The new Hyderabad International Airport will commence commercial operations from Sunday, its developers announced on Thursday.
A week after the airport was formally inaugurated and the scheduled commercial launch was postponed at the last minute, the airport developers received a nod from the Civil Aviation Ministry to start operations from 0001 hours on March 23.
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“This is in pursuance of clause 5.5 of the Concession Agreement signed between the Government of India and GHIAL on December 20, 2004,” said a statement by GMR Hyderabad International Airport Limited (GHIAL), which has built the Rajiv Gandhi International Airport at Shamshabad. The statement also said that on commissioning of the new airport, the existing airport at Begumpet in the heart of the city, will be shut down for civil aviation operations.
General aviation services (other than those relating to commercial aircraft, charter flights, aircraft hired or operated under commercial arrangements) may continue to be provided at the existing airport, it said.
The new airport was inaugurated by United Progressive Alliance (UPA) Chairperson Sonia Gandhi on March 14 and the commercial operations were to start from 0001 hrs on March 16. Minutes after the formal inauguration, the Ministry announced in New Delhi that the opening was delayed by a few days.
The move came in the backdrop of reported objections by low-cost airlines over the higher ground handling charges at the new airport and the criticism over the poor road connectivity between Shamshabad and the city.
Last week, Airports Authority of India (AAI) employees had gone on strike protesting the closure of the existing airports in Hyderabad and Bangalore in favour of new ones.
India's first greenfield airport built in public-private partnership was completed six months ahead of the schedule. It is being seen as a model for public-private partnership in infrastructure projects.
The Rs 25 billion airport with the longest run-way in Southeast Asia has been built by GHIAL, a joint venture in which GMR Infrastructure Limited holds 63 percent, Malaysia Airports Holding Berhad 11 percent, AAI 13 percent and the Andhra Pradesh government 13 percent.
Thursday, March 20, 2008
IPL's official beverage supplier for 5 years: Pepsi news
PepsiCo India will officially supply beverages to the DLF Indian Premier League for five years.
The deal, worth $12.5 million according to a release by the company, will see Pepsi supply beverages to the DLF Indian Premier League.
Punita Lal, marketing head at PepsiCo India said, ''Pepsico is proud to associate with the DLF IPL. DLF IPL and the new format will have a large youth audience which is a key target for our brands.''
Lalit Modi, Chairman and Commissioner of IPL said, ''Pepsi has a long history of supporting cricket in the sub-continent and to have them as our beverage supplier for this league will give our cricket extravaganza a solid boost.''
The deal, worth $12.5 million according to a release by the company, will see Pepsi supply beverages to the DLF Indian Premier League.
Punita Lal, marketing head at PepsiCo India said, ''Pepsico is proud to associate with the DLF IPL. DLF IPL and the new format will have a large youth audience which is a key target for our brands.''
Lalit Modi, Chairman and Commissioner of IPL said, ''Pepsi has a long history of supporting cricket in the sub-continent and to have them as our beverage supplier for this league will give our cricket extravaganza a solid boost.''
Sunday, March 16, 2008
something for you
hi, friends....
in my blog (http://karunabharghav.blogspot.com) u might have noticed about my posts namely,
doors and ,types...,windows,stairway,sedimentation,cogulation,yeast flocculation,evaporation.transpiration and evapotanspiration.i have choosen this topics for a particular reson to place them in my blog.they are included in my second sessional exams.
so i want to place them in my blog.so tht i will be revising them once again.
doors and types....,windows,stairways comes under the subject called building material and technology.but in short we will term it as BMT.next topics,sedimentation,coagulation,yeast flocculation comes under environmental engineering.evaporation,transpiration and evapotanspiration comes under hydrology.
all this subjects nmaely BMT,environmental engineering,hydrology comes under civil enggineering 2nd year 4th semester in my college namely VNIT....
in my blog (http://karunabharghav.blogspot.com) u might have noticed about my posts namely,
doors and ,types...,windows,stairway,sedimentation,cogulation,yeast flocculation,evaporation.transpiration and evapotanspiration.i have choosen this topics for a particular reson to place them in my blog.they are included in my second sessional exams.
so i want to place them in my blog.so tht i will be revising them once again.
doors and types....,windows,stairways comes under the subject called building material and technology.but in short we will term it as BMT.next topics,sedimentation,coagulation,yeast flocculation comes under environmental engineering.evaporation,transpiration and evapotanspiration comes under hydrology.
all this subjects nmaely BMT,environmental engineering,hydrology comes under civil enggineering 2nd year 4th semester in my college namely VNIT....
EVAPOTRASPIRATION
Evapotranspiration (ET) is a term used to describe the sum of evaporation and plant transpiration from the earth's land surface to atmosphere. Evaporation accounts for the movement of water to the air from sources such as the soil, canopy interception, and waterbodies. Transpiration accounts for the movement of water within a plant and the subsequent loss of water as vapour through stomata in its leaves. Evapotranspiration is an important part of the water cycle. An element (such as a tree) that contributes to evapotranspiration can be called an evapotranspirator.[1]
Potential evapotranspiration (PET) is a representation of the environmental demand for evapotranspiration and represents the evapotranspiration rate of a short green crop, completely shading the ground, of uniform height and with adequate water status in the soil profile. It is a reflection of the energy available to evaporate water, and of the wind available to transport the water vapour from the ground up into the lower atmosphere. Evapotranspiration is said to equal potential evapotranspiration when there is ample water.
Evapotranspiration and the water cycle:
Evapotranspiration is a significant water loss from a watershed. Types of vegetation and land use significantly affect evapotranspiration, and therefore the amount of water leaving a watershed. Because water transpired through leaves comes from the roots, plants with deep reaching roots can more constantly transpire water. Thus herbaceous plants transpire less than woody plants because herbaceous plants usually lack a deep taproot. Also, woody plants keep their structure over long winters while herbaceous plants must grow up from seed in the spring in seasonal climates, and will contribute almost nothing to evapotranspiration in the spring. Conifer forests tend to have much higher rates of evapotranspiration than deciduous forests.[citation needed] This is because their needles give them superior surface area,[dubious ] resulting in more pores for transpiration, and allowing for more droplets of rain to be suspended in and around the needles and branches, where some of the droplets can then be evaporated. Factors that affect evapotranspiration include the plant's growth stage or level of maturity, percentage of soil cover, solar radiation, humidity, temperature, and wind.
Through evapotranspiration, forests reduce water yield, except for in unique ecosystems called cloud forests. Trees in cloud forests condense fog or low clouds into liquid water on their surface, which drips down to the ground. These trees still contribute to evapotranspiration, but often condense more water than they evaporate or transpire.
In areas that are not irrigated, actual evapotranspiration is usually no greater than precipitation, with some buffer in time depending on the soil's ability to hold water. It will usually be less because some water will be lost due to percolation or surface runoff. An exception is areas with high water tables, where capillary action can cause water from the groundwater to rise through the soil matrix to the surface. If potential evapotranspiration is greater than actual precipitation, then soil will dry out, unless irrigation is used.
Estimating evapotranspiration:
Evapotranspiration cannot be measured directly. Pan evaporation data can be used to estimate lake evaporation, but transpiration and evaporation of intercepted rain on vegetation are unknown. There are three general approaches to estimate evapotranspiration indirectly.
Catchment water balance:
Evapotranspiration may be estimated by creating an equation of the water balance of a catchment (or watershed). The equation balances the change in water stored within the basin (S) with inputs and exports:
The input is precipitation (P), and the exports are evapotranspiration (which is to be estimated), streamflow (Q), and groundwater recharge (D). If the change in storage, precipitation, streamflow, and groundwater recharge are all estimated, the missing flux, ET, can be estimated by rearranging the above equation as follows:
Hydrometeorological equations:
The most general and widely used equation for calculating reference ET is the Penman equation. The Penman-Monteith variation is recommended by the Food and Agriculture Organization.[2] The simpler Blaney-Criddle equation was popular in the Western United States for many years but it is not as accurate in regions with higher humidities. Other solutions used includes Makkink, which is simple but must be calibrated to a specific location, and Hargreaves. To convert the reference evapotranspiration to actual crop evapotranspiration, a crop coefficient and a stress coeficient must be used.
Energy balance:
A third methodology to estimate the actual evapotranspiration is the use of the energy balance.
where λE is the energy needed to change the phase of water from liquid to gas, Rn is the net radiation, G is the soil heat flux and H is the sensible heat flux. Using instruments like a sentillometer, soil heat flux plates or radiation meters, the components of the energy balance can be calculated and the energy available for actual evapotranspiration can be solved.
Potential evapotraspiration:
Potential evapotranspiration (PET) is the amount of water that could be evaporated and transpired if there was sufficient water available. This demand incorporates the energy available for evaporation and the ability of the lower atmosphere to transport evaporated moisture away from the land surface. PET is higher in the summer, on less cloudy days, and closer to the equator, because of the higher levels of solar radiation that provides the energy for evaporation. PET is also higher on windy days because the evaporated moisture can be quickly moved from the ground of plants, allowing more evaporation to fill its place.
PET is expressed in terms of a depth of water, and can be graphed during the year (see figure). There is usually a pronounced peak in summer, which results from higher temperatures.
Potential evapotranspiration is usually measured indirectly, from other climatic factors, but also depends on the surface type, such free water (for lakes and oceans), the soil type for bare soil, and the vegetation. Often a value for the potential evapotranspiration is calculated at a nearby climate station on a reference surface, conventionally short grass. This value is called the reference evapotranspiration, and can be converted to a potential evapotranspiration by multiplying with a surface coefficient. In agriculture, this is called a crop coefficient. The difference between potential evapotranspiration and precipitation is used in irrigation scheduling.
Let us see briefly about lysimeter which is used to measure evapotanspiration.
Potential evapotranspiration (PET) is the amount of water that could be evaporated and transpired if there was sufficient water available. This demand incorporates the energy available for evaporation and the ability of the lower atmosphere to transport evaporated moisture away from the land surface. PET is higher in the summer, on less cloudy days, and closer to the equator, because of the higher levels of solar radiation that provides the energy for evaporation. PET is also higher on windy days because the evaporated moisture can be quickly moved from the ground of plants, allowing more evaporation to fill its place.
PET is expressed in terms of a depth of water, and can be graphed during the year (see figure). There is usually a pronounced peak in summer, which results from higher temperatures.
Potential evapotranspiration is usually measured indirectly, from other climatic factors, but also depends on the surface type, such free water (for lakes and oceans), the soil type for bare soil, and the vegetation. Often a value for the potential evapotranspiration is calculated at a nearby climate station on a reference surface, conventionally short grass. This value is called the reference evapotranspiration, and can be converted to a potential evapotranspiration by multiplying with a surface coefficient. In agriculture, this is called a crop coefficient. The difference between potential evapotranspiration and precipitation is used in irrigation scheduling.
TRASPIRATION
Transpiration is the evaporation of water from the aerial parts of plants, especially leaves but also stems, flowers and roots. Leaf transpiration occurs through stomata, and can be thought of as a necessary "cost" associated with the opening of stomata to allow the diffusion of carbon dioxide gas from the air for photosynthesis. Transpiration also cools plants and enables mass flow of mineral nutrients from roots to shoots. Mass flow is caused by the decrease in hydrostatic (water) pressure in the upper parts of the plants due to the diffusion of water out of stomata into the atmosphere. Water is absorbed at the roots by osmosis, and any dissolved mineral nutrients travel with it through the xylem.
The rate of transpiration is directly related to the degree of stomatal opening, and to the evaporative demand of the atmosphere surrounding the leaf. The amount of water lost by a plant depends on its size, along with the surrounding light intensity, temperature, humidity, and wind speed (all of which influence evaporative demand). Soil water supply and soil temperature can influence stomatal opening, and thus transpiration rate.
A fully grown tree may lose several hundred gallons (a few cubic meters) of water through its leaves on a hot, dry day. About 90% of the water that enters a plant's roots is used for this process. The transpiration ratio is the ratio of the mass of water transpired to the mass of dry matter produced; the transpiration ratio of crops tends to fall between 200 and 1000 (i.e., crop plants transpire 200 to 1000 kg of water for every kg of dry matter produced) (Martin, Leonard & Stamp 1976, p. 81).
Transpiration rate of plants can be measured by a number of techniques, including potometers, lysimeters, porometers, and heat balance sap flow gauges.
Desert plants and conifers have specially adapted structures, such as thick cuticles, reduced leaf areas, sunken stomata and hairs to reduce transpiration and conserve water. Many cacti conduct photosynthesis in succulent stems, rather than leaves, so the surface area of the shoot is very low. Many desert plants have a special type of photosynthesis, termed Crassulacean acid metabolism or CAM photosynthesis in which the stomata are closed during the day and open at night when transpiration will be lower.
EVAPORATION
Evaporation is the process by which molecules in a liquid state (e.g. water) spontaneously become gaseous (e.g. water vapor). It is the opposite of condensation. Generally, evaporation can be seen by the gradual disappearance of a liquid, when exposed to a significant volume of gas.
On average, the molecules do not have enough energy to escape from the liquid, or else the liquid would turn into vapor quickly. When the molecules collide, they transfer energy to each other in varying degrees, based on how they collide. Sometimes the transfer is so one-sided that one of the molecules ends up with enough energy to be considered past the boiling point of the liquid. If this happens near the surface of the liquid it may actually fly off into the gas and thus "evaporate".
Liquids that do not appear to evaporate visibly at a given temperature in a given gas (e.g. cooking oil at room temperature) have molecules that do not tend to transfer energy to each other in a pattern sufficient to frequently give a molecule the "escape velocity" - the heat energy - necessary to turn into vapor. However, these liquids are evaporating, it's just that the process is much slower and thus significantly less visible.
Evaporation is an essential part of the water cycle. Solar energy drives evaporation of water from oceans, lakes, moisture in the soil, and other sources of water. In hydrology, evaporation and transpiration (which involves evaporation within plant stomata) are collectively termed evapotranspiration.
THEORY:
For molecules of a liquid to evaporate, they must be located near the surface, be moving in the proper direction, and have sufficient kinetic energy to overcome liquid-phase intermolecular forces.[1] Only a small proportion of the molecules meet these criteria, so the rate of evaporation is limited. Since the kinetic energy of a molecule is proportional to its temperature, evaporation proceeds more quickly at higher temperature. As the faster-moving molecules escape, the remaining molecules have lower average kinetic energy, and the temperature of the liquid thus decreases. This phenomenon is also called evaporative cooling. This is why evaporating sweat cools the human body. Evaporation also tends to proceed more quickly with higher flow rates between the gaseous and liquid phase and in liquids with higher vapor pressure. For example, laundry on a clothes line will dry (by evaporation) more rapidly on a windy day than on a still day.Three key parts to evaporation are heat, humidity and air movement.
Evaporative equilibrium:
If the evaporation takes place in a closed vessel, the escaping molecules accumulate as a vapor above the liquid. Many of the molecules return to the liquid, with returning molecules becoming more frequent as the density and pressure of the vapor increases. When the process of escape and return reaches an equilibrium,[1] the vapor is said to be "saturated," and no further change in either vapor pressure and density or liquid temperature will occur. For a system consisting of vapor and liquid of a pure substance, this equilibrium state is directly related to the vapor pressure of the substance, as given by the Clausius-Clapeyron relation:
where P1, P2 are the vapor pressures at temperatures T1, T2 respectively, ΔHvap is the enthalpy of vaporization, and R is the universal gas constant. The rate of evaporation in an open system is related to the vapor pressure found in a closed system. If a liquid is heated, when the vapor pressure reaches the ambient pressure the liquid will boil.
The ability for a molecule of a liquid to evaporate is largely based on the amount of kinetic energy an individual particle may possess. Even at lower temperatures, individual molecules of a liquid can potentially evaporate if they have more than the minimum amount of kinetic energy required for vaporization.
Factors influencing the rate of evaporation:
- Concentration of the substance evaporating in the air: If the air already has a high concentration of the substance evaporating, then the given substance will evaporate more slowly.
- Concentration of other substances in the air: If the air is already saturated with other substances, it can have a lower capacity for the substance evaporating.
- Flow rate of air: This is in part related to the concentration points above. If fresh air is moving over the substance all the time, then the concentration of the substance in the air is less likely to go up with time, thus encouraging faster evaporation. This is result of the boundary layer at the evaporation surface decreasing with flow velocity, decreasing the diffusion distance in the stagnant layer.
- Concentration of other substances in the liquid(Impurities): If the liquid contains other substances, it will have a lower capacity for evaporation.
- Temperature of the substance: If the substance is hotter, then evaporation will be faster.
- Inter-molecular forces: The stronger the forces keeping the molecules together in the liquid state the more energy that must be input in order to evaporate them.
- Surface Area: A substance which has a larger surface area will evaporate faster as there are more surface molecules which are able to escape.
- Heating : The thickness of the object being heated was thick at a time of heating, the heat being delivered for evaporation of the water could be reduced. If there was no thickness, the heat might have been delivered more to the evaporation of the water.
In the US, the National Weather Service measures the actual rate of evaporation from a standardized "pan" open water surface outdoors, at various locations nationwide. Others do likewise around the world. The US data is collected and compiled into an annual evaporation map.[1] The measurements range from under 30 to over 120 inches per year. Formulas for calculating the rate of evaporation from a water surface such as a swimming pool of can be found here[2] and here[3].
Applications:
When clothes are hung on a laundry line, even though the ambient temperature is below the boiling point of water, water evaporates. This is accelerated by factors such as low humidity, heat (from the sun), and wind. In a clothes dryer hot air is blown through the clothes, allowing water to evaporate very rapidly.
Yeast Flooculation
Yeast flocculation typically refers to the clumping together of brewing yeast once the sugar in a beer brew has been converted into alcohol. In the case of ale yeast Saccharomyces cerevisiae the yeast floats to the top of an open tank, whereas with lager yeast Saccharomyces pastorianus the yeast will sink to the bottom of the tank.
Cell aggregation occurs throughout microbiology, in bacteria, filamentous algae, fungi and yeast (Lewin, 1984; Stratford, 1992). Yeast are capable of forming three aggregates; mating aggregates, for DNA exchange; chain formation, for development and differentiation; and flocs as a survival strategy in adverse conditions (Calleja, 1987). Brewing strains are polyploid so mating aggregates do not occur. Therefore only chain formation and flocculation are of relevance to the brewing industry.
Flocculation is distinct from agglomeration (‘grit’ formation), which is irreversible and most commonly in bakers yeast strains of fail to separate when resuspended (Guinard and Lewis, 1993). Agglomeration only occurs following the pressing and rehydration of yeast cakes and both flocculent and non-flocculent yeast strains have been shown to demonstrate agglomeration (Guinard and Lewis, 1993). It is also distinct from the formation of biofilms, which occur on a solid substrate.
Pasteur first described flocculation of brewer’s yeast in 1876 (Pasteur, 1876) which has since been the subject of many reviews (Stewart et al, 1975; Stewart and Russell, 1986; Calleja, 1987; Speers et al, 1992; Stratford, 1992; Jin and Speers, 1999, Smart, 2001). Flocculation has been defined as the reversible, non-sexual aggregation of yeast cells that may be dispersed by specific sugars (Burns, 1937; Lindquist, 1953, Eddy, 1955; Masy et al, 1992) or EDTA (Burns, 1937; Lindquist, 1953). The addition of nutrients other than sugars has been demonstrated not to reverse flocculation (Soares et al, 2004). This is as opposed to mating aggregates formed as a prelude to sexual fusion between complimentary yeast cells (Calleja, 1987; Stratford, 1992).
Flocculation is a bimodal process in which a non-flocculent population develops into one comprising of flocculent and non-flocculent cells (Miki et al, 1982). The efficiency of flocculation is determined by the timing of flocculation onset and the rate of flocculation in conjunction with the ratio of flocculent to non-flocculent cells (Stratford and Keenan, 1987; 1988; van Hamersveld et al, 1996). The rate-limiting step is doublet formation, requiring the presence of active surface proteins (Stan and Despa, 2000). The mechanism by which this occurs is thought to be the lectin interaction theory.
Lectin Interaction Theory The accepted mechanism of flocculation involves a protein-carbohydrate model (Miki et al, 1982) (figure 1.3). Fully flocculent yeast cells exhibit carbohydrate α-mannan receptors and protein lectins (section 1.5.4). It has been suggested that lectin like interactions between the two results in the flocculation phenotype (section 4.1) with Ca2+ ions required for the correct conformation of the flocculation lectins. Coflocculation between Kluyveromyces and Schizosaccharomyces has been shown to be by a “lectinic” mechanism (El-Behhari et al, 2000). This theory explains the essential role of calcium and how deproteinisation affects flocculation.
Flocculation Lectins and Phenotypes Three flocculation phenotypes have been elucidated based on the lectins they produce: Flo1 (Stratford and Assinder, 1991) NewFlo (Stratford and Assinder, 1991) and Mannose Insensitive (MI) (Masy et al, 1992; Dengis and Rouxhet, 1997). These flocculation phenotypes differ in the time of the onset of flocculation and the sugar inhibition of flocculation. Flocculation has also been classified according to time of onset and floc morphology.
Gilliland Class Flocculation Characteristics I Completely Dispersed II Flocculating into small, loose lumps late in fermentation III Flocculating into dense masses late in fermentation IV Flocculating very early in fermentation owing to non-separation of daughter cells
The genetic control of yeast flocculation has not been extensively studied. Recent reports suggest genes encoding lectin-like proteins exhibit close sequence homology (Jin and Speers, 1991, 1999; Smart, 2001). Furthermore it seems that FLO genes have interchangeable functions that can compensate for one another (Guo et al, 2000).
Flocculation Phenotypes The Flo1 phenotype is inhibited by mannose (Burns, 1937; Miki et al, 1982; Nishihara and Toraya, 1987; Kihn et al, 1988; Stratford, 1989; Stratford and Assinder, 1991) occurs in both ale and lager strains (Miki, 1982; Stratford and Assinder, 1991; Masy et al, 1992; Smit et al, 1982; Stratford, 1993; Stratford and Carter, 1993; Teunissen et al, 1993; Teunissen et al, 1995a, b; Bony et al, 1997; Braley and Chaffin, 1999; Fleming and Pennings, 2001; He et al, 2002; Verstrepen et al, 2003) and is associated with the FLO1 gene (Watari, 1991 Masy et al, 1992; Stratford, 1993; Stratford and Carter, 1993; Teunissen et al, 1993; Teunissen et al, 1995a, b; Bony et al, 1997; Braley and Chaffin, 1999).
The NewFlo phenotype differs from that of FLO1 in several ways. Firstly NewFlo flocculation is inhibited by mannose, glucose and maltose (Stratford and Assinder, 1991; Masy, 1992; Rhymes, 1999). Secondly the NewFlo lectin is putatively encoded by the FLO10 gene (Guo et al, 2000; Smart, 2001) and is not expressed until stationary phase onset (Stratford, 1989; Stratford and Assinder, 1991; D’Hautcourt and Smart, 1999). Thirdly lectin maturation occurs some fourteen hours after the cessation of cell division (Stratford, 1989; Stratford and Assinder, 1991; Masy 1992; D’Hautcourt and Smart, 1999) and is therefore not concomitant with entry into stationary phase, although this is strain dependent (D’Hautcourt and Smart, 1999; Verstrepen et al, 2003).
The MI phenotype appears to occur in ale (Saccharomyces cerevisiae, but not lager (saccharomyces pastorianus) strains (Masy et al, 1992; Dengis and Rouxhet, 1997; Jin and Speers, 1999) and is considered to be a rare phenotype. The FLO11 gene has however been identified as being essential for flocculation in S. bayanus (Ishigami et al, 2004) and characteristics such as invasive growth and pseudohyphal formation in Saccharomyces cerevisiae (Lo and Dranginis, 1998; Gagiano et al, 1999; Gancedo, 2001; Gagiano et al, 2002; Gagiano et al, 2003; Verduzco-Luque et al, 2003; Vivier et al, 2003; Guldener et al, 2004). Although this flocculation phenotype has not been fully characterised, it is differentiated from other flocculation phenotypes by a lack of inhibition of the lectin like reaction in the presence of mannose (Dengis and Rouxhet, 1997; Guo et al, 2000; Smart, 2001).
Coagulation is a complex process by which blood forms solid clots. It is an important part of hemostasis (the cessation of blood loss from a damaged vessel) whereby a damaged blood vessel wall is covered by a platelet- and fibrin-containing clot to stop bleeding and begin repair of the damaged vessel. Disorders of coagulation can lead to an increased risk of bleeding and/or clotting and embolism.
Coagulation is highly conserved throughout biology; in all mammals, coagulation involves both a cellular (platelet) and a protein (coagulation factor) component. The system in humans has been the most extensively researched and therefore is the best understood.
Coagulation is initiated almost instantly after an injury to the blood vessel damages the endothelium (lining of the vessel). Platelets immediately form a hemostatic plug at the site of injury; this is called primary hemostasis. Secondary hemostasis occurs simultaneously—proteins in the blood plasma, called coagulation factors, respond in a complex cascade to form fibrin strands which strengthen the platelet plug.PHYIOLOGY:
Platelet activation
Damage to blood vessel walls exposes collagen normally present under the endothelium. Circulating platelets bind to the collagen with the surface collagen-specific glycoprotein Ia/IIa receptor. This adhesion is strengthened further by the large multimeric circulating protein von Willebrand factor (vWF), which forms links between the platelet glycoprotein Ib/IX/V and collagen fibrils.
The platelets are then activated and release the contents of their granules into the plasma, in turn activating other platelets. The platelets undergo a change in their shape which exposes a phospholipid surface for those coagulation factors that require it. Fibrinogen links adjacent platelets by forming links via the glycoprotein IIb/IIIa. In addition, thrombin activates platelets.
THE COGULENT CASCADE:
The coagulation cascade of secondary hemostasis has two pathways, the contact activation pathway (formerly known as the intrinsic pathway) and the tissue factor pathway (formerly known as the extrinsic pathway) that lead to fibrin formation. It was previously thought that the coagulation cascade consisted of two pathways of equal importance joined to a common pathway. It is now known that the primary pathway for the initiation of blood coagulation is the tissue factor pathway. The pathways are a series of reactions, in which a zymogen (inactive enzyme precursor) of a serine protease and its glycoprotein co-factor are activated to become active components that then catalyze the next reaction in the cascade, ultimately resulting in cross-linked fibrin. Coagulation factors are generally indicated by Roman numerals, with a lowercase a appended to indicate an active form.
The coagulation factors are generally serine proteases (enzymes). There are some exceptions. For example, FVIII and FV are glycoproteins and Factor XIII is a transglutaminase. Serine proteases act by cleaving other proteins at specific sites. The coagulation factors circulate as inactive zymogens.
The coagulation cascade is classically divided into three pathways. The tissue factor and contact activation pathways both activate the "final common pathway" of factor X, thrombin and fibrin.
Tissue factor pathway:
The main role of the tissue factor pathway is to generate a "thrombin burst", a process by which thrombin, the most important constituent of the coagulation cascade in terms of its feedback activation roles, is released instantaneously. FVIIa circulates in a higher amount than any other activated coagulation factor.
- Following damage to the blood vessel, endothelium Tissue Factor (TF) is released, forming a complex with FVII and in so doing, activating it (TF-FVIIa).
- TF-FVIIa activates FIX and FX.
- FVII is itself activated by thrombin, FXIa, plasmin, FXII and FXa.
- The activation of FXa by TF-FVIIa is almost immediately inhibited by tissue factor pathway inhibitor (TFPI).
- FXa and its co-factor FVa form the prothrombinase complex which activates prothrombin to thrombin.
- Thrombin then activates other components of the coagulation cascade, including FV and FVII (which activates FXI, which in turn activates FIX), and activates and releases FVIII from being bound to vWF.
- FVIIIa is the co-factor of FIXa and together they form the "tenase" complex which activates FX and so the cycle continues. ("Tenase" is a contraction of "ten" and the suffix "-ase" used for enzymes.)
Contact activation pathway:
The contact activation pathway begins with formation of the primary complex on collagen by high-molecular weight kininogen (HMWK), prekallikrein, and FXII (Hageman factor). Prekallikrein is converted to kallikrein and FXII becomes FXIIa. FXIIa converts FXI into FXIa. Factor XIa activates FIX, which with its co-factor FVIIIa form the tenase complex, which activates FX to FXa. The minor role that the contact activation pathway has in initiating clot formation can be illustrated by the fact that patients with severe deficiencies of FXII, HMWK, and prekallikrein do not have a bleeding disorder.
Cofactors:
Various substances are required for the proper functioning of the coagulation cascade:
- Calcium and phospholipid (a platelet membrane constituent) are required for the tenase and prothrombinase complexes to function. Calcium mediates the binding of the complexes via the terminal gamma-carboxy residues on FXa and FIXa to the phospholipid surfaces expressed by platelets as well as procoagulant microparticles or microvesicles shedded from them. Calcium is also required at other points in the coagulation cascade.
- Vitamin K is an essential factor to a hepatic gamma-glutamyl carboxylase that adds a carboxyl group to glutamic acid residues on factors II, VII, IX and X, as well as Protein S, Protein C and Protein Z. Deficiency of vitamin K (e.g. in malabsorption), use of inhibiting anticoagulants (warfarin, acenocoumarol and phenprocoumon) or disease (hepatocellular carcinoma) impairs the function of the enzyme and leads to the formation of PIVKAs (proteins formed in vitamin K absence) this causes partial or non gamma carboxylation and affects the coagulation factors ability to bind to expressed phospholipid.
Inhibitors:
Three mechanisms keep the coagulation cascade in check. Abnormalities can lead to an increased tendency toward thrombosis:
- Protein C is a major physiological anticoagulant. It is a vitamin K-dependent serine protease enzyme that is activated by thrombin into activated protein C (APC). The activated form (with protein S and phospholipid as a cofactor) degrades Factor Va and Factor VIIIa. Quantitative or qualitative deficiency of either may lead to thrombophilia (a tendency to develop thrombosis). Impaired action of Protein C (activated Protein C resistance), for example by having the "Leiden" variant of Factor V or high levels of FVIII also may lead to a thrombotic tendency.
- Antithrombin is a serine protease inhibitor (serpin) that degrades the serine proteases; thrombin and FXa, as well as FXIIa, and FIXa. It is constantly active, but its adhesion to these factors is increased by the presence of heparan sulfate (a glycosaminoglycan) or the administration of heparins (different heparinoids increase affinity to F Xa, thrombin, or both). Quantitative or qualitative deficiency of antithrombin (inborn or acquired, e.g. in proteinuria) leads to thrombophilia.
- Tissue factor pathway inhibitor (TFPI) inhibits F VIIa-related activation of F IX and F X after its original initiation.
Testing of coagulation:
Numerous tests are used to assess the function of the coagulation system:
- Common: aPTT, PT (also used to determine INR), fibrinogen testing (often by the Clauss method), platelet count, platelet function testing (often by PFA-100).
- Other: TCT, bleeding time, mixing test (whether an abnormality corrects if the patient's plasma is mixed with normal plasma), coagulation factor assays, antiphosholipid antibodies, D-dimer, genetic tests (eg. factor V Leiden, prothrombin mutation G20210A), dilute Russell's viper venom time (dRVVT), miscellanous platelet function tests, thromboelastography (TEG or ROTEM), euglobulin lysis time (ELT), .
The contact factor pathway is initiated by activation of the "contact factors" of plasma, and can be measured by the activated partial thromboplastin time (aPTT) test.
The tissue factor pathway is initiated by release of tissue factor (a specific cellular lipoprotein), and can be measured by the prothrombin time (PT) test. PT results are often reported as ratio (INR value) to monitor dosing of oral anticoagulants such as warfarin.
The quantitative and qualitative screening of fibrinogen is measured by the thrombin clotting time (TCT). Measurement of the exact amount of fibrinogen present in the blood is generally done using the Clauss method for fibrinogen testing. Many analysers are capable of measuring a "derived fibrinogen" level from the graph of the Prothrombin time clot.
If a coagulation factor is part of the contact or tissue factor pathway, a deficiency of that factor will affect only one of the tests: thus hemophilia A, a deficiency of factor VIII, which is part of the contact factor pathway, results in an abnormally prolonged aPTT test but a normal PT test. The exceptions are prothrombin, fibrinogen and some variants of FX which can only be detected by either aPTT or PT. If an abnormal PT or aPTT is present additional testing will occur to determine which (if any) factor is present as aberrant concentrations.
Role in disease:
Platelet disorders:
Platelet conditions may be inborn or acquired. Some inborn platelet pathologies are Glanzmann's thrombasthenia, Bernard-Soulier syndrome (abnormal glycoprotein Ib-IX-V complex), gray platelet syndrome (deficient alpha granules) and delta storage pool deficiency (deficient dense granules). Most are rare conditions. Most inborn platelet pathologies predispose to hemorrhage. von Willebrand disease is due to deficiency or abnormal function of von Willebrand factor, and leads to a similar bleeding pattern; its milder forms are relatively common.
Decreased platelet numbers may be due to various causes, including insufficient production (e.g. in myelodysplastic syndrome or other bone marrow disorders), destruction by the immune system (immune thrombocytopenic purpura/ITP), and consumption due to various causes (thrombotic thrombocytopenic purpura/TTP, hemolytic-uremic syndrome/HUS, paroxysmal nocturnal hemoglobinuria/PNH, disseminated intravascular coagulation/DIC, heparin-induced thrombocytopenia/HIT). Most consumptive conditions lead to platelet activation, and some are associated with thrombosis.
Factor disorders and thrombosis:
The best-known coagulation factor disorders are the hemophilias. The three main forms are hemophilia A (factor VIII deficiency), hemophilia B (factor IX deficiency or "Christmas disease") and hemophilia C (factor XI deficiency, mild bleeding tendency). Together with von Willebrand disease (which behaves more like a platelet disorder except in severe cases), these conditions predispose to bleeding. Most hemophilias are inherited. In liver failure (acute and chronic forms) there is insufficient production of coagulation factors by the liver; this may increase bleeding risk.
Thrombosis is the pathological development of blood clots, and embolism is said to occur when a blood clot (thrombus) migrates to another part of the body, interfering with organ function there. Most cases of thrombosis are due to acquired extrinsic problems (surgery, cancer, immobility, obesity, economy class syndrome), but a small proportion of people harbor predisposing conditions known collectively as thrombophilia (e.g. antiphospholipid syndrome, factor V Leiden and various other rarer genetic disorders).
Mutations in factor XII have been associated with an asymptomatic prolongation in the clotting time and possibly a tendency to thrombophebitis. Other mutations have been linked with a rare form of hereditary angioedema (type III).
Coagulation factors:
The remainder of the biochemical factors in the process of coagulation were largely discovered in the 20th century.
A first clue as to the actual complexity of the system of coagulation was the discovery of proaccelerin (initially and later called Factor V) by Paul Owren (1905-1990) in 1947. He also postulated that its function was the generation of accelerin (Factor VI), which later turned out to be the activated form of V (or Va); hence, VI is not now in active use.[8]
Factor VII (also known as serum prothrombin conversion accelerator or proconvertin, precipitated by barium sulfate) was discovered in a young female patient in 1949 and 1951 by different groups.
Factor VIII turned out to be deficient in the clinically recognised but etiologically elusive hemophilia A; it was identified in the 1950s and is alternatively called antihemophilic globulin due to its capability to correct hemophilia A.[8]
Factor IX was discovered in 1952 in a young patient with hemophilia B named Stephen Christmas (1947-1993). His deficiency was described by Dr. Rosemary Biggs and Professor R.G. MacFarlane in Oxford, UK. The factor is hence called Christmas Factor or Christmas Eve Factor. Christmas lived in Canada, and campaigned for blood transfusion safety until succumbing to transfusion-related AIDS at age 46. An alternative name for the factor is plasma thromboplastin component, given by an independent group in California.[8]
Hageman factor, now known as factor XII, was identified in 1955 in an asymptomatic patient with a prolonged bleeding time named of John Hageman. Factor X, or Stuart-Prower factor, followed, in 1956. This protein was identified in a Ms. Audrey Prower of London, who had a lifelong bleeding tendency. In 1957, an American group identified the same factor in a Mr. Rufus Stuart. Factors XI and XIII were identified in 1953 and 1961, respectively.[8]
The view that the coagulation process was a "cascade" or "waterfall" was enunciated almost simultaneously by MacFarlane[9] in the UK and by Davie and Ratnoff[10] in the USA, respectively.
Saturday, March 15, 2008
SEDIMENTATION
Sedimentation describes the motion of molecules in solutions or particles in suspensions in response to an external force such as gravity, centrifugal force or electric force. Sedimentation may pertain to objects of various sizes, ranging from suspensions of dust and pollen particles to cellular suspensions to solutions of single molecules such as proteins and peptides. Even small molecules such as aspirin can be sedimented, although it can be difficult to apply a sufficiently strong force to produce significant sedimentation.
In a sedimentation experiment, the applied force accelerates the particles to a terminal velocity vterm at which the applied force is exactly canceled by an opposing drag force. In general, the drag force varies linearly with the terminal velocity, i.e., Fdrag = fvterm where f depends only on the properties of the particle and the surrounding fluid. Similarly, the applied force generally varies linearly with some coupling constant (denoted here as q) that depends only on the properties of the particle, Fapp = qEapp. Hence, it is generally possible to define a sedimentation coefficient that depends only on the properties of the particle and the surrounding fluid. Thus, measuring s can reveal underlying properties of the particle.
In many cases, the motion of the particles is blocked by a hard boundary; the resulting accumulation of particles at the boundary is called a sediment. The concentration of particles at the boundary is opposed by the diffusion of the particles.
The sedimentation of particles under gravity is described by the Mason-Weaver equation, which has a simple exact solution. The sedimentation coefficient s in this case equals mb / f, where mb is the buoyant mass.
The sedimentation of particles under the centrifugal force is described by the Lamm equation, which likewise has an exact solution. The sedimentation coefficient s also equals mb / f, where mb is the buoyant mass. However, the Lamm equation differs from the Mason-Weaver equation because the centrifugal force depends on radius from the origin of rotation, whereas gravity is presumed constant. The Lamm equation also has extra terms, since it pertains to sector-shaped cells, whereas the Mason-Weaver equation pertains to box-shaped cells (i.e., cells whose walls are aligned with the three Cartesian axes).
Particles with a charge or dipole moment can be sedimented by an electric field or electric field gradient, respectively. These processes are called electrophoresis and dielectrophoresis, respectively. For electrophoresis, the sedimentation coefficient corresponds to the particle charge divided by its drag (the electrophoretic mobility). Similarly, for dielectrophoresis, the sedimentation coefficient equals the particle's electric dipole moment divided by its drag.
In a sedimentation experiment, the applied force accelerates the particles to a terminal velocity vterm at which the applied force is exactly canceled by an opposing drag force. In general, the drag force varies linearly with the terminal velocity, i.e., Fdrag = fvterm where f depends only on the properties of the particle and the surrounding fluid. Similarly, the applied force generally varies linearly with some coupling constant (denoted here as q) that depends only on the properties of the particle, Fapp = qEapp. Hence, it is generally possible to define a sedimentation coefficient that depends only on the properties of the particle and the surrounding fluid. Thus, measuring s can reveal underlying properties of the particle.
In many cases, the motion of the particles is blocked by a hard boundary; the resulting accumulation of particles at the boundary is called a sediment. The concentration of particles at the boundary is opposed by the diffusion of the particles.
The sedimentation of particles under gravity is described by the Mason-Weaver equation, which has a simple exact solution. The sedimentation coefficient s in this case equals mb / f, where mb is the buoyant mass.
The sedimentation of particles under the centrifugal force is described by the Lamm equation, which likewise has an exact solution. The sedimentation coefficient s also equals mb / f, where mb is the buoyant mass. However, the Lamm equation differs from the Mason-Weaver equation because the centrifugal force depends on radius from the origin of rotation, whereas gravity is presumed constant. The Lamm equation also has extra terms, since it pertains to sector-shaped cells, whereas the Mason-Weaver equation pertains to box-shaped cells (i.e., cells whose walls are aligned with the three Cartesian axes).
Particles with a charge or dipole moment can be sedimented by an electric field or electric field gradient, respectively. These processes are called electrophoresis and dielectrophoresis, respectively. For electrophoresis, the sedimentation coefficient corresponds to the particle charge divided by its drag (the electrophoretic mobility). Similarly, for dielectrophoresis, the sedimentation coefficient equals the particle's electric dipole moment divided by its drag.
STAIRWAY
Stairs, staircase, stairway, and flight of stairs are all names for a construction designed to bridge a large vertical distance by dividing it into smaller vertical distances, called steps. Stairways may be straight, round, or may consist of two or more straight pieces connected at angles.
Special stairways include escalators and ladders. Alternatives to stairways are elevators, stairlifts and inclined moving sidewalks.
COMPONENTS AND TERMINOLOGY:
Step
The step is composed of the tread and riser.
tread - The part of the step that is stepped on. It is constructed to the same specifications (thickness) as any other flooring. The tread "width" is measured from the outer edge of the step to the vertical "riser" between steps.
riser - The vertical portion of the step between steps. This may be missing for an "open" stair effect.
nosing - An edge part of the tread that protrudes from the riser beneath. If it is present, this means that horizontally, the total "run" length of the stairs is not simply the sum of the tread lengths, the treads actually overlap each other slightly
bullnose - Where stairs are open on one or both sides, the first step above the lower floor may be wider than the other steps and rounded. The rounded portion of the step is called a "bullnose". The pickets typically form a semi-circle around the circumference of the bullnose and the handrail has a horizontal spiral called a "volute". Besides the cosmetic appeal, bullnoses allow the pickets to form a wider, more stable base for the end of the handrail. Handrails that simply end at a post at the foot of the stairs are usually unstable, even with a thick post. A double bullnose can be used when both sides of the stairs are open.
winders - Winders are steps that are narrower on one side than the other. They are used to change the direction of the stairs without landings. A series of winders form a circular or spiral stairway. When three steps are used to turn a 90° corner, the middle step is called a kite winder due to its similarity to a diamond-shaped kite.
stringer, stringer board or sometimes just string - The structural member that supports the treads. There are typically two stringers, one on either side of the stairs; though the treads may be supported many other ways. The stringers are notched so that the risers and treads fit into them. Stringers on open-sided stairs are often open themselves so that the treads are visible from the side. Such stringers are called "cut" stringers. Stringers on a closed side of the stairs are closed, with the support for the treads routed into the stringer.
trim - Trim (e.g. quarter-round or baseboard trim) is normally applied where walls meet floors. Within a flight of stairs there is no trim as the trim thickness will significantly eat into the tread width. Shoe moulding may be used between the lower floor and the first riser. Trimming a bullnose is a special challenge as the last riser above the lower floor is rounded. Today, special flexible, plastic trim is available for this purpose. Scotia is concave moulding that is underneath the nosing between the riser and the tread above it.
THE RAILING SYSTEM:
The balustrade is the complete system of railings and pickets that prevents people from falling over the edge.
banister, railing or handrail - The angled member for handholding, as distinguished from the vertical pickets which hold it up for stairs that are open on one side; there is often a railing on both sides, sometimes only on one side or not at all, on wide staircases there is sometimes also one in the middle, or even more. The term "banister" is sometimes used to mean just the handrail, or sometimes the handrail and the balusters or sometimes just the balusters[1].
volute - A handrail for the bullnose step that is shaped like a spiral. Volutes may be right or lefthanded depending on which side of the stairs they occur when facing up the stairs.
turnout - Instead of a complete spiral volute, a turnout is a quarter-turn rounded end to the handrail.
gooseneck - The vertical handrail that joins a sloped handrail to a higher handrail on the balcony or landing is a gooseneck.
rosette - Where the handrail ends in the wall and a half-newel is not used, it may be trimmed by a rosette.
easings - Wall handrails are mounted directly onto the wall with wall brackets. At the bottom of the stairs such railings flare to a horizontal railing and this horizontal portion is called a "starting easing". At the top of the stairs, the horizontal portion of the railing is called a "over easing".
core rail - Wood handrails often have a metal core to provide extra strength and stiffness, especially when the rail has to curve against the grain of the wood. The archaic term for the metal core is "core rail".
baluster - A term for the vertical pickets that hold the handrail. Sometimes simply called guards or spindles. Treads often require two balusters. The second baluster is closer to the riser and is taller than the first. The extra height in the second baluster is typically in the middle between decorative elements on the baluster. That way the bottom decorative elements are aligned with the tread and the top elements are aligned with the railing angle. However, this means the first and second balusters are manufactured separately and cannot be interchanged. Balusters without decorative elements can be interchanged.
newel - A large picket or post used to anchor the handrail. Since it is a structural element, it extends below the floor and subfloor to the bottom of the floor joists and is bolted right to the floor joist. A half-newel may be used where a railing ends in the wall. Visually, it looks like half the newel is embedded in the wall. For open landings, a newel may extend below the landing for a decorative newel drop.
baserail or shoerail - For systems where the baluster does not start at the treads, they go to a baserail. This allows for identical balusters, avoiding the second baluster problem.
fillet - A decorative filler piece on the floor between balusters on a balcony railing.
Handrails may be continuous (sometimes called over-the-post) or post-to-post (or more accurately ""newel-to-newel""). For continuous handrails on long balconies, there may be multiple newels and tandem caps to cover the newels. At corners, there are quarter-turn caps. For post-to-post systems, the newels project above the handrails.
Another, more classical, form of handrailing which is still in use is the Tangent method. A variant of the Cylindric method of layout, it allows for continuous climbing and twisting rails and easings. It was originally defined from principles set down by architect Peter Nicholson in the 18th century.
OTHER TERMS:
balcony - For stairs with an open concept upper floor or landing, the upper floor is functionally a balcony. For a straight flight of stairs, the balcony may be long enough to require multiple newels to support the length of railing. In modern homes, it is common to have hardwood floors on the first floor and carpet on the second. The homeowner should consider using hardwood nosing in place of carpet. Should the carpet be subsequently replaced with hardwood, the balcony balustrade may have to be removed to add the nosing.
flight - A flight is an uninterrupted series of steps.
floating stairs - A flight of stairs is said to be "floating" if there is nothing underneath. The risers are typically missing as well to emphasize the open effect. There may be only one stringer or the stringers otherwise minimized. Where building codes allow, there may not even be handrails.
landing or platform - A landing is the area of a floor near the top or bottom step of a stair. An intermediate landing is a small platform that is built as part of the stair between main floor levels and is typically used to allow stairs to change directions, or to allow the user a rest. As intermediate landings consume floor space they can be expensive to build. However, changing the direction of the stairs allows stairs to fit where they would not otherwise, or provides privacy to the upper level as visitors downstairs cannot simply look up the stairs to the upper level due to the change in direction.
runner - Carpetting that runs down the middle of the stairs. Runners may be directly stapled or nailed to the stairs, or may be secured by specialized bar that holds the carpet in place where the tread meets the riser.
spandrel - If there is not another flight of stairs immediately underneath, the triangular space underneath the stairs is called a "spandrel". It is frequently used as a closet.
staircase - This term is often reserved for the stairs themselves: the steps, railings and landings; though often it is used interchangeably with "stairs" and "stairway".
stairway - This term is often reserved for the entire stairwell and staircase in combination; though often it is used interchangeably with "stairs" and "staircase".
MEASURMENTS:
The rise height of each step is measured from the top of one tread to the next. It is not the physical height of the riser; the latter excludes the thickness of the tread.
The tread depth or length is measured from the edge of the nosing to the vertical riser. It is sometimes called the going.
The total run of the stairs is the horizontal distance from the first riser to the last riser. It is often not simply the sum of the individual tread lengths due to the nosing overlapping between treads.
The total rise of the stairs is the height between floors (or landings) that the flight of stairs is spanning.
The slope of the stairs is the total rise divided by the total run (not the individual riser and treads due to the nosing). It is sometimes called the rake or pitch of the stairs. The pitch line is the imaginary line along the tip of the nosing of the treads.
Headroom is the height above the nosing of a tread to the ceiling above it.
Walkline - For curved stairs, the inner radius of the curve may result in very narrow treads. The "walkline" is the imaginary line some distance away from the inner edge on which people are expected to walk. Building code will specify the distance. Building codes will then specify the minimum tread size at the walkline.
To avoid confusion, the number of steps in a set of stairs is always the number of risers, not the number of treads.
Ergonomics and Building Code requirements:
Ergonomically and for safety reasons, stairs have to have certain measurements in order for people to comfortably use them. Building codes will typically specify certain measurements so that the stairs are not too steep or narrow. Building codes will specify [2]:
minimum tread length, typically 9 inches (229 mm) including the nosing. However, most human feet are longer than 9 inches (229 mm), thus people's feet don't actually fit on the tread of the step.
maximum riser height, typically 8.25 inches (210 mm). Note that by specifying the maximum riser height and minimum tread length, a maximum slope is established. Residential building codes will typically allow for steeper stairs than public building codes.
minimum riser height: Some building codes also specify a minimum riser height, often 5 inches (125 mm).
Riser-Tread formula: Sometimes the stair parameters will be something like riser + tread equals 17-18 inches[3] or another formula is 2 times riser + tread equals 24 inches (610 mm). Thus a 7 inch (178 mm) rise and a ten inch (254 mm) tread exactly meets this code. If only a 2 inch (51 mm) rise is used then a 20 inch (508 mm) tread is required. This is based on the principle that a low rise is more like walking up a gentle incline and so the natural swing of the leg will be longer. This makes low rise stairs very expensive in terms of the space consumed. Such low rise stairs were built into the Winchester Mystery House to accommodate the infirmities of the owner, Sarah Winchester, before the invention of the elevator. These stairways, called "Easy Risers" consist of five flights wrapped into a multi turn arrangement with a total width equal to more than four times the individual flight width and a depth roughly equal to one flight's run plus this width. The flights have varying numbers of steps.
variance on riser height and tread depth between steps on the same flight should be very low. Building codes may specify variances as small as 0.25 inches (6.4 mm). The reason is that on a continuous flight of stairs, people get used to a regular step and may trip if there is a step that is different, especially at night. The general rule is that all steps on the same flight must be identical. Hence, stairs are typically custom made to fit the particular floor to floor height and horizontal space available. Special care must be taken on the first and last risers. Stairs must be supported directly by the subfloor. If thick flooring (e.g. thick hardwood planks) are added on top of the subfloor, it will cover part of the first riser, reducing the effective height of the first step. Likewise at the top step, if the top riser simply reaches the subfloor and thick flooring is added, the last rise at the top may be higher than the last riser. The first and last riser heights of the rough stairs are modified to adjust for the addition of the finished floor.
maximum nosing protrusion, typically 1.25 inches (32 mm) to prevent people from tripping on the nosing.
height of the handrail. This is typically between 34 and 38 inches (864 and 965 mm), measured to the nose of the tread. The minimum height of the handrail for landings may be different and is typically 36 inches (914 mm).
railing diameter. The size has to be comfortable for grasping and is typically between 1.25 and 2.675 inches (37 and 68 mm).
maximum space between the pickets of the handrail. This is typically 4 inches (102 mm).
openings (if they exist) between the bottom rail and treads are typically no bigger than 6 inches (152 mm).
minimum headroom
maximum vertical height between floors or landings. This allows people to rest and limits the height of a fall.
mandate handrails if there is more than a certain number of steps (typically 2 risers)
minimum width of the stairway, with and without handrails
not allow doors to swing over steps; the arc of doors must be completely on the landing/floor.
A Stairwell may be designated as an Area of refuge as well as a fire escape route, due to its fire-resistance rated design and fresh air supply.
Jacques Francois Blondel in his 1771 Cours d'architecture [4]was the first known person to establish the ergonomic relationship of tread and riser dimensions[5]. He specified that 2 x riser + tread = step length.[6]
It is estimated that a noticeable mis-step once in 7,398 uses and a minor accident on a flight of stairs occurs once in 63,000 uses.[7]
Stairs are not suitable for wheelchairs and other vehicles. A stairlift is a mechanical device for lifting wheelchairs up and down stairs. For sufficiently wide stairs, a rail is mounted to the treads of the stairs. A chair or lifting platform is attached to the rail. A person on the chair or platform is lifted as the chair or platform moves along the rail.
FORMS:
Stairs can take an infinite number of forms, combining winders and landings.
The simplest form is the straight flight of stairs, without any winders nor landings. It is not often used in modern homes because:
The upstairs is directly visible from the bottom of a straight flight of stairs.
It is dangerous in that a fall is not stopped until the bottom of the stairs.
A straight flight requires enough space for the entire run of the stairs.
Most modern stairs incorporate at least one landing. "L" shaped stairways have one landing and a change in direction by 90 degrees. "U" shaped stairs may employ a single wider landings for a change in direction of 180 degrees, or 2 landings for two changes in direction of 90 degrees each. Use of landings and a change of direction have the following advantages:
The upstairs is not directly visible from the bottom of the stairs, providing more privacy for the upper floor.
Falls are arrested at the landings
Even though the landings consume total floor space, there is no large single dimension, allowing better floorplan designs.
SPERICAL AND HERICAL STAIRS:
Spiral stairs wind around a central pole. They typically have a handrail on the outer side only, and on the inner side just the central pole. A squared spiral stair assumes a square stairwell and expands the steps and railing to a square, resulting in unequal steps (larger where they extend into a corner of the square). A pure spiral assumes a circular stairwell and the steps and handrail are equal and positioned screw-symmetrically. A tight spiral stair with a central pole is very space efficient in the use of floor area. A user of these stairs must take care to not step too close to the central pole as it becomes more likely that one or more steps may be missed, especially when going down. One should always take care to continuously use the handrail so that additional support is available in the event that a step is missed. Using the handrail will also direct the user to the safer outer portion of the treads.Spiral stairs in medieval times were generally made of stone and typically wound in a clockwise direction (from the ascendor's point of view), in order to place at a disadvantage attacking swordsmen who were most often right handed). This asymmetry forces the right handed swordsman to engage the central pike and degrade his mobility compared with the defender who is facing down the stairs. Extant 14th to 17th century examples of these stairways can be seen at Muchalls Castle, Crathes Castle and Myres Castle in Scotland.
Recent developments in manufacturing and design have led to the introduction of kit form spiral stair. Steps and handrails can be bolted together to form a complete unit. These stairs can be made out of steel, timber, concrete or a combination of materials.
Helical or circular stairs do not have a central pole and there is a handrail on both sides. These have the advantage of a more uniform tread width when compared to the spiral staircase. Such stairs may also be built around an elliptical or oval planform. A double helix is possible, with two independent helical stairs in the same vertical space, allowing one person to ascend and another to descend, without ever meeting if they choose different helixes (there is one at Château de Chambord). Fire escapes, though built with landings and straight runs of stairs, are often functionally double helixes, with two separate stairs intertwinned and occupying the same floor space. This is often in support of legal requirements to have two separate fire escapes.
Both spiral and helical stairs can be characterized by the number of turns that are made. A "quarter-turn" stair deposits the person facing 90 degrees from the starting orientation. Likewise there are half-turn, three-quarters-turn and full-turn stairs. A continuous spiral may make many turns depending on the height. Very tall multi turn spiral staircases are usually found in old stone towers within fortifications, churches and in lighthouses.
Winders may be used in combination with straight stairs to turn the direction of the stairs. This allows for a large number of permutations.
Special stairways include escalators and ladders. Alternatives to stairways are elevators, stairlifts and inclined moving sidewalks.
COMPONENTS AND TERMINOLOGY:
Step
The step is composed of the tread and riser.
tread - The part of the step that is stepped on. It is constructed to the same specifications (thickness) as any other flooring. The tread "width" is measured from the outer edge of the step to the vertical "riser" between steps.
riser - The vertical portion of the step between steps. This may be missing for an "open" stair effect.
nosing - An edge part of the tread that protrudes from the riser beneath. If it is present, this means that horizontally, the total "run" length of the stairs is not simply the sum of the tread lengths, the treads actually overlap each other slightly
bullnose - Where stairs are open on one or both sides, the first step above the lower floor may be wider than the other steps and rounded. The rounded portion of the step is called a "bullnose". The pickets typically form a semi-circle around the circumference of the bullnose and the handrail has a horizontal spiral called a "volute". Besides the cosmetic appeal, bullnoses allow the pickets to form a wider, more stable base for the end of the handrail. Handrails that simply end at a post at the foot of the stairs are usually unstable, even with a thick post. A double bullnose can be used when both sides of the stairs are open.
winders - Winders are steps that are narrower on one side than the other. They are used to change the direction of the stairs without landings. A series of winders form a circular or spiral stairway. When three steps are used to turn a 90° corner, the middle step is called a kite winder due to its similarity to a diamond-shaped kite.
stringer, stringer board or sometimes just string - The structural member that supports the treads. There are typically two stringers, one on either side of the stairs; though the treads may be supported many other ways. The stringers are notched so that the risers and treads fit into them. Stringers on open-sided stairs are often open themselves so that the treads are visible from the side. Such stringers are called "cut" stringers. Stringers on a closed side of the stairs are closed, with the support for the treads routed into the stringer.
trim - Trim (e.g. quarter-round or baseboard trim) is normally applied where walls meet floors. Within a flight of stairs there is no trim as the trim thickness will significantly eat into the tread width. Shoe moulding may be used between the lower floor and the first riser. Trimming a bullnose is a special challenge as the last riser above the lower floor is rounded. Today, special flexible, plastic trim is available for this purpose. Scotia is concave moulding that is underneath the nosing between the riser and the tread above it.
THE RAILING SYSTEM:
The balustrade is the complete system of railings and pickets that prevents people from falling over the edge.
banister, railing or handrail - The angled member for handholding, as distinguished from the vertical pickets which hold it up for stairs that are open on one side; there is often a railing on both sides, sometimes only on one side or not at all, on wide staircases there is sometimes also one in the middle, or even more. The term "banister" is sometimes used to mean just the handrail, or sometimes the handrail and the balusters or sometimes just the balusters[1].
volute - A handrail for the bullnose step that is shaped like a spiral. Volutes may be right or lefthanded depending on which side of the stairs they occur when facing up the stairs.
turnout - Instead of a complete spiral volute, a turnout is a quarter-turn rounded end to the handrail.
gooseneck - The vertical handrail that joins a sloped handrail to a higher handrail on the balcony or landing is a gooseneck.
rosette - Where the handrail ends in the wall and a half-newel is not used, it may be trimmed by a rosette.
easings - Wall handrails are mounted directly onto the wall with wall brackets. At the bottom of the stairs such railings flare to a horizontal railing and this horizontal portion is called a "starting easing". At the top of the stairs, the horizontal portion of the railing is called a "over easing".
core rail - Wood handrails often have a metal core to provide extra strength and stiffness, especially when the rail has to curve against the grain of the wood. The archaic term for the metal core is "core rail".
baluster - A term for the vertical pickets that hold the handrail. Sometimes simply called guards or spindles. Treads often require two balusters. The second baluster is closer to the riser and is taller than the first. The extra height in the second baluster is typically in the middle between decorative elements on the baluster. That way the bottom decorative elements are aligned with the tread and the top elements are aligned with the railing angle. However, this means the first and second balusters are manufactured separately and cannot be interchanged. Balusters without decorative elements can be interchanged.
newel - A large picket or post used to anchor the handrail. Since it is a structural element, it extends below the floor and subfloor to the bottom of the floor joists and is bolted right to the floor joist. A half-newel may be used where a railing ends in the wall. Visually, it looks like half the newel is embedded in the wall. For open landings, a newel may extend below the landing for a decorative newel drop.
baserail or shoerail - For systems where the baluster does not start at the treads, they go to a baserail. This allows for identical balusters, avoiding the second baluster problem.
fillet - A decorative filler piece on the floor between balusters on a balcony railing.
Handrails may be continuous (sometimes called over-the-post) or post-to-post (or more accurately ""newel-to-newel""). For continuous handrails on long balconies, there may be multiple newels and tandem caps to cover the newels. At corners, there are quarter-turn caps. For post-to-post systems, the newels project above the handrails.
Another, more classical, form of handrailing which is still in use is the Tangent method. A variant of the Cylindric method of layout, it allows for continuous climbing and twisting rails and easings. It was originally defined from principles set down by architect Peter Nicholson in the 18th century.
OTHER TERMS:
balcony - For stairs with an open concept upper floor or landing, the upper floor is functionally a balcony. For a straight flight of stairs, the balcony may be long enough to require multiple newels to support the length of railing. In modern homes, it is common to have hardwood floors on the first floor and carpet on the second. The homeowner should consider using hardwood nosing in place of carpet. Should the carpet be subsequently replaced with hardwood, the balcony balustrade may have to be removed to add the nosing.
flight - A flight is an uninterrupted series of steps.
floating stairs - A flight of stairs is said to be "floating" if there is nothing underneath. The risers are typically missing as well to emphasize the open effect. There may be only one stringer or the stringers otherwise minimized. Where building codes allow, there may not even be handrails.
landing or platform - A landing is the area of a floor near the top or bottom step of a stair. An intermediate landing is a small platform that is built as part of the stair between main floor levels and is typically used to allow stairs to change directions, or to allow the user a rest. As intermediate landings consume floor space they can be expensive to build. However, changing the direction of the stairs allows stairs to fit where they would not otherwise, or provides privacy to the upper level as visitors downstairs cannot simply look up the stairs to the upper level due to the change in direction.
runner - Carpetting that runs down the middle of the stairs. Runners may be directly stapled or nailed to the stairs, or may be secured by specialized bar that holds the carpet in place where the tread meets the riser.
spandrel - If there is not another flight of stairs immediately underneath, the triangular space underneath the stairs is called a "spandrel". It is frequently used as a closet.
staircase - This term is often reserved for the stairs themselves: the steps, railings and landings; though often it is used interchangeably with "stairs" and "stairway".
stairway - This term is often reserved for the entire stairwell and staircase in combination; though often it is used interchangeably with "stairs" and "staircase".
MEASURMENTS:
The rise height of each step is measured from the top of one tread to the next. It is not the physical height of the riser; the latter excludes the thickness of the tread.
The tread depth or length is measured from the edge of the nosing to the vertical riser. It is sometimes called the going.
The total run of the stairs is the horizontal distance from the first riser to the last riser. It is often not simply the sum of the individual tread lengths due to the nosing overlapping between treads.
The total rise of the stairs is the height between floors (or landings) that the flight of stairs is spanning.
The slope of the stairs is the total rise divided by the total run (not the individual riser and treads due to the nosing). It is sometimes called the rake or pitch of the stairs. The pitch line is the imaginary line along the tip of the nosing of the treads.
Headroom is the height above the nosing of a tread to the ceiling above it.
Walkline - For curved stairs, the inner radius of the curve may result in very narrow treads. The "walkline" is the imaginary line some distance away from the inner edge on which people are expected to walk. Building code will specify the distance. Building codes will then specify the minimum tread size at the walkline.
To avoid confusion, the number of steps in a set of stairs is always the number of risers, not the number of treads.
Ergonomics and Building Code requirements:
Ergonomically and for safety reasons, stairs have to have certain measurements in order for people to comfortably use them. Building codes will typically specify certain measurements so that the stairs are not too steep or narrow. Building codes will specify [2]:
minimum tread length, typically 9 inches (229 mm) including the nosing. However, most human feet are longer than 9 inches (229 mm), thus people's feet don't actually fit on the tread of the step.
maximum riser height, typically 8.25 inches (210 mm). Note that by specifying the maximum riser height and minimum tread length, a maximum slope is established. Residential building codes will typically allow for steeper stairs than public building codes.
minimum riser height: Some building codes also specify a minimum riser height, often 5 inches (125 mm).
Riser-Tread formula: Sometimes the stair parameters will be something like riser + tread equals 17-18 inches[3] or another formula is 2 times riser + tread equals 24 inches (610 mm). Thus a 7 inch (178 mm) rise and a ten inch (254 mm) tread exactly meets this code. If only a 2 inch (51 mm) rise is used then a 20 inch (508 mm) tread is required. This is based on the principle that a low rise is more like walking up a gentle incline and so the natural swing of the leg will be longer. This makes low rise stairs very expensive in terms of the space consumed. Such low rise stairs were built into the Winchester Mystery House to accommodate the infirmities of the owner, Sarah Winchester, before the invention of the elevator. These stairways, called "Easy Risers" consist of five flights wrapped into a multi turn arrangement with a total width equal to more than four times the individual flight width and a depth roughly equal to one flight's run plus this width. The flights have varying numbers of steps.
variance on riser height and tread depth between steps on the same flight should be very low. Building codes may specify variances as small as 0.25 inches (6.4 mm). The reason is that on a continuous flight of stairs, people get used to a regular step and may trip if there is a step that is different, especially at night. The general rule is that all steps on the same flight must be identical. Hence, stairs are typically custom made to fit the particular floor to floor height and horizontal space available. Special care must be taken on the first and last risers. Stairs must be supported directly by the subfloor. If thick flooring (e.g. thick hardwood planks) are added on top of the subfloor, it will cover part of the first riser, reducing the effective height of the first step. Likewise at the top step, if the top riser simply reaches the subfloor and thick flooring is added, the last rise at the top may be higher than the last riser. The first and last riser heights of the rough stairs are modified to adjust for the addition of the finished floor.
maximum nosing protrusion, typically 1.25 inches (32 mm) to prevent people from tripping on the nosing.
height of the handrail. This is typically between 34 and 38 inches (864 and 965 mm), measured to the nose of the tread. The minimum height of the handrail for landings may be different and is typically 36 inches (914 mm).
railing diameter. The size has to be comfortable for grasping and is typically between 1.25 and 2.675 inches (37 and 68 mm).
maximum space between the pickets of the handrail. This is typically 4 inches (102 mm).
openings (if they exist) between the bottom rail and treads are typically no bigger than 6 inches (152 mm).
minimum headroom
maximum vertical height between floors or landings. This allows people to rest and limits the height of a fall.
mandate handrails if there is more than a certain number of steps (typically 2 risers)
minimum width of the stairway, with and without handrails
not allow doors to swing over steps; the arc of doors must be completely on the landing/floor.
A Stairwell may be designated as an Area of refuge as well as a fire escape route, due to its fire-resistance rated design and fresh air supply.
Jacques Francois Blondel in his 1771 Cours d'architecture [4]was the first known person to establish the ergonomic relationship of tread and riser dimensions[5]. He specified that 2 x riser + tread = step length.[6]
It is estimated that a noticeable mis-step once in 7,398 uses and a minor accident on a flight of stairs occurs once in 63,000 uses.[7]
Stairs are not suitable for wheelchairs and other vehicles. A stairlift is a mechanical device for lifting wheelchairs up and down stairs. For sufficiently wide stairs, a rail is mounted to the treads of the stairs. A chair or lifting platform is attached to the rail. A person on the chair or platform is lifted as the chair or platform moves along the rail.
FORMS:
Stairs can take an infinite number of forms, combining winders and landings.
The simplest form is the straight flight of stairs, without any winders nor landings. It is not often used in modern homes because:
The upstairs is directly visible from the bottom of a straight flight of stairs.
It is dangerous in that a fall is not stopped until the bottom of the stairs.
A straight flight requires enough space for the entire run of the stairs.
Most modern stairs incorporate at least one landing. "L" shaped stairways have one landing and a change in direction by 90 degrees. "U" shaped stairs may employ a single wider landings for a change in direction of 180 degrees, or 2 landings for two changes in direction of 90 degrees each. Use of landings and a change of direction have the following advantages:
The upstairs is not directly visible from the bottom of the stairs, providing more privacy for the upper floor.
Falls are arrested at the landings
Even though the landings consume total floor space, there is no large single dimension, allowing better floorplan designs.
SPERICAL AND HERICAL STAIRS:
Spiral stairs wind around a central pole. They typically have a handrail on the outer side only, and on the inner side just the central pole. A squared spiral stair assumes a square stairwell and expands the steps and railing to a square, resulting in unequal steps (larger where they extend into a corner of the square). A pure spiral assumes a circular stairwell and the steps and handrail are equal and positioned screw-symmetrically. A tight spiral stair with a central pole is very space efficient in the use of floor area. A user of these stairs must take care to not step too close to the central pole as it becomes more likely that one or more steps may be missed, especially when going down. One should always take care to continuously use the handrail so that additional support is available in the event that a step is missed. Using the handrail will also direct the user to the safer outer portion of the treads.Spiral stairs in medieval times were generally made of stone and typically wound in a clockwise direction (from the ascendor's point of view), in order to place at a disadvantage attacking swordsmen who were most often right handed). This asymmetry forces the right handed swordsman to engage the central pike and degrade his mobility compared with the defender who is facing down the stairs. Extant 14th to 17th century examples of these stairways can be seen at Muchalls Castle, Crathes Castle and Myres Castle in Scotland.
Recent developments in manufacturing and design have led to the introduction of kit form spiral stair. Steps and handrails can be bolted together to form a complete unit. These stairs can be made out of steel, timber, concrete or a combination of materials.
Helical or circular stairs do not have a central pole and there is a handrail on both sides. These have the advantage of a more uniform tread width when compared to the spiral staircase. Such stairs may also be built around an elliptical or oval planform. A double helix is possible, with two independent helical stairs in the same vertical space, allowing one person to ascend and another to descend, without ever meeting if they choose different helixes (there is one at Château de Chambord). Fire escapes, though built with landings and straight runs of stairs, are often functionally double helixes, with two separate stairs intertwinned and occupying the same floor space. This is often in support of legal requirements to have two separate fire escapes.
Both spiral and helical stairs can be characterized by the number of turns that are made. A "quarter-turn" stair deposits the person facing 90 degrees from the starting orientation. Likewise there are half-turn, three-quarters-turn and full-turn stairs. A continuous spiral may make many turns depending on the height. Very tall multi turn spiral staircases are usually found in old stone towers within fortifications, churches and in lighthouses.
Winders may be used in combination with straight stairs to turn the direction of the stairs. This allows for a large number of permutations.
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