Archive:New Draft of the Week

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The New Draft of the Week is a chance to highlight a recently created Citizendium article that has just started down the road of becoming a Citizendium masterpiece.
It is chosen each week by vote in a manner similar to that of its sister project, the Article of the Week.

Current Nominees

The next New Draft of the Week will be the article with the most votes at 1 AM UTC on Thursday, 11 June 2009. I did the honors this time. Milton Beychok 07:06, 5 June 2009 (UTC)

Text in this section is transcluded from the respective Citizendium entries and may change when these are edited.

Nominated article Supporters Specialist supporters Dates Score
Developing Article Air preheater: A general term to describe any device designed to preheat the combustion air used in a fuel-burning furnace for the purpose of increasing the thermal efficiency of the furnace. [e]
(PD) Image: Milton Beychok
Schematic diagram of a steam generator in a conventional coal-fired power plant.

An air preheater (APH) is a general term to describe any device designed to preheat the combustion air used in a fuel-burning furnace for the purpose of increasing the thermal efficiency of the furnace.

In particular, this article describes the combustion air preheaters for the large fuel-burning furnaces used to generate steam in thermal power plants. The air preheater increases the steam generator's thermal efficiency by preheating the combustion air with heat recovered from the hot combustion flue gases (see the adjacent diagram).

Types

The two most often used categories of air preheaters in thermal power plants are regenerative air preheaters and tubular air preheaters.[1][2][3][4]

Regenerative air preheaters

The two most common types of regenerative air preheaters are

  • The rotating-plate regenerative air preheater, often referred to as a RAPH. The RAPH was invented by Fredrik Ljungström, who was a Swedish engineer, and is also called a Ljungström air preheater.
  • The stationary-plate regenerative air preheater, often referred to as a Rothemuhle because Rothemühle is the German town where the original manufacturer produced them for many years.

Regenerative air preheaters may also be categorized as recuperators, which are special types of heat exchangers designed to recover or reclaim heat in order to reuse or recycle it.

Rotating-plate regenerative air preheater

(PD) Image: U.S. Environmental Protection Agency
A typical rotating-plate regenerative air preheater.[2]
The rotating-plate air preheater (RAPH) consists of a central rotating-plate element installed within a casing that is divided into sectors. There are three basic designs for the rotating-plate element:[5][6]
(PD) Image: U.S. Environmental Protection Agency
A typical rotating-plate regenerative air preheater.[2]
  • The bi-sector design has two sectors.
  • The tri-sector design has three sectors.
  • The quad-sector design has four sectors.

In the tri-sector design, the steam generator's hot flue gas flows through the largest sector (usually spanning about half the cross-section of the casing) and transfers some of its heat into the heat-absorbing material within the rotating wheel element. The cooled flue gas is then routed to further treatment in dust removal and other equipment before being vented from the flue gas stack. Ambient air is blown through the second, smaller sector by a centrifugal fan and absorbs heat from the heated material as it rotates through that smaller sector. The heated air then flows into the steam generating furnace as combustion air. The third sector is the smallest one and it heats a portion of the ambient air which is then routed into the coal pulverizations and is used to transport the coal-air mixture to coal burners. Thus, the total air heated in the RAPH provides: heated primary combustion air, heated air to remove moisture from the pulverized coal and carrier air for transporting the pulverized coal to the coal burners. Since the flue gas pressure is lower than the pressure of the air being heated, there is some small leakage (between the sectors) of flue gas into the air.

The bi-sector design is used in thermal power plants burning fuels (such as oil or gas) that do not require pulverizing or removal of moisture and therefore have need for heated air other than for combustion air.

The quad-sector design has a large sector heated by flue gas and three air-heating sectors: one is for the combustion air and that sector is flanked by two smaller air sectors. In applications such as circulating fluid bed (CFB) combustion systems where the differential between the air pressure and the flue gas pressure is even higher than in a conventional coal-fired steam generator, flue gas pressure, such a design is ideal since it acts to reduce the leakage of air into the flue gas.[6]

The rotating wheel element rotates quite slowly (around 3-5 revolutions per minute) to allow optimum heat transfer first from the hot exhaust gases to the element and then, as it rotates, from the element to the air in the other sectors.

Construction features

The heat-absorbing material in the rotating wheel element consists of vertical corrugated plates pressed into steel baskets, with sufficient space between the plates for the flue gas to pass through. The plates are corrugated to provide more surface area for the heat to be absorbed and also to provide needed rigidity. The baskets are designed to be replaceable as needed.

The vertical shaft that rotates the wheel is supported on thrust bearings at the lower end lubricated with an oil bath that is cooled by water circulating in coils inside the oil bath. Cooling of the bottom end of the shaft is needed since that is where the hot flue gas enters the preheater. The top end of the shaft has a simple roller bearing to hold the shaft in a vertical position.

Radial supports and cages for holding the corrugated plate baskets in position are attached to the rotating shaft. Radial and circumferential seal plates are also provided to minimize leakage of flue gas or air between the sectors.

For cleaning of the baskets while in operation, steam jets are provided to blow any fly ash (deposited by the flue gas) into an ash hopper below the preheater.

The rotating shaft is driven by a motor and gearing. To avoid uneven thermal expansion and contraction resulting in damage to the rotating wheel, the rotation must be started before starting the steam generator and must also be kept in rotation for some time after the steam generator is shut down.

The baskets of corrugated plates are subject to abrasive and corrosive wear from the fly ash and corrosive gases in the flue gas. Hence frequent replacements are required and new baskets are always kept on hand and ready for use.

Stationary-plate regenerative air preheater

(PD) Image: Milton Beychok
A typical stationary-plate regenerative air preheater.

The heat absorbing element in this type of regenerative air preheater is stationary rather than rotating. Instead, the air ducts in the preheater are rotated so as to alternately expose sections of the heating absorbing element to the upflowing air.

The hot flue gas enters at the top of the preheater and flows down through those exposed sections of the stationary heat-absorbing element that are not blocked by the rotating air outlet ducts, thus heating those sections of the stationary element. As the air ducts slowly rotate around, they pass over the heated sections and the incoming air is heated as it flows upward through those heated sections.

As indicated in the adjacent drawing, there are rotating inlet air ducts (inside the outer casing) at the bottom of the stationary heat absorbing element as well as the rotating outlet air ducts at the top of the stationary element.

The basic heat transfer principals of the stationary-plate regenerative preheater are the same as for the rotating-plate regenerative preheater. The table below provides a comparison of some design parameters between the rotating-plate and stationary-plate preheaters:

Some Comparisons Between Rotating-plate
and Stationary-plate Regenerative Air Preheaters[7]
  Rotating-plate Stationary-plate
Revolutions per minute 1.5 – 4.0 (a) 0.7 – 1.4 (b)
Gas flow area, % of total 40 – 50 50 – 60
Air flow area, % of total 35 – 45 35 – 45
Seal section area, % of total 8 – 17 5 – 10
(a) Revolutions per minute of the rotating plate element
(b) Revolutions per minute of the rotating air ducts

Tubular type

(PD) Image: Milton Beychok
A typical tubular air preheater[8]

Tubular air preheaters may have a number of configurations:[2][8][9]

  1. A bundle of vertical tubes through which the flue gas flows downward (see adjacent diagram) and exchanges heat with ambient air flowing horizontally across the exterior of the tubes. Baffles are usually provided so that the air flows across the tubes a number of times. For example, as shown in the adjacent diagram, the air flow across the tubes three times and is referred to as 3-pass tubular air preheater.
  2. The same as (1) above except that the flue gas flows upward rather than downward.
  3. A bundle of horizontal tubes through which the air flows and exchanges heat with the hot flue gas flowing downward across the tube bundle. In some designs, there may be three separate horizontal tube bundles one above the other. The air enters the lower tube bundle from the right-hand side, exits on the left-hand side and then enters the middle tube bundle on the left-hand side and exits on the right-hand side. Finally, the air enters the upper tube bundle on the right-hand side and exits on the left-hand side. In essence, such a design is similar to the 3-pass design of (1) above except that the air is in the tubes rather than outside the tubes.

A number of new circulating fluid bed (CFB) and bubbling fluid bed (BFB) steam generators are using tubular air preheaters, which avoids the air leakage associated with regenerative air preheaters.

Dew point corrosion

The water dew point of air or any other gas containing water vapor usually refers to the temperature (for a given pressure) at which the air or gas is saturated with water vapor. That means that the air or gas is at the point where the water vapor will start to condense into liquid water if the temperature is lowered beyond that point.

As a broad generality, the combustion flue gases from steam generators fueled by coal, fuel oil, natural gas, or biomass are composed of carbon dioxide (CO2) and water vapor (H2O) as well as nitrogen and excess oxygen remaining from the intake combustion air. Typically, more than two-thirds of the flue gas is nitrogen. The combustion flue gases may also contain small percentages of air pollutants such as particulate matter, carbon monoxide, nitrogen oxides, and sulfur oxides in the form of gaseous sulfur dioxide (SO2) and gaseous sulfur trioxide (SO3). The SO3 is present because a portion of the SO2 formed in the combustion of the sulfur compounds in the steam generator's furnace fuel is further oxidized to SO3 as the flue gas travels through the superheater and reheater sections of the steam generator (see the above diagram of a steam generator). The gas phase SO3 then combines the vapor phase H2O to form gas phase sulfuric acid H2SO4:[10]

H2O + SO3 → H2SO4

Because of the presence of gaseous sulfuric acid, the dew point of most flue gases is much higher than the water dew point of air and the flue gas dew point is referred to as the acid dew point. That is the flue gas temperature at which acid will begin to condense out of the flue gas if the temperature is lowered beyond that point. For example, a flue gas with 5 volume % water vapor and containing no acid gases has a water dew point of about 32 °C (90 °F). The same flue gas with the addition of only 0.01 volume percent of SO3 will have an acid dew point of about 118 °C (244 °F).[11]

The acid dew point of a combustion flue gas depends upon the composition of the specific fuel being burned and the resultant composition of the flue gas. Given a flue gas composition, its acid dew point can be predicted fairly closely. As an approximation, the acid dew points of flue gases from thermal power plants range from about 120 °C to about 150 °C (250 to 300 °F).

All of the air preheater types incur erosion problems to some extent from the fly ash particles in the flue gas. If the hot flue gas temperature in an air preheater is lowered to below its acid dew point, then the air preheater also incurs corrosion problems which can be quite severe. That is especially true of the tubular air preheaters. For that reason, many air preheaters have a means for the air to partially bypass the air preheater (see above tubular air preheater diagram) so that the amount of heat exchange can be controlled to avoid lowering the flue gas temperature below the acid dew point.

To mitigate dew point corrosion, the tubular air preheaters may use ceramic or Teflon-coated tubes and the regenerative air preheaters may use special corrosion-resistant steels or enameled materials.

The addition of limestone (CaCO3) into circulating fluidized bed (CFB) steam generators results in capturing 95% or more of the gaseous SO2 in the combustion product gases as solid calcium sulfate (Ca2SO4) and that occurs before the SO2 has time to be further oxidized to SO3. Thus, the acid dew point of the flue gas from a CFB steam generator is higher than from conventional thermal power plant steam generators. That means that the air preheaters in CFB units have considerably less dew point corrosion problems. That may also be one of the reasons why a number of the newer CFB units are using tubular preheaters.

References

  1. ↑ Sadik Kakaç and Hongtan Liu (2002). Heat Exchangers: Selection, Rating and Thermal Design, 2nd Edition. CRC Press. ISBN 0-8493-0902-6. 
  2. ↑ 2.0 2.1 2.2 2.3 Course SI:428A Online publication of the U.S. Environmental Protection Agency‎'s Air Pollution Training Institute, known as APTI (Scroll down to page 23 of 28)
  3. ↑ Sadik Kakaç (Editor) (April, 1991). Boilers. Evaporators and Condensers. Wiley Interscience. ISBN 0-471-62170-6.  (See Chapter 8 by Z.H. Lin)
  4. ↑ Lawrence Drbak, Patricia Boston, Kalya Westra, and R. Bruce Erickson (Editors) (1996). Power Plant Engineering (Black and Veatch). Chapman & Hall. ISBN 0-412-06401-4. 
  5. ↑ The Ljungström® Air Preheater
  6. ↑ 6.0 6.1 Ljungström® Air Preheater Arrangements
  7. ↑ Prabir Basu, Kefa Cen and Louis Jestin (1999). Boilers and Burners: Design and Theory, 1st Edition. Springer. ISBN 0-387-98703-7. 
  8. ↑ 8.0 8.1 http://www.egcfe.ewg.apec.org/Documents/Costs&EffectivenessofUpgradingOlderCoal-FiredPowerPlantsFina.pdf Costs and effectiveness of upgrading and refurbishing older coal-fired power plants in developing APEC economies] Asia-Pacific Economic Cooperation (APEC) Energy Working Group, Expert Group on Clean Fossil Energy, June 2005
  9. ↑ Performance Analysis of Primary Air Heater Under Particulate Condition in Lignite-Fired Power Plant Journal of Engineering, Computing and Architecture, Vol. 1, Issue 2, 2007
  10. ↑ Predicting Sulfuric Acid Emissions from Power Plants]
  11. ↑ Burning Sulfur Compounds A publication of the Banks Engineering Company of Oklahoma.
 (Read more...) 		Daniel Mietchen;
Caesar Schinas 		Milton Beychok 5


Developing Article Proteus mirabilis: A Gram-negative, rod-shaped bacteria belonging to the enterobacteriaceae family; causes 90% of human infections with Proteus species, usually community-acquired [e]
Proteus Mirabilis
800px-Proteus mirabilis 01.jpg
Scientific classification
Kingdom: Bacteria
Phylum: Proteobacteria
Class: Gamma Proteobacteria
Order: Enterobacteriales
Family: Enterobacteriaceae
Genus: Proteus
Species: Mirabils
Binomial name
Proteus mirabilis

Proteus mirabilis is a Gram-negative, rod-shaped bacterium belonging to the enterobacteriaceae family.[1] It is facultatively anaerobic, not requiring oxygen for survival and reproduction and may even die in the presence of oxygen. Proteus mirabilis are found free-living in moist habitats, such as [water] and soil. They are mostly inhabitants of urinary tracts of human where they cause infections that are related with formation of renal and bladder calculi, also known as bladder stones.

It is a significant, if not highly lethal, pathogen of humans, most often in the urinary tract. This species causes 90% of human Proteus infections and is usually community-acquired. P. vulgaris is more likely to be hospital-acquired (i.e., nosocomial).

Genome structure

Similarly to other Gram-negative bacteria, Proteus mirabilis contains an extracytoplamic outer membrane. In addition, the outer membrane contains a lipid bilayer, lipoproteins, polysaccharides, and lipopolysaccharides.[1] Various components of the membrane interplay with the host to determine virulence. Proteus mirabilis possesses flagella which play an important role in the bacteria's swarming motility and pathogenicity.[2]

Its genome has been completely sequenced. Pearson says. "Part of our goal is finding potential targets for new vaccines that could protect people from infection." In cases where stones form, the bacteria can become resistant to antibiotics," says Harry L.T. Mobley, Ph.D., professor and chair of microbiology and immunology in the U-M Medical School. Mobley is an expert on urease. Pearson's study explains why the bacterium has the ability to stick to some surfaces such as those of kidney or bladder stones. "This bacterium has an unusually high number of genes that encode for 15 different adherence factors or fimbriae on its surface," Pearson explains. "All these different fimbriae help the bacterium stick to bladder cells, catheters, kidney stones or each other.

Pearson also discovered that the Proteus mirabilis genome is made up of 24 genes that encode components of a system used to inject bacterial proteins into host cells. In future research, Pearson will use gene micro arrays to identify the Proteus mirabilis genes that are turned on, or expressed, during the infection stage. Genes involved in the infection process will be prime targets for future vaccine development, according to Pearson, although she says that years of additional research will be needed before vaccines could be commercially available.[3]

The genome of Proteus mirabilis is .063 Mb long and has a G+C content of 38.88%. There is a single plasmid consisting of 36,289 nucleotides. Annotation of the genome is identified 3,685 coding sequences and seven rRNA loci. Analysis of the sequence confirmed the presence of previously identified virulence determinants, as well as a contiguous 54-kb flagellar regulon and 17 types of fimbriae. Genes encoding a potential type III secretion system were identified on a low-G+C-content genomic island containing 24 intact genes that appear to encode all components necessary to assemble a type III secretion system needle complex. In addition, the P. mirabilis HI4320 genome possesses four tandem copies of the zapE metalloprotease gene, genes encoding six putative autotransporters, an extension of the atf fimbrial operon to six genes, including an mrpJ homolog, and genes encoding at least five iron uptake mechanisms, two potential type IV secretion systems, and 16 two-component regulators.[4]

Morphology

Raft formation

Proteus can display two different morphological and physiological forms; one is known as the swimmer cells and the other as swarmer cells. In aqueous suspension Proteus mirabilis is found in the swimmer state, which is a small rod-like cells1 to 2 μm in length. They contain 8 to 10 flagella that aid in their swimming motility. On contact with a surface, Proteus mirabilis changes to the swarmer state where the cell considerably increases in length to form highly flagellated filaments that are 20 to 80 μm in length. These cells line up in parallel to form rafts that are able to move rapidly over surfaces en masse. On semi-solid surfaces such as an agar surface, they form concentric rings of growth. This pattern is caused by the coordinated burst of swarming activity interspeded with a consolidation to the swimmer state..[5]

P. mirabilis on agar

An important feature of Proteus mirabilis is their swarming motility, facilitated by peritrichous flagella, which is a rapid and coordinated translocation of a bacterial population across solid or semi-solid surfaces. This ability aids them in food acquisition, reproduction and growth. It also aids the bacteria in expressing its virulence factors and invading hosts’ urothelial cells.

Metabolism

Metabolism of P. mirabilis

They have the ability to produce urease, which is an enzyme that hydrolyzes urea to ammonia. In fact, Proteus mirabilis utilizes urea and citrate. It is therefore trivial for them to live in highly alkalinated environments. The bacterium also produces hydrogen sulfide gas, which aids in forming clear films on growth media, which can be distinguished as growth or concentric rings.[5].

Ecology

Proteus mirabilis are found free-living in moist habitats, such as water and soil. They are also found in putrid meat, infusions, and abscesses. They are mostly inhabitants of urinary tracts of human where it is believed to cause urinary tract infections associated with formation of renal and bladder calculi, often known as bladder stones. Proteus mirabilis require an environment that has high alkalinity, meaning that the concentration of alkali in the solution, which is measured in terms of pH, must be high. A suitable environment for Proteus mirabilis must have a pH higher than 7.[1]

Pathology

This organism causes 90% of human infections with Proteus species. It is primarily community-acquired, and most frequent in the urinary tract. [1]

Proteus mirabilis is a significant pathogen of the urinary tract. Urinary tract infection is a process following certain steps; it first starts with colonization of the bladder, which causes cystitis. Then, the infection proceeds to the kidneys, which leads to acute pyelonephritis, chronic inflammation and at last renal failure, which if left untreated, can cause death.[2]

Proteus mirabilis is highly virulent and contains many characteristics that aid in its pathogenicity. It possesses a flagella which is necessary for motility and is involved in causing infections. It also produces urease, which is responsible for the formation of bladder and kidney stones as a result of the hydrolysis of urea to ammonia. Furthermore, the hemolysin that the bacterium secretes is cytotoxic for urinary tract epithelial cells which are subject to invasion by the proteus.[2] The bacterium's swarming motility also plays an important role in renal infections, which involve colonization of the lower urinary tract, followed by ascending movement of the bacterium. It is believed that the swarming motility is correlated with the effective invasion of hosts’ epithelia cells, as it provides the ability to move rapidly and therefore to rapidly colonize and invade the cells.

Inhibition of virulence factor expression and swarming differentiation of Proteus mirabilis by p-nitrophenylglycerol (PNPG)

It was found that PNPG could prevent Proteus mirabilis from growing and moving rapidly. according to a journal, PNPG inhibits the growth rate and swarming differentiation and activities of Proteus mirabilis. PNPG also inhabits the production of virulence factors such as urease, protease and hemolysin. It was found that in the presence of PNPG, the invasion hosts' epithelial cells diminished dramatically. This is due to the fact that PNPG contains certains agents that impair the proper function of Proteus mirabilis; the clinical significance needs to be assessed.[2]

Reference

  1. ↑ 1.0 1.1 1.2 1.3 Kelley Struble, Michael Stuart Bronze, Rhett L Jackson, Gus Gonzalez, (31 July 2009), "Proteus Infections: Overview", eMedicine
  2. ↑ 2.0 2.1 2.2 2.3 Liaw S-J et al. (2000), "Inhibition of virulence factor expression and swarming expresssion in P. mirabilis by p-nitrophenyglycerol", J. Medical Microbiology 49: 725-731
  3. ↑ "Proteus Mirabilis Will Give Up Its Genetic Secrets At ASM Meeting", Medical News Today, 25 May 2006
  4. ↑ Pearson MM et al. (June 2008; epub March 2008), "Complete genome sequence of uropathogenic Proteus mirabilis, a master of both adherence and motility.", J Bacteriol. 190 (11): 4027-37
  5. ↑ 5.0 5.1 Proteus mirabilis, Biomed Health Technology Cooperative
 (Read more...) 		Milton Beychok Daniel Mietchen 4


Developing Article Wrench (tool): A fastening tool used to tighten or loosen threaded fasteners, with one end that makes firm contact with flat surfaces of the fastener, and the other end providing a means of applying force [e]

A wrench (American English), or spanner (British English), is a fastening tool used to manipulate threaded fasteners such as nuts, studs and bolts. They also may manipulate threaded structural elements such as pipes. The wrench is sized and shaped to put pressure and leverage on flat faces of the fastener, and then is moved in the direction of rotation needed to loosen or tighten the fastening assembly.

Hand tools

The most common hand wrenches are made either from a flat bar of steel, or from cylinders. Even with these two types, the wrench can either completely or partially surround the fastener.

Flat Bar

The most common hand wrenches either are open-ended, such that they have sides parallel to two or more facets of the nut, or box, which surrounds all sides of the nut. These types can drop over the nut no matter how much of the screw or bolt protrudes.

The longer the handle of the wrench, the more force can be applied to the fastener. One technique is to carry a length of pipe, which can slip over the wrench and act as a handle extender. Do be warned, however, that a sufficiently long pipe can exert enough force to break the wrench or the fastener.

Double-sided open-end wrench
Double-sided box-end wrench

Still, there are times when it is absolutely necessary to release a stuck fastener. It is usually wise first to apply a penetrating lubricant to the fastener, and tap it gently to let the lubricant reach the threads, waiting briefly before applying force. Yet another dangerous but sometimes necessary technique is to hit the handle of the wrench with a hammer; do remember to hit it in the direction in which the fastener needs to turn. Gloves and eye protection are wise precautions when hammering a wrench. An even more desperate expedient is to heat the fastener to expand it, which may destroy the hardness or toughness of the metal. Occasionally, it is possible to chill the piece to which the fastener is attached, contracting it and helping break the adhesion.

For some specialized applications, typically where only authorized persons are to adjust the fastener, the sides of the wrench head may not be parallel. For example, the nuts on fire hydrants are pentagonal, so they cannot be manipulated with a standard wrench shape.

Combination wrench

(CC) Photo: Derek Hodges
A combination wrench
A combination wrench has a one open and one box end, usually of the same size. The open end is more useful when there is limited access to the fastener. Box ends can get a better grip when the flats of the nut are deformed.

Adjustable open wrench

PD Image
Adjustable wrench

An adjustable wrench has one fixed jaw, and one that is adjustable by means of a screw adjustment, usually made in one piece with the adjustable jaw. In the U.S., this is often called a Crescent wrench after the first well-known manufacturer, while it is a Bahco wrench in Dutch usage, after the Swedish manufacturer. The obvious advantage of the adjustable wrench is that an entire set of wrenches need not be carried when the size of the fastener to be adjusted is not known. The disadvantage is that the adjustment can slip, and generally cannot apply as much force as a solid wrench.

It should be mentioned, if mostly to condemn the practice, that pliers are sometimes used to adjust nuts. Most types of pliers, however, do not have parallel jaws, but angled ones. These are apt to deform a nut if heavy pressure is applied.

Pipe wrench

Pipe wrench

Pipe wrenches grasp threaded pipes and turn them, so they do not have flat jaws. One common type has curved jaws, with the wrench designed to slip slightly so it can be repositioned as the pipe moves under it. These were called Stillson wrenches after the inventor; they are sometimes, incorrectly, called monkey wrenches.

Another type does not have jaws, but instead a chain that tensions against the pipe.

Some plumbing fixtures have a nut-like shape molded into the metal, so that a flat-jawed wrench can be used. This is the application intended for the increasingly rare monkey wrench.

Socket wrenches and nutdrivers

Sockets proper are single pieces of cast or machined metal, with one end shaped to slip over the fastener to be manipulated, and the other to receive a driveshaft to turn it. The shaft end may actually have a depression, or even a spring-loaded bearing, to help lock the shaft into place. In combination, the driveshaft and socket are extremely strong in rotation, but should separate easily with linear traction.

Where the English measurement system is used, the shaft diameter is most often 3/8" or 1/4" for general purposes. 1/2", 3/4", and 1" drives are used for heavy equipment. Both metric and English system sockets, however, can snap onto the male end of the shaft.

Adapters are available to convert between shaft sizes. For example, one might have a large nut but only a 1/4" shaft system, so an adapter can allow a 3/8" socket to be used with that shaft.

Basic handle and extension

The most basic driver is a shaft with a handle, much like a screwdriver, but with a socket-mating connector rather than a screwdriver bit. Another very common variant, called an extension, has a male connector that mates with the socket at one end, and a female connector that accepts another socket tool at the other. Multiple extensions can be snapped together for extra length.

Nutdrivers

Nutdrivers are a permanently attached set of socket, driveshaft, and handle. Some nutdrivers have hollow shafts, so bolt length protruding above the nut goes into the hollow and does not interfere with rotation.

Aids to leverage

Most often, however, at the end of the extension away from the socket, a tool to improve the leverage of driving is attached. One such tool is a ratchet, which, at first, looks like an open-ended or box wrench. The male connector, however, is attached to a disk and mechanical components inside the ratchet head. There is a small control that selects the direction (i.e., loosening or tightening) in which the socket is to be moved. Once that control is set, the ratchet moves freely in the other direction, so it can be repositioned easily; it is not necessary to have 360 degree access above the fastener -- just enough working space to move the ratchet handle.

Other ways to improve leverage include various pivoting handles. One type looks like the brace (tool) used to drive hand drills; there is a socket fitting rather than a chuck at the working end. The operator holds a knob, fitted with bearings in which the shaft turns, and cranks a handle.

Another type, called a flex handle, is related to the rachet, but, rather than rotating, the handle pivots 180 degrees so it can be repositioned quickly. A flex handle is simpler, cheaper, and may be able to apply more force than a rachet.

Torque wrenches

A torque wrench is both a fastening tool and a measuring device. It is used where precise measurement of the tightness of a bolt is necessary.

It has been suggested that a quantum mechanical torque wrench can measure either the torque, or find the bolt, but not both.

Spanners (precision)

While a spanner is a general term in British English for "wrench", there is a specialized tool always known as a spanner. It consists of a bar with two or more protruding pins, sometimes adjustable in distance, that fit into corresponding holes in a fastener an allow it to be turned. The bar is connected to a shaft or other mechanism to allow turning, or sometimes the spanner is built not as a bar, but as a pliers-like device with the pins at the work end. Spanners are often used in optical work, on the retaining rings of lens elements.

Power wrenches

Impact wrenches

One of the most common types is a power-operated driver for sockets, the sockets usually made of extra-strong metal. Pneumatically driven impact wrenches are extremely common in the automotive industry; air drive does not generate the sparks that an electric motor could produce, which would be hazardous in the presence of petroleum products.

For other applications, however, electric impact wrenches are increasingly common, especially cordless battery-powered wrenches with great portability. For some heavy applications, the impact energy may be provided by an explosive cartridge.

There are impact wrenches that are hand-powered, but by hitting a specific part with a hammer, allowing great force to be applied.

Power torque wrench

Intended for industrial applications, these are often powered hydraulically, which allows great precision. (Read more...)

Howard C. Berkowitz 3


Developing Article Three Week Hero Milton Beychok;
Meg Ireland 		18 May 2009
19 June 2009 		2
Developing Article Immigrant Song Daniel Mietchen;
Meg Ireland 		11 May 2009
10 June 2009 		2
Recently created pages are listed on Special:NewPages.

Current Winner

To change, click edit and follow the instructions, or see documentation at {{Featured Article}}.

The 2009 H1N1 influenza virus, commonly referred to as swine flu, is an influenza A virus first discovered in April 2009, which contains human, porcine and avian genes.[1] Those infected with the H1N1 virus report symptoms similar to those observed in most influenza A viral infections, namely fever, cough, sore throat, body aches, headache, chills and fatigue, and a significant fraction of those afflicted report diarrhea and vomiting. It may cause severe illness and death. Although seasonal influenza normally differentially affects certain populations, including young children, people over 65 years of age, pregnant women, and the chronically ill, population related risks are yet to be determined for this virus. The virus is contagious so common health care precautions should be taken to avoid contracting this flu.

Epidemiology

The 2009 H1N1 influenza virus is a novel H1N1 strain.[2] Although in the prior 2007-2008 season, H1N1 was about a third of all cases[3], starting in April 2009 a H1N1 strain emerged that was initially untypeable. The 2009 novel H1N1 influenza virus contains genes normally found in North American swine as well as two genes found in European and Asian swine and has been called a triple-reassortant of genes.[2][4]

Prevention

General good health practices should be taken to avoid this and other illnesses. Most importantly, wash your hands often, and avoid sick persons and unnecessarily touching surfaces. Stay fit by eating a well-balanced, nutritious diet, drink plenty of water, get sufficient sleep each day, and exercise. The use of antibacterial soaps are no better than regular soaps at removing this virus from your hands.

Once infected, one may reduce the spread of the flu in a number of simple ways.

Hygiene

  • Do not cough or sneeze into your hands directly, but cover your nose and mouth with a tissue (or shirt sleeve - the current suggestion is, in the absence of a tissue, cough or sneeze into the crux of your elbow rather than your hands).
  • Throw the tissue away directly, without setting it on other surfaces, such as desk tops or kitchen counters.
  • Wash your hands often with soap and water, especially after you cough or sneeze.
  • Avoid touching your eyes, nose or mouth, and wash your hands afterwards.
  • Stay home for 7 days after symptoms begin or you have been symptom free for 24 hours.
  • Avoid close contact with sick people.
  • Avoid shopping after becoming ill. Buy at least a one week supply of medications, tissues, soaps, and so on.

Medications and Infectivity

The antiviral drugs oseltamivir and/or zanamivir are recommended by the Centers for Disease Control for the treatment and/or prevention of 2009 H1N1. These antiviral drugs inhibit the reproductive cycle of the virus, thereby ameliorating the severity and length of illness. Although the period of infectivity for a person with H1N1 has yet to be determined, persons with influenza are typically contagious beginning 1 day before the onset of symptoms and 7 days after symptom onset. Childrem may be contagious for a longer time period.

Food, Water and Recreation

One can not become infected by the swine flu from eating properly cooked pork products. Based on previous studies of the H5N1 avian flu, it is expected that chlorine levels used in municipal water supplies should be sufficient to kill the H1N1 virus. Likewise, properly treated water at swimming pools, spas, water parks, interactive fountains, and other treated recreational water venues should be free of the virus. The virus is contagious so common health care precautions should be taken to avoid contracting this flu.

Seeking Medical Attention

One should seek immediate medical attention when patients experience any of the following warning signs:

In Adults or Children:

  • difficult or rapid breathing,
  • Chest/Abdominal pain or pressure
  • Sudden dizziness or confusion
  • Severe or persistent vomiting

Additional warning signs in children:

  • Bluish or gray skin color
  • Insufficient fluid intact
  • Not waking up or interacting
  • Being so irritable that the child does not want to be held
  • Flu-like symptoms improve but then return with fever and worse cough
  • Fever with a rash

Treatment

Peramivir is an investigational intravenous neuraminidase inhibitor that can be used.[5]

Complications

Various pulmonary complications may occur including pulmonary embolism.[6]

References

  1. ↑ NCBI list of deposited sequences for 2009 H1N1
  2. ↑ 2.0 2.1 Novel Swine-Origin Influenza A (H1N1) Virus Investigation Team. Dawood FS, Jain S, Finelli L, Shaw MW, Lindstrom S et al. (2009). "Emergence of a novel swine-origin influenza A (H1N1) virus in humans.". N Engl J Med 360 (25): 2605-15. DOI:10.1056/NEJMoa0903810. PMID 19423869. Research Blogging.
  3. ↑ 2007-08 U.S. INFLUENZA SEASON SUMMARY, Centers for Disease Control and Prevention
  4. ↑ Swine Flu & You
  5. ↑ Birnkrant D, Cox E (2009). "The Emergency Use Authorization of Peramivir for Treatment of 2009 H1N1 Influenza.". N Engl J Med. DOI:10.1056/NEJMp0910479. PMID 19884645. Research Blogging.
  6. ↑ Agarwal PP et al (2009) Chest Radiographic and CT Findings in Novel Swine-Origin Influenza A (H1N1) Virus (S-OIV) Infection American Journal of Radiology

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Previous Winners

Rules and Procedure

Rules

  • The primary criterion of eligibility for a new draft is that it must have been created no more than one month before the date of the next selection (Currently every Thursday).
  • Articles must be ranked 1 or 2 (developed or developing).
  • Any Citizen may nominate a draft.
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  • The article's nominator is indicated simply by the first name in the list of votes (see below).
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Nomination

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Voting

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Ranking

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Updating

  • Each Thursday, one of the admins listed below should move the winning article to the Current Winner section of this page, announce the winner on Citizendium-L and update the "previous winning drafts" section accordingly.
  • The winning article will be the article at the top of the list (ie the one with the most votes).
  • In the event of two or more having the same number of votes :
    • The article with the most specialist supporters is used. Should this fail to produce a winner, the article appearing first by English alphabetical order is used.
    • The remaining winning articles are guaranteed this position in the following weeks, again in alphabetical order. No further voting should take place on these, which remain at the top of the table with notices to that effect. Further nominations and voting take place to determine future winning articles for the following weeks.
    • Winning articles may be named New Draft of the Week beyond their last eligible date if their circumstances are so described above.

Administrators

The Administrators of this program are the same as the admins for CZ:Article of the Week.

References

See Also


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