Nutritional Requirements

Nutritional Requirements

Types of Water

SPARKLING WATER:

Carbonated water obtained either through natural underground springs or made by dissolving CO2 gas in water. Carbonation lasts longer in naturally carbonated waters.

MINERAL WATER:

Contains dissolved minerals. Various brands will contain different levels of minerals. Some mineral waters are made from tap water, then minerals are added or removed as desired.

CLUB SODA:

Usually tap water that has been filtered and carbonated. Minerals and mineral salts are added. Club soda will also take tomato juice stains out of your carpet.

SELTZER:

Usually tap water filtered and carbonated. No mineral or mineral salts are added.

SOFT WATER:

Low mineral content water. Usually comes from deep in the earth with its principal mineral being sodium. Will dissolve soap better and will not leave a ring around the bathtub. Will dissolve minerals such as lead from pipes.

HARD WATER:

High mineral content water. Usually comes from shallow ground that has high concentrations of calcium and magnesium. Hard water leaves rock-like crystals.

SPRING WATER:

Water without gas bubbles, usually tap water or natural spring water. Bottled bulk water falls into this category. When purchasing bottled water, try buying it in glass bottles labeled natural.

http://www.bellybytes.com/foodfacts/types_of_water.html

Solar Cells

Solar Cells

Solar cells (as the name implies) are designed to convert (at least a portion of) available light into electrical energy. They do this without the use of either chemical reactions or moving parts.

History
The development of the solar cell stems from the work of the French physicist Antoine-César Becquerel in 1839. Becquerel discovered the photovoltaic effect while experimenting with a solid electrode in an electrolyte solution; he observed that voltage developed when light fell upon the electrode. About 50 years later,

Charles Fritts constructed the first true solar cells using junctions formed by coating the semiconductor selenium with an ultrathin, nearly transparent layer of gold.

Fritts's devices were very inefficient, transforming less than 1 percent of the absorbed light into electrical energy.

By 1927 another metalÐsemiconductor-junction solar cell, in this case made of copper and the semiconductor copper oxide, had been demonstrated

.

By the 1930s both the selenium cell and the copper oxide cell were being employed in light-sensitive devices, such as photometers, for use in photography.

These early solar cells, however, still had energy-conversion efficiencies of less than 1 percent. This impasse was finally overcome with the development of the silicon solar cell by Russell Ohl in 1941. In 1954, three other American researchers, G.L. Pearson, Daryl Chapin, and Calvin Fuller, demonstrated a silicon solar cell capable of a 6-percent energy-conversion efficiency when used in direct sunlight. By the late 1980s silicon cells, as well as those made of gallium arsenide, with efficiencies of more than 20 percent had been fabricated. In 1989 a concentrator solar cell, a type of device in which sunlight is concentrated onto the cell surface by means of lenses, achieved an efficiency of 37 percent due to the increased intensity of the collected energy. In general, solar cells of widely varying efficiencies and cost are now available.

Structure

Modern solar cells are based on semiconductor physics -- they are basically just P-N junction photodiodes with a very large light-sensitive area.

The photovoltaic effect, which causes the cell to convert light directly into electrical energy, occurs in the three energy-conversion layers.

Diagram courtesy U.S. Department of Energy

The first of these three layers necessary for energy conversion in a solar cell is the top junction layer (made of N-type semiconductor ). The next layer in the structure is the core of the device; this is the absorber layer (the P-N junction). The last of the energy-conversion layers is the back junction layer (made of P-type semiconductor).

As may be seen in the above diagram, there are two additional layers that must be present in a solar cell. These are the electrical contact layers. There must obviously be two such layers to allow electric current to flow out of and into the cell. The electrical contact layer on the face of the cell where light enters is generally present in some grid pattern and is composed of a good conductor such as a metal. The grid pattern does not cover the entire face of the cell since grid materials, though good electrical conductors, are generally not transparent to light. Hence, the grid pattern must be widely spaced to allow light to enter the solar cell but not to the extent that the electrical contact layer will have difficulty collecting the current produced by the cell. The back electrical contact layer has no such diametrically opposed restrictions. It need simply function as an electrical contact and thus covers the entire back surface of the cell structure. Because the back layer must be a very good electrical conductor, it is always made of metal.

Operation

Solar cells are characterized by a maximum Open Circuit Voltage (Voc) at zero output current and a Short Circuit Current (Isc) at zero output voltage. Since power can be computed via this equation:

P = I * V

Then with one term at zero these conditions (V = Voc / I = 0, V = 0 / I = Isc ) also represent zero power. As you might then expect, a combination of less than maximum current and voltage can be found that maximizes the power produced (called, not surprisingly, the "maximum power point"). Many BEAM designs (and, in particular, solar engines) attempt to stay at (or near) this point. The tricky part is building a design that can find the maximum power point regardless of lighting conditions.

Source--http://encyclobeamia.solarbotics.net/articles/solar_cell.html

Solar Cooker

:: Solar Cooker

Domestic Solar Cooker

What is Solar Cooker ? A solar cooker looks like a simple square aluminium suitcase, with five main components with an outer box measuring 500 x 500 x 165 mm with three containers.

Benefits of using the solar cooker

• In an age where domestic fuel costs are rising each year, the solar cooker is a real boon.
• Reasonably priced, easy-to-use and completely trouble-free, the solar cooker is an ideal supplement to the conventional cooking appliances.
• Can be used 300 days a year.
• No fuel required for cooking.
• All items can be cooked except the fried and chapatis.
• Cooking is safe and clean.
• Solar cooking is entirely non-polluting and has no ill effects on health.
• Food cooked in solar cooker tastes better, is more nutritious and healthy.
• No need to keep close watch during cooking as the process is slow.
• Cooking time is around 1.30 to 2.30 hours.
• Food remains hot as long as the glass assembly is not opened.
• Three LPG cylinders can be saved annually as a result of solar cooking.
• Pay-back period is around three years.
• Life is around 10-15 years.
• O & M cost is almost negligible.

Did you know?

• The first box type solar cooker was built by Horace de Saussure, a Swiss naturalist, in 1767! He is said to have cooked fruits in it.
• That box type solar cookers can be fabricated using just cardboard and aluminum foil? Check out this website for the design http://www.i4at.org/surv/solarbox.htm
• In the 1950’s UN and other funding agencies commissioned studies to design solar cookers. The conclusion was encouraging – that solar cooker can cook food thoroughly and nutritiously and was easy to make and use.
• Based on the above study, UN sponsored programmes to introduce them in communities where there was a felt need, but this did not meet with much success.
• A World Conference on Solar Cooking was held in Stockton, California, in 1992. (http://solarcooking.org/stockton.htm )

THE INDIAN SCENE: Some of the policy initiatives taken by the Indian Government to promote the use of solar energy in general are:

• 1981 - Recognising the importance of renewable energy sources as the best alternative to conventional fuels, the Government of India set up a Commission for Additional Sources of Energy (CASE) in the Department of Science and Technology
• 1982 - A full-fledged, independent department, the Department of Non-conventional Energy Sources, is set up.
• 1992 - This ‘department’ is made into a ‘Ministry’, called the Ministry of Non-conventional Energy Sources (MNES).
• Gave subsidy for box type solar cookers from 1984 to 1994.

MNES is the nodal agency of the Government of India for all matters relating to non-conventional/renewable energy.

For more information click on www.mnes.nic.in

As the MNES felt that the use of solar energy for cooking and water heating was on the increase, the subsidy on solar water heaters and solar cookers were withdrawn in 1993-94. It is interesting to note that the Government continues to subsidize cooking gas, at a heavy cost to the exchequer, but is doing little about solar cookers. With over 40manufacturers of different types ofsolar cookers in the India, the combined capacity is to the tune of 75, 000 cookers pre annum. The manufacturers are mostly in the north - Delhi, Gujarat, Himachal Pradesh, Madhya Pradesh, Maharashtra, Punjab, Uttar Pradesh and West Bengal. The cookers have to adhere to the norms recommended by the MNES and the end product needs to be approved by the Bureau of Indian Standards. We understand that an estimated ‘potential’ demand for solar cookers in India is nearly 10 million!

MNES has also opened Aditya Solar Shops across the country,

which serves as convenient consumer points for sales, service and repair of renewable energy devices.

Box Cookers	Panel Cookers	Parabolic Cookers
When a glass covered chamber coated black inside and insulated all around is exposed to sunlight the temperature inside exceeds 100 degree Celsius, which is sufficient to cook food. More heat can be achieved by having an exterior reflector. The solar box cooker incorporates these features.	Roger Bernard in France came up with this design, where various flat panels concentrate the sun's rays on to a pot inside a plastic bag or under a glass bowl. The advantage of this design is that they can be built in an hour or so, from next to nothing. In Kenya, these are being manufactured for the Kakuma Refugee Camp project for US$2 each.	These are usually concave disks that focus the light onto the bottom of a pot. The advantage is that foods cook about as fast as on a conventional stove. Seen above is one model and there are many others possible.
Slow, even cooking of large quantities of food is possible Takes more than 3 hours to cook	Relatively quicker, but can cook only smaller quantities	Food can be cooked in half an hour. The disadvantage is that they are complicated to make, they must be focused often to follow the sun, and they can cause burns and eye injury if not used correctly.
With a single-reflector box cooker, once the food is cooked, it just stays warm and doesn't scorch.You can put in a few pots with different foods and then come back later in the day and each pot will cook to perfection and stay hot until you take it out.	Some people have reported the need to stir food every once in a while when using this kind of cooker, to ensure that the food heats evenly.	Cooking with a parabolic cooker is very similar to cooking on one burner of a conventional stove. Since the concentrated sunlight shines directly on the bottom of a pot, the pot heats up and cooks very quickly. The food will burn though. So you have to stir it and watch it carefully.
Box cookers with one back reflector don't need to be turned unless you are cooking beans, which take up to 5 hours.	Panel cookers need to be turned more often than box cookers, since they have side reflectors that can shade the pot.	Parabolic cookers are the most difficult to keep in focus. These need to be turned every 10 to 30 minutes, depending on the focal length.

Courtesy--www.mnes.nic.in

Meristematic Tissues

Meristematic Tissues

Tissues where cells are constantly dividing are called meristems or meristematic tissues. These regions produce new cells. These new cells are generally small, six-sided boxlike structures with a number of tiny vacuoles and a large nucleus, by comparison. Sometimes there are no vacuoles at all. As the cells mature the vacuoles will grow to many different shapes and sizes, depending on the needs of the cell. It is possible that the vacuole may fill 95% or more of the cell’s total volume.

There are three types of meristems:

1. Apical Meristems
2. Lateral Meristems
3. Intercalary Meristems

Apical meristems

are located at or near the tips of roots and shoots. As new cells form in the meristems, the roots and shoots will increase in length. This vertical growth is also known as primary growth. A good example would be the growth of a tree in height. Each apical meristem will produce embryo leaves and buds as well as three types of primary meristems: protoderm, ground meristems, and procambium. These primary meristems will produce the cells that will form the primary tissues.

Lateral meristems account for secondary growth in plants. Secondary growth is generally horizontal growth. A good example would be the growth of a tree trunk in girth. There are two types of lateral meristems to be aware of in the study of plants.

The vascular cambium, the first type of lateral meristem, is sometimes just called the cambium. The cambium is a thin, branching cylinder that, except for the tips where the apical meristems are located, runs the length of the roots and stems of most perennial plants and many herbaceous annuals. The cambium is responsible for the production of cells and tissues that increase the thickness, or girth, of the plant.

The cork cambium, the second type of lateral meristem, is much like the vascular cambium in that it is also a thin cylinder that runs the length of roots and stems. The difference is that it is only found in woody plants, as it will produce the outer bark.

Both the vascular cambium and the cork cambium, if present, will begin to produce cells and tissues only after the primary tissues produced by the apical meristems have begun to mature.

Intercalary meristems are found in grasses and related plants that do not have a vascular cambium or a cork cambium, as they do not increase in girth. These plants do have apical meristems and in areas of leaf attachment, called nodes, they have the third type of meristematic tissue. This meristem will also actively produce new cells and is responsibly for increases in length. The intercalary meristem is responsible for the regrowth of cut grass.

There are other tissues in plants that do not actively produce new cells. These tissues are called nonmeristematic tissues. Nonmeristematic tissues are made of cells that are produced by the meristems and are formed to various shapes and sizes depending on their intended function in the plant. Sometimes the tissues are composed of the same type of cells throughout, or sometimes they are mixed.

Courtesy---

Dose--Permanent Tissues

Permanent Tissues

The cells of permanent tissues do not have the ability to divide. These cells are already differentiated in different tissue types and is now specialized to perform specific functions. They are subdivided into two groups, viz, simple tissues consisting of cells which are more or less similar, e.g. epidermis, parenchyma, chlorenchyma, collenchyma, sclerenchyma and complex tissues consisting of different kinds of cells, e.g. xylem and phloem.

Simple tissues are:

Epidermis
Parenchyma
Chlorenchyma
Collenchyma
Sclerenchyma

Complex tissues are:

Xylem
Phloem

Sclerenchyma

Mature sclerenchyma cells are dead and have secondary cell walls thickened with cellulose and usually impregnated with lignin. In contrast to collenchyma, which is pliable, sclerenchyma is elastic. The cell cavity orlumen is very small or it may disappear completely. There are two types of sclerenchyma cells, namely sclereids and fibres.

1. Sclereids: The cells are irregular in shape. The cell walls are thick, hard and lignified which makes the lumen very small. Simple pits (canals) are found in the thickened cell walls and link adjacent cells. Sclereids are commonly found in fruit and seeds.
2. Fibres: The cells are needle-shaped with pointed tips, thick walls and rather small lumen. Secondary cell walls, impregnated with, are formed. Simple pits are also present. Fibres are abundant in the vascular tissue of angiosperms, i.e. flowering plants.

Functions:

• sclerenchyma is an important supporting tissue in plants,
• sclereids are responsible for the hardness of date seeds and the shell of walnut,
• fibres probably play a role in the transport of water in the plant,
• starch granules are stored in the young, living fibres.

A line drawing of a sclerenchyma cell.

Epidermis

The epidermis is the outermost cellular layer which covers the whole plant structure, i.e. it covers roots, stem, leaves, flowers and fruit. It is composed of a single layer of living cells, although there are exceptions. Epidermis is usually closely packed, without intercellular spaces or chloroplasts. The outer walls, which are exposed to the atmosphere and usually thickened, and may be covered by a waxy, waterproof cuticle which are made up of cutin. Apart from the normal epidermal cells there are also stomata in the epidermis of leaves and stem. A stoma is an opening (pore) which is bounded by two beanshaped cells called guard cells . The guard cells differ from normal epidermal cells in that they have chloroplasts and the cell walls are thickening unevenly; the outer wall is thin and the inner wall (nearest the opening) is thick. The thin-walled epidermal cells of roots give rise to root hairs. Hair- like outgrowths may also be found in the epidermis of leaves and stems.

Functions:

• the epidermal cells protect the underlying cells,
• the waxy cuticle prevents the loss of moisture from the leaves and stems,
• the transparent epidermal cells allow sunlight (for photosynthesis) to pass through to the chloroplasts in the mesophyll tissue,
• the stomata of leaves and stems allow gaseous exchange to take place which is necessary for photosynthesis and respiration,
• water vapour may be given off through the stomata during transpiration,
• the root-hairs absorb water and dissolved ions from the soil.

A diagrammatic representation of a stomata, when open and close.

Parenchyma

Parenchyma is the most common plant tissue. It is relatively unspecialized and makes up a substantial part of the volume of a herbaceous plant and of the leaves, flowers and the fruits of woody plants. The thin-walled parenchyma cells have large vacuoles and distinct intercellular spaces.

Functions:

• the most important function of the parenchyma cells of roots and stem is the storage of food (e.g. starch) and water,
• the intercellular air spaces permit gaseous exchange.

A line drawing of a parenchyma cell.

Chlorenchyma

Chlorenchyma cells are actually parenchyma cells, but they contain chloroplasts, e.g. the parenchyma cells of leaves and stems. The mesophyll cells of leaves can thus be regarded as chlorenchyma.

Functions:

• the chlorenchyma are the main photosynthetic cells of the plant and manufacture carbohydrates during photosynthesis.

Collenchyma

Collenchyma tissues are mainly found under the epidermis in young stems in the large veins of leaves. The cells are composed of living, elongated cells running parallel to the length of organs that it is found in. Collenchyma cells havethick cellulose cell walls which thickened at the corners. Intercellular air spaces are absent or very small. The cells contain living protoplasm and they sometimes contain chloroplasts.

Functions:

• the collenchyma serve as supporting and strengthening tissue,
• in collenchyma with chloroplasts, photosynthesis takes place.

A line drawing of a collenchyma cell.

Xylem

Xylem is a complex tissue composed of xylem vessels, xylem tracheids, xylem fibres and xylem parenchyma.

1. Xylem vessels: Xylem vessels comprise a vertical chain of lengthened, dead cells known as vessel elements. The cells are arranged end to end and the cross-walls dissolve completely or have simple or complex perforation plates between successive cells. The secondary walls of vessels are impregnated with lignin and are thickened unevenly. The walls of the vessels may be thickened in different ways, e.g. annular, spiral and pitted thickening may be observed.
2. Xylem tracheids: A tracheids is an elongated cell, the contents of which are non-living. The cell walls are thickened, impregnated with lignin and the lumen is smaller. As in the case of vessels, there is a differentiation between annular, spiral and pitted tracheids again caused by the type of thickening of the secondary walls. Tracheids have no perforation plates.
3. Xylem fibres and xylem parenchyma bear a strong resemblance to normal fibres and parenchyma. Xylem fibres are sometimes separated by thin cross walls and the walls of xylem parenchyma are sometimes thicker than those of normal parenchyma.

Functions:

• xylem is an important strengthening tissue,
• xylem vessels and tracheids transport water and mineral salts,
• starch is sometimes stored in the xylem fibres and xylem parenchyma.

A line drawing of the different xylem cells.

Phloem

Phloem is a complex tissue composed of sieve tubes, companion cells, phloem fibres and phloem parenchyma

1. Sieve Tubes: A sieve tube, like xylem vessels, is a series of cells (sieve elements) joined end to end. The cross walls between successive cells (sieve elements) become perforated forming sieve plates. The cell walls arethin. Although the cell contents are living, the nucleus disintegrates and disappears. The lumen is filled with a slimy sap which is composed mainly of protein.
2. Companion Cells: Companion Cells are specialized parenchyma cells which always appear with the sieve tube element. They are also elongated, thin-walled and there is a distinct nucleus in the cytoplasm of the companion cell. Companion cells are linked with the sieve tubes by small canals filled with cytoplasm, which are smaller than pits.
3. Phloem Fibres: These cells are elongated tapering cells, found particular in the stem. They have thickened walls.
4. Phloem Parenchyma: Phloem Parenchyma is living and has thin cell walls. These cells form the packing tissue between all the other types of cells.

Functions:

• sieve tubes transport organic compounds,
• companion cells helps to regulate the metabolic activities of the sieve tube elements,
• the phloem fibres give the plant mechanical strength,
• the phloem parenchyma stores compounds such as starch.

A line drawing of the different phloem cells.

Courtesy---http://www.botany.uwc.ac.za/SCI_ED/grade10/plant_tissues/index.htm

Wavelength

-

Wavelength is the distance between identical points in the adjacent cycles of a waveform signal propogated in space or along a wire, as shown in the illustration. In wirelesssystems, this length is usually specified in meters,centimeters, or millimeters.

Inthe case of infrared, visible light, ultraviolet, and gammaradiation, the wavelength ismore often specified in nanometers (units of 10^-9meter) or Angstrom units(units of 10^-10 meter).

Wavelength is inversely related to frequency. The higher the frequency of the signal, the shorter the wavelength. Iff is the frequency of the signal as measured in megahertz, and w isthe wavelength as measuredin meters, then

w = 300/f

and conversely

f = 300/w

Wavelength is sometimes represented by the Greek letter lambda.

Source---

Fungus Infections

Skin fungus infections are hard to recognize. The itching, flaking, redness, and thickened skin of fungal infections can look just like other types of dermatitis or skin allergies. In fact, eczematous skin often becomes infected with fungi, so both are present simultaneously. Doctors use microscopes to help them diagnose skin fungus infections, so there’s no way you can really be sure at home. The Advisory will focus on the five most easily recognized skin fungus infections, but even after looking at the pictures don’t be too confident.

Athlete’s Foot (tinea pedis).

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Every year, over 10% of the U.S. population develops this problem. Probably 75% of us will have athlete’s foot at some time during our lives. The most common form occurs between your third, fourth, and fifth toes, sometimes spreading to the sole. Between the toes, your skin becomes white, moist, and easily rubbed off; the tops of the toes may be red, dry, and flaky. Intense itching and burning are the rule. Athlete’s foot usually occurs with hot, moist conditions, or if you wear shoes constantly.

Jock Itch (tinea cruris). The same conditions of heat, moisture (sweat) and poor air circulation leading to athlete’s foot also cause fungus infections of the groin, or jock itch. As its name implies, intense itching and burning are the usual symptoms. You will also find redness, flaking and peeling on the inner thighs, pubic area, and scrotum.

Ringworm (tinea corpora).

It is caused by a microscopic fungus, not a worm. The infected area spreads out slowly from its central starting point and creates a slightly raised, intensely red ring surrounding a less red, flaky, itchy area. Over weeks, the ring slowly enlarges. It can occur anywhere on the body and in multiple sites at once, so it’s often confused with other kinds of dermatitis.

Candidiasis.

Image via Wikipedia

Theis brownish-red, itchy discoloration affects the underarms, corners of the mouth, rectal area, and beneath the breasts. The same type of fungus causes vaginal yeast infections (candida albicans).

Tinea Versicolor. This fungus actually changes the color of the skin it infects; the patches may be lighter or darker than your normal surrounding skin. This spotted pattern and the fine scaly flakes at the

margins make this fungal infection the easiest to identify. Since itching and irritation are mild, it’s also the least bothersome.

Warmth, humidity, sweating, and poor air circulation all help bring about these fungal infections. But they are contagious, too. Athlete’s foot is believe to be passed on locker room and shower floors, and by sharing footwear and socks; you can acquire tinea versicolor from vinyl surfaces of weight lifting benches; and of course ringworm is contagious through direct contact (usually kids).

Because of all these factors, prevention is a matter of both personal hygiene and minimizing contact with potential carriers or contaminated objects.

There are several effective OTC anti-fungal medications. Because different fungi affect different locations, medications are sometimes specific for those locations. The recommendations below should help you sort it out.

Athlete’s Foot - Tolnaftate is the only OTC medicine approved for both prevention and treatment of athlete’s foot. Be patient, though. It could take a month or more of daily treatment for it to completely clear. Consider preventive use if the condition recurs.

Tinea Versicolor - Although not a Category I agent, selenium sulfide shampoo is universally recognized by dermatologists as an effective OTC remedy for tinea versicolor. Since it often affects large areas of the trunk, applying this shampoo once a day for five minutes, then washing off, is a lot easier and cheaper than using a whole tube of anti-fungal cream twice daily. Tinea versicolor also tends to recur easily, but this shampoo can prevent it if used once a week after the initial 2-4 week treatment cycle.

Candidiasis, Ringworm, and Jock Itch - Miconazole or clotrimazole are quickly effective (1-2 weeks) for each one of these conditions, and come in cream, lotion, or spray. Avoid alcohol-based products since they can sting chafed and delicate skin.

Courtesy--http://quickcare.org/skin/fungus.html

Images-- Wikipedia,Flickr

hEALTH dOSE (BCG)

BCG - the current vaccine for tuberculosis

Bacille Calmette Guerin (BCG) is the current vaccine for tuberculosis. It was first used in 1921. BCG is the only vaccine available today for protection against tuberculosis.

It is most effective in protecting children from the disease.

History of the vaccine

Bacille Calmette Guerin (BCG) containes a live attenuated (weakened) strain of Mycobacterium bovis. It was originally isolated from a cow with tuberculosis by Calmette and Guren who worked in Paris at the Institute Pasteur. This strain was carefully subcultured every three weeks for many years. After about thirteen years the strain was seen to be less virulent for animals such as cows and guinea pigs. During these thirteen years many undefined genetic changes occurred to change the original stain of M. bovis. This altered organism was called BCG. In addition to the loss of virulence, other changes to BCG were noted. These included a pronounced change in the appearance of colonies grown in the laboratory. Colonies of M. bovis have a rough granular appearance whereas colonies of BCG are moist and smooth.

Today there are several strains of “BCG”.

BCG was first used as a vaccine to protect humans against tuberculosis in 1921.

At first, cultures of BCG were maintained in Paris. Later, it was subcultured and distributed to several laboratories throughout the world where the vaccine strain called BCG continued to be maintained by continuous subculture. After many years it became clear that the various strains maintained ain different laboratories were no longer identical to each other. Indeed, it was likely that all the various strains maintained by continuous subculture continued to undergo undefined genetic changes. Indeed, the "original" strain of BCG maintained at in Paris had continued to change during the subcultures needed to maintain the viability of the culture. To limit these continuing changes the procedures needed to maintain the strain were modified. Today, the organism is maintained in several laboratories using a "seed lot" production technique to limit further genetic variation using freeze-dried (also called lyphilized) cells so that each batch starts with the same cells.

Safety

After extensive tests in animals, BCG was first used as a vaccine in 1921. It was given orally to infants. Since this time the vaccine has been widely used. Today, it is estimated that more than 1 billion people have received BCG.

BCG is widely used and the safety of this vaccine has not been a serious issue until recently. There is a concern that use of the vaccine in persons who are immune compromised may result is an infection caused by the BCG itself. Also, even among immune competent persons, local reactions, including ulceration at the site of vaccination may result in shedding of live organisms which could infect others who may be immune compromised.

The early use of BCG was marked by a tragic accident. In Lubeck more than 25% of the approximately 250 infants who received a batch of the vaccine developed tuberculosis. It was later recognized that this batch was accidentally contaminated with a virulent strain of M. tuberculosis.

BCG production and substrains

The BCG vaccines that are currently in use are produced at several (seven?) sites throughout the world. These vaccines are not identical. To what extent they differ in efficacy and safety in humans is not clear at present. Some differences in molecular and genetic characteristics are known. What is not known is if the "BCG" from one manufacturer is "better" than one produced at another site. Each BCG is now know by the location where it is produced. For example, we have BCG (Paris), BCG (Copenhagen), BCG (Tice) and BCG (Montreal) among others.

Elasticity

An important property of many structural materials is their ability to regain their original shape after a load is removed. These materials are called elastic.

Steel, glass and rubber are elastic; putty or modeling clay are not elastic. Each of these materials is elastic to varying degrees; steel and glass are both more elastic than rubber. The degree of elasticity, or "stiffness" of a material is called its Modulus of Elasticity (E). Given the modulus of elasticity, possible deformations can be calculated for any material and loading.

All materials are assumed to be elastic except when indicated otherwise in this course.

Robert Hooke (1635 - 1703), a great English scientist, experimented with springs, clocks and watches. During his investigation of the spring he discovered that in elastic materials, stress and strain are proportional. He first presented this in a lecture in 1678 and it is known today simply as Hooke's Law.

Hooke's Law applies as long as the material stress does not pass a certain point known as its proportional limit. This is the point at which the physical properties of the material actually change. Any time an elastic material is loaded between zero and the proportional limit, the stress and strain are directly proportional and if the load is released the material will regain its initial dimensions. If the stress is doubled the strain is doubled; if the stress is tripled the deformation is three times as great, etc.

The English physician and physicist Thomas Young (1773 - 1829) noted that if stress is proportional to strain, then for any given material, stress divided by strain would be a constant. This constant is known today as Young's Modulus or the Modulus of Elasticity.

The Modulus of Elasticity is represented by E = Stress / Strain.

This relationship is found as the slope of the curve of the stress-strain curve from initial loading to the proportional limit. A higher value of the modulus indicates a more brittle material (i.e. glass, ceramics). A very low value represents a ductile material (i.e. rubber).

Modulus of Elasticity

The values of the modulus of elasticity for structural materials have been determined by tests and are readily available in references such as the AISC manual. Some of the more common values are:

* Steel: E=29,000 KSI (sometimes rounded to 30,000 KSI)
* Aluminum: E=10,000 KSI
* Wood: E=1,000 - 2,000 KSI (usual range)
* Concrete E=2,500 - 5,000 KSI (usual range)

It is often necessary to be able to determine the deformation of a structural member once the loads and physical properties of the structural member are known. This is simply derived and is developed from the stress/strain relationships that have already been established.

dOSE -- pHYSICS

1. Piezomagnetism is a phenomenon observed in some antiferromagnetic crystals. It is characterised by a linear coupling between the system's magnetic polarisation and mechanical strain. In a piezomagnetic, one may induce a spontaneous magnetic moment by applying physical stress, or a physical deformation by applying a magnetic field.
2. In materials that exhibit antiferromagnetism, the magnetic moments of atoms or molecules, usually related to the spins of electrons, align in a regular pattern with neighboringspins (on different sublattices) pointing in opposite directions. This is, like ferromagnetism and ferrimagnetism, a manifestation of ordered magnetism.
3. An electron is a subatomic particle that carries a negative electric charge. It has no known components or substructure, and therefore is believed to be anelementary particle. An electron has a mass that is approximately 1/1836 that of the proton.
4. In physics, subatomic particles are the particles composing nucleons and atoms. There are two types of subatomic particles: elementary particles, which are not made of other particles, and composite particles.Particle physics and nuclear physics study these particles and how they interact.
5. In physics, a nucleon is a collective name for two baryons: the neutron and the proton.
6. Baryons are the family of composite particles made of three quarks, as opposed to the mesons which are the family of composite particles made of one quark and one antiquark. Both baryons and mesons are part of the larger particle family comprising all particles made of quarks—the hadrons. The term baryon is derived from the Greek βαρύς (barys), meaning "heavy", because at the time of their naming it was believed that baryons were characterized by having greater masses than other particles.
7. A quark is an elementary particle and a fundamental constituent of matter. Quarks combine to form composite particlescalled hadrons, the most stable of which are protons and neutrons, the components of atomic nuclei.
8. In particle physics, a hadron is a particle made of quarks held together by the strong force (similar to how molecules are held together by theelectromagnetic force). Hadrons are either mesons (made of one quark and one antiquark) or baryons (made of three quarks). Other combinations, such as tetraquarks (an "exotic" meson) and pentaquarks (an"exotic" baryon), may be possible but no evidence conclusively suggests their existence as of 2009. The best known mesons are pions and kaons, while the best known baryons are protons and neutrons.
9. In particle physics, a pion (short for pi meson; denoted π) is any of three subatomic particles: π⁰, π⁺ and π⁻. Pions are the lightest mesons and play an important role in explaining low-energy properties of the strong nuclear force.
10. In particle physics, a kaon is any one of a group of four mesons distinguished by the fact that they carry a quantum number called strangeness. In the quark model they are understood to contain a single strange quark (or antiquark).

11. In particle physics, strangeness S is a property of particles, expressed as a quantum number, for describing decay of particles in strong and electromagnetic reactions, which occur in a short period of time. The strangeness of a particle is defined as:

    

    where n_s represents the number of strange quarks (s) and n_s represents the number of strange antiquarks (s).