Ten Facts About Cells and Cell Function

Ten Facts About Cells and Cell Function Cells are the fundamental units of life. Whether they be unicellular or multicellular life forms, all living organisms are composed of and depend on cells to function normally. Scientists estimate that our bodies contain anywhere from 75 to 100 trillion cells. In addition, there are hundreds of different types of cells in the body. Cells do everything from providing structure and stability to providing energy and a means of reproduction for an organism. The following 10 facts about cells will provide you with well known and perhaps little known tidbits of information about cells. Cells are too Small to be Seen Without Magnification Cells range in size from 1 to 100 micrometers. The study of cells, also called cell biology, would not have been possible without the invention of the microscope. With the advance microscopes of today, such as the Scanning Electron Microscope and Transmission Electron Microscope, cell biologists are able to obtain detailed images of the smallest of cell structures. Primary Types of Cells Eukaryotic and prokaryotic cells are the two main types of cells. Eukaryotic cells are called so because they have a true nucleus that is enclosed within a membrane. Animals, plants, fungi, and protists are examples of organisms that contain eukaryotic cells. Prokaryotic organisms include bacteria and archaeans. The prokaryotic cell nucleus is not enclosed within a membrane. Prokaryotic Single-Celled Organisms were the Earliest and Most Primitive Forms of Life on Earth Prokaryotes can live in environments that would be deadly to most other organisms. These extremophiles are able to live and thrive in various extreme habitats. Archaeans for example, live in areas such as hydrothermal vents, hot springs, swamps, wetlands, and even animal intestines. There are More Bacterial Cells in the Body than Human Cells Scientists have estimated that about 95% of all the cells in the body are bacteria. The vast majority of these microbes can be found within the digetive tract. Billions of bacteria also live on the skin. Cells Contain Genetic Material Cells contain DNA (deoxyribonucleic acid) and RNA (ribonucleic acid), the genetic information necessary for directing cellular activities. DNA and RNA are molecules known as nucleic acids. In prokaryotic cells, the single bacterial DNA molecule is not separated from the rest of the cell but coiled up in a region of the cytoplasm called the nucleoid region. In eukaryotic cells, DNA molecules are located within the cells nucleus. DNA and proteins are the major components of chromosomes. Human cells contain 23 pairs of chromosomes (for a total of 46). There are 22 pairs of autosomes (non-sex chromosomes) and one pair of sex chromosomes. The X and Y sex chromosomes determine sex. Organelles Which Carry Out Specific Functions Organelles have a wide range of responsibilities within a cell that include everything from providing energy to producing hormones and enzymes. Eukaryotic cells contain several types of organelles, while prokaryotic cells contain a few organelles (ribosomes) and none that are bound by a membrane. There are also differences between the kinds of organelles found within different eukaryotic cell types. Plant cells for example, contain structures such as a cell wall and chloroplasts that are not found in animal cells. Other examples of organelles include: Nucleus - controls cell growth and reproduction.Mitochondria - provide energy for the cell.Endoplasmic Reticulum - synthesizes carbohydrates and lipids.Golgi Complex - manufactures, stores, and ships certain cellular products.Ribosomes - involved in protein synthesis.Lysosomes - digest cellular macromolecules. Reproduce Through Different Methods Most prokaryotic cells replicate by a process called binary fission. This is a type of cloning process in which two identical cells are derived from a single cell. Eukaryotic organisms are also capable of reproducing asexually through mitosis. In addition, some eukaryotes are capable of sexual reproduction. This involves the fusion of sex cells or gametes. Gametes are produced by a process called meiosis. Groups of Similar Cells Form Tissues Tissues are groups of cells with both a shared structure and function. Cells that make up animal tissues are sometimes woven together with extracellular fibers and are occasionally held together by a sticky substance that coats the cells. Different types of tissues can also be arranged together to form organs. Groups of organs can in turn form organ systems. Varying Life Spans Cells within the human body have different life spans based on the type and function of the cell. They can live anywhere from a few days to a year. Certain cells of the digestive tract live for only a few days, while some immune system cells can live for up to six weeks. Pancreatic cells can live for as long as a year. Cells Commit Suicide When a cell becomes damaged or undergoes some type of infection, it will self destruct by a process called apoptosis. Apoptosis works to ensure proper development and to keep the bodys natural process of mitosis in check. A cells inability to undergo apoptosis can result in the development of cancer.

The Palliative Care Essay Example | Topics and Well Written Essays - 4000 words

The Palliative Care - Essay Example Palliative care may be achieved by offering psychological, physical, and spiritual relief for the patient. In the United Kingdom, palliative care services are not only applied to the end of life patients but are also increasingly widely used in the management of incurable diseases alongside other medical procedures such as diagnosis and treatment. This is particularly attributed to the growing empirical evidence suggesting that the cost –efficacy of palliative care significantly outweighs attempts at disease cure, with regard to quality of life for both the patient and the family. The provision of palliative care is often affected by a number of external influences such as pathways, government policies and agendas and hospice availability as well as internal influences some of which may include psychological and physical aspects of the patients or their families. Other internal factors may also include the knowledge of the caregivers regarding the principles and practices of palliative care, attitudes of the caregiver on life and death and support from relatives and family members. This paper is based on a case study of Mrs. Janet, an end of life cancer patient who was admitted in a hospital in the United Kingdom 28 years after her initial diagnosis of cervical cancer (see Appendix A). The case study analysis attempts to highlight some of the potential external influences that may have directly influenced her end-of-life care, as well as the strategies applied by concerned practitioners in facilitating the delivery of palliative care services of the required quality. In addition, the present case analysis also seeks to critically evaluate the variable factors, including the social, physical, and psychological factors, together with their respective impacts on the experience of the client in relation to the provided palliative care. There exist a diverse number of factors that influence the end-of-life palliative care provided to patients with life-limiting health conditions. In the case study, Mrs. Janet’s end of life care is likely to be directly influenced by external factors such as such as cultural factors, care pathways, government policies and agendas and hospice availability.

Summary Essay Example | Topics and Well Written Essays - 250 words - 105

Summary - Essay Example There are different structuring considerations for different types of businesses. Canadian businesses need registration from the concerned provincial and federal governments for getting the tax account numbers. An allocation formula is used to allocate each corporation’s income to the provinces of permanent establishment. Capital Taxes have been mostly waived, whereas interest expenses are financed and deducted according to the set principles. Canada follows the guidelines set by OECD for the arm-length’s principle for transfer pricing. Earnings of a Canadian subsidiary are distributed through dividends, and the cash is repatriated. Canada applies withholding tax upon the non-residents’ services in Canada. Canada treats leasehold improvements as capital expenditures for the purposes of tax. Tax planning opportunities are there for companies having significant real estate amount in Canada. Canadian income tax laws apply on non-resident businessmen in Canada under domestic law, though sales made over the Internet are exempt from the income tax

Global relevance from a diversity of perspectives in International Essay

Global relevance from a diversity of perspectives in International Relations Theory - Essay Example This paper will evaluate the issue of global relevance from a diversity of perspectives in relation to International Relations Theory. The paper will discuss the issues surrounding global relevance and the implications on the how the various international relations theories relate to global relevance. Specifically, the paper will discuss critical theoretical perspectives in International Relations Theory such as Constructivism, Feminism and Marxism in regards to global relevance. The study will investigate the various aspects that can influence the global relevance of a state or a country and how these aspects can be controlled. It is important to note that global relevance is critical; especially in this era of globalization. Therefore, the study will endeavor to establish the critical issues that surround the issue of global relevance and how International Relations Theory affects global relevance. In order to attain the purpose of this paper, the first section will describe the is sue of global prominence in the context of global relations. The normative and theoretical perspectives in International Relations Theory that influence global relevance from a diversity of perspectives will be discussed. ... No country in the globe can prosper in solidarity and international cooperation is essential for every country. It is imperative that countries which dominate the international landscape have put in place policies that make them globally relevant (Hobson, 2009). Despite the diversity that is evident throughout the world, all countries are interlinked for mutual benefit. The aspect of global relevance can be evaluated from a diversity of perspectives that influence international relations. One of the major aspects of global relevance is economic status. The economy of a country is an important indicator of its development rate. It is important to note that economically powerful countries benefit the most in the realm of international trade. The formation of international and regional trade bodies such the World Trade Organizations imply that the exchange of goods and services is an important issue for every country. Suffice to say, trade is implemented through the principle of willing buyer and willing buyer. Therefore, in order to be able to dominate in the international trade, it is necessary for a country to improve its production capabilities (Hobson, 2009). The manufacturing, services and agricultural industries are some of the main areas of international trade. Thus, countries that can export more products and services while keeping their imports at a low level have the capability to stay globally relevant. The challenge for emerging economies that aspire for global dominance is the policies that they have to put in place in order to attain this goal. Countries that are unable to be globally relevant may invariably end up lagging behind economically. The political landscape in a country is an important

The Construction Material Concrete Construction Essay

The Construction Material Concrete Construction Essay The process of curing concrete, handling it in different climatic conditions and the various diseases that can arise in concrete structures are the key points of this paper. The word concrete is derived from a latin word concretuswhich means compact or condensed. Concrete is a thick composite artificial stone like material which is made by mixing cement (generally Portland cement) and various other aggregates, such as sand, pebbles, gravel, shale, etc., with water and allowing the mixture to harden by hydration. Since the ancient times it had been used in constructing structures and today also it is used more than any other man made construction material in the world. COMPOSITION Depending upon the reqirement of the structure,the proportions of the main ingredients discussed below are varied to avail different types of concrete. By doing so the finished product can be tailored to its application with varying strength, density, or chemical and thermal resistance properties. CEMENT Portland cement is a basic ingredient of concrete. It consists of a mixture of oxides of calcium, silicon and aluminium. Portland cement and similar materials are made by heating limestone (a source of calcium) with clay, and grinding this product (called clinker) with a source of sulfate (most commonly gypsum). WATER When water is added in a cementitious material, cement paste is formed through the process of hydration. The cement paste glues the aggregate together, fills voids within it, and allows it to flow more smoothly. Water should be added in the mix very carefully as less water in the cement paste will yield a stronger, more durable concrete; more water will give an free-flowing concrete with a higher slump. Impure water used to make concrete can cause problems when setting or in causing premature failure of the structure. In the process of hydration many different reactions occur at the same time. As the reactions proceed, the products of the cement hydration process gradually bond together the individual sand and gravel particles, and other components of the concrete, to form a solid compact mass. AGGREGATES The presence of aggregate greatly increases the robustness of concrete above that of cement.Following are the different items which could be used as aggregates: Sand, natural gravel and crushed stone Recycled aggregates (from construction, demolition and excavation waste) and manufactured aggregates like air-cooled blast furnace slag and bottom ash Decorative stones such as quartzite, small river stones or crushed glass are sometimes added to the surface of concrete for a decorative exposed aggregate finish. CURING OF CONCRETE The term curing concrete signifies the process of stopping freshly poured concrete from drying out too quickly. Unless the concrete mass is not cured, or if it is left out to dry out on its own, it will not develop the full bond between all of its ingredients. In order to form a water cement paste, water is added in Portland cement after which chemical reactions take place in the mixture turns the paste into a bonding agent. This reaction is known as hydration and it produces a stone-like compact substancethe hardened cement paste. Both the rate and degree of hydration, and the resulting strength of the final concrete, depend on the curing process that follows placing and consolidating the plastic concrete. As long as the mixture contains water and the temperature conditions are favorable, the process of Hydration continues ,though at a decreasing rate . The strength of concrete is dependent on crystal growth within the concrete matrix through the process of hydration If water is not adequate, the crystals cannot grow, due to which the concrete is unable to attain the desired strength. The presence of water through proper curing of the concrete facilitates the crystal growth that encloses the gravel and sand mix, causing interweaving with each other. .The time-span of the process of Curing begins from the time of consolidation and ends at the point where the concrete reaches its design strength. The period can vary from a few days to a month or longer. For most structural use, the curing period for cast-in-place concrete is usually 3 days to 2 weeks. During this period, the concrete mass should be kept moist and as near 73F as practical. Bridge decks and other slabs exposed to weather and chemical attack usually require longer curing periods. The time span of the curing period also depends on the factors such as type of cement used mix proportions required strength size and shape of the concrete mass weather conditions and temperature future exposure conditions SIGNIFICANCE OF CURING A proper and effective curing process helps in improving various properties of concrete such as freeze and thaw resistance strength watertightness wear resistance volume stability. Serviceability and apperance The compressive strength of concrete that has been properly cured is 75 to 95 per cent more than the concrete that has not been cured. Figure 1 illustrates this by comparing the compressive strength of concrete(at 180 days) for which the surface has been either kept moist for the entire duration of 180 days or is kept moist for various periods of time and allowed to dry out or is allowed to dry out from the time it was first made.It is quite clearly depicted that the compressive strength of the concrete is highest when it is fully cured for the entire period of 180 days. Fig 1:Moist curing effect on compressive strength of concrete source:www.tpub.com The permeability and absorptivity of concrete mix depends upon the porosity of the mix ie whether the pores and capillaries are discrete or interconnected. The porosity of the mix is reduced overtime through proper and effective curing of concrete thereby increasing the durability of concrete. Also, proper curing of concrete mix will reduce crazing, dusting and scaling of the slab thereby ensuring better serviceability and appearance. STAGES IN CURING PROCESS After the concrete mix have been placed, it is imperative to keep it moist and maintain specified concrete temperatures.The process of curing starts immediately after the placement of concrete and it goes through two stages : Initial curing stage: time of placement to initial set. This stage would include all the deliberate action taken between placement and final finishing of concrete. Approximate conditions during the initial curing period should be forecast prior to construction. Under this stage,the rate of strength gain of the concrete is minimal. The various aspects to be dealt with construction initial curing period as shown in diagram below are : verifying evaporation conditions: concrete temperatures, wind velocity, air temperature, and relative humidity are required to be taken into account during placement. These elements are used to make nomograph to calculate the evaporation rate and to determine whether critical drying rates exist. Using the concrete placing temperature, the time of initial setting can be estimated. The time of initial setting is the optimal time for application of final curing. Major items requiring attention during construction-initial curing period. Source : www.fhwa.dot.govt Onsite adjustments for Excessive drying: In order to reduce evaporation rates of bleed water the following two adjustments could be made- reducing concrete placing temperatures- Cooling aggregate stockpiles, cooling mixing water, or using ice for mixing water are very effective ways of reducing concrete temperatures. use of evaporation reducers. Evaporation reducers are water emulsions of film-forming compounds. The film-forming compound is the active ingredient that slows down evaporation of water. There is also a benefit from the water fraction of the evaporation reducers, in that it compensates to a small degree for losses of mixing water to evaporation.Evaporation reducers may need to be applied several times, depending on the conditions. Concrete that are liable to quick drying is required to be covered with wet gunny bag or wet hessian cloth properly squeezed, so that the water does not drip and at the same time, does not allow the concrete to dry. This condition should be maintained for 24 hours or at least till the final setting time of cement at which duration the concrete will have assumed the final volume. The Final curing stage: The final curing period is defined as the time interval between application of curing procedures and the end of deliberate curing. Final curing methods fall into four categories: Water curing : Water curing can be done in various ways like immersion,ponding, spraying or fogging and wet covering.This is by far the best method of curing as it satisfies all the requirements of curing, namely, promotion of hydration, elimination of shrinkage and absorption of the heat of hydration. Curing a house slab by flooding. Source: http://www.builderbill-diy-help.com/curing-concrete.html The precast concrete items are normally immersed in curing tanks for a certain duration. Pavement slabs, roof slab etc. are covered under water by making small ponds. Vertical retaining wall or plastered surfaces or concrete columns etc. are cured by spraying water. In some cases, wet coverings such as wet gunny bags, hessian cloth, jute matting, straw etc., are wrapped to vertical surface for keeping the concrete wet. For horizontal surfaces saw dust, earth or sand are used as wet covering to keep the concrete in wet condition for a longer time so that the concrete is not unduly dried to prevent hydration. The diagram below summarises the major criteria for using water-added curing methods. Major features of curing with added water. Membrane curing : this curing method is mostly used when there is less availability of water in the region where curing is done. Under this method, concrete could be covered with membrane which will effectively seal off the evaporation of water from concrete. A continuous seal over the concrete surface is maintained by means of a firm impervious film to prevent moisture in concrete from escaping by evaporation. Some of the materials, which can be used for this purpose, are bituminous compounds, polyethylene PLASTIC SHEETING source:www.builderbill-diy-help.com or polyester film, waterproof paper, rubber compounds etc. When waterproofing paper or polyethylene film are used as membrane, care must be taken to see that these are not punctured anywhere and also see whether adequate lapping is given at the junction and this lap is effectively sealed. Application of heat : When concrete is subjected to higher temperature it accelerates the hydration process resulting in faster development of strength. Concrete cannot be subjected to dry heat to accelerate the hydration process as the presence of moisture is also an essential requisite. Therefore, subjecting the concrete to higher temperature and maintaining the required wetness can be achieved by subjecting the concrete to steam curing. The exposure of concrete to higher temperature can be done by Steam curing at ordinary pressure, Steam curing at high pressure ,Curing by Infra-red radiation ,Electrical curing. Traditional steam curing of concrete pipes (www.construction-int.com) Miscellaneous : Calcium chloride is used either as a surface coating or as an admixture. It has been used satisfactorily as a curing medium. Both these methods are based on the fact that calcium chloride being a salt shows affinity for moisture. The salt not only absorbs moisture from atmosphere but also retains it at the surface. This moisture held at the surface prevents the mixing water from evaporation and thereby keeps the concrete wet for a long time to promote hydration. Formwork prevents escaping of moisture from the concrete, particularly, in the case of beams and columns. Keeping the form work intact and sealing the joint with wax or any other sealing compound prevents the evaporation of moisture from the concrete. This procedure of promoting hydration can be considered as one of the miscellaneous methods of curing. At the end of the curing process majority of cement gets hydrated.There is slow rate of compressive strength gain of around 50-100 psi/hours and little exothermic heat generation. In the entire process of curing if one of the curing procedures is used initially, it may be replaced by one of the other procedures after the concrete is 1 day old, provided that the concrete surface is not permitted to become dry at any time. After the termination of the curing process the adequacy of a curing program could be verified.Although strength is the primary variable around which curing specifications are based several other approaches can also be used like Surface Water Absorption: the amount of water a dry concrete specimen absorbs in the first minute or so after contact with liquid water is directly related to the quality of the curing of the near-surface zone of the concrete. This method has direct applicability to verifying curing. The method is reasonably applied to cores, which can be dried to a constant low moisture content before testing. Rebound Hammer: The rebound hammer method basically measures the modulus of elasticity of the nearsurface concrete. This may actually recommend the method for use in evaluating the curing of concrete pavements, where near-surface effects are considered most important. The test method is suitable for in-place measurements. Laboratory work has shown that rebound numbers of uncured concrete exposed to modestly severe drying are reduced by about 50 percent at 7 days relative to well-cured concrete. Strength of Cores: The strength of concrete is strongly affected by inadequate curing, and, in theory, could be detected by measuring strength of cores. the effects of poor curing are only strongly apparent in the properties of the top 50 mm of concrete, and sometimes even less. Ultrasonic Pulse Velocity: The ultrasonic pulse velocity (UPV) method is an indirect measure of the modulus of elasticity of concrete. The modulus of elasticity of concrete tends to increase with increasing hydration (or quality of curing) of the cement paste fraction of the concrete. UPV testing can be set up in a number of configurations, each of which tends to focus on slightly different features of the concrete. A simple pulse velocity taken through a piece of concrete, which is the traditional way of using UPV to investigate concrete properties, gives information on the average quality of the concrete. Abrasion Resistance: The degree of curing has been shown in numerous research publications to be strongly reflected in the abrasion resistance of the cement-paste fraction of concrete. This truth is easily verified qualitatively using an electrically powered wire brush and observing the ease with which the near-surface mortar can be removed from a small spot of concrete. Poorly cured concrete is easily abraded away, while well-cured concrete is quite difficult to abrade away with such equipment. DISEASES OF CONCRETE Deterioration of concrete buildings is becoming a cause of concern now a days. Often the structures located along open water, lakes, rivers and oceans are extremely vulnerable to attack from the harsh environment i.e. salt, moisture, humidity, carbon dioxide, etc. cracks, spalls and rust stains are some of the visual symptoms of the deterioration of concrete. CRACK Crack is the most common diseases of concrete structures and it occurs as a result of material discontinuity. Thermal and shrinkage cracks can be associated with high cement content and high strength concrete. Usually cracks occur in the concrete structures due to various reasons such as excess water in the mix ,rapid drying of the concrete, improper strength concrete poured on the job, lack of control joints, if Concrete is poured on frozen ground, alkali-silica reactionetc. In order to prevent cracks in concrete structures, following preventive measures could be taken: Estimate in advance the quantity of water to be mixed to get the required concrete mix. Adding too much water in the mix is one of the main causes of cracked concrete Do not pour concrete on the frozen ground .A compacted subgrade could be used to pour concrete upon to prevent cracking Cut control joints into the concrete so that the slab will be able to shrink and expand with temperature changes. Control joints should be cut the same depth of the slab and spaced a maximum of three times the thickness of the concrete. The slab must retain enough moisture so that the drying and shrinking happens as slowly as possible in the days and weeks after pouring. Curing helps the concrete to retain moisture in the concrete so that it can continue to gain strength to resist cracking. CRACKS ON CONCRETE SURFACE Source:www.homebuildinginformation.com FROST When the concrete is critically saturated i.e. approximately 91% of its pores are filled with water then deterioration of concrete from freeze thaw actions may occur. When water freezes to ice it occupies 9% more volume than that of water.In case there is no space in concrete for this expanded volume , a kind of distress is caused which will result in loss of concrete surface. A surface active agent should be added to the concrete mixture in order to prevent frost in a concrete structure. This creates a large number of closely spaced, small air bubbles in the hardened concrete which would act as expansion chambers to relieve the pressure build-up. It is to be noted that concrete with high water content and high water to cement ratio is less frost resistant than concrete with lower water content. ABRASION AND CAVITATION Hydraulic Concrete structures are affected by Abrasion-erosion due to the action of debris rolling and grinding against surface. The sources of the debris include construction trash left in a structure, riprap brought back into a basin by eddy currents because of poor hydraulic design or asymmetrical discharge, and riprap or other debris thrown into a basin by the public. Mechanical abrasion is usually characterized by long shallow grooves in the concrete surface and spalling along monolith joints. general abrasion and cavitation erosion results in coarse aggregate exposed concrete surface, concrete uneven surface, resulting in holes. In order to prevent the structure to suffer from abrasion the concrete should include the maximum amount of the hardest coarse aggregate that is available and the lowest practical w/c. In addition to this,high-range water-reducing admixtures (HRWRA) and condensed silica fume have been used to develop high compressive strength concrete 97 MPa (14,000 psi) , at this strength the concrete mix assumes a greater role in resisting abrasion-erosion damage. Also vacuum-treated concrete, polymer concrete, polymer-impregnated concrete, and polymer portland cement concrete could also be used to increase the abrasion resistance. In existing structures, balanced flows should be maintained into basins by using all gates to avoid discharge conditions where eddy action is prevalent. ABRASION source:www.nrc-cnrc.gc.ca CARBONATION Carbonation is a chemical reaction between atmospheric carbon dioxide and hydrated cement compounds which causes a reduction in the alkalinity of the concrete. The permeability and moisture content of the concrete directly affects the rate of carbonation . Pop-corn like calcite crystals present in carbonated paste. source:www.concrete-experts.com In the process of carbonation the calcium bearing phases present in the concrete mass are attacked by carbon dioxide of the air and converted to calcium carbonate.In this process the alkalinity of the concrete is lowered from an initial pH of around 13.5 to around 8.5 over some years. One method of testing a structure for carbonation is to drill a fresh hole in the surface and then treat the cut surface with phenolphthalein indicator solution. This solution will turn [pink] when in contact with alkaline concrete, making it possible to see the depth of carbonation. In order to combat the process of carbonation aquron products from Allcrete industries could be used which helps in the following ways seals out moisture to a depth of 100mm or more reduces oxygen permeability by a pore-blocking process brings up the alkalinity of the concrete purging and binding chlorides in the colloidal silicate hydrogel formed in the pores and capillaries of the concrete It is to be noted that when Concrete is treated within 24 hours of casting ,it will be protected for life against carbonation problems and aged concrete, once treated, will become immune to further deterioration. CORROSION Corrosion of steel reinforcement in concrete structures is well known to be Concrete Cancer, which happens to be a significant area of concern in the area of infrastructure and building across the world. Corrosive species can enter the concrete mix if the ingredients of the concrete mix such as water, aggregates, additives are contaminated.When such corrosive species reacts with the chemical compounds under the porous nature of concrete,the problem of corrosion occurs. Corrosion damage to the reinforcing steel results in the build-up of voluminous corrosion products, generating internal stresses and subsequent cracking and spalling of the concrete as shown schematically in the diagram below: Figure 2source:www.corrosion-club.com source:www.zoranthepainter.com Corrosion mechanism Concrete Cancer The most frightening thing is that the corrosion can be going on under the surface and will not be noticed until the concrete starts visibly disintegrating. The outcome of such corrosion is that concrete reduces its strength and also the steel re-enforcing within the concrete can rust and the pressure this creates can cause the concrete to crack and crumble. Buildings in coastal areas are especially at risk. The preventive measures to avoid such kind of concrete cancer are listed below: Epoxy coating: The concrete structures that are exposed to deicing salt may benifit from use of epoxy-coated, hot dip galvanised or stainless steel rebar. Epoxy coated rebar can easily be identified by the light green colour of its epoxy coating. Applying Sealants: After the process of curing, penetrating sealants must be applied. Sealants include paint, plastic foams, films and aluminum foil, felts or fabric mats sealed with tar, and layers of bentonite clay, sometimes used to seal roadbeds. corrosion inhibitors: calcium nitrite can also be added to the water mix before pouring concrete. Generally, 12 wt. % of calcium nitrate with respect to cement weight is needed to prevent corrosion of the rebars. Extreme weather conditions such as high ambient and concrete temperature, low relative humidity or a mere 40 F or less average daily air temperature for more than 3 consecutive days, tend to impair the quality of freshly mixed or hardened concrete thereby giving detrimental results. Therefore, it becomes imperative to handle concrete with caution both in extreme hot and cold weather. EFFECTS OF HOT WEATHER AND PROPER HANDLING On the compressive strength: When the temperature of concrete is high cement hydrates at a much faster rate, it sucks up water and grows crystals around the aggregate particles but dont have time to grow strong . Although, the early strength will be higher but 28-day strength suffers. If the concrete is about 18 hotter than normal (for example, 88 instead of 70), the ultimate compressive strength of the mix will be about 10% lower. On the colors of integrally colored concrete: under hot weather conditions , slump decreases rapidly as the cement sets up and and more mixing water is needed. In integrally colored concrete,this can lead to variations in water content which can result in significant differences in concrete color between adjacent pours. Surface drying: high concrete temperature and hot dry wind across the concrete can cause more drying and surface shrinkage. Thermal differentials: sometimes the hot weather condition makes one part of the concrete mass warmer than another part. If this differential is greater than about 20F then concrete gets cracks. Difficulty in maintaining air content can be a problem in warm concrete. Mixing is more likely to drive air out of the concrete making the level difficult to control. Dealing with hot weather concreting Plastic shrinkage is a particular problem in hot weather concreting. As a general rule, each 10o F increase in ambient temperature reduces slump about 1. A switch from ASTM C494 Type A to Type D water reducing and set retarding mix may be part of an effective plan for hot-weather concreting. Aggregates forms a major part in a concrete mix so its temperature has the greatest effect on concrete temperature. Shading of aggregate piles is ideal, although not always possible. Using cool water is another way to get cool concrete. Ready mix producers in hot climates use chilled water or ice to lower the concrete temperature. Retarding admixtures can also contribute towards controlling concrete in warm weather. When the concrete is hot, the setting time is very quick .At that time Retarder can be added at the plant or on the job site . Retarders delays the setting time but they also give the concrete more time to dry out, so curing is critical. Retarders come as straight retarders or as water-reducing and retarding admixtures. Mid-range water reducers can increase the air content of the concrete. For concrete that is to be stamped, consider using step retardationadding retarder to the mix after half of the batch or after one-third and two-thirds have been placed. For textured concrete one of the strongest things to do in hot weather is step retardation. In order to avoid slump loss superplasticizer (high-range water reducer) could be used. These admixtures can increase slump without affecting the concretes final strength or appearance. Before placing the concrete on a subgrade wet down everything, subgrade and forms, with cool water so moisture isnt absorbed from the concrete, which can lead to cracking. In order to prevent the evaporation of surface water use a monomolecular film or evaporation retarder as soon as the concrete is down and bull floated. These materials evaporate after a couple of hours. Monomolecular film will prevent plastic shrinkage cracking and surface crusting. In hot and dry weather curing needs to start as soon as finishing operations are completed. A white pigmented curing compound could be used with plain gray concretein order reflect sunshine. Also the white curing blanket could be used for the same purpose. A white pigmented curing compound on plain gray concrete white curing blankets keep the concrete cooler by reflecting can help reflect some heat from the sun the sun In a hot climate, stain the concrete in the coolest part of the day as staining concrete relies on a chemical reaction that happens faster in hot weather.If concrete is stained in 95 to 100 weather ,it can ruin the entire job. Staining is best done early in the day when the concrete is cooler For an overlay installation it is advisable that the concrete surface temperature should be between 50 and 80.Installing an overlay during the hottest part of the day amidst direct sunlight could adversely affect the quality of the result. EFFECTS OF COLD WEATHER AND PROPER HANDLING During cold weather until the concrete gains compressive strength of 500psi , it is under threat of either getting freezed up which in turn could break up the matrix or the concrete mix sets at a very slow pace. Below 40F the hydration reaction basically stops and the concrete doesnt gain any further strength. when the ground is cold, the concrete in contact with it will be cold and will set more slowly. This can lead to the problem of crusting, with the top part of the concrete set and the bottom still soft. During the process of shifting the concrete mix from the ready mix plant to the job site there will be some heat loss. While placing concrete in cold it is advisable to remove all snow and ice from that area. Also any standing water should also be removed that could get mixed into the concrete. In case of a frozen land, it is advisable to thaw it using hydronic heat pipes and blankets (such as those from Ground Heaters), or electric blankets (check out Power Blanket). It is also suggested to Warm up anything that will come in contact with the concrete, including forms and any embedments, to at least 32F. Covering everything with tarps the day before the pour, will keep it dry and warm enough.also blankets could be used for the same purpose as well. Place triple layers of insulating blankets at corners and edges that could freeze. Wrap any protruding rebars. Make sure the blankets wont blow off during the night. Ground heaters Inc Portland cement association While placing decorative concrete in cold weather it is suggested to use a dial pocket thermometer or an infrared thermometer to test the concrete temperature as it is needed to be kept above 50F for the concrete to keep gaining strength. Also on exterior concrete, customers should be reminded to keep deicing chemicals off the surface during the first winter. Deicers can lead to spalling of newer concrete. During the process of finishing concrete in cold weather, it is advisable to let all the bleed water to evaporate first otherwise water-cement ratio would increase surface of concrete would get weak. Bleed water is basically the concrete particles settling (like mud in a stirred up pond) and squeezing out all the extra water. Vacuums can also be used for this purpose. It should also be noted that sealing concrete in cold weather conditions is very risky. Power blanket Layfield Group In order to keep the slab warm hydronic heating pipes or electric heating blankets could be used. These are laid on top of the slab and insulated. Also, in case it is too cold to even place the concrete, then the only option left is to enclose the work and heat the air. In case of an enclosure,it is required to consider the potential problem of carbonation. With unvented heaters (salamanders), or even with gas-powered equipment, the carbon dioxide levels can increase. This carbon reacts with the concrete, creating a chalky carbonated layer at the surface which is unacceptable. To fix this problem use heaters that exhaust to the outside of an enclosure or building and just blow in warm air. Maintain the concrete temperature above 40 degree

Struggles of African Americans in Langston Hughes’ Poems, Mother to Son

Struggles of African Americans in Langston Hughes’ Poems, Mother to Son and Lenox Avenue: Midnight The experiences, lessons, and conditions of one’s life provide a wellspring of inspiration for one’s creative expressions and ideas. Throughout life people encounter situations and circumstances that consequently help to mold them into individualized spirits. An individual’s personality is a reflection of his or her life. Langston Hughes, a world-renowned African American poet and self-professed defender of African American heritage, boldly defies the stereotypical and accepted form of poetry at his own discretion. Although Langston Hughes is a successful African American poet, he, like many other Harlemites, faces obstacles and opposition along his journey through life; however, Hughes embraces his hardships and infuses his life experiences into poetical works that his fellow African Americans can relate to on some level. In both his poems â€Å"Mother to Son† and â€Å"Lenox Avenue: Midnight† Hughes reveals the constant struggle of a ty pical African American living during the 1920’s. In â€Å"Mother to Son† Hughes expresses the desperation of a mother who is anxious for her son to succeed. In the poem the mother hopes to offer her son encouraging words and impart to him the wisdom and knowledge she gains through persevering. While in the latter poem, â€Å"Lenox Avenue: Midnight,† Hughes reveals the cultural aspects of a city during the Harlem Renaissance and conveys the emotions of a quintessential African American Harlemite based on his own his experiences as an African American poet living in Harlem, NY. Hughes exposes in both poems the true nature, as he perceives it, of life as an African American in 1920’s white America. ... ...g hidden within the words of his poem. Works Cited Harper, Donna. Thomson Gale. 12, March 2003. Hughes, Langston. â€Å"The Harlem Renaissance.† Literature: An Introduction to Fiction, Poetry, and Drama. Ed. X.J. Kennedy and Dana Gioia. 3rd Compact ed. New York: Longman, 2003. 767-769. Hughes, Langston. â€Å"Lenox Avenue: Midnight.† Literature: An Introduction to Fiction, Poetry, and Drama. Ed. X.J. Kennedy and Dana Gioia. 3rd Compact ed. New York: Longman 2003. 760. Hughes, Langston. â€Å"Mother to Son.† Literature: An Introduction to Fiction, Poetry, and Drama. Ed. X.J. Kennedy and Dana Gioia. 3rd Compact ed. New York: Longman 2003. 759. Pinckney, Darryl. â€Å"Black Identity in Langston Hughes.† Literature: An Introduction to Fiction, Poetry, And Drama. Ed. X.J. Kennedy and Dana Gioia. 3rd Compact ed. New York: Longman 2003. 772-773.

Data Warehouse Case Study Essay

History of the CDR When the project began in 1995–96, the CDR, initially referred to as the â€Å"clinical research database,† was intended to support and enhance clinical research at the University of Virginia by providing clinicians, students, and researchers with direct, rapid access to retrospective clinical and administrative patient data. Re? ecting this intent, the system was funded by the School of Medicine and housed in the Academic Computing Health Sciences group, which is distinct from the medical center’s IT group. With considerable assistance and cooperation from data owners and stewards, legacy data from several different sources were loaded into a single relational database and periodically updated. Authorized users accessed the CDR through a standard Web browser and viewed or downloaded data to their personal computers for further analysis. Initially, emphasis was placed on getting the CDR running as quickly as possible and with a minimum of resources; consequently, extensive transformation of data to an enterprise data model was not performed. The CDR project team consists of 2. 5–3. 0 FTEs (full-time equivalents)— one developer, one developer-database administrator, and portions of analyst, clinician, and administrative FTEs. To date, the costs of developing and operating the CDR have been approximately $200,000 per year, underwritten by the School of Medicine. Over the course of the project, there have been signi? cant enhancements to the user interface, incorporation of additional data sources, and the development of an integrated data model. There has also been increasing interest in using the CDR to serve a broader audience than researchers and to support management and administrative functions—â€Å"to meet the challenge of providing a way for anyone with a need to know—at every level of the organization—access to accurate and timely data necessary to support effective decision making, clinical research, and process improvement. In the area of education, the CDR has become a core teaching resource for the Department of Health Evaluation Science’s master’s program and for the School of Nursing. Students use the CDR to understand and master informatics issues such as data capture, vocabularies, and coding, as well as to perform Case Study: A Data Warehouse for an Academic Medical Center 167 exploratory analyses of healthcare questions. Starting in Spring 2001, the CDR will also be introduced into the university’s undergraduate medical curriculum. System Description Following is a brief overview of the CDR application as it exists at the University of Virginia. System Architecture. The CDR is a relational data warehouse that resides on a Dell PowerEdge 1300 (Dual Intel 400MHz processors, 512MB RAM) running the Linux operating system and Sybase 11. 9. 1 relational database management system. For storage, the system uses a Dell Powervault 201S 236GB RAID Disk Array. As of October 2000, the database contained 23GB of information about 5. 4 million patient visits (16GB visit data, 7GB laboratory results). Data loading into Sybase is achieved using custom Practical Extraction and Report Language (Perl) programs. CDR Contents. The CDR currently draws data from four independent systems (see Table 1). In addition, a number of derived values (for example, number of days to next inpatient visit, number of times a diagnostic code is used in various settings) are computed to provide summary information for selected data elements. Data from each of these source systems are integrated into the CDR’s data model. In addition to the current contents listed in Table 1, users and the CDR project team have identi? ed additional data elements that might be incorporated Table 1. Contents of the CDR Type of Data Inpatient, outpatient visits Source of Data Shared Medical Systems Description Patient registration and demographic data, diagnoses, procedures, unit and census information, billing transactions, including medications, costs, charges, reimbursement, insurance information Physician billing transactions from inpatient and outpatient visits, diagnoses, and procedures Laboratory test results Available Dates Jul 1993–Jun 2000 Professional billing Laboratory results Cardiac surgery IDX billing system HL-7 messages from SunQuest Lab System Cardiac surgery outcomes data (de? ned by Society of Thoracic Surgeons Oct 1992–Jun 2000 Jan 1996–Jun 2000 Clinical details for thoracic surgery cases Jul 1993–Jun 2000 168 Einbinder, Scully, Pates, Schubart, Reynolds into the CDR, including microbiology results, discharge summaries (and other narrative data), outpatient prescribing information, order entry details, and tumor registry information. As of October 2000, we have just ? nished incorporating death registry data from the Virginia Department of Health into the CDR. These data will provide our users with direct access to more comprehensive mortality outcomes data than are contained in local information systems, which generally are restricted to an in-hospital death indicator. User Interface. The user interface runs in a standard Web browser and consists of a data dictionary, a collection of common gateway interface (CGI) programs implemented using the â€Å"C† programming language, and JavaScriptenabled HTML pages. Structured query language (SQL) statements are generated automatically in response to point-and-click actions by the user, enabling submission of ad hoc queries without prior knowledge of SQL. The SQL queries are sent to the CGI programs that query the database and return results in dynamically created HTML pages. The entire process is controlled by the contents of the data dictionary, which is used to format SQL results, set up HTML links for data drill-down, and provide on-line help. Data may be downloaded immediately into Microsoft Excel or another analysis tool on the user’s workstation. Query Formulation. Most CDR users use the Guided Query function to retrieve data. This process involves three steps: 1. De? ne a population of interest by setting conditions, for example, date ranges, diagnostic codes, physician identi? ers, service locations, and lab test codes or values. 2. Submit the query, specifying how much data the CDR should return (all matching data or a speci? ed number of rows). 3. After the CDR returns the population of interest, use the Report Menu to explore various attributes of the population on a case-by-case or group level. Custom reports can also be de? ned, and the results of any report can be downloaded into Microsoft Excel, Access, or other analysis tool. Generally, the query process requires several iterations to modify the population conditions or report options. In addition, â€Å"browsing† the data may help the user generate ideas for additional queries. We believe that it is helpful for end users to go through this query process themselves—to directly engage the data. However, many users, especially those with a pressing need for data for a meeting, report, or grant, prefer to use CDR team members as intermediaries or analysts. To date, we have attempted to meet this preference, but as query volume increases, our ability to provide data in a timely manner may fall off. Security. A steering committee of clinicians guided the initial development of the CDR and established policies for its utilization and access. Only authorized users may log onto the CDR. To protect con? dentiality, all patient and physician identifying information has been partitioned into a â€Å"secure† Case Study: A Data Warehouse for an Academic Medical Center 169 database. Translation from or to disguised identi? ers to or from actual identi? ers is possible but requires a written request and appropriate approval (for example, from a supervisor or the human investigations committee). All data transmitted from the database server to the user’s browser are encrypted using the secure Netscape Web server, and all accesses to the database are logged. In addition, CDR access is restricted to personal computers that are part of the â€Å"Virginia. edu† domain or that are authenticated by the university’s proxy server. Evaluation Understanding user needs is the basis for improving the CDR to enable users to retrieve the data independently and to increase usage of the CDR at our institution. Thus, assessing the value of the CDR—how well we meet our users’ needs and how we might increase our user base—has been an important activity that has helped guide planning for changes and enhancements and for allocation of our limited resources. Efforts to evaluate the CDR have included several approaches: †¢ Monitoring user population and usage patterns †¢ Administering a CDR user survey †¢ Tracking queries submitted to the CDR and performing follow-up telephone interviews Usage Statistics. Voluntary usage of an IS resource is an important measure of its value and of user satisfaction. 5 However, usage of a data warehouse is likely to be quite different than for other types of information resources, such as clinical information systems. A clinical system is likely to be used many times per day; a data warehouse may be used sporadically. Thus, although we monitor system usage as a measure of the CDR’s value, we believe that frequency of usage cannot be viewed in isolation in assessing the success of a data warehouse. Since the CDR went â€Å"live,† more than 300 individuals have requested and obtained logon IDs. As of September 30, 2000, 213 individuals had logged on and submitted at least one query. This number does not include usage by CDR project team members and does not re? ect analyses performed by team members for end users. Figure 1 shows the cumulative number of active users (those who submitted a query) and demonstrates a linear growth pattern.