Investigating the effects of heat treatment on metals Essay Example for Free

Investigating the effects of heat treatment on metals Essay Metals have various uses in a wide range of industry, where the properties of each metal determine what the metal will be used for. When a metal properties need to be changed to satisfy particular needs, it can be modified by processing the metals with treatments such as cold working and heat treatments. Structure of metals Metals are made from their ore, at extremely high temperature. In this form, metals are in a liquid form. The liquid metals are cast by pouring it into moulds where it is cools down and solidifies. When metals are frozen, crystals start forming. These crystals begin to form throughout the metal, where they keep they keep rapidly growing until they reach a neighboring growing crystal structure. These crystals are called grains, where crystals that meet with one another are called grain boundary. Dislocation Dislocation are formed when defects are found in the crystal structures. This is often caused by when atoms are missing in a layer, This is shown in figure one. Secondly, the metal trip should be placed on top of the hottest part of bunsen burner. The metal should be kept there until is is seen glowing red. Once the metal has gone red, it should immediately be plunged into the previously filled beaker in step 1. Lastly swirl the beaker vigorously for thirty seconds. Tempering With any metal strip that has been quenched, place the strip unto a bunsen flamer until the metal strip goes a dull red. Once the metal has gone dull red, slowly remove the metal from the bunsen flame and pace on a heat proof mat, where it should be left to cool to room temperature. Annealing Firstly, heat metal strip for five minutes on the hottest part of bunsen flame. the whole length should of the strip metal should be heated. Next, half close the bunsen flame and continue heating the metal on the non luminous flame. When a minute or two has passed, starting moving the metal strip in and out of the flame, top start cooling down the metal. After a couple of minutes, remove the strip from the flame and place it on a heat proof mat, where it can cool to room temperature. Cold working Once the metal has been cooled down, a marker should be made 30mm from the tip of the metal suing a felt tip pen. The shorter end of the metal strip should then be put in between two wooden blocks(the marker line should still be visible). The wooden blocks should be clamped firmly on the table or bench to keep the two blocks in place. With leather gloves, bend the metal strip through 90 degrees where the strip is lying alongside the wooden block ( shown in picture B). The metal should be bending where the marker was made. Now the metal should be bent 180 degrees from its position, this is shown in picture C. This in total counts as two bends. To conclude, the strongest metal in the cold working was steel where it snapped after 44 bends. This changed when the metals where quenched, copper showed the most significant change, where the metal bent 64 times before snapping; indicating an increase in strength of copper. Significant changes was also present in aluminum. Quenching on the other hand had very little affect on steel, as the data shows that steel bent 43, slight decrease compared to cold working where the steel bent on average 44 times. Overall the most affected by quenching was copper, followed closely by aluminum, with the lowest being aluminum which has broke on average after 42 bends. In annealing, copper by far was the strongest metal where the average number of bends was 75. Aluminum and steel however, only bent 32 and 35 times, respectively. This shows that annealing heat treatment does little in increasing the strength of steel and aluminum. The heat treatment tempering, managed to increase the strength of copper and aluminum by a large margin, compared to the other two treatments. This indicates that tempering may be the best heat treatment due to it making copper bend on average 84 times and aluminum 64 times, which are the highest average for both metals. The strength of steel on the other hand decreased under tempering. Generally, aluminum showed the most changes on all three treatment, with tempering having the most effect. Copper strength also increased under all heat treatment, with it also showing the most significant change under tempering. Steel however, was either unaffected or decreased under all heat treatments, this may due to experimental errors Evaluation The procedure for each metal on the table above was repeated three times, to ensure that the experiment was reliable. New strips of metals were used for each new treatment to ensure that the accuracy of the results is not changed. In addition, the length was each metal was made the same, to make the results valid. The metals also needs to be bent as close to the strip as possible, as bending the strips to far may cause the metal to bend quicker, affecting the accuracy of the results.

Endosymbiotic Theory of Eukaryotic Cell Development

Endosymbiotic Theory of Eukaryotic Cell Development Abstract The defining feature of eukaryotic cells is that they contain membrane-bound organelles and a true nucleus. The endosymbiotic theory is based upon the idea that eukaryotic cells evolved in steps beginning with the stable incorporation of chemo-organotrophic and phototrophic symbionts from the domain bacteria. This essay reviewed the evidence that supports this theory. After investigating the molecular, physiological and morphological evidence, it is almost certain that chloroplasts and mitochondria are from the domain bacteria, and that many of the genes required for the survival of these organelles are contained within the nuclear DNA of the eukaryotic cell rather than the organelles own independent DNA. It is for this reason that I believe that endosymbiosis was the process whereby eukaryotes began to form and evolve. It was found that the genome of a protozoan, Reclinomonas, contained all the protein-coding found in sequenced mitochondrial genomes, providing support for the specul ative process of endosymbiotic gene transfer. The hydrogen hypothesis seems to be the most likely scenario for the formation of eukaryotes, which explains the need for compartmentalisation with increasing host genome size to improve efficiency of function throughout the cell, and the chimeric nature of eukaryotes. Introduction Based upon data collected from slow decaying radioactive isotopes, Earth is thought to have formed approximately 4.55 billion years ago. From this time of origin, a continual process of geological and physical change has occurred, which created conditions leading to the origin of life about 4 billion years ago. Life is thought to have undergone the process of evolution, defined as DNA sequence change and the inheritance of that change, often under the selective pressures of a changing environment. (1) Microfossil evidence suggests that unicellular eukaryotes arose on Earth approximately 2 billion years ago, after the development of an oxic environment and the invention of respiratory metabolism in cyanobacteria. This timing infers that the availability of oxygen was a large influence on the biological evolution that led to the emergence of Eukarya. (1) The defining characteristic of eukaryotes is the presence of a well-defined nucleus within each cell. (2) Typical eukaryotic cells contain a membrane bound nucleus and organelles enclosed by an outer plasma membrane; these organelles are organised into compartmentalised structures which have their own function(s) within the cell, often working together with other organelles to complete vital biological processes. This compartmentation in cells is essential in organisms as it allows differing compositions of nutrients to exist inside each compartment as opposed to outside, creating perfect conditions for biochemical reactions to occur.(3) The differences between eukaryotes and prokaryotes are shown in Table 1: Mitochondria are membrane-bound organelles found in the cytoplasm of most eukaryotic cells and are most concentrated in cells associated with active processes, such as muscle cells which constantly require energy for muscle contraction. The two surrounding membranes that encompass a mitochondrion differ in function and composition, creating distinct compartments within the organelle. The outer membrane is regular in appearance and composed of proteins and lipids, in roughly equal measure, whilst the outer membrane contains porin proteins rendering it more permeable. The inner membrane is only freely permeable to oxygen, water and carbon dioxide; it contains many infoldings, or cristae, that protrude into the central matrix space, significantly increasing the surface area and giving it an irregular shape. As can be seen in Figure 1, mitochondria contain ribosomes and have their own genetic material, mitochondrial DNA (mtDNA), separate from the nuclear DNA. (4) Mitochondria are the principle sites of ATP production- in a process known as oxidative phosphorylation. Products of the Krebs cycle, NADH + H+ and FADH2, are carried forward to the electron transport chain (ETC) and are oxidised to NAD+ and FAD, releasing hydrogen atoms. These hydrogen atoms split to produce protons and electrons, and the electrons are passed down the ETC between electron carriers, losing energy at each level. This energy is utilised by pumping the protons into the intermembranal space causing an electrochemical gradient between the intermembranal space and the mitochondrial matrix. The protons diffuse down the electrochemical gradient through specific channels on the stalked particles of the cristae, where ATPsynthase located at the stalked particles, supplies electrical potential energy to convert ADP and inorganic phosphate to ATP. In mammalian cells, enzymes in the inner mitochondrial membrane and central matrix space carry out the terminal stages of glucose and fatty acid oxidation in the process of ATP synthesis. Mitochondria also play an important role in the regulation of ionised calcium concentration within cells, largely due to their ability to accumulate substantial amounts of calcium. (3)(5) Chloroplasts are membrane-bound organelles found within photosynthetic eukaryotes. Chloroplasts are surrounded by a double membrane, the outer membrane being regular in appearance whilst the inner membrane contains infoldings to form an interconnected system of disc-shaped sacs named thylakoids. These are often arranged in to stacks called grana. Enclosed within the inner membrane of the chloroplast is a fluid-filled region called the stroma, containing water and the enzymes necessary for the light-independent reactions (the Calvin cycle) in photosynthesis. The thylakoid membrane is the site of the light dependent reactions in photosynthesis, and contains photosynthetic pigments (such as chlorophyll and carotenoids) and electron transport chains. Chloroplasts, like mitochondria, contain ribosomes and their own independent DNA (ctDNA), which is central to the theory of endosymbiosis. The structure of a typical chloroplast is shown by Figure 2: Radiant energy is trapped by photosynthetic pigments and used to excite electrons in order to produce ATP by photophosphorylation. The light dependent reactions occur in the thylakoid membrane (Photosystem II or P680) and ultimately, these reactions produce the ATP and NADPH required for photosynthesis to continue in the stroma (where Photosystem I or P700 is located). A series of light independent reactions occur within the stroma producing carbohydrates from carbon dioxide and water using ATP and NADPH. The most supported hypothesis (put forward by Lynn Margulis) for the origin of the eukaryotic cell is that of endosymbiosis which is suitably named as symbiosis occurs when two different species benefit from living and working together. When one organism actually lives inside the other its called endosymbiosis.'(6) The endosymbiosis hypothesis states that the modern, or organelle-containing eukaryotic cell evolved in steps through the stable incorporation of chemo-organotrophic and phototrophic symbionts from the domain Bacteria. In other words, chloroplasts and mitochondria of modern-day eukaryotes arose from the stable incorporation into a second type of cell of a chemoorganotrophic bacterium, which underwent facultative aerobic respiration, and a cyanobacterium, which carried out oxygenic photosynthesis. The beneficial association between the engulfed prokaryote and eukaryote would have given the eukaryote an advantage over neighbouring cells, and the theory is that the prokaryote and eukaryote lost the ability to live independently. (1) Oxygen was an important factor in endosymbiosis and in the rise of the eukaryotic cell through its production in photosynthesis by the ancestor of the chloroplast and its consumption in energy-producing metabolic processes by the ancestor of the mitochondrion. It is worth noting that eukaryotes underwent rapid evolution, most probably due to their ability to exploit sunlight for energy and the greater yields of energy released by aerobic respiration. Support for the endosymbiosis hypothesis can be found in the physiology and metabolism of mitochondria and chloroplasts, as well as the structure and sequence of their genomes.(1) Similarities between modern-day chloroplasts, mitochondria, and prokaryotes relative to eukaryotes are shown in table 2: Molecular Evidence When Margulis proposed the endosymbiotic theory, she predicted that if the organelles really were prokaryotic symbionts, they would contain their own independent DNA. This was proven to be the case in the 1980s for mitochondria and chloroplasts.(7)Furthermore, mitochondrial DNA (mtDNA) was found to have a proportionally higher ratio of guanine-cytosine base pairs than in eukaryotic nuclear DNA, as found in bacteria. These findings are significant as they strongly suggest that mitochondria and chloroplasts are of prokaryotic origin and nature, supporting the possibility that the eukaryotic cell evolved from the stable incorporation of symbionts from the domain Bacteria. Another striking similarity between mitochondria and bacteria is that they both contain 70S ribosomes and contain a comparable order of genes encoding ribosomal proteins a shown in Figure 4: It is only fair that the molecular problems associated with the endosymbiosis hypothesis that have been put forward are considered. Firstly, mitochondria and chloroplasts can only arise from pre-existing mitochondria and chloroplasts, having lost many essential genes needed for survival. It has been suggested that this is because of the large timespan that the mitochondria/chloroplasts have co-existed. During this time, systems and genes that were no longer needed were either simply deleted or transferred into the host genome. Hence, mitochondria and chloroplasts have lost the ability to live independently over time. This supports the endosymbiotic theory as it provides a reason as to why the ancestors of the chloroplasts and mitochondria were able to survive independently whilst chloroplast and mitochondria are unable to do so now. The study of mitochondrial genomes so far has suggested that mitochondrial genomes actually encode less than 70 of the proteins that mitochondria need to function; most being encoded by the nuclear genome and targeted to mitochondria using protein import machinery that is specific to this organelle.(7) It has been found that the genome of Reclinomonas contains all the protein-coding genes found in all the sequenced mitochondrial genomes: (8) The importance of Figure 5 is that it shows that the mitochondrial genome no longer contains many of the protein-coding genes, and hence, mitochondria are no longer able to live independently. The mitochondrial endosymbiont is believed to have belonged to the proteobacteria since several genes and proteins still encoded by the mitochondrial genome branch in molecular trees among homologues from this group. Interestingly, mitochondrial proteins such as the 60- and 70-kDa heat shock proteins (Hsp60, Hsp70), also branch amongst proteobacterial homologues, but the genes are encoded by the host nuclear genome.(9) This can be explained by a theory called endosymbiotic gene transfer which states that during the course of mitochondrial genome reduction, genes were transferred from the endosymbionts genome to the hosts chromosomes, but the encoded proteins were reimported into the organelle where they originally functioned. (7) This theory is central to the endosymbiotic theory, as it explain s the inability of chloroplasts and mitochondria to live independently even though these organelles are believed to have originated from the domain Bacteria. It is also believed that this gene transfer has provided an essential way in which mitochondrial or chloroplast activity can be regulated. The studies of protists raise  the possibility that mitochondria originated at essentially  the same time as the nuclear component of the eukaryotic cell  rather than in a separate, subsequent event. (10) T This would fit in with the hydrogen hypothesis as described later. A further problem to consider is the extent to which genes were transferred to the cell nucleus. Why did some genes remain in the cytoplasmic organelles? This question has been addressed by the Co-location for  Redox  Regulation (CoRR) hypothesis, which states that the location of  genetic information  in  cytoplasmic  organelles  permits regulation of its expression by the reduction-oxidation  (redox) state of its  gene products. Therefore, evolution by natural selection would have favoured mitochondrial or chloroplast cells that had deleted or transferred some genes to the host genome but had kept those that were still beneficial in the regulation of the organelles activity. (11) Physiological Evidence Evidence for the endosymbiosis theory can be found in the physiology of mitochondria and chloroplasts. For example, both mitochondria and chloroplasts have their own protein-synthesising machinery which closely resembles that of Bacteria rather than that of Eukaryotes. Ribosome function in mitochondria and chloroplasts are inhibited by the same antibiotics that inhibit ribosome function in free-living bacteria. Hence, it is no surprise that both these organelles contain 70S ribosomes typical of prokaryotic cells, and show 16S ribosomal RNA gene sequences, a characteristic of certain Bacteria such as Escherichia coli.(1) For example, human mitochondrial ribosomes can be affected by chloramphenicol (an antibiotic used to inhibit protein synthesis), further evidence that mitochondria are likely to be of bacterial origin. Chloramphenicol is a relatively simple molecule containing a nitrobenzene ring responsible for some of the toxicity problems associated with the drug: Chloramphenicol inhibits protein synthesis due to its high affinity for the large (50S) ribosomal subunit, which when bound to chloramphenicol, blocks the action of peptidyl transferase, preventing peptide bond synthesis. It has also been discovered that chloramphenicol prevents the maturation of the 30S ribosomal subunits, decreasing the number of competent subunits and significantly decreasing the proportion of mitochondrial ribonucleoprotein present as monomers. (12) Also, the antibiotic rifampicin which inhibits the RNA polymerase of Bacteria has been found to inhibit the RNA polymerase within bacteria. Proteins of chloroplast or mitochondrion origin, like bacteria, always use N-formylmethionine as their initiating amino acid of their transcript.(13) Mitochondria replicate, like bacteria, only by the process of binary fission inferring that mitochondria did indeed originate from prokaryotes. The completion of the genome sequence of the cyanobacterium Synechocystis, has provided e vidence for the origin of chloroplast translocation apparatus. Just as the endosymbiosis theory predicts, analysis of this sequence showed that three key translocation components within chloroplasts, Toc75, Tic22 and Tic20, evolved from existing proteins within the cyanobacterial genome.(14)Mitochondria and chloroplasts have remarkably similar mechanisms by which ATP is produced. These ATP-generating pathways often include electron transport chains and proton pumps, similar to that found in prokaryotic energy production mechanisms. One of the most recent problems with the endosymbiosis theory is found within the physiology of mitochondria. Mounting evidence suggests that key components of the mitochondrial transcription and replication apparatus are derived from the T-odd lineage of  bacteriophage  rather than from an ÃŽÂ ±-Proteobacterium, as the endosymbiont hypothesis would predict.'(15) It has been discovered that three of the essential elements of the replication and transcription apparatus; the RNA polymerase, the replicative primase-helicase and the DNA polymerase do not resemble those of eubacteria as predicted by the symbiosis theory, but instead appears to resemble proteins encoded by T-odd bacteriophages. However, this does not disprove the theory of endosymbiosis as it is conceivable that numerous mitochondrial genes were acquired together from an ancestor of T-odd phage early in the formation of the eukaryotic cell, at the time when the mitochondrial symbiont was incorporated. (15) Morphological Evidence Another characteristic that further supports the hypothesis is that mitochondria and chloroplasts contain small amounts of DNA that is different from that of the cell nucleus which is arranged in a covalently closed, circular structure, with no associated histones, typical of Bacteria. Mitochondria are surrounded by two membranes, separated by the inter-membranal space and each with a different composition. Mitochondrial membranes more closely resemble membranes found in Gram-negative bacteria in terms of lipid composition than eukaryotic membranes. (16) The inner-membrane infoldings in the mitochondria lends more credibility to the endosymbiosis theory as the cristae are adaptations that increase the surface area of oxidative enzymes, evolutionary analogues to the mesosomal membranes of many prokaryotes (16)Further evidence that mitochondria and chloroplasts are of a prokaryotic origin is the lack of cholesterol in their membranes. This is significant because it is an essential stru ctural component in many eukaryotic membranes, mainly in mammalian cell membrane, but it almost completely absent amongst prokaryotes. Another problem is that recent genetic analysis of small eukaryotes that lack many characteristics that are associated with eukaryotic cells, most importantly mitochondria, show that they all still retain genes involved in the synthesis of mitochondrial proteins. In 1983, the taxon Archezoa was proposed to unite this group of odd eukaryotes, and the belief was that these cells had diverged from other eukaryotes before these characteristics evolved and hence represented primitive eukaryotic lineages. Before the recent genetic breakthrough that shows that these eukaryotes contain genes involved in mitochondrial protein synthesis, molecular work supported their primitive status, as they consistently fell deep into the branches of eukaryotic trees. This recent genetic analysis implies that all these eukaryotes once had mitochondria, suggesting that they evolved after the mitochondrial symbiosis. There is also the question of how the eukaryotic cell arose, including the nature and propert ies of the cell that acquired mitochondria and later chloroplasts, and how the nuclear membrane was formed which touches upon the compatmentalisation within cells and its importance in the functioning of the eukaryotic cell. (7) Formation of the eukaryotic cell There have been two hypotheses put forward to explain how the eukaryotic cell arose. One states that eukaryotes started as a nucleus-bearing lineage that later acquired the bacterial ancestor of the mitochondrion and the cyanobacterial ancestor of the chloroplast by the process of endosymbiosis. This nucleated line then diverged into the lineages giving rise to animals and plants. It is thought that the nucleus arose spontaneously in an early cell. One possible cause for the spontaneous formation of the nucleus is that it arose in response to the increasing genome size of early eukaryotes. (1) The second hypothesis, also known as the hydrogen hypothesis, states that the bacterial ancestor of the mitochondrion was taken up by a member of the Archaea via endosymbiosis, and from this association, the nucleus later emerged, followed by a later acquisition of the cyanobacterial ancestor of the chloroplast. The main difference between these two hypotheses is the position of the mitochondrion relative to the formation of the nucleus in time and hence on the universal phylogenetic tree. The hydrogen hypothesis put forward by William F. Martin and Miklos Muller in 1998, proposes that the eukaryotic cell arose from a symbiotic association of an anaerobic, hydrogen dependent, autotrophic archaebacterium (the host) with a hydrogen producing, oxygen consuming eubacterium (the symbiont), which released molecular hydrogen as a waste product of anaerobic heterotrophic metabolism. (17) The dependence of the host upon the molecular hydrogen as an energy source, produced as a waste product b y the symbiont is thought to be what lead to the association. In this scenario, the nucleus arose following the formation of this stable association between these two kinds of cells, and genes involved in lipid synthesis were transferred from the symbiont to the host chromosome. This may have lead to the synthesis of bacterial (symbiont) lipids by the host, eventually leading to the creation of an internal membrane system, the endoplasmic reticulum and the early stages of a eukaryotic nucleus. As the size of the host genome increased with time, changes were made to maximise the efficiency of replication and gene expression via the process of evolution. Hence, over time, this kind of cell compartmentalised and sequestered the genetic coding information within a protected membrane away from the cytoplasm. The formation of a mitochondrion-containing nucleated cell line was complete, which then later acquired chloroplasts by endosymbiosis. The hydrogen hypothesis has explains the observ ation that eukaryotes are of chimeric nature, containing attributes of both Bacteria and Archaea. (1) Conclusions In summary, molecular, physiological and morphological evidence can be found to support the endosymbiosis theory put forward by Lynn Margulis. Most compelling of which is the numerous similarities between organelles such as chloroplasts and mitochondria with prokaryotes, coupled with the inability of the organelles to live independently despite having their own independent DNA due to most of the genes required for the survival of the organelle being stored in the nuclear DNA of the host. The importance of this should not be underestimated, as it does all but prove that the ancestors of mitochondria and chloroplasts were of a prokaryotic origin and thus were once able to live independently. Therefore, this does lend credibility to the endosymbiosis theory as the symbionts that were allegedly incorporated were likely to have been from the domain bacteria, and that something must have occurred which stopped the symbionts being able to live independently, an event which many scientists n ow believe to be the process of endosymbiotic gene transfer. The hydrogen hypothesis appears to be the likely scenario for how the eukaryotic cell evolved, as it explains the formation of the nucleus as being a response to the growing size of the nuclear genome of the host, which would have maximised efficiency of gene expression. Endosymbiosis also explains why the eukaryotic cell appears to be of a chimeric nature; containing attributes of Archaea (e.g. similar transcription and translation apparatus) and Bacteria (e.g. contain same type of lipids).

Safety Assessment: Benzalkonium Chloride as Sanitising Agent

Safety Assessment: Benzalkonium Chloride as Sanitising Agent Benzalkonium Chloride Benzalkonium chloride or BAC is an antibacterial agent belonging to the quaternary ammonium compound group. It is widely used in the health care industry and cosmetic industry as an antimicrobial and cleansing agent. According to the Food and Drug Administration (FDA), 0.1-0.13% w/w BAC is considered safe and effective as an â€Å"antiseptic drug product†.55 BAC has also been recognized as safe and effective when incorporated into oral mouth rinses.56 BAC is also popularly used as a rinse-free hand sanitizer and for hand washing.57 Short-term and long-term clinical studies have shown that BAC incorporated in intranasal products is safe and well-tolerated. 58 Furthemore, BAC meets the performance criteria under the Tentative Final Monograph for Health Care Antiseptic Drug Products as an active component in rinse-free hand sanitizers. Sufficient evidence exists to support the usage of BAC as a Category I active ingredient in 1994. It was analyzed as a leave-on sanitizer at the Final Monograph for Healthcare Personnel Antiseptic Drug Products. 59 A study by Dyer et al concluded that a hand sanitizer with BAC as the main component was a safe and effective way of decreasing illness absenteeism in grade schools.60 The safety of BAC was reviewed by an expert panel and they concluded that at concentrations of up to 0.1%, free active ingredient is â€Å"safe for human use†.61 It was acknowledged that BAC can be used beyond being an active ingredient for leave-on products because of its safety and antimicrobial effectiveness profiles. The FDA has also agreed upon the usefulness of biocidal quaternary amino actives, particularly BAC, in their previous rulemaking. As an example, the FDA stated that â€Å"it was not seriously concerned with the safety of ‘quats’ for first aid uses like wound cleansers, skin wound protectants, and skin antiseptics† in the 1991 Proposed Rule for Topical Antiseptic Drug Products for Over-the-Counter Human Use; Tentative Final Monograph for First Aid Antiseptic Drug Products. BAC was found to meet the requirements for first-aid antiseptic applications as reviewed by the expert panel at that time. Furthermore, the FDA has permitted the combination of BAC and Benzethonium Chloride homologues at concentrations of up to 0.004% as a food preservative or for long-term ingestible applications.62 At the 2002 16th Report of the Cosmetic Ingredients Review Expert Panel, BAC was announced to be safe at concentrations of up to 0.1% w/w. The cosmetic applications studied here were those that encompassed a daily-use regimen. A publication was done on a cross-over study of 420 grade-school children (5-12 years old) for a period of 10 weeks. They were told to use a leave-on sanitizer with BAC as soon as they entered the classroom, before eating their snacks and lunch, after sneezing or coughing inside the classroom, and after using the restroom. They observed that even with frequent use, there was no adverse reaction such as edema, rash or erythema, among the students during or after the study.40 Another study published in 1998 investigated the performance of an alcohol-free hand sanitizer with BAC. They concluded that the product exceeded the minimum performance standards indicated by the FDA for reducing bacteria.63 BAC has been reported to be effective against a wide variety of microorganisms, such as mixed-type viruses and non-enveloped viruses. BAC even demonstrated on some instances, a significantly higher virucidal activity as compared to alcohol applications. One important aspect of BAC that should not be over-looked is its non-flammable nature. In fact, during the SARS epidemic in 2003, BAC-containing sanitizers were very effective against human coronavirus especially in use in airlines and airports as alcohol-containing products were banned because of issues in flammability. In a study on BAC at reducing illness in public and private schools, they observed a 44.2% decrease in incidence of gastrointestinal illnesses and a 50.2% reduction in respiratory-related illnesses. In a different double-blinded study with 769 students, there was a 33% reduction in illness-related absenteeism. It was recommended that alcohol-free leave-on sanitizers, like those with BAC, are the only appropriate composition for usage in settings as school. This is due to the possible misuse of alcohol-containing sanitizers as a fire accelerant or by intentional ingestion. An excellent review on the issue of bacterial resistance to antibacterial  sanitizers was also recently submitted by SDA to FDA in response to the reopening of the docket for comments. However, the FDA advised that further studies should be done regarding antimicrobial resistance and the potential development of resistance to these agents, including BAC. This was stated at the joint meeting in 1997 of the FDA Advisory Committees. In the field of Orthodontics, Othman et al 64 confirmed that adding BAC to an adhesive produces antibacterial properties. In the study, BAC was incorporated into a light-cured composite resin, and an evaluation of its antimicrobial and physical properties was done. BAC was incorporated into Reliance Phase II adhesive to produce BAC concentration from 0.25% to 2.50% wt/wt. The modified samples were cut into disks and incubated in Strep. mutans for two days. Amount of bacterial inhibition was measured with agar disk diffusion assay. Other disks were placed in brain-heart infusion medium with Strep. sobrinus to measure its adherence. Cells that adhered were measured. Tensile bond strength was analyzed using a universal testing machine by attaching traction hooks to bovine teeth with the modified adhesives. Results showed an increase in antimicrobial activity in composites with higher BAC. Antimicrobial activity was negative for the composites without BAC. The composite with BAC and with out BAC did not show any difference with regard to their diametral tensile stress and tensile bond strength. Therefore, they concluded that when BAC was combined with an orthodontic adhesive, it added antimicrobial properties without changing its mechanical properties. Another study that aimed to create an antibacterial adhesive without compromising its bond strength was done by Saito et al.65 Their aim was to find the dose of BAC that exhibited antibacterial effect and did not compromise bond strength. In Saito’s study, Superbond CB resin cement was used. A mixture of the polymer, monomer, catalyst and BAC was produced according to the instructions of the manufacturer. Composite disks with the following BAC concentration were produced: 0.25%, 0.75%, 1.25%, 1.75%, 2.5%, and 5% (wt/wt). Composite disks of the same size (0.8 mm x 2 .0 mm thickness) were made. The test bacteria used were Strep. mutans 10449 and PS14, and Strep. sobrinus 6715 and B13. A brain-heart infusion medium was used to grow the bacteria. To evaluate the antibacterial activity, disk diffusion assay was utilized. To analyze the release of BAC as shown by an inhibition of growth of the bacteria, the semidiameter of the growth inhibition zone was measured. The bacteria were grown overnight in a broth and diluted. An optical density of 0.5 (550nm) was used. An inoculation of 80  µL (60-fold dilution) was performed on the brain-heart infusion agar plates. A glass rod was used to spread the inoculums evenly providing uniform bacterial growth. The BAC-infused composite disks were placed on the agar and were incubated at 37 ºC. Two days after incubation, the inhibition zones were measured. Saito also tested the shear bond strength using 70 extracted human premolars. The teeth were randomly distributed into seven groups and embedded in acrylic except for the buccal areas which were used for bonding. The teeth were polished using rubber prophylactic cups with pumic for 10 seconds. The teeth were etched with 65% phosphoric acid for 30 seconds and washed for 20 seconds then orthodontic metal brackets were bonded. Composite with the following BAC concentrations were used to bond the brackets: 0%, 0.25%, 0.75%, 1.25%, 2.5%, and 5%. A 300-gram force was applied on each bracket (based on the study of Bishara et al66). The results were presented in standard deviation and mean and analyzed with ANOVA to determine if there were significant differences among the groups. For multiple comparisons, Fisher test was used. Statistical differences were detected by a Chi-square test. Significance was predetermined at P 0.5.38 Results showed that there were significant differences among the composites with different BAC concentrations. No significant differences were found among the bacterial strains. When placed on the agar plate with Strep. mutans or Strep. sobrinus, no inhibition zone was observed on the composite with 0% BAC. The composite disks with BAC demonstrated a significant antibacterial property when compared with the composite without BAC. The antibacterial effect was found to increase as BAC concentration increased. This was indicated by an increase in the bacterial inhibition zones that were measured. The disks with 5% BAC had the highest amount of antibacterial activity. A significant difference in bond strength was noted among the different composites with BAC. However, as BAC concentration was raised, they observed a decline in shear bond strength. The study of Saito et al concluded that adding BAC into composite resin attributes antimicrobial properties strong enough to inhibit Streptococcus mutans and Streptococcus sobrinus. A clinically acceptable range of shear bond strength is yet to be established scientifically. Saito noted that incorporation of BAC does not lessen the strength to less than 10 MPa when an etchant (phosphoric acid) is used. The range of shear bond strength in study was 10.12 MPa – 20.94 MPa. Saito et al further concluded that a composite incorporated with BAC â€Å"has a possibility for clinical application as a bonding adhesive†. It was recommended in the study that it is essential to acquire a long-term release behaviour of an antibacterial agent. Therefore, a study investigating the release behaviour of BAC should be done. It was mentioned in the study by Saito that BAC has been a popular choice of contact lens antiseptic. However, the quantity of BAC used in the study was less than the amount used in contact lenses. A typical bonding procedure in an orthodontic patient requires around 150 mg of composite adhesive. Therefore, 0.7 mg of BAC is required to achieve 0.5% BAC concentration. The same author in 2009 evaluated the antibacterial activity and cytotoxicity of an orthodontic adhesive containing BAC. To achieve the desired concentration of BAC, it was initially diluted to 50% by mixing it with the orthodontic polymer (wt/wt). It was diluted further with polymer to achieve the required concentration. 65 They achieved the following BAC concentrations: 0.25%, 0.75%. 1.25%, 1.75%, 2.5%, and 5.0% (wt/wt). Custom-made molds were used to produce BAC-composite disks of the same size (8.0 mm x 2.0 mm). The disks were evaluated using antibacterial and cytotoxicity assays with three independent runs. To perform the disk diffusion assay, the BAC composite disks were soaked in distilled water at 37 ºC for 0, 30, 90, and 180 days prior to the assessment of antibacterial activity. The test bacteria used were Strep. mutans 10449 and PS14 and Strep. sobrinus 6751 and B13. They were routinely grown in a brain-heart infusion medium for 24 hours. The growth inhibition of Strep. mutans and / or Strep. sobrinus showed the release of BAC into the agar medium. Electric digital callipers were used to take measurements of the zone of growth inhibition around each BAC composite disk. To test the cytotoxicity, human gingival fibroblast cultures were grown from the cells of healthy gingival tissues from patients who were undergoing extraction prior to orthodontic treatment. This was copied from the method of Somerman, et al. After the patients underwent extraction, a part of the gingival tissue attached to the interdental papilla was taken. The samples were washed twice in phosphate-buffered saline solution (PBS). The acquired tissues were dissected into 1-mm cubes and were transferred to 35-mm tissue culture dishes with ÃŽ ±-minimal essential medium supplemented with 100  µg/mL of penicillin G, 500  µg/mL gentamicin sulphate, 0.3  µg/mL amphotericin B, and 10% fetal bovine serum. Incubation of the cultures was done in a 37 ºC humidified incubator with 95% air and 5% carbon dioxide. When confluence was reached, the cells were detached using 0.05% trypsin in PBS for 10 minutes. They were subcultured in flasks and seeded.38 The controls used in the study were the resin disks without BAC. The harvested gingival cells were laid under resin disks. In between the disks and the gingival cells was an 8  µm PET membrane that allowed the passage of the components of the resins to make contact with the human gingival cells. This was based on the study of Tang et al. Incubation with the gingival cells were done at 37 ºC for 1, 3, and 6 days.38 A reduction assay kit containing tetrazolium bromide was used to assess the cytotoxicity. This was based on the reduction that occurs to MTT when exposed to living cell mitochondria. It becomes purple fromazan. After 1, 3, and 6 days, the cells were cleaned with PBS after removal of the resins and the medium. Addition of 0.5 mL MTT medium solution was made to the wells. The solution was incubated at 37 ºC for 3 hours. A microplate reader was used to measure the purplish lysate. They observed significant differences among the different lengths of time the samples were soaked in distilled water and among the BAC concentration. With the different bacteria, they did not detect any significant differences. No difference that was significant enough was also observed between the bacterial strain and BAC. There were significant differences noted regarding the antibacterial activity at 0 day between samples with 5% BAC compared to other BAC concentrations. There were also significant differences observed regarding antibacterial activity among 0.25%, 0.75%, and 1.25% BAC, and 1.75%, 2.5%, and 5% BAC concentration. However, there was not any significant difference detected among 1.75%. 2.5%, and 5% BAC concentrations. There was a significant difference at 180 days between 0.25%, 0.75%, and between 1.25% and 5% concentrations. They observed that the higher the concentration of BAC in the composite, the greater the decrease that occurred in antibacterial property based on the assay time prolongation. They concluded that when the samples were not soaked in water, they exhibited higher antibacterial activity. The resins with 5% BAC had the highest antibacterial property. There was a significant decrease in antibacterial activity after soaking the samples in water for 180 days at all BAC concentrations. The samples incorporated with 5% BAC had the highest antibacterial activity compared to the resin with 0.25% at all periods of the experiment. In fact, the antibacterial activity exhibited by the resin with 5% BAC soaked for 180 days was the same as the antibacterial activity shown by the resin containing 0.25% and 1.75% BAC prior to immersion in water. There were significant differences in MTT activity percentages among the BAC composites with regard to cytotoxicity to the human gingival cells. Saito’s study concluded that resins with 1.25% or 1.75% BAC exhibited constant antibacterial properties when immersed in water for 180 days due to the continuous BAC release. However, an increase in cytotoxicity was noted as the antibacterial activity increased. Therefore, composites with a higher concentration of BAC were shown to be more cytotoxic. A concentration of BAC that was 0.25% or 0.75% exhibited cytotoxicity similar to the resins without BAC or the controls at all test periods. Saito et al recommended that a similar study be made using saliva instead of water as the immersing medium. This is due to the presumption that the oral environment is different that it may influence the antibacterial activity and cytotoxicity of the resins with BAC. The study confirmed that adding BAC to a composite resin exhibits an antibacterial effect against Strep. mutans and Strep. sobrinus. The author suggested that BAC be tested in vivo for safety before it is tested clinically.

Travel Restrictions to Cuba :: essays research papers

The US travel policy restricts Cuban-Americans to travel to Cuba once every three years. Some agree that this attacks Family Values. Others agree with the travel restriction. Many feel its the only way to stop funding the Communist Dictatorship. Recently a policy is the US travel restrictions to Cuba. The policy has many restrictions, But the most controversial states that Cuban American citizens may visit Cuba only once every three years( Farley and Thale, pg.1 ). The Policy represent a tightening o f the US embargo against Cuba( Farley and Thale, pg.1 ). This policy stops aiding the Cuban Economy and bans Americans from buying fine cigars and cheap sugar, on top of other things at the cost of our national honor, but when it comes to family issues, the policy is really effective in a wrong way. The new policy goes against family values.   Ã‚  Ã‚  Ã‚  Ã‚  Through the History , The United State citizens have indirectly supported the Cuban economy ( Sullivan, pg. 1 ). This policy stops the flow of money into the Cuban Economy. In effective does damage to the relationships between Cuban-Americans and their families in Cuba. But the policy effectively stops giving money to Castro, and his terrorist and murderous ways( Farley and Thale, pg.1 ). The policy claims it stops efforts to influence conditions in Cuba. Stopped conditions of aiding Castro, basically stopping the flow of information and abridging the rights of ordinary American( Sullivan, pg. 2 ).   Ã‚  Ã‚  Ã‚  Ã‚  Through the years the policy has gone through many revisions. New amendments have been added adds new restrictions and has left previous part of the policy in place. The New policy rules are claimed to attack family values. While some strongly argue that new revision are necessary order to stop funding a communist dictatorship( Farley and Thale, pg.2 ). The policy has gone through a very recent and controversial change. The policy Now only allow Cuban - Americans to visit Cuba only once ever Three years, as oppose to when ever you wanted. Basically before recent revisions, you had the freedom to come and go to Cuba as you pleased.   Ã‚  Ã‚  Ã‚  Ã‚  The policy over has gone through very effective revisions. Cuban-Americans are the ones who are most effected by the policy. Basically those who have Cuban- American family in US with family in Cuba. The policy effects the families in Cuba because the policy limits the amount of humanitarian assistance that Cuban-American families can give to their family.

Corporate Valuation - Dandy Fashion Berhad :: Business Finance Stock Market

The value of public companies is determined by the stock market. The value of companies not publicly quoted will be greatly influenced by the same market. Therefore, we will focus on the main stock-market-related ratios. They are:  · Market Capitalization  · Share values, nominal, book, market  · Earnings Per Share (EPS)  · Dividends Per Share (DPS)  · Dividend Cover and Pay-Out Ratio  · Earnings Yield  · Dividend Yield  · Price To Earnings Ratio (PE)  · Market To Book Ratio Below is the balance sheet for Dandy Fashion Berhad: Dandy Fashion Berhad BALANCE SHEET AS AT 31 DECEMBER 2006 ($000,000s) Assets Liabilities & Shareholder's Equity Long Investment $ $ Owners Funds $ $ Net Fixed Assets 440 Issued Capital 80 Investment 40 Capital Reserves 60 Revenue Reserves 220 360

Success of Mcdonalds

As a husband and Father of two children, I’d like to say I’m an expert on McDonalds, especially the modern day McDonalds which is a lot different than when I was a kid. Today, McDonald’s is practically everywhere in the world and is a part of their cultures. The explanation of McDonald’s success can be derived from many things, but the ones that stand out are first their branding. They have been around for over sixty-five years and that certainly helps with branding. As of today, McDonald’s success in the public’s eye is that they have quality food at a low price that is given to the customer quickly with great service and clean facilities. The planning, organization, leadership and controlling by McDonald’s are about as cutting edge as you can get when it comes to fast food restaurants. I’m going to talk about these four points and they will tell you why McDonald’s is the number one fast food chain in the world. The McDonald’s chain is composed of company owned restaurants as well as franchised restaurants which make up over sixty-five percent of the operating McDonald’s outlets. Now because of this many of the restaurants are controlled and run separate from one another. McDonald’s is not just around to gain profits, but to survive not only the American recession, but also the global market. They strive to be the best employer for people in each community around the world, deliver operational quality to their customers in each and every restaurant and achieve profitable growth by continuing to expand their brand and using their strengths to continue to be innovative and take advantage of modern technology. So yes, McDonald’s knows what they are doing, but that wasn’t always the case. Back when they first opened, they were only open for lunch and dinner. So approximately from 7:00 a. m. to 7:00 p. m. and they did well, but today most McDonald’s restaurants are open twenty-four hours a day. Many fast food chains have copied this idea in order to keep up with McDonalds. From a planning standpoint, McDonald’s is always coming up with innovative ideas to continue to their branding. When you watch a couple hours of television in the evening, no matter what channel, you are going to see a McDonald’s commercial. They are typically very fresh and memorable and that’s without a doubt on purpose. The planning that goes into McDonald’s marketing is to always be two steps ahead of their competition. You also probably can’t help but see at least one billboard from McDonald’s on the way to work. Again, this to McDonald’s in your head for breakfast, lunch and dinner. Another big part of McDonald’s planning is to stay modern. Our American culture has gotten increasingly obese over the decades and McDonald’s takes a lot of heat for this. This is why they came up with their healthy menu a few years back so people had the choice to eat healthy. I believe another big part of McDonald’s planning is to tap into markets that they haven’t reached before. Sure McDonald’s has been serving coffee for years, but who doesn’t like a good cup of Starbuck’s coffee? I know I love my Starbuck’s in the morning and this is where McDonald’s decided to tap into the gourmet coffee drinker market recently by coming up with the McCafe. They now serve frappuccinos, gourmet coffee and iced coffees. This was brilliant in my opinion because now when you go to McDonald’s in the morning for your Egg McMuffin, you can now get a Starbucks quality gourmet coffee. McDonald’s has done very well with this addition to their menu and this is why McDonald’s has been and will continue to be the number one fast food chain in the world. As far as organizing, McDonald’s has franchises all over the world now and they continue to grow at a blistering pace. Their goal is to make sure that globally, each restaurant caters to specific cultures. What is on the menu in my southern California McDonald’s is different that say a McDonald’s in Europe. Having been stationed in Germany, I can definitely attest to this. So organizationally, McDonald’s continues their success by globally rganizing and implementing innovations to each of their franchises all over the world. Even the McCafe, as new as it is, is launching in McDonald’s franchises across the globe. Leadership is vital the McDonald’s success. Without strong leadership, who knows what would have happened to the McDonald’s brand. In 2001, the Hu man Resource Design Center for McDonald’s Corporation initiated the development of a special leadership development program for a select number of high potential managers identified as candidates for possible promotion into a key role in its system, that of regional manager. The program was entitled â€Å"McDonald’s Leadership Development Experience†. This program, now twelve years young, is breeding leadership within its own walls. Having read about the program, it’s very extensive and well thought out and this is just one of the reasons why McDonald’s continues to have strong leadership. Now as far as McDonald’s controlling is concerned, they do have very strict controls and guidelines in place to ensure that all of their restaurants are uniform. This is really one of the qualities that separate themselves from the competition. The strict controls in place for each McDonald’s franchise don’t just apply to the ones here in the United States, but all over the world. Things like uniform restaurant hours, quality control standards and strict hiring criteria for employees are just a few of the things that McDonald’s has in place to ensure that all of their restaurants in the world have a high standard of excellence. McDonald’s has been successful for quite some time now and the four points I just wrote about are some of the reasons for their success. McDonald’s will continue to be innovative and hold a high standard of excellence. I be in twenty year there will be new and exciting products from McDonald’s as they continue to be the number one fast food chain in the world. McDonald's 24/7; By focusing on the hours between traditional mealtimes, the fast-food giant is sizzling, by Michael Arndt. Business Week. New York: Feb 05, 2007. , Iss. 4020; pg. 64, retrieved at 07/22/2010 from: http://www. businessweek. com/magazine/content/07_06/b4020001. htm Helm, B. (2010). Ethnic Marketing: McDonalds' Is Lovin' It. Bloomberg Business Week, retrieved May 15, 2011 at http://www. usinessweek. com/magazine/content/10_29/b4187022876832. htm A Golden Recipe for McDonald’s Europe, by Kerry Capell(2010). A Golden Recipee for McDonalds' Europe. Business Week (on line), New York, July 18, 2008, retrieved at 07/200/2010 from: http://www. businessweek. com/globalbiz/content/jul2008/gb20080717_293203. htm Patton, L. (2011). Ronald McDonald Sidelined as Chain Toutes Lattes. Bloomberg Business Week, retrieved May 15, 20 11, at: http://www. businessweek. com/news/2011-03-02/ronald-mcdonald-sidelined-as-chain-touts-lattes. html

Rhetorical Crtique Essay

On this rhetorical critique, I will be talking about the driving community of the state of Florida. As we all know, Florida is infamous for it’s terrible accidents. John Couwels and Vivian Kuo, journalists for CNN, prepared an article about the multi-car crash that occurred on January 29th,2012, where 11 people were killed and 46 others were injured. I chose this article because car accidents are a daily event in the state of Florida. However, the roads are spacious and for the most part, well designed. Florida drivers are being held accountable for the wreck due to their lack of safety precautions used while driving through a high fog/smoke area, caused by a nearby forest fire. This article is great for a project proposal; it addresses the drivers bad decision making when faced with cautious situations. The article named â€Å"Florida Highway Patrol: Some drivers didn’t slow before crashes†, explains that the Florida Highway Patrol prepared a traffic report holding the drivers of the crash, responsible for their actions by continuing to drive without headlights or warning signals, and without slowing down. The highway patrol quadrupled their staff on the road, and reported that conditions were clear enough to drive. Barely half an hour later, a car crash involving 25 vehicles closes the I-75 by gainesville. According to the report, drivers did not take the proper precautions assigned after fog and smoke warnings were placed on the road, causing more vehicles to smash into accidents that did not have enough time to be cleared from the road. This article informs us really well of a community problem. The authors use quotes from people who attended the scene giving a sense of complete reasoning or â€Å"truth† over emotion. The article continues by saying that the highway patrol has already accepted different measures and policies to promote a more secure Florida through professional law enforcement and traffic safety awareness. The specific type of writing is quoted when witnesses or police officials are interviewed. The writing that is used in the article is useful for making the reader visualize the event through a witness’ eyes.