Conductivity :: essays research papers

Super conductivity is a natural phenomenon in which certain materials such as metals, alloys, and ceramics, can conduct electricity without resistance. These materials are what we call superconductors. In a superconductor, once the flow of electrons begins, it essentially goes on forever, making it an important material to humans. Superconductivity was discovered by a Dutch scientist by the name of Heike Kamerlingh Onnes in 1911. While researching properties of materials at absolute zero, this man found out that certain materials lost its resistance to the flow of electrons. For years to come, his discovery was at the head of theoretical interest. The only problem though, was that people at that time could not even think of a way to produce such a temperature, to allow materials to be superconductors at all times. This all changed in 1986 when Karl Muller and George Bednorz were working at the IBM Research Division in Zurich, Switzerland. They found a material that reached supercond uctivity at around 35 degrees Kelvin or –238 degrees Celsius. In the next year, a team of Chinese-American physicists declared that they had found a material that reached superconductivity at 92 degrees Kelvin. This was a big improvement. 92 degrees Kelvin is not a very high temperature, in fact, it is the equivalent of –181 degrees Celsius. Locating superconducting material above 77 degree Kelvin is a good thing because it means that the material will be easily produced and used. A theoretical understanding of superconductivity was advanced in 1957 by American physicists John Bardeen, Leon Cooper, and John Schrieffer. Their Theories of Superconductivity became know as the BCS theory (which came from each mans last name) and won them a Nobel prize in 1972. The BCS theory explained superconductivity at temperatures close to absolute zero. However, at higher temperatures and with different superconductor systems, the BCS theory has consequently became insufficient to ful ly explain electron behavior. The Type 1 category of superconductors is basically made up of pure metals that normally show conductivity at room temperature. They require really cold temperatures to slow down molecular vibrations enough to facilitate unrestrained electron flow in agreement to the BCS theory. BCS theory suggests that electrons team up in cooper pairs in order to help each other overcome molecular obstacles. Type 1 superconductors were discovered first and require the coldest temperatures to become superconductive. They are characterized by a very sharp transition to a superconducting state.

Microbiology Coursework: Bacillus Cereus

Microbiology Coursework: Bacillus cereus After investigation following on outbreak of food poisoning at a pizza restaurant, it was found that all suffers had consumed a portion of side salad from the self-service salad bar alongside their main dish. Subsequently, this was further traced to a rice salad. Environmental Health Officers investigating this outbreak suspected it may have been caused by Bacillus cereus (B. cereus). The presence of large numbers of B. cereus in a food is indicative of active growth and proliferation of the organism and is consistent with a potential hazard to health. The diagnosis of B. ereus can be confirmed by the isolation of more than 105 B. cereus organisms per gram from epidemiologically implicated food, but such testing is often not done because the illness is relatively harmless and usually self-limiting 1. Design a method(s) to enumerate the: i)Total bacterial count ii)Bacillus cereus count In the rice saladThis outbreak of food poisoning could be i nvestigated by performing an enumeration (plate count) of the total viable bacteria in the rice salad on a general non-selective agar using either the pour or the spread plate method. To confirm that the outbreak had been caused by any B. ereus present in the rice salad a selective media agar, such as mannitol egg yolk polymixin agar (MEYP/MYP), should be used. Once B. cereus has been confirmed a further enumeration of the B. cereus should be performed on the MEYP/MYP agar selective media plate to show whether the amount of B. cereus present is within the range known to cause food poisoning 105–107 cells g? 1 of food for Diarrhoeal syndrome, or 105–108 cells g? 1 of food for Emetic syndrome. (Granum & Lund, 2006) To perform a total cell count and the confirmation of B. cereus by either the pour or spread plate method the equipment required is as follows:General non-selective agar Mannitol egg yolk polymixin agar (MEYP/MYP) Petri dishes Glass or disposable â€Å"hockey stick† spreader Bunsen burner Test tubes Ringers solution Pastettes / Pippettes Food blender Before a cell count can be performed a serial dilution of an homogenate of the rice salad is required. For this one part rice salad is blended to nine part ringers solution, from this initial homogenate that the serial dilution is created by taking 1ml of this original and adding it to 9ml of ringers solution thereby creating a 1:10 dilution of the original.This step is repeated a further 5 times, each time taking 1ml from the dilution created in the previous tube and adding it to 9ml of ringers solution thereby with each step the original sample is diluted by a further factor of 10, (Figure 1). Once the serial dilution has been completed down to a dilution of 1:1,000,000 (10-6) either the pour or spread plate method of plating out of the samples can be performed Figure 1: Serial dilution When using a general non-selective agar both the pour and spread plate methods can be used for en umeration of the total bacteria in the rice salad.With both methods all plates are performed in triplicate. Along-side the non-selective agar, an agar such as MEYP/MYP selective agar which is selective for B. cereus can be used to confirm that B. cereus is present in the original sample. In the pour plate method 1ml or 0. 1ml of each of the dilutions prepared earlier within the serial dilution are added to individual petri dishes and a nutrient agar which is held at around 50oC is poured over each of these samples, the petri dishes are swirled causing gentle agitation and mixing the bacteria with the agar.After the agar has solidified the plates are incubated, after this incubation the pour plates show bacterial growth both on and within the agar due to aerobic and anaerobic bacteria. In the spread plate method 0. 1ml of each of the serial dilution solutions is pipetted onto the surface of a pre-poured agar plate and spread using a â€Å"hockey stick† spreader, the agar plate s are then incubated. Bacterial colonies only grow on the surface of the spread plate, (Figure 2) Figure 2: Method of Pour and spread plate technique. Microbial Growth, 2011) Once the plates have been incubated they are examined and the number of colonies counted, only plates that show between 30-300 colonies are counted, if the number of colonies is above 300 then the plate is discarded as too numerous to count, if below 30 it is discarded as too few to count. After the plates showing between 30-300 colonies have been counted the number of bacteria in the original sample can be worked out using the calculation Number of colonies on plate x dilution of sample = number of bacteria / mlIf growth has occurred on the MEYP/MYP plates, a Gram stain can be performed on a sample from one of the colonies, when the gram stain is examined under oil immersion B. cereus should appear as large Gram-positive bacilli in short-to-long chains; with spores that are ellipsoidal, central to subterminal, and that do not swell the sporangium. (Tallent, Rhodehamel , Harmon, & Bennett, 2012) (Figure 3) Figure 3: flow diagram showing order of events leading to the enumeration of total bacteria and Bacillus cereus in a sample of food. 2.Explain why MEYP/MYP agar is selective for Bacillus cereus B. cereus is mannitol-negative. The mannitol content of the medium thus allows differentiation of the accompanyingmannitol-positive microbial flora which are identified by a change in colour of the indicator phenol red to yellow. B. cereus is not affected by concentrations of polymyxin which inhibit the common accompanying microbial flora (Donovan, 1958). Addition of polymyxin is necessary, however, if the sample material is suspected to contain high-numbers of accompanying microorganisms B. cereus produces lecithinase.The insoluble degradation products of egg-yolk lecithin accumulate around the Cereus colonies to form a white precipitate. A lecithinase reaction occurs very early in many strains, Cereus colonies can, therefore, often be rapidly identified before accompanying polymyxin-resistant microorganisms have had a chance to fully develop. Incubation: 18-40 hours at 32  °C. B. cereus appears as rough, dry colonies with a pink to purple base which are surrounded by a ring of dense precipitate. Colonies surrounded by a yellow or a clear zone are not Bacillus cereus.Further tests should be performed to confirm the identity of Bacillus cereus (anaerobic degradation of D(+)glucose, degradation of gelatin, positive nitrate reduction). (Merck, 2012) 3. Suggest how health officers may have come to the tentative conclusion of B. cereus poisoning. Health officers may have come to this conclusion based on the short incubation time to the sudden onset of illness, and due to rice already being implicated as the source of this type of food poisoning in other cases. 4. Suggest ways in which: i. The rice salad might have been infected by the Bacillus cereus; ii.The Bacillus cereus c ould have survived the normal cooking process of the rice; iii. Bacillus cereus causes food poisoning. B. cereus is present in the outer casing of rice and, because it is able to form spores that are very resistant to low or high temperatures, it can therefore easily survive cooking and less-than perfect refrigeration. Improper storage of food stuffs is the issue. Bacillus cereus spores can survive boiling and if the food, in this case rice is stored at ambient temperature, the spores can germinate into toxin producing bacteria. Herriman, 2009) Bacillus cereus has been reported to be present in stools of healthy humans at varying levels (Johnson, 1984) therefore if an individual had not washed their hands after going to the toilet then handled the serving spoon any B. cereus from the hands could be transferred to the serving spoon which in turn could either infect the rice salad or the hand of the person next using the spoon. When rice is boiled and then stored in the fridge without being cooled first, these spores can germinate on the cooked rice and grow well at 4oC.If the rice is then used in a stir fry or similar dish, where the cooking time is relatively short, or the rice is held at an insufficient temperature enough of the bacteria survive to be ingested. Bacillus cereus causes food poisoning of two different types, emetic and diarrhoeal. (Table 1) Table 1. Characteristics of the two types of disease caused by Bacillus cereus Diarrhoeal syndromeEmetic syndrome Infective dose105–107 (total)105–108 (cells g? 1) Toxin producedIn the small intestine of the hostPreformed in foods Type of toxinProteinCyclic peptide Incubation period8–16 h (occasionally >24 h)0. –5 h Duration of illness12–24 h (occasionally several days)6–24 h SymptomsAbdominal pain, watery diarrhoea and occasionally nauseaNausea, vomiting and malaise (sometimes followed by diarrhoea, due to additional enterotoxin production? ) Foods most frequently implicatedMeat products, soups, vegetables, puddings/sauces and milk/milk productsStarch-rich foods; Fried and cooked rice, pasta, pastry and noodles The form that produces diarrhoea is accompanied by symptoms that are virtually indistinguishable from those caused by the Clostridium perfingens bacteria.The affected person experiences abdominal cramps and severe watery diarrhoea within about 15 hours of eating the contaminated rice. Vomiting rarely occurs but the diarrhoea carries on between 1 and 2 days. The diarrhetic syndromes observed in patients are thought to stem from the three toxins Hemolysin BL Hbl, Nonhemolytic Enterotoxin Nhe and Cytotoxin K CytK. These enterotoxins are all produced in the small intestine of the host, thus thwarting the issue of digestion by host endogenous enzymes. Some strains of the bacteria have an extra plasmid that carries a gene for a toxin that causes severe vomiting.These strains cause the emetic form of Bacillus cereus and produce symptoms very similar to food poisoning by Staphylococcus aureus. After ingesting rice contaminated with these strains, vomiting begins between 1 and 5 hours. The effects are fairly short-lived and the digestive system usually returns to normal within about 24 hours. The emetic form is commonly caused by rice that is not cooked for a time and temperature sufficient to kill any spores present, then improperly refrigerated. It can produce a toxin, cereulide, which is not inactivated by later reheating. This form leads to nausea and vomiting 1–5 hours after consumption.It can be difficult to distinguish from other short-term bacterial foodborne pathogens such as Staphylococcus aureusReferences Microbial Growth. (2011). Retrieved March 3, 2012, from The Growth Of Bacterial Cultures: http://classes. midlandstech. com/carterp/Courses/bio225/chap06/Microbial%20Growth%20ss5. htm Donovan, K. O. (1958). A selective medium for Bacillus cereus in milk. J. Appl. Bact. (21), 100-103. Granum, P. , & Lun d, T. (2006, January 17). Bacillus cereus and its food poisoning toxins. FEMS Microbiology Letters, 157(2), 223-228. doi:10. 1111/j. 1574-6968. 1997. tb12776. x Herriman, R. (2009, September 13). Food-Borne Intoxication – Bacillus Cereus. Retrieved March 6, 2012, from ezinearticles. com: http://ezinearticles. com/? Food-Borne-Intoxication—Bacillus-Cereus&id=2915150 Johnson, K. M. (1984). Bacillus cereus food-borne illness. An update. J Food Prot, 47, 145–153. Merck. (2012). MYP Agar. Retrieved March 01, 2012, from Merck Microbiology Manual 12th Edition: http://www. mibius. de/out/oxbaseshop/html/0/images/wysiwigpro/MYP_Agar_105267_engl. pdf Tallent, S. M. , Rhodehamel , E. , Harmon, S. M. , & Bennett, R. W. (2012, February 02). BAM: Bacillus cereus. Retrieved March 05, 2012, from FDA U. S. Food and Drug Administration:

The Day At West Hill High School - 1963 Words

Shadows Die I ve never been able to go to a month school without ending up in the hospital in some way. Whether I was the one getting treatment, or seeing a dying family member. I was somehow always there. I have been bullied for months. I always get called an emo, or I m told that I should just kill myself because I m just a waste of space. My parents are highly abusive and they are drunks, so they thought I was lying when I said I was being bullied. They soon started to see that I was coming home with marks on me. They transferred me to a new school. Tomorrow was my first day at West Hill High School on the outskirts of Seattle, Washington. You probably would†¦show more content†¦I didn t listen, I just wanted to get out of this class, I looked out the window, figuring out my plan to end everything. The bell rings, and it s our 10 minute passing period. You should just die, a girl with blonde hair, a very expensive manicure, and clothes said to me. I just ignored it. But then things to a turn for the worse. Why aren t you looking at me when I speak to you! the girl screamed in my face as she pulled my head by my hair towards her. I said, kill yourself, nobody even likes you anyway That got me. I looked in her eyes, and then I felt a pain in my fist, and the girl screamed, blood rushing from her nose. Evelyn, office now! one of the aids yelled. I walked to the office, only to find Mason is sitting in the principles part. Week of detention. That s my punishment for punching a prep who was telling me to die, what is wrong with people? ~Lunch~ I walk into detention, crowded with the rebels and no popular jocks and girls to be heard, smelled, or seen. I then see that the seat next to mason was the only one that was open. You know, it kinda rude to stare, Mason says, slightly annoyed by my presence. Oh, I m sorry, I didn t mean too. I didn t realize I was. I am very sorry, I say to him. It s fine, by the way, the name is Mason, I know, So, I hear your in her because you punched the queen bee and