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Wednesday, March 31, 2010

general science#7

PHYSICS: NUCLEAR PHYSICS

Nuclear Fission

  • Nuclear fission is a reaction in which the nucleus of an atom splits into smaller parts
  • Nuclear fission can either release energy or absorb energy: for nuclei lighter than iron fission absorbs energy, while for nuclei heavier than iron it releases energy
  • Energy released can be in the form of electromagnetic radiation or kinetic energy
  • The amount of free energy contained in nuclear fuel is about a million times that contained in a similar mass of chemical fuel (like petrol)
  • The atom bomb or fission bomb is based on nuclear fission
  • Example: fission of Uranium-235 to give Barium, Krypton and neutrons
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Nuclear Fusion

  • Nuclear fusion is the process by which multiple nuclei join together to form a heavier nucleus
  • Nuclear fusion can result in either the release or absorption of energy: for nuclei lighter than iron fusion releases energy, while for nuclei heavier than iron it absorbs energy
  • Nuclear fusion is the source of energy of stars.
  • Nuclear fusion is responsible for the production of all but the lightest elements in the universe. This process is called nucleosynthesis
  • Controlled nuclear fusion can result in a thermonuclear explosion – the concept behind the hydrogen bomb
  • The energy density of nuclear fusion is much greater than that of nuclear fission
  • Only direct conversion of mass into energy (collision of matter and anti matter) is more energetic than nuclear fusion
  • Example: fusion of hydrogen nuclei to form helium
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PIONEERS OF NUCLEAR PHYSICS RESEARCH
Scientist
Nationality
Discovery
Recognition
J J Thomson
Britain
Electron (1897)
Nobel in Physics (1906)
Henri Becquerel
Belgium
Radioactivity (1896)
Nobel in Physics (1903)
Ernest Rutherford
New Zealand
Structure of atom (1907)
Nobel in Chemistry (1908)
He is regarded as the father of nuclear physics
Franco Rasetti
Italy/USA
Nuclear spin (1929)

James Chadwick
Britain
Neutron (1932)
Nobel in Physics (1935)
Enrico Fermi
Italy/USA
Nuclear chain reaction (1942)
Neutron irradiation
Nobel in Physics (1938)
Hideki Yukawa
Japan
Strong nuclear force (1935)
Nobel in Physics (1949)
Hans Bethe
Germany/USA
Nuclear fusion (1939)
Nobel in Physics (1967)
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APPLICATIONS OF NUCLEAR PHYSICS
Application
Developed by
Working principle
Use
Nuclear power
Enrico Fermi (Italy, 1934)
Nuclear fission
Power generation
Nuclear weapons
Enrico Fermi (Italy, 1934)
Edward Teller (USA, 1952)
Nuclear fission
Nuclear fusion
Weapons
Radioactive pharmaceuticals
Sam Seidlin (USA, 1946)
Radioactive decay
Cancer, endocrine tumours, bone treatment
Medical imaging
David Kuhl, Roy Edwards (USA, 1950s)
Nuclear magnetic resonance (for MRI)
Positron emission (for PET)
MRI: Musculosketal, cardiovascular, brain, cancer imaging
PET: cancer, brain diseases imaging
Radiocarbon dating
Willard Libby (USA, 1949)
Radioactive decay of carbon-14
Archaeology
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IMPORTANT NUCLEAR RESEARCH FACILITIES
Nuclear research facilities in the world

Facility
Location
Established
Famous for
Brookhaven National Lab
New York
1947
Until 2008 world’s largest heavy-ion collider
European Organization for Nuclear Research (CERN)
Geneva
1954
World’s largest particle physics lab
Birthplace of the World Wide Web
Large Hadron Collider (LHC)
Fermilab
Chicago
1967
Tevatron – world’s second largest particle accelerator
ISIS
Oxfordshire (England)
1985
Neutron research
Joint Institute for Nuclear Research
Dubna, Russia
1956
Collaboration of 18 nations including former Soviet states, China, Cuba
Lawrence Berkeley National Lab
California
1931
Discovery of multiple elements including astatine, and plutonium
Lawrence Livermore National Lab
California
1952

Los Alamos National Lab
New Mexico, USA
1943
The Manhattan Project
National Superconducting Cyclotron lab
Michigan
1963
Rare isotope research
Oak Ridge National Lab
Tennessee
1943
World’s fastest supercomputer – Jaguar
Sudbury Neutrino Lab
Ontario
1999
Located 2 km underground
Studies solar neutrinos
TRIUMF (Tri University Meson Facility)
Vancouver
1974
World’s largest cyclotron
Yongbyon Nuclear Scientific Research Centre
Yongbyon, North Korea
1980
North Korea’s main nuclear facility
Sandia National Lab
New Mexico, USA
1948
Z Machine (largest X-ray generator in the world)
Institute of Nuclear Medicine, Oncology and Radiotherapy (INOR)
Abbottabad, NWFP (Pakistan)


Pakistan Institute of Nuclear Science and Technology (PINSTECH)
Islamabad
1965

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Nuclear research facilities in India

Facility
Location
Established
Famous for
Bhabha Atomic Research Centre
Bombay
1954
India’s primary nuclear research centre
India’s first reactor Apsara
Variable Energy Cyclotron Centre (VECC)
Calcutta
1977
First cyclotron in India
Institute for Plasma Research (IPR)
Gandhinagar
1982
Plasma physics
Indira Gandhi Centre for Atomic Research (IGCAR)
Kalpakkam
1971
Fast breeder test reactor (FBTR)
KAMINI (Kalapakkam Mini) light water reactor
Built the reactor for Advanced Technology Vessel (ATV)
Saha Institute for Nuclear Physics
Calcutta
1949

Tata Institute for Fundamental Research (TIFR)
Bombay
1945

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CHEMISTRY: POLYMERS

Overview

  • A polymer is a large molecule consisting of repeating structural units
  • The repeating units are usually connected by covalent chemical bonds
  • Polymers can be of two types
    • Natural polymers: shellac, amber, rubber, proteins etc
    • Synthetic polymers: nylon, polyethylene, neoprene, synthetic rubber etc
  • Synthetic polymers are commonly referred to as plastics
  • The first plastic based on a synthetic polymer to be created was Bakelite, by Leo Baekeland(Belgium/USA) in 1906
  • Vulcanization of rubber was invented by Charles Goodyear (USA) in 1839. Vulcanization is the process of making rubber more durable by addition of sulphur
  • The first plastic to be created was Parkesine (aka celluloid) invented by Alexander Parkes (England) in 1855
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Synthesis of polymers

  • The synthesis of polymers – both natural and synthetic – involves the step called polymerization
  • Polymerization is the process of combining many small molecules (monomers) into a covalently bonded chain (polymer)
  • Synthetic polymers are created using of two techniques
    • Step growth polymerization: chains of monomers are combined directly
    • Chain growth polymerization: monomers are added to the chain one at a time
  • Natural polymers are usually created by enzyme-mediated processes, such as the synthesis of proteins from amino acids using DNA and RNA
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Categories of polymers

  • Organic polymers are polymers that are based on the element carbon. Eg: polyethylene, cellulose etc
  • Inorganic polymers are polymers that are not based on carbon. Eg: silicone, which uses silicon and oxygen
  • Copolymer is one that is derived from two or more monomeric units. Eg: ABS plastic
  • Fluoropolymers are polymers based on fluorocarbons. They have high resistance to solvents, acids and bases. Eg: teflon
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TYPES OF BIOPOLYMERS
DNA as a biopolymer
DNA as a biopolymer
  1. Structural proteins
    1. Structural proteins are proteins that provide structural support to tissues
    2. They are usually used to construct connective tissues, tendons, bone matrix, muscle fibre
    3. Examples include collagen, keratin, elastin
  2. Functional proteins
    1. Proteins that perform a chemical function in organisms
    2. Usually used for initiate or sustain chemical reactions
    3. Examples include hormones, enzymes
  3. Structural polysaccharides
    1. They are carbohydrates that provide structural support to cells and tissues
    2. Examples include cellulose, chitin
  4. Storage polysaccharides
    1. Carbohydrates that are used for storing energy
    2. Eg: starch, glycogen
  5. Nucleic acids
    1. Nucleic acids are macromolecules composed of chains of nucleotides
    2. Nucleic acids are universal in living beings, as they are found in all plant and animal cells
    3. Eg: DNA, RNA
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TYPES OF SYNTHETIC POLYMERS
  1. Thermoplastics
    1. Thermoplastics are plastics that turn into liquids upon heating
    2. Also known as thermosoftening plastic
    3. Thermoplastics can be remelted and remoulded
    4. Eg: polyethylene, Teflon, nylon
    5. Recyclable bottles (such as Coke/Pepsi) are made from thermoplastics
  2. Thermosetting plastics
    1. Thermosettings plastics are plastics that do not turn into liquid upon heating
    2. Thermosetting plastics, once cured, cannot be remoulded
    3. They are stronger, more suitable for high-temperature applications, but cannot be easily recycled
    4. Eg: vulcanized rubber, bakelite, Kevlar
  3. Elastomers
    1. Elastomers are polymers that are elastic
    2. Elastomers are relatively soft and deformable
    3. Eg: natural rubber, synthetic polyisoprene
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IMPORTANT NATURAL POLYMERS AND THEIR APPLICATIONS
Polymer
Application
Notes
Collagen
Connective tissue
Gelatine (food)
Most abundant protein in mammals
Keratin
Hair, nails, claw etc

Enzymes
Catalysis

Hormones
Cell signalling

Cellulose
Cell wall of plants
Cardboard, paper
Most common organic compound on Earth
Chitin
Cell wall of fungi, insects

Starch
Energy storage in plants
Most important carbohydrate in human diet
Glycogen
Energy storage in animals

DNA
Genetic information

RNA
Protein synthesis

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IMPORTANT SYNTHETIC POLYMERS AND THEIR APPLICATIONS
Polymer
Developed by
Constituent elements
Application
Notes
Parkesine
Alexander Parkes (Britain, 1855)
Cellulose
Plastic moulding
First man-made polymer
Bakelite
Leo Baekeland (USA, 1906)
Phenol and formaldehyde
Radios, telephones, clocks
First polymer made completely synthetically
Polyvinylchloride (PVC)
Henri Regnault (France, 1835)
Vinyl groups and chlorine
Construction material
Third most widely used plastic
Styrofoam
Ray McIntre (USA, 1941)
Phenyl group
Thermal insulation
Brand name for polystyrene
Nylon
Wallace Carothers (USA, 1935)
Amides
Fabric, toothbrush, rope etc
Family of polyamides
First commercially successful synthetic polymer
Synthetic rubber
Fritz Hoffman (Germany, 1909)
Isoprene
Tyres, textile printing, rocket fuel

Vulcanized rubber
Charles Goodyear (USA, 1839)
Rubber, sulphur
Tyres
Vulcanized rubber is much stronger than natural rubber
Polypropylene
Karl Rehn and Guilio Natta (Italy, 1954)
Propene
Textiles, stationary, automotive components
Second most widely used synthetic polymer
Polyethylene
Hans von Pechmann (Germany, 1898)
Ethylene
Packaging (shopping bags)
Most widely used synthetic polymer
Teflon
Roy Plunkett (USA, 1938)
Ethylene
Cookware, construction, lubricant
Brand name for polytetrafluoroehtylene (PTFE)
Very low friction, non-reactive
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DEGRADATION OF POLYMERS
Ozone cracking in natural rubber tubing
Ozone cracking in natural rubber tubing
  • Degradation of polymers can be desirable as well undesirable: desirable when looking for biological degradation, undesirable when faced with loss of strength, colour etc
  • Polymer degradation usually occurs due to hydrolysis of covalent bonds connecting the polymer chain
  • Polymer degradation can happen because of heat, light, chemicals and galvanic action
  • Ozone cracking is the cracking effect of ozone on rubber products such as tyres, seals, fuel lines etc. Usually prevented by adding antiozonants to the rubber before vulcanization
  • Chlorine can cause degradation of plastic as well, especially plumbing
  • Resin Identification Code is the system of labelling plastic bottles on the basis of their constituent polymers. This Code helps in the sorting and recycling of plastic bottles
  • Degradation of plastics can take hundreds to thousands of years
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Biodegradable plastics

  • Biodegradable plastics are plastics than can break down upon exposure to sunlight (especially UV), water, bacteria etc
  • Biopol is a biodegradable polymer synthesized by genetically engineered bacteria
  • Ecoflex is a fully biodegradable synthetic polymer for food packaging
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Bioplastics

  • They are organic plastics derived from renewable biomass sources such as vegetable oil, corn, starch etc
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Oxy-biodegradable plastics

  • Plastics to which a small amount of metals salts have been added
  • As long as the plastic has access to oxygen the metal salts speed up process of degradation
  • Degradation process is shortened from hundreds of years to months
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BIOLOGY: GENETIC DISORDERS

About genetic disorders
Huntington's disease is inherited in the autosomal dominant fashion
Huntington's disease is inherited in the autosomal dominant fashion

  • Genetic disorders are disorders that are passed on from generation to generation
  • They are caused by abnormalities in genes or chromosomes
  • Some genetic disorders may also be influenced by non-genetic environmental factors. Eg: cancer
  • Most genetic disorders are relatively rare and only affect one person in thousands or millions
  • To recollect, males have XY chromosome pairs while females have XX pairs
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Single Gene Disorders

  • Single gene disorders result from the mutation of a single gene
  • They can be passed onto subsequent generations in multiple ways
  • Single gene disorders include sickle cell disease, cystic fibrosis Huntington disease
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Multiple gene disorders

  • Multiple gene disorders result from mutation on multiple genes in combination with environmental factors
  • They do not have a clear pattern of inheritance, which makes it difficult to assess risk of inheriting a particular disease
  • Examples include heart disease, diabetes, hypertension, obesity, autism
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TYPES OF SINGLE GENE GENETIC DISORDERS
  1. Autosomal dominant
    Sickle cell disease is inherited in the autosomal recessive pattern
    Sickle cell disease is inherited in the autosomal recessive pattern

    1. Only one mutated copy of the gene is necessary for inheritance of the mutation
    2. Each affected person usually has one affected parent
    3. There is a 50% chance that the child will inherit the mutated gene
    4. Autosomal dominant disorders usually have low penetrance i.e. although only one mutated copy is needed, only a small portion of those who inherit that mutation will develop the disorder
    5. Eg: Huntington’s disease, Marfan syndrome
  2. Autosomal recessive
    1. Two copies of the gene must be mutated for a person to be affected
    2. An affected person usually has unaffected parents who each have one mutated gene
    3. There is a 25% chance that the child will inherit the mutated gene
    4. Eg: Cystic fibrosis, sickle cell disease, Tay-Sachs disease, dry earwax, Niemann-Pick disease
  3. X-linked dominant
    1. X-linked dominant disorders are caused by mutations on the X chromosome
    2. Males and females are both affected by such disorders. However, males are affected more severely
    3. For a man with a X-linked dominant disorder, his sons will all be unaffected (since they receive their father’s Y chromosome) while his daughters will all be affected (since they receive his X chromosome)
    4. A woman with a X-linked dominant disorder has a 50% chance of passing it on to progeny
    5. Eg: Hypophosphatemic rickets, Rett syndrome, Aicardi syndrome
  4. X-linked recessive
    X-linked recessive with a carrier mother
    X-linked recessive with a carrier mother

    1. Caused by mutations on the X-chromosome
    2. Males are affected more frequently than females
    3. The sons of a man affected by a X-linked recessive disorder will not be affected, while his daughters will carry one copy of the mutated gene
    4. The sons of a woman affected by a X-linked recessive disorder will have have a 50% chance of being affected by the disorder, while the daughters of the woman have a 50% chance of becoming carriers of the disorder
    5. Eg: colour blindness, muscular dystrophy, hemophilia A
  5. Y-linked disorders
    1. Caused by mutations on the Y chromosome
    2. Y chromosomes are present only in males
    3. The sons of a man with Y-linked disorders will inherit his Y chromosome and will always be affected while the daughters will inherit his X chromosome and will never be affected
    4. Eg: male infertility
  6. Mitochondrial disorders
    1. These disorders are caused by mutations in the mitochondrial DNA
    2. Only mothers can pass on mitochondrial disorders to children, since only egg cells (from the mother) contribute mitochondria to the developing embryo
    3. Eg: Leber’s Heriditary Optic Neuropathy

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