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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

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APPLICATIONS OF NUCLEAR PHYSICS

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IMPORTANT NUCLEAR RESEARCH FACILITIES

Nuclear research facilities in the world

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Nuclear research facilities in India

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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

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

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IMPORTANT SYNTHETIC POLYMERS AND THEIR APPLICATIONS

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DEGRADATION OF POLYMERS

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

• 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

   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

   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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