CSIR NET flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Hückel's rule

A planar, cyclic, fully conjugated system is aromatic when it has 4n+2 pi electrons (n = 0, 1, 2...); 4n pi electrons instead give antiaromatic character. Benzene is the n = 1 case.

Chemical shift

The resonance frequency of a nucleus in NMR measured relative to a standard (TMS defined as 0 ppm) and expressed in ppm, reflecting the local electron density and magnetic environment.

Crystal field stabilization energy

The net energy lowering gained when d electrons occupy split orbitals in a ligand field, measured relative to the unsplit barycentre; it explains site preferences and hydration enthalpies of transition metals.

Beer–Lambert law

A = epsilon times c times l links absorbance to molar absorptivity, concentration and path length. It stays linear only for dilute solutions, monochromatic light and no shifting equilibria.

Markovnikov's rule

In electrophilic addition of HX to an alkene, the hydrogen adds to the carbon already bearing more hydrogens, because the more substituted, more stable carbocation intermediate is formed.

Le Chatelier's principle

When an equilibrium system is disturbed by a change in concentration, pressure or temperature, it shifts in the direction that partly counteracts the disturbance; a catalyst leaves the position unchanged.

Coriolis parameter

f = 2 times Earth's angular velocity times the sine of latitude. It measures the local vertical component of planetary rotation, vanishes at the equator and is maximal at the poles.

Potential temperature

The temperature a parcel would reach if moved dry-adiabatically to 1000 hPa, given by theta = T (1000/p)^(R/cp). It is conserved in dry adiabatic motion and diagnoses static stability.

Ekman transport

The depth-integrated wind-driven water transport in the surface boundary layer, directed 90 degrees to the right of the wind in the Northern Hemisphere and 90 degrees left in the Southern.

Milankovitch cycles

Quasi-periodic changes in Earth's orbit and spin axis: eccentricity near 100 kyr, obliquity near 41 kyr and axial precession near 23 kyr. They modulate seasonal insolation and glacial cycles.

Mohorovičić discontinuity

The seismic boundary between crust and mantle, identified by an abrupt increase in P- and S-wave velocities at roughly 5 to 40 km depth, deeper beneath continents than oceans.

Albedo

The fraction of incident solar radiation reflected by a surface or planet. Fresh snow is about 0.8 to 0.9, open ocean about 0.06, and Earth's planetary average about 0.30.

Hardy–Weinberg equilibrium

In an ideal population with random mating and no selection, mutation, migration or drift, genotype frequencies remain p squared, 2pq and q squared for alleles of frequency p and q.

Polymerase chain reaction

An in vitro DNA amplification method cycling through denaturation near 95 degrees Celsius, primer annealing near 55 to 65 degrees Celsius, and extension by a thermostable polymerase near 72 degrees Celsius.

PAM sequence

Protospacer adjacent motif: a short DNA sequence, 5'-NGG-3' for SpCas9, that must lie next to the target before Cas9 binds and cleaves, preventing attack on the CRISPR locus itself.

Southern blotting

A method that separates DNA by gel electrophoresis, transfers it to a membrane, and detects specific sequences with labelled probes. Northern blots analyse RNA; Western blots analyse proteins.

Wobble hypothesis

Crick's proposal that the third codon base pairs loosely with the first anticodon base, allowing one tRNA to read several synonymous codons and explaining the degeneracy of the genetic code.

Turnover number

k_cat, the maximum number of substrate molecules converted per active site per unit time at saturating substrate; numerically equal to Vmax divided by total enzyme concentration.

Cauchy–Riemann equations

For f = u + iv, differentiability as a complex function requires u_x = v_y and u_y = −v_x; with continuity of the partial derivatives these conditions are also sufficient.

Residue theorem

If f is analytic inside and on a simple closed contour except at isolated poles, the contour integral of f equals 2πi times the sum of residues at those interior poles.

Rank–nullity theorem

For a linear map on an n-dimensional space, the dimension of the image plus the dimension of the kernel equals n; equivalently rank(A) + nullity(A) = n for an m by n matrix.

Central limit theorem

For independent, identically distributed random variables with finite mean and variance, the standardised sample mean converges in distribution to the standard normal as the sample size grows.

Lagrange's theorem

The order of any subgroup divides the order of a finite group, so the order of every element divides the group order; Fermat's little theorem follows as a special case.

Uniform convergence

A sequence converges uniformly when the supremum of the difference from the limit tends to zero. Unlike pointwise convergence, it preserves continuity and allows term-by-term integration.

Newton–Raphson method

Root-finding iteration x(n+1) = x(n) − f(x(n))/f'(x(n)). It converges quadratically near a simple root but fails where the derivative vanishes or the initial guess is poor.

Heisenberg uncertainty principle

Position and momentum cannot both be sharply defined: the product of their uncertainties is at least h-bar over two. A similar relation links energy uncertainty to state lifetime.

Wien's displacement law

The wavelength of peak blackbody emission is inversely proportional to temperature, lambda_max times T = 2.898 times 10 to the minus 3 metre-kelvin, so hotter bodies peak at shorter wavelengths.

Bragg's law

Constructive interference of X-rays scattered from parallel lattice planes of spacing d occurs when 2d sin(theta) = n times lambda, with theta the glancing angle and n an integer.

Poynting vector

S = (1/mu-zero) E cross B describes the direction and rate of electromagnetic energy flow; for a plane wave the time-averaged intensity equals E-zero squared divided by 2 mu-zero c.

Fermi energy

The energy of the highest occupied single-particle state for non-interacting fermions at absolute zero; at that temperature every state below it is filled and every state above is empty.

Time dilation

A clock moving at speed v relative to an observer runs slow by the factor gamma = 1/sqrt(1 minus v squared over c squared), so the measured interval is gamma times the proper interval.

Maxwell relations

Equalities among second partial derivatives of thermodynamic potentials, such as the entropy derivative of temperature with volume equalling minus the pressure derivative with entropy, obtained from exact differentials.