Theory of multilayer solar cells

432-438An expression has been derived for the absorption coefficient of an incident radiation with energy ħw by a semiconductor with band-gap E0. For a multilayer solar cell composed of seven layers that facilitate the solar cell to use the seven colours of the white light for maximum efficiency, the expression for the solar current ISC has been used to calculate the value of the charge carrier density n in each layer. ISC should be the same through all the layers for the layers to be connected in optical series. For such an arrangement, the efficiency of the multilayer solar cell turns out to be more than 42%

Transition temperature for ⁴He liquid adsorbed in disordered media

351-354For pure 4He liquid the superfluid fraction starts having a finite value at and below the -transition temperature 2.176K, whereas for 4He in a disordered media the superfluid fraction starts having a finite value at 2.168K, a temperature that is lower compared to the temperature at which superfluidity appears in pure 4He. Relations for transition temperatures for both cases that are in agreement with experimental values have been obtained. Adsorption, which normally leads to a decrease in the degrees of freedom, consequently results in a release of heat, which destroys superfluidity. Hence for the liquid 4He flowing into a disordered medium, the transition temperature is expected to be lower

Four-level approximation in disordered medium

355-360The adsorption of superfluid 4He into a disordered medium, the disappearance of superfluidity due to adsorption, and the subsequent appearance of superfluidity when more 4He flows into the disordered medium have been described by the four-level approximation. The adsorption of superfluid 4He into a disordered medium depletes the ZMS as the particles shift to higher excited levels resulting in ‘four-level approximation’. Superfluidity reappears on further adsorption but at a lower temperature implying that the Tc value of a four-level system should be lower than the Tc value for a three-level system, which is in agreement with the experimental observations

Anharmonic perturbation of neutron-proton pairs by the unpaired neutrons in heavy finite nuclei

7-15The properties of a finite heavy nucleus in which the number of neutrons N is not equal to the number of protons Z, N > Z, have been studied. It is assumed that the core of the nucleus is composed of proton-neutron pairs and the excess neutrons constitute the surface region of the nucleus. The interaction between a neutron and a proton constituting the neutron-proton pair is assumed to be harmonic. The unpaired neutrons in the surface region are assumed to interact with the neutron–proton pairs in the core of the nucleus anharmonically. Many body perturbation theory has been used to calculate the total energy of the nucleus, and thereby, we have calculated the binding energy per nucleon, called the binding fraction, the specific heat and the transition temperature. Speculation, as to how the alpha, beta and gamma radiations are emitted by a heavy nucleus, is also presented

Pair distribution function for interacting bosons and the ground-state energy of solid helium-4

325-331The pair distribution function g(r) for a system of bosons interacting through a two-body potential composed of a hard core followed by a square well has been obtained using the reaction matrix formalism for the energy excitation spectrum Ek and the fundamental definition relating the structure factor S(k) and g(r) . This has been used in obtaining the ground state energy of solid 4He using the kinetic energy and potential energy expressions of Hansen and Levesque. The most stable ground state of solid 4He corresponds to a potential width of b=3.8Ǻ ,but the corresponding E>/N for the density, ρ, of solid 4He is very large compared with the experimental value. However, for b =4.81Ǻ and ρ=2.8×1022 particles/ cm3, E>/N =-11.24 K= -93.4Joule/mol. and for b=4.82Ǻ and ρ=2.5×1022 particles/cm3, E>/N = -6.84 K=56.8 Joule/mol. The experimental value for the ground state energy of solid 4He =-59.5J/mol

Specific heat jump in anisotropic YBa₂Cu₃O₇₋δ superconductor

991-993Using the exotic pairing model, the jump in the specific heat ΔC/Tc in YBa₂Cu₃O₇₋δ, for both breathing mode and buckling mode has been calculated. Its value was compared with the experimental values and it has been found that the specific heat jump in superconductor and the density of states were one fifth of the earlier reported values. This is indicative of the small fraction of carriers close to the Fermi level, which are paired and exotic pairing due to anharmonic perturbation of the apical oxygen ions leads to a lowering of ΔC/Tc

<link rel="File-List" href="file:///C:%5CDOCUME%7E1%5Ccharu%5CLOCALS%7E1%5CTemp%5Cmsohtml1%5C01%5Cclip_filelist.xml"> Correlation amplitude for quasi-particles in high <i>T_c</i> superconductors

758-763 The correlation amplitude for the quasi-particles in high Tc superconductors has been deduced. From this amplitude, the maximum critical transition temperature has been calculated. The assumption, which has been made is that, the superconductivity is due to condensation of electron pairs, which may be in a parallel spin-state, an antiparallel spin-state, or a mixture of the two states. It has been established that the maximum transition temperature in the optical phonon frequency is Tc = 262.6 K irrespective of the state of the electron pair

Elastic scattering of ⁴He atoms at the surface of liquid helium

743-748Elastic scattering of 4He atoms when they approach the surface of 4He liquid, has been studied. The liquid surface is assumed to be uniform and the density profile is the same along and perpendicular to the surface. The incident 4He atom will interact with a large number of 4He atoms in the liquid near the surface of liquid 4He. Hence, the effective interaction of the incident particle will be due to many-body forces. The many-body forces are represented by the t-matrix. In the equation for potential energy per atom in the bulk liquid, the pair potential was replaced by the t-matrix. The Gaussian potential used in calculating the expectation value of the t-matrix is equivalent to the Lennard-Jonnes potential. The results give quantitative agreement with the corresponding experimental values for 4He for the various values of c2. The potential energy per atom in the bulk liquid obtained in this calculation is -20.130 K. The experimental energy of interaction is -20.81K, which implies that the formula derived by us for the potential energy per atom in the bulk liquid works wel