Excitonic effects of bilayer graphene: A simple approach

The present work investigates the excitonic effects on the bilayer graphene with layers of different thickness under the influence of external electric field through a simple numerical approach. The band structure and energy gap have been calculated using a tight-binding model including parameters like the second-nearest-neighbor-hopping energies t′ (in-plane) and γ (intra-layer) and the on-site energy Δ, in details. The binding energy of exciton for bilayer graphene has been calculated by Wannier model and Hartree–Fock approximation through the Bethe–Salpeter equation. Finally the optical conductivity spectrum of bilayer graphene has been calculated by using the effective mass approximation in two band model.     

Symmetry and surface energy coefficients with an effective interaction

Symmetry energy coefficients in the first and second order have been estimated by using an effective interaction developed in a previous paper. The rearrangement contribution to the first-order symmetry energy coefficient has also been estimated. The effect of neutron excess on the first- and second-order single particle energies of nuclear matter have been studied by determining the isotopic spin dependent part of the single particle potential. The 1s state single particle energies of²⁰⁸Pb and¹⁶O have been estimated from the single particle energy of nuclear matter by incorporating the values of the isotopic spin dependent part of the single particle potential. The surface energy coefficient has been determined by using the semi-infinite model in the Thomas Fermi approach.Financial assistance from University Grants Commission, New Delhi, is gratefully acknowledged. The authors are also grateful to Professor K. C. Pande and Dr. S. P. Pandya for helpful suggestions.     

Measurement of the neutron-induced deuteron breakup reaction cross-section between 5 and 25 MeV

High-spin states in ¹⁸⁷Pt have been studied by means of ??-ray spectroscopy techniques. Known bands have been significantly extended and new bands have been found. The band structures are discussed in the framework of the cranking model and negative-parity states are compared with calculations performed with a semi-microscopic axial-rotor plus one-quasiparticle coupling model. Shape coexistence is observed from low excitation energy.     

Giant resonances in90Zr and116Sn

The giant resonance region in⁹⁰Zr and¹¹⁶Sn excited by 270 MeV helions has been measured up to about 35 MeV excitation energy. The low and the high energy octupole resonances are seen prominently in addition to the quadrupole and the monopole resonances. The angular distribution data for the various multipoles are satisfactorily explained by the collective model calculations. The percentatge energy weighted sum rule strengths have been determined for all the prominent resonances.     

Zum Drei- und Vierkörperproblem der Kernphysik

The independent pair model has been applied to the nuclear three- and four-body problem. The equations of the model have been solved by a perturbation approach in the case of spin- and charge-independent central two-body forces with hard-core. In lowest order of perturbation theory the nuclear average potential has been approximated by an oscillator potential including an effective mass, the parameters of which were so chosen as to give as nearly a self-consistent potential as possible. For a sqare well two-body interaction the lowest order equations have been solved exactly, the corrections are shown to be small. Some tests for the internal consistency of the approach have been developped and are shown to be well fulfilled by our solutions. According to a proposal byLipkin we succeeded in separating off the energy of the center of mass motion. The results for the binding energy of He⁴(27,9 MeV), the binding energy of H³ (7,1 MeV), the energy difference between H³ and He³ (0,735 MeV) and the RMS-radius of He⁴ (1,75f) are in rather good agreement with experimental results.     

The Energy Dissipation,Productions of the Subthreshold Pion Mesons and Flowangle in Interdediate-Energy 86Kr+197Au Reaction

The dissipative energy,productions of subthreshold pion mesons and flowangle in intermediate-energy heavy system ⁸⁶Kr+¹⁹⁷Au reaction have been calculated by the extended BUU model,meanwhile,the relation of the energy dissipation to the charge number of PLF and the correlation of the charge number between the PLF and TLF have been reproduced.     

The effects of mean field and two-body collision on the radial expansion energy

The expansion energy has been studied by using BUU model based on the Skyrme interaction to obtain the information of equation of state. The effects of radial expansion energy on the mean field and two-body collision have been discussed. The results are that at intermediate energy heavy ion collision the radial expansion energy is sensitive to effective massm* and insensitive to the incompressibility. The reasonable effects massm*=0.8 m is obtained by comparison of expansion energy with experiment. Cross section has a little influence on the expansion energy and the effect of cross section on expansion energy increases with increasing beam energy.     

Effects of disorder on the correlation energy of rings of hydrogen atoms

The correlation energy of disordered systems has been calculated by means of second-order Rayleigh-Schrödinger perturbation theory in the M?ller-Plesset partitioning. Rings of hydrogen atoms have been chosen as model systems and the degree of disorder has been varied from complete delocalization to complete localization of the one-particle states. The correlation energy was found to have an extremum at an intermediate degree of disorder, corresponding to incomplete localization.     

Refractive indices and related properties of some potential mixed crystals

The high frequency refractive indices of some binary, ternary and quaternary mixed crystals have been evaluated from the knowledge of plasmon energy and the lowest gap energy of the crystals for their applications in heterojunctionled and solar cells. The Fermi energy screening factor correction has been applied to effect accuracy in prediction. The model has been used to study the temperature and pressure dependence of refractive index. The calculated value agrees with experiment (within a few percent) justifying the validity of the model.     

Étude de la dissipation d'énergie dans la fission de 234u à l'aide de la réaction 233U(d,pf)

The energy balance in the fission of ²³⁴U has been investigated on the basis of experimental results from the ²³³U(d, pf) reaction. Taking into account the neutron evaporation we have deduced the total kinetic energy and excitation energy distributions of the primary fragments as functions of the excitation energy of the fissioning nucleus. The neutron evaporation temperatures have been adjusted so as to reproduce the average value and width of the measured kinetic energy distributions for each fragmentation. Excitation energy distributions of the fragments have been deduced. The data are discussed in the framework of the liquid-drop model with shell corrections. Evidence for energy dissipation in the fission of ²³⁴U, involving drastic changes in the scission configuration, is shown for some fragmentation modes.     

Vibration-inversion-rotation spectra of ammonia: A vibration-inversion-rotation Hamiltonian for NH2D and ND2H

The model Hamiltonian developed previously for ammonia NH₃ has been used to study the vibration-inversion-rotation energy levels of the isotopic species of ammonia NH₂D and ND₂H. In this model the inversion motion is removed from the vibrational problem by allowing the molecular reference configuration to be a function of the large amplitude motion coordinate.The ground state inversion-rotation energy levels of NH₂D and ND₂H have been calculated with the use of the zeroth-order inversion-rotation Hamiltonian, and the calculated transition frequencies have been compared with the experimental data.     

Effects of the second and third neighbor hopping interactions on the electronic states of soliton in polyacetylene

We have studied the energy spectra and the electronic states of a soliton in the weakly coupled electron-phonon systems using an extension of SSH model that includes non-nearest neighbor hopping interactions. The results show that: (1) the electron-hole symmetry of the energy band structure implied by SSH model is broken, and the energy gap 2 increases. (2) for a negative charged soliton, only two bound states have been found, one of them is the midgap state, another is a new shallow state near the bottom of the conduction band; for a neutral soliton, all three bound states exist as in the SSH model, but their localizations are strengthened; for a positive charged soliton, four bound states have been found, one of which is an additional state near the top of the conduction band.     

Energy spectrum of C60 fullerene

The energy spectrum of the C₆₀ fullerene has been calculated in terms of the Shubin-Vonsovskii-Hubbard model using an approximation of static fluctuations. Based on the spectrum, the optical absorption bands at 4.84, 5.88, and 6.30 eV observed experimentally have been successfully explained. It has been concluded that the model used is applicable for the calculation of the energy spectrum and the energy properties of other nanosystems, such as fullerenes of higher orders, carbon nanotubes, and grafen planes.     

Quantum molecular dynamics approach to estimate spallation yield from<Emphasis Type="Italic">p</Emphasis> +<Superscript>208</Superscript>Pb reaction at 800 MeV

The spallation yield of neutrons and other mass fragments produced in 800 MeV proton induced reaction on²⁰⁸Pb have been calculated in the framework of quantum molecular dynamics (QMD) model. The energy spectra and angular distribution have been calculated. Also, multiplicity distributions of the emitted neutrons and kinetic energy carried away by them have been estimated and compared with the available experimental data. The agreement is satisfactory. A major contribution to the neutron emission comes from statistical decay of the fragments. For mass and charge distributions of spallation products the QMD process gives rise to target-like and projectile-like fragments only.     

长脉冲高能激光能量测试技术的研究

用锥形腔量热式激光能量计,测量了在不同脉冲宽度条件下,脉冲激光能量和激光吸收腔温升之间的关系,并用传统的方法得到不同激光能量对应的温升,并按照有关公式计算得到激光能量,结果表明实际激光能量和按传统方法计算得到的激光能量之间存在较大的差距;我们从理论上分析了由于热辐射、热传导影响,得出锥形吸收腔时间温度曲线关系的数学模型;用该数学模型对测量得到温度时间曲线进行最小二乘法拟合,拟合曲线和实际曲线非常吻合;通过该曲线我们对测量结果进行修正,和传统数据处理方法比较,该方法得到的结果更接近真值.     

Fluorescence characteristics of Dy ions in calcium fluoroborate glasses

Calcium fluoroborate (CFB) glasses doped with different concentrations of trivalent dysprosium ions were prepared and investigated by the FTIR, optical absorption, photoluminescence and decay analysis. Free-ion Hamiltonian model and Judd-Ofelt theory have been used to analyze the energy level scheme and the spectral intensities of Dy³⁺ ions in CFB glasses. From the emission spectra it is observed that the samples emit intense light yellowish color which is nearer to white light. Chromaticity color coordinates have been calculated and the dominant emission wavelength has also been indicated. Decay curves of ⁴F_9/2 level for the samples with different concentrations have been analyzed using the Inokuti-Hirayama model and the energy transfer and non-radiative decay rates have been determined.     

Collective potentials and dipole and quadrupole giant resonances

The dynamic collective model is extended into the energy region immediately above the giant dipole resonances, i.e. into an energy region between 20 and 28 MeV. The total Hamiltonian is constructed and the dynamical problem is solved by diagonalizing the Hamiltonian in the basis of a five-dimensional harmonic oscillator. In schematical studies the splitting of giant quadrupole resonances is shown. For some elements the potential energy surfaces (PES) are constructed within the collective model developed by Gneuss et al. and the quadrupole resonances have been calculated in the framework of the dynamic collective model. In the last part the agreement with experimental data is shown.     

The 63,65Cu(e,p0) reactions in the giant resonance region

Angular distributions of the ^63,65Cu(e, p₀) reactions have been measured in the giant resonance energy region. The resulting differential cross sections have been decomposed into E1 and E2 components by a resonance model. The excitation functions for the two isotopes are significantly different, clearly reflecting threshold effects. The transition strengths of the low- and high-energy parts of the cross sections are reproduced by the statistical model and the direct-semidirect model, respectively, and the overall fit to the data is obtained by the sum of these two results.     

An empirical fit to estimated neutron emission cross sections from proton induced reactions

Neutron emission cross section for various elements from⁹Be to²⁰⁹Bi have been calculated using the hybrid model code ALICE-91 for proton induced reactions in the energy range 25 MeV to 105 Me V. An empirical expression relating neutron emission cross section to target mass number and incident proton energy has been obtained. The simple expression reduces the computation time significantly. The trend in the variation of neutron emission cross sections with respect to the target mass number and incident proton energy has been discussed within the framework of the model used.