Simple wavefunction for an impurity in a parabolic quantum dot

A simple variational wavefunction is proposed for calculating the ground-state energy of a hydrogenic donor located at the centre of a spherical parabolic quantum dot. Binding energies are calculated for three values of the parameter which gives the strength of the confining parabolic potential by the proposed wavefunction as well as by a wavefunction used by Xiaoet al. [Superlattices and Microstructures,19, 137 (1996)]. The results are compared to the ‘exact’ energies obtained by numerical integration of the Schrodinger equation. It is shown that the proposed wavefunction gives considerably better results than the wavefunction used by Xiaoet al. in all cases.     

Conductivity of carbon nanotubes in a longitudinal magnetic field

Multiwall carbon nanotubes exhibit oscillations of magnetoresistance with the period Φ₀=hc/2e [A. Bachtold, C. Strunk, J.-P. Salvetat, et al., Nature 397, 673 (1999)]. This effect is analogous to the Sharvin effect for a normal metal [D. Yu. Sharvin and Yu. V. Sharvin, Pis’ma Zh. Éksp. Teor. Fiz. 34, 285 (1981)]. It is shown that, along with the magnetoresistance peaks corresponding to the flux values that are multiples of Φ ₀, additional peaks with a period three times shorter can be observed in carbon nanotubes.     

Fluorescence Spectroscopic Properties Analysed within the Extended Förster Theory with Application to Biomacromolecular Systems

The extended Förster theory (EFT) of electronic energy transport accounts for translational and rotational dynamics, which are neglected by the classical Förster theory (FT). EFT has been developed for electronic energy transfer within donor-acceptor pairs [Isaksson, et al, Phys. Chem. Chem. Phys., 9, 1941(2007)] and donor-donor pairs [Johansson, et al, J. Chem. Phys., 105, 10896 (1996); Norlin, et al, Phys. Chem. Chem. Phys., 10, 6962(2008)]. For donors that exhibit different or identical non-exponential fluorescence relaxation within a donor-donor pair, the process of reverberating energy migration is reversible to a higher or lower degree. Here the impact of the EFT has been studied with respect to its influence on fluorescence quantum yields, fluorescence lifetimes as well as depolarisation experiments. The FT predicts relative fluorescence quantum yields which usually agree with the EFT within experimental accuracy, however, substantial deviations occurs in the steady-state and in particular the time-resolved depolarisation data.     

Stiffness constant measurement in NiFe alloys by neutron inelastic scattering

Stiffness constant D has been measured in Ni-Fe alloys in a concentration range up to 68% of iron by neutron inelastic scattering, at room temperature and low temperature. Stiffness constant D decreases more strongly in the range of 60–68% iron concentration and a noticeable enhancement of the spin-wave width occurs in that region.     

On the characterization of the ω-phase in Zr0.8Nb0.2 from intensities of b.c c. Bragg reflections

A reanalysis of the study of Keating and LaPlaca [J. Phys. Chem, Solids35,879 (1974)] shows that the Bragg reflection integrated intensities can be fit almost equally well by quite different models and thus do not suffice to characterize the ω-phase in this alloy without other data. This limitation should be expected for other alloys in which the ω-particles are not large.     

The analysing power in the elastic scattering of 14 MeV neutrons by deuterons

The analysing power for the elastic scattering of 14.1 MeV neutrons by deuterons has been measured at 17 angles between 44.5° and 161.6° in the centre of mass. A polynomial fit to this data combined with that at the same energy by Preiswerk et al. and Fischer et al. has been made and compared with a similar fit to the p-d data of Duder et al. Significant differences are found over the full angular range. Similar comparisons have also been made on existing data at other energies between 8 and 50 MeV. The polynomial expansion coefficients have been determined as a function of energy and show differences between p-d and n-d scattering which vary smoothly with energy and appear to be greater than the experimental errors.     

Magnetization measurements for AuFe spin-glass alloys in fields up to 40 T

High-field magnetization curves are presented for AuFe alloys of Fe concentrations: c = 3.1, 5.1, 6.5 and 10.4 at.%, at T = 4.2 K in pulsed fields up to 40 T. For c = 10.4 at.% additional data were taken at T = 1.2 K and 77 K. From these results we conclude that the nearest-neighbour interaction between the Fe atoms in Au is ferromagnetic, of order of 80 K. The behaviour of the magnetization curves can be qualitatively explained in terms of ferromagnetic clusters that are antiferromagnetically coupled.     

The effect of inelastic electron scattering on the conductivity of very thin wires

The behaviour of the conductivity of a thin wire is calculated in the regime in which inelastic scattering between localized states is beginning to limit the metallic conductivity apparent at higher temperatures. The implications of this for the experiments of Giordano et al. and of Chaudhari and Habermeier, and the possibility of using it to detect inelastic scattering of electrons when elastic scattering is dominant, are discussed.     

A note on surface magnetoplasmons in semiconductors

The results of Brion et al. [Phys. Rev. Lett.28, 1455 (1972)] are reinterpreted to predict, in facile manner, the type of inequalities that need to be satisfied by the surface parameters for the existence of gaps and multiple branches in the dispersion curves for surface waves along the interface of a semiconductor-semiconductor structure.     

Dust ion-acoustic shock-wave structures: Theory and laboratory experiments

An evolutionary theoretical model is developed that describes dust ion-acoustic shock waves in dusty plasma consisting of ions (treated in the hydrodynamic approximation), Boltzmann electrons, and variable-charge dust grains. Account is taken not only of ionization, absorption, momentum loss by electrons and ions in collisions with dust grains, and gas-kinetic pressure effects but also of the processes peculiar to laboratory plasmas. It is shown that the model is capable of describing all the main experimental results on dust ion-acoustic shock waves [Q.-Z. Luo et al., Phys. Plasmas 6, 3455 (1999); Y. Nakamura et al., Phys. Rev. Lett., 83, 1602 (1999)].     

A second Br-site or a third water position in the crystal structure of K2[Pt(CN)4]Br0.3·3H2O(KCP)?

A discussion of the paper “A neutron diffraction study of structural changes in one-dimensional K₂[Pt(CN)₄]Br_0.3·3H₂O from 77–323°K” which appeared in Solid State Commun.17, 45–48 (1975) and of related papers.Single crystal X-ray and neutron diffraction investigations show without any doubt that the crystal structure of KCP contains a third not fully occupied water position, whereby the correspondent water molecule fills alternatively with Br the center of the unit cell. Furthermore the D-atoms of this water position show occupational disorder. We found four possible arrangements for the D₂O molecule. A second Br-site as reported by Williams et al. does not exist.     

X-ray diffraction study of the CDW phase in (TaSe4)2I: Determination of the CDW modulation amplitude

An extensive X-ray diffraction study of charge density wave (CDW) phase in (TaSe₄)₂I is reported. We have observed the superstructure satellites at 2q in addition to those at q reported by Fujishita et al. The results imply a sinusoidal lattice modulation with polarization almost perpendicular to q (i.e. transverse) and the existence of CDW domains. At 15 K we have extracted an approximate value for the amplitude of the lattice modulation perpendicular to q to be μ_⊥ ∽ 0.087 Å.     

Mössbauer effect study of γ-FeMn alloys

The disordered antiferromagnetic γ-FeMn alloys in the range of Mn concentration from 0 up to 50 at.% Mn were investigated by means of X-ray diffraction analysis (XRD), differential scanning calorimeter (DSC) and Mössbauer spectroscopy (ME) at room temperature and at 80 K. The lattice parameter is constant for Mn contents below 27 at.% and increases linearly for higher Mn concentration. The RT Mössbauer spectra for the alloys with less than 20 at.% Mn were fitted with quadrupole splitting (QS) distribution, and above 20 at.% Mn they were fitted with magnetic hyperfine field (HF) distribution. The averageQS decreases, while the HF maintain a constant value by increasing the Mn concentration. At 80 K, the HF increases linearly up to 30 at.% Mn and then maintains a constant value at about 38 kOe. The peak of the specific heat (c _p) at the Néel temperature changes from broad to sharp as the Mn content increases. The Néel temperature increases with Mn concentration.     

Lattice dynamics of zinc and cadmium

Present work studies the phonon dispersion in Zn and Cd on the basis of a model which considers short range pairwise forces effective upto sixth nearest neighbours and long range forces on the lines of Krebs' work with the assumption that the first derivatives of the paired potential occurring in the zz elements are different from those in the xx elements, equivalent to the work of de Wames et al. We consider complete equilibrium of the ionic lattice in a medium of uniform electron gas similar to our previous work (J. Phys. Chem. Solids36, 975 (1975)) but now we obtain the two equilibrium conditions in a modified form. Further our earlier scheme is not applicable in the study of the lattice dynamics of Zn and Cd and the present scheme at one hand removes this difficulty and on the other it explains the phonon dispersion along [0001], [0110] and [1120] symmetry directions with sufficiently good agreements with the experimental data.     

Hypersurface-homogeneous Universe filled with perfect fluid in <Emphasis Type="Italic">f</Emphasis>(<Emphasis Type="Italic">R</Emphasis>, <Emphasis Type="Italic">T</Emphasis>) theory of gravity

The exact solutions of the field equations with respect to hypersurface-homogeneous Universe filled with perfect fluid in the framework of f(R, T) theory of gravity (Harko et al, Phys. Rev. D 84, 024020 (2011)) is derived. The physical behaviour of the cosmological model is studied.     

A phenomenological approach to the equation of state of a unitary Fermi gas

We propose a phenomenological approach for the equation of state of a unitary Fermi gas. The universal equation of state is parametrized in terms of Fermi–Dirac integrals. This reproduces the experimental data over the accessible range of fugacity and normalized temperature, but cannot describe the superfluid phase transition found in the MIT experiment [Ku et al, Science 335, 563 (2012)]. The most sensitive data for compressibility and specific heat at phase transition can, however, be fitted by introducing into the grand partition function a pair of complex conjugate zeros lying in the complex fugacity plane slightly off the real axis.     

Size effect on different impurity levels in semiconductors — A comment

The results obtained for the strain energy corrections to O and Se donor ionization energies in GaP (at the P site) by Van Cong et al. in a recent communication [1] are shown to be fortuitous. It is pointed out that the results of Weinreich [2] are of the correct order unlike the results of Van Cong et al. which are too high in many cases and are not in agreement with experiment.     

X-ray emission spectra and electronic structure of Mn impurities in diluted Al,Ni and Cu-based solid solutions

Mn L_α emission spectra of pure metal and AlMn, CuMn and NiMn alloys are presented. For CuMn and NiMn alloys, the dependence of the width of structureless emission band on Mn concentration is discussed. For Al_0.995Mn_0.005 alloy, distoted shape of the emission spectrum reveals the spin splitting of impurity virtual bound states.     

Effect of Fe substitution on the thermal expansion of the highT c superconductor Y1Ba2Cu3O y

Thermal expansion measurements have been carried out on Fe substituted superconducting compounds Y₁Ba₂(Cu_1−x Fe _x )₃O _y (0<x<4%) using a high resolution dilatometer employing the three terminal capacitance technique. The experimental set up is sensitive enough to detect changes in α of less than 10⁻⁸K⁻¹. Results show that the jump Δα in the coefficient of linear thermal expansion at the superconducting transition temperature,T _c, increases almost linearly with Fe concentration. The normal state thermal expansion coefficient α first decreases, attains a minimum value aroundx=1% and then increases for higher Fe concentrations. The oxygen content per unit formula is almost constant up tox=1% and then increases rapidly withx. It has also been observed that the anomalous behaviour of α around 260 K observed by Meingastet al [22] for Fe concentrationx=5% is due to inadequate annealing of the sample.     

Intensity of the atomic oxygen lines at 8446 and 7771 A in an Ar-O2 d.c. glow discharge

An equation for the intensity ofO(3³P?3³S) at 8446 A and ofO(3⁵P?3⁵S) at 7771 A has been derived as a function of electron-, Ar- and O₂-densities assuming applicability of the excitation processes proposed by Bennett et al. and by Tunitskii and Cherkasov. The electron temperature has been assumed to be constant. The results are compared with experimental data obtained in the d.c. glow discharge of Ar-O₂ mixtures.