On the Bose-Einstein correlation in inelastic collisions of nuclei

The Bose-Einstein correlation function for two pions of same charge produced in a high energy nucleus-nucleus collision is computed in the framework of the reggeon theory. We obtain a coherence parameter λ=1 and a transverse radius of the sourceR _T close to the radius of the smaller of the colliding nuclei.

     

Dimensionality Effects on the Mixed Spin-1/2 and Spin-2 Blume-Capel Model: Renormalization Group Theory

We have used the real-space Migdal-Kadanoff renormalization group technique on d-dimensional hypercubic lattice to study the mixed spin-1/2 and spin-2 Blume-Capel model. First, we indicate a critical dimension d_C ≈?2.05, above and below which different topologies of phase diagrams occur. The phase diagrams have been plotted in the (crystal field, temperature) plane around d_C, in which there is a second-order phase transition. Moreover, using the variation of the free energy at low temperatures, we have established the ground-state phase diagrams in the (?/J, C/J) plane for d?<?d_C and d?≥?d_C. In particular, we have seen the appearance of two first-order transitions at very low temperatures by the use of the free energy and its isotherm derivative. A detailed analysis of fixed points and flow diagrams indicates that there is no tricritical point.

     

Energy and momentum of general spherically symmetric frames on the regularizing teleparallelism

In the context of the covariant teleparallel framework, we use the 2-form translational momentum to compute the total energy of two general spherically symmetric frames. The first one is characterized by an arbitrary function H(r), which preserves the spherical symmetry and reproduces all the previous solutions, while the other one is characterized by a parameter ξ which ensures the vanishing of the axial of trace of the torsion. We calculate the total energy by using two procedures, i.e., when the Weitzenböck connection Γ_α^β is trivial, and show how H(r) and ξ play the role of an inertia that leads the total energy to be unphysical. Therefore, we take into account Γ_α^β and show that although the space×we use contain an arbitrary function and one parameter, they have no effect on the form of the total energy and momentum as it should be.     

Long Distance Electronic Effects on the Rotational Potential Barriers Around the Caromatic-Cethylenic Bond

A systematic study of the rotational activation free energy around the C_aromatic-C_ethylenic bond of para-substituted styrene systems is carried out in the present work from a quantum chemistry point of view.

Calculations of the rotational potential barriers in the AM1 approach are developed as function of the electron-donor groups localized on the aromatic ring. Based on these calculations and thermodynamical data, we predict changes in the activation free energy barriers due to the long distance electronic effects of the substituents in acetophenones, cinnamaldehydes and benzalketones according to the following equation:

Our results agree the experimental measurements registered up to date and the standard deviations are similar to experimental determinations.     

Abnormal photonic energy — a signal of Quark matter possibly seen in exotic cosmic ray events

A phenomenological method is proposed to select possible Quark matter forming events in ultra-relativistic nucleus-nucleus interactions. We compare the released photonic and hadronic energies from a Quark matter forming event and from a normal Hadronic event and derive a relation, which may be used in an event-by-event analysis to differentiate the two phases. We determine thus two regions of QCD deconfinement. We also discuss the hadronic, photonic energy and multiplicity contents and the 〈P_T〉 of several exotic cosmic ray events at ultra high energies. On the basis of the phenomenological model, we suggest that the “Centauro” type are Quark matter events near the projectile fragmentation region with very large baryochemical potential,μ _b. The “Anti-Centauro” type events are created by vacuum excitation in the central region with near zeroμ _b.

     

The dependence of sputtering efficiency on ion energy and angle of incidence

Abstract

Earlier measurements of sputtering efficiency of polycrystalline targets (fraction of impinging ion energy leaving the target through sputtering and backscattering) have been extended to higher energies. Lead and copper targets were bombarded with several different projectiles with energies between 80 and 1200 keV. The sputtering efficiency decreases with increasing energy. This decrease is ascribed to the combined influence of changes in the scattering cross section with energy, and to electronic stopping. The results may be described as a function of the mass ratio M ₂/M ₁ and the reduced energy ? only.

The sputtering efficiency was measured as a function of angle of incidence of the bombarding ions. To ensure complete collection of sputtered and backscattered particles, it was possible to cover only the region of incidence angle from 0° to 45°. Targets of copper, silver, and lead were investigated with 17 different ion-target combinations. The sputtering efficiency increased with angle of incidence. This increase is described well by a simple interpolation formula by Sigmund.     

On the dependence of the critical temperature on pressure in the bisoliton model of high temperature superconductors

Abstract

In the framework of the bisoliton model we have studied the critical temperature T _c, as a function of the pressure P and of the hole concentration δ for the high temperature superconductors YBa₂Cu₃O_x and (La_1-xM_x)₂CuO₄. Our results for δ ln T_c/δ ln V as a function of T _c describe quite satisfactorily the general trend of the experimental data. Furthermore we show that in the bisoliton model the energy gap δ (in units of Jg³/3, where J is the nearest-neighbour exchange integral and g is the nonlinearity parameter) is an universal function of δ/g. An analogous property is valid for T _c By fitting the maximum value of T _c we are able also to reproduce the experimental data for T _c(δ).     

Isospin and symmetry energy study in nuclear EOS

This paper summarizes the isoscaling and isospin related studies in asymmetry nuclear reactions by different dynamic and statistical models. Isospin dependent quantum molecular dynamics model (IQMD) and lattice gas model (LGM) are used to study the isoscaling properties and isoscaling parameters dependence on incident energies, impact parameters, temperature and other parameters. In the LGM model, the signal of phase transition has been found in free neutron (proton) chemical potential difference Δµ_n or Δµ_p as a function of temperature, or in free neutron and proton chemical potential difference Δµ_n−Δµ_p. Density dependence of symmetry energy coefficient C _sym(ρ/ρ ₀) is also studied in the frame of LGM, with the potential parameters which can reproduce the nuclear ground state property, soft density dependence of symmetry energy is deduced from the simulation results. Giant dipole resonance (GDR) induced by isospin asymmetry in entrance channel is also studied via IQMD model, and the dynamic dipole resonance shows isospin sensitivity on the isospin asymmetry of entrance channel and symmetry energy of the nuclear equation of state (EOS). GDR can also be regarded as a possible isospin sensitive signature.

     

Measurements of hall-effect and sheet resistivity as a function of temperature on hot,phosphorous implants in silicon

Abstract

Results of Hall-effect measurements as a function of temperature on a layer formed by hot, phosphorous (P³¹) implant in Si at 400 keV energy in a random direction are presented; the dose used was 10¹⁵ ions cm^?2. The electrical behaviour of the layer as a function of isochronal annealing was examined.

A detailed analysis of the measured quantities n _8eff, the effective surface density of free carriers, and μ_eff, the effective mobility, down to 4.2°K is presented using the integral equations:

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These formulae were solved numerically, the input data viz: the distribution of donor centres and compensating damage centres being assumed from the current literature.

Results from this analysis indicate a rather complicated distribution of current flow in the layer as a function of temperature, indicating that the traditional interpretation of Hall measurements based on a homogeneous distribution model is of questionable validity.     

Isotope effect of protonic conductivity in LiNbO3

Abstract

The electrical DC conductivity [sgrave] of LiNbO₃ :H, D was studied as a function of temperature, electric field and proton/deuteron dopant concentration. The conductivity follows linearly the hydrogen content over two orders of magnitude. Independent holographic measurements on the same samples confirm these results in the temperature range 75 – 150 °C. The activation energy for protonic and deuteronic migration turns out to be equal, E_{act, H} = E_{act, D} = 1.23 ± 0.04eV. The isotope effect of the pre-exponential factor reflects the mass dependence of the attempt frequency and shows the protons to be the migrating species rather than hydroxyl ions.     

The early high-energy afterglow emission from short GRBs

We calculate the high energy afterglow emission from short Gamma-Ray Bursts (SGRBs) in the external shock model. There are two possible components contributing to the high energy afterglow: electron synchrotron emission and synchrotron self-Compton (SSC) emission. We find that for typical parameter values of SGRBs, the early high-energy afterglow emission in 10 MeV-10 GeV is dominated by synchrotron emission. For a burst occurring at redshift z = 0.1, the high-energy emission can be detectable by Fermi LAT if the blast wave has energy E ⩾ 10⁵¹ ergs and the fraction of electron energy ɛ _e ⩾ 0.1. This provides a possible explanation for the high energy tail of SGRB 081024B.

     

Structural Phase Transition and the Dielectric Permittivity of the Model Lipid Bilayer [(CH2)12(NH3)2]CuCl4

Structural phase transitions in the lipid-like bilayer material [(CH₂)₁₂(NH₃)₂]CuCl₄ have been observed using differential thermal scanning. The compound shows an irreversible thermochromic transition at ? 465 K and three reversible transitions at T ₁ = 433 ± 4 K and T ₂ = 411 ± 2 K and T ₃ = 358 K. The transition at 350 K is ascribed to chain melting. The other two correspond to crystalline phase transformation.

Phase (IV) T₃ = 358 ± 2K Phase (III) T₂ = 411 ± 2K Phase (II) T₁ = 433 ± 4K Phase (I)

Dielectric permittivity is studied as a function of temperature in the range 300-440 K and frequency, range (60 Hz-100 kHz). It confirms the observed transitions. The dielectric permittivity reflects rotational and conformational transitions for the compound. The variation of the real part of the conductivity with temperature is thermally activated in the temperature range above 350 K, with frequency-dependent activation energy, the values of activation energy lie in the range of ionic hopping. The dependence of the conductivity on frequency follows the universal power law σ = σ₀ + A(T) ω ^{s ( T )} with 0<s<1. Comparison of this material with other members of the series is discussed     

The Study on the Arc Plasma Temperature Measurement by Optical Emission Spectroscopy with Fiber Optical Transmission

Abstract

A method for transmitting radiation of the arc plasma with multimode fused quartz fiber onto the spectrograph has been studied. The plot of the Boltzmann function in emission spectral analysis is used for measuring temperature of the arc plasma. The measured temperature of the arc plasma is 5946.6K from least square linear regression of ln[λI/(gA)] and E_i for a number of the emission line intensities of the excited copper atom. Its regression coefficient and measured precision are ?0.97% and 1.7%, respectively. The advantages of the method of the diagnostic temperature for the arc plasma are absolute measurements of the temperature, remote sensing, precision and suitable for mal-environment, such as high temperature, toxic, explosion, strong magnetic or/and electrical fields.

In addition, we have discussed the effect of the spectroscopic constants, such as transition probability, A , the statistical weight of the upper level, g , and the energy of the upper level, E_i , of copper lines on calculating temperature with a plot of the Boltzmann function in detail. The results show that the accurate measurement of the temperature for the arc plasma is obtained only when the spectroscopic constants are selected correctly.     

Numerical studies on the anderson localization problem

The electron localization is studied for Anderson's tight-binding model with diagonal and off-diagonal disorder for a very large square lattice (10,000 sites) and diamond lattice (27,000 sites). The numerical investigations are based on the Lanczos recursion method. The convergence of the recursion coefficientsa _n ,b _n is discussed with regard to the electron localization.From Anderson's criterion and an exact real space renormalization method the energy of the localization edge is found as a function of the degree of disorder. Also the dependence of the spatial decay rate of localized wave functions on the energy and the degree of disorder is evaluated. Near the Anderson transition, where all states become localized, we get two critical exponentsv _E andv _W , which lead us to the tentative suggestion of multicritical scaling laws for this transition.     

Density functional study of ternary AuxAgyCuz and AuxAgyCuz+ clusters (x + y+z = 5, 6)

ABSTRACT

We report a theoretical investigation of neutral Au_xAg_yCu_z and cationic Au_xAg_yCu_z⁺ ternary clusters, for x?+?y+z?=?5 and 6. Our study is performed within density functional theory at the TPSSTPSS/SDD level. The geometries, chemical order, binding energy, mixing energy, second difference in the energy, adiabatic ionisation potential of these clusters are evaluated as a function of the whole concentration range. The most probable dissociation channels and the corresponding dissociation energies for the most stable clusters are also determined and discussed.     

Electron energy loss studies in solids; The transition metal dichalcogenides

The theory of characteristic electron energy losses is discussed in terms of the electronic band structure of a solid. The relationship between the observed plasmon energies, the average interband energy gap and the background dielectric constant of the solid is developed.

The transmission energy loss spectra of a number of the layer-type transition metal dichalcogenides, MX₂, where M=Zr, Hf, Nb, Ta, Mo and W and X=S and Se, have been measured in the range of 0–50 eV. In the experiments, a beam of 50 keV electrons is incident along the c-axis of the crystals and electrons inelastically scattered through an angle of 1 m radian are selected for energy analysis. This ensures that the momentum transfer and hence the electric vector for the excitations lies in the basal plane of the crystal (E⊥c).

Kramers-Kronig analysis has been applied to the energy loss data to deduce the complex dielectric function of each material. From this function, all other ‘optical’ constants, such as the reflectivity, and the oscillator integral function and joint density of states function have been calculated.

The results give substantial support to the existing band model for the family of materials and, in addition, provide the basis for a quantitative understanding of the band structure of individual compounds.     

Reconstruction of <Emphasis Type="Italic">f</Emphasis>(<Emphasis Type="Italic">T</Emphasis>) gravity according to holographic dark energy

We develop the reconstruction of the f(T) gravity model according to the holographic dark energy. T is the torsion scalar and its initial value from the teleparallel gravity is imposed for fitting the initial value of the function f(T). The evolutionary nature of the holographic dark energy is essentially based on two important parameters, Ω _V  and ω _V , respectively, the dimensionless dark energy and the parameter of the equation of state, related to the holographic dark energy. The result shows a polynomial function for f(T), and we also observe that, when Ω _V →1 at the future time, ω _V may cross −1 for some values of the input parameter b. Another interesting aspect of the obtained model is that it provides a unification scenario of dark matter with dark energy.     

Analysis of the Al content in semiconductor materials by null ellipsometric spectrometry

In this paper, we demonstrate two methods by which the aluminum content in Al_xGa_0.51−xIn_0.49P and Si-doped Al_xGa_0.51−xIn_0.49P film deposited on GaAs substrates by MOVCD can be measured nondestructively. The first method is to calculate the Al content by means of effective medium approximation theory based on the optical parameters of the samples determined from ellipsometric spectrometry at room temperature for different wavelengths. The second method is to obtain the values of the energy gap E_g by analyzing the third derivatives of the imaginary part of the dielectric function. The aluminum content in the samples is then evaluated by substituting the value of E_g into the linear interpolation equation. The results of both methods agreed well with that obtained by the energy dispersive X-ray analysis method.