Synthesis of sterically congested 1,3,4-oxadiazole derivatives from aromatic carboxylic acids, <Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>-dicyclohexylcarbodiimide and (<Emphasis Type="Italic">N</Emphasis>-isocyanimino)triphenylphosphorane

Reactions of (N-isocyanimino)triphenylphosphorane with N,N-dicyclohexylcarbodiimide in the presence of aromatic (or heteroaromatic) carboxylic acids proceed smoothly at room temperature and in neutral conditions to afford sterically congested 1,3,4-oxadiazole derivatives in high yields. The reaction proceeds smoothly and cleanly under mild conditions, and no side reactions were observed.     

EPR Features of Spin-Crossover in Tris(<Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>-Dialkyl-Dithiocarbamato)Iron(III)

The temperature dependence of electron paramagnetic resonance (EPR) spectra of a series of dithiocarbamates Fe(RR′dtc)₃ was studied in the temperature range from 5 to 300 K. A small part of solvated complexes serving as spin probes in the EPR-silent matrix enabled the observation of EPR of the Fe(III) ion in the whole temperature range. The spin transition was revealed in the reduction of the integral intensity of the signal from the high-spin complexes and in the non-monotonous change of the line width with temperature decrease due to the effect of the low-spin complexes with short spin–lattice relaxation times. Below ca. 60 K, the ferromagnetic ordering of the magnetic moments in low-spin particles (“domains”) arising at the spin transition was observed.     

Reconstruction of some cosmological models in <Emphasis Type="Italic">f</Emphasis>(<Emphasis Type="Italic">R</Emphasis>,<Emphasis Type="Italic">T</Emphasis>) cosmology

In this paper, we reconstruct cosmological models in the framework of f(R,T) gravity, where R is the Ricci scalar and T is the trace of the stress-energy tensor. We show that the dust fluid reproduces ΛCDM, phantom–non-phantom era and phantom cosmology. Further, we reconstruct different cosmological models, including the Chaplygin gas, and scalar field with some specific forms of f(R,T). Our numerical simulation for the Hubble parameter shows good agreement with the BAO observational data for low redshifts, z<2.     

Ferromagnetism and ferroelectricity in Eu<Emphasis Type="Italic">X</Emphasis> (<Emphasis Type="Italic">X</Emphasis> = <Emphasis Type="Italic">O</Emphasis>, <Emphasis Type="Italic">S</Emphasis>): pressure effects

Ferromagnetism and ferroelectricity in Eu monochalcogenides have been investigated by ab initio density functional theory in the DFT+U approach. Exchange interaction parameters and Curie temperatures under pressure are studied and discussed using Heisenberg Hamiltonian with first and second-nearest-neighbor interactions. The calculations showed that the hydrostatic pressure perfectly improves the Curie temperature (EuO: T _C = 175 K; EuS: T _C = 33.8 K) and in the other hand it cannot induce the spontaneous polarization (P _s ). The effect of uniaxial and biaxial pressure is also studied. Although the uniaxial strains slightly increases the Curie temperature, it ensures the ferrolectricity in these systems by producing a spontaneous polarization of the order of P _s (EuO) = 57.50 μC/cm² and P _s (EuS) = 42.86 μC/cm² with pressures of 5% and 4%, respectively. The search for new model systems is a necessity to better understand the physics related to multiferroïc materials and to consider possible applications.     

Spherical Symmetric Perfect Fluid Collapse in <Emphasis Type="Italic">f</Emphasis>(<Emphasis Type="Italic">R</Emphasis>, <Emphasis Type="Italic">T</Emphasis>) Gravity

This paper contains the study of spherically symmetric perfect fluid collapse in the frame work of f(R, T) modified theory of gravity. We proceed our work by considering the non-static spherically symmetric background in the interior and static spherically symmetric background in the exterior regions of the star. The junction conditions between exterior and interior regions are presented by matching the exterior and interior regions. The field equations are solved by taking the assumptions that the Ricci scalar as well as the trace of energy-momentum tensor are to be constant, for a particular f(R, T) model. By inserting the solution of the field equations in junction conditions, we evaluate the gravitational mass of the collapsing system. Also, we discuss the apparent horizons and their time formation for different possible cases. It is concluded that the term f(R ₀, T ₀) behaves as a source of repulsive force and that’s why it slowdowns the collapse of the matter.     

Study of <Emphasis Type="Italic">N</Emphasis> = <Emphasis Type="Italic">Z</Emphasis> nuclei in variation-after-projection framework

Variation-after-projection (VAP) calculations in conjunction with the Hartree- Bogoliubov (HB) ansatz have been carried out for A = 68-88, N = Z nuclei. In this framework, the yrast spectra with , B(E2) transition probabilities and deformation parameter ( ) have been obtained. A pairing interaction for like particles as well as protons and neutrons has been included in the model for a two-body interaction.Received: 28 April 2003, Revised: 20 March 2004, Published online: 14 September 2004PACS: 21.10.-k Properties of nuclei; nuclear energy levels - 21.60.-n Nuclear structure models and methods - 27.50. + e      

Forward on the <Emphasis Type="Italic">N</Emphasis> = <Emphasis Type="Italic">Z</Emphasis> line with GASP

The experimental study of the proton-rich nuclei close to the N = Z line is a constant challenge for nuclear spectroscopy, mainly due to the difficulty to produce them with the currently available beam/target combinations. Significant advances on this direction were obtained from experiments performed with the GASP array during the last two years: the yrast line of ⁸⁴Mo was extended up to 10 ⁺ , ⁸⁸Ru observed for the first time, and the N = Z + 1 line was mapped from ⁸¹Zr to ⁹⁵Ag. These new results allow us to have a more complete image of the transition from the well-deformed shell closure at N,Z = 40 to the spherical-shell closure at N,Z = 50, and highlights some particular effects that can be observed only in the vicinity of the N = Z line.Received: 10 January 2003, Published online: 23 March 2004PACS: 21.10.-k Properties of nuclei; nuclear energy levels - 21.10.Pc Single-particle levels and strength functions - 21.10.Re Collective levels - 23.20.-g Electromagnetic transitions     

Ionization of <Emphasis Type="Italic">nS</Emphasis>, <Emphasis Type="Italic">nP</Emphasis>, and <Emphasis Type="Italic">nD</Emphasis> lithium,potassium, and cesium Rydberg atoms by blackbody radiation

The results of theoretical calculations of the blackbody ionization rates of lithium, potassium, and cesium atoms residing in Rydberg states are presented. The calculations are performed for nS, nP, and nD states in a wide range of principal quantum numbers, n = 8?65, for blackbody radiation temperatures T = 77, 300, and 600 K. The calculations are performed using the known quasi-classical formulas for the photoionization cross sections and for the radial matrix elements of transitions in the discrete spectrum. The effect of the blackbody-radiation-induced population redistribution between Rydberg states on the blackbody ionization rates measured under laboratory conditions is quantitatively analyzed. Simple analytical formulas that approximate the numerical results and that can be used to estimate the blackbody ionization rates of Rydberg atoms are presented. For the S series of lithium, the rate of population of high-lying Rydberg levels by blackbody radiation is found to anomalously behave as a function of n. This anomaly is similar to the occurrence of the Cooper minimum in the discrete spectrum.     

Dark Energy Models in <Emphasis Type="Italic">f</Emphasis>(<Emphasis Type="Italic">R</Emphasis>, <Emphasis Type="Italic">T</Emphasis>) Theory with Variable Deceleration Parameter

In this communication we have investigated Bianchi type-II dark energy (DE) cosmological models with and without presence of magnetic field in modified f(R, T) gravity theory as proposed by Harko et al. (Phys. Rev. D, 84, 024020, 2011). The exact solution of the field equations is obtained by setting the deceleration parameter q as a time function along with suitable assumption the scale factor \(a(t)= [sinh(\alpha t)]^{\frac {1}{n}}\), α and n are positive constant. We have obtained a class of accelerating and decelerating DE cosmological models for different values of n and α. The present study believes that the mysterious dark energy is the main responsible force for accelerating expansion of the universe. For our constructed models the DE candidates cosmological constant (Λ) and the EoS parameter (ω) both are found to be time varying quantities. The cosmological constant Λ is very large at early time and approaches to a small positive value at late time whereas the EoS parameters is found small negative at present time. Physical and kinematical properties of the models are discussed with the help of pictorial representations of the parameters. We have observed that our constructed models are compatible with recent cosmological observations.     

<Emphasis Type="Italic">f</Emphasis>(<Emphasis Type="Italic">R</Emphasis>) Cosmology from <Emphasis Type="Italic">q</Emphasis>-theory

From a macroscopic theory of the quantum vacuum in terms of conserved relativistic charges (generically denoted by q ^(a) with label a), we have obtained, in the low-energy limit, a particular type of f(R) model relevant to cosmology. The macroscopic quantum-vacuum theory allows us to distinguish between different phenomenological f(R) models on physical grounds. The text was submitted by the authors in English.     

Friedmann Cosmology with Matter Creation in Modified <Emphasis Type="Italic">f</Emphasis>(<Emphasis Type="Italic">R</Emphasis>, <Emphasis Type="Italic">T</Emphasis>) Gravity

The theoretical and observational consequences of thermodynamics of open systems which allow matter creation, are investigated in modified f(R, T) (R is the Ricci scalar and T is the trace of energy-momentum tensor) theory of gravity within the framework of a flat Friedmann-Robertson-Walker line element. The simplest model f(R, T)=R+2f(T) with “gamma-law” equation of state p = (γ?1)ρ is assumed to obtain the exact solution. A power-law expansion model is proposed by considering the natural phenomenological particle creation rate ψ = 3β n H, where β is a pure number of the order of unity, n the particle number density and H is the Hubble parameter. A Big Rip singularity is observed for γ<0 describing phantom cosmology. The accelerated expansion of the Universe is driven by the particle creation. The density parameter shows the negative curvature of the Universe due to particle creation. The entropy increases with the evolution of the Universe. Some kinematics tests such as lookback time, luminosity distance, proper distance, angular diameter versus redshift are discussed in detail to observe the role of particle creation in early and late time evolution of the Universe.     

Exact Results for Topological Strings on Resolved <Emphasis Type="Italic">Y</Emphasis><Superscript><Emphasis Type="Italic"> p</Emphasis>,<Emphasis Type="Italic">q</Emphasis></Superscript> Singularities

We obtain exact results in α′ for open and closed A-model topological string amplitudes on a large class of toric Calabi-Yau threefolds by using their correspondence with five dimensional gauge theories. The toric Calabi-Yaus that we analyze are obtained as minimal resolution of cones over Y ^p,q manifolds and give rise via M-theory compactification to SU(p) gauge theories on . As an application we present a detailed study of the local case and compute open and closed genus zero Gromov-Witten invariants of the orbifold. We also display the modular structure of the topological wave function and give predictions for higher genus amplitudes. The mirror curve in this case is the spectral curve of the relativistic A ₁ Toda chain. Our results also indicate the existence of a wider class of relativistic integrable systems associated to generic Y ^p,q geometries.     

1/<Emphasis Type="Italic">N</Emphasis><Subscript><Emphasis Type="Italic">c</Emphasis></Subscript> countings in baryons

The 1/N _c -power countings for baryon decays and configuration mixings are determined by means of a nonrelativistic quark picture. Such countings are expected to be robust under changes in the quark masses and, therefore, valid as these become light. It is shown that excited baryons have natural widths of \(\mathcal{O}(N_c^0 )\). These dominant widths are due to the decays that proceed directly to the ground-state baryons, with cascade decays being suppressed to \(\mathcal{O}(1/N_c )\). Configuration mixings, defined as mixings between states belonging to different O(3) × SU(2N _f ) multiplets, are shown to be subleading in an expansion in \(1/\sqrt {N_c }\) when they involve the ground-state baryons, while the mixings between excited states can be \(\mathcal{O}(N_c^0 )\).     

Tsallis <Emphasis Type="Italic">p</Emphasis>,<Emphasis Type="Italic">q</Emphasis>-deformed Touchard polynomials and Stirling numbers

In this paper, we develop and investigate a new two-parametrized deformation of the Touchard polynomials, based on the definition of the NEXT q-exponential function of Tsallis. We obtain new generalizations of the Stirling numbers of the second kind and of the binomial coefficients and represent two new statistics for the set partitions.     

Pairing of Neutrons and Protons in <Emphasis Type="Italic">N</Emphasis> = <Emphasis Type="Italic">Z</Emphasis> Nuclei

Values of neutron–proton pairing based on mass relations are estimated. It is shown that substantially different formulas for calculating the np-pairing energy in self-conjugate nuclei yield similar results. Comparison of the obtained values and the structure of ground state multiplet spectra shows that mass relations can be used to describe the isovector (T = 1) component of np-pairing to sufficient accuracy, but provides little or no information on isoscalar component T = 0.     

A reanalysis of finite temperature <Emphasis Type="Italic">SU</Emphasis>(<Emphasis Type="Italic">N</Emphasis>) gauge theory

We revise the SU(N _c ), N _c =3,4,6, lattice data on pure gauge theories at finite temperature by means of a quasi-particle approach. In particular, we focus on the relation between the effective mass of the quasi-particle and the order of the deconfinement transition, the scaling of the interaction measure with N²_c -1N^{2}_{c} -1, the role of gluon condensate, and the screening mass.     

Improvement of <Emphasis Type="Italic">n</Emphasis>-ZnO/<Emphasis Type="Italic">p</Emphasis>-Si photodiodes by embedding of silver nanoparticles

The photo-current of n-ZnO/p-Si heterojunction photodiodes was improved by embedding Ag nanoparticles in the interface (ZnO/nano-P_Ag/p-Si), and the ratio between photo- and dark-current increased by about three orders more than that of a n-ZnO/p-Si specimen. The improvement in the photo-current resulted from the light scattering of embedded Ag nanoparticles. The I–V curve of n-ZnO/p-Si degraded after thermal treatment (A-ZnO/p-Si) because the silicon robbed the oxygen from ZnO to form amorphous silicon dioxide and left an oxygen vacancy. Notably, the properties of ZnO/nano-P_Ag/p-Si were better in the time-dependent photoresponse under 10 V bias. Ag nanoparticles (15–20 nm) scattered the UV light randomly and increased the probability for the absorption of ZnO to enhance the properties of the photodiode.     

The <Emphasis Type="Italic">N</Emphasis> = <Emphasis Type="Italic">Z</Emphasis><Emphasis Type="Italic">f</Emphasis><Subscript>7/2</Subscript>-shell nuclei: Experimental highlights

During the last decade, as the experimental and computing means and techniques have rapidly evolved, the experimental investigation of the f_7/2-shell nuclei has gained renewed interest. TheN = Z nuclei studied with the GASP array range from ⁴⁴Ti to ⁵²Fe. The results extended the knowledge of their structure up to high spins and excitation energies, above band terminations, where the competition with the charged-particles emission was initially thought to obscure the possibility of gamma-ray spectroscopy investigation. The paper highlights some of the most outstanding properties of these nuclei such as the nuclear rotation and backbending effects, band termination states, yrast traps, non-natural parity bands, competition between T = 0 and T = 1 pn pairing modes.Received: 30 October 2002, Published online: 16 March 2004PACS: 21.10.-k Properties of nuclei; nuclear energy levels - 21.60.Cs Shell model - 23.20.Lv transitions and level energies - 27.40. + z C.A. Ur: On leave from NIPNE Bucharest, Romania     

Cosmology from <Emphasis Type="Italic">f</Emphasis>(<Emphasis Type="Italic">R</Emphasis>,<Emphasis Type="Italic">T</Emphasis>) Theory in a Variant Speed of Light Scenario

In this work I present a generalization of f(R, T) gravity, by allowing the speed of light to vary. Cosmological solutions are presented for matter and radiation-dominated universes, the former allowing the universe expansion to accelerate while the latter contemplating a possible alternative to inflationary scenario. Remarkably, standard gravity is always retrieved for a special case of f(R, T).