2D degenerate electron gas at Ba/<Emphasis Type="Italic">n</Emphasis>-AlGaN and Ba/<Emphasis Type="Italic">n</Emphasis>-GaN interfaces

Ba/n-GaN(0001) and Ba/n-AlGaN(0001) interfaces were investigated for the first time by means of ultraviolet photoelectron spectroscopy. The spectra of the photoemission from a valence band along with the spectra of the core levels of Ga 3d, Al 2p, and Ba 4d were studied. The formation of a 2D degenerate electron gas (an accumulated layer on the n-GaN and n-AlGaN surfaces during adsorption of Ba atoms) was revealed.     

Temperature dependence of dark current-voltage characteristics of <Emphasis Type="Italic">n</Emphasis>InSb-<Emphasis Type="Italic">n</Emphasis>PbTe-<Emphasis Type="Italic">n</Emphasis>CdTe isotype structure

The temperature dependence of dark current-voltage characteristics of an nInSb-nPbTe-nCdTe structure is investigated. It is shown that in the temperature range from 115 K to 125 K an energy barrier exists for charge carriers through the InSb layer, which is strictly connected with different temperature dependences of electron concentrations in nInSb and nPbTe.     

Electronic structure of crystal-forming fulborenes B<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript>N<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript>

A general approach is formulated to the design of crystal-forming fullerene-like clusters X _n Y _n from which zeolite-like covalent crystals based on IV-IV, III-V, and II-VI binary semiconductor compounds with diamond-like sp ³ bonds can be constructed and synthesized by means of copolymerization through faces. A number of the smallest sized crystal-forming boron nitride clusters are constructed, such as the B₁₂N₁₂, B₁₆N1₆, B₁₈N₁₈, B₂₄N₂₄, B₃₆N₃₆, and B ₆₀N₆₀ fulborenes. The optimized configurations, electronic structures, charge transfers, band gaps, total energies, cohesive energies, and electron density maps of the clusters are calculated using the spin-restricted Hartree-Fock method in the 6–31G basis set. Comparative calculations of the B₆₀N₆₀ fulborene with the use of the density functional theory method have demonstrated that the spin-restricted Hartree-Fock method in the 6–31G basis set is optimum from the standpoint of the accuracy and efficiency.     

Discussion of isomeric ratios in (<Emphasis Type="Italic">p,n</Emphasis>) and (<Emphasis Type="Italic">d</Emphasis>, 2<Emphasis Type="Italic">n</Emphasis>) reaction

Isomeric ratios (IR) in the (p, n) and (d, 2n) reactions are considered. The dependence of IR values on the projectile type and energy, the target- and product-nucleus spin, the spin difference between the isomeric and ground states of products, and the product mass number is discussed. The isomeric ratios for 46 product nuclei (from ^44m,gSc to ^127m,gXe) obtained in reactions where target and product nuclei have identical mass numbers were calculated at energies from the reaction threshold to 50 MeV (with a step of ΔE = 1 MeV). The calculations in question were performed with the aid of the TALYS 1.4 code package. The calculated IR values were compared with their experimental counterparts available from the literature (EXFOR database). In the majority of cases, the calculated IR values agree well with the experimental data in question. It is noteworthy that the IR values obtained in (d, 2n) reactions are substantially greater than those in (p, n) reactions.     

The difference between <Emphasis Type="Italic">n</Emphasis>-dimensional regularization and <Emphasis Type="Italic">n</Emphasis>-dimensional reduction in QCD

We discuss the difference between n-dimensional regularization and n-dimensional reduction for processes in QCD which have an additional mass scale. Examples are heavy flavor production in hadron-hadron collisions or on-shell photon-hadron collisions where the scale is represented by the mass m. Another example is electroproduction of heavy flavors where we have two mass scales given by m and the virtuality of the photon . Finally we study the Drell-Yan process where the additional scale is represented by the virtuality of the vector boson ( ). The difference between the two schemes is not accounted for by the usual oversubtractions. There are extra counter terms which multiply the mass scale dependent parts of the Born cross sections. In the case of the Drell-Yan process it turns out that the off-shell mass regularization agrees with n-dimensional regularization.Received: 12 January 2005, Published online: 21 February 2005PACS: 11.15.Bt, 12.38.Bx, 13.85.NiJ. Smith: Partially supported by the National Science Foundation grant PHY-0354776.     

Role of (<Emphasis Type="Italic">n</Emphasis>,2<Emphasis Type="Italic">n</Emphasis>) reactions in transmutation of long-lived fission products

The conditions under which (n,γ) and (n,2n) reactions can help or hinder each other in neutron transmutation of long-lived fission products (LLFPs) are considered. Isotopic and elemental transmutation for the main long-lived fission products, ⁷⁹Se, ⁹³Zr, ⁹⁹Tc, ¹⁰⁷Pd, ¹²⁶Sn, ¹²⁹I, and ¹³⁵Cs, are considered. The effect of (n,2n) reactions on the equilibrium amount of nuclei of the transmuted isotope and the neutron consumption required for the isotope processing is estimated. The aim of the study is to estimate the influence of (n,2n) reactions on efficiency of neutron LLFP transmutation. The code TIME26 and the libraries of evaluated nuclear data ABBN-93, JEF-PC, and JANIS system are applied. The following results are obtained: (1) The effect of (n,2n) reactions on the minimum number of neutrons required for transmutation and the equilibrium amount of LLFP nuclei is estimated. (2) It is demonstrated that, for three LLFP isotopes (¹²⁶Sn, ¹²⁹I, and ¹³⁵Cs), (n,γ) and (n,2n) reactions are partners facilitating neutron transmutation. The strongest effect of (n,2n) reaction is found for ¹²⁶Sn transmutation (reduction of the neutron consumption by 49% and the equilibrium amount of nuclei by 19%).     

Phase behaviour of <Emphasis Type="Italic">n</Emphasis>-hexane/perfluoro-<Emphasis Type="Italic">n</Emphasis>-hexane binary thin wetting films

We present X-ray reflectivity investigations of the concentration distribution in binary liquid thin films on silicon substrates. The liquid-vapor coexistence of the binary mixture investigated, hexane and perfluorohexane, is far from criticality. Therefore, a sharp interface separates the liquid film from the vapor. The data reveal a separation of the film in layers parallel to the substrate. A phase diagram is constructed as a projection to the (composition difference, temperature) space, covering a temperature range corresponding to the one-phase and the two-phase regime of the bulk liquid. Although the composition data indicate a mixing gap similar to that of the bulk system, there are two major differences: i) only the near-surface phase changes its composition significantly, and ii) a composition gradient in the film exists also at higher temperatures where in the bulk system the one-phase regime exists.Received: 28 April 2004, Published online: 21 September 2004PACS: 61.10.Kw X-ray reflectometry (surfaces, interfaces, films) - 64.75. + g Solubility, segregation, and mixing; phase separation - 68.15. + e Liquid thin films     

Bidirectional Quantum Teleportation of a Class of <Emphasis Type="Italic">n</Emphasis>-Qubit States by Using (2<Emphasis Type="Italic">n</Emphasis> + <Emphasis Type="Bold">2</Emphasis>)-Qubit Entangled States as Quantum Channel

A new protocol of bidirectional quantum teleportation (BQT) is proposed in which the users can transmit a class of n-qubit state to each other simultaneously, by using (2n + 2)-qubit entangled states as quantum channel. The state of the art approaches can only transmit two-qubit states in each round. This scheme is based on control-not operation, single-qubit measurements and appropriate single-qubit unitary operations. It is shown that the protocol is secure in preparation phase.     

Mechanism of charge transfer in <Emphasis Type="Italic">n</Emphasis>-CdS/<Emphasis Type="Italic">p</Emphasis>-CdTe heterojunctions

The capacitance-voltage and current-voltage characteristics of the n-CdS/p-CdTe heterosystem are investigated. Analysis of these characteristics demonstrates that the CdTe_1?x S _x solid solution formed at the n-CdS/p-CdTe heterointerface is inhomogeneous in both the conductivity and composition. The thickness of solid solutions is estimated from the capacitance-voltage characteristics. It is shown that, for the n-CdS/p-CdTe heterosystem, the current-voltage characteristic in the current density range 10^?8-10^?5 A cm^?2 is governed by the thermal electron emission, whereas the current in the heterostructure at current densities in the range 10^?4-10^?2 A cm^?2 is limited by recombination of charge carriers in the electroneutral region of the CdTe_1?x S _x solid solution. The lifetime and the diffusion length of minority charge carriers in the CdTe_1?x S _x solid solution and the surface recombination rate at the interface between the CdS layer and the CdTe_1?x S _x solid solution are determined. It is demonstrated that the n-CdS/p-CdTe heterostructure operates as a p-i-n structure in which CdTe is a p layer, CdTe_1?x S _x is an i layer, and CdS is an n layer.     

Experimental study of the ignition of <Emphasis Type="Italic">n</Emphasis>-hexane- and <Emphasis Type="Italic">n</Emphasis>-decane-based surrogate fuels

Surrogate fuels on the basis of mixtures of n-hexane, n-decane, and benzene are fuels alternative to petroleum motor fuels, similar to the former in thermodynamic and kinetic properties. The fact the surrogate fuels are composed of a limited number of components makes it possible to develop both detailed and global kinetic mechanisms of their ignition in mixtures with oxidizers. In turn, the possibility of the kinetic modeling of the ignition of such fuels over wide temperature and pressure ranges is of critical importance for the numerical modeling of combustion-to-detonation transition phenomena. An experimental method for measuring ignition delay times of mixtures of air with liquid fuels with low vapor pressure under normal conditions is developed and tested. In the present work, the ignition of stoichiometric mixtures of air with n-hexane, n-decane, and surrogate fuels composed of 20% n-hexane and 80% n-decane, 20% benzene and 80% n-decane, and 9.1% n-hexane, 18.2% benzene, and 72.7% n-decane is experimentally investigated in a static reactor. The ignition delay time is determined by recording pressure oscillograms at temperatures of 530–1030 K and pressures of 1–9 atm.     

Charge accumulation layer in Cs,Ba/<Emphasis Type="Italic">n</Emphasis>-GaN(0001) ultrathin interfaces: Electronic and photoemission properties

Experimental studies and theoretical calculations of the photoemission from Cs/n-GaN(0001) and Ba/n-GaN(0001) ultrathin interfaces were carried out. The electronic properties of the interfaces were studied in situ using threshold photoemission spectroscopy under vacuum at a residual pressure of P ～ 5 × 10^?11 Torr. A new effect was revealed, namely, photoemission with a high quantum yield under excitation with light in the transparency region of GaN. It was shown that adsorption of Cs or Ba on n-GaN brings about the formation of a quasi-two-dimensional electron channel, i.e., a charge accumulation layer directly near the surface. The dependences of the photoemission spectra and work function on the thickness of Cs and Ba coatings were investigated. It was established that adsorption of Cs and Ba leads to a sharp decrease in the work function by ～1.45 and ～1.95 eV, respectively. The photoemission spectra were calculated, and parameters of the accumulation layer, such as the energy position of the layer below the Fermi level for different Cs and Ba coverages, were determined. It was demonstrated that the energy parameters of the accumulation layer on the n-GaN(0001) surface can be controlled by properly varying the Cs or Ba coverage. The layer thickness was found to reach a maximum for a cesium coverage of ～0.5 monolayer.     

Non-vacuum Bianchi types <Emphasis Type="Italic">I</Emphasis> and <Emphasis Type="Italic">V</Emphasis> in <Emphasis Type="Italic">f</Emphasis> (<Emphasis Type="Italic">R</Emphasis>) gravity

In a recent paper (Sharif and Shamir in Class. Quantum Grav. 26:235020, 2009), we have studied the vacuum solutions of Bianchi types I and V spacetimes in the framework of metric f (R) gravity. Here we extend this work to perfect fluid solutions. For this purpose, we take stiff matter to find energy density and pressure of the universe. In particular, we find two exact solutions in each case which correspond to two models of the universe. The first solution gives a singular model while the second solution provides a non-singular model. The physical behavior of these models has been discussed using some physical quantities. Also, the function of the Ricci scalar is evaluated.     

<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.     

Charge accumulation layer on the <Emphasis Type="Italic">n</Emphasis>-GaN (0001) surface with ultrathin Ba coatings

The adsorption of Ba on the n-type GaN(0001) surface is studied. It is found that submonolayer Ba coatings induce cardinal changes in the electronic properties of the surface with the formation of a charge accumulation layer in the region of the near-surface band bending. The excitation of the Ba/n-GaN system by light from the region of GaN transparency results in photoemission. The lowest value of the work function corresponds to ～1.90 eV at a Ba coverage of ～0.4 ML. Two surface bands induced by Ba adsorption are found in the surface photoemission spectra.     

Metastable-state population in <Emphasis Type="Italic">n</Emphasis>-GaAs

The population of metastable states in n-GaAs is determined by investigating the low-temperature slow edge photoluminescence as a function of temperature, uniaxial compression, and magnetic-field strength. Analysis of the evolution of the integrated intensity of slow afterglow revealed that in the allowed band, there is a free-carrier trapping state located a few millielectronvolts above the band edge and not related to the direct (Γ) band. The filling of this trap occurs through carrier tunneling exchange between the free-carrier subsystem and the reservoir of metastable localized states and is resonant in character.     

Raman Spectra of <Emphasis Type="Italic">n</Emphasis>-Butane,Isobutane, <Emphasis Type="Italic">n</Emphasis>-Pentane,and Isopentane in a Methane Environment

We have studied the particular features of the Raman spectra of gaseous n-butane, isobutane, n-pentane, and isopentane in a methane medium at a pressure of 25 atm. It has been found that, under these conditions, changes in the conformational equilibria of these molecules are negligible, and most significant changes in the spectra are observed in the range of 2850–3000 cm^–1, in which bands corresponding to the stretching vibrations of CH₂ and CH₃ groups shift to lower frequencies. The data obtained will be usefull in determining the composition of natural gas using Raman spectroscopy.     

Verifiable Quantum (<Emphasis Type="Italic">k</Emphasis>,<Emphasis Type="Italic">n</Emphasis>)-threshold Secret Key Sharing

Based on Lagrange interpolation formula and the post-verification mechanism, we show how to construct a verifiable quantum (k,n) threshold secret key sharing scheme. Compared with the previous secret sharing protocols, ours has the merits: (i) it can resist the fraud of the dealer who generates and distributes fake shares among the participants during the secret distribution phase; Most importantly, (ii) It can check the cheating of the dishonest participant who provides a false share during the secret reconstruction phase such that the authorized group cannot recover the correct secret.     

Empirical relation and establishment of shell effects in (<Emphasis Type="Italic">n</Emphasis>, 2<Emphasis Type="Italic">n</Emphasis>) reaction cross-sections at 14 MeV

The experimental data for (n, 2n) reaction cross-sections around 14 MeV neutron energy have been collected from the literature and analysed for the isotopes having 1 ≤ Z ≤ 82. The empirical relations for the reaction cross-sections have been obtained, which show fairly good fits with the experimental values. The shell effects have been established at magic nucleon numbers for (n, 2n) reaction cross-sections around 14 MeV neutron energy. The odd-even effects have also been observed as the cross-sections for odd-mass nuclei are higher than their neighbouring even-even nuclei.      

AQFT from <Emphasis Type="Italic">n</Emphasis>-Functorial QFT

There are essentially two different approaches to the axiomatization of quantum field theory (QFT): algebraic QFT, going back to Haag and Kastler, and functorial QFT, going back to Atiyah and Segal. More recently, based on ideas by Baez and Dolan, the latter is being refined to “extended” functorial QFT by Freed, Hopkins, Lurie and others. The first approach uses local nets of operator algebras which assign to each patch an algebra “of observables”, the latter uses n-functors which assign to each patch a “propagator of states”.In this note we present an observation about how these two axiom systems are naturally related: we demonstrate under mild assumptions that every 2-dimensional extended Minkowskian QFT 2-functor (“parallel surface transport”) naturally yields a local net, whose locality derives from the 2-categorical exchange law, and which is covariant if the 2-functor is equivariant. This is obtained by postcomposing the propagation 2-functor with an operation that mimics the passage from the Schrödinger picture to the Heisenberg picture in quantum mechanics. The argument has a straightforward generalization to general Lorentzian structure, bare lightcone structure and higher dimensions. It does not, however, by itself imply anything about the existence of a vacuum state or about positive energy representations.     

<Emphasis Type="Italic">O</Emphasis>(1) eV sterile neutrino in <Emphasis Type="Italic">f</Emphasis>(<Emphasis Type="Italic">R</Emphasis>) gravity

We refer [1] to the role of an additional O(1) eV sterile neutrino in modified gravity models. We find parameter constraints in particular f(R) gravity model using following up-to-dated cosmological data: measurements of the cosmic microwave background (CMB) anisotropy, the CMB lensing potential, the baryon acoustic oscillations (BAO), the cluster mass function and the Hubble constant. It was obtained for the sterile neutrino mass 0.47 eV < m _ν,sterile < 1 eV (2σ) assuming that the sterile neutrinos are thermalized and the active neutrinos are massless, not significantly larger than in the standard cosmology model within the same data set: 0.45 eV < m _ν,sterile < 0.92 eV (2σ). But, if the mass of sterile neutrino is fixed and equals ≈ 1.5 eV according to various anomalies in neutrino oscillation experiments, f(R) gravity is much more consistent with observation data than the CDM model.