Magnetic properties of some RCo2B2 and RCo4B4 compounds

RCo₂B₂ (R=Pr, Nd, Sm, Gd) and RCo₄B₄ (R=Pr, Nd, Sm) compounds have been investigated by X-ray and magnetometry techniques in the temperature range 4.2-300 K. These compounds crystallize in tetragonal crystal structures of the types CeAl₂Ga₂ and CeCo₄B₄, respectively, with lattice parameters decreasing for increasing atomic weight of the rare earth ion. All compounds order magnetically with the Curie temperatures much below room temperature. Anomalous magnetic behavior is observed for RCo₄B₄ alloys.     

Interplay of superconductivity and antiferromagnetism in SmRh4B4

A microscopic theory of interplay of superconductivity and antiferromagnetism in rare earth ternary systems is developed from first principles for less than half filledf atomic shells. Self consistent equations for the superconducting order parameter Δ and magnetic order parameter Γ, are derived using a Green’s function technique and equation of motion method. The theory is applied to explain the experimental results in the antiferromagnetic superconductor SmRh₄B₄. The present model explains true coexistence of superconductivity and antiferromagnetism and the suppression of superconductivity by antiferromagnetism. The behaviour of superconducting order parameter (Δ), magnetic order parameter (Γ), the specific heat, the density of states, free energy and critical field (H _c) is also studied for the system SmRh₄B₄.     

Magnetic field dependence of the neutron scattering from ErRh4B4

Magnetism in the reentrant superconductor ErRh₄B₄ has been studied by neutron scattering as a function of an applied magnetic field. For a temperature of 1.69 K long-range ferromagnetism is found in fields higher than 1 kOe. Considerable hysteresis is found in the neutron scattering intensity vs magnetic field curve and long-range order with a small Er moment remains when the field is reduced to small values.     

LTE-Advanced and the evolution to Beyond 4G (B4G) systems

Cellular networks have been undergoing an extraordinarily fast evolution in the past years. With commercial deployments of Release 8 (Rel-8) Long Term Evolution (LTE) already being carried out worldwide, a significant effort is being put forth by the research and standardization communities on the development and specification of LTE-Advanced. The work started in Rel-10 by the Third Generation Partnership Project (3GPP) had the initial objective of meeting the International Mobile Telecommunications-Advanced (IMT-Advanced) requirements set by the International Telecommunications Union (ITU) which defined fourth generation (4G) systems. However, predictions based on the wireless traffic explosion in recent years indicate a need for more advanced technologies and higher performance. Hence, 3GPP’s efforts have continued through Rel-11 and now Rel-12. This paper provides a state-of-the-art comprehensive view on the key enabling technologies for LTE-Advanced systems. Already consolidated technologies developed for Rel-10 and Rel-11 are reviewed while novel approaches and enhancements currently under consideration for Rel-12 are also discussed. Technical challenges for each of the main areas of study are pointed out as an encouragement for the research community to participate in this collective effort.     

Coxeter groups A4, B4 and D4 for two-qubit systems

The Coxeter–Weyl groups W(A₄), W(B₄), and W(D₄) have proven very useful for two-qubit systems in quantum information theory. A simple technique is employed to construct the unitary matrix representations of the groups, based on quaternionic transformation of the usual reflection matrices. The von Neumann entropy of each reduced density matrix is calculated. It is shown that these unitary matrix representations are naturally related to various universal quantum gates and they lead to entangled states. Canonical decomposition of generators in terms of fundamental gate representations is given to construct the quantum circuits.     

The deformation of B4C particle in the B4C/2024Al composites after high velocity impact

In the present work, B₄C/2024Al composites with volume fraction of 45% were prepared by a pressure infiltration method. The microstructure of the crater bottom of B₄C/2024Al composite after impact was characterized by transmission electron microscope (TEM), which indicated that recovery and dynamic recrystallization generated in Al matrix, and the grain size distribution was about from dozens of nanometer to 200 nm. Furthermore, the plastic deformation was observed in B₄C ceramic, which led to the transformation from monocrystal to polycrystal ceramic grains. The boundary observed in this work was high-angle grain boundary and the two grains at the boundary had an orientation difference of 30°.     

Temperature dependence features of the photoluminescence spectral distribution of Li2B4O7 and Li2B4O7:Cu

The temperature dependence of the photoluminescence (PhL) spectral distributions has been reported for the lithium tetraborate Li₂B₄O₇ (LTB) and Li₂B₄O₇:Cu (LTB:Cu) single crystals and for glassy LTB:Cu. It was found that the emission peaks of the LTB and LTB:Cu single crystals are non-elementary and splittable by temperature increase into several elementary peaks. By the sample heating the temperature quenching of PhL as well as the redistribution of the PhL intensity among elementary peaks was observed. Heating of the LTB:Cu single crystal samples caused no shift of the spectral maxima of the individual PhL peaks. The curve describing the temperature dependency of individual PhL peaks for the LTB:Cu single crystal is characterized by maxima resulting from combination of PhL and thermostimulated luminescence (TSL). The PhL intensity for glassy LTB:Cu is significantly lower than that for LTB:Cu single crystal with the equivalent copper dopant content. As compared to the LTB:Cu single crystal, the PhL spectral maximum for glassy LTB:Cu is wider and shifted to the lower energy range. Heating of the glassy LTB:Cu sample results in the PhL temperature quenching without any shift of the spectral maximum.     

4B9B束线低能分支的性能改进

分析了北京同步辐射实验室4B9B原束线低能分支的构造及弊病,在不影响束线高能分支性能及总体机械结构的基础上提出了改进方案.详细介绍了该设计方案和光束线调试工作及出光后束线的性能测试工作,该测试结果完全符合束线的设计.该束线在同步辐射专用光实验中充分发挥了改进后的优势,取得了令人满意的结果     

X-ray properties and interface study of B4C/Mo and B4C/Mo2C periodic multilayers

We present a comparative study of B₄C/Mo and B₄C/Mo₂C periodic multilayer structures deposited by magnetron sputtering. The characterization was performed by grazing incidence X-ray reflectometry at two different energies and high resolution transmission electron microscopy. The experimental results indicate the existence of an interdiffusion layer at the B₄C-on-Mo interface in the B₄C/Mo system. Thus, the B₄C/Mo multilayers were modeled by an asymmetric structure with three layers in each period. The thickness of B₄C-on-Mo interfacial layer was estimated about 1.1 nm. The B₄C/Mo₂C multilayers present less interdiffusion and are well modeled by a symmetric structure without interfacial layers. This study shows that B₄C/Mo₂C structure is an interesting alternative to B₄C/Mo multilayer for X-ray optic applications.     

Persistence of superconductivity in magnetically ordered SmRh4B4

Measurements of the thermal conductivity and the electrical resistivity between 50 mK and 4 K in zero magnetic field and in fields exceeding the superconducting critical field H_c2 indicate the persistance of bulk superconductivity in magnetically ordered SmRh₄B₄.     

Elastic scattering of B on B in the energy range from 4 to 15 MeV

Angular distributions (at E_c.m. = 4, 6.5 and 10.5 MeV) and excitation functions (at 30°, 60° and 90°) are given for the elastic scattering of ¹⁰B on ¹⁰B. The results of an optical model (OM) analysis are presented and discussed. In the energy range covered the Sommerfeld parameter η varies from 4.4 to 2.3.     

Walking the path from B4- to B1-type structures in GaN

Molecular dynamics simulations are performed on the wurtzite-type structure (B4) to the rocksalt-type structure (B1) pressure-induced phase transition in GaN. From this, a nucleation and growth mechanism through a tetragonal metastable configuration is found. An intermediate of h-MgO type structure suggested from static calculations is ruled out. However, the pathway through the tetragonal intermediate may be altered by defect incorporation. While the overall transformation mechanism is preserved for both vacancies and Ga substitution by indium, already a 5% aluminum substitution establishes a transition route which avoids the tetragonal structure. Changes in the transformation mechanism and the resulting stabilization of the previously metastable high-pressure modification is elaborated by tracing the interplay of phase nucleation and growth and defect incorporation.     

Determination of crystalline electric fields in RERh4B4 compounds

Using the Mössbauer effect of ¹⁵⁵Gd, the quadrupole interaction in GdRh₄B₄ has been measured, which yields the A⁰₂ term in the crystalline electric field Hamiltonian to be 1165 ± 100 K/a.u. Using this, the B⁰₂ terms for the other RERh₄B₄ (RE = Gd to Tm) have been deduced, and the physical properties predicted by the resulting Hamiltonian are compared with the experimental results.     

Measurement of the polarization for soft X-ray magnetic circular dichroism at the BSRF beamline 4B7B

Three ultra-short-period W/B₄C multilayers （1.244 nm, 1.235 nm and 1.034 nm） have been fabricated and used for polarization measurement at the 4B7B Beamline at the Beijing Synchrotron Radiation Facility （BSRF）. By using the rotating analyzer ellipsometry method, the linear polarization degree of light emerging from this beamline has been measured and the circular polarization evaluated for 700-860 eV. The first soft X-ray magnetic circular dichroism measurements are carried out at BSRF by positioning the beamline aperture out of the plane of the electron storage ring.     

Measurement of the branching fraction of Gamma(4S) --> B0B0

We report the first measurement of the branching fraction f(00) for Gamma(4S) --> B(0)B(0). The data sample consists of 81.7 fb(-1) collected at the Gamma(4S) resonance with the BABAR detector at the SLAC PEP-II asymmetric-energy e(+)e(-) storage ring. Using partial reconstruction of the decay B(0) --> D(*+) l(-)nu(l) in which only the charged lepton and the soft pion from the decay D(*+) --> D(0)pi(+) are reconstructed, we obtain f(00) = 0.487 +/- 0.010(stat) +/- 0.008(syst). Our result does not depend on the branching fractions of B(0) --> D(*+)l(-)nu(l) and D(*+) --> D(0)pi(+) decays, on the ratio of the charged and neutral B meson lifetimes, nor on the assumption of isospin symmetry.     

Second-order and third-order elastic constants of B4C ceramics

The linear and nonlinear elastic properties of B₄C boron carbide ceramics have been studied. The second-order elastic constants and other parameters of the theory of elasticity in the linear approximation have been calculated based on the experimentally measured density and velocity values of longitudinal and shear bulk acoustic waves in the samples. The Thurston-Brugger method has been used to determine the third-order elastic constants of B₄C. To achieve this, we have measured the relative changes of the longitudinal and shear bulk acoustic wave velocities depending on the uniaxial compression applied to the sample.