Simulation of the xenon gamma spectrometer for analyzing radioactive materials

The results of the calculation of the detection efficiency of gamma-rays for the xenon gamma spectrometer (XGS) obtained using the GEANT4 Monte Carlo simulation are presented. The gamma spectra of the set of basic standard gamma-sources (OSGI) are analyzed for a real detector, and the calculated and actual detection efficiencies are compared. The XGS spectra are analyzed to determine the minimum concentration of the ¹⁵²Eu radio nuclide in the ¹³⁷Cs and ⁶⁰Co mixture. It is shown that the xenon gamma spectrometer is capable of detecting the isotope at concentrations above 40% in the mixture.     

Microfabrication of stacks of acoustic matching layers for 15 MHz ultrasonic transducers

This paper presents a novel method used to manufacture stacks of multiple matching layers for 15 MHz piezoelectric ultrasonic transducers, using fabrication technology derived from the MEMS industry. The acoustic matching layers were made on a silicon wafer substrate using micromachining techniques, i.e., lithography and etch, to design silicon and polymer layers with the desired acoustic properties. Two matching layer configurations were tested: a double layer structure consisting of a silicon–polymer composite and polymer and a triple layer structure consisting of silicon, composite, and polymer. The composite is a biphase material of silicon and polymer in 2-2 connectivity. The matching layers were manufactured by anisotropic wet etch of a (1 1 0)-oriented Silicon-on-Insulator wafer. The wafer was etched by KOH 40 wt%, to form 83 μm deep and 4.5 mm long trenches that were subsequently filled with Spurr’s epoxy, which has acoustic impedance 2.4 MRayl. This resulted in a stack of three layers: The silicon substrate, a silicon–polymer composite intermediate layer, and a polymer layer on the top. The stacks were bonded to PZT disks to form acoustic transducers and the acoustic performance of the fabricated transducers was tested in a pulse-echo setup, where center frequency, −6 dB relative bandwidth and insertion loss were measured. The transducer with two matching layers was measured to have a relative bandwidth of 70%, two-way insertion loss 18.4 dB and pulse length 196 ns. The transducers with three matching layers had fractional bandwidths from 90% to 93%, two-way insertion loss ranging from 18.3 to 25.4 dB, and pulse lengths 326 and 446 ns. The long pulse lengths of the transducers with three matching layers were attributed to ripple in the passband.     

Velocity of domain-wall motion induced by electrical current in the ferromagnetic semiconductor (Ga,Mn)As

Current-induced domain-wall motion with velocity spanning over 5 orders of magnitude up to 22 m/s has been observed by the magneto-optical Kerr effect in (Ga,Mn)As with perpendicular magnetic anisotropy. The data are employed to verify theories of spin transfer by the Slonczewski-like mechanism as well as by the torque resulting from spin-flip transitions in the domain-wall region. Evidence for domain-wall creep at low currents is found.     

Measurement of the p to s wave branching ratio of 187Re beta decay from beta environmental fine structure

The mixed occurrence of s-wave and p-wave contributions in a first forbidden unique Gamow-Teller beta decay has been investigated for the first time by measuring the beta environmental fine structure (BEFS) in a 187Re crystalline compound. The experiment has been carried out with an array of eight AgReO4 thermal detectors operating at a temperature of approximately 100 mK. A fit of the observed BEFS spectrum indicates the p-wave electron emission as the dominant channel. The complete understanding of the BEFS distortion of the 187Re beta decay spectrum is crucial for future experiments aiming at the precise calorimetric measurement of the antineutrino mass.     

Integrable field theories with defects

The structure of integrable field theories in the presence of defects is discussed in terms of boundary functions under the Lagrangian formalism. Explicit examples of bosonic and fermionic theories are considered. In particular, the boundary functions for the super sinh-Gordon model is constructed and shown to generate the Backlund transformations for its soliton solutions.     

Relativistic lattice kinetic theory: Recent developments and future prospects

In this paper, we review recent progress in relativistic lattice kinetic theory and its applications to relativistic hydrodynamics. Two methods for constructing the discretised distribution function, moment matching and projection onto orthogonal polynomials, are described. Extensions to ultra-high velocities as well as improved dissipation models are discussed. We show that the existing models can successfully cover a wide range of velocities (from weak-relativistic to ultra-relativistic) and viscous regimes. Various applications, from quark-gluon plasma and relativistic Richtmyer-Meshkov instability to flows in curved manifolds are also explored. Finally, potential developments for general relativity are outlined along with future prospects for solving the full set of Einstein equations of general relativity.     

Ricci dark energy in Chern–Simons modified gravity

In this work, we have considered the Ricci dark energy model, where the energy density of the universe is proportional to the Ricci scalar curvature, in the dynamic Chern–Simons modified gravity. We show that in this context the evolution of the scale factor is similar to that displayed by the modified Chaplygin gas.     

Full vectorial band structure computation of photonic crystals with hexagonal lattice and a staircase approximation of the slanted unit cells

This paper describes band structure computations of photonic crystals with a hexagonal lattice. Particularly, the full vectorial three-dimensional case is considered. The unit cells are approximated with a staircase approximation. Due to their periodicity, fields inside the computational window can be related to those outside of this area. Numerical results are compared with those from the literature and show a very good agreement.     

Phenomenology tools on cloud infrastructures using OpenStack

We present a new environment for computations in particle physics phenomenology employing recent developments in cloud computing. On this environment users can create and manage “virtual” machines on which the phenomenology codes/tools can be deployed easily in an automated way. We analyze the performance of this environment based on “virtual” machines versus the utilization of physical hardware. In this way we provide a qualitative result for the influence of the host operating system on the performance of a representative set of applications for phenomenology calculations.     

Time resolved scattering relaxation mechanisms of microcavity polaritons

We study the polariton relaxation dynamics for different scattering mechanisms as: Phonon and electron scattering procesess. The relaxation polariton is obtained at very short times by solving the Boltzman equation. Instead of the well-known relaxation process by phonons, we show that the bottleneck effect relaxes to the ground state more efficiently at low pump power intensity when the electron relaxation process is included. In this way, we clearly demonstrate that different relaxation times exist, for which any of these two mechanism is more efficient to relax the polariton population to the ground state.