Modeling the efficiency of neutron detection scintillators in the energy range of 5–70 MeV

The instrumental functions for neutron godoscope detectors used in studying the nd-breakup reaction are obtained. The effect on light output of contributions from different processes that occur in a scintillator under the effect of neutrons is examined at different energies of the incident neutrons. The relationship between the detector??s efficiency and neutron energies ranging from 5 to 70 MeV is obtained for different thresholds.     

Simulation of superconducting single photon detector coupled with metal–insulator–metal concentric ring grating

Sub-wavelength metal–insulator–metal (MIM) concentric ring grating structure has been introduced to couple with superconducting single photon detector (SSPD) to enhance its response. The effects of the coupling structure parameters on the enhancement factor have been studied systematically. Our numerical simulation results show that the optical density arriving at the detection area of SSPD can be greatly enhanced by the structure of MIM concentric ring grating, corresponding to the improvement of detection response of the detector. A high enhancement factor more than 40 times can be obtained at wavelength of \(1.55~\upmu \hbox {m}\) with proper structure parameters.     

Controlling the size of ZnO quantum dots using the dressed photon–phonon-assisted sol–gel method

We developed a sol–gel method using the dressed photon–phonon (DPP) process. DPPs are selectively exited in nanoscale structures at photon energies that are lower than the bandgap energy, which allows one to increase the growth rate of smaller ZnO quantum dots (QDs). Thus, we obtained a smaller size variance of ZnO QDs. The growth rate was proportional to the power of the light used for DPP excitation. The results were confirmed using a rate equation that accounted for the concentration of the sol–gel solution.     

Experimental search for neutron–mirror neutron oscillations using storage of ultracold neutrons

The idea of a hidden sector of mirror partners of elementary particles has attracted considerable interest as a possible candidate for dark matter. Recently it was pointed out by Berezhiani and Bento that the present experimental data cannot exclude the possibility of a rapid oscillation of the neutron n to a mirror neutron n′ with oscillation time much smaller than the neutron lifetime. A dedicated search for vacuum transitions n→n^′$\mathrm{n}\to {\mathrm{n}}^{\prime }$ has to be performed at weak magnetic field, where both states are degenerate. We report the result of our experiment, which compares rates of ultracold neutrons after storage at a weak magnetic field well below 20 nT and at a magnetic field strong enough to suppress the seeked transitions. We obtain a new limit for the oscillation time of n–n′ transitions, τosc(90% C.L.)>414 s${\tau }_{\mathrm{osc}}(90\mathrm{\%}\text{C.L.})>414\text{s}$. The corresponding limit for the mixing energy of the normal and mirror neutron states is δm(90% C.L.)<1.5×¹⁰⁻¹⁸ eV$\delta m(90\mathrm{\%}\text{C.L.})<1.5\times {10}^{\mathrm{-18}}\text{eV}$.     

The effect of the metal cylinder in the slot on the transmission properties of the metal–insulator–metal waveguide

The effects of the size, the position and the shape of the metal cylinder in the slot waveguide on the transmittance properties at the communication wavelength of 1.55 μm are investigated using the finite difference time domain method. Since the surface plasmon polartions excites the local surface plasmon resonance of the metal cylinder, the attenuation in the metal–insulator–metal waveguide is enhanced. Those results provide us with the theoretical foundation for the prediction of the effect of the imperfection in the preparation process on the transmittance properties of the metal–insulator–metal waveguides.     

Gradient models of the axion–photon coupling

We establish an extended version of the Einstein–Maxwell-axion model by introducing into the Lagrangian cross-terms, which contain the gradient four-vector of the pseudoscalar (axion) field in convolution with the Maxwell tensor. The gradient model of the axion–photon coupling is applied to cosmology: we analyze the Bianchi-I type Universe with an initial magnetic field, electric field induced by the axion–photon interaction, cosmological constant and dark matter, which is described in terms of the pseudoscalar (axion) field. Analytical, qualitative and numerical results are presented in detail for two distinguished epochs: first, for the early Universe with magnetic field domination; second, for the stage of late-time accelerated expansion.     

On the absolute efficiency of large neutron detectors for μCF

The absolute efficiency for a large organic scintillator neutron detector has been calculated via Monte Carlo simulation for neutrons of 14 MeV. The influence of the environmental geometry (source scattering, etc.) has been taken into account. Full differential cross-sections, including resonances, have been used. The calculated response function compares well with the measured one. This revised version was published online in August 2006 with corrections to the Cover Date.     

Fabrication and analysis of the structural phase transition of ZrO2 nanoparticles using modified facile sol–gel route

The synthesis of zirconia nanoparticles is achieved through a modified facile sol–gel route. The as-prepared gel is analyzed thermally using TGA and DTA techniques to spot the crystallization process of zirconia nanoparticles. The prepared gel is then annealed at different temperatures and the structure was found to change between tetragonal and monoclinic crystal systems. The first stable tetragonal phase is achieved after annealing for 2?h at 400°C. The annealed powders between 600°C and 800°C demonstrate mixed tetragonal/monoclinic phases. Annealing at 1000°C and higher temperatures up to 1200°C resulted in pure monoclinic phase. Cubic phase was not detected within the annealing temperature range in this study. The elemental analysis of the annealed powder confirmed the formation of zirconia nanoparticles with the chemical formula ZrO₂. The FTIR spectra of the annealed samples introduced a variation in the vibrational bands especially around the phase transition temperature. HR-TEM images reported the formation of nano-zirconia crystals with apparently large particle sizes. The optical energy gap of zirconia nanoparticles is investigated and determined.     

Negative differential resistance of a metal–insulator–metal device with gold nanoparticles embedded in polydimethylsiloxane

Metal–insulator–metal (MIM) devices play an important role in information storage cells. In this research, a MIM with an insulator made from polydimethylsiloxane blended with gold nanoparticles has been investigated. The current–voltage characteristic demonstrates a negative differential resistance (NDR) and memory effect. This article attempts to explain the NDR and memory effect, using the charge trapping and releasing mechanisms of the gold nanoparticles and also electron tunneling mechanisms.     

Analysis of the photon–photon resonance influence on the direct modulation bandwidth of dual-longitudinal-mode distributed feedback lasers

The paper explores the possibilities to extend the direct modulation bandwidth in dual-longitudinal-mode distributed feedback lasers by exploiting the photon–photon resonance induced by the interaction of the two modes in the laser cavity. The effects on the direct amplitude modulation and on the direct modulation of the difference frequency between the two modes are analyzed using simulation and experimental results. When the photon–photon resonance, which occurs at the difference frequency between the two modes, is properly placed at a higher frequency than the carrier-photon resonance, the small-signal amplitude modulation (AM) bandwidth of the laser can be significantly increased. However, both simulations and experiments point out that a high small-signal AM bandwidth does not lead to a high large-signal AM bandwidth if the small-signal modulation response has significant variations across the modulation bandwidth. The paper shows that a high large-signal AM bandwidth is obtained when the two modes are significantly unbalanced, whereas a high-bandwidth difference frequency modulation can be best detected when the two modes are balanced and the DC bias is properly chosen.     

The use of Herschel–Quincke tubes to improve the efficiency of lined ducts

The scattering matrix results of Herschel–Quincke (HQ) resonators installed in combination with an acoustic liner (HQ-Liners) are presented in this paper. This approach aims at controlling both tonal and broadband noise to improve the liner efficiency. It uses circumferential arrays of Herschel–Quincke tubes on a main duct in a serial association with a locally reacting liner of known impedance. Results for the scattering matrix of this system are deduced from an analytical model and compared with experimental and numerical data showing a good agreement. Analysis of the scattering matrix coefficients points out the modal conversion properties that depend on the number of HQ tubes along the circumference. Results of the transmission loss show that the choice of an optimal HQ configuration with respect to the liner properties can substantially improve the liner efficiency.     

Shedding light on correlated electron–photon states using the exact factorization

The exact factorization framework is extended and utilized to introduce the electronic-states of correlated electron–photon systems. The formal definitions of an exact scalar potential and an exact vector potential that account for the electron–photon correlation are given. Inclusion of these potentials to the Hamiltonian of the uncoupled electronic system leads to a purely electronic Schrödinger equation that uniquely determines the electronic states of the complete electron–photon system. For a one-dimensional asymmetric double-well potential coupled to a single photon mode with resonance frequency, we investigate the features of the exact scalar potential. In particular, we discuss the significance of the step-and-peak structure of the exact scalar potential in describing the phenomena of photon-assisted delocalization and polaritonic squeezing of the electronic excited-states. In addition, we develop an analytical approximation for the scalar potential and demonstrate how the step-and-peak features of the exact scalar potential are captured by the proposed analytical expression.     

Probing Ho?ava-Lifshitz gravity using particle and photon dynamics in the presence of plasma

We study the particle motion around a black hole(BH) in Ho?ava-Lifshitz(HL) gravity with the Kehagias-Sfetsos(KS) parameter. First, the innermost stable circular orbit(ISCO) is obtained for massive particles around the BH in HL gravity. We find that the radii of the ISCOs decrease as the KS parameter decreases, meaning that the parameter ? causes the orbits of particles to move inward with respect to that of the Schwarzschild BH case.Then, the optical properties of a KS BH are studied in detail,...     

Green synthesis and characterization of Au@Pt core–shell bimetallic nanoparticles using gallic acid

In this study, we developed a facile and benign green synthesis approach for the successful fabrication of well-dispersed urchin-like Au@Pt core–shell nanoparticles (NPs) using gallic acid (GA) as both a reducing and protecting agent. The proposed one-step synthesis exploits the differences in the reduction potentials of AuCl₄⁻ and PtCl₆²⁻, where the AuCl₄⁻ ions are preferentially reduced to Au cores and the PtCl₆²⁻ ions are then deposited continuously onto the Au core surface as a Pt shell. The as-prepared Au@Pt NPs were characterized by transmission electron microscope (TEM); high-resolution transmission electron microscope (HR-TEM); scanning electron microscope (SEM); UV-vis absorption spectra (UV-vis); X-ray diffraction (XRD); Fourier transmission infrared spectra (FT-IR). We systematically investigated the effects of some experimental parameters on the formation of the Au@Pt NPs, i.e., the reaction temperature, the molar ratios of HAuCl₄/H₂PtCl₆, and the amount of GA. When polyvinylpyrrolidone K-30 (PVP) was used as a protecting agent, the Au@Pt core–shell NPs obtained using this green synthesis method were better dispersed and smaller in size. The as-prepared Au@Pt NPs exhibited better catalytic activity in the reaction where NaBH₄ reduced p-nitrophenol to p-aminophenol. However, the results showed that the Au@Pt bimetallic NPs had a lower catalytic activity than the pure Au NPs obtained by the same method, which confirmed the formation of Au@Pt core–shell nanostructures because the active sites on the surfaces of the Au NPs were covered with a Pt shell.     

Chemical microanalysis of rare-earth–transition metal–boron alloys and magnets using scanning electron microscopy

This paper reports the results of investigations of chemical microanalyses of various alloys and sintered magnets with well-known compositions. Analyses of neodymium, praseodymium, iron, cobalt, niobium and copper have been carried out using energy-dispersive X-ray spectrometry. Quantitative analyses of boron have been carried out using wavelength-dispersive X-ray spectrometry. The resulting mean values were compared with data reported in the literature for the various phases present in these magnetic materials.     

Dimensional dependences of the interfacial tension at a solid—liquid interface and the melting temperature of metal nanoparticles

New coordinating relationships are obtained for the dimensional dependences of melting temperature T(r) and interfacial tension ?? _SL (r) of a solid spherical nanoparticle at the boundary with its own melt. The Thomson formula for T(r) and the Tolman formula for ?? _SL (r) follow from the expressions obtained at large radii of curvature. Numerical calculations are performed for metals. Results from calculations on the dimensional dependences of the melting temperature for Pt, Au, and Al that conform fairly well with experimental data are given as examples.     

Evaluation of the neutron production rate using D–D and D–T fuel in an inertial electrostatic confinement fusion device

The correlation between the neutron production rate and fuel species in a spherical inertial electrostatic confinement fusion (IECF) device is investigated by solving the Poisson equation for various ion and electron distribution functions. The fuel ion energy distribution function is determined at each radial point. The fusion reaction rate is evaluated from the energy distribution function. The dependence of the neutron production rate (NPR) on some important parameters, like the ion convergence, the broadening of the distributions in the energy space, working pressure and fuel species, are also investigated. Compared with the IECF device with D–D, numerical calculations show that by increasing the percentage of tritium in the D–T mixture fuel the neutron production rate grows significantly.