Radiation attenuation and nuclear properties of high density concrete made with steel aggregates

Abstract

The fast neutron and gamma ray spectra measured behind different thickness of steel scrap concrete with density of 4 g/cm³ have been studied. The mix proportions by weight of this type of concrete were 1 cement: 6.89 steel scrap: 2.9 sand and 0.5 Water. Comparison with a standard ordinary concrete of density 2.3 g/cm³ have been carried out. The measurements were made using a collimated beam of both gamma rays and neutrons emitted from one of the horizontal channel of the Egyptian Research Reactor-1. A fast neutron and gamma ray spectrometer with a stilbene crystal was used to measure the spectra of fast neutrons and gamma rays. Pulse shape discrimination using the zero cross over technique was used to separate the photon pulses from the electron pulses. The equation due to Schmidt has been modified and applied for determining the neutron effective removal cross sections (～_R) for steel scrap, ordinary, hematite–serpentine, ilmenite–limonite and ilmenite concretes. This equation gives results which are in good agreement with the measured values. The derived empirical equation in a previous work to calculate the neutron integral flux behind different thicknesses of different types of concretes, gives good results for steel scrap concrete under investigation comparing with the corresponding experimental data. Total neutron macroscopic cross sections, linear attenuation coefficients for gamma rays and the half-value layers for both radiations at different energies have been obtained for steel scrap concrete and comparing with the corresponding values of ordinary concrete. The results show that steel scrap concrete is better than ordinary, hematite–serpentine, ilmenite–limonite and ilmenite concretes from the radiation shielding point of view.     

Prevention of blow-up by fast diffusion in chemotaxis

In this paper, we study a strongly coupled parabolic system with cross diffusion term which models chemotaxis. The diffusion coefficient goes to infinity when cell density tends to an allowable maximum value. Such ‘fast diffusion’ leads to global existence of solutions in bounded domains for any given initial data irrespective of the spatial dimension, which is usually the goal of many modifications to the classical Keller–Segel model. The key estimates that make this possible have been obtained by a technique that uses ideas from Moser's iterations.     

Construction of triangular DP surface and its application

In this paper, a new type of bivariate basis on a triangle is presented, which is constructed by extending the univariate NTP basis proposed by Delgado and Peña. Some algebraic properties and its recursive formulae are given. Then a new type of surfaces that is called triangular DP surface is defined, and its recursive evaluation algorithm is obtained. Also, in the case of low degree, its subdivision algorithm and degree elevation algorithm are derived. It is shown that this type of surfaces is obviously more advantageous than triangular Bézier surface, and hence extremely useful for geometric design, especially for the situation in which the surface needs to be evaluated quickly.     

On a class of signals and matrices giving very fast algorithms for linear problems

In this paper is presented a class of stochastic signals and of correlation matrices introducing very fast algorithms for solving linear problems. These signals are derived from white noise by using three kinds of operations combined in various orders: summation, difference and instantaneous modulation. The discrete time Brownian motion is a particular example of such signals.     

基于单片机和AD9858的4频点快速跳频设计

在分析了DDS基本原理以及AD9858基本特点的基础上，介绍了AD9858的送数方式及单片机接口程序。给出了利用AD9858内部寄存器来实现跳频时间小于50ns的4频点快速跳频的具体方法。     

High speed analysis of underivatized drugs by gas chromatography–mass spectrometry

The technique of choice for many types of forensic drug confirmations is gas chromatography/mass spectrometry (GC/MS). Significant amounts of analytical time can be involved in a GC/MS run. The use of a 0.1 mm i.d. fused silica capillary column with hydrogen carrier gas can significantly increase the speed of an analysis without sacrificing resolution. Nanogram levels of underivatized drugs, from amphetamine to strychnine, can be eluted in less than twelve minutes. The multitasking system permits data acquisition, while performing data reduction on the previous run.     

CU encoding depth prediction,early CU splitting termination and fast mode decision for fast HEVC intra-coding

High Efficiency Video Coding (HEVC) is a new video coding standard achieving about a 50% bit rate reduction compared to the popular H.264/AVC High Profile with the same subjective reproduced video quality. Better coding efficiency is attained, however, at the cost of significantly increased encoding complexity. Therefore, fast encoding algorithms with little loss in coding efficiency is necessary for HEVC to be successfully adopted for real applications. In this paper we propose a fast encoding technique applicable to HEVC all intra encoding. The proposed fast encoding technique consists of coding unit (CU) search depth prediction, early CU splitting termination, and fast mode decision. In CU search depth prediction, the depth of encoded CU in the current coding tree unit (CTU) is limited to predicted range, which is mostly narrower than the full depth range. Early CU splitting skips mode search of its sub-CUs when rate distortion (RD) cost of current CU is below the estimated RD cost at the current CU depth. RD cost and encoded CU depth distribution of the collocated CTU of the previous frame are utilized both to predict the encoding CU depth search range and to estimate the RD cost for CU splitting termination. Fast mode decision reduces the number of candidate modes for full rate distortion optimized quantization on the basis of the low complexity costs computed in the preceding rough mode decision step. When all these three methods are applied, proposed fast HEVC intra encoding technique reduces the encoding time of the reference encoder by 57% on the average, with only 0.6% of coding efficiency loss in terms of Bjontegaard delta (BD) rate increase under the HEVC common test conditions.     

Fast analysis of doping agents in urine by ultra-high-pressure liquid chromatography–quadrupole time-of-flight mass spectrometry: I. Screening analysis

The general strategy to perform anti-doping analyses of urine samples starts with the screening for a wide range of compounds. This step should be fast, generic and able to detect any sample that may contain a prohibited substance while avoiding false negatives and reducing false positive results. The experiments presented in this work were based on ultra-high-pressure liquid chromatography coupled to hybrid quadrupole time-of-flight mass spectrometry. Thanks to the high sensitivity of the method, urine samples could be diluted 2-fold prior to injection. One hundred and three forbidden substances from various classes (such as stimulants, diuretics, narcotics, anti-estrogens) were analysed on a C₁₈ reversed-phase column in two gradients of 9 min (including two 3 min equilibration periods) for positive and negative electrospray ionisation and detected in the MS full scan mode. The automatic identification of analytes was based on retention time and mass accuracy, with an automated tool for peak picking. The method was validated according to the International Standard for Laboratories described in the World Anti-Doping Code and was selective enough to comply with the World Anti-Doping Agency recommendations. In addition, the matrix effect on MS response was measured on all investigated analytes spiked in urine samples. The limits of detection ranged from 1 to 500 ng/mL, allowing the identification of all tested compounds in urine. When a sample was reported positive during the screening, a fast additional pre-confirmatory step was performed to reduce the number of confirmatory analyses.     

Bursting and synchronization transition in the coupled modified ML neurons

Bursting is an important electrical behavior in neuron’s firing. In this paper, based on the fast/slow dynamical bifurcation analysis and the phase plane analysis, two types of bursting are presented in the modified Morris–Lecar neuronal model, and the associated bifurcation mechanisms of switching between the active phase and the silent phase are analyzed. For two coupled bursters, it is found that the same type of coupled bursters may have different synchronization transition path from that of two different types of coupled bursters. The analysis of bursting types and the transition to synchronization may provide us with better insight into neuronal encoding and information transmission.