Space- and time-like electromagnetic pion form factors in light-cone pQCD

We present a combined analysis of the space- and time-like electromagnetic pion form factors in light-cone perturbative QCD with transverse momentum dependence and Sudakov suppression. Including the genuine non-perturbative “soft” QCD and the power suppressed twist-3 corrections to the standard twist-2 perturbative QCD result, the experimental form factor data available at moderate energies/momentum transfers can be explained reasonably well. To this end, the bulk of the existing discrepancy between the space- and time-like experimental data is ostensibly reconciled.     

Experimental evaluation of dual acceptance window weighting function for right coronary MR angiography at 3.0T

To shorten scanning time and increase the feasibility of experimental results, we performed right coronary artery magnetic resonance angiography (CMRA) at 3.0 T using dual acceptance window weighting function in 25 normal subjects. We examined these subjects using conventional navigator with fixed gating window and 6 dual acceptance window weighted gating (DAWG) sequences with different central weighted ratio (CWR). Compared with the conventional navigator sequence, DAWG sequences with CWRs of 20% and 25% increased the scanning efficiency by 30% and 26% respectively (P<.05), while maintaining good image quality; further the corresponding scanning time decreased from 2.12–1.64 and 1.69 min, respectively (P<.05). However, CWRs less than 15% caused image degradation to some extent. The coronary artery lengths and diameters did not show statistically significant differences between the two techniques (P>.05). Briefly, to avoid the problems caused by low navigator efficiency and to maintain comparable image quality, the weighted gating parameters of 3 mm width central acceptance window and 15 mm width outer acceptance window with CWR between 20% and 25% are recommended for right CMRA at 3 T.     

X波段高功率微波选模定向耦合器

高功率、长脉冲是高功率微波技术发展的趋势,提高微波器件的功率容量成为一项重要的任务,使用过模器件可以有效提高微波源的功率容量,然而却会带来微波源中同时存在多种模式的问题。为了识别一个X波段长脉冲过模高功率微波源的输出主模TM01模式,设计了一种在线选模定向耦合器,进行了理论分析和模拟优化设计。当频率范围为9.2~9.6 GHz时,模拟结果显示该选模耦合器对TM01模的耦合度为-54 dB,在400 MHz带宽内定向性大于35 dB,对TM02模的抑制度大于15 dB,功率容量可达到3 GW以上。     

Review of Fluorescence Suppression Techniques in Raman Spectroscopy

Abstract

Raman spectroscopy is an important and powerful technique for analyzing the chemical composition of biological or nonbiological samples in many fields. A serious challenge frequently encountered in Raman measurements arises from the existence of the concurrent fluorescence background. The fluorescence intensity is normally several orders of magnitude larger than the Raman scattering signal, especially in biological samples. Such fluorescence background must be suppressed in order to obtain accurate Raman spectra. Several different techniques have been explored for this purpose. These techniques could be generally grouped into time-domain, frequency-domain, wavelength-domain, and computational methods in addition to various Raman enhancement techniques and other unconventional methods. This review briefly describes the fundamental principles of each group of methods, reports the most recent advances, and makes comparison across those major categories of techniques in terms of cost and performance in a hope to guide interested readers to select proper methods for specific applications.     

Radiation hardness of gas discharge tubes and avalanche diodes used for transient voltage suppression

The widespread use of gas discharge tubes (GDTs) and avalanche diodes for transient voltage suppression (TVS) in many cases results in their exposure to ionizing radiation. The aim of this paper is to investigate the influence of irradiation on these TVS devices’ characteristics, by exposing them to a combined neutron/gamma radiation field. Experimental results show that irradiation of TVS diodes causes a lasting degradation of their protective characteristics. On the other hand, GDTs exhibit a temporary change of performance. The observed effects are presented with the accompanying theoretical interpretations, based on the interaction of radiation with materials constituting the investigated devices.     

Suppression of slag foaming by a sound wave

The aim of this work was to study the effects of sound frequency, sound intensity and viscosity of slag on the slag foaming rate and the steady-state foam height. Experiments were carried out using two slags (BaO–B₂O₃) melted at a temperature of 1223 or 1273 K, as well as water–glycerin solutions at room temperature. Low frequency sound waves (<1.3 kHz) are found to be more effective in the slag foaming suppression than high frequency waves (1.3–12 kHz). The steady-state foam height decreases abruptly when the sound pressure reaches a threshold value that depends on sound frequency and liquid viscosity. The results can be explained in terms of enhancing the rates of liquid drainage and film rupture induced by sound.     

基于散射模型设计外遮光罩

通过对粗糙表面散射情况的分析发现,普通金属材料的表面散射能量主要集中在10°散射角内。针对这种现象,提出了基于该散射特性的光学系统外遮光罩设计方法,该遮光罩的杂散光抑制角比基于反射理论计算的大5°,具有良好的散射杂散光的抑制作用。最后以Ritchey-Chirtien(R-C)光学系统为例,为其设计了合适的遮光罩,并在TracePro软件中对比性地建模、分析。结果证明了该模型的正确性,且该遮光罩对抑制杂散光起到了很好的效果,点源透射比(PST)相对较低。     

Removal of J-coupling peak distortion in PGSE experiments

Peak distortion caused by homonuclear J-coupling is a major problem that limits the utility of the pulsed-field gradient spin–echo (PGSE) method for studying translational diffusion. This unwanted effect can be removed by incorporation of anti-phase magnetization purging pulse elements at the end of the spin–echo sequence. Three methods, namely, trim-pulse, homospoil pulse gradient and chirp based z-filter were evaluated as potential candidates for an improved NMR diffusion method that is less sensitive to J-coupling peak distortion. The chirp based z-filter was found to be excellent in suppressing anti-phase magnetization while leaving the in-phase magnetization basically intact in spin–echo and stimulated-echo based experiments. The incorporation of chirp based z-filter into PGSE could allow diffusion analysis that would otherwise be impossible by conventional means.     

The transient suppression for piezoelectric ceramic emission transducer

A transient suppression method for piezoelectric ceramic transducer is presented. By adding some special pedestal pulses to the original transmitted signal, the transient effects in the output of the transducer can be just precisely transmission by use of a narrowband transducer. canceled, thereby achieving the broadband The experimental results show that the transient responses of the sinusoid pulses and coded signals are suppressed successfully and the acoustic waveforms radiated into the surrounding water are improved significantly.