MHz cut-off frequency and permeability mechanism of iron-based soft magnetic composites

The lack of soft magnetic composites with high power density in MHz frequency range has become an obstacle in the efficient operation of the electrical and electronic equipments.Here,a promising method to increase the cut-off frequency of iron-based soft magnetic composites to hundreds of MHz is reported.The cut-off frequency is increased from 10 MHz to 1 GHz by modulating the height of the ring,the distribution of particles,and the particle size.The mechanism of cut-off frequency and permeability is the coherent rotation of domain modulated by inhomogeneous field due to the eddy current effect.An empirical formula for the cut-off frequency in a magnetic ring composed of iron-based particles is established from experimental data.This work provides an effective approach to fabricate soft magnetic composites with a cut-off frequency in hundreds of MHz.

Collector optimization for tradeoff between breakdown voltage and cut-off frequency in SiGe HBT

As is well known, there exists a tradeoff between the breakdown voltage BVcEO and the cut-off frequency fT for a standard heterojunction bipolar transistor （HBT）. In this paper, this tradeoff is alleviated by collector doping engineering in the SiGe HBT by utilizing a novel composite of P＋ and N- doping layers inside the collector-base （CB） space-charge region （SCR）. Compared with the single N-type collector, the introduction of the thin P＋ layers provides a reverse electric field weakening the electric field near the CB metallurgical junction without changing the field direction, and the thin N layer further effectively lowers the electric field near the CB metallurgical junction. As a result, the electron temperature near the CB metallurgical junction is lowered, consequently suppressing the impact ionization, thus BVcEO is improved with a slight degradation in fT. The results show that the product of fTXBVcEo is improved from 309.51 GHz.V to 326.35 GHz.V.

Effect of Cut-Off Frequency of Butterworth Filter on Detectability and Contrast of Hot and Cold Regions in Tc-99m SPECT

In SPECT, noise is one of the major limitations that degrade image quality. To suppress the noisy signals in an image, digital filters are most commonly applied. However, in SPECT image reconstruction, selection of an appropriate filter and its functions has always remained a difficult task. In this work an attempt was made to investigate the effects of varying cut-off frequencies and in keeping the order of Butterworth filter constant on detectability and contrast of hot and cold re-gions images. A new insert simulating hot and cold regions which provides similar views in a reconstructed image was placed in the phantom’s cylindrical source tank and imaged. Tc-99m radionuclide was distributed uniformly in the phantom. SPECT data were collected in a 20% energy window centered at 140 keV by a Philips ADAC Forte dual head gamma camera mounted with a LEHR collimator. Images were generated by using the filtered backprojection technique. A Butterworth filter of order 5 with cut-off frequencies 0.35 and 0.45 cycles·cm-1 was applied. Images were examined in terms of hot and cold regions, detectability and contrast. Results show that the hot and cold regions’ detectability and contrast vary with the change of cut-off frequency. With a 0.45 cycles·cm-1 cut-off frequency, a significant enhancement in contrast of cold regions was achieved as compared to a 0.35 cycles·cm-1 cut-off frequency. Furthermore, the detectability of hot and cold regions improved with the use of a 0.45 cycles·cm-1 cut-off frequency. In conclusion, image quality of hot and cold regions affected in a different way with a change of cut-off frequency. Thus, care should be taken in selecting the filter cut-off frequency prior to reconstruction of images;particularly, when both types of regions are expected in the reconstructed image.

Feasibility of applying the lower cut-off frequency for the density radial coverage extension in EAST reflectometry measurement

The extraordinary mode(X-mode)lower cut-off frequency is proposed for use in the reflectometry diagnostic on ITER for the electron density profile measurement,which is a trade-off between extreme plasma parameters and the accessible probing frequency.In contemporary experiments,the lower cutoff frequency can be identified at the probing frequency below the electron cyclotron frequency(f_(ce)) under certain plasma conditions.We provide here,for the first time,the experimental validation of the use of the lower cut-off frequency for the density profiles via the reflectometry measurement on EAST.The corresponding group delay of the lower cut-off frequency evolves continuously with the upper one,revealing a reasonable radial coverage extension of reflectometry measurement toward the plasma core.It is concluded that the lower cut-off frequency can be used as a supplement to the upper one in the density profile inversion process,which is of particular interest in the high magnetic field and/or density discharge to extend the radial coverage of reflectometry measurement.

Low Frequency Oscillations of the Heat Distribution in the Global Upper Ocean Layers

The heat distributions in the upper layers of the ocean have been studied and some important low frequency oscillations （LFOs） are already found and quantified by using various characteristic factors. In this paper, the ‘heat center＇ of a sea area is defined with a simple method. Then the temperature data set of the upper layer of the global ocean （from surface down to 400 m, 1955-2003） is analyzed to detect the possible LFOs. Not only some zonal LFOs, which were reported early, but also some strong LFOs of the vertical and meridional heat distribution, which might imply some physical sense, are detected. It should be noted that the similar vertical oscillation pattern can be found in the Pacific Ocean, Atlantic Ocean and Indian Ocean. Results from some preliminary studies show that the vertical LFO might be caused by the solar irradiance anomalies. This study may help reveal some unknown dynamical processes in the global oceans and may also benefit other related studies.

An Experimental Method to Determine the Cut-Off Frequency of an Acoustical Free Field in a Non-Ideal Environment

The availability of ideal conditions like anechoic chamber to characterize some sound parameters, like sound intensity and sound power necessities the determination of free field and cut off frequency measurements. In this article, full experiment was executed at Wayne State University (Detroit-Michigan), to determine the cut off frequency in all directions;the obtained results showed that the free field can be determined for a specified space. So other tests can take place in this space avoiding regions where reflections and consequently noise can be found. Upon these results tests related to noise abatement in vehicles can be done in such environment.

THE APPLICATION OF WEINSTEIN-CHIEN′S METHOD——THE UPPER AND LOWER LIMITS OF FUNDAMENTAL FREQUENCY OF RECTANGULAR PLATES WITH EDGES ARE THE MIXTURE OF SIMPLY SUPPORTED PORTIONS AND CLAMPED PORTIONS

In this paper, the method of relaxed boundary conditions is applied to rectangular plates with edges which are a sort of the mixture of simply supported portions and clamped portions, so that the lower limit of fundamental frequency of such plates is evaluated. A kind of polynomial satisfying the displacement boundary conditions is designed, os that it is enabled to evaluate the upper limit of fundamental frequency by Ritz' method. The practical calculation examples solved by these methods have given satisfactory results. At the end of this paper, it is pointed out that the socalled exact solution of such plates usually evaluated by the force superposition method is essentially a kind of lower limit of solution, if the truncated error of series which occurs in actual calculation is considered.

The Impact of Cut-off Lows on Ozone in the Upper Troposphere and Lower Stratosphere over Changchun from Ozonesonde Observations

In situ measurements of the vertical structure of ozone were made in Changchun （43.53°N, 125.13°E）, China, by the Institute of Atmosphere Physics, in the summers of 2010-13. Analysis of the 89 validated ozone profiles shows the vari- ation of ozone concentration in the upper troposphere and lower stratosphere （UTLS） caused by cut-off lows （COLs） over Changchun. During the COL events, an increase of the ozone concentration and a lower height of the tropopause are observed. Backward simulations with a trajectory model show that the ozone-rich airmass brought by the COL is from Siberia. A case study proves that stratosphere-troposphere exchange （STE） occurs in the COL. The ozone-rich air mass transported from the stratosphere to the troposphere first becomes unstable, then loses its high ozone concentration. This process usually happens during the decay stage of COLs. In order to understand the influence of COLs on the ozone in the UTLS, statistical analysis of the ozone profiles within COLs, and other profiles, are employed. The results indicate that the ozone concentrations of the in-COL profiles are significantly higher than those of the other profiles between ±4 km around the tropopause. The COLs induce an increase in UTLS column ozone by 32% on average. Meanwhile, the COLs depress the lapse-rate tropopause （LRT）/dynamical tropopause height by 1.4/1.7 km and cause the atmosphere above the tropopause to be less stable. The influence of COLs is durable because the increased ozone concentration lasts at least one day after the COL has passed over Changchun. Furthermore, the relative coefficient between LRT height and lower stratosphere （LS） column ozone is -0.62, which implies a positive correlation between COL strength and LS ozone concentration.

Analysis and compensation of low frequency characteristics of sensors for vibration testing

In view of the influence and harm of low frequency vibration environment on the structure of spaceflight products,a low frequency dynamic study method for piezoelectric sensor based on the dynamic system of sinusoidal pressure is proposed.This method uses a sinusoidal pressure dynamic system with two-way dual channel import and export synchronization technology to study the low frequency characteristics of a piezoelectric sensor of PCB company,and its lower cut-off frequency is 0.26 Hz.It is also studied that when the frequency of the measured vibration or shock signal is 1-200 kHz,the error range of signal positive pressure action time is 4.87%-0.03%.The dynamic compensation for the low frequency of the vibration sensor is carried out,and the compensation effect is good.

Effects of different frequencies of repetitive transcranial magnetic stimulation on the recovery of upper limb motor dysfunction in patients with subacute cerebral infarction

Studies have confirmed that low-frequency repetitive transcranial magnetic stimulation can decrease the activity of cortical neurons, and high-frequency repetitive transcranial magnetic stimulation can increase the excitability of cortical neurons. However, there are few studies concerning the use of different frequencies of repetitive transcranial magnetic stimulation on the recovery of upper-limb motor function after cerebral infarction. We hypothesized that different frequencies of repetitive transcranial magnetic stimulation in patients with cerebral infarction would produce different effects on the recovery of upper-limb motor function. This study enrolled 127 patients with upper-limb dysfunction during the subacute phase of cerebral infarction. These patients were randomly assigned to three groups. The low-frequency group comprised 42 patients who were treated with 1 Hz repetitive transcranial magnetic stimulation on the contralateral hemisphere primary motor cortex （M1）. The high-frequency group comprised 43 patients who were treated with 10 Hz repetitive transcranial magnetic stimulation on ipsilateral M1. Finally, the sham group comprised 42 patients who were treated with 10 Hz of false stimulation on ipsilateral M1. A total of 135 seconds of stimulation was applied in the sham group and high-frequency group. At 2 weeks after treatment, cortical latency of motor-evoked potentials and central motor conduction time were significantly lower compared with before treatment. Moreover, motor function scores were significantly improved. The above indices for the low- and high-frequency groups were significantly different compared with the sham group. However, there was no significant difference between the low- and high-frequency groups. The results show that low- and high-frequency repetitive transcranial magnetic stimulation can similarly improve upper-limb motor function in patients with cerebral infarction.

Radio-frequency transistors from millimeter-scale graphene domains

Graphene is a new promising candidate for application in radio-frequency （RF） electronics due to its excellent elec- tronic properties such as ultrahigh carrier mobility, large threshold current density, and high saturation velocity. Recently, much progress has been made in the graphene-based RF field-effect transistors （RF-FETs）. Here we present for the first time the high-performance top-gated RF transistors using millimeter-scale single graphene domain on a SiO2/Si substrate through a conventional microfabrication process. A maximum cut-off frequency of 178 GHz and a peak maximum os- cillation frequency of 35 GHz are achieved in the graphene-domain-based FET with a gate length of 50 nm and 150 nm, respectively. This work shows that the millimeter-scale single graphene domain has great potential applications in RF devices and circuits.

准噶尔盆地盆1井西凹陷石炭系火山岩凝析气藏的发现与勘探启示

准噶尔盆地石炭系火山岩油气藏是油气勘探的重点领域之一。根据录测井资料、地球化学分析数据及岩石薄片鉴定资料,结合地球物理方法,厘清了准噶尔盆地盆1井西凹陷石炭系火山岩油气成藏的主控因素,总结出深层火山岩气藏富集规律,明确了有利勘探方向。研究结果表明:(1)准噶尔盆地盆1井西凹陷风城组烃源岩厚度为100~300 m,面积约为5 400 km2,整体进入生凝析油—干气阶段,生气强度大于20×108m3/km2,为凹陷提供了丰富的天然气源。(2)研究区石炭系火山岩岩性复杂,爆发作用形成的安山质火山角砾岩受到风化淋滤作用,可形成物性较好的风化壳型储层。石炭系—二叠系大型不整合面和广泛发育的深大断裂是重要的输导体系,二叠系上乌尔禾组泥岩作为区域盖层,为凝析气成藏提供了保存条件,油藏主要分布在高部位,气藏分布于低部位。(3)通过“两宽一高”(宽方位、宽频带、高密度)技术,提高地震成像精度,联合时-频电磁技术(TFEM),实现了石炭系火山岩的精细刻画,为深层油气藏的勘探提供了有力支撑。石西16井的重大突破,证实了盆1井西凹陷石炭系火山岩具有巨大的勘探潜力。

黄河上游降水变化分析

黄河上游是黄河流域重要的水源涵养区,径流占流域多年平均(1956—2000年)总径流的62%,降水变化不仅是水源的主要影响因素,也关系到涵养能力的变化。本文利用黄河上游43个气象站1960—2021年逐日降水系列数据,基于小波分析划分周期,采用Mann-Kendall检验法、距平法、频率曲线法等对上游区降水变化进行分析,结果表明:(1)黄河上游降水可划分出1963—1981年、1981—1999年、1999—2018年三个明显的周期;(2)1960—2021年年降水量以4.9 mm 10a的趋势增加,三个周期时段内年降水量的倾向率分别为-0.9 mm 10a,-1.0 mm 10a,46mm 10a;(3)1960—2021年年降水量距平百分率在-15%~15%的正常年份占比74%,距平百分率在-30%~-15%的轻旱年份和15%~30%的轻涝年份分别占比15%和8%;距平百分率在30%~40%的中涝年份占3%,旱涝年份基本发生在1963—1981年、1999—2018年两个周期;(4)三个周期时段日降水量具有差异的主要是频率小于10%的降水,且随海拔变化有差异,表现为1999—2018年玛沁站25~45.4 mm d降水量比以往增强,1999—2018年临夏站20~50 mm d降水量比以往增强,1963—1981年乌审召站50~65 mm d降水量比以往增强。

基于遥感影像的上荆江典型洲滩植被适宜区分布特征研究

江心洲滩是长江中游河漫滩重要组成部分,厘清洲滩上植被生长适宜区域的分布特征,以及这些区域所应满足的淹没频率临界条件,是生态护滩规划设计和三峡建库后洲滩植被变化预测的重要前提。本文选取上荆江关洲和突起洲分别作为卵石夹沙和沙质型洲滩的典型代表,基于Landsat遥感影像提取了1986—2002年的长时序洲滩淹水范围和植被信息,改进并利用水文特性与影像数据相结合的方法计算了滩面上不同位置的淹没频率和植被频率,分析了二者间的响应规律,确定了植被生长适宜区对应的淹没率条件。研究结果表明:两类洲滩上都存在低、高植被频率区像元相对集中,而中等植被频率区像元较为分散的规律,根据植被频率分布特征,可将滩面区域划分为高频次植被覆盖区、中频次植被覆盖区、过渡区和不适宜区,各区之间的植被频率临界值分别为80%、50%、20%;滩面不同位置的淹没频率是影响植被频率的主导因素,从长时期平均来看两类洲滩上的淹没频率-植被频率响应关系符合统一的Logistic曲线,根据该曲线可确定出各区域的临界淹没条件分别为年均18 d、43 d、92 d。在年均淹没天数大于92 d的区域内,随着淹没天数增加,植被频率迅速减少至10%以下。本文的方法和认识可为三峡建库后坝下游洲滩植被演替趋势预测提供参考。

不同强度的高频重复经颅磁刺激对脑梗死早期患者上肢功能的影响

目的:观察不同强度高频重复经颅磁刺激(high-frequency repetitive transcranial magnetic stimulation,HF-rTMS)对脑梗死恢复早期患者上肢功能障碍恢复的影响。方法:选取60例脑梗死恢复早期患者,采用随机数字表法分为HF-rTMS 80%RMT组、100%RMT组和假刺激组,每组各20例。三组患者均给予基础治疗(药物治疗及常规康复训练),在此基础上分别给予不同强度的HF-rTMS治疗。记录治疗前及治疗4周后3组患者的Fugl-Meyer上肢运动功能评定(Fugl-Meyer assement-upper extremity,FMA-UE)和改良Barthel指数(modified Barthel Index,MBI)分值,检测运动诱发电位(motor evoked potential,MEP)潜伏期,计算中枢运动传导时间(central motor conduction time,CMCT),测量患侧大脑中动脉(middle cerebral artery,MCA)血流速度。结果:治疗前,3组患者的FMA-UE评分、MBI评分、MEP潜伏期、CMCT及MCA血流速度均无显著性差异(P>0.05)。治疗4周后,3组患者的上述指标均较治疗前提高,具有显著性差异(P<0.05);其中80%RMT组、100%RMT组指标改善均较假刺激组显著(P<0.05);除MBI外,100%RMT组各项指标改善最为显著(P<0.05)。结论:HF-rTMS可以改善脑梗死恢复早期患者上肢功能和日常生活能力,100%RMT HF-rTMS在提高功能、运动神经兴奋性,改善脑血流等方面较80%RMT更有优势。

矿用提升机电控系统智能化设计及应用分析

针对提升机所用的传统电控系统存在控制效率低、精度差、运行安全可靠性差等不足,为有效解决上述问题,本文基于提升机系统的主要结构,通过应用PLC可编程控制器,高压变频器及上位机等设备,创建了新的提升机智能电控系统,经应用高压变频器来优化改造原调速系统,电动机实现了平滑调速,应用上位机与PLC合理结合,提升机实现了变频调速,改造后不仅提升机电控系统的自动化、智能化水平显著提升,而且提升机运行更节能、更高效,取得了较好的应用效果,可为类似工况下提升机电控系统的改造提供参考。

超微针刀联合高低频重复经颅磁刺激治疗脑卒中后上肢痉挛的临床观察

【目的】观察超微针刀联合高低频重复经颅磁刺激(rTMS)治疗脑卒中后上肢痉挛的临床疗效。【方法】将106例脑卒中后上肢痉挛患者随机分为观察组和对照组,每组各53例,2组患者均给予常规药物与运动疗法治疗,对照组给予高低频rTMS治疗,观察组在对照组治疗的基础上,给予超微针刀治疗。2组均治疗4周。治疗2、4周后,分别评价2组临床疗效,观察2组患者治疗前后改良Ashworth量表(MAS)评分的变化情况,以及上肢Fugl-Meyer量表评分的情况。比较2组患者治疗前后Berg平衡量表(BBS)评分与改良Barthel指数(BI)评分的变化情况。并评价2组的安全性及不良反应的发生情况。【结果】(1)治疗2周后,观察组总有效率为81.13%(43/53),对照组为62.26%(33/53)。观察组疗效优于对照组,差异有统计学意义(P<0.05)。(2)治疗4周后,观察组总有效率为90.57%(48/53),对照组为73.58%(39/53)。观察组疗效优于对照组,差异有统计学意义(P<0.05)。(3)治疗2、4周后,观察组MAS评分与上肢Fugl-Meyer评分均明显改善(P<0.05),且观察组在改善MAS评分与上肢Fugl-Meyer评分方面明显优于对照组,差异均有统计学意义(P<0.05)。(4)治疗2、4周后,观察组BBS评分与改良Barthel指数评分均明显改善(P<0.05),且观察组在改善BBS评分与改良Barthel指数评分方面明显优于对照组,差异均有统计学意义(P<0.05)。(5)观察组与对照组不良反应发生率比较,差异无统计学意义(P>0.05)。【结论】超微针刀联合高低频重复经颅磁刺激治疗脑卒中后上肢痉挛,能明显改善患者的临床症状,改善患者上肢的肌力状态,提高上肢运动与平衡能力,提高患者日常生活能力,疗效显著。

低频脉冲电疗联合经颅直流电刺激对老年卒中患者上肢功能障碍的疗效研究

目的探讨低频脉冲电疗(LFPE)联合经颅直流电刺激(t DCS)对老年卒中患者上肢功能障碍的疗效。方法回顾性选取2021年1月至2023年8月浙江中医药大学附属第三医院(庆春院区)收治的120例卒中导致上肢功能障碍的老年患者为研究对象,采用LFPE、t DCS、LFPE+t DCS治疗各40例,分别为LFPE组、t DCS组、LFPE+t DCS组。观察并比较3组患者治疗前及治疗4周后上肢运动功能[采用简式Fugl-Meyer量表(FMA)评估]、痉挛程度[采用改良Ashworth痉挛评定量表(MAS)评估]、血清指标[包括血清神经元特异性烯醇化酶(NSE)、S-100β蛋白、髓鞘碱性蛋白(MBP)水平]、自理能力[采用改良Barthel指数(MBI)评估]及生活质量[采用脑卒中专用生活质量量表(SS-QOL)评估]等指标。结果与治疗前比较,治疗4周后3组患者上肢FMA评分以及MBI、SS-QOL评分均明显升高(均P<0.01),上肢MAS评分以及血清NSE、S-100β蛋白、MBP水平均明显降低(均P<0.01)。治疗4周后,LFPE+t DCS组FMA评分以及MBI、SS-QOL评分均明显高于LFPE组、t DCS组(均P<0.05),而MAS评分以及血清NSE、S-100β蛋白、MBP水平均低于LFPE组、t DCS组(均P<0.05)。结论LFPE联合t DCS能有效改善老年卒中患者上肢功能障碍,提高患者自理能力和生活质量。

变频调速器控制系统在煤矿提升机上的应用

针对提升机控制设备陈旧、自动化水平低、无故障预警以及实时监控功能等问题进行了改造与设计。首先对系统的组成与技术要求进行简要分析,结合某煤矿提升机实际情况提出控制系统的总体设计方案;对调速系统变频器进行选型与参数分析,并搭建控制电路,经测试达预期效果;采用PLC与Win CC组态软件完成系统监控系统与软件的设计,实现实时监控,提升了自动化水平。最后,对变频调速控制系统的应用效果进行了综合验证。

不同频率的重复经颅磁刺激对脑卒中上肢运动功能恢复的影响

上肢运动功能障碍是脑卒中患者常见的后遗症之一,使患者部分或完全丧失独立生活能力,在降低了患者的生活质量的同时也影响了家庭的幸福指数。近年来,重复经颅磁刺激被广泛应用于临床治疗中。但目前针对不同的患者如何选择最佳频率治疗,尚未做出统一的定论。本研究主要根据脑卒中患者运动功能恢复的分期与脑损伤程度来分析高频、低频、联合治疗之间的疗效差异,并且针对重复经颅磁刺激对运动功能恢复的机制、理论基础、作用靶点进行综述,以期为以后的临床研究和应用提供参考。