Generation of self-oscillations from a singly resonant periodically poled potassium titanyl phosphate crystal frequency doubler

We report on the generation of self-oscillations from a continuously pumped singly resonant frequency doubler based on a periodically poled potassium titanyl phosphate crystal （PPKTP）. The sustained square-wave and staircase curve of self-oscillations are obtained when the incident pump powers are below and above the threshold of subharmonic-pumped parametric oscillation （SPO）, respectively. The self-oscillations can be explained by the competition between the phase shifts induced by cascading nonlinearity and thermal effect, and the influence of fundamental nonlinear phase shift by the generation of SPO. The simulation results are in good agreement with the experiment data.

Stability analysis of a liquid crystal elastomer self-oscillator under a linear temperature field

Self-oscillating systems abound in the natural world and offer substantial potential for applications in controllers,micro-motors,medical equipments,and so on.Currently,numerical methods have been widely utilized for obtaining the characteristics of self-oscillation including amplitude and frequency.However,numerical methods are burdened by intricate computations and limited precision,hindering comprehensive investigations into self-oscillating systems.In this paper,the stability of a liquid crystal elastomer fiber self-oscillating system under a linear temperature field is studied,and analytical solutions for the amplitude and frequency are determined.Initially,we establish the governing equations of self-oscillation,elucidate two motion regimes,and reveal the underlying mechanism.Subsequently,we conduct a stability analysis and employ a multi-scale method to obtain the analytical solutions for the amplitude and frequency.The results show agreement between the multi-scale and numerical methods.This research contributes to the examination of diverse self-oscillating systems and advances the theoretical analysis of self-oscillating systems rooted in active materials.

Epidemiological, Diagnostic and Evolutionary Profile of Seizures in Young Infants at Albert Royer (Dakar/Senegal)

Introduction: Seizures are one of the most common neurological complications in the infant period. The aim of our study was to describe the epidemiological, clinical, therapeutic and prognostic features of seizures in infants at the Albert Royer Children’s Hospital (Senegal). Materials and Methods: This was a retrospective, descriptive study from 1 January 2012 to 30 September 2018 of infants aged 0 days to 2 months who presented with seizures. Results: The hospital rate was 8.5%. Almost all the mothers (99.1%) had undergone at least 3 antenatal visits. Urogenital infection, gestational arterial hypertension and funicular anomalies were the main pregnancy-related pathologies. Delivery was vaginal in the majority of cases (80.9%). Most infants (43.6%) had not cried at birth. The majority of infants (63%) were born at term. Trophicity was normal in 68% of cases. The average age of the infants was 6.7 days. The main causes of seizures were hypoxic-ischemic encephalopathy (48.7%), metabolic disturbances (48.1%) and central ոеrvοսѕ system infections (15.6%). Phenobarbital was the 1st-line anticonvulsant. The case fatality rate was 39.5%. The main sequela observed were delayed psychomotor development (20.6%). Conclusion: Optimal management of infant seizures requires early diagnosis and etiological treatment by improving the quality of perinatal care to ensure better management of risk factors, as well as increasing the availability of neuroimaging equipment.

LCD背光照明CCFL罗耶(Royer)谐振变换器设计

大屏幕LCD背光照明使用的CCFL驱动电路大多采用推挽拓扑结构。文中介绍了基于FAN7548控制器的CCFL罗耶(Royer)谐振变换器的工作原理与设计方法。

Self-Oscillating Structural Polymer Gels

self-oscillating polymer gel has become a distinguished class of smart soft materials. Here we fabricated and demonstrated a self-oscillating structural gel network with the incorporation of the Belousov-Zhabotinsky (BZ) reaction. The structural polymer gel oscillates at a macroscopic level with remarkably faster kinetics compared to a normal gel of similar chemical compositions. The structural polymer gel also displays larger oscillating amplitude compared to the normal gel because of the increased diffusion of fluids surrounding the gel particles. This type of structural polymer gels can be harnessed to provide novel and feasible applications in a wide variety of fields, such as drug delivery, nanopatterning, chemical and biosensing, and photonic crystals.

Self-Oscillating Mixer(SOM) With 0.18 μm CMOS Technology

self-oscillating mixer is introduced in this paper, with fundamental signal generated by the oscillator subcircuit in the process of mixing. The oscillator core consumes 3 mA of the current from a 1.8 V DC supply and leads to an output power of –0.88 dBm per oscillator, and a measured phase noise of –91, –102 and –107 dBc/Hz at 100 KHz, 600 KHz and 1 MHz from the carrier, respectively. The proposed mixer achieved IIP3 of 0 dBm in the process of mixing, with conversation gain of 1.93 dB. Designing and simulation the circuit was done in 0.18 μm CMOS technology by ADS2010.

Tropical cyclone, as powerful natural self-oscillatory systems, and wind-energetic a way of struggle against it—The analysis of a cyclone from a position of the theory of vibrations

It is considered three phases of development of a tropical cyclone: the origin, the steady-state regime and the termination, coinciding with three phases of self-oscillatory process: oscillation buid-up, dynamic balance and failure of self-oscillations. The rough size of energy of a cyclone, as column of air rotating with high speed, at initial and final stages of development and comparison of the received sizes with nuclear and hydrogen bombs is calculated. The model of the electronic oscillator with negative active conductivity by the numerical solution of the equation of the Van-der-Pol is analyzed. Formal coincidence of transient in this model with increase of capacity of vortical air formation, that allows to make mnemonic model of a cyclone in the form of volume self-oscillatory system is shown. The numerical solution of the made equations allows to construct schedules of dynamic process for each of particles of the investigated environment. The general recipe on restraint of development of a cyclone by compulsory entering into it of attenuation is given. Realization of this recipe by means of group of platforms with powerful wind-electrogenerator and the fans and uses of a principle of negative feedback is shown. The results of laboratory experiment confirming idea, taken as a principle struggle against an arising air whirlwind, by transformation of a laminar stream in chaotic, turbulent are resulted. For fuller check offered a wind-energetic method of struggle against a cyclone carrying out of more scale experiment is necessary.

Pb同位素链(178≤A≤220)的α衰变的理论研究

利用统一裂变模型(UFM),在考虑预形成因子的情况下系统地研究了Pb同位素链(178≤A≤220)的α衰变情况,并利用包含离心势的推广的Royer(G−Royer)公式和the Viola-Seaborg Semi-empirical relationship(VSS)公式做了计算.通过理论计算值与实验值的对比分析,结果表明离心势在原子核的α衰变过程中起着非常重要的作用.同时实验值与理论值良好的一致性表明统一裂变模型、G−Royer公式和VSS公式对于Pb同位素链的α衰变的预测是可靠的,并给出了部分Pb同位素的α衰变半衰期的预测值.

基于罗耶谐振的微型X射线管高压电源的设计

根据现有的微型X射线管高压电源的基本性能要求,设计了一种输出从0至30 kV可调的微型X射线管用高压直流电源。主电路采用直流电源供电,经过罗耶谐振逆变电路、高频变压器、正负双向倍压整流电路而达到产生直流高压的目的。在稳压电路中采用了反馈控制谐振三极管基极电流的方式,整个电路处于线性工作状态。实测数据表明,电路实现了低噪声、低纹波、低功耗的高压稳压电源设计。

低纹波微型X射线管高压电源的研制

国内研发的X射线高压电源体积普遍较大,不适合微型X射线管的要求。针对微型X射线管的特点,本文设计了一种低纹波、小体积高压电源,其输出电压在0^-40kV范围内可调。电源的逆变电路采用罗耶谐振电路,并引入UCC2973控制芯片以提高其效率。在电源的升压部分设计了高频变压器、双向倍压整流电路,以进行两级升压。通过电阻分压后取样反馈的方式进行稳压。电路工作在线性状态,无开关噪声。测试结果表明,电源的输出电压纹波低于0.3%、稳定度优于0.12%/10h,可满足微型X射线管的需求。

手持式X荧光仪电源系统的设计

手持式X荧光仪所获取谱线的能量分辨率除了决定于荧光脉冲信号处理电路、数字成形滤波算法等,更重要的取决于整套仪器电源系统的合理设计。论文提出一种采用罗耶谐振升压方式给SI-PIN半导体探测器提供+170 V偏置电压的高压电源供电设计方案,避免传统采用PWM波控制变压器升压方式纹波大、效率低的缺陷;同时系统采用电制冷片的温度反馈信号控制供电电源MOS管的导通程度,从而实现对电制冷片温度的控制。实际测试显示该供电方案的高压输出纹波低于10 mV,功耗比传统设计方案低了9.1%,系统同时具有功耗低、纹波小、稳定好等特点,满足手持式X荧光仪野外工作的需要。

混合模式低噪声3kV高压直流电源设计

高压直流电源是电离室等核辐射探测器的关键部件。针对需要3kV左右高压的电离室,本文研制了0~3kV连续可调的低噪声、高效率、小体积及高稳定性的高压直流电源。该高压直流电源系统采用线性与开关混合模式设计,兼顾了转换效率与低噪声。核心部分升压转换部分采用线性罗耶谐振电路与高频变压器实现,保证足够低的高压电源输出纹波。罗耶谐振电路的供电电源则由边沿时间控制型超低噪声开关稳压器LT1534提供,从而实现了混合模式高压直流电源的设计。高压直流电源输出部分采用二阶RC滤波电路进一步降低了输出电压的纹波。实测输出电压范围为0~3kV,静态功耗为0.4 W,3kV输出时纹波为16.55mV,由此可知该电源可用于低噪声的核辐射探测器供电场合。

低成本微型臭氧电源的设计

为节省制造成本,采用Royer电路作为微型臭氧发生器的主电路。分析了臭氧发生器的等效电路,介绍了Royer电路驱动臭氧发生器的工作原理及臭氧产量调节的方法。采用AVR单片机作为系统的主控芯片,给出了系统总体控制方案,介绍了脉冲宽度调制(PWM)信号的产生过程。制作了一台试验样机,实验结果表明,整体方案设计合理,电路运行稳定可靠。

超重核区原子核的α衰变寿命的研究

对超重核区(Z≥110)中的30个原子核运用文献[1]给出的新参数的Violar-Seaborg公式和文献[2]所给出的三个公式及其参数分别计算α衰变寿命,将所得的计算结果与实验值进行比较,得出上述四个计算α衰变寿命公式中最理想的公式是新参数的Violar-Seaborg公式的结论.

10kV电缆绝缘监测用直流电源的设计

针对靠岸船舶供电系统中10 kV XLPE电力电缆绝缘监测系统的需求,采用洛埃耶逆变-变压-全桥整流-稳压输出的方案,并利用可调式集成稳压器设计12 VDC输入,80 VDC输出的直流电源。给出了Ap法变压器的设计过程。测试结果表明该电源性能好,结构简单,工作可靠,可以满足绝缘监测系统的需求。

国际医学史学会的建立与历史演进

为推进有关医学科学、诊疗技术和公共卫生的历史研究,加强世界各国医学史研究人员和学会之间的交流,促进医学文化的交流与传播,国际医学史学会(International Society for the History of Medicine,ISHM)于1921年在巴黎宣布成立。利用ISHM的相关档案和口述访谈等辅助资料,还原其建立和演进的过程,并在全球政治和医学发展格局中,批判性地审视ISHM从以法国和比利时为主导,逐步走向欧洲大陆、欧洲和北美,最后走向全球,从以医生/医学史家为主体到融合科学技术史、生物医学史、医疗史和历史学家等多元学科的历史进程。

小型化可编程电泳仪电源设计

针对传统电泳仪电源不能自动切换电压的问题,采用含有单片机的开关电源技术,研究了一种小型化可编程电泳仪电源设计方案。采用单片机输出PWM作为控制信号,升压电路采用改进的Royer电路。能够做到对时间和电压混合编程,同时满足电泳仪电源的需求,符合YY/T0087-2004标准的要求,其负载效应在稳压状态下不大于2%。在微流控芯片凝胶电泳试验中起到了定时自动电压输出与切换的作用。

航天器用胶体推进器10kV高压可调束流电源仿真分析研究

近年来,随着微纳卫星编队飞行成为诸如引力波探测等领域的研究热点,推力量级更小的新兴电推进器,例如胶体推进器(Colloid Thruster,CT)的应用前景越来越广泛,尤其是对其电源处理单元(Power Processing Unit,PPU)的需求越来越高。文章针对航天器胶体推进器电源处理单元中10kV高压可调束流电源,设计了一种双管Buck-Boost预稳压电路+罗耶自激震荡器+双向倍压整流的三级式电压升举电路拓扑;选取合适的电路参数,并使用电路仿真软件Saber对前级电路和后级电路分别进行仿真,以证实电路拓扑及参数选择的可行性,进而对整体电路进行仿真,验证设计的准确性。同时,选取了两种由反激构成的备选高压电路进行仿真分析验证,从中甄选出最佳的电路拓扑。仿真结果表明,设计的3种电路都能实现最高至10kV的电压输出,同时,能够实现3kV到10kV之间的大范围调节,满足胶体推进器PPU束流电源的工作指标。

Coupling processes between self-oscillation of formation pressure and periodic migration-accumulation of natural gases in Yinggehai Basin, South China Sea

The modeling of formation pressure in Yinggehai shows that DF1-1 diapir has oscilla-torily released thermal fluids twice since 5.0 Ma, which may be controlled by the multi-structural subsidences and their accompanying thermal events. Using thermal indicators of formation temperature by DST, I/S mixed clay minerals, homogeneous temperature of inorganic fluid inclusion and δ13C of methane to trace the thermal fluid migrating order and path, we found that there are two orders of natural gas migration-accumulation in the upper site over the top of the overpres-sured compartment. Based on the oscillatory development of formation pressure, we postulate there would exist earlier (before 5.0 Ma) gas accumulation in their deeper site.

Canards in a rheodynamic model of cardiac pressure pulsations

This paper reports on the canard phenomenon occurring in a rheodynamic model of cardiac pressure pulsations. By singular perturbation techniques the corresponding parameter value at which canards exist is obtained. The physiological significance of canards in this model is given.