具有响应与强度约束的凸轮机构动态设计

以滚子从动件平面凸轮机构为分析对象 ,结合从动件相对变形理论 ,提出了输出响应限制与构件强度约束相结合的凸轮机构动态设计与修改方法 ,并从理论上进行了阐述。最后 ,通过一实例对不同频率比λ、不同摆臂截面形状及截面积下的摆臂最大变形、最大弯应力及凸轮与转子间最大压应力进行了数值计算 ,为凸轮机构动态设计与修改 。

影响凸轮机构动态性能的相对变形函数性质研究

以滚子从动件平面凸轮机构为分析对象 ,提出了相对变形函数这一新概念 ,并从理论上对其进行了研究 ,最后借助于一凸轮机构在不同参数下其摆臂最大相对变形量的数值计算过程与结果 ,阐述了基于该理论的凸轮机构动态设计与修改的具体实现步骤与方法。

人行天桥竖向振动控制

该文介绍了国内外规范和标准关于人行天桥在人群荷载激励下产生竖向振动时的相关控制要求。为了解决人桥共振问题,设计上采用的基本方法主要有两种:频率调整法和限制动力响应值法[1];调整结构基频可以通过改变板厚、梁高或结构形式等实现;目前国内外也广泛采用调频质量阻尼器(Tuned Mass Damper,TMD)来限制结构的动力响应。该文以天津市南京路人行天桥工程为背景,详细分析了各种竖向振动控制方法的效果。计算表明:增加梁高和改变结构形式均能较大幅度的提高结构基频;采用TMD减振系统则可有效削减人行桥的共振反应。

在线总有机碳(TOC)分析仪系统适用性试验

对在线总有机碳(TOC)分析仪系统适用性试验方法进行了合理改进,此方法符合USP 28和EP 5标准,操作简单,有效降低了试验成本。

浅析某立交桥振动舒适性评价

通过对某立交桥进行动载试验,测定该桥结构的自振频率及振动加速度,并与理论计算的结果及相应规范的要求进行比较,通过限制动力响应值法对该桥进行舒适性评价。并通过避开敏感频率法改善桥梁频率,从而达到改善桥梁振动舒适性。

约束线方法在生态学研究中的应用

生态系统格局和过程往往受到多个因子的共同影响,故此反映两个生态学变量相互关系的散点图常常会表现为有边界的散点云。基于数据均值或中值分析的传统统计方法不适用于散点云数据的分析。散点云所表征的不是两变量之间的相关关系,而是限制作用关系。约束线(包络)方法为提取散点云边界、理解限制变量对响应变量的作用,以及预测响应变量的潜在最大值提供了有效手段。该文对应用约束线方法研究生态学问题所取得的成果进行总结与归纳,介绍了约束线概念的发展历程、提取方法,从物种分布、种群行为及作物产量优化三个方面总结了约束线方法的优点及适用性,概述了当前约束线方法应用研究面临的问题与挑战,指出约束线方法应结合其他统计方法,实现对生态过程的准确理解,此外,还应重视约束线方法的尺度依赖性。最后,该文展望了约束线方法在研究生态系统服务关系和土地系统优化等方面的应用前景。

具有60分贝动态范围的音量单位表

一种音频音量单位表能显示与峰值相关的音频幅度．来帮助精确设定录音电平．或用于显示放大器的工作状况。一个简单的二极管和电容器网络提供了经典的音量单位表的峰值加权式响应．但是电路一般把响应限制在大约23分贝的可显示动态范围．并且音量单位表指针的惯性和机械式“冲击”会带来误差。

Artemisinin mimics calorie restriction to extend yeast lifespan via a dual-phase mode: a conclusion drawn from global transcriptome profiling

Calorie restriction(CR) promotes longevity among distinct organisms from yeast to mammals. Although CR-prolonged lifespan is believed to associate with enhanced respiratory activity, it is apparently controversial for accelerated energy consumption regardless of insufficient nutrient intake. In reconciling the contradiction of less food supply versus much metabolite dispense, we revealed a CR-based mode of dual-phase responses that encompass a phase of mitochondrial enhancement(ME) and a phase of post-mitochondrial enhancement(PME), which can be distinguished by the expression patterns and activity dynamics of mitochondrial signatures. ME is characterized by global antioxidative activation, and PME is denoted by systemic metabolic modulation. CR-mediated aging-delaying effects are replicated by artesunate, a semi-synthetic derivative of the antimalarial artemisinin that can alkylate heme-containing proteins, suggesting artesunate-heme conjugation functionally resembles nitric oxide-heme interaction. A correlation of artesunate-heme conjugation with cytochrome c oxidase activation has been established from adduct formation and activity alteration. Exogenous hydrogen peroxide also mimics CR to trigger antioxidant responses, affect signaling cascades, and alter respiratory rhythms, implying hydrogen peroxide is engaged in lifespan extension. Conclusively, artesunate mimics CR-triggered nitric oxide and hydrogen peroxide to induce antioxidative networks for scavenging reactive oxygen species and mitigating oxidative stress, thereby directing metabolic conversion from anabolism to catabolism, maintaining essential metabolic functionality, and extending life expectancy in yeast.

Transient response of carbon nanotube integrated circuits

The speed of frequency response of all published carbon nanotube （CNT） integrated circuits （ICs） is far from that predicted. The transient response of CNT ICs is explored systematically through the combination of experimental and simulation methods. Complementary field-effect-transistor （FET） based inverters were fabricated on a single semiconducting CNT, and the dynamic response measurement indicates that it can only work at an unexpectedly low speed, i.e. with a large propagation delay of 30 }_ts. Owing to the larger output resistance of CNT FETs, the existence of parasitic capacitances should induce much larger resistive-capacitive （RC） delay than that in Si ICs. Through detailed analysis combining simulation and experimental measurements, several kinds of parasitic capacitances dragging down the actual speed of CNT FET ICs are identified one by one, and each of them limits the speed at different levels through RC delay. It is found that the parasitic capacitance from the measurement system is the dominant one, and the large RC delay lowers the speed of CNT FETs logic circuits to only several kHz which is similar to the experimental results. Various optimized schemes are suggested and demonstrated to minimize the effect of parasitic capacitances, and thus improve the speed of CNT ICs.

Competition and abiotic stress affect the size of mangroves near their geographic range limit

Studies of competition in mangroves are mostly limited to seedlings and artificial settings like forestry projects.We conducted the first experimental study of intraspecific competition among adult mangroves in a natural mangrove forest to examine how important competition is in determining tree size compared with abiotic conditions.We conducted a study near Port Aransas,TX,USA,which is near the geographical limit of mangroves and dominated by monospecific stands of‘scrub’form black mangroves,Avicennia germinans.We thinned 10 plots to create a gradient of mangrove cover,and quantified the effects of mangrove cover on the growth of tagged mangroves from 2013 to 2019,and the mangrove canopy height in 2019.The relative growth rate of tagged mangroves declined as mangrove cover increased,and plants in the plot with 100%mangrove cover did not grow,indicating that they had attained their maximum size.In plots with reduced mangrove cover,plant height increased sharply,with plants in the plot with 11%mangrove cover growing~52%taller over 6 years.Canopy height was~30%taller in the plot fringe than in the interior,and canopy height in both fringe and interior declined as mangrove cover increased.Measures of leaf chlorophyll concentration and light interception suggested that plants were primarily limited by nitrogen.Our results showed that scrub mangroves compete strongly despite being limited by abiotic conditions,and that the importance of competition was greater in magnitude than that of abiotic differences between the fringe and interior.

A microwave photonic filter based on multi-wavelength fiber laser and infinite impulse response

A microwave photonic filter(MPF) based on multi-wavelength fiber laser and infinite impulse response(IIR) is proposed. The filter uses a multi-wavelength fiber laser as the light source, two sections of polarization maintaining fiber(PMF) and three polarization controllers(PCs) as the laser frequency selection device. By adjusting the PC to change the effective length of the PMF, the laser can obtain three wavelength spacings, which are 0.44 nm, 0.78 nm and 1.08 nm, respectively. And the corresponding free spectral ranges(FSRs) are 8.46 GHz, 4.66 GHz and 3.44 GHz, respectively. Thus changing the wavelength spacing of the laser can make the FSR variable. An IIR filter is introduced based on a finite impulse response(FIR) filter. Then the 3-d B bandwidth of the MPF is reduced, and the main side-lobe suppression ratio(MSSR) is increased. By adjusting the gain of the radio frequency(RF) signal amplifier, the frequency response of the filter can be enhanced.