Theoretical and experimental study of a bi-stable piezoelectric energy harvester under hybrid galloping and band-limited random excitations

In the practical environment,it is very common for the simultaneous occurrence of base excitation and crosswind.Scavenging the combined energy of vibration and wind with a single energy harvesting structure is fascinating.For this purpose,the effects of the wind speed and random excitation level are investigated with the stochastic averaging method(SAM)based on the energy envelope.The results of the analytical prediction are verified with the Monte-Carlo method(MCM).The numerical simulation shows that the introduction of wind can reduce the critical excitation level for triggering an inter-well jump and make a bi-stable energy harvester(BEH)realize the performance enhancement for a weak base excitation.However,as the strength of the wind increases to a particular level,the influence of the random base excitation on the dynamic responses is weakened,and the system exhibits a periodic galloping response.A comparison between a BEH and a linear energy harvester(LEH)indicates that the BEH demonstrates inferior performance for high-speed wind.Relevant experiments are conducted to investigate the validity of the theoretical prediction and numerical simulation.The experimental findings also show that strong random excitation is favorable for the BEH in the range of low wind speeds.However,as the speed of the incoming wind is up to a particular level,the disadvantage of the BEH becomes clear and evident.

股权质押与会计稳健性

本文采用我国沪深两市A股上市公司2009-2016年的数据检验了股权质押和会计稳健性的关系。研究发现,存在股权质押的上市公司会计稳健性会降低,股权质押与会计稳健性的负相关关系在非国有企业与经营业绩较差的企业中更显著。研究结果表明,在股权质押后上市公司会通过提前释放"好消息"和隐藏"坏消息"的方式进行市值管理。本文认为财务报告使用者应该重视股权质押后上市公司会计信息质量下降的风险,同时监管机构应做好应对股权质押带来的系统性金融风险的防范工作。

高管薪酬差距与研发投入

本文利用2007~2015年我国A股上市公司数据,研究高管团队薪酬差距对企业研发投入的影响。本文发现,CEO与其他高管的薪酬差距越大,企业研发投入越多。上述结果在控制内生性问题后仍然稳健,从而有力支撑了锦标赛理论。进一步研究发现,只有在股权集中度较低、公司成长性较高以及CEO为内部继任的样本中,高管团队薪酬差距才能有效激发企业投入研发。本文认为我国上市公司需要从长远发展角度考虑,构建更加有效的薪酬激励机制,以增强企业创新能力。

A seismic model for crustal structure in North China Craton

We present a digital crustal model in North China Craton(NCC). The construction of crustal model is based on digitization of original seismic sounding profiles, and new results of three-dimensional structure images of receiver functions. The crustal model includes seismic velocity and thickness of crustal layers. The depths to Moho indicate a thinning crust ~30 km in the east areas and a general westward deepening to more than 40 km in the west. The P wave velocity varies from 2.0 to 5.6 km/s in the sedimentary cover,from 5.8 to 6.4 km/s in the upper crust, and from 6.5 to 7.0 km/s in the lower crust. By analyzing regional trends in crustal structure and links to tectonic evolution illustrated by typical profiles, we conclude that:(1) The delimited area by the shallowing Moho in the eastern NCC represents the spatial range of the craton destruction. The present structure of the eastern NCC crust retains the tectonic information about craton destruction by extension and magmatism;(2) The tectonic activities of the craton destruction have modified the crustal structure of the convergence boundaries at the northern and southern margin of the NCC;(3) The Ordos terrene may represent a relatively stable tectonic feature in the NCC, but with the tectonic remnant of the continental collision during the assembly of the NCC in the north-east area and the response to the lateral expansion of the Tibetan Plateau during the Cenozoic in the south-west.

A new approach for inversion of receiver function for crustal structure in the depth domain

A method for reconstructing crustal velocity structure using the optimization of stacking receiver function amplitude in the depth domain,named common conversion amplitude(CCA)inversion,is presented.The conversion amplitude in the depth domain,which represents the impedance change in the medium,is obtained by assigning the receiver function amplitude to the corresponding conversion position where the P-to-S conversion occurred.Utilizing the conversion amplitude variation with depth as an optimization objective,imposing reliable prior constraints on the structural model frame and velocity range,and adopting a stepwise search inversion technique,this method efficiently weakens the tendency of easily falling into the local extremum in conventional receiver function inversion.Synthetic tests show that the CCA inversion can reconstruct complex crustal velocity structures well and is especially suitable for revealing crustal evolution by estimating diverse velocity distributions.Its performance in reconstructing crustal structure is superior to that of the conventional receiver function imaging method.

高效光催化二氧化碳还原钻单原子催化剂的多尺度结构工程

人工光合作用将二氧化碳转化为增值化学品和燃料,在克服全球环境能源危机方面具有巨大潜力.然而,由于CO_(2)的热力学稳定性和动力学滞后性,开发高效的CO_(2)RR光催化剂是一个巨大的挑战.本文在微介孔氮掺杂碳(0.8-Co-ISAS/MMNC-900)上制备了一种具有高度分散Co单原子位的分级多孔钴单原子光催化剂,该催化剂显著促进了CO_(2)-to-CO的光还原.0.8-Co-ISAS/MMNC-900催化剂的CO生成速率高达7261μmol g^(-1)h^(-1),CO选择性高达90.1%,并且在四次循环测试中表现出良好的稳定性.实验数据和理论结果表明,分层多孔结构可以促进电荷分离引起的外部局部电场的形成,Co隔离的单原子位和微介孔构型协同作用,促进光激发电子积累、CO_(2)吸附活化和*COOH中间体的形成.本研究通过多尺度多孔结构工程,提出了一种合成CO_(2)还原光催化剂的新策略.

生物大分子的量子计算模拟:并行量子算法的初步探索

Quantum computing is a rapidly-emerging technology that is widely expected to solve valuable problems in physics and chemistry.After quantum computational advantage in the task of sampling has been demonstrated on both photonic and superconductor quantum platforms[1,2],quantum computing is urgently seeking to solve problems of practical interest that are often intractable or at least computationally demanding for classical computers[3].

Interfacial engineering of SnO_(2)/Bi_(2)O_(2)CO_(3)heterojunction on heteroatoms-doped carbon for high-performance CO_(2)electroreduction to formate

Electrochemical CO_(2)reduction is a viable,economical,and sustainable method to transform atmospheric CO_(2)into carbon-based fuels and effectively reduce climate change and the energy crisis.Constructing robust catalysts through interface engineering is significant for electrocatalytic CO_(2)reduction(ECR)but remains a grand challenge.Herein,SnO2/Bi_(2)O_(2)CO_(3)heterojunction on N,S-codoped-carbon(SnO_(2)/BOC@NSC)with efficient ECR performance was firstly constructed by a facile synthetic strategy.When the SnO_(2)/BOC@NSC was utilized in ECR,it exhibits a large formic acid(HCOOH)partial current density(JHCOOH)of 86.7 mA·cm^(−2)at−1.2 V versus reversible hydrogen electrode(RHE)and maximum Faradaic efficiency(FE)of HCOOH(90.75%at−1.2 V versus RHE),respectively.Notably,the FEHCOOH of SnO_(2)/BOC@NSC is higher than 90%in the flow cell and the JHCOOH of SnO_(2)/BOC@NSC can achieve 200 mA·cm^(−2)at−0.8 V versus RHE to meet the requirements of industrialization level.The comparative experimental analysis and in-situ X-ray absorption fine structure reveal that the excellent ECR performance can be ascribed to the synergistic effect of SnO_(2)/BOC heterojunction,which enhances the activation of CO_(2)molecules and improves electron transfer.This work provides an efficient SnO_(2)-based heterojunction catalyst for effective formate production and offers a novel approach for the construction of new types of metal oxide heterostructures for other catalytic applications.

Integrated guidance and control design of a flight vehicle with side-window detection

This paper considers the guidance and control problem of a flight vehicle with sidewindow detection. In order to guarantee the target remaining in the seeker＇s sight of view, the line of sight and the attitude of the flight vehicle should be under some constraints caused by the sidewindow, which leads to coupling between the guidance and the attitude dynamics model. To deal with the side-window constraints and the coupling, a novel Integrated Guidance and Control（IGC）design approach is proposed. Firstly, the relative motion equations are derived in the body-Line of Sight（LOS） coordinate system. And the guidance and control problem of the flight vehicle is formulated into an IGC problem with state constraints. Then, based on the singular perturbation method, the IGC problem is decomposed into the control design of the quasi-steady-state subsystem and the boundary-layer subsystem which can be designed separately. Finally, the receding horizon control is applied to the control design for the two subsystems. Simulation results show the effectiveness of the proposed approach.

Insights into the Origin of Natural Gas Reservoirs in the Devonian System of the Marsel Block, Kazakhstan

The genetic type and accumulation model of the Devonian reservoirs in the Marsel Block remain unclear, despite decades of exploration history. According to the well testing, logging interpretations and sample testing results, the Devonian natural gas reservoir in the Marsel Block has five typical characteristics:(1) It is obvious that the traps contain continuous gas accumulations. Not only the apexes of the structures are enriched in natural gas, but also the slopes and depressions contain gas accumulations.(2) The gas reservoirs are classified as tight reservoirs, but there are also reservoirs with high porosity and permeability in some areas.(3) The general negative or low-pressure in the gas reservoir is obvious, although the pressure in the target layers of some wells is close to normal.(4) The yields of single wells in the Devonian reservoir are quite different: some wells have low yields or are dry, whereas the gas production from high-yield wells has reached 700 000 m3/day.(5) The gas-water relationship is complicated: there is no obvious gas-water interface, but the water-producing layer is generally located at the apexes of structures. Research and analysis have shown that using the model of the conventional gas reservoirs genetic type can only explain the characteristics of parts of the gas reservoir, while the model of accumulation in a deep-basin gas reservoir cannot fully explain the distribution characteristics of the Devonian reservoir. However, the model of accumulation in a stacked complex continuous oil and gas reservoir can reasonably explain the geological and distribution characteristics of the Devonian reservoir. Moreover, the predicted gas distribution along a cross-section of the reservoir is also in agreement with the geological background and tectonic environment of the Marsel Block, therefore, the genetic type of the Devonian natural gas reservoir in the Marsel Block is a stacked complex continuous tight-gas reservoir. Finally, by comprehensively analyzing the source rock, reservoir and cap rocks, as well as the structural characteristics, it is verified that Devonian in the Marsel Block has favorable geological conditions for formation of a superimposed continuous tight gas reservoir.

Three Novel Mutations of Microphthalmos Identified in Two Chinese Families

Genetic alterations are a major cause of microphthalmos,while novel-related genes and mutations in microphthalmos have rarely been explored.To identify the underlying genetic defect responsible for microphthalmos eyes in two three-generation Chinese families,we screened 425 genes involved in common inherited non-syndromic eye diseases with next-generation sequencing-based target capture sequencing of the two probands of two three-generation Chinese families diagnosed with microphthalmos.Variants were filtered and analyzed to identify possible disease-causing variants before Sanger sequencing validation.We enrolled two families with microphthalmos(Family 1:microphthalmos with congenital ocular coloboma and Family 2:simple microphthalmos).Two novel heterozygous mutations,Peroxidasin(PXDN)c.3165C>T(p.Pro1055Pro)and PXDN c.2640C>G(p.Arg880Arg),were found in Family 1,and Crystallin Beta B2(CRYBB2)c.481G>A(p.Gly161Arg)was found in Family 2,but none of the mutations were found in the unaffected individuals,who were phenotypically nor-mal.Multiple orthologous sequence alignment(MSA)revealed that the CRYBB2 p.Gly161Arg mutation was a deleterious effect mutation.In conclusion,the three novel mutations found in our study extend our current understanding of the genetic basis of microphthalmos and provide early pre-symptomatic diagnosis and emphasize the significance of genetic diagnosis of microphthalmos.