火炮内弹道挤进过程导转侧力特性

为研究弹丸挤进过程膛线导转侧与弹带的力学响应,基于能量法推导弹丸挤进过程弹带运动、变形及其与膛线相互作用的力学机理,根据经典内弹道理论分析了弹带挤进后与膛线导转侧受力关系,分别得到挤进过程和挤进后导转侧受力的一般表达式,并分析了挤进过程及挤进后导转侧受力的主要影响因素。采用弹塑性有限元方法模拟弹丸膛内运动过程,获取多种工况下导转侧受力动态响应,分析导转侧受力变化特性,以及挤进过程中导转侧力受挤进速度和坡膛角的影响规律。研究表明:弹丸挤进过程导转侧受力与挤进速度、坡膛角正相关,挤进后导转侧受力与弹底压力变化趋势一致;在一定速度范围内,弹丸挤进过程的导转侧受力远大于最大膛压时刻,且随着速度增加,挤进过程导转侧受力与最大膛压时刻的比值有明显增大的趋势;对于弹丸启动后自由行程较长的埋头弹火炮,挤进过程受力更为恶劣,需加强装药结构及优化坡膛结构为提高身管寿命创造条件。研究结果可为弹丸结构设计及弹炮匹配性分析提供理论参考。

直升机滚转侧滑耦合的响应分析

滚转侧滑耦合是直升机飞行品质试验的重要内容。结合某型直升机的飞行试验,通过参数辨识及数值仿真,给出了不同气动参数下直升机滚转侧滑耦合响应结果,并对气动参数对直升机滚转侧滑耦合及飞行品质的影响规律进行了分析总结,对后续直升机品质试飞有着重要意义。

身管膛线类型及其动力学影响研究

为了比较火炮身管等齐膛线、渐速膛线和混合膛线之间的动力学响应差异,采用动力学分析方法分析了身管膛线导转侧力、膛线约束下的弹丸轴向加速度,以及不同身管膛线条件下的炮口振动响应的变化规律.结果表明,在弹丸出炮口位置附近,等齐膛线导转侧力最小,渐速膛线导转侧力最大;等齐膛线导转侧力曲线光滑,而混合膛线导转侧力变化剧烈、曲线载荷梯度非常大;当弹头刚露出炮口时,混合膛线导转侧力突变范围达3倍之多,混合膛线约束下的弹丸轴向加速度在炮口附近有突跳;与等齐膛线相比,混合膛线引起的炮口绕身管轴线转动角速度和角加速度分别增加了92.7%和367.5%.等齐膛线有利于弹丸膛内平稳运动,有利于减小炮口振动响应.

基于液柱平衡体的单兵筒式武器动力学特性研究

为探究发射过程中液柱平衡体对单兵筒式武器射击稳定性的影响,对基于液柱平衡体的单兵筒式武器动力学特性进行研究。通过分析采用液体平衡发射技术的单兵筒式武器发射过程,建立其受力模型;利用Fluent流体仿真软件建立喷管气液两相流仿真模型,重点分析液体工质对喷管推力的影响特性;并分析了液柱平衡体影响下单兵筒式武器膛线导转侧力的变化规律。研究结果表明:液柱平衡体对单兵筒式武器射击稳定性影响较大,有必要进一步优化设计。

人在回路红外成像导弹搜捕概率建模与仿真

针对人在回路的导弹搜捕概率计算问题,通过分析人在回路特点、红外成像导弹末端捕控的实际过程,建立了红外成像瞬时航向视场、纵向视场计算模型,研究了导引头最大搜索扇面、目标区边界制约下的转侧搜扫条件,给出了综合距离与方位约束的发现目标判据模型。根据计算流程,仿真分析了导弹进入航向、开机距离、目标区边长等因素对搜捕概率的影响。结果显示,导弹从目标区对角线方向进入时的搜捕概率比最低值高出21%;最佳开机距离因目标区边长而异,边长小于7 km可使发现概率大于0.85;增强红外成像导引头作用距离、提高操作员转动光轴的速率均能极大提高搜捕概率。

偏心隔震结构扭转效应机理分析及关键参数限值研究

相较于传统抗震结构,隔震结构更易通过调整隔震支座布置方案,控制关键参数在合理范围内,减少上部结构偏心带来的不利影响。为此,从偏心隔震结构扭转效应机理角度,分析了在不同取值范围内,隔震结构转侧频率比、隔震层偏心率对扭转效应的影响规律和影响程度。研究结果表明:转侧频率比越小,扭转反应越明显,且此时较小的隔震层偏心率就会使得隔震结构扭转加剧;当转侧频率比大于1.2后,其影响逐渐减弱;隔震层的偏心率与扭转响应接近正相关。然后,以支座位移不超过容许值为限制条件,推导出距离质心最远处支座在有无偏心时的位移比值显式。分析结果表明,存在一个最大隔震周期使该比值取得极小值。据此,可推导出不同转侧频率比时隔震层偏心率的限值,在该限值范围内偏心隔震结构的扭转可得到有效控制,为设计人员在进行隔震结构抗扭设计时提供参考。

Isolation of the Flanking Sequences Adjacent to Transgenic T-DNA in Brassica napus Genome by an Improved Inverse PCR Method

[Objective] The research aimed to isolate flanking sequences adjacent to the transgenic T-DNA in Brassica napus by an improved inverse PCR method.[Method] Using single clone of transgenic FS4 in Brassica napus as the research materials,total DNA was extracted from transgenic Brassica napus by using modified CTAB method.After enzyme digestion and purification,self-joining was made.Two circles of nested PCR and the sequence alignment were carried out.[Result] A fragement with the size of 4.0 kb was amplified ...

经方治验二则

刘××,男,45岁,工人。1979年去外地公差,因路旁施工扔跳板打伤头部,当即送医院,经抢救治疗,半年后出院。遗有头晕,头痛,恶心,多梦等证,曾多处医治不效而来我院。证见:头晕、头痛、恶心、夜多恶梦,项背强难以转侧,无汗,偶得汗自觉轻松,微喘,口渴不甚,舌质稍红,苔薄黄,右寸脉浮而有力。

书法欹中取正的审美规律

书法艺术的欹中取正之美体现了动态平衡的审美效果,具有生动的神采,表现出灵动、骏健、奇险、潇洒、奔放等审美意境。仰俯、转侧、向背是书法欹中取正的主要结构规律。书法史中的不同书体作品具有丰富多样的欹中取正的审美风貌。

Prospects of China's Agricultural Development

Remarkable achievements have been made in China＇s agricultural development since the late 1970s. Nevertheless, deep-rooted problems are arising from inefficient farming practices. From mid- and long-term perspectives, migration of China＇s agricultural labor will slow and large-scale operation of farmland will accelerate. Although grain supply and demand have maintained a tight balance, new potentials still exist in improving grain production. Under the pressures of resource and environmental constraints, advancing the green and efficient transition of agriculture will become a new trend in China＇s agricultural development. In this context, the treatment of agricultural pollution, supply-side structural reform and innovation of agricultural subsidy policy are of strategic significance to the transition and upgrade of China＇s agriculture.

Novel high torque bearingless two-sided rotary ultrasonic motor

Applications are limited at present because the currently available ultrasonic motors (USMs) do not provide suffi-ciently high torque and power. The conventional travelling-wave USM needs the bearing to support, which required lubricant. To solve the above problem, a bearingless travelling-wave USM is designed. First, a novel structure of the two-sided USM consisting of a two-sided teeth stator and two disk-type rotors is designed. And the excitation principle of the two-sided travelling-wave USM is analyzed. Then, using ANSYS software, we set up the model of the stator to predict the excitation frequency and modal response of the stator. The shape of the vibration mode was obtained. Last, the load characteristics of the USM are measured using ex-perimental method. The maximum stall torque and the no-load speed were obtained. The results showed that the characteristics of the two-sided USM are better than those of the conventional one-sided USM.

Topology evolutions of silhouettes

We give the topology changing of the silhouette in 3D space while others study the projections in an image. Silhou- ettes play a crucial role in visualization, graphics and vision. This work focuses on the global behaviors of silhouettes, especially their topological evolutions, such as splitting, merging, appearing and disappearing. The dynamics of silhouettes are governed by the topology, the curvature of the surface, and the view point. In this paper, we work on a more theoretical level to give enu- merative properties of the silhouette including: the integration of signed geodesic curvature along a silhouette is equal to the view cone angle; in elliptic regions, no silhouette can be contained in another one; in hyperbolic regions, if a silhouette is homotopic to a point, then it has at least 4 cusps; finally, critical events can only happen when the view point is on the aspect surfaces (ruled surface of the asymptotic lines of parabolic points with surface itself). We also introduce a method to visualize the evolution of silhouettes, especially all the critical events where the topologies of the silhouettes change. The results have broad applications in computer vision for recognition, graphics for rendering and visualization.

Analysis of the Flanking Sequence and EventSpecific Detection of Transgenic Line W-4 of Brassica napus

The genetically modified high-oleic rapeseed （Brassica napus L.） line W-4 was obtained by transforming a binary vector which harbored an inverted repeat expression cassette of fad2 gene into the rapeseed cultivar Westar.The transformation was mediated by Agrobacterium.The flanking sequences to both the left and right borders of T-DNA insertion site were amplified by thermal asymmetric interlaced PCR （TAIL-PCR） from the genomic DNA of the transgenic rapeseed line W-4.The flanking sequences to the right border was 290 bp in length and the nucleotide composition was 31.27％ for G＋C content while 68.73％ for A＋T content.The flanking sequence to the left border was 365 bp in length and the G＋C content was 32.6％ and the A＋T content was 67.4％,indicating that the T-DNA was integrated in the A/T-rich region.Further more,sequence alignment analysis showed a deletion of 62 bp including the right border of pCNFIRnos and the integration of the whole left border except a change of G to A.That was to say,the integration of the T-DNA in the transgenic line W-4 not involved in the vector sequences.Based on both flanking sequences as well as the left and right borders of the T-DNA sequences,two pairs of specific primers TLF/TLR and TRF/TRR were designed.Using the primers the event-specific PCR detection method for transgenic rapeseed line W-4 was established.By the PCR,two fragments of 485 and 405 bp were amplified from the W-4 genomic DNA as expected,while no products were amplified from the genomic DNA of other transgenic rapeseed lines and non-transgenic rapeseed line.And by the PCR it is possible to detect the W-4 genomic DNA from a mixed sample of genomic DNA.The limit of the detection for the qualitative PCR assay was 0.1％.The method developed in this work is highly specific,sensitive and suitable for event-specific detection of the transgenic rapeseed line W-4.

Ac/Ds Transposition Activity in Transgenic Rice Population and DNA Flanking Sequence of Ds Insertion Sites

The Agrobacterium mediated transgenic rice ( Oryza saliva L.) population with inserts of maize transposon Activator/Dissociation (Ac/Ds) was investigated. DNA sequences flanking the T-DNA were analyzed with inverse PCR. Results showed that 65.4% of the T-DNA was integrated in different locations of rice genome, and some T-DNA flanking sequences were located on certain chromosomes. A number of T-DNA was found to have inserted into protein coding regions. In order to induce transposition of the inserted Ds elements, 354 crosses of Ac x Ds and Ds x Ac were constructed. The excision frequency of Ds element trans-activated by Ac transposase was 22.7% in the F-2 populations, and the transposition was confirmed with analyses of DNA sequences flanking the Ds elements. In addition to the transposition due to 'cut-paste' mechanism, Ds can replicate itself and integrate into a new locus, and inaccurate excisions were also found. A proportion of DNA segments flanking the Ds elements showed no homologies to sequences published in GenBank, of which two were registered under the accession numbers AF355153 and AF355770. The strategy of using transposon tagging for rice genomics study was discussed.

Supply-Side Solutions to China's Energy Transition

Compared with the first two energy transitions in human history, the current third energy transition is characterized by the changing concepts of development. Considering its energy mix dominated by fossil fuels, China is faced with a daunting task of transition. This paper discusses the following policy recommendations on China＇s energy transition, including building a renewables-friendly electric power system, developing smart grids and electric vehicles, promoting cross-regional electric power transactions, encouraging financial innovation, and creating new energy industry investment funds to broaden financing channels and diversify investment entities.

Experimental Study on Airflow Reversal Within Bypass Branch During Mine Fire

Based on the analysis of conditions for airflow reversal within a bypass branch, the airflow reversal phenomena were successfully simulated in the laboratory experiments. Data obtained indicate that airflow reversal within a bypass branch is mainly caused by fire pressure yielded in the combustion branch. In addition, the maximum reversal quantity of airflow occurs in step with the highest temperature of fire, the highest concentration of CO 2 and the lowest concentration of O 2. Moreover, the time that fire size reaches the maximum value corresponds to the time airflow reversal in the bypass branch is most possible. The results are of great significance for guiding rescue work to avoid airflow reversal.

Xom interacts with and stimulates transcriptional activity of LEFI/TCFs: implications for ventral cell fate determination during vertebrate embryogenesis

LEF1/TCFs are high mobility group box-containing transcriptional factors mediating canonical Wnt/β-catenin signaling during early embryogenesis and tumorigenesis. β-Catenin forms a complex with LEF 1/TCFs and transactivates LEF1/TCF-mediated transcriptions during dorsalization. Although LEF-mediated transcription is also implicated in ventralization, the underlying molecular mechanism is not well understood. Using the vertebrate Xenopus laevis model system, we found that Xom, which is a ventralizing homeobox protein with dual roles of transcriptional activation and repression, forms a complex with LEF 1/TCF through its homeodomain and transactivates LEF 1/TCF-mediated transcription through its N-terminal transactivation domain （TAD）. Our data show that Xom lacking the N-terminal TAD fails to transactivate ventral genes, such as BMP4 and Xom itself, but retains the ability to suppress transcriptional activation of dorsal gene promoters, such as the Goosecoid promoter, indicating that transactivation and repression are separable functions of Xom. It has been postulated that Xom forms a positive re-enforcement loop with BMP4 to promote ventral- ization and to suppress dorsal gene expression. Consistent with an essential role of Xom transactivation of LEF1/TCFs during early embryogenesis, we found that expression of the dominant-negative Xom mutant that lacks the TAD fails to re-enforce the ventral signaling of BMP4 and causes a catastrophic effect during gastrulation. Our data suggest that the functional interaction of Xom and LEF 1/TCF-factors is essential for ventral cell fate determination and that LEF 1/TCF factors may function as a point of convergence to mediate the combined signaling of Wnt/β-catenin and BMP4/Xom pathways during early embryogenesis.

Distortional buckling analysis of steel-concrete composite box beams considering effect of stud rotational restraint under hogging moment

Restrained distortional buckling is an important buckling mode of steel-concrete composite box beams(SCCBB)under the hogging moment.Rotational and lateral deformation restraints of the bottom plate by the webs are essential factors affecting SCCBB distortional buckling.Based on the stationary potential energy principle,the analytical expressions for the rotational restraint stiffness(RRS)of the web upper edge as well as the RRS and the lateral restraint stiffness(LRS)of the bottom plate were derived.Also,the SCCBB critical moment formula under the hogging moment was derived.Using twenty specimens,the theoretical calculation method is compared with the finite-element method.Results indicate that the theoretical calculation method can effectively and accurately reflect the restraint effect of the studs,top steel flange,and other factors on the bottom plate.Both the RRS and the LRS have a nonlinear coupling relationship with the external loads and the RRS of the web’s upper edge.Under the hogging moment,the RRS of the web upper edge has a certain influence on the SCCBB distortional buckling critical moment.With increasing RRS of the web upper edge,the SCCBB critical moment increases at first and then tends to be stable.

Animal Idioms＇ Teaching in Cognitive Perspective——from the Contrastive Analysis on Chinese ＂Hu＂ Idioms and English ＂Lion＂ Idioms

In the actual idioms teaching, most students feel that idioms are difficult to comprehend, memorize and make actual application just because the overall meanings of idioms are unpredictable. Since cognitive linguistics is based on embodiment, it can change the abstract things into comparatively concrete things, which provides a shortest way to grasp these idioms. Actually, most idioms are based on conceptual metaphor and metonymy composed of conceptual mappings between the source domain and the target one. Therefore, this paper is trying to probe into the role of cognitive principles in idioms teaching, especially animal idioms from the contrastive analysis on Chinese ＂hu＂ idioms and English ＂lion＂ idioms.