Reversing histone methylation

Histones package DNA, and post-translational modifications of histones can regulate access to DNA. Until recently, histone methylation-unlike all other histone modifications-was considered a permanent mark. The discovery of enzymes that reverse the methylation of lysines and arginines challenges our current thinking on the unique nature of histone methylation, and substantially increases the complexity of histone modification pathways.     

Reconstruction of an enzyme by domain substitution effectively switches substrate specificity

The polar domains of the two transcarbamoylases, aspartate transcarbamoylase (ATCase) and ornithine transcarbamoylase, (OTCase) from Escherichia coli bind the common substrate carbamoyl phosphate and share extensive amino-acid sequence homology. The equatorial domains of the two enzymes differ in their substrate specificity (ATCase binds aspartate, OTCase binds ornithine) and have decreased sequence identity. While addressing the conservation of specific protein interactions during the evolution of these enzymes, we were able to switch one of their amino-acid-specific equatorial domains to produce a viable chimaeric enzyme. This was achieved by the in vitro fusion of DNA encoding the polar domain of OTCase to DNA encoding the equatorial domain of ATCase. The resulting gene fusion successfully transformed an argI-pyrB deletion strain of E. coli to pyrimidine prototrophy, giving rise to Pyr+ transformants that expressed ATCase but not OTCase activity. The formation of this active chimaeric enzyme shows that by exchanging protein domains between two functionally divergent enzymes we have achieved a switching in substrate specificity.     

可逆式轧机几种电气控制方法

冷轧可逆式轧机在轧制过程中主要用到的几种关于传动控制器的原理及对这几种控制方式的详细介绍,其中包括了速度控制原理控制器的设计,△V的控制原理,张力控制原理,直接张力控制,间接张力控制,加速转矩控制以及钢卷内径计算的方法。     

浅谈逆向工程的应用

在当今竞争日趋激烈的产品市场中,能否快速生产出符合市场需求的产品就成为企业成败的关键,但往往都会遇到这样的难题,就是客户给你的只是一个实物样品或手板模型,在没有图纸及任何数据的情况下,工程技术人员无法得到其准确的尺寸,这给企业的生产带来了很大的困难,至少会拖延交货时间．文章从逆向工程的角度阐述了类似问题的解决方法。     

变速箱倒挡开关故障分析

文中对变速箱倒挡开关的工作原理进行介绍,同时对比较常见的故障模式进行分析,找到可行的改进措施,为今后应对变速箱倒挡问题实际操作提供了相关参考依据。     

Reversing pathological neural activity using targeted plasticity

Brain changes in response to nerve damage or cochlear trauma can generate pathological neural activity that is believed to be responsible for many types of chronic pain and tinnitus. Several studies have reported that the severity of chronic pain and tinnitus is correlated with the degree of map reorganization in somatosensory and auditory cortex, respectively. Direct electrical or transcranial magnetic stimulation of sensory cortex can temporarily disrupt these phantom sensations. However, there is as yet no direct evidence for a causal role of plasticity in the generation of pain or tinnitus. Here we report evidence that reversing the brain changes responsible can eliminate the perceptual impairment in an animal model of noise-induced tinnitus. Exposure to intense noise degrades the frequency tuning of auditory cortex neurons and increases cortical synchronization. Repeatedly pairing tones with brief pulses of vagus nerve stimulation completely eliminated the physiological and behavioural correlates of tinnitus in noise-exposed rats. These improvements persisted for weeks after the end of therapy. This method for restoring neural activity to normal may be applicable to a variety of neurological disorders.     

A hybrid recognition sequence in a recombinant restriction enzyme and the evolution of DNA sequence specificity

Early attempts to generate new restriction specificities by recombination between allelic restriction-modification systems have been unsuccessful. Bullas et al. succeeded in isolating a new specificity, SQ, in Salmonella that they interpreted as being the result of a recombination event between the parental strains, Salmonella typhimurium and S. postdam, which encode the SB and SP restriction systems, respectively. This interpretation has recently been confirmed by DNA heteroduplex studies with the SB, SP and SQ structural genes. We have determined the DNA sequences recognized by the SB and SP enzymes and found that, like all type I restriction sequences, they are split into two specific domains by a spacer of nonspecific sequence that, for both SB and SP, is 6 base pairs (bp) long. We have now determined the sequence recognized by the recombinant SQ enzyme and find that it is a hybrid between the SB and SP sequences, containing one specific domain from each parental strain. This result implies that each of the two specific domains is recognized by a physically distinct part of the enzyme.     

立柱式双向旋转钢闸门静力数值分析

基于大型有限元分析软件ANSYS,对立柱式双向旋转钢闸门进行了建模和分析,通过静力分析获得了闸门不同工况下的应力和应变的分布规律,对闸门的强度和刚度进行了校核.结果表明,闸门的强度和刚度满足设计要求,闸门整体结构设计合理,所作研究对同类闸门结构的设计计算具有一定的参考价值.     

倒车雷达预警系统的设计和实现

倒车雷达能告知汽车驾驶员车尾障碍物的情况,帮助驾驶员扫除视野死角,提高安全性。现在生产的中高档小轿车,大多数配有倒车雷达。而很多经济型车没有配置倒车雷达,所以设计一个成本低、性能好的倒车雷达系统就很有必要了。文中介绍基于单片机控制的倒车雷达系统,该系统采用通用型单片机作为控制电路,方便系统功能扩展。系统电路主要采用集成器件构成,外围元件少,电路简洁、调试方便、成本低,利于商品化生产。     

倒车防撞报警系统的设计

基于超声波测距原理,介绍了一种以单片机AT89C51为主控制器的倒车防撞报警系统。此系统在汽车倒车时自动启动,由装置于车尾保险杠上的探头发送超声波,遇到障碍物产生回波信号,传感器接收到回波信号后经控制器进行数据处理,判断出障碍物的位置,达到设定的距离时显示并播报。为了减小测距的误差在数据处理部分还采用了温度补偿和最小二乘法来修正距离。实验表明该倒车系统在30 cm~500 cm范围内可实现准确测距,具有可靠性较高、外围电路简单、实用性强等优点。     

依那普利逆转心室重构的研究进展

详述了血管紧张转化酶抑制剂———依那普利（enalapril,Ena）临床用于治疗高血压、心肌梗死、心力衰竭、心肌缺血和脑缺血等疾病的现状,并发现Ena具有逆转高血压、心肌缺血、心肌炎、心肌梗死等引起的心室重构（ventricular remodeling,VR）作用,同时对Ena逆转VR及作用机制进行了研究.     

测量误差对照片反求精度的影响

根据拍摄的零件照片反求其三维模型,再生成二维工程图样,以取代传统零件测绘方法,其具有成本低、效率高的优点.但要使其真正成为工程实用方法,反求精度是一个重要因素.通过分析产生照片反求误差的关键因素,研究了因拍摄条件的测量误差而引起的空间坐标反求精度的计算方法,提出了在影像反求过程中,应在照片采集阶段设计专门的标定相机与目标物相对位置的装置,以便从源头上控制反求误差.     

空调器换向过程动态特性模拟

采用控制容积法建立四通换向阀动态模型 ,并将其接入空调器动态仿真模型 ,从而建立起研究空调器换向过程动态特性的仿真平台 .通过仿真研究 ,分析了换向过程中制冷系统及阀体压力 ,运动部件位移、速度、加速度等参数的变化过程 ,得出了影响换向可靠性的关键因素 .     

四通换向阀对家用热泵空调系统性能的影响

四通换向阀对热泵系统的热性能和效率会产生一定的影响．只要热泵系统处于运行状态,该性能影响就一直存在．通过搭建的实验台,测定了家用分体式热泵型空调器中四通换向阀的传热、压降和制冷剂泄漏损失的具体值,得出了相应的特性系数;建立了包括四通换向阀在内的热泵系统稳态仿真模型,并经实验验证．通过实例,定量分析了四通换向阀的各种损失对热泵系统热性能和ＣＯＰ所产生的影响．结果表明,四通换向阀使家用热泵系统的ＣＯＰ下降了２．５％左右．通过改进四通换向阀的特性,可减少其对热泵性能的影响,有利于热泵系统的节能．     

Reversing EphB2 depletion rescues cognitive functions in Alzheimer model

Amyloid-β oligomers may cause cognitive deficits in Alzheimer's disease by impairing neuronal NMDA-type glutamate receptors, whose function is regulated by the receptor tyrosine kinase EphB2. Here we show that amyloid-β oligomers bind to the fibronectin repeats domain of EphB2 and trigger EphB2 degradation in the proteasome. To determine the pathogenic importance of EphB2 depletions in Alzheimer's disease and related models, we used lentiviral constructs to reduce or increase neuronal expression of EphB2 in memory centres of the mouse brain. In nontransgenic mice, knockdown of EphB2 mediated by short hairpin RNA reduced NMDA receptor currents and impaired long-term potentiation in the dentate gyrus, which are important for memory formation. Increasing EphB2 expression in the dentate gyrus of human amyloid precursor protein transgenic mice reversed deficits in NMDA receptor-dependent long-term potentiation and memory impairments. Thus, depletion of EphB2 is critical in amyloid-β-induced neuronal dysfunction. Increasing EphB2 levels or function could be beneficial in Alzheimer's disease.     

基于工业相机的汽车倒车影像系统设计

汽车倒车影像系统以影像显示及语音提示告知驾驶员后方障碍物的情况,提高驾驶的方便性和安全性。为解决传统汽车倒车影像系统经常出现的黑屏、闪屏等情况,提出了一种使用工业相机搭配工控机和PLC的设计,减少了导线的使用,简化了信息的传输过程。通过实验测试验证了新型倒车影像系统的有效性,系统不仅成像稳定,而且维修检测较为简便。     

数控线切割贮丝筒换向监控技术研究

在实际生产活动中,数控线切割机床的贮丝筒换向功能失效属于数控线切割机床常见故障,贮丝筒换向功能失效,会引起加工工件报废,对数控线切割机床走丝丝杠造成损伤,严重会损坏整个机械系统.为保证生产效益,对数控线切割贮丝筒换向失效故障进行分析,提出建立于OMRON C200HE型的可编程序逻辑控制器的一种监控技术,并对这种监控技术的软件及硬件实现进行研究.实践证明,应用该监控技术可以有效实现数控线切割机床计算机控制,能够准确检测出数控线切割机床故障,保障在故障发生后机床可以正常运行,有益于实现数控线切割作业的综合效益.     

基于物体影子反求特定时空

根据物体在太阳光照射下将产生影子的自然现象,研究物体影子的形成原理,通过分析物体实形与其影子关系建立数学模型.进一步利用影子的形成原理进行逆向变换,通过Visual Basic和Visual Lisp编程实现反求算法,研制了计算机反求实验平台,实现对影子的反求,并通过实验反求实际模型,比较分析数据误差从而验证算法的有效性,最后提出了一种新的反求方法.