用瞬心法快速求四杆机构的速度

用解析法和矢量方程图解法,求四杆机构的各点速度是很容易的,但当四杆机构中有一连架杆与连杆组成的运动副为直移副时,再用解析法和矢量方程图解法求解速度就变得繁锁与困难了,为此利用数学,三心定理导出新等式求解四杆机构各点的速度,又变成十分简单、易解,这为求解四杆机构的速度带来了快捷简便的方法理论。     

平面应变镦粗问题的变分分析

应用希尔分析金属加工过程的一般方法计算了平面应变镦粗问题的载荷和自由表面的鼓形形状并将分析结果与其它理论分析结果及有关实验进行了对比．结果表明，应用希尔法所获得的结果与其它理论分析结果及实验符合较好，但结果的精度较其它理论方法没有改善．     

点的速度合成定理在牵连运动为平面运动时的应用

把作平面运动的实际刚体概念扩展成一个作平面运动的抽象质点系,以此为动系,用刚体平面运动理论来求解无载体牵连点在平面上的合成运动问题,并对此解法加以验证.     

基于等效耦合刚度的平面折展滑块机构分析

柔性铰链是实现平面折展柔顺机构运动的关键部分.如何设计得到柔度好、精度高的柔性铰链一直是柔顺机构研究的关键问题.综合考虑影响平面折展机构铰链刚度和精度特性的等效弯扭及拉压刚度,以LET铰链为例,分析在不同载荷下各个参数对弯扭与拉压等效耦合刚度的影响趋势,从而提出弯扭与拉压等效耦合刚度的概念.通过大量的实例计算和分析,推导出LET铰链弯扭与拉压等效耦合刚度的经验公式.基于等效耦合刚度经验公式,对平面折展柔顺滑块机构进行分析.应用等效耦合刚度公式与不应用等效耦合刚度公式两种情况的分析结果和有限元仿真结果表明,应用等效耦合刚度经验公式的滑块位移计算精度得到很大的提高,验证了等效耦合刚度经验公式的适用性.     

Auto CAD环境中作图法对平面连杆机构运动分析的探讨

通过对 Auto CAD软件所具备的几何精确作图功能和矢量运算功能的研究 ,探讨在 Auto CAD软件中以作图法对平面连杆机构进行运动分析的新方法 ,进一步开发 Auto CAD软件的辅助设计功能。     

Possible role(s) of neurokinins in CNS development and neurodegenerative or other disorders

The present review is an attempt to summarize the diverse literature that suggests a role for neurokinins in a variety of CNS developmental or disease processes. The role of neurokinins in (anti)nociception is well known and is the subject of other comprehensive reviews. The focus of this review is on associations that implicate substance P or other neurokinins in certain aspects of CNS development and in various neuropathologic disorders that have neurodegenerative, psychiatric or other clinical manifestations. Also included are associations related to the central control of some "peripheral" functions. The amount of and degree of evidence for neurokinin involvement in each situation vary from strong to speculative--critical analyses and commentaries on individual methodologies and studies are available from other sources. When viewed in this broad context, the information suggests intrinsic neuroprotective or neurodegenerative properties of neurokinins. It is proposed that these properties delineate a specialized area within the broader field of neurokinin research.     

Identification of a nasal nematode (Eucoleus boehmi) in greyhounds

A tri-functional in vitro evaluation has been utilized to analyze peripheral blood mononuclear cells (BMNC) from HIV-infected patients, which allows for the classification of these individuals into convenient stages, according to the number of in vitro parameters affected. The classifying functional parameters are: the mitochondrial metabolic activity of freshly isolated BMNC, measured by an MTT reduction assay, the detection of apoptosis in 72 hour cultures of these cells assessed by propidium iodide staining and dual parametric flow cytometric analysis, and their proliferative response to pokeweed mitogen. Our results indicate that HIV-infected patients at different stages of their clinical disease, can present dysfunctions in one, two or three of the above-mentioned parameters. Based on these results, patients can be classified into four newly-described stages which are Stage 0, including uninfected controls and all patients with unaffected parameters, and Stages 1, 2 and 3, including patients having one, two or all three parameters affected, respectively. This type of immunological evaluation and classification of HIV-infected patients has the potential of becoming a predictive tool in the longitudinal follow-up of their HIV infection.     

Identification and Monitoring of Modal Parameters in Aircraft Structures Using the Natural Excitation Technique (NExT) Combined with the Eigensystem Realization Algorithm (ERA)

The early detection of cracks, fatigue, corrosion, and structural failure in aging aircraft is one of the major challenges in the aircraft industry. Common inspection techniques are time consuming and hence can have strong economic implications due to aircraft downtime. As a result, during the past decade a number of methodologies have been proposed for detecting structural damage based on variations in the structure’s dynamic characteristics. This paper describes the implementation of the natural excitation technique (NExT) combined with the eigensystem realization algorithm (ERA) to determine the dynamic characteristics of a T-34A Mentor acrobatic category aircraft and a modified DC-3 cargo/transport category aircraft. In-flight acceleration data were processed using NExT-ERA to monitor the predominant natural frequencies and associated mode shapes of the aircraft for varying flight conditions. The results show the effectiveness of this modal identification methodology and the possibility of implementing it in a real-time structural health monitoring system for aircraft.     

Identification of the coding region for a second poly(A) polymerase in Escherichia coli

We had earlier identified the pcnB locus as the gene for the major Escherichia coli poly(A) polymerase (PAP I). In this report, we describe the disruption and identification of a candidate gene for a second poly(A) polymerase (PAP II) by an experimental strategy which was based on the assumption that the viability of E. coli depends on the presence of either PAP I or PAP II. The coding region thus identified is the open reading frame f310, located at about 87 min on the E. coli chromosome. The following lines of evidence support f310 as the gene for PAP II: (i) the deduced peptide encoded by f310 has a molecular weight of 36,300, similar to the molecular weight of 35,000 estimated by gel filtration of PAP II; (ii) the deduced f310 product is a relatively hydrophobic polypeptide with a pI of 9.4, consistent with the properties of partially purified PAP II; (iii) overexpression of f310 leads to the formation of inclusion bodies whose solubilization and renaturation yields poly(A) polymerase activity that corresponds to a 35-kDa protein as shown by enzyme blotting; and (iv) expression of a f310 fusion construct with hexahistidine at the N-terminus of the coding region allowed purification of a poly(A) polymerase fraction whose major component is a 36-kDa protein. E. coli PAP II has no significant sequence homology either to PAP I or to the viral and eukaryotic poly(A) polymerases, suggesting that the bacterial poly(A) polymerases have evolved independently. An interesting feature of the PAP II sequence is the presence of sets of two paired cysteine and histidine residues that resemble the RNA binding motifs seen in some other proteins.     

T-cell recognition of a cross-reactive antigen(s) in erythrocyte stages of Plasmodium falciparum and Plasmodium yoelii: inhibition of parasitemia by this antigen(s)

In the current study, we investigated the presence of a cross-reactive antigen(s) in the erythrocyte stage from Plasmodium yoelii (265 BY strain) and Plasmodium falciparum through recognition by T cells primed in vivo with antigens from each of these parasites. BALB/c mice are naturally resistant to P. falciparum but are susceptible to P. yoelii infection. Mice that had recovered from P. yoelii primary infection became resistant to a second infection. A higher in vitro proliferative response to a soluble blood stage preparation of P. falciparum was observed in splenic cells from immune animals than in those from mice with a patent P. yoelii infection. The antigen-induced proliferative response was enhanced when animals were exposed to a secondary infection. Animals exposed to a challenge infection were treated with anti-CD4 or anti-CD8 monoclonal antibodies to deplete the corresponding subset of T cells. There was a marked diminution in P. falciparum antigen-induced proliferative response in the total splenic cell populations from CD8-depleted but not from CD4-depleted mice. In CD8-depleted and nondepleted animals, the antigen-induced proliferation in the total cell populations was markedly lower than in the T-cell-rich populations, indicating inhibitory activities of B cells and/or macrophages. There was no such difference in the stimulation between total and T-enriched cell populations from CD4-depleted animals. Flow cytometry analysis demonstrated the presence of an almost equal percentage of CD8+ (59.6%) and CD4+ (64%) T cells in the spleen preparations following in vivo depletion of CD4- and CD8-bearing T cells, respectively. When cultured with P. yoelii blood stage antigen, splenocytes from animals immunized with P. falciparum antigen displayed a significant proliferative response which was markedly diminished by treatment with anti-Thy-1.2 antibody plus complement. Animals immunized with P. falciparum antigen and then challenged with P. yoelii blood stage parasites displayed about a 50% lower level of parasitemia. These results demonstrated the existence of a cross-reactive antigen(s) between a murine and a human Plasmodium species, as determined from both in vivo and in vitro biological assays, and indicated the reactivity of mainly CD8+ T cells with this antigen.     

A Feasibility Study on Manufacturing of Functionally Graded Structures Using SiC Ceramic Powder in a Steel‐Based Matrix by Gas Tungsten Arc Welding (GTAW)

The paper presents a feasibility study on application of the gas tungsten arc welding (GTAW) process to obtain metal composite functional coating for advanced tribological application. Silicon carbide (SiC) particles in the form of powder was added to a weld pool in autogenous mode as well as with an additional filler wire. Powder feeding was carried out at different angles and with varying separation distance from the welding torch. The metallurgical characterization of the cladded structure was carried out using optical as well as scanning electron microscopy (SEM). Energy dispersive X‐ray spectroscopy (EDS) was performed to analyze the composition of the deposited weld metal. It has been observed that due to low SiC density it was difficult for particles to penetrate the weld pool. Also the added SiC was found to be dissociated into Si and carbon (C) and the large amount of dissolved C in the weld pool resulted in formation of graphite phases.