Fabrication of a Cam Using Metal Matrix Composites

This work reports on studies on Al-SiC as a possible alternative material for a cam. Powder metal composite cams when mounted on hollow shafts provide a high strength to weight ratio. The coefficient of thermal expansion is also low. A mixture of four different compositions (10, 20, 25, 30 wt %) of SiC powder were prepared and mixed with A1 powders. Cams were fabricated using cold isostatic compaction and subsequent sintering. A die was also fabricated to cast the cams. The various properties of fabricated composite cams, namely, compressive strength, hardness, density, and surface roughness were measured, and their variation with reinforcement content was studied.     

Characterization & evaluation of Al7075 MMCs reinforced with ceramic particulates and influence of age hardening on their tensile behavior

Aluminium has a massive demand in the areas of automobile, aerospace and diverse engineering applications in order to furnish the requirement in those fields. But this technological evolution needs something more than aluminium. Materialogists are struggling hard to find out a material which owns sound mechanical and thermal properties and also superior than aluminium in each extent. Metal matrix composite (MMC) is a solution. Generally, metal matrix composites contain a low density material, i.e. aluminium or magnesium, reinforced with fibers or particulate of a ceramic material, i.e. silicon carbide or graphite. They show greater specific strength, high stiffness, elevated operating temperature, and superior wear resistance, along with the possibility to customize these properties for a specific use. In this study, Al 7075 is taken as a base matrix material, whereas ceramic materials like SiC, Al₂O₃, B4C and TiB₂ are used as reinforcements. There are different methods available for fabricating metal matrix composite materials and in this work, stir casting technique, which is a liquid state process, is used. Four different MMC specimens were produced with 15 % SiC, 15 % Al₂O₃, 15 % B4C and 15 % TiB₂. Mechanical properties i.e. tensile strength, hardness, and impact strength were studied for the prepared specimens. The results were charted and presented graphically to describe these materials characteristics.     

CDM potential of bagasse cogeneration in India

 So far, the cumulative capacity of renewable energy systems such as bagasse cogeneration in India is far below their theoretical potential despite government subsidy programmes. One of the major barriers is the high investment cost of these systems. The Clean Development Mechanism (CDM) provides industrialized countries with an incentive to invest in emission reduction projects in developing countries to achieve a reduction in CO₂ emissions at lowest cost that also promotes sustainable development in the host country. Bagasse cogeneration projects could be of interest under the CDM because they directly displace greenhouse gas emissions while contributing to sustainable rural development.     

Characterization and modeling of hot carrier injection in LDMOS for L-band radar application

This paper reports a methodology to correlate Hot Carrier Injection (HCI) degradation mechanism and electrical figures of merit on Lateral-Diffused Metal-Oxide-Semiconductor (LDMOS) transistor. This method is based on RF life test in radar operating conditions coupled to a high drain voltage in order to make visible HCI degradation. We propose drain current modeling vs. time based on a simple extraction procedure. The electron density trapped in the oxide is extracted from hot carrier induced series resistance enhancement model (HISREM - i.e. ΔR_d model). From this methodology, the degradation of RF-LDMOS due to HCI is quantified and could be simulated with EDA.     

汽车安全系统中的摄像头技术

在上世纪60年代,汽车业将注意力转向寻找能够保证驾驶者和乘客安全的创新方法。结果如何呢?出现了缓冲方向盘和仪表板、座椅安全带,以及其后的安全气囊和电子稳定性控制系统。自那时起,汽车工程师便一     

Design of 84 GHz 500 kW Gyrotron for Technological Millimeter Wave Applications

In this paper, the design and the numerical simulation of the 84 GHz, 500 kW gyrotron at first harmonic operation for technological applications is described. The operating mode of the gyrotron is TE_{10, 4}. Various in-house developed and commercially available computer codes are used for the design purpose. The triode-type magnetron injection gun with the accelerating voltage 70-kV, the beam current 10-A and the maximum transverse velocity spread less than 5% is designed. The preliminary design is obtained by using some trade-off equations. The mode selection, the cold cavity and the beam-wave interaction analysis are discussed for the design of weakly tapered open resonator type of the interaction cavity. The parametric analysis of the interaction cavity and the electron gun is also presented.     

Microwave-Triggered Thermo-Responsive Shape Memory Polymer (Polyurethane)/GNPS/MWCNTS Composites

Strength of Materials - The work reported herein, analysis of microwave irradiations triggered thermo-responsive shape memory polyurethane (PU)/Graphene nanoplatelets (GNPs)/Multiwalled Carbone...     

Numerical Simulation of a Double-anode Magnetron Injection Gun for 110 GHz, 1 MW Gyrotron

A 40 A double-anode magnetron injection gun for a 1 MW, 110 GHz gyrotron has been designed. The preliminary design has been obtained by using some trade-off equations. The electron beam analysis has been performed by using the commercially available code EGUN and the in-house developed code MIGANS. The operating mode of the gyrotron is TE_22,6 and it is operated in the fundamental harmonic. The electron beam with a low transverse velocity spread (db _^max = 2.26% \delta {\beta_{ \bot \max }} = 2.26\% ) and the transverse-to-axial velocity ratio of the electron beam (α) = 1.37 is obtained. The simulated results of the MIG obtained with the EGUN code have been validated with another trajectory code TRAK. The results on the design output parameters obtained by both the codes are in good agreement. The sensitivity analysis has been carried out by changing the different gun parameters to decide the fabrication tolerance.     

Centrosome defects and genetic instability in malignant tumors

Genetic instability is a common feature of many human cancers. This condition is frequently characterized by an abnormal number of chromosomes, although little is known about the mechanism that generates this altered genetic state. One possibility is that chromosomes are missegregated during mitosis due to the assembly of dysfunctional mitotic spindles. Because centrosomes are involved in spindle assembly, they could contribute to chromosome missegregation through the organization of aberrant spindles. As an initial test of this idea, we examined malignant tumors for centrosome abnormalities using antibodies to the centrosome protein pericentrin. We found that centrosomes in nearly all tumors and tumor-derived cell lines were atypical in shape, size, and composition and were often present in multiple copies. In addition, virtually all pericentrin-staining structures in tumor cells nucleated microtubules, and they participated in formation of disorganized mitotic spindles, upon which chromosomes were missegregated. All tumor cell lines had both centrosome defects and abnormal chromosome numbers, whereas neither was observed in nontumor cells. These results indicate that centrosome defects are a common feature of malignant tumors and suggest that they may contribute to genetic instability in cancer.     

Postmortem studies in schizophrenia

The past decade has seen renewed interest in the neuropathology of schizophrenia. The advent of new postmortem techniques and functional imaging, along with a greater understanding of the neuropsychology of schizophrenia, have provided many new clues to the nature of the underlying brain dysfunction in this disorder. There has also been a greater understanding of the presence of severe cognitive dysfunction among many elderly persons with schizophrenia. In this article, a series of investigations are described that seek to answer basic questions about the neuropathology of schizophrenia, in particular as it pertains to cognitive impairment. The first study describes neuropathological findings in 100 consecutively autopsied persons with schizophrenia, the majority of whom had had detailed antemortem assessments. Results from this first study prompted the conclusion that schizophrenia is not characterized by classical, histologically identifiable neuropathology. Moreover, most cases of dementia in schizophrenia are probably not the result of neuropathologically identifiable dementing illnesses. The next four studies examined chemical markers that are altered in Alzheimer's disease and some other dementing conditions and have also been suggested to be abnormal in schizophrenia: choline acetyltransferase, catecholamines and indolamines, neuropeptides, and synaptic proteins. Schizophrenia cases as a group did not show a cholinergic deficit; nor did they differ from elderly comparison cases with respect to cortical catecholamines and indolamines. Among the schizophrenia cases, however, cognitive impairment was negatively correlated with choline acetyltransferase activity. Those with cognitive impairment showed evidence of cortical noradrenergic and serotonergic deficits. Neuropeptide deficits were also present in schizophrenia, but their pattern differed from that seen in Alzheimer's disease. Increased synaptic protein activity was found in the cingulate cortex of persons with schizophrenia, and this activity was correlated with schizophrenia symptoms. From this second series of studies, it was concluded that some biological measures in schizophrenia may be related to cognitive impairment (e.g., cortical amines), whereas others may be related to diagnosis (e.g., neuropeptide deficits). In addition, synaptic organization may correlate with schizophrenia symptoms.