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Time-dependent Maxwell's equations in differential and conservation form are solved numerically, and field components are computed for scattering and penetration involving arbitrary 2-D objects using upwind computational fluid dynamics (CFD) based techniques. The Lax-Wendroff explicit scheme, which is second-order accurate in time and space, is used. The object and surrounding space are divided into a number of zones, and the Cartesian coordinate system is converted to local body-fitted coordinate systems in those zones, to handle more conveniently arbitrary geometry cross sections as well as to facilitate implementation of the boundary conditions. The method of characteristic subpath integration, better known as the Riemann solver in CFD, is then applied to the transformed Maxwell's equations, yielding the solution for the field components in the time domain. Both steady-state and transient fields can be computed. A fast Fourier transform is used to obtain frequency-domain information. Both radar cross sections and near field distributions are presented for some canonical geometries 相似文献
104.
A simple circuit modification is presented for reducing the output jitter of the self-sustaining monostable multivibrator clock recovery circuit. Jitter is reduced by preventing the monostable multivibrator from being triggered by pulses that arrive early. Experimental results in a fibre-optic system employing the Petrovic code show that, with this modification, the jitter variance can easily be reduced by a factor of 6. 相似文献
105.
Dr. Alexander A. Aksenov Christian E. Sandrock Dr. Weixiang Zhao Shankar Sankaran Michael Schivo Richart Harper Dr. Carol J. Cardona Dr. Zheng Xing Dr. Cristina E. Davis 《Chembiochem : a European journal of chemical biology》2014,15(7):1040-1048
Volatile organic compounds (VOCs) emanating from humans have the potential to revolutionize non‐invasive diagnostics. Yet, little is known about how these compounds are generated by complex biological systems, and even less is known about how these compounds are reflective of a particular physiological state. In this proof‐of‐concept study, we examined VOCs produced directly at the cellular level from B lymphoblastoid cells upon infection with three live influenza virus subtypes: H9N2 (avian), H6N2 (avian), and H1N1 (human). Using a single cell line helped to alleviate some of the complexity and variability when studying VOC production by an entire organism, and it allowed us to discern marked differences in VOC production upon infection of the cells. The patterns of VOCs produced in response to infection were unique for each virus subtype, while several other non‐specific VOCs were produced after infections with all three strains. Also, there was a specific time course of VOC release post infection. Among emitted VOCs, production of esters and other oxygenated compounds was particularly notable, and these may be attributed to increased oxidative stress resulting from infection. Elucidating VOC signatures that result from the host cells response to infection may yield an avenue for non‐invasive diagnostics and therapy of influenza and other viral infections. 相似文献
106.
Hemant Ramaswami Raj Shankar Shaw Sam Anand 《The International Journal of Advanced Manufacturing Technology》2011,53(9-12):963-977
Selection of the optimal set of cutting tools is one of the most important steps in process planning for 2.5-D pocket machining. Conventional CAM software requires considerable input from the user in terms of selection of tool sizes and machining strategy. This trial-and-error procedure to determine the optimal process sequence tends to generate conservative and suboptimal results. This paper presents a methodology for optimal selection of a sequence of tools to minimize the total time required to end mill a non-convex polygonal pocket with or without islands using the staircase milling strategy. The algorithm decomposes the pocket geometry into convex regions and mills each region independently by selecting a sequence of tools based on the accessibility of various tools to the region. Strategies have been developed for machining the main pass and the subsequent leftover areas in order to obtain the final pocket geometry. Subsequently, the machining times for each decomposed area are aggregated while accounting for the need to use multiple passes, non-cutting time, and the tool change time. A dynamic programming approach is used to determine the optimal set of tools which minimizes the total processing time. The effect of varying the non-cutting speed and tool change time on the tool path length and number of tool selection is studied. 相似文献
107.
The present paper investigates the effect of fibre content and alkali treatment on tensile, flexural and impact properties of unidirectional Roystonea regia natural-fibre-reinforced epoxy composites which are partially biodegradable. The reinforcement Roystonea regia (royal palm) fibre was collected from the foliage of locally available royal palm tree through the process of water retting and mechanical extraction. The poor adhesion between fibre and matrix is commonly encountered problem in natural-fibre-reinforced composites. To overcome this problem, specific physical and chemical treatments were suggested for surface modification of fibres by investigators. Alkali treatment is one of the simple and effective surface modification techniques which is widely used in natural fibre composites. In the present study both untreated and alkali-treated fibres were used as reinforcement in Roystonea regia epoxy composites and the tensile, flexural and impact properties were determined at different fibre contents. The alkali treatment found to be effective in improving the tensile and flexural properties while the impact strength decreased. 相似文献
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Ruptures in wet-steam and single-phase water lines at fossil and nuclear plants due to erosion/corrosion of of the inside surface have resulted in comprehensive measurement of wall thickness of components prone to failure. The large number of components to be inspected as well as the required resolution to make that inspection require effective management of the large amounts of ultrasonic testing data. Recognizing this need, Northern States Power (NSP) Company initiated compilation and organization of a database which contained inspection history, component type and history, flow conditions in the component along with detailed wall thickness measurements. The database was organized using a commercially available personal computer (PC)-based database management software package.This paper discusses the background of erosion/corrosion (E/C) damage at U.S. utilities; the industry response; NDE approaches to wall thinning examination; and practical techniques used to analyze wall thickness data from components and compare data between inspection intervals. The data were compiled from nuclear and fossil units. 相似文献
110.
D Daphna-Iken DB Shankar A Lawshé DM Ornitz GM Shackleford CA MacArthur 《Canadian Metallurgical Quarterly》1998,17(21):2711-2717
Prior studies have identified Fibroblast Growth Factor-8 (Fgf8) as a possible proto-oncogene in mouse mammary tumorigenesis. We now report on the generation of two types of Fgf8 transgenic mice that each utilize the mouse mammary tumor virus (MMTV) promoter. The first transgene (MMTV-Fgf8b) results in the overexpression of the FGF8b isoform exclusively. Male and female MMTV-Fgf8b transgenic mice are viable and fertile. RNA for FGF8b is detected in mammary gland and salivary gland tissues of transgenic mice by Northern blot analysis. Nearly 85% of breeding transgenic female mice developed mammary lobular adenocarcinomas by 12 months of age, while no tumors developed in non-transgenic littermates. Salivary gland tumors occurred in some animals, always in association with mammary tumors. Several MMTV-Fgf8b transgenic mice had lung metastases at necropsy. The second transgene (MMTV-Fgf8) uses the entire Fgf8 gene and potentially encodes all FGF8 isoforms. Fgf8 is expressed by this transgene in several tissues in addition to those described above, notably the ovaries. The two MMTV-Fgf8 founders developed mammary ductal adenocarcinomas at five and eight months of age, and both displayed ovarian stromal hyperplasia. The founders expressing either transgene did not successfully nurse their pups. These results demonstrate that production of FGF8b, and possibly other FGF8 isoforms, in the mammary and salivary glands contributes to oncogenesis, and that ovarian expression results in stromal hyperplasia. 相似文献