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1.
Field R. D. Hartwig K. T. Necker C. T. Bingert J. F. Agnew S. R. 《Metallurgical and Materials Transactions A》2002,33(13):965-972
The equal-channel angular extrusion (ECAE) technique has been applied to a powder metallurgy (P/M) source Be alloy. Extrusions
have been successfully completed on Ni-canned billets of Be at approximately 425°C. No cracking was observed in the billets,
and significant grain refinement was achieved. In this article, microstructural features and dislocation structures are discussed
for a singlepass extrusion, including evidence of <c> and <c+a> dislocations. Significant crystallographic texture developed during ECAE, which is discussed in terms of this unique deformation
processing technique and the underlying physical processes which sustain the deformation.
S.R. AGNEW, formerly with the Oak Ridge National Laboratory, Oak Ridge, TN 37831-6115
This article is based on a presentation made in the symposium entitled “Defect Properties and Mechanical Behavior of HCP Metals
and Alloys” at the TMS Annual Meeting, February 11–15, 2001, in New Orleans, Louisiana, under the auspices of the following
ASM committees: Materials Science Critical Technology Sector, Structural Materials Division, Electronic, Magnetic & Photonic
Materials Division, Chemistry & Physics of Materials Committee, Joint Nuclear Materials Committee, and Titanium Committee. 相似文献
2.
F Davodeau MA Peyrat A Necker R Dominici F Blanchard C Leget J Gaschet P Costa Y Jacques A Godard H Vie A Poggi F Romagné M Bonneville 《Canadian Metallurgical Quarterly》1997,158(12):5603-5611
Several studies have demonstrated the existence of a murine NK1.1+ alphabeta T cell subset expressing V alpha14+ TCR alpha-chains with highly conserved invariant junctional sequences and able to secrete Th2 cytokines when exposed to CD1+ stimulator cells. In humans, alphabeta T cells carrying invariant V alpha24+ TCR alpha-chains highly homologous to those expressed by murine NK1.1 cells have been recently described. Here we show that these cells (referred to as V alpha24inv T cells) and murine NK1.1+ alphabeta T cells resemble each other in several ways. First, like their murine counterparts, T cells expressing high levels of V alpha24inv TCRs can be either CD4- CD8- double negative (DN) or CD4+, but they never express heterodimeric CD8 molecules. Second, most V alpha24inv T cells are brightly stained by NKRP1-specific mAb but not by mAb directed against other type II transmembrane proteins of the NK complex. Third, DN and particularly CD4+ V alpha24inv T cells are greatly enriched for IL-4 producers. The concomitant expression of highly conserved TCRs of a particular set of NK markers and of Th2 cytokines in human and murine alphabeta T cells suggests a coordinate acquisition of these phenotypic and functional properties. Furthermore, the relatively high frequency of human V alpha24inv T cells, which are presently shown to represent on average 1/500 PBL, and the high interindividual variations of the size of this cell subset under physiologic conditions go for a major role played by alphabeta T cells carrying invariant TCR in a large array of immune responses. 相似文献
3.
Marc C. Necker 《Mobile Networks and Applications》2009,14(4):539-550
The currently emerging 802.16e (WiMAX) and 3GPP Long Term Evolution (LTE) cellular systems are based on Orthogonal Frequency
Division Multiple Access (OFDMA). OFDMA suffers from heavy inter-cell interference if neighboring base stations use the same
frequency range. One approach to solve this issue is the application of beamforming antennas in combination with interference
coordination (IFCO) mechanisms between base stations. In this paper, we trace the problem of IFCO back to the graph coloring
problem and investigate the achievable resource utilization of the interference coordinated system. We develop a heuristic
that allows the combination of arbitrary scheduling algorithms with the IFCO mechanism. This allows an efficient utilization
of the radio system’s frequency resources while still obeying scheduling constraints, such as Quality of Service requirements.
Finally, we study the tradeoff between fairness and the total system throughput.
相似文献
Marc C. NeckerEmail: |
4.
Xianping Wu Surya R. Kalidindi Carl Necker Ayman A. Salem 《Metallurgical and Materials Transactions A》2008,39(12):3046-3054
5.
A new two-dimensional blind channel estimation scheme for coherent detection of orthogonal frequency-division multiplexing (OFDM) signals in a mobile environment is presented. The channel estimation is based on the a posteriori probability (APP) calculation algorithm. The time-variant channel transfer function is completely recovered without phase ambiguity with no need for any pilot or reference symbols, thus maximizing the spectral efficiency of the underlying OFDM system. The phase ambiguity problem is solved by using a 4-QAM (quadrature amplitude modulation) scheme with asymmetrical arrangement. The results clearly indicate that totally blind channel estimation is possible for virtually any realistic time-variant mobile channel. 相似文献
6.
I. J. Beyerlein R. D. Field K. T. Hartwig C. T. Necker 《Journal of Materials Science》2008,43(23-24):7465-7473
Texture development and substructure evolution are described for pure beryllium given two-pass equal channel angular extrusion (ECAE) processing following routes A and C. These routes impose different strain paths between the first and second passes—the former cross-shearing and the latter reversal. Polycrystal calculations that are in good agreement with the texture measurements suggest that basal slip and, secondly, prismatic slip are operative in both passes of both routes. Multi scale polycrystal modeling is shown to effectively predict texture evolution to strains of two caused by both ECAE processing routes. Shear-like deformation textures observed in the second pass of route C are explained by differences in deformation characteristics between the first and second passes. 相似文献
7.
Interference Coordination in Cellular OFDMA Networks 总被引:1,自引:0,他引:1
Orthogonal frequency division multiple access is the basis for several emerging mobile communication systems. Prominent examples are the 3GPP Long Term Evolution as the successor of UMTS high-speed packet access and the IEEE 802.16 system, advanced by the WiMAX forum. On a system level, OFDMA is basically a combination of time and frequency division multiple access. In cellular TDM/FDM systems, inter-cell interference is a major issue that traditionally has been solved by avoiding the use of the same frequency bands in adjacent cells. However, this solution incurs a waste of precious frequency resources. An attractive alternative is the use of beamforming antennas in combination with interference coordination mechanisms, where the transmission of adjacent base stations is coordinated to minimize inter-cell interference. Interference coordination is an important aspect of the system level, which influences many other issues, such as network planning or scheduling mechanisms. In this article, we give an overview of interference coordination as it would apply, for example, to IEEE 802.16e and review the relevant literature. We also discuss and compare interference coordination algorithms, which can be based either on global system knowledge or purely on local system knowledge. 相似文献
8.
Analysis of steam and hydrogen distributions with PAR mitigation in NPP containments 总被引:1,自引:0,他引:1
P. Royl H. Rochholz W. Breitung J. R. Travis G. Necker 《Nuclear Engineering and Design》2000,202(2-3)
The 3-D-field code, GASFLOW is a joint development of Forschungszentrum Karlsruhe and Los Alamos National Laboratory for the simulation of steam/hydrogen distribution and combustion in complex nuclear reactor containment geometries. GASFLOW gives a solution of the compressible 3-D Navier–Stokes equations and has been validated by analysing experiments that simulate the relevant aspects and integral sequences of such accidents. The 3-D GASFLOW simulations cover significant problem times and define a new state-of-the art in containment simulations that goes beyond the current simulation technique with lumped-parameter models. The newly released and validated version, GASFLOW 2.1 has been applied in mechanistic 3-D analyzes of steam/hydrogen distributions under severe accident conditions with mitigation involving a large number of catalytic recombiners at various locations in two types of PWR containments of German design. This contribution describes the developed 3-D containment models, the applied concept of recombiner positioning, and it discusses the calculated results in relation to the applied source term, which was the same in both containments. The investigated scenario was a hypothetical core melt accident beyond the design limit from a large-break loss of coolant accident (LOCA) at a low release location for steam and hydrogen from a rupture of the surge line to the pressurizer (surge-line LOCA). It covers the in-vessel phase only with 7000 s problem time. The contribution identifies the principal mechanisms that determine the hydrogen mixing in these two containments, and it shows generic differences to similar simulations performed with lumped-parameter codes that represent the containment by control volumes interconnected through 1-D flow paths. The analyzed mitigation concept with catalytic recombiners of the Siemens and NIS type is an effective measure to prevent the formation of burnable mixtures during the ongoing slow deinertization process after the hydrogen release and has recently been applied in backfitting the operational German Konvoi-type PWR plants with passive autocatalytic recombiners (PAR). 相似文献
9.
In birds, the output system of the cerebellum, the cerebellar nuclei, has not yet been studied electrophysiologically. Recordings from nuclear cells during electrical stimulation of the radial nerve revealed a uniform type of response consisting of an initial inhibition followed by a clear cut excitation. Responses with an initial excitation were rare. Response patterns and latencies suggest an input from Purkinje cells of the cerebellar cortex and a lack of collateral input from spinocerebellar pathways. This points to a fundamental difference from cerebellar nuclear cells in mammals, in which collateral input provides a prominent excitatory response under comparable experimental conditions. 相似文献
10.
Equal-channel angular extrusion of beryllium 总被引:1,自引:0,他引:1
R. D. Field C. T. Necker K. T. Hartwig J. F. Bingert S. R. Agnew 《Metallurgical and Materials Transactions A》2002,33(3):965-972
The equal-channel angular extrusion (ECAE) technique has been applied to a powder metallurgy (P/M) source Be alloy. Extrusions
have been successfully completed on Ni-canned billets of Be at approximately 425 °C. No cracking was observed in the billets,
and significant grain refinement was achieved. In this article, microstructural features and dislocation structures are discussed
for a single-pass extrusion, including evidence of 〈c〉 and 〈c+a〉 dislocations. Significant crystallographic texture developed during ECAE, which is discussed in terms of this unique deformation
processing technique and the underlying physical processes which sustain the deformation.
This article is based on a presentation made in the symposium entitled “Defect Properties and Mechanical Behavior of HCP Metals
and Alloys” at the TMS Annual Meeting, February 11–15, 2001, in New Orleans, Louisiana, under the auspices of the following
ASM committees: Materials Science Critical Technology Sector, Structural Materials Division, Electronic, Magnetic & Photonic
Materials Division, Chemistry & Physics of Materials Committee, Joint Nuclear Materials Committee, and Titanium Committee. 相似文献