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71.
The capacity-achieving coding scheme for the multiple-input multiple-output (MIMO) broadcast channel is dirty-paper coding.
With this type of transmission scheme the optimal number of active users that receive data and the optimal power allocation
strategy are highly dependent on the structure of the channel matrix and on the total transmit power available. In the context
of packet-data access with adaptive transmission where mobile users are equipped with a single receive antenna and the base
station has multiple transmit antennas, we study the optimal number of active users and the optimal power allocation. In the
particular case of two transmit antennas, we prove that the optimal number of active users can be a non-monotonic function
of the total transmit power. Thus not only the number of users that should optimally be served simultaneously depends on the
user channel vectors but also on the power available at the base station transmitter. The expected complexity of optimal scheduling
algorithms is thus very high. Yet we then prove that at most as many users as the number of transmit antennas are allocated
a large amount of power asymptotically in the high-power region in order to achieve the sum-capacity. Simulations confirm
that constraining the number of active users to be no more than the number of transmit antennas incurs only a marginal loss
in spectral efficiency. Based on these observations, we propose low-complexity scheduling algorithms with sub-optimal transmission
schemes that can approach the sum-capacity of the MIMO broadcast channel by taking advantage of multiuser diversity. The suitability
of known antenna selection algorithms is also demonstrated. We consider the cases of complete and partial channel knowledge
at the transmitter. We provide simulation results to illustrate our conclusions. 相似文献
72.
Cuzner R.M. Nowak D.J. Bendre A. Oriti G. Julian A.L. 《Industry Applications, IEEE Transactions on》2007,43(5):1284-1294
A mathematical model that Is developed for a generalized drive system, including common-mode passive and active elements, is used to explore the issues of paralleling soft-switched resonant dc-link drive systems. Differences between the modulation pattern for each drive system cause common voltage disturbances, which lead to significant circulating currents between the drive systems. Control methods for actively compensating for common-mode circulating currents or reducing the common- mode voltage disturbances are investigated. Practical modifications to the drive system controls are implemented to reduce the circulating currents between paralleled systems. 相似文献
73.
Witold Charatonik 《国际计算机数学杂志》2013,90(6):1150-1170
There are many decision problems in automata theory (including membership, emptiness, inclusion and universality problems) that are NP-hard for some classes of tree automata (TA). The study of their parameterized complexity allows us to find new bounds of their nonpolynomial time algorithmic behaviours. We present results of such a study for classical TA, rigid tree automata, TA with global equality and disequality and t-DAG automata. As parameters we consider the number of states, the cardinality of the signature, the size of the term or the t-dag and the size of the automaton. 相似文献
74.
Vanessa Kohl Oliver Drews Victor Costina Miriam Bierbaum Ahmed Jawhar Henning Roehl Christel Weiss Susanne Brendel Helga Kleiner Johanna Flach Birgit Spiess Wolfgang Seifarth Daniel Nowak Wolf-Karsten Hofmann Alice Fabarius Henning D. Popp 《International journal of molecular sciences》2021,22(11)
Non-targeted effects (NTE) of ionizing radiation may initiate myeloid neoplasms (MN). Here, protein mediators (I) in irradiated human mesenchymal stromal cells (MSC) as the NTE source, (II) in MSC conditioned supernatant and (III) in human bone marrow CD34+ cells undergoing genotoxic NTE were investigated. Healthy sublethal irradiated MSC showed significantly increased levels of reactive oxygen species. These cells responded by increasing intracellular abundance of proteins involved in proteasomal degradation, protein translation, cytoskeleton dynamics, nucleocytoplasmic shuttling, and those with antioxidant activity. Among the increased proteins were THY1 and GNA11/14, which are signaling proteins with hitherto unknown functions in the radiation response and NTE. In the corresponding MSC conditioned medium, the three chaperones GRP78, CALR, and PDIA3 were increased. Together with GPI, these were the only four altered proteins, which were associated with the observed genotoxic NTE. Healthy CD34+ cells cultured in MSC conditioned medium suffered from more than a six-fold increase in γH2AX focal staining, indicative for DNA double-strand breaks, as well as numerical and structural chromosomal aberrations within three days. At this stage, five proteins were altered, among them IQGAP1, HMGB1, and PA2G4, which are involved in malign development. In summary, our data provide novel insights into three sequential steps of genotoxic signaling from irradiated MSC to CD34+ cells, implicating that induced NTE might initiate the development of MN. 相似文献
75.
Grzegorz Nowak Włodzimierz Wróblewski Iwona Nowak 《International Journal of Heat and Mass Transfer》2012,55(17-18):4511-4520
This paper discusses the problem of blade cooling system optimization connected with conjugate heat transfer (CHT) analysis for reliable thermal field prediction within a steam cooled component. Since the full CHT solution, which involves the main flow, blade material and the coolant flow domains is computationally expensive from the point of view of optimization process, it was decided to reduce the problem by fixing the boundary conditions at the blade surface and solving the task for the interior only (both solid material and coolant). Such assumption, on one hand, makes the problem computationally feasible, and on the other, provides more reliable thermal field prediction than it used to be with the empirical relationships.The analysis involves shape optimization of internal cooling passages within an airfoil. The cooling passages are modeled with a set of four Bezier splines joined together to compose a closed contour. Each passage is fed with cooling steam of constant parameters at the inlet. In the present study the airfoil profile is taken as aerodynamically optimal. The search problem is solved with evolutionary algorithm and the final configuration is to be found among the Pareto optimal cooling candidates. 相似文献
76.
The surface tension of liquid tin of three different grades of purity (99.85, 99.96, and 99.999%) was measured by the classical
sessile drop method over the temperature range 523–1023 K, in heating and cooling regimes. The results obtained show that
the metal purity affects the values of surface tension and its temperature dependence. The highest values of surface tension
and smooth linear temperature dependence were obtained in cooling regime for tin of the highest purity. With increasing content
of impurities, both surface tension and its temperature coefficient decrease while the scatter of the data increases. The
surface tension values measured on heating regime show higher scatter, compared to those obtained in cooling regime, and the
temperature dependence of the surface tension is curvilinear rather than linear. 相似文献
77.
Wu E.Y. McKenna J.M. Lai W. Nowak E. Vayshenker A. 《Electron Device Letters, IEEE》2001,22(12):603-605
We report the effect of change of voltage acceleration on temperature dependence of oxide breakdown for ultra-thin oxides below 6 nm. The time- or charge-to-breakdown (TBD/QBD) is directly measured over a wide range of temperatures (-30°C to 200°C) for several fixed voltages using different area capacitors and long-term stress. Using extensive experimental evidence, we unequivocally demonstrate that this strong temperature dependence of oxide breakdown on ultra-thin oxides is not a thickness effect as previously suggested at least for thickness range investigated in this work. It is a consequence of two experimental facts: 1) voltage-dependent voltage acceleration and 2) temperature-independent voltage acceleration within a fixed TBD window. These results provide a coherent picture for TBD in both voltage and temperature domains for ultra-thin oxides 相似文献
78.
79.
80.
Mieczyslaw Witold Krasny 《Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment》2005,540(2-3):222-234
A method of delivering a small energy spread electron beam to the LHC interaction points is proposed. In this method, heavy ions are used as carriers of projectile electrons. Acceleration, storage and collision-stability aspects of such a hybrid beam is discussed and a new beam-cooling method is presented. This discussion is followed by a proposal of the Parasitic Ion–Electron collider at LHC (PIE@LHC). The PIE@LHC provides an opportunity, for the present LHC detectors, to enlarge the scope of their research program by including the program of electron–proton and electron–nucleus collisions with minor machine and detector investments. 相似文献