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31.
Samples of the copper-cadmium ferrite series Cd
x
Cu1–x
Fe2O4 (x=0 to 1) have been investigated by means of Mössbauer spectroscopy at 77 K. Mössbauer spectra forx=0.0 to 0.7 suggest the existence of two hyperfine fields, one due to the Fe3+ tetrahedral ions (A-sites) and the other due to the Fe3+ octahedral ions (B-sites), while forx=0.8 it shows relaxation behaviour and forx0.9 it exhibits a paramagnetic quadrupole doublet. The systematic dependence of the isomer shifts, line widths, quadrupole interactions and nuclear magnetic fields of57Fe3+ ions in both A and B sites has been determined as a function of cadmium content. The variation of nuclear magnetic fields at the A and B sites is explained on the basis of the A-B and B-B supertransferred hyperfine interactions. Analysis of the average Mössbauer line widths as a function of cadmium concentration suggests that the relaxation spectrum observed atx=0.8 (77 K) is possibly due to domain wall oscillations. It has been found here that QS (B) increases from CuFe2O4to CdFe2O4 as the cadmium concentration is increased. 相似文献
32.
Proactive thermal management in green datacenters 总被引:1,自引:1,他引:0
Eun Kyung Lee Indraneel Kulkarni Dario Pompili Manish Parashar 《The Journal of supercomputing》2012,60(2):165-195
The increasing demand for faster computing and high storage capacity has resulted in an increase in energy consumption and
heat generation in datacenters. Because of the increase in heat generation, cooling requirements have become a critical concern,
both in terms of growing operating costs as well as their environmental and societal impacts. Presently, thermal management
techniques make an effort to thermally profile and control datacenters’ cooling equipment to increase their efficiency. In
conventional thermal management techniques, cooling systems are triggered by the temperature crossing predefined thresholds.
Such reactive approaches result in delayed response as the temperature may already be too high, which can result in performance
degradation of hardware. 相似文献
33.
T. K. Vishnuvardhan V. R. Kulkarni C. Basavaraja S. C. Raghavendra 《Bulletin of Materials Science》2006,29(1):77-83
Conducting polymer composites of polypyrrole/yttrium oxide (PPy/Y2O3) were synthesized byin situ polymerization of pyrrole with Y2O3 using FeCl3 as an oxidant. The Y2O3 is varied in five different weight percentages of PPy in PPy/Y2O3 composites. The synthesized polymer composites are characterized by infrared and X-ray diffraction techniques. The surface
morphology of the composite is studied by scanning electron microscopy. The glass transition temperature of the polymer and
its composite is discussed by DSC. Electrical conductivity of the compressed pellets depends on the concentration of Y2O3 in PPy. The frequency dependent a.c. conductivity reveals that the Y2O3 concentration in PPy is responsible for the variation of conductivity of the composites. Frequency dependent dielectric constant
at room temperature for different composites are due to interfacial space charge (Maxwell Wagner) polarization leading to
the large value of dielectric constant. Frequency dependent dielectric loss, as well as variation of dielectric loss as a
function of mass percentage of Y2O3 is also presented and discussed. 相似文献
34.
Total radiation dose at geostationary orbit 总被引:1,自引:0,他引:1
Active semiconductor components in satellites are sensitive to accumulated ionization radiation dose. Radiation dose and shielding estimations for electronic components are usually carried out using NASA models of space radiation particle flux. Accurate measurement of accumulated dose during the life of a satellite is essential for optimizing radiation shielding design for electronic components. Dosimeters were designed using radiation sensitive field-effect transistors (RADFETs) and accumulated dose at geostationary orbit was measured. Radiation dose as measured by these dosimeters with spherical aluminum shields are presented and compared with NASA model doses. 相似文献
35.
A comparative dielectric relaxation study of PMN–PT and PMN–PZ ceramics using impedance spectroscopy
Surya M. Gupta Pragya Pandit Pankaj Patro Ajit R. Kulkarni Vinod K. Wadhawan 《Materials Science and Engineering: B》2005,120(1-3):194-198
AC-impedance spectroscopic studies in the temperature range of 30–400 °C are carried out on solid solutions of lead magnesium niobate (PMN) with lead titanate (PT) and lead zirconate (PZ), both of them in the 65/35 atomic ratio. For PMN–PT this corresponds to the morphotropic phase boundary composition (with normal ferroelectric behaviour), and for PMN–PZ it is near the phase boundary between normal ferroelectric and relaxor ferroelectric compositions. The variation of dielectric permittivity with temperature at different frequencies shows normal ferroelectric and relaxor-like dependence for PMN–PT and PMN–PZ, respectively. Temperature-dependent spectroscopic modulus plots reveal a much broader peak for PMN–PZ compared to that for PMN–PT, which is consistent with the dielectric behaviour. PMN–PT shows nearly ideal Debye behaviour below Tm (the temperature of the permittivity maximum) and the behaviour departs from ideality above Tm, whereas non-ideal Debye behaviour is seen both below and above Tm for PMN–PZ. Complex modulus plots fit well with two depressed semicircles and three depressed semicircles, respectively, for PMN–PT and PMN–PZ. The relaxation observed in the spectroscopic plots around 1 MHz for PMN–PT has been assigned to polarisation relaxation expected for normal-sized domains. No such relaxation could be observed for PMN–PZ around 1 MHz because of the mesoscopic domain sizes. 相似文献
36.
S. Di Gennaro C. Horn S. R. Kulkarni P. J. Ramadge 《Discrete Event Dynamic Systems》1998,8(4):343-351
We consider a class of hybrid dynamical systems and obtain conditions under which the behavior of these systems can be reduced to a finite state automaton. Specifically, we consider timed automata with more general enabling regions coupling the continuous and discrete dynamics than those previously considered. We provide a necessary condition for the existence of a finite state reduction, together with examples showing that this condition is not sufficient. We then give two sufficient conditions that provide a large class of systems with general enabling regions which admit finite reductions. 相似文献
37.
Shrirang Mare Jacob Sorber Minho Shin Cory Cornelius David Kotz 《Mobile Networks and Applications》2014,19(3):331-344
As healthcare in many countries faces an aging population and rising costs, mobile sensing technologies promise a new opportunity. Using mobile health (mHealth) sensing, which uses medical sensors to collect data about the patients, and mobile phones to act as a gateway between sensors and electronic health record systems, caregivers can continuously monitor the patients and deliver better care. Furthermore, individuals can become better engaged in monitoring and managing their own health. Although some work on mHealth sensing has addressed security, achieving strong privacy for low-power sensors remains a challenge. We make three contributions. First, we propose an mHealth sensing protocol that provides strong security and privacy properties at the link layer, with low energy overhead, suitable for low-power sensors. The protocol uses three novel techniques: adaptive security, to dynamically modify transmission overhead; MAC striping, to make forgery difficult even for small-sized Message Authentication Codes; and asymmetric resource requirements, in recognition of the limited resources in tiny mHealth sensors. Second, we demonstrate its feasibility by implementing a prototype on a Chronos wrist device, and evaluating it experimentally. Third, we provide a security, privacy, and energy analysis of our system. 相似文献
38.
Digital video has many applications varying from telecommunications to broadcasting and so on. Video compression techniques have evolved over the past two decades with prominent technique being developed using fractal. However, this technique was not so popular because of its computationally intensive nature. This paper proposes an inter frame video compression technique, which consists of a combination of a block matching using fractal compression. The proposed algorithm is implemented on CUDA-enabled GPU which significantly reduces the encoding time of the video and provides a very high compression ratio with reasonable quality of the decoded video. Extensive simulations were carried out to analyze the performance of the proposed algorithm. 相似文献
39.
40.
To avoid stockouts and maintain product availability, retailers typically carry excess units and subsequently incur higher cost. In case of style/fashion goods, demand forecasting is extremely difficult due to short selling cycles. The purpose of this study was to minimise the cost of excess stocking without compromising product availability. To achieve these conflicting objectives, our study includes two ordering instances and two returns policies. The time between orders subsequently helps resolve demand uncertainty. Existing studies consider only one type of returns policy, that is, returns on the entire purchase quantity; whereas our study considers two types of returns policies: returns on the first order size and returns on the entire purchase quantity. This study also includes models for the retailer and the supply chain system. Analytical and numerical insights into our study enable the retailer to select his appropriate returns policies to maximise his as well as system’s expected profits. We also show that perfect coordination of partners will help them improve their profits considerably. 相似文献