排序方式: 共有22条查询结果,搜索用时 630 毫秒
1.
Markovic Maja D. Seslija Sanja I. Ugrinovic Vukasin Dj. Kunaver Matjaz Panic Vesna V. Pjanovic Rada V. Spasojevic Pavle M. 《Cellulose (London, England)》2021,28(17):11109-11132
Cellulose - pH- and magnetic-sensitive hybrid hydrogels based on poly(methacrylic acid) (PMAA), nanocellulose (NC), carboxymethyl cellulose (CMC) and magnetite particles (MN) were prepared as... 相似文献
2.
Vojislav Spasojevic Ana Mrakovic Marija Perovic Vladan Kusigerski Jovan Blanusa 《Journal of nanoparticle research》2011,13(2):763-771
Single-phase perovskite compound La0.7Ca0.3MnO3 was synthesised by a high-energy ball milling in a single step processing. Structure and morphology characterizations revealed
nanoparticle nature of this mixed valent manganite with the average particle diameter of 9 nm. Comprehensive set of magnetic
measurements showed that the system can be described as an ensemble of interacting magnetic nanoparticles where each particle
possesses high magnetic moment, i.e., superspin. Furthermore, magnetic behavior showed contributions from both superspin-glass
(SSG) and superparamagnetic (SP) states, and the prevailing properties depended on the experimental conditions. It was established
that SSG state dominated in low magnetic fields up to 500 Oe while in higher applied fields suppression of collective behavior
occurred and individual characteristics of nanoparticles prevailed. It was also concluded that the applied method of synthesis
produced system with high magnetic anisotropy as well as with the large nanoparticle shell whose thickness amounts 30% of
a particle diameter. 相似文献
3.
Luo J. Yates R. Spasojevic P. 《IEEE transactions on information theory / Professional Technical Group on Information Theory》2005,51(7):2594-2611
The service outage based allocation problem explores variable-rate transmission schemes and combines the concepts of ergodic capacity and outage capacity for fading channels. A service outage occurs when the transmission rate is below a given basic rate r/sub o/. The allocation problem is to maximize the expected rate subject to the average power constraint and the constraint that the outage probability is less than /spl epsi/. A general class of probabilistic power allocation schemes is considered for an M-parallel fading channel model. The optimum power allocation scheme is derived and shown to be deterministic except at channel states of a boundary set. The resulting service outage achievable rate ranges from 1-/spl epsi/ of the outage capacity up to the ergodic capacity with increasing average power. Two near-optimum schemes are also derived by exploiting the fact that the outage probability is usually small. The second near-optimum scheme significantly reduces the computational complexity of the optimum solution; moreover, it has a simple structure for the implementation of transmission of mixed real-time and non-real-time services. 相似文献
4.
Lin L. Yates R.D. Spasojevic P. 《IEEE transactions on information theory / Professional Technical Group on Information Theory》2006,52(5):1847-1860
This work examines a transmission system which adapts a finite set of code rates and a continuously varying transmit power. We propose a technique for finding the average reliable throughput (ART)-maximizing policy satisfying an average power constraint for a slow fading additive white Gaussian noise (AWGN) channel. ART is a measure motivated by the information outage and can, for example, be argued to characterize the long-term average throughput of a data packet transmission system with a transmit queue and a feedback protocol which requests retransmission of erroneously received packets. Given the size of the code rate set L, the ART-maximizing policy has the following properties. 1. For a given set of code rates, the optimum allocation policy suggests quantizing the fading state space into a set of L+1 corresponding intervals. For each quantization interval the optimal policy specifies a minimum transmitted power assignment which guarantees zero information outage. The optimum average power assignments across quantization intervals have a waterfilling relationship with respect to the interval channel quality measure. 2. The joint optimization of quantization intervals and the corresponding rate assignments are shown to have multiple local maxima. Nevertheless, this optimization problem can be reduced to a simple one-dimensional search over a parameter which determines the outage interval. Numerical results show that, in a Rayleigh-fading channel, there is only a 1-dB gap between the ergodic capacity and the throughput of a two-rate adaptive transmission system when the throughput is less than 6 bits/s/Hz. A special case of our optimal policy assignment is the optimal power and rate policy for an adaptive M-QAM system. 相似文献
5.
Spasojevic P. Xiaodong Wang Host-Madsen A. 《Communications, IEEE Transactions on》2001,49(9):1631-1641
A nonlinear group-blind technique is developed for joint detection of some given users' data in a CDMA uplink environment with the presence of unknown interference. This method performs the so-called “slowest-descent search” over a likelihood function of the desired users, starting from the estimate closest to the unconstrained maximizer of the likelihood function, and along mutually orthogonal directions where this likelihood function drops to the slowest. Simulation results show that this new nonlinear technique offers substantial performance improvement over the previously proposed linear group-blind multiuser detectors with little attendant increase in computational complexity. The problem of group-blind multiuser detection in the presence of both unknown interference and impulsive ambient noise is also treated under the framework of slowest-descent search, with the aid of a novel subspace-based robust interference cancellation scheme. It is seen that this robust group-blind method significantly outperforms the robust blind multiuser detection scheme proposed previously 相似文献
6.
Ruoheng Liu Maric I. Spasojevic P. Yates R.D. 《IEEE transactions on information theory / Professional Technical Group on Information Theory》2008,54(6):2493-2507
We study information-theoretic security for discrete memoryless interference and broadcast channels with independent confidential messages sent to two receivers. Confidential messages are transmitted to their respective receivers while ensuring mutual information-theoretic secrecy. That is, each receiver is kept in total ignorance with respect to the message intended for the other receiver. The secrecy level is measured by the equivocation rate at the eavesdropping receiver. In this paper, we present inner and outer bounds on secrecy capacity regions for these two communication systems. The derived outer bounds have an identical mutual information expression that applies to both channel models. The difference is in the input distributions over which the expression is optimized. The inner bound rate regions are achieved by random binning techniques. For the broadcast channel, a double-binning coding scheme allows for both joint encoding and preserving of confidentiality. Furthermore, we show that, for a special case of the interference channel, referred to as the switch channel, derived bounds meet. Finally, we describe several transmission schemes for Gaussian interference channels and derive their achievable rate regions while ensuring mutual information-theoretic secrecy. An encoding scheme in which transmitters dedicate some of their power to create artificial noise is proposed and shown to outperform both time-sharing and simple multiplexed transmission of the confidential messages. 相似文献
7.
V. Kusigerski D. Markovic V. Spasojevic M. Tadic M. Zentkova M. Mihalik 《Journal of nanoparticle research》2010,12(4):1299-1306
Pressure effects on magnetic properties of two La0.7Ca0.3MnO3 nanoparticle samples with different mean particle sizes were investigated. Both the samples were prepared by the glycine-nitrate
method: sample S—as-prepared (10 nm), and sample S900—subsequently annealed at 900 °C for 2 h (50 nm). Magnetization measurements revealed remarkable differences in magnetic properties
with the applied pressure up to 0.75 GPa: (i) for S sample, both transition temperatures, para-to-ferromagnetic T
C = 120 K and spin-glass-like transition T
f = 102 K, decrease with the pressure with the respective pressure coefficients dT
C/dP = −2.9 K/GPa and dT
f/dP = −4.4 K/GPa; (ii) for S900 sample, para-to-ferromagnetic transition temperature T
C = 261 K increases with pressure with the pressure coefficient dT
C/dP = 14.8 K/GPa. At the same time, saturation magnetization M
S recorded at 10 K decreases/increases with pressure for S/S900 sample, respectively. Explanation of these unusual pressure effects on the magnetism of sample S is proposed within the scenario
of the combined contributions of two types of disorders present in the system: surface disorder introduced by the particle
shell, and structural disorder of the particle core caused by the prominent Jahn–Teller distortion. Both disorders tend to
vanish with the annealing of the system (i.e., with the nanoparticle growth), and so the behavior of the sample S900 is similar to that previously observed for the bulk counterpart. 相似文献
8.
Jovan Blanusa Miodrag Mitric Vojislav Spasojevic Janez Pirnat 《Solid State Communications》2005,133(3):157-161
The ErxY1−xF3 (x=0.1, 0.2, 0.7, 0.9, 1) solid solutions were synthesized and characterized by X-ray powder diffraction and magnetic measurements. The crystal structure refinements done by the Rietveld profile method show that no significant change of the structure parameters with the erbium concentration occurs. On the basis of DC susceptibility measurements in the 2-300 K range the lowest four crystal field levels have been determined, giving the ground level magnetic moment value of 6.7 μB. Results of M(H) studies point to the presence of complex exchange interactions between erbium ions. 相似文献
9.
Marija Perovic Ana Mrakovic Vladan Kusigerski Jovan Blanusa Vojislav Spasojevic 《Journal of nanoparticle research》2011,13(12):6805-6811
Spin dynamics in mechanochemically obtained nanoparticle manganite La0.70Ca0.30MnO3 was investigated in this study by means of a series of AC and DC magnetic measurements. AC susceptibility indicates the presence
of sizeable interparticle interactions, yielding collective magnetic behavior. The related properties were probed by experiments
in weak DC field: memory effects were analyzed in both field-cooled (FC) and zero field-cooled (ZFC) regimes, while, after
ZFC aging, magnetic relaxation was recorded. The system appears to be sensitive to magnetothermal history, in analogy with
spin-glass-like compounds. The analysis of the data indicates the occurrence of slow dynamics in an ensemble of strongly interacting
super spins. 相似文献
10.
People,Places, Things: Web Presence for the Real World 总被引:2,自引:1,他引:1
Kindberg Tim Barton John Morgan Jeff Becker Gene Caswell Debbie Debaty Philippe Gopal Gita Frid Marcos Krishnan Venky Morris Howard Schettino John Serra Bill Spasojevic Mirjana 《Mobile Networks and Applications》2002,7(5):365-376
The convergence of Web technology, wireless networks, and portable client devices provides new design opportunities for computer/communications systems. In the HP Labs' Cooltown project we have been exploring these opportunities through an infrastructure to support web presence for people, places and things. We put web servers into things like printers and put information into web servers about things like artwork; we group physically related things into places embodied in web servers. Using URLs for addressing, physical URL beaconing and sensing of URLs for discovery, and localized web servers for directories, we can create a location-aware but ubiquitous system to support nomadic users. On top of this infrastructure we can leverage Internet connectivity to support communications services. Web presence bridges the World Wide Web and the physical world we inhabit, providing a model for supporting nomadic users without a central control point. 相似文献