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61.
N. Bolleé P. Hertogen G. J. Adriaenssens C. Sénémaud A. Gheorghiu-de La Rocque 《Semiconductors》1998,32(8):873-878
The influence of the presence of Cu in the amount between 1% and 6% in arsenic chalcogenide glasses is examined through a
study of the electronic energy levels by means of x-ray photoelectron and x-ray emission spectroscopy, through an investigation
of the low-energy tunneling systems by means of phonon echoes at 0.37 K, and through an examination of the photodarkening
and the photoinduced dichroism caused by polarized Ar+ laser irradiation. Possible links between the various effects are examined. The Cu atoms become an integral part of the amorphous
lattice structure and strongly influence the photodarkening, but they do not have a significant effect on the tunneling systems
or the dichroism. It is concluded that the tunneling levels and the dichroism involve only local configurations, while the
photodarkening involves larger-scale areas of the lattice.
Fiz. Tekh. Poluprovodn. 32, 976–981 (August 1998) 相似文献
62.
La Porta Thomas F. Ramjee Ramachandran Woo Thomas Sabnani Krishan K. 《Mobile Networks and Applications》1998,3(2):123-141
Wireless networks are characterized by simple end devices and limited bandwidth. One solution to address these and other limitations
of the wireless mobile environment that has been widely pursued is the placement of proxies, or agents, inside the network
to assist with application processing that would normally take place on end devices. These agents can additionally manipulate
data to reduce bandwidth requirements and assist in providing services. The design and implementation of a user agent is heavily
impacted by the application it supports. In this paper we present our experiences with user agents in two different types
of applications: telephony-based Personal Communication Services (PCS) and two-way messaging. To provide low latency service,
the PCS user agents are mobile so that they may be kept close to their end devices. The design of the PCS agents limits migration
overhead to the transfer of approximately 100 bytes of information in about 150 milliseconds. To provide advanced messaging
services, the messaging user agent supports flexible messages while limiting air interface bandwidth usage. The messaging
agents reduce uplink bandwidth usage by approximately 35% when applied to a cellular PCS system, and reduce message payloads
by 97%.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
63.
The design and performance evaluation of multimedia systems require the availability of adequate models to mimic the statistical properties of the traffic generated by a multimedia source. In this paper the authors propose a very simple method for the generation of discretetime and discretestate autocorrelated random variables which can be used to model a traffic source by simulation. The probability distribution and autocorrelation sequence of the variables generated exactly match the corresponding experimental histograms of the source to be modelled when the experimental autocorrelation sequence is decreasing with downward convexity. In this paper an analytical demonstration of the method proposed is given and its use is illustrated by three telecommunications examples. 相似文献
64.
65.
Pedro X. La Hera Leonid B. Freidovich Anton S. Shiriaev Uwe Mettin 《Mechatronics》2009,19(8):1240-1250
The problem of swinging up inverted pendulums has often been solved by stabilizing a particular class of homoclinic structures present in the dynamics of a physical pendulum. Here, new arguments are suggested to show how other homoclinic curves can be preplanned for dynamics of the passive-link of the robot. This is done by reparameterizing the motions according to geometrical relations among the generalized coordinates, which are known as virtual holonomic constraints. After that, conditions that guarantee the existence of periodic solutions surrounding the planned homoclinic orbits are derived. The corresponding trajectories, in contrast to homoclinic curves, admit efficient design of feedback control laws ensuring exponential orbital stabilization. The method is illustrated by simulations and supported by experimental studies on the Furuta pendulum. The implementation issues are discussed in detail. 相似文献
66.
MoSi_2以其高熔点(2030℃)、高使用温度(>1600℃)、良好的导热性和导电性等优良性能,被认为是继镍基高温合金之后极具竞争力的新型高温结构候选材料之一。但是,MoSi_2的低温脆性和中温氧化碎裂(PEST)难以克服。本文以Mo、Si合金粉末为原料,采用激光熔覆技术,在纯镍基材上制成MoSi_2金属硅化物复合材料涂层。分析了涂层的显微组织,测试了涂层的显微硬度。 相似文献
67.
3GPP Release 5 is the first step toward an all-IP cellular network. While Release 99 is still heavily based on a core network inherited from 2G networks, Release 5 introduces a new core network architecture based on IETF protocols. In particular, SIP is used for initiating, managing, and terminating media sessions. However, the use of SIP can result in a significant increase of the signaling and computational loads inside the core network, due to its larger message size and increased requirements on network nodes. This article compares the core network signaling loads of 3GPP Release 99 and Release 5, and elaborates on possible enhancements to improve the bandwidth efficiency of the signaling in Release 5. 相似文献
68.
Scuderi A. La Paglia L. Carrara F. Palmisano G. 《Solid-State Circuits, IEEE Journal of》2005,40(3):611-621
This paper presents the design and measured performance of a 1.8-GHz power amplifier featuring load mismatch protection and soft-slope power control. Load-mismatch-induced breakdown can be avoided by attenuating the RF power to the final stage during overvoltage conditions. This was accomplished by means of a feedback control system, which detects the peak voltage at the output collector node and clamps its value to a given threshold by varying the circuit gain. The issue of output power control has been addressed as well. To this end, a temperature-compensated bias network is proposed, which allows a moderate power control slope (dB/V) to be achieved by varying the circuit quiescent current according to an exponential law. The nonlinear power amplifier was fabricated using a low-cost silicon bipolar process with a 6.4-V breakdown voltage. It delivers a 33.5-dBm saturated output power with 46% maximum power-added efficiency and 36-dB gain at a nominal 3.5-V supply voltage. The device is able to tolerate a 10:1 load standing-wave ratio up to a 5.1-V supply voltage. Power control slope is lower than 80 dB/V between -15 dBm and the saturated output power level. 相似文献
69.
Stefano Mariani Antonino Amedeo La Mattina Alessandro Paghi Lucanos Strambini Giuseppe Barillaro 《Advanced functional materials》2021,31(26):2100774
Here, a fluoride-assisted route for the controlled in-situ synthesis of metal nanoparticles (NPs) (i.e., AgNPs, AuNPs) on polydimethylsiloxane (PDMS) is reported. The size and coverage of the NPs on the PDMS surface are modulated with time and over space during the synthetic process, leveraging the improved yield (10×) and faster kinetics (100×) of NP formation in the presence of F− ions, compared to fluoride-free approaches. This enables the maskless preparation of both linear and step gradients and patterns of NPs in 1D and 2D on the PDMS surface. As an application in flexible plasmonics/photonics, continuous and step-wise spatial modulations of the plasmonic features of PDMS slabs with 1D and 2D AgNP gradients on the surface are demonstrated. An excellent spatially resolved tuning of key optical parameters, namely, optical density from zero to 5 and extinction ratio up to 100 dB, is achieved with AgNP gradients prepared in AgF solution for 12 minutes; the performance are comparable to those of commercial dielectric/interference filters. When used as a rejection filter in optical fluorescence microscopy, the AgNP-PDMS slabs are able to reject the excitation laser at 405 nm and retain the green fluorescence of microbeads (100 µm) used as test cases. 相似文献
70.
La Agusu T. Idehara O. Dumbrajs 《Journal of Infrared, Millimeter and Terahertz Waves》2004,25(7):1023-1036
The TE6,11 mode has been selected as a candidate for the second harmonic operation of a terahertz gyrotron at 1007.68 GHz. The predicted efficiency is 8.6 percent for the output power 0.38 kW. Time-dependent, multi-mode calculations have been carried out to investigate stability of a single-mode operation at second harmonic. It has been found that with the beam current 0.111 A and the magnetic field 19.282 T the second harmonic operation in the TE6,11 mode is possible. 相似文献