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971.
972.
R. Gerbaldo G. Ghigo G. Giunchi L. Gozzelino F. Laviano E. Mezzetti 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(3):297-300
We present results from an extended magneto-optical (MO) analysis of two samples cut from high-density pellets of MgB2. The first sample was studied in order to show that no matter how large the sample is and despite the bulk granularity, the
material enters into a critical state in a crystal-like fashion. The second sample was chosen for the quantitative analysis.
A numerical approach based on an inverted 2D Biot-Savart model was used to calculate the current paths across the homogeneous
polycrystalline bulk, as well as in the vicinity and across some morphological defects. Local current densities in the homogeneous
part were estimated as a function of the applied magnetic field at different temperatures, in three regimes: below full penetration,
at full penetration and above full penetration, respectively. A hypothesis of interpretation of the apparent absence of magnetic
granularity inside the polycrystalline microstructure is presented. It is related to a critical state likely reached by a
network of strongly coupled Josephson junctions.
Received 31 May 2001 and Received in final form 5 December 2001 相似文献
973.
Understanding of the basic nature of arc root fluctuation is still one of the unsolved problems in thermal arc plasma physics.
It has direct impact on myriads of thermal plasma applications being implemented at present. Recently, chaotic nature of arc
root behavior has been reported through the analysis of voltages, acoustic and optical signals which are generated from a
hollow copper electrode arc plasma torch. In this paper we present details of computations involved in the estimation process
of various dynamic properties and show how they reflect chaotic behavior of arc root in the system. 相似文献
974.
单重态氧O2 (a1Δg)是迄今唯一能用纯化学反应高效产生的具有长寿命的亚稳激发态分子 .为了考察提出的用两个O2 (1Δ)能量汇集反应生成氧第二单重激发态O2 (b1Σ+ g)以实现近可见短波长化学激光方案的现实性 ,设计和实验了一个氯流量为 3~ 10mmol/s的射流式单重态氧发生器 (JSOG) .考察了三种具有不同孔径和孔数目的喷头、氯气流量和脱水冷阱温度等对JSOG出口的O2 (1Δ)浓度、O2 (1Δ)分压、氯利用率及水蒸气含量的影响 .发现用聚氯乙烯管作冷阱时 ,最佳冷阱介质温度为 - 140~ - 15 0℃ ,对此提出了O2 (1Δ)表面脱活与脱水互相竞争的解释 .在最佳条件下 ,可将O2 (1Δ)气中水分压降低至 4Pa ,这一结果是首次报导 相似文献
975.
Dielectric effect on the rf characteristics of a helical groove travelling wave tube 总被引:1,自引:0,他引:1
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A new type of partial-dielectric-loaded helical groove slow-wave structure (SWS) for millimetre wave travelling wave tube (TWT) is presented in this paper.The radio-frequency characteristics including the dispersion properties,the longitudinal electric field distribution and the beam-wave coupling impedance of this structure are analysed.The results show that the dispersion of the helical groove circuit is weakened,the phase velocity is reduced and the position of the maximum Ez is moved from the mouth to the inside of the groove after partially filling the dielectric materials in the helical groove SWS.Therefore,the dielectric-loaded helical groove SWS is suitable for a multi-beam TWT with broad band and high gain. 相似文献
976.
G. Kh. Panova M. N. Khlopkin N. A. Chernoplekov A. A. Shikov 《Physics of the Solid State》2002,44(7):1218-1223
The specific heats of the Ni2B amorphous system and of its crystal analog were studied in the temperature range 3–270 K. The data obtained permitted us to isolate the contribution due to atomic vibrations from the experimentally measured specific heat, determine the electronic density of states at the Fermi level and the temperature dependence of the characteristic Debye parameter Θ, and to calculate some average frequencies (moments) of the vibrational spectrum. The electronic density of states at the Fermi level increases under amorphization. An analysis of the temperature dependence of the lattice specific heat showed that amorphization brings about a substantial growth in the density of vibrational states at low frequencies, whereas the spectrum-averaged and rms frequencies change very little, which is in good agreement with neutron diffraction measurements. 相似文献
977.
A simple model has been developed to describe the Zeeman patterns of far-infrared laser magnetic resonance spectra of the monobromomethyl radical CH2Br observed at 447.3 and 671.1μm. A satisfactory agreement between the experimental spectra of the radical and their simulation with this simple model has been achieved. This approach can be used to gain further information about the structure and the spectrum of this interesting radical. 相似文献
978.
This paper reports on the results of experimental investigations into the thermal conductivity of GaS and GaSe layered semiconductor crystals in directions parallel and perpendicular to the crystal layers in the temperature range 5–300 K. Specific features of the thermal conductivity of these crystals are analyzed. 相似文献
979.
Study on the in—plane electrical resistivity and thermoelectric power in single crystals of La2—xBaxCuO4
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The in-plane electrical resistivity and thermoelectric power have been measured on single crystals of La2-xBaxCuO4 at around x=0.125. The room temperature resistivity and thermopower have their maximum values at x=0.125, indicating that the carrier concentration is the minimum and the carriers are most strongly localized at x=0.125. The observed semiconductor-like behaviour can be well described by the weak-localized quasi-two-dimensional state. The steep rise in electric resistivity of the sample at x=0.125 below 70K is attributed to the formation of static stripe-order of holes and spins, which are pinned by the low-temperature tetragonal (LTT) structure, as discovered in La1.48Nd0.4Sr0.12CuO4. The temperature dependence of electric resistivity below 70K is still well described by the formula ρ∝ lnT. A definite change in the slope of thermopower is observed at the low-temperature orthorhombic-LTT structural phase transition temperature. The origin of the 1/8 anomaly is discussed in the text. 相似文献
980.
N. H. Al-Assady 《Journal of Optimization Theory and Applications》1997,94(3):747-755
We present a method which generates conjugate search directions and maintains the quadratic convergence property, when applied to a quadratic function, even when the line searches are not exact. The method is similar to that given by Dixon, but needs one less vector store. When the method is applied to a number of general functions of different dimensionality, results show the efficiency of the method. 相似文献