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We have carried out extensive studies on the self-injection problem in barrierless heterojunctions between La0.7Ca0.3MnO3 (LCMO) and YBa2Cu3O7-δ (YBCO) thin films. The heterojunctions were formed in situ by sequentially growing LCMO and YBCO films on 〈100〉 LaAlO3 (LAO) substrate using a pulsed laser deposition (PLD) system. YBCO micro-bridges with 64 μm width were patterned both on the LAO (control) and LCMO side of the substrate. Critical current, I c, was measured at 77 K on both the control side as well as the LCMO side for different YBCO film thickness. It was observed that while the control side showed a J c of ∼ 2 × 106 A/cm2, the LCMO side showed about half the value for the same thickness (1800 ?). The difference in J c indicates that a certain thickness of YBCO has become ‘effectively’ normal due to self-injection. From the measurement of J c at two different thicknesses (1800 ? and 1500 ?) of YBCO films both on the LAO as well as the LCMO side, the value of self-injection length (at 77 K) was estimated to be ∼ 900 ?. To the authors’ best knowledge, this is the first time that self-injection length has been quantified. A control experiment carried out with LaNiO3 deposited by PLD on YBCO did not show any evidence of self-injection.  相似文献   
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The detection of early-stage tumors in the breast by microwave imaging is challenged by both the moderate endogenous dielectric contrast between healthy and malignant glandular tissues and the spatial resolution available from illumination at microwave frequencies. The high endogenous dielectric contrast between adipose and fibroglandular tissue structures increases the difficulty of tumor detection due to the high dynamic range of the contrast function to be imaged and the low level of signal scattered from a tumor relative to the clutter scattered by normal tissue structures. Microwave inverse scattering techniques, used to estimate the complete spatial profile of the dielectric properties within the breast, have the potential to reconstruct both normal and cancerous tissue structures. However, the ill-posedness of the associated inverse problem often limits the frequency of microwave illumination to the UHF band within which early-stage cancers have sub-wavelength dimensions. In this computational study, we examine the reconstruction of small, compact tumors in three-dimensional numerical breast phantoms by a multiple-frequency inverse scattering solution. Computer models are also employed to investigate the use of exogenous contrast agents for enhancing tumor detection. Simulated array measurements are acquired before and after the introduction of the assumed contrast effects for two specific agents currently under consideration for breast imaging: microbubbles and carbon nanotubes. Differential images of the applied contrast demonstrate the potential of the approach for detecting the preferential uptake of contrast agents by malignant tissues.  相似文献   
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CoFe2O4-BaTiO3 composites were prepared using conventional ceramic double sintering process with various compositions. Presence of two phases in the composites was confirmed using X-ray diffraction. The dc resistivity and thermoemf as a function of temperature in the temperature range 300 K to 600 K were measured. Variation of dielectric constant (ɛ′) with frequency in the range 100 Hz to 1 MHz and also with temperature at a fixed frequency of 1 kHz was studied. The ac conductivity was derived from dielectric constant (ɛ′) and loss tangent (tan δ). The nature of conduction is discussed on the basis of small polaron hopping model. The static value of magnetoelectric conversion factor has been studied as a function of magnetic field.  相似文献   
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This is a continuation of our earlier investigation (Gurtuet al 1974Phys. Lett. 50 B 391) on multiparticle production in proton-nucleus collisions based on an exposure of emulsion stack to 200 GeV/c beam at the NAL. It is found that the ratioR em = 〈n s〉/〈n ch〉, where 〈n ch〉 is the charged particle multiplicity in pp-collisions, increases slowly from about 1 at 10 GeV/c to 1·6 at 68 GeV/c and attains a constant value of 1·71 ± 0·04 in the region 200 to 8000 GeV/c. Furthermore,R em = 1·71 implies an effectiveA-dependence ofR A =A 0.18,i.e., a very weak dependence. Predictions ofR em on various models are discussed and compared with the emulsion data. Data seem to favour models of hadron-nucleon collisions in which production of particles takes place through adouble step mechanism,e.g., diffractive excitation, hydrodynamical and energy flux cascade as opposed to models which envisage instantaneous production.  相似文献   
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This is the report of Heavy Ion Physics and Quark-Gluon Plasma at WHEPP-09 which was part of Working Group-4. Discussion and work on some aspects of quark-gluon plasma believed to have created in heavy-ion collisions and in early Universe are reported.  相似文献   
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The composition of dissolved organic matter (DOM) in a soil is the product of a variety of soil processes. Changes in the composition of DOM in water discharged from soil should, therefore, give an important insight into modifications in these soil processes. We hypothesise that these processes in soils, under different grassland management regimes, would be affected to different extents by the short-term disturbance of a storm event and that evidence of this could be detected in delta(13)C and delta(15)N signatures in drainage and surface runoff waters. During a storm event we collected discharge waters from 1 ha grassland lysimeters, with or without artificial drainage, which received contrasting fertiliser inputs, and delta(13)C and delta(15)N signatures were determined. Changes in (13)C enrichment during the storm event were clearly identifiable, as were differences between plots for (13)C and (15)N, illustrating that this technique has potential to be a useful tool for identifying and investigating short- and long-term changes in soil organic matter dynamics. Copyright 1999 John Wiley & Sons, Ltd.  相似文献   
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We present a theoretical analysis for simultaneous optical wavelength interchange and isolation of a pair of collinear input optical signals by use of two concurrent difference-frequency-generation processes in a two-dimensional second-order nonlinear photonic crystal. We have derived a set of relations, including a general nonlinear Bragg condition, that we use to determine the parameters of the nonlinear lattice, given the input wavelengths and desired exit angles of the wavelength-interchanged outputs.  相似文献   
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We report the realization and demonstration of novel semiconductor waveguide-coupled microcavity ring and disk resonators. For a 10.5-microm-diameter disk resonator, we measure a finesse of 120, a resonant linewidth of 0.18 nm, and a free-spectral range of 21.6 nm in the 1.55-mum-wavelength region. We present the nanofabrication methods and the experimental results for 10.5- and 20.5-mum-diameter ring and disk resonators to show the feasibility of such devices.  相似文献   
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