考虑损伤的蠕变问题的变形场与损伤场

本文研究了考虑损伤的蠕变介质的变形场与损伤场的解。求得了下列三个问题的新解:(1)考虑损伤的指数律蠕变材料在小损伤条件下的变形场与损伤场;(2)幂律蠕变材料在大损伤条件下的裂纹尖端场;(3)全耦合蠕变损伤的圆柱扭转问题的变形场与损伤场,这三个新解均可用解析的形式表达。     

Identifying the global core-periphery structure of science

While there is a consensus that there is a core-periphery structure in the global scientific enterprise, there have not been many methodologies developed for identifying this structure. This paper develops a methodology by looking at the differences in the power law structure of article outputs and degree centrality distributions of countries. This methodology is applied to five different scientific fields: astronomy and astrophysics, energy and fuels, nanotechnology and nanosciences, nutrition, and oceanography. This methodology uncovers a two-tiered power law structure that exists in all examined fields. The core-periphery structure that is unique to each field is characterized by the core’s size, minimum degree, and exponent of its power law distribution. Stark differences are identified between technology and non-technology intensive scientific fields.     

Microwave power dependence in Gd 123 and Tl 2212 thin films: Examining the evidence for limiting behavior

Using a 5-GHz parallel-plate resonator, several Gd 123 films and one Tl 2212 film have been studied as a function of microwave power. The variation of the surface resistance as a function of dc magnetic fields applied parallel to the crystallographicc axis reflects the gross microstructure of the films. Two broad categories of behavior are observed in dc field. The evidence for intrinsically limited power dependence is discussed in terms of impedance plane analysis.     

Conditions for and limitations of high-power handling capabilities of planar YBa2Cu3O7-x filters

The conditions for the design of compact high-power HTS filters are deduced from basic considerations, and related to the microwave properties of the HTS films and the substrates. Potential mechanisms limiting the linear microwave response of HTS films are analyzed systematically. Magnetic and thermal field breakdowns are found to confine the power handling capability to comparable field levels. While magnetic limitation is related to flux penetration at the lower critical field B_c1, thermally induced quenches occur dependent on the presence of defects and on the thermal conductivity of the substrate. The detrimental role of film inhomogeneities for the linear microwave response is confirmed experimentally for microwave fields at 19 GHz and for dc fields at 87 GHz.     

The skewness of science in 219 sub-fields and a number of aggregates

This paper studies evidence from Thomson Scientific (TS) about the citation process of 3.7 million articles published in the period 1998–2002 in 219 Web of Science (WoS) categories, or sub-fields. Reference and citation distributions have very different characteristics across sub-fields. However, when analyzed with the Characteristic Scores and Scales (CSS) technique, which is replication and scale invariant, the shape of these distributions over three broad categories of articles appears strikingly similar. Reference distributions are mildly skewed, but citation distributions with a 5-year citation window are highly skewed: the mean is 20 points above the median, while 9–10% of all articles in the upper tail account for about 44% of all citations. The aggregation of sub-fields into disciplines and fields according to several aggregation schemes preserve this feature of citation distributions. It should be noted that when we look into subsets of articles within the lower and upper tails of citation distributions the universality partially breaks down. On the other hand, for 140 of the 219 sub-fields the existence of a power law cannot be rejected. However, contrary to what is generally believed, at the sub-field level the scaling parameter is above 3.5 most of the time, and power laws are relatively small: on average, they represent 2% of all articles and account for 13.5% of all citations. The results of the aggregation into disciplines and fields reveal that power law algebra is a subtle phenomenon.     

Roughness of glancing angle deposited titanium thin films: an experimental and computational study

The characterization of roughness at the nanoscale by the means of atomic force microscopy (AFM) was performed on high aspect ratio glancing angle deposited titanium thin films. With the use of scanning electron microscopy as well as x-ray photoelectron spectroscopy, it was shown that the AFM measurements gave rise to incorrect roughness values for the films consisting of the highest aspect ratio structures. By correcting for this experimental artefact, the difference between the saturated roughness value of a film grown with conventional physical vapour deposition and films grown with a glancing angle of deposition was shown to behave as a power law function of the deposition angle, with a saturated roughness exponent of κ?=?7.1?±?0.2. This power law scaling was confirmed by three-dimensional molecular dynamics simulations of glancing angle deposition, where the saturated roughness exponent was calculated to κ?=?6.7?±?0.4.     

Asymptotic crack-tip fields in anisotropic power law material under antiplane shear

A hodograph transformation in conjunction with an appropriate affine transformation are both used to investigate the strain and stress fields near the crack tip in an anisotropic power law material under antiplane shear. Stress and strain exponents as well as angular distributions for the asymptotic stress and strain fields are obtained analytically. All the stress strain exponents are independent of material anisotropy, and the effect of material anisotropy on the asymptotic stress and strain field is discussed including higher order terms.     

Influence of coercive force on low-frequency creep in bloch-wall permalloy films

A very high resolution Bitter pattern technique is used to observe the motion of Bloch walls in Permalloy films excited by slowly rising and slowly falling hard-axis fields. For low coercive force films, the basic motion consists of approximately equal and opposite jumps induced by simultaneous wall structure changes at two transition fields. Net motion begins with the application of small easy-axis bias fields. For high coercive force films, although the wall structure changes continue to occur, the wall jumps and a net displacement do net occur until the easy-axis bias field exceeds a certain critical value which is a function of the wall coercive force.     

Humidity-sensitive electrical properties and switching characteristics of BN films

This paper reports on the electrical properties of polycrystalline boron nitride (BN) films deposited on silicon substrates in a B₂H₆---NH₃---H₂ system. Virgin (unformed) samples exhibit humidity-sensitive electrical resistances. A current obeying Ohm's law at low humidities and low fields becomes space-charge-limited at high humidities and high fields. Some of the properties fundamental to their use as humidity sensors are also examined. After electroforming, BN films in the form of Ag/BN/Si/Al sandwiches begin to exhibit threshold switching only in atmospheres containing moisture. This switching behavior depends not only on the humidity but also on the sweep speed, the frequency of oscillation and the polarity of the applied sawtooth voltage pulse trains. A revised form Dearnaley's filamentary model is proposed.     

Oscillations in longitudinal magnetoresistance in single-crystal films of bismuth

Theoretically, it has been shown by Erukhimov and Tavger that, when the magnetic and electric fields are in the same direction and parallel to the film surface, a change in the film thickness or the magnetic field leads to oscillations in conductivity for experimentally attainable conditions. We report small amplitude oscillations in the longitudinal magnetoresistance of single-crystal bismuth films in weak magnetic fields at liquid nitrogen temperature, due to the influence of the magnetic field on size quantization.     

Three-dimensional nonlinear thermo-elastic analysis of functionally graded cylindrical shells with piezoelectric layers by differential quadrature method

Three-dimensional nonlinear thermo-elastic analysis of a functionally graded cylindrical shell with piezoelectric layers under the effect of asymmetric thermo-electro-mechanical loads is carried out. The strain–displacement relations are based on the nonlinear Lagrangian strain–displacement relations; that is, nonlinear terms containing derivatives of the displacement in the radial direction are included. Material properties of the shell are assumed to be graded in the radial direction according to a power law but the Poisson’s ratio is assumed to be constant. Cylindrical shells are assumed to be under the effect of pressure loading in cosine form, ring pressure loads, electric and temperature fields. Numerical results of stress, displacement, electric and thermal fields are obtained by using two versions of the differential quadrature methods, namely polynomial and Fourier quadrature methods. The convergence of the solution is studied, and results of the axisymmetric loadings are verified with reported results for a cylindrical shell with material properties obeying a power law. Effects of the grading index of material properties, the temperature difference, the ratio of the mean radius to the thickness of the shell, boundary conditions, the thickness of piezoelectric layers and electric excitation on stress, displacement, electric and temperature fields are presented.     

Optimization of Geomagnetic Shielding for MKIDs Mounted on a Rotating Cryostat

Superconducting detectors, such as microwave kinetic inductance detectors (MKIDs), are sensitive to the effects of ambient magnetic fields. There are two effects magnetic fields have on the response of MKIDs; the trapping of magnetic fields inside the superconducting materials degrades the resonator quality, and the time variation of the magnetic fields results in a baseline fluctuation. In the case of radio astronomy, this means the detector must be protected from the geomagnetic field. Here, we construct a test system to evaluate the effects described. We also evaluate the impact of the magnetic shield. We find that a shielding power of 47 dB is necessary in the case of application with a noise equivalent power of \(2.4 \times 10^{-16}\,\text {W}/\sqrt{\text {Hz}}\). We also confirm that the measured shielding power obtained using permalloy films is consistent with simulations based on the finite element method to an accuracy of 1 dB. We have designed magnetic shields for the GroundBIRD CMB telescope using these results. We achieve a sufficient shielding power of 55 dB.     

聚酰亚胺的侧链功能化

侧链功能化的聚酰亚胺是一类特殊的高性能聚合物,可用来制备非线性光学材料,绝缘薄膜,耐高温气液分离膜,射线屏蔽膜,柔性印刷电路板基膜和宇来得及航材料等,用于航天航空。国防军工,电子,电机电器,核动力学各个工业领域。本文就近１０年来国内外对聚酰亚胺侧链功能化的研究现状和应用前景进行了综述。     

新型红外二氧化碳传感器

本文介绍了一种具有不切光单光束结构的新型红外二氧化碳传感器，该传感器基于朗伯－比尔吸收定律，采用光源稳流，附加误差补偿与单片机数据处理及选用高性能红外探测器等技术，能够对二氧化碳气体进行准确有效的探测和分析。     

Anisotrophy control of Ni-Fe films through sequenced-field deposition

Anisotropy of nickel-iron films of 82, 74, and 66 per cent nickel compositions was controlled by time-sequenced application of orthogonal fields during deposition. Resulting anisotropy values are in agreement with simpleM-induced anisotropy principles. Coercive forces show small but definite decrease with anisotropy constant. Dispersion angle is proportional to the reciprocal of the anisotropy constant. The technique is suitable for production of low-Hkfilms. It permits nonanomalous inverted films to be produced and allows the study of other anisotropy sources.     

Singular crack-tip fields for pressure sensitive plastic solids

Plain strain mode-I singular plastic fields are examined for cracks embedded in pressure sensitive solids. Material response is described by a small strain deformation theory in conjunction with elliptic yield criterion and plastic potential. Non-associativity is accounted for and a pure power law is assumed to characterize strain hardening. The material does not admit a strain energy function hence it is not possible to deduce a-priori the J-integral motivated stress singularities. A standard separation of variables representation of near-tip eigenfunctions has been evaluated numerically, over a range of material parameters. It has been found that stress singularities may deviate from J-integral predictions, with increasing non-associativity, by up to nearly 20%. Sample illustrations are provided for singular field profiles and some aspects of pressure sensitive non- associated plasticity are discussed.     

Growth and characteristics of ZnO films on growth side of freestanding diamond substrate dependent on buffer layer thickness

We report the growth and properties of highly c-axis oriented ZnO films, by radio-frequency magnetron sputtering, on the growth side of freestanding chemical vapor deposited diamond film-substrate. Low-temperature ZnO buffer layer is required for the formation of continuous ZnO films. The morphology, structure, and optical properties of the ZnO films deposited are strongly dependent on the thickness of the buffer layer. The optimized thickness of ZnO buffer layer is about 10 nm to realize high-quality ZnO films having small compressive stress and high intensity ultraviolet emission. The ZnO/diamond (growth side) system is available for the applications in numerous fields, especially for high performance surface acoustic wave devices.     

Nanomagnetic behavior of fullerene thin films in Earth magnetic field in dark and under polarization light influences

In this paper magnetic fields intensity of C60 thin films of 60 nm and 100 nm thickness under the influence of polarization lights are presented. Two proton magnetometers were used for measurements. Significant change of magnetic field intensity in range from 2.5 nT to 12.3 nT is identified as a difference of dark and polarization lights of 60 nm and 100 nm thin films thickness, respectively. Specific power density of polarization light was 40 mW/cm2. Based on 200 measurement data average value of difference between magnetic intensity of C60 thin films, with 60 nm and 100 nm thickness, after influence of polarization light, were 3.9 nT and 9.9 nT respectively.     

A Soffer-Cottey model for the galvanomagnetic properties of thin polycrystalline metal films

Theoretical equations for the galvanomagnetic parameters of thin polycrystalline metal films are derived within the frameworks of the Soffer-Cottey model for electron scattering at rough surfaces and of the three-dimensional model for electron scattering at grain boundaries. Influences of the surface roughness and of the strength of the transverse magnetic field are investigated, showing the absence of oscillations in the transport parameters with increasing magnetic field even for very thin films with rough surfaces. In the limits of small reduced thicknesses and weak magnetic fields, analytical expressions for the Hall coefficient and for the electrical conductivity are proposed in order to provide an easier experimental determination of the roughness and grain parameters.     

Dynamical properties of gapless superconductors

The system of time-dependent equations is obtained for superconductors in the gapless region (strong magnetic fields). The thin films in a presence of uhf power are considered in more detail. It is shown that the whole picture is very different in comparison with the simple diffusion type extension of the Ginsburg—Landau theory. It is pointed out that a new characteristic time has to be introduced corresponding to processes of the energy relaxation.