The resistivity of the intermediate state of type-I superconductors

The interaction between transport current and flux spots in the intermediate state of a superconductor is investigated. It is shown that the force on the flux spots depends on factors such as current lead configuration, and it is therefore not possible to define a unique flow resistivity for type-I superconductors. The conclusions are supported by experimental evidence.     

Investigation of surface acceptor state density and resistivity jump of ytterbium-doped (Ba, Sr)TiO3 materials

The acceptor state density was calculated by a new method based on Heywang Model. By using the plot of natural logarithm of resistivity versus 1/_appT, the acceptor state density of Yb-doped BaTiO₃ was calculated. The doping effects of Yb and Mn were also investigated. Yb doped after preheating can decrease the acceptor state density and resistivity jump; Mn doped after preheating may increase the acceptor state density and resistivity jump.     

The impurity dependence of the electrical resistivity in the intermediate state

Measurements have been made of the electrical resistivity in the intermediate state of a superconducting cylinder of tin showing the resistivity to have the expected temperature and field dependence, but indicating that the dependence on the electron mean free path appears to be inadequately characterized by present theory.     

Study on the normal state resistivity of doped Ru-1222 system

The present work investigates the effect of Sb substitution on the transport properties Ru_1-xSb_xSr₂Gd_1.4Ce_0.6Cu₂O_10-δ system. The onset superconducting transition temperature is found to decrease with Sb substitution. The normal state resistivity data could be described by 3D variable range hopping in lower temperature region (below T_M) and small polaron hopping model in higher temperature region (above T_M).     

Stress-strain state of a longitudinal-bending converter under resonant oscillations

Institute of Mechanics, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Problemy Prochnosti, No. 6, pp. 81–84, June, 1989.     

Do density oscillations exist near the free surface of 4He?

Variational calculations are carried out for liquid ⁴He with a free surface. Five classes of wave functions are studied, four of which permit the density profile to exhibit oscillations near the surface. We conclude that it is not possible to determine with certainty whether density oscillations exist by variational methods alone. On the other hand, certain qualitative features of the layered structure and quantitative bounds on the extent of the oscillations can be observed, if the latter indeed exist. These observations lead us to believe that effects of a layered structure on, e.g., evaporation, surface scattering, and properties of adsorbates are probably too weak to be detectable.Work supported in part by the National Science Foundation through Grant No. DMR74-09661.Work carried out in connection with honors research for the B.A. degree.     

On the stability of the equilibrium state and small oscillations of non-holonomic systems

The stability of small oscillations of non -holonomic systems is discussed. In contrast to Neimark and Fufaev, we have shown here that a non-holonomic system does indeed possess an isolated equilibrium state under certain conditions. We provide conditions under which there exists asymptotic stability of small oscillations of a non-holonomic system about its equilibrium position. The connection between a holonomic and non-holonomic system is also discussed. The results obtained here can be useful for the control of a non-holonomic system     

Shape-dependent regularization for the retrieval of atmospheric state parameter profiles

We present an adaptive regularization approach to retrieve vertical state parameter profiles from limb-sounding measurements with high accuracy. This is accomplished by introducing a dedicated regularization functional based on a reasonable assumption of the profile characteristics. The approach results in shape-dependent weighting during least-squares computations and relies on a Cholesky decomposition of a preselected L(T)L matrix. Our method is compared with established regularization functionals such as optimal estimation and Tikhonov with respect to errors and achievable height resolution. The results show an improved height resolution of the retrieved profiles together with a reduction of absolute and relative errors obtained by test-bed simulations.     

Subgap peak and Tomash-McMillan-Anderson oscillations in the density of states of SNS Bridges

The quasiparticle spectra and the densities of states of superconducting-normal-superconducting junctions are computed from the WKBJ transformed Bogoliubov-de Gennes Equations (BdGE), which are solved by Picard iteration and numerical integration. It is shown that the influence of the proximity effect on the bound states can be modeled by a rectangular pair potential well of effective normal layer thickness 2a*= _–L ^L [1–(z)/]dz, where (z) is the pair potential of the junction, is its asymptotic constant value, and 2L is the total length of the sample. The density of states exhibits a subgap peak at energies less than besides the BCS peak atE=; forE> there are geometrical resonances which are due to electron-hole interferences in finiteS layers of thicknessL-a*.     

Electric field affects the charge state in ion-implanted Si-SiO2 structures

Using the method of depth profiling based on the measurement of high-frequency voltage-capacitance characteristics in an electrolyte-insulator-semiconductor structure in combination with the insulator layer etching, it was found that Ar ion implantation into the oxide film of a Si-SiO₂ structure (oxide thickness, 250 nm) leads to the formation of positively charged (outer) and negatively charged (inner) layers in the SiO₂ film beginning with an implanted ion dose of 10¹⁴ cm⁻². The effect of an external electric field upon the charge state in these ion-implanted structures was studied. It was established that the negatively charged centers represent hole traps, which are recharged by the applied field to a neutral state. It is suggested that these centers are related to the appearance of nonbridging oxygen atoms as a result of the silicon oxide film reconstruction induced by the ion implantation to a dose exceeding 10¹⁴ cm⁻².     

Resolution analysis of tomographic reconstruction of electron density profiles in the Ionosphere

Traditionally, knowledge of the ionospheric electron density is obtained using Faraday rotation or differential Doppler techniques which measure total electron content in columns of the ionosphere. Conventional data processing can only image the electron density in the direction perpendicular to these columns, thereby forming one-dimensional images. Because this data is proportional to line integrals through the region of interest, tomographic techniques may be used to reconstruct two-dimensional electron density images. In this paper, the resolution limit of the image reconstruction process is analyzed in terms of limited-angle tomography.     

Current state of Fe-Mn-Al-C low density steels

Fe-Mn-Al-C steels, previously developed in the 1950s for replacing Fe-Cr-Ni steels, are currently generating a lot of interest with potential applications for structural parts in the automotive industry because they are lighter. This paper provides a review on the physical metallurgy, processing strategies, strengthening mechanisms and mechanical properties of Fe-Mn-Al-C steels from the published literature over a period of many years, and suggests avenues for future applications of these alloys in the automotive sector.The addition of Al to Fe-C steels leads to a reduction in both density and Young’s modulus. A 1.3% reduction in density and a 2% reduction in Young’s modulus are obtained per 1 wt% addition of Al. Due to the addition of the high amounts of Al, together with Mn and C, the physical metallurgy, general processing, microstructural evolutions and deformation mechanisms of these steels are largely different from those of the conventional steels.The addition of Al to high-Mn austenitic steels brings two other important effects: increasing the stacking fault energy (SFE) and producing short-range ordering (SRO) and/or κ′-carbide precipitation. Plastic deformation of low-density Fe-Mn-Al-C steels with a high SFE, which involves SRO, is dominated by planar glide. New deformation mechanisms such as the microband induced plasticity (MBIP), the dynamic slip band refinement (DSBR) and the shear band induced plasticity (SIP) are introduced to describe plastic deformation of Fe-Mn-Al-C austenitic steels in addition to the transformation-induced plasticity (TRIP) and the twinning-induced plasticity (TWIP), which are often observed in Mn TWIP steels. These new deformation mechanisms are related to the formation and uniform arrangement of the SRO or nano-sized κ′-carbides which are coherent with the austenitic matrix. The κ′-carbide precipitation is a unique strengthening mechanism in the austenitic Fe-Mn-Al-C steels bearing high amounts of Al and C.The lightweight Fe-Mn–Al-C alloys can produce a variety of microstructures and achieve a wide range of properties. These alloys can be classified into four categories: ferritic steels, ferrite based duplex steels, austenite based duplex steels and austenitic steels. The austenitic steels are the most promising in terms of properties and processing. The tensile properties of the austenitic lightweight steels are similar to those of high Mn TWIP steels. The impact toughness of these steels in the solution treated condition is slightly lower than that of Cr-Ni stainless steels but is higher than that of the conventional high strength steels. The energy absorption at high strain rate is similar to that of high Mn TWIP steels and higher than that of conventional deep drawing steels. The ferrite based duplex low-density steels is another promising alternative. A bimodal microstructure can be obtained here through process control for steels with lower alloying contents, in which the plastic deformation of the ferrite and the TRIP and/or TWIP effects from the retained austenite can be profitably used. This type of Fe-Mn-Al-C steels exhibits an improved combination of strength and ductility compared with the first generation advanced high strength steels. The ferritic Fe-Al steels have tensile properties comparable with HSLA steels of 400–500 MPa strength level. The corrosion behaviour of Fe-Mn-Al-C steels is not improved in comparison with the conventional high strength steels. The application properties such as the fatigue behaviour and formability of Fe-Mn-Al-C steels cannot be properly understood at this stage, because of the limited experimental results so far. Some other application aspects such as weldability, coatability are not well documented.The applications of the Fe-Mn-Al-C steels in the automobiles is still not prevalent due to the lack of knowledge related to application properties so far. Above all, the reduced Young’s modulus of these steels and the processing problems as a result of the high Al and high Mn contents are the main issues. The future developments will therefore have to concentrate on the alloying and processing strategies and also on the methods to increase the Young's modulus. An improved processing strategy and a high value for the Young’s modulus will go a long way towards upscaling these steels to real automotive applications.     

Effects of current density and deposition time on electrical resistivity of electroplated Cu layers

This study was performed to investigate the effects of current density and deposition time on sheet resistance and resistivity of electroplated Cu layer. Cu layer covered on sputtered Si/Ta/22Cu-78Ta/Cu films was electroplated with current densities of 1, 1.5 and 2 A/dm², and the deposition times varied from 20 to 100 min. The effects of current density and deposition time on the thickness of Cu layers and the current efficiency were investigated. The variation in sheet resistance and resistivity were discussed with respect to thickness, surface roughness, microstructure, grain size, and texture. In general, it was found that surface roughness might not be the dominate parameter, but the density of nodule boundary in the porous films would affect the electrical property of the electroplating Cu. An increasing extent of the (1 1 1) preferred orientation tends to loosen the nodules and lower the sheet resistance and resistivity of Cu layers. A decrease in the current density and an increase in deposition time tend to produce a Cu layer with (1 1 1) preferred orientation and results in relatively low sheet resistance and resistivity.     

Effects of current density and deposition time on electrical resistivity of electroplated Cu layers

This study was performed to investigate the effects of current density and deposition time on sheet resistance and resistivity of electroplated Cu layer. Cu layer covered on sputtered Si/Ta/22Cu-78Ta/Cu films was electroplated with current densities of 1, 1.5 and 2 A/dm², and the deposition times varied from 20 to 100 min. The effects of current density and deposition time on the thickness of Cu layers and the current efficiency were investigated. The variation in sheet resistance and resistivity were discussed with respect to thickness, surface roughness, microstructure, grain size, and texture. In general, it was found that surface roughness might not be the dominate parameter, but the density of nodule boundary in the porous films would affect the electrical property of the electroplating Cu. An increasing extent of the (1 1 1) preferred orientation tends to loosen the nodules and lower the sheet resistance and resistivity of Cu layers. A decrease in the current density and an increase in deposition time tend to produce a Cu layer with (1 1 1) preferred orientation and results in relatively low sheet resistance and resistivity.     

电阻率用于混凝土养护状态与效率评价研究

通过测量电阻率可望实现对混凝土养护过程的监测。测量不同养护条件下混凝土1～5cm表层区域内电阻率随养护龄期的变化,然后测量不同条件养护28d的混凝土浸水后表层区域电阻率随浸水时间的变化,最后对比分析混凝土表层区域不同位置的电阻率变化规律。结果显示,采用混凝土表层1～2cm与4～5cm区域电阻率的差值可以反映混凝土养护状态,差值越大表明混凝土的养护不良;根据水分侵入条件下混凝土表层不同区域电阻率降低程度,可以判断混凝土养护效率,电阻率降低幅度大表明混凝土养护不良。     

The state primary standard of the unit of heat-flux surface density

The results of the construction of the State Primary Standard of the unit of heat-flux surface density at the Siberian State Research Institute of Metrology are considered.     

Energy scale of the pairing model with energy-dependent density of state

The critical temperature of a pairing model for HT _c S has been calculated using an energy-dependent density of states. We showed that the problem which is connected with the van Hove scenario is very sensitive to the energy scale and to the behavior of the density of states at low and high energy.