Limitation of the field emission current density by the space charge of the emitted electrons

Rigorous and exact calculations are used to show that in earlier analytic studies of this problem by Barbour et al. [Phys. Rev. 92, 45 (1953)] and A $\overset{\lower0.5em\hbox{$\overset{\lower0.5em\hbox{ zenberg [Zh. Tekh. Fiz 11, 2079 (1954)], the influence of the electron space charge was not taken into account very accurately. It is shown that the real field of action is much weaker than that calculated geometrically.     

Features of the relaxation polarization of a polar dielectric under conditions of large electrothermal loads

In a polar dielectric occurring under the conditions of large electrothermal loads, it is necessary to take into account the temperature dependence of the conductivity γ(T) and complex permittivity $\overset{\lower0.5em\hbox{$\overset{\lower0.5em\hbox{ . An allowance for this circumstance in the simplest model of the Debye relaxation polarization leads to deviation of the ε″=f(ε′) curve from the well-known Cole-Cole semicircle. Exact solutions of the model problems for a flat capacitor are presented for the cases when the temperature gradient is caused by an external source and by relaxation losses in the dielectric material.     

One-dimensional fractal walk at a finite free motion velocity

We consider one-dimensional symmetric fractal walk of a particle with free path lengths distributed according to an asymptotic power law ( $\overset{\lower0.5em\hbox{$\overset{\lower0.5em\hbox{ ) modeling the transport in a strongly inhomogeneous fractal media. The spatial distribution of particles is determined, which is a Gaussian distribution for α>2, a stable Lévy distribution for 1<α<2, and is confined within a finite segment for α<1, exhibiting a minimum in the middle and integrable singularities at the ends. Qualitative differences between these distributions are explained by the predominance of one of the two competitive processes: diffusion (α>1) and ballistic (α<1).     

Combined effect of partial calcination and sintering condition on low loss Mn-Zn ferrite

In order to achieve highly densified lower loss Mn-Zn ferrite materials, various powder processing routes have been under investigation. In this report, a lower sintering temperature with lower oxygen partial pressure and proper attrition milling duration are suggested. From the previous study, a partial calcination procedure was studied and an optimum partial calcination level was found. Accordingly, Mn_0.71Zn_0.22Fe_2.07O₄ ferrite was prepared by calcination with small amounts of CaCO₃, SiO₂, Nb₂O₅ and SnO₂. The partially calcined ferrites were made by calcining the mixture of the whole amount of ZnO and amount of Fe₂O₃ and Mn₃O₄ and sintering the mixture of the calcined powders and the remaining of Fe₂O₃ and Mn₃O₄. Initially, from the 40 min secondary milling and the partial calcination, lower temperature (1300°C) sintered samples showed a power loss of 340 mW cm^–3 at 90°C. Secondly, several milling durations showed secondary milling had a more profound effect on magnetic properties than primary milling. The 20 min primary and 90 min secondary milling showed lower core loss around 320 mW cm^–3 at 1300°C and 1250°C, suggesting the sintering temperature could be reduced to 1250°C. Thus, the proper sintering condition of lower oxygen partial pressure at 1250°C was studied. As a result, lower loss with higher density was realized.     

On the contribution of the superconductor to the resistance of a superconductor-normal metal system

The problem of dc current flow through a superconductor-normal metal interface near the critical temperature T _c is considered. The equations for the Green's functions integrated with respect to the variable = v(p–p₀) are used to calcuate the resistance of the pure and dirty superconductor S. It is shown that the electric field E decays exponentially over a length % MathType!MTEF!2!1!+-% feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXafv3ySLgzGmvETj2BSbqefm0B1jxALjhiov2D% aebbfv3ySLgzGueE0jxyaibaiiYdd9qrFfea0dXdf9vqai-hEir8Ve% ea0de9qq-hbrpepeea0db9q8as0-LqLs-Jirpepeea0-as0Fb9pgea% 0lrP0xe9Fve9Fve9qapdbaqaaeGacaGaaiaabeqaamaabaabcaGcba% acbaGaa8xmamaaBaaaleaacaWFIbaabeaakiabg2da9iaacIcadaWc% gaqaaiaa-reacqaHepaDdaWgaaWcbaGaa8xzaaqabaacbiGccaGF0a% Gaa8hvaaqaaiabec8aWjabgs5aejaa-LcadaahaaWcbeqaamaaliaa% baGaa8xmaaqaaiaa-jdaaaaaaaaaaaa!49B4!\[1_b = ({{D\tau _e 4T} \mathord{\left/ {\vphantom {{D\tau _e 4T} {\pi \Delta )^{{\raise0.7ex\hbox{$1$} \!\mathord{\left/ {\vphantom {1 2}}\right.\kern-\nulldelimiterspace}\!\lower0.7ex\hbox{$2$}}} }}} \right. \kern-\nulldelimiterspace} {\pi \Delta )^{{\raise0.7ex\hbox{$1$} \!\mathord{\left/ {\vphantom {1 2}}\right.\kern-\nulldelimiterspace}\!\lower0.7ex\hbox{$2$}}} }}\] within the superconductor and at the S-N interface there is a jump of E [strictly speaking, E varies over the correlation length (T)]; here D is the diffusion coefficient, and _e is the energy relaxation time. The magnitude of the jump of E is of the order of or less than the value of E at the boundary of the S region. In the case of a pure superconductor this jump is caused by the Andreev reflection of quasiparticles at the S-N interface.     

On characteristic lengths used in notch fracture mechanics

In this paper, four kinds of characteristic length parameters used in a local notch fracture criterion are presented: (1) a characteristic length ${\uprho }_{\mathrm{c}}$ generally connecting to the notch radius, (2) a characteristic distance $\hbox {X}_{\mathrm{c}}$ considered as intrinsic to material and connected to the microstructure, (3) a critical distance $\hbox {d}_{0}$ considered as intrinsic to material and connected to the fracture process zone, (4) an effective distance $\hbox {X}_{\mathrm{ef}}$ considered as a characteristic of the stress distribution. Each approach is discussed. The paper ends with the author’s opinion about the different methods.     

Surface Recombination Velocity Dependence on Morphological Properties of CdTe Thin Films Prepared by Close-Spaced Sublimation

Cadmium telluride (CdTe) thin films were prepared on glass substrates by employing the close-spaced sublimation technique. Different source ( $T_\mathrm{sou}$ ) and substrate temperatures ( $T_\mathrm{sub}$ ) were used in order to change the structural properties of layers. The ranges chosen were: $550\,^{\circ }\hbox {C} \le T_\mathrm{sou} \le 650\,^{\circ }\hbox {C}$ and $400\,^{\circ }\hbox {C} \le T_\mathrm{sub} \le 600\,^{\circ }\hbox {C}$ . The environment in the growing chamber was also changed with the purpose to study its influence on the crystalline properties of the surface and volume of the material. Three different surroundings were used: vacuum, high-purity argon, and high-purity oxygen. The surface recombination velocity (SRV) was calculated from photoacoustic (PA) measurements by employing the open PA cell configuration. The behavior of the experimental results was analyzed as a function of the structural characteristics of the films: texture and grain size. Scanning electron microscopy, optical absorption, X-ray diffraction, and dark resistivity measurements were also employed to analyze the properties of the CdTe films. The minimum value for the SRV was found for $T_\mathrm{sou} = 650\,^{\circ }\hbox {C},\, T_\mathrm{sub} = 600\,^{\circ }\hbox {C}$ in an oxygen ambient.     

Exploratory Characterization of a Perfluoropolyether Oil as a Possible Viscosity Standard at Deepwater Production Conditions of 533 K and 241 MPa

DuPont’s perfluoropolyether oil Krytox $^{\textregistered }$ GPL 102 is a promising candidate for the high-temperature, high-pressure Deepwater viscosity standard (DVS). The preferred DVS is a thermally stable liquid that exhibits a viscosity of roughly 20  $\hbox {mPa} \cdot \hbox {s}$ at 533 K and 241 MPa; a viscosity value representative of light oils found in ultra-deep formations beneath the deep waters of the Gulf of Mexico. A windowed rolling-ball viscometer designed by our team is used to determine the Krytox $^{\textregistered }$ GPL 102 viscosity at pressures to 245 MPa and temperatures of 311 K, 372 K, and 533 K. At 533 K and 243 MPa, the Krytox $^{\textregistered }$ GPL 102 viscosity is $(27.2 \pm 1.3)\,\hbox {mPa} \cdot \hbox {s}$ . The rolling-ball viscometer viscosity results for Krytox $^{\textregistered }$ GPL 102 are correlated with an empirical 10-parameter surface fitting function that yields an MAPD of 3.9 %. A Couette rheometer is also used to measure the Krytox $^{\textregistered }$ GPL 102 viscosity, yielding a value of $(26.2 \pm 1)\,\hbox {mPa} \cdot \hbox {s}$ at 533 K and 241 MPa. The results of this exploratory study suggest that Krytox $^{\textregistered }\, \hbox {GPL}$ 102 is a promising candidate for the DVS, primarily because this fluoroether oil is thermally stable and exhibits a viscosity closer to the targeted value of 20 mPa $\cdot $ s at 533 K and 241 MPa than any other fluid reported to date. Nonetheless, further studies must be conducted by other researcher groups using various types of viscometers and rheometers on samples of Krytox GPL $^{\textregistered }$ 102 from the same lot to further establish the properties of Krytox GPL $^{\textregistered }$ 102.