Large-aperture plasma-assisted deposition of inertial confinement fusion laser coatings

Plasma-assisted electron-beam evaporation leads to changes in the crystallinity, density, and stresses of thin films. A dual-source plasma system provides stress control of large-aperture, high-fluence coatings used in vacuum for substrates 1m in aperture.     

Solubility of β-stabilizers in α-titanium

Conclusions We have determined the solubilities of iron, chromium, manganese, silicon, copper, molybdenum, vanadium, and tantalum in -titanium (Table 1) and in the -solid solution of Ti+6% Al (Table 2).Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 2, pp. 13–16, February, 1963     

Feedback control of congestion in packet switching networks: the case of multiple congested nodes

In this paper, an analytical method for the design of a congestion control scheme in packet switching networks is presented. This scheme is particularly suitable for implementation in ATM switches, for the support of the available bit rate (ABR) service in ATM networks. The control architecture is rate-based with a local feedback controller associated with each switching node. The controller itself is a generalization of the standard proportional-plus-derivative controller, with the difference that extra higher-order derivative terms are involved to accommodate the delay present in high-speed networks. It is shown that, under the specific service discipline introduced here, there exists a set of control gains that result in asymptotic stability of the linearized network model. A method for calculating these gains is given. In addition, it is shown that the resulting steady state rate allocation possesses the so-called max-min fairness property. The theoretical results are illustrated by a simulation example, where it is shown that the controller designed, using the methods developed here, works well for both the service discipline introduced in this paper and for the standard FCFS scheme. © 1997 John Wiley & Sons, Ltd.     

Mathematical Modeling of Monovalent Permselectivity of a Bilayer Ion-Exchange Membrane as a Function of Current Density

Modification of an ion-exchange membrane with a thin layer, the charge of which is opposite to the charge of the substrate membrane, has proven to be an effective approach to obtaining a composite membrane with permselectivity towards monovalent ions. However, the mechanism of permselectivity is not clear enough. We report a 1D model based on the Nernst–Planck–Poisson equation system. Unlike other similar models, we introduce activity coefficients, which change when passing from one layer of the membrane to another. This makes it possible to accurately take into account the fact that the substrate membranes usually selectively sorb multiply charged counterions. We show that the main cause for the change in the permselectivity coefficient, P_1/2, with increasing current density, j, is the change in the membrane/solution layer, which controls the fluxes of the competing mono- and divalent ions. At low current densities, counterion fluxes are controlled by transfer through the substrate membrane, which causes selective divalent ion transfer. When the current increases, the kinetic control goes first to the modification layer (which leads to the predominant transfer of monovalent ions) and then, at currents close to the limiting current, to the depleted diffusion layer (which results in a complete loss of the permselectivity). Thus, the dependence P_1/2 − j passes through a maximum. An analytical solution is obtained for approximate assessment of the maximum value of P_1/2 and the corresponding fluxes of the competing ions. The maximum P_1/2 values, plotted as a function of the Na⁺ ion current density at which this maximum is reached, gives the theoretical trade-off curve between the membrane permselectivity and permeability of the bilayer monovalent selective ion-exchange membrane under consideration.     

A novel route to superhard nanocrystalline cubic boron nitride: Emulsion detonation and high-pressure high-temperature transformation-assisted consolidation

Synthesizing bulk nanocrystalline materials is challenging since grain growth should be suppressed whereas densification promoted. Here, we demonstrate a novel route to synthesize superhard bulk nanocrystalline cubic boron nitride (cBN), which combines the use of emulsion detonation and high-pressure high-temperature transformation-assisted consolidation. The emulsion detonation process activates BN to possess unique structure and chemistry, i.e. wurtzitic BN nanograins in hexagonal BN matrix with enhanced structural disordering and oxygen impurity, a combination that enhances the nucleation rate of cBN and its densification leading to the formation of bulk nanocrystalline cBN at reduced conditions. The cBN, synthesized at 7.5 GPa and 1800 °C, displayed Vickers hardness values of 50?62 GPa for 5?20 N loads. The findings in the study suggest a feasible solution to synthesize bulk nanocrystalline cBN in a more scalable way, while also providing design insights on how to refine grain growth while enhancing densification to synthesize bulk nanocrystalline materials.     

In situ investigation of electrical inhomogeneity of ion exchange membrane surface using scanning electrochemical microscopy

Scanning electrochemical microscopy (SECM) is a relatively new, but well-developed method to study the electrochemical characteristics of the surface of heterogeneous materials, such as microelectrodes and biological cells. This paper presents the adaptation of this method to studying the distribution of electric potential near the surface of a heterogeneous ion exchange membrane. A special electrodialysis flow-through cell whose design allows for in situ 3D SECM measurements has been developed. The cell provides a laminar flow of liquid along the membrane surface, thereby making it possible to control the thickness of the diffusion layer. The SECM method has been verified by examining a model heterogeneous ion exchange membrane with preset surface and bulk properties. It has been found that the potential distribution is axisymmetric in the presence of cylindrical pores and the method allows the unambiguous determination of the position of the centers of conductive and nonconductive areas. An extremely nonuniform distribution of the potential with no signs of symmetry has been revealed in the case of MK-40 membrane. Unlike other methods for investigating inhomogeneous surfaces, SECM enable the determination of the distribution and evaluation of the size of conductive and nonconductive areas of heterogeneous ion exchange membranes in the swollen state.     

A spectrometer of polarized neutrons

A polarized neutron spectrometer intended for studies of interactions of nuclei and condensed matter with polarized neutrons with energies in the range from thermal energies to several electron volts was designed at the IBR-2 pulsed reactor (JINR, Dubna). Diffraction on magnetized Co(92%)–Fe(8%) single crystals was used to polarize neutrons and analyze the polarization. The attained neutron polarization was ∼95% within the entire energy range.     

Lean buffering in serial production lines with non-exponential machines

In this paper, lean buffering (i.e., the smallest level of buffering necessary and sufficient to ensure the desired production rate of a manufacturing system) is analyzed for the case of serial lines with machines having Weibull, gamma, and log-normal distributions of up- and downtime. The results obtained show that: (1) the lean level of buffering is not very sensitive to the type of up- and downtime distributions and depends mainly on their coefficients of variation, CV _up and CV _down ; (2) the lean level of buffering is more sensitive to CV _down than to CV _up but the difference in sensitivities is not too large (typically, within 20%). Based on these observations, an empirical law for calculating the lean level of buffering as a function of machine efficiency, line efficiency, the number of machines in the system, and CV _up and CV _down is introduced. It leads to a reduction of lean buffering by a factor of up to 4, as compared with that calculated using the exponential assumption. It is conjectured that this empirical law holds for any unimodal distribution of up- and downtime, provided that CV _up and CV _down are less than 1. Correspondence to: Semyon M. Meerkov     

Regularities in the Sorption of Plutonium Hexafluoride

When implemented, the modern methods for reprocessing nuclear fuel which are based on the volatility of fluorides are complicated by the physical adsorption of uranium and plutonium hexafluorides on inorganic compounds. The lack of the required experimental data in this field makes it impossible to describe the kinetics of the behavior of the indicated hexafluorides in the various processes involved in obtaining and reprocessing them. Consequently, the study of the adsorption of uranium and plutonium hexafluorides and the determination of the heat and entropy of adsorption are of interest from the scientific standpoint and for applications. This paper is devoted to the study of these questions.__________Translated from Atomnaya Energiya, Vol. 98, No. 5, pp. 341–348, May 2005.