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261.
A detailed knowledge of dependence of mechanical properties on orientation in materials prepared by directional processes
may present an important factor influencing the design of construction parts. Toward this end, the compressive creep testing
of short specimens may be useful. Three different magnesium-based materials were subjected to this testing: (i) pure magnesium,
(ii) magnesium matrix composite reinforced with 10 vol.% of titanium, and (iii) magnesium alloy WE54. All three materials
were prepared through a powder metallurgical route with final hot extrusion. The specimens for creep tests were cut in such
a way that their longitudinal axis (i.e., the direction of compressive creep stress) and the axis of extruded bar contained
a predestined angle. Two extreme cases can be observed: In pure Mg and in Mg-Ti composites, the dependence of the creep rate
is very sensitive to the orientation especially at small inclinations from extrusion axis. The greatest creep resistance is
observed in specimens with stress axis parallel to the extrusion axis, the lowest at declinations from 45 to 90°. On the other
hand, in WE54 no orientation dependence was observed. Possible explanations of the behavior based on microstructural observations
are discussed.
__________
Translated from Problemy Prochnosti, No. 1, pp. 125–128, January–February, 2008. 相似文献
262.
Betekhtin V. I. Kadomtsev A. G. Sklenička V. Narykova M. V. 《Technical Physics Letters》2011,37(10):977-979
The influence of hydrostatic pressure on the structure and durability of ultrafine-grained aluminum obtained equal-channel angular pressing (ECAP) has been studied. It is established that the experimentally observed initial growth in the durability of ECAP-processed metal is due to the healing of nanopores, whereas a decrease in this growth with increasing number of passes is caused by the related increase in the fraction of large-angle grain boundaries.
相似文献263.
J. Szamos Anna Jánosi Boróka Tamás éva Kiss 《Zeitschrift für Lebensmitteluntersuchung und -Forschung A》1998,206(3):208-212
This paper describes a practical application of the interfacial protein enrichment method, called three-phase partitioning
(TPP), and outlines its significance in the differentiation of multicomponent protein systems, such as homogenates and drips
of different meats (pork, beef, chicken, turkey and wild-boar). The results obtained using the single-protein model system
are also reported to demonstrate the basic process and some characteristic features of TPP. For meat-protein-partitioning
experiments, ammonium sulphate (41% relative saturation) and 23.7% tert-butanol were used at 20 – 25°C. Using this two-liquid system, a characteristic distribution of three phases (including a
semi-solid midlayer) was obtained for homogenates of eight different meats following centrifugation. Compressibility, expressed
as a ratio of layer thickness obtained by low-speed (200 g) and medium-speed (4500 g) centrifugation, allowed us to distinguish between beef and pork drips. A good correlation was
found between layer thickness and storage time for wild-boar samples. The partitioning presented here can be considered as
a rapid and simple method for comparison between raw meat samples of different origin.
Received: 9 July 1997 / Revised version: 1 October 1997 相似文献
264.
Hájek M Dezortová M Wagnerová D Skoch A Voska L Hejlová I Trunečka P 《Magma (New York, N.Y.)》2011,24(5):297-304
Object
Among several non-invasive methods of liver fat analysis, the most important role is played by MR imaging and spectroscopy (MRS). This study describes the 1H MRS at 3T measurement of liver fat volume fraction ffat{\phi_{{\rm fat}}} in a group of liver transplant patients, an at-risk group for the development of de novo steatosis. 相似文献265.
The active DC glow discharge sustained in pure O2 and O2-Ar mixtures with Ar/O2 concentration ratios up to 50% has been studied in a Pyrex discharge tube for pressures up to 500 Pa and for discharge currents up to 40 mA. The electric field strength and emission spectra parameters of the discharge were studied by means of the double-probe method and optical emission spectroscopy.The electric field strength was found to increase with the pressure and decrease with the discharge current, which is typical for DC glow discharges. Considering O2-Ar mixtures, the values of electric field strength decreased with Ar/O2 ratio.We have focused on the emitted radiation. The rotational temperature Trot of molecular oxygen was determined from the well-resolved atmospheric A-band at 760 nm. The increase of the rotational temperature with increasing deposited power has been observed for all studied Ar/O2 ratios. Moreover, it has been found that values of Trot are independent of the mixture composition. 相似文献
266.
Pavel Jnský Jakub Zlmal Bohumila Lencov Martin Zoba
Ivan Vl
ek Tom Radli
ka 《Vacuum》2009,84(2):357-362
The paper presents numerical simulations of a hairpin thermionic electron gun, an electron source for an electron-beam welding machine. New algorithm for the simulation of emission limited by space charge has been developed and implemented in the program EOD, which enables us to simulate the optical system as whole. The results of the simulation were compared with the experimental measurements. 相似文献
267.
Active DC glow discharges in oxygen have been studied in Silica and Pyrex discharge tubes for medium pressures up to 550 Pa and for discharge currents up to 40 mA. Electric field strength measured by a double-probe technique was found to increase with the pressure and to decrease with the discharge current, which is typical for DC glow discharges. We have focused on the emitted radiation. The rotational temperature (Trot) of molecular oxygen was determined from the PP and PQ branches of the well-resolved atmospheric A-band of molecular oxygen at 760 nm. Good agreement between values of Trot obtained from particular branches was found. The increase of the rotational temperature with increasing pressure and discharge current has been observed in both discharge tubes, however, the values of rotational temperature were systematically higher in the tube made of Pyrex glass. This difference was explained by the particular thermal conductivity of the tube material. 相似文献
268.
The extended dynamic plane source (EDPS) method is one of the transient methods for measurements of the thermal conductivity
and thermal diffusivity in solids. This technique uses a transient plane source (TPS) sensor, which serves as the heat source
and thermometer. Its calibration consists of measuring the temperature dependence of the TPS sensor resistance and computing
the temperature coefficient of resistance (TCR) using least-squares (LS) estimation. The goal of this study is to calibrate
the TPS sensor directly in the apparatus for the EDPS method. The article presents an uncertainty assessment of the TCR measurement.
The main sources of uncertainty stem from resistance measurements of the constant resistor and platinum thermometer calibration.
The LS estimate of the TCR in a nickel TPS sensor is 4.83 × 10−3 K−1 at 20 °C and 4.57 × 10−3 K−1 at 45 °C with a combined standard uncertainty better than 0.04 × 10−3 K−1, which is 0.7 %. 相似文献
269.
Thin film colorimetric interferometry was used in combination with phase shifting interferometry for the detailed experimental investigation of changes in real surface microgeometry within the elastohydrodynamic conjunction formed between a real, random, rough surface, a steel ball and a smooth glass disc. Three real roughness features were studied in detail — the transverse ridge, transverse groove and longitudinal groove. The ridge was found to be heavily deformed within lubricated contact and its height increased with increasing rolling speed. For the transverse groove, a local reduction in film thickness at the leading edge was observed, while the longitudinal groove maintained its undeformed shape. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
270.
Petr Jákl Mojmír Šerý Jan Ježek Alexandr Jonáš Miroslav Liška Pavel Zemánek 《Journal of Modern Optics》2013,60(10):1615-1625
Abstract The way in which reflection of the trapping beam from a dielectric interface influences the distance of the trapped sphere from the beam waist is studied theoretically and experimentally. The reflected wave interferes with the incident wave and they create a standing-wave component in the total axial intensity distribution. This component then modulates the trapping potential and creates several possible equilibrium positions for the trapped sphere. When the beam waist approaches the surface, the potential profile changes, which consequently causes jumps of the trapped probe from its current location to a deeper potential well. We suggested theoretically and proved experimentally that the magnitude of these unwanted jumps between the neighbouring equilibrium positions can be decreased by a suitable size of the sphere. 相似文献