共查询到20条相似文献,搜索用时 31 毫秒
1.
J. Boronat F. Arias de Saavedra E. Buendia A. Polls 《Journal of Low Temperature Physics》1994,94(3-4):325-349
A variational microscopic calculation of the binding energy of a4He impurity (i) in homogeneous liquid3He at zero temperature is presented. Starting on an extended Jastrow-Slater wave function including three-body correlations, the expression for I is derived and the appropriated FHNC formalism for this problem is reviewed. In the framework of the Average Correlation Approximation (ACA), it is proved that it is possible to obtain the chemical potential of the impurity only from liquid3He magnitudes with a good accuracy. Our results are consistent with both a recent experimental determination of I at zero pressure and the non-solubility of4He in3He. However, numerical uncertainties preclude a firm conclusion about the latter property. 相似文献
2.
A thermomechanical effect has been found in normal liquid3He. The effect appears only when the temperature gradient is established across liquid3He confined in small pores so that the3He quasiparticle scattering is boundary limited. This was achieved with a porous plug of packed 70 nm copper-oxide powder. The magnitude of P/gDT varies from 4 C at 2 mK to C at 20 mK, where P is pressure, T is temperature and C is the heat capacity per unit volume. The sign is positive, meaning that the3He moves from cold to hot. If viewed as an analogue of thermoelectricity, the magnitude of this thermomechanical effect is unsurprising. However, as shown in the following paper, it is an order of magnitude larger than a theoretical prediction for liquid3He. 相似文献
3.
We have investigated the viscosity of liquid3He-4He mixtures at various3He - concentrations (0.98%x9.5%) in the temperature range1 mK T 100 mK and at pressures 0 bar P 20 bar. At T10 mK the Fermi-liquid behaviour T2 = const. as well as x4/3 could be confirmed. However, there are significant deviations from theoretical predictions for the magnitude of the viscosity as well as for its pressure dependence. 相似文献
4.
J. H. Merkin 《Journal of Engineering Mathematics》1985,19(3):189-201
Summary The similarity solutions for free convection on a vertical plate when the (non-dimensional) plate temperature is x
and when the (non-dimensional) surface heat flux is –x
are considered. Solutions valid for 1 and 1 are obtained. Further, for the first problem it is shown that there is a value 0, dependent on the Prandtl number, such that solutions of the similarity equations are possible only for >0, and for the second problem that solutions are possible only for >–1 (for all Prandtl numbers). In both cases the solutions becomes singular as 0 and as –1, and the natures of these singularities are discussed. 相似文献
5.
Ewout ter Haar Raymond Wagner Clemens M. C. M. van Woerkens Stephen C. Steel Giorgio Frossati Ladislav Skrbek Mark W. Meisel Valdir Bindilatti Alexandre R. Rodrigues Ramon Valls Martin Nei F. Oliveira Jr. 《Journal of Low Temperature Physics》1995,99(1-2):151-166
A new design for conventional,3He re-circulating, dilution refrigerators has been developed and tested. The units are made out of plastic and can be designed to have very small diameters (<15mm). These characteristics make them ideal to cool samples below 100 mK in high or time-varying magnetic fields. Furthermore, they are inexpensive, reliable and easily constructed. The best refrigerators reach continuous temperatures of around 10 mK at low circulation rates ( 100 mol/s). The cooling power at high temperatures is limited by the speed of the circulation pump and not by the refrigerator itself. The basic design and construction methods are discussed. 相似文献
6.
Stephen A. Langer Keith DeConde D. L. Stein 《Journal of Low Temperature Physics》1984,57(3-4):249-263
We investigate the possibility of using the techniques of dynamic nuclear polarization on liquid3He. We calculate the polarization rate resulting from the saturation of the electron spin resonance in a substrate immersed in the liquid. For metallic substrates, the rate will be too slow to overcome relaxation at the walls of the container. For insulating substrates, liquid polarizations enhanced by a factor B/N103 can be achieved on the order of seconds. 相似文献
7.
Cylindrical stand-alone tubes of plasma-sprayed alumina were tested in uniaxial compression at room temperature, using strain gages to monitor axial strains. The effect of lamella size on the mechanical response was investigated by employing different starting powders to fabricate samples. The average powder sizes investigated included 9 m, 19 m and 32 m alumina; the resulting effective lamella diameters were 10 m, 28 m, and 55 m, respectively. Similar stress-strain hysteresis was observed on unloading in all tubes, independent of lamella size. A strong correlation between the failure stress and the cumulative strain at failure was also observed for tubes fabricated from the three powders. For samples with approximately constant densities, tubes plasma sprayed with the 9 m powder exhibited greater moduli than tubes sprayed from either 19 or 32 m powders. This difference was attributed to the greater percentage of unmelted -Al2O3 in the coating. 相似文献
8.
The microdeformation and fracture mechanisms of a densely crosslinked, polydomain, smectic liquid crystalline thermoset (LCT) were investigated in order to gain some insight into its interesting mechanical properties (e.g. improved fracture toughness). A difunctional LC epoxy monomer, diglycidyl ether of 4,4-dihydroxy--methylstilbene (DGDHMS), was crosslinked with the tetrafunctional, aromatic crosslinker, 4,4-methylene dianiline (MDA) to produce the LCT. Thermoset films (30 m in thickness) were bonded to copper grids, strained in tension, and observed under the polarizing optical microscope. A new type of microdeformation and fracture mechanism was observed for the smectic LCT. At small strains, numerous microcracks formed which were oriented at various angles to the straining direction. Many smaller isolated and interconnected defects (of the order of a single LC domain, 1 m in size) surrounded and emanated from the crack tips. At larger strains, the microcracks propagated slowly and stably until reaching a critical size of 250 m, at which time they began to widen and change direction, indicative of plastic deformation which extended over many LC domains. Film failure occurred through microcrack interconnection. A fracture mechanism for the LCT is proposed based on microscopic voiding near the crack tip through the failure of individual LC domains. 相似文献
9.
The thermomechanical coefficient P/T has been measured for liquid3He from 2–20 mK. The temperature difference was established across3He in a porous plug with 90 nm pore diameter. The coefficient was 5 kPa K–1 and only weakly temperature dependent; in terms of the heat capacity per unit volume, the coefficient varies from 4C at 2 mK to C at 20 mK. 相似文献
10.
E. M. Dianov V. G. Plotnichenko Yu. N. Pyrkov I. V. Smol'nikov S. A. Koleskin G. G. Devyatykh M. F. Churbanov G. E. Snopatin I. V. Skripachev R. M. Shaposhnikov 《Inorganic Materials》2003,39(6):627-630
Single-mode As–S glass fibers with a core diameter from 3 to 20 m and a clad diameter of 125 m are prepared by the double-crucible method. The cutoff wavelength of the fibers is 0.9–6 m. The lowest transmission losses in the fibers at 2.2–2.3 m are 100 dB/km, and their mean bending strength is 800–1000 MPa. 相似文献
11.
This paper deals with the problem of twisting of a non-homogeneous, isotropic, half-space by rotating a circular part of its boundary surface (0ra, z = 0) through a given angle. A ring (a<r<b, z = 0) outside this circle is stress-free and the remaining part (r>b, z = 0) is rigidly clamped. The shear modulus is assumed to vary with the cylindrical coordinates r, z by the power law ( = ,
r
z
). Such a dependence is of practical interest in the context of Soil Mechanics. The problem leads to a Fredholm integral equation of the second kind which is solved numerically, giving an evaluation of the influence of non-homogeneity on the torque at the surface and the stress intensity factor. The homogeneous case studied in [16] is recovered. Expressions for some quantities of physical importance such as the torque applied at the surface and stress intensity factor are obtained. It appears from our investigation that the influence of clamping dies out with increasing and . Quantitative evaluations are given and some curves for the relative increase, due to clamping, in the torque and in the stress intensity factor are presented. 相似文献
12.
Microstructure-property studies in friction-stir welded, Thixomolded magnesium alloy AM60 总被引:5,自引:0,他引:5
Thixomolded magnesium alloy AM60 plates joined by friction-stir welding were observed to be as strong or stronger than the unwelded base material. The thixotropic microstructures of the as-molded plates consisted of either 3% or 18% primary solid fraction of -Mg globules (45 m average size) in a eutectic mixture consisting of -Mg grains (10 m) surrounded by Mg17Al12 intermetallic grains in the -Mg grain boundaries (having an average size of 1–2 m). This complex, composite microstructure became a homogeneous (Mg + 6% Al)), recrystallized, equiaxed grain (10–15 m) microstructure in the weld zone. 相似文献
13.
W. Wendler T. Herrmannsdörfer S. Rehmann F. Pobell 《Journal of Low Temperature Physics》1998,111(1-2):99-118
We have measured ac susceptibility, nuclear magnetic resonance, and nuclear heat capacity of two PtFe
x
samples with concentrations of magnetic impurities x = 11 ppm and 41 ppm at magnetic fields (0 ± 0.05) mTB248 mT. The susceptibility data have been measured at temperatures of 0.3 KT100 mK, no hint for nuclear magnetic ordering could be detected to a temperature of 0.3 K. The nuclear heat capacity data taken at 1.4 KT10 mK show enhanced values which scale with x at low polarization. This effect is described by a model assuming an internal magnetic field caused by the impurities. No indication for nuclear magnetic ordering could be detected to 1.4 K. The nuclear magnetic resonance experiments have been performed on these samples at 0.8 KT0.5 mK and 2.5 mTB22.8 mT as well as on three other samples with x = 5, 10, 31 ppm in a different setup at 40 KT0.5 mK and at 5.4 mTB200 mT. Spin-lattice and effective spin-spin relaxation times
1and
2
*
of 195
Pt strongly depend on x and on the external magnetic field. No temperature dependence of
1and
2
*
could be detected and the NMR data, too, give no hint for nuclear magnetic ordering to 0.8 K. 相似文献
14.
R. Nomura H. H. Hensley T. Matsushita T. Mizusaki 《Journal of Low Temperature Physics》1994,94(5-6):377-383
We have measured the growth rate of single crystal U2D2 solid3He in the superfluid B phase as a function of chemical potential difference between the solid and liquid for temperatures between 0.4 and 0.9 TN. The growth rate was not proportional to , with very slow growth rates for less than about 10 erg/cm3. For larger values of the growth rate depended weakly on temperature and the growth was attributed to a quantum growth mechanism due to screw dislocations. The melting rate was too fast to be measured quantitatively, but was slower at higher temperatures. 相似文献
15.
-Si3N4 whiskers that are 1–10 mm long and 0.5–1.1 m thick were obtained by the reaction of wheat husks with NH3 at 1250–1450 °C. A maximum whisker yield of about 30% was obtained at 1450 °C with the addition of an iron impurity. Whiskers with 1.3–2.2 m thickness (average 1.6 m) were obtained by the addition of an H2S impurity. Thin whiskers with periodic thick and thin diameters were also obtained. 相似文献
16.
S. B. Artemenko A. T. Belonozhko G. P. Vyatkin Yu. G. Izmailov S. A. Plokhov V. G. Rechkalov 《Journal of Engineering Physics and Thermophysics》1988,55(4):1132-1136
The application of the methods of laser and holographic interferometry to the problems of measuring evaporation rates is examined. Mass transfer accompanying evaporation in the region of extradiffusion monitoring is studied.Notation jv
specific mass flux of the vapor, kg/(m2·sec)
- c
coefficient of condensation
- v
coefficient of evaporation
- D
coefficient of diffusion
- m2/sec,
wetting angle
- R
radius of the vessel, m
-
time, sec
- h
height of the segment, m
-
wavelength of the laser radiation, m
- N
order of the interference fringe or the number of fringes passing through a given point
-
density of the matter, kg/m3
-
length of the cell with the liquid of interest, m
- T
temperature, K
- n
refractive index of the medium
- m
mass
- kg, V
volume of the spheroidal segment, m3
- liq and g
molar mass, kg/mole
- C0 and Cp
concentration of vapor in the gas, kg/m3
- a and b
semiaxes of the spheroid, m
- e
ellipsoidal coordinate of a point on the surface, m2
- c/n
derivative along the normal
- r
coordinate of a point on the surface of evaporation, m
- n
change in the refractive index of the medium
Indices st
standard liquid
- liq
liquid
- g
gas
- 0
starting state
- p
equilibrium pressure
Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 55, No. 4, pp. 605–611, October, 1988. 相似文献
17.
The dynamic viscosity () of stimulated whole saliva in a typical pre-orthodontic sample population was characterized as a function of temperature (T). Samples were collected from 30 adolescents or young adults, after screening for factors that are known to have an effect on salivary viscosity. Using a cone and plate viscometer, 1.5 ml of stimulated whole saliva was evaluated at a constant shear rate of 450 s-1 from T=20°C to T=40°C. Data from the -T plots showed a negative dependence of the form, =a–bT, over a range of from 1.08 to 2.45 centipoise (cps) at 34°C. Most of the samples fell into a narrow envelope, where the mean of the saliva samples ranged from 2.42±0.61 cps at 20°C to 1.57±0.32 cps at 37°C. With regard to sample stability, viscosity-time plots indicated that a small but predictable decrease in occurred during the 3 h period. The -T plots generated from fresh and frozen saliva samples demonstrated an appreciable change in as a result of refrigeration. With regard to sample reproducibility, viscometric data obtained from a typical pre-orthodontic patient over a 1-week period fluctuated within a fairly broad envelope of values.Presented, in part, at the 21st Annual Meeting and Exhibition of the A.A.D.R., Boston, Massachusetts, March, 1992. 相似文献
18.
The present paper examines the elastostatic problem related to the axisymmetric rotation of a rigid circular disc bonded to a non-homogeneous half-space containing a penny-shaped crack. The shear modulus of the half-space is assumed to vary with depth according to the relation (z) = 1(z + c), c > 0 and 1, are constants. Using Hankel transforms, the solution of the problem is reduced to integral equations and finally to simultaneous Fredholm integral equations of the second kind. By solving numerically the simultaneous Fredholm integral equations, results are obtained which are used to estimate the stress intensity factor at the crack tip and the torque required to rotate the disc through an angle 0. 相似文献
19.
M. D. Mikhailov B. K. Shishedzhiev 《Journal of Engineering Physics and Thermophysics》1975,28(4):509-513
A minimax approximation, uniform for Bi [0, ), is developed for the roots of the equation BiW()=V(), by means of Chebyshev polynomials.Translated from Inzhenero-Fizicheskii Zhurnal, Vol. 28, No. 4, pp. 710–715, April, 1975. 相似文献
20.
An Al-6061 metal matrix composite, reinforced with 10 vol % Al2O3 particulates, was subjected to equal-channel angular (ECA) pressing at room temperature to a total strain of 5. It is shown that the intense plastic straining introduced by ECA pressing reduces the grain size from 35 m to 1 m and this leads to an increase in the microhardness measured at room temperature. Inspection revealed some limit cracking of the larger Al2O3 particulates as a consequence of the ECA pressing. Tensile testing after ECA pressing gave a maximum ductility of 235% at a temperature of 853 K when testing at strain rates from 10–4 to 10–3 s–1. It is suggested that high strain rate superplasticity is not achieved in this material after ECA pressing due to the presence of relatively large Al2O3 particulates. 相似文献