共查询到20条相似文献,搜索用时 281 毫秒
1.
2.
Summary We present the negative result of a search for the radiative decay of a light neutral fermion, that might be the neutrino
(if massive) or the photino, gravitationally bounded to our Galaxy. The limit obtained for the radiative lifetime of a particle
of mass between 12.5 and 21.5 eV is ≈1018 years. These new data on UV background in the range (1250÷2000) ? show the presence of continuum emission and diffuse lines
emission at high galactic latitude (|b
II|>45°). The lines are identifiable with C IV, λ-1549 ? and N III, λ=1749 ?. The continuum level sharply rises at 1680 ? to
the level of (314±136) photons/(cm2s sr ?) and remains nearly constant up to 2000 Å. Below 1680 Å we found no emission with an upper limit of ≈100 units. These
new data are briefly discussed in comparison with the results of previous experiments and theoretical expectations.
Paper presented at the Congress ?Galactic and Extragalactic Dark Matter?, Roma, 28 to 30 June 1983. 相似文献
3.
A. N. Chumakov S. A. Petrov N. A. Bosak E. N. Shcherbakova 《Journal of Applied Spectroscopy》2012,79(4):664-669
We have obtained carbon thin films on silicon and glass substrates with multipulse pulsed laser irradiation of graphite under vacuum (p ≈ 2.6 Pa) using a high-frequency series of nanosecond laser pulses (τ = 85 ns, λ = 1060 nm) with pulse repetition frequency f ≈ 10–20 kHz and laser power density q ≈ 15–40 MW/cm2. We established the optimal laser power density and laser pulse repetition frequency for obtaining amorphous nanostructured diamond-like films. 相似文献
4.
Guang S. He Yiping Cui Paras N. Prasad 《Journal of Experimental and Theoretical Physics》1997,85(5):850-856
The spectral structure of backward stimulated scattering from a 10 cm-long CS2-liquid cell is investigated by using Q-switched 10-ns and 532-nm laser pulses with different spectral linewidths. Under a narrow spectral line (∼0.1 cm−1) pump condition, very strong sharp lines near the pump wavelength (λ
0) position and the first-order stimulated Raman scattering (λ
s1) position can be observed. However, under a wide line (≈1 cm−1) pump condition, only a strong and superbroadening spectral band can be observed mainly in the red-shift side of the pump
wavelength. The different spectral features under these two conditions can be explained by a competition between stimulated
Brillouin, Raman, and Rayleigh-Kerr scattering. Under both pump conditions, the broadening spectral distributions are not
consistent with the predictions given by stimulated Rayleigh-wing scattering theories, but can be interpreted well utilizing
the theoretical model of stimulated Rayleigh-Kerr scattering.
Zh. éksp. Teor. Fiz. 112, 1563–1573 (November 1997)
Published in English in the original Russian journal. Reproduced here with stylistic changes by the Translation Editor. 相似文献
5.
S. P. Gavrilov A. A. Vertiy 《International Journal of Infrared and Millimeter Waves》1997,18(9):1739-1760
Tomographic methods of image reconstruction of two-dimensional cross-sections of volumetric objects in millimeter wavelengths
band are suggested and considered.
It is shown that in the frequency band under consideration, the images of investigated objects may be obtained by first-order
diffraction tomography method (Born, Rytov or high frequency approximation of the first-order for scattered electromagnetic
field). 相似文献
6.
A. A. Vertiy S. P. Gavrilov 《International Journal of Infrared and Millimeter Waves》1998,19(9):1201-1220
Tomographic methods of image reconstruction of two-dimensional cross-sections of volumetric objects in millimeter wavelengths band are suggested and considered.It is shown that in the frequency band under consideration, the images of investigated objects may be obtained by first-order diffraction tomography method (Born, Rytov or high frequency approximation of the first-order for scattered electromagnetic field). 相似文献
7.
N. V. Denisova V. S. Egorov V. V. Kozlov N. M. Reutova P. Yu. Serdobintsev É. E. Fradkin 《Journal of Experimental and Theoretical Physics》1998,86(1):39-48
The coherent V-configuration interaction between an optically dense resonantly-absorbing three-level medium (neon) and two ultrashort superradiance
pulses with converging wave fronts is investigated experimentally and theoretically. Both separate and combined propagation
of pulses with wavelengths λ
1=614.3 nm (strong field, θ
1⩾π) and λ
3=594.5 nm (weak field, θ
3≈/20) are studied. For propagation of a separate strong-field pulse, supertransparency of the absorbing medium was observed,
which is associated with the generation of a soliton-like pulse at the difference frequency (Δν≈1700 MHz) and the dispersion-diffraction stabilization effect. Under these conditions a weak-field pulse is completely absorbed.
Combined propagation of the pulses leads to novel effects. A below-threshold pulse (weak field) was observed to pass through
the absorber while interacting coherently with a strong-field pulse at a neighboring transition. It is shown theoretically
that absorption of the weak pulse is reduced for two reasons: first, as a result of incoherent transparency of the resonance
transition caused by emptying of the lower level by the field of the strong pulse, and second, as a result of coherent transfer
of polarization between the upper levels via the two-photon processes. When the conditions for combined propagation are met,
the latter mechanism ensures inversionless amplification of a weak pulse over a wide band of frequencies. In this case, the
gain can even exceed the linear absorption coefficient in absolute value. A difference in propagation velocities of the weak
and strong pulses was recorded experimentally, along with a shift in the carrier frequency of the weak field towards the red
(≈600 MHz). A mechanism for transfer of phase modulation from a strong pulse to a weak pulse via the common lower level is
discussed theoretically.
Zh. éksp. Teor. Fiz. 113, 71–88 (January 1998) 相似文献
8.
Summary Reflectivity measurements have been done on dopedn-type HgCr2Se4 (n≈(1015÷1019) cm−3), at various temperatures ((4÷300) K) in the infra-red range
. The spectra show the structure of a plasma edge and reststrahlbands. Data have been analysed by a Kramers-Kronig procedure.
The deduced dynamical conductivity shows an anomaly near the plasma frequency ωp. The transmitivity measurements show a strong temperature dependence of the conduction band.
Paper presented at the ?V International Conference on Ternary and Multinary Compounds?, held in Cagliari, September 14–16,
1982. 相似文献
9.
L. A. Ageev K. S. Beloshenko E. D. Makovetsky V. K. Miloslavsky 《Optics and Spectroscopy》2009,107(5):796-802
Quartz glass samples with a thin photosensitive AgCl-Ag film, prepared by successive evaporation of AgCl (h
AgCl ≈ 35 nm) and Ag (h
Ag ≈ 8 nm) in vacuum have been investigated. A periodic structure with a period of d = 375 nm formed by Ag particles was obtained in films using a p-polarized laser beam (λ = 532 nm, P = 25 mW) at an angle of incidence of ϕ = 20°. After removing AgCl in a fixing agent, the periodic structure remained on the
glass surface. Subsequent irradiation by a CO2 laser (λ = 10.6 μm, P ≈ 20 W) led to the implantation of this structure into the glass with the conservation of its period d and partial conservation of the related dichroism. The fact of implantation is confirmed by the high mechanical and chemical
stability of the structure obtained. A possible implantation mechanism, taking into account the thermionic emission, Ag ionic
transport, and the presence of free voids in the quartz glass and defects in its structural network, is discussed. 相似文献
10.
The surface of polyethylene terephthalate films (the degree of crystallinity is 0.12–0.18) subjected to uniaxial drawing near
the glass transition temperature of 353 K has been studied by electron microscopy and IR spectroscopy. Formation of a percolation
cluster of densely packed particles, which is deformed as a whole entity, has been revealed in the films. The volume fraction
of the cluster (Ω ≈ 0.5) and the degree of chain unfolding (β ≈ 0.7) at 343 K are independent of the drawing ratio in the
region 1.1 ≤ λ ≤ 3.0. Near λ = 2.5, plane orientation of chains, for which the radius of particles in the amorphous phase
is close to the radius of unperturbed coil, has been found. At 363 K, the cluster framework formation (Ω ≈ 0.6 and β ≈ 1)
terminates near λ = 2.5. The drawing ratio λ ≥ 4 corresponds to microfibrils of chains with the parameters Ω ≈ 0.15 and β
≈ 1 and the fractal dimensionality D ≈ 1. 相似文献
11.
Cai Lingcang Chen Qifeng Gu Yunjun Zhang Ying Zhou Xianming Jing Fuqian 《中国科学G辑(英文版)》2005,48(2):695-705
Hugoniot curves and shock temperatures of gas helium with initial temperature 293 K and three initial pressures 0.6, 1.2,
and 5.0 MPa were measured up to 15000 K using a two-stage light-gas gun and transient radiation pyrometer. It was found that
the calculated Hugoniot EOS of gas helium at the same initial pressure using Saha equation with Debye-Hückel correction was
in good agreement with the experimental data. The curve of the calculated shock wave velocity with the particle velocity of
gas helium which is shocked from the initial pressure 5 MPa and temperature 293 K, i.e., theD ≈u relation,D=C
0+λu (u<10 km/s, λ=1.32) in a low pressure region, is approximately parallel with the fittedD ≈u (λ=1.36) of liquid helium from the experimental data of Nellis et al. Our calculations show that the Hugoniot parameter λ
is independent of the initial density p{in0}. TheD≈u curves of gas helium will transfer to another one and approach a limiting value of compression when their temperature elevates
to about 18000 K and the ionization degree of the shocked gas helium reaches 10−3. 相似文献
12.
CAI Lingcang CHEN Qifeng GU Yunjun ZHANG Ying ZHOU Xianming & JING Fuqian Laboratory for Shock Wave Detonation Physics Research Institute of Fluid Physics Mianyang China 《中国科学G辑(英文版)》2005,48(6):695-705
Helium, hydrogen, and their isotopes are the simplest monoatomic and diatomic molecules. It is relatively easy to describe their properties using the basic principles of quantum mechanics. In condensed matter physics, hydrogen and helium serve as the models for the condensed matter properties at extreme conditions so that both experi- mental and theoretical physicists pay much attention to the study of their properties[1], especially the insulator-metal transition of hydrogen[2]. The aim to st… 相似文献
13.
A self consistent formulation of the Jeans instability of a dusty plasma with proper inclusion of charge dynamics is described.
It is shown that charge fluctuations significantly affect the Jeans as well as the Buneman mode. For plasma particles (electrons
and ions) in local thermal equilibrium, the Jeans lengthλ
J is given byλ
J≈λ
g
F(R, ε, β/η), whereλ
g is the Debye length of the charged grains,R is the square of the ratio of the Jeans to the plasma frequency of the grains,ε is the square of the ratio of the Debye length of the grains and the plasma particles andβ/η is the ratio of the attachment to the decay frequency of the electronic charges to the grain surface. The functional form
ofF is given in the text. Numerical investigation of the Jeans-Buneman mode for a two and three component plasma shows that the
Jeans mode dominates atkλ
D≪1 (wherek is the wave number andλ
D is the Debye length of plasma particles), whereas atkλ
D≫1 only the Buneman mode operates. Charge fluctuations reduce the area of overlap of the two modes. Furthermore, in the absence
of gravity, there exists a new, charge fluctuation induced unstable mode in a streaming dusty plasma. Astrophysical applications
of the results are discussed. 相似文献
14.
Filler-matrix thermal boundary resistance of diamond-copper composite with high thermal conductivity 总被引:1,自引:0,他引:1
A composite material with a high thermal conductivity is obtained by capillary infiltration of copper into a bed of diamond
particles of 400 μm size, the particles having been pre-coated with tungsten. The measured thermal conductivity of the composite
decreases from 910 to 480 W m−1 K−1 when the coating thickness is increased from 110 to 470 nm. Calculations of the filler/matrix thermal boundary resistance
R and the thermal conductivity of the coating layer λ
i
using differential effective medium, Lichtenecker’s and Hashin’s models give similar numerical values of R and λ
i
≈ 1.5 W m−1 K−1. The minimal thickness of the coating h ∼ 100 nm necessary for ensuring production of a composite while maximizing its thermal conductivity, is of the same order
as the free path of the heat carriers in diamond (phonons) and in copper (electrons). The heat conductance of the diamond/tungsten
carbide coating/copper interface when h is of this thickness is estimated as (0.8–1) × 108 W m−2 K−1 and is at the upper level of values characteristic for perfect dielectric/metal boundaries. 相似文献
15.
Vysotsky S. L. Nikitov S. A. Novitskii N. N. Stognii A. I. Filimonov Yu. A. 《Technical Physics》2011,56(2):308-310
The spectrum and propagation losses of a surface magnetostatic wave in a 1D ferrite magnon crystal are experimentally studied
as a function of angle φ between the wavevectors of the surface magnetostatic wave and periodic crystal lattice. Variation
in the positions of Bragg forbidden bands with angle φ is described. A wide transmission band is discovered near long-wave
frequency boundary f
0 of the surface magnetostatic wave in a narrow interval of angles around φ ≈ 57°. In the interval 70° < φ < 90° and at frequencies
below f
0, there exists a magnetostatic wave with a wavevector that is normal to the bias field. 相似文献
16.
Summary The data of 46 months of the GEOGRAV gravitational-wave antenna are analysed to search for monochromatic Doppler-shifted signals
from rotating neutron stars, in the frequency band (856.2÷859.2) Hz. Two different methods were used. With the first, the
gravitational radiation from the whole sky is investigated and a limit ofh≤1·10−21 is found. With the second method only the radiation from a single source is searched. The Galactic Centre and the Large Magellanic
Cloud are considered as sources and the limit ofh≤6·10−22 is found. 相似文献
17.
A vector field q (the order parameter of the molecular packing) describing the packing (specifically, the orientation) of membrane-forming
amphiphilic molecules is introduced to describe the structures of lyotropic phases constructed from membranes. In the general
case q·n≠0 (where n is the unit normal vector) and therefore the singularities of the vector field q are not determined uniquely by the topology of the surface. The condition q·n=0 signifies disruption of the packing of the molecules. This corresponds to holes, which can form in membranes when lyotropic
systems are diluted. As an illustration, the simplest type of such singularities, in which the distribution of the field q around a hole is described by a part of an instanton with unit topological charge, is studied. It is shown that such a distribution
guarantees the existence of a local minimum under the condition that the tension per unit length λ of the hole boundary is small compared with the deformation energy of the field q:
λh/K≪l (K is the modulus of the orientational elasticity of the field q and h is the thickness of the membrane). The radius of the hole which is formed equals L≈2.52(K/λh)1/3 and the energy E≈59.79K(λh/K)1/3.
Pis’ma Zh. éksp. Teor. Fiz. 64, No. 8, 575–580 (25 October 1996) 相似文献
18.
L. S. Lunin I. A. Sysoev D. L. Alfimova S. N. Chebotarev A. S. Pashchenko 《Journal of Surface Investigation: X-ray, Synchrotron and Neutron Techniques》2011,5(3):559-562
The possibility of obtaining ion-beam-deposited InAs/GaAs heterostructures with quantum dots for photovoltaic converters is
shown. The surface morphology of the grown heterostructures is analyzed by scanning probe microscopy. Quantum dots and InAs
nanoclusters with planar dimensions from 20 to 100 nm and a height from 5 to 80 nm are detected. The average surface density
of quantum-dimensional InAs objects with a size below 35 nm is 105 mm−2. In the photoluminescence spectra (T = 300 K), a peak is revealed with a maximum at the wavelength λ = 1150 nm (hν ≈ 1.1 eV), which shows that the grown heterostructures contain InAs quantum dots of various sizes. 相似文献
19.
Experimental absorption spectra of benzene, isooctane, and their mixtures are obtained in the wavelength range λ = 1620–1820
nm in which the first overtones of vibrational frequencies of CH, CH2, and CH3 hydrocarbon groups are located. Positions of fundamental absorption bands of benzene are refined. Absorption spectra of benzene-isooctane
mixtures are shown to intersect in a narrow area near λ ≈ 1695 nm. The main maximum of benzene absorption at λ = 1671.5 ±
0.5 nm, where the influence of isooctane absorption is practically absent, is proposed for determining the content of benzene
in benzene-isooctane mixtures. A linear calibration curve for λ = 1671.5 nm that encompasses the full range of benzene concentrations
(0–100%) is presented.
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 5, pp. 631–634, September–October, 2008. 相似文献
20.
T. M. Burbaev M. N. Gordeev D. N. Lobanov A. V. Novikov M. M. Rzaev N. N. Sibeldin M. L. Skorikov V. A. Tsvetkov D. V. Shepel 《JETP Letters》2010,92(5):305-309
The electron-hole liquid (EHL) in SiGe layers of Si/Si1 − x
Ge
x
/Si quantum-confinement heterostructures is discovered. It is composed of quasi-two-dimensional holes in the quantum well
formed by the SiGe layer and quasi-three-dimensional electrons, which occupy a wider region of space centered on this layer.
The densities of electrons and holes in the EHL are determined to be p
0 ≈ 8.5 × 1011 cm−2 and n
0 ≈ 4.8 × 1018 cm−3, respectively. It is demonstrated that the gas phase consists of excitons and excitonic molecules. The conditions on the
band parameters of the structure under which the formation of the EHL of this kind and biexcitons is possible are formulated. 相似文献