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1.
A new method is proposed to enhance microwave radiation with a wavelength of λ ∼ 1 cm in an active medium comprising elongated
conducting nanotubes dispersed in air, which is energy pumped by a nonstationary electric field. For a volume fraction of
nanoparticles c
0 ≈ 10−3 in air at atmospheric pressure, the necessary value of the nonstationary pumping electric field (generated by a high-power
nanosecond pulsed voltage source) is estimated at ∼ 200 J/m3 and the weak signal gain is estimated at Γ0 = 0.055 m−1. One possible mechanism of microwave radiation enhancement in a spatial resonator is considered. 相似文献
2.
The concentration of O2(a
1Δ) molecules have been measured in the direct current discharge in an oxygen flow were measured in various cross sections
in the gas flow channel after the discharge. It is shown that the decrease in the concentration can be described by a quadratic
dependence of rate on the O2(a
1Δ) concentration. The rate constant of such a process is estimated to be ∼1 × 10−31 cm6/sec. Potential processes are considered. A three-body process in which an O(P) atom participates as the second particle apparently plays the key role 相似文献
3.
V. P. Domanov 《Radiochemistry》2010,52(3):230-236
Gas thermochromatographic experiments aimed to prepare volatile oxygen-containing americium compounds were performed. Under
the experimental conditions, Am formed three volatile compounds: AmO2, previously unknown trioxide AmO3, and, presumably, acid of the composition H2AmO4, with centers of the adsorption zones at ∼475, ∼315, and ∼140°C. The calculated enthalpies of adsorption −ΔH
a0 of these compounds on the quartz surface (kJ mol−1) are 180 ± 10, 144 ± 7, and 109 ± 8, respectively. Americium di- and trioxide are less volatile than the respective oxides
of U, Np, and Pu. The same trend was observed with the presumed acids. 相似文献
4.
M. Aidaraliev N. V. Zotova S. A. Karandashev B. A. Matveev M. A. Remenny N. M. Stus’ G. N. Talalakin 《Technical Physics Letters》1998,24(6):472-474
The directional patterns, current-voltage characteristics, and spectral characteristics of mesastripe lasers with InGaAsSb
active layers, emitting at λ=3.0–3.6 μm (77 K) and having threshold currents ≥15 mA (j
th≥200 A/cm2), are investigated. The maximum output power is 1.4 mW (λ∼3.3 μm), the differential quantum efficiency ∼3%(τ=5–30 μs, f=500 Hz) for lasing in a longitudinal mode with beam divergences ΔΘ∥∼15° and ΔΘ ⊥ ∼30°. The relationship of the differential
quantum efficiency to the order of the spatial mode of the lasing is demonstrated. A single-mode, current-tunable (−30 cm−1/A) laser is used to measure the transmission of methane in the region of the ν
3 absorption band.
Pis’ma Zh. Tekh. Fiz. 24, 40–45 (June 26, 1998) 相似文献
5.
R. H. Dauskardt B. J. Dalgleish D. Yao R. O. Ritchie P. F. Becher 《Journal of Materials Science》1993,28(12):3258-3266
The characteristics of subcritical crack growth by cyclic fatigue have been examined in a silicon carbide whisker-reinforced
alumina composite, with specific reference to the role of load ratio (ratio of minimum to maximum applied stress intensity,
R=K
min/K
max); results are compared with similar subcritical crack-growth data obtained under constant load conditions (static fatigue).
Using compact-tension samples cycled at ambient temperatures, cyclic fatigue-crack growth has been measured over six orders
of magnitude from ∼10−11–10−5 m cycle−1 at load ratios ranging from 0.05–0.5. Growth rates (da/dN) display an approximate Paris power-law dependence on the applied stress-intensity range (ΔK), with an exponent varying between 33 and 50. Growth-rate behaviour is found to be strongly dependent upon load ratio; the
fatigue threshold, ΔK
TH, for example, is found to be increased by over 80% at R=0.05 compared to R=0.5. These results are rationalized in terms of a far greater dependency of growth rates on K
max(da/dN ∞ K
max
30
) compared to ΔK(da/dN ∞ ΔK
5), in contrast to fatigue behaviour in metallic materials where generally the reverse is true. Micromechanisms of crack advance
underlying such behaviour are discussed in terms of timedependent crack bridging involving either matrix grains or unbroken
whiskers. 相似文献
6.
T. N. Mukhamedjanov O. P. Sushkov J. M. Cadogan 《Journal of Superconductivity and Novel Magnetism》2007,20(2):193-196
We suggest to use insulating garnets doped by rare-earth ions for measurements of nuclear anapole moments. A parity violating
shift of the NMR frequency arises due to the combined effect of the lattice crystal field and the anapole moment of the rare-earth
nucleus. We show that there are two different observable effects related to frequency: (a) shift of the NMR frequency in an
external electric field applied to the solid; the value of the shift is about Δν1 ∼ 10−5 Hz with E = 10 kV/cm, and (b) splitting of the NMR line into two lines. The second effect is independent of the external electric field.
The value of the splitting is about Δν2 ∼ 0.5 Hz; it depends on the orientation of the crystal with respect to magnetic field. Both estimates are presented for the
magnetic field of about 10 T. 相似文献
7.
E. Yu. Loktionov A. V. Ovchinnikov Yu. Yu. Protasov D. S. Sitnikov 《High Temperature》2011,49(3):403-412
Experimental research results are presented on the formation dynamics and macrostructure of optical discharges of condensed
matter of a polymer series ((C2F4)
n
, (CH2O)
n
) under the action of a femtosecond laser (τ
0.5 ∼ 45–70 fs) pulses (I
0 ∼ 1013−1015 W/cm2) in the UV — NIR spectral region (λ ∼ 266, 400, 800 nm) under air and vacuum conditions. Electron density distributions in
the near-surface area of the optical discharge, vapor expansion, and velocities of shock-wave front propagation are determined
for the first time by precise laser pulse micro-interferometry with high spatial and time resolution. The correspondence is
shown of the values of the laser ablation spectral-energy threshold, as determined by interference microscopy and the interferometry
of a gas-plasma flow. An estimation technique for the total momentum of light-erosion gas-plasma flow in the sub-nanonewton
range is proposed and implemented for the first time. The results of comparative analysis are presented on the laser radiation
conversion efficiency at different stages of femtosecond optical discharges. 相似文献
8.
Flow stress, Young’s Modulus, energy and strain of fracture of poly(methyl methacrylate) (PMMA) and polystyrene (PS) were studied under compressive loading at strain rates of 10−4–10 s−1 and temperatures from 293 K to temperatures ∼20 K below T
g. It was found that the energy of fracture shows an increase in the quasi-static strain rate (10−4–10−3 s−1) region and becomes constant in the low strain rate (10−2–10 s−1) region, while the strain of fracture shows a slow decrease with rate over the strain rate range tested. The activation energies and volumes of PMMA and PS at yield stress, 20% and 30% strain were evaluated using Eyring’s theory of viscous flow. ΔG was found to be constant for all strain rates and strains for both PMMA and PS. The activation volume for both materials increased as a function of strain. 相似文献
9.
A. V. Abramov A. G. Deryagin N. G. Deryagin S. I. Kokhanovskii V. I. Kuchinskii E. U. Rafailov G. S. Sokolovskii D. N. Tret’yakov 《Technical Physics Letters》1997,23(3):172-174
Results are presented of studies of the photoluminescence properties of epitaxial layers of AlxGa1−x
As solid solutions grown by liquid-phase epitaxy with nonequilibrium crystallization achieved by ultrafast rates of cooling
of the flux (V∼102–103 °C/s). The photoluminescence characteristics obtained indicate that the epitaxial layers are of high quality. It is also
observed that when samples with x
buff=0.5–0.55 are exposed to laser radiation of power density ∼1 kW/cm2 at a temperature of 77 K, the spectral composition of the radiation undergoes irreversible changes caused by the formation
of an arsenic vacancy (V
As)-donor impurity complex.
Pis’ma Zh. Tekh. Fiz. 23, 8–13 (March 12, 1997) 相似文献
10.
In this paper, the enthalpies of dissolution of matrine in ethanol (EtOH) were measured using a RD496-2000 Calvet microcalorimeter
at 309.65 K under atmospheric pressure. The differential enthalpy (Δdif
H
m) and molar enthalpy (Δsol
H
m) of dissolution of matrine in ethanol were determined. And the relationship between heat and the amount of solute was also
established. Based on the thermodynamic and kinetic knowledge, the corresponding kinetic equation that described the dissolution
process was determined to be
\fracdadt=2.36×10-4(1-a)1.09{\frac{{\rm d}\alpha}{{\rm d}t}=2.36\times 10^{-4}(1-\alpha )^{1.09}} . Moreover, the half-life, t
1/2 = 48.89 min, Δsol
H
m = −12.40 kJ · mol−1, Δsol
S
m = −354.7 J · mol−1 · K−1, and Δ sol
G
m = 97.43 kJ · mol−1 of the dissolution process were also obtained. The results show that this work not only provides a simple method for the
determination of the half-life for a drug but also offers a theoretical reference for the clinical application of matrine. 相似文献
11.
CdGa2S4 single crystals have been grown from a presynthesized source material by closed-tube iodine vapor transport, and their X-ray
dosimetric properties have been studied. Their X-ray sensitivity coefficient K ranges from K = 1.26 × 10−11 to 1.39 × 10−10 A min/(V R) at effective X-ray hardnesses V
a = 25–50 keV and dose rates E = 0.75–78.05 R/min, and increases with X-ray dose. The K(V
a) curve has a negative slope, in contrast to the K(E) curve. The photocurrent-dose curves of the CdGa2S4 single crystals demonstrate that the steady-state X-ray photocurrent is a power-law function of X-ray dose rate: ΔI
E,0 ∼ E
α
. With increasing V
a, the slope of the curves sharply decreases and α approaches unity. 相似文献
12.
Takeyuki Suzuki Yoshitaka Dansui Tetsuji Shirai Chikako Tsubaki 《Journal of Materials Science》1985,20(9):3125-3130
The solid solubility limit, grain orientation, defect structure and electrical conductivity of solidified rhombohedral specimens
in the Bi2O3-BaO system are described. The c-axes (in hexagonal notation) of solidified specimens were almost entirely oriented along the platelet/film thickness. Slow-cooling
(∼ 10−2° Csec−1) of the system gave solid solutions with substitutional type of 2BaO → 2BaBi′ + 20+ V
0
..
for 12 to 32 mol % BaO. High-temperature modification of slowly-cooled sample (16 mol % BaO) showed a conductivity of 8.8×10−1 Ω−1 cm −1 at 600° C along the conduction plane (perpendicular to the c-axis). Rapid quenching (∼ 105° C sec−1) produced solid solutions for 8 to 20 mol % BaO introducing interstitial Ba2+ (10–12 mol % BaO) and Schottky type defects such as VBi‴ and V
Bi
‴
and V
0
..
(16 to 20 mol % BaO), however the high-temperature modification of the rhombohedral structure could not be frozen. 相似文献
13.
V. G. Shengurov V. Yu. Chalkov S. A. Denisov D. V. Shengurov R. Kh. Zhukavin M. N. Drozdov 《Technical Physics Letters》2011,37(7):601-604
Controlled boron doping of Si1 − x
Ge
x
epilayers has been achieved during low-temperature growth of SiGe/Si(100) heterostructures by sublimation of boron-doped
silicon in a germane medium. Boron-doped single-crystalline silicon plate was sublimed by resistive heating to ∼1300°C. Using
this source, heterostructures with selectively doped layers, sharp dopant concentration profiles, and a maximum boron concentration
of ∼1 × 1019 cm−3 were obtained. 相似文献
14.
Mahendra Nath Roy Bhoj Bahadur Gurung Vikas Kumar Dakua 《International Journal of Thermophysics》2006,27(5):1539-1550
Electrolytic conductivities of potassium halides, KX (X = Cl−, Br−, I−) have been investigated in 10, 20, and 30 mass% glycerol + H2O mixtures at 298.0, 308.0, and 318.0 K. The conductance data have been analyzed by the Fuoss-conductance–concentration equation in terms of the limiting molar conductance (Λ0), the association constant (K
A
), and the distance of closest approach of ion (R). The association constant (K
A
) tends to increase in the order: 10 mass% < 20 mass% < 30 mass% glycerol + water mixtures, while it decreases with temperature. Thermodynamic parameters ΔH
0, ΔG
0, and ΔS
0 are obtained and discussed. Also, Walden products (Λ0η) are reported. The results have been interpreted in terms of ion–solvent interactions and structural changes in the mixed solvents. 相似文献
15.
16.
B. I. Belevtsev Yu. F. Komnik V. I. Odnokozov A. V. Fomin 《Journal of Low Temperature Physics》1984,54(5-6):587-605
Electrical and superconducting properties of indium films condensed in a H2 atmosphere (pressurep
H
2=6×10−6 to 1.4×10−4 Torr) onto a substrate cooled with liquid helium are investigated. As hydrogen content is increased, a continuous increase
in residual resistivity ρ* is observed, permitting systematic study of the resistance vs. temperature dependenceR(T) and the superconducting transition temperatureT
c on approaching the metal-insulator transition (MIT). With regard to ρ*, four regimes of conductivity can be observed: (1)
conductivity with a positive temperature resistance coefficient (TRC), (2) conductivity with a small, constant, negative TRC,
(3) conductivity under weak localization with ΔR (T) ∼ln T or
type corrections, (4) hopping conductivity.T
c rises continuously with ρ* and reaches its peak (∼5.2K) in the second regime. A further increase of ρ* leads to a decrease
ofT
c and complete suppression of superconductivity. The experimental dependenceR(T) is compared with theory. TheT
c variation on approaching the MIT and the relation between Mooij's rule and the superconducting properties are discussed. 相似文献
17.
Kenji Uchino Shoichiro Nomura Leslie E. Cross Robert E. Newnham Sei J. Jang 《Journal of Materials Science》1981,16(3):569-578
Properties of new electrostrictive materials for displacive transducers are reviewed including theoretical, material and design
studies. Intensive investigation of the electrostrictive effects in ferroelectric and antiferroelectric perovskites have led
to some empirical rules: the product of the electrostriction coefficientQ and the Curie-Weiss constantC is constant for all perovskite crystals and theQ value is proportional to the square of the thermal expansion coefficient,α. Consistent with the empirical rules, the relaxor ferroelectric ceramic 0.9 Pb(Mg1/3Nb2/3)O3 −0.1 PbTiO3 possesses much larger strain with lower hysteresis, aging effects and thermal expansion than that obtained with piezoelectric
lead zirconate titanate (PZT). Using a multilayer configuration similar to commercial capacitors, a new mirror control device
capable of large strains with high reproducibility, up toΔL/L ∼ 10−3, with only 200 V applied has been developed. 相似文献
18.
K. R. Nagabhushana B. N. Lakshminarasappa Fouran Singh 《Bulletin of Materials Science》2009,32(5):515-519
Polycrystalline aluminum oxide is synthesized by combustion technique and XRD studies of the sample revealed the α-phase. The synthesized sample is irradiated with 120 MeV swift Au9+ ions for the fluence in the range from 1 × 1011 to 1 × 1013 ions cm−2. A broad photoluminescence (PL) emission with peak at ∼ 447 nm and two sharp emissions with peak at ∼ 679 and ∼ 695 nm are
observed in pristine when sample was excited with 326 nm. However, in the irradiated samples the PL intensity at ∼ 447, 679
and 695 nm decreases with increase in ion fluence. The α-Al2O3 gives rise to seven Raman modes with Raman intensity with peaks at ∼ 253, 396, 417, 546, 630, 842, 867 cm−1 observed in pristine. The intensity of these modes decreases with increase in ion fluence. However, the Raman modes observed
at lower fluences are found to disappear at higher fluence. 相似文献
19.
The thermo-emf ΔV of the touching p- and n-type Cu/Bi-Te/Cu composites with different thicknesses of t
Bi-Te and t
Cu was measured as a function of time by alternating the temperature difference ΔT at periods of T = 20, 60, 120, 240 and ∞ sec, where t
Bi-Te was varied from 0.1 to 2.0 mm and t
Cu from 0 to 4.0 mm. As a result, ΔV changes significantly with t
Bi-Te, t
Cu and T. The effective thermo-emf ΔV
eff increases significantly with an increase of 1/T and exhibited a local maximum at 1/T = 1/240 s−1. The resultant | α | and the effective temperature difference ΔT
eff were increased significantly by optimizing t
Bi-Te and t
Cu at 1/T = 1/240 s−1. The power generation ΔW
eff (= ΔV
eff2/4R
calc) estimated using the measured ΔV
eff and calculated R
calc also exhibited a local maximum at 1/240 s−1 for an optimum combination of t
Bi-Te = 0.1 mm and t
Cu = 2.0 mm, so that the maxima ΔW
eff at 1/T = 1/240 s−1 for the p- and n-type composites were 2.28 and 2.92 times higher than those obtained at 1/T = 0 s−1. This significant increase in ΔW
eff is owing to both the increase in ΔT
eff and the increase in ZT due to the increase in |α|. The power generation was thus found to be enhanced significantly by imposing the alternating
temperature gradients on touching Cu/Bi-Te/Cu composites. 相似文献
20.
The energy distribution of the density of occupied surface states (N
ss) at the cathode insulatorphosphor interface in ZnS:Mn electroluminescent thin-film (ELTF) emitters has been modeled on the
basis of experimental data. Changes in this distribution depending on the parameters of exciting voltage pulses have been
studied. It is established that the energy distribution of N
ss shifts toward deeper levels upon a decrease in the frequency of the exciting signal and the resulting increase in the pause
between the adjacent switch-on states. This behavior corresponds to a cascade relaxation mechanism of electrons trapped on
the surface states. Maximum values of the N
ss (∼2.5 × 1013 cm−2) and the specific density of surface states per unit energy (2 × 1014–1015 cm−2 eV−1) are determined for the cathode insulator-phosphor interface from which electrons are tunneling. Positions of the equilibrium
(∼1.25 eV below the conduction-band bottom) and the quasi-equilibrium (0.6–1.25 eV) Fermi levels during the ELTF emitter operation
are estimated. 相似文献