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1.
The performance of a compact uv photo-preionized TE laser is studied in the pressure range 1–5 bar. As the pressure is increased, the laser pulse shape is little altered, but both the peak power and the total output pulse energy increase significantly with pressure, even for constant input electrical energy. For various gas mixtures and excitation source capacitors the measurements suggest approximate output energy scaling with the product of the source charge per unit electrode area [C.m–2] and the molecular partial pressure [CO2+N2+CO]. This is explained in terms of the pressure-dependent discharge impedance. An input-energy-related discharge instability limits the optimum laser pressure to 1.5–2.5 bar, and we show that, at constant input energy, the instability boundary depends on the molecular partial pressure alone. The pre-ionization photo-electron yield varies negligibly with pressure, but the discharge tolerance to added oxygen decreases asp –3 top –4, dependent on gas mixture. Nevertheless sealed operation for >105 shots has been obtained with a 5% CO25% CO3% N22% H285% He gas mixture at a total pressure of 5 bar.  相似文献   

2.
It was shown in a previous communication that the nonlinear Schrödinger equation exhibits a spectrum of eigenfunctions of the form = k,A k (coshkx) –k and = k B k (coshkx) –k–1sinhkx, and the corresponding eigenvalues of the energy are related to a band structure with a characteristic energy gap as a significant feature. In the present paper, it is shown that a further spectrum exists exhibiting the general structure = k=0 A k(cosh kx)–k–1/2and = k=0 Bk(cosh kx)–k–3/2sinhkx and yielding also a band structure. An extension of the solution spectrum to a nonlinear Klein-Gordon equation and a nonlinear Dirac equation does not imply essential difficulties, and the corresponding characteristic band structure has to be related to a mass spectrum.  相似文献   

3.
ArF laser-induced CVD has been employed to generate hydrogenated amorphous silicon (a-Si:H) from Si2H6 gas dilute with He, Ar, or H2. The formation of amorphous films or powder is found to depend critically on the kind of buffer gas, the stationary total and partial gas pressures, and the substrate temperature. These dependences have been investigated in the 1–5 Torr pressure and 100–400 °C temperature ranges. They are semiquantitatively discussed in terms of ArF laser photolysis of disilane, gas heating by heat flow from the substrate and laser irradiation, diffusion, and gas phase polymerization. Furthermore, photo ionization has been observed but found irrelevant for the a-Si:H layer properties. The photo and dark conductivities ( ph, d) of the semiconductor layers are determined by the substrate temperature. The ph values range between 10–7 and 10–4 –1 cm–1 and the d values between 10–11 and 10–8 –1 cm–1. The maximum ratio ph/ d amounts to 4×104. The layers are further characterized by their optical band gap and activation energy. The layer properties are compared to literature values of amorphous films prepared by various photo, HOMO, and plasma CVD methods.  相似文献   

4.
The rare-earth site of samples having the compositions (Fe,Cu)Sr2(Eu,Ce) n Cu2O4+2n+z (n=2 and 3) were studied by151Eu Mössbauer spectroscopy. The results obtained are compared with measurements of EuBa2Cu3O7– (123) and Bi2Sr2(Ca1–yEuy)Cu2O8+E (2212) samples. The full quadrupole Hamiltonian of the 21.5-keV -transition was applied in analyzing the measured spectra. Simultaneous fitting of spectra recorded from crystallites oriented in various directions was used to determine the hyperfine parameters of then= 2 and 3 samples. Two different electric field gradients, not discernible in simple random crystallite measurements, were obtained for then=3 series.  相似文献   

5.
Letw = {w(x)xZd} be a positive random field with i.i.d. distribution. Given its realization, letX t be the position at timet of a particle starting at the origin and performing a simple random walk with jump rate w–1(Xt). The processX={X t:t0} combined withw on a common probability space is an example of random walk in random environment. We consider the quantities t =(d/dt) E (X t 2M –1 t and t(w) = (d/dt)Ew(X t 2 – M 1t). Here Ew. is expectation overX at fixedw and E = Ew (dw) is the expectation over bothX andw. We prove the following long-time tail results: (1) limt td/2t= V2Md/2–3(d/2)d/2 and (2) limt td/4 st(w)= Zs weakly in path space, with {Zs:s>0} the Gaussian process with EZs=0 and EZrZs= V2Md/2–4(d)d/2 (r + s)–d/2. HereM and V2 are the mean and variance of w(0) under . The main surprise is that fixingw changes the power of the long-time tail fromd/2 tod/4. Since , with 0 the stationary measure for the environment process, our result (1) exhibits a long-time tail in an equilibrium autocorrelation function.  相似文献   

6.
Refait  Ph.  Drissi  S.  Abdelmoula  M.  Génin  J.-M. R. 《Hyperfine Interactions》2002,139(1-4):651-655
Green rust-like compounds (GRs) were discovered as natural minerals in various hydromorphic soils, where anoxic conditions allow their stability. They may control some redox processes in aquifers and participate to the transformation of various pollutants. Since Mg(II) cations are present in the fields where GRs were discovered, a partial substitution of Mg(II) to Fe(II) leading to intermediate compounds between GRs and usual Mg(II)–Fe(III) hydroxysalts is suspected. Mg(II)–Fe(II)–Fe(II) hydroxycarbonates can be obtained as intermediate oxidation products of (Mg, Fe)(OH)2 in carbonate-containing aqueous media obeying to [FeII 4(1–x)MgII 4x FeIII 2(OH)12]2+ [CO3 2– nH2O]–2. TMS spectra at 12 K are similar to those of GRs, i.e., two quadrupole doublets, one due to Fe(II) with a large isomer shift =1.29 mms–1 (with respect to -iron at room temperature) and quadrupole splitting E Q=2.76 mms–1, the other one due to Fe(III) with smaller hyperfine parameters =0.49 mms–1 and E Q=0.44 mms–1. Fe(II) ions oxidise rapidly into Fe(III) with dissolved O2. The reactivity is similar to that of Fe(II)–Fe(III) hydroxysalts GR, and thus the potential of Mg(II)–Fe(II)–Fe(III) compounds for reducing pollutants.  相似文献   

7.
The nature of the optical absorption gap in NiO at 4.0 eV is investigated. It is found that this gap is due to a band to band transition, where an electron is taken out of the valence band and placed into the conduction band. The optical gap of 6.0 eV found in NiMgO is of a nature, where an electron is taken out of the oxygen 2p band and placed into the first affinity level of the Ni2+ ion (3d 8L»3d 9L–1). The impurity band created in Ni1–x Li x O by the Li ions is found 2.3 eV below the bottom of the conduction band in agreement with model predictions.  相似文献   

8.
The119Sn-Mössbauer spectra ofxSnO·(70–x)SnF2·30P2O5 glasses (0 x70) measured at 78 K comprised a doublet due to Sn2+ (=3.30–3.36 mm s–1, = 1.70–1.72 mm s–1) and a weak singlet due to Sn4+ located at –0.23 mm s–1 with respect to BaSnO3. The and of Sn2+ were comparable to those of Sn2P2O7. Small Debye temperatures (146 and 155 K) were obtained from the low-temperature measurements. These results indicate that Sn2+ and Sn4+ occupied interstitial sites, being loosely and ionically bonded to distorted PO4–x F x tetrahedra.  相似文献   

9.
For the radial Schrödinger equation with a potentialq(x) decreasing at infinity asq 0 q , (0, 2), the low energy asymptotics of spectral and scattering data is found. In particular, it is shown that forq 0>0 the spectral function vanishes exponentially as the energyk 2 tends to zero. On the contrary, there is always a zero-energy resonance forq 0<0. These results determine the local asymptotics of solutions of the time-dependent Schrödinger equation for large timest. Specifically, for positive potentials its solutions decay as exp(–0 t (2–)/(2+), 0>0,t. In the case (1, 2) it is shown that for ±q 0>0 the phase shift tends to ± ask0 and its asymptotics is evaluated.  相似文献   

10.
Thed-dimensional random Cantor set is a generalization of the classical middle-thirds Cantor set. Starting with the unit cube [0, 1] d , at every stage of the construction we divide each cube remaining intoM d equal subcubes, and select each of these at random with probabilityp. The resulting limit set is a random fractal, which may be crossed by paths or (d–1)-dimensional sheets. We examine the critical probabilityp s(M, d) marking the existence of these sheet crossings, and show that ps(M,d)1–pc(M d) asM, where pc(M d) is the critical probability of site percolation on the lattice (M d) obtained by adding the diagonal edges to the hypercubic lattice d. This result is then used to show that, at least for sufficiently large values ofM, the phases corresponding to the existence of path and sheet crossings are distinct.  相似文献   

11.
We derive the exact stationary probability distribution for the coupled system of Langevin equationsd t u=uu s,d t s=–s+d 2+F(t).  相似文献   

12.
The integrated density of states has C-like singularities, ln|k(E)–k(E c )|=–|EE c |v/2 c (E), with c >0, a milder function at the edges of the spectral gaps which appear when the distribution function of the potentiald has a sufficiently large gap. The behaviour of c nearE c is determined by the local continuity properties ofd near the relevant edge: c (E)=O(1) ifd has an atom and =O(ln|EE c |) if is (absolutely) continuous and power bounded.  相似文献   

13.
Magnetic and electric hyperfine interactions in the system EuSm were investigated with the isomeric 11/2 state in145Eu by applying the time-differential perturbed angular distribution (TDPAD) method. The temperature dependence of paramagnetism was studied between 90 K and 1000 K by measuring the magnetic hyperfine interaction frequency L=gNN1 (T)Bext. The paramagnetic correction factor strictly follows the Curie-Weiss relation =1+C/(T-), withC=–50(2) K and =–29(5) K. This is compatible with a hyperfine field ofB int(0)=–25(1) T, a valence of two for Eu in Sm, and antiferromagnetic order at low temperatures.The temperature dependence of the electric quandrupole coupling constant vQ, investigated between 100 K and 400 K, can be reproduced by a linear temperature variation vQ(T)=vQ(0) (1-AT), with vQ(0)=16.2(4) MHz andA=7.2(8)·10–4 K–1.The paramagnetic relaxation time rel of the nuclear alignment is proportional to the temperature of the sample, with rel T–1=3.7(2) ·10–9s K–1.This leads to the Korringa relation J T=const=5.1(5)·10–11s K for the relaxation time of the 4f electronic spinJ. Assuming that the relaxation ofJ is mainly caused by exchange interaction between conduction electrons and localized 4f electrons at the Eu site, an exchange integral of |J eff|=0.10(2) eV can be deduced.  相似文献   

14.
The infra-red spectra of a large number of ternary Cu(II) oxides with at least a quasi square-planar coordination of oxygen around the copper ions have been studied. The frequency of the bands with the highest frequency,v max, is found to correlate extremely well with the shortest Cu–O distance.v max increases at an impressive rate of 20 cm–1 per 0.01 Å when the Cu–O distance becomes less than 1.97 Å, which is the Cu2+–O2– distance in square-planar CuO4 complexes as obtained from empirical ionic radii considerations. The marked sensitivity may be used as a titration procedure not only to assign bands but also to obtain diagnostic information about local coordination in compounds derived, for example, from the YBa2Cu3O7–d structure such as LaCaBaCu3O7–d . The only example where this correlation fails is in the two-layer non-superconducting oxides derived from La2(Ca, Sr)Cu2O6. The significance of this result is discussed. The marked dependence of frequency on the bond-distance is qualitatively examined in terms of an increased electron-phonon coupling to account for the observed tendency of the superconducting transition temperature to go through a maximum as the average basal plane Cu–O distance is decreased.  相似文献   

15.
We present a method for obtaining bounds on the magnetic moment of the lepton. In order to do this, we study the radiative decayW as a function of the anomalous magnetic moment of the ,a . One can obtain bounds as good asa < 4.05×10–2, 2.25×10–2, 4.5×10–3, and 2.5×10–3 at the present Fermilab, future Fermilab, SSC, and LHC, respectively.  相似文献   

16.
For the reaction +d2n+v is shown that the momentum dependence of the N*(1236) propagator in the N*-excitation current of the pion range could he neglected only for the square of the effective mass M2 10(M *2–M2).Dedicated to Academician Václav Votruba on the occasion of his seventieth birthday.  相似文献   

17.
A suitable dual for the k-acceleration bundle(T k M, k ,M) is the fiberedbundle (T k–1 M× M T*M). The mentioned bundle carries a canonicalpresymplectic structure and k canonical Poisson structures. By means of thisdual we define the notion of Hamilton spaces of orderk, whose total spaceconsists of points x of the configuration spaceM, accelerations of order 1,...,k – 1, y (1),...,y (k–1), and momenta p. Some remarkable Hamiltonian systemsare pointed out. There exists a Legendre mapping from the Lagrange spaces oforder k to the Hamilton space of order k.  相似文献   

18.
Investigations were made of the electrical properties, the cathodolumiescence and photoconductivity spectra, and the temperature dependence of the majority carrier lifetime in gallium arsenide with a high concentration of tin (n=2·1018 cm–3, 1.5·1017 cm–3) that was doped with copper under different diffusion regimes. Measurements of the Hall effect revealed centers with an ionization energy 0.175 ± 0.005 eV, their concentration depending on the rate of cooling of the samples. The cathodoluminescence and Hall effect data suggest that the cathodoluminescence band observed at 1.35 eV in GaAsSnCu is associated with radiative transitions of electrons to centers with a =Ev + 0.175 eV. The hole lifetime in GaAsSnCu has a complicated temperature dependence which can be explained qualitatively by the presence of two types of capture center.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 58–63, September, 1980.  相似文献   

19.
Turbulent fluctuations are treated using a stationary distribution functionw st for an order parameter field representing a fluid. Naive scale invariance ofw st yields thek –5/3 spectral law in three dimensions andk –3 in two dimensions. The noise parameter of the stationary distribution is connected with energy flow or enstrophy conservation, respectively. In order to include fluctuations of the local energy dissipation a grand distribution function is introduced.  相似文献   

20.
Highly unstable FeO is chemically passivated by incorporating Cr3+ ions by solid solution technique and forming FexOCr3+ single phase material. XRD, chemical analysis and Mossbauer spectroscopy are used for the characterization of the freshly prepared as well as samples aged in the desiccator for nearly three months. Optimum concentration range — 0.25 to 0.75 mole% — of Cr2O3 has been found to be necessary for stabilizing FexOCr3+. x is determined by chemical analysis. Mossbauer and XRD studies have confirmed the chemical passivation of unstable FeO.NCL Communication No. 3905  相似文献   

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