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1.
Bulk and grain boundary (GB) diffusion of 14C in Nb has been studied by the radiotracer serial sectioning technique. B and C kinetic regimes were realized for GB diffusion in the temperature range from 800 to 1173 K. The values of P = sD
gb, D
gb and s follow the Arrhenius dependencies: P = 5.15 × 10–15 exp[–(83.1 kJ/mol)/RT] m3/s (973–1173 K), D
gb = 2.3 × 10–6 exp[–(133.0 kJ/mol)/RT] m2/s (800–950 K), and s = 4.7 exp[(49.9 kJ/mol)/RT].The increase in the GB diffusion compared with self-diffusion is very large despite the probable retardation effect due to the strong segregation.The results for GB diffusion of C in Nb as well as for other interstitial solutes (P, S) in bcc transition metals (- Fe, Mo) are discussed in the framework of the transition state theory. It is assumed that GB segregation decreases the energy of the ground state whereas the change in the diffusion mechanism (e.g. from vacancy to interstitial) leads to a strong decrease of the transition state energy. This change in the diffusion mechanism results in a fast GB diffusion of interstitial solutes in spite of their large tendency to segregate to GBs. 相似文献
2.
A parallel algorithm for the enumeration of isolated connected clusters on a regular lattice is presented. The algorithm has been implemented on 17 RISC-based workstations to calculate the perimeter polynomials for the plane triangular lattice up to clustersizes=21. New data for perimeter polynomials Ds up toD
21, total number of clustersg
s up tog
22, and coefficientsb
r in the low-density series expansion of the mean cluster size up tob
21 are given. 相似文献
3.
V. Starý 《Czechoslovak Journal of Physics》1978,28(9):1036-1046
A simple model of the intermediate stage of thin film growth was established for the case of the three-dimensional growth. In this stage, the film growth is strongly influenced by the growth and the coalescence of islands, often occurring via the so-called liquid-like manner; this process is controlled by the surface self-diffusion of evaporated material. Thus, the characteristic of thin film in this stage measured experimentally, can be employed for the determination of some parameters: the coefficient of surface self-diffusion Ds = D0 exp (-Qs/kT), especially activation energy Qs and pre-exponential factor D0 of the evaporated material and adhesion energy for the system film/substrate. 相似文献
4.
Molecular constants of LiCl(X~1Σ~+) and elastic collisions of two ground-state Cl and Li atoms at low and ultralow temperatures 下载免费PDF全文
Interaction potentials for LiCl(X 1 Σ +) are constructed by the highly accurate valence internally contracted mul-tireference configuration interaction in combination with a number of large correlation-consistent basis sets,which are used to determine the spectroscopic parameters (D 0,D e,R e,ω e,ω e χ e,B e and α e).The potentials obtained at the basis sets,i.e.,aug-cc-pV5Z-JKFI for Cl and cc-pV5Z for Li,are selected to study the elastic collision properties of Li and Cl atoms at the impact energies from 1.0×10 12 to 1.0×10 4 a.u.The derived total elastic cross sections are very large and almost constant at ultralow temperatures,and their shapes are mainly dominated by the s-partial wave at very low impact energies.Only one shape resonance can be found in the total elastic cross sections over the present collision energy regime,which is rather strong and obviously broadened by the overlap contributions of the abundant resonances coming from various partial waves.Abundant resonances exist for the elastic partial-wave cross sections until l=22 partial waves.The vibrational manifolds of the LiCl(X 1 Σ +) molecule,which are predicted at the present level of theory and the basis sets cc-pV5Z for Li and the aug-cc-pV5Z-JKFI for Cl,should achieve much high accuracy due to the employment of the large correlation-consistent basis sets. 相似文献
5.
D. Ebert R. N. Faustov V. O. Galkin 《The European Physical Journal C - Particles and Fields》2010,66(1-2):197-206
The masses of the ground, orbitally and radially excited states of heavy-light mesons are calculated within the framework of the QCD-motivated relativistic quark model based on the quasipotential approach. Both light (q=u,d,s) and heavy (Q=c,b) quarks are treated fully relativistically without application of the heavy-quark 1/m Q expansion. The Regge trajectories in the (M 2,J) and (M 2,n r ) planes are investigated and their parameters are obtained. The results are in good agreement with available experimental data except for the masses of the anomalous $D^{*}_{s0}(2317)$ , D s1(2460) and $D_{sJ}^{*}(2860)$ states. 相似文献
6.
First principles calculations of alloying element diffusion coefficients in Ni using the five-frequency model 下载免费PDF全文
The diffusion coefficients of several alloying elements(Al,Mo,Co,Ta,Ru,W,Cr,Re) in Ni are directly calculated using the five-frequency model and the first principles density functional theory.The correlation factors provided by the five-frequency model are explicitly calculated.The calculated diffusion coefficients show their excellent agreement with the available experimental data.Both the diffusion pre-factor(D 0) and the activation energy(Q) of impurity diffusion are obtained.The diffusion coefficients above 700 K are sorted in the following order:DAl>DCr>DCo>DTa>DMo>DRu>DW>D Re.It is found that there is a positive correlation between the atomic radius of the solute and the jump energy of Ni that results in the rotation of the solute-vacancy pair(E 1).The value of E 2-E 1(E 2 is the solute diffusion energy) and the correlation factor each also show a positive correlation.The larger atoms in the same series have lower diffusion activation energies and faster diffusion coefficients. 相似文献
7.
G. Fricke H. Kopfermann S. Penselin K. Schlüpmann 《Zeitschrift für Physik A Hadrons and Nuclei》1959,156(3):416-424
The hyperfine structure splittings of the electronic ground states2 D 3/2 and2 D 3/2 of the stable isotope Sc45 have been measured by the atomic beam magnetic resonance method. From these splittings the magnetic dipole and electric quadrupole interaction constants are found to bea 3/2=(269,560±0,02) Mc/sb 3/2=?(26,37±0,1) Mc/sa 5/2=(109,034±0,01) Mc/sb 5/2=?(37,31±0,1) Mc/s. The values of the electric quadrupole moment calculated fromb 3/2 andb 5/2 differ by about 5% indicating that the configuration 3d 4s 2 of the ground states is perturbed by higher configurations. Averaging these two values we obtain for the quadrupole moment of Sc45 Q(Sc45)=?(0,22±0,01) · 10?24 cm2. 相似文献
8.
Evren Ataman 《Journal of Macromolecular Science: Physics》2013,52(4):705-715
Small molecule sorption and desorption in and out of Iota‐Carrageenan was studied by using steady‐state fluorescence (SSF) technique. Pyranine dissolved in water used as fluorescence probe. Fluorescence emission intensity, I p from pyranine was monitored for studying sorption and desorption processes at various temperatures. The Fickian model was applied to produce sorption, Ds, early desorption, Ded, and desorption, Dd, coefficients. Corresponding activation energies were obtained and found to be 20.5 kJ mol?1, 7.0 kJ mol?1 and 34.9 kJ mol?1, respectively. The observed Ded value is an order of magnitude smaller than the Ds and Dd coefficients. On the other hand, sorption processes were shown to be twice as fast as desorption processes. 相似文献
9.
Measurement of the diffractive cross section in deep inelastic scattering using ZEUS 1994 data 总被引:1,自引:0,他引:1
The DIS diffractive cross section, dsdiffg* p ? XN/dMXd\sigma^{di\!f\!f}_{\gamma^* p \to XN}/dM_X, has been measured in the mass range MX < 15M_X < 15 GeV for g*p\gamma^*p c.m. energies 60 < W < 20060 < W < 200 GeV and photon virtualities Q2 = 7Q^2 = 7 to 140 GeV2^2. For fixed Q2Q^2 and MXM_X, the diffractive cross section rises rapidly with WW, dsdiffg*p ? XN(MX,W,Q2)/dMX μ Wadiffd\sigma^{di\!f\!f}_{\gamma^*p \to XN}(M_X,W,Q^2)/dM_X \propto W^{a^{diff}} with adiff = 0.507 ±0.034 (stat)+0.155-0.046(syst)a^{diff} = 0.507 \pm 0.034 (stat)^{+0.155}_{-0.046}(syst) corresponding to a t-averaged pomeron trajectory of [`( a\mathbb P )] = 1.127 ±0.009 (stat)+0.039-0.012 (syst)\overline{ \alpha_{_{{\mathbb P}}} } = 1.127 \pm 0.009 (stat)^{+0.039}_{-0.012} (syst) which is larger than [`( a\mathbb P )]\overline{ \alpha_{_{{\mathbb P}}} } observed in hadron-hadron scattering. The W dependence of the diffractive cross section is found to be the same as that of the total cross section for scattering of virtual photons on protons. The data are consistent with the assumption that the diffractive structure function FD(3)2F^{D(3)}_2 factorizes according to x\mathbb P FD(3)2 (x\mathbb P,b,Q2) = (x0/ x\mathbb P)n FD(2)2(b,Q2)x_{_{{\mathbb P}}} F^{D(3)}_2 (x_{_{{\mathbb P}}},\beta,Q^2) = (x_0/ x_{_{{\mathbb P}}})^n F^{D(2)}_2(\beta,Q^2). They are also consistent with QCD based models which incorporate factorization breaking. The rise of x\mathbb P FD(3)2x_{_{{\mathbb P}}} F^{D(3)}_2 with decreasing x\mathbb Px_{_{{\mathbb P}}} and the weak dependence of FD(2)2F^{D(2)}_2 on Q2Q^2 suggest a substantial contribution from partonic interactions. 相似文献
10.
Creep experiments were conducted on Zn-22%?Al in which SiC particulates were introduced by variable co-deposition of multi-phase materials (VCM). The objective of the investigation is to determine the effect of SiC particulates on the creep behaviour in region I (the low-stress region) and region II (the intermediate-stress or superplastic region) of the sigmoidal plot between stress and strain rate, which was previously reported for the reinforcement-free Zn-22%?Al. The creep data show that the presence of SiC particulates has no effect on the sigmoidal trend between stress and strain rate; and that in region II, the stress exponent, n, and the activation energy for creep, Q, agree well with those reported for SiC-free grades of Zn-22%?Al; n?=?2.5 and Q?~?Q gb, where Q gb is energy for grain boundary diffusion in the alloy. However, the data indicate that the presence of the particulates results in narrowing region II and reducing maximum ductility. An analysis of the creep data reveals the presence of a threshold stress that depends strongly on temperature. The microstructural data inferred from an examination of the crept specimens by the means of transmission electron microscopy (TEM) suggest that the origin of τ 0 may be related to the interaction between moving dislocations and dispersion particles. These particles are introduced in the material as a result of processing the material by thermal spray and deposition. 相似文献
11.
s , the surface diffusion coefficient, Ds
′, and the surface reaction rate coefficient, βs
′, of Cu on alumina are determined in the temperature range 1048–1198 K. Measuring simultaneously the time dependence of the
effective thickness, Heff(t), the lateral shift of the boundary, y(t) of beaded films (BF) and using vapour pressure data we concluded that the process
is controlled by surface reaction at the perimeters of beads. Supposing Arrhenius-type temperature dependence for Ds
′, βs
′ and λs the activation energies and preexponential factors have been calculated.
Received: 2 October 1996/Accepted: 27 November 1996 相似文献
12.
Ye.S. Golubeva W. Cassing L.A. Kondratyuk 《The European Physical Journal A - Hadrons and Nuclei》2002,14(2):255-263
We study the perspectives of resonant and nonresonant charmed-meson production in ˉp + A reactions within the Multiple Scattering Monte Carlo (MSMC) approach. We calculate the production of the resonances Ψ(3770),Ψ(4040)
and Ψ(4160) on various nuclei, their propagation and decay to D,ˉD, D
*,ˉD*, D
s,ˉDs in the medium and vacuum, respectively. The modifications of the open charm vector mesons in the nuclear medium are found
to be rather moderate or even small such that dilepton spectroscopy will require an invariant mass resolution of a few MeV.
Furthermore, the elastic and inelastic interactions of the open charm mesons in the medium are taken into account, which can
be related to (u, d )-, s- or c-quark exchange with nucleons. It is found that by studying the D/ˉD ratio for low momenta in the laboratory ( ? 2 - 2.2 GeV/c) as a function of the target mass A stringent constraints on the c-quark exchange cross-section can be obtained. On the other hand, the ratios D
-
s/D
+
s as well as D/D
-
s and D/D
+
s at low momenta as a function of A will permit to fix independently the strength of the s-quark exchange reaction in D
-
s
N scattering.
Received: 1 March 2002 / Accepted: 21 March 2002 相似文献
13.
The nonadiabatic corrections to the self-energy part Σs(q, ω) of the phonon Green’s function are studied for various values of the phonon vectors q resulting from electron-phonon interactions. It is shown that the long-range electron-electron Coulomb interaction has no
direct influence on these effects, aside from a possible renormalization of the corresponding constants. The electronic response
functions and Σs(q, ω) are calculated for arbitrary vectors qand energy ω in the BCS approximation. The results obtained for q=0 agree with previously obtained results. It is shown that for large wave numbers q, vertex corrections are negligible and Σs(q, ω) possesses a logarithmic singularity at ω=2Δ, where Δ is the superconducting gap. It is also shown that in systems with nesting, Σs(Q, ω) (where Q is the nesting vector) possesses a square-root singularity at ω=2Δ, i.e., exactly of the same type as at q=0. The results are used to explain the recently published experimental data on phonon anomalies, observed in nickel borocarbides
in the superconducting state, at large q. It is shown, specifically, that in these systems nesting must be taken into account in order to account for the emergence
of a narrow additional line in the phonon spectral function S(q, ω)≈−π
−1 Im D
s
(q, ω), where D
s
(q, ω) is the phonon Green’s function, at temperatures T<T
c
.
Zh. éksp. Teor. Fiz. 115, 1799–1817 (May 1999) 相似文献
14.
Jörn Manz 《Molecular physics》2013,111(3):899-910
Exact quantum transition probabilities for collinear F + H2 → FH + H on two different potential energy surfaces are analyzed in terms of regional effects of the potentials. The potentials considered are (a) a weakly curved rotated harmonic model potential and (b) a strongly curved rotated Morse potential fitted to the ab initio SCFCI surface of Bender et al. In both potentials a, b the energy along the reaction path has the same parameters, and three successive regions 1–3 are analysed. The main results are: (1) at very low total energies the reactants are reflected from the activation barrier (region 1 of potentials a, b). (2) in the downhill region 2 of potentials a and b the molecules are weakly and strongly excited, respectively. Region 2 of the realistic potential b also causes H2 back reflection, depending on the total energy (although there is no barrier in region 2!); (3) In the final shallow sloped, weakly curved region 3 of potential a, part of the excited molecules are again de-excited before reaching the product's configuration. On the contrary, region 3 of potential b has a non-curved reaction path, and the reaction is adiabatic therein, i.e. the van der Waals minimum is irrelevant for vibrational excitation. Practical aspects of the state path sum method are discussed in detail. 相似文献
15.
R.?P.?Hildebrandt H.?W.?Grie?hammer T.?R.?Hemmert 《The European Physical Journal A - Hadrons and Nuclei》2010,46(1):111-137
We examine elastic Compton scattering from the deuteron for photon energies ranging from zero to 100MeV, using state-of-the-art
deuteron wave functions and NN potentials. Nucleon-nucleon rescattering between emission and absorption of the two photons is treated by Green’s functions
in order to ensure gauge invariance and the correct Thomson limit. With this Green’s function hybrid approach, we fulfill
the low-energy theorem of deuteron Compton scattering and there is no significant dependence on the deuteron wave function
used. Concerning the nucleon structure, we use the chiral effective field theory with explicit D \Delta(1232) degrees of freedom within the small-scale expansion up to leading-one-loop order. Agreement with available data is
good at all energies. Our 2-parameter fit to all elastic g \gamma
d data leads to values for the static isoscalar dipole polarizabilities which are in excellent agreement with the isoscalar
Baldin sum rule. Taking this value as additional input, we find aEs \alpha_{E}^{s} = (11.3±0.7(stat)±0.6(Baldin)±1(theory)).10-4 fm^3 and bMs \beta_{M}^{s} = (3.2±0.7(stat)±0.6(Baldin)±1(theory)).10-4 fm^3 and conclude by comparison to the proton numbers that neutron and proton polarizabilities are the same within rather
small errors. 相似文献
16.
Ag grain boundary (GB) diffusion was measured in the Cu-0.2at%Ag alloy in a wide temperature range from 473 to 970 K. The direct measurements of Ag GB diffusivity D
alloy
gb under conditions of the Harrison C regime revealed that D
alloy
gb is almost identical to D
pure
gb determined earlier for Ag diffusion in high-purity Cu (Divinski, Lohmann, and Herzig, 2001). The penetration profiles determined in the Harrison B regime showed a complex, multi-stage shape. This diffusion behavior can be rationalized assuming that besides GBs significantly covered by segregated Ag atoms, some fraction of GBs remains almost free from Ag atoms in the studied temperature interval. The total amount of pure GBs drastically decreases with decreasing temperature. This hypothesis was proven by measurements of Ag GB diffusion in Cu near 5 bicrystals, which allowed us to analyze in detail the non-linear segregation of Ag in Cu GBs. 相似文献
17.
H. Yuki J. Kasagi A. G. Lipson T. Ohtsuki T. Baba T. Noda B. F. Lyakhov N. Asami 《JETP Letters》1998,68(11):823-829
Yields of protons emitted in the D+D reaction in Pd, Au/Pd/PdO, Ti, and Au foils are measured by a d
E-E counter telescope for bombarding energies between 2.5 and 10 keV. The experimental yields are compared with those predicted
from a parametrization of the cross section and stopping power at higher energies. It is found that for Ti and Au target the
enhancement of the D(d,p)T reaction is similar to that observed with a deuterium gas target (several tens of eV). The dependence of the yields on the
bombarding energy corresponds well to the screening potential parameters U
s=250±15 eV for Pd and 601 ±23 eV for Au/Pd/PdO. Possible models of the enhancement obtained are discussed.
Pis’ma Zh. éksp. Teor. Fiz. 68, No. 11, 785–790 (10 December 1998)
Published in English in the original Russian journal. Edited by Steve Torstveit. 相似文献
18.
In yttrium iron garnet, Y3Fe5O12, the oxygen vacancy concentration at high temperatures depends on the partial oxygen pressure. Due to the electron donating nature of the vacancies, changes in the oxygen vacancy concentration can be measured by electrical conductivity measurements. We discuss a dynamic method for studying the diffusion of oxygen vacancies by measurements of the time dependence of the electrical conduction after a change in the oxygen partial pressure has taken place. It is shown that the interpretation of the measurements is straightforward if the relative change in conductivity remains small (? 10%). Measurements were performed on single crystals and on polycrystalline samples at temperatures 900–1400°C. The samples were made n-type by substitution with Si or p-type by substitution with Ca, Zn or Pb. The partial oxygen pressure was changed between 1 and 0.1 atm. For all samples the diffusion coefficient D of the oxygen vacancies can be represented by , where A = 8400 cm2s?1 and Q = 2.90 eV. It is shown that the activation energy of 2.90 eV is due to the migration enthalpy of the vacancies only. 相似文献
19.
M. A. Khorosheva V. I. Orlov N. V. Abrosimov V. V. Kveder 《Journal of Experimental and Theoretical Physics》2010,110(5):769-774
A method is proposed for determining the nonequilibrium concentration of vacancies and vacancy complexes in silicon crystals
by measuring the concentration of electrically active nickel atoms at the sites of the silicon lattice, [Ni
s
], after the diffusion of nickel at temperatures from 550 to 650°C. It is shown experimentally that, after the diffusion of
nickel from the surface into silicon samples with different initial nonequilibrium concentrations of vacancy complexes, [V]init, formed during crystal growth, the concentration [Ni
s
] in the bulk of a sample to a good degree of accuracy corresponds to the vacancy concentration [V]init determined by a standard method based on the analysis of the concentration profiles of [Au
s
] after the diffusion of gold from the surface. This method for determining the concentration of vacancies is much simpler
than the standard method and allows one to use lower temperatures and a lower thermal budget. 相似文献
20.
We present a two-dimensional model to account for the role of heat-conducting walls in the measurement of heat transport and Soret-effect-driven mass transport in transient holographic grating experiments. Heat diffusion into the walls leads to non-exponential decay of the temperature grating. Under certain experimental conditions it can be approximated by an exponential function and assigned an apparent thermal diffusivity Dth, app < Dth, s, where Dth,s is the true thermal diffusivity of the sample. The ratio Dth, app/Dth, s depends on only three dimensionless parameters, d /ls, κs/κw, and Dth, s/Dth, w. d is the grating period, ls the sample thickness, κs and κw the thermal conductivities of sample and wall, respectively, and Dth,w the thermal diffusivity of the wall. If at least two measurements are performed at different d /ls, both Dth,s and κs can be determined. Instead of costly solving PDEs, Dth,s can be obtained by finding the zero of an analytic function. For thin samples and large grating periods, heat conduction into the walls plays a predominant role and the concentration grating in binary mixtures is no longer one-dimensional. Nevertheless, the normalized heterodyne diffraction efficiency of the concentration grating remains unaffected and the true thermal and collective diffusion coefficient and the correct Soret coefficient are still obtained from a simple one-dimensional model. 相似文献