A mathematical analysis of the etching of {111} diamond surfaces is developed. The slopes of etch pit faces are computed in terms of the specific rate constants, k2 and k3, for removal of two- and three-bonded atoms along 〈1̄10〉 steps and the specific rate constant, kd, for step nucleation at the central initiating defect. Interactions between neighboring steps are neglected. Two limiting etching regimes are found, i.e., one in which the step velocity increases linearly with step length and a regime of constant step velocity. If kd is limited by a no overhang criterion, i.e., nucleation of a new step cannot occur until the prior step has moved out of the way, kd and etch pit slope are functions of the size of the initiating defect. This allows etch pits of vastly different slope to be formed at the same ratio. Point bottom pits with shallow (less than 2°) slopes form from small initiating defects, e.g., dislocation outcrops. At the same ratio flat bottom pits with steep (70° 32') outer faces are formed by etching from large shallow defects, e.g., ring cracks or inclusions. Some preliminary conclusions are drawn about the chemical environment present during the latter stages of diamond genesis. 相似文献
If resonance decaying into KS,L (the short- and long-lived kaon) and a neutral system So of pions, one can isolate the C-even and C-odd, crossed-channel contributions to by using the reactions whether So is a C-eigenstate, or a mixture of C-even and C-odd states. Applications to the production of K1(890) and the Q-meson are discussed, and simple numerical predictions made for QS,L production. Q-production data indicate approximate t-channel helicity conservation for the ω and P' exchanges at vertices involving a spin change, in similarity to the belief for the pomeron. QS,L production data can give information also on Q-decays. 相似文献
We show that the enhancement mechanism proposed for non-leptonic decays of charmed mesons (D0, F+) is still important for decays of pseudoscalar mesons with b flavor, while its effect is small for mesons with t flavor. For the semi-leptonic branching ratios of B? (b), B0(b) and BS0(b) we predict BR (B? → evX ~' 9%, BR(B0 → evX) ~' BR(Bs0 → evX) ~' 5%. We can also derive the enhancement of the branching ratios of uncharmed final states in B decays, i.e. ~' 20 %, ≈ 10%, where = π + ... + K + ... . 相似文献
Surface atomic transport on Ni was measured by mass transport technique on a sinusoidal profile. One of the studied surfaces was within 15' of a singular (001) orientation. Others were vicinal surfaces. Kinetic damping coefficients are shown to be dependent on the profile parameters, i.e. of the density ntot, of all the monoatomic steps and also of the density σc of kinks of the monoatomic steps. If the parameter describes the random motion of adatoms on isolated terraces and if α and k are two coefficients linked to adsorption/emission processes from steps and kinks, a sinusoidal profile with 5 μm periodicity obeys to the relation: . This result demonstrates the importance of surface atomic structure which has been neglected in Mullins' theory, which may be non-negligible in all processes where surface mass transport is involved. 相似文献
The branching ratio has been determined to be (2.68±0.15)×10?3 for photon energies greater than 50 MeV in the KS0 rest frame. The decay KS0→π+π?γ is found to be dominated by the internal bremsstrahlung transition. The branching rato of a possible direct transition is found to be less than 0.06 × 10?3 at 90% confidence level for . 相似文献
The k-particle, infinite-volume distribution functions and modified Ursell correlation functions of a classical system of particles with the two-body potential are considered. The limiting values of the functions and in the limit γ → 0 are calculated, under fairly weak conditions on q and K, by a method involving functional differentiation. These limiting functions are used to describe the molecular structure of the various states of the system both in the range of the potential q(r) and in the rage of the potential γνK(γr). The direct correlation function c? (r, γ) is also considered and it is shown that for , , for all one-phase states, where β is the reciprocal temperature. Special cases of our results confirm those of other authors, including the well-known results of Ornstein and Zernike. 相似文献
A new modification of molecular beam relaxation spectrometry (MBRS) of surface processes is described making use of partial modulation in order to study nonlinear processes: a constant particle beam is directed towards the catalyst surface, the surface temperature is modulated due to absorption of a modulated beam of UV light, reaction products are analyzed by use of phase sensitive mass spectrometric detection. The application of the method is shown by a study of catalytic decomposition of methanol on polycrystalline NiO. Formation of CO was found to be a monomolecular, formation of H2 and H2O bimolecular processes. The resulting mechanism may be described as follows: Rate constants in dependence from surface temperature T0 are η = 1.8 × 103; kd1 = 1.8 × 1010 s?1; kd2 = 1.2 × 10?2 cm2 particles?1 s?1; kd3 = 3.5 × 10?4 cm2 particles?1 s?1. Average surface residence times of the intermediates are: at 550 ? T0 ? 650 K; at 540 ?T0 ? 610 K; at 550 ? T0 ? 645 K. 相似文献
The irreducible components of the Raman scattering tensor operator under the symmetry of a general point group are calculated. The unitary transformations U(ΓγΓksΓk′s′, ρσ) from the Cartesian and spherical components, respectively, to the irreducible components for the 32 crystallographic point groups are collected in tables. As an example the unitary transformation U(ΓγΓksΓk′s′, ρσ) is used to discuss the behavior of the scattering tensor in a resonance Raman experiment. With the help of the general formalism the scattering tensor for electronic Raman transitions of transition metal ions is calculated. As an example the scattering tensors of electronic Raman transitions within the 5T2 state of the high-spin trigonal distorted octahedral Fe2+ are calculated and the refinement of the selection rules is discussed. 相似文献
Using the ARGUS detector at DORIS II, we have observed a signal of 36.7±8.0 events in the decay channel D0→Ks0φ. In the same data sample, we have observed the well established decay D0→Ks0π+π?, and find the ratio, , to be 0.186±0.052. The substantial value of (0.99±0.32±0.17)% then derived for the branching ratio for gives direct evidence that W exchange contributes D0 decay. 相似文献
Granular composites consisting of 25% nickel as 8 nm diameter particles dispersed in an aluminium oxide matrix display excess conduction noise. Co-deposited films with resistance per square about 105 ohms and negative temperature coefficient show a noise power spectral density where α ? 1.10 ± 0.03 over the accessible spectral range of 0.1 Hz ? ? ? 5000 Hz. The amplitude 3 × 10?15 ? Sv(1) ? 5 × 10?12 V2Hz?1, appears to increase approximately quadratically as the applied voltage Vs up to Vs ? 2.5 V and as the first power of Vs for 2.5 ? Vs < 35 V. 相似文献
Using the re-equilibration kinetic method the chemical diffusion coefficient in nonstoichiometric chromium sesquisulfide, Cr2+yS3, has been determined as a function of temperature (1073–1373 K) and sulphur vapour pressure (10?104 Pa). It has been found that this coefficient is independent of sulphur pressure and can be described by the following empirical equation: . It has been shown that the mobility of the point defects inCr2+yS3 is independent of their concentration and that the self-diffusion coefficient of chromium in this sulfide has the following function of temperature and sulphur pressure: . (cm2s?1). 相似文献
The model assumes that when two high energy particles collide each behaves as a geometrical object which has a Gaussian density and is spherically symmetric except for the Lorentz-contraction in the incident direction. Folding the two spatial distribution together we obtain the slope (b) of the elastic diffraction peak in terms of the c.m. velocities (βi and βj) and the sizes (Ai and Aj) of the two incident particles. These sizes are assumed to have the experimental s-dependence of σtot ∝ πA2 for each reaction. The combined s-dependence of the σtot's and the β's gives the s-dependence of the elastic slope . This formula agrees with the experimental slope for p-p, -p, K+-p, K?-p and π±-p elastic scattering from 3 to 1500 GeV/c, with only 3 parameters: Aπ2 = 6.1, AK2 = 3.3 and Ap2 = 10.5 (GeV/c)?2. 相似文献
In the presence of right-handed currents including , it is emphasized that the dominant parity-violating (-conserving) Hamiltonian for nonleptonic decays of charmed hadrons transforms like of SU(4), and leads to distinctive results especially in D+ → KSπ+, F+ → μ+νμ and D0 → K?e+νe, etc. 相似文献
The cyclotron resonance of inversion-layer electrons on (100)p-type Si is found to depend sensitively on an externally applied compressive stress. At low temperatures (T ? 10 K) we observe a considerable increase of the cyclotron mass m1c with stress S along the [001] direction. The effect is most strongly observed at low electron densities ns. For and ns~2 × 1011cm-2 we obtain instead of the expected 0.2m0. Along with this change of a strong narrowing of the resonance is noted. Raising the temperature gives an additional ns- dependent increase of . 相似文献
The results of precise measurements of the energies of the muonic X-ray transitions of 92Mo, 94Mo, 95Mo, 96Mo, 97Mo, 98Mo and 100Mo are reported. The data were analyzed in terms of the Barrett moments 〈rke?αr〉 of the nuclear charge distributions from which the equivalent nuclear radii Rk and the differences ΔRk between neighboring isotopes were computed. Systematic shell effects have been observed at the neutron numbers N = 50 and N = 56. 相似文献
We construct a potential for qurkonium systems using as the basic ingredients the gluon condensate, i.e., 〈0∥GμνaGμνa∥0〉 ≠ 0 to incorporate nonperturbative effects and using quark screening. The potential is able to account satisfactorily for the s, c and b bound states with a flavor independent, essentially constant value for the effective coupling constant . We also investigate heavier quark systems with the constant and find that for quark mass ? 20 GeV the potential is essentially coulombic. 相似文献
Results are presented on two-jet and three-jet cross sections, measured in the UA1 experiment at the CERN Super Proton Synchrotron (SPS) pp? Collider, at the highest available subprocess cms energies (). Precise measurements of the two-jet angular distribution are consistent with previous results but show significant scale-breaking effects. The three-jet Dalitz plot and the three-jet angular distributions show evidence for final- and initial-state bremsstrahlung processes, in agreement with the leading-order QCD predictions. A comparison of the yield of wide-angle three-jet events with the yield of two-jet events at smaller scattering angles gives for the strong interaction coupling constant: at Q2≈4000 GeV2, where the factor may plausibly be assumed to be close to unity. 相似文献