On the relative intensities of the Raman active fundamentals,r0 structural parameters,and pathway of chair–boat interconversion of cyclohexane and cyclohexane‐d12

Raman spectra of liquid cyclohexane, C₆H₁₂, and deuterated cyclohexane, C₆D₁₂, were recorded with both parallel and perpendicular polarizations. The observed vibrational wavenumbers, depolarization ratios, and their intensities were measured and compared with the corresponding predicted values as well as the experimental values previously reported. The conformational energetics were obtained with the Møller–Plesset perturbation method to the second order [MP2(full)] as well as with density functional theory by the B3LYP method utilizing a variety of basis sets. The average ab initio predicted difference in energy between the more stable chair form (D_3d) and the less stable twisted‐boat form (D₂) is 2213 cm⁻¹ (26.47 kJ/mol), with a similar value of 2223 cm⁻¹ (26.59 kJ/mol) from the density function theory calculations. By using two dihedral angles as variables, we calculated the chair–boat interconversion pathway for cyclohexane at the MP2(full)/6‐31G(d) level. The harmonic force constants, Raman intensities, depolarization values, and the potential energy distribution were predicted from both MP2(full) and B3LYP calculations with the 6‐31G(d) basis set and compared with the experimental values for the chair form when available. The ‘adjusted’ r₀ structural parameters were obtained from MP2/6‐311 + G(d,p) calculations and previously reported microwave rotational constants of five isotopomers of cyclohexane: i.e. 1,1‐d₂, ¹³C‐1,1‐d₂, 1,1,2,2,3,3‐d₆, and d₁ (equatorial and axial). The determined distances in Å are: r(CC) = 1.536(3), r(CH)_ax = 1.098(1); r(CH)_eq = 1.095(1); and the angles in degrees: ∠CCH_ax = 108.8(3); ∠CCH_eq = 110.2(3); ∠CCC = 111.1(3); and ∠HCH = 107.6(3) with dihedral angle ∠CCCC = 55.7(3). These values are compared with those previously reported and it is found that the difference in the r₀ distances (0.003 Å) between the two CH values is much smaller than the difference (0.008 Å) previously reported for the r_s values. Copyright © 2008 John Wiley & Sons, Ltd.     

ICP-AES法直接测定地热温泉水样中的钾、钠、钙、镁、硅、锂、硼的研究

采用顺序扫描式ＩＣＰ光谱仪,直接测定了地热温泉水样中的７种元素,并对最佳测试条件的选择进行了探讨,方法简便,快速、准确,检出限及精密度均可满足分析要求。     

On the burst activity of the Crab Nebula, as observed by air shower arrays

Recent experiments with the Fermi-LAT and AGILE satellite gamma-ray telescopes, in which bursts of gamma-rays from the Crab Nebula were detected in the energy range of ～100 MeV, have aroused keen interest, if not a sensation. However, data on a possible burst in the Crab Nebula at much higher energies of ～100 TeV were published more than 20 years ago. Characteristics of transient and stationary fluxes of gamma rays from the Crab Nebula in various energy ranges are discussed in this work, and it is shown that the old data obtained at ultra-high energies is reasonably consistent with the latest pattern of the source’s burst activity.     

On the validity and properties of the atom-atom potential as a function of intermolecular separation,configuration, and partial wave order

The intermolecular partial wave expansion of the atom-atom potential U is reviewed briefly and developed, by using results due to Sack, so that the radial components of the expansion can be evaluated to arbitrary accuracy for all relevant partial wave orders and values of the intermolecular distance r. These results are used to study the convergence of the partial wave expansion of U as a function of partial wave order, r, intermolecular orientation, and the anisotropy of the interacting molecules. In marked contrast to previous work it is found that many of the higher order partial wave components of U are important relative to the isotropic term even for the interaction of relatively spherical molecules and that the results obtained from a truncated partial wave expansion depend significantly upon the method of summation due to the generally poor convergence of the expansion. The validity of the atom-atom potential as a representation of the correct attractive intermolecular potential is also discussed in some detail. There are basic problems associated with the representations furnished by both the isotropic and the anisotropic parts of the atom-atom potential at intermediate and large r. The different convergence properties of the r ^-1 expansions of the partial wave expansions of U and of the correct potential for these values of r is illustrated by using model interactions. While it appears that it may be possible to obtain a qualitatively reasonable representation of the attractive part of an intermolecular potential over a useful range of r from atom-atom results, this apparently cannot be achieved for wider ranges of r or for the purely anisotropic part of the potential.     

On the degradation of ZnS:Cu,Al,Au phosphor powder: The effects of temperature

Abstract

The effects of temperature are discussed when the ZnS:Cu,Al,Au (P22G) phosphor powder is bombarded by a 2 keV electron beam with a current density of 88 mA/cm² at an oxygen pressure of 2 × 10^?6 Torr at temperatures between 25 and 300°C. The rate of surface reaction decreases at higher temperatures due to the reduction in the mean stay time of the O₂ on the surface which is vital for the reactions according to an electron stimulated surface chemical reaction model. A direct correlation between the temperature and the initial cathodoluminescence (CL) brightness which depicts thermal quenching of the CL was observed.     

On the prediction of impact noise,V: The noise from drop hammers

In earlier papers in this series, the concepts of “acceleration” and “ringing” noise have been studied in relation to impact machines, and values of radiation efficiency have been obtained for the various types of structural components. In the work reported in this paper the predicted and measured noise radiation from a drop hammer, both in full-scale and in $\text{1}\text{3}\text{-}\text{scale}$ model form, were examined. It is found that overall noise levels (L_eq per event) can be predicted from vibration measurements to within ± 1·5 dB, and to within ±2·5 dB in one-third octave bands. In turn this has permitted noise reduction techniques to be examined by studies of local component vibration levels rather than overall noise, a method which provides considerable enlightenment at the design stage. It is shown that on one particular drop hammer, the noise energy is shared surprisingly uniformly over four or five sources, and that when these have been reduced, the overall noise reduction is severely limited by the “acceleration” noise from the “tup” or “hammer” itself. As this is difficult to eliminate without a basic change in forging technology, it follows that “tup” enclosure or modification of the sharpness of the final “hard” impact are the only means available for any serious noise reduction. Also indicated is the reliability of using model techniques, suitably scaled in frequency and impulse magnitude, in developing machinery with impact characteristics.     

The ground-level cosmic-ray event of September 29, 1989 as recorded by the rome detectors

Summary An extraordinary increase in cosmic-ray intensity has been recorded on September 29, 1989 by the Rome detectors (rigidity threshold ∼6.2 GV). We show the time evolution of the event as recorded at Rome in the nucleonic component and in the total ionizing and muon components; as well as at Campo Imperatore (2300 m a.s.l. near Rome) in the nucleonic component by a special monitor designed for the detection of solar-neutron events. The one-minute time resolution of the Campo Imperatore data offers the possibility to follow in detail the development of the event for most of the time. The possible contribution of solar neutrons to the early phase of the Campo Imperatore event has been not clarified so far, further results may be obtained by the analysis of the multiplicity data registered in the event.     

On the prediction of impact noise,Part IX: The noise from punch presses

The punch press is a further classical example of impact noise: the force is built up in the punch relatively slowly, and the whole machine is strained until the load on the material being punched reaches a yield and shortly afterwards a fracture level. At this stage the strain energy in the machine and its workpiece must be redistributed and this leads to vibration of the whole machine and to noise radiation. In this paper work which has been carried out at ISVR over a number of years is presented. It describes the way the Energy Accountancy Equation [1] can be modified to relate the noise radiated directly to the sum of the squares of the large rates of change of force against time, and illustrates clearly the way that noise control, with use of passive or active methods in designing the punch tooling, can be related directly to the one parameter 10 log Σ[f(t)]_max². It is shown that noise levels can be reduced by up to 30 dB under ideal conditions by fracture pulse tailoring while still cutting metal, but that more realistically, 10 dB reductions may be obtained below those of current practice by practical tool design. An explanation is given of why large open presses are never likely to achieve the proposed factory noise levels and that the noise from double-sided presses can be controlled effectively by tooling modifications and by the addition of damping. The paper describes work carried out on passive and active cancellation systems used to arrest and springback of the press structure following workpiece material fracture and explains the practical limitations of such systems. Active techniques are limited by the difficulties obtained, with brittle hard materials, of finding a trigger and load freezing system which can operate fast enough to reduce adequately the force parameter 10 log Σ (f_max(t))². Where punching finish allows, it has been found that well-designed shear and/or cutting with low percentage clearance is superior to active cancellation, since this provides a surer method of reducing the above force parameter, especially for harder materials. The Energy Accountancy Equation suggests that the use of increased structural damping can be an effective method of noise reduction, particularly if the punch press structure is initially only lightly damped. Experiments on a third-scale model of a 200 tonne double-sided press suggest that this damping needs to be added selectively in areas where the vibrational energy density is high and coincides with areas of high noise radiation. Thus, in the experiments described, 12 dB reduction has been obtained under such conditions, only 1 or 2 dB reduction being obtained when damping of the base plate has been unaltered.