Construction of a New Set of fpc＇s for the Composite Pair

A new set of fpc is introduced to build the orthogonal set of basis for the states with many S and D pairs in the microscopic theory of low-lying collective motion.     

Orbital fractional parentage coefficients for the harmonic oscillator shell model

The Hamiltonian ofn particles moving in a common harmonic oscillator potential has as its symmetry group the unitary groupU(3n) in 3n dimensions,n particle states of the harmonic oscillator shell model can be characterized as bases of irreducible representations (BIR) of the groupU(3n) and of certain subgroups of this group. Use is made of these subgroups for the factorization and calculation of 2, 3, and 4 particle fractional parentage coefficients (fpc) of the harmonic oscillator shell model. Recoupling coefficients for subgroup chains of the symmetric groupS (n) appear as factors in the fpc. These coefficients are analyzed and calculated explicitly. The 2, 3 and 4 particle fpc of the 1s 1p shell configuration are obtained as products of these recoupling coefficients with known reduced Wigner coefficients of the unitary groupU(3) in 3 dimensions. Possible applications are indicated.     

Phase noise suppression in a DPSK transmission system by the use of an attenuation-imbalanced NOLM

A nonlinear optical loop mirror (NOLM) imbalanced by attenuation has been used for the suppression of nonlinear phase noise in a DPSK transmission system. It has been experimentally shown that such a passive, NOLM-based regenerator can significantly improve the performance of a phase-encoded transmission when it is limited by nonlinear phase noise. A brief overview over the advantages und limitations of different NOLM-based phase-preserving amplitude regenerators is also given.     

A simple carbon dioxide laser amplifier suitable for optically pumped infra-red laser applications

A simple amplifier tube has been designed which, when used with already well-developed, stable single-frequency CO₂ laser oscillators, produces a cw power output of up to 40 W suitable for pumping far infra-red lasers.     

碲化铅/硫化锌红外多层滤光片的光谱漂移研究

采用碲化铅和硫化锌作为镀膜材料,研制了空间红外光学系统使用的红外多层带通滤光片。本文首次利用导纳轨迹图解技术,当在空间低温条件下使用时,对由碲化铅的折射率变化引起的光谱漂移机理进行了研究。根据多层膜各膜层间存在的光学厚度的补偿效应,建立了光谱漂移模型。并对设计的滤光片采用对分法计算了它在低温条件下波长的漂移量,计算结果与研制出的滤光片实测结果吻合很好。并成功地将研究结果应用于滤光片的设计,对原设计结果进行了准确的修正,使得最终研制的滤光片在低温下完全满足使用要求。     

时间分辨晶体谱仪在Z箍缩等离子体中的应用

在装置阳加速器上,使用椭圆弯晶谱仪对Al丝阵Z箍缩实验的X射线辐射特性进行了研究。在谱仪结构中,使用椭圆面的晶体作为分光元件,采用PIN阵列作为记录元件实现时间分辨测量,同时用成像板记录时间积分结果。在Al丝阵Ｚ箍缩实验中,获得了时间分辨的Al等离子体Ｋ壳层辐射谱,用基于碰撞-辐射模型的K壳层线辐射谱分析程序对Al丝阵Z箍缩的实验数据进行了分析,获得了Al丝阵等离子体的时间分辨的电子温度和时空平均的电子数密度参数。     

Diffusion controlled ice growth with soft impingement inside biological cells during freezing

An iterative method has been proposed to determine the relationship between the temperature depression of intracellular ice formation (IIF) and the equilibrium melting point depression for initial cryoprotective agent (CPA) concentrations larger than 1.5M. Using the iterative method coupling with a water transport model for freezing induced cell dehydration and intracellular ice growth, the temperature of IIF has been determined. The new model of temperature of IIF has been applied to predict nucleation parameters at various temperature and initial CPA concentrations according to Karlsson's approach. A geometrical model of soft impingement proposed by Bruna has been incorporated into Karlsson's diffusion limited crystal growth model to include the effect of soft impingement. The new crystal growth model has been verified by a comparison between the predicted critical cooling rates for vitrification with the reported values in literature. With the new crystal growth model, it has been found that the limiting value of the crystallized volume fraction increases as cooling progresses and decreases as the initial CPA concentration increases. A comparison of simulated crystallized volume fractions when soft impingement, hard impingement and no corrections are used has also been made and the result shows that soft impingement could not be omitted in the prediction of intracellular ice formation and growth, especially when the final crystallized volume fraction is larger than 0.1.     

Simulated performance and model measurements of an SIS waveguide mixer using integrated tuning structures

A three-port approximation of the quantum mixer theory is employed to perform mixer gain calculations at 230 GHz for SIS junctions with integrated tuning structures. In addition, the embedding impedance range of a waveguide mixer mount has been obtained from model measurements and has been included in the gain calculations. The results show that even moderately small junctions can perform well in a waveguide environment when an integrated tuning structure is used. A three-element tuning circuit is presented that would allow broad band operation with a fixed embedding impedance which is important for applications using a planar antenna structure.     

An efficient,robust, domain-decomposition algorithm for particle Monte Carlo

A previously described algorithm [T.A. Brunner, T.J. Urbatsch, T.M. Evans, N.A. Gentile, Comparison of four parallel algorithms for domain decomposed implicit Monte Carlo, Journal of Computational Physics 212 (2) (2006) 527–539] for doing domain decomposed particle Monte Carlo calculations in the context of thermal radiation transport has been improved. It has been extended to support cases where the number of particles in a time step are unknown at the beginning of the time step. This situation arises when various physical processes, such as neutron transport, can generate additional particles during the time step, or when particle splitting is used for variance reduction. Additionally, several race conditions that existed in the previous algorithm and could cause code hangs have been fixed. This new algorithm is believed to be robust against all race conditions. The parallel scalability of the new algorithm remains excellent.     

The diffuse and channel stages in the overvoltage breakdown of a gas gap

An interrupted discharge has been used to examine the production of light in the breakdown of an overvoltage gas gap in air under conditions of E/p = 90–110 V/cm-mm Hg. It is found that there are two types of discharge, the type being dependent on the number of initial electrons: diffuse when there are many electrons and of channel type when there is a single initiating electron. The observed voltage-fall curves for the first type of discharge agree well with theoretical ones derived from the avalanche theory. A study has been made of the dependence of the delay time and switching time on the relative intensity of the illumination used to produce the initial electrons.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii Fizika, No. 9, pp. 45–49, September, 1971.We are indebted to Dr. G. A. Mesyats for proposing the problem and discussing the results.     

Perturbation theory of low-V optical fibres with dip in the refractive index

A simple perturbation theory has been used to study the characteristics of low-V, step-index optical fibres with a dip in the centre of the refractive index profile. Analytical expressions have been derived for the cut-off frequency and propagation constant of an arbitrary mode on such a fibre. In particular, it has been shown that even when the dip is quite large, the perturbation theory results for the propagation constant of the fundamental mode and cut-off frequency of the second mode are virtually indistinguishable from exact numerical results calculated by series expansion techniques.     

High-pressure single-crystal X-ray diffraction facilities on station 9.8 at the SRS Daresbury Laboratory--hydrogen location in the high-pressure structure of ethanol

A new high-pressure single-crystal diffraction facility has been constructed on station 9.8 at the Synchrotron Radiation Source, Daresbury Laboratory, for a range of studies on a variety of systems of relevance to physics, chemistry and materials science that would otherwise prove intractable with conventional laboratory-based methods. The station has been equipped with a modified Enraf-Nonius CAD4 four-circle diffractometer for high-pressure studies which can be conveniently, and rapidly, interchanged with the Bruker SMART CCD area-detector system when more routine ambient-pressure diffraction work is to be undertaken. This rapid change-over has been achieved by permanently mounting the CAD4 on its own jacking table, formerly used for the station's white-beam diffraction mode, which allows the alignment of the SMART diffractometer to remain undisturbed when the CAD4 is in use. Early results on the test low-melting-point compound ethanol (CH3CH2OH) reveal that excellent refined structures can be obtained, including the location and refinement of the H atoms, demonstrating that one of the original, and major, objectives of the station has been accomplished.     

MCNPX modelling of the NPL manganese bath facility based on a converted CAD model

A detailed CAD model of the new manganese bath facility of the UK National Physical Laboratory has been converted into MCNPX format using the conversion program MCAM. The model has been used to evaluate a number of important parameters of the new facility such as the fraction of neutrons that escape from the manganese sulphate solution but subsequently return and are captured by it, and the degree of irradiation of the solution when a source is being transferred to and from the bath. It has also been used to recalculate the correction factors for the fraction of neutrons captured by nuclei other than manganese, the fraction captured by the source and the source mounting assembly and the fraction escaping from the bath itself, and compare these with values from an earlier simplified model.     

Experimental and theoretical investigation of formation of the oxygen-containing precipitate-dislocation loop system in silicon

A model of coherent and incoherent oxygen-containing precipitates formed in an anisotropic silicon crystal due to the decomposition of a supersaturated oxygen solid solution has been considered. The stresses acting inside and outside the precipitate have been determined in the framework of the classical Eshelby’s approach. A criterion has been proposed for the generation of the misfit dislocation and the onset of motion of the perfect interstitial dislocation loop lying in the precipitate plane. The proposed precipitate model and criterion have been used for determining the dependence of the precipitate radius that corresponds to the formation of the misfit dislocation and the onset of motion of the perfect interstitial dislocation loop when an external load is applied to the sample. The results obtained are compared with the available experimental data.     

Evaluation of holographic emulsion movement using phase difference amplification

A real-time holographic interferometry technique is typically used in the evaluation of aberrations caused by movement of the photographic emulsion. However, this technique is insufficiently accurate when an emulsion, with strain which has been released prior to exposure, is used. A proposed solution is based on the difference amplification method, which uses the higher diffraction orders of a non-linearly recorded hologram.     

Gamma-rays from Mössbauer sources: a low-dose approach to cancer therapy

Summary A new approach to cancer treatment using low-energy gamma-rays is discussed. Cultures of bone marrow mononuclear cells collected from normal donors and patients with chronic myelogenous leukaemia have been studied after the addition of hematin, at different concentrations, and irradiation by a M?ssbauer gamma-ray source. Growth stimulation has been observed when hematin is added to normal bone marrow cultures, while growth inhibition is observed when hematin is added to leukaemic cultures. The effect becomes then more pronounced when hematin is used in combination with M?ssbauer gamma-rays.     

On the dynamics of a novel ocean wave energy converter

Buoy-type ocean wave energy converters are designed to exhibit resonant responses when subject to excitation by ocean waves. A novel excitation scheme is proposed which has the potential to improve the energy harvesting capabilities of these converters. The scheme uses the incident waves to modulate the mass of the device in a manner which amplifies its resonant response. To illustrate the novel excitation scheme, a simple one-degree of freedom model is developed for the wave energy converter. This model has the form of a switched linear system. After the stability regime of this system has been established, the model is then used to show that the excitation scheme improves the power harvesting capabilities by 25-65 percent even when amplitude restrictions are present. It is also demonstrated that the sensitivity of the device's power harvesting capabilities to changes in damping becomes much smaller when the novel excitation scheme is used.     

L-shell ionization of atoms by relativistic electrons

A theoretical study of theL-shell ionization of atoms by relativistic electrons is made for atomic numbers in the range 47 to 92. A new potential model recently proposed by Das and Chakraborty dealing with atomic screening effect in a better way has been used. The results are in satisfactory agreement when compared with some available experimental results and also with the theoretical results of Scofield.