Performance of three different unfolding procedures connected to Bonner sphere data

This paper presents the results obtained in a comparison of three neutron spectrum unfolding procedures based on the SAND, MINCHI and UNFANA computer programs. The calculations were performed with data obtained previously from measurements using the PTB Bonner sphere spectrometer and taken from the literature; the neutron dosimetry was done with the Leake rem-meter. The evaluation of some spectrum hardness quantifiers is also reported. The codes give comparable neutron spectrum results. Relative to ambient dose equivalent derived from the Bonner sphere system, as a function of the unfolding code used, the Leake calculated readings were typically 1.16 to 1.91 and 1.58 to 2.69 times larger for the environment of a transport cask with spent fuel elements (Clab) and inside the containment building of a pressurised water reactor (Ring-G), respectively, depending on the calibration fields.     

微型夹钳的最新研究

~~微型夹钳的最新研究@王晓东$大连理工大学微系统研究中心!大连116024 @刘冲$大连理工大学微系统研究中心!大连116024 @王立鼎$大连理工大学微系统研究中心!大连116024~~~~~~~~     

New surface flattening scheme and its application in the visualization of the human cortex unfolding

Abstract

It is a difficult problem to interpret the spatial relationship between different locations on the human cortical surface. The main reason for this difficulty is that the surface of the human cerebral cortex is highly folded and therefore much of it is obscured from view. In this paper, we present an efficient and distortion‐less flattening algorithm to unfold the cortical surface. Using the proposed technique, we can quickly visualize and precisely measure the cortical surface. Experimental results are shown to evaluate the usefulness of the proposed method.     

Investigation of combined unfolding of neutron spectra using the UMG unfolding codes

An investigation of the simultaneous unfolding of data from neutron spectrometers using the UMG codes MAXED and GRAVEL has been performed. This approach involves combining the data from the spectrometers before unfolding, thereby performing a single combined unfolding of all the data to yield a final combined spectrum. The study used measured data from three proton recoil counters and also Bonner sphere and proton recoil counter responses calculated from their response functions. In each case, the spectrum derived from combined unfolding is compared with either the spectrum obtained from merging the independently unfolded spectra or the spectrum used to calculate the responses. The advantages and disadvantages of this technique are discussed.     

New aspects in electrical measurement accreditation

Modern technology involves increasingly more accurate measurements over a much wider range of values and parameters; this situation is particularly true in the field of electrical measurements, where new concepts have required accreditation services to modify and adapt their criteria accordingly. This article describes how criteria have been developed to make accreditation possible in three different, newly-developed circumstances: (a) instruments in which software plays a vital part in the measurement process; (b) instruments which are primary standards where conventional direct traceability is not appropriate; and (c) techniques by which calibration can be carried out at a customer's premises without any laboratory staff from the higher level laboratory needing to be present during the work     

New aspects of the microhardness of ultraoriented polyethylene

The influence of extrusion conditions on the microhardness of ultradrawn polyethylene (PE) has been investigated. The micromechanical behaviour of ultradrawn PE fibres can be defined in terms of a creep constant and a microhardness value (MH) at 0.1 min, relating to the size of indentation under load rather than to the residual dimension. The PE strands show, in addition, a conspicuous anisotropic shape of the indentation pattern (MH >MH ) which involves a local elastic recovery of the material parallel to the fibre axis. The hardening of the fibres in the parallel and perpendicular direction to the fibre axis is an increasing function of both extrusion temperature and extrusion pressure and can be explained in terms of a simultaneous improvement in the strength and the lateral packing of fibrils and microfibrils in fibre direction. For extrusion temperatures (T _e) greater than 134° C the microhardness shows, however, a decrease which is thought to be related to the molecular relaxation occurring in the vicinity of the melting point. In the range of extrusion temperatures (90 to 137° C) and extrusion pressures (0.24 to 0.5 GPa) investigated, the hardness anisotropy on the fibre surface, MH, is a unique increasing function of draw ratio . It is completely independent of both the extrusion temperature and pressure. MH in the core of cleaved fibres shows a constant value which is independent of and equals the extrapolated value at the surface for the maximum attainable value of . The results can be satisfactorily explained if one considers the existing morphological differences between the outer sheath and the inner core of the fibres.     

New aspects in the microstructure of YBCO melt-textured high-T c superconductors

The microstructure and phase constitution of bulk textured YBCO samples prepared by the modified MTG method in the longitudinal temperature gradient have been investigated. We found the existence of an unusual phase between stacked platelets. Microanalysis shows that this phase may be characterized as Y-143. This phase forms ellipsoid-like particles with a typical size about 0.05–2μ which can play the role of effective pinning centers. The reason for the phase formation is discussed. We assume that this phase exists commonly in melt-textured samples prepared in the temperature field gradient.     

New aspects of nanopharmaceutical delivery systems

Nanobiotechnology, involving biological systems manufactured at the molecular level, is a multidisciplinary field that has fostered the development of nanoscaled pharmaceutical delivery devices. Micelles, liposomes, solid lipid nanoparticles, polymeric nanoparticles, functionalized nanoparticles, nanocrystals, cyclodextrins, dendrimers, nanotubes and metallic nanoparticles have been used as strategies to deliver conventional pharmaceuticals or substances such as peptides, recombinant proteins, vaccines and nucleotides. Nanoparticles and other colloidal pharmaceutical delivery systems modify many physicochemical properties, thus resulting in changes in the body distribution and other pharmacological processes. These changes can lead to pharmaceutical delivery at specific sites and reduce side effects. Therefore, nanoparticles can improve the therapeutic efficiency, being excellent carriers for biological molecules, including enzymes, recombinant proteins and nucleic acid. This review discusses different pharmaceutical carrier systems, and their potential and limitations in the field of pharmaceutical technology. Products with these technologies which have been approved by the FDA in different clinical phases and which are on the market will be also discussed.     

Propagation of uncertainties in unfolding procedures

A review of methods currently used to unfold particle spectra from measured pulse height distributions or other detector readings is given. It is pointed out that most of the measurements in particle spectrometry reveal ill-conditioned or ill-posed problems. The presentation which is given here for examples of such inverse problems is focussed on the algorithms used in the HEPRO unfolding program package of PTB. The question of uncertainty propagation is discussed for least-squares algorithms as well as for those based on maximum entropy. A first attempt has been made to quantify generally the “ambiguity” in ill-posed unfolding problems. The maximum entropy algorithm realized in the MIEKE code allows a clear distinction to be made between two parts of uncertainty, one part coming from ambiguity and one part coming from the usual uncertainty propagation. The resulting uncertainty matrix of the MIEKE code provides these two parts.     

Stability of the unfolding of the predator-prey model

We prove a conjecture of Zeeman that any generic unfolding of the Volterra's original predator-prey model is stable. This well-known two-dimensional model has co-dimension one in the planar Lotka- Volterra system and all its orbits are closed in the region of physical interest. Any generic unfolding of the model locally induces a degenerate Hopf bifurcation, but the presence of a cycle of saddles makes the global stability analysis quite involved. We solve the problem by working in the equivalent replicator system. Our proof of stability uses a family of Lyapunov functions for the unfolding. There are two other co-dimension one bifurcations in the planar replicator (equivalently Lotka- Volterra) system, which involve cycles of saddles and are therefore non-trivial. In one case we prove the stability of the bifurcation and in the other we determine a topologically versa! unfolding of the co-dimension one flow. This then, together with previous work on the subject, completes the study of co-dimension one bifurcations of the system     

Random perturbations of codimension one homoclinic tangencies in dimension 3

Adding small random parametric noise to an arc of diffeomorphisms of a manifold of dimension 3, generically unfolding a codimension one quadratic homoclinic tangency q associated to a sectionally dissipative saddle fixed point p , we obtain not more than a finite number of 'physical' probability measures, whose ergodic basins cover the orbits which are recurrent to a neighbourhood of the tangency point q . This result is in contrast to the extension of Newhouse's phenomenon of coexistence of infinitely many sinks obtained by Palis and Viana in this setting. There is a similar result for the simpler bidimensional case whose proof relies on geometric arguments. We now extend the arguments to cover three-dimensional manifolds.     

The unsteady evolution of the singularity at separation

Summary The unsteady boundary layer equations are studied close to a separation point. A perturbation procedure, based on an idea of Kaplun, leads to a nonlinear integro-differential equation for the skin-friction. A uniformly valid small-time analysis of this equation shows how an initial square-root singularity at a separation point is smoothed out by unsteady processes.     

New aspects of fatigue and fracture mechanics

Recent Scanning Electron Microscope observations of the development of microstructural changes under reversed cyclic straining in soft, medium-strong and high strength metals have established the existence of two dominant fatigue mechanisms associated with, respectively, the development of glide fissures by reversed plastic slip in soft metals and of slip-less shear cracking in strong metals, as well as of combinations of various complexity of both in medium-strength metals. The stage of micro-crack multiplication and growth preceding the stage of propagation of the final macro-crack and following a very short stage of formation of point-defects, the significance of which has essentially been lost between the attempts to reduce fatigue either to a lattice defect phenomenon in physics or to a single crack-propagation phenomenon in mechanics represents the principal engineering aspect of fatigue except when, as the result of the pre-existence of a dominant local defect or stress-concentration, the fatigue life is completely determined by the propagating crack. Analytical treatment of this stage for consideration in fatigue life prediction and reliability assessment must await the development of suitable methods of statistical fracture mechanics. Some aspects of this approach are discussed.     

Isolation of the singularity in the solution of a heat conduction problem

A finite-difference method is used to solve a problem with a singularity in the solution. A scheme suitable for describing the behavior of the solution near the singularity is constructed.     

On the performance of the enthalpy method in the region of a singularity

A test problem is presented which provides a realistic challenge for computational techniques designed for the prediction of temperature distributions in melting/freezing processes. It is shown that a suitably modified finite difference implementation of the enthalpy method produces results that are perhaps adequate for practical purposes. However, the best approach to problems typified by the test problem remains to be found.     

压电材料切口奇性指数计算

利用一种数值方法分析压电材料切口尖端包括奇异应力场和奇异电位移场在内的双重奇异性.基于切口尖端的位移场按幂级数渐近展开假设,从应力平衡方程和Maxwell方程出发,推导出关于压电材料切口奇性指数的特征方程组,同时将切口的力学和电学边界条件转化为奇性指数和特征函数的组合表达,从而将压电材料双重奇性分析问题转化为在相应边界条件下微分方程组的特征值求解问题,采用插值矩阵法,可以一次性地计算出压电材料切口的各阶奇性指数.裂纹作为切口的特例,其尖端的电弹性奇性指数亦可以根据本法求出.     

压电材料切口奇性指数计算

利用一种数值方法分析压电材料切口尖端包括奇异应力场和奇异电位移场在内的双重奇异性。基于切口尖端的位移场按幂级数渐近展开假设, 从应力平衡方程和Maxwell方程出发, 推导出关于压电材料切口奇性指数的特征方程组, 同时将切口的力学和电学边界条件转化为奇性指数和特征函数的组合表达, 从而将压电材料双重奇性分析问题转化为在相应边界条件下微分方程组的特征值求解问题, 采用插值矩阵法, 可以一次性地计算出压电材料切口的各阶奇性指数。裂纹作为切口的特例, 其尖端的电弹性奇性指数亦可以根据本法求出。     

On the stress singularity in steady-state transonic shear crack propagation

The steady-state problem of a semi-infinite shear crack propagating with a velocity greater than the shear-wave velocity was considered. The crack was modeled by a straight cut which extended in its own plane under the action of in-plane shear stresses uniformly distributed over a segment of the crack lips. In this paper we were particularly interested in the stress singularity which was found to be different from that corresponding to the subsonic case. Complex variable methods have been employed exclusively.

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Résumé On considère le problème stationnaire d'une fissure semi-infinie de cisaillement qui se propage à une vitesse supérieure à la vitesse des ondes de cisaillement. La fissure est représentée par une coupure droite qui s'étend suivant son propre plan sous l'effet de contraintes de cisaillement agissant sur celui-ci et distribuées de manière uniforme sur un segment des lèvres de la fissure.Dans l'étude, on s'est surtout intéressé à la singularité de contrainte, que l'on a trouvé être différente de celle qui correspond à un cas subsonique.C'est la méthode des variables complexes qui a été utilitsée à l'exclusion de toute autre.

     

An introduction to the theory of unidimensional unfolding

Despite its 55 year presence in the field of mathematical psychology, the theory of unidimensional unfolding remains an enigma for many psychometricians and applied practitioners. This paper is the first of a three part series; and it aims to introduce unidimensional unfolding theory. The paper begins with a simple hypothetical example presenting an idealised distinction between responses to cumulative and unfolding dichotomous items. This followed by an accessible presentation of the theory of unidimensional unfolding as first articulated by Clyde H. Coombs (1950, 1964). The concept of the single peaked preference function (Coombs and Avrunin, 1977) which underpins unfolding theory is then presented. The article then progresses to the class of Rasch (1960) based IRT models developed by Andrich (1995) and Luo (2001). It was shown these models propose arguments not inconsistent with Coombs's (1964) original theory. The presumption of additive structure in psychological attributes was concluded to be the key weakness of the theories of unidimensional unfolding discussed.