Search

An instrumental technique for recording monochromatic X-ray images of laser-produced plasmas has been developed using a Layered Synthetic Microstructure in combination with a pinhole camera. Well resolved images in 6 A X-ray emission from 10 μm gold microdots are demonstrated.

The formation and the deexcitation of the composite nucleus formed during the Ni + Al reaction at 28 A·MeV has been studied with the 4 π multidetector AMPHORA. A rigourous selection of the experimental data is described in order to extract a central collision sample. Then different models are compared to the data. The incomplete fusion process is in agreement with the data. The azimuthal angle correlations of He-Li and Li-Li pairs have been used to discriminate sequential or instantaneous emission. The sequential deexcitation is more consistent with all the data. The different analyses allow to describe all the characteristics of the compound nucleus and finally a fusion cross section of 300 ± 100 mbarn has been measured.

In nuclear physics, the term multifragmentation refers to the instantaneous break-up (partition) of a highly excited atomic nucleus into several fragments. We present a description of this process and an introduction to the application of equilibrium statistical mechanics in the analysis of the probabilities associated with partitions. La multifragmentation en physique nucleaire fait reference a la cassure instantannee (partition) d'un noyau fortement excite en plusieurs fragments. Nous proposons une description de ce processus et une introduction a l'application de la mecanique statistique a l'analyse des probabilites associees aux partitions.

We apply the Boltzmann distribution to charge partition probabilities measured with the AMPHORA multidetector in the reaction 32S + 27Al at 37.5 MeV/ nucleon. Approximate corrections to the data for pre-equilibrium emission are made and modifications to the basic formalism due to detection e?ciency and evaporation are treated explicitly. The data are well reproduced with a temperature of 5.0 MeV and a freeze-out volume which corresponds to densities which are 20 times smaller than normal density.

The paper describes a soft-systems method for the capture, representation and analysis of process knowledge as a platform for process improvement in capital goods manufacture. It is based on the formative results of some collaborative work, funded by two EPSRC grants, between manufacturing companies, including an MNE and an SME. The paper reports on: the problem addressed by the collaborative programme; the approach taken; the results obtained thus far; and the response of the problem-owners to those results and to the prospects of future work. It proposes specific deliverables based on formative results which may enable strategists in certain manufacturing enterprises to begin to design and implement process improvement programmes based on a system approach. The paper describes a novel form of systemic diagram (systemigram) which is used as the means to capture process understanding. Process models, represented by systemigrams, have proved useful to multifunction teams charged with the responsibility of implementing concurrent engineering philosophies by their companies who are seeking significant reductions in product cycle time.

Gas ionization chambers of a special shape adapted for 4π detector systems are presented. Different anode wire configurations are discussed for three working gases: Ar + methane(10%), isobutane, and tetrafluoromethane.

We present an analysis which aims at explaining the similarities (and differences) which exist between a simple bond percolation process on a cubic lattice and the fragmentation of highly excited atomic nuclei. Emphasis is placed on discussing percolation in terms of concepts which are well known in nuclear physics such asQ-value and particle emission thresholds. Similarities and differences between the bond percolation process and nuclear fragmentation are discussed. An approximate expression for the microcanonical partition sum (number of microstates) corresponding to any given percolation partition is shown to provide a good starting point for predicting fragment size distributions.

This article presents a new analysis of primary projectile-like fragments produced in peripheral and mid-peripheral collisions in the reaction $^{40}\mathrm{Ca}$${+}^{\mathrm{nat}}$Cu at 35 MeV/nucleon. The data were obtained using the charged particle amphora array. The distributions of multiplicity, inclusive charge, and heaviest fragment charge of the deexcitation products as well as the moments characterizing the single event charge partitions are remarkably well reproduced by a statistical sequential binary decay model even up to excitation energies of more than 8 MeV/nucleon. The results produced by the sequential binary decay model and a simple bond percolation model are qualitatively very similar. However the sequential binary decay mechanism leads to charge fluctuations which are in better agreement with the data than those predicted by the percolation model.

We describe an experimental study of the [sup 32]S+[sup 27]Al reaction at 37.5 MeV/nucleon carried out with the AMPHORA multidetector. A small fraction of events in which the total charge was detected and which are shown to originate mainly from central collisions have been isolated and compared with statistical decay model predictions. Dynamical properties provide strong evidence for a radial directed collective component (blast wave) in the fragment energies which dominates the interfragment Coulomb repulsion and the thermal motion.

Starting from a parametrized canonical expression for partition weights we investigate effects of uncorrelated stochastic fluctuations in the parameters. A special class of weights which are not affected by uncorrelated fluctuations is isolated and used as a reference for a systematic analysis of fluctuations. The technique is appled to partition weights obtained from a simple bond breaking percolation simulation. Strong evidence for the existence of uncorrelated fluctuations is obtained. The effects of fluctuations and of finite size effects on scaled factorial moments of the mass distribution are analyzed and discussed.

Properties of projectile fragments produced in peripheral and midperipheral collisions in the reaction [sup 40]Ca + [sup nat]Cu at 35 MeV/nucleon were investigated using the AMPHORA multidetector. A reconstruction of the primary projectilelike fragments enabled simultaneous determination of their excitation energy and angular momentum. These quantities are in good agreement with predictions of simple macroscopic and microscopic collision models. Partition of excitation energy between primary projectile and targetlike fragments is discussed. The multiplicity and charge distributions of the primary projectilelike fragment deexcitation products are fairly well reproduced by a statistical binary-decay model.

The multidetector AMPHORA was used to investigate the reaction of 35 MeV per nucleon $^{40}\mathrm{Ca}$ ions with a $^{\mathrm{nat}}\mathrm{Cu}$ target. For 150 000 events corresponding to peripheral and midperipheral collisions, it was possible to reconstruct the primary projectilelike fragments and to calculate event by event the center of mass and the excitation energy. Comparison with a percolation simulation (charge moments, critical exponent) and a momentum ellipsoid analysis are presented and commented. No evidence for a change in disintegration mechanism with increasing excitation energy is found.

We discuss the effect of geometrical efficiency and detection energy thresholds of a typical heavy-ion 4π detector (AMPHORA at the ISN) on measurements at energies near 35 MeV/nucleon. The study is based on simulation data generated by two different models: a microscopic interaction code which describes central as well as peripheral collisions, and a statistical code that describes the emission of pre-equilibrium nucleons followed by evaporation from an equilibrated incomplete-fusion system. Two reactions are studied, 32 S+ 27 Al at 37.5 MeV/nucleon and 40 Ca+ 40 Ca at 35 MeV/nucleon. We have investigated the effect of the incomplete (and selective) detection of the charged particles on several variables (parallel momentum, multiplicities, charge distribution), momentum distribution variables and moments of the event-by-event charge distribution. The results show that the response of the detector severely distorts the variable distributions and that a selection is required to obtain a set of data that represents the original ensemble. Total detected charge ( Z P + Z T ) selection can give, depending on the system, an acceptable representation of some of the variables in central and semi-peripheral reactions but the effect of the detector depends strongly on the kinematics of the studied reaction. The optimum application of this selection appears to be associated to relatively light systems studied under conditions of inverse kinematics.

Azimuthal angle correlations have been measured for Li-Li pairs from $^{40}\mathrm{Ar}$ + $^{197}\mathrm{Au}$, $^{\mathrm{nat}}\mathrm{Ag}$, $^{\mathrm{nat}}\mathrm{Cu}$, $^{27}\mathrm{Al}$ (17A, 27A, and 34A MeV). Many of these correlations exhibit enhancements at \ensuremath{\Delta}cphi of 0\ifmmode^\circ\else\textdegree\fi{} and 180\ifmmode^\circ\else\textdegree\fi{}, the classical pattern for evaporation from a hot, high-spin source. A very different pattern is predicted by a simple multifragmentation model, i.e., a peak at \ensuremath{\Delta}cphi\ensuremath{\approxeq}60\ifmmode^\circ\else\textdegree\fi{}. This peak is driven by the rapid Coulomb explosion of a nonrotating nucleus. The latter pattern is not observed experimentally, however, if collective rotation is included in the multifragmentation model, its predictions are more consistent with the observations. Such comparisons can give a promising test for sequential emission from a rotating source versus instantaneous explosive multifragmentation, but one needs a very good selection of collision centrality to reduce the role of the collective rotation. For most of these data the dominant driving forces seem to be rotational motion perturbed by final-state Coulomb repulsions for time delays of the order of ${10}^{\mathrm{\ensuremath{-}}22}$ s between successive emissions of Li fragments.

Presentation du programme de recherche et developpement, en fonction des differents procedes et utilisations dans les secteurs secondaire et tertiaire, notamment dans l'habitat et les bâtiments

Recurrent or prolonged seizures cause selective neuronal injury in vulnerable structures in animal models and in humans. Considerable evidence suggests that seizure-induced neuronal injury is epileptogenic. For example, a large fraction of animals that experience chemoconvulsant-induced status epilepticus and associated neuronal loss in limbic structures go on to develop spontaneous recurrent seizures. In contrast to adult animals, immature animals manifest little, if any, neuronal injury after status epilepticus. We and others have shown that even in the absence of seizure-induced injury, animals that experience status epilepticus, when immature, manifest enhanced injury and an enhanced behavioral response to status epilepticus later in life. We have termed this the two-hit phenomenon: a single apparently noninjurious event confers enhanced vulnerability to later life events. The mechanism of the two-hit phenomenon remains uncertain.

Brain imaging is a mainstay in the approach to patients with epilepsy. With the advent of magnetic resonance imaging (MRI), it became possible to identify the cause, and sometimes the consequences, of epileptic seizures in perhaps 50% of patients with epilepsy. Over the last decade, it has become increasingly apparent that, in addition to identifying genetic, congenital, and acquired lesions that lead to seizures, MRI also has the ability to reveal acute brain changes related to epileptic activity that we have termed ‘peri-ictal’ imaging abnormalities. Peri-ictal MRI abnormalities may be reversible, evolving, or permanent – and may occur in the region of the epileptic discharge or remote from it. Their occurrence seems highly variable but frequently correlates with the duration and severity of ictal activity, the so-called duration–severity integral. Here, we propose a classification of peri-ictal imaging findings, provide examples, and comment on potential pathophysiological mechanisms for their occurrence.

This paper outlines a way of using a computer-based handbook for the dissemination of company and project knowledge which alleviates the problems of paper-based procedure manuals. An online facility, a handbook, is created to allow instant access to up-to-date information about a company and the way it operates. The data is organised using a series of models built using the Boardman Soft Systems Methodology and a unique pictorial representation called the 'Systemigram'. >

Matière Nucléaire; The shape of the velocity distributions of charged particles projected on the beam direction can be explained if emissions from the hot projectile-like fragment and the target-like fragment are supplemented by an emission from an intermediate velocity source located between them. The creation of this source is predicted by a two-stage reaction model where, in the second stage, some of the nucleons identified in the first stage as participants form a group of clusters located in the region between the colliding nuclei. The cluster coalescence process is governed on the average by the maximum value of entropy, although its fluctuations are also significant. The properties of the intermediate velocity source are precisely described, including the isotopic composition of the emitted particles. (Springer)

Matière Nucléaire; The creation of hot Ca-like fragments was investigated in the 40Ca +40Ca reaction at 35 AMeV.Using the AMPHORA 4π detector system, the primary projectile-like fragment was reconstructed and itsproperties were determined. Both primary and secondary distributions are compared with the predictionsof a Monte Carlo code describing a heavy-ion collision as a two-step process. Some of the nucleons whichare identified as participants in the first step are transferred in the second step to these final states, whichcorrespond on the average to the maximum value of entropy (thermodynamic probability). The modelallows for competition between mean-field effects and nucleon-nucleon interactions in the overlap zone ofthe interacting nuclei. The analysis presented here suggests a thermalized source picture of the decay ofthe projectile-like fragment. The validity of the reconstruction procedure for projectile-like fragments isdiscussed. (Springer)

Summary form only given. The top-level business process architecture should be derived from the business strategy. The detail of the processes within a top-level process architecture cannot be founded on logic alone, there is a need to utilise the collective knowledge of the workforce to derive the business processes and for the workforce to learn more about their business in the experience. In engaging employees in the process definition, shared values as to the new processes are more likely to emerge. Indeed, a commonly reported failure of BPR initiatives (business process reengineering) is the failure to achieve buy-in from employees regarding the changes that need to be made to day-to-day operations. What better method to employ than soft systems methodology (SSM) (Checkland, 1981). This paper illustrates how a soft systems approach can be used to define integrated business processes, resulting in a notation that clearly shows how each function/department contributes to the process objective.

The density of states in statistical approaches to nuclear multifragmentation includes a contribution from permutations of fragment positions in the physical space (the volume V{sub F}) occupied by the fragments. For N pointlike noninteracting particles (perfect gas) this factor is simply proportional to V{sub F}{sup N}. We propose a correction due to the finite size of fragments which is based on an evaluation of the two-body overlap probability. The correction exhibits an approximate exponential dependence on the multiplicity N. {copyright} {ital 1997} {ital The American Physical Society}

In this paper we attempt to explain the success of equilibrium statistical models in the analysis of products of small impact parameter heavy ion collisions. Our argument is based on an examination of restrictions on the space of microscopic states due to the dynamics of the collision process. We then proceed to consider the example of a simple cubic bond breaking percolation process. We show that slow convergence of certain physical observables near the phase transition is related to the fact that all partitions of the total number of sites have small probabilities (entropy maximum). We discuss the importance of similar behaviour for decay of highly excited nuclei.

A neutron which enters a detector can be scattered into a neighbouring detector. If the neutron is registered in each detector the effect will be calle

Coincidences between light particles (Z ⩽ 4) and heavy ions (A ⩾ 9) have been measured for the 20Ne + 12C reaction at E lab ( 20 Ne ) = 160 MeV . α, 16O events from the 12C(20Ne, α16O)12C reaction and α, 20Ne events from 12C(20Ne, α20Ne)8Be have been found. Energy distributions and angular correlations of these events are consistent with α-decay from the intermediate nuclei 20Ne and 24Mg formed by inelastic scattering and α-transfer in a first reaction step.

Measurements of the elastic scattering of /sup 12/C on /sup 12/C at ten laboratory energies between 120 and 290 MeV were made to determine the reaction cross section sigma/sub R/ and the total nuclear cross section sigma/sub T/. Analysis of these data and existing data at lower energies shows that sigma/sub R/ reaches a maximum at around 200 MeV in the laboratory whereas sigma/sub T/ shows little variation with bombarding energy.

Elastic scattering angular distributions were measured for 46-MeV $^{3}\mathrm{He}$ over the \ensuremath{\sim} 30\ifmmode^\circ\else\textdegree\fi{}-110\ifmmode^\circ\else\textdegree\fi{} range and for 41-MeV $\ensuremath{\alpha}$ particles over the \ensuremath{\sim} 25\ifmmode^\circ\else\textdegree\fi{}-150\ifmmode^\circ\else\textdegree\fi{} range for the neighboring targets $^{27}\mathrm{Al}$, $^{28,29,30}\mathrm{Si}$. For $\ensuremath{\alpha}$ particles, $l=2$ inelastic scattering data were also obtained at angles beyond \ensuremath{\sim} 50\ifmmode^\circ\else\textdegree\fi{}. For $^{3}\mathrm{He}$ the three Si targets yield similar angular distributions that are different from that of $^{27}\mathrm{Al}$ at angles larger than \ensuremath{\sim} 55\ifmmode^\circ\else\textdegree\fi{}. The elastic $\ensuremath{\alpha}$-particle data supplement earlier back angle data to yield almost complete angular distributions. The $^{28}\mathrm{Si}$ $\ensuremath{\alpha}$-particle elastic angular distribution exhibits an anamoly in the 80\ifmmode^\circ\else\textdegree\fi{}-150\ifmmode^\circ\else\textdegree\fi{} region. The $^{3}\mathrm{He}$ data were fitted by optical model potentials with either volume or surface absorption. To fit all of the $\ensuremath{\alpha}$-particle elastic scattering data, potentials with both volume and surface absorption, with separate geometry parameters, were needed. Distorted-wave Born-approximation analyses of the $\ensuremath{\alpha}$-particle inelastic scattering data yield values of ${\ensuremath{\beta}}_{2}$ that are in reasonable agreement with values obtained from analyses of scattering at other energies and incident particles.NUCLEAR REACTIONS ($^{3}\mathrm{He}$, $^{3}\mathrm{He}$) at MeV and ($\ensuremath{\alpha}, {\ensuremath{\alpha}}^{\ensuremath{'}}$) at 41 MeV from, $^{27}\mathrm{Al}$, $^{28,29,30,}\mathrm{Si}$; enriched targets. Measured $\ensuremath{\sigma}(\ensuremath{\theta})$; performed optical model and DWBA analyses; deduced scattering potentials and ${\ensuremath{\beta}}_{2}$ values.

60, 62 Ni(p, t) 58, 60 Ni experiments have been undertaken at 46.5 MeV. More than twenty new levels are identified with J π , T assignments. The angular distributions obtained are analysed using zero range DWBA calculations in which the usual Hankel function is replaced at the nuclear surface by a dineutron wave function calculated in a Saxon-Woods potential. Level structure information is obtained from comparison with other experiments.

We have studied the breakup of 140 MeV 16 O into 12 C + α by targets of 12 C, 13 C and 28 Si. At least two mechanisms contribute. One can be identified as the coherent excitation of the 16 O projectile to components of the giant resonance states. Another dominant mechanism may be the quasi-free scattering of the α or 12 C constituents of the projectile by the target.

A high resolution study of the breakup of /sup 16/O and /sup 20/Ne has been made at 9 MeV per nucleon. The experimental configuration preferentially detects sequential breakup events. The dominant source of ..cap alpha..-/sup 12/C and ..cap alpha..-/sup 16/O coincidence events is the decay of excited states in /sup 16/O and /sup 20/Ne, respectively. The experimental technique and the reaction mechanism leading to sequential breakup are discussed.

An 86 MeV/nucleon 12C beam has been used to bombard targets of C, Ag and Au. Energy spectra of reaction products with Z = 3−6 and A = 6−12 have been measured at angles between 3° and 20°. A simple fragmentation model, while predicting approximately the gross features of the data, fails to describe the results in detail.

Recent experiments to study the laser driven compression of CH shell targets and the effects of increasing aspect ratio using x-ray shadowgraph techniques are described. This work has been carried out at the Rutherford Appleton Laboratory's Central Laser Facility with 12 beam, 0·53 μm, 1·0 ns irradiation. X-ray shadowgraphy techniques have been used with a frame time of ∼100ps and spatial resolution of 5 to lOμm to obtain density profiles for the compressed targets. A systematic study of 150–200 μm targets with aspect ratios from ∼7 to ∼20 has been performed. The x-ray shadowgraphy techniques used are described, results in the form of x-radiographs presented and a discussion of preliminary results given.

The production of large yields of thermonuclear neutrons in 12 beam laser driven implosion of deuterium filled glass microballoons of very high aspect ratio has been studied. It has been found that significantly enhanced yield is obtained when the target irradiation is symmetrical but locally concentrated. A simple model satisfactorily describes a wide range of experimental results.

Explicit mappings from the first n2p base n Gray code integers into the ordered vertices of the pth Peano polygon and vice versa are derived. The result is generalised to r-dimensional Peano polygons. Algorithms to achieve the transformations directly are discussed.

Complete identification of products of the reaction 20Ne (110 MeV) + 12C has been carried out using time of flight and Δ E - E measurements. Angular distributions of reaction products and energy spectra were obtained between laboratory angles of 3.7° and 17°. The evaporation residue cross-sectionwas measured to be 1 270 + 150 mb. Analysis of the data has been carried out using the Hauser-Feshbach angular momentum dependent formalism. Nuclear reactions 12C(20Ne, X) E = 110 MeV. Simultaneous identification in mass and charge. Measured yields, energy spectra and angular distributions for 6 < A < 32. Evaporation analysis.

Spectra of 48Ti, 56Fe, 59Co and 60Ni have been investigated for excitation energies of 10–20 MeV by inelastic scattering of 80 MeV 3He particles. Broad peaks with excitation energies of about 63±1 A − 1 3 MeV and FWHM of 6 MeV have been observed. Much narrower satellite peaks occur at excitation energies about 51±1 A − 1 3 MeV . The angular distributions of the sum of these peaks were compared to extended optical model DWBA calculations which confirm the predominant L = 2 character of the GR. A tentative assignment of L = 2 or 4 was made for the 13.5 MeV satellite peak in 56Fe. We see no definite evidence for the presence of an L = 1 GR component.

A frequency doubled Nd glass laser was used to irradiate plane solid targets. Temporally and spectrally resolved measurements of the backscattered light were obtained together with calorimeter measurements of the backreflected energy. The results show the presence of stimulated Brillouin scattering and an estimate is made of the coronal electron temperature.

Measurements of projectile-like-fragment--target-like-fragment coincidences in the reaction {sup 40}Ar+{sup 27}Al are simulated using a Monte Carlo version of the random walk model. The predictions of the model are compared with recent measurements. The good agreement between predictions and data obtained here and elsewhere indicates that the underlying physical picture constitutes a viable model of the reaction mechanism.

Recent results from the new 12-beam compression facility at Rutherford Appleton Laboratory are discussed and novel experiments are described which use thermonuclear particle spectroscopy to measure compression uniformity, fast particle dE/dx and hydro instabilities.

Differential cross sections have been measured for the elastic scattering of 33 MeV 3 He particles from targets of 58,60,62,64 Ni, 63,65 Cu and 64,66,68 Zn over the angular range 5° to 175°. The data have been analysed with the optical model, with particular emphasis on the investigation of the ambiguities in the real potential, the form of the imaginary potential and the use of a spin-orbit term.

The advent of high-frequency transistors has created a need for improved oscillographs. Present instruments are neither fast enough nor sufficiently sensitive to display the low-amplitude high-impedance waveforms generated by these high-frequency transistors. A transistor oscillograph using the sampling principle has therefore been designed having a response extending from d.c. to 300 Mc/s, corresponding to a rise time of about 1.5 millimicrosec, and a sensitivity which gives a full-scale deflection for an input of a few hundred millivolts; the input impedance is equal to 1 pF and 1 megohm parallel. With one exception, all the transistors employed have ? cut-off frequencies in the region of 10 Mc/s. A basic oscillograph using a total of ten transistors is described the first part of the paper, followed by a more sophisticated version with improved linearity and double-beam display.

In certain computer applications to engineering problems such as the automatic control of machine tools the computing equipment derives its input in digital form, from, for example, an angle-indicating device on a rotating shaft. The indicating device may take the form of a multiple commutator or a coded disc read by photoelectric means. Since the shaft is rotating at mechanical speeds and the reading device is operating at electronic speeds a possibility of false readings exists when for example a change from 1999 to 2000 is taking place. In fact any of the readings 1999, 1990, 1900, 1000 or 2000 may occur in the same sort of way that a mileage recorder could be misread under similar circumstances.

The risk of instability when negative feedback is applied to a multistage amplifier is minimized by dividing the amplifier into sections, each with its own feedback. If there are not more than two 90° phase-shifts in each feedback loop, the circuit will be stable. Since the interaction between cascaded stages depends on their input and output impedances, various methods of controlling these impedances have been examined. Several practical wide-band amplifier circuits are described, and it is shown that such circuits can be made to accept wide variations in transistor characteristics.When operation is required near the cut-off frequency of the transistor, a transformer coupling is proposed. The relatively poor low-frequency response of this circuit is improved by the addition of an RC coupling.Bias currents in the transistor circuits are fixed by a d.c. feedback which is decoupled at signal frequencies. Operation at very low frequency (