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Projectile binary breakup has been investigated in 58 Ni+ 12 C, 24 Mg, 197 Au at 34.5 MeV/A and 58 Ni+ 70 Zn at 40 MeV/A. The fragment angular distributions exhibit an anisotropic pattern showing that breakup is aligned with the direction of scattered quasi-projectile (QP). The correlation functions of the two heaviest fragments have been studied as a function of charge asymmetry. They suggest that the QP decays while still in close proximity of the target. The correlation between the charge and velocity of the two heavy fragments shows that the binary breakup of the QP might originate from an important deformation of the projectile by the target, and that the lighter of the colliding partners also contributes to the aligned emission pattern.

Complete events with at least 83% of the total charge of the 24Mg+12C system has been investigated at 45 A MeV with a large multidetector array. Central single-source events are selected by use of the Statistical Discriminant Analysis Method. Two-fragment reduced-velocity correlation functions are measured for the emission of intermediate-mass fragments from single-source events. Many-body trajectory calculations with a surface sequential model indicate an emission time of ≈400 fm/c suggesting that a large part of the single-source data can be described in a sequential decay picture. At the highest reconstructed excitation energy limit (≈8–10 A MeV), a mean emission time of ≈200 fm/c is deduced showing that part of the data may be explained by an instantaneous multifragmentation scenario.

The peripheral and semiperipheral reactions in ${}^{35}\mathrm{Cl}{+}^{197}\mathrm{Au}$ have been studied at 30 and 43 MeV/nucleon. The nonequilibrium $\ensuremath{\alpha}$ and IMF components have been observed in the experiment. The fraction of nonequilibrium emission decreases with an increase in the atomic number of the projectilelike fragments but, for a given projectilelike fragment, it increases with the charge of the emitted particles. The characteristics of quasiprojectiles reconstructed from their decay products reveal several features reminiscent of damped reactions at lower bombarding energies. The atomic number and deflection angle of projectilelike fragments depend strongly on their kinetic energy or dissipated energy. At 30 MeV/nucleon, the experimental data can be explained by a deep inelastic transfer model. One-body dissipation is still the main mechanism for the energy and angular momentum dissipation. However, at 43 MeV/nucleon, deep inelastic transfer models can predict only the experimental tendency. Two-body dissipation plays a more important role at higher incident energies. The similarity observed in the decay product distributions, as a function of excitation energy, suggests that the excited quasiprojectiles formed in binary collisions might approach thermal equilibrium for both incident energies. The decay products have been analyzed with sequential-binary and simultaneous-disassembly statistical decay models. Both statistical models are able to provide good agreement with the experimental observables except for the mean kinetic energy of the products.

The experimental signature of the formation of a necklike structure, with a velocity between that of the projectilelike emitter and that of the targetlike emitter, is investigated with the same beam and experimental setup for targets lighter and heavier than the projectile. The reactions are {sup 35}Cl on {sup 12}C and on {sup 197}Au at 43 MeV/nucleon. Particle velocity distributions are compared with two-source statistical simulations and the presence of a necklike structure is inferred from the data. In the second part of the paper, dynamical model simulations with the formation of a necklike structure are presented for the {sup 35}Cl+{sup 12}C system at 43 MeV/nucleon. {copyright} {ital 1997} {ital The American Physical Society}

The reverse kinematics light heavy-ion system 35 Cl+ 12 C at 43 MeV/nucleon is investigated in the framework of a dynamical-statistical hybrid model. The modified quantum molecular dynamics model which includes a Pauli potential is used to describe the initial non-equilibrium stage of the reaction and the formation of highly excited pre-fragments. The decay of pre-fragments is further described with a statistical sequential decay code. The distributions of global observables from filtered simulations, such as the center-of-mass velocity of products, fragment charge, anisotropy ratio and flow angle, reproduce the experimental results remarkably well. The evolutions between the number of sources and flow angle with impact parameter are investigated and compared with experimental results. For the light heavy-ion system, binary dissipative collision is a dominant reaction process. The process is still present even in central collisions. The formation of a neck-like structure can be observed at mid-central collision in the simulations. From a comparison to Boltzmann-Uehling-Uhlenbeck model calculations, a possible origin of the neck-like structure for the present system could be the mean-field instabilities which originate from dynamical fluctuations through the time evolution of the collision.

The breakup of the projectile 24 Mg, excited in peripheral collisions on a gold target, has been investigated at 25 and 35 A MeV with a large scintillation-detector array allowing exclusive measurements. Absolute breakup cross sections were deduced and the projectile-like nucleus velocity and excitation energy have been reconstructed. The excitation energy partition between the projectile and the target is found to lay between the limits of equal excitation energy sharing and equal temperature with some evolution from one limit to the other. The statistical nature of the decay mechanism is inferred from global variables. Small-relative-angle analysis is applied to the six-alpha exit channel and the corresponding data were found to be consistent with a sequential evaporation decay mechanism, with some contribution from sequential fission at higher excitation energies. The time scale involved in the breakup of 24 Mg projectiles into the 6α and the 5αHH channels has been investigated by examining distortions in the fragment velocity distributions due to the Coulomb field of the target. A decrease in the quasi-projectile lifetime is observed as the mean excitation energy increases from 3.4 to 4.5 A MeV.

iwm2001

XL Bormio

Light charged particle emission has been investigated as a function of excitation energy in exclusive experiments on the decay of $^{16}\mathrm{O}$, $^{24}\mathrm{Mg}$, and $^{35}\mathrm{Cl}$ projectiles between 25A and 70A MeV. The systematics of excitation energy removed by Z=1 and Z=2 particles were deduced. The results are similar to a previous study of proton and \ensuremath{\alpha}-particle evaporation in compound nucleus reactions at beam energies below 20A MeV, supporting the idea of a common statistical process.

A study of the most violent collisions in the 24Mg+12C reactions at 25A and 35A MeV has been carried out. Experimental data, for those events in which the total charge of the system has been detected, are compared to simulations based on statistical fragmentation codes. For violent events, a binary mechanism appears to be competing successfully with compound nucleus formation.

This study examined the relationship between the EEG (spectral edge frequency 90-SEF90) and the occurrence of awareness defined for the purpose of this study as responsiveness to verbal commands. Fifty women undergoing general anaesthesia for elective Caesarean section were examined. Responsiveness to verbal commands was detected every minute in the period from the induction of anaesthesia to the delivery of the newborn using the Tunstall isolated forearm technique and correlated with the SEF90 value. The patients were assigned by a randomized code to receive either thiopentone (4 mg.kg-1) or ketamine (1 mg.kg-1) for induction of anaesthesia. Before the administration of succinylcholine a tourniquet was applied to the free arm, and inflated to 200 mmHg, to maintain motor function to one arm. The EEG recordings started five minutes before induction and were recorded throughout anaesthesia. The incidence of responsiveness to verbal commands was lower in the ketamine group (24%) where the average SEF90 was 12.0 +/- 3 Hz, than in the thiopentone group (52%), where the average SEF90 was 18.09 +/- 3 Hz (P = 0.01). The results suggest that SEF values ofor = 8.6 Hz were sufficient to avoid responsiveness to verbal commands.

The fragmentation of the projectile 24 Mg, excited in peripheral collisions on 197 Au and 12 C targets, has been investigated at 25A MeV and 35A MeV with a large scintillator detector array. Projectile breakup events were selected in the off-line analysis, by requiring that the total detected charge in one event be equal to that of the projectile. The projectile-like nucleus (PLN) excitation energies have been reconstructed and compared to results at 50A MeV and 70A MeV. The branching ratios of 2-, 4-, 5-, and 6-fold decays show a linear dependence, characteristic of statistical decay. Global variable analysis in terms of relative angles was applied to the six-alpha exit channel and the corresponding data have been compared to theoretical calculations based on simultaneous and sequential binary decay. The latter have been divided into sequential fission and sequential evaporation decays. The data has been found to be consistent with a sequential evaporation decay mechanism for a wide range of the intermediate-energy domain.

In this paper an original energy relation for light scintillation in a CsI(T1) detector is established. It is dependent on the charge and mass of the particle (fragment) and is a direct light-to-energy function suitable for the calibration of CsI(T1) detectors used in heavy-ion studies at intermediate energies. Resulting calibration with this function and energy spectra for light ions, obtained from a heavy ion experiment, are presented.

Simultaneous measurement of both neutrons and charged particles emitted in the reaction {sup 64}Zn + {sup 64}Zn at 45 MeV/nucleon allows comparison of the neutron to proton ratio at midrapidity with that at projectile rapidity. The evolution of N/Z in both rapidity regimes with increasing centrality is examined. For the completely reconstructed midrapidity material one finds that the neutron to proton ratio is above that of the overall {sup 64}Zn + {sup 64}Zn system. In contrast, the reconstructed ratio for the quasiprojectile is below that of the overall system. This difference provides the most complete evidence to date of neutron enrichment of midrapidity nuclear matter at the expense of the quasiprojectile.

The formation and deexcitation of fusionlike events selected in events with a total charge equal or greater than 16 in ${}^{24}\mathrm{Mg}{+}^{12}\mathrm{C}$ system has been investigated at 25, 35, and 45 MeV/nucleon with a large multidetector array. Central single-source events are selected by use of the statistical discriminant analysis method applied to a set of 26 global variables. The fusion cross section has been extracted for the three bombarding energies and compared to other experimental data and to theoretical predictions. The total multiplicity is found to first increase to a maximum value and then decrease with increasing beam energy. It is shown that this behavior is connected to the opening of multifragmentation channels at 45 MeV/nucleon and the disappearance of channels with only light charged particles.

Concern about the side effects of allogeneic blood transfusion has led to increased interest in methods of minimizing peri-operative transfusion. Technologies to minimize allogeneic transfusion include drugs such as aprotinin, desmopressin, tranexamic acid and erythropoietin, and techniques such as acute normovolemic hemodilution, cell salvage and autologous pre-donation.To survey the current use in Israel of these seven technologies to minimize allogeneic blood transfusion.Our survey was conducted in 1996-97 in all hospitals in Israel with more than 50 beds and at least one of the following departments: cardiac or vascular surgery, orthopedics, or urology. All departments surveyed were asked: a) whether the technologies were currently being used or not, b) the degree of use, and c) the factors influencing their use and non-use. The survey was targeted at the heads of these departments.Pharmaceuticals to reduce allogeneic blood transfusion were used in a much higher proportion in cardiac surgery departments than in the other three departments. Pre-operative blood donation was used in few of the cardiac, urologic and vascular surgery departments compared to its moderate use in orthopedic departments. The use of acute normovolemic hemodilution was reported in a majority of the cardiac departments only. Moderate use of cell salvage was reported in all departments except urology where it was not used at all.There is considerable practice variation in the use of technologies to minimize exposure to peri-operative allogeneic blood transfusion in Israel.

It is now well known that collisions between heavy ions in the Fermi energy domain produce mainly binary type events[1]-[5]. It seems that this binary character dominates even for the most violent reactions[1, 3, 4]. However, what is still not well understood is the deexcitation stage of the two principal emitters and the effects produced by the entrance channel dynamics. An important factor in this energy range is that many processes are possibly in competition and it is experimentaly difficult to isolate each of them. Processes such as the progressively vanishing fusion, binary deep inelastic collisions and the appearance of nucleon-nucleon scattering are all present in the Fermi energy range. Furthermore, detected particles could have been emitted on a large time scale from very different stages of the decay, ranging from pre-equilibrium process to evaporation. Within the statistical break-up hypothesis, where the two principal emitters are considered as thermalized nuclei, we expect only the excitation energy of each emitter, and not the way it is reached, to be a determinant quantity for the disintegration exit channels. On the other hand, typical violence of these collisions can also lead to important deformations of the two main products of the reaction. Such deformations were observed recently by the rupture of neck-like structures linking the reaction partners[6]-[9]. In an asymmetric collision, we could expect the biggest nucleus to sustain the largest deformation. By its subsequent disintegration toward a more stable state, it could be possible to observe the effects of such a deformation on the deexcitation mode of the nucleus.

The same hot nuclear system ({Sigma}{ital Z}=18) has been studied for two different entrance channels with reaction products detected in a forward array of scintillators: central collisions of {sup 24}Mg on a {sup 12}C target at 25{ital A} and 35{ital A} MeV and peripheral pickup reactions of {sup 35}Cl on a {sup 197}Au target at 43{ital A} MeV. The detection-efficiency-corrected charge distributions, multiplicity of charged particles and cross sections as a function of excitation energy are compared. The reaction mechanism is investigated, through comparison to simulations with statistical observables. The central reaction {sup 24}Mg+{sup 12}C at 35{ital A} MeV is well characterized by a dissipative binary collision scenario. Data at 25{ital A} MeV show less evidence of such dynamical characteristics. The intermediate-mass fragments (3{le}{ital Z}{le}8) production for each reaction is compared to model calculations for different values of excitation energy. The systems formed in the central collision at 25{ital A} MeV and the pickup reaction at 43{ital A} MeV show similar source characteristics, both statistically and in momentum space. However, the yields of the various exit channels, from evaporation and/or fission to multifragmentation and vaporization, differ for the two reactions. {copyright} {ital 1996 The American Physical Society.}

Intermediate-mass fragment (IMF) production, typically 3≤;Z≤20, is a widely observed decay mode in heavy-ion reactions[1]. Possible scenarios to explain such a decay mode include bulk instabilities based on the expansion of hot nuclear matter with an initial compression stage in near-central collisions [2]–[4]. However, for such collisions, dynamical IMF production is also present as is evident from the observation of neck emission[5]–[7]. Also, the persistence of binary dissipative collisions[8]–[11] leaves a very small cross section for forming a hot and dense single source[12, 13]

Fragment production has been studied as a function of the source mass and excitation energy in peripheral collisions of $^{35}$Cl+$^{197}$Au at 43 MeV/nucleon and $^{70}$Ge+$^{nat}$Ti at 35 MeV/nucleon. The results are compared to the Au+Au data at 600 MeV/nucleon obtained by the ALADIN collaboration. A mass scaling, by $A_{source} \sim$ 35 to 190, strongly correlated to excitation energy per nucleon, is presented, suggesting a thermal fragment production mechanism. Comparisons to a standard sequential decay model and the lattice-gas model are made. Fragment emission from a hot, rotating source is unable to reproduce the experimental source size scaling., Comment: 13 pages LaTeX file, including 3 postscript figures (in .tar.gz fornmat), accepted in Phys. Rev. C . Also available at http://thomson.phy.ulaval.ca/ions_lourds/gil-en.html

The time scale involved in the breakup of 24 Mg projectiles into the 6α and the 5αpH channels has been investigated by examining distortions and shifts in the fragment velocity distributions due to the Coulomb field of the target. Assuming a fixed angular momentum range of 4 to 8 ħ strok; for both channels, we deduce time scales of (5.1 – 6.8) × 10 −22 s for the six-alpha channel at 3.4 MeV of excitation per nucleon and (3.0–5.9) × 10 −22 s for the 5αpH channel at 4.5A MeV of excitation.

A study of the reaction mechanisms in central 24Mg + 12C collisions at 25A and 35A MeV has been carried out. Global variables, such as anisotropy ratios and source-velocity ratios, computed for those events in which the total charge of the system has been detected, are compared to simulations based on statistical fragmentation codes. For violent events, a binary mechanism appears to be competing successfully with compound nucleus formation.

Tellerium 135 and 137 nuclei were produced in thermal neutron fission of235U separated by on-line isotope separator and deposited on a movable tape. Gamma ray singles,γ-γ, β-γ coincidences and time sequencedγ spectra were collected using Ge(Li) detectors and scintillator (NE 102 A) telescope. The half-lives and mass excesses of135Te and137Te were measured and level schemes of135I and135I have been established. The level scheme of135I has been compared to different shell model calculations.

The different paradigms on which traditional information retrieval systems are built are reused to design Web search engines. However, designers have to innovate in order to adapt to this particular documentary context, which has an important impact on the way tools operate. Through an analysis of French and English scientific literature, and observations made during Web search training sessions, we try to define how far users are taken into account in the design of such systems, by comparing paradigm implementation to recent researches on information needs and the informational process. An analysis of the different steps of an information retrieval process highlights the complexity and the many dimensions of the concept of relevance in document retrieval.

Vaporization and high multiplicity events, where the nuclear system is almost completely disassembled in light charged particles $(Zl~2),$ were analyzed for events with total charge detected $(\ensuremath{\Sigma}Z=23)$ in the ${}^{35}{\mathrm{C}\mathrm{l}+}^{12}\mathrm{C}$ reaction at 43 MeV/nucleon. Kinematic characteristics have been studied separately for $Z=1,$ $Z=2,$ and $Z=3\char21{}4$ particles. When those are compared to simulations, noticeable differences in privileged emission direction have been found between $Zg~2$ particles and protons. For violent reactions, these differences could be explained by the apparent ``symmetrization'' of the reaction partners via the formation of a large necklike structure, and its subsequent breakup into many light ions.

Matière Nucléaire NIM; By combining data from a charged particle $^{58}$Ni+$^{58}$Ni experiment at 52 MeV/nucleon with an $^{36}$Ar+$^{58}$Ni experiment at 50 MeV/nucleon for which free neutrons have been detected, an increase in the neutron to proton ratio of the whole nuclear material at midrapidity has been experimentally observed in the reaction $^{58}$Ni+$^{58}$Ni at 52 MeV/nucleon. The neutron-to-proton ratio of the quasi-projectile emission is analyzed for the same reactions and is seen to decrease below the ratio of the initial system. Those observations suggest that an asymmetric exchange of neutrons and protons between the quasiprojectile and the midrapidity region exists.