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Negative ion formation in electron transfer experiments from fast neutral potassium (K) atom collisions with neutral tetrachloromethane (CCl

In the Drowned Cayes area of Belize, manatees (Trichechus manatus manatus) are commonly observed resting in depressions in the substrate, locally referred to as manatee resting holes. To understand why manatees prefer locations with resting holes, the physical and environmental attributes of the depressions were characterized and diurnal and nocturnal use by manatees at four resting hole sites were documented over two summers. Twelve resting hole sites were compared with 20 non-resting hole sites in the Drowned Cayes, using water depth, substrate type, vegetation, water velocity, salinity, and water temperature. Four resting holes were chosen for repeated diurnal and nocturnal observations, during which sea and weather conditions were recorded in addition to the presence/absence of manatees. Resting holes were significantly deeper and had slower surface water velocity than areas without resting holes. A total of 168 point scans were conducted over 55 d, resulting in 39 manatee sightings over two summers. There was a significant difference in the number of sightings between research years and between day and night scans. Given the large number of resting holes in the Drowned Cayes, many of which are in sheltered areas with slow currents, it is possible that manatees select these spots based on the tranquility of the water and environment. The combination of slow currents, protection from waves, low numbers of boats, and nearby seagrass beds would make these ideal resting areas. These findings have implications for the conservation of important manatee habitat.

The efficiency of different time-independent and time-dependent wave packet methods to calculate charge-exchange cross sections is discussed. The time-independent spectral projection method is based on the Chebyshev expansion of the resolvent function and represents an interesting alternative to the usual Fourier method which involves a time propagation. On the other hand, the flux operator method still requires propagation in time but uses the properties of absorbing potentials in order to calculate the flux operator matrix elements. We show the necessity of introducing the appropriate Hankel–Riccati functions when the full Hamiltonian contains a centrifugal term in 1/R2 in order to reduce the computational time. The collisional system Si4++He is studied as a test case.

multicharged ion on helium have been determined by means ofconfiguration-interaction methods. The total and partial electron capture cross sections have been determinedusing a semiclassical approach in the 2-eV–60-keV laboratory energy range. A sharp resonance has beenexhibited for a 45.455-eV collision energy.@S1050-2947~98!00808-7#PACS number~s!: 34.70.1eI. INTRODUCTION

The potential energy curves and the coupling matrix elements of the1∑1 and1Π states involved in the collision of the B3+(1s 2) multicharged ion on a He target have been calculated by means of an ab initio method with configuration interaction. The total and partial capture cross-sections have been determined, using a semi-classical method. The results are in good agreement with experiment, exhibiting a strong influence of rotational coupling even at low energies.

Introduction – objectifs Exploration du reservoir dans les sous-populations CD4 circulantes (SP) apres 2 ans d’un traitement antiretroviral initie en primoinfection VIH (PHI2). Materiels et methodes 12 patients randomises de l’essai OPTIPRIM. J0 et M24 : quantification de l’ADN-VIH total et analyse phylogenetique de la quasiespece virale dans les cellules triees quiescentes, naives (TN), memoires centrales (TCM), transitionnelles (TTM), effectrices (TEM). M24 : capacite des SP a produire des virus par activation in vitro et comparaison des niveaux d’ADN-VIH dans les SP des PHI2 versus 9 patients traites en PHI 6 ans en mediane (PHI6) et 11 controleurs post-traitement traites en PHI (PTC). Resultats De J0 a M24 : augmentation du nombre des SP (p Conclusion Un traitement precoce de deux ans en PHI protege les TCM et TN de l’infection. Un traitement de plus longue duree est necessaire pour atteindre une reduction profonde du reservoir VIH et augmenter les cas de PTC.

Cross sections are calculated for the charge transfer of O2+ ions in collision with helium at impact energies up to 625 eV amu-1. The adiabatic potential energies and the relevant radial coupling matrix elements of the quasi-molecular system are calculated by means of ab initio methods. The collision dynamics are subsequently treated by a semiclassical formalism. The results are found to be in fair agreement with experimental measurements and improve previous theoretical calculations.

Test case collision systems for direct and indirect processes in the action of radiation on the biological medium have been investigated theoretically by means of ab initio quantum chemistry molecular methods followed by a semiclassical dynamical treatment. As a direct process, we have studied the charge transfer of the RNA base uracil on Cq+ ions (q = 2,4). The process depends strongly on the orientation of the projectile towards the uracil target, in particular for the C4++uracil reaction, and shows a significant delocalization of the π electrons of the uracil ring towards the carbon ion. The collision of C2+ ions on the OH radical has been also investigated as a model of the action of ions on OH radicals created in the medium, in order to have a look to some possible indirect processes. The approach in the linear geometry with consideration of the relaxation of the OH target has been considered.

The anisotropy effect in charge transfer induced by collision of C{sup q+} ions (q=2,4) on uracil has been studied theoretically using ab initio molecular methods followed by a semiclassical dynamical treatment. The process depends strongly on the orientation of the projectile in the C{sup 4+}+uracil reaction and is favored around the perpendicular direction. The effect is weaker in the C{sup 2+}+uracil collision system where cross-sections remain low.

Wave packet simulations using ab initio potential energy surfaces (PES) have been developed within the framework of the constrained Hamiltonian methodology. The approach is presented with the example of bromoacetyl chloride photodissociation. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem 106: 670 - 675, 2006

Ab initio potential-energy curves and rotational and radial coupling matrix elements of the S and P molecular states involved in the collision of N with He are determined by means of configuration interaction methods. In the 1–50-keV laboratory energy range, the total and the partial electron capture cross sections have been obtained using a semiclassical approach. Comparison with experiment shows the importance of the double capture channels.

The most abundant decay channels have been studied quantitatively for high-energy (60 keV/amu) cluster ions H (3) (+)(H (2))(m = 1-14) colliding with He atoms employing a recently developed multicoincidence technique for the simultaneous detection of the correlated fragments on an event-by-event basis. This allows us to identify decay reactions and their underlying decay mechanisms responsible for the occurrence of the U-shaped fragmentation pattern.

Although single electron capture remains generally the main process in most ion-atom charge-transfer reactions, double and eventually multiple electron capture may be important in the understanding of such processes. An illustration of these mechanisms is presented on the example of the B2+ + H and B4+ + He collisions. A complete ab-initio molecular treatment of the potential energy curves and coupling matrix elements followed by a semiclassical collision dynamics has been performed for these systems. An adiabatic representation providing an unambiguous description of the molecular states has been used throughout this work. The results compare well to experimental data and improve markedly previous theoretical work.

IPM; International audience; Electron capture cross sections of hydrogen cluster ions Hn+ colliding with atomic helium have been measured in a large range of cluster size (5⩽n⩽35) for the same velocity (1.5v0, 60 keV/u). While the electron capture cross section decreases from the H+ ion to the H3+ one, the cluster electron capture cross section is found to be independent of the cluster size and nearly equal to the capture cross section of the H3+ ion. Electron capture by hydrogen clusters on a helium atom is a process involving only the H3+ core of the cluster where the positive charge is localized. It appears that this very localized electron capture is not disturbed by the presence of molecules, up to sixteen, around the H3+ core.

Recent experimental measurements [1] show evidence of production of fast He− ions by means of a one‐step double electron caputre process in He+(1s)+He(ls2)→He−+HHe2+ collision. The molecular calculation has been performed by means of a configuration interaction method using the CIPSI algorithm. It show an orientation of the capture towards formation of He−(1s2p2) ions, corroborating electric‐field detachment experiment [5], when a double collision mechanism should lead to He−(1s2s2p). (AIP)

On account of genetic homologies trisomy 16 in the mouse is regarded as an animal model of Down's syndrome. A detailed evaluation of the cardiovascular system in 109 fetuses with trisomy 16 and 422 balanced siblings was performed in order to systematize the cardiovascular anomalies and to elucidate the pathogenetic mechanisms responsible for their formation. 92% of fetuses with experimentally induced trisomy 16 exhibited cardiovascular anomalies. The most common types of anomalies were hypoplasia and aplasia of the aortic arch, which appeared in 85% of the fetuses. Situs inversus of the aortic arch system was remarkably frequent (20%). Hypoplasia or aplasia of the pulmonary artery was seen in 10% of the fetuses. A too proximal insertion of the pulmonary artery into the ascending aorta was observed in 8% of the fetuses.

The matrix elements of the operator d/dR between the first three 1 Sigma + singlets of HeNe2+ have been calculated by the rigorous finite differences technique and by Levy's projection method, based on the determination of the effective Hamiltonian in a quasi-diabatic basis. A numerical diabatisation procedure based on the knowledge of the d/dR matrix elements has also been applied. The results of the two methods for determining non-adiabatic couplings and quasidiabatic states have been compared. The nature of the avoided crossing between the A and B 1 Sigma + states of HeNe2+ is discussed.

A method is described that permits the generation of four isolated blastomeres after embryo splitting of murine four-cell eggs and the subsequent chromosomal analysis of one of the obtained 1/4-blastomeres. According to the karyograms obtained, embryos can be selected for reimplantation and furthermore triplicated via the embryo splitting procedure. By employing the described experimental setup, it is possible specifically to produce trisomy 16----2n aggregation chimeras as a postnatal model system of human Down's syndrome. The design can also be used for embryo sexing in stock farming and the selective reproduction of sexed farm animals via embryo transfer. Furthermore the application of blastomere karyotyping in human genetic counseling is discussed for the descendants of carriers of Robertsonian translocations. In addition the reported method could be employed for the genotypic identification of early homozygous embryonic stages from persons carrying frequent recessive mutations. The proposed design could, therefore, widen the spectrum of prenatal diagnosis.

Skeletal anomalies present in trisomy 16 in the mouse--an animal model of human trisomy 21--are described. Altogether 27 fetuses with trisomy 16 and 118 chromosomally balanced siblings were examined radiographically and by alizarin staining on day 20 of gestation; the radiographs were analyzed by computer-aided densitometry and structural differentiation. Extensive asymmetry or abnormal fusion of the vertebral centers and alterations of the vertebral arches were observed along with rib malformations (rib-vertebra syndrome). The skull primarily exhibited anomalies of the occipital bone. Ossification of the humerus, femur, and tibia was characterized by reduced mineralization. Typical, fracture-like alterations affecting only the tibia were also observed. Measurement of the lengths of the humeri of fetuses of comparable weight revealed a growth retardation not correlatable with the degree of mineralization. The significance of these skeletal abnormalities with regard to the trisomy 21 syndrome is discussed.

The profile of the Lyman- alpha line of hydrogen in the presence of an argon plasma has been determined in the frame of the 'Unified Franck-Condon' lineshape developed by Szudy and Baylis (1975) and using an ab initio potential. A non-adiabatic representation has been introduced as an intermediate in the calculation to provide an accurate description of the states at the crossing points.

Murine trisomy 19 (Ts19) can be regarded as a general model of human trisomies. It is the only autosomal trisomy in the mouse that survives the perinatal period. Therefore, it is the only animal model available for postnatal investigations of trisomy-specific mental retardation. To evaluate the extent of developmental retardation during the late-embryonic and fetal period of gestation, total body weight development was documented for 60 Ts19-fetuses and compared with that of 219 euploid in utero-mates. In addition, a postnatal study on body-weight development of 77 Ts19-neonates and 74 euploid littermates was performed starting on day 1 postpartum and continuing until spontaneous death or until day 22. Forty-seven Ts19-individuals were further tested in nine behavioural test systems in order to determine their neurophysiological developmental profile. Findings were compared with age-dependent morphologic and physiologic parameters. The data obtained in the present study show a significant retardation of organ- and body-weight development in Ts19-mice starting on day 14 of gestation. Retardation of physiological parameters is progressive and persists throughout the perinatal and postnatal periods. Furthermore, the trisomic individuals showed specific behavioural abnormalities.

On account of genetic homologies, trisomy 16 in the mouse is generally regarded as a direct animal model of Down's syndrome. Mouse trisomy 19, on the other hand, can be seen as a general model of human trisomies. A detailed evaluation of the cardiovascular system and skeleton in 109 fetuses with trisomy 16 and 422 balanced siblings was carried out in order to systematize the cardiovascular anomalies and the pathogenetic mechanisms responsible for their formation according to (1) general retardation, (2) genetically determined impairment of neural-crest cell migration, and (3) direct gene action on organogenesis. Skeletal malformations in the form of a rib-vertebra syndrome encountered in Ts 16 are described here for the first time. In 108 fetuses and 219 neonates resulting from cross-breeding to induce trisomy 19, we found no significant increase in the frequency of the foregoing anomalies. These results are discussed with regard to a chromosome-specific genetic influence as opposed to a general effect of chromosome imbalance. The specificity of the Ts16 syndrome is compared with that of individual organ anomalies as can be induced by teratogenic agents. Our investigation shows that specific malformation patterns of a particular type can be produced by a variety of methods. However, the overall patterns of the two syndromes are highly chromosome-specific. On detailed examination, the malformation pattern of mouse trisomy 16 shows significant similarities with that of human trisomy 21.