Evolution of the decay mechanisms in central collisions of XeXe + SnSn from E/AE/A = 8 to 29 MeVMeV

Collisions of Xe+Sn at beam energies of $E/A$ = 8 to 29 $MeV$ and leading to fusion-like heavy residues are studied using the $4\pi$ INDRA multidetector. The fusion cross section was measured and shows a maximum at $E/A$ = 18-20 $MeV$. A decomposition into four exit-channels consisting of the number of heavy fragments produced in central collisions has been made. Their relative yields are measured as a function of the incident beam energy. The energy spectra of light charged particles (LCP) in coincidence with the fragments of each exit-channel have been analyzed. They reveal that a composite system is formed, it is highly excited and first decays by emitting light particles and then may breakup into 2- or many- fragments or survives as an evaporative residue. A quantitative estimation of this primary emission is given and compared to the secondary decay of the fragments. These analyses indicate that most of the evaporative LCP precede not only fission but also breakup into several fragments.Comment: Invited Talk given at the 11th International Conference on Nucleus-Nucleus Collisions (NN2012), San Antonio, Texas, USA, May 27-June 1, 2012. To appear in the NN2012 Proceedings in Journal of Physics: Conference Series (JPCS

Modeling Nutrient and Plankton Processes in the California Coastal Transition Zone: 3. Lagrangian Drifters

Two types of numerical Lagrangian drifter experiments were conducted, using a set of increasingly complex and sophisticated models, to investigate the processes associated with the plankton distributions in the California coastal transition zone (CTZ). The first experiment used a one-dimensional (1-D; vertical) time-dependent physical-bio-optical model, which contained a nine-component food web. Vertical velocities, along the track of simulated Lagrangian drifters, derived from a three-dimensional (3-D), primitive equation circulation model developed to simulate the flow observed within the CTZ; were used to parameterize the upwelling and downwelling processes. The second experiment used 880 simulated Lagrangian drifters from a 3-D primitive equation circulation model which was coupled to the same food web and bio-optical model used in the first experiment. Parameterization of the biological processes in both experiments were based upon data obtained during the CTZ field experiments. Comparison of simulations with data provided insight into the role of the biological and physical processes in determining the development of the subsurface chlorophyll maximum and other related features. In both studies, the vertical velocities experienced by a simulated Lagrangian drifter as it was advected offshore while entrained within a filament played a major role in determining the depth to which the euphotic zone and the chlorophyll maximum developed. Also, as the drifters moved offshore, the food web changed from a coastal, neritic food web to an offshore, oligotrophic food web due to the decrease in nutrient availability. The temporal development of the food web constituents following the simulated drifters was dependent upon the environment to which the drifter was exposed. For example, the amount of time upwelled or downwelled and the initial location in the CTZ region greatly affected the development of the food web

Atomic oxygen studies on polymers

The purpose was to study the effects of atomic oxygen on the erosion of polymer based materials. The development of an atomic oxygen neutral beam facility using a SURFATRON surface wave launcher that can produce beam energies between 2 and 3 eV at flux levels as high as approx. 10 to the 17th power atoms/cm (2)-sec is described. Thin film dielectric materials were studied to determine recession rates and and reaction efficiencies as a function of incident beam energy and fluence. Accelerated testing was also accomplished and the values of reaction efficiency compared to available space flight data. Electron microscope photomicrographs of the samples' surface morphology were compared to flight test specimens

Modeling Nutrient and Plankton Processes in the California Coastal Transition Zone: 1. A Time- and Depth-Dependent Model

A time- and depth-dependent, physical-bio-optical model was developed for the California coastal transition zone (CTZ) with the overall objective of understanding and quantifying the processes that contribute to the vertical and temporal development of nutrient and plankton distributions in the CTZ. The model food web components included silicate, nitrate, ammonium, two phytoplankton size fractions, copepods, doliolids, euphausiids, and a detritus pool. The wavelength-dependent subsurface irradiance field was attenuated by sea water and phytoplankton pigments. The one-dimensional (1-D) model adequately simulated the development and maintenance of a subsurface chlorophyll maximum in different regions within the CTZ. An analysis of the individual terms in the model governing equations revealed that phytoplankton in situ growth was primarily responsible for the creation and maintenance of the subsurface chlorophyll maximum at both coastal and oceanic regions in the CTZ. The depth to which the maximum in situ growth occurred was controlled by the combined effect of light and nutrient limitation. Also, the simulated bio-optical fields demonstrated the effect of nonlinear couplings between food web components and the subsurface irradiance field on vertical biological distributions. In particular, the epsilon-folding scale of the subsurface photosynthetically available radiation (PAR) was influenced by the level of zooplankton grazing

Expression of the Ladybird-like homeobox 2 transcription factor in the developing mouse testis and epididymis

<p>Abstract</p> <p>Background</p> <p>Homeoproteins are a class of transcription factors that are well-known regulators of organogenesis and cell differentiation in numerous tissues, including the male reproductive system. Indeed, a handful of homeoproteins have so far been identified in the testis and epididymis where a few were shown to play important developmental roles. Through a degenerate PCR approach aimed at identifying novel homeoproteins expressed in the male reproductive system, we have detected several homeoproteins most of which had never been described before in this tissue. One of these homeoproteins is Ladybird-like homeobox 2 (Lbx2), a homeobox factor mostly known to be expressed in the nervous system.</p> <p>Results</p> <p>To better define the expression profile of Lbx2 in the male reproductive system, we have performed <it>in situ </it>hybridization throughout testicular and epididymal development and into adulthood. Lbx2 expression was also confirmed by real time RT-PCR in those tissues and in several testicular and epididymal cell lines. In the epididymis, a highly segmented tissue, Lbx2 shows a regionalized expression profile, being more expressed in proximal segments of the caput epididymis than any other segment. In the testis, we found that Lbx2 is constitutively expressed at high levels in Sertoli cells. In interstitial cells, Lbx2 is weakly expressed during fetal and early postnatal life, highly expressed around P32-P36, and absent in adult animals. Finally, Lbx2 can also be detected in a population of germ cells in adults.</p> <p>Conclusion</p> <p>Altogether, our data suggest that the homeoprotein Lbx2 might be involved in the regulation of male reproductive system development and cell differentiation as well as in male epididymal segmentation.</p

Observed mechanisms of El Nino SST evolution in the Pacific

Tropical Pacific Ocean SST and velocity observations are used to construct NINO3 and NINO4 area average, 20-year long interannual time series of local and advective convergences of thermal energy. The variability of the sum of these observed convergences in each region is balanced by the vertical convergence of thermal energy due to the latent surface flux (86% in NINO3; 84% in NINO4). The latitude scale of the El Nino SST anomalies is shown to be equal to the ratio of the poleward mean speed of water parcels to the time scale at which thermal energy is given back to the atmosphere by a negative SST feedback through latent heat flux anomaly. Simultaneous observations and analyses of velocity and SST underscore the importance of the time-mean, wind-driven, poleward circulation in the establishment of the patterns of El Nino/SST anomalies directly north and south of the Pacific equator