Super-strong magnetic field-dominated ion beam dynamics in focusing plasma devices.

High energy density physics is the field of physics dedicated to the study of matter and plasmas in extreme conditions of temperature, densities and pressures. It encompasses multiple disciplines such as material science, planetary science, laboratory and astrophysical plasma science. For the latter, high energy density states can be accompanied by extreme radiation environments and super-strong magnetic fields. The creation of high energy density states in the laboratory consists in concentrating/depositing large amounts of energy in a reduced mass, typically solid material sample or dense plasma, over a time shorter than the typical timescales of heat conduction and hydrodynamic expansion. Laser-generated, high current-density ion beams constitute an important tool for the creation of high energy density states in the laboratory. Focusing plasma devices, such as cone-targets are necessary in order to focus and direct these intense beams towards the heating sample or dense plasma, while protecting the proton generation foil from the harsh environments typical of an integrated high-power laser experiment. A full understanding of the ion beam dynamics in focusing devices is therefore necessary in order to properly design and interpret the numerous experiments in the field. In this work, we report a detailed investigation of large-scale, kilojoule-class laser-generated ion beam dynamics in focusing devices and we demonstrate that high-brilliance ion beams compress magnetic fields to amplitudes exceeding tens of kilo-Tesla, which in turn play a dominant role in the focusing process, resulting either in a worsening or enhancement of focusing capabilities depending on the target geometry.

Multisegmented kinoform phase plate for spatial and temporal control of the focal-plane irradiance profile.

Kinoform phase plates (KPPs) are widely used in inertial confinement fusion to improve energy efficiency and to produce an optimum irradiance profile on the target plane. However KPPs are sensitive to beam aberrations and offer little flexibility in temporally tailoring the far-field pattern. To overcome these problems, we developed a multisegmented KPP and demonstrated temporal control of a focusing pattern and protection against phase distortions by numerical simulations.

MGSA/GRO-mediated melanocyte transformation involves induction of Ras expression.

The MGSA/GRO protein is endogenously expressed in almost 70% of the melanoma cell lines and tumors, but not in normal melanocytes. We have previously demonstrated that over-expression of human MGSA/GROalpha, beta or gamma in immortalized murine melanocytes (melan-a cells) enables these cells to form tumors in SCID and nude mice. To examine the possibility that the MGSA/GRO effect on melanocyte transformation requires expression of other genes, differential display was performed. One of the mRNA's identified in the screen as overexpressed in MGSA/GRO transformed melan-a clones was the newly described M-Ras or R-Ras3 gene, a member of the Ras gene superfamily. Over-expression of MGSA/GRO upregulates M-Ras expression at both the mRNA and protein levels, and this induction requires an intact glutamine-leucine-arginine (ELR)-motif in the MGSA/GRO protein. Western blot examination of Ras expression revealed that K- and N-Ras proteins are also elevated in MGSA/GRO-expressing melan-a clones, leading to an overall increase in the amount of activated Ras. MGSA/GRO-expressing melan-a clones exhibited enhanced AP-1 activity. The effects of MGSA/GRO on AP-1 activation could be mimicked by over-expression of wild-type M-Ras or a constitutively activated M-Ras mutant in control melan-a cells as monitored by an AP-1-luciferase reporter, while expression of a dominant negative M-Ras blocked AP-1-luciferase activity in MGSA/GRO-transformed melan-a clones. In the in vitro transformation assay, over-expression of M-Ras mimicked the effects of MGSA/GRO by inducing cellular transformation in control melan-a cells, while over-expression of dominant negative M-Ras in MGSA/GROalpha-expressing melan-a-6 cells blocked transformation. These data suggest that MGSA/GRO-mediated transformation requires Ras activation in melanocytes.

Small GTPase RhoD suppresses cell migration and cytokinesis.

Rho family small GTPases regulate organization of the actin cytoskeleton. Among them, RhoA plays essential roles in the formation of the actin stress fibers, the associated focal adhesions, and the contractile rings necessary for cytokinesis. Recently, RhoD, a novel member of Rho family has been identified. The amino acid sequences of its effector domain is distinct from those of the other Rho family proteins, suggesting its unique cellular functions. Introduction of the constitutively active form of RhoD(G26V) into fibroblasts by microinjection or transfection resulted in disassembly of the actin stress fibers and the focal adhesions, whereas the dominant negative form of RhoD(T31K) did not affect these structures. The degree of cell migration assessed by the phagokinetic tracks on a substrate covered with gold particles was diminished by the expression of RhoD(G26V) but not by RhoD(T31K). Thus, cytoskeletal alterations including the loss of stress fibers and focal adhesions by RhoD seems to lead to the retardation of cell migration. Transfection of RhoD(G26V) cDNA into cultured cells also induced multinucleation. Moreover, RhoD(G26V) microinjected into fertilized eggs and embryos of Xenopus laevis caused cleavage arrest only in the injected cells, and the uncleaved cells contained multiple nuclei. These results imply that RhoD does not affect nuclear division but can interfere with cytokinesis presumably by preventing the formation of the actin-based contractile ring. Enhancement of the stress fibers by RhoA or RhoA-activating lysophosphatidic acid was reversed by the transfection of RhoD cDNA. Accordingly, the cellular functions of RhoD are likely to be antagonistic to those of RhoA.

Serum proteins and secretory component in human carious dentin.

By the use of the peroxidase-labeled antibody method, significant localization of IgG, IgA, albumin and transferrin was demonstrated in the deep lesion of 20 carious teeth, where the secretory component was absent. These serum proteins formed a distinct zone, surrounding the overlying, shallow lesion infected with bacteria.