Possibility of deexcitation of isomeric nuclei in plasmas produced by subpicosecond laser pulses

Possible schemes of X-ray-activated deexcitation of isomers of rhodium, silver, tellurium, and bismuth are considered. It is shown that conditions necessary for deexcitation of rhodium isomer can, in principle, be achieved in a high-temperature solid-body-density plasma produced by an ultrashort laser pulse.     

Interaction of plasma clouds produced from two laser targets

Results are presented from studies of the interaction of two plasma clouds produced from two different-type laser targets in an ambient gas in the MKV-4 stand of the Iskra-5 facility. The experimental data are compared with the results of numerical simulations.     

Interaction of laser plasmas with noble gases

The interaction of a noble gas jet (Xe, Kr, He) with a laser plasma at a distance of ～1 cm from a solid target (Mg, (CH₂)_n, LiF, or CF₄) was studied for the first time. The line spectra that were excited in the course of charge exchange of multicharged ions with noble gas atoms in the interaction region were recorded. A clean (debris-free) soft X-ray source excited by laser pulses focused into a xenon jet was designed and investigated.     

Studies of the optical properties of the proflavine–DNA complex

We report studies of the optical properties of the proflavine–DNA complex, using absorbance and circular dichroism spectroscopy. From comparison of the absorption spectra of proflavine complexed with calf thymus and T2 DNA, we conclude that stacking of the dyes external to the double helix is comparatively much weaker with T2 DXA, probably because of its glucosylation. Several sources are found for the circular dichroism induced in proflavine when it is complexed with DNA. There is a relatively weak circular dichroism induced when the dye is infinitely dilute on the DNA lattice; this presumably arises from the environmental asymmetry of the binding site. Stronger circular dichroism effects are induced by interaction of intercalated and stacked dyes; studies with T2 DNA, for which stacking seems to be blocked, permit a tentative resolution of effects due to the two modes of binding. One recurring theme of these studies is the observation that the optical properties are quite dependent on environment. The most dramatic example is a strong variation with salt concentration of the amplitude of the circular dichroism induced in the isolated (intercalated) monomer by the surrounding DNA. This suggests that the structure of the intercalated complex is quite sensitive to external conditions.     

Studies on the properties of the singlet oxygen-like factor produced during lipid peroxidation

The singlet oxygen reaction product of various trapping agents is observed during enzymic and nonenzymic peroxidation of microsomes as well as during the peroxidation of pure lipids extracted from microsomes. We now wish to report that purified fatty acid hydroperoxide alone, as well as peroxidized microsomal lipid and cumene hydroperoxide also form the singlet oxygen reaction product with 2,5-diphenylfuran. The reaction product (cis-1,2-dibenzoylethylene) was observed to be formed in an anaerobic system, with or without EDTA. The data indicate that a reaction of hydroxyl radicals with 2,5-diphenylfuran cannot account for the formation of dibenzoylethylene in these systems. These results are consistent with a hypothesis that the singlet oxygen-like factor was formed from the lipid peroxides per se and, in addition, supports the possibility that either the peroxides can react directly with diphenylfuran to produce dibenzoylethylene or that the self-reaction of organic peroxides may form an intermediate product which can react directly with singlet oxygen-trapping agents to produce substances which are identical to a reaction of the trapping agents with singlets oxygen.     

Investigation of the angular distribution and energy spectrum of fast ions produced during irradiation of targets by short laser pulses in the SOKOL-P facility

Results are presented from experimental investigations of the angular distributions and energy spectra of fast ions produced in deuterium polyethylene targets under irradiation by picosecond laser pulses with intensities of up to 2 × 10¹⁸ W/cm² in the SOKOL-P facility. The parameters of ion fluxes were measured by time-of-flight spectrometers based on semiconductor detectors.     

Simulation of perturbation produced by an absorbing spherical body in collisionless plasma

A steady plasma state reached in the course of charging of an absorbing spherical body is found using computational methods. Numerical simulations provide complete information on this process, thereby allowing one to find the spatiotemporal dependences of the physical quantities and observe the kinetic phenomena accompanying the formation of stable electron and ion distributions in phase space. The distribution function of trapped ions is obtained, and their contribution to the screening of the charged sphere is determined. The sphere charge and the charge of the trapped-ion cloud are determined as functions of the unperturbed plasma parameters.     

Studies of the extracellular proteolytic activity produced by Propionibacterium acnes

Of several commercial media tested, trypticase soya both containing 0.4% (w/v) D-sorbitol was superior as a growth medium for the production of extracellular proteinase by Propionibacterium acnes (strain P-37). Extracellular proteinase, production of which was shown to be growth-associated by both batch and continuous culture studies, was partially purified by 70% (NH4)2SO4 saturation. Sephadex G-75 chromatography and ion exchange on DEAE-Sephadex A-50. It was shown to be a heterogeneous mixture of at least three molecular species of enzyme. Proteinase I was inhibited by EDTA (10(-3) mol/l) and PMSF (5 millimol/l) and stimulated by CaCl2 (190% at 10(-3) mol/l). It had a molecular weight of 20 to 30000 and a broad pH optimum from 6.5 to 7.5. Proteinase II was an alkaline proteinase with a molecular weight of 30 to 40000 which was not significantly inhibited by EDTA (10(-2) mol/l) nor stimulated by CaCl2. Proteinase III represented a minor proportion of the recovered proteolytic activity, had a molecular weight of 20 to 30000 and was most active in the alkaline pH range. This enzyme was inhibited by EDTA (10(-4) mol/l) and PMSF (5 millimol/l), and stimulated by CaCl2 (250% at 10(-2) mol/l).     

Studies of the extracellular proteolytic activity produced by Propionibacterium acnes

Of several commercial media tested, trypticase soya broth containing 0.4% (w/v) D-sorbitol was superior as a growth medium for the production of extracellular proteinase by Propionibacterium acnes (strain P-37). Extracellular proteinase, production of which was shown to be growth-associated by both batch and continuous culture studies, was partially purified by 70% (NH₄)₂SO₄ saturation, Sephadex G-75 chromatography and ion exchange on DEAE-Sephadex A-50. It was shown to be a heterogeneous mixture of at least three molecular species of enzyme. Proteinase I was inhibited by EDTA (10^-3 mol/l) and PMSF (5 millimol/l) and stimulated by CaCl₂ (190% at 10^-3 mol/l). It had a molecular weight of 20 to 30000 and a broad pH optimum from 6.5 to 7.5. Proteinase II was an alkaline proteinase with a molecular weight of 30 to 40000 which was not significantly inhibited by EDTA (10^-2 mol/l) nor stimulated by CaCl₂. Proteinase III represented a minor proportion of the recovered proteolytic activity, had a molecular weight of 20 to 30000 and was most active in the alkaline pH range. This enzyme was inhibited by EDTA (10^-4 mol/l) and PMSF (5 millimol/l), and stimulated by CaCl₂ (250% at 10^-2 mol/l).     

Mechanical properties of neuronal growth cone membranes studied by tether formation with laser optical tweezers.

Many cell phenomena involve major morphological changes, particularly in mitosis and the process of cell migration. For cells or neuronal growth cones to migrate, they must extend the leading edge of the plasma membrane as a lamellipodium or filopodium. During extension of filopodia, membrane must move across the surface creating shear and flow. Intracellular biochemical processes driving extension must work against the membrane mechanical properties, but the forces required to extend growth cones have not been measured. In this paper, laser optical tweezers and a nanometer-level analysis system were used to measure the neuronal growth cone membrane mechanical properties through the extension of filopodia-like tethers with IgG-coated beads. Although the probability of a bead attaching to the membrane was constant irrespective of treatment; the probability of forming a tether with a constant force increased dramatically with cytochalasin B or D and dimethylsulfoxide (DMSO). These are treatments that alter the organization of the actin cytoskeleton. The force required to hold a tether at zero velocity (F0) was greater than forces generated by single molecular motors, kinesin and myosin; and F0 decreased with cytochalasin B or D and DMSO in correlation with the changes in the probability of tether formation. The force of the tether on the bead increased linearly with the velocity of tether elongation. From the dependency of tether force on velocity of tether formation, we calculated a parameter related to membrane viscosity, which decreased with cytochalasin B or D, ATP depletion, nocodazole, and DMSO.(ABSTRACT TRUNCATED AT 250 WORDS)     

Studies of the optical properties of a nonequilibrium plasma in the MKV-4 facility

Results are presented from experimental and theoretical studies of a glowing plasma object emerging behind a shock front that propagates through the background gas at a pressure of p₀ = 6 torr after laser irradiation of a hollow spherical target. The results of calculations are compared to the experimental results obtained in the MKV-4 device (a component of the Iskra-5 facility).