Comparative study of the spatial structure of the X-ray and ion emission sources in the micropinch discharge plasma

Images of ion emission sources in the micropinch discharge plasma are obtained by the pinhole camera technique. A region that is the source of the most intense ion emission has a length of about 3 mm along the discharge axis and a width of ≤1 mm. It seems that the image of the emitting region recorded in the axial direction reflects the action of the discharge current magnetic field on the directional pattern of the ion flow.     

Spatial structure of the neck and acceleration processes in a micropinch

It is shown that the spatial structure of the micropinch neck during the transition from magnetohydrodynamic to radiative compression and the bremsstrahlung spectrum of the discharge in the photon energy range of up to 30 keV depend on the configuration of the inner electrode of the coaxial electrode system of the micropinch discharge. Analysis of the experimental results indicates that the acceleration processes in the electron component of the micropinch plasma develop earlier than radiative compression.     

Correlation between the parameters of ion and X-ray emissions from the plasma of a micropinch discharge

Ion emission from the plasma of a micropinch discharge is studied by analyzing the plasma flow from the discharge region with the help of time-of-flight technique and probe diagnostics. Concurrently, soft Xray emission from the micropinch is recorded. The experimental data are interpreted using the radiative contraction model.     

Studies of the structure and dynamics of the radiating plasma of a micropinch discharge

Space-resolved X-ray spectra and electron emission spectra from a micropinch discharge are measured with the help of tracking detectors. Results from measurements of the discharge optical emission with a high temporal and spatial resolution are also presented.     

Refinement of the spatial structure of the gramicidin A ion channel]

The spatial structure of the gramicidin A (GA) transmembrane ion-channel was refined on the base of cross-peak volumes measured in NOESY spectra (mixing time tau m = 100 and 200 ms). The refinement methods included the comparison of experimental cross-peak volumes with those calculated for low-energy GA conformations, dynamic averaging of the low-energy conformation set and restrained energy minimization. Accuracy of the spatial structure determination was estimated by the penalty function Fr defined as a root mean square deviation of interproton distances corresponding to the calculated and experimental cross-peak volumes. As the initial conformation we used the right-handed pi 6,3 LD pi 6,3 LD helix established on the base of NMR data regardless of the cross-peak volumes. The conformation is in a good agreement with NOE cross-peak volumes (Fr 0.2 to 0.5 A depending on NOESY spectrum). For a number of NOEs formed by the side chain protons, distances errors were found as much as 0.5-2.0 A. Restrained energy minimization procedure had little further success. However some of these errors were eliminated by the change in torsional angle chi 2 of D-Leu12 and dynamic averaging of the Val7 side chain conformations. Apparently, majority of deviations of the calculated and experimental cross-peak volumes are due to the intramolecular mobility of GA and cannot be eliminated within the framework of rigid globule model. In summary the spatial structure of GA ion-channel can be thought as a set of low-energy conformations, differing by the side chain torsion angles chi 1 Val7 and chi 2 D-Leu4 and D-Leu10 and the orientation of the C-terminal ethanolamine group. Root mean square differences between the atomic coordinates of conformations are in the range of 0.3-0.8 A.     

Cell analysis with the new Leipzig high-energy ion nanoprobe

The high-energy ion nanoprobe LIPSION at the University of Leipzig has been in operation since 1998. The ultrastable, 3.5 MV SINLETRON accelerator supplies the H+ or He+ ion beam. A magnetic scanning system moves the focused beam across the sample. At present, a resolution of 41 +/- 4 nm in the low current mode and 300 nm at 5 pA can be achieved. The experimental chamber is equipped with electron-, energy dispersive X-ray-, and particle detectors. They can be used simultaneously to analyse the sample by means of PIXE (particle induced X-ray emission), RBS (Rutherford backscattering), and in the case of thin sections or monolayer samples STIM (scanning transmission ion microscopy). A goniometer allows the application of channeling measurements in single crystals in combination with these methods. In contrast to previous publication describing microbeam facility at LIPSION, the current biomedical research has concentrated on microscopy and tomography on chondrocytes in pig cartilages and fixed single endothelial cells (HUVEC). For the irradiation of single living cells, an external beam facility with irradiation platform, fast beamgate and mini-Petri dishes is under construction.     

Generation of superthermal electrons in a micropinch discharge

Results are presented from experimental studies of the formation of the superthermal electron component in a micropinch discharge plasma. Radiative collapse in a Z-pinch is found to affect the energy of the accelerated electrons. That the radiative collapse has been reached may be inferred from the energy of the emitted hard X-ray photons.     

Estimating and controlling for spatial structure in the study of ecological communities

Aim Variation partitioning based on canonical analysis is the most commonly used analysis to investigate community patterns according to environmental and spatial predictors. Ecologists use this method in order to understand the pure contribution of the environment independent of space, and vice versa, as well as to control for inflated type I error in assessing the environmental component under spatial autocorrelation. Our goal is to use numerical simulations to compare how different spatial predictors and model selection procedures perform in assessing the importance of the spatial component and in controlling for type I error while testing environmental predictors. Innovation We determine for the first time how the ability of commonly used (polynomial regressors) and novel methods based on eigenvector maps compare in the realm of spatial variation partitioning. We introduce a novel forward selection procedure to select spatial regressors for community analysis. Finally, we point out a number of issues that have not been previously considered about the joint explained variation between environment and space, which should be taken into account when reporting and testing the unique contributions of environment and space in patterning ecological communities. Main conclusions In tests of species‐environment relationships, spatial autocorrelation is known to inflate the level of type I error and make the tests of significance invalid. First, one must determine if the spatial component is significant using all spatial predictors (Moran's eigenvector maps). If it is, consider a model selection for the set of spatial predictors (an individual‐species forward selection procedure is to be preferred) and use the environmental and selected spatial predictors in a partial regression or partial canonical analysis scheme. This is an effective way of controlling for type I error in such tests. Polynomial regressors do not provide tests with a correct level of type I error.     

Fluorescent probe study of the spatial structure of membranes and lipoproteins

A review is devoted to principles of studies in spatial structure of the model and biological membranes and lipoproteins on the basis of measuring radiationless energy transfer between fluorescent probes and from proteins to the probes. Recently the theory has been developed for energy transfer in membranes of various geometry and in lipoproteins of different size and structure. Special fluorescent probes are designed and made. The measurement procedure was tested in simulated systems and used to study a series of membranes as well as blood plasma lipoproteins of main classes. Everything above-mentioned resulted in obtaining data on the size of protein molecules in membranes and lipoproteins, proteins location relative to the lipid phase, on the surface area of the membranes (isolated and directly in a cell), association of protein molecules, state of near-protein lipid layer, membrane asymmetry, spreading of proteins on the lipoprotein surface, on the cholesterol effect on the lipid bilayer size etc.     

Comparative study of gamma-ray and high-energy carbon ion irradiation on negative gravitaxis inEuglena gracilisZ

The effects of ⁶⁰Co gamma-ray and 290 MeV/amu carbon ion irradiation on negative gravitaxis was studied in the photosynthetic flagellate Euglena gracilis strain Z in a dose-response dependent manner. Cells were exposed to the doses (0-200 Gy for water). The negative gravitaxis was quantified by the r-value observed in a recently developed biomonitoring system. The present results demonstrate the inhibitory effects of gamma-rays and 290 MeV/amu carbon ions on negative gravitaxis of the Euglena gracilis strain Z. The 290 MeV/amu carbon ions had a greater impact at a low dose (<40 Gy) than the ⁶⁰Co gamma-rays.     

Current scaling for the radiative characteristics of a micropinch discharge

The absolute VUV and soft X-ray (hν > 100 eV) yield from a micropinch discharge is measured for a fixed current of 150 kA. The current scaling in the range of 30–250 kA is found for a number of the discharge parameters: the VUV and soft X-ray yield, the electron temperature, the effective temperature of suprathermal electrons, and the energy of bremsstrahlung emission from thermal electrons. The experimental data are in good agreement with the simulations performed by using the model of radiative collapse in fast Z-pinches in plasmas of high-Zelements.     

A practical approach to the study of spatial structure in simple cases of heterogeneous vegetation

Abstract. Spatial heterogeneity is a characteristic of most natural ecosystems which is difficult to handle analytically, particularly in the absence of knowledge about the exogenous factors responsible for this heterogeneity. While classical methods for analysis of spatial point patterns usually require the hypothesis of homogeneity, we present a practical approach for partitioning heterogeneous vegetation plots into homogeneous subplots in simple cases of heterogeneity without drastically reducing the data. It is based on the detection of endogenous variations of the pattern using local density and second‐order local neighbour density functions that allow delineation of irregularly shaped subplots that could be considered as internally homogeneous. Spatial statistics, such as Ripley's K‐function adapted to analyse plots of irregular shape, can then be computed for each of the homogeneous subplots. Two applications to forest ecological field data demonstrate that the method, addressed to ecologists, can avoid misinterpretations of the spatial structure of heterogeneous vegetation stands.     

Resolving the spatial kinetics of electric pulse-induced ion release

Exposure of cells to nanosecond pulsed electric fields (nsPEF) causes a rapid increase in intracellular calcium. The mechanism(s) responsible for this calcium burst remains unknown, but is hypothesized to be from direct influx through nanopores, the activation of specific ion channels, or direct disruption of organelles. It is likely, however, that several mechanisms are involved/activated, thereby resulting in a complex chain of events that are difficult to separate by slow imaging methods. In this letter, we describe a novel high-speed imaging system capable of determining the spatial location of calcium bursts within a single cell following nsPEF exposure. Preliminary data in rodent neuroblastoma cells are presented, demonstrating the ability of this system to track the location of calcium bursts in vitro within milliseconds of exposure. These data reveal that calcium ions enter the cell from the plasma membrane regions closest to the electrodes (poles), and that intracellular calcium release occurs in the absence of extracellular calcium. We believe that this novel technique will allow us to temporally and spatially separate various nsPEF-induced effects, leading to powerful insights into the mechanism(s) of interaction between electric fields and cellular membranes.     

Effect of the anode material on the X-ray spectrum of micropinch discharge plasma

The effect of the elemental composition of the anode material on the parameters and X-ray spectrum of micropinch discharge plasma have been studied using a low-inductance vacuum spark device. It is shown that the plasma electron temperature T _e and intensity of hard X-ray emission increase with increasing nuclear charge number Z of the anode material of the discharge system.     

Competing sound sources reveal spatial effects in cortical processing

Why is spatial tuning in auditory cortex weak, even though location is important to object recognition in natural settings? This question continues to vex neuroscientists focused on linking physiological results to auditory perception. Here we show that the spatial locations of simultaneous, competing sound sources dramatically influence how well neural spike trains recorded from the zebra finch field L (an analog of mammalian primary auditory cortex) encode source identity. We find that the location of a birdsong played in quiet has little effect on the fidelity of the neural encoding of the song. However, when the song is presented along with a masker, spatial effects are pronounced. For each spatial configuration, a subset of neurons encodes song identity more robustly than others. As a result, competing sources from different locations dominate responses of different neural subpopulations, helping to separate neural responses into independent representations. These results help elucidate how cortical processing exploits spatial information to provide a substrate for selective spatial auditory attention.     

Electrostatic modeling of ion pores. Multipolar sources

We present calculations of the polarization energy required when a multipolar source enters a transmembrane ion channel. The polarization energy for polar, but uncharged, sources is nearly independent of channel length if the length/diameter ratio is greater than 1.25; however, it is strongly dependent on channel radius. All significant changes in the polarization energy occur within a distance of +/- one channel radius of the entrance to the channel. Our calculational method also provides a means of estimating the change in polarization energy that occurs when an ion is not located axially; this contribution can be significant for smaller ions, for which the binding sites may be far from the axis.     

Dispersal strategies, few dominating or many coexisting: the effect of environmental spatial structure and multiple sources of mortality

Interspecific competition, life history traits, environmental heterogeneity and spatial structure as well as disturbance are known to impact the successful dispersal strategies in metacommunities. However, studies on the direction of impact of those factors on dispersal have yielded contradictory results and often considered only few competing dispersal strategies at the same time. We used a unifying modeling approach to contrast the combined effects of species traits (adult survival, specialization), environmental heterogeneity and structure (spatial autocorrelation, habitat availability) and disturbance on the selected, maintained and coexisting dispersal strategies in heterogeneous metacommunities. Using a negative exponential dispersal kernel, we allowed for variation of both species dispersal distance and dispersal rate. We showed that strong disturbance promotes species with high dispersal abilities, while low local adult survival and habitat availability select against them. Spatial autocorrelation favors species with higher dispersal ability when adult survival and disturbance rate are low, and selects against them in the opposite situation. Interestingly, several dispersal strategies coexist when disturbance and adult survival act in opposition, as for example when strong disturbance regime favors species with high dispersal abilities while low adult survival selects species with low dispersal. Our results unify apparently contradictory previous results and demonstrate that spatial structure, disturbance and adult survival determine the success and diversity of coexisting dispersal strategies in competing metacommunities.     

Interaction of ion tracks in spatial and temporal proximity

In the present work, a systematic analysis of the impact of spatial and temporal proximity of ion tracks on the yield of higher-order radiolytic species as well as of DNA damage patterns is presented. This potential impact may be of concern when laser-driven particle accelerators are used for ion radiation therapy. The biophysical Monte Carlo track structure code PARTRAC was used and, to this end, extended in two aspects: first, the temporal information about track evolution has been included in the track structure module and, second, the simulation code has been modified to enable parallel multiple track processing during simulation of subsequent modelling stages. Depending on the spatial and temporal separation between ion-track pairs, the yield of chemical species has been calculated for incident protons with start energies of 20 MeV, for He²⁺ ions with start energies of 1 and 20 MeV, and for 60 MeV C⁶⁺ ions. Provided the overlap of the considered ion tracks is sufficient in all four dimensions (space and time), the yield of hydroxyl radicals was found to be reduced compared to that of single tracks, for all considered ion types. The biological endpoints investigated were base damages, single-strand breaks, double-strand breaks, and clustered lesions for incident pairs of protons and He²⁺ ions, each with start energies of 20 MeV. The yield of clustered lesions produced by 20 MeV protons turned out to be influenced by the spatial separation of the proton pair; in contrast, no influence was found for different start times of the protons. The yield of single-strand breaks and base hits was found neither to depend on the spatial separation nor on the temporal separation between the incident protons. For incident 20 MeV He²⁺ ions, however, a dependence on the spatial and temporal separation of the ion pair was found for all considered biological endpoints. Nevertheless, spatial proximity conditions where such intertrack effects were obtained are not met in the case of tumour radiation therapy; thus, no impact on radiation effects due to short pulse duration of laser-driven accelerators can be expected from alterations during the chemical stage.