Weibel instability in the field of a short laser pulse

The growth rate of Weibel instability in a plasma interacting with a high-frequency pulse with a duration less or comparable with the electron mean free time is determined. The growth rate is shown to decrease with decreasing pulse duration. It is found that instability can develop after the short pulse is switched off and the generated magnetic field no longer affects electron motion in the high-frequency field.     

Process of commutation of a vacuum electric-discharge gap by laser plasma

The temporal parameters of a process of vacuum gap commutation under exposure to a nanosecond pulse of laser radiation incident on the cathode has been studied depending on the radiation energy. Based on the experiment data, it is suggested that a glow discharge is initially ignited in electrode erosion products under exposure to the laser pulse, which due to development of the ionization-overheating instability undergoes the contraction of current channel and transits to an arc discharge. With the radiation energy exceeding a threshold value, the radiation (incident on the cathode) accelerates directly the instability development and the glow discharge transition to the arc discharge due to the radiation absorption in the discharge plasma.     

Dispersion properties of a plasma produced by a short X-ray pulse

A collisionless plasma produced by a short ionizing pulse from an X-ray laser is characterized by an anisotropic monoenergetic electron distribution governed by the classical photoeffect. The dispersion properties of such a photoionized plasma are studied. The spectra of high-frequency plasma waves and their damping, as well as the parameters of the aperiodic instability of a photoionized plasma, are described. The relationship between the electrostatic and magnetic perturbations generated by this instability is investigated, and an analysis is made of how the instability transforms into a purely longitudinal (two-stream-like) instability and into a purely transverse (Weibel-like) instability, depending on the absolute value and direction of the wave vector.     

Decay instability of a laser pulse propagating in a transverse direction in a magnetized plasma

The decay instability of a lser pulse propagating across an external magnetic field in a subscritical plasma is investigated analytically and numerically. It is shown that, when the relaxation of the pulse is taken into account, the hydrodynamic growth rate of the decay instability is slower than that obtained earlier in the constant-amplitude pump wave approximation. The results of numerical simulations by a particle-in-cell method demonstrate that an increase in the amplitude of the parametrically excited waves is accompanied by a decrease in their group velocity; in this case, up to 85% of the laser energy is converted into the energy of the plasma particles. It is found that, under resonance conditions, the magnetic field acts to increase the energy of the accelerated ions that escape from the plasma slab through its front boundary.     

Electromagnetic radiation from a plasma slab during the development of Weibel instability

Electromagnetic radiation from an anisotropic plasma slab formed by ionization of matter in the field of a high-power femtosecond pulse is studied. It is shown that the growth of initial field perturbations in the course of Weibel instability is accompanied by the generation of nonmonochromatic radiation with a characteristic frequency on the order of the instability growth rate. It is found that perturbations with characteristic scale lengths less than or on the order of the ratio of the speed of light to the Langmuir frequency are excited and radiated most efficiently, provided that the slab is thicker than this ratio.     

Photoionization two-stream instability in a collisional plasma

An analysis is made of how electron collisions influence the development of photoionization two-stream instability of a plasma produced in the irradiation of matter by a short X-ray pulse from a free-electron laser. The cases of a weakly ionized and a completely ionized plasma are discussed.     

Temperature-Dependent Electrical and Ultrastructural Characterizations of Porcine Skin upon Electroporation

The mechanism of high-voltage pulse-induced permeabilization of the stratum corneum, the outer layer of the skin, is still not completely understood. It has been suggested that joule heating resulting from the applied pulse may play a major role in disrupting the stratum corneum. In this study, electrical and ultrastructural measurements were conducted to examine the temperature dependence of the pulse-induced permeabilization of the stratum corneum. The stratum corneum resistance was measured using a vertical diffusion holder, with the stratum corneum placed between two electrode-containing chambers. The stratum corneum resistance was reduced manyfold during the applied pulse. The extent of resistance reduction increased with pulse voltage until reaching a threshold value, above which the resistance reduction was less dependent on the pulse voltage. The stratum corneum was more susceptible to permeabilization at high temperature, the threshold voltage being lower. The stratum corneum resistance recovered within milliseconds after a single 0.3-ms pulse. High-temperature samples had a more prolonged recovery time. Using time-resolved freeze fracture electron microscopy, aggregates of lipid vesicles were observed in all samples pulsed above the threshold voltage. The sizes and fractional areas occupied by aggregates of lipid vesicles at 4°C and at 25°C were measured at different time points after the applied pulse. Aggregates of vesicles persisted long after the electric resistance was recovered. After pulsing at the same voltage of 80 V, samples at 4°C were found to have slightly more extensive aggregate formation initially, but recovered more rapidly than those at 25°C. The more rapid recovery of the 4°C samples was likely due to a lower supra-threshold voltage. Viscoelastic instability propagation created by the pulse may also play a role in the recovery of the aggregates.     

Modeling of processes of heat transfer in whole-body hyperthermia

The method of whole-body hyperthermia in which the body temperature for a short time reaches values up to 43-44 degrees C holds currently much promise. However, at body temperatures above 42 degrees C, the risks associated with the hemodynamic instability and the appearance of arrhythmia in the patient increase. A model of heat transfer has been created to increase the efficiency and safety of the immersion-convectional method of whole-body hyperthermia. This model takes into account changes in the skin blood flow and the dynamics of pulse rate depending on body temperature. The model of heat transfer adequately reflects processes of heating of the organism and can form a basis for the calculation of distribution of heat inside the organism.     

Experimental study of radiation in the wavelength range 12.2–15.8 nm from a pulsed high-current plasma diode

Results are presented from experimental studies of the temporal and integral characteristics of radiation in the 12.2-to 15.8-nm spectral range from the anode region of an extended high-current (I ～ 30 kA) pulsed discharge in Sn vapor. It is found that the radiation pulse consists of intense spikes with a duration much shorter than the half-period of the discharge current. The spikes are shown to correlate with the onset of instability in the plasma column. It is supposed that the radiation spikes in the given wavelength range can be generated by a long-lived dense plasma core optimally supplied with energy. A method for achieving a highly efficient quasi-steady radiation regime is proposed.     

Psb27, a cyanobacterial lipoprotein, is involved in the repair cycle of photosystem II

Photosystem II (PSII) performs one of the key reactions on our planet: the light-driven oxidation of water. This fundamental but very complex process requires PSII to act in a highly coordinated fashion. Despite detailed structural information on the fully assembled PSII complex, the dynamic aspects of formation, processing, turnover, and degradation of PSII with at least 19 subunits and various cofactors are still not fully understood. Transient complexes are especially difficult to characterize due to low abundance, potential heterogeneity, and instability. Here, we show that Psb27 is involved in the assembly of the water-splitting site of PSII and in the turnover of the complex. Psb27 is a bacterial lipoprotein with a specific lipid modification as shown by matrix-assisted laser-desorption ionization time of flight mass spectrometry. The combination of HPLC purification of four different PSII subcomplexes and (15)N pulse label experiments revealed that lipoprotein Psb27 is part of a preassembled PSII subcomplex that represents a distinct intermediate in the repair cycle of PSII.     

Cyclic Alternating Pattern Is Associated with Cerebral Hemodynamic Variation: A Near-Infrared Spectroscopy Study of Sleep in Healthy Humans

The cyclic alternating pattern (CAP), that is, cyclic variation of brain activity within non-REM sleep stages, is related to sleep instability and preservation, as well as consolidation of learning. Unlike the well-known electrical activity of CAP, its cerebral hemodynamic counterpart has not been assessed in healthy subjects so far. We recorded scalp and cortical hemodynamics with near-infrared spectroscopy on the forehead and systemic hemodynamics (heart rate and amplitude of the photoplethysmograph) with a finger pulse oximeter during 23 nights in 11 subjects. Electrical CAP activity was recorded with a polysomnogram. CAP was related to changes in scalp, cortical, and systemic hemodynamic signals that resembled the ones seen in arousal. Due to their repetitive nature, CAP sequences manifested as low- and very-low-frequency oscillations in the hemodynamic signals. The subtype A3+B showed the strongest hemodynamic changes. A transient hypoxia occurred during CAP cycles, suggesting that an increased CAP rate, especially with the subtype A3+B, which may result from diseases or fragmented sleep, might have an adverse effect on the cerebral vasculature.     

A membrane model of plant cell extension

A theory is presented for the mechanics of plant cell wall extension and is based on the analogy of the cell wall with a membrane structure made of material capable of large non-linear deformations. These wall deformations may be elastic, elastic-plastic or visco-elastic. Mathematical analyses of such membrane structures show that there is, generally, a critical internal pressure at which dimensional instability occurs. This instability is characterized by a sudden drop in internal pressure accompanied by a large increase in the physical proportions of the membrane structure. The theory proposes that cell wall extension occurs when the cell turgor pressure reaches this critical instability value. The cell wall thus stretched is fixed by biochemical synthesis of wall material. Osmotic regulation re-establishes the turgor pressure and the instability cycle repeats itself as long as the critical instability pressure of the cell is below the osmotic pressure of the cell contents. Equalization of these pressures stops cell extension. The rate of cell extension depends on the frequency of the instability cycle and is thus dependent on the various rate processes associated with the instability cycle. The theory appears to be able to explain most of the known facts regarding cell extension such as the influence of temperature and the action of some growth substances.     

Dynamics of a biological fixed film for phenol degradation in a fluidized-bed bioreactor

Experimental and modeling studies were conducted to analyze the dynamic response behavior of a phenol-oxidizing fixed film using a differential, fluidized-bed bioreactor in a recycle loop with a well-mixed reservoir. With the bioreactor at steady state, a pulse of phenol was added to perturb the system, and the phenol concentration was monitored continuously until steady state was again achieved.The experimental dynamics were compared with a dynamic mathematical model based on diffusion and reaction within the biofilm, liquid mixing, and biofilm growth. Constant-pH experiments could be adequately described using an unstructured, double-Monod kinetic expression with substrate inhibition by phenol.However, in dynamic experiments without pH control, the pH of the liquid phase dropped, and damped oscillations were observed in the phenol concentration and reaction rate trajectories. Oscillatory solutions could not be induced in the model, even when product inhibition was included, and a linear stability analysis did not reveal tendencies toward instability. The cause of the experimental oscillations remains unknown.     

Repetitively rated plasma relativistic microwave oscillator with a controllable frequency in every pulse

A repetitively rated microwave oscillator whose frequency can be varied electronically from pulse to pulse in a predetermined manner is created for the first time. The microwave oscillator has a power on the order of 10⁸ W and is based on the Cherenkov interaction of a high-current relativistic electron beam with a plasma preformed before each pulse. Electronic control over the plasma properties allows one to arbitrarily vary the microwave frequency from pulse to pulse at a pulse repetition rate of up to 50 Hz.     

链霉菌遗传不稳定性研究进展与展望

摘要： 链霉菌中广泛存在着遗传不稳定性现象,这种遗传不稳定性影响着链霉菌的诸多表型,尤其是工业生产上的菌种退化,抗生素产量不稳定等,给工业生产和实验研究带来很大麻烦。经多年深入研究,已逐步揭示了链霉菌遗传不稳定性和染色体不稳定性的关系。链霉菌遗传不稳定性机制的揭示,可为改良生产菌种,构建高产而又稳定的基因工程菌奠定理论基础。本文综述了链霉菌遗传不稳定性的研究进展,并对后续研究进行讨论与展望。     

Gene instability induced by mobile genetic elements in Drosophila melanogaster]

The genetic instability of Drosophila melanogaster genes induced by the mobile genetic elements is reviewed. The main attention is paid to genetic instability depended on types of crossing. Data on the possibility of genetic instability induction by the chemical and physical (X-rays, heat-shock) agents and their complex effect are cited. It was shown that a number of agents which cause mutagenic effect realize their action by involving of mobile genetic elements.     

The labile brain. II. Transients, complexity and selection

The successive expression of neuronal transients is related to dynamic correlations and, as shown in this paper, to dynamic instability. Dynamic instability is a form of complexity, typical of neuronal systems, which may be crucial for adaptive brain function from two perspectives. The first is from the point of view of neuronal selection and self-organizing systems: if selective mechanisms underpin the emergence of adaptive neuronal responses then dynamic instability is, itself, necessarily adaptive. This is because dynamic instability is the source of diversity on which selection acts and is therefore subject to selective pressure. In short, the emergence of order, through selection, depends almost paradoxically on the instabilities that characterize the diversity of brain dynamics. The second perspective is provided by information theory.     

The genetics of phenotypic plasticity. XIII. Interactions with developmental instability

In a heterogeneous environment, natural selection on a trait can lead to a variety of outcomes, including phenotypic plasticity and bet‐hedging through developmental instability. These outcomes depend on the magnitude and pattern of that heterogeneity and the spatial and temporal distribution of individuals. However, we do not know if and how those two outcomes might interact with each other. I examined the joint evolution of plasticity and instability through the use of an individual‐based simulation in which each could be genetically independent or pleiotropically linked. When plasticity and instability were determined by different loci, the only effect on the evolution of plasticity was the elimination of plasticity as a bet‐hedging strategy. In contrast, the effects on the evolution of instability were more substantial. If conditions were such that the population was likely to evolve to the optimal reaction norm, then instability was disfavored. Instability was favored only when the lack of a reliable environmental cue disfavored plasticity. When plasticity and instability were determined by the same loci, instability acted as a strong limitation on the evolution of plasticity. Under some conditions, selection for instability resulted in maladaptive plasticity. Therefore, before testing any models of plasticity or instability evolution, or interpreting empirical patterns, it is important to know the ecological, life history, developmental, and genetic contexts of trait phenotypic plasticity and developmental instability.     

Zinc and cadmium accumulation in cabbage aphid (Brevicoryne brassicae) host plants and developmental instability

Developmental instability in morphological characters can occur during individual development due to various environmental stresses. Fluctuating asymmetry (FA) is often used as a measurement of developmental instability, but within-environment variation (CV_e) is also considered an indicator of developmental instability. Cabbage aphid ( Brevicoryne brassicae ) populations were reared on zinc- (Zn) or cadmium- (Cd) contaminated cabbage and radish plants. Developmental instability indicators were measured and their relations with fitness were explored. Results revealed that cabbage aphids exposed to Cd and Zn displayed considerable developmental instability, particularly fluctuating asymmetry. Differences in developmental instability between the two metals were also detected, as well as differences between the two developmental instability measurements. For almost all measured traits, FA was greater on Cd- and Zn-contaminated compared to non-contaminated host plants. In contrast, CV_e of some traits was greater on non-contaminated host plants, yet for other traits CV_e was greater on contaminated host plants. There were also non-significant inverse relationships between FA and fitness of cabbage aphid populations. Due to weak correlations between FA and different patterns of two developmental instability measurements, this study does not support the hypothesis that developmental instability is a useful bioindicator of environmental quality.     

Excitation of magnetic fields by a circularly polarized laser pulse in a plasma channel

The excitation of quasistatic magnetic fields by a circularly polarized laser pulse in a plasma channel is considered. It is shown that, to second order in the amplitude of the electric field of the laser pulse, circular rotation of the plane of polarization of the laser radiation in a radially nonuniform plasma gives rise to a nonlinear azimuthal current and leads to the excitation of the radial and axial components of the magnetic field. The dependence of the magnetic field distribution over the plasma channel on the spatial dimensions of the pulse and on the channel width is investigated for a moderate-power laser pulse. The structure of the magnetic fields excited by a relativistic laser pulse in a wide plasma channel is analyzed.