On the Possibility of Generating Harmonics of the Electron Plasma Frequency in the Solar Atmosphere due to Explosive Instability in a System of Interpenetrating Electron and Ion Flows

An alternative mechanism is proposed for the generation of harmonics of the electron plasma frequency due to the development of explosive instability in a system of interpenetrating electron and proton flows in the solar atmosphere. The efficiency of the new mechanism in comparison with the earlier discussed mechanisms involving multistage processes of nonlinear interaction of waves in plasma is determined. It is shown that the development of explosive instability can lead to the excitation of the second and third harmonics of the plasma frequency with comparable amplitudes.     

Quasilinear theory of the ion Weibel instability in the Earth's magnetospheric tail

The quasilinear equation for the ion Weibel instability is solved for waves propagating along the magnetic field. The energy of the excited waves is estimated and the moments of the ion distribution function in the saturation stage are determined as functions of the current velocity for parameters characteristic of the neutral sheet of the Earth's magnetotail. The question is studied of whether the current disruption at the beginning of the explosive phase of a substorm can be explained as being due to the onset of the ion Weibel instability.     

Nonlinear theory of the excitation of azimuthal surface waves during dissipative instability

A theoretical study is made of the surface electromagnetic eigenmodes that are excited by an annular charged-particle beam due to dissipative instability and propagate across the external axial magnetic field in a cylindrical metal waveguide partially filled with plasma. A self-consistent set of differential equations for a cold low-density charged-particle beam moving above the plasma surface is constructed in the single-mode approximation and is solved numerically. It is shown that the larger the dissipation, the slower the instability growth rate and the larger the wave amplitude in the saturation stage of the instability. An increase in the transverse dimensions of a charged-particle beam results in a slower growth of the dissipative instability, in which case, however, the beam transfers a larger fraction of its kinetic energy to the wave.     

Theoretical and experimental investigations of the excitation of high-frequency oscillations in an ion collective accelerator model based on the Doppler effect

Results are presented from studies of a two-beam scheme of ion acceleration by a high-frequency field excited by an electron beam due to the instabilities associated with anomalous and normal Doppler effects. The dynamics of the excitation of eigenmodes in a periodic slow wave structure (SWS) by a relativistic electron beam via the anomalous Doppler effect is investigated theoretically. Mechanisms for the saturation of the instability are considered, analytical expressions for the maximum field amplitude and the efficiency with which the energy of beam electrons is converted into the energy of the excited wave are derived, and the results of numerical simulations of such excitation are presented. An experimental stand designed to test the principles and possibility of proton acceleration up to an energy of 8 MeV at a current up to 3 A is described. A double resonance (associated with anomalous and normal Doppler effects) occurring in the interaction of an electron beam with a helical SWS is studied experimentally. In this case, an increase in the efficiency with which the accelerating high-frequency field is excited is observed.     

Concerning mechanisms for the zebra pattern formation in the solar radio emission

The nature of the zebra patterns in continuous type-IV solar radio bursts is discussed. The most comprehensively developed models of such patterns involve mechanisms based on the double plasma resonance and plasma wave-whistler interaction. Over the last five years, there have appeared a dozen papers concerning the refinement of the mechanism based on the double plasma resonance, because, in its initial formulation, this mechanism failed to describe many features of the zebra pattern. It is shown that the improved model of this mechanism with a power-law distribution function of hot electrons within the loss cone is inapplicable to the coronal plasma. In recent papers, the formation of the zebra pattern in the course of electromagnetic wave propagation through the solar corona was considered. In the present paper, all these models are estimated comparatively. An analysis of recent theories shows that any types of zebra patterns can form in the course of radio wave propagation in the corona, provided that there are plasma inhomogeneities of different scales on the wave path. The superfine structure of zebra stripes in the form of millisecond spikes with a strict period of ～30 ms can be attributed to the generation of continuous radio emission in the radio source itself, assuming that plasma inhomogeneities are formed by a finite-amplitude wave with the same period.     

Species differences in courtship acoustic signals among five Lake Malawi cichlid species (Pseudotropheus spp.)

Male courtship acoustic signals from five Lake Malawi cichlid fish species of the Pseudotropheus zebra complex were recorded and compared. Sounds made by males of P. zebra , Pseudotropheus callainos and the undescribed species known as Pseudotropheus 'zebra gold' from Nkhata Bay, and Pseudotropheus emmiltos and Pseudotropheus faizilberi from Mphanga Rocks, differed significantly in the number of pulses and in pulse period. The largest differences in acoustic variables were found among the sympatric Mphanga Rocks species that, in contrast to the other three species, show relatively minor differences in male colour and pattern. These findings suggest that interspecific mate recognition is mediated by multimodal signals and that the mass of different sensory channels varies among sympatric species groups. This study also showed that sound peak frequency was significantly negatively correlated with male size and that sound production rate increased significantly with courtship rate.     

Songbirds use pulse tone register in two voices to generate low-frequency sound

The principal physical mechanism of sound generation is similar in songbirds and humans, despite large differences in their vocal organs. Whereas vocal fold dynamics in the human larynx are well characterized, the vibratory behaviour of the sound-generating labia in the songbird vocal organ, the syrinx, is unknown. We present the first high-speed video records of the intact syrinx during induced phonation. The syrinx of anaesthetized crows shows a vibration pattern of the labia similar to that of the human vocal fry register. Acoustic pulses result from short opening of the labia, and pulse generation alternates between the left and right sound sources. Spontaneously calling crows can also generate similar pulse characteristics with only one sound generator. Airflow recordings in zebra finches and starlings show that pulse tone sounds can be generated unilaterally, synchronously or by alternating between the two sides. Vocal fry-like dynamics therefore represent a common production mechanism for low-frequency sounds in songbirds. These results also illustrate that complex vibration patterns can emerge from the mechanical properties of the coupled sound generators in the syrinx. The use of vocal fry-like dynamics in the songbird syrinx extends the similarity to this unusual vocal register with mammalian sound production mechanisms.     

Contrasting patterns of density‐dependent selection at different life stages can create more than one fast–slow axis of life‐history variation

There has been much recent research interest in the existence of a major axis of life‐history variation along a fast–slow continuum within almost all major taxonomic groups. Eco‐evolutionary models of density‐dependent selection provide a general explanation for such observations of interspecific variation in the "pace of life." One issue, however, is that some large‐bodied long‐lived “slow” species (e.g., trees and large fish) often show an explosive “fast” type of reproduction with many small offspring, and species with “fast” adult life stages can have comparatively “slow” offspring life stages (e.g., mayflies). We attempt to explain such life‐history evolution using the same eco‐evolutionary modeling approach but with two life stages, separating adult reproductive strategies from offspring survival strategies. When the population dynamics in the two life stages are closely linked and affect each other, density‐dependent selection occurs in parallel on both reproduction and survival, producing the usual one‐dimensional fast–slow continuum (e.g., houseflies to blue whales). However, strong density dependence at either the adult reproduction or offspring survival life stage creates quasi‐independent population dynamics, allowing fast‐type reproduction alongside slow‐type survival (e.g., trees and large fish), or the perhaps rarer slow‐type reproduction alongside fast‐type survival (e.g., mayflies—short‐lived adults producing few long‐lived offspring). Therefore, most types of species life histories in nature can potentially be explained via the eco‐evolutionary consequences of density‐dependent selection given the possible separation of demographic effects at different life stages.     

The relation between ATPASE activity and light chains of myosin in developing, adult and denervated muscles of several animals species.

Ca2+ATPase activity and light chains of myosin, fractionated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, in developing, adult and denervated fast, slow and cardiac muscles of the rat, guinea-pig, cat, rabbit and chick were studied. It has been shown that in normal adult muscles the electrophoretic pattern of light chains of myosin reflects the myosin ATPase activity only when muscles from the same animal species are compared. In homologous muscles from adult animals differing in size, the size-dependent difference in myosin ATPase activity is not revealed in the electrophoretic pattern. Both in developing and in denervated muscle, changes in myosin ATPase activity are either connected with changes in the pattern of light chains of myosin or this pattern does not change. This relation is different in fast and slow muscles and also differs in chick and rabbit muscles. There are several possibilities of explaining the relation between ATPase activity of myosin and the pattern of light chains of myosin. The observation that myosin from the soleus muscle of 1-month-old rabbit contains light chains corresponding to both fast and slow type of myosin, indicates that the change in myosin ATPase activity during development is due to changes in the ratio between the fast and slow type of myosin.     

New mechanism for the formation of discrete stripes in the solar radio spectrum

Dispersion relations are derived for the eigenfrequency spectrum of a spatially periodic nonlinear plasma resonators created in the solar atmosphere due to the development of thermal instability. The eigenfrequency spectra of such resonators are calculated, and it is shown that they are capable of generating tens of discrete stripes (a so-called zebra structure) the number of which is independent of the ratio of the plasma frequency to the gyrofrequency in the source. This may help to overcome all difficulties in explaining the large number of stripes in the zebra structure, as well as the small magnitude of the magnetic field. The spatially periodic plasma resonators under consideration act as a filter with numerous transparency windows separated from one another by opaque regions. The number of stripes and their frequencies in the zebra structure depend on the spatial period of plasma nonuniformity, which is equal to meters or decameters for conditions typical of the solar atmosphere. The high brightness temperature of radio emission in the zebra structure is attributed to coherent emission from a large number of identical small-scale plasma sources. Some regular properties of the observed zebra structure are explained.     

Nonlinear mechanism for the generation of electromagnetic fields in a magnetized plasma by the beatings of waves

The modulational instability in a plasma in a strong constant external magnetic field is considered. The plasmon condensate is modulated not by conventional low-frequency ion sound but by the beatings of two high-frequency transverse electromagnetic waves propagating along the magnetic field. The instability reduces the spatial scales of Langmuir turbulence along the external magnetic field and generates electromagnetic fields. It is shown that, for a pump wave with a sufficiently large amplitude, the effect described in the present paper can be a dominant nonlinear process.     

Block by internal Mg2+ causes voltage-dependent inactivation of Kv1.5

Internal Mg2+ blocks many potassium channels including Kv1.5. Here, we show that internal Mg2+ block of Kv1.5 induces voltage-dependent current decay at strongly depolarised potentials that contains a component due to acceleration of C-type inactivation after pore block. The voltage-dependent current decay was fitted to a bi-exponential function (tau(fast) and tau(slow)). Without Mg2+, tau(fast) and tau(slow) were voltage-independent, but with 10 mM Mg2+, tau(fast) decreased from 156 ms at +40 mV to 5 ms at +140 mV and tau(slow) decreased from 2.3 s to 206 ms. With Mg2+, tail currents after short pulses that allowed only the fast phase of decay showed a rising phase that reflected voltage-dependent unbinding. This suggested that the fast phase of voltage-dependent current decay was due to Mg2+ pore block. In contrast, tail currents after longer pulses that allowed the slow phase of decay were reduced to almost zero suggesting that the slow phase was due to channel inactivation. Consistent with this, the mutation R487V (equivalent to T449V in Shaker) or increasing external K+, both of which reduce C-type inactivation, prevented the slow phase of decay. These results are consistent with voltage-dependent open-channel block of Kv1.5 by internal Mg2+ that subsequently induces C-type inactivation by restricting K+ filling of the selectivity filter from the internal solution.     

A cyclic model for bimodal activation of calcium activated potassium channels in radish vacuoles.

This paper presents the mathematical framework of a cyclic model proposed for describing the transition between a fast and a slow mode (fast-slow effect) induced by the application of step membrane potentials to ion channels from radish vacuoles. A voltage stimulation pulse with frequency in the range of 2 Hz or higher increased the activation time (slow mode) of the recorded currents. When the frequency of the stimulation pattern was restored to 0.1 Hz the activation time decreased twofold (fast mode). This experimental result cannot be explained by classical kinetic theory. The model, based on a simple extension of the Hodgkin and Huxley chain, describes the whole current experimental data and provides hints on the structural conformation of ion channels.     

Multishot tomography for high-resolution in situ subtomogram averaging

Cryo-electron tomography (cryo-ET) and subtomogram averaging (STA) can resolve protein complexes at near atomic resolution, and when combined with focused ion beam (FIB) milling, macromolecules can be observed within their native context. Unlike single particle acquisition (SPA), cryo-ET can be slow, which may reduce overall project throughput. We here propose a fast, multi-position tomographic acquisition scheme based on beam-tilt corrected beam-shift imaging along the tilt axis, which yields sub-nanometer in situ STA averages.     

Interaction of the sulfate ion with the active site of succinate dehydrogenase

A new type of slow changes of the succinate dehydrogenase (EC 1.3.99.1) activity induced by the sulphate ion is described. After preincubation of submitochondrial particles or soluble succinate dehydrogenase with sulphate both preparations catalyze the phenazine methosulphate reductase reaction with a significant lag. When added to the assay medium, the sulphate ion induces biphasic time-dependent competitive inhibition of the enzyme. The sulphate-induced inhibition is due to a rapid interaction of the anion with the active site of the enzyme followed by a slow pH-dependent (pKa=7.2) transformation of the enzyme-inhibitor complex. The pH-profiles of the overall succinate dehydrogenase reaction and of equilibrium between the fast and slow enzyme-sulphate complexes suggest that the same protolytic step is involved in the formation of an active intermediate and inactive enzyme-sulphate complex.     

Neural responses in the inferior colliculus of echolocating bats to artificial orientation sounds and echoes

The responses of single units and evoked potentials to a pair of artificial sounds, mimicking theorientation sound and echo, and to tape recorded actual orientation sounds were studied in terms of recovery cycle. the recovery cycle of single units could be classified into four groups: (1) short suppression (4%), (2) delayed inhibition (11%), (3) temporal recovery with or without a supernormal phase (7%), and (4) undelayed inhibition (78%) lasting 4 to 26 msec. therefore the majority of neurons were not excited by the second sound (echo) of a pair when it was delivered within several milliseconds after the first (out-going orientation sound). the duration of the recovery cycle was a function of the intensity of a pair of sounds. the weaker the first tone pulse relative to the second, the more rapid the recovery to the second. therefore, the reception of echoes is probably improved by contraction of middle ear muscles resulting in attenuation of self-stimulation by the out-going pulse. The collicular evoked potential consisted of two components, a fast one mainly due to the incoming fibers from lower levels and a slow one due to the main body of the inferior colliculus. The slow component showed slow recovery cycles as did the majority of single units while the fast one recovered very quickly. No noticeable difference in recovery cycles was found between awake and anesthetized animals. The functional meaning of inhibitory periods in the recovery cycle and role of the inferior colliculus in echo-location are discussed.     

Divalent cation binding properties of slow skeletal muscle troponin in comparison with those of cardiac and fast skeletal muscle troponins

1. New methods of preparing troponins from slow skeletal and cardiac muscle of the chicken have been developed. The electrophoretic mobilities of slow skeletal muscle troponin subunits were different from those of the corresponding fast skeletal muscle subunits. 2. A new method for determining the amount of divalent cations bound to troponin was developed. The principle of the method is to immobilize troponin by conjugating it with Sepharose 4B resin, thus making it readily sedimentable. 3. The numbers of Sr and Ca ions bound to slow muscle troponin at concentrations sufficient to produce maximum contraction were 1.73 and 1.36 mol per mol, respectively, being nearly equal to those of cardiac troponin but half of those of fast muscle troponin. 4. The concentrations of Sr and Ca ions giving half-maximal ion binding to slow muscle troponin (K50%) were 5.5 X 10(-6) M and 4.6 X 10(-7) M, respectively. 5. K50% for Sr of cardiac troponin was significantly higher than that of slow muscle troponin. Although K50% for Sr of cardiac troponin was the same as that of fast muscle troponin, cardiac troponin bound more Sr ions than fast muscle troponin at lower Sr ion concentrations. The mechanism underlying the high sensitivity of cardiac muscle contraction to Sr ions is discussed in comparison with that of slow muscle.     

Fast ignition of an inertial fusion target with a solid noncryogenic fuel by an ion beam

The burning efficiency of a preliminarily compressed inertial confinement fusion (ICF) target with a solid noncryogenic fuel (deuterium-tritium beryllium hydride) upon fast central ignition by a fast ion beam is studied. The main aim of the study was to determine the extent to which the spatial temperature distribution formed under the heating of an ICF target by ion beams with different particle energy spectra affects the thermonuclear gain. The study is based on a complex numerical modeling including computer simulations of (i) the heating of a compressed target with a spatially nonuniform density and temperature distributions by a fast ion beam and (ii) the burning of the target with the initial spatial density distribution formed at the instant of maximum compression of the target and the initial spatial temperature distribution formed as a result of heating of the compressed target by the ion beam. The threshold energy of the igniting ion beam and the dependence of the thermonuclear gain on the energy deposited in the target are determined.