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.     

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.     

Reflection and transmission coefficients for radio waves incident obliquely on N identical plane plasma layers and zebra patterns in the spectrum of solar radio emission

The reflection and transmission coefficients for quasi-monochromatic radio waves incident at an arbitrary angle on an arbitrary number of identical piecewise-homogeneous plane plasma layers are calculated analytically and numerically. It is shown that alternating transparency and opacity stripes in the spectrum of radio waves passing through such a plasma structure (the zebra pattern effect) can be observed at any angle of incidence. The opacity stripes for ordinary waves are wider than those for extraordinary waves. For the zebra pattern to be well pronounced, the radio wave flux in the Sun??s atmosphere should be narrowly directed, which is possible during bursts.     

Nonlinear periodic space-charge waves in plasma

A solution is obtained in the form of coupled nonlinear periodic space-charge waves propagating in a magnetoactive plasma. The wave spectrum in the vicinity of the critical point, where the number of harmonics increases substantially, is found to fall with harmonic number as ∝ s ^?1/3. Periodic space-charge waves are invoked to explain the zebra pattern in the radio emission from solar flares.     

A possible interpretation of the zebra pattern in solar radiation

The nature of the zebra pattern in continual type-IV solar radio bursts is discussed. It is shown that, when a weakly relativistic monoenergetic proton beam propagates in a highly nonisothermal plasma, the energy of the slow beam mode can be negative and explosive instability can develop due to the interaction of the slow and fast beam modes with ion sound. Due to weak spatial dispersion, ion sound generation is accompanied by cascade merging, which leads to stabilization of explosive instability. The zebra pattern forms due to the scattering of fast protons by ion sound harmonics. The efficiency of the new mechanism is compared with that of previously discussed mechanisms.     

Dynamics of accelerated ions in coronal loops and model of a gamma-ray source

The dynamics of ions accelerated to energies of 10–100 MeV/nucleon in an electric field of ～0.01–0.1 V/cm, which has a component directed along the magnetic field of solar coronal loops with a characteristic size of ～100000 km, is considered. The motion of fast ions trapped in a current-carrying magnetic loop that has a magnetic mirror at its base (the mirror trap model) is analyzed. The applicability of the obtained theoretical results to interpret gamma-ray bursts that, according to the data of the RHESSI space observatory, occurred on July 23, 2002 and October 28, 2003, is discussed. In those two bursts, a single and a pair gamma source displaced relative to the hard X-ray sources were localized in the 2.223-MeV neutron-capture line. On the basis of complex analysis of multi-wavelength (X-ray, gamma-ray, and optical) observations and the data on fast solar protons, a new topological model of the source of accelerated particles (of the mirror trap type) and a new scenario of the event that occurred on July 23, 2002 are proposed. Evidence of the possibility of particle acceleration by the electric field in coronal mass-ejection loops during large solar flares is obtained. The simulation results indicate that the gamma-ray source in the excitation lines (4.1–6.7 MeV) should coincide with the region where the accelerated ions interact with the background plasma of the solar atmosphere above the spot of the flare active region.     

Study of bioengineered zebra fish olfactory receptor 131-2: receptor purification and secondary structure analysis

How fishes are able to detect trace molecules in large bodies of water is not understood. It is plausible that they use olfactory receptors to detect water-soluble compounds. How the zebra fish Danio Rerio, an organism with only 98 functional olfactory receptors, is able to selectively detect and recognize numerous compounds in water remains a puzzling phenomenon. We are interested in studying the biochemical and molecular mechanisms of olfaction in fish. Here, we report on the study of a bioengineered zebra fish olfactory receptor OR131-2, affinity-purified from a HEK293S tetracycline-inducible system. This receptor was expressed and translocated to the cell plasma membrane as revealed by confocal microscopy. Circular dichroism spectroscopy showed that the purified zebra fish receptor folded into an α-helical structure, as observed for other G-protein coupled receptors (GPCRs). Our study shows that it is possible to produce viable quantities of the zebra fish olfactory receptor. This will not only enable detailed structural and functional analyses, but also aid in the design of biosensor devices in order to detect water-soluble metabolites or its intermediates, which are associated with human health.     

Heliospheric current sheet and effects of its interaction with solar cosmic rays

The effects of interaction of solar cosmic rays (SCRs) with the heliospheric current sheet (HCS) in the solar wind are analyzed. A self-consistent kinetic model of the HCS is developed in which ions with quasiadiabatic dynamics can present. The HCS is considered an equilibrium embedded current structure in which two main plasma species with different temperatures (the low-energy background plasma of the solar wind and the higher energy SCR component) contribute to the current. The obtained results are verified by comparing with the results of numerical simulations based on solving equations of motion by the particle tracing method in the given HCS magnetic field with allowance for SCR particles. It is shown that the HCS is a relatively thin multiscale current configuration embedded in a thicker plasma layer. In this case, as a rule, the shear (tangential to the sheet current) component of the magnetic field is present in the HCS. Taking into account high-energy SCR particles in the HCS can lead to a change of its configuration and the formation of a multiscale embedded structure. Parametric family of solutions is considered in which the current balance in the HCS is provided at different SCR temperatures and different densities of the high-energy plasma. The SCR densities are determined at which an appreciable (detectable by satellites) HCS thickening can occur. Possible applications of this modeling to explain experimental observations are discussed.     

The acoustic expression of stress in a songbird: Does corticosterone drive isolation-induced modifications of zebra finch calls?

Animal vocalizations convey multiple pieces of information about the sender. Some of them are stable, such as identity or sex, but others are labile like the emotional or motivational state. Only a few studies have examined the acoustic expression of emotional state in non-human animals and related vocal cues to physiological parameters. In this paper, we examined the vocal expression of isolation-induced stress in a songbird, the zebra finch (Taeniopygia guttata). Although songbirds use acoustic communication extensively, nothing is known to date on how they might encode physiological states in their vocalizations. We tested the hypothesis that social isolation in zebra finches induces a rise of plasma corticosterone that modifies the vocal behavior. We monitored plasma corticosterone, as well as call rate and acoustic structure of calls of males in response to the playback of female calls of varied saliences (familiar versus stranger) in two situations: social isolation and social housing. Social isolation induced both a rise in plasma corticosterone, and a range of modifications in males' vocal behavior. Isolated birds showed a lower vocal activity, an abolition of the difference of response between the two stimuli, and evoked calls with longer duration and higher pitch. Because some of these effects were mimicked after oral administration of corticosterone in socially housed subjects, we conclude that corticosterone could be partly responsible for the isolation-related modifications of calls in male zebra finches. To our knowledge, this is the first demonstration of the direct implication of glucocorticoids in the modulation of the structure of vocal sounds.     

Song retuning with tutor model by adult zebra finches

Songbirds first memorize a tutor song in youth and develop their own song after the remembered model. As birds sexually mature, their song becomes crystallized and refractory to further tutoring. Here, we show that the song syllables of adult zebra finches gradually drift from their once crystallized forms, when individual birds are kept in auditory isolation or in company of cage mates singing different song syllables. Furthermore, when birds with drifted syllables are tutored with the same model again, they amend the fine structure of their syllables towards the model. In contrast, retutoring does not affect syllable sequences that differ from those of the original tutor.     

Radiative damping of coronal-loop oscillations

A theoretical interpretation is given to the coronal-loop oscillations that have been recently detected by the UV telescope of the TRACE spacecraft. It is shown that the anomalously rapid damping of coronal-loop oscillations initiated by an external action (a shock wave from a solar flare) is completely explained in terms of the radiative damping mechanism. A coronal loop oscillating with a small but finite (observable) amplitude in an external magnetic field efficiently generates fast magnetosonic modes. As a result, the perturbation energy is completely dissipated during several periods of free oscillations of the loop. The problem is studied in the perfectly conducting plasma approximation. The effect is explained without making any hypotheses about anomalous properties of the plasma inside the coronal loops.     

Light microscopic studies on the pineal organ in teleost fishes with special regard to its function

The antennal flagellum of the male sorghum midge is about a millimeter long and may bear over 500 sense organs. These consist of (1) tactile hairs, (2) thin-walled pegs, (3) circumfila and (4) very small pegs of unknown function. Each of the 12 subsegments of the flagellum is divided into two globular nodes and each of these is encircled by a circumfilum of from 6 to 14 loops. The circumfila are attached to the antennal surface by short stalks. The loops of the circumfila have the basic structure of thin-walled chemoreceptors: (1) very small pores in their delicate wall and (2) a lumen filled with branches of dendrites from sensory neurons. The outer surface of the circumfilum is covered with a labyrinth of fine ridges between which the pores are located. Some evidence was obtained that the circumfila are produced in the pupa by bifurcate trichogen cells. The flagellum of the female is shorter than that of the male and composed of 12 cylindrical subsegments. The circumfila of the female lie close to the surface to which they are attached by short stalks. Each is composed of two parts that encircle the subsegment and of two others that run lengthwise between the circles. The surface is nearly smooth, perforated by fine openings and lacks the complex pattern of ridges seen in the male. It also has more dendrite branches but, otherwise, has the same basic structure.     

Developmental changes at the node and paranode in human sural nerves: morphometric and fine-structural evaluation

Developmental alterations of paranodal fiber segments have not been investigated systematically in human nerve fibers at the light- and electron-microscopic level. We have therefore analyzed developmental changes in the fine structure of the paranode in 43 human sural nerves during the axonal growth period up to 5 years of age, and during the subsequent myelin development up to 20 years and thereafter. The nodal, internodal, and paranodal axon diameters reach their adult values at 4–5 years of age. The ratio between internodal and paranodal axon diameters remains constant at 1.8–2.0. Despite a considerable increase in myelin sheath thickness, the length of the paranodal myelin sheath attachment zone at the axon does not increase correspondingly, because of attenuation, separation from the axolemma, and piling up of myelin loops in the paranode. Separation of variable numbers of terminal myelin loops from the underlying axolemma results in the formation of bracelets of Nageotte, whereas the transverse bands of these loops disappear. The adaptation of the paranodal myelin sheath to axonal expansion during development probably occurs by uneven gliding of the paranodal myelin loops simultaneously with internodal slippage of myelin lamellae. Since mechanically stabilizing structures (tight junctions and desmosomes between adjacent paranodal myelin processes; transverse bands between myelin loops and paranodal axolemma) are unevenly arranged, especially during rapid axonal growth, paranodal axonal growth with simultaneous adaptation of the myelin sheath is probably discontinuous with time.Presented in part at the 10th Biennial Meeting of the Peripheral Nerve Study Group at Arden House, Harriman, New York, USA, June 30th–July 3rd, 1991, and as a doctoral thesis (M. Bertram) at the RWTH Aachen in 1991     

Invasive ecosystem engineers and biotic indices: Giving a wrong impression of water quality improvement?

Benthic component of an ecosystem is considered in ecological status assessment of the key European Directives. Most of the metrics proposed for the benthic quality assessment are biodiversity based. Their robustness and applicability are widely discussed in many recent studies. However an impact of invasive alien species on biotic indices and environmental quality assessments has been largely overlooked by researchers so far. In the current study we assessed Benthic Quality Index (BQI) in a coastal ecosystem, highly affected by the invasive zebra mussel Dreissena polymorpha. Zebra mussel is able of modifying benthic habitats and enhancing local biodiversity. In the analyzed ecosystem it affected benthic species richness, abundance and community structure. As a result the calculated BQI values were significantly higher in the presence of zebra mussel with evident outliers in samples with particularly high zebra mussel abundances. Therefore we found that BQI determined in our study was artificially elevated providing false signal of the ecological status improvement. Based on the results presented, we suggested data correction framework that has been tested on the current dataset and proved to be effective minimizing zebra mussel impact on BQI assessment. Our experience could be applied for other coastal ecosystems invaded by the zebra mussel or any other aquatic invasive species with resembling biological traits and bioinvasion impacts.     

Species differences in auditory processing dynamics in songbird auditory telencephalon

The caudomedial nidopallium (NCM) of songbirds is a telencephalic area involved in the auditory processing and memorization of complex vocal communication signals. We used pure tone stimuli and multiunit electrophysiological recordings in awake birds to investigate whether the basic properties of song-responding circuits in NCM differ between canaries and zebra finches, two species whose songs are markedly different in their spectral and temporal organization. We found that the responses in zebra finch NCM are characterized by broad tuning and sustained responses that may facilitate the integration of zebra finch song syllables and call notes that are of long duration and have a broad harmonic structure. In contrast, we found that the responses in canary NCM show narrower tuning and less sustained responses over the time periods analyzed. These characteristics may contribute to enhanced processing of the narrow-band whistles, rapid trills, and steep frequency modulations that are prominent features of canary song. These species differences are much less pronounced in field L2, the direct thalamorecipient region that represents a preceding station in the central avian auditory pathway. NCM responses did not differ across sexes of either species, but field L2 did show wider tuning in zebra finch females relative to males. In sum, species differences in the response properties of NCM likely reflect selectivity for the acoustic elements of each species' vocal repertoire.     

Anhydrolutein in the zebra finch: a new,metabolically derived carotenoid in birds

Many birds acquire carotenoid pigments from the diet that they deposit into feathers and bare parts to develop extravagant sexual coloration. Although biologists have shown interest in both the mechanisms and function of these colorful displays, the carotenoids ingested and processed by these birds are poorly described. Here we document the carotenoid-pigment profile in the diet, blood and tissue of captive male and female zebra finches (Taeniopygia guttata). Dietary carotenoids including: lutein; zeaxanthin; and β-cryptoxanthin were also present in the plasma, liver, adipose tissue and egg-yolk. These were accompanied in the blood and tissues by a fourth pigment, 2′,3′-anhydrolutein, that was absent from the diet. To our knowledge, this is the first reported documentation of anhydrolutein in any avian species; among animals, it has been previously described only in human skin and serum and in fish liver. We also identified anhydrolutein in the plasma of two closely related estrildid finch species (Estrilda astrild and Sporaeginthus subflavus). Anhydrolutein was the major carotenoid found in zebra finch serum and liver, but did not exceed the concentration of lutein and zeaxanthin in adipose tissue or egg yolk. Whereas the percent composition of zeaxanthin and β-cryptoxanthin were similar between diet and plasma, lutein was comparatively less abundant in plasma than in the diet. Lutein also was proportionally deficient in plasma from birds that circulated a higher percentage of anhydrolutein. These results suggest that zebra finches metabolically derive anhydrolutein from dietary sources of lutein. The production site and physiological function of anhydrolutein have yet to be determined.     

姜黄素类似物EF24对HepG2及斑马鱼胚胎发育的影响

为探讨姜黄素类似物EF24对肝癌细胞的影响以及对脊椎动物的毒性,以EF24对HepG2和斑马鱼胚胎进行处理,发现低浓度的EF24对HepG2达到较好的杀伤效果,IC50为29.38umol／L。对斑马鱼胚胎,当受精卵发育6h为敏感期,EF24的安全浓度达100mg／L。而从400mg／L高浓度开始出现畸形和死亡,如卵黄弥散、胚胎在外包期死亡、囊胚期胚胎动物极弥散、脊柱弯曲、发育不全等现象。EF24是一种对肝癌细胞有较强的杀伤效果且安全的潜在药物。     

Population structuring in mountain zebras (<Emphasis Type="Italic">Equus zebra</Emphasis>): The molecular consequences of divergent demographic histories

The endangered mountain zebra (Equus zebra) is endemic to the semi-arid inhospitable mountainous escarpments of southern Africa. The species is divided taxonomically into two geographically separated subspecies, each with differing recent population histories. In Namibia, Hartmann’s mountain zebra (E. z. hartmannae) is common and occurs in large free-ranging populations, whereas in South Africa, prolonged hunting and habitat destruction over the last 300 years has decimated populations of the Cape mountain zebra (E. z. zebra). In this study, we investigate the consequences of these divergent demographic histories for population genetic diversity and structure. We also examine the phylogeographic relationship between the two taxonomic groups. Genetic information was obtained at 15 microsatellite loci for 291 individuals from a total of 10 populations as well as 445 bp of the mitochondrial control region sequence data from 77 individuals. Both model-based and standard analytical approaches were used to examine the data. Both types of marker returned levels of diversity and structure that were consistent with population history. Low genetic variation within individual Cape mountain zebra populations, the characteristic indicator of population fragmentation and drift, was offset by moderate variation in the entire E. z. zebra sample. This implies that higher levels of diversity still exist within the Cape mountain zebra gene pool. A management strategy that entailed the mixing of aboriginal populations is therefore advocated in order to halt the further loss of Cape mountain zebra genetic diversity. Allele frequencies in Hartmann’s mountain zebra were relatively resilient to demographic fluctuations. Due to the high incidence of mitochondrial haplotype sharing between populations, the hypothesis that Cape and Hartmann’s mountain zebra mitochondrial lineages were reciprocally monophyletic was not supported. However, the presence of private alleles at nuclear loci rendered the two subspecies genetically distinct evolutionary significant units.     

Mitochondrial DNA of the extinct quagga: Relatedness and extent of postmortem change

Sequences are reported for portions of two mitochondrial genes from a domestic horse and a plains zebra and compared to those published for a quagga and a mountain zebra. The extinct quagga and plains zebra sequences are identical at all silent sites, whereas the horse sequence differs from both of them by 11 silent substitutions. Postmortem changes in quagga DNA may account for the two coding substitutions between the quagga and plains zebra sequences. The hypothesis that the closest relative of the quagga is the domestic horse receives no support from these data. From the extent of sequence divergence between horse and zebra mitochondrial DNAs (mtDNAs), as well as from information about the fossil record, we estimate that the mean rate of mtDNA divergence in Equus is similar to that in other mammals, i.e., roughly 2% per million years.