bluuebunny/crossref_metadata_2025 huggingface dataset:
Seven lizard species and a blind snake: activity, body condition and growth of desert herpetofauna in relation to rainfall
Authors: Schlesinger Christine A. , Christian Keith A. , James Craig D. , Morton Stephen R.
Published: January 2011

In the Australian arid zone, primary productivity is highly variable in response to irregular and unpredictable rainfall and this has major flow-on effects for desert fauna. We measured temporal patterns of activity and body condition of eight reptile species, and growth for the three most abundant species, in a dry and a wet year. Activity and body condition of the diurnal lizards Ctenophorus nuchalis and Amphibolurus gilberti (Agamidae) and Ctenotus leonhardii and Ctenotus schomburgkii (Scincidae) varied predictably. In the dry year the onset of warm-season activity was delayed and body condition was low, whereas high levels of activity and body condition were observed in the wet year. Growth rates of C. schomburgkii, C. leonhardii, and C. nuchalis did not differ between the two years. Body condition of the nocturnal lizards Diplodactylus conspicillatus and Rhynchoedura ornata (Gekkonidae) and Lerista labialis (Scincidae) did not differ between years but the nocturnal blind snake Ramphotyphlops centralis (Typhlopidae) had higher condition in the wet year. Nocturnal species were active only in warmer months and this apparently limited their ability to respond to favourable conditions in the wet year. Temporal patterns of activity may be important determinants of how effectively lizards can make use of available resources after rain.
Activity levels in the left hemisphere caudate–fusiform circuit predict how well a second language will be learned
Authors: Tan Li Hai , Chen Lin , Yip Virginia , Chan Alice H. D. , Yang Jing , Gao Jia-Hong , Siok Wai Ting
Published: January 2011

How second language (L2) learning is achieved in the human brain remains one of the fundamental questions of neuroscience and linguistics. Previous neuroimaging studies with bilinguals have consistently shown overlapping cortical organization of the native language (L1) and L2, leading to a prediction that a common neurobiological marker may be responsible for the development of the two languages. Here, by using functional MRI, we show that later skills to read in L2 are predicted by the activity level of the fusiform–caudate circuit in the left hemisphere, which nonetheless is not predictive of the ability to read in the native language. We scanned 10-y-old children while they performed a lexical decision task on L2 (and L1) stimuli. The subjects’ written language (reading) skills were behaviorally assessed twice, the first time just before we performed the fMRI scan (time 1 reading) and the second time 1 y later (time 2 reading). A whole-brain based analysis revealed that activity levels in left caudate and left fusiform gyrus correlated with L2 literacy skills at time 1. After controlling for the effects of time 1 reading and nonverbal IQ, or the effect of in-scanner lexical performance, the development in L2 literacy skills (time 2 reading) was also predicted by activity in left caudate and fusiform regions that are thought to mediate language control functions and resolve competition arising from L1 during L2 learning. Our findings suggest that the activity level of left caudate and fusiform regions serves as an important neurobiological marker for predicting accomplishment in reading skills in a new language.
A chromatin insulator driving three-dimensional Polycomb response element (PRE) contacts and Polycomb association with the chromatin fiber
Authors: Comet Itys , Schuettengruber Bernd , Sexton Tom , Cavalli Giacomo
Published: January 2011

Regulation of gene expression involves long-distance communication between regulatory elements and target promoters, but how this is achieved remains unknown. Insulator elements have been proposed to modulate the communication between regulatory elements and promoters due to their ability to insulate genes from regulatory elements or to take part in long-distance interactions. Using a high-resolution chromatin conformation capture (H3C) method, we show that the
Drosophila gypsy
insulator behaves as a conformational chromatin border that is able to prohibit contacts between a Polycomb response element (PRE) and a distal promoter. On the other hand, two spaced
gypsy
elements form a chromatin loop that is able to bring an upstream PRE in contact with a downstream gene to mediate its repression. Chromatin immunoprecipitation (ChIP) profiles of the Polycomb protein and its associated H3K27me3 histone mark reflect this insulator-dependent chromatin conformation, suggesting that Polycomb action at a distance can be organized by local chromatin topology.
Selection of distinct Hox–Extradenticle interaction modes fine-tunes Hox protein activity
Authors: Saadaoui Mehdi , Merabet Samir , Litim-Mecheri Isma , Arbeille Elise , Sambrani Nagraj , Damen Wim , Brena Carlo , Pradel Jacques , Graba Yacine
Published: January 2011

Hox
genes encode transcription factors widely used for diversifying animal body plans in development and evolution. To achieve functional specificity, Hox proteins associate with PBC class proteins, Pre-B cell leukemia homeobox (Pbx) in vertebrates, and Extradenticle (Exd) in
Drosophila
, and were thought to use a unique hexapeptide-dependent generic mode of interaction. Recent findings, however, revealed the existence of an alternative, UbdA-dependent paralog-specific interaction mode providing diversity in Hox–PBC interactions. In this study, we investigated the basis for the selection of one of these two Hox–PBC interaction modes. Using naturally occurring variations and mutations in the
Drosophila
Ultrabithorax protein, we found that the linker region, a short domain separating the hexapeptide from the homeodomain, promotes an interaction mediated by the UbdA domain in a context-dependent manner. While using a UbdA-dependent interaction for the repression of the limb-promoting gene
Distalless
, interaction with Exd during segment-identity specification still relies on the hexapeptide motif. We further show that distinctly assembled Hox–PBC complexes display subtle but distinct repressive activities. These findings identify Hox–PBC interaction as a template for subtle regulation of Hox protein activity that may have played a major role in the diversification of Hox protein function in development and evolution.
Regulatory T cells facilitate the nuclear accumulation of inducible cAMP early repressor (ICER) and suppress nuclear factor of activated T cell c1 (NFATc1)
Authors: Vaeth Martin , Gogishvili Tea , Bopp Tobias , Klein Matthias , Berberich-Siebelt Friederike , Gattenloehner Stefan , Avots Andris , Sparwasser Tim , Grebe Nadine , Schmitt Edgar , Hünig Thomas , Serfling Edgar , Bodor Josef
Published: January 2011

Inducible cAMP early repressor (ICER) is a transcriptional repressor, which, because of alternate promoter use, is generated from the 3′ region of the cAMP response modulator (Crem) gene. Its expression and nuclear occurrence are elevated by high cAMP levels in naturally occurring regulatory T cells (nTregs). Using two mouse models, we demonstrate that nTregs control the cellular localization of ICER/CREM, and thereby inhibit IL-2 synthesis in conventional CD4+T cells. Ablation of nTregs in depletion of regulatory T-cell (DEREG) mice resulted in cytosolic localization of ICER/CREM and increased IL-2 synthesis upon stimulation. Direct contacts between nTregs and conventional CD4+T cells led to nuclear accumulation of ICER/CREM and suppression of IL-2 synthesis on administration of CD28 superagonistic (CD28SA) Ab. In a similar way, nTregs communicated with B cells and induced the cAMP-driven nuclear localization of ICER/CREM. High levels of ICER suppressed the induction of nuclear factor of activated T cell c1 (Nfatc1)gene in T cells whose inducibleNfatc1P1 promoter bears two highly conserved cAMP-responsive elements to which ICER/CREM can bind. These findings suggest that nTregs suppress T-cell responses by the cAMP-dependent nuclear accumulation of ICER/CREM and inhibition of NFATc1 and IL-2 induction.
Requirement for ribosomal protein S6 kinase 1 to mediate glycolysis and apoptosis resistance induced by Pten deficiency
Authors: Tandon Preeti , Gallo Catherine A. , Khatri Shikha , Barger Jennifer F. , Yepiskoposyan Hasmik , Plas David R.
Published: January 2011

Pten inactivation promotes cell survival in leukemia cells by activating glycolytic metabolism. We found that targeting ribosomal protein S6 kinase 1 (S6K1) in Pten-deficient cells suppressed glycolysis and induced apoptosis. S6K1 knockdown decreased expression of HIF-1α, and HIF-1α was sufficient to restore glycolysis and survival of cells lacking S6K1. In the Pten
fl/fl
Mx1-Cre
+
mouse model of leukemia, S6K1 deletion delayed the development of leukemia. Thus, S6K1 is a critical mediator of glycolytic metabolism, cell survival, and leukemogenesis in Pten-deficient cells.
The chromatin-remodeling enzyme BRG1 modulates vascular Wnt signaling at two levels
Authors: Griffin Courtney T. , Curtis Carol D. , Davis Reema B. , Muthukumar Vijay , Magnuson Terry
Published: January 2011

The ATP-dependent chromatin-remodeling enzyme brahma-related gene 1 (BRG1) regulates transcription of specific target genes during embryonic and postnatal development. Deletion of
Brg1
from embryonic blood vessels results in yolk sac vascular remodeling defects. We now report that misregulation of the canonical Wnt signaling pathway underlies many
Brg1
mutant vascular phenotypes.
Brg1
deletion resulted in down-regulation of several Wnt receptors of the
frizzled
family, degradation of the intracellular Wnt signaling molecule β-catenin, and an overall decrease in Wnt signaling in endothelial cells. Pharmacological stabilization of β-catenin significantly rescued
Brg1
mutant vessel morphology and transcription of Wnt target genes. Our data demonstrate that BRG1 impacts the canonical Wnt pathway at two different levels in vascular endothelium: through transcriptional regulation of both Wnt receptor genes and Wnt target genes. These findings establish an epigenetic mechanism for the modulation of Wnt signaling during embryonic vascular development.
Identification of a brain center whose activity discriminates a choice behavior in zebrafish
Authors: Lau Billy Y. B. , Mathur Priya , Gould Georgianna G. , Guo Su
Published: January 2011

The ability to make choices and carry out appropriate actions is critical for individual survival and well-being. Choice behaviors, from hard-wired to experience-dependent, have been observed across the animal kingdom. Although differential engagement of sensory neuronal pathways is a known mechanism, neurobiological substrates in the brain that underlie choice making downstream of sensory perception are not well understood. Here, we report a behavioral paradigm in zebrafish in which a half-light/half-dark visual image evokes an innate choice behavior, light avoidance. Neuronal activity mapping using the immediate early gene
c-fos
reveals the engagement of distinct brain regions, including the medial zone of the dorsal telencephalic region (Dm) and the dorsal nucleus of the ventral telencephalic area (Vd), the teleost anatomical homologs of the mammalian amygdala and striatum, respectively. In animals that were subjected to the identical sensory stimulus but displayed little or no avoidance, strikingly, the Dm and Vd were not engaged, despite similar levels of activation in the brain nuclei involved in visual processing. Based on these findings and previous connectivity data, we propose a neural circuitry model in which the Dm serves as a brain center, the activity of which predicates this choice behavior in zebrafish.
Interactions of anthrax lethal factor with protective antigen defined by site-directed spin labeling
Authors: Jennings-Antipov Laura D. , Song Likai , Collier R. John
Published: January 2011

The protective antigen (PA) moiety of anthrax toxin forms oligomeric pores that translocate the enzymatic moieties of the toxin—lethal factor (LF) and edema factor (EF)—across the endosomal membrane of mammalian cells. Here we describe site-directed spin-labeling studies that identify interactions of LF with the prepore and pore conformations of PA. Our results reveal a direct interaction between the extreme N terminus of LF (residues 2–5) and the Φ-clamp, a structure within the lumen of the pore that catalyzes translocation. Also, consistent with a recent crystallographic model, we find that, upon binding of the translocation substrate to PA, LF helix α1 separates from helices α2 and α3 and binds in the α-clamp of PA. These interactions, together with the binding of the globular part of the N-terminal domain of LF to domain 1′ of PA, indicate that LF interacts with the PA pore at three distinct sites. Our findings elucidate the state from which translocation of LF and EF proceeds through the PA pore.
Bioluminescence imaging of Aβ deposition in bigenic mouse models of Alzheimer's disease
Authors: Watts Joel C. , Giles Kurt , Grillo Sunny K. , Lemus Azucena , DeArmond Stephen J. , Prusiner Stanley B.
Published: January 2011

Transgenic (Tg) mouse models of Alzheimer's disease have served as valuable tools for investigating pathogenic mechanisms related to Aβ accumulation. However, assessing disease status in these animals has required time-consuming behavioral assessments or postmortem neuropathological analysis. Here, we report a method for tracking the progression of Aβ accumulation in vivo using bioluminescence imaging (BLI) on two lines of Tg mice, which express luciferase (luc) under control of the
Gfap
promoter as well as mutant human amyloid precursor protein. Bigenic mice exhibited an age-dependent increase in BLI signals that correlated with the deposition of Aβ in the brain. Bioluminescence signals began to increase in 7-mo-old Tg(CRND8:
Gfap
-luc) mice and 14-mo-old Tg(APP23:
Gfap
-luc) mice. When Tg(APP23:
Gfap
-luc) mice were inoculated with brain homogenates from aged Tg(APP23) mice, BLI detected the accelerated disease onset and induced Aβ deposition at 11 mo of age. Because of its rapid, noninvasive, and quantitative format, BLI permits the objective repeated analysis of individual mice at multiple time points, which is likely to facilitate the testing of Aβ-directed therapeutics.
Point mutation in the glycoprotein of lymphocytic choriomeningitis virus is necessary for receptor binding, dendritic cell infection, and long-term persistence
Authors: Sullivan Brian M. , Emonet Sébastien F. , Welch Megan J. , Lee Andrew M. , Campbell Kevin P. , de la Torre Juan C. , Oldstone Michael B.
Published: January 2011

Arenaviruses are a major cause of hemorrhagic fevers endemic to Sub-Saharan Africa and South America, and thus a major public health and medical concern. The prototypic arenavirus lymphocytic choriomeningitis virus (LCMV) is widely used as a model system for studying persistent and acute infections, as well as for gaining an understanding of mammalian immune function. When originally characterized three decades ago, the LCMV isolate, Armstrong, which causes an acute infection in adult mice, was found to differ from the LCMV Clone 13 strain that causes a persistent infection by two amino acid changes, one within the virus surface glycoprotein (GP1: F260L) and the other within the virus L polymerase (K1076Q). Mutation F260L was considered solely responsible for the exceptionally strong binding affinity of Clone 13 (L at GP1 260) to its cellular receptor, α-dystroglycan, which among cells of the immune system is preferentially expressed on dendritic cells, and consequently, alters dendritic cell function leading to viral persistence. Recently, we noted a previously overlooked nucleotide difference between these two strains that results in an additional amino acid change in GP1, N176D. To investigate the potential contribution of this newly identified mutation to the Clone 13 phenotype, we used reverse-genetics approaches to generate recombinant LCM viruses with each of these individual mutations. Phenotypic characterization of these rLCMV showed that mutation F260L, but not N176D, in the GP1 of LCMV is essential for mediating the long-term persistence of Clone 13 infections. This work emphasizes the importance of subtle differences in viral strains that determine disease outcomes.
Human thrombopoietin knockin mice efficiently support human hematopoiesis in vivo
Authors: Rongvaux Anthony , Willinger Tim , Takizawa Hitoshi , Rathinam Chozhavendan , Auerbach Wojtek , Murphy Andrew J. , Valenzuela David M. , Yancopoulos George D. , Eynon Elizabeth E. , Stevens Sean , Manz Markus G. , Flavell Richard A.
Published: January 2011

Hematopoietic stem cells (HSCs) both self-renew and give rise to all blood cells for the lifetime of an individual. Xenogeneic mouse models are broadly used to study human hematopoietic stem and progenitor cell biology in vivo. However, maintenance, differentiation, and function of human hematopoietic cells are suboptimal in these hosts. Thrombopoietin (TPO) has been demonstrated as a crucial cytokine supporting maintenance and self-renewal of HSCs. We generated RAG2
−/−
γ
c
−/−
mice in which we replaced the gene encoding mouse TPO by its human homolog. Homozygous humanization of TPO led to increased levels of human engraftment in the bone marrow of the hosts, and multilineage differentiation of hematopoietic cells was improved, with an increased ratio of myelomonocytic verus lymphoid lineages. Moreover, maintenance of human stem and progenitor cells was improved, as demonstrated by serial transplantation. Therefore, RAG2
−/−
γ
c
−/−
TPO-humanized mice represent a useful model to study human hematopoiesis in vivo.
Stability of plasmas penetrated by neutral gas
Authors: Lehnert B.
Published: January 2011

For a plasma body of density n and characteristic macroscopic dimension Lcthere exists a critical ion density nc= 1/σcmLcwhere σcm≃ 3 × 10−19m2for hydrogen. When n ⪅ ncthe plasma is permeable to neutral gas, whereas it becomes impermeable to the same gas when n ≫ nc. Permeable and impermeable plasmas have different equilibrium and stability properties. So far, tokamak experiments have been performed in the range of permeable plasmas, whereas full-scale steadystate fusion reactors are likely to operate in the impermeable range.

The effects of plasma-neutral-gas interaction, finite resistivity, and viscosity on the gravitational instability modes of a magnetized plasma have been investigated:

There are both direct and indirect neutral-gas effects on the ballooning and flute modes. The direct effects are due to frictional forces from collisions, and the indirect ones to the influence of the plasma-neutral-gas balance on the unperturbed pressure and density distributions.

In an impermeable plasma, the driving mechanism of the ballooning and flute instabilities can be localized to a narrow, dense and cool, partially ionized boundary region, in which plasma-neutral-gas collisions and viscosity strongly reduce the instability growth rates. Further reductions of these rates are expected to arise in more advanced and non-linear approaches.

In tokamaks, resistive ballooning modes should be practically unaffected by neutral-gas collisions. However, when n approaches ncfrom below, a collisionless ballooning mode is expected to arise from an increase of the gradients in the boundary region. This behaviour is consistent with observations, including adiabatic-compression experiments.
Flute perturbations of plasma in a helical magnetic field
Authors: Mikhailovskaya L.V. , Kikhailovsky A.B.
Published: January 2011

This paper investigates flute perturbations of a plasma that is in a helical, cylindrically symmetric magnetic field. In a geometricaloptics approximation an- equation has been obtained that relates the frequency and the wave vector of the flute perturbations of the plasma for an arbitrary relation of the gas pressure and the magnetic pressure and for an arbitrary ratio ϱ/λ of the Larmor radius of the ions to the wavelength. This equation, is used to obtain stability criteria and increments (decrements) of flute-type oscillations under conditions when the shear in the lines of force is insignificant. The stability condition obtained thus in an approximation of zero ion Larmor radius coincides with the corresponding results that follow from the hydrodynamics of Chew, Goldberger, Low. For small values of β and a finite ratio ϱ/λ a criterion was obtained for the stabilization of perturbations with finite ion Larmor radius.

Consideration of interaction between resonance particles and the wave in a number of cases leads to the buildup of flute perturbations. It is shown that such a type of buildup—residual instability—in the case of a helical magnetic field differs essentially from the residual instability for a model with a force of gravity discussed in the paper by Rosenbluth. Krall and Rostoker which is due to differences in the direction of the drift of the resonance particles in the two cases.

We have elucidated the connection between the waves that are responsible for flute instability of a hydrodynamic type and waves that have been revealed in the work of Yu. A. Tserkovnikov. We have considered transition to the case of a magnetic field with an infinitely large radius of curvature of lines of force. We have elucidated the question of the spatial structure (in a radial direction) of waves of the type discussed in Ref 5, and it has been shown that their radial wavelength is essentially connected with the ion Larmor radius, and the wavelength of hydrodynamic flute perturbations does not depend on the value of the latter.

The effect of curvature of lines of force on flute perturbations of the type of transverse drift waves has been discussed. We have shown that for not too large a radius of curvature of the line of force R <a/β (a is the characteristic dimension for the change of plasma pressure), the instability predicted in the work of Krall and Rosenbluth [6] for such a type of oscillations in a field with R→ ∞ is stabilized.
Scattering of electromagnetic waves by a cylindrical plasma in a steady magnetic field: I. Anisotropy effects
Authors: Vandenplas P. E. , Messiaen A. M.
Published: January 2011

The experimental resonance pattern of a cylindrical plasma in a steady magnetic field is compared to theory. The scattering of a plane homogeneous wave by a cold plasma column with a glass wall is studied theoretically. The Poynting vector of this wave is perpendicular to the axis of the cylinder. The static magnetic field B0 is parallel either to the axis or to the Poynting vector S, or perpendicular to both the axis and S.

The equilibrium density of the cold plasma is assumed constant in this paper and the anisotropy effects due to the homogeneous steady magnetic fields are studied through the equivalent tensorial permittivity. This permittivity is written in a general form so that the treatment also includes the anisotropie dielectric rod. When B0 lies in the cross-section of the cylinder, the partial differential equations cannot be solved in cylindrical co-ordinates. The solution is however obtained to second order in β (dimensionless parameter proportional to B0) in a Cartesian co-ordinate system and it is then transformed to a cylindrical system in which the boundary conditions are stated. It is found in most cases that the effect of B0 is much greater for the experimental phenomena than that predicted by the theoretical approach. This discrepancy arises from Laplace forces due to B0 in the cross-section and to the drift velocity of the electrons along the axis of the cylinder, and results in an inhomogeneity of magnetic origin studied in part II. This magnetically induced inhomogeneity accounts for the data not explained by the anisotropie approach.

When B0 is parallel to the cylinder axis, the problem is solved exactly. The aforesaid Laplace forces do not intervene as B0 is then parallel to the drift velocity. The quantitative agreement is very satisfactory for relatively small values of B0 and poorer results for higher B0 are probably linked to non-proportionality between equilibrium electron density and the discharge current in the plasma column.
MHD theory of stationary interaction between a high-frequency field and a plasma in non-homogeneous fields
Authors: Teichmann Jiří
Published: January 2011

Using the MHD (magneto-hydrodynamic) model of the three-component plasma, we discuss the forces affecting unit volume of an unbounded plasma in a space occupied by generally nonuniform high-frequency and magnetostatic fields. In the metric defined by the geometry of the magnetic field lines, we derive the forces affecting the three-fluid plasma arising from a high-frequency field with a high1E/1Hratio. Effects of collisions among plasma components and viscosity are included. The solution has been obtained by applying the method of successive approximations. Similarly, anisotropic plasma is studied in the collision-free approximation. Stationary hf forces in fundamental field configurations are quantitatively discussed; there are some characteristic effects in fields with curved field lines. The role of the temperature correction is discussed. The hf forces, especially near the cyclotron frequencies, can be used for the limitation of plasma escape along magnetic lines and for the acceleration and injection of plasma in nonuniform magnetostatic fields. The possibilities of the application in magnetic traps are demonstrated by some examples.
Drift cyclotron instability of a plasma with hot ions
Authors: Mikhailovsky A.B.
Published: January 2011

The author analyzes the role of drift-cyclotron instability, alluded to in ref. 2, in a spatially inhomogeneous plasma. This instability can occur in a not-too-dilute plasma with a finite Larmor radius of the ions, (ϱ/a)2 > (CA/C)2; (CA is the Alfvén velocity, ϱ is the Larmor radius of the ions, and a is the characteristic dimension of the inhomogeneity).

The paper contains a detailed investigation of the effects on the instability criterion of various factors: the curvature of the lines of force and the inhomogeneity of the magnetic field, the form of the equilibrium particle velocity distribution function, the relationship between the transverse and longitudinal dimensions of the system, and the ratio of electron to ion temperature.

The author concludes that, if the flute (hydrodynamic) instability is stabilized, the drift-cyclotron instability is the most dangerous for a system with a finite Larmor radius of the ions. This instability may be overcome by creating a system with finite intersection of the magnetic lines of force (shear). In short systems this instability need not occur if there is cold plasma of finite density between the hot plasma and the conducting ends of the apparatus.
Flute instability of a dilute inhomogmeous plasma in an inhomogeneous electric field
Authors: Arsenin V.V.
Published: January 2011

Flute perturbations of a strongly inhomogeneous dilute plasma in an inhomogeneous electric field are discussed. An inhomogeneous electric field, appearing at weak charge separation in a region with a width of the order of an ion Larmor radius in which plasma, is inhomogeneous, does not affect the stability of long-wave oscillations of low frequency. Also examined is the case of a very strong inhomogeneity in which the characteristic dimension at which the electric field changes is the order of an electron Debye length. In this case perturbations with a wavelength the order of an inhomogeneity dimension can be unstable.
Lagrangian formulation of wave kinetics in a weakly turbulent plasma
Authors: Suramlishvili G. I.
Published: January 2011

In this paper kinetic equations for plasma oscillations are derived. The method is the following: the complete Lagrangian function for a system of charged particles in an electromagnetic field is written down; the amplitude of the oscillations is defined explicitly and an expansion in powers of it is performed. As a result, a power series for the Lagrangian is obtained. The zeroth order Lagrangian gives only the equilibrium state: the first order Lagrangian vanishes identically; the second order Lagrangian contains the natural oscillations of the plasma; the higher order Lagrangians give the interactions of the natural oscillations. The distribution for oscillators in phase space is introduced and the oscillation interaction Lagrangian is written in the second quantization representation. The kinetic equation for the oscillation distribution function is then obtained by the usual method.
Corrections to “Flute instability of an axially-symmetric plasma with a finite ion Larmor radius”
Authors: Mikhailovskaya L. V. , Mikhailovsky A. B.
Published: January 2011

Even in the case of a large ion Larmor radius, the first mode of flute perturbations is unstable (for arbitrary distributions of the pressure and density of the plasma).
Electrical conductance of a turbulent plasma
Authors: Petviashvili V.I. , Ramazashvili R.R. , Tsintsadze N.L.
Published: January 2011

We investigate the electrical conductance of a homogeneous, weakly turbulent magnetoactive plasma under the assumption that oscillation is possible. Under certain onditions the electrical conductance of such a plasma can be anomalously small. This phenomenon can be explained by an effective increase in the frequency of ion electron collisions that is caused by collective particle interaction. Only low-frequency oscillations (in which both electrons and ions participate) give a significant contribution to turbulent-plasma resistance.

A formula was found, through the turbulent oscillation spectrum, for the electrical conductance of the weakly turbulent plasma. Comparison of the conductance with the anomalous diffusions across the magnetic field shows that they both contain the same quantity (determined by the oscillation spectrum), which can be interpreted as an effective collision frequency; hence we draw the conclusion that this effective collision frequency will play the role of ordinary collisions in other macroscopic processes also.

The effective collision frequency was evaluated for the Drummond-Rosenbluth instability, and with it we found the width of the weak shock wave in collisionless plasma. Also found was the formula for the effective collision frequency of an isotropic plasma.
Turbulence of inhomogeneous plasma in a strong magnetic field
Authors: Václavik J.
Published: January 2011

This paper is a study of plasma turbulence arising from magnetohydrodynamic drift instability. It deals with the derivation of equations of strong plasma turbulence from equations of two component magnetohydrodynamics by using a diagram technique. Based on these equations an estimate is carried out of the maximum value of the distribution function of the electric fields of the oscillations and the coefficient of turbulent plasma diffusion. For a more exact determination of these values and the shape of the distribution function, it is necessary to solve the system of equations numerically; therefore the system is transformed into a dimensionless form so that automatic computers can be applied.
Diffusion perpendicular to the magnetic field in the universal instability
Authors: Buchelnikova N. S.
Published: January 2011

Diffusion perpendicular to the magnetic field is investigated in a potassium plasma of non-uniform density in which the “universal” instability is excited. A qualitative picture of such diffusion is obtained by studying the relationship between the radial distribution of plasma density and the magnetic field, and by comparing the experimental densities with calculated ones on the assumption of classical diffusion. For densities of 109—1010 cm−3, the radial distribution and the peak density do not depend on the magnetic field. At higher densities, however, the half-width of the distribution becomes smaller and the peak diminishes as the field increases. At densities of 7 × 1010—5 × 1011 cm−3 the curves for the radial distribution agree well with the calculations.

Direct measurements of the diffusion coefficient come from measurements of the plasma flux perpendicular to the magnetic field. In the density range 109—1010 cm−3, the diffusion coefficient does not depend on magnetic field or on density. At higher densities it does depend on the magnetic field H, and at densities greater than 2 × 1011 cm−3 a 1/H
2 relationship is observed; the diffusion coefficient agrees with the classical coefficient in absolute value. The spread in the diffusion coefficients obtained from a single series of experiments, representing the statistical accuracy of the measurements and the stability of the diffusion coefficient, is ∼40%. The average value of the diffusion coefficient for low densities is (2.3 ± 0.9) × 102 cm2/s, greater than the classical coefficient by 1 to 2 orders of magnitude. The diffusion coefficient and the oscillation amplitude are correlated. As density is varied they remain constant until a certain critical density is reached, after which they begin to decline simultaneously. Classical diffusion is observed in the region where instability is control. Ion-ion diffusion and wall diffusion play no part in the experiments. The conclusion is drawn that the diffusion coefficient measured in the density range 109—1010 cm−3 is the result of the universal instability in a collisionless plasma.
Geodesic curvature in closed plasma configurations
Authors: Coppi B.
Published: January 2011

The stability of a plasma toroidal configuration is affected by the component of the magnetic field curvature that lies within the magnetic surface. The analysis is simplified by introducing an appropriate one-dimensional model. Because the mentioned magnetic curvature component is periodic along the field lines and has a zero average, when the periodicity is shorter than a given amount no instability localized in a particular region along the field can be found. Then the stability analysis is reduced to consider modes that extend along the magnetic field and adapt themselves to the periodicity. Attention is also devoted to modes which arise when there is shear and the periodicity is relatively long.
Stabilité électrostatique des plasmas de longueur finie
Authors: Cotsaftis M.
Published: January 2011

Using a plane-geometry model developed previously for the study of flute instabilities having a general equilibrium state, and taking into account the finite dimension of the plasma along the magnetic field and the possible presence of a cold plasma between the plasma and the conducting plates, the author resumes the study of electrostatic instabilities which, when the plasma becomes infinite, give rise to instabilities propagated “perpendicular” to the magnetic field. He determines the dispersion relation for the flutes, for the Mikhailovski-Timofeev gradient instabilities and for the loss cone instabilities, which he analyses in greater detail since they entail particularly stringent criteria in infinite geometry. The stability limit is presented as a set of curves depending on two parameters. The values assumed by these two parameters can be divided into two quite distinct groups corresponding to longitudinal and transverse injection. The two groups of values lie in the plane to either side of a critical line that divides the stability analysis into two distinct regions. Starting from this dividing line it is possible to write in each region “approximate” criteria that are more simple but indicate general trends. Devices with longitudinal injection cannot be stabilized by cold plasma and finite length effects. Devices with transverse injection offer better stabilization possibilities; under present conditions, however, it is probably necessary to increase the plasma density by one or two orders of magnitude. The flute instabilities are stabilized at the same time. Since the effect of gravity appears to be slight, the results accordingly suggest that, for obtaining a stable plasma, “short” high-density devices with a simple mirror are preferable to “long” devices with a magnetic sink. It remains to be seen, however, whether the effect that has been described mathematically is physically acceptable.
Equilibrium of a toroidal plasma column in steady-state and high-frequency magnetic fields
Authors: Gutkin T.I. , Lozovsky S.N. , Boleslavskaya G.I.
Published: January 2011

The authors consider the equilibrium of a toroidal plasma column in a steady-state magnetic field on which is superimposed a multipole high-frequency field produced by currents flowing around the major circumference of the torus which are proportional to exp[i (ωt-nψ)], where ψ is the polar angle in the meridional cross-section of the torus and ω is the frequency determined by the generator.

They demonstrate the possibility of achieving equilibrium when the pressure of the high-frequency field is less than the kinetic pressure of the plasma, ignoring the reaction of the circuit to the displacement of the plasma column; i.e. it is assumed that this displacement does not give rise to image currents in the circuit.

An expression is derived for displacement of the column as a function of the amplitude of the high-frequency field, the kinetic pressure of the plasma, the depth of the skin layer, the multipole order (n), and of geometric parameters such as the radius of the plasma column rp, the radius of the circuit rk and the radius of the torus R. The displacement of the column is proportional to the kinetic pressure of the plasma, inversely proportional to the square of the amplitude of the current in the circuit, and independent of the steady-state magnetic field. Expressed as a function of the multipole order (n), displacement is at a minimum when n is equal to the whole number closest to 1 + [1/2 ln(rk/rp)]. When rk/rp∼2, the optimum value of n is 2 (quadrupole). When n = 1 (dipole), displacement increases in proportion to ln(c/ωrp). On the assumption of a quasi-steady state (c/ωrp ≫ 1) equilibrium containment of the plasma in the dipole case is found to be difficult to achieve in practice. When n = 0 equilibrium is quite impossible to achieve. The validity of this conclusion is dependent on the assumption of a quasi-steady state and on the further assumption that the circuit will not react to displacement of the column.
Application of lasers to the production of high-temperature and high-pressure plasma
Authors: Kidder R.E.
Published: January 2011

A brief account is given of the historical evolution of giant pulse lasers and of the level of performance of such lasers that has so far been achieved. Those aspects of the interaction of light with a plasma that are of importance in plasma heating are briefly reviewed, and a detailed treatment including the results of computer calculations is given of the heating of a spark within a homogeneous gas, the subsonic heating of an isolated gas sphere, and the pressure resulting from light-induced blow-off.

It is concluded that existing giant pulse lasers have sufficient brightness to be potentially capable of producing plasmas with kilovolt temperatures and tens of megabar pressures, but that a major increase in output power will be required before this potential can be realized. The design of future giant pulse lasers that are particularly well suited to the achievement of extremely high output power at high brightness is discussed.
Energy transfer of a quasi-monochromatic wave in an inhomogeneous medium
Authors: Jungwirth K.
Published: January 2011

The paper presents the derivation of more general expressions than those usually obtained for the energy density W, the energy flux density S⃗, and the energy dissipation Γ of a quasi-monochromatic wave. The corrections as computed can be substantial, for example, in an inhomogeneous plasma in the region of frequencies ω for which the drift effects play an important role.
Kinetics of slightly relativistic plasma, II
Authors: Trubnikov B.A.
Published: January 2011

A solution has been found to the equation obtained earlier for the binary correlation function of an electron plasma; this equation takes into account, in the first non-vanishing approximation, effects of interaction retardation. Transverse interactions of particles at great distances are shown to diminish proportionally to r−3, as a result of which an isolated particle in the plasma is surrounded by a very extensive correlation cloud of currents.

The collision integral obtained on the basis of Darwin's Lagrangian is shown to differ from one making precise allowance for retardation only in terms of the order (v/c)6.
Sensitivity of a stripping analyser for neutral hydrogen atoms in the energy range from 50 to 300 eV
Authors: Fleischmann H.H. , Tuckfield R.G.
Published: January 2011

The sensitivity of a neutral-hydrogen energy analyser consisting of a gas-stripping cell and an electric ion analyser was investigated in the energy range from 50 to 300 eV. A neutral atom flux is produced by means of a plasma gun and multipole guide field. The density of this flux at the analyser entrance was determined using a calibrated secondary emission detector. The conversion efficiencies of various gases and their pressure dependence was examined. So far the use of oxygen as stripping gas seems to be the optimal choice. However, for all investigated stripping gases the sensitivity was found to be a steep function of the particle energy. This might limit the applicability of this analyser to energies above 100 eV, using the investigated gases for stripping. The overall energy resolution is estimated to be ΔE/E = 10 − 15%.
Area waves in a theta pinch
Authors: Newton A.A.
Published: January 2011

Measurements made in the mid-plane of a theta pinch plasma indicate a sudden decrease in line density. This is interpreted as the arrival of a rarefaction wave due to axial plasma loss. Detailed predictions of density, and β given by an axial MHD computation, are in good agreement with the observations.
Field line trajectories in a Skornyakov trap
Authors: Bickerton R.J. , Lenamon L.
Published: January 2011

Skornyakov has proposed a magnetic trap in which a spiral conductor connects diametrally opposite points on the inside surface of a superconducting sphere. He has argued that such a system will have nested toroidal magnetic surfaces and that these surfaces will have favourable stability properties both in terms of ‘average minimum B’ and of ‘shear’. Further he has maintained that the field distribution in such a trap can be closely reproduced by substituting an outer return spiral for the superconducting sphere and traps of this technically simpler type have been constructed. In this note we discuss the results of numerical calculations of the trajectories of magnetic field lines in such a two-spiral trap. We find that there are always some field lines originating near the centre of the system which leave it after one or two transits across the machine. Other lines are contained but trace out surfaces which are not topologically toroidal. Thus traps of the two-spiral type will not contain plasma effectively.
Langmuir probes compared with other diagnostic techniques in a Q-device
Authors: Van Der Houven Van Oordt A.J. , Wegrowe J.-G.
Published: January 2011

A comparison of density measurements between cylindrical Langmuir probes, resonance fluorescence scattering and microwave methods is performed in a singly ionized barium plasma of a Q-device by varying the following parameters: 1) Density n: 3 × 108 cm−3 ≤ n ≤ 3 × 1011 cm−3; 2) Plate temperature Tp: 2100°K ≤ Tp ≤ 2500°K; 3) Plate material: Re and W; 4) Magnetic field B: 2 kG ≤ B ≤ kG; 5) Mode of operation: Double and single ended operations; 6) Ion temperature Ti down to about room temperature, keeping the electron temperature Te = Tp; 7) Degree of ionization γ: 0.1% ≤ γ ≤ 100%; 8) Probe dimensions.

If the density n is evaluated by equating the extrapolated ion saturation current Is at the plasma potential Vs to the random ion current, it is shown that this yields a reliable relative value of the plasma density, which is by a factor of about 2.5 higher than the most probable value.
Thermalization of the kinetic energy of a plasma flow by a magnetic mirror field in BSG-I experiments
Authors: Uchida T. , Miyamoto K. , Fujita J. , Kawasaki S. , Inoue N. , Suzuki Y. , Adati K.
Published: January 2011

The purpose of the experiment using the BSG-I device described here is to study the expansion of a plasma, produced in a strong magnetic field by a theta pinch, into a weak magnetic channel and the thermalization of the kinetic energy of this plasma flow by a magnetic mirror field. The plasma, to which the fluid model is applicable, treated here is collision dominated and low-β. Shock phenomena due to the mirror field at the far end of the device are observed by several kinds of measurements and it was concluded that some part of the kinetic energy of the plasma flow was changed to thermal energy by the shock phenomenon. Plasma parameters measured in front of and behind the shock front were consistent with the Rankine-Hugoniot relations. Thus the ion temperature rises after the shock and approaches that of the initial plasma as produced in the theta pinch region before the expansion.
Equations of the electromagnetic field containing plasma
Authors: Karlovitz Béla
Published: January 2011

Plasma differs from all other media in the nature of its diamagnetic moment. The motion of the free ions and electrons, responsible for the magnetic moment of the plasma, is not restricted by quantum rules. Consequently, the energy transfer mode cE⃗⋅curlM⃗, which is forbidden by Maxwell's equations for all other media, does exist between plasma and field. Full description of an electromagnetic field containing plasma therefore requires additional terms in the field equations. These terms allow the existence of a new phenomenon: the generation of steady-state electrical vortex fields measured in a coordinate system at rest relative to the time-constant magnetic field.

The characteristic properties of this plasma-generated induction phenomenon are described briefly. The need for an experimental test of the predicted phenomenon is stressed, particularly in view of the great simplifications it may offer for the realization of thermonuclear power.
Excitations of electrostatic ion-cyclotron oscillations in weakly ionized plasma placed in an external d. c. electric field
Authors: Milić B. , Sünder D.
Published: January 2011

The excitation of ion-cyclotron oscillations in a weakly ionized plasma placed in an external d.c. electric field parallel to the field of magnetization is considered and the threshold electron drift is determined. The process is treated kinetically, and elastic collisions of charged particles with neutrals are described by Boltzmann collision integral. It is shown that the oscillations begin in the long-wave region and that their excitation may depend on ion collisions. In moderate magnetic fields (νe ≫ Ωi ≫ νi) electron collisions significantly facilitate the process of excitation.
Relativistic corrections to the distribution functions of particles in a high-temperature plasma
Authors: Kosachev V.V. , Trubnikov B.A.
Published: January 2011

Single- and double-particle functions for a high-temperature plasma in thermodynamic equilibrium are found by integrating the general Gibbs distribution. The plasma itself is described by Darwin's Lagrangian so that relativistic effects can be taken into account with an accuracy to terms of the order of v2/c2. The single-particle distribution functions are shown to be somewhat different from the Maxwellian ones in this approximation.
Temperature in laser-created deuterium plasmas
Authors: Bobin J.L. , Delobeau F. , De Giovanni G. , Fauquignon C. , Floux F.
Published: January 2011

The beam of a powerful neodymium glass laser is focused into a solid deuterium stick. The temperature of the created plasma is measured by Jahoda's X-ray absorption method. The electron temperature has been found to range up to 450 eV and exhibits a 2/3-power dependence on the power flux density.

These results are in agreement with a theoretical model involving a strong shock and a deflagration front propagating inwards the D2 ice whereas the plasma expands in the vacuum towards the incoming beam.