bluuebunny/crossref_metadata_2025 huggingface dataset:
EHD/EMHD Transport Processes and Electric Reconnection in Dusty and Dirty Plasmas
Authors: KIKUCHI HIROSHI
Published: February 2006

ABSTRACT:For dusty and dirty plasmas, fully or partially ionized, collisionless or collisional, containing dust grains or aerosols, charged and/or uncharged, an electrohydrodynamics (EHD)/electromagnetohydrodynamics (EMHD) is presented on the basis of a new equation of electric field transport in a charged fluid, supplemented by the equations of fluid vorticity, magnetic field, energy transport, and heat transfer extended for this new regime. The ‘electric Reynolds number’,RE=ɛμvL/T(ɛ: dielectric constant; μ: permeability;v: fluid velocity;L: characteristic length;T: characteristic time) plays an important role in the EHD/EMHD regime as a criterion of relative importance of convection, diffusion, dissipation, propagation, and radiation. The equation of electric field transport recovers the Kelvin‐Helmholtz theorem for high electric Reynolds numbers with a space‐charge related frozen‐in field concept. Tenuous cosmic plasmas where dust particles can be highly charged, need to be considered a multi‐component fluid, composed of electrons, ions, charged and/ or uncharged dust, and specifications are given briefly to a multi‐ component fluid model. By analogy with fluid vortex merging in the HD regime and magnetic reconnection in the MHD regime, electric reconnection is newly introduced in the EHD/EMHD regime. Following dust‐related electric reconnection, subsequent processes are divided into two cases, depending on whether the local electric fields on the grain surface are below or beyond the breakdown threshold of the background gas. For the former case, some of the electrostatic energy tends to be converted into the kinetic energy of the particle, leading to its rapid acceleration. For the latter case, a local surface discharge will take place due to sufficiently high local electric fields, forming a corona around the dust or object and leading to critical ionization flow in the form of streamer and leader followed by an eventual main discharge, or rarely by a plasma layer formation around the dust grain. Applications of EHD/EMHD and electric reconnection to a number of examples are indicated, including the formation of diffuse dust layers or dust distributions between the clouds and the ionosphere with reference to pre‐earthquake effects, natural and triggered lightning, tornadic thunderstorms, cloud‐to‐ionosphere discharges, ball lightning, nebular lightning, Chondrule production in meteorites, and a new universal electric‐cusp type plasma reactor.
Helix String Model for Turbulent Vorticity and Cavitation in Shearing Arc Plasma
Authors: DIJKHUIS GEERT C.
Published: February 2006

ABSTRACT: This paper models turbulent vorticity in shearing plasma layers as strings of identical helix units smoothly joined at their junctions. We obtain helix strings tying loops, knots, links and braids on tetragonal and cubic lattices. In state diagrams for conduction electrons in cool, dense discharge plasma we find a subdomain for cavitation and curves with zero chemical potential for equilibrium of fermi and bose systems. We present a scaling cycle of vortex stretching, twisting, breaking and reconnection at high Reynolds number forming vortex lattices at arbitrary mesh refinement. Its exponential particle acceleration brings ion circulation energy within range of high‐energy events associated with lightning and ball lightning. This vortex plasma has a state equation with negative pressure for self‐confinement. We argue that its energy surface in phase space favours self‐organization. And we discuss vortex plasma with steady‐state energy conversion by buoyancy in the nuclear fusion regime.
Non‐Equilibrium Effects Induced by Mobilities Along Steep Gradients
Authors: VAN DER MULLEN JOOST , JONKERS JEROEN
Published: February 2006

ABSTRACT: A general treatment or non‐equilibrium aspects of plasmas is presented. This is done by relating transport fluxes to equilibrium restoring processes in so‐called disturbed bilateral relations. Especially for small plasmas with consequently steep gradients this leads among others to a relatively simple characterization of the plasma as a whole.
Mechanisms of Heat Transfer between non Equilibrium Plasma and a Target Covered by a Semiconductor
Authors: CAUQUOT PASCAL , CAVADIAS SIMEON , AMOUROUX JACQUES
Published: February 2006

ABSTRACT: Elementary phenomena of heat and mass transfer from a non equilibrium low pressure plasma to an oxide target such as ‐n or ‐p type semiconductors have been measured by using an oxygen plasma. The aim of this work is to establish a correlation between the electronic properties of the semiconductors (electronic gap) and their reactivity (activation energy of the recombination reaction). The energetic transfer of a material is defined by the recombination and accommodation coefficients, respectively γ and β. The γ coefficient is measured in a pulsed oxygen plasma reactor in non equilibrium conditions, using an actinometric method. The test materials are ‐p type semiconductors (CoO, MnO, PbO and Sb2O3) and ‐n type semiconductors (SnOx). An experimental study on more complex ceramic material (SiC) is undertaken on a large temperature range (300 K‐1123 K) in order to point out a change in the recombination mechanism when the surface temperature raises. The chemical structure of the material is followed by XPS analyses and shows an oxidation of SiC to SiO2 structure.
Transient Phenomena in d.c. Plasma‐Spray Torches
Authors: COUDERT Jean François , FAUCHAIS Pierre
Published: February 2006

ABSTRACT: D.c. plasma torches have been involved for many years in industrial applications such as welding, cutting or deposit elaboration by plasma spraying or plasma assisted vapor deposition. These techniques use specific properties of plasmas produced by d.c. arcs where high temperatures (up to 25000 K) and high flow velocities (up to few km/s) are available. A considerable amount of experimental work was devoted, in the past, to characterize the properties of arc jets as a function of arc current, torch design and configuration, plasma forming gas thermophysical properties and flowrate. In the same time models approached more and more accurately the behavior of arc jets, testifying of a real advance in both knowledge and understanding of the different implicated processes and mechanisms.

Nevertheless, and mainly because of experimental difficulties, transient phenomena due to arc instabilities have been less intensively studied and their interest has only been underlined the last decade, although they were mentioned more than thirty years ago.

Due to the extraordinary progress accomplished in the field of instrumentation, new diagnostic techniques have become available, accompanied by powerful signal processing methods which are now easy to apply thanks to the development of computers and associated software. It has been experimentally demonstrated in plasma torches that the arc is submitted to gas dynamic forces which give rise to two different modes of instability among which two major cases can be distinguished. The first one is the so‐called “take‐over” mode, characterized by rather low fluctuations of arc voltage compared to the mean value, the second one being the “restrike” mode, for which the fluctuations of arc voltage are about the same in amplitude than the mean value. The restrike mode is clearly identified as the result of the stretching of the arc by the cold gas flow, followed by electrical breakdown of the cold gas layer which gives rise to a new arc‐anode attachment. The stretching‐rearcing sequences are repeated at a frequency which is governed by experimental conditions and give a sawtooth shaped voltage signal, the analysis of which provides clear information about the arc dynamics. The fluctuations of arc length generate strong voltage variations which are correlated to the electrical power supplied to the gas and, as a consequence, to the variations of the arc jet temperature and velocity. The amplitude and frequency of voltage fluctuations can be related to the torch working and geometrical parameters and dimensional analysis allow to establish reliable semi‐empirical correlations. Temperature and velocity distributions are strongly correlated to the torch working conditions and the resulting fluctuations. It will be illustrated for different operating conditions of a d.c. spray torch.
Characteristics of Turbulence in the Boundary Layer Between a Plasma Jet and an Ambient Gas Investigated by Electric Probesb
Authors: HRABOVSKÝ MILAN , KONRÁD MILOŠ , KOPECKÝ VLADIMÍR
Published: February 2006

ABSTRACT:Electric probe measurements are used to investigate the characteristics of turbulence in the interaction zone of a plasma jet with ambient air. An array of 6 probes made of Mo wire with diameter of 1 mm and length of 1 mm was moved through the plasma jet at different positions downstream of the torch exit. The maps of the probe current contours in coordinates corresponding to radial position and time represent the structure of the plasma flow. Basic characteristics of the turbulence ‐ mean size of perturbations and characteristic length ‐ were determined by statistical analysis of probe signals. The dependence of these characteristics on plasma velocity and distance from the torch exit was studied.
Particle Behavior in a Fluctuating Plasma Jet
Authors: PARK J. H. , HEBERLEIN J. , PFENDER E. , LAU Y. C. , RUUD J. , WANG H. P.
Published: February 2006

ABSTRACT: This paper reports numerical studies of the fluctuations of a plasma jet and behavior of the powder particles injected into such a fluctuating plasma jet. A radially fluctuating plasma jet is assumed to represent rotational fluctuations by forcing a steady‐state plasma jet to oscillate radially with a specified frequency. Axial fluctuations are considered by applying a transient input voltage to the two‐dimensional LAVA code. The trajectories and temperature histories of yttria‐stabilized zirconia particles injected into a fluctuating N2/H2 plasma jet flowing into air are monitored and compared with experimental data. The results show that the radial fluctuation significantly affects the plasma conditions and particle behavior, while the axial fluctuation leads to results closely resembling those of steady‐state plasma jets.
The Kinetic Theory of Transport Processes in Turbulent Media of Moderate Density
Authors: AZNAKAEV EMIR G.
Published: February 2006

ABSTRACT:The purpose of this paper is to develop the kinetic theory of transport processes (energy, momentum and mass transfer) in turbulent media of moderate density by methods of statistical mechanics and to determine their equilibrium and non‐equilibrium properties. New analytical and evaluated expressions for turbulent transport coefficients have been founded. Hydrodynamic equations of Euler and Navier‐Stokes type are obtained from kinetic equations by multiplying on additive invariants and integrating them on the particle coordinates.
RESONANCE IN A TRANSITIONAL PLASMA PLUMEa
Authors: KREJČÍ LUDĚK , DOLÍNEK VLADIMÍR , SOPUCH PAVEL , NĚNIČKA VÁCLAV , HLÍNA JAN
Published: February 2006

ABSTRACT: In the paper an insight into the mechanisms of a strong feedback between the thermal events taking place in the plasma plume core and in the arc chamber cavity during the plume transition to turbulence is given. The piece of knowledge is confronted with the data obtained in flapping plumes where such interplay does not exist practically.
Mobile Gene Cassettes and Integrons in Evolution
Authors: HALL RUTH M. , COLLIS CHRISTINA M. , KIM MI‐JURNG , PARTRIDGE SALLY R. , RECCHIA GAVIN D. , STOKES H. W.
Published: February 2006

ABSTRACT: Integrons and the site‐specific recombination systems encoded by them provide a simple mechanism for the addition of new genes to bacterial chromosomes. Although there is substantial divergence among the four known integron‐encoded integrases, they all recognize the recombination sites, known as 59‐base elements, that are associated with genes that are packaged in gene cassettes. In contrast, the integron‐associated recombination sites, attI sites, are preferentially recognized by the cognate integrase.
RNA Processing in Evolution: The Logic of Soft‐Wired Genomesa
Authors: HERBERT ALAN , RICH ALEXANDER
Published: February 2006

ABSTRACT:Direct read‐out of information from DNA into RNA allows the genome to be faithfully reproduced in RNA. This outcome occurs in what may be called “hard‐wired” organisms. On the other hand, in what we refer to as “soft‐wired” organisms, RNA is processed extensively, allowing a number of different messages to be produced from the same gene. As a consequence, the nucleotide sequences present in RNA (referred to here as the ribotype) differ from those present in DNA (the genotype). In soft‐wired organisms, RNA processing can be thought of as a series of steps, one or more of which have two mutually exclusive outcomes: a “default” outcome and an “alternative” outcome. In the presence of appropriate regulatory signals, the RNA is processed using the alternative pathway, while the default pathway is used in their absence. The setup is functionally equivalent to that found in binary “logic gates.” In both cases, “logical operations” are implemented by using regulatory signals to establish a conditional relationship between input and output and can be described using the Boolean operators AND, OR, and NOT. In the case of RNA processing events, the outcomes can be used either to directly regulate cellular responses or to control other RNA processing events. In the latter case, “networks” are established that make processing of one RNA contingent on another. Such networks allow cells to respond to their surroundings by changing the connectivity between different RNA processing events, using RNA as a substrate to compute an appropriate response. As such logical operations impact phenotype, they are subject to natural selection. Through reverse transcription, successful outcomes can be incorporated into the genome.
Mechanisms of Mutation in Nondividing Cells: Insights from the Study of Adaptive Mutation in Escherichia colia
Authors: FOSTER PATRICIA L. , ROSCHE WILLIAM A.
Published: February 2006

ABSTRACT: When populations of cells are subjected to nonlethal selection, mutations arise in the absence of cell division, a phenomenon that has been called “adaptive mutation.” In a strain of Escherichia coli that cannot metabolize lactose (Lac−) but that reverts to lactose utilization (Lac+) when lactose is its sole energy and carbon source, the mutational process consists of two components. (1) A highly efficient, recombination‐dependent mechanism giving rise to mutations on the F′ episome that carries the Lac− allele; and (2) a less efficient, unknown mechanism giving rise to mutations elsewhere in the genome. Both selected and nonselected mutations arise in the Lac− population, but nonselected mutations are enriched in Lac+ mutants, suggesting that some Lac+ cells have passed though a transient period of increased mutation. These results have several evolutionary implications. (1) DNA synthesis initiated by recombination could be an important source of spontaneous mutation, particularly in cells that are not undergoing genomic replication. (2) The highly active mutational mechanism on the episome could be important in the horizontal transfer of variant alleles among species that carry and exchange conjugal plasmids. (3) A subpopulation of cells in a state of transient mutation could be a source of multiple variant alleles and could provide a mechanism for rapid adaptive evolution under adverse conditions.
Evolution of Evolvabilitya
Authors: RADMAN MIROSLAV , MATIC IVAN , TADDEI FRANÇOIS
Published: February 2006

ABSTRACT: Genomic sequence data provide evidence for a common origin of life and for its evolution by genetic variation via mutation and recombination. This paper discusses the fundamental dialectic paradigm of evolution‐stability versus variability‐at the crossroads of molecular genetics, population genetics, ecology, and the emerging science of experimental evolution. Experimental evolution of molecules, viruses, and bacteria can be used not only to test some basic evolutionary hypotheses but also to create new organisms for applications in biotechnology, agriculture, and medicine.
Evolution of Chordate Hox Gene Clustersa
Authors: RUDDLE FRANK H. , AMEMIYA CHRIS T. , CARR JANET L. , KIM CHANG‐BAE , LEDJE CHRISTINA , SHASHIKANT COODUVALLI S. , WAGNER GÜNTER P.
Published: February 2006

ABSTRACT: In this article, we consider the role of the Hox genes in chordate and vertebrate evolution from the viewpoints of molecular and developmental evolution. Models of Hox cluster duplication are considered with emphasis on a threefold duplication model. We also show that cluster duplication is consistent with a semiconservative model of duplication, where following duplication, one daughter cluster remains unmodified, while the other diverges and assumes a new architecture and presumably new functions. Evidence is reviewed, suggesting that Hox gene enhancers have played an important role in body plan evolution. Finally, we contrast the invertebrates and vertebrates in terms of genome and Hox cluster duplication which are present in the latter, but not the former. We question whether gene duplication has been important in vertebrates for the introduction of novel features such as limbs, a urogenital system, and specialized neuromuscular interactions.
Transposable Elements As a Molecular Evolutionary Force
Authors: FEDOROFF NINA V.
Published: February 2006

ABSTRACT: This essay addresses the paradoxes of the complex and highly redundant genomes. The central theses developed are that: (1) the distinctive feature of complex genomes is the existence of epigenetic mechanisms that permit extremely high levels of both tandem and dispersed redundancy; (2) the special contribution of transposable elements is to modularize the genome; and (3) the labilizing forces of recombination and transposition are just barely contained, giving a dynamic genetic system of ever increasing complexity that verges on the chaotic.
Floricultural Traits and Transposable Elements in the Japanese and Common Morning Gloriesaa
Authors: IIDA SHIGERU , HOSHINO ATSUSHI , JOHZUKA‐HISATOMI YASUYO , HABU YOSHIKI , INAGAKI YOSHISHIGE
Published: February 2006

ABSTRACT: The Japanese morning glory has an extensive history of genetic studies and over 200 different spontaneous mutant lines have been described. Of these, we identified that two mutable alleles, flecked and speckled, for flower variegations are caused by integration of transposable elements, belonging to the En/Spm family, into the DFR‐B and CHI genes for flower pigmentation, respectively. The mutable flaked allele of the common morning glory bearing variegated flowers is caused by insertion of a new transposable element, Tip 100, into one of the CHS genes for pigmentation and that Tip 100 belongs to the Ac/Ds family. These results are discussed with regard to spontaneous transposon mutagenesis and generation of floricultural traits of morning glories.
Dynamic Evolution of Genomes and the Concept of Genome Space
Authors: BELLGARD MATTHEW I. , ITOH TAKESHI , WATANABE HIDEMI , IMANISHI TADASHI , GOJOBORI TAKASHI
Published: February 2006

ABSTRACT: A new era in the elucidation of genome evolution has been heralded with the availability of numerous genome sequences. With these data, it has been possible to study evolutionary processes at a greater level of detail in order to characterize features such as gene shuffling, genome rearrangements, base bias composition, and horizontal gene transfer. In this paper, we discuss the evolutionary implications of significant rearrangements within genomes as well as characteristic genomic regions that have been conserved across genomes. This is based on our analysis of orthologous and paralogous genes. We argue that genome plasticity has most likely contributed substantially to the dynamic evolution of genomes. We also describe the characteristic mosaic features of an archaea genome that is comprised of both bacterial and eukaryal elements. Here we investigate base compositional differences as well as the similarity of this species' genes to either bacteria or eukarya. We conclude that these features can be largely explained by the mechanism of horizontal gene transfer. Finally, we introduce the concept of genome space which is defined as the entire set of genomes of all living organisms. We explain its usefulness to describe as well as to gain deeper insight into the general features of the dynamic genomic evolutionary process.
Detecting Alien Genes in Bacterial Genomesa
Authors: MRÁZEK JAN , KARLIN SAMUEL
Published: February 2006

ABSTRACT: We present new methods for calculating codon bias of a group of genes or an individual gene relative to a standard gene class. This method is suitable for identifying alien (e.g., horizontally transferred) and highly expressed genes. In yeast and several bacterial genomes, highly expressed genes typically include ribosomal protein genes, elongation factors, chaperonins (heat shock proteins), and a subset of genes involved in glycolysis generally essential in exponential growth. Highly expressed genes of the Synechocystis genome feature several photosystem II genes, and highly expressed genes in several methanogens (Methanococcus jannaschii, M. thermoautotrophicum) are essential for methanogenesis. Alien genes mostly consist of ORFs of unknown function, transposases, prophage genes, and restriction/modification enzymes. Notably, nuclear ribosomal proteins of yeast are highly expressed, whereas mitochondrial ribosomal protein genes appear to be alien genes. Alien genes often occur in clusters, suggesting in these cases that transfer events entail several genes.
Stimulus Processing by Type II Hair Cells in the Mouse Utricle
Authors: HOLT JEFFREY R. , VOLLRATH MELISSA A. , EATOCK RUTH ANNE
Published: February 2006

Abstract: In type II and neonatal hair cells in the mouse utricle, the receptor potentials evoked by low‐frequency sinusoidal deflections of the hair bundle are attenuated by adaptation of the mechanoelectrical transduction current and the voltage‐dependent activation of a large potassium (K)‐selective outwardly rectifying conductance, gDR. These processes may contribute to high‐pass filtering of the responses of some utricular afferents to sinusoidal linear accelerations below 2 Hz. Depolarizing receptor potentials are more attenuated by gDR than are hyperpolarizing receptor potentials. It may therefore reduce nonlinear distortion introduced by mechanoelectrical transduction, which generates larger depolarizing currents than hyperpolarizing currents.

The discharge properties of utricular afferents vary according to whether they innervate the striolar or extrastriolar zones of the sensory epithelium. Regional variation in hair‐cell properties is likely to contribute. Preliminary results suggest that the outwardly rectifying K conductances of type II cells are slower and larger in the striola than in the extrastriola, consistent with regional variation in the relative numbers of delayed rectifier and A‐current K channels.
The Planes of the Utricular and Saccular Maculae of the Guinea Pig
Authors: CURTHOYS I. S. , BETTS G. A. , BURGESS A. M. , MacDOUGALL H. G. , CARTWRIGHT A. D. , HALMAGYI G. M.
Published: February 2006

Abstract: To establish a link between otolith anatomy and function it is necessary to know the regions of the utricular and saccular maculae, which are stimulated by any arbitrary linear acceleration stimulus. That requires accurate information about the location and orientation of the spatially extended maculae in head‐fixed coordinates and referred to head‐fixed landmarks (such as Reid's line). New data showing the location of the otolithic maculae in the guinea pig with respect to head‐fixed stereotaxic coordinates are presented. Guinea pigs were perfused with Karnovsky's fixative and the maculae were exposed while the head was held in a guinea pig stereotaxic device. An electrolytically sharpened fine wire held in a calibrated micromanipulator was touched to points all over the surface of each macula under visual observation with the aid of a high‐power operating microscope. The x, y, z coordinates of these points were plotted using a three‐dimensional plotting program. Both maculae have pronounced curvature so that dorsoventral shear forces will stimulate regions of both the utricular and saccular maculae.
A Review of Otolith Pathways to Brainstem and Cerebellum
Authors: BÜTTNER‐ENNEVERA J. A.
Published: February 2006

Abstract: Our knowledge of otolith pathways is developing rapidly, but is still far from complete. Primary afferents from the sacculus and utricle terminate mainly in the lateral, inferior and caudal superior vestibular nuclei, and the ventral cerebellum, in particular the nodulus. Otolith signals descend via reticulo‐ and vestibulospinal pathways in the spinal cord to influence neck motoneurons and ascending proprioceptive afferents. Utricular information can reach the extraocular eye muscles via mono‐, di‐, and multisynaptic pathways, but saccular afferents probably only by multisynaptic pathways.

The otolith signals are relayed from the vestibular nuclei, medullary reticular formation, inferior olive, and lateral reticular nucleus to sagittal zones in the caudal cerebellar vermis (nodulus and uvula), and influence the deep cerebellar nuclei. The graviceptive information could be channeled by the cerebellar efferents back to the vestibular and inferior olive complex, or fed into ascending pathways that would innervate the mescencephalon, the thalamus, and cerebral cortex.
Functional Organization of Primate Translational Vestibulo‐Ocular Reflexes and Effects of Unilateral Labyrinthectomy
Authors: ANGELAKI DORA E. , McHENRY M. QUINN , NEWLANDS SHAWN D. , DICKMAN J. DAVID
Published: February 2006

Abstract: Translational vestibulo‐ocular reflexes (trVORs) are characterized by distinct spatio‐temporal properties and sensitivities that are proportional to the inverse of viewing distance. Anodal (inhibitory) labyrinthine stimulation (100 μA, >2 s) during motion decreased the high‐pass filtered dynamics, as well as horizontal trVOR sensitivity and its dependence on viewing distance. Cathodal (excitatory) currents had opposite effects. Translational VORs were also affected after unilateral labyrinthectomy. Animals lost their ability to modulate trVOR sensitivity as a function of viewing distance acutely after the lesion. These deficits partially recovered over time, albeit a significant reduction in trVOR sensitivity as a function of viewing distance remained in compensated animals. During fore‐aft motion, the effects of unilateral labyrinthectomy were more dramatic. Both acute and compensated animals permanently lost their ability to modulate fore‐aft trVOR responses as a function of target eccentricity. These results suggest that (1) the dynamics and viewing distance‐dependent properties of the trVORs are very sensitive to changes in the resting firing rate of vestibular afferents and, consequently, vestibular nuclei neurons; (2) the most irregularly firing primary otolith afferents that are most sensitive to labyrinthine electrical stimulation might contribute to reflex dynamics and sensitivity; (3) inputs from both labyrinths are necessary for the generation of the translational VORs.
Inertial Processing of Vestibulo‐Ocular Signals
Authors: HESS BERNHARD J. M. , ANGELAKI DORA E.
Published: February 2006

Abstract: New evidence for a central resolution of gravito‐inertial signals has been recently obtained by analyzing the properties of the vestibulo‐ocular reflex (VOR) in response to combined lateral translations and roll tilts of the head. It is found that the VOR generates robust compensatory horizontal eye movements independent of whether or not the interaural translatory acceleration component is canceled out by a gravitational acceleration component due to simultaneous roll‐tilt. This response property of the VOR depends on functional semicircular canals, suggesting that the brain uses both otolith and semicircular canal signals to estimate head motion relative to inertial space. Vestibular information about dynamic head attitude relative to gravity is the basis for computing head (and body) angular velocity relative to inertial space. Available evidence suggests that the inertial vestibular system controls both head attitude and velocity with respect to a gravity‐centered reference frame. The basic computational principles underlying the inertial processing of otolith and semicircular canal afferent signals are outlined.
Clinical Testing of Otolith Function
Authors: HALMAGYI G. M. , CURTHOYS I. S.
Published: February 2006

Abstract: The subjective visual horizontal and vestibular‐evoked myogenic potentials are simple, robust, and reproducible tests of otolith dysfunction that can prove clinically useful diagnostic information in patients with vertigo and other balance disorders. While they appear to have high specificity for unilateral otolith dysfunction, further clinical research will be required to establish their sensitivity.
Assessing Otolith Function by the Subjective Visual Vertical
Authors: BÖHMER ANDREAS , MAST FRED
Published: February 2006

Abstract: The effects of peripheral vestibular diseases on the subjective visual vertical (SVV) are resumed and provide the basis for some insights into the otolith pathophysiology. With a normal range of 0 ± 2 deg (when measured in an upright body position), the SVV was shifted by 11 ± 6 deg toward the ipsilateral ear in 40 patients following an acute unilateral vestibular deafferentiation (UVD), but in the opposite direction in 9 of 52 patients after stapes surgery. These opposite effects suggest a push‐pull mechanism of the pairs of otolith organs with respect to the SVV. The dissociation between the SVV and the perception of body position indicates influences by unconscious reflexive mechanisms such as ocular cyclotorsion on the SVV. In chronic UVD patients, lateral shifts of the subjects during constant angular velocity rotation into various eccentric positions (± 16 cm) revealed a shift of the “center of graviception” close to the remaining intact contralateral inner ear. To date, this seems to be the most consistent test for clinical identification of a chronic compensated unilateral loss of otolith function. The findings regarding asymmetries in otolithic sensitivity to medially and laterally directed roll‐tilts remain controversial, probably mainly because of influences of extravestibular cues.
Horizontal Linear Vestibulo‐Ocular Reflex Testing in Patients with Peripheral Vestibular Disorders
Authors: LEMPERT THOMAS , GRESTY MICHAEL A. , BRONSTEIN ADOLFO M.
Published: February 2006

Abstract: Horizontal eye movements in response to lateral head translation [linear vestibulo‐ocular reflex (LVOR)] in normal subjects and in patients with bilateral vestibular failure (n= 14), unilateral vestibular nerve section (n= 9), and benign positional vertigo (n= 14), were studied.2 LVORs were elicited in darkness by step acceleration (0.24 g) of the whole body along the interaural axis. Results and conclusions: (1) in patients with bilateral vestibular failure, LVORs were either absent or abnormal with asymmetries, diminished velocities, and prolonged latencies. Measurements of dynamic visual acuity during linear self‐motion showed decreased performance in patients at 1.0 and 1.5 Hz, which correlated with absent or delayed LVORs. These findings demonstrate the functional role of LVORs for dynamic visual acuity. (2) Early after vestibular nerve section, LVORs were diminished or absent with head acceleration toward the operated ear and normal in the opposite direction. After 6‐10 weeks, responses were symmetrical again. Thus, a single utricle appears to be polarized with respect to the LVOR early after unilateral vestibular loss generating mostly contraversive responses. (3) Patients with benign positional vertigo showed mostly normal LVORs, which can be explained by minor utricular damage or central compensation of a chronic unilateral deficit.
Linear Vestibular Self‐Motion Signals in Monkey Medial Superior Temporal Area
Authors: BREMMER F. , KUBISCHIK M. , PEKEL M. , LAPPE M. , HOFFMANN K.‐P.
Published: February 2006

Abstract: The present study was aimed at investigating the sensitivity to linear vestibular stimulation of neurons in the medial superior temporal area (MST) of the macaque monkey. Two monkeys were moved on a parallel swing while single‐unit activity was recorded. About one‐half of the cells (28/51) responded in the dark either to forward motion (n= 10), or to backward motion (n= 11), or to both (n= 7). Twenty cells responding to vestibular stimulation in darkness were also tested for their responses to optic flow stimulation simulating forward and backward self‐motion. Forty‐five percent (9/20) of them preferred the same self‐motion directions, that is, combined visual and vestibular signals in a synergistic manner. Thirty percent (6/20) of the cells were not responsive to visual stimulation alone. The remaining 25% (5/20) preferred directions that were antialigned. Our results provide strong evidence that neurons in the MST area are at least in part involved in the processing of self‐motion.
The Contributions of Vestibular Signals to the Representations of Space in the Posterior Parietal Cortex
Authors: ANDERSEN RICHARD A. , SHENOY KRISHNA V. , SNYDER LAWRENCE H. , BRADLEY DAVID C. , CROWELL JAMES A.
Published: February 2006

Abstract: Vestibular signals play an important role in spatial orientation, perception of object location, and control of self‐motion. Prior physiological research on vestibular information processing has focused on brainstem mechanisms; relatively little is known about the processing of vestibular information at the level of the cerebral cortex. Recent electrophysiological experiments examining the use of vestibular canal signals in two different perceptual tasks are described: computation of self motion and localization of visual stimuli in a world‐centered reference frame. These two perceptual functions are mediated by different parts wof the posterior parietal cortex, the former in the dorsal aspect of the medial superior temporal area (MSTd) and the latter in area 7a.
The Vestibular Cortex: Its Locations, Functions, and Disorders
Authors: BRANDT THOMAS , DIETERICH MARIANNE
Published: February 2006

Abstract: Evidence is presented that the multisensory parieto‐insular cortex is the human homologue of the parieto‐insular vestibular cortex (PIVC) in the monkey and is involved in the perception of verticality and self‐motion. Acute lesions (patients with middle cerebral artery infarctions) of this area caused contraversive tilts of perceived vertical, body lateropulsion, and, rarely, rotational vertigo. Brain activation studies using positron emission tomography or functional magnetic resonance tomography showed that PIVC was activated by caloric irrigation of the ears or by galvanic stimulation of the mastoid. This indicates that PIVC receives input from both the semicircular canals and otoliths. PIVC was also activated during small‐field optokinetic stimulation, but not when the nystagmus was suppressed by fixation. Activation of vestibular cortex areas, visual motion‐sensitive areas, and ocular motor areas exhibited a significant right‐hemispheric dominance. The vestibular cortex intimately interacts with the visual cortex to match the two 3‐D orientation maps (perception of verticality, room‐tilt illusion) and mediates self‐motion perception by means of a reciprocal inhibitory visual‐vestibular interaction. This mechanism of an inhibitory interaction allows a shift of the dominant sensorial weight during self‐motion perception from one sensory modality (visual or vestibular) to the other, depending on which mode of stimulation prevails: body acceleration (vestibular input) or constant velocity motion (visual input).
Cortical Areas Activated by Bilateral Galvanic Vestibular Stimulation
Authors: LOBEL ELIE , KLEINE JUSTUS F. , LEROY‐WILLIG ANNE , VAN DE MOORTELE PIERRE‐FRANÇOIS , BIHAN DENIS LE , GRÜSSER OTTO‐JOACHIM , BERTHOZ ALAIN
Published: February 2006

Abstract: The brain areas activated by bilateral galvanic vestibular stimulation (GVS) were studied using functional magnetic resonance imaging. In six human volunteers, GVS led to activation in the region of the temporoparietal junction, the central sulcus, and the anterior interior intraparietal sulcus, which may correspond to macaque areas PIVC, 3aV, and 2v, respectively. In addition, activation was found in premotor regions of the frontal lobe, presumably analogous to areas 6pa and 8a in the monkey. Since these areas were not detected in previous studies using caloric vestibular stimulation, they could be related to the modulation of otolith afferent activity by GVS. However, the simple paradigm used did not allow separation of the otolithic and semicircular canal effects of GVS. Further studies must be performed to clarify the question of cortical representation of the otolithic information in the human and monkey brain.
The Interaction of Otolith and Proprioceptive Information in the Perception of Verticality: The Effects of Labyrinthine and CNS Disease
Authors: BRONSTEIN ADOLFO M.
Published: February 2006

Abstract: A review of recent experiments in patients with labyrinthine and neurological disorders assessing the subjective postural vertical (SPV) and the subjective visual vertical (SVV) is presented. The SPV was measured with subjects (Ss) seated in a motorized flight simulator tilting at 1.5 deg/s in roll and pitch; the Ss' task was to indicate when they entered and left self‐verticality. The SVV was measured by Ss adjusting a straight line to what they perceived as gravitational upright. Clear dissociations between the SVV and SPV were found, for example, patients with acute unilateral vestibular disorders had marked tilts of the SVV toward the side of the lesion but a “lean” (bias, tilt) of the SPV was never found. Dissociations of the SPV and SVV could also be induced in normal subjects by roll‐plane visual motion stimuli: the SVV was tilted in the direction of motion, but the SPV was not. Prolonged lateral body tilt did, however, bias the SVV (the “A” effect) and the SPV, but these effects are likely to be mediated by somatosensory rather than otolithic input. Evidence for the latter came from (i) findings in patients with absent vestibular function, who showed an enhanced “A” effect, and (ii) from a patient with a thalamic infarction, who showed absence of the “A” effect when leaning on the hemihypesthetic side. In separate experiments where normal Ss indicated space‐vertical and space‐horizontal with saccadic eye movements, we found differences between these percepts, that is, subjective external space lost orthogonality. The findings in these various experiments can be interpreted if we abandon the idea of a single, “internal representation” of verticality. Different sensory modalities convey different and sometimes conflicting messages about verticality. Otolithic and somatosensory signals can have opposite sign effects during verticality estimates while tilted. In man, somatosensory cues have a prominent role in verticality perception.
The Role of the Otoliths in Perception of the Vertical and in Path Integration
Authors: MITTELSTAEDT HORST
Published: February 2006

Abstract: The role of the otoliths in essential performances of human orientation is analyzed. The following interactions of the otoliths are considered:

1. The otoliths cooperate with graviceptors in the trunk in the perception of body posture. The truncal graviceptors turn out to yield on average 60% of the total gain.

2. The otoliths cooperate with proprioceptors in the head‐to‐trunk coordinate transformation. However, under static conditions, proprioceptors in the legs, although effective in the control of posture, neither affect the perception of posture nor of the visual vertical.

3. In contrast to the perception of posture, the perception of the visual vertical (SVV) receives the necessary gravity information exclusively from the otoliths. However, their output appears to be affected by a central nervous component that tends to rotate the SVV into the z‐axis of head and trunk. A theory of vectorial summation of this component, the “idiotropic vector,” with the otolithic vector is able to explain the cause of the A‐ and E‐ effects, the increase of the variance of the SVV with the tilt angle, and the asymmetrical effect of rotatory visual flow.

4. Finally, it is shown that the otoliths, by the separation of the effects of tilt from those of translation, play an essential role in navigation by path integration.
Artificial Gravity Considerations for a Mars Exploration Mission
Authors: YOUNG LAURENCE R.
Published: February 2006

Abstract: Artificial gravity (AG), as a means of preventing physiological deconditioning of astronauts during long‐duration space flights, presents certain special challenges to the otolith organs and the adaptive capabilities of the CNS. The key issues regarding the choice of AG acceleration, radius, and rotation rate are reviewed from the viewpoints of physiological requirements and human factors disturbances. Head movements and resultant Coriolis forces on the rotating platform may limit the usefulness of economical short centrifuges for other than brief periods of intermittent stimulation.
Cardiac Hypertrophy: Signal Transduction, Transcriptional Adaptation, and Altered Growth Control
Authors: WAGNER MICHAEL , MASCARENO EDUARDO , SIDDIQUI M.A.Q.
Published: February 2006

Abstract: Cardiac hypertrophy results from the enlargement of cardiac muscle and fibroblast cells. This abnormal pattern of growth can be elicited by a number of hypertrophic agents, such as cytokines and hormones that participate in normal cell‐cell signaling events during development. Under conditions yet to be defined, these same signaling molecules can cause hypertrophy of the heart. Intracellular signal transduction pathways appear to be the prime means by which the hypertrophic signal is transduced in cardiomyocytes. There is no evidence that the signal transduction pathways in hypertrophic cardiomyocytes differ from those of normal cardiomyocytes. Perhaps the signal itself is aberrant, mistimed, misplaced, or occurring at non‐physiological concentrations. Alternatively, as a quiescent cell, the cardiomyocyte may not be able to respond completely to a growth signal by turning on its proliferative machinery. Three avenues of research are described: (1) the study of the upregulation of the cardiac MLC‐2 gene, (2) STAT proteins and activation of angiotensin II, and (3) hypertrophy as a perturbation of cell cycle controls.
Amplification of Angiotensin II Signaling in Cardiac Myocytes by Adenovirus‐Mediated Overexpression of the AT1 Receptora
Authors: BOOZ GEORGE W. , CARL LOIS L. , BAKER KENNETH M.
Published: February 2006

Abstract: Low levels of AT1 receptor can make studying the growth‐related signal transduction events mediated by this angiotensin II receptor in cardiac myocytes technically difficult. The purpose of the present study was to establish whether an adenovirus expression system could be used to increase the number of plasma membrane AT1 receptors in neonatal rat ventricular myocytes, thereby amplifying the signaling pathways activated by this receptor. Cardiac myocytes infected with adenovirus expressing the AT1 receptor exhibited increased ligand binding. The overexpressed receptor appeared to function like the endogenous receptor, in regard to agonist‐induced internalization, as well as coupling to MAPK activation and protein tyrosine phosphorylation events. In addition, adenovirus‐mediated overexpression of the AT1 receptor resulted in the amplification of angiotensin II intracellular signaling. In conclusion, adenovirus‐mediated overexpression of angiotensin II receptors appears to be a useful strategy for studying the signal transduction events activated by this hormone in cardiac myocytes and for unraveling the molecular means by which this receptor type couples to a hypertrophic pattern of growth and gene expression.
Myocardial Response to Stress in Cardiac Hypertrophy and Heart Failure: Effect of Antihypertensive Drugsa
Authors: SEN SUBHA
Published: February 2006

Abstract: The myocardium's response to increased stress or load is not stereotyped. Differences have been observed in the heart's molecular composition and performance characteristics when exposed to stress. Myosin isoforms gradually change during development of hypertrophy, whereas collagen levels change only during the chronic phase of hypertrophy. Cardiac hypertrophy can regress if treated with antihypertensive drugs, but the myocardium of the post‐hypertrophic heart no longer has the same composition as it did before hypertrophy. In rat studies of the effects of antihypertensive drugs on cardiac functional reserve, captopril showed a regression of hypertrophy associated with a lower baseline stroke volume and, after dobutamine stress, a dose‐dependent rise in stroke volume. In untreated rates captopril showed no change in stroke volume. In hydralazine‐treated rats, there was no change in reserve after dobutamine stress, whereas propranolol treatment resulted in partial regression and a slight change in stroke volume. Overall, our data suggests that development of hypertension and hypertrophy plays a role in changes in the molecular structure of the myocardium, especially during the chronic phase of hypertrophy and heart failure. This complex process cannot be explained by one factor but involves a combination of factors. Identification of each factor would be of importance for the development of appropriate therapeutic agents.
Oxidized LDL and Atherogenesisa
Authors: YLÄ‐HERTTUALA SEPPO
Published: February 2006

Abstract: A brief review of recent findings regarding the role of oxidized low‐density lipoproteins (Ox‐LDL) in atherogenesis. Lipid peroxidation and oxidative damage to LDL make arteries susceptible to chronic inflammation, which is known to cause alterations in arterial gene expression and promote lesion development. Treatment protocols implementing antioxidants for preventing cardiovascular diseases are suggested.
Effect of Antioxidant Trace Elements on the Response of Cardiac Tissue to Oxidative Stressa
Authors: BARANDIER CHRISTINE , TANGUY STÉPHANE , PUCHEU SYLVIE , BOUCHER FRANCOIS , DE LEIRIS JOËL
Published: February 2006

Abstract:It is now well established that several trace elements, because of their involvement in the catalytic activity and spatial conformation of antioxidant enzymes, may contribute to the prevention of oxidative stress such as occurs upon reperfusion of ischemic tissue. The aim of this paper is (1) to review the role of these trace elements (Cu, Mn, Se, and Zn) in antioxidant cellular defenses in the course of post‐ischemic reperfusion of cardiac tissue, (2) to provide experimental data suggesting that variations in trace element dietary intake may modulate the vulnerability of cardiac tissue to ischemia‐reperfusion, and (3) to discuss in more detail the effect of Mn ions, which seem to play a special protective role against reperfusion injury. Some results obtained from experiments in animal models of myocardial reperfusion have shown that the dietary intake of such trace elements can modulate cardiac activity of antioxidant enzymes and, consequently, the degree of reperfusion damage. In addition, experimental data on the protective effects of an acute treatment with Mn are presented. Finally, experimental evidence on the protective role of salen‐Mn complexes, which exhibit catalytic SOD‐ and CAT‐like activities against reperfusion injury, are described. These complexes should be of considerable interest in clinical conditions.