bluuebunny/crossref_metadata_2025 huggingface dataset:
ON THE QUESTION OF REGULAR SOLITONS IN A NONCOMMUTATIVE MAXWELL–CHERN–SIMONS–HIGGS MODEL
Authors: MUKHERJEE PRADIP , SAHA ANIRBAN
Published: May 2007

The Maxwell–Chern–Simons model with scalar matter in the adjoint representation is analyzed from an alternative approach which is regular in the θ→0 limit. This method is complementary to the usual operator formalism applied to explore the nonperturbative solutions which give singular results in the θ→0 limit. The absence of any regular non-trivial lumpy solutions satisfying B–P–S bound has been conclusively demonstrated.
MOTION OF A VECTOR PARTICLE IN A CURVED SPACETIME IV: ASYMPTOTICAL SHAPE OF CAUSTIC
Authors: MUMINOV A. T. , YA. TURAKULOV Z.
Published: May 2007

The studies of influence of spin on a photon motion in a Schwarzschild spacetime is continued. In the previous paper2the first-order correction to the geodesic motion is reduced to a non-uniform linear ordinary differential equation and the equation obtained has been solved by the standard method of integration of the Green function. If each photon draws a world line specified by this solution, then light rays from infinitely distant source form a caustic which does not appear without the spin-gravity interaction. The goal of this work is to obtain explicit form of caustic.
CP VIOLATION IN BEAUTY DECAYS
Authors: GRONAU MICHAEL
Published: May 2007

Precision tests of the Kobayashi–Maskawa model of CP violation are discussed, pointing out possible signatures for other sources of CP violation and for new flavor-changing operators. The current status of the most accurate tests is summarized.
CONSTRAINTS ON THE COSMOLOGICAL DENSITY PARAMETERS AND COSMIC TOPOLOGY
Authors: REBOUÇAS M. J.
Published: May 2007

A nontrivial topology of the spatial section of the universe is an observable which can be probed for all homogeneous and isotropic universes, without any assumption on the cosmological density parameters. We discuss how one can use this observable to set constraints on the density parameters of the universe by using a specific spatial topology along with type Ia supernovae and X-ray gas mass fraction data sets.
QUARK MATTER MAGNETIZATION: PHASE TRANSITION OR UPPER LIMIT OF MAGNETIC FIELD?
Authors: MARTÍNEZ A. PÉREZ , ROJAS H. PÉREZ , MOSQUERA CUESTA H. J. , ORSARIA M.
Published: May 2007

Quark matter is expected to exist in the interior of compact stellar objects as neutron stars or even the more exotic strange stars. In a previous paper [Int. J. Mod. Phys. D14(11) (2005) 1959], the equations of state for a degenerate quark gas were studied in the presence of ultra strong magnetic fields, starting from the modified MIT Bag Model which included the electromagnetic interaction. In the present paper, we revise the behavior of a system made up of quarks with anomalous magnetic moment (AMM) and we discuss its effect in terms of the magnetization and susceptibility. It can be understood as a phase transition or as a criterion of the limited value for the magnetic field in quark stars.
THE NUCLEAR MATTER COMPRESSIBILITY FUNCTION IN A PARAMETERIZED COUPLING MODEL
Authors: DEXHEIMER VERÔNICA A. , VASCONCELLOS CÉSAR A. Z. , BODMANN BARDO E. J.
Published: May 2007

In the framework of an effective derivative-coupling model with scalar and vector mesons coupled to the octet of baryons and leptonic degrees of freedom, we have calculated in detail the nuclear property known as the compressibility function, using the mean-field theory formalism and taking into account chemical equilibrium, baryon number and electric charge conservation. The parameters of the model are chosen in order to reproduce phenomenology: an effective nucleon mass between 0.7–0.8 MN and a compression modulus between 200–300 MeV.
PHASE TRANSITIONS IN ASYMMETRIC NUCLEAR MATTER
Authors: DUTRA M. , LOURENÇO O. , DELFINO A. , SÁ MARTINS J. S.
Published: May 2007

We study the thermodynamics of an asymmetric system with arbitrary proton fraction. The system is described by a mean-field theory, with terms for the surface and Coulombian contributions to the interaction energy. Consistently with the binary nature of the system under study, we impose baryon number and isospin conservation and investigate the coexistence surface (binodal). The chemical instability, as well as the mechanical instability, are taken into account in the construction of the meta-stability region as a function of the proton fraction and temperature. The effect of including surface and Coulombian terms is also discussed.
FINITE TEMPERATURE NUCLEAR MATTER IN THE RELATIVISTIC MEAN FIELD THEORY
Authors: PASSAMANI TOMAZ , CESCATO MARIA LUIZA
Published: May 2007

The nuclear matter density at finite temperature was evaluated analytically in the relativistic mean field theory using Sommerfeld approximation at low temperature. These analytical results are interesting since they allow a more transparent analysis of the contributions of the involved parameters.
QUARK CORE FORMATION IN SPINNING-DOWN PULSARS
Authors: MARRANGHELLO G. F. , REGIMBAU T. , DE FREITAS PACHECO J. A.
Published: May 2007

A pulsars spins down due to magnetic torque reducing its radius and increasing the central energy density. Some pulsars which are born with central densities close to the critical value of quark deconfinement may undergo a phase transition and suffer a structural re-arrangement. This process may excite oscillation modes and emit gravitational waves. We determine the rate of quark core formation in neutron stars using a realistic population synthesis code.
DETECTING QUASI-NORMAL MODES FROM NEUTRON STARS AND BLACK HOLES
Authors: MARRANGHELLO G. F.
Published: May 2007

The properties of relativistic perturbations of neutron stars and black holes are discussed. They are of great relevance in the study of gravitational wave astronomy. In this work, we review the properties of quasi-normal modes of neutron stars and Schwarzschild black holes and the main features of their detection by actual gravitational wave interferometers.
A CLASS OF NONLINEAR RELATIVISTIC MODELS FOR NUCLEAR MATTER AND THE BINARY PULSAR J0737-3039A
Authors: RAZEIRA MOISÉS , VASCONCELLOS CÉSAR A. Z. , BODMANN BARDO E. J. , HADJIMICHEF DIMITER
Published: May 2007

In this work, we calculate the moment of inertia of the pulsar of the binary system J0737-3039A in the framework of Einstein's gravitational theory combined with a relativistic field theoretical approach for nuclear matter in the slow rotating regime, taking into account that the star's frequency is much smaller than Kepler's frequency. In the description of the EoS for nuclear matter, we consider a generalized class of relativistic multi-baryon Lagrangian density mean field approach which contains adjustable nonlinear couplings of the meson fields with the baryon fields. Upon adjusting the model parameters to describe bulk static properties of ordinary nuclear matter, we determine the EoS of the pulsars. By analyzing the results, dynamical constraints for neutron star models are identified.
A GENERAL SELF-SIMILAR MODEL AND THE P-D DIAGRAM OF EXTRAGALACTIC RADIO SOURCES
Authors: LIMA A. P. , CARVALHO J. C. , O'DEA C. P.
Published: May 2007

The great majority of analytical models for extragalactic radio sources suppose self-similarity and can be classified into three types. We have developed a model that represents a generalization of most models found in the literature and show that these three types are particular cases. The model assumes that the area of the head of the jet varies with the jet size according to a power law and the jet luminosity is a function of time. As is usually done, the basic hypothesis is that there is an equilibrium between the pressure exerted both by the head of the jet and the cocoon walls and the ram pressure of the ambient medium. The equilibrium equations and energy conservation equation allow us to express the size and width of the source and the pressure in the cocoon as a power law and find the respective exponents. Once we find these exponents, we can determine the initial values of the source size, the cocoon radius and of the pressure inside the cocoon. We also suppose that, near the nucleus, the jet propagates in a constant density atmosphere and, as it leaves the central region of the host galaxy, it propagates in a decaying atmosphere. All these assumptions can be used to calculate the evolution of the source radio luminosity allowing us to draw a P-D diagram. This can then be compared with the observed P-D diagram of both compact (GPS and CSS) and extended sources from the 3CR catalogue. The comparison makes it possible to determine the various parameters of the model and understand the physical processes involved in the evolution of extragalactic radio sources.
EXTENDED RADIO SOURCES EVOLUTION AND THE ANGULAR SIZE REDSHIFT RELATION
Authors: CARVALHO J. C. , ALCANIZ J. S. , LIMA J. A. S.
Published: May 2007

The angular diameter versus redshift relation in the standard FRW model is rediscussed. The present data imply that the standard FRW flat cosmology (q0 = 1/2) cannot be the best-fit model when evolution is absent. By using a simple analytical model to describe the expansion of jets in extended radio sources, a redshift dependence of the proper length of the sources is obtained. For these sources, we show that evolution contributes in such a way that the models can be compatible with the observations of the angular diameter versus redshift cosmological test.
A NOTE ON THE LARGE-ANGLE ANISOTROPIES IN THE WMAP CUT-SKY MAPS
Authors: BERNUI A. , MOTA B. , REBOUÇAS M. J. , TAVAKOL R.
Published: May 2007

Recent analyses of the WMAP data seem to indicate the possible presence of large-angle anisotropy in the Universe. If confirmed, these can have important consequences for our understanding of the Universe. A number of attempts have recently been made to establish the reality and nature of such anisotropies in the CMB data. Among these is a directional indicator recently proposed by the authors. A distinctive feature of this indicator is that it can be used to generate a sky map of the large-scale anisotropies of the CMB maps. Applying this indicator to full-sky temperature maps we found a statistically significant preferred direction. The full-sky maps used in these analyses are known to have residual foreground contamination as well as complicated noise properties. Thus, here we performed the same analysis for a map where regions with high foreground contamination were removed. We find that the main feature of the full-sky analysis, namely the presence of a significant axis of asymmetry, is robust with respect to this masking procedure. Other subtler anomalies of the full-sky are on the other hand no longer present.
GRAVITATIONAL PERTURBATIONS AND QUASINORMAL MODES OF BLACK HOLES WITH NON-SPHERICAL TOPOLOGY
Authors: MIRANDA ALEX S. , ZANCHIN VILSON T.
Published: May 2007

In the present work we investigate the physical interpretation of gravitational perturbations of static asymptotically anti-de Sitter black holes with non-spherical topology. For zero wavenumber modes, the axial perturbations yield only small rotations on the system, while the polar perturbations lead to a change in the mass and may also produce gravitational waves. Additionally, it is verified that perturbations with any nonzero wavenumber are able to produce gravitational waves in these space–times. On the basis of these results, the quasinormal frequencies corresponding to polar perturbation modes with null wavenumber are calculated and briefly analyzed.
ON THE THERMODYNAMICS OF DARK ENERGY
Authors: SILVA R. , ALCANIZ J. S. , LIMA J. A. S.
Published: May 2007

Recent astronomical observations suggest that the bulk of energy in the Universe is repulsive and appears like a dark energy component (which accounts for ~2/3 of the energy content of the Universe) with negative pressure (ω ≡ px/ρx < 0). In this work, we discuss the thermodynamic behavior by considering three different parametrizations, describing the dark energy component: (1) Model 1: [Formula: see text]; (2) Model 2: ω(z) = ω0 + ω2 z; (3) Model 3: ω(z) = ω0 - ω3 ln (1 + z). It is found that its energy and temperature grow during the evolution of the Universe since work is done on the system. The case of phantom energy (ω < -1), however, seems to be physically meaningless because its entropy is negative. Our analysis also implies that the ultimate fate of the Universe may be considerably modified. Actually, the future of the Universe depends on the kind of parametrization. For Models 1 and 3, the Universe will becoming increasingly hot, while for Model 2 it cools during evolution.
THE INTERACTION BETWEEN EXTRAGALACTIC JETS AND THE INTERSTELLAR MEDIUM
Authors: CARVALHO J. C. , O'DEA C. P.
Published: May 2007

Observations of compact (GPS) and semi-compact (CSS) extragalactic radio sources indicate the existence of an alignment between radio and optical emission. In this work, we study the interaction between the expanding lobes of radio sources and the interstellar medium. We develop a simple analytical model to calculate the expansion speed of the radio lobes and calculate the optical luminosity of the compressed gas cloud. Qualitative maps of the optical and radio emission are produced for a variety of clouds and ambient gas density and jet power. The maps show the observed alignment and the trailing of the optical emission relative to the radio. It is proposed that a more detailed comparison between the model results and the observed data will allow the use of these calculations as a diagnostic of the diffuse and clump gas surrounding the nucleus of active galaxies.
GENERAL RELATIVISTIC EFFECTS OF STRONG MAGNETIC FIELDS ON THE GRAVITATIONAL FORCE: A DRIVING ENGINE FOR BURSTS OF GAMMA RAYS IN SGRS?
Authors: MALHEIRO MANUEL , RAY SUBHARTHI , CUESTA HERMAN J. MOSQUERA , DEY JISHNU
Published: May 2007

In General Relativity, all forms of energy contribute to gravity and not only just ordinary matter as in Newtonian Physics. This fact can be seen in the modified hydrostatic equilibrium equation for relativistic stars pervaded by magnetic (B) fields. It has an additional term coupled to the matter part as well as an anisotropic term which is purely of magnetic origin. That additional term coming from the pressure changed by the radial component of the diagonal electromagnetic field tensor weakens the gravitational force when B is strong enough and can even produce an unexpected change in the attractive nature of the force by reversing its sign. In an extreme case, this new general relativistic (GR) effect can even trigger an instability in the star as a consequence of the sudden reversal of the hydrostatic pressure gradient. We suggest here that this GR effect may be the possible central engine driving the transient giant outbursts observed in Soft Gamma-ray Repeaters (SGRs). In small regions of the neutron star (NS), strong magnetic condensation can take place. Beyond a critical limit, these highly magnetized bubbles may explode releasing the trapped energy as a burst of γ-rays of ~1036–40 erg.
CAPTURE CONDITIONS FOR STRANGELETS IN THE GEOMAGNETIC FIELD
Authors: PAULUCCI L. , HORVATH J. E. , MEDINA-TANCO G. A.
Published: May 2007

Strangelets coming from the interstellar medium are an interesting target in experiments searching for evidence of this hypothetic state of hadronic matter. For a stationary population of strangelets to be trapped by the geomagnetic field, these particles would have to fulfill certain conditions, namely having magnetic rigidities above the geomagnetic cutoff and below a certain threshold for adiabatic motion. For totally ionized strangelets these two conditions prevent them to be stably trapped if one considers that a similar mechanism resulting in the anomalous cosmic rays belt should also be responsible for strangelet trapping. The situation could be different if those particles could reach the earth with an effective charge less than total ionization, since it would lower the particle's magnetic rigidity, but cross sections are much too low to allow interstellar electronic recombination for strangelets in the low baryonic number range. If traces of strangelets are indeed measured as a component of the radiation belt, alternative methods for their capture have to be proposed.
A SIMPLIFIED TOP DOWN MODEL FOR COSMIC RAY PARTICLE PRODUCTION
Authors: AMORIM L. C. S. , GONÇALVES V. P. B. , BODMANN B. E. J. , SANTOS S. MITTMANN DOS
Published: May 2007

We investigate the implications of a minimal top down model on cosmic ray particle production from super heavy vector boson annihilation with subsequent pseudo-scalar boson decay. Super heavy particles are assumed to exist according to a homogeneous distribution. Besides the particle production via decay, the thermal momentum distribution of the initial state as well as expansion effects and cosmic temperature corrections are considered in the context of a Friedmann–Robertson–Walker universe.
THE SCHWARZSCHILD STATIC COSMOLOGICAL MODEL
Authors: PEREYRA P. H.
Published: May 2007

The present work describes an immersion in 5D of the interior Schwarzschild solution of the general relativity equations. The model-theory is defined in the context of a flat 5D space–time-matter Minkowski model, using a Tolman-like technique, which shows via Lorentz transformations that the solution is compatible with homogeneity and isotropy, thus obeying the cosmological principle. These properties permit one to consider the solution in terms of a cosmological model. In this model, the Universe may be treated as an idealized star with constant density and variable pressure, where each observer can be the "center" of the same. The observed redshift appears as a static gravitational effect which obeys the sufficiently verified and generally accepted square distance law. The Buchdahl stability theorem establishes a limit of distance observation with density dependence.
SPECTRAL STABILITY CONDITIONS FOR SHOCK WAVE PATTERNS
Authors: LEWICKA MARTA , ZUMBRUN KEVIN
Published: May 2007

We compare inviscid stability conditions obtained by Lewicka for large-amplitude shock wave patterns with "slow eigenvalue", or low-frequency, stability conditions obtained by Lin and Schecter through a vanishing viscosity analysis of the Dafermos regularization. Under the structural condition that scattering coefficients for each component wave are positive, we show that BV and L1 inviscid stability are equivalent to respective versions of low-frequency Dafermos-regularized stability. When scattering coefficients appear with different signs, the conditions are in general distinct. We give various examples demonstrating this phenomenon and indicating the subtle role of cancellation in linearized behavior in the presence of negative scattering coefficients.
3,5-Diiodothyronine in vivo maintains euthyroidal expression of type 2 iodothyronine deiodinase, growth hormone, and thyroid hormone receptor β1 in the killifish
Authors: García-G C. , López-Bojorquez L. , Nuñez J. , Valverde-R C. , Orozco A.
Published: May 2007

Until recently, 3,5-diiodothyronine (3,5-T2) has been considered an inactive by-product of triiodothyronine (T3) deiodination. However, studies from several laboratories have shown that 3,5-T2has specific, nongenomic effects on mitochondrial oxidative capacity and respiration rate that are distinct from those due to T3. Nevertheless, little is known about the putative genomic effects of 3,5-T2. We have previously shown that hyperthyroidism induced by supraphysiological doses of 3,5-T2inhibits hepatic iodothyronine deiodinase type 2 (D2) activity and lowers mRNA levels in the killifish in the same manner as T3and T4, suggesting a pretranslational effect of 3,5-T2(Garcia-G C, Jeziorski MC, Valverde-R C, Orozco A. Gen Comp Endocrinol 135: 201–209, 2004). The question remains as to whether 3,5-T2would have effects under conditions similar to those that are physiological for T3. To this end, intact killifish were rendered hypothyroid by administering methimazole. Groups of hypothyroid animals simultaneously received 30 nM of either T3, reverse T3, or 3,5-T2. Under these conditions, we expected that, if it were bioactive, 3,5-T2would mimic T3and thus reverse the compensatory upregulation of D2 and tyroid receptor β1 and downregulation of growth hormone that characterize hypothyroidism. Our results demonstrate that 3,5-T2is indeed bioactive, reversing both hepatic D2 and growth hormone responses during a hypothyroidal state. Furthermore, we observed that 3,5-T2and T3recruit two distinct populations of transcription factors to typical palindromic and DR4 thyroid hormone response elements. Taken together, these results add further evidence to support the notion that 3,5-T2is a bioactive iodothyronine.
Behavioral, metabolic, and molecular stress responses of marine bivalve Mytilus galloprovincialis during long-term acclimation at increasing ambient temperature
Authors: Anestis Andreas , Lazou Antigone , Pörtner Hans O. , Michaelidis Basile
Published: May 2007

The present study aimed to determine the thermal response of the Mediterranean mussel Mytilus galloprovincialis by integrating information from various levels of biological organization including behavior, metabolic adjustments, heat shock protein expression, and protein kinase activity. Behavioral responses were determined by examining the effect of warming on valve closure and opening. Metabolic impacts were assessed by examining the activity of the key glycolytic enzyme pyruvate kinase (PK). Molecular responses were addressed through the expression of Hsp70 and Hsp90 and the phosphorylation of stress-activated protein kinases, p38 mitogen-activated protein kinase (p38 MAPK) and cJun-N-terminal kinases (JNKs). Mussels increased the duration of valve closure by about sixfold when acclimated to 24°C rather than to 17°C. As indicated by the activity of PK, such behavior caused metabolic depression and probably a shift from aerobic to anaerobic metabolism. Acclimation to temperatures higher than 24°C caused an increase in mortality and induced the expression of Hsp72. Increased phosphorylation of p38 MAPK and JNKs indicated activation of MAPK signaling cascades. The potential involvement of MAPKs in the induction of Hsp genes in the tissues of M. galloprovincialis is discussed. In conclusion, it seems that M. galloprovincialis lives close to its acclimation limits and incipient lethal temperature and that a small degree of warming will elicit stress responses at whole organism and molecular levels.
Effect of cigarette smoke on placental antioxidant enzyme expression
Authors: Sidle Elizabeth H. , Casselman Richard , Smith Graeme N.
Published: May 2007

Cigarette smoking is associated with systemic oxidative stress leading to an upregulation of antioxidant systems [superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), and heme oxygenase (HO)] in some tissues, but the response in the human placenta is unknown. The aim of this study was to determine the effect of cigarette smoke exposure on placental antioxidant expression in vivo, as well as the effect on antioxidant expression in the human trophoblast choriocarcinoma (HTR)-8SVNeo cell line. In the in vivo experiment, normal-term placentas were obtained following elective caesarean section. The chorionic villi (CV), anchoring villi (AV), and basal plate (BP) were dissected, and Western blot analysis was carried out for HO-1, HO-2, SOD, CAT, and GPx. In vitro experiment, a cigarette smoke extract (CSE) was prepared by bubbling the smoke form three cigarettes through 15 ml of RPMI. This 100% CSE was syringe filtered and diluted to 0.1, 0.5, 1, 2, 5, and 10% concentrations. HTR-8SVNeo cells were cultured with the CSE for 48 h. The cells were harvested, protein was extracted, and run on SDS-PAGE gels, and Western blot analysis was carried out for HO-1, HO-2, SOD, and CAT. Immunofluorescence for HTR-8SVNeo cells HO-1 was carried out following increasing concentrations of CSE. In the in vivo experiment, HO-1 and HO-2 expression was increased in the BP of placentas from smokers compared with nonsmokers. CAT, GPx, and SOD levels in all placental regions, as well as HO-1 and HO-2 expression in the AV and CV were unchanged. In the in vitro experiment, The 5%, 10%, and 20% dilutions were toxic to the cells. The 0.1% CSE solution did not significantly alter HO-1 expression. Treatment with the 0.5%, 1% and 2% CSE solutions resulted in a dose-dependent increase in HO-1 expression. None of the CSE treatments resulted in a significant alteration in HO-2, SOD, GPx, or CAT expression. HO-1 immunoflourescence confirmed the HO-1 expression studies. Cigarette smoke exposure increases HO-1 and HO-2 expression in the placental basal plate and increases HO-1 expression in the HTR-8SVNeo cell line. Increased HO-1 and HO-2 protein expression may increase the production of the antioxidants biliverdin and bilirubin, which are products of heme metabolism. This could function to reduce the oxidative load that is released into the maternal plasma from the preeclamptic placenta and may contribute to the observed decreased incidence of preeclampsia in smokers.
Metabolic inhibition-induced transient Ca2+increase depends on mitochondria in a human proximal renal cell line
Authors: Caplanusi Adrian , Fuller Andrew J. , Gonzalez-Villalobos Romer A. , Hammond Timothy G. , Navar L. G.
Published: May 2007

During ischemia or hypoxia an increase in intracellular cytosolic Ca2+induces deleterious events but is also implicated in signaling processes triggered in such conditions. In MDCK cells (distal tubular origin), it was shown that mitochondria confer protection during metabolic inhibition (MI), by buffering the Ca2+overload via mitochondrial Na+-Ca2+exchanger (NCX). To further assess this process in cells of human origin, human cortical renal epithelial cells (proximal tubular origin) were subjected to MI and changes in cytosolic Ca2+([Ca2+]i), Na+, and ATP concentrations were monitored. MI was accomplished with both antimycin A and 2-deoxyglucose and induced a 3.5-fold increase in [Ca2+]i, reaching 136.5 ± 15.8 nM in the first 3.45 min. Subsequently [Ca2+]idropped and stabilized to 62.7 ± 7.3 nM by 30 min. The first phase of the transient increase was La3+sensitive, not influenced by diltiazem, and abolished when mitochondria were deenergized with the protonophore carbonylcyanide p-trifluoromethoxyphenylhydrazone. The subsequent recovery phase was impaired in a Na+-free medium and weakened when the mitochondrial NCX was blocked with 7-chloro-5-(2-chlorophenyl)-1,5-dihydro-4,1-benzothiazepin-2(3H)-one (CGP-37157). Thus Ca2+entry is likely mediated by store-operated Ca2+channels and depends on energized mitochondria, whereas [Ca2+]irecovery relied partially on the activity of mitochondrial NCX. These results indicate a possible mitochondrial-mediated signaling process triggered by MI, support the hypothesis that mitochondrial NCX has an important role in the Ca2+clearance, and overall suggest that mitochondria play a preponderant role in the regulation of responses to MI in human renal epithelial cells.
The alternative pathway of complement is activated in the glomeruli and tubulointerstitium of mice with adriamycin nephropathy
Authors: Lenderink Amanda M. , Liegel Katharine , Ljubanović Danica , Coleman Kathrin E. , Gilkeson Gary S. , Holers V. Michael , Thurman Joshua M.
Published: May 2007

The complement system effectively identifies and clears invasive pathogens as well as injured host cells. Uncontrolled complement activation can also contribute to tissue injury, however, and inhibition of this system may ameliorate many types of inflammatory injury. Several studies have demonstrated that the filtration of complement proteins into the renal tubules, as occurs during proteinuric renal disease, causes tubular inflammation and injury. In the present study, we tested the hypothesis that activation of the complement system in the urinary space requires an intact alternative pathway. Using a model of adriamycin-induced renal injury, which induces injury resembling focal segmental glomerulosclerosis, we examined whether mice deficient in factor B would be protected from the development of progressive tubulointerstitial injury. Complement activation was attenuated in the glomeruli and tubulointerstitium of mice with congenital deficiency of factor B ( fB−/−) compared with wild-type controls, demonstrating that complement activation does occur through the alternative pathway. Deficiency in factor B did not significantly protect the mice from tubulointerstitial injury. However, treatment of wild-type mice with an inhibitory monoclonal antibody to factor B did delay the development of renal failure. These results demonstrate that complement activation in this nonimmune complex-mediated model of progressive renal disease requires an intact alternative pathway.
Rapid and Precise Retinotopic Mapping of the Visual Cortex Obtained by Voltage-Sensitive Dye Imaging in the Behaving Monkey
Authors: Yang Zhiyong , Heeger David J. , Seidemann Eyal
Published: May 2007

Retinotopy is a fundamental organizing principle of the visual cortex. Over the years, a variety of techniques have been used to examine it. None of these techniques, however, provides a way to rapidly characterize retinotopy, at the submillimeter range, in alert, behaving subjects. Voltage-sensitive dye imaging (VSDI) can be used to monitor neuronal population activity at high spatial and temporal resolutions. Here we present a VSDI protocol for rapid and precise retinotopic mapping in the behaving monkey. Two monkeys performed a fixation task while thin visual stimuli swept periodically at a high speed in one of two possible directions through a small region of visual space. Because visual space is represented systematically across the cortical surface, each moving stimulus produced a traveling wave of activity in the cortex that could be precisely measured with VSDI. The time at which the peak of the traveling wave reached each location in the cortex linked this location with its retinotopic representation. We obtained detailed retinotopic maps from a region of about 1 cm2 over the dorsal portion of areas V1 and V2. Retinotopy obtained during <4 min of imaging had a spatial precision of 0.11–0.19 mm, was consistent across experiments, and reliably predicted the locations of the response to small localized stimuli. The ability to rapidly obtain precise retinotopic maps in behaving monkeys opens the door for detailed analysis of the relationship between spatiotemporal dynamics of population responses in the visual cortex and perceptually guided behavior.
Influence of Viscous Loads on Motor Planning
Authors: Thoroughman Kurt A. , Wang Wei , Tomov Dimitre N.
Published: May 2007

Here we computationally investigate how encumbering the hand could alter predictions made by the minimum torque change (MTC) and minimum endpoint variance hypotheses (MEPV) of movement planning. After minutes of training, people have made arm trajectories in a robot-generated viscous force field that were similar to previous baseline trajectories without the force field. We simulate the human arm interacting with this viscous load. We found that the viscous forces clearly differentiated MTC and MEPV predictions from both minimum-jerk predictions and from human behavior. We conclude that learned behavior in the viscous environment could arise from minimizing kinematic costs but could not arise from a minimization of either torque change or endpoint variance.
Loss of Betaglycan Expression in Ovarian Cancer: Role in Motility and Invasion
Authors: Hempel Nadine , How Tam , Dong Mei , Murphy Susan K. , Fields Timothy A. , Blobe Gerard C.
Published: May 2007

The transforming growth factor-β (TGF-β) superfamily members, TGF-β, activin, and inhibin, all have prominent roles in regulating normal ovarian function. Betaglycan, or the type III TGF-β receptor, is a coreceptor that regulates TGF-β, activin, and inhibin signaling. Here, we show that betaglycan expression is frequently decreased or lost in epithelial derived ovarian cancer at both the mRNA and protein level, with the degree of loss correlating with tumor grade. Treatment of ovarian cancer cell lines with the methyltransferase inhibitor 5-aza-2-deoxycytidine and the histone deacetylase inhibitor trichostatin A resulted in significant synergistic induction of betaglycan message levels and increased betaglycan protein expression, indicating that epigenetic silencing may play a role in the loss of betaglycan expression observed in ovarian cancer. Although restoring betaglycan expression in Ovca429 ovarian cancer cells is not sufficient to restore TGF-β–mediated inhibition of proliferation, betaglycan significantly inhibits ovarian cancer cell motility and invasiveness. Furthermore, betaglycan specifically enhances the antimigratory effects of inhibin and the ability of inhibin to repress matrix metalloproteinase levels in these cells. These results show, for the first time, epigenetic regulation of betaglycan expression in ovarian cancer, and a novel role for betaglycan in regulating ovarian cancer motility and invasiveness. [Cancer Res 2007;67(11):5231–8]
Aging Effects on the Activation of the Auditory Cortex during Binaural Speech Listening in White Noise: An fMRI Study
Authors: Hwang Juen-Haur , Li Chia-Wei , Wu Chang-Wei , Chen Jyh-Horng , Liu Tien-Chen
Published: May 2007

The functional significance of age-related pathology of the auditory cortex is not well established. The purpose of this study was to elucidate the activation pattern of the auditory cortex in aged subjects in response to speech signals. Functional magnetic resonance imaging was performed on 12 elderly subjects with normal hearing acuity during selective listening with both ears to speech sounds in quiet and in white noise. Twelve young, normal-hearing subjects served as controls. Our results showed that activation of the auditory cortex during selective listening to speech decreased in elderly subjects compared to young subjects, especially in noise. Reduced activation occurred in the anterior and posterior regions of the bilateral superior temporal gyrus (STG), but mainly in the posterior part of the left STG. In addition, background noise had a greater masking effect on speech perception in the elderly subjects than in the young ones. These findings suggest that early functional changes associated with central presbycusis occur mainly in the posterior part of the left STG.
Predictors of Cessation of Regular Leisure-Time Physical Activity in Community-Dwelling Elderly People
Authors: Shimada Hiroyuki , Lord Stephen R. , Yoshida Hideyo , Kim Hunkyung , Suzuki Takao
Published: May 2007

Background: Maintaining regular physical activity is important for physical and mental health, providing benefits including protection against chronic disease. However, little is known about the causes of cessation of habitual physical activity in olderpeople. Objectives: To identify predictors of cessation of regular physical activity in community-dwelling elderly people. Methods: 582 community-dwelling people aged 70 years and over who were living in Tokyo, Japan, were surveyed regarding physical activity levels 2 years after completing an initial survey where they indicated they took part in physical activity at least 5 days a week. Baseline demographic, health, physical functioning and psychological status measures were used as predictors of exercise cessation. Results: At the 2-year follow-up, 192 subjects (33%) had ceased taking part in regular physical activity. In univariate analyses, women, smokers, those who reported a fear of falling and those with a slower walking speed at baseline were significantly more likely to cease regular physical activity. Multiple logistic regression analysis identified 3 of these variables as significant and independent predictors of activity cessation: female gender (adjusted OR = 1.67, 95% CI = 1.13–2.47); smoking (OR = 2.34, 95% CI = 1.33–4.13), and slow walking speed (OR = 1.79, 95% CI = 1.07–2.98). Conclusions: The study identified simple screening measures for identifying elderly people at risk of ceasing regular physical activity. Currently active older people with these factors may benefit from counseling and interventions to enable them to continue participating in regular physical activity.
Single Parenthood and Childhood Outcomes in the Mid-Nineteenth-Century Urban South
Authors: Bodenhorn Howard
Published: May 2007

Data from the urban South reveal two notable consequences of single parenthood during the mid-nineteenth century. First, white children residing with single mothers left school earlier than children residing with two parents, and black children in single mother homes started school later and left school earlier. Second, white youths in single-mother homes faced an increased incidence of labor-force participation, but black youths in the same situation did not. Single parenthood imposed costs, in terms of foregone human-capital formation, on children in the mid-nineteenth century, but the consequences of single motherhood were mitigated by social norms regarding childhood education.
Estimating Information Rates with Confidence Intervals in Neural Spike Trains
Authors: Shlens Jonathon , Kennel Matthew B. , Abarbanel Henry D. I. , Chichilnisky E. J.
Published: May 2007

Information theory provides a natural set of statistics to quantify the amount of knowledge a neuron conveys about a stimulus. A related work (Kennel, Shlens, Abarbanel, & Chichilnisky, 2005) demonstrated how to reliably estimate, with a Bayesian confidence interval, the entropy rate from a discrete, observed time series. We extend this method to measure the rate of novel information that a neural spike train encodes about a stimulus—the average and specific mutual information rates. Our estimator makes few assumptions about the underlying neural dynamics, shows excellent performance in experimentally relevant regimes, and uniquely provides confidence intervals bounding the range of information rates compatible with the observed spike train. We validate this estimator with simulations of spike trains and highlight how stimulus parameters affect its convergence in bias and variance. Finally, we apply these ideas to a recording from a guinea pig retinal ganglion cell and compare results to a simple linear decoder.
Input-Driven Oscillations in Networks with Excitatory and Inhibitory Neurons with Dynamic Synapses
Authors: Marinazzo Daniele , Kappen Hilbert J. , Gielen Stan C. A. M.
Published: May 2007

Previous work has shown that networks of neurons with two coupled layers of excitatory and inhibitory neurons can reveal oscillatory activity. For example, Börgers and Kopell (2003) have shown that oscillations occur when the excitatory neurons receive a sufficiently large input. A constant drive to the excitatory neurons is sufficient for oscillatory activity. Other studies (Doiron, Chacron, Maler, Longtin, & Bastian, 2003; Doiron, Lindner, Longtin, Maler, & Bastian, 2004) have shown that networks of neurons with two coupled layers of excitatory and inhibitory neurons reveal oscillatory activity only if the excitatory neurons receive correlated input, regardless of the amount of excitatory input. In this study, we show that these apparently contradictory results can be explained by the behavior of a single model operating in different regimes of parameter space. Moreover, we show that adding dynamic synapses in the inhibitory feedback loop provides a robust network behavior over a broad range of stimulus intensities, contrary to that of previous models. A remarkable property of the introduction of dynamic synapses is that the activity of the network reveals synchronized oscillatory components in the case of correlated input, but also reflects the temporal behavior of the input signal to the excitatory neurons. This allows the network to encode both the temporal characteristics of the input and the presence of spatial correlations in the input simultaneously.
Selectivity and Stability via Dendritic Nonlinearity
Authors: Morita Kenji , Okada Masato , Aihara Kazuyuki
Published: May 2007

Inspired by recent studies regarding dendritic computation, we constructed a recurrent neural network model incorporating dendritic lateral inhibition. Our model consists of an input layer and a neuron layer that includes excitatory cells and an inhibitory cell; this inhibitory cell is activated by the pooled activities of all the excitatory cells, and it in turn inhibits each dendritic branch of the excitatory cells that receive excitations from the input layer. Dendritic nonlinear operation consisting of branch-specifically rectified inhibition and saturation is described by imposing nonlinear transfer functions before summation over the branches. In this model with sufficiently strong recurrent excitation, on transiently presenting a stimulus that has a high correlation with feed- forward connections of one of the excitatory cells, the corresponding cell becomes highly active, and the activity is sustained after the stimulus is turned off, whereas all the other excitatory cells continue to have low activities. But on transiently presenting a stimulus that does not have high correlations with feedforward connections of any of the excitatory cells, all the excitatory cells continue to have low activities. Interestingly, such stimulus-selective sustained response is preserved for a wide range of stimulus intensity. We derive an analytical formulation of the model in the limit where individual excitatory cells have an infinite number of dendritic branches and prove the existence of an equilibrium point corresponding to such a balanced low-level activity state as observed in the simulations, whose stability depends solely on the signal-to-noise ratio of the stimulus. We propose this model as a model of stimulus selectivity equipped with self-sustainability and intensity-invariance simultaneously, which was difficult in the conventional competitive neural networks with a similar degree of complexity in their network architecture. We discuss the biological relevance of the model in a general framework of computational neuroscience.
Imposing Biological Constraints onto an Abstract Neocortical Attractor Network Model
Authors: Johansson Christopher , Lansner Anders
Published: May 2007

In this letter, we study an abstract model of neocortex based on its modularization into mini- and hypercolumns. We discuss a full-scale instance of this model and connect its network properties to the underlying biological properties of neurons in cortex. In particular, we discuss how the biological constraints put on the network determine the network's performance in terms of storage capacity. We show that a network instantiating the model scales well given the biologically constrained parameters on activity and connectivity, which makes this network interesting also as an engineered system. In this model, the minicolumns are grouped into hypercolumns that can be active or quiescent, and the model predicts that only a few percent of the hypercolumns should be active at any one time. With this model, we show that at least 20 to 30 pyramidal neurons should be aggregated into a minicolumn and at least 50 to 60 minicolumns should be grouped into a hypercolumn in order to achieve high storage capacity.
Feature Selection via Coalitional Game Theory
Authors: Cohen Shay , Dror Gideon , Ruppin Eytan
Published: May 2007

We present and study the contribution-selection algorithm (CSA), a novel algorithm for feature selection. The algorithm is based on the multiperturbation shapley analysis (MSA), a framework that relies on game theory to estimate usefulness. The algorithm iteratively estimates the usefulness of features and selects them accordingly, using either forward selection or backward elimination. It can optimize various performance measures over unseen data such as accuracy, balanced error rate, and area under receiver-operator-characteristic curve. Empirical comparison with several other existing feature selection methods shows that the backward elimination variant of CSA leads to the most accurate classification results on an array of data sets.
Outliers Detection in Multivariate Time Series by Independent Component Analysis
Authors: Baragona Roberto , Battaglia Francesco
Published: May 2007

In multivariate time series, outlying data may be often observed that do not fit the common pattern. Occurrences of outliers are unpredictable events that may severely distort the analysis of the multivariate time series. For instance, model building, seasonality assessment, and forecasting may be seriously affected by undetected outliers. The structure dependence of the multivariate time series gives rise to the well-known smearing and masking phenomena that prevent using most outliers' identification techniques. It may be noticed, however, that a convenient way for representing multiple outliers consists of superimposing a deterministic disturbance to a gaussian multivariate time series. Then outliers may be modeled as nongaussian time series components. Independent component analysis is a recently developed tool that is likely to be able to extract possible outlier patterns. In practice, independent component analysis may be used to analyze multivariate observable time series and separate regular and outlying unobservable components. In the factor models framework too, it is shown that independent component analysis is a useful tool for detection of outliers in multivariate time series. Some algorithms that perform independent component analysis are compared. It has been found that all algorithms are effective in detecting various types of outliers, such as patches, level shifts, and isolated outliers, even at the beginning or the end of the stretch of observations. Also, there is no appreciable difference in the ability of different algorithms to display the outlying observations pattern.
Accurate Monitoring of Terrestrial Aerosols and Total Solar Irradiance: Introducing the Glory Mission
Authors: Mishchenko Michael I. , Cairns Brian , Kopp Greg , Schueler Carl F. , Fafaul Bryan A. , Hansen James E. , Hooker Ronald J. , Itchkawich Tom , Maring Hal B. , Travis Larry D.
Published: May 2007

The NASA Glory mission is intended to facilitate and improve upon long-term monitoring of two key forcings influencing global climate. One of the mission's principal objectives is to determine the global distribution of detailed aerosol and cloud properties with unprecedented accuracy, thereby facilitating the quantification of the aerosol direct and indirect radiative forcings. The other is to continue the 28-yr record of satellite-based measurements of total solar irradiance from which the effect of solar variability on the Earth's climate is quantified. These objectives will be met by flying two state-of-the-art science instruments on an Earth-orbiting platform. Based on a proven technique demonstrated with an aircraft-based prototype, the Aerosol Polarimetry Sensor (APS) will collect accurate multiangle photopolarimetric measurements of the Earth along the satellite ground track within a wide spectral range extending from the visible to the shortwave infrared. The Total Irradiance Monitor (TIM) is an improved version of an instrument currently flying on the Solar Radiation and Climate Experiment (SORCE) and will provide accurate and precise measurements of spectrally integrated sunlight illuminating the Earth. Because Glory is expected to fly as part of the A-Train constellation of Earth-orbiting spacecraft, the APS data will also be used to improve retrievals of aerosol climate forcing parameters and global aerosol assessments with other A-Train instruments. In this paper, we detail the scientific rationale and objectives of the Glory mission, explain how these scientific objectives dictate the specific measurement strategy, describe how the measurement strategy will be implemented by the APS and TIM, and briefly outline the overall structure of the mission. It is expected that the Glory results will be used extensively by members of the climate, solar, atmospheric, oceanic, and environmental research communities as well as in education and outreach activities.