bluuebunny/crossref_metadata_2025 huggingface dataset:
Toroidal Triblock Copolymer Assemblies
Authors: Pochan Darrin J. , Chen Zhiyun , Cui Honggang , Hales Kelly , Qi Kai , Wooley Karen L.
Published: September 2004

A stable phase of toroidal, or ringlike, supramolecular assemblies was formed by combining dilute solution characteristics critical for both bundling of like-charged biopolymers and block copolymer micelle formation. The key to toroid versus classic cylinder micelle formation is the interaction of the negatively charged hydrophilic block of an amphiphilic triblock copolymer with a positively charged divalent organic counterion. This produces a self-attraction of cylindrical micelles that leads to toroid formation, a mechanism akin to the toroidal bundling of semiflexible charged biopolymers such as DNA. The toroids can be kinetically trapped or chemically cross-linked. Insight into the mechanism of toroid formation can be gained by observation of intermediate structures kinetically trapped during film casting.
Multicompartment Micelles from ABC Miktoarm Stars in Water
Authors: Li Zhibo , Kesselman Ellina , Talmon Yeshayahu , Hillmyer Marc A. , Lodge Timothy P.
Published: September 2004

By combining three mutually immiscible polymeric components in a mixed-arm star block terpolymer architecture, we have observed the formation of a previously unknown class of multicompartment micelles in dilute aqueous solution. Connection of water-soluble poly(ethylene oxide) and two hydrophobic but immiscible components (a polymeric hydrocarbon and a perfluorinated polyether) at a common junction leads to molecular frustration when dispersed in aqueous solution. The incompatible hydrophobic blocks form cores that are protected from the water by the poly(ethylene oxide) blocks, but both are forced to make contact with the poly(ethylene oxide) by virtue of the chain architecture. The structures that emerge depend on the relative lengths of the blocks and can be tuned from discrete multicompartment micelles to extended wormlike structures with segmented cores.
Riboflavin Production in
Lactococcus lactis
: Potential for In Situ Production of Vitamin-Enriched Foods
Authors: Burgess Catherine , O'Connell-Motherway Mary , Sybesma Wilbert , Hugenholtz Jeroen , van Sinderen Douwe
Published: October 2004

This study describes the genetic analysis of the riboflavin (vitamin B
2
) biosynthetic (
rib
) operon in the lactic acid bacterium
Lactococcus lactis
subsp.
cremoris
strain NZ9000. Functional analysis of the genes of the
L. lactis rib
operon was performed by using complementation studies, as well as by deletion analysis. In addition, gene-specific genetic engineering was used to examine which genes of the
rib
operon need to be overexpressed in order to effect riboflavin overproduction. Transcriptional regulation of the
L. lactis
riboflavin biosynthetic process was investigated by using Northern hybridization and primer extension, as well as the analysis of roseoflavin-induced riboflavin-overproducing
L. lactis
isolates. The latter analysis revealed the presence of both nucleotide replacements and deletions in the regulatory region of the
rib
operon. The results presented here are an important step toward the development of fermented foods containing increased levels of riboflavin, produced in situ, thus negating the need for vitamin fortification.
Bacterial Community Structure and Diversity in a Century-Old Manure-Treated Agroecosystem
Authors: Sun H. Y. , Deng S. P. , Raun W. R.
Published: October 2004

Changes in soil microbial community structure and diversity may reflect environmental impact. We examined 16S rRNA gene fingerprints of bacterial communities in six agroecosystems by PCR amplification and denaturing gradient gel electrophoresis (PCR-DGGE) separation. These soils were treated with manure for over a century or different fertilizers for over 70 years. Bacterial community structure and diversity were affected by soil management practices, as evidenced by changes in the PCR-DGGE banding patterns. Bacterial community structure in the manure-treated soil was more closely related to the structure in the untreated soil than that in soils treated with inorganic fertilizers. Lime treatment had little effect on bacterial community structure. Soils treated with P and N-P had bacterial community structures more closely related to each other than to those of soils given other treatments. Among the soils tested, a significantly higher number of bacterial ribotypes and a more even distribution of the bacterial community existed in the manure-treated soil. Of the 99 clones obtained from the soil treated with manure for over a century, two (both
Pseudomonas
spp.) exhibited 100% similarity to sequences in the GenBank database. Two of the clones were possible chimeras. Based on similarity matching, the remaining 97 clones formed six major clusters. Fifty-six out of 97 were assigned taxonomic units which grouped into five major taxa: α-, β-, and γ-
Proteobacteria
(36 clones),
Acidobacteria
(16 clones),
Bacteroidetes
(2 clones),
Nitrospirae
(1 clone), and
Firmicutes
(1 clone). Forty-one clones remained unclassified. Results from this study suggested that bacterial community structure was closely related to agroecosystem management practices conducted for over 70 years.
Composition and Diversity of Microbial Communities Recovered from Surrogate Minerals Incubated in an Acidic Uranium-Contaminated Aquifer
Authors: Reardon Catherine L. , Cummings David E. , Petzke Lynn M. , Kinsall Barry L. , Watson David B. , Peyton Brent M. , Geesey Gill G.
Published: October 2004

Our understanding of subsurface microbiology is hindered by the inaccessibility of this environment, particularly when the hydrogeologic medium is contaminated with toxic substances. In this study, surrogate geological media contained in a porous receptacle were incubated in a well within the saturated zone of a pristine region of an aquifer to capture populations from the extant communities. After an 8-week incubation, the media were recovered, and the microbial community that developed on each medium was compared to the community recovered from groundwater and native sediments from the same region of the aquifer, using 16S DNA coding for rRNA (rDNA)-based terminal restriction fragment length polymorphism (T-RFLP). The groundwater and sediment communities were highly distinct from one another, and the communities that developed on the various media were more similar to groundwater communities than to sediment communities. 16S rDNA clone libraries of communities that developed on particles of a specular hematite medium incubated in the same well as the media used for T-RFLP analysis were compared with those obtained from an acidic, uranium-contaminated region of the same aquifer. The hematite-associated community formed in the pristine area was highly diverse at the species level, with 25 distinct phylotypes identified, the majority of which (73%) were affiliated with the β-
Proteobacteria
. Similarly, the hematite-associated community formed in the contaminated area was populated in large part by β-
Proteobacteria
(62%); however, only 13 distinct phylotypes were apparent. The three numerically dominant clones from the hematite-associated community from the contaminated site were affiliated with metal- and radionuclide-tolerant or acidophilic taxa, consistent with the environmental conditions. Only two populations were common to both sites.
Comparison of Different Primer Sets for Use in Automated Ribosomal Intergenic Spacer Analysis of Complex Bacterial Communities
Authors: Cardinale Massimiliano , Brusetti Lorenzo , Quatrini Paola , Borin Sara , Puglia Anna Maria , Rizzi Aurora , Zanardini Elisabetta , Sorlini Claudia , Corselli Cesare , Daffonchio Daniele
Published: October 2004

ITSF and ITSReub, constituting a new primer set designed for the amplification of the 16S-23S rRNA intergenic transcribed spacers, have been compared with primer sets consisting of 1406F and 23Sr (M. M. Fisher and E. W. Triplett, Appl. Environ. Microbiol. 65:4630-4636, 1999) and S-D-Bact-1522-b-S-20 and L-D-Bact-132-a-A-18 (L. Ranjard et al., Appl. Environ. Microbiol. 67:4479-4487, 2001), previously proposed for automated ribosomal intergenic spacer analysis (ARISA) of complex bacterial communities. An agricultural soil and a polluted soil, maize silage, goat milk, a small marble sample from the façade of the Certosa of Pavia (Pavia, Italy), and brine from a deep hypersaline anoxic basin in the Mediterranean Sea were analyzed with the three primer sets. The number of peaks in the ARISA profiles, the range of peak size (width of the profile), and the reproducibility of results were used as indices to evaluate the efficiency of the three primer sets. The overall data showed that ITSF and ITSReub generated the most informative (in term of peak number) and reproducible profiles and yielded a wider range of spacer sizes (134 to 1,387) than the other primer sets, which were limited in detecting long fragments. The minimum amount of DNA template and sensitivity in detection of minor DNA populations were evaluated with artificial mixtures of defined bacterial species. ITSF and ITSReub amplified all the bacteria at DNA template concentrations from 280 to 0.14 ng μl
−1
, while the other primer sets failed to detect the spacers of one or more bacterial strains. Although the primer set consisting of ITSF and ITSReub and that of S-D-Bact-1522-b-S-20 and L-D-Bact-132-a-A-18 showed similar sensitivities for the DNA of
Allorhizobium undicula
mixed with the DNA of other species, the S-D-Bact-1522-b-S-20 and L-D-Bact-132-a-A-18 primer set failed to detect the DNA of
Pseudomonas stutzeri
.
Movements of lingcod (Ophiodon elongatus) in southeast Alaska: potential for increased conservation and yield from marine reserves
Authors: Starr Richard M , O'Connell Victoria , Ralston Stephen
Published: October 2004

Residence time and movement rates of lingcod (Ophiodon elongatus) were recorded in an area closed to fishing in southeast Alaska to evaluate the potential effects of reserves on mortality, egg production, and fishery yield. In 1999, 43 lingcod were tagged with sonic transmitters, and an array of receivers moored in the reserve recorded signals transmitted from tagged fish for 14 months. Most of the tagged fish frequently left the reserve but were only absent for short time periods. Tagged fish showed a high degree of site fidelity. Models generated from the tag data provided a way to predict the effects of marine reserves on yield and eggs per recruit for a cohort of female lingcod. Model results indicated that for lingcod stocks with low abundance, marine reserves could improve egg production while having a small effect on fishery yield. For more abundant stocks, if a portion of the stock is protected in reserves, fishing rates could be increased outside reserves without reducing egg production relative to egg production levels in the absence of reserves.
Molecular and morphological variation within swim bladder nematodes, Cystidicola spp.
Authors: Miscampbell Allyson E , Lankester Murray W , Adamson Martin L
Published: October 2004

We sequenced four rDNA regions (ITS-1, ITS-2, 5.8S, and D3 region of 28S) from the parasitic nematode Cystidicola spp. from seven species of fish host and 11 locations in Canada and Finland to elucidate suspected unresolved genetic variation within the genus. A holarctic species, Cystidicola farionis from the swim bladder of Salmonidae and Osmeridae, and a nearctic species, Cystidicola stigmatura from trout and char (Salvelinus spp.), differ in life history, host and geographic range, reproductive strategy, and adult and egg morphology. These nematodes were identical at three rDNA regions (ITS-1, 5.8S, and D3); however, two ITS-2 variants were found that differed at four nucleotide positions: variant I (366 bp) was found in British Columbia populations of C. farionis and in C. stigmatura and variant II (369 bp) was found in Ontario and Finnish populations of C. farionis. These results demonstrate that two species with distinct morphology and biology can have identical rDNA sequences, while two morphologically identical isolates have different ITS-2 sequences. Thus, rDNA spacer regions may not be useful for distinguishing biologically valid species or subspecies in some nematode groups. Although phenotypic variation suggested a third undescribed species of Cystidicola from lake whitefish (Coregonus clupeaformis), rDNA analysis did not provide meaningful evidence of its uniqueness.
MIRROR WORLD AND ITS COSMOLOGICAL CONSEQUENCES
Authors: BEREZHIANI ZURAB
Published: September 2004

We briefly review the concept of a parallel 'mirror' world which has the same particle physics as the observable world and couples to the latter by gravity and perhaps other very weak forces. The nucleosynthesis bounds demand that the mirror world should have a smaller temperature than the ordinary one. By this reason its evolution should substantially deviate from the standard cosmology as far as the crucial epochs like baryogenesis, nucleosynthesis etc. are concerned. In particular, we show that in the context of certain baryogenesis scenarios, the baryon asymmetry in the mirror world should be larger than in the observable one. Moreover, we show that mirror baryons could naturally constitute the dominant dark matter component of the Universe, and discuss its cosmological implications.
EXPERIMENTAL IMPLICATIONS OF MIRROR MATTER-TYPE DARK MATTER
Authors: FOOT ROBERT
Published: September 2004

Mirror matter-type dark matter is one dark matter candidate which is particularly well motivated from high energy physics. The theoretical motivation and experimental evidence are pedagogically reviewed, with emphasis on the implications of recent orthopositronium experiments, the DAMA/NaI dark matter search, anomalous meteorite events etc.
NEW PHYSICS AND INVISIBLE DECAY OF ORTHOPOSITRONIUM
Authors: CRIVELLI PAOLO
Published: September 2004

We propose an experiment to search for invisible decays of orthopositronium (o-Ps) with the 90% confidence sensitivity in the branching ratio as low as 10-8. Evidence for this decay mode would unambiguosly signal new physics: either the existence of extra–dimensions or fractionally charged particles or new light gauge bosons. The experimental approach and the detector components of the proposed experiment are described.
EXPERIMENTAL TESTS OF FUNDAMENTAL SYMMETRIES IN POSITRONIUM ANNIHILATION
Authors: VETTER PAUL A.
Published: September 2004

Using the Gammasphere array of high-purity germanium detectors at the 88" Cyclotron at Lawrence Berkeley National Laboratory, we have made several measurements to test discrete fundamental symmetries in positronium annihilation. We tested charge conjugation symmetry (C) by searching for decays of ortho- and para-positronium to the "wrong" number of photons. We measured the five-photon annihilation mode of ortho-positronium, finding agreement with tree-level QED calculations at order α8. In a second experiment, we searched for decays of polarized ortho-positronium which violate the combined symmetry operation CPT. We improved existing limits on this CPT test by roughly a factor of ten. We are studying the feasibility of an experiment to search for "invisible" decays of ortho-positronium. Invisible decays could be caused by extra dimensions (invoked in string theories). General requirements for an experiment sensitive to decay branching ratios of order 10-9 are discussed.
PRECISION STUDY OF POSITRONIUM: TESTING BOUND STATE QED THEORY
Authors: KARSHENBOIM SAVELY G.
Published: September 2004

As an unstable light pure leptonic system, positronium is a very specific probe atom to test bound state QED. In contrast to ordinary QED for free leptons, the bound state QED theory is not so well understood and bound state approaches deserve highly accurate tests. We present a brief overview of precision studies of positronium paying special attention to uncertainties of theory as well as comparison of theory and experiment. We also consider in detail advantages and disadvantages of positronium tests compared to other QED experiments.
HIGH ORDER QED CORRECTIONS IN POSITRONIUM PHYSICS
Authors: PENIN ALEXANDER A.
Published: September 2004

High-order perturbative corrections to positronium decays and hyperfine splitting are briefly reviewed. Theoretical predictions are compared to the most recent experimental data. Perspectives of future calculations are discussed.
DESIGN OF A HIGH-EFFICIENCY PULSED POSITRON BEAM FOR EXPERIMENTS WITH ORTHOPOSITRONIUM IN VACUUM
Authors: GNINENKO S. N.
Published: September 2004

A new design of a high-efficiency pulsed slow positron beam for experiments with orthopositronium in vacuum is described. The new method is based on a RF waveform pulse applied to a double gap buncher system for adjusting the time-of-flight of positrons. Simulations show that compression of positrons emitted from the moderator during 300 ns into a pulse of 2 ns width is achievable. Preliminary results on the design and requirements for the pulsing system components are presented.
THE QUANTIZED HALL INSULATOR: A "QUANTUM" SIGNATURE OF A "CLASSICAL" TRANSPORT REGIME?
Authors: SHIMSHONI EFRAT
Published: September 2004

Experimental studies of the transitions from a primary quantum Hall (QH) liquid at filling factor ν=1/k (with k an odd integer) to the insulator have indicated a "quantized Hall insulator" (QHI) behavior: while the longitudinal resistivity diverges with decreasing temperature and current bias, the Hall resistivity remains quantized at the value kh/e2. We review the experimental results and the theoretical studies addressing this phenomenon. In particular, we discuss a theoretical approach which employs a model of the insulator as a random network of weakly coupled puddles of QH liquid at fixed ν. This model is proved to exhibit a robust quantization of the Hall resistivity, provided the electron transport on the network is incoherent. Subsequent theoretical studies have focused on the controversy whether the assumption of incoherence is necessary. The emergent conclusion is that in the quantum coherent transport regime, quantum interference destroys the QHI as a consequence of localization. Once the localization length becomes much shorter than the dephasing length, the Hall resistivity diverges. We conclude by mentioning some recent experimental observations and open questions.
RELAXATION OF FEMTOSECOND PHOTOEXCITED ELECTRONS IN A METALLIC SAMPLE
Authors: SINGH NAVINDER
Published: September 2004

A model calculation is given for the energy relaxation of a nonequilibrium distribution of hot electrons prepared in a metallic sample that has been subjected to homogeneous photo-excitation by a femtosecond laser pulse. The model assumes that the photoexcitation creates two interpenetrating electronic subsystems, initially comprising of a dilute energy-wise higher-lying nondegenerate hot electron subsystem, and a relatively dense, lower-lying electron subsystem which is degenerate. The relaxation process is taken to be dominated by the electron–(multi)phonon interaction, resulting in a quasi-continuous electron energy loss to the lattice bath. A novel physical feature of the kinetics considered here is the slowing down of the electron–phonon relaxation in the vicinity of the Fermi energy of the degenerate subsystem, due to the fermionic blocking of the interaction phase space. This leads to a peaking of the calculated hot electron distribution at the Fermi energy. This feature, as well as the entire evolution of the hot electron distribution, may be time-resolved by a pump-probe study. The model is particularly applicable to disordered metallic systems with low electron concentrations and strong electron–phonon coupling, and that are at high temperatures, where the usual two-temperature model1–3 may not be appropriate.
MAGNETIC BIAS FIELD DEPENDENCE OF THE MAGNETOELECTRIC EFFECT IN A MAGNETOELECTRIC STRUCTURE: A SIMPLE MODEL
Authors: WAN Y. P. , ZHONG Z.
Published: September 2004

The magnetoelectric (ME) effect in a ME composite structure in which a magnetostrictive component is bonded with a piezoelectric component was studied theoretically, based on the hyperbolic nonlinear constitutive relation of magnetostriction and the piezoelectric equations. A quantitative relation was established analytically for the ME effect and the influencing factors, such as the magnetic bias field and the structure dimensions. It was verified that the theoretical model agrees qualitatively with the experimental results published in Ref. 7. It can also be predicted by the model that the ME effect can be improved by optimizing the structure dimensions.
THE OPTICAL PROPERTIES OF NITROGENATED AMORPHOUS CARBON FILMS GROWN BY A NOVEL SURFACE WAVE MICROWAVE PLASMA CVD METHOD
Authors: RUSOP M. , ADHIKARI S. , OMER A. M. M. , ADHIKARY S. , UCHIDA H. , JIMBO T. , SOGA T. , UMENO M.
Published: September 2004

The effects of annealing temperature on the optical properties of nitrogenated amorphous carbon (a-C:N) films grown on quartz substrates by a novel surface wave microwave plasma chemical vapor deposition (SWMP-CVD) method are reported. The thickness, optical, structural and bonding properties of the as-grown and anneal-treated a-C:N films were measured and compared. The film thickness decreased rapidly with increasing annealing temperature above 350°C. A wide range of optical absorption characteristics is observed, depending on the annealing temperature. The optical band gap of as-grown a-C:N films is approximately 2.8 eV, gradually decreasing to 2.5 eV for the films anneal-treated at 300°C, and beyond that decreasing rapidly down to 0.9 eV at 500°C. The Raman and FTIR spectroscopy measurements have shown that the structural and composition of the films can be tuned by optimizing the annealing temperature. The change of optical, structural and bonding properties of SWMP-CVD-grown a-C:N films with higher annealing temperature was attributed to the fundamental changes in the bonding and band structures of the films.
ON THE EXISTENCE OF TURNING POINTS IN d-DIMENSIONAL SCHWARZSCHILD–De SITTER AND ANTI-De SITTER SPACETIMES
Authors: BÉSSA CARLOS H. G. , LIMA JOSÉ A. S.
Published: September 2004

We investigate the motion of a test particle in a d-dimensional, spherically symmetric and static spacetime supported by a mass M plus a Λ-term. The motion is strongly dependent on the sign of Λ. In Schwarzschild–de Sitter (SdS) space–time (Λ>0), besides the physical singularity at r=0 there are cases with two horizons and two turning points, one horizon and one turning point and the complete absence of horizon and turning points. For Schwarzschild–Anti de Sitter (SAdS) spacetime (Λ<0) the horizon coordinate is associated to an unique turning point.
NÄIVE DIMENSIONAL ANALYSIS IN AN EFFECTIVE FIELD THEORY FOR NEUTRON STARS
Authors: MAEKAWA CLÁUDIO M. , RAZEIRA MOISÉS , LÜTZ EDUARDO F. , VASCONCELLOS CÉSAR A. Z. , DILLIG MANFRED
Published: September 2004

In the investigation of the role of naturalness in effective theory, we focus on dense hadronic matter in a generalized relativistic multi-baryon Lagrangian density mean field approach which contains nonlinear self-couplings of the σ and δ meson fields interacting with the fundamental baryon octet and with the ω and ϱ meson fields and compare its predictions with estimates obtained within a phenomenological naive dimensional analysis based on the naturalness of the coupling constants of the Lagrangian model; our investigation is limited however to the scalar sector of the theory. Upon adjusting the model parameters to describe bulk static properties of ordinary nuclear matter, we show that our approach represents a natural modelling of nuclear matter under the extreme conditions of density as found in the interior of neutron stars.
The XMM-NEWTON VIEW ON NEUTRON STARS AND BLACK HOLES
Authors: MOTCH CHRISTIAN
Published: September 2004

The improved sensitivity of the XMM-Newton satellite is quickly expanding our knowledge of X-ray emission mechanisms and physical conditions in and around compact objects. Thanks to the large collecting power and high energy resolution of the EPIC and RGS instruments, detailed X-ray spectral analysis can be performed in the 0.2 to 12 keV energy range. In this short review, I highlight the most significant results obtained by XMM-Newton on neutron stars both isolated and in binary systems and on accreting stellar mass black holes.
THE DEVELOPMENT AND SCIENTIFIC IMPACT OF THE CHANDRA X-RAY OBSERVATORY
Authors: SCHWARTZ DANIEL A.
Published: September 2004

I review the operational capabilities of the Chandra X-ray Observatory, including some of the spectacular results obtained by the general observer community. A natural theme of this talk is that Chandra is revealing outflows of great quantities of energy that were not previously observable. I highlight the Chandra studies of powerful X-ray jets. This subject is only possible due to the sub-arcsecond resolution of the X-ray telescope.
EQUATION OF STATE OF NEUTRON STAR MATTER
Authors: WEBER FRIDOLIN
Published: September 2004

The physical properties of neutron star matter at supernuclear densities are highly uncertain and the associated equation of state is only very poorly known. This has its origin in numerous sources which are discussed in this paper.
ON THE STOCHASTIC EVOLUTION OF THE INFLATON FIELD
Authors: SILVA JOÃO MARIA , LIMA JOSÉ A. S.
Published: September 2004

During the inflationary regime, the expansion of the Universe is driven by a scalar field ϕ(t) which may be in thermal contact with the radiation fluid. In this work, we study the influence of the thermal bath assuming that it is responsible for the stochastic evolution of the inflaton field. Assuming that the fluctuation dynamics is described by a Langevin-type equation of motion, a large set of analytical solutions including white and colored noises are derived. It is found that even in the case of white noise the field experience an anomalous diffusion. Such results may be important for studying thermally induced initial density perturbations in inflationary cosmologies, mainly in the framework of warm inflation.
MICROWAVE PHOTON TRAJECTORIES IN HYPERBOLIC UNIVERSES
Authors: FIUZA K. , Prado S. D.
Published: September 2004

In models of universes that have constant negative spatial curvature, photon trajectories are exponentially unstable, which imply chaotic photonic dynamics. This has been put forward as an explanation of pre-inflationary homogeneity and to the fact that fluctuations in the cosmic microwave background are close to Gaussian. We show here that additional random fluctuations in the curvature can lead to stochastic stabilization of photon trajectories implying in several consequences for the statistic of temperature fluctuations of the Cosmic Microwave Background.
PRIMORDIAL BUBBLES OF COLOUR SUPERCONDUCTING QUARK MATTER
Authors: MASPERI LUIS , ORSARIA MILVA
Published: September 2004

We analyze the possibility that bubbles of quark matter surviving the confinement phase transition might have become colour superconducting due to the enormous compression suffered by them.
OF CHARGED STARS AND CHARGED BLACK HOLES
Authors: MALHEIRO MANUEL , PICANÇO RODRIGO , RAY SUBHARTHI , LEMOS JOSÉ P. S. , ZANCHIN VILSON T.
Published: September 2004

Effect of maximum amount of charge a compact star can hold, is studied here. We analyze the different features in the renewed stellar structure and discuss the reasons why such huge charge is possible inside a compact star. We studied a particular case of a polytropic equation of state (EOS) assuming the charge density is proportional to the mass density. Although the global balance of force allows a huge charge, the electric repulsion faced by each charged particle forces it to leave the star, resulting in the secondary collapse of the system to form a charged black hole.
WHAT WE KNOW AND WHAT WE DON'T KNOW ABOUT THE UNIVERSE
Authors: GLEISER MARCELO
Published: September 2004

I present a non-technical and necessarily biased and incomplete overview of our present understanding of the physical universe and its constituents, emphasizing what we have learned from the explosive growth in cosmological and astrophysical data acquisition and some of the key open questions that remain. The topics are organized under the labels space, time, and matter. Most bibliographical references are for the non-expert.
ANISTROPIC STARS: EXACT SOLUTIONS AND STABILITY
Authors: GLEISER MARCELO , DEV KRSNA
Published: September 2004

I report on recent work concerning the existence and stability of self-gravitating spheres with anisotropic pressure. After presenting new exact solutions, Chandrasekhar's variational formalism for radial perturbations is generalized to anisotropic objects and applied to investigate their stability. It is shown that anisotropy can not only support stars of mass M and radius R with 2M/R≥8/9 and arbitrarily large surface redshifts, but that stable configurations exist for values of the adiabatic index γ smaller than the corresponding isotropic value.
A NEW LOOK INTO THE GRAVITON MASS
Authors: NOVELLO MÁRIO
Published: September 2004

We analyze the concept of graviton mass in the presence of a "cosmological" Λ term in Einstein equations of gravity. We point out a connection between the mass of the graviton and Λ.
NATURALNESS IN AN EFFECTIVE FIELD THEORY FOR NEUTRON STAR MATTER
Authors: RAZEIRA MOISÉS , VASCONCELLOS CÉSAR A. Z.
Published: September 2004

High density hadronic matter is studied in a generalized relativistic multi-baryon Lagrangian density mean field approach which contains nonlinear couplings of the σ, ω, ϱ fields. We compare the predictions of our model with estimates obtained within a phenomenological naive dimensional analysis based on the naturalness of the coefficients of the theory. Upon adjusting the model parameters to describe bulk static properties of ordinary nuclear matter, we show that our approach represents a natural modelling of nuclear matter under the extreme conditions of density as the ones found in the interior of neutron stars. Moreover, we show that naturalness play a major role in effective field theory and, in combination with experiment, could represent a relevant criterium to select a model among others in the description of global static properties of neutron stars.
ON THE WIDTH OF THE LAST SCATTERING SURFACE
Authors: PIRES NILZA , NOBRE MARIA ASSUNTA S. , LIMA JOSÉ A. S.
Published: September 2004

We discuss the physical effects of some accelerated world models on the width of the last scattering surface (LSS) of the cosmic microwave background radiation (CMBR). The models considered in our analysis are X-matter (XCDM) and a Chaplygin type gas. The redshift of the LSS does not depend on the kind of dark energy (if XCDM of Chaplygin). Further, for a Chaplygin gas, the width of the LSS is also only weakly dependent on the kind of scenario (if we have dark energy plus cold dark matter or the unified picture).
NEUTRINO OPACITY IN HIGH DENSITY NUCLEAR MATTER
Authors: DOS SANTOS SÉRGIO M. , RAZEIRA MOISÉS , VASCONCELLOS CÉSAR A. Z. , LEINSON LEV
Published: September 2004

We estimate in this work the contribution of the nucleon weak magnetism on the neutrino absorption mean free path inside high density nuclear matter. Our main contribution to this subject involves basically, in the mean field approach, three different ingredients: (a) a relativistic generalization of the approach developed by Sanjay and collaborators; (b) the inclusion of the nucleon weak-magnetism; (c) the inclusion of the pseudo-scalar interaction involving the nucleons. Our preliminary results indicate the consistency of our approach. The novel results we have obtained, considering similar physical conditions as the ones assumed by Sanjay and collaborators, is that the neutrino absorption mean free path is three times the corresponding result obtained by those authors.
MATTER UNDER STRONG GRAVITY: THE NUCLEAR REGIONS OF AGN
Authors: BOLLER THOMAS
Published: September 2004

X-ray observations of Seyfert galaxies and quasars currently provide the most powerful way to study the environments of supermassive black holes. Our ability to probe these environments, some of the most extreme found in nature, is rapidly improving driven by dramatic advances in X-ray spectroscopic instrumentation. In addition to the well known 'hard X-ray power law' that is probably formed in a hot 'corona' above a cooler accretion disc, substantial spectral complexity has also been revealed. For example, soft X-ray excess emission above the power law is often seen at low X-ray energies, and this emission is thought to be associated with the inner disc. Atomic absorption/emission processes in nuclear gas flows are also observed to imprint characteristic features on X-ray spectra. Iron Kα emission lines from 6.40–6.97 keV are formed at least partially by fluorescence in the inner disc, and absorption edges seen mainly below 2 keV reveal major flows of ionized gas in the nucleus. Studies of the complex X-ray spectra of Seyferts and quasars have undergone a revolution wit the launches of Chandra in 1998 and XMM-Newton in 1999. The era of high-resolution X-ray spectroscopy has been initiated by the Chandra and XMM-Newton grating spectrometers. These detectors provide X-ray spectra with 6–100 times higher spectral resolution than those previously available, and they have dramatically enlarged the arsenal of diagnostics available for investigating Seyfert/quasar nuclei. The new generation of X-ray observatories is used to intensively address some of the leading questions about Seyfert/quasar X-ray emission. Some of the most important scientific issues for the next years are: — Matter under strong gravity: Why are relativistically blurred Fe K lines so rare? — What are the extreme X-ray spectral and variability properties of ultrasoft Narrow-Line Seyfert 1 galaxies telling us about Seyferts and quasars more generally? — What is the physical nature of the sharp spectral cut-off in Seyfert galaxies? While the advances expected from the new generation of X-ray observatories are so large and widespread that precise predictions are difficult, it is believed that particularly important progress will be made towards answering these central questions. Below is explained why the questions I have stated are fundamental and timely.
CHARGED (n+1)-DIMENSIONAL EINSTEIN–MAXWELL SYSTEMS
Authors: ZANCHIN VILSON T.
Published: September 2004

In the present work we consider Einstein–Maxwell equations in (n+1)-dimensional spacetimes and show that there are Majumdar–Papapetrou type solutions for all n≥3. In the case of charged perfect fluids, the solutions with nonzero pressure are singular. It is verified that, for zero pressure, the equilibrium is independent of the shape of the distribution of the charged matter.
A GAME THEORETICAL MODEL OF INTERNATIONAL FISHING WITH TIME DELAY
Authors: SZIDAROVSZKY FERENC , ENGEL ANDREW , CHIARELLA CARL
Published: October 2004

This paper studies the evolution of a fish stock that is exploited by an n-country oligopoly. A feature of the economic structure is that the countries exploiting the fish stock experience time lags in obtaining and implementing information on the fish stock. The local asymptotic behavior of the equilibrium is analyzed, including asymptotic stability, instability, and cyclical behavior. Under the assumption of symmetric countries, two special cases are examined in detail. In the first case identical time delays are assumed, and in the second case it is assumed that one country has a different time delay from the others. This semi-symmetric case gives some insight into the consequence of asymmetry of the countries on the asymptotic behavior of the fish stock.
Role of Voluntary Drive in Encoding an Elementary Motor Memory
Authors: Kaelin-Lang Alain , Sawaki Lumy , Cohen Leonardo G.
Published: September 2004

Motor training consisting of repetitive thumb movements results in encoding of motor memories in the primary motor cortex. It is not known if proprioceptive input originating in the training movements is sufficient to produce this effect. In this study, we compared the ability of training consisting of voluntary (active) and passively-elicited (passive) movements to induce this form of plasticity. Active training led to successful encoding accompanied by characteristic changes in corticomotor excitability, while passive training did not. These results support a pivotal role for voluntary motor drive in coding motor memories in the primary motor cortex.
Effects of Intratympanic Gentamicin on Vestibular Afferents and Hair Cells in the Chinchilla
Authors: Hirvonen Timo P. , Minor Lloyd B. , Hullar Timothy E. , Carey John P.
Published: September 2004

Gentamicin is toxic to vestibular hair cells, but its effects on vestibular afferents have not been defined. We treated anesthetized chinchillas with one injection of gentamicin (26.7 mg/ml) into the middle ear and made extracellular recordings from afferents after 5–25 (early) or 90–115 days (late). The relative proportions of regular, intermediate, and irregular afferents did not change after treatment. The spontaneous firing rate of regular afferents was lower ( P < 0.001) on the treated side (early: 44.3 ± 16.3; late: 33.9 ± 13.2 spikes·s−1) than on the untreated side (54.9 ± 16.8 spikes·s−1). Spontaneous rates of irregular and intermediate afferents did not change. The majority of treated afferents did not measurably respond to tilt or rotation (82% in the early group, 76% in the late group). Those that did respond had abnormally low sensitivities ( P < 0.001). Treated canal units that responded to rotation had mean sensitivities only 5–7% of the values for untreated canal afferents. Treated otolith afferents had mean sensitivities 23–28% of the values for untreated otolith units. Sensitivity to externally applied galvanic currents was unaffected for all afferents. Intratympanic gentamicin treatment reduced the histological density of all hair cells by 57% ( P = 0.04). The density of hair cells with calyx endings was reduced by 99% ( P = 0.03), although some remaining hair cells had other features suggestive of type I morphology. Type II hair cell density was not significantly reduced. These findings suggest that a single intratympanic gentamicin injection causes partial damage and loss of vestibular hair cells, particularly type I hair cells or their calyceal afferent endings, does not damage the afferent spike initiation zones, and preserves enough hair cell synaptic activity to drive the spontaneous activity of vestibular afferents.
5-HT Prolongs Ventral Root Bursting Via Presynaptic Inhibition of Synaptic Activity During Fictive Locomotion in Lamprey
Authors: Schwartz Eric J. , Gerachshenko Tatyana , Alford Simon
Published: September 2004

Locomotor pattern generation is maintained by integration of the intrinsic properties of spinal central pattern generator (CPG) neurons in conjunction with synaptic activity of the neural network. In the lamprey, the spinal locomotor CPG is modulated by 5-HT. On a cellular level, 5-HT presynaptically inhibits synaptic transmission and postsynaptically inhibits a Ca2+-activated K+current responsible for the slow afterhyperpolarization (sAHP) that follows action potentials in ventral horn neurons. To understand the contribution of these cellular mechanisms to the modulation of the spinal CPG, we have tested the effect of selective 5-HT analogues against fictive locomotion initiated by bath application of N-methyl-d-aspartate (NMDA). We found that the 5-HT1Dagonist, L694-247, dramatically prolongs the frequency of ventral root bursting. Furthermore, we show that L694-247 presynaptically inhibits synaptic transmission without altering postsynaptic Ca2+-activated K+currents. We also confirm that 5-HT inhibits synaptic transmission at concentrations that modulate locomotion. To examine the mechanism by which selective presynaptic inhibition modulates the frequency of fictive locomotion, we performed voltage- and current-clamp recordings of CPG neurons during locomotion. Our results show that 5-HT decreases glutamatergic synaptic drive within the locomotor CPG during fictive locomotion. Thus we conclude that presynaptic inhibition of neurotransmitter release contributes to 5-HT–mediated modulation of locomotor activity.
Synaptically Recruited Apical Currents Are Required to Initiate Axonal and Apical Spikes in Hippocampal Pyramidal Cells: Modulation by Inhibition
Authors: Canals S. , López-Aguado L. , Herreras O.
Published: September 2004

Dendritic voltage-dependent currents and inhibition modulate the information flow between synaptic and decision areas. Subthreshold and spike currents are sequentially recruited by synaptic potentials in the apical shaft of pyramidal cells, which may also decide cell output. We studied the global role of proximal apical recruited currents on cell output in vitro and in the anesthetized rat after local blockade of Na+ currents in the axon initial segment (AIS) or the proximal apical shaft and their modulation by inhibition. Microejection of TTX, field potentials, and intrasomatic and intradendritic recordings were employed. Dendritic population spikes (PSs) were much smaller in vitro, but the gross relations between synaptic and active currents are similar to in vivo. Activation of Schaffer collaterals triggered PSs and action potentials (APs) in the apical shaft that fully propagated to the axon. However, the specific blockade of proximal Na+ currents avoided cell firing, although antidromic PSs and APs readily invaded somata. The somatic depolarization of subthreshold excitatory postsynaptic potentials (EPSPs) also decreased to about 50%. These results were not due to decreased excitatory input by TTX. However, when GABAA inhibition was locally removed, Schaffer synaptic currents skipped the proximal dendrite and fired somatic PSs, although initiated at the AIS. It is concluded that apical currents recruited en passant by Schaffer synaptic potentials in the apical shaft constitute a necessary amplifier for this input to cause output decision. Local inhibition decides when and where an AP will initiate, constituting an efficient mechanism to discriminate and weight different inputs.
Prehension Synergies in Three Dimensions
Authors: Shim Jae Kun , Latash Mark L. , Zatsiorsky Vladimir M.
Published: September 2004

The goal of this study was to investigate the conjoint changes of digit forces/moments in 3 dimensions during static prehension under external torques acting on the object in one plane. The experimental paradigm was similar to holding a book vertically in the air where the center of mass of the book is located farther from the hand than the points of digit contacts. Three force and 3 moment components from each digit were recorded during static prehension of a customized handle. Subjects produced forces and moments in all 3 directions, although the external torques were exerted on the handheld object about only the Z-axis. The 3-dimensional response to a 2-dimensional task was explained by the cause–effect chain effects prompted by the noncollinearity of the normal forces of the thumb and the 4 fingers (represented by the “virtual finger”). Because the forces are not collinear (not along the same line), they generate moments of force about X- and Y-axes that are negated by the finger forces along the Y- and X-directions. The magnitudes of forces produced by lateral fingers (index and little) with longer moment arms were larger compared with the central fingers (middle and ring). At the virtual finger (an imaginary digit whose mechanical action is equivalent to the summed action of the 4 fingers) level, the relative contribution of different fractions of the resistive moment produced by subjects did not depend on the torque magnitude. We conclude that the CNS 1) solves a planar prehension task by producing forces and moments in all 3 directions, 2) uses mechanical advantage of fingers, and 3) shares the total torque among finger forces and moments in a particular way disregarding the torque magnitude.
An application of the method of matched asymptotic expansions for low Reynolds number flow past a cylinder of arbitrary cross section
Authors: Kohr Mirela
Published: September 2004

We study the low Reynolds number flow of an incompressible
Newtonian fluid of infinite expanse past a cylinder of arbitrary
cross section by using the method of matched asymptotic
expansions. The analysis that will be made in this paper is
equivalent to that developed by Power (1990) in
order to solve the resulting inner (or Stokes) problems with the
completed double‐layer boundary integral equation method
(CDLBIEM) due to Power and Miranda (1987). We will
solve these problems by the boundary integral method developed by
Hsiao and Kress (1985).
Some exact inequalities of Hardy‐Littlewood‐Polya type for periodic functions
Authors: Azar Laith Emil
Published: September 2004

We investigate the following problem: for a given A ≥ 0, find
the infimum of the set of B ≥ 0 such that the inequality
, for k, r ∈ ℕ ∪ {0}, 0 ≤ k < r, holds for all sufficiently
smooth functions.
Critical values lie on a line
Authors: Ainouline Azat
Published: September 2004

We prove that critical values set of a differentiable map lies on a line of certain smoothness class.
On a class of nonlinear reaction‐diffusion systems with nonlocal boundary conditions
Authors: Bouziani Abdelfatah
Published: September 2004

We prove the existence, uniqueness, and continuous dependence of a generalized solution of a nonlinear reaction‐diffusion system with only integral terms in the boundaries. We first solve a particular case of the problem by using the energy‐integral method. Next, via an iteration procedure, we derive the obtained results to study the solvability of the stated problem.
Production of Prednisolone by Pseudomonas oleovorans Cells Incorporated Into PVP/PEO Radiation Crosslinked Hydrogels
Authors: Abd El-Hady Abeer , Abd El-Rehim Hassan A.
Published: September 2004

In order to rise the yield of prednisolone from hydrocortisone, the Pseudomonas oleovorans cells were entrapped into radiation crosslinked poly (vinyl pyrrolidone)/poly(ethylene oxide) (PVP/PEO) hydrogel of different gel contents. The factors affecting the gel content and swelling behavior of the polymeric gel, such as polymer composition, polymer blend concentration, and irradiation doses, were investigated. The formation of gels having a good strength with the ability to retain a desirable amount of water in their three‐dimensional network can be achieved by using PVP/PEO copolymer of composition (90 : 10) and concentration of 15% prepared at 20 kGy irradiation dose. At these conditions the prepared hydrogel is considered the most favorable one that gave the highest hydrocortisone bioconversion and prednisolone yield, 81% and 62.8%, respectively. The improvement of prednisolone yield was also achieved by increasing substrate concentration. Maximum hydrocortisone bioconversion (86.44) was obtained at 18 hours by using substrate concentration of 30 mg. Reusability of immobilized Pseudomonas oleovorans entrapped into PVP/PEO copolymer hydrogel was studied. The results indicated that the transformation capacity of hydrocortisone to prednisolone highly increased by the repeated use of copolymer for 4 times. This was accompanied by an increase in prednisolone yield to 89% and the bioconversion of hydrocortisone was 98.8%.