bluuebunny/crossref_metadata_2025 huggingface dataset:
STUDIES ON FUSARIUM WILT OF BANANAS: IV. CLONAL DIFFERENTIATION AMONG WILD TYPE ISOLATES OF F. OXYSPORUM f. CUBENSE
Authors: Stover R. H.
Published: January 2008

F. oxysporum f. cubense exists in diseased rhizomes and pseudostems of Gros Michel bananas in two major clonal groups or cultivars designated 'Odoratum' and 'Inodoratum' because of the presence or absence of a pronounced distinctive odor from cultures after 4 to 8 days on various media. Three clones of the 'Inodoratum' cultivar, difficult to distinguish morphologically on peptone dextrose agar, were distinguishable by cultural interaction and pathogenicity tests in the field. Some clones of the 'Inodoratum' and 'Odoratum' cultivars were shown to differ quantitatively in pathogenicity in the field. Clone C from Honduras, which is limited in distribution, induced the most rapid disease spread and destruction of banana mats, followed by clone E from Panama. There was an association between the 'Inodoratum'and 'Odoratum' cultivars and the syndromes induced in Honduras. The former usually induced strong yellowing of erect leaves whereas the latter usually induced leaf collapse at the petiole with little or no leaf yellowing.
NUMERICAL SIMULATION OF STREAMER PROPAGATION IN OXYGEN
Authors: SETTAOUTI A. , SETTAOUTI L.
Published: January 2008

Glow discharges are being used in many fields of application. For the improvement of performance in these applications, it is necessary to understand discharge dynamics experimentally and numerically. In this paper, a Monte Carlo simulation is carried out in oxygen ( O 2) in uniform electric fields. The electron motion and avalanche growth are simulated by tracing individual paths, and the technique also accounts for the effect of the rapid spatial and temporal space charge variations by solving the Poisson equation. The streamer propagation, electron, positive and negative-ion distribution, and space charge fields are studied in detail as time increases.
SIMPLE AND COST EFFECTIVE FABRICATION OF ZnO THIN FILMS ON HYDROGEN TERMINATED SILICON SUBSTRATES BY NEBULISED SPRAY PYROLYSIS
Authors: CHANDRA SEKHAR M.
Published: January 2008

Pure and Al doped nanocrystalline ZnO films have been prepared on Hydrogen terminated Si(100) substrates by nebulized spray pyrolysis. The dependence of the structural, compositional and electrical properties were investigated using XRD, EDX, AFM and spectrophotometer. The X-ray diffraction data coincide well with the pattern of ZnO reported with the Standard Database. Films annealed at higher temperatures show better orientation, as revealed from X-ray diffraction patterns. Annealing the films in air improved the electrical properties. From the I-V characteristics, the nonlinear coefficient α value has been estimated. Reflectance measurements show good reflectance in the IR region for pure ZnO films, and Al doping improved the reflectance values.
QUANTUM SPIN CURRENT INDUCED THROUGH OPTICAL DIPOLE TRANSITION PROCESS IN SEMICONDUCTORS
Authors: LIU XIONG-JUN , KWEK L. C. , Oh C. H.
Published: January 2008

We propose a scheme to generate quantum spin current via linear optical process. By interacting a three-level system based on the spin states of charged particles (electrons or holes in semiconductor, etc) with the angular momentum states of an optical field, we show that the dynamics of charged particles equipped with different spin polarizations are governed by different (opposite) additional effective magnetic fields. In this way, a pure dissipationless quantum spin current can be generated. No spin-orbit interaction (e.g., Rashba or Dresselhaus term) is needed in this scheme. We also calculate the effect of nonmagnetic impurities on the created spin currents and show that the vertex correction of the spin hall conductivity in the ladder approximation is exactly zero.

Paper presented at NTU Spintronics Workshop, Singapore, May 2006.
SPIN RELATED TRANSPORT IN RASHBA 2DEG SYSTEMS
Authors: NITTA JUNSAKU
Published: January 2008

Transport in mesoscopic conductors is determined not only by orbital motion of carriers but also by quantum interference effect. However, it is well known that the quantum interference such as weak localization is much modified in the presence of spin-orbit interaction (SOI), leading to weak anti-localization. We discuss the origin of the Rashba SOI and spin related mesoscopic transport in InGaAs based two dimensional electron gases (2DEG) affected by the Rashba SOI.

It is experimentally shown that the strength of the Rashba SOI in InGaAs 2DEG systems can be controlled by the gate voltage.1 The spin dynamics in solid systems is commonly determined by the competition between Zeeman effect and SOI. The spin relaxation time and dephasing time are studied from weak anti-localization analysis as a function of the relative strength of the Zeeman energy (EZ) and the Rashba SOI energy (E SOI ). The (EZ) was introduced by applying magnetic field parallel to the 2DEG plane. This in-pane magnetic field does not affect the orbital motion of electrons. The spin relaxation time increases with the Zeeman energy. The dephasing time associated with the spin-induced time reversal symmetry (TRS) breaking saturates when EZ becomes comparable to E SOI . Moreover, we show that the spin-induced TRS breaking mechanism is a universal function of the ratio EZ/E SOI within the experimental accuracy.2

Note from Publisher: This article contains the abstract only.
CONTROLLING SPIN COHERENCE WITH SEMICONDUCTOR NANOSTRUCTURES
Authors: AWSCHALOM DAVID D.
Published: January 2008

We present two emerging opportunities for manipulating and communicating coherent spin states in semiconductors. First, we show that semiconductor microcavities offer unique means of controlling light-matter interactions in confined geometries, resulting in a wide range of applications in optical communications and inspiring proposals for quantum information processing and computational schemes. Studies of spin dynamics in microcavities — a new and promising research field — have revealed novel effects such as polarization beats, stimulated spin scattering, and giant Faraday rotation. Here, we study the electron spin dynamics in optically-pumped GaAs microdisk lasers with quantum wells and interface-fluctuation quantum dots in the active region. In particular, we examine how the electron spin dynamics are modified by the stimulated emission in the disks, and observe an enhancement of the spin coherence time when the optical excitation is in resonance with a high quality ( Q ~ 5000) lasing mode.1 This resonant enhancement, contrary to expectations from the observed trend in the carrier recombination time, is then manipulated by altering the cavity design and dimensions. In analogy to devices based on excitonic coherence, this ability to engineer coherent interactions between electron spins and photons may provide novel pathways towards spin dependent quantum optoelectronics.

In a second example, the nitrogen-vacancy (N-V) center in diamond has garnered interest as a room-temperature solid-state system not only for exploring electronic and nuclear spin phenomena but also as a candidate for spin-based quantum information processing. Spin coherence times of up to 50 microseconds have been reported for ensembles of N-V centers and a two-qubit gate utilizing the electron spin of a N-V center and the nuclear spin of a nearby C-13 atom has been demonstrated. Here, we present experiments using angle-resolved magneto-photoluminescence microscopy to investigate anisotropic spin interactions of single N-V centers in diamond at room temperature.2 Negative peaks in the photoluminescence intensity are observed as a function of both magnetic field magnitude and angle, and can be explained by coherent spin precession and anisotropic relaxation at spin-level anticrossings. Additionally, precise field alignment with the symmetry axis of a single N-V center reveals the resonant magnetic dipolar coupling of a single "bright" electron spin of an N-V center to small numbers of "dark" spins of nitrogen defects in its immediate vicinity, which are otherwise undetected by photoluminescence. Most recently, we are exploring the possibility of utilizing this magnetic dipole coupling between bright and dark spins to couple two spatially separated single N-V center spins by means of intermediate nitrogen spins.

Note from Publisher: This article contains the abstract only.
MAGNETO-GYROTROPIC PHOTOGALVANIC EFFECTS IN SEMICONDUCTOR QUANTUM WELLS
Authors: GANICHEV S. D.
Published: January 2008

The spin-orbit coupling provides a versatile tool to generate and to manipulate the spin degree of freedom in low-dimensional semiconductor structures. The spin Hall effect, where an electric current drives a transverse spin current and causes a nonequilibrium spin accumulation near the sample boundary,1,2 the spin-galvanic effect, where a nonequilibrium spin polarization drives an electric current3,4 or the reverse process, in which an electrical current generates a non-equilibrium spin-polarization,5–9 are all consequences of spin-orbit coupling. In order to observe a spin Hall effect a bias driven current is an essential prerequisite. Then spin separation is caused via spin-orbit coupling either by Mott scattering (extrinsic spin Hall effect) or by spin splitting of the band structure (intrinsic spin Hall effect). Recently an elementary effect causing spin separation which is fundamentally different from that of the spin Hall effect has been observed.10 In contrast to the spin Hall effect it does not require an electric current to flow: it is spin separation achieved by spin-dependent scattering of electrons in media with suitable symmetry. It is show that by free carrier (Drude) absorption of terahertz radiation spin separation is achieved in a wide range of temperatures from liquid helium temperature up to room temperature. Moreover the experimental results demonstrate that simple electron gas heating by any means is already sufficient to yield spin separation due to spin-dependent energy relaxation processes of non-equilibrium carriers.

In order to demonstrate the existence of the spin separation due to asymmetric scattering the pure spin current was converted into an electric current. It is achieved by application of a magnetic field which polarizes spins. This is analogues to spin-dependent scattering in transport experiments: spin-dependent scattering in an unpolarized electron gas causes the extrinsic spin Hall effect, whereas in a spin-polarized electron gas a charge current, the anomalous Hall effect, can be observed. As both magnetic fields and gyrotropic mechanisms were used authors introduced the notation "magneto-gyrotropic photogalvanic effects" for this class of phenomena. The effect is observed in GaAs and InAs low dimensional structures at free-carrier absorption of terahertz radiation in a wide range of temperatures from liquid helium temperature up to room temperature. The results are well described by the phenomenological description based on the symmetry. Experimental and theoretical analysis evidences unumbiguously that the observed photocurrents are spin-dependent. Microscopic theory of this effect based on asymmetry of photoexcitation and relaxation processes are developed being in a good agreement with experimental data.

Note from Publisher: This article contains the abstract only.
THIRD-ORDER NONLINEAR OPTICAL PROPERTIES OF [(C2H5)4N][Co(dmit)2] USING Z-SCAN TECHNIQUE
Authors: ZHANG XI , REN QUAN , GUO WEN-FENG , SUN XIANG-BING , WANG XIN-QIANG , YANG HONG-LIANG , ZHANG FU-JUN , GAO YI , XU DONG
Published: January 2008

A novel dmit 2- complex: [( C 2 H 5)4 N][Co(dmit) 2], abbreviated as EtCo , was synthesized and its third-order optical nonlinearities were characterized by Z-scan technique at the wavelength of 1064 nm with laser duration of 40 ps. Z-scan curves revealed a negative nonlinear refraction at 1064 nm and a positive absorption was observed. The nonlinear refraction coefficient n2, the nonlinear absorption coefficient β and the molecular second hyperpolarizability γ have been determined to be as large as 9.51×10-19 m 2/ W , 2.19×10-12 m/W and 5.41×10-31 esu respectively, suggesting that this material has potential applications in optical limiting.
ASYNCHRONOUS LASER TRANSPONDERS: A NEW TOOL FOR IMPROVED FUNDAMENTAL PHYSICS EXPERIMENTS
Authors: DEGNAN JOHN J.
Published: January 2008

Since 1964, the NASA Goddard Space Flight Center (GSFC) has been using short pulse lasers to range to artificial satellites equipped with passive retroreflectors. Today, a global network of 40 satellite laser ranging (SLR) stations, under the auspices of the International Laser Ranging Service (ILRS), routinely tracks two dozen international space missions with few-millimeter precision using picosecond pulse lasers in support of Earth science. Lunar laser ranging (LLR) began in 1969, shortly after NASA's Apollo 11 mission placed the first of five retroreflector packages on the Moon. An important LLR data product has been the verification of Einstein's equivalence principle and other tests of general relativity. In 1975, the University of Maryland used a laser ranging system to continuously transfer time between two sets of atomic clocks — one set on the ground and the other in an aircraft — to observe the predicted relativistic effects of gravity and velocity on the clock rates. Two-way asynchronous laser transponders promise to extend these precise ranging and time transfer capabilities beyond the Moon to the planets, as evidenced by two successful experiments carried out in 2005 at distances of 24 and 80 million km respectively.
FUNDAMENTAL PHYSICS AT NASA: TWO CRITICAL ISSUES AND FAIRBANK'S PRINCIPLE
Authors: EVERITT C. W. FRANCIS
Published: January 2008

Space offers eight distinct paths to controlled laboratory-style experiments in fundamental physics beyond the reach of any Earth-based laboratory. This impressive range of opportunity has already led to important physics but we are only at the beginning. Meanwhile, NASA is in crisis. This paper follows the wisdom of a great and inspiring physicist, William Fairbank, that every setback or difficulty is an opportunity. NASA needs new science; fundamental physics can provide it and with it fascinating new technologies — and training for a new generation of imaginative physicists and engineers.
EXPERIMENTAL GRAVITY IN SPACE — HISTORY, TECHNIQUES AND PROSPECTS
Authors: HELLINGS RONALD W.
Published: January 2008

This is more an after-dinner talk than it is a presentation of research — nothing new, no references, incomplete. It is, rather, a somewhat personal view of: (1) the history of experimental gravity in space, (2) a discussion on the theoretical basis for the two major thrusts in the field — tests of post-Newtonian gravity and gravitational astronomy, and (3) a couple of brief comments on two of the future space opportunities that are discussed at this meeting, LATOR and LISA. My judgment is that we have done a lot to provide an experimental basis for the theory of gravity, and that we can do even more.
LESSONS FROM INTRODUCING NEW SCIENTIFIC DISCIPLINES INTO EUROPEAN SPACE RESEARCH
Authors: HUBER MARTIN C. E.
Published: January 2008

Physics experiments in space will permit us to investigate natural phenomena that cannot be observed on the ground, such as low-frequency gravitational waves, and to reach uncharted realms of accuracy — accessible only through experiments carried out in space — where current foundations of physics can be further tested and potentially falsified. Such projects require technologies that have not been in hand for a long time but are available now.

To avoid conflict of interest, the merit of space projects in physics, from the proposal stage through development, ought to be judged by experts in physics, rather than by space scientists from other fields. It is time now to set aside some funding to let missions in fundamental physics compete fairly with the established space sciences, thereby enriching and deepening the space enterprise — and broadening its advocacy base.

We look, in the context of the European space scene, at the measures and events that resurrected the initially suppressed planetary sciences and brought solar physics to blooming after a long drought; and derive ideas on how to increase the number of flight opportunities for fundamental physics in space.
LASER RANGING FOR GRAVITATIONAL, LUNAR AND PLANETARY SCIENCE
Authors: MERKOWITZ STEPHEN M. , DABNEY PHILIP W. , LIVAS JEFFREY C. , MCGARRY JAN F. , NEUMANN GREGORY A. , ZAGWODZKI THOMAS W.
Published: January 2008

More precise lunar and Martian ranging will enable unprecedented tests of Einstein's theory of general relativity as well as lunar and planetary science. NASA is currently planning several missions to return to the Moon, and it is natural to consider if precision laser ranging instruments should be included. New advanced retroreflector arrays at carefully chosen landing sites would have an immediate positive impact on lunar and gravitational studies. Laser transponders are currently being developed that may offer an advantage over passive ranging, and could be adapted for use on Mars and other distant objects. Precision ranging capability can also be combined with optical communications for an extremely versatile instrument. In this paper we discuss the science that can be gained by improved lunar and Martian ranging along with several technologies that can be used for this purpose.
EXPERIMENTAL VALIDATION OF A HIGH ACCURACY TEST OF THE EQUIVALENCE PRINCIPLE WITH THE SMALL SATELLITE "GALILEO GALILEI"
Authors: NOBILI ANNA M. , COMANDI GIAN LUCA , DORAVARI SURESH , MACCARRONE FRANCESCO , BRAMANTI DONATO , POLACCO ERSEO
Published: January 2008

The small satellite "Galileo Galilei" (GG) has been designed to test the equivalence principle (EP) to 10-17 with a total mass at launch of 250 kg. The key instrument is a differential accelerometer made up of weakly coupled coaxial, concentric test cylinders rapidly spinning around the symmetry axis and sensitive in the plane perpendicular to it, lying at a small inclination from the orbit plane. The whole spacecraft spins around the same symmetry axis so as to be passively stabilized. The test masses are large (10 kg each, to reduce thermal noise), their coupling is very weak (for high sensitivity to differential effects), and rotation is fast (for high frequency modulation of the signal). A 1 g version of the accelerometer ("Galileo Galilei on the Ground" — GGG) has been built to the full scale — except for coupling, which cannot be as weak as in the absence of weight, and a motor to maintain rotation (not needed in space due to angular momentum conservation). GGG has proved: (i) high Q; (ii) auto-centering and long term stability; (iii) a sensitivity to EP testing which is close to the target sensitivity of the GG experiment provided that the physical properties of the experiment in space are going to be fully exploited.
COSMIC ACCELERATION AND MODIFIED GRAVITY
Authors: TRODDEN MARK
Published: January 2008

I briefly discuss some attempts to construct a consistent modification to general relativity (GR) that might explain the observed late-time acceleration of the Universe and provide an alternative to dark energy. I describe the issues facing extensions to GR, illustrate these with a specific example, and discuss the resulting observational and theoretical obstacles.
LASER ASTROMETRIC TEST OF RELATIVITY: SCIENCE, TECHNOLOGY AND MISSION DESIGN
Authors: TURYSHEV SLAVA G. , SHAO MICHAEL
Published: January 2008

The Laser Astrometric Test of Relativity (LATOR) experiment is designed to explore the general theory of relativity in close proximity to the Sun — the most intense gravitational environment in the solar system. Using independent time series of highly accurate measurements of the Shapiro time delay (interplanetary laser ranging accurate to 3 mm at ~2 AU) and interferometric astrometry (accurate to 0.01 picoradian), LATOR will measure gravitational deflection of light by the solar gravity with an accuracy of one part in a billion — a factor of ~30,000 better than what is currently available. LATOR will perform a series of highly accurate tests in its search for cosmological remnants of the scalar field in the solar system. We present the science, technology and mission design for the LATOR mission.
CONSTRAINING TEVES GRAVITY AS EFFECTIVE DARK MATTER AND DARK ENERGY
Authors: ZHAO HONGSHENG
Published: January 2008

The phenomena customarily described with the standard ΛCDM model are broadly reproduced by an extremely simple model in TeVeS, Bekenstein's1 modification of general relativity motivated by galaxy phenomenology. Our model can account for the acceleration of the Universe seen at SNeIa distances without a cosmological constant, and the accelerations seen in rotation curves of nearby spiral galaxies and gravitational lensing of high-redshift elliptical galaxies without cold dark matter. The model is consistent with BBN and the neutrino mass between 0.05 eV to 2 eV. The TeVeS scalar field is shown to play the effective dual roles of dark matter and dark energy, with the amplitudes of the effects controlled by a μ function of the scalar field, called the μ essence here. We also discuss outliers to the theory's predictions on multiimaged galaxy lenses and outliers on the subgalaxy scale.
SPACE-BASED TESTS OF GRAVITY WITH LASER RANGING
Authors: TURYSHEV SLAVA G. , WILLIAMS JAMES G.
Published: January 2008

Existing capabilities of laser ranging, optical interferometry, and metrology, in combination with precision frequency standards, atom-based quantum sensors, and drag-free technologies, are critical for space-based tests of fundamental physics; as a result of the recent progress in these disciplines, the entire area is poised for major advances. Thus, accurate ranging to the Moon and Mars will provide significant improvements in several gravity tests, namely the equivalence principle, geodetic precession, PPN parameters β and γ, and possible variation of the gravitational constant G. Other tests will become possible with the development of an optical architecture that allows one to proceed from meter to centimeter to millimeter range accuracies on interplanetary distances. Motivated by anticipated accuracy gains, we discuss the recent renaissance in lunar laser ranging and consider future relativistic gravity experiments with precision laser ranging over interplanetary distances.
THE IMPACT OF ADVERTISING IN A DUOPOLY GAME
Authors: SCHOONBEEK LAMBERT , KOOREMAN PETER
Published: January 2008

We investigate the impact of advertising in a static differentiated duopoly. First, we consider the Nash equilibrium if firms compete with both prices and advertising. Second, we examine the Nash equilibrium if firms only compete in prices and do not advertise. We characterize the circumstances in which the profit, output, and/or price of each firm is greater (or smaller) with advertising than without advertising.
ANTI-COORDINATION GAMES AND DYNAMIC STABILITY
Authors: KOJIMA FUHITO , TAKAHASHI SATORU
Published: January 2008

We introduce the class of anti-coordination games. A symmetric two-player game is said to have the anti-coordination property if, for any mixed strategy, any worst response to the mixed strategy is in the support of the mixed strategy. Every anti-coordination game has a unique symmetric Nash equilibrium, which lies in the interior of the set of mixed strategies. We investigate the dynamic stability of the equilibrium in a one-population setting. Specifically we focus on the best response dynamic (BRD), where agents in a large population take myopic best responses, and the perfect foresight dynamic (PFD), where agents maximize total discounted payoffs from the present to the future. For any anti-coordination game we show (i) that, for any initial distribution, BRD has a unique solution, which reaches the equilibrium in a finite time, (ii) that the same path is one of the solutions to PFD, and (iii) that no path escapes from the equilibrium in PFD once the path reaches the equilibrium. Moreover we show (iv) that, in some subclasses of anti-coordination games, for any initial state, any solution to PFD converges to the equilibrium. All the results for PFD hold for any discount rate.
CONTAGION AND THE SPEED OF ADJUSTMENT IN SMALL WORLDS
Authors: CARTWRIGHT EDWARD J.
Published: January 2008

We model a simple dynamic process in which myopic agents are matched amongst each other to play a coordination game. The network of player interaction is varied between a regular lattice and a random network allowing us to model contagion in small world networks. Weighting times for an equilibrium shift from the risk dominated to risk dominant equilibrium are shown to be smallest in small world networks.
E-POINTS FOR DIAGONAL GAMES I
Authors: MARCHI EZIO
Published: January 2008

In this paper we study and compute E-points in an explicit way for diagonal games of three, four, five and n-players.
EVOLUTION AND THE COMPLEXITY OF FINITE AUTOMATA
Authors: KILANI MOEZ
Published: January 2008

Prisoner's dilemma played by finite automata is reviewed again using a slightly modified measure of complexity. At a first step, an equilibrium with a large number of possible outcomes is shown to hold. At a second stage, we consider a game of repeated interaction, and show that on (limit) equilibrium only cooperative actions are played. We conclude that cooperation is the result of a (complex) long interaction.
INVESTIGATIONS ON NANOCRYSTALLINE SUPERPARAMAGNETIC PARTICLES OF CoFe2O4
Authors: PANT R. P. , KUMAR VINOD , HALDER S. K. , GUPTA S. K. , SINGH SUKHVIR
Published: January 2008

Superparamagnetic (SP) crystalline cobalt ferrite ( CoFe 2 O 4) nanoparticles are synthesized by chemical co-precipitation method. Grown nanoparticles are annealed in air at various temperatures in the range 373 K to 1173 K to understand the variation in properties in nanoregion. Physical properties are analyzed for crystalline phase, crystallite size, particle size, shape, magnetization and relaxation behavior by using various characterization techniques viz. X-ray diffractometer (XRD), transmission electron microscope (TEM), vibrating sample magnetometer (VSM) and electron paramagnetic resonance (EPR). Annealing effect on various physical properties of particles are investigated. Particles are used in the development of stable ferrofluid.
SYNTHESIS OF ALLOY METAL NANOCLUSTERS IN SILICA GLASS BY SEQUENTIAL ION IMPLANTATION
Authors: JOSEPH B. , LENKA H. P. , KUIRI P. K. , MAHAPATRA D. P. , KESAVAMOORTHY R.
Published: January 2008

High fluence low energy negative ion implantation has been used to synthesize embedded metal nanoclusters of Au , Ag and Sb in silica glass. The Au - and Ag -implanted samples showed peaks, corresponding to surface plasmon resonance (SPR) in the optical absorption (OA) spectra, confirming the formation of metallic nanoparticles in the matrix. No SPR peak was observed in case of Sb -implanted samples which is attributed to the absence of pure metallic precipitates which could be detected in the OA spectrum. Low frequency Raman scattering (LFRS) measurements also confirm this. Cross-sectional transmission electron microscopy has been used to infer about the size distribution of the nanoparticles. Sequential implantations of Au and Ag or Au and Sb have been found to result in SPR peaks at locations in between those for nanoparticles of the constituent atoms, indicating the formation of alloy nanoparticles in the system. In case of the Au + Ag system, Rutherford backscattering spectrometry has been used to infer about the composition of the nanoparticles in terms of the concentrations of the metallic constituents. A direct, one-to-one correspondence between the SPR peak position and composition has been observed.
MAGNETIC IMPURITY EFFECTS IN ZIGZAG CARBON NANOTUBES
Authors: MORADIAN ROSTAM , FATHALIAN ALI
Published: January 2008

We investigate effects of magnetic impurity doping on the Curie critical temperature (Tc) of semiconducting carbon nanotubes. Variation of Tc as a function of impurity concentration for different coupling constant (J), and spin value (S) are calculated. We found by increasing J and S, the critical temperature is increased. Also we calculated Tc in terms of band filling for different impurity concentration, exchange coupling and impurity spin magnitude.
COPOLYMER-MEDIATED FABRICATION OF VERSATILE ELECTRO-ACTIVE AND INFLAMMATION ATTENUATING SUBSTRATES FOR BIOLOGICAL INTERROGATION
Authors: CHOW EDWARD K. , CHU BENJAMIN , CHENG GENHONG , TAI YU-CHONG , PIERSTORFF ERIK , HO DEAN
Published: January 2008

Serving as platforms for both cellular interrogation as well as biomembrane mimicry, biotic–abiotic functionalized materials, such as block copolymeric membranes, offer the opportunity for tailored biology, where specific embedded functionalities can be rapidly engineered, on demand, without the need for genetic processing. These versatile materials enable rapid, thin film deposition of a plethora of biologically-relevant materials at the air–water interface given their amphiphilic properties, meaning that they possess alternating hydrophilic and hydrophobic components. This property confers to these materials the ability to be transferred to a wide range of substrates and materials, further enhancing their interfacial versatility. In addition, their biologically-inert, and tunable, thickness-dependent insulating properties serve as ideal bio-active substrates while maintaining the functionality of the integrated molecule (e.g., protein, effector molecule, etc.). Here, we report the application of a polyethyleneoxide–polymethylmethacrylate (PEO–PMMA) diblock and polymethyloxazoline–polydimethylsiloxane–polymethyloxazoline (PMOXA–PDMS–PMOXA) triblock copolymers as molecular anchors for tethering a broad spectrum of materials. These include carbon nanotubes for the fabrication of bioelectrodes to measure cytochrome c-mediated oxidation-reduction, as well as the anti-inflammatory molecule, dexamethasone, for the suppression of lipopolysaccharide (LPS)-induced inflammation in murine macrophages. As such, this work demonstrates the versatility, and broad applicability and impact of this platform approach towards the fabrication of multifunctional arrays of biologically-active surfaces for experimentation ranging from bio-electroactivity to studies of cellular immunity.
TUNABLE ELECTRIC CONDUCTIVITIES OF Au-DOPED BORON NITRIDE NANOTUBES
Authors: CHEN Y. J. , FU L. , CHEN Y. , ZOU J. , LI J. , DUAN W. H.
Published: January 2008

Tunable electronic properties of nanotubes are an essential requirement for building nanotube circuits and devices. We have produced BN nanotube films with controlled electric conductivities by Au doping. The Au -doped BN nanotube films have been found to exhibit from semiconducting to metallic behavior under different Au contents. Both experimental and computing simulation studies reveal that the conductivities of the doped film are improved by the incorporation of Au atoms into nanotube walls. The doped BN nanotubes and films are expected to have potential applications in catalysts, sensors and nanoelectronics.
SPIN-COHERENT TRANSPORT IN MESOSCOPIC INTERFERENCE DEVICE
Authors: ZEIN WALID A. , PHILLIPS ADEL H. , OMAR OMAR A.
Published: January 2008

We investigate the quantum size effect in the phase coherent mesoscopic ring. A quantum dot is embedded in one arm and it is connected to one lead via tunnel barrier. Both Aharonov–Casher and Aharonov–Bohm effects are studied. A spin-dependent conductance has been deduced and it depends on the intrinsic parameters. Our results show that the strength of spin-orbit coupling depends on the size of the present device. This investigation is valuable for fabricating such spintronics devices.
The Neoproterozoic Quatipuru ophiolite and the Araguaia fold belt, central-northern Brazil, compared with correlatives in NW Africa
Authors: Paixão M. A. P. , Nilson A. A. , Dantas E. L.
Published: January 2008

The Araguaia Belt, the northern branch of Neoproterozoic Tocantins tectonic province, developed during West Gondwana amalgamation as a result of collision between the Amazon and West African and/or São Francisco/Congo cratons. The external zone of the belt consists of ophiolitic slices and fragments, sedimentary rocks derived from magmatic arc sources, volcanic rocks, and part of a passive continental margin with low-grade metamorphic rocks, while the internal zone corresponds to a pile of low- to medium-grade metasedimentary rocks. The largest and best preserved ophiolitic bodies occur in the southern part of the belt, where the Quatipuru and Morro do Agostinho ophiolites are composed predominantly of mantle peridotites (mainly residual harzburgite) representing the base of the Moho transition zone. They contain chromitite pods, dunitic lensoid bodies and a suite of mafic–ultramafic dykes and/or sills resulting from partial melting, magma impregnation and diapiric up-rise. A Sm–Nd isochron age of 757±49 Ma indicates oceanic crust formation during the Early Neoproterozoic. NW African correlatives of the Araguaia Belt, the Mauritanide–Bassaride–Rokelide belt, show similarities with respect to lithostratigraphic units, the ages of basement and supracrustal rocks, the presence of Neoproterozoic ophiolitic slices and fragments, suture zones characterized by high gravity anomalies and centrifugal tectonic vergence. We conclude that these belts were probably formed around the same Neoproterozoic ocean or several small coeval oceans.
Late Neoproterozoic and Early Cambrian palaeogeography: models and problems
Authors: Pisarevsky S. A. , Murphy J. B. , Cawood P. A. , Collins A. S.
Published: January 2008

We present two alternative sets of global palaeogeographical reconstructions for the time interval 615–530 Ma using competing high and low-latitude palaeomagnetic data subsets for Laurentia in conjunction with geological data. Both models demonstrate a genetic relationship between the collisional events associated with the assembly of Gondwana and the extensional events related to the opening of the Tornquist Sea, the eastern Iapetus Ocean (600–550 Ma), and the western Iapetus Ocean (after 550 Ma), forming a three-arm rift between Laurentia, Baltica, and Gondwana. The extensional events are probably plume-related, which is indicated in the reconstructions by voluminous mafic magmatism along the margins of palaeo-continents. The low-latitude model requires a single plume event, whereas the high-latitude model needs at least three discrete plumes. Coeval collisions of large continental masses during the assembly of Gondwana, as well as slab pull from subduction zones associated with those collisions, could have caused upper plate extension resulting in the rifted arm that developed into the eastern Iapetus Ocean and Tornquist Sea but retarded development of the western Iapetus Ocean. As a result, the eastern Iapetus Ocean and the Tornquist Sea opened before the western Iapetus Ocean.
Proterozoic evolution of the Nigeria–Boborema province
Authors: Dada S. S.
Published: January 2008

Structural, geochronological, geochemical and mineralization patterns in the Nigeria–Borborema province of western Africa and NE Brazil reflect a complex Proterozoic evolution culminating in the Neoproterozoic Pan-African/Brasiliano orogenesis (
c
. 600 Ma). Reworking of the Archaean–early Proterozoic crust produced heterogeneous deformation exemplified by prevalent shears, migmatization, granitization and intrusion of large volumes of granitoids typical of a Himalayan-type thickened crust resulting from continent–continent collision. Dominant north–south to east–west structures, with prominent penetrative fabric and mylonitised wrench faults, refolded, transpressed, or even obliterated older structural trends, which are preserved in nappes of the central Sahara region (NW Africa to Nigeria) and in NE Brazil. Anatexis and recrystallisation were coeval with emplacement of Pan-African granitoids throughout this mobile belt. Bulk chemical modification, especially affecting magmatophile elements and REE patterns, attest to chemical exchange between Archaean basement and Pan-African/Brasiliano rocks. Older crust is present in both regions, including early (3.6–3.5 Ga), mid (3.1 Ga) and late (2.7–2.5 Ga) Archaean, as well as large areas of Palaeoproterozoic rocks reworked by the
c
. 600 Ma tectono-thermal events. The extent and interpretation of Eburnian/Transamazonian (2.1–2.0 Ga) events have not yet been resolved due to inadequate structural and isotopic data. Litho-structural control of Au, Sn, Nb and Ta mineralization relates to main or late-stage Pan-African deformation.
Fever response to intravenous prostaglandin E2 is mediated by the brain but does not require afferent vagal signaling
Authors: Ootsuka Youichirou , Blessing William W. , Steiner Alexandre A. , Romanovsky Andrej A.
Published: January 2008

PGE2 produced in the periphery triggers the early phase of the febrile response to infection and may contribute to later phases. It can be hypothesized that peripherally synthesized PGE2 transmits febrigenic signals to the brain via vagal afferent nerves. Before testing this hypothesis, we investigated whether the febrigenic effect of intravenously administered PGE2 is mediated by the brain and is not the result of a direct action of PGE2 on thermoeffectors. In anesthetized rats, intravenously injected PGE2 (100 μg/kg) caused an increase in sympathetic discharge to interscapular brown adipose tissue (iBAT), as well as increases in iBAT thermogenesis, end-expired CO2, and colonic temperature (Tc). All these effects were prevented by inhibition of neuronal function in the raphe region of the medulla oblongata using an intra-raphe microinjection of muscimol. We then asked whether the brain-mediated PGE2 fever requires vagal signaling and answered this question by conducting two independent studies in rats. In a study in anesthetized rats, acute bilateral cervical vagotomy did not affect the effects of intravenously injected PGE2 (100 μg/kg) on iBAT sympathetic discharge and Tc. In a study in conscious rats, administration of PGE2 (280 μg/kg) via an indwelling jugular catheter caused tail skin vasoconstriction, tended to increase oxygen consumption, and increased Tc; none of these responses was affected by total truncal subdiaphragmatic vagotomy performed 2 wk before the experiment. We conclude that the febrile response to circulating PGE2 is mediated by the brain, but that it does not require vagal afferent signaling.
A novel minimal model to describe NEFA kinetics following an intravenous glucose challenge
Authors: Boston Ray C. , Moate Peter J.
Published: January 2008

Dynamics of nonesterified fatty acid (NEFA) metabolism in humans requires quantification if we are to understand the etiology of such diseases as type 1 and 2 diabetes, as well as metabolic syndrome and obesity, or if we are to elucidate the mechanism of action of various interventions. We present a new compartmental model that employs the pattern of plasma glucose concentrations in healthy young adults to predict dynamic changes that occur in plasma NEFA concentrations during either a glucose-only intravenous glucose tolerance test, or an insulin-modified intravenous tolerance test, or a modified protocol during which variable-rate glucose infusions were administered to prevent plasma glucose from declining below 100 mg/dl. The model described all of the major features of NEFA response to an intravenous glucose tolerance test, including an initial latency phase, a phase during which plasma NEFA concentrations plummet to a nadir, and a rebound phase during which plasma NEFA concentrations may rise to a plateau concentration, which may be substantially higher than the initial basal NEFA concentration. This model is consistent with physiological processes and provides seven adjustable parameters that can be used to quantify NEFA production (lipolysis) and utilization (oxidation). When tested on data from the scientific literature, the range in estimated rate of lipolysis was 24–36 μmol·l−1·min−1and for NEFA oxidation rate was 25–54 μmol·l−1·min−1. All model parameters were well identified and had coefficients of variation < 15% of their estimated values. It is concluded that this model is suitable to describe NEFA kinetics in human subjects.
Interactions between subtotal nephrectomy and salt: effects on blood pressure and renal function in pregnant and nonpregnant ewes
Authors: Gibson Karen J. , Boyce Amanda C. , Thomson Clare L. , Chinchen Sarah , Lumbers Eugenie R.
Published: January 2008

The effects of high salt intake on blood pressure and renal function were studied in nine subtotally nephrectomized pregnant ewes (STNxP) and seven intact pregnant ewes (IntP) in late gestation and in eight subtotally nephrectomized nonpregnant ewes (STNxNP) and seven intact nonpregnant ewes (IntNP). STNxP had higher mean arterial pressures ( P < 0.02) and plasma creatinine levels ( P < 0.001) than IntP. High salt (0.17 M NaCl as drinking water for 5 days) did not change blood pressure in either STNxP or IntP. STNxNP had higher mean arterial pressures ( P = 0.03) and plasma creatinine levels ( P < 0.001) than IntNP. In STNxNP, blood pressure increased with high salt intake and there was a positive relationship between diastolic pressure and sodium balance ( r = 0.497, P = 0.05). This relationship was not present in IntNP, STNxP, or IntP. Because high salt intake did not cause an increase in blood pressure in STNxP, it is concluded that they were protected by pregnancy from further rises in blood pressure. The observed increase in glomerular filtration rate ( P < 0.03) and depression of fractional proximal sodium reabsorption ( P = 0.003) that occurred in STNxP, but not in STNxNP, in response to high salt may have contributed to this protection. As well, the increased production of vasorelaxants in pregnancy may selectively protect against the occurrence of salt-sensitive hypertension in pregnancy.
Renal nerves and nNOS: roles in natriuresis of acute isovolumetric sodium loading in conscious rats
Authors: Kompanowska-Jezierska Elżbieta , Wolff Helle , Kuczeriszka Marta , Gramsbergen Jan B. , Walkowska Agnieszka , Johns Edward J. , Bie Peter
Published: January 2008

It was hypothesized that renal sympathetic nerve activity (RSNA) and neuronal nitric oxide synthase (nNOS) are involved in the acute inhibition of renin secretion and the natriuresis following slow NaCl loading (NaLoad) and that RSNA participates in the regulation of arterial blood pressure (MABP). This was tested by NaLoad after chronic renal denervation with and without inhibition of nNOS by S-methyl-thiocitrulline (SMTC). In addition, the acute effects of renal denervation on MABP and sodium balance were assessed. Rats were investigated in the conscious, catheterized state, in metabolic cages, and acutely during anesthesia. NaLoad was performed over 2 h by intravenous infusion of hypertonic solution (50 μmol·min−1·kg body mass−1) at constant body volume conditions. SMTC was coinfused in amounts (20 μg·min−1·kg−1) reported to selectively inhibit nNOS. Directly measured MABPs of acutely and chronically denervated rats were less than control (15% and 9%, respectively, P < 0.005). Plasma renin concentration (PRC) was reduced by renal denervation (14.5 ± 0.2 vs. 19.3 ± 1.3 mIU/l, P < 0.005) and by nNOS inhibition (12.4 ± 2.3 vs. 19.6 ± 1.6 mlU/l, P < 0.005). NaLoad reduced PRC ( P < 0.05) and elevated MABP modestly ( P < 0.05) and increased sodium excretion six-fold, irrespective of renal denervation and SMTC. The metabolic data demonstrated that renal denervation lowered sodium balance during the first days after denervation ( P < 0.001). These data show that renal denervation decreases MABP and renin secretion. However, neither renal denervation nor nNOS inhibition affects either the renin down-regulation or the natriuretic response to acute sodium loading. Acute sodium-driven renin regulation seems independent of RSNA and nNOS under the present conditions.
The Spatial Scale of Attention Strongly Modulates Saccade Latencies
Authors: Harwood Mark R. , Madelain Laurent , Krauzlis Richard J. , Wallman Josh
Published: January 2008

We have previously shown that when a stimulus consisting of two concentric rings moves, saccade latencies are much longer (by 150 ms) when attention is directed to the larger ring than to the smaller ring. Here, we investigated whether this effect can be explained by a deferral of the “cost” of making a saccade while the target remains inside the attentional field, or by purely visual factors (eccentricity or contrast). We found 1) latencies were shorter when attention was directed to small features irrespective of retinal eccentricity; 2) saccade latency distributions were systematically determined by the ratio between the amplitude of the stimulus step and the diameter of the attended ring: stimulus steps that were larger than the attended ring resulted in short latencies, whereas steps smaller than the attended ring resulted in proportionally longer and more variable latencies; 3) this effect was not seen in manual reaction times to the same target movement; and 4) suprathreshold changes in the contrast of targets, mimicking possible attentional effects on perceived contrast and saliency, had little effect on latency. We argue that the spatial scale of attention determines the urgency of saccade motor preparation processes by changing the rate and rate variability of the underlying decision signal, to defer the cost of saccades that result in little visual benefit.
Serotonin Activates Presynaptic and Postsynaptic Receptors in Rat Globus Pallidus
Authors: Hashimoto Kenji , Kita Hitoshi
Published: January 2008

Although recent histological, behavioral, and clinical studies suggest that serotonin (5-HT) plays significant roles in the control of pallidal activity, only little is known about the physiological action of 5-HT in the pallidum. Our recent unit recording study in monkeys suggested that 5-HT provides both presynaptic and postsynaptic modulations of pallidal neurons. The present study using rat brain slice preparations further explored these presynaptic and postsynaptic actions of 5-HT. Bath application of 5-HT or the 5-HT1A/1B/1D/5/7receptor (R) agonist 5-carboxamidotryptamine maleate (5-CT) depolarized some and hyperpolarized other pallidal neurons. Pretreatments of slices with blockers of the hyperpolarization–cyclic nucleotide-activated current or with the 5-HT2/7R–selective antagonist mesulergine occluded 5-CT–induced depolarization. The 5-HT1AR–selective blocker N-[2[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]- N-2-pyridinylcyclohex- anecarboxamide maleate occluded the 5-CT–induced hyperpolarization. These results suggested involvement of 5-HT7R and 5-HT1AR in the postsynaptic depolarization and hyperpolarization, respectively. 5-CT presynaptically suppressed both internal capsule stimulation–induced excitatory postsynaptic currents (EPSCs) and striatal stimulation–induced inhibitory postsynaptic currents (IPSCs). The potencies of 5-CT on the presynaptic effects were 20- to 25-fold higher than on postsynaptic effects, suggesting that 5-HT mainly modulates presynaptic sites in the globus pallidus. Experiments with several antagonists suggested involvement of 5-HT1B/DR in the presynaptic suppression of EPSCs. However, the receptor type involved in the presynaptic suppression of IPSCs was inconclusive. The present results provided evidence that 5-HT exerts significant control over the synaptic inputs and the autonomous activity of pallidal neurons.