bluuebunny/crossref_metadata_2025 huggingface dataset:
Obligatory Role of Inducible Nitric Oxide Synthase in Ischemic Preconditioning
Authors: Cho Sunghee , Park Eun-Mi , Zhou Ping , Frys Kelly , Ross M Elizabeth , Iadecola Costantino
Published: February 2005

Sublethal insults can induce a transient tolerance toward subsequent lethal ischemia, a phenomenon termed ischemic preconditioning (IPC). In the myocardium, nitric oxide derived from ‘inducible’ nitric oxide synthase (iNOS or NOS II) plays a critical role in the expression of IPC produced by sublethal ischemia. Here, we investigated whether iNOS is involved in IPC in brain. Ischemic preconditioning was produced in mice by three episodes of 1-min bilateral common carotid artery (BCCA) occlusion, each followed by 5 mins of reperfusion. After 24 h, mice underwent middle cerebral artery (MCA) occlusion for 20 mins. Intraischemic cerebral blood flow was monitored during both in BCCA and MCA occlusion (MCAO) by laser-Doppler flowmetry. Mice were killed 3 days after MCAO, and infarct volume was determined in thionine-stained sections. Infarct volume was significantly reduced 24 h after IPC (70%; P<0.05). Treatment with the iNOS inhibitor aminoguanidine (400 mg/kg), abolished the IPC-induced protection. Furthermore, IPC failed to induce ischemic tolerance in iNOS-null mice. In wild-type mice, IPC increased the resistance to Ca2+-mediated depolarization in isolated brain mitochondria. However, in iNOS-null mice IPC failed to induce such resistance. We conclude that iNOS is required for the full expression of IPC and that such effect is coupled to an increased resistance of mitochondria to injury. Thus, iNOS-derived nitric oxide, in addition to its deleterious effects on the late stages of ischemic brain damage, can also be beneficial by promoting ischemic tolerance through signaling, ultimately resulting in mitochondrial protection.
Bio-hydrogen: microbes have their own agenda
Authors: Cammack R.
Published: February 2005

The international hydrogenase community stages a meeting every 3–4 years, and this time it was held in the University of Reading. Each congress has revealed new aspects of the complex nature of hydrogenases: their structure, molecular mechanisms and biosynthesis are all yielding up their secrets. This following introduction provides background information, and the highlights of the meeting are presented in the papers that follow.
Electrocatalytic proton reduction by dithiolate-bridged diiron carbonyl complexes: a connection to the H-cluster?
Authors: Borg S.J. , Bondin M.I. , Best S.P. , Razavet M. , Liu X. , Pickett C.J.
Published: February 2005

Spectroscopic and electrochemical investigation of electrocatalytic proton reduction by Fe2(μ-pdt)(CO)6, 1, have been interpreted in terms of a reaction scheme involving sequential electron–proton reactions to give a two-electron, two-proton product that undergoes rate-limiting dihydrogen elimination. Further reduction, at slightly higher negative potentials, gives a more reactive product and this process dominates reactions conducted at higher acid concentrations. Inhibition of the electrocatalytic reaction by CO is due to the more efficient loss of catalyst and this is best modelled by a reaction that is second order in terms of 1−. During electrocatalytic proton reduction a new species is observed, which features a bridging CO group and the wavenumbers of the ν(CO) modes of the terminally bound carbonyl groups are similar to those of the carbonyl groups bound to the oxidized form of the H-cluster.
Eukaryotic Fe-hydrogenases – old eukaryotic heritage or adaptive acquisitions?
Authors: Hackstein J.H.P.
Published: February 2005

All eukaryotes seem to possess proteins that most probably evolved from an ancestral Fe-hydrogenase. These proteins, known as NARF or Nar, do not produce hydrogen. Notably, a small group of rather unrelated unicellular anaerobes and a few algae possess Fe-hydrogenases, which produce hydrogen. In most, but not all organisms, hydrogen production occurs in membrane-bounded organelles, i.e. hydrogenosomes or plastids. Whereas plastids are monophyletic, hydrogenosomes evolved repeatedly and independently from mitochondria or mitochondria-like organelles. A systematic analysis of the various hydrogenosomes and their hydrogenases will contribute to an understanding of the evolution of the eukaryotic cell, and provide clues to the evolutionary origin(s) of the Fe-hydrogenase.
Construction of a [NiFe]-hydrogenase deletion mutant of Desulfovibrio vulgaris Hildenborough
Authors: Goenka A. , Voordouw J.K. , Lubitz W. , Gärtner W. , Voordouw G.
Published: February 2005

A mutant of Desulfovibrio vulgaris Hildenborough lacking a gene for [NiFe] hydrogenase was generated. Growth studies, performed for the mutant in comparison with the wild-type, showed no strong differences during the exponential growth phase. However, the mutant cells died more rapidly in the stationary growth phase.
Uptake hydrogenase in cyanobacteria: novel input from non-heterocystous strains
Authors: Tamagnini P. , Leitão E. , Oxelfelt F.
Published: February 2005

Most of the research to date on cyanobacterial uptake hydrogenases has been performed on filamentous heterocystous strains. However, recent results on the hup gene cluster organization and its transcriptional regulation in non-heterocystous strains has contributed to the widening of knowledge in this field. In the present study, we outline the recent findings on uptake hydrogenases from non-heterocystous cyanobacteria, comparing it with the presently available data from heterocystous strains, and draw attention to potential areas for future research.
NifU and NifS are required for the maturation of nitrogenase and cannot replace the function of isc-gene products in Azotobacter vinelandii
Authors: Johnson D.C. , Dos Santos P.C. , Dean D.R.
Published: February 2005

In recent years, it has become evident that [Fe-S] proteins, such as hydrogenase, nitrogenase and aconitase, require a complex machinery to assemble and insert their associated [Fe-S] clusters. So far, three different types of [Fe-S] cluster biosynthetic systems have been identified and these have been designated nif, isc and suf. In the present work, we show that the nif-specific [Fe-S] cluster biosynthetic system from Azotobacter vinelandii, which is required for nitrogenase maturation, cannot functionally replace the isc [Fe-S] cluster system used for the maturation of other [Fe-S] proteins, such as aconitase. The results indicate that, in certain cases, [Fe-S] cluster biosynthetic machineries have evolved to perform only specialized functions.
Molybdate-dependent expression of the periplasmic nitrate reductase in Bradyrhizobium japonicum
Authors: Bonnard N. , Tresierra-Ayala A. , Bedmar E.J. , Delgado M.J.
Published: February 2005

The napEDABC genes of Bradyrhizobium japonicum encode the periplasmic nitrate reductase, an Mo-containing enzyme which catalyses the reduction of nitrate to nitrite when oxygen concentrations are limiting. In this bacterium, another set of genes, modABC, code for a high affinity ABC-type Mo transport system. A B. japonicum modA mutant has been obtained that is not capable of growing anaerobically with nitrate and lacks nitrate reductase activity. Under nitrate respiring conditions, when Mo concentrations are limiting, the B. japonicum modA mutant lacked both the 90 kDa protein corresponding to the NapA component of the periplasmic nitrate reductase, and the membrane-bound 25 kDa c-type cytochrome NapC. Regulatory studies using a napE–lacZ fusion indicated that napE expression was highly reduced in the modA mutant background when the cells were incubated anaerobically with nitrate under Mo-deficient conditions.
Microaerobic denitrification in Neisseria meningitidis
Authors: Rock J.D. , Moir J.W.B.
Published: February 2005

The major aetiological agent of human bacterial meningitis is Neisseria meningitidis. During the course of disease and host colonization, the bacterium has to withstand limited oxygen availability. Nitrogen oxide and nitrogen oxyanions are thought to be present, which may constitute an alternative sink for electrons from the N. meningitidis respiratory chain. A partial denitrification pathway is encoded by the aniA nitrite reductase gene and the norB nitric oxide reductase gene. Analysis of the completed genome sequences of two N. meningitidis strains is used to generate a model for the membrane-associated respiratory chain of this organism. Analysis of aniA expression indicates it to be controlled primarily by oxygen and secondarily by nitrite. The ability of N. meningitidis to denitrify relies on microaerobic growth conditions. Here we show that under microaerobic conditions nitrite supplements oxygen as an alternative respiratory substrate.
N-oxide sensing in Pseudomonas aeruginosa: expression and preliminary characterization of DNR, an FNR–CRP type transcriptional regulator
Authors: Rinaldo S. , Giardina G. , Brunori M. , Cutruzzolà F.
Published: February 2005

In denitrifying bacteria, the concentration of NO is maintained low by a tight control of the expression and activity of nitrite and NO reductases. Regulation involves redox-linked transcription factors, such as those belonging to the CRP-FNR (cAMP receptor protein–fumarate and nitrate reductase regulator) superfamily, which act as oxygen and N-oxide sensors. Given that few members of this superfamily have been characterized in detail, we have cloned, expressed and purified the dissimilative nitrate respiration regulator from Pseudomonas aeruginosa. To gain insights on the structural properties of the dissimilative nitrate respiration regulator, we have also determined the aggregation state of the purified protein and its ability to bind hydrophobic compounds such as 8-anilino-1-naphthalenesulphonic acid.
The concentrative nucleoside transporter family (SLC28): new roles beyond salvage?
Authors: Aymerich I. , Duflot S. , Fernández-Veledo S. , Guillén-Gómez E. , Huber-Ruano I. , Casado F.J. , Pastor-Anglada M.
Published: February 2005

The concentrative nucleoside transporter (CNT) family (SLC28) has three members: SLC28A1 (CNT1), SLC28A2 (CNT2) and SLC28A3 (CNT3). The CNT1 and CNT2 transporters are co-expressed in liver parenchymal cells and macrophages, two suitable models in which to study cell cycle progression. Despite initial observations suggesting that these transporter proteins might contribute to nucleoside salvage during proliferation, their subcellular localization and regulatory properties suggest alternative roles in cell physiology. In particular, CNT2 is a suitable candidate for modulation of purinergic responses, since it is under the control of the adenosine 1 receptor. Increasing evidence also suggests a role for CNT2 in energy metabolism, since its activation relies on the opening of ATP-sensitive K+ channels. Animal and cell models genetically modified to alter nucleoside transporter expression levels may help to elucidate the particular roles of CNT proteins in cell physiology.
Sucrose-induced translational repression of plant bZIP-type transcription factors
Authors: Wiese A. , Elzinga N. , Wobbes B. , Smeekens S.
Published: February 2005

Sugars as signalling molecules exert control on the transcription of many plant genes. Sugar signals also alter mRNA and protein stability. Increased sucrose concentrations specifically repress translation of the S-class basic region leucine zipper (bZIP) type transcription factor AtbZIP11/ATB2. This sucrose-induced repression of translation (SIRT) depends on translation of a highly conserved upstream open reading frame (uORF) in the 5′ UTR of the gene. This conserved uORF is exclusively encoded in 5′ UTRs of several plant S-class bZIP transcription factors. Arabidopsis homologues of ATB2/AtbZIP11, which harbour the conserved uORF, also show SIRT. Therefore, SIRT emerges as a general sucrose translational control mechanism of a group of transcription factors. SIRT might be part of a sucrose-specific signalling pathway, controlling expression of plant bZIP transcription factor genes.
Allometry, root/shoot ratio and root architecture in understory saplings of deciduous dicotyledonous trees in central Japan
Authors: CAO KUN‐FANG , OHKUBO TATSUHIRO
Published: February 2005

Plant allometry that is related to plant architecture and biomass allocation strongly influences a plant's ability to grow in shaded forest understory. Some allometric traits can change with plant size. The present study compared crown and trunk allometries, root/shoot biomass allometry, and root architecture among understory saplings (0.25–5 m height, except for two trees> 5 < 7 m) of seven deciduous dicotyledonous species in central Japan. Associations of the crown and trunk allometries with several plant morphological attributes were analyzed. Branch morphology (plagiotropy vs orthotropy) and life size were correlated with sapling crown and trunk allometries. Both large leaves and orthotropic branches were associated with a narrow small crown and slender trunk. The root/shoot ratio decreased rapidly with increasing plant height for saplings shorter than about 1.5 m. Less shade‐tolerant species tended to have smaller root/shoot ratios for saplings taller than 1.5 m. With an increase in plant height, the branch/trunk biomass ratio decreased for saplings with plagiotropic branches but increased for saplings with orthotropic branches. Four subcanopy species (Acer distylum, Carpinus cordata, Fraxinus lanuginosa and Acanthopanax sciadophylloides) had superficial root systems; a common understory species (Sapium japonica) had a deep tap root system; and a canopy species (Magnolia obovata) and a subcanopy species (Acer tenuifolium) had heart root systems of intermediate depth. The root depth was not related to shade tolerance. Among species of the same height, the difference in fine root length can be 30‐fold.
Control by Signaling Modulators of the Sorting of Canalicular Transporters in Rat Hepatocyte Couplets: Role of the Cytoskeleton
Authors: Roma Marcelo G. , Milkiewicz Piotr , Elias Elwyn , Coleman Roger
Published: February 2005

Hormonal control of the restoration of hepatocanalicular polarity in short–term cultured hepatocyte couplets was analyzed. One hour following isolation, couplets were unable to accumulate the fluorescent bile acid analogue, cholyl–lysyl–fluorescein (CLF), and showed a nonpolarized distribution of F–actin and mrp2 over the cell body. A progressive, time–dependent restoration of couplet–polarized function and morphology was reached after 4 hours of culture. Both dibutyryl cyclic adenosine monophosphate (DBcAMP) and the Ca2+–elevating compound, thapsigargin, accelerated restoration of normal couplet morphology and function. The DBcAMP–mediated stimulus was inhibited by the Ca2+ chelator, 1,2–bis–(o–aminophenoxy)–ethene–N,N,N′,N′–tetra–acetate tetra–(acetomethyl)ester (BAPTA/AM), but not by the protein kinase A (PKA) inhibitors, KT5720 or H89, suggesting that Ca2+ elevation rather than PKA activation is involved. N–(6–aminohexyl–5–chloro–1–napththalenesulfonamide (W–7), a calmodulin inhibitor, and the protein kinase C (PKC) activator, phorbol dibutyrate, inhibited both the basal and the DBcAMP–stimulated recovery of functional polarity, whereas staurosporine and Gö 6976, 2 PKC inhibitors, accelerated the basal recovery of polarized function. Disruption of the microtubule cytoskeleton by colchicine induced only minor changes under basal, but not under DBcAMP–stimulated, conditions. The Golgi complex disruptor, brefeldin A, significantly delayed, and the microfilament–disrupting agent, cytochalasin D, fully blocked, both processes. However, DBcAMP stimulated trafficking of vesicles containing CLF to the pericanalicular region under the last condition. Our results indicate that restoration of couplet polarity following isolation occurs via a Ca2+–calmodulin–mediated mechanism, which depends on microfilament, but not on microtubule integrity. A second pathway is activated by DBcAMP activation via Ca2+–calmodulin formation, whose requirements with respect to cytoskeletal components are opposite. PKC has a negative regulatory role in both pathways.
Tissue Inhibitor of Metalloproteinases–1 Promotes Liver Fibrosis Development in A Transgenic Mouse Model
Authors: Yoshiji Hitoshi , Kuriyama Shigeki , Miyamoto Yoji , Thorgeirsson Unnur P. , Gomez Daniel E. , Kawata Mitsuhiro , Yoshii Junichi , Ikenaka Yasuhide , Noguchi Ryuichi , Tsujinoue Hirohisa , Nakatani Toshiya , Thorgeirsson Snorri S. , Fukui Hiroshi
Published: February 2005

Tissue inhibitor of metalloproteinases–1 (TIMP–1) has been shown to be increased in liver fibrosis development both in murine experimental models and human samples. However, the direct role of TIMP–1 during liver fibrosis development has not been defined. To address this issue, we developed transgenic mice overexpressing human TIMP–1 (hTIMP–1) in the liver under control of the albumin promoter/enhancer. A model of CCl4–induced hepatic fibrosis was used to assess the extent of fibrosis development in TIMP–1 transgenic (TIMP–Tg) mice and control hybrid (Cont) mice. Without any treatment, overexpression of TIMP–1 itself did not induce liver fibrosis. There were no significant differences of pro–(α1)–collagen–I, (α2)–collagen–IV, and α–smooth muscle actin (α–SMA) mRNA expression in the liver between TIMP–Tg and Cont–mice, suggesting that overexpression of TIMP–1 itself did not cause hepatic stellate cell (HSC) activation. After 4–week treatment with CCl4, however, densitometric analysis revealed that TIMP–Tg–mice had a seven–fold increase in liver fibrosis compared with the Cont–mice. The hepatic hydroxyproline content and serum hyaluronic acid were also significantly increased in TIMP–Tg–mice, whereas CCl4–induced liver dysfunction was not altered. An active form of matrix metalloproteinases–2 (MMP–2) level in the liver of TIMP–Tg–mice was decreased relative to that in Cont–mice because of the transgenic TIMP–1. Immunohistochemical analysis revealed that collagen–I and collagen–IV accumulation was markedly increased in the liver of CCl4–treated TIMP–Tg–mice with a pattern similar to that of α–SMA positive cells. These results suggest that TIMP–1 does not by itself result in liver fibrosis, but strongly promotes liver fibrosis development.
A comparison between different semiclassical approximations for optical response functions in nonpolar liquid solutions
Authors: Shi Qiang , Geva Eitan
Published: February 2005

The temporal behavior of optical response functions (ORFs) reflects the quantum dynamics of an electronic superposition state, and as such lacks a well-defined classical limit. In this paper, we consider the importance of accounting for the quantum nature of the dynamics when calculating ORFs of different types. To this end, we calculated the ORFs associated with the linear absorption spectrum and the nonlinear two-pulse photon-echo experiment, via the following approaches: (1) the semiclassical forward-backward approach; (2) an approach based on linearizing the path-integral forward-backward action in terms of the difference between the forward and backward paths; (3) an approach based on ground state nuclear dynamics. The calculations were performed on a model that consists of a two-state chromophore solvated in a nonpolar liquid. The different methods were found to yield very similar results for the absorption spectrum and “diagonal” two-pulse photon echo (i.e., the homodyne-detected signal at time t=t0 after the second pulse, where t0 is the time interval between the two pulses). The different approximations yielded somewhat different results in the case of the time-integrated photon-echo signal. The reasons for the similarity between the predictions of different approximations are also discussed
Contracted basis sets for density functional calculations: Segmented versus general contraction
Authors: Jensen Frank
Published: February 2005

The differences between segmented and general contracted basis sets of double and triple zeta quality are analyzed for first and second row elements. Based on coverage of the exponent space and the performance for molecular properties, it is shown that a segmented contraction requires duplication of one primitive function compared to a general contraction for double zeta type basis sets. For triple zeta basis sets, segmentation necessitates either addition of one primitive function and expanding to a quadruple valence space, or addition of two primitive functions. For molecular properties depending on the valence orbitals, such as atomization energies, equilibrium distances, and vibrational frequencies, some of the inner functions describing the core orbitals can be removed without significantly affecting the accuracy. Several of the popular basis sets in common use correspond to such core-pruned basis sets.
Remarkable interplay of electron correlation and relativity in the photodetachment spectrum of PtCl62−
Authors: Pernpointner Markus , Breidbach Jörg , Cederbaum Lorenz S.
Published: February 2005

In this work we calculate the photoelectron spectrum of the PtCl62− dianion by application of the recently developed third-order Dirac–Hartree–Fock implementation of the one-particle propagator technique allowing for a consistent treatment of spin-orbit and scalar relativistic effects together with electron correlation. For PtCl62− a gas phase photoelectron spectrum is available showing clearly discernible structures not reproducible by a nonrelativistic or purely scalar-relativistic computation. A population analysis of the valence orbitals allows for an assignment of the photoelectron peaks and reveals the strong influence of relativity in combination with electron correlation.
Integrable couplings of vector AKNS soliton equations
Authors: Ma Wen-Xiu
Published: February 2005

By enlarging the associated matrix spectral problems, two specific classes of multicomponent integrable couplings of the physically important vector AKNS soliton equations are constructed, which can be linked to each other by a Bäcklund transformation. The resulting two hierarchies of integrable couplings possess the enlarged zero curvature representations and recursion structures, and thus each system in the two hierarchies has infinitely many commuting symmetries.
High temperature structures and orientational disorder in compressed solid nitrogen
Authors: Tassini Leonardo , Gorelli Federico , Ulivi Lorenzo
Published: February 2005

An experimental study of the phase transitions at high temperature in compressed solid nitrogen has been performed using Raman spectroscopy. Knowledge of the equilibrium phase diagram in the region of the ordered ϵ phase and the two disordered δ and δloc phases, at pressures between 10 and 20GPa, has been extended up to 500K. The Raman scattering line shape and line width of the active vibrons has been measured accurately, along isobaric scans, across the phase transitions. Analysis of the width and of its different behavior with increasing temperature in the three phases led to more precise conclusions about the nature of the disorder in the different phases. Observation of an evident shoulder in the ν2 band of the δloc phase suggests the possibility that sites of two different symmetries may be occupied by the disk molecules in this structure.
On the difference in scattering behavior of cyclic and linear polymers in bulk
Authors: Gagliardi S. , Arrighi V. , Ferguson R. , Dagger A. C. , Semlyen J. A. , Higgins J. S.
Published: February 2005

It has been suggested that, due to topological constraints, rings in the melt may assume a more compact shape than Gaussian chains. In this paper, we exploit the availability of narrow fractions of perdeuterated linear and cyclic polydimethylsiloxane (PDMS) and, through the analysis of the small angle neutron scattering (SANS) profiles, demonstrate the difference in scattering properties of linear and cyclic PDMS molecules. As expected for Gaussian chains, for the H/D linear PDMS samples, log-log plots of the scattered intensity versus scattering vector Q display a Q(−2) dependence. However, for H/D cyclic blends, the scaling exponent is higher than 2, as predicted by computer simulations reported in the literature. We show that cyclic molecules in bulk display the characteristic maximum in plots of scattered intensity versus Q(−2) that is expected on the basis of Monte Carlo calculations and from the Casassa equation [E. F. Casassa, J. Polym. Sci. A 3, 605 (1965)]. It is also shown that, for rings, the Debye equation [P. Debye, J. Appl. Phys. 15, 338 (1944)] is no longer appropriate to describe the SANS profiles of H/D cyclic blends, at least up to Mw≈10000. For these samples, the Casassa form factor gives a better representation of the SANS data and we show that this function which was developed for monodisperse cyclics is still adequate to describe our slightly polydisperse samples. Deviations from all above observations are noted for Mw>11000 and are attributed to partial contamination of cyclic samples with linear chains. The failure of both the Debye and the Casassa form factors could be due to contamination of the cyclic fractions by linear polymers or to a real conformational change.
Topological derivation of shape exponents for stretched exponential relaxation
Authors: Macdonald J. R. , Phillips J. C.
Published: February 2005

In homogeneous (ideal) glasses, the important dimensionless stretched-exponential shape parameter β is described by magic (not adjusted) simple fractions derived from fractal configuration spaces of effective dimension d* determined by different topological axioms (rules) in the presence (absence) of a forcing electric field. The rules are based on a new central principle for defining glassy states: equal a priori distributions of fractal residual configurational entropy. Our approach and its β estimates are fully supported by the results of relaxation measurements involving many different glassy materials and probe methods. The present unique topological predictions for β typically agree with observed values to ∼1% and indicate that for field-forced conditions β should be constant for appreciable ranges of such exogenous variables as temperature and ionic concentration, as indeed observed using appropriate frequency-domain data analysis. The present approach can also be inverted and used to test sample homogeneity and quality.
High-resolution three-dimensional imaging of flat objects by synchrotron-radiation computed laminography
Authors: Helfen L. , Baumbach T. , Mikulík P. , Kiel D. , Pernot P. , Cloetens P. , Baruchel J.
Published: February 2005

Computed laminography with synchrotron radiation is developed and carried out for three-dimensional imaging of flat, laterally extended objects with high spatial resolution. Particular experimental conditions of a stationary synchrotron source have been taken into account by a scanning geometry different from that employed with movable conventional laboratory x-ray sources. Depending on the mechanical precision of the sample manipulation system, high spatial resolution down to the scale of 1μm can be attained nondestructively, even for objects of large lateral size. Furthermore, high beam intensity and the parallel-beam geometry enables easy use of monochromatic radiation for optimizing contrast and reducing imaging artifacts. Simulations and experiments on a test object demonstrate the feasibility of the method. Application to the inspection of solder joints in a flip-chip bonded device shows the potential for quality assurance of microsystem devices.
Enhanced semiconductor optical absorption via surface plasmon excitation in metal nanoparticles
Authors: Schaadt D. M. , Feng B. , Yu E. T.
Published: February 2005

Surface plasmon resonances in metallic nanoparticles are of interest for a variety of applications due to the large electromagnetic field enhancement that occurs in the vicinity of the metal surface, and the dependence of the resonance wavelength on the nanoparticle’s size, shape, and local dielectric environment. Here we report an engineered enhancement of optical absorption and photocurrent in a semiconductor via the excitation of surface plasmon resonances in spherical Au nanoparticles deposited on the semiconductor surface. The enhancement in absorption within the semiconductor results in increased photocurrent response in Si pn junction diodes over wavelength ranges that correspond closely to the nanoparticle plasmon resonance wavelengths as determined by measurements of extinction spectra. These observations suggest a variety of approaches for improving the performance of devices such as photodetectors, imaging arrays, and photovoltaics.
Ultrafast spin-polarized electrical currents injected in a strained zinc blende semiconductor by single color pulses
Authors: Bieler M. , Laman N. , van Driel H. M. , Smirl Arthur L.
Published: February 2005

Ultrafast ballistic electrical currents are generated through interband excitation of strained InGaAs∕GaAs quantum well samples at 295 K by 810 nm, 60 fs circularly polarized optical pulses. These currents are generated through quantum interference of optical absorption pathways associated with the orthogonally polarized components of the light field, and although the spin of the currents is not directly measured, they should also be spin polarized. The femtosecond transient currents are detected via the emitted tetrahertz (THz) radiation which has a bandwidth of ∼8THz. The THz amplitude scales linearly with injected carrier density up to ∼1018cm−3 beyond which state filling and carrier–carrier scattering cause a sublinear dependence. A peak current density of 9kA∕cm2 is obtained for a peak pump intensity of 250MW∕cm2.
Enhancing laser beam directional stability by single-mode optical fiber and feedback control of drifts
Authors: Zhao Weiqian , Tan Jiubin , Qiu Lirong , Zou Limin , Cui Jiwen , Shi Zi
Published: February 2005

A system, which uses a single-mode optical fiber to suppress the laser beam drifts, and uses feedback control to further reduce the drifts of a primary collimated beam, is proposed to enhance the directional stability of laser beams. The linear and angular drifts of laser beams are separated through light path arrangement and detected using quadrant position detectors, and are controlled using two-dimensional linear and angular drift feedback control systems according to their magnitudes detected. Theoretical analyses and experimental results indicate that the collimation accuracy of 0.7×10−7rad can be achieved at a collimation distance of 500 mm using single-mode optical fiber and separate control of linear and angular drifts.
Enhanced magnetoresistance in strain-free manganite network
Authors: Wu T. , Mitchell J. F.
Published: February 2005

A network structure of a ferromagnetic metallic (FMM)∕charge-ordered insulator (COI) mixed phase manganite has been obtained by annealing a 150Å Pr0.65(Ca0.75Sr0.25)0.35MnO3 film under tensile strain on a SrTiO3 substrate. Under the same deposition and annealing conditions, a film deposited on a LaAlO3 substrate, which provides compressive strain, remains continuous. The network structure also manifests a larger magnetoresistance than the continuous film. It is suggested that the lateral confinement in this filamentary structure may affect the percolative transport in this mixed FMM∕COI system.
Origin of dark counts in In0.53Ga0.47As∕In0.52Al0.48As avalanche photodiodes operated in Geiger mode
Authors: Karve G. , Wang S. , Ma F. , Li X. , Campbell J. C. , Ispasoiu R. G. , Bethune D. S. , Risk W. P. , Kinsey G. S. , Boisvert J. C. , Isshiki T. D. , Sudharsanan R.
Published: February 2005

A dark count rate in InP-based single photon counting avalanche photodiodes is a limiting factor to their efficacy. The temperature dependence of the dark count rate was studied to understand its origin in In0.53Ga0.47As∕In0.52Al0.48As separate-absorption-charge-multiplication avalanche photodiodes. The dark count rate was observed to be a very weak function of temperature in the range from 77Kto300K. Various mechanisms for dark count generation were considered. Simulations of band-to-band tunneling in the In0.52Al0.48As multiplication layer were found to agree well with the experimental temperature dependence of dark count rate at various excess biases. To reduce tunneling-induced dark counts, a suitable design change to the detector structure is proposed.
Enhanced sensitivity due to current redistribution in the Hall effect of semiconductor-metal hybrid structures
Authors: Holz Matthias , Kronenwerth Oliver , Grundler Dirk
Published: February 2005

Experimental and theoretical studies have shown that nonmagnetic semiconductor-metal hybrid structures can exhibit a very large magnetoresistance effect, the so-called extraordinary magnetoresistance (EMR) effect. The EMR can be useful in magnetic-field sensors and read heads. We show that the sensitivity of a linear hybrid structure can be further enlarged by using an optimized configuration of current leads and voltage probes. Strikingly, we find that the EMR and the Hall effect cooperate and thereby improve the performance. Our findings also explain the origin of the recently reported sensitivity increase in a nanostructured EMR device obtained via interchanging one lead and one probe [J. Moussa et al., J. Appl. Phys. 94, 1110 (2003)].
Tracing deeply buried InAs∕GaAs quantum dots using atomic force microscopy and wet chemical etching
Authors: Fasching G. , Unterrainer K. , Brezna W. , Smoliner J. , Strasser G.
Published: February 2005

We present cross-sectional atomic-force-microscope measurements of buried self-assembled quantum dots. The used method needs a minimum of time and sample preparation (cleaving and etching) to obtain the dot density, dot distribution, and give an estimate of the dot dimensions. Etching only the cleaved surface of the sample opens up the opportunity to determine the properties of a buried dot layer before or even after device fabrication.
Internal photoemission in solar blind AlGaN Schottky barrier photodiodes
Authors: Duboz Jean-Yves , Grandjean Nicolas , Omnes Franck , Mosca Mauro , Reverchon Jean-Luc
Published: February 2005

We have analyzed the photoresponse of solar blind AlGaN Schottky barrier photodiodes below the alloy band gap energy, in the 3.5–4.5eV range, and we show that it is dominated by internal photoemission. The n-type Schottky barrier height is shown to increase linearly with the band gap energy of the AlGaN alloy. The amplitude of the internal photoemission signal is about 20 times smaller than the value given by the Fowler theory based on a free electron model. We explain this result by taking into account the interband transitions and the ballistic transport of photoexcited electrons in the metal. This low value of internal photoemission allows us to achieve a spectral rejection ratio between 280 and 320nm of more than 3 decades.
Improved superlensing in two-dimensional photonic crystals with a basis
Authors: Wang X. , Ren Z. F. , Kempa K.
Published: February 2005

We study propagation of light in square and hexagonal two-dimensional photonic crystals. We show, that slabs of these crystals focus light with subwavelength resolution. We propose a systematic way to increase this resolution, at an essentially fixed frequency, by employing a hierarchy of crystals of the same structure, and the same lattice constant, but with an increasingly complex basis.
Surface plasmon propagation in an elliptical corral
Authors: Drezet A. , Stepanov A. L. , Ditlbacher H. , Hohenau A. , Steinberger B. , Aussenegg F. R. , Leitner A. , Krenn J. R.
Published: February 2005

We report the experimental realization of an elliptical Bragg reflector acting as an interferometer for propagating surface plasmon (SP) waves. We investigate SP interferometry in this device using a leakage radiation microscope and we compare our observations with a theoretical model for SP propagation. Strong SP focalization as a function of laser polarization orientation is observed and justified.
Expertise and Attunement to Kinematic Constraints
Authors: Abernethy Bruce , Zawi Khairi , Jackson Robin C
Published: February 2005

Three experiments were undertaken to ascertain the extent to which expertise in natural anticipatory tasks is characterised by superior attunement to the biomechanical (kinematic) constraints of the movement pattern being observed. Twelve world-class and twelve non-expert badminton players were required to predict the depth of an opponent's stroke from either video displays or point-light displays of the opposing player's hitting action. The information available within the displays was manipulated through temporal and/or spatial occlusion. Consistent with predictions that can be derived from the constraint-attunement hypothesis (Vicente and Wang, 1998 Psychological Review105 33–57), experts showed: (i) an unchanged pattern of information pick-up when the display was reduced from video to point-light and only kinematic information was available; (ii) superior information pick-up from kinematic features that non-experts could use; and (iii) attunement to early kinematic information from the lower body to which non-experts were not sensitive. Consistent with predictions that can be derived from a common-coding perspective (Prinz, 1997 European Journal of Cognitive Psychology9 129–154), the anticipation of stroke depth was facilitated more for experts than non-experts when the perceptual display provided linked segment information reminiscent of the cross-segmental torque transfers that occur during expert movement production.
A shortened adeno-associated virus expression cassette for
CFTR
gene transfer to cystic fibrosis airway epithelia
Authors: Ostedgaard Lynda S. , Rokhlina Tatiana , Karp Philip H. , Lashmit Philip , Afione Sandra , Schmidt Michael , Zabner Joseph , Stinski Mark F. , Chiorini Jay A. , Welsh Michael J.
Published: February 2005

Adeno-associated viruses (AAVs) such as AAV5 that transduce airway epithelia from the apical surface are attractive vectors for gene transfer in cystic fibrosis (CF). However, their utility in CF has been limited because packaging of the insert becomes inefficient when its length exceeds ≈4,900–5,000 bp. To partially circumvent this size constraint, we previously developed a CF transmembrane conductance regulator (CFTR) transgene that deleted a portion of the R domain (CFTRΔR). In this study, we focused on shortening the other elements in the AAV expression cassette. We found that portions of the CMV immediate/early (
CMVie
) enhancer/promoter could be deleted without abolishing activity. We also tested various intervening sequences, poly(A) signals, and an intron to develop an expression cassette that meets the size restrictions imposed by AAV. We then packaged these shortened elements with the CFTRΔR transgene into AAV5 and applied them to the apical surface of differentiated CF airway epithelia. Two to 4 weeks later, the AAV5 vectors partially corrected the CF Cl
–
transport defect. These results demonstrate that a single AAV vector can complement the CF defect in differentiated airway epithelia and thereby further the development of effective CF gene transfer.
Remembering one year later: Role of the amygdala and the medial temporal lobe memory system in retrieving emotional memories
Authors: Dolcos Florin , LaBar Kevin S. , Cabeza Roberto
Published: February 2005

The memory-enhancing effect of emotion can be powerful and long-lasting. Most studies investigating the neural bases of this phenomenon have focused on encoding and early consolidation processes, and hence little is known regarding the contribution of retrieval processes, particularly after lengthy retention intervals. To address this issue, we used event-related functional MRI to measure neural activity during the retrieval of emotional and neutral pictures after a retention interval of 1 yr. Retrieval activity for emotional and neutral pictures was separately analyzed for successfully (hits) vs. unsuccessfully (misses) retrieved items and for responses based on recollection vs. familiarity. Recognition performance was better for emotional than for neutral pictures, and this effect was found only for recollection-based responses. Successful retrieval of emotional pictures elicited greater activity than successful retrieval of neutral pictures in the amygdala, entorhinal cortex, and hippocampus. Moreover, in the amygdala and hippocampus, the emotion effect was greater for recollection than for familiarity, whereas in the entorhinal cortex, it was similar for both forms of retrieval. These findings clarify the role of the amygdala and the medial temporal lobe memory regions in recollection and familiarity of emotional memory after lengthy retention intervals.
Complete genome sequence of
Vibrio fischeri
: A symbiotic bacterium with pathogenic congeners
Authors: Ruby E. G. , Urbanowski M. , Campbell J. , Dunn A. , Faini M. , Gunsalus R. , Lostroh P. , Lupp C. , McCann J. , Millikan D. , Schaefer A. , Stabb E. , Stevens A. , Visick K. , Whistler C. , Greenberg E. P.
Published: February 2005

Vibrio fischeri
belongs to the Vibrionaceae, a large family of marine γ-proteobacteria that includes several dozen species known to engage in a diversity of beneficial or pathogenic interactions with animal tissue. Among the small number of pathogenic
Vibrio
species that cause human diseases are
Vibrio cholerae, Vibrio parahaemolyticus
, and
Vibrio vulnificus
, the only members of the Vibrionaceae that have had their genome sequences reported. Nonpathogenic members of the genus
Vibrio
, including a number of beneficial symbionts, make up the majority of the Vibrionaceae, but none of these species has been similarly examined. Here we report the genome sequence of
V. fischeri
ES114, which enters into a mutualistic symbiosis in the light organ of the bobtail squid,
Euprymna scolopes
. Analysis of this sequence has revealed surprising parallels with
V. cholerae
and other pathogens.
Recruitment and interaction dynamics of plant penetration resistance components in a plasma membrane microdomain
Authors: Bhat Riyaz A. , Miklis Marco , Schmelzer Elmon , Schulze-Lefert Paul , Panstruga Ralph
Published: February 2005

Many fungal pathogens must enter plant cells for successful colonization. Barley
mildew resistance locus o
(
Mlo
) is required for host cell invasion upon attack by the ascomycete powdery mildew fungus,
Blumeria graminis
f.sp.
hordei
, and encodes the founder of a family of heptahelical integral membrane proteins unique to plants. Recessively inherited loss-of-function mutant alleles (
mlo
) result in effective penetration resistance to all isolates of the biotrophic parasite. We used noninvasive fluorescence-based imaging to show that fluorescently tagged MLO protein becomes redistributed in the plasma membrane (PM) and accumulates beneath fungal appressoria coincident with the initiation of pathogen entry into host cells. Polarized MLO accumulation occurs once upon attack and appears to be independent of actin cytoskeleton function. Likewise, barley ROR2 syntaxin, a genetically defined component of penetration resistance to
B. graminis
f.sp.
hordei
, and a subset of predicted PM-resident proteins become redistributed to fungal entry sites. We previously identified calmodulin, a cytoplasmic calcium sensor, as an interactor and positive regulator of MLO activity and demonstrate here by FRET microscopy an increase in MLO/calmodulin FRET around penetration sites coincident with successful host cell entry. Our data provide evidence for the formation of a pathogen-triggered PM microdomain that is reminiscent of membrane microdomains (lipid rafts) induced upon attempted entry of pathogenic bacteria in animal cells.
Extinction probabilities and times to extinction for populations of tsetse flies Glossina spp. (Diptera: Glossinidae) subjected to various control measures
Authors: Hargrove J.W.
Published: February 2005

A stochastic branching process was used to derive equations for the mean and variance of the probability of, and time to, extinction in tsetse populations. If the remnant population is a single inseminated female, the extinction probability increases linearly with adult mortality and is always certain if this mortality >3.5% per day even for zero pupal mortality. If the latter mortality is 4% per day, certain extinction is only avoided if adult mortality <1.5% per day. For remnant female populations >1, the extinction probability increases in a non-linear manner with adult mortality. Extinction is still certain for adult mortality >3.5% per day but, when the remnant population is >16, extinction is highly unlikely for adult mortality <2.5% per day if all females are inseminated. Extinction probability increases with increasing probability of sterile mating in much the same way as it does with increasing adult mortality. Extinction is assured if the probability of insemination can be reduced to 0.1. The required reduction decreases with increasing adult mortality. For adult mortality = 6–8% per day, the time to extinction increases only by one generation per order of magnitude increase in the starting population. Time to extinction is less sensitive to changes in the pupal than in the adult mortality. Reductions in the probability of insemination only become important when adult mortality is small; if the adult mortality is 8% per day, reducing the insemination probability from 1 to 0.1 only reduces the expected time to extinction by two generations. Conversely, increases in adult mortality produce important reductions in the required time even when the probability of insemination is 0.1. The practical, economic implication for the sterile insect technique is that the low-tech methods used to suppress tsetse populations should not be halted when the release of sterile males is initiated. The sterile insect technique should only be contemplated when it has been demonstrated that the low-tech methods have failed to effect eradication. The theory is shown to be in good accord with the observed results of tsetse control campaigns involving the use of odour-baited targets in Zimbabwe and the sterile insect technique on Unguja Island, Zanzibar.
A new silverleaf-inducing biotype Ms ofBemisia tabaci(Hemiptera: Aleyrodidae) indigenous to the islands of the south-west Indian Ocean
Authors: Delatte H. , Reynaud B. , Granier M. , Thornary L. , Lett J.M. , Goldbach R. , Peterschmitt M.
Published: February 2005

Following the first detection of tomato yellow leaf curl virus (TYLCV) from R=union (700 km east of Madagascar) in 1997 and the upsurge ofBemisia tabaci(Gennadius) on vegetable crops, two genetic types ofB. tabaciwere distinguished using RAPD–PCR and cytochrome oxidase I (COI) gene sequence comparisons. One type was assigned to biotype B and the other was genetically dissimilar to the populations described elsewhere and was named Ms, after the Mascarenes Archipelago. This new genetic type forms a distinct group that is sister to two other groups, one to which the B biotype is a member and one to which the Q biotype belongs. The Ms biotype is thought to be indigenous to the region as it was also detected in Mauritius, the Seychelles and Madagascar. Both B and Ms populations ofB. tabaciinduced silverleaf symptoms onCucurbitasp., and were able to acquire and transmit TYLCV. Taken together these results indicate that the Ms genetic type should be considered a new biotype ofB. tabaci.