bluuebunny/crossref_metadata_2025 huggingface dataset:
Contributions of an orthopteran to the understanding of neuronal pathfinding
Authors: SANCHEZ DIEGO , GANEORNINA MARIA D , BASTIANI MICHAEL J
Published: July 2007

During the development of the nervous system neurons extend axons through a complex embryonic environment. To find a correct target, often located at a long distance, the neuronal growth cones travel along highly specific and stereotyped pathways. Proper neuronal pathfinding is thought to be accomplished by the specific interaction of receptors on the neuronal surface with molecular cues in the environment. We review the information obtained in an invertebrate model system, the grasshopper embryo, about the specific role of the cell surface in wiring the nervous system.
Marginal condition for the onset of thermoacoustic oscillations of a gas in a tube
Authors: Sugimoto N. , Yoshida M.
Published: July 2007

This paper revisits a classical problem to derive a marginal condition for the onset of spontaneous thermoacoustic oscillations of a gas in a circular tube with one end open and the other closed by a flat wall, subjected to a temperature gradient along the side wall. Formulation is given in the framework of the linear theory and the first-order theory in the ratio of a boundary-layer thickness to the tube radius. An eigenvalue problem is posed on the second-order differential equation with variable coefficients of the axial coordinate for the excess pressure in the main-flow region outside of the boundary layer. A boundary layer on the end wall is taken into account in the form of an appropriate boundary condition. By using the idea of renormalization, the pressure is rescaled and a complex axial coordinate is introduced so that the pressure equation is transformed into a tractable form. It turns out that the equation includes a factor (frequency) determined by the product of the local sound speed and the logarithmic temperature gradient, though the boundary-layer effect is not completely eliminated. When this factor is constant everywhere, the temperature distribution is parabolic and solutions are obtained in a closed form. The frequency equation is then derived from the boundary conditions at both ends of the tube, from which the marginal condition is obtained for the ratio of temperature at the hot, closed end to the one at the cold, open end against the tube radius relative to the thickness of the boundary layer at the open end. The spatial modes of the oscillations are also analytically obtained and their profiles are displayed. Finally, some discussions on marginal oscillations are given from the viewpoint of energy balance.
Reduction effect of neutral density on the excitation of turbulent drift waves in a linear magnetized plasma with flow
Authors: Saitou Y. , Yonesu A. , Shinohara S. , Ignatenko M. V. , Kasuya N. , Kawaguchi M. , Terasaka K. , Nishijima T. , Nagashima Y. , Kawai Y. , Yagi M. , Itoh S.-I. , Azumi M. , Itoh K.
Published: July 2007

The importance of reducing the neutral density to reach strong drift wave turbulence is clarified from the results of the extended magnetohydrodynamics and Monte Carlo simulations in a linear magnetized plasma. An upper bound of the neutral density relating to the ion-neutral collision frequency for the excitation of drift wave instability is shown, and the necessary flow velocity to excite this instability is also estimated from the neutral distributions. Measurements of the Mach number and the electron density distributions using Mach probe in the large mirror device (LMD) of Kyushu University [S. Shinohara et al., Plasma Phys. Control. Fusion 37, 1015 (1995)] are reported as well. The obtained results show a controllability of the neutral density and provide the basis for neutral density reduction and a possibility to excite strong drift wave turbulence in the LMD.
Photomechanics of mono- and polydomain liquid crystal elastomer films
Authors: Dunn Martin L.
Published: July 2007

The coupling of optical and mechanical energy has recently been demonstrated in a class of liquid crystal elastomers that contain light-sensitive molecules. Their molecular structure consists of stiff, ordered, rod-like molecules (the liquid crystal feature) connected to long cross-linked molecular chains (the elastomer feature). This connection leads to a coupling between the orientational order of the rods and mechanical deformation of the network. Irradiation with light at appropriate wavelengths leads to isomerization of the stiff rod-like molecules, resulting in bending (straightening) of the molecules which dilutes (enhances) the orientational order, thus causing macroscopic deformation. This deformation, photostrain, can be as much as hundreds of percent. These materials are typically fabricated as thin monodomain or polydomain films. If uniformly irradiated through the thickness, they undergo anisotropic incompressible deformation in the film plane. If the light intensity varies through the thickness, then the photostrain also varies and the film bends. The nature of the deformation depends on, among other things, whether the film is a monodomain or polydomain, whether the light is polarized or not, and if so, in what direction. In all cases, molecules with axes aligned with the polarization component preferentially isomerize; the relationship between the molecular alignment and polarization determines the nature of the resulting strain. In this study, we analyze the deformation of such photoactuated thin films with anisotropic photostrains that are uniform or vary through the thickness. Building on existing work we incorporate the effects of geometric nonlinearity, while retaining the assumptions of isotropic linear elastic material behavior, to develop fairly simple analytical estimates of the overall deformation. By virtue of their simplicity these provide considerable insight into the deformation phenomena and at the same time are in good agreement with more accurate nonlinear finite element calculations. Consistent with reports in the literature, we find that large shape changes can occur, and that the effects of geometric nonlinearity can be significant. Our analysis explains the recently reported phenomena of photoinduced anisotropic saddle-shaped films [M. Camacho-Lopez, H. Finkelmann, P. Palffy-Muhoray, and M. Shelley, Nat. Mater. 3, 307 (2004)] and directionally-dependent bending of polydomain films [T. Ikeda, M. Nakano, Y. L. Yu, O. Tsutsumi, and A. Kanazawa, Adv. Mater. 15, 201 (2003)]. These results have somewhat broad applicability, including technological applications such as actuators, artificial muscles, and energy harvesting.
Langevin dynamics simulations of ds-DNA translocation through synthetic nanopores
Authors: Forrey Christopher , Muthukumar M.
Published: July 2007

We have implemented a coarse-grained model to study voltage-driven as-DNA translocation through nanopores located in synthetic membranes. The simulated trajectory of the DNA through the nanopores was calculated using Langevin dynamics. We present the results based on more than 120 000 individual translocations. We are particularly interested in this work in probing the physical basis of various experimentally observed—yet poorly understood—phenomena. Notably, we observe in our simulations the formation of ds-DNA hairpins, widely suspected to be the basis for quantized blockage. We study the translocation time, a measurable quantity crucially important in polyelectrolyte characterization, as a function of hairpin vertex location along the polymer backbone, finding that this behavior can be tuned to some degree by simulation parameters. We also study the voltage dependence of the tendency of hairpins to serve as the initiators of translocation events. Surprisingly, we find that the resulting probability depends vitally upon whether the events counted are ultimately successful or not. Further details lead us to propose that failed attempts in experimental translocation studies may be more common—and deceptive—than is generally recognized. We find the time taken by successful single file translocations to be directly proportional to the ratio of chain length to the applied voltage. Finally, we address a common yet puzzling phenomenon in translocation experiments: translocation events in which the current through the pore is highly, yet incompletely, blocked. We present the findings that offer a new explanation for such events.
Mobility of electrons in supercritical krypton: Role of density fluctuations
Authors: Nishikawa Masaru , Holroyd Richard A. , Preses Jack M.
Published: July 2007

Excess electrons were generated in supercritical krypton by means of pulsed x-ray irradiation, and the electron transport phenomena were studied. Electron signals immediately after a 30ps pulse showed a distinctive feature characteristic of the presence of the Ramsauer-Townsend minimum in the momentum transfer cross section. The dependence of the drift velocity vD on field strength was found to be concave upward in the low field region and then to go through a maximum with increasing field strength, which is also typical of the presence of a minimum in the scattering cross section at an intermediate field strength. A minimum in the electron mobility was observed at about one-half the critical density. The acoustical phonon scattering model, which successfully explained the mobility change in this density region in supercritical xenon, was again found to account for the mobility in supercritical krypton.
Optical phonon behavior in strain-free dilute Ga(As,N) studied by Raman scattering
Authors: Ibáñez J. , Alarcón-Lladó E. , Cuscó R. , Artús L. , Hopkinson M.
Published: July 2007

We present a Raman-scattering study on strain-free dilute Ga(As,N) epilayers grown by molecular beam epitaxy. The aim of our work is to discriminate the effect of alloying from the effect of biaxial strain on the frequency behavior of the optical phonon modes of Ga(As,N). In the relaxed epilayers, we observe the following: (i) for the GaN-like LO mode, an upward frequency shift with increasing N which is larger than previously observed in strained samples; (ii) for the GaAs-like LO mode, a redshift with increasing N content which is lower than those reported in the literature on strained samples; and (iii) for the GaAs-like TO mode, we observe a very minor blueshift with increasing N fraction. We discuss the origin of the observed shifts, with particular attention to the reduction of the GaAs-like TO-LO splitting in Ga(As,N). Our data and analysis suggest that such reduction cannot be explained only by a reduction of the total number of Ga–As oscillators due to the substitution of As by N. We discuss the effects of disorder and of ionic plasmon coupling between the GaAs and GaN sublattices of Ga(As,N) on the behavior of the GaAs-like LO mode of the alloy. We conclude that the behavior of this mode is determined by long-range effects.
Novel instrument to characterize dry granular materials at low consolidations
Authors: Castellanos A. , Quintanilla M. A. S. , Valverde J. M. , Soria-Hoyo C.
Published: July 2007

The performance of traditional instruments for measuring the flow properties of dry granular materials at small consolidation stresses is not fully satisfactory. Generally, commercial quick tests, as, for example, the angle repose method, do not yield intrinsic material properties. This difficulty is solved in currently available ring shear testers, in which the externally applied torque necessary for shearing the sample is measured as a function of the normal stress previously applied through an annular lid. In this article we show a novel device in which the shear stress is caused by the action of a centrifugal force on a vertical layer of unconsolidated material, which is rotated around its vertical axis. At a critical point the shear stress is large enough to drive material avalanches. From a theoretical analysis of these avalanches based on Coulomb’s method of wedges, we derive the angle of internal friction and cohesion of the granular material. To illustrate the functioning of the instrument, measurements on steel, ferrite, and magnetite beads of different particle size are presented. The data obtained are used to analyze the gravity-driven avalanches of these materials in a slowly rotated drum.
Characterization of a new open cylindrical ion cyclotron resonance cell with unusual geometry
Authors: Kanawati B. , Wanczek K. P.
Published: July 2007

A new cylindrical ion cyclotron resonance cell with electrodes of different diameters is characterized. It consists of a central segmented electrode for ion trapping and detection and two planar trapping electrodes with a center bore, to which two small tube electrodes are fitted. The cell can trap either positive or negative ions or both ion polarities in the center region. For trapping both ion polarities, an unsymmetrical double well potential can be generated. Ions generated from SF6 by electron impact or electron attachment are investigated. In depth analysis of radial excitation patterns of positive and negative ions trapped simultaneously in different stability regions reveals sharp discrimination in the extent of radial acceleration. SIMION simulations of the radial excitation show different trajectories of positive and negative ions. Axial component of radial dipolar excitation field exists in the terminal stability regions.
Improvement of luminescence degradation in pure water of nanocrystalline silicon particles covered by a hydrogenated amorphous carbon layer
Authors: Sato Keisuke , Kishimoto Naoki , Oku Takahiro , Hirakuri Kenji
Published: July 2007

The stability of luminescence in pure water of surface-modified nanocrystalline silicon (nc-Si) particles has been studied. The surfaces of nc-Si particles were modified with more stable silicon-oxygen (Si-O) and silicon-carbon (Si-C) bonds by the formation of a thin native oxide layer and a hydrogenated amorphous carbon (a-C:H) layer consisting of both disordered regions and graphite bands. The peak position of luminescence in pure water of the sample with the a-C:H layer was similar to that in the sample without the a-C:H layer. Moreover, the degradation rate of the luminescence intensity of the sample with the a-C:H layer was less than that of the sample without the a-C:H layer, for immersion in pure water above 100 h. The luminescence in pure water of the a-C:H coated sample could be seen with the naked eye even after aging for 200 h. The degradation of the luminescence in pure water can be improved remarkably by the formation of Si-O and Si-C bonds with strong bond strengths on the surfaces of the nc-Si particles.
High-load, high-temperature deformation apparatus for synthetic and natural silicate melts
Authors: Hess K.-U. , Cordonnier B. , Lavallée Y. , Dingwell D. B.
Published: July 2007

A unique high-load, high-temperature uniaxial press was developed to measure the rheology of silicate melts and magmatic suspensions at temperature up to 1050°C. This new apparatus is designed to operate at constant stresses (up to 300kN) or constant strain rates (∼10−7 to 100s−1) and further allows us to carry on experiments on samples with high viscosities (∼108 to 1012Pas). The rheological instrument represents an advance in that it accommodates homogeneously heated samples (±2°C) of voluminous sizes (up to 790cm3) which permit the insertion of thermocouples to monitor temperature distribution evolutions during measurements. At last this setup allows for accurate measurements of viscosity of natural multiphase materials at strain rates and temperatures common to natural systems. The apparatus aspires to precisely (1) describe the onset of non-Newtonian behavior and its evolution with increasing strain rate until the point of rupture in the brittle regime, (2) constrain the effect of crystals and bubbles on the viscosity, and (3) record heating dissipated through viscous deformation. Here, we present a series of measurements on NIST standard material SRM 717a to calibrate the instrument. We couple the viscosity determined via Gent’s equation with certified viscosity data of the standard material to calibrate this state-of-the-art apparatus. This work shows that we can resolve the viscosity of voluminous melt sample within 0.06 logarithmic unit and furthermore present the detection of minor viscous dissipation for a high-temperature, high strain rate experiment.
Modeling and simulation for the enhancement of electron storage in a stacked multilayer nanocrystallite silicon floating gate memory
Authors: Yu L. W. , Chen K. J. , Ding H. L. , Xu J. , Liu K. , Li W. , Wang X. , Huang X. F.
Published: July 2007

In this article, we investigate the storage enhancement mechanism of stacked multilayer nanocrystallite silicon (nc-Si) structures in a master-equation-based equivalent circuit model. As a theoretical extension from our previous experimental works, we reveal the detail injection sequence of electrons into the multilayer nc-Si structure via a direct tunneling process, and how the retention property is enhanced by the stacked structures. Seeking a further improvement in the multilayer nc-Si-based nonvolatile memory structure, we compare two major approaches for that purpose, i.e. (1) by further increasing the number of stacked layers or (2) by adopting an asymmetric double-layer structure. It is shown that the latter is more promising for achieving better nonvolatile storage property and shows a more effective threshold shifting, while retaining the virtues of direct tunneling process like fast write/erase and low operation voltage. We suggest that these results provide important guides for practical design of memory devices based on multilayer nc-Si floating gate structures.
Enhancement of the photoluminescence of silicon oxide defect states by combining silicon oxide with silicon nanowires
Authors: Noé P. , Guignard J. , Gentile P. , Delamadeleine E. , Calvo V. , Ferret P. , Dhalluin F. , Baron T.
Published: July 2007

The authors show an efficient room-temperature visible photoluminescence source obtained by combining silicon nanowires (SiNWs) and silicon oxide (SiO2) defect states. The SiNWs are synthesized by a Vapor-Liquid-Solid mechanism and then covered by SiO2 deposited by standard deposition techniques. SiNW samples have been observed by scanning electron microscopy. The photoluminescence spectra of SiO2/SiNWs samples exhibit a blue-green-light emission centered at 500 nm attributed to the carrier recombination at oxygen relative defects at the SiNWs/SiO2 interface and defect centers in the SiO2 layer. Such structures are very promising for optoelectronic devices in order to achieve an efficient silicon-based source under electrical injection.
Nitride-based light emitting diodes with indium tin oxide electrode patterned by imprint lithography
Authors: Chang S. J. , Shen C. F. , Chen W. S. , Kuo C. T. , Ko T. K. , Shei S. C. , Sheu J. K.
Published: July 2007

The authors propose a simple, low cost, and mass producible imprint lithography method to texture indium tin oxide (ITO) contact layer of nitride-based light emitting diodes (LEDs). Under 20mA current injection, it was found that forward voltages were 3.24, 3.25, and 3.24V while the LED output powers were 11.7, 12.6, and 13.3mW for the conventional ITO LED, ITO LED patterned with 1.75μm holes, and ITO LED patterned with 0.85μm holes, respectively.
ac susceptibility of a melt-textured YBa2Cu3Ox ring closed by a strong-coupling contact
Authors: Chen D.-X. , Pardo E. , Sanchez A.
Published: July 2007

The complex ac susceptibility χ=χ′−jχ″ of a melt-textured YBa2Cu3Ox ring closed by a strong-coupling contact is measured after zero-field cooling to 77K as a function of the ac field amplitude Hm and frequency f. The resulting χ(Hm,f) is similar to that derived from a power-law relation between the local current density and electric field but with maximum χ″(Hm) increasing steadily with increasing f, which is explained by the creep of Abrikosov-Josephson vortices along the contact driven by the London force of supercurrents and the Lorentz force of the induced normal currents.
Using the temperature dependence of resonator quality factor as a thermometer
Authors: Hopcroft M. A. , Kim B. , Chandorkar S. , Melamud R. , Agarwal M. , Jha C. M. , Bahl G. , Salvia J. , Mehta H. , Lee H. K. , Candler R. N. , Kenny T. W.
Published: July 2007

Silicon micromechanical resonators have been designed to have a quality factor (Q) that is a strong function of temperature. This is an ideal sensor for the temperature of the resonator—it is instantaneous, consumes no power, and indicates the temperature of the resonator structure with high sensitivity. The authors present a practical implementation of an oscillator system using these resonators with a temperature resolution of better than 0.002°C. The Q(T) signal is uniquely suited for implementing feedback control of the resonator temperature, thereby stabilizing the frequency silicon micromechanical resonators and enabling their use in high-stability frequency reference applications.
Strain induced internal potentials of compositionally graded epitaxial ferroelectric thin films
Authors: Akcay G. , Zhong S. , Allimi B. S. , Alpay S. P. , Mantese J. V.
Published: July 2007

Compositionally graded ferroelectrics produce internal potentials that manifest themselves as asymmetric hysteresis in polarization versus applied field plots. The direction and magnitude of the built-in fields depend on the sense of the chemical gradient in unclamped graded ferroelectrics. A thermodynamic model was employed to understand how these potentials would be affected by an inhomogeneous internal strain in epitaxial compositionally graded ferroelectric structures. The analysis indicates that the strain field can be employed to control both the magnitude and direction of the internal potentials. Indeed, the sense of the polarization gradient may be completely reversed with the appropriate strain gradient.
Effects of a long-term fire retardant chemical (Fire-Trol 934) on seed viability and germination of plants growing in a burned Mediterranean area
Authors: Luna Belén , Moreno José M. , Cruz Alberto , Fernández-González Federico
Published: July 2007

This work documents the effect of a common, long-term fire retardant chemical, Fire-Trol 934, on seed viability and germination of 36 plant species growing in a burned Mediterranean area, covering different life-form types, regenerative strategies and distribution ranges. Seeds were subjected to four treatments: control, and application of Fire-Trol 934 at concentrations of 0.02, 0.2 and 2%. Fire-Trol 934 significantly decreased both seed viability and germination in the group of species studied, which suggests that Fire-Trol 934 may be toxic for seeds, at least when applied at high concentrations. Whereas seed viability generally showed a progressive decrease with increased Fire-Trol 934 concentration, germination percentages generally increased when intermediate Fire-Trol 934 concentrations were used, but tended to be drastically reduced when seeds were exposed to the highest (2%) concentration. The reduction observed in germination at the highest Fire-Trol 934 concentration was greater than that observed in viability, which suggests that the effect of Fire-Trol 934 on seeds may not be lasting. Little differences in the response to Fire-Trol 934 emerged among plant groups, all of which followed the general tendency described above.
Resprouting responses of Acacia shrubs in the Western Desert of Australia - fire severity, interval and season influence survival
Authors: Wright Boyd R. , Clarke Peter J.
Published: July 2007

The hummock grasslands of arid Australia are fire-prone ecosystems in which the perennial woody plants mostly resprout after fire. The resprouting ability among these species is poorly understood in relation to environmental variation; consequently, little is known about the impacts that contemporary fire regimes are having on vegetation within these systems. We examined the resprouting ability of adults and juveniles of four widespread Acacia species (A. aneura, A. kempeana, A. maitlandii, A. melleodora) by experimentally testing the effects of fire severity, interval and season. We found that fire severity and season strongly affected survival, but the magnitude of the effects was variable among the species. Unexpectedly, a short fire interval of 2 years did not have a strong negative effect on resprouting of any species. Fire severity had variable effects among the four species, with those species with more deeply buried buds being more resilient to high-severity soil heating than those with shallow buds. Season of fire also strongly affected survival of some species, and we propose that seasonal variation in soil heating and soil moisture mediated these effects. The species by environment interactions we observed within one functional group (resprouters with a soil-stored seed bank) and in one genus suggest that modelling landscape response to fire regimes will be complex in these arid ecosystems. We predict, however, that the dominant resprouting acacias in hummock grasslands of central Australia are highly resilient to a range of fire regimes.
Discovery of antiandrogen activity of nonsteroidal scaffolds of marketed drugs
Authors: Bisson W. H. , Cheltsov A. V. , Bruey-Sedano N. , Lin B. , Chen J. , Goldberger N. , May L. T. , Christopoulos A. , Dalton J. T. , Sexton P. M. , Zhang X.-K. , Abagyan R.
Published: July 2007

Finding good drug leadsde novofrom large chemical libraries, real or virtual, is not an easy task. High-throughput screening is often plagued by low hit rates and many leads that are toxic or exhibit poor bioavailability. Exploiting the secondary activity of marketed drugs, on the other hand, may help in generating drug leads that can be optimized for the observed side-effect target, while maintaining acceptable bioavailability and toxicity profiles. Here, we describe an efficient computational methodology to discover leads to a protein target from safe marketed drugs. We applied anin silico“drug repurposing” procedure for identification of nonsteroidal antagonists against the human androgen receptor (AR), using multiple predicted models of an antagonist-bound receptor. The library of marketed oral drugs was then docked into the best-performing models, and the 11 selected compounds with the highest docking score were testedin vitrofor AR binding and antagonism of dihydrotestosterone-induced AR transactivation. The phenothiazine derivatives acetophenazine, fluphenazine, and periciazine, used clinically as antipsychotic drugs, were identified as weak AR antagonists. Thisin vitrobiological activity correlated well with endocrine side effects observed in individuals taking these medications. Further computational optimization of phenothiazines, combined within vitroscreening, led to the identification of a nonsteroidal antiandrogen with improved AR antagonism and marked reduction in affinity for dopaminergic and serotonergic receptors that are the primary target of phenothiazine antipsychotics.
Fibrinogen inhibits neurite outgrowth via β3 integrin-mediated phosphorylation of the EGF receptor
Authors: Schachtrup Christian , Lu Paul , Jones Leonard L. , Lee Jae K. , Lu Jerry , Sachs Ben D. , Zheng Binhai , Akassoglou Katerina
Published: July 2007

Changes in the molecular and cellular composition of the CNS after injury or disease result in the formation of an inhibitory environment that inhibits the regeneration of adult mammalian CNS neurons. Although a dramatic change in the CNS environment after traumatic injury or disease is hemorrhage because of vascular rupture or leakage of the blood–brain barrier, the potential role for blood proteins in repair processes remains unknown. Here we show that the blood protein fibrinogen is an inhibitor of neurite outgrowth that is massively deposited in the spinal cord after injury. We show that fibrinogen acts as a ligand for β3 integrin and induces the transactivation of EGF receptor (EGFR) in neurons. Fibrinogen-mediated inhibition of neurite outgrowth is reversed by blocking either β3 integrin or phoshorylation of EGFR. Inhibition of Src family kinases that mediate the cross-talk between integrin and growth factor receptors rescue the fibrinogen-induced phosphorylation of EGFR. These results identify fibrinogen as the first blood-derived inhibitor of neurite outgrowth and suggest fibrinogen-induced EGFR transactivation on neuronal cells as a molecular link between vascular and neuronal damage in the CNS after injury.
Class selection of amino acid metabolites in body fluids using chemical derivatization and their enhanced
13
C NMR
Authors: Shanaiah Narasimhamurthy , Desilva M. Aruni , Nagana Gowda G. A. , Raftery Michael A. , Hainline Bryan E. , Raftery Daniel
Published: July 2007

We report a chemical derivatization method that selects a class of metabolites from a complex mixture and enhances their detection by
13
C NMR. Acetylation of amines directly in aqueous medium with 1,1′-
13
C
2
acetic anhydride is a simple method that creates a high sensitivity and quantitative label in complex biofluids with minimal sample pretreatment. Detection using either 1D or 2D
13
C NMR experiments produces highly resolved spectra with improved sensitivity. Experiments to identify and compare amino acids and related metabolites in normal human urine and serum samples as well as in urine from patients with the inborn errors of metabolism tyrosinemia type II, argininosuccinic aciduria, homocystinuria, and phenylketonuria demonstrate the method. The use of metabolite derivatization and
13
C NMR spectroscopy produces data suitable for metabolite profiling analysis of biofluids on a time scale that allows routine use. Extension of this approach to enhance the NMR detection of other classes of metabolites has also been accomplished. The improved detection of low-concentration metabolites shown here creates opportunities to improve the understanding of the biological processes and develop improved disease detection methodologies.
Thioredoxin is required for S-nitrosation of procaspase-3 and the inhibition of apoptosis in Jurkat cells
Authors: Mitchell Douglas A. , Morton Sarah U. , Fernhoff Nathaniel B. , Marletta Michael A.
Published: July 2007

S-nitrosation is a posttranslational, oxidative addition of NO to cysteine residues of proteins that has been proposed as a cGMP-independent signaling pathway [Hess DT, Matsumoto A, Kim SO, Marshall HE, Stamler JS (2005)
Nat Rev Mol Cell Biol
6:150–166]. A paradox of S-nitrosation is that only a small set of reactive cysteines are modified
in vivo
despite the promiscuous reactivity NO exhibits with thiols, precluding the reaction of free NO as the primary mechanism of S-nitrosation. Here we show that a specific transnitrosation reaction between procaspase-3 and thioredoxin-1 (Trx) occurs in cultured human T cells and prevents apoptosis. Trx participation in catalyzing transnitrosation reactions in cells may be general because this protein has numerous protein–protein interactions and plays a key role in cellular redox homeostasis [Powis G, Montfort WR (2001)
Annu Rev Pharmacol Toxicol
41:261–295], nitrosothiol content in cells [Haendeler J, Hoffmann J, Tischler V, Berk BC, Zeiher AM, Dimmeler S (2002)
Nat Cell Biol
4:743–749], and antiapoptotic signaling.
Directed evolution of aryl carrier proteins in the enterobactin synthetase
Authors: Zhou Zhe , Lai Jonathan R. , Walsh Christopher T.
Published: July 2007

The recognition of carrier proteins by multiple catalytic partners occurs in every cycle of chain elongation in the biosynthesis of fatty acids and of the pharmacologically important polyketide and nonribosomal peptide natural products. To dissect the features of carrier proteins that determine specific recognition at distinct points in assembly lines, we have used the two-module
Escherichia coli
enterobactin synthetase as a model system. Using an
entB
knockout strain, we developed a selection for growth on iron-limiting medium to evolve aryl carrier protein domains. The aryl carrier proteins from VibB of
Vibrio cholerae
vibriobactin and HMWP2 of
Yersinia pestis
yersiniabactin assembly lines were evolved by random mutagenesis to support growth under selection conditions, yielding a convergent set of mutations. Subsequent
in vitro
biochemical characterizations with partner enzymes EntE, EntF, and Sfp on the evolved VibB aryl carrier protein revealed a ≈500-fold improvement in reconstituted enterobactin production activity. Mechanistic characterization identified three distinct specific recognition surfaces of VibBArCP for three catalytic partners in enterobactin biosynthesis. Our results suggest that heterologous carrier protein interactions can be engineered with a small number of mutations given a suitable selection scheme and provide insights for reprogramming nonribosomal peptide biosynthesis.
ARE FIXED-TERM JOBS BAD FOR YOUR HEALTH?: A COMPARISON OF WEST-GERMANY AND SPAIN
Authors: Gash Vanessa , Mertens Antje , Gordo Laura Romeu
Published: July 2007

In this paper we analyse the health effects of fixed-term contract status for men and women in West-Germany and Spain using panel data. This paper asks whether changes in the employment relationship, as a result of the liberalisation of employment law, have altered the positive health effects associated with employment (Jahoda 1982; Goldsmith et al. 1996). Using information on switches between unemployment and employment by contract type we analyze whether transitions to different contracts have different health effects. We find that unemployed workers show positive health effects at job acquisition, and also find the positive effect to be smaller for workers who obtain a fixed-term job. We also establish surprising differences by gender and country, with women less likely to report positive health effects at job acquisition. For West-Germany, this was found to be a function of the dual-burden of paid and unpaid care within the home.
EMPLOYEE CONTROL IN THE ERA OF FLEXIBILITY: A STRESS BUFFER OR A STRESS AMPLIFIER?
Authors: Grönlund Anne
Published: July 2007

Traditionally, employee control has been considered a buffer against stress, but debate about the transformation of work raises new questions. Can individual control really counteract the high demands in downsized organisations? Or does it make flexible work even more difficult to define and delimit, physically and emotionally? This article, based on survey data from 800 Swedish employees, studies the effect of job control on work hours, work-family conflict and psychological wellbeing. The results show that high job demands are associated with longer work hours, more work-family conflict and lower wellbeing, while control has positive effects, even when demands are high.
POLICY FOR THE ‘PEAK HOUR’ OF LIFE: LESSONS FROM THE NEW DUTCH LIFE COURSE SAVING SCHEME
Authors: Maier Robert , de Graaf Willibrord , Frericks Patricia
Published: July 2007

The Dutch government attempts to base its social policy on a life course perspective, and it promotes such a perspective in Europe. This has led to the introduction of a Life Course Saving Scheme (starting in 2006), which aims to enable good management of the ‘peak hour’ of life and to facilitate transitions between and combinations of the activities of working, caring and learning. This important and ambitious policy can be seen as a pioneering example for European countries, however, the present realisation is not sufficient according to research and problems to deal with. This article examines (1) whether the Dutch government's life course policy is based on a sound scientific basis and (2) whether the new Life Course Saving Scheme can realise the policy aims as formulated.
Functionally independent components of prey capture are architecturally constrained in spider orb webs
Authors: Blackledge Todd A , Eliason Chad M
Published: July 2007

Evolutionary conflict in trait performance under different ecological contexts is common, but may also arise from functional coupling between traits operating within the same context. Orb webs first intercept and then retain insects long enough to be attacked by spiders. Improving either function increases prey capture and they are largely determined by different aspects of web architecture. We manipulated the mesh width of orbs to investigate its effect, along with web size, on prey capture by spiders and found that they functioned independently. Probability of prey capture increased with web size but was not affected by mesh width. Conversely, spiders on narrow-meshed webs were almost three times more likely to capture energetically profitable large insects, which demand greater prey retention. Yet, the two functions are still constrained during web spinning because increasing mesh width maximizes web size and hence interception, while retention is improved by decreasing mesh width because more silk adheres to insects. The architectural coupling between prey interception and retention has probably played a key role in both the macroevolution of orb web shape and the expression of plasticity in the spinning behaviours of spiders.
Transmission electron microscopy study of the cell–sensor interface
Authors: Wrobel Günter , Höller Matthias , Ingebrandt Sven , Dieluweit Sabine , Sommerhage Frank , Bochem Hans Peter , Offenhäusser Andreas
Published: July 2007

An emerging number of micro- and nanoelectronics-based biosensors have been developed for non-invasive recordings of physiological cellular activity. The interface between the biological system and the electronic devices strongly influences the signal transfer between these systems. Little is known about the nanoscopic structure of the cell–sensor interface that is essential for a detailed interpretation of the recordings. Therefore, we analysed the interface between the sensor surface and attached cells using transmission electron microscopy (TEM). The maximum possible resolution of our TEM study, however, was restricted by the quality of the interface preparation. Therefore, we complemented our studies with imaging ellipsometry.

We cultured HEK293 cells on substrates, which had been precoated with different types of proteins. We found that contact geometry between attached cell membrane and substrate was dependent on the type of protein coating used. In the presence of polylysine, the average distance of the membrane–substrate interface was in the range of 35–40 nm. However, the cell membrane was highly protruded in the presence of other proteins like fibronectin, laminin or concanavalin-A. The presented method allows the nanoscopic characterization of the cell–sensor interface.
The effect of population structure on the emergence of drug resistance during influenza pandemics
Authors: Débarre Florence , Bonhoeffer Sebastian , Regoes Roland R
Published: July 2007

The spread of H5N1 avian influenza and the recent high numbers of confirmed human cases have raised international concern about the possibility of a new pandemic. Therefore, antiviral drugs are now being stockpiled to be used as a first line of defence. The large-scale use of antivirals will however exert a strong selection pressure on the virus, and may lead to the emergence of drug-resistant strains. A few mathematical models have been developed to assess the emergence of drug resistance during influenza pandemics. These models, however, neglected the spatial structure of large populations and the stochasticity of epidemic and demographic processes. To assess the impact of population structure and stochasticity, we modify and extend a previous model of influenza epidemics into a metapopulation model which takes into account the division of large populations into smaller units, and develop deterministic and stochastic versions of the model. We find that the dynamics in a fragmented population is less explosive, and, as a result, prophylaxis will prevent more infections and lead to fewer resistant cases in both the deterministic and stochastic model. While in the deterministic model the final level of resistance during treatment is not affected by fragmentation, in the stochastic model it is. Our results enable us to qualitatively extrapolate the prediction of deterministic, homogeneous-mixing models to more realistic scenarios.
How it happened that a portion of a treatise entitled
New Improvements of Planting and Gardening both Philosophical and Practical
by Richard Bradley FRS, which dealt with blights of trees and plants, provided the first report of an environment that contained green sulphur photosynthetic bacteria
Authors: Santer Melvin
Published: July 2007

Richard Bradley proposed that biological agents caused infectious disease. He agreed that air could transmit disease, but it had to contain a living agent, either visible or microscopic. To dismiss the idea that air alone could cause disease he included evidence provided by Robert Balle about a toxic grotto near Lake Averna, close to Naples, whose fumes were lethal to animals and humans yet that lethality was not contagious and occurred quickly, not a characteristic of ‘pestilential fevers’. In this grotto the surface water was covered with a ‘green scum’, a layer of green sulphur photosynthetic bacteria that could live in that anoxic environment, which contained hydrogen sulphide and carbon dioxide gas and was accessible to visible light. This environment was a natural enrichment culture for these bacteria. It was the first time that the presence of these bacteria was disclosed in the scientific literature.
Entanglement in single-particle systems
Authors: Cunha Marcelo O. Terra , Dunningham Jacob A , Vedral Vlatko
Published: July 2007

We address some of the most commonly raised questions about entanglement, especially with regard to the so-called occupation number entanglement. To answer unambiguously whether entanglement can exist in a one-atom delocalized state, we propose an experiment capable of showing violations of Bell's inequality using only this state and local operations. We review previous discussions for one-photon non-locality and propose a specific experiment for creating one-atom entangled states, showing that the superselection rule of atom number can be overcome. As a by-product, this experiment suggests a means of creating an entangled state of two different chemical species. By comparison with a massless system, we argue that there should be no fundamental objection to such a superposition and its creation may be within reach of present technology.
The complex structure of hunter–gatherer social networks
Authors: Hamilton Marcus J , Milne Bruce T , Walker Robert S , Burger Oskar , Brown James H
Published: July 2007

In nature, many different types of complex system form hierarchical, self-similar or fractal-like structures that have evolved to maximize internal efficiency. In this paper, we ask whether hunter-gatherer societies show similar structural properties. We use fractal network theory to analyse the statistical structure of 1189 social groups in 339 hunter-gatherer societies from a published compilation of ethnographies. We show that population structure is indeed self-similar or fractal-like with the number of individuals or groups belonging to each successively higher level of organization exhibiting a constant ratio close to 4. Further, despite the wide ecological, cultural and historical diversity of hunter-gatherer societies, this remarkable self-similarity holds both within and across cultures and continents. We show that the branching ratio is related to density-dependent reproduction in complex environments and hypothesize that the general pattern of hierarchical organization reflects the self-similar properties of the networks and the underlying cohesive and disruptive forces that govern the flow of material resources, genes and non-genetic information within and between social groups. Our results offer insight into the energetics of human sociality and suggest that human social networks self-organize in response to similar optimization principles found behind the formation of many complex systems in nature.
Inhibitor development in haemophilia B: an orphan disease in need of attention
Authors: DiMichele Donna
Published: July 2007

Factor IX (FIX) inhibitors develop in 1·5–3% of haemophilia B patients. Due to its low incidence compared with that in haemophilia A, few comparable data exist on host and treatment‐related risk factors, and immunological processes associated with FIX inhibitor development. Moreover, the safety and efficacy of bypass therapy as well as the outcome predictors of successful inhibitor eradication have been poorly characterised. The lack of a useful evidence‐based approach to the diagnosis and management of FIX inhibitors complicates their significant morbidity due to the frequency of allergic reactions that often herald antibody development. This review discusses what is currently known about the epidemiology, natural history and immunology of anti‐FIX antibody development. It addresses several special considerations in the approach to the treatment of bleeding and inhibitor eradication. A case is made for moving forward with an integrated international collaboration for the further study of the nature and treatment of this problem.
Optimized methods for fungal α‐amylase airborne exposure assessment in bakeries and mills
Authors: Sander I. , Zahradnik E. , Bogdanovic J. , Raulf‐Heimsoth M. , Wouters I. M. , Renström A. , Harris‐Roberts J. , Robinson E. , Rodrigo M. J. , Goldscheid N. , Brüning T. , Doekes G.
Published: July 2007

Background
In order to enable reproducible and comparable exposure measurements of fungal alpha‐amylase (α‐amylase) in different laboratories and countries, the entire procedure from sampling of airborne dust to measuring extracted samples (including standards and the used enzyme) immunoassays must be standardized. The aim of this study was to establish optimal elution and assay conditions.

Methods
A parallel sampler was used for simultaneous collection of 10 samples of inhalable dust in bakeries and mills in Germany, England, the Netherlands and Spain. Three enzyme‐immunoassays (EIAs) for detection of fungal α‐amylase based on monoclonal antibodies or polyclonal antibodies were used for the measurement of the parallel‐sampled filters (n=432) extracted using several methods. The results were analysed by regression analysis of variance. Additional filters (n=54) were extracted and analysed using two EIAs to investigate the storage stability of the extracts.

Results
Although α‐amylase concentrations correlated well (r0.88), differences were found between the EIAs in the sensitivity and nominal values (up to a mean factor 5.8). The best elution medium for airborne filters (phosphate‐buffered saline ‘PBS’ with 0.05% Tween‐20) led to 1.2 to two times higher α‐amylase allergen yields than extraction in PBS only, while higher Tween‐20 concentrations decreased the extracted α‐amylase yield. During storage of frozen dust/filter extracts for 3–4 months at −20°C, a loss of approximately 40% of measurable α‐amylase was observed, which could be partially prevented by addition of 0.1% casein to the medium directly after extraction.

Conclusion
Although the effects of only a few of many possible causes of variation were investigated, for these factors a clear choice could be made with regard to optimal elution conditions and the use of validated EIAs with calibrated standards, thus making significant progress towards a completely standardized procedure for airborne α‐amylase measurements.