bluuebunny/crossref_metadata_2025 huggingface dataset:
Reappraisal of biosafety risks posed by PERVs in xenotransplantation
Authors: Louz Derrick , Bergmans Hans E. , Loos Birgit P. , Hoeben Rob C.
Published: November 2007

Donor materials of porcine origin could potentially provide an alternative source of cells, tissues or whole organs for transplantation to humans, but is hampered by the health risk posed by infection with porcine viruses. Although pigs can be bred in such a way that all known exogenous microorganisms are eliminated, this is not feasible for all endogenous pathogens, such as the porcine endogenous retroviruses (PERVs) which are present in the germline of pigs as proviruses. Upon transplantation, PERV proviruses would be transferred to the human recipient along with the xenograft. If xenotransplantation stimulates or facilitates replication of PERVs in the new hosts, a risk exists for adaptation of the virus to humans and subsequent spread of these viruses. In a worst‐case scenario, this might result in the emergence of a new viral disease. Although the concerns for disease potential of PERVs are easing, only limited pre‐clinical and clinical data are available. Small‐scale, well‐designed and carefully controlled clinical trials would provide more evidence on the safety of this approach and allow a better appreciation of the risks involved. It is therefore important to have a framework of protective measures and monitoring protocols in place to facilitate such initially small scale clinical trials. This framework will raise ethical and social considerations regarding acceptability. Copyright © 2007 John Wiley & Sons, Ltd.
Caloplaca fuscorufa—a misunderstood species in northern Europe
Authors: ARUP Ulf , ARNENG Emma , SØCHTING Ulrik
Published: November 2007

Caloplaca fuscorufa H. Magn. is a poorly known species that for a long time was known only from a single locality in Jämtland, northern Sweden, where it was collected in 1910. It has been suggested to be synonymous with C. crenularia (With.) J. R. Laundon, but has also been confused with C. exsecuta (Nyl.) Dalla Torre & Sarnth. We have compared the isotype of C. fuscorufa and material collected in Sweden, Norway and Svalbard, with presumably related species, using morphology, anatomy and chemistry as well as molecular data. The results show that C. fuscorufa is a distinct species, differing from C. crenularia mainly in its somewhat larger spores with wider septa, different colour of the apothecia and a more northern distribution. It differs from C. exsecuta mainly in its chemistry and smaller spores with smaller septa. Caloplaca crenularia is shown to have a more southern distribution in Sweden than previously understood. Chemical data and a molecular analysis based on ITS data show that C. fuscorufa is related to C. crenularia and C. ammiospila, but clearly separated from these species.
A new species of Xanthoparmelia (Ascomycota: Parmeliaceae) from the Canary Islands
Authors: PÉREZ-VARGAS Israel , HERNÁNDEZ-PADRÓN Consuelo , ELIX John A.
Published: November 2007

Xanthoparmelia perezdepazii from the Canary Islands is described as new to science. It is characterized by an isidiate upper surface, the presence of usnic, constipatic and protoconstipatic acids in the medulla and a brown lower surface.
D. Z. Phillips on God and evil
Authors: HICK JOHN
Published: November 2007

This a response to D. Z. Phillips's stringent critique of theodicies, including that suggested by myself. I offer counters to his array of arguments, and point to what I see as a fundamental flaw in his philosophy of religion. He appealed to religious language as used by ordinary religious persons. But his account of the meaning of this language was not that of the ordinary religious believer. He thus claimed, by implication, to know better than they did what they really meant. I conclude that he was a non-realist concerning both religious language and the reality of God.
Dynamics of continental deformation in Asia
Authors: Vergnolle M. , Calais E. , Dong L.
Published: November 2007

The relevance of plate tectonics concepts to the description of deformation of large continental areas like Asia is subject to much debate. For some, the deformation of continents is better described by rigid motion of lithospheric blocks with strain concentrated along narrow fault zones. For others, it is better described by viscous flow of a continuously deforming solid in which faults play a minor role. Discriminating these end‐member hypotheses requires spatially dense measurements of surface strain rates covering the whole deforming area. Here we revisit the issue of the forces and rheological structure that control present‐day deformation in Asia. We use the “thin sheet” theory, with deformation driven by the balance of boundary and buoyancy stresses acting on a faulted lithosphere with laterally varying strength. Models are validated against a recent, homogeneous, GPS velocity field that covers most of Asia. In the models, deformation in compressional areas (Himalayas, Tien Shan, Altay) is well reproduced with strong coupling at the India/Eurasia plate contact, which allows for boundary forces to transfer into Asia. Southeastward motions observed in north and south China, however, require tensional, oceanward directed stresses, possibly generated by gravitational potential energy gradients across the Indonesian and Pacific subductions. Model and observed strain rates show that a large part of Asia undergoes no resolvable strain, with a kinematics apparently consistent with block‐ or plate‐like motions. Internal strain, possibly continuous, is limited to high‐elevation, mechanically weaker areas. Lateral variations of lithospheric strength appear to control the style of deformation in Asia, with a dynamics consistent with the thin sheet physical framework.
Stochastic simulation and spatial estimation with multiple data types using artificial neural networks
Authors: Besaw Lance E. , Rizzo Donna M.
Published: November 2007

A novel data‐driven artificial neural network (ANN) that quantitatively combines large numbers of multiple types of soft data is presented for performing stochastic simulation and/or spatial estimation. A counterpropagation ANN is extended with a radial basis function to estimate parameter fields that reproduce the spatial structure exhibited in autocorrelated parameters. Applications involve using three geophysical properties measured on a slab of Berea sandstone and the delineation of landfill leachate at a site in the Netherlands using electrical formation conductivity as our primary variable and six types of secondary data (e.g., hydrochemistry, archaea, and bacteria). The ANN estimation fields are statistically similar to geostatistical methods (indicator simulation and cokriging) and reference fields (when available). The method is a nonparametric clustering/classification algorithm that can assimilate significant amounts of disparate data types with both continuous and categorical responses without the computational burden associated with the construction of positive definite covariance and cross‐covariance matrices. The combination of simplicity and computational speed makes the method ideally suited for environmental subsurface characterization and other Earth science applications with spatially autocorrelated variables.
Voltage-Gated K+ Channel Dysfunction in Myocytes from a Dog Model of Subarachnoid Hemorrhage
Authors: Jahromi Babak S , Aihara Yasuo , Ai Jinglu , Zhang Zhen-Du , Nikitina Elena , Macdonald Robert Loch
Published: November 2007

Delayed cerebral vasospasm after subarachnoid hemorrhage is primarily due to sustained contraction of arterial smooth muscle cells. Its pathogenesis remains unclear. The degree of arterial constriction is regulated by membrane potential that in turn is determined predominately by K+ conductance (GK). Here, we identified the main voltage-gated K+ (Kv) channels contributing to outward delayed rectifier currents in dog basilar artery smooth muscle as Kv2 class through a combination of electrophysiological and pharmacological methods. Kv2 current density was nearly halved in vasospastic myocytes after subarachnoid hemorrhage (SAH) in dogs, and Kv2.1 and Kv2.2 were downregulated in vasospastic myocytes when examined by quantitative mRNA, Western blotting, and immunohistochemistry. Vasospastic myocytes were depolarized and had a smaller contribution of GK toward maintenance of their membrane potential. Pharmacological block of Kv current in control myocytes mimicked the depolarization observed in vasospastic arteries. The degree of membrane depolarization was found to be compatible with the amount of vasoconstriction observed after SAH. We conclude that Kv2 dysfunction after SAH contributes to the pathogenesis of delayed cerebral vasospasm. This may confer a novel target for treatment of delayed cerebral vasospasm.
Pancreatic beta-cell granule peptides form heteromolecular complexes which inhibit islet amyloid polypeptide fibril formation
Authors: JAIKARAN Emma T. A. S. , NILSSON Melanie R. , CLARK Anne
Published: November 2007

Islet amyloid polypeptide (IAPP), or ‘amylin’, is co-stored with insulin in secretory granules of pancreatic islet β-cells. In Type 2 diabetes, IAPP converts into a β-sheet conformation and oligomerizes to form amyloid fibrils and islet deposits. Granule components, including insulin, inhibit spontaneous IAPP fibril formation in vitro. To determine the mechanism of this inhibition, molecular interactions of insulin with human IAPP (hIAPP), rat IAPP (rIAPP) and other peptides were examined using surface plasmon resonance (BIAcore), CD and transmission electron microscopy (EM). hIAPP and rIAPP complexed with insulin, and this reaction was concentration-dependent. rIAPP and insulin, but not pro-insulin, bound to hIAPP. Insulin with a truncated B-chain, to prevent dimerization, also bound hIAPP. In the presence of insulin, hIAPP did not spontaneously develop β-sheet secondary structure or form fibrils. Insulin interacted with pre-formed IAPP fibrils in a regular repeating pattern, as demonstrated by immunoEM, suggesting that the binding sites for insulin remain exposed in hIAPP fibrils. Since rIAPP and hIAPP form complexes with insulin (and each other), this could explain the lack of amyloid fibrils in transgenic mice expressing hIAPP. It is likely that IAPP fibrillogenesis is inhibited in secretory granules (where the hIAPP concentration is in the millimolar range) by heteromolecular complex formation with insulin. Alterations in the proportions of insulin and IAPP in granules could disrupt the stability of the peptide. The increase in the proportion of unprocessed pro-insulin produced in Type 2 diabetes could be a major factor in destabilization of hIAPP and induction of fibril formation.
Transcriptional activation of the murine Muc5ac mucin gene in epithelial cancer cells by TGF-beta/Smad4 signalling pathway is potentiated by Sp1
Authors: JONCKHEERE Nicolas , van der SLUIS Maria , VELGHE Amélie , BUISINE Marie-Pierre , SUTMULLER Marjolein , DUCOUROUBLE Marie-Paule , PIGNY Pascal , BÜLLER Hans A. , AUBERT Jean-Pierre , EINERHAND Alexandra W. C. , VAN SEUNINGEN Isabelle
Published: November 2007

Changes in the expression of mucin genes in gastrointestinal cancers is thought to contribute to the development of the disease. In our laboratory we have shown previously that MUC5AC is aberrantly expressed in rectosigmoid villous adenomas. However, the regulatory mechanisms underlying that altered profile of expression is unknown. In order to study its regulation at the transcriptional level, we have isolated and characterized 5.5 kb of the 5´-flanking region of the mouse Muc5ac mucin gene. The promoter is flanked by a TATA box and a transcriptional start site is located 22 bp downstream of the TATA box. Analysis of the sequence showed a high density of binding sites for Smad4, an essential factor in the signalling cascade activated by TGF-β (transforming growth factor-β), and Sp1, an important factor in the regulation of MUC5AC. This led us to study Muc5ac regulation by TGF-β. We show that exogenous addition of TGF-β to the cells induces Muc5ac endogenous expression, promoter activity and Smad4 binding to the promoter. By co-transfection studies we show that Smad4 is essential for Muc5ac promoter activation and that it does not synergize with Smad2 or Smad3. By gel-retardation and co-transfection assays, we identified Sp1 and Sp3 as important regulators of Muc5ac expression and showed that Smad4 and Sp1 act in a co-operative manner to transactivate Muc5ac promoter activity. Altogether these results bring new insights into the molecular mechanisms of TGF-β-mediated up-regulation of Muc5ac and enhance our understanding as to how Muc5ac is regulated in certain pathologies of the gastrointestinal tract.
Functional polypeptides can be synthesized from human mitochondrial transcripts lacking termination codons
Authors: CHRZANOWSKA-LIGHTOWLERS Zofia M. A. , TEMPERLEY Richard J. , SMITH Paul M. , SENECA Sara H. , LIGHTOWLERS Robert N.
Published: November 2007

The human mitochondrial genome (mtDNA) is a small, circular DNA duplex found in multi-copy in the mitochondrial matrix. It is almost fully transcribed from both strands to produce large polycistronic RNA units that are processed and matured. The 13 mtDNA-encoded polypeptides are translated from mt-mRNAs that have been matured by polyadenylation of their free 3´-termini. A patient with clinical features consistent with an mtDNA disorder was recently shown to carry a microdeletion, resulting in the loss of the termination codon for MTATP6 and in its juxtaposition with MTCO3. Cell lines from this patient exhibited low steady-state levels of RNA14, the bi-cistronic transcript encoding subunits 6 and 8 of the FoF1-ATP synthase, complex V, consistent with a decreased stability. Recent reports of ‘non-stop’ mRNA decay systems in the cytosol have failed to determine the fate of gene products derived from transcripts lacking termination codons, although enhanced decay clearly required the ‘non-stop’ transcripts to be translated. We wished to determine whether functional translation products could still be expressed from non-stop transcripts in the human mitochondrion. Although a minor defect in complex V assembly was noted in the patient-derived cell lines, the steady-state level of ATPase 6 was similar to controls, consistent with the pattern of de novo mitochondrial protein synthesis. Moreover, no significant difference in ATP synthase activity could be detected. We conclude that, in the absence of a functional termination codon, although mitochondrial transcripts are more rapidly degraded, they are also translated to generate stable polypeptides that are successfully integrated into functional enzyme complexes.
Chronic myeloid leukaemia: stem cell derived but progenitor cell driven
Authors: MARLEY Stephen B. , GORDON Myrtle Y.
Published: November 2007

The biology of CML (chronic myeloid leukaemia) has been extensively investigated as the disease is a paradigm of neoplasms induced when a translocation results in expression of a novel fusion protein, in this instance p210BCR-ABL. Although CML manifests itself principally as unregulated expansion of the myeloid lineage, the lesion is present in the stem cell population and it has long been assumed that disregulated stem cell kinetics must underlie the basic pathology of the disease. In this review, we present evidence that, in normal haemopoiesis, less primitive precursor cells retain considerable flexibility in their capacity to undergo self-renewal, allowing them to maintain lineage-specific homoeostasis without inflicting proliferative stress upon the stem cell population. This mechanism is dysregulated in CML and we have developed a self-renewal assay for CFU-GM (colony-forming unit-granulocyte/macrophage) which demonstrates that, in CML, the PI (proliferative index) of the myeloid progenitor cell population is increased. The ability to measure the PI as an endpoint of p210BCR-ABL expression gives considerable versatility to the in vitro investigation of putative therapeutic regimes in CML.
Assessment of cerebral autoregulation from ectopic heartbeats
Authors: EAMES Penelope J. , POTTER John F. , PANERAI Ronney B.
Published: November 2007

Transfer function analysis of spontaneous fluctuations in BP (blood pressure) and CBFV (cerebral blood flow velocity) has been widely used to study dynamic CA (cerebral autoregulation). The inverse Fourier transform and its integral, giving the impulse and step responses, have been used to gain perspective of the state of dynamic CA from the frequency and time domains respectively. The occurrence of ectopic heartbeats in the data has usually been treated as an artefact. Data containing multiple ectopic heartbeats were selected from a data set compiled for an acute stroke study which also included bilateral middle CBFV, concurrent surface ECG and non-invasive beat-to-beat BP recordings. Transfer function analysis and impulse and step responses were calculated from these data by (i) retaining ectopic heartbeats, (ii) after removal of ectopic heartbeats and replacement by linear interpolation, and (iii) using a narrow window of data surrounding selected ectopic heartbeats. Coherent averaging of the raw data of the selected ectopic heartbeats also allowed direct visualization of the relationship between BP changes and CBFV. The impulse and step responses were similar in shape whether or not ectopic heartbeats had been removed and showed characteristics of active dynamic CA. Removal of ectopic heartbeats from the CBFV and BP tracings, by linear interpolation or other methods, is not necessary to provide reliable estimates of dynamic autoregulation in subjects with ectopic heartbeat rates of up to eight per min. Additionally, impulse-like disturbances of BP induced by single-beat ectopic heartbeats provide enough information to characterize the autoregulatory response of the subject in agreement with more traditional methods of dynamic autoregulation assessment.
Effect of acetazolamide on leg endurance exercise at sea level and simulated altitude
Authors: Fulco Charles S. , Muza Steven R. , Ditzler Dan , Lammi Eric , Lewis Steven F. , Cymerman Allen
Published: November 2007

Acetazolamide can be taken at sea level to prevent acute mountain sickness during subsequent altitude exposure. Acetazolamide causes metabolic acidosis at sea level and altitude, and increases SaO2 (arterial oxygen saturation) at altitude. The aim of the present study was to determine whether acetazolamide impairs muscle endurance at sea level but not simulated altitude (4300 m for <3 h). Six subjects (20±1 years of age; mean±S.E.M.) performed exhaustive constant work rate one-leg knee-extension exercise (25±2 W) once a week for 4 weeks, twice at sea level and twice at altitude. Each week, subjects took either acetazolamide (250 mg) or placebo orally in a double-blind fashion (three times a day) for 2 days. On day 2, all exercise bouts began approx. 2.5 h after the last dose of acetazolamide or placebo. Acetazolamide caused similar acidosis (pH) in all subjects at sea level (7.43±0.01 with placebo compared with 7.34±0.01 with acetazolamide; P<0.05) and altitude (7.48±0.03 with placebo compared with 7.37±0.01 with acetazolamide; P<0.05). However, endurance performance was impaired with acetazolamide only at sea level (48±4 min with placebo compared with 36±5 min with acetazolamide; P<0.05), but not altitude (17±2 min with placebo compared with 20±3 min with acetazolamide; P=not significant). In conclusion, lack of impairment of endurance performance by acetazolamide compared with placebo at altitude was probably due to off-setting secondary effects resulting from acidosis, e.g. ventilatory induced increase in SaO2 for acetazolamide compared with placebo (89±1 compared with 86±1% respectively; P<0.05), which resulted in an increased oxygen pressure gradient from capillary to exercising muscle.
Effective potential and resummation procedure to multidimensional complex cubic potentials for weak and strong coupling
Authors: Yahiaoui S.-A. , Cherroud O. , Bentaiba M.
Published: November 2007

The method for the recursive calculation of the effective potential is applied successfully in case of weak-coupling limit (g→0) to a multidimensional complex cubic potential. In strong-coupling limit (g→∞), the result is resumed using the variational perturbation theory (VPT). It is found that the convergence of VPT results approaches those expected.
Core ionization potentials from self-interaction corrected Kohn-Sham orbital energies
Authors: Tu Guangde , Carravetta Vincenzo , Vahtras Olav , Ågren Hans
Published: November 2007

We propose a simple self-interaction correction to Kohn-Sham orbital energies in order to apply ground state Kohn-Sham density functional theory to accurate predictions of core electron binding energies and chemical shifts. The proposition is explored through a series of calculations of organic compounds of different sizes and types. Comparison is made versus experiment and the “ΔKohn-Sham” method employing separate state optimizations of the ground and core hole states, with the use of the B3LYP functional and different basis sets. A parameter α is introduced for a best fitting of computed and experimental ionization potentials. It is found that internal parametrizations in terms of basis set expansions can be well controlled. With a unique α=0.72 and basis set larger than 6-31G, the core ionization energies (IPs) of the self-interaction corrected Kohn-Sham calculations fit quite well to the experimental values. Hence, self-interaction corrected Kohn-Sham calculations seem to provide a promising tool for core IPs that combines accuracy and efficiency.
Comparative study of the interaction of pyridine with polycrystalline Ag and amorphous solid water
Authors: Bahr S. , Kempter V.
Published: November 2007

The interaction of pyridine (C5H5N) with polycrystalline Ag and amorphous solid water (D2O) is compared. Metastable impact electron spectroscopy (MIES) and reflection-absorption infrared spectroscopy (RAIRS) were utilized to obtain information on the structure of the pyridine-Ag and pyridine-water interfaces. On polycrystalline Ag, C5H5N adsorbs with its molecular axis perpendicular to the surface whereby a work function decrease of 1.5eV takes place during the build up of the first layer. In the second layer the molecular axis is tilted with respect to the surface normal. On amorphous solid water, C5H5N is initially adsorbed on top with its ring plane oriented preferentially near parallel with respect to the surface, reflecting the contribution of two different interactions to the bonding, the formation of a π-hydrogen bond, and competitive bonding via the nitrogen lone pair. Coverage-driven reorientation takes place during the completion of the first monolayer and increases the average tilt angle. We have followed the growth of pyridine films up to the third layer which, according to RAIRS, shows clear signs of condensation. No embedding of pyridine species into the underlying water film can be noticed when heating up to desorption. The exposure of a pyridine film at 124K to D2O molecules does not lead to on top adsorption. Instead, D2O becomes initially embedded into the pyridine film, and RAIRS indicates solvation of the pyridine species.
Theoretical elastic moduli for disordered packings of interconnected spheres
Authors: Zaccone Alessio , Lattuada Marco , Wu Hua , Morbidelli Massimo
Published: November 2007

A theoretical model has been developed which provides analytical expressions for the elastic moduli of disordered isotropic ensembles of spheres interconnected by physical bonds. Young’s and shear moduli have been derived assuming an ideal random isotropic network and the radial distribution function for disordered packings of spheres. The interparticle interactions are accounted for in terms of surface forces for the two distinct cases of perfectly rigid spheres and spheres deformable at contact. A theoretical expression is also derived in a similar way for the bulk or compressibility modulus. In this case, an atomistic approach has been followed based on the analogy with noble gas solids and colloidal crystals. Also in this case, disordered spatial distribution of the spheres is described statistically. For the case of colloidal aggregates, a total two-body mean-field interaction potential is used which includes the Born repulsion energy. This latter contribution plays an essential role in determining the compression behavior of systems of particles aggregated in the primary minimum of the potential well and, therefore, must not be neglected. Both the expression of the Young’s modulus and that of the compressibility modulus derived in this work are found to be consistent with two distinct sets of experimental data which recently appeared in the literature.
Sensitivity of an exothermic chemical wave front to a departure from local equilibrium
Authors: Nowakowski B. , Lemarchand A.
Published: November 2007

We study the propagation of an exothermic chemical wave front in a reactive dilute gas and show that the particle velocity distribution departs from the Maxwellian form in the front zone. The analytical corrections to the balance equations for concentrations, temperature, and stream velocity induced by the departure from local equilibrium are derived from a perturbative solution of the Boltzmann equation. Our analytical predictions of the front properties, including its propagation speed, compare well with microscopic simulations of the particle dynamics.
Vacuum ultraviolet spectroscopic properties of rare earth (RE=Ce,Tb,Eu,Tm,Sm)-doped hexagonal KCaGd(PO4)2 phosphate
Authors: Zhang Z. J. , Yuan J. L. , Duan C. J. , Xiong D. B. , Chen H. H. , Zhao J. T. , Zhang G. B. , Shi C. S.
Published: November 2007

Hexagonal KCaGd(PO4)2:RE3+ (RE=Ce,Tb,Eu,Tm,Sm) were synthesized by coprecipitation method and their vacuum ultraviolet–ultraviolet (VUV-UV) spectroscopic properties were investigated. The bands at about 165nm in the VUV excitation spectra are attributed to the host lattice absorptions. For Ce3+-doped samples, the bands at 207, 256, 275, and 320nm are assigned to the 4f-5d transitions of Ce3+ in KCaGd(PO4)2. For Tb3+-doped sample, the bands at 203 and 222nm are related to the 4f-5d spin-allowed transitions. For Eu3+-doped sample, the O2−–Eu3+ charge-transfer band (CTB) at 229nm is observed, and the fine emission spectrum of Eu3+ indicates that Eu3+ ions prefer to occupy Gd3+ or Ca2+ sites in the host lattice. For Tm3+- and Sm3+-doped samples, the O2−–Tm3+ and O2−–Sm3+ CTBs are observed to be at 176 and 186nm, respectively. From the standpoints of the absorption band, color purity, and luminescent intensity, Tb3+-doped KCaGd(PO4)2 is a potential candidate for 172nm excited green plasma display phosphors.
Terahertz gain on shallow donor transitions in silicon
Authors: Zhukavin R. Kh. , Shastin V. N. , Pavlov S. G. , Hübers H.-W. , Hovenier J. N. , Klaassen T. O. , van der Meer A. F. G.
Published: November 2007

Small signal gain measurements of optically excited terahertz silicon lasers are reported. Two types of lasers, Si:P and Si:Bi, were investigated. They were optically excited with radiation from a free electron laser or a CO2 laser. The experiments were performed with an oscillator-amplifier scheme where one sample serves as a laser while the other one is an amplifier. In case of the free electron laser the pump frequency corresponds to intracenter excitation of the 2p0 or 2p± states of the P and Bi Coulomb centers, and the gain was determined for the 2p0→1s(E), 2p0→1s(T2) transitions in Si:P and the 2p±→1s(E) transition in Si:Bi. Pumping with a CO2 laser leads to photoexcitation of the Coulomb centers. In this case the gain was determined for the 2p0→1s(T2) of Si:P transition. The gain for intracenter pumping is in the range 5−10 cm−1 while for photoexcitation the gain is considerably less, namely ∼0.5 cm−1. The experimental results are analyzed and found to be in good agreement with theoretical calculations based on balance equations.
Investigation of a cavitation bubble between a rigid boundary and a free surface
Authors: Gregorčič Peter , Petkovšek Rok , Možina Janez
Published: November 2007

When a high-intensity laser pulse is focused into a liquid the energy is converted into mechanical energy via an optodynamic process. The conversion starts with plasma formation; this is followed by shock-wave propagation and the expansion of a cavitation bubble. A cavitation bubble developed near boundaries results in an asymmetrical collapse, with the generation of a liquid jet during the bubble’s rebound. In the case of a free surface this liquid jet is directed away from the surface and the oscillation times are prolonged. On the other hand, in the case of a rigid boundary, the liquid jet is directed toward the boundary and the oscillation times are shortened. We present measurements of a cavitation bubble oscillating between a free surface and a rigid boundary using deflections of a laser beam as the optical probe. Shadow photography was used simultaneously as a comparison during the experiments. With the beam-deflection probe we also measured the shortening of the oscillation times near a free surface as well as the prolongation of oscillation times near a rigid boundary. In order to explain this shortening of the cavitation-bubble oscillation times near a free surface, Rayleigh’s model was extended and compared with our experimental results.
Estimation of parametric gain in GaAs∕AlOx waveguides by fluorescence and second harmonic generation measurements
Authors: Ravaro M. , Le Dû M. , Likforman J.-P. , Ducci S. , Berger V. , Leo G. , Marcadet X.
Published: November 2007

Efficient parametric fluorescence is obtained from a pump wavelength λ=1.06μm in low-loss, form-birefringent GaAs∕AlOx waveguides. Besides showing a 1μm wide tuning range and the onset of amplification regime for continuous-wave pump levels around 50mW, an 8% parametric gain is determined. This is the highest figure reported to date in semiconductor waveguides, and confirms GaAs∕AlOx waveguides as a candidate for an integrated parametric optical source.
Spin valve effect in self-exchange biased ferromagnetic metal/semiconductor bilayers
Authors: Zhu M. , Wilson M. J. , Sheu B. L. , Mitra P. , Schiffer P. , Samarth N.
Published: November 2007

We report magnetization and magetoresistance measurements in hybrid ferromagnetic metal/semiconductor heterostructures comprised of MnAs∕(Ga,Mn)As bilayers. Our measurements show that the (metallic) MnAs and (semiconducting) (Ga,Mn)As layers are exchange coupled, resulting in an exchange biasing of the magnetically softer (Ga,Mn)As layer that weakens with layer thickness. Magnetoresistance measurements in the current-perpendicular-to-the-plane geometry show a spin valve effect in these self-exchange biased bilayers. Similar measurements in MnAs∕p-GaAs∕(Ga,Mn)As trilayers show that the exchange coupling diminishes with spatial separation between the layers.
Stimulated emission of CdS nanowires grown by thermal evaporation
Authors: Pan Hui , Xing Guichuan , Ni Zhenhua , Ji Wei , Feng Yuan Ping , Tang Zhe , Chua Daniel H. C. , Lin Jianyi , Shen Zexiang
Published: November 2007

High-quality CdS nanowires with wurtzite structure were produced by thermal evaporation of CdS powder. The nanowires were core-shell structures, consisting of crystalline core and amorphous/polycrystal shell. The intensity of the second-order longitudinal phonon mode in the Raman spectrum of the CdS nanowires is higher than that of the first-order mode due to exciton-phonon coupling. The photoluminescence of the CdS nanowires is power dependent, and the photoluminescence peak at 516.5nm becomes narrower with increase in excitation power, indicating the stimulated emission characteristics of CdS nanowires. The population inversion generated by two-photon absorption is mainly attributed to the occurrence of stimulated emission.
Application of NaYF4:Yb, Er upconversion fluorescence nanocrystals for solution-processed near infrared photodetectors
Authors: Sun Cheng-Jun , Xu Zhihua , Hu Bin , Yi G. S. , Chow G. M. , Shen Jian
Published: November 2007

In an attempt to overcome the technical challenges in the conventional solution-processed near infrared (NIR) photodetectors, we have used NaYF4:Yb, Er upconversion fluorescence nanocrystals to replace the semiconductor quantum dots in conjugated polymers. Under NIR excitation, the NaYF4:Yb, Er nanocrystals emit visible light in the solution-processed NIR photodetectors. The emitted visible light is simultaneously absorbed by the host conjugated polymer to generate photocurrent, which indicates that our approach is applicable to fabricate NIR photodetectors while avoiding the major technical challenges associated with semiconductor quantum dot based NIR photodetectors.
Domestic Sourcing by Foreign-Owned Subsidiaries
Authors: Williams David , McDonald Frank , Tüselmann Heinz J , Turner Colin
Published: November 2007

This paper investigates the development of domestic sourcing by foreign-owned subsidiaries (FOS) in the UK. The regional development and international-business literatures are used to develop a conceptual framework on the links between autonomy, the use of networks, and domestic sourcing. Data from a survey of German, French, and US FOS in the UK is used to test the model. The results indicate that increased use of networks and increased operational decision-making autonomy are associated with increased domestic sourcing, but that only a minority of FOS are increasing their use of domestic sourcing. The growing importance of global sourcing is considered as a possible explanation for the low proportion of FOS that are increasing their use of domestic sourcing. The implications for regional-development policy of the findings are also assessed.
The systematics and biology of the spider genus Nephila (Araneae:Nephilidae) in the Australasian region
Authors: Harvey Mark S. , Austin Andrew D. , Adams Mark
Published: November 2007

Five species of the nephilid genus Nephila Leach are found in the Australasian region, which for the purposes of this study was defined as Australia and its dependencies (including Lord Howe I., Norfolk I., Christmas I., Cocos (Keeling) Is), New Guinea (including Papua New Guinea and the Indonesian province of West Papua), Solomon Is, Vanuatu, New Caledonia, Fiji, Tonga, Niue, New Zealand and other parts of the south-west Pacific region. All species are redescribed and illustrated. Nephila pilipes (Fabricius) occurs in the closed forests of eastern and northern Australia, New Guinea, Solomon Is and Vanuatu (through to South-East Asia); N. plumipes (Latreille) is found in Australia (including Lord Howe I. and Norfolk I.), New Guinea, Vanuatu, Solomon Is and New Caledonia; N. tetragnathoides (Walckenaer) inhabits Fiji, Tonga and Niue; N. antipodiana (Walckenaer) occurs in northern Australia (as well as Christmas I.), New Guinea and Solomon Is (through to South-East Asia); and N. edulis (Labillardière) is found in Australia (including Cocos (Keeling) Is), New Guinea, New Zealand and New Caledonia. Epeira (Nephila) walckenaeri Doleschall, E. (N.) hasseltii Doleschall, N. maculata var. annulipes Thorell, N. maculata jalorensis Simon, N. maculata var. novae-guineae Strand, N. pictithorax Kulczyński, N. maculata var. flavornata Merian, N. pictithorax Kulczyński, N. maculata var. flavornata Merian, N. maculata piscatorum de Vis, and N. (N.) maculata var. lauterbachi Dahl are proposed as new synonyms of N. pilipes. Nephila imperialis var. novaemecklenburgiae Strand, N. ambigua Kulczyński, N. sarasinorum Merian and N. celebesiana Strand are proposed as new synonyms of N. antipodiana. Meta aerea Hogg, N. meridionalis Hogg, N. adelaidensis Hogg and N. meridionalis hermitis Hogg are proposed as new synonyms of N. edulis. Nephila picta Rainbow is removed from the synonymy of N. plumipes and treated as a synonym of N. edulis, and N. nigritarsis insulicola Pocock is removed from the synonymy of N. plumipes and treated as a synonym of N. antipodiana. Allozyme data demonstrate that N. pilipes is distinct at the 80% FD level from N. edulis, N. plumipes and N. tetragnathoides. Nephila plumipes and N. tetragnathoides, deemed to represent sister-taxa owing to the shared presence of a triangular protrusion of the male pedipalpal conductor, were found to differ at 15% FD in the genetic study. No genetic differentiation was found between 10 populations of N. edulis sampled across mainland Australia. Species of the genus Nephila have been extensively used in ecological and behavioural studies, and the biology of Nephila species in the Australasian region is extensively reviewed and compared with studies on Nephila species from other regions of the world.
Mechanism of degradation of CPEB during
Xenopus
oocyte maturation
Authors: Setoyama Daiki , Yamashita Masakane , Sagata Noriyuki
Published: November 2007

CPEB, a cytoplasmic polyadenylation element-binding protein, plays an important role in translational control of maternal mRNAs in early animal development. During
Xenopus
oocyte maturation, CPEB undergoes a Cdc2-mediated phosphorylation- and ubiquitin-dependent degradation that is required for proper entry into meiosis II. However, the precise mechanism of CPEB degradation, including the identity of the responsible E3 ubiquitin ligase, is not known. Here, we show that the SCF
β-TrCP
E3 ubiquitin ligase complex targets CPEB for degradation during
Xenopus
oocyte maturation. β-TrCP, the F-box protein of SCF
β-TrCP
, specifically binds to a sequence
190
TSGFSS
195
(termed here the TSG motif) of CPEB, thereby targeting CPEB for degradation. β-TrCP binding depends on phosphorylation of Thr-190, Ser-191, and Ser-195 in the TSG motif. Among these residues, Ser-191 is phosphorylated by the Polo-like kinase Plx1, which binds CPEB at a specific Thr-125 residue prephosphorylated by Cdc2. Finally, Cdc2-mediated phosphorylation of other multiple Ser residues, previously implicated in CPEB degradation, is required for both Thr-125 phosphorylation and β-TrCP binding, presumably causing conformational changes of CPEB. We propose that Cdc2 and Plx1 sequentially phosphorylate CPEB and target it for SCF
β-TrCP
-dependent degradation in
Xenopus
oocytes. We suggest that many other proteins carrying the TSG-like motif may be targeted by SCF
β-TrCP
.
Targeted polyphosphatase expression alters mitochondrial metabolism and inhibits calcium-dependent cell death
Authors: Abramov Andrey Y. , Fraley Cresson , Diao Catherine T. , Winkfein Robert , Colicos Michael A. , Duchen Michael R. , French Robert J. , Pavlov Evgeny
Published: November 2007

Polyphosphate (polyP) consists of tens to hundreds of phosphates, linked by ATP-like high-energy bonds. Although polyP is present in mammalian mitochondria, its physiological roles there are obscure. Here, we examine the involvement of polyP in mitochondrial energy metabolism and ion transport. We constructed a vector to express a mitochondrially targeted polyphosphatase, along with a GFP fluorescent tag. Specific reduction of mitochondrial polyP, by polyphosphatase expression, significantly modulates mitochondrial bioenergetics, as indicated by the reduction of inner membrane potential and increased NADH levels. Furthermore, reduction of polyP levels increases mitochondrial capacity to accumulate calcium and reduces the likelihood of the calcium-induced mitochondrial permeability transition, a central event in many types of necrotic cell death. This confers protection against cell death, including that induced by β-amyloid peptide, a pathogenic agent in Alzheimer's disease. These results demonstrate a crucial role played by polyP in mitochondrial function of mammalian cells.
Correspondence Between Quantum and Classical Dynamics in Photodetachment Near Elastic Wall
Authors: Yang Guang-can , Rui Kui-kui , Zheng Yi-zhuang
Published: November 2007

The photodetachment of H near an elastic wall was investigated and an analytical formula of the cross section was derived. It was found that the cross section is a superposition of a smooth background and sinusoidal oscillation, which depends on the distance between the ion and the elastic wall. The classical dynamics of the photo-detached electron and its quantum correspondence was analyzed. In this model, the semiclassical photodetachment cross section is exactly the same as the quantum result.
Influence of New Interaction Potential on MD Simulation of MgSiO3 Perovskite Thermodynamic Properties
Authors: Chen Qiong , Cheng Xin-lu , Yang Xiang-dong
Published: November 2007

The interaction potential plays an important role in molecular dynamics (MD) simulations. Pair potential has been used to simulate the melting temperature of MgSiO3 perovskite in previous studies, but considerable discrepancy of melting temperature exists between these simulations. Comparisons of potential energy curves are performed to explain the discrepancy. To further investigate the influence of the interaction potential parameters on the MD simulation result, a new set of potential parameters is developed based on two fitting potential parameters of previous studies, and is applied in the present study. The simulated molar volume MgSiO3 perovskite agrees well with the study by Belonoshko and Dubrovinsky at ambient condition. The equations of state, constant-pressure heating capacity and the constant-pressure thermal expansivity of MgSiO3 perovskite are close to the experimental data. Calculated melting temperatures are also comparable with those derived from previous studies.
First-principles Periodic Density Functional Study of CO Adsorption on Spinel-type CuCr2O4 (100) Surface
Authors: Xu Xiang-lan , Chen Wen-kai , Sun Bao-zhen , Wang Xia , Lu Chun-hai
Published: November 2007

The catalytic properties of CuCr2O4 with the cubic normal spinel-type structure were discussed by means of studying CO adsorption on the CuCr2 O4 (100) surface in the framework of density functional theory. The results of geometry optimization show that CO prefers to adsorb at a Cu site with the adsorption energy of 133.2 kJ/mol. The adsorptions at all sites lead to a decrease in C-O stretching frequency, an increase in C-O bond length and a net positive Mulliken charge for the CO molecule. Population analysis indicates that the charges transfer from the CO molecule to substrate. The density of states for CO molecule before and after adsorption are also computed to discuss the bonding mechanism of CO.
Uncoupling the effects of shade and food resources of vegetation on Mediterranean ants: an experimental approach at the community level
Authors: Arnan Xavier , Rodrigo Anselm , Retana Javier
Published: November 2007

Vegetation is one of the main factors affecting the composition and structure of ant communities. The effect of vegetation is both by offering food resources and by modifying the proportion of ground cover exposed to shade conditions. However, it is difficult in field studies to uncouple the effects of food resources and shade on animal communities. The goal of this study was to analyze experimentally the effects of vegetation through food and shade supply on the structure and composition of a Mediterranean ant community. We have crossed these two factors in a factorial design where we have eliminated vegetation in experimental treatments and we have simulated the effects of vegetation by manipulating separately the supply of food resources and shade. The expected decrease in ant abundance and richness in plots without food resources but with shade was only partially confirmed by the results, because there was a decrease in the number of ant species but not a significant decrease in overall ant abundance in plots without food resources. We did not confirm the second hypothesis that the decrease in shade while maintaining food resources resulted in an increase of heat‐tolerant, subordinate species and, consequently, ant richness. Species composition differed in the different experimental treatments. Stress‐tolerant species were abundant in areas without shade and without food resources. Heat‐tolerant species were mainly present in plots without shade but with food resources. Finally, species with high requirements of shade and/or food resources were associated to control plots with both shade and food resources from vegetation. Overall, this study provides an experiment that uncouples experimentally shade and food resources and dissects their effects on the whole ant community, and shows that the effects of the two factors are independent and affect different components of ant community structure and composition.
Shifting altitudinal distribution of outbreak zones of winter moth Operophtera brumata in sub‐arctic birch forest: a response to recent climate warming?
Authors: B. Hagen Snorre , U. Jepsen Jane , A. Ims Rolf , G. Yoccoz Nigel
Published: November 2007

Climatic change is expected to affect the extent and severity of geometrid moth outbreaks, a major disturbance factor in sub‐arctic birch forests. Previous studies have reported that the two geometrid species involved, autumnal moth and winter moth, differ in their temperature requirements and, consequently, in their altitudinal and latitudinal distribution patterns. In this study, we document the altitudinal distribution of winter moth outbreaks in a large coastal area in northern Norway. We show that, in the present winter moth outbreak, defoliated birch stands were seen as distinct zones with a rather constant width in the uppermost part of the forest and where the upper limit coincided with the forest line. The outbreak zone closely followed the spatially variable forest line as an undulating belt, although some of the variation in outbreak zone width was also related to variation in topographical variables, such as distance from the coast, forest line altitude, and slope of the terrain. A distinct outbreak zone at the altitudinal forest line is the typical picture that has been depicted in more qualitative historical records on previous outbreaks of autumnal moth rather than winter moth. We suggest that the recent documented climate warming in this region may have induced a shift in distribution of the winter moth both relative to topography and geography. Further investigation is, however, required to substantiate these suspicions.
Predation risk is unlikely to account for the failure of subordinate speckled warblersChthonicola sagittatato help at the nest
Authors: Gardner Janet L.
Published: November 2007

The predator avoidance hypothesis suggests that the failure of subordinate birds to provision nestlings in communally breeding species is a consequence of increased predation risk. Parents exclude subordinates from the nest area and thus reduce the frequency of predator‐attracting visits when the nest is most vulnerable, leading to increased reproductive success. I evaluated this hypothesis for the speckled warblerChthonicola sagittata, a group‐living member of the Pardalotidae in which subordinate males never feed nestlings or fledglings even though they are unrelated to the primary pair, compete for copulations and sometimes sire young in the brood. Parents did not modify provisioning behaviour relative to the risk of nest predation; provisioning rates to 10 d‐old nestlings were similar on high and low risk territories. Furthermore, there was no evidence that parents modified the timing of deliveries or adjusted the relative size of deliveries in relation to predation risk. The condition (residual mass) of nestlings differed between high and low risk territories because nestlings on high risk territories had smaller tarsi but similar body mass to those at low risk. Tarsus length was the result of parental phenotype, not modified provisioning behaviour. Given that parents were unresponsive to predation risk, it seems unlikely that predation can account for the failure of subordinates to provision at the nest.