bluuebunny/crossref_metadata_2025 huggingface dataset:
Rapid 3‐D forward model of potential fields with application to the Palinuro Seamount magnetic anomaly (southern Tyrrhenian Sea, Italy)
Authors: Caratori Tontini F. , Cocchi L. , Carmisciano C.
Published: February 2009

We show a set of forward model equations in the Fourier domain for calculating the 3‐D gravity and magnetic anomalies of a given 3‐D distribution of density or magnetization. One property of the potential field equations is that they are given by convolution products, providing a very simple analytic expression in the Fourier domain. Under this assumption, the domain of the density or magnetization parameters is connected by a biunivoc relationship with the data space, and potential field anomalies can be seen as filtered versions of the corresponding density or magnetization distributions. A very fine spatial discretization can be obtained by using a large number of points within a unique 3‐D grid, where both the source distributions and field data are defined. The main advantage of this formulation is that it dramatically reduces execution times, providing a very fast forward model tool useful for modeling anomalies at different altitudes. We use this method to evaluate an average magnetization of 8A/mfor the Palinuro Seamount in the Tyrrhenian Sea (southern Italy), thus performing a joint interpretation of morphological and newly acquired magnetic data.
Seasonal variations of sea ice and ocean circulation in the Bering Sea: A model‐data fusion study
Authors: Wang Jia , Hu Haoguo , Mizobata Kohei , Saitoh Sei‐ichi
Published: February 2009

A 9‐km coupled ice‐ocean model (CIOM) was implemented in the entire Bering Sea to investigate seasonal cycles of sea ice and ocean circulation under atmospheric forcing. Sea ice cover with a maximum of 0.6 × 106 km2 in February to late March was reasonably reproduced by the Bering‐CIOM and validated by Special Sensor Microwave/Imager (SSM/I) measurements. The model also captures some important spatial variability and downscaling processes such as polynyas and ridging, which the SSM/I measurements cannot reproduce because of their coarse (25 km) resolution. There are two distinct surface ocean circulation patterns in winter and summer on the Bering shelves because of the dominant winds, which are northeasterly in winter and southwesterly in summer. Summer low‐temperature, high‐salinity water mass (<3°C) on the Bering shelf is formed locally during winter because of strong vertical convection caused by salt injection when ice forms, wind, and wind‐wave mixing on the shelf. The northward volume transport across the 62.5°N line, with an annual mean of 0.8 ± 0.33 Sv (1 Sv = 106 m3 s−1) that is consistent with the measurements in the Bering Strait, has barotropic structure, which transports heat flux (with an annual mean of 7.74 TW; 1 TW = 1012 W) northward. The Anadyr Current advects warmer, saltier water northward during summer; nevertheless, it reverses its direction to southward during winter because of predominant northeasterly and northerly wind forcing. Therefore, the Anadyr Current advects cold, salty water southward. The volume transport on the broad midshelf is northward year round, advecting heat (3.3 ± 2.4 TW) and freshwater (−8 ± 10 × 104 practical salinity unit (psu) m3 s−1) northward. One important finding is that the Anadyr Current and the midshelf current are out of phase in volume and heat transports. The Alaskan Coastal Current also transports heat and freshwater northward on an annual basis. The Bering‐CIOM also captures the winter dense water formation along the Siberian coast, which is promoted by the downwelling favorable northeasterly wind, and the summer upwelling due to the basin‐scale upwelling favorable southwesterly wind, which brings up the cold, salty, and nutrient‐rich water from the subsurface to the surface within a narrow strip along the west coast. This upwelling found in the model was also confirmed by satellite measurements in this study.
A model for DNA replication showing how dormant origins safeguard against replication fork failure
Authors: Blow J Julian , Ge Xin Quan
Published: February 2009

Replication origins are ‘licensed’ for a single initiation event before entry into S phase; however, many licensed replication origins are not used, but instead remain dormant. The use of these dormant origins helps cells to survive replication stresses that block replication fork movement. Here, we present a computer model of the replication of a typical metazoan origin cluster in which origins are assigned a certain initiation probability per unit time and are then activated stochastically during S phase. The output of this model is in good agreement with experimental data and shows how inefficient dormant origins can be activated when replication forks are inhibited. The model also shows how dormant origins can allow replication to complete even if some forks stall irreversibly. This provides a simple explanation for how replication origin firing is regulated, which simultaneously provides protection against replicative stress while minimizing the cost of using large numbers of replication forks.
Discriminative detection and enumeration of microbial life in marine subsurface sediments
Authors: Morono Yuki , Terada Takeshi , Masui Noriaki , Inagaki Fumio
Published: February 2009

Detection and enumeration of microbial life in natural environments provide fundamental information about the extent of the biosphere on Earth. However, it has long been difficult to evaluate the abundance of microbial cells in sedimentary habitats because non-specific binding of fluorescent dye and/or auto-fluorescence from sediment particles strongly hampers the recognition of cell-derived signals. Here, we show a highly efficient and discriminative detection and enumeration technique for microbial cells in sediments using hydrofluoric acid (HF) treatment and automated fluorescent image analysis. Washing of sediment slurries with HF significantly reduced non-biological fluorescent signals such as amorphous silica and enhanced the efficiency of cell detachment from the particles. We found that cell-derived SYBR Green I signals can be distinguished from non-biological backgrounds by dividing green fluorescence (band-pass filter: 528/38 nm (center-wavelength/bandwidth)) by red (617/73 nm) per image. A newly developed automated microscope system could take a wide range of high-resolution image in a short time, and subsequently enumerate the accurate number of cell-derived signals by the calculation of green to red fluorescence signals per image. Using our technique, we evaluated the microbial population in deep marine sediments offshore Peru and Japan down to 365 m below the seafloor, which provided objective digital images as evidence for the quantification of the prevailing microbial life. Our method is hence useful to explore the extent of sub-seafloor life in the future scientific drilling, and moreover widely applicable in the study of microbial ecology.
The alkaline phosphatase PhoX is more widely distributed in marine bacteria than the classical PhoA
Authors: Sebastian Marta , Ammerman James W
Published: February 2009

Phosphorus (P) is a vital nutrient for all living organisms and may control the growth of bacteria in the ocean. Bacteria induce alkaline phosphatases when inorganic phosphate (Pi) is insufficient to meet their P-requirements, and therefore bulk alkaline phosphatase activity measurements have been used to assess the P-status of microbial assemblages. In this study, the molecular basis of marine bacterial phosphatases and their potential role in the environment were investigated. We found that only a limited number of homologs to the classical Escherichia coli alkaline phosphatase (PhoA) were present in marine isolates in the Bacteroidetes and γ-proteobacteria lineages. In contrast, PhoX, a recently described phosphatase, was widely distributed among diverse bacterial taxa, including Cyanobacteria, and frequently found in the marine metagenomic Global Ocean Survey database. These taxa included ecologically important groups such as Roseobacter and Trichodesmium. PhoX was induced solely upon P-starvation and accounted for approximately 90% of the phosphatase activity in the model marine bacterium Silicibacter pomeroyi. Analysis of the available transcriptomic datasets and their corresponding metagenomes indicated that PhoX is more abundant than PhoA in oligotrophic marine environments such as the North Pacific Subtropical Gyre. Those analyses also revealed that PhoA may be important when Bacteroidetes are abundant, such as in algal bloom episodes. However, PhoX appears to be much more widespread. Its identification as a gene that mediates organic P acquisition in ecologically important groups, and as a marker of Pi-stress, constitutes an important step toward a better understanding of the marine P cycle.
Quantitative detection of culturable methanogenic archaea abundance in anaerobic treatment systems using the sequence-specific rRNA cleavage method
Authors: Narihiro Takashi , Terada Takeshi , Ohashi Akiko , Wu Jer-Horng , Liu Wen-Tso , Araki Nobuo , Kamagata Yoichi , Nakamura Kazunori , Sekiguchi Yuji
Published: February 2009

A method based on sequence-specific cleavage of rRNA with ribonuclease H was used to detect almost all known cultivable methanogens in anaerobic biological treatment systems. To do so, a total of 40 scissor probes in different phylogeny specificities were designed or modified from previous studies, optimized for their specificities under digestion conditions with 32 methanogenic reference strains, and then applied to detect methanogens in sludge samples taken from 6 different anaerobic treatment processes. Among these processes, known aceticlastic and hydrogenotrophic groups of methanogens from the families Methanosarcinaceae, Methanosaetaceae, Methanobacteriaceae, Methanothermaceae and Methanocaldococcaceae could be successfully detected and identified down to the genus level. Within the aceticlastic methanogens, the abundances of mesophilic Methanosaeta accounted for 5.7–48.5% of the total archaeal populations in mesophilic anaerobic processes, and those of Methanosarcina represented 41.7% of the total archaeal populations in thermophilic processes. For hydrogenotrophic methanogens, members of the Methanomicrobiales, Methanobrevibacter and Methanobacterium were detected in mesophilic processes (1.2–17.2%), whereas those of Methanothermobacter, Methanothermaceae and Methanocaldococcaceae were detected in thermophilic process (2.0–4.8%). Overall results suggested that those hierarchical scissor probes developed could be effective for rapid and possibly on-site monitoring of targeted methanogens in different microbial environments.
Plasma membrane microdomains from hybrid aspen cells are involved in cell wall polysaccharide biosynthesis
Authors: Bessueille Laurence , Sindt Nicolas , Guichardant Michel , Djerbi Soraya , Teeri Tuula T. , Bulone Vincent
Published: February 2009

Detergent-resistant plasma membrane microdomains [DRMs (detergent-resistant membranes)] were isolated recently from several plant species. As for animal cells, a large range of cellular functions, such as signal transduction, endocytosis and protein trafficking, have been attributed to plant lipid rafts and DRMs. The data available are essentially based on proteomics and more approaches need to be undertaken to elucidate the precise function of individual populations of DRMs in plants. We report here the first isolation of DRMs from purified plasma membranes of a tree species, the hybrid aspen Populus tremula × tremuloides, and their biochemical characterization. Plasma membranes were solubilized with Triton X-100 and the resulting DRMs were isolated by flotation in sucrose density gradients. The DRMs were enriched in sterols, sphingolipids and glycosylphosphatidylinositol-anchored proteins and thus exhibited similar properties to DRMs from other species. However, they contained key carbohydrate synthases involved in cell wall polysaccharide biosynthesis, namely callose [(1→3)-β-D-glucan] and cellulose synthases. The association of these enzymes with DRMs was demonstrated using specific glucan synthase assays and antibodies, as well as biochemical and chemical approaches for the characterization of the polysaccharides synthesized in vitro by the isolated DRMs. More than 70% of the total glucan synthase activities present in the original plasma membranes was associated with the DRM fraction. In addition to shedding light on the lipid environment of callose and cellulose synthases, our results demonstrate the involvement of DRMs in the biosynthesis of important cell wall polysaccharides. This novel concept suggests a function of plant membrane microdomains in cell growth and morphogenesis.
Magnetocaloric effect and spin reorientation transition in single-crystal Er2(Co0.4Fe0.6)17
Authors: Ilyn M. , Andreev A. V. , Zhukova V. , Zhukov A. , Tishin A. , Gonzalez J.
Published: February 2009

Magnetic and magnetocaloric properties of single crystal Er2(Co0.4Fe0.6)17 were investigated. First order spin reorientation phase transition was observed at 272 K. Magnetic easy-axis anisotropy was found below this temperature and the easy-plane one above. Magnetocaloric effect accompanying field induced first order magnetic reorientation has been measured directly. It reaches −0.25 and 0.15 K, respectively, provided that the field is perpendicular to the easy-magnetization direction. These values were satisfactorily compared with thermodynamic calculations.
Mössbauer spectroscopy study on the magnetic transition in Mn1.1Fe0.9P0.8Ge0.2
Authors: Liu X. B. , Altounian Z. , Ryan D. H. , Yue Ming , Li Zhiqiang , Liu Danmin , Zhang Jiuxing
Published: February 2009

The magnetic transition has been studied in Mn1.1Fe0.9P0.8Ge0.2 by magnetic measurements and F57e Mössbauer spectroscopy. The alloy crystallizes in the hexagonal Fe2P-type structure with lattice constants of a=6.0476(4) Å and c=3.4766(7) Å. Both bulk magnetization measurements and Mössbauer spectroscopy show that the as-prepared sample has a significantly lower transition temperature on first cooling (TC1≈200 K) than after it has undergone thermal cycling to 20 K (TC20 K=240 K). The behavior of the material stabilizes after the first cooling/heating cycle and no further changes are observed in TC. Working with a stabilized sample, we find that the temperature dependence of the hyperfine field, Bhf(T), is more rapid than that predicted by a simple mean field Brillouin function, and in addition, Bhf(T) shows a thermal hysteresis of 10 K upon cooling versus heating. These results show that the magnetic transition at TC is definitely first order and suggest that there is an additional irreversible magnetostructural change during the first cooling process of the as-prepared sample.
Numerical study on microwave-assisted magnetization reversal of magnetic particles several tens of nanometers wide with perpendicular anisotropy
Authors: Nozaki Y. , Ohta M. , Narita N. , Matsuyama K.
Published: February 2009

Microwave-assisted magnetization reversal (MAMR) is numerically investigated for perpendicularly magnetized particles with a natural ferromagnetic resonance frequency of 22.5 GHz. The precession angle of magnetization can be enhanced intensively by increasing the amplitude of the ac hard-axis field with an optimum frequency. However, the precession of magnetization about the easy axis becomes unstable as the precession angle reaches a critical value because the easy-axis component of the effective field exerted on the magnetization becomes zero. The analysis of magnetization dynamics in MAMR showed that the precession of magnetization about an in-plane axis, appearing after the easy-axis component of the effective field becomes zero, plays an important role in the irreversible switching of magnetization.
Intensity tracking for theoretical infrared spectroscopy of large molecules
Authors: Luber Sandra , Neugebauer Johannes , Reiher Markus
Published: February 2009

We present an approach for the direct calculation of vibrational normal modes with high infrared intensities based on a mode-tracking-like algorithm [M. Reiher and J. Neugebauer, J. Chem. Phys. 118, 1634 (2003)] but with distinct features: no collective guess vibration is utilized but high-intensity distortions are constructed. Only the modes of interest with the highest infrared intensities are then targeted irrespective of a predefinition of the underlying collective normal coordinates. This leads to a fast access to the most important features in infrared spectra. The different implementations of the mode selection procedure are validated on a set of small organic molecules as well as on the metal complex Δ(δδδ)-tris(ethylenediaminato)cobalt(III) and the peptide all-(S)-decaalanine. As a critical test case, approximate infrared spectra of Schrock’s dinitrogen molybdenum complex are calculated via intensity tracking.
Contracted Gaussian basis sets for Douglas–Kroll–Hess calculations: Estimating scalar relativistic effects of some atomic and molecular properties
Authors: Jorge F. E. , Canal Neto A. , Camiletti G. G. , Machado S. F.
Published: February 2009

Douglas–Kroll–Hess (DKH) contracted Gaussian basis sets of double, triple, and quadruple zeta valence qualities plus polarization functions (XZP, X=D, T, and Q, respectively) for the atoms H–Ar and DZP and TZP for K–Kr are presented. They have been determined from the corresponding nonrelativistic basis sets generated previously by Jorge et al. We have recontracted the original XZP basis sets, i.e., the values of the contraction coefficients were reoptimized using the relativistic DKH Hamiltonian. The effect of DKH at the coupled-cluster level of theory on the ionization energy of some atoms and dissociation energy and geometric parameters for a sample of molecules is discussed. Our results were compared with theoretical and experimental values reported in the literature.
Linear-scaling atomic orbital-based second-order Møller–Plesset perturbation theory by rigorous integral screening criteria
Authors: Doser Bernd , Lambrecht Daniel S. , Kussmann Jörg , Ochsenfeld Christian
Published: February 2009

A Laplace-transformed second-order Møller–Plesset perturbation theory (MP2) method is presented, which allows to achieve linear scaling of the computational effort with molecular size for electronically local structures. Also for systems with a delocalized electronic structure, a cubic or even quadratic scaling behavior is achieved. Numerically significant contributions to the atomic orbital (AO)-MP2 energy are preselected using the so-called multipole-based integral estimates (MBIE) introduced earlier by us [J. Chem. Phys. 123, 184102 (2005)]. Since MBIE provides rigorous upper bounds, numerical accuracy is fully controlled and the exact MP2 result is attained. While the choice of thresholds for a specific accuracy is only weakly dependent upon the molecular system, our AO-MP2 scheme offers the possibility for incremental thresholding: for only little additional computational expense, the numerical accuracy can be systematically converged. We illustrate this dependence upon numerical thresholds for the calculation of intermolecular interaction energies for the S22 test set. The efficiency and accuracy of our AO-MP2 method is demonstrated for linear alkanes, stacked DNA base pairs, and carbon nanotubes: e.g., for DNA systems the crossover toward conventional MP2 schemes occurs between one and two base pairs. In this way, it is for the first time possible to compute wave function-based correlation energies for systems containing more than 1000 atoms with 10 000 basis functions as illustrated for a 16 base pair DNA system on a single-core computer, where no empirical restrictions are introduced and numerical accuracy is fully preserved.
Device loss of (Ba,Sr)TiO3 film-based capacitors at 1–20 GHz
Authors: Chang Wontae , Alldredge L. M. B. , Kirchoefer Steven W. , Pond Jeffrey M.
Published: February 2009

Device loss of BaxSr1−xTiO3 (BST, x=0.5 and 0.6) film-based interdigitated capacitors as a function of frequency (1–20 GHz) at room temperature is observed to range broadly from less than 0.01 to larger than 1 while the commonly observed device losses are around 0.05. Frequency dependence of the device loss tends to be larger for the higher device losses (>0.05) and at the higher frequencies (>10 GHz). The various characteristics of the microwave device loss are examined by analyzing the complex power applied in the devices, P=Pactive+jPreactive, where Pactive is the dissipated power and Preactive is the stored power in the devices. The dissipated power at the devices (Pactive), subsequently resulting in the device loss, e.g., device loss=−Pactive/Preactive, is well fitted with the dissipated powers associated with the dielectric resistance and the electrode resistance (including the conduction and radiation resistances) of the devices.
The chemistry of nitrogen oxides on small size-selected cobalt clusters, Con+
Authors: Anderson Marie L. , Lacz Agnieszka , Drewello Thomas , Derrick Peter J. , Woodruff D. Phil , Mackenzie Stuart R.
Published: February 2009

Fourier transform ion cyclotron resonance mass spectrometry has been employed to study the reactions of gas-phase cationic cobalt clusters, Con+ (n=4–30), with nitric oxide, NO, and nitrous oxide, N2O, under single collision conditions. Isolation of the initial cluster permits detailed investigation of fragmentation channels which characterize the reactions of all but the largest clusters studied. In reaction with N2O, most clusters generate the monoxides ConO+ without fragmentation, cobalt atom loss accompanying only subsequent reactions. By contrast, chemisorption of even a single NO molecule is accompanied by fragmentation of the cluster. The measured rate coefficients for the Con++N2O reaction as a function of cluster size are significantly smaller than those calculated using the surface charge capture model, while for NO the rates are comparable. The reactions have been studied under high coverage conditions by storing clusters for extended periods to permit multiple reactions to occur. This leads to interesting chemistry on the surface of the cluster resulting in the formation of stable oxide clusters and/or the decomposition of nitric oxide on the cluster with the resulting loss of molecular nitrogen.
Effect of magnetic field direction on the remanent resistance levels and vortex chirality of a multilayered magnetic ring
Authors: Nam Chunghee , Ng B. G. , Castaño F. J. , Ross C. A.
Published: February 2009

The effect of applied field direction on the magnetoresistance response of a 5 μm diameter Co/Cu/NiFe thin film ring has been examined. When the Co layer of the ring is placed in a vortex state, four possible remanent magnetization configurations exist, in which the NiFe layer is in one of four states: forward onion, reverse onion, clockwise vortex or counterclockwise vortex. The resistance levels of these four remanent states depend on the field angle with respect to the electrical contact leads, and measured values agree well with an electrical model. The chirality of the Co vortex can be determined from measurements of the minor loop, and the chirality of the NiFe vortex can be set using two-step field cycling at two different field angles.
Magnetic properties of NiMn-based Heusler alloys influenced by Fe atoms replacing Mn
Authors: Passamani E. C. , Xavier F. , Favre-Nicolin E. , Larica C. , Takeuchi A. Y. , Castro I. L. , Proveti J. R.
Published: February 2009

The influence of the Mn substitution by Fe atoms on the magnetocaloric and magnetic properties of the martensitic Ni50Mn36Sn14 Heusler-type compound has been investigated using magnetization measurements. The insertion of Fe atoms reduces the Mn-Mn AF interactions resulting in (i) a systematic decrease in the martensitic transition temperature, down to its disappearance at 15 at. % of Fe, (ii) an enhancement of the saturation magnetization, and (iii) a monotonic increase in the L21-type phase Curie temperature. The Fe substitution also induces metamagnetic transition from an incipient AF to a noncollinear spin configuration for applied magnetic fields higher than 3 T in the case of 3 and 7 at. % Fe substitutional. The exchange-bias effect is only found in compounds with a well-defined martensitic phase transition (Fe content lower than 10 at. %). The maximum of the inverse magnetic entropy change, for a field variation of 5 T, is about +12 J kg−1 K−1 and it is nearly constant for Fe content up to 7 at. %. This observation suggests that the Ni50(Mn1−xFex)36Sn14 Heusler-type compounds could be used to prepare composites with potential for technological application in magnetic refrigerators.
Analysis of optical gain property in the InGaN/GaN triangular shaped quantum well under the piezoelectric field
Authors: Yang Ziwen , Li Rui , Wei Qiyuan , Yu Tao , Zhang Yanzhao , Chen Weihua , Hu Xiaodong
Published: February 2009

InGaN/GaN triangular quantum wells (QWs) are investigated theoretically, and the electron-hole wave-function overlap and optical gain characteristics are analyzed. The strong internal piezoelectric field is taken into account to explain the major difference between the optical properties of triangular QWs and conventional rectangular QWs. Our calculations reveal that triangular QWs, in comparison to rectangular QWs, provide higher electron-hole wave-function overlap and are less affected by the quantum confined Stark effect. Furthermore, triangular QWs exhibit increased optical gain and higher polarization degree, which are beneficial to GaN-based light emitting devices.
Effect of chemical synapse on vibrational resonance in coupled neurons
Authors: Deng Bin , Wang Jiang , Wei Xile
Published: February 2009

The response of three coupled FitzHugh–Nagumo neurons, under high-frequency driving, to a subthreshold low-frequency signal is investigated. We show that an optimal amplitude of the high-frequency driving enhances the response of coupled excited neurons to a subthreshold low-frequency input, and the chemical synaptic coupling is more efficient than the well-known electrical coupling (gap junction), especially when the coupled neurons are near the canard regime, for local signal input, i.e., only one of the three neurons is subject to a low-frequency signal. The influence of additive noise and the interplay between vibrational and stochastic resonance are also analyzed.
Realization of a high mobility dual-gated graphene field-effect transistor with Al2O3 dielectric
Authors: Kim Seyoung , Nah Junghyo , Jo Insun , Shahrjerdi Davood , Colombo Luigi , Yao Zhen , Tutuc Emanuel , Banerjee Sanjay K.
Published: February 2009

We fabricate and characterize dual-gated graphene field-effect transistors using Al2O3 as top-gate dielectric. We use a thin Al film as a nucleation layer to enable the atomic layer deposition of Al2O3. Our devices show mobility values of over 8000 cm2/V s at room temperature, a finding which indicates that the top-gate stack does not significantly increase the carrier scattering and consequently degrade the device characteristics. We propose a device model to fit the experimental data using a single mobility value.
Recursive calculation of effective resistances in distance-regular networks based on Bose–Mesner algebra and Christoffel–Darboux identity
Authors: Jafarizadeh M. A. , Sufiani R. , Jafarizadeh S.
Published: February 2009

Recently, Jafarizadeh et al. [ J. Phys. A: Math. Theor. 40, 4949 (2007)] have given a method for calculation of effective resistance (two-point resistance) on distance-regular networks, where the calculation was based on stratification introduced by Jafarizadeh and Salimi [J. Phys. A 39, 1 (2006)] and Stieltjes transform of the spectral distribution (Stieltjes function) associated with the network. Also,Jafarizadeh et al. [ J. Phys. A: Math. Theor. 40, 4949 (2007)] have shown that effective resistances between a node α and all nodes β belonging to the same stratum with respect to α (Rαβ(i), β belonging to the ith stratum with respect to α) are the same. In this work, an algorithm for recursive calculation of the effective resistances in an arbitrary distance-regular resistor network is provided, where the derivation of the algorithm is based on the Bose–Mesner algebra, stratification of the network, spectral techniques, and Christoffel–Darboux identity. It is shown that the effective resistance on a distance-regular network is a strictly increasing function of the shortest path distance defined on the network. In other words, the effective resistance Rαβ(m+1) is strictly larger than Rαβ(m). The link between effective resistance and random walks on distance-regular networks is discussed, where average commute time and its square root (called Euclidean commute time) as distance are related to effective resistance. Finally, for some important examples of finite distance-regular networks, effective resistances are calculated.
Electronic and chemical properties of molybdenum oxide doped hole injection layers in organic light emitting diodes
Authors: Wu Chih-I , Lin Chang-Ting , Lee Guan-Ru , Cho Ting-Yi , Wu Chung-Chih , Pi Tun-Wen
Published: February 2009

The origins of barrier lowering leading to high efficient organic light emitting devices with incorporation of molybdenum oxide (MoOx) in anode structures are investigated. Ultraviolet and x-ray photoemission spectra reveal that p-type doping effects in the organic films and carrier concentration increase at the anode interfaces cause the hole injection barrier lowering. The gap states, which help carrier injection from the anodes, resulted from the oxygen deficiency in MoOx due to the interaction of organic materials and MoOx.
First-principles study of the dielectric properties of Ba(Zn1/3Nb2/3)O3 and Ba(Mg1/3Nb2/3)O3
Authors: Dai Yadong , Zhao Guanghui , Liu Hanxing
Published: February 2009

Microwave dielectric ceramics Ba(M1/32+M2/35+)O3 have been studied for many years, but the exact relations between the B-site ions and the ceramics’ dielectric properties are still unclear. We take 2:1-ordered Ba(Zn1/3Nb2/3)O3 (BZN) and Ba(Mg1/3Nb2/3)O3 (BMN) as examples and discuss their static permittivity and intrinsic loss based on first-principles calculation. The larger mode-effective charges and lower frequencies of the normal modes are found to be responsible for the larger permittivity in BZN, but further analysis indicates that the dipole interaction, which is strengthened by the covalent bonding among Zn, Nb, and O, is the origin of these phenomena. In fact, the measured loss is found to be very close to the intrinsic loss in both BZN and BMN; we conclude that the difference in the measured loss is mainly the reflection of the difference in the intrinsic loss which is caused by the difference in permittivity between BZN and BMN. Moreover, our calculation results are in good agreement with the experimental values, a characterization of the Raman spectra of BZN and BMN is suggested based on our results.
Lattice Boltzmann study of droplet motion inside a grooved channel
Authors: Huang Jun Jie , Shu Chang , Chew Yong Tian
Published: February 2009

A droplet moving inside a grooved channel is studied by using a new lattice Boltzmann model for multiphase flows with large density ratio. A constant body force is applied to drive the droplet. Flows under different surface tensions, driving forces, density ratios, wall wettabilities, and groove geometries are investigated. It is found that the drag on the droplet and the flow pattern are strongly affected by the wall wettability and topography when the system scale is small. The effects of the driving force on the droplet are investigated through comparison of two different ways of applying it. Besides, the density ratio is varied over a wide range to assess its effects in the present setup. Special attention is paid to grooved hydrophilic walls which tend to enhance the droplet-wall contact. For such walls, two distinctive types of shape of the interface inside the groove are found and series of numerical investigations are carried out to find the critical wall contact angle, groove width and depth that determine which kind of shape the droplet assumes. Some typical cases are chosen for detailed analyses and compared to some other work. This study is expected to improve our understanding on the lotus effect and the physics of small scale flows near rough walls.
From thermally activated to viscosity controlled fracture of biopolymer hydrogels
Authors: Baumberger T. , Ronsin O.
Published: February 2009

We report on rate-dependent fracture energy measurements over three decades of steady crack velocities in alginate and gelatin hydrogels. We evidence that irrespective of gel thermoreversibility, thermally activated “unzipping” of the noncovalent cross-link zones results in slow crack propagation, prevailing against the toughening effect of viscous solvent drag during chain pull-out, which becomes efficient above a few mm s−1. We extend a previous model [T. Baumberger et al., Nat. Mater. 5, 552 (2006)] to account for both mechanisms and estimate the microscopic unzipping rates.
Measurement of magnetic losses by thermal method applied to power ferrites at high level of induction and frequency
Authors: Loyau V. , Lo Bue M. , Mazaleyrat F.
Published: February 2009

Classically, low frequency losses in soft magnetic materials and ferrites in particular are measured by flux metric method under sinusoidal waveform excitation voltage. However, in typical application of modern power electronics, the frequency currently exceeds 100 kHz. This feature is at the origin of a difficulty: the phase shift between current and voltage can be disturbed by current probe delay. Thus, the results can be affected by large errors. As a consequence, it becomes more and more important to develop alternative methods to measure losses in magnetic materials. It is proposed to use calorimetric method which is by principle free of the above mentioned problems. The experimental device is described in details and the results are reported for experiments conducted on a commercial Mn–Zn ferrite under sinusoidal waveform regime for frequencies varying from 10 to 200 kHz. Comparisons with flux metric measurement show that significant differences appear typically for Bf products above 5000 V/m2 (50 kHz×100 mT).
The substrate thickness dependence of the photovoltage in LaAlO3−δ/Si heterostructures
Authors: Wen Juan , Jin Kui-juan , He Meng , Lu Huibin , Yang Fang , Yang Guozhen
Published: February 2009

The photoelectric properties of LaAlO3−δ/Si heterostructures with different substrate thicknesses were systematically investigated, in which the LaAlO3−δ thin films were epitaxially grown on p-type Si substrates by a computer-controlled laser molecular-beam epitaxy system. Picosecond photoelectric response was observed, and the photoelectric sensitivity was improved greatly by decreasing the thickness of the Si substrates. The maximum photoelectric sensitivity reached 85.6 V/W, and faster photoelectric response was obtained with thinner Si substrate. The experimental results demonstrate that the photoelectrical effects on heterostructures consisting of perovskite oxide and thin silicon substrate are not only with fast response but also with high sensitivity.
Rationalising the Policy Mess? Ex Ante Policy Assessment and the Utilisation of Knowledge in the Policy Process
Authors: Hertin Julia , Turnpenny John , Jordan Andrew , Nilsson Mans , Russel Duncan , Nykvist Björn
Published: February 2009

Procedures for the ex ante assessment of public policies are currently in vogue across the OECD. Their design is typically informed by a rational-instrumental model of problem solving, which assumes that knowledge is collected, evaluated, and then translated straightforwardly into ‘better policies’. But this model has been little affected by more than three decades of academic research which has demonstrated that the reality of everyday policy making is far messier. In this paper we analyse whether the uptake of ex ante assessment of policies is nonetheless capable of creating opportunities for policy deliberation and learning informed by new assessment knowledge. Drawing on an analysis of policy assessment procedures in three countries and the European Union, we find that there are several ways in which assessment knowledge is used in the policy process. Moreover, we argue that policy learning occurs despite, rather than because of, the instrumental design of new assessment procedures, which tends to act as a barrier to open deliberation and knowledge utilisation.
Fit and Working Again? The Instrumental Leisure of the ‘Creative Class’
Authors: Banks Mark
Published: February 2009

The utopianization of ‘creative work’ is a pronounced feature of postindustrial societies. The author analyzes the attendant promotion of ‘creative leisure’, and its role in supporting discourses and practices of creative work. Through an analysis of Richard Florida's influential text The Rise of the Creative Class, it is argued that, while creative leisure is offered up as a means of free and autonomous expression, it may be leading, paradoxically, to the erosion of freedom as the terrain of critical and disinterested leisure is pervasively colonized by discourses of economic rationality. Secondly, it is contended that whereas, traditionally, capital has always sought to regulate and administer leisure ‘from above’—with workers variably ‘resisting’ below—such a model may no longer apply since (according to Florida) creative-class subjects now appear to be actively choosing to perform (rather than being coerced into) economically directed leisure.
The fractions of short- and long-range connections in the visual cortex
Authors: Stepanyants Armen , Martinez Luis M. , Ferecskó Alex S. , Kisvárday Zoltán F.
Published: February 2009

When analyzing synaptic connectivity in a brain tissue slice, it is difficult to discern between synapses made by local neurons and those arising from long-range axonal projections. We analyzed a data set of excitatory neurons and inhibitory basket cells reconstructed from cat primary visual cortex in an attempt to provide a quantitative answer to the question: What fraction of cortical synapses is local, and what fraction is mediated by long-range projections? We found an unexpectedly high proportion of nonlocal synapses. For example, 92% of excitatory synapses near the axis of a 200-μm-diameter iso-orientation column come from neurons located outside the column, and this fraction remains high—76%—even for an 800-μm ocular dominance column. The long-range nature of connectivity has dramatic implications for experiments in cortical tissue slices. Our estimate indicates that in a 300-μm-thick section cut perpendicularly to the cortical surface, the number of viable excitatory synapses is reduced to about 10%, and the number of synapses made by inhibitory basket cell axons is reduced to 38%. This uneven reduction in the numbers of excitatory and inhibitory synapses changes the excitation–inhibition balance by a factor of 3.8 toward inhibition, and may result in cortical tissue that is less excitable than in vivo. We found that electrophysiological studies conducted in tissue sections may significantly underestimate the extent of cortical connectivity; for example, for some projections, the reported probabilities of finding connected nearby neuron pairs in slices could understate the in vivo probabilities by a factor of 3.
Rescuing Z
+
agrin splicing in
Nova
null mice restores synapse formation and unmasks a physiologic defect in motor neuron firing
Authors: Ruggiu Matteo , Herbst Ruth , Kim Natalie , Jevsek Marko , Fak John J. , Mann Mary Anne , Fischbach Gerald , Burden Steven J. , Darnell Robert B.
Published: February 2009

Synapse formation at the neuromuscular junction (NMJ) requires an alternatively spliced variant of agrin (Z
+
agrin) that is produced only by neurons. Here, we show that Nova1 and Nova2, neuron-specific splicing factors identified as targets in autoimmune motor disease, are essential regulators of Z
+
agrin.
Nova1
/
Nova2
double knockout mice are paralyzed and fail to cluster AChRs at the NMJ, and breeding them with transgenic mice constitutively expressing Z
+
agrin in motor neurons rescued AChR clustering. Surprisingly, however, these rescued mice remained paralyzed, while electrophysiologic studies demonstrated that the motor axon and synapse were functional-spontaneous and evoked recordings revealed synaptic transmission and muscle contraction. These results point to a proximal defect in motor neuron firing in the absence of Nova and reveal a previously unsuspected role for RNA regulation in the physiologic activation of motor neurons.
A role for Orai in TRPC-mediated Ca
2+
entry suggests that a TRPC:Orai complex may mediate store and receptor operated Ca
2+
entry
Authors: Liao Yanhong , Plummer Nicholas W. , George Margaret D. , Abramowitz Joel , Zhu Michael Xi , Birnbaumer Lutz
Published: February 2009

TRPC and Orai proteins have both been proposed to form Ca
2+
-selective, store-operated calcium entry (SOCE) channels that are activated by store-depletion with Ca
2+
chelators or calcium pump inhibitors. In contrast, only TRPC proteins have been proposed to form nonselective receptor-operated calcium entry (ROCE) cation channels that are activated by Gq/Gi-PLCβ signaling, which is the physiological stimulus for store depletion. We reported previously that a dominant negative Orai1 mutant, R91W, inhibits Ca
2+
entry through both SOCE and ROCE channels, implicating Orai participation in both channel complexes. However, the argument for Orai participating in ROCE independently of store depletion is tenuous because store depletion is an integral component of the ROCE response, which includes formation of IP3, a store-depleting agent. Here we show that the R91W mutant also blocks diacylglycerol (DAG)-activated Ca
2+
entry into cells that stably, or transiently, express DAG-responsive TRPC proteins. This strongly suggests that Orai and TRPC proteins form complexes that participate in Ca
2+
entry with or without activation of store depletion. To integrate these results with recent data linking SOCE with recruitment of Orai and TRPCs to lipid rafts by STIM, we develop the hypothesis that Orai:TRPC complexes recruited to lipid rafts mediate SOCE, whereas the same complexes mediate ROCE when they are outside of lipid rafts. It remains to be determined whether the molecules forming the permeation pathway are the same when Orai:TRPC complexes mediate ROCE or SOCE.
A MULTIWAVELENGTH VIEW OF STAR FORMATION IN INTERACTING GALAXIES IN THE PAVO GROUP
Authors: Machacek M. , Ashby M. L. N. , Jones C. , Forman W. R. , Bastian N.
Published: February 2009

We combine Spitzer Infrared Array Camera mid-infrared and Chandra X-ray observations of the dominant galaxies NGC 6872 and NGC 6876 in the Pavo group with archival optical and H i data to study interaction-induced star formation. In the spiral galaxy NGC 6872, 8.0 μm and 5.8 μm nonstellar emission having colors consistent with polycyclic aromatic hydrocarbons (PAHs) is concentrated primarily in clumps in three regions: in a 5 kpc radius outer ring about the center of the spiral galaxy, in a bridge of emission connecting NGC 6872's northern spiral arm to IC 4970, and along the full extent of both NGC 6872's tidal arms. PAH emission is correlated with young star clusters and dense H i regions. We find no strong differences in the mid-infrared colors of the star-forming regions in the spiral galaxy NGC 6872 as a function of position relative to the tidally interacting companion galaxy IC 4970. We find 11 very luminous X-ray sources (≳ (0.5–5) ×1039  erg s−1 ) clustered to the southwest in NGC 6872, near bright star-forming regions. In NGC 6872's tidal features, young star clusters form at the boundaries of diffuse X-ray gas, suggesting that stars form as gas stripped by the interactions cools. The nucleus of NGC 6872 is a weak X-ray point source with 0.5–8 keV luminosity of 8.5 × 1039  erg s−1 , but there is little evidence in the inner 1 kpc of NGC 6872 for PAH emission from recent star formation or nuclear activity. However, a 4 kpc “stream,” leading from the outer ring of NGC 6872 to the nucleus, may signal the transport of interstellar matter into NGC 6872's nuclear region. Nonstellar emission, consistent with PAH emission, is also found in the central region of elliptical galaxy NGC 6877, companion to the dominant Pavo group elliptical galaxy NGC 6876. However, in the central region of NGC 6876, the dust emission is more likely due to silicate emission from old asymptotic giant branch stars.
Mirković-Vilonen cycles and polytopes for a symmetric pair
Authors: Hong Jiuzu
Published: February 2009

Let

G
G

be a connected, simply-connected, and almost simple algebraic group, and let

σ
\sigma

be a Dynkin automorphism on

G
G

. Then

(
G
,

G
σ

)

(G,G^\sigma )

is a symmetric pair. In this paper, we get a bijection between the set of

σ
\sigma

-invariant MV cycles (polytopes) for

G
G

and the set of MV cycles (polytopes) for

G
σ

G^\sigma

, which is the fixed point subgroup of

G
G

; moreover, this bijection can be restricted to the set of MV cycles (polytopes) in irreducible representations. As an application, we obtain a new proof of the twining character formula.
A flexible two-stage procedure for identifying gene sets that are differentially expressed
Authors: Heller Ruth , Manduchi Elisabetta , Grant Gregory R. , Ewens Warren J.
Published: February 2009

Motivation: Microarray data analysis has expanded from testing individual genes for differential expression to testing gene sets for differential expression. The tests at the gene set level may focus on multivariate expression changes or on the differential expression of at least one gene in the gene set. These tests may be powerful at detecting subtle changes in expression, but findings at the gene set level need to be examined further to understand whether they are informative and if so how.

Results: We propose to first test for differential expression at the gene set level but then proceed to test for differential expression of individual genes within discovered gene sets. We introduce the overall false discovery rate (OFDR) as an appropriate error rate to control when testing multiple gene sets and genes. We illustrate the advantage of this procedure over procedures that only test gene sets or individual genes.

Availability: R code (www.r-project.org) for implementing our approach is included as supplementary material.

Contact:  ruheller@whatron.upenn.edu