bluuebunny/crossref_metadata_2025 huggingface dataset:
New lower bounds for the Capacitated Arc Routing Problem
Authors: Pearn Wen Lea
Published: May 2007

The Capacitated Arc Routing Problem (CARP), a generalization of the arc routing problems such as the Chinese Postman Problem (CPP), is a very practical distribution management problem which has many real‐world applications. This paper briefly reviews two existing lower bounding procedures—the Matching Lower Bound and the Node Scanning Lower Bound, then introduces a new bounding technique to provide tighter lower bounds on the problem solutions.
Data transfers in networks with transceivers
Authors: Choi Hyeong‐Ah , Louis Hakimi S.
Published: May 2007

The scheduling of data transfers in networks, where the schedule does not permit interruption and each communication module can be used as a transmitter and as a receiver (i.e., as a transceiver) was studied by Coffman et al. The same problem when interruption in the schedule is permitted and the transmitting and receiving modules are distinct was studied by Choi and Hakimi among others. Hajek and Sasaki studied another interesting variation of the problem where interruption is permitted but each communication module is a transmitter and a receiver. This paper presents certain generalizations and improvements of Hajek and Sasaki's results.
Spherulitic structures of poly [tetrafluoroethylene‐co‐(perfluoroalkyl vinyl ether)]
Authors: Fujimori Atsuhiro , Hasegawa Masahiro , Masuko Toru
Published: May 2007

Spherulitic textures of poly[tetrafluoroethylene‐co‐(perfluoropropyl vinyl ether)] (PFA) were examined in detail using polarized optical microscopy. The PFA consisting of random comonomer units among the tetrafluoroethylene units crystallizes as spherulites composed of lamellae, although polytetrafluoroethylene usually forms extended‐chain crystals because of the rigid nature of 13/6 helices. The spherulites obtained exhibit positive birefringence since the polymer crystal has a larger refractive index in the direction normal to the chain than that along it. These fluorocopolymers exhibit a thicker long period of at least 30 nm in small‐angle X‐ray scattering profiles than is generally the case for hydrogenated crystalline polymers. In these copolymers, we consider the formation of a switchboard‐type lamellae model according to P. J. Flory's suggestion. In addition, we find the overlooked reflections near 2θ = 8.5° based on the superlattice in wide‐angle X‐ray diffraction profiles of fluorocopolymers with high reproducibility. From this result, it was found that the lattice constant that was previously proposed is required to be refined to twice the value on the a‐ and b‐axes of the reciprocal lattice to assign all the reflection indices. Copyright © 2007 Society of Chemical Industry
Proteomic analysis of high‐molecular‐weight protein polymers in a doxorubicin‐resistant breast‐cancer cell line
Authors: Park Sung‐Soo , Kim Dae‐Seok , Park Kang‐Seo , Song Hye‐Jin , Kim Soo‐Youl
Published: May 2007

We recently reported that increased transglutaminase 2 (TGase 2) expression correlates with increased resistance to the cancer drug doxorubicin in breast‐cancer cell lines. Interestingly, high‐molecular‐weight (HMW) proteins also increased with increased TGase 2 expression in the drug‐resistant cell lines. TGase 2 is likely to be responsible for the formation of HMW proteins, because TGase 2 catalyzes cross‐linking between proteins. Although the role of the HMW proteins is unclear, we demonstrated that TGase 2 inhibition increases drug sensitivity in breast‐cancer cells. Herein we find that TGase 2 inhibition by cystamine dramatically reduces the level of HMW proteins. Identification of the HMW proteins may suggest the mechanism of cancer drug resistance associated with aberrant TGase 2 function. To explore the identities of HMW proteins, we performed in‐gel tryptic digestions of unresolved HMW proteins and analyzed the resulting peptides using LC‐MALDI‐MS/MS. Most of the identified proteins were associated with gene regulation, such as polyadenylate‐binding proteins, translation initiation factors, and ribonucleoproteins. This finding suggests that TGase 2 may participate in gene regulation, in addition to its role in cell adhesion.
Twistor strings and supergravity
Authors: Abou‐Zeid M.
Published: May 2007

I survey the recent construction of a family of new twistor string theories which are free from world‐sheet anomalies and give the space‐time spectra of Einstein supergravities, with second order field equations instead of the higher derivative conformal supergravities that arose from earlier twistor strings.
Metastable supersymmetry breaking and gauge/gravity duality
Authors: Argurio R. , Bertolini M. , Franco S. , Kachru S.
Published: May 2007

We discuss metastable supersymmetry breaking states in gauge theories and in their gravity duals. We then engineer a quiver gauge theory with several interesting features by studying D‐branes at a simple Calabi‐Yau singularity. At weak 't Hooft coupling we argue using field theory techniques that it admits, besides the supersymmetric vacua, also metastable non‐supersymmetric vacua, though the arguments indicating the existence of the latter are not decisive. At strong 't Hooft coupling we present a simple candidate gravity dual description for both sets of vacua.
BPS preons in M‐theory and supergravity
Authors: Bandos I.A. , de Azcárraga J.A.
Published: May 2007

After introducing the notion of BPS preons as the basic constituents of M‐theory, we discuss the recent negative results in the search for solutions of the D = 10 and D = 11 supergravity equations preserving 31/32 supersymmetries i.e., of preonic solutions. The absence of these supergravity preonic solutions may point out to a pure quantum nature of BPS preons, manifesting itself in the need of incorporating quantum (stringy/M‐theoretic) corrections to the supergravity equations.
Twistor string as tensionless superstring
Authors: Bandos I.A. , de Azcárraga J.A. , Miquel‐Espanya C.
Published: May 2007

We give a brief review of the twistor string approach to supersymmetric Yang‐Mills theories with an emphasis on the different formulations of (super)string models in supertwistor space and their superspace form. We discuss the classical equivalence among the Siegel closed twistor string and the Lorentz harmonics formulation of the (N = 4) tensionless superstring, and notice the possible relation of the twistor string to the D = 10 Green‐Schwarz superstring action, as well as to models in the enlarged, tensorial superspaces that are relevant in higher spin theories.
Instanton calculus with R‐R background and topological strings
Authors: Billó M.
Published: May 2007

The non‐perturbative low energy effective action of N = 2 SYM is studied within a microscopic string realization via D3/D‐instanton systems. The localization deformation of instanton moduli space which has allowed the exact computation of multi‐instanton contributions is, in this setting, due to a RR graviphoton background. The relation of deformed instanton contributions to topological string amplitudes on CY, argued by Nekrasov, appears quite natural in this framework. Based on Billo, et al., J. High Energy Phys. 0611, 012 (2006) [arXiv:hep‐th/0606013].
Meson decays from string splitting
Authors: Bigazzi F. , Cotrone A.L. , Martucci L. , Troost W.
Published: May 2007

We discuss exclusive decays of large spin mesons into mesons in models of large Nc quenched QCD at strong coupling using string theory. The rate of the processes are calculated by studying the splitting of a macroscopic string on the relevant dual gravity backgrounds. We study analytic formulas for the decay rates of mesons made up of very heavy or very light quarks.
Calibrations on spaces with G × G‐structure
Authors: Gmeiner F. , Witt F.
Published: May 2007

In these notes we give an introduction to the concept of spaces with G × G‐structure and their structured submanifolds. These objects generalise the classical notion of a calibrated submanifold. Therefore, they are interesting from a string theory viewpoint as they are relevant to describe D‐branes in string compactifications on backgrounds with fluxes. This article is based on a talk given by the first author at the RTN Workshop “Constituents, Fundamental Forces and Symmetries of the Universe”, Naples, Italy, 9–13 Oct 2006.
Evidence for new seven‐branes
Authors: Bergshoeff E.A. , Hartong J. , Ortín T. , Roest D.
Published: May 2007

In order to construct globally well‐defined 7‐brane solutions we postulate the existence of a new type of 7‐brane. We show that these new 7‐branes play an important role in understanding both the existing F‐theory 7‐brane configurations as well as more general 7‐brane configurations.
pp‐wave matrix models from point‐like gravitons
Authors: Lozano Y. , Rodríguez‐Gómez D.
Published: May 2007

The BFSS Matrix model can be regarded as a theory of coincident M‐theory gravitons. In this spirit, we summarize how using the action for coincident gravitons proposed in hep‐th/0207199 it is possible to go beyond the linear order approximation of Kabat and Taylor, and to provide a satisfactory microscopical description of giant gravitons in AdSm × Sn backgrounds. We then show that in the M‐theory maximally supersymmetric pp‐wave background, the action for coincident gravitons, besides reproducing the BMN Matrix model, predicts a new quadrupolar coupling to the M‐theory 6‐form potential, which supports the so far elusive fuzzy 5‐sphere giant graviton solution. Finally, we discuss similar Matrix models that can be derived in Type II string theories using dualities.
Unfrozen hyperscalars and supersymmetry
Authors: Meessen P.
Published: May 2007

We discuss the effect that non‐constant hyperscalars have in supersymmetric solutions, discuss the equations governing such solutions and show some intriguing solutions.
BPS solutions in AdS/CFT
Authors: Milanesi G. , Gava E. , Narain K.S. , O'Loughlin M.
Published: May 2007

We study a class of exact supersymmetric solutions of type IIB Supergravity. They have an SO(4) SU(2) × U(1) isometry and preserve generically 4 of the 32 supersymmetries of the theory. Asymptotically AdS5 × S5 solutions in this class are dual to 1/8 BPS chiral operators which preserve the same symmetries in the 𝒩 = 4 SYM theory. They are parametrized by a set of four functions that satisfy certain differential equations. We analyze the solutions to these equations in a large radius asymptotic expansion: they carry charges with respect to two U(1) KK gauge fields and their mass saturates the expected BPS bound. We show how the same formalism is suitable for the description of excitations of the AdS5 × Yp,q geometries.
Higher genus superstring amplitudes and the measure on the moduli space
Authors: Volpato R.
Published: May 2007

Recent derivations of completely gauge‐invariant two‐loop superstring amplitudes renewed the interest in the possible form of higher genus contributions. In this respect, two main points are discussed: a. At genus greater than 3, the Schottky problem actually represents a formidable obstruction for the explicit expression of the integration measure on the moduli space in terms of Riemann period matrices. As a first step toward such a construction, a modular invariant measure for all genera is derived, corresponding to the restriction to the Schottky locus of the Siegel metric on the upper half‐space. b. A class of natural generalizations of the 2 loop D'Hoker and Phong formula is discussed for the higher genus contributions to the 4‐gravitons amplitude in type II theories. Such expressions also satisfy the non‐trivial requirements of modular invariance and gauge slice independence.
Quasinormal modes and meson decay rates
Authors: Hoyos C. , Landsteiner K. , Montero S.
Published: May 2007

We model meson melting in a hot plasma by the quasinormal modes of D7‐brane fluctuations of embeddings that fall into the horizon of a black hole in Ads5 × S5 geometry. The inverse of the imaginary part of the quasinormal frequency gives the lifetime of the meson in the plasma. We briefly comment on the possible application of our model to quarkonium suppression.
Supersymmetric black holes in string theory
Authors: Mohaupt T.
Published: May 2007

We review recent developments concerning supersymmetric black holes in string theory. After a general introduction to the laws of black hole mechanics and to black hole entropy in string theory, we discuss black hole solutions in N = 2 supergravity, special geometry, the black hole attractor equations and the underlying variational principle. Special attention is payed to the crucial role of higher derivative corrections. Finally we discuss black hole partition functions and their relation with the topological string, mainly from the supergravity perspective. We try to summarize the state of art and discuss various open questions and problems.
Gauge theory and knot homologies
Authors: Gukov S.
Published: May 2007

Topological gauge theories in four dimensions which admit surface operators provide a natural framework for realizing homological knot invariants. Every such theory leads to an action of the braid group on branes on the corresponding moduli space. This action plays a key role in the construction of homological knot invariants. We illustrate the general construction with a simple example based on surface operators in 𝒩 = 4 twisted gauge theory which lead to a categorification of a variant of the Casson invariant.
High breakdown field of pnp GaN/InGaN/AlGaN DHBTs with AlGaN collector
Authors: Kumakura Kazuhide , Nishikawa Atsushi , Makimoto Toshiki
Published: May 2007

We have investigated the characteristics of pnp GaN/InGaN/(Al)GaN double heterojunction bipolar transistors (DHBTs) grown by metalorganic vapour phase epitaxy. In GaN‐collector DHBTs, the collector–base breakdown voltage under the open‐emitter condition increased with increasing collector thickness. By fitting the experimental results to the theoretical model of the punch‐through diode, we obtained the breakdown field of 3.1 MV/cm and the residual carrier concentration of 8.5 × 1016 cm–3 for the GaN collector layer. On the other hand, in a 500 nm thick AlGaN collector, the breakdown voltage was 190 V. Assuming that the bias was uniformly applied in the AlGaN collector, the corresponding breakdown field was calculated to be 3.8 MV/cm. The results indicate that the use of an AlGaN collector in HBTs is a promising way to increase the breakdown voltage without increasing the collector thickness. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Comparison between optical gain spectra of InxGa1–xN/In0.02Ga0.98N laser diodes emitting at 404 nm and 470 nm
Authors: Kojima K. , Funato M. , Kawakami Y. , Braun H. , Schwarz U. T. , Nagahama S. , Mukai T.
Published: May 2007

We investigate the gain formation properties of Inx Ga1–x N laser diodes emitting at 404 nm and 470 nm (sample A and B, respectively). Employing the Hakki–Paoli method, their optical gain spectra were measured at 298 K and 333 K. Since spatial fluctuations of the well width and In composition are considerable for long‐wavelength laser diodes, broadening of the optical gain and luminescence spectra are clearly enhanced in sample B when compared with sample A. Moreover, population inversion occurs in at least two discrete energy levels for the gain spectra of sample B. It was found that only the modal gain of the higher gain peak can overcome the mirror loss, therefore the lower one does not contribute to lasing action. We also estimate internal loss of A and B to be 25 cm–1 and 30 cm–1, respectively. The maximum gain value of A increases linearly with increasing injected current even at 333 K, while that of B grows sub‐linearly. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
UV LED arrays at 280 and 340 nm for spectroscopic biosensing
Authors: Davitt K. , Song Y.‐K. , Patterson W. , Nurmikko A. V. , Ren Z. , Sun Q. , Han J.
Published: May 2007

We demonstrate the application of linear arrays of ultraviolet light emitting diodes (UV LEDs) at the wavelengths of 280 nm and 340 nm to the acquisition of fluorescence spectra from single particles in real‐time. A compact optical system and custom electronics are employed to produce a compact, standalone biosensor. The detection sensitivity of the UV LED system is established using the biofluorophores tryptophan and NADH, and the capability of the sensor to sort particles based on weak spectra is demonstrated using micron‐sized polystyrene latex (PSL) spheres. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Trends in electrospinning of natural nanofibers
Authors: Haghi A. K. , Akbari M.
Published: May 2007

Nanotechnology has become in recent years a topic of great interest to scientists and engineers, and is now established as prioritized research area in many countries. The reduction of the size to the nanometer range brings an array of new possibilities in terms of material properties, in particular with respect to achievable surface to volume ratios. Electrospinning of natural fibers is a novel process for producing superfine fibers by forcing a solution through a spinneret with an electric field. An experimental study on this technique has been made in this paper and the effect of systematic parameters on electrospun nanofibers were critically analyzed. Based on this study, the key process parameters have been identified according to our experimental observations. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Synthesis of carbon nanotubes, nanofibers and encapsulated nanoparticles by decomposition of acetylene on Ge modified Pd catalysts
Authors: Segura Rodrigo A. , Tello Alejandra , Häberle Patricio
Published: May 2007

Different carbon nanostructures were synthesized by decomposition of acetylene over alumina supported palladium–germanium catalysts. The addition of small amounts of Ge to the Pd(1%)/γ‐Al2O3 catalyst increases the yield of carbon nanotubes among other carbon products, in the decomposition of acetylene. The use of a higher Ge concentration (0.3%) in the catalyst induces the formation of carbon nanofibers. For larger Ge concentrations (0.5%) the bimetallic catalyst particles become encapsulated in a graphitic structure. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
High‐frequency performance of multiple‐channel carbon nanotube transistors
Authors: Narita Kaoru , Hongo Hiroo , Ishida Masahiko , Nihey Fumiyuki
Published: May 2007

We have measured the high‐frequency characteristics of carbon nanotube field effect transistors (CNTFETs) and obtained a cut‐off frequency of 10.3 GHz and maximum oscillation frequency of 3.5 GHz. These values are among the highest ever published. We achieved them by developing a high‐density multiple‐channel CNTFET structure whose output impedance is much lower than conventional single channel CNTFETs, and by accurately measuring S‐parameters, e.g., using the de‐embedding procedure that removes existing errors in measured S‐parameters of small‐signal devices. We also described an equivalent circuit RF model consistent with the experimental results. Detailed analysis revealed that decreasing parasitic capacitances of electrodes and resistances of carbon nanotube extensions greatly improve the high‐frequency performance of CNTFETs. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Weighted nonparametric maximum likelihood estimate of a mixing distribution in nonrandomized clinical trials
Authors: Liu Chaofeng , Xie Jun , Zhang Ying
Published: May 2007

Hierarchical models have a variety of applications, including multi‐center clinical trials, local estimation of disease rates, longitudinal studies, risk assessment, and meta‐analysis. In a hierarchical model, observations are sampled conditional on individual unit‐specific parameters and these parameters are sampled from a mixing distribution. In observational studies or nonrandomized clinical trails, observations may be biased samples from a population and heterogeneous with respect to some confounding factors. Without controlling the heterogeneity in the sample, the standard estimation of the mixing distribution may lead to inaccurate statistical inferences. In this article, we propose a weighted nonparametric maximum likelihood estimate (NPMLE) of the mixing distribution and its smoothed versionviaweighted smoothing by roughening. The proposed estimator reduces bias by assigning a weight to each subject in the sample. The weighted NPMLE is shown to be weighted self‐consistent and therefore can be easily calculated through a recursive approach. Simulation studies were conducted to evaluate the performance of the proposed estimator. We applied this method to clinical trial data evaluating a new treatment for stress urinary incontinence. Copyright © 2007 John Wiley & Sons, Ltd.
Inelastic behavior of staggered truss systems
Authors: Kim Jinkoo , Lee Joon‐Ho , Kim Young‐Moon
Published: May 2007

In this study 4‐, 10‐, and 30‐story staggered truss systems (STS) were designed and their seismic performances were evaluated by pushover analysis. The results were compared with the seismic performance of conventional moment‐resisting frames and braced frames. According to the analysis results, the STS showed relatively satisfactory lateral load‐resisting capability compared with conventional braced frames. However, in the mid‐ to high‐rise STS, plastic hinges formed at horizontal and vertical chords of a Vierendeel panel, which subsequently led to brittle collapse of the structure. Based on these observations, reinforcing schemes were applied and their effects on enhancing lateral load‐resisting capacity were investigated. Copyright © 2007 John Wiley & Sons, Ltd.
Seismic analysis, design, and review for tall buildings
Authors: Moehle Jack P.
Published: May 2007

Whereas current building codes legally apply to seismic design of tall buildings, their prescriptive provisions do not adequately address many critical aspects. Performance‐based engineering provides a desirable alternative. Application of performance‐based procedures requires: an understanding of the relation between performance and nonlinear modeling; selection and manipulation of ground motions appropriate to design hazard levels; selection of appropriate nonlinear models and analysis procedures; interpretation of results to determine design quantities based on nonlinear dynamic analysis procedures; careful attention to structural details; and peer review by independent qualified experts to help assure the building official that the proposed materials and system are acceptable. These topics are discussed with an emphasis on tall buildings. Copyright © 2006 John Wiley & Sons, Ltd.
Antibiotic from the marine environment with antimicrobial fouling activity
Authors: Wigglesworth‐Cooksey B. , Cooksey K. E. , Long Richard
Published: May 2007

The degradation in performance of submerged marine structures through their colonization by micro‐ and macrobiota is well known. Historically, toxic surface coatings have been used to control both types of fouling. Legislative requirements worldwide now require alternative non‐ or minimally toxic coatings to be used. Here we report on the potential for synthetic 2‐pentyl‐4‐quinolinol (PQ), an antibiotic from an Alteromonas sp., as a candidate antifoulant. Hundred micromolar PQ reduces the growth of four marine diatoms that usually grow as biofilms. Furthermore, PQ inhibits the initial adhesive process in Amphora coffeaeformis in a logarithmic dose‐dependent manner, but not the adhesion of a Navicula sp., indicating differing adhesive processes in these two diatoms. Treatment of established biofilms with PQ causes a rapid and complete loss of motility in both Amphora and Navicula and eventually, as seen by Sytox Green staining, cell death, and lysis. We conclude that PQ, or one of its chemical analogues, holds promise as an antifoulant molecule for inclusion in marine surface coating. © 2007 Wiley Periodicals, Inc. Environ Toxicol 22: 275–280, 2007.
Long‐lifetime current‐driven rotating kink modes in a non‐line‐tied plasma column with a free end
Authors: Intrator T. P. , Furno I. , Ryutov D. D. , Lapenta G. , Dorf L. , Sun X.
Published: May 2007

We show the first experimental evidence for a magnetohydrodynamic kink instability in a current rope with one end that is free to move. This free end is partially insulated by sheath resistivity, so that the usual frozen in flux assumption for magnetohydrodynamics is violated in this region. The free end is therefore not line‐tied to the axial boundary. We find the instability threshold is well below the classical Kruskal‐Shafranov threshold, culminating in a long‐lifetime saturated state. The presence of an axial flow further lowers the kink threshold and gives rise to a doppler‐shifted frequency from rotation of the kink, where the eigenfunction is axially pushed in the flow direction. This lowered threshold may give rise to kink instabilities in situations with small magnetic twist that would otherwise be considered stable. Striking agreement with a theoretical analysis is demonstrated. The existence of a free end may be important for open flux tubes attached to the Sun, galactic jets associated with accretion discs, and spheromak startup.
High‐resolution multifluid simulations of the plasma environment near the Martian magnetic anomalies
Authors: Harnett E. M. , Winglee R. M.
Published: May 2007

Three‐dimensional high‐resolution (∼40 km), multifluid simulations of the solar wind interaction at Mars during the southern hemisphere summer solstice indicate that the region around the magnetic anomalies can be complex and highly structured. The anomalous magnetic field leads to the formation of multiple cusps and a void region where the ionosphere is eroded. Most importantly, the anomalous magnetic field changes the nature of the magnetic pileup layer (MPL) when compared to over unmagnetized regions. While the altitude of the MPL is approximately the same in both the northern and southern hemispheres for this orientation, plasma in the MPL near the magnetic anomalies is cooler, with less solar wind and more of ionospheric origin. The solar wind density is reduced by a factor of 3 in the southern MPL, in comparison to the northern MPL, while the ionospheric density is 10–600 times more dense in the southern MPL, depending on altitude, location, and species.
Technique: Large‐scale ionospheric conductance estimated from combined satellite and ground‐based electromagnetic data
Authors: Green D. L. , Waters C. L. , Korth H. , Anderson B. J. , Ridley A. J. , Barnes R. J.
Published: May 2007

A technique for estimating the large‐scale spatial distribution of the height‐integrated electrical conductivity (conductance) of the Earth's high‐latitude ionosphere is presented. By combining satellite magnetic perturbation data with ground‐based magnetometer and HF radar observations the Hall (ΣH) and Pedersen (ΣP) conductances are independently calculated. Magnetic perturbations observed at the Earth's surface are combined with those recorded by satellites to calculate the horizontal ionospheric current (⊥). Combined HF radar and satellite ion drift data give the ionospheric electric field (⊥), which combined with ⊥ allows ΣH and ΣP to be estimated from Ohm's law. Conductance results from preliminary application of the technique to an event with a 1 hour integration time are presented. Significant uncertainties arise due to sparse ground magnetometer and electric field coverage. The resulting conductance distribution shows an enhancement in the auroral regions as expected from a statistical model conductance. However, the calculated conductance enhancement is located between the region 1 and region 2 Birkeland currents. This agrees with the statistical model data in the morning sector but disagrees in the evening sector. Comparison of the conductance results with conductance data inferred from in situ precipitating particle observations shows colocated enhancements. The calculated data also show a low (<1) Hall to Pedersen conductance ratio in regions near downward Birkeland current.
Climatology of the equatorial thermospheric mass density anomaly
Authors: Liu Huixin , Lühr Hermann , Watanabe Shigeto
Published: May 2007

The equatorial anomaly is an interesting and important feature of the Earth's thermosphere‐ionosphere coupling in tropical regions. It is an anomalous latitudinal distribution found in both the ionized and unionized part of the atmosphere. Its equinox configuration consists of a minimum near the dip equator flanked by two maxima on both sides. The ionospheric side of this anomaly, often referred to as the equatorial ionization anomaly (EIA), has long been recognized since the 1930s. However, its thermospheric counterpart was only to be glimpsed by the Dynamic Explorer 2 satellite in the 1970s. A global picture of it has been rather recently revealed by the CHAMP satellite in 2005. In this paper we complement previous studies by investigating the climatology of the equatorial mass anomaly (EMA) in the thermosphere using 4 years of CHAMP measurements. Our analysis has revealed strong variation of the EMA with season and solar flux level. The EMA structure is most prominent around equinox, with a crest‐to‐trough ratio about 1.05 for F10.7 = 150. Near solstices, it is asymmetric about the dip equator. The density crest attains maximum 1–2 hours earlier and reaches higher values in the summer hemisphere than in the winter hemisphere. The density in EMA regions varies semiannually, with maxima near equinoxes. The latitudinal locations of the EMA crests undergo a seasonal variation, obviously following the movement of the subsolar point. The EMA structure has also been found to become more pronounced at higher solar flux levels. Both the location and magnitude of the EMA crests closely follow those of the EIA in corresponding seasons and solar flux levels, hence demonstrating strong plasma‐neutral interaction. Furthermore, two seasonal asymmetries clearly present in the globally averaged density, with the density in March/December being ∼15–20% higher than that in September/June.
Exchange bias in [Pt∕Co]n∕IrMn multilayers with perpendicular magnetic anisotropy
Authors: Rhee Jang Roh
Published: May 2007

An unusual peak in ferromagnetic thickness dependence of exchange bias properties is observed for [Pt(15)∕Co(tCo)]4–IrMn(50) (in angstrom) multilayer prepared by magnetron sputtering. The exchange coupling field (Hex) shows the maximum value of 291Oe for tCo=3Å. Such atypical behavior is ascribed to a reduction of the perpendicular effective magnetic anisotropy and the concomitant reduction of MR∕MS (remanence to saturation magnetization ratio) for either very thin or exceedingly thick tCo. The hysteresis loops become asymmetric at intermediate angle with a shift not only along the field axis but also along the magnetization axis. Hex and coercivity (Hc) show a 1∕cosθ and 1∕∣cosθ∣ dependence on the angle (θ) between the applied measuring field (Ha) and the perpendicular-plane cooling field, respectively. This 1∕cosθ dependence can be accounted for by considering the strong out-of-plane magnetic anisotropy introduced during the field cooling.
Carrier relaxation dynamics and steady-state charge distributions in coupled InGaN∕GaN multiple and single quantum wells
Authors: Khatsevich S. , Rich D. H. , Keller S. , DenBaars S. P.
Published: May 2007

We have examined the carrier capture dynamics and excitation dependent charge distributions of coupled InGaN∕GaN multiple quantum well samples. We measured the temporal evolution of time-delayed cathodoluminescence (CL) spectra to study the temperature- and excitation-dependent transfer of carriers from a surrounding confinement region into a coupled single quantum well. Samples possessing two different structures for the confinement region [i.e., number of quantum wells (QWs) and varying widths] were examined with CL. In order to study state filling of the SQW and QWs in the confinement region, we calculated the quasi-Fermi levels and carrier densities by utilizing a model that involves self-consistent solutions of the nonlinear Poisson-Schrödinger equation for wurtzite QWs including strain, deformation potentials, and polarization fields. Band-edge and effective mass parameters were first obtained from a strain- and In composition-dependent k⋅p calculation for wurtzite InxGa1−xN, using a 6×6 k⋅p Hamiltonian in the {0001} representation. The model shows that the difference in the quasi-Fermi levels between the confinement and SQW regions decreases with increasing excitation and temperature. Likewise, a reversal in the relative magnitude of the carrier densities between these two regions occurs at a certain temperature and excitation. Furthermore, the results for the model describing the steady-state excitation are consistent with those for the transient excitation in time-resolved CL, which also exhibit a marked increase in the rate of carrier transfer to the SQW region as the temperature increases.
Small scale response and modeling of periodically forced turbulence
Authors: Bos Wouter J. T. , Clark Timothy T. , Rubinstein Robert
Published: May 2007

The response of the small scales of isotropic turbulence to periodic large scale forcing is studied using two-point closures. The frequency response of the turbulent kinetic energy and dissipation rate, and the phase shifts among production, energy, and dissipation are determined as functions of the Reynolds number. It is observed that the amplitude and phase of the dissipation exhibit nontrivial frequency and Reynolds number dependence that reveals a filtering effect of the energy cascade. Perturbation analysis is applied to understand this behavior which is shown to depend on distant interactions between widely separated scales of motion. Finally, the extent to which finite dimensional models (standard two-equation models and various generalizations) can reproduce the observed behavior is discussed.
Atomistic analysis of the annealing behavior of amorphous regions in silicon
Authors: López Pedro , Pelaz Lourdes , Marqués Luis A. , Santos Iván
Published: May 2007

We have analyzed the features of recrystallization of amorphous regions, using an atomistic amorphization-recrystallization model that considers the Si interstitial-vacancy pair as the building block for the amorphous phase. Both small amorphous pockets and large continuous amorphous layers are modeled as an accumulation of Si interstitial-vacancy pairs. In our model recrystallization is envisioned as a local rearrangement of atoms, the recrystallization rate of Si interstitial-vacancy pairs being determined by their local coordination. This feature explains the differences in the annealing behavior of amorphous regions with different topologies, the faster regrowth velocity of the damage tail compared with the continuous amorphous layer, and the independence of the regrowth velocity on the amorphous layer depth.
Effects of ZnO buffer layers on the fabrication of GaN films using pulsed laser deposition
Authors: Man B. Y. , Yang C. , Zhuang H. Z. , Liu M. , Wei X. Q. , Zhu H. C. , Xue C. S.
Published: May 2007

GaN thin films were deposited on Si (111) substrates using ZnO buffer layers by pulsed laser deposition of a GaN target in a nitrogen atmosphere. High-quality GaN thin films were obtained after annealing at 950 °C for 15 min in a NH3 atmosphere. The crystalline quality, composition, and surface morphology of the films were characterized by x-ray diffraction, Fourier transform infrared spectroscopy, and atomic force microscopy. Through analysis of the measured results, a conclusion was drawn that ZnO buffer layers and their crystalline quality affected the structural properties (crystalline quality, composition, and surface morphology) of GaN films. Crystalline ZnO buffer layers improved nucleation and growth of GaN films. Zn–O bonds are destroyed when the GaN films are annealed in ammonia (NH3) ambience; a few O and Zn atoms depart from their positions, while N and Ga atoms fill in the empty positions and form a hexagonal structure of a special component. The structure is propitious to the epitaxial growth of GaN, while the motion of atoms gives the grains of GaN more chances to move and form Ga–N bonds. The annealing time markedly affects the preparation of GaN films and the least annealing time is 15 min under our experimental conditions.
Stability of natural convection in superposed fluid and porous layers: Influence of the interfacial jump boundary condition
Authors: Hirata Silvia C. , Goyeau Benoît , Gobin Dominique
Published: May 2007

Macroscopic modeling of momentum transport at a fluid-porous interface has been improved by the derivation of a stress jump boundary condition related to the spatial variations of the effective properties of the porous medium at the interfacial region. This Communication concerns the influence of this jump condition on the onset of thermal natural convection in fluid/porous stratified layers. A linear stability analysis shows that, for small depth ratio, the effective jump coefficient strongly influences the bimodal marginal stability curves. At large wave numbers, the “fluid mode” (the convective flow is confined in the fluid layer) is found to be more unstable while the porous mode, corresponding to small wave numbers, remains unchanged. The influence of the thickness and the dimensionless permeability of the porous layer is also presented.
Magnetic properties of postoxidized Pt∕Co∕Al layers with perpendicular anisotropy
Authors: Lacour D. , Hehn M. , Alnot M. , Montaigne F. , Greullet F. , Lengaigne G. , Lenoble O. , Robert S. , Schuhl A.
Published: May 2007

The magnetic properties of ultrathin Co layers sandwiched between Pt and Al layers are studied as a function of the Al layer oxidation time. The association of three batches of complementary experiments (extraordinary Hall effect, x-ray photoelectron spectroscopy, and tunneling magnetoresistance) allows the authors to finely characterize their samples both magnetically and chemically. The authors show that their oxidation process reduces the coercive field of ultrathin Co layers with perpendicular anisotropy (case of short oxidation time) and can even induce transition from a ferromagnetic to a superparamagnetic state (lengthy oxidation time).
Observation of the Purcell effect in high-index-contrast micropillars
Authors: Bennett A. J. , Ellis D. J. P. , Shields A. J. , Atkinson P. , Farrer I. , Ritchie D. A.
Published: May 2007

The authors have fabricated pillar microcavity samples with Bragg mirrors consisting of alternate layers of GaAs and aluminum oxide. Compared to the more widely studied GaAs∕AlAs micropillars, these mirrors can achieve higher reflectivities with fewer layer repeats and reduce the mode volume. The authors have studied a number of samples containing a low density of InGaAs∕GaAs self-assembled quantum dots in a cavity and here report observation of a threefold enhancement in the radiative lifetime of a quantum dot exciton state due to the Purcell effect.
Photo-leakage-current characteristic of F incorporated hydrogenated amorphous silicon thin film transistor
Authors: Wang M. C. , Chang T. C. , Liu Po-Tsun , Tsao S. W. , Chen J. R.
Published: May 2007

The photo-leakage-current (IPLC) characteristic of F incorporated a-Si:H thin film transistor (TFT) has been studied. The device activation energy (Ea) of a-Si:H(:F) TFTs is higher than those of typical a-Si:H TFTs, and resulted in the shift down of Fermi level in a-Si:H(:F). Experimental results show that the IPLC of a-Si:H(:F) TFTs is smaller than that of conventional a-Si:H TFTs in the density of states limited region, stemmed from the higher recombination centers present in a-Si:H(:F) material. However, the higher IPLC is observed in the hole conduction region, resulted from the larger Ea in the a-Si:H(:F) TFTs.
Heritability, correlated response, and indirect selection involving spectral reflectance indices and grain yield in wheat
Authors: Babar M. A. , van Ginkel M. , Reynolds M. P. , Prasad B. , Klatt A. R.
Published: May 2007

The objectives of this study were to assess the potential of using spectral reflectance indices (SRIs) as an indirect selection tool for grain yield in wheat under irrigated conditions. This paper demonstrates the genetic correlation between grain yield and SRIs, heritability and expected response to selection for grain yield and SRIs, correlated response to selection for grain yield estimated from SRIs, and efficiency of indirect selection for grain yield using SRIs in different spring wheat populations. Four field experiments, GHIST (15 CIMMYT globally adapted genotypes), RLs1 (25 random F3-derived families), RLs2 (36 random F3-derived families), and RLs3 (64 random F5-derived families) were conducted under irrigated conditions at the CIMMYT research station in north-west Mexico in 3 different years. Spectral reflectance was measured at 3 growth stages (booting, heading, and grain filling) and 7 SRIs were calculated using average values of spectral reflectance at heading and grain filling. Five previously developed SRIs (PRI, WI, RNDVI, GNDVI, SR), and 2 newly calculated SRIs (NWI-1 and NWI-2) were evaluated in the experiments. In general, the within- and between-year genetic correlations between grain yield and SRIs were significant. Three NIR-based indices (WI, NWI-1, and NWI-2) showed higher genetic correlations (0.73–0.92) with grain yield than the other indices (0.35–0.67), and these observations were consistent in all populations. Broad-sense heritability estimates for all indices were in general moderate to high (0.60–0.80), and higher than grain yield (0.45–0.70). The realised heritability for the 3 NIR-based indices was higher than for the other indices and for grain yield itself. Expected response to selection for all indices was moderate to high (0.54–0.85). The correlated response for grain yield estimated from the 3 NIR-based indices (0.59–0.64) was much higher than the correlated response for grain yield estimated from the other indices (0.31–0.46), and the efficiency of indirect selection for these 3 NIR-based indices was 90–96% of the efficiency of direct selection for grain yield. These results demonstrate the potential for using the 3 NIR-based SRI tools in breeding programs for selecting for increased genetic gains for yield.
Genotypic variation in phosphorus utilisation of soybean [Glycine max (L.) Murr.] grown in various sparingly soluble P sources
Authors: Tang C. , Qiao Y. F. , Han X. Z. , Zheng S. J.
Published: May 2007

This study compared the utilisation of sparingly soluble P among soybean genotypes selected from 3 geographical regions with contrasting soil pH. Plants of 5 genotypes from each region were grown for 72 days in soil columns supplied with hydroxyapetite (Ca-P), AlPO4 (Al-P), or FePO4 (Fe-P) at a rate of 25 mg P/kg soil. NaH2PO4 (Na-P) was used as control at the same rate. Shoot weights ranged from 2.4 to 5.9 g/plant. On average, the genotypes selected from calcareous soils of north-west China produced the highest shoot biomass whereas those from neutral soils of the north-east region the least. Root biomass and root surface area followed the same trend. In contrast, the root-to-shoot weight ratio was highest in Fe-P and lowest in Na-P while root length in Na-P and Fe-P was greater than in the other P forms. The genotypes from the north-east region had higher P concentration in the shoot than those from the other 2 regions. Total P uptake ranged from 9.0 to 15.9 mg/plant for Na-P, and from 6.3 to 12.4 for the sparingly soluble P. Average total P uptake was the highest for the genotypes from the north-west region, and was greatest in Na-P and lowest in Fe-P. The genotypes from the north-east region displayed the greatest ability to use sparingly soluble P, and those from the north-west the least relative to Na-P. Total P uptake from the sparingly soluble P correlated highly with plant biomass production, N2 fixation and nodulation, and seed P, while the relative P uptake correlated highly with P concentration in shoots but neither correlated with root carboxylate release nor leachate pH. The results suggest that there is a substantial genotypic variation in utilisation of sparingly soluble P, which is related to early vigour, nodulation, and seed P reserve but not to origin site pH or root exudation.
Genotypic variability in sequence and expression of HVA1 gene in Tibetan hulless barley, Hordeum vulgare ssp. vulgare, associated with resistance to water deficit
Authors: Qian Gang , Han Zhaoxue , Zhao Tao , Deng Guangbing , Pan Zhifen , Yu Maoqun
Published: May 2007

Late embryogenesis abundant (LEA) proteins are thought to protect against water stress in plants. Characteristics of sequence and expression of barley gene HVA1, a member of LEA group 3 protein, were investigated in hulless barley (Hordeum vulgare ssp. vulgare), associated with phenotypically diverse drought-tolerant genotypes. Sensitive and tolerant genotypes were identified from Tibetan populations of cultivated hulless barley, based on scores of water loss rate (WLR), maldondialdehyde (MDA), and proline content. The results indicated that lower MDA contents, lower scores of WLR, and higher proline contents were associated with drought-tolerant genotypes in hulless barley. Notably, differential trends of expression patterns were detected among the selected contrasting genotypes, depending on the duration of dehydration stress. The HVA1 gene tended to respond earlier in the tolerance (after 2 h) compared with sensitive genotypes (after 4 h). Results of quantitative real-time PCR indicated that the relative level of HVA1 expression was always higher in tolerant genotypes, rapidly increasing at the earlier stages (after 2–4 h of dehydration). However, HVA1 expressions of sensitive genotypes had a fast increase from 8 to 12 h of stress. Variable numbers of the 11-amino-acid-motif in LEA3 proteins were not consistent with the lines of drought resistance in hulless barley. Molecular characteristic of LEA3 protein in tolerant lines existed in the consistency of Gln32, Arg33, and Ala195 in Tibetan hulless barley. The present study may indicate that the differential HVA1 gene has a functional role in the dehydration tolerance in hulless barley. The authors suggested that the observed variability in sequence and expression of HVA1 could be related to the diverse drought-tolerant genotypes in crops.
Angiotensin II up-regulates soluble epoxide hydrolase in vascular endothelium
in vitro
and
in vivo
Authors: Ai Ding , Fu Yi , Guo Deliang , Tanaka Hiromasa , Wang Nanping , Tang Chaoshu , Hammock Bruce D. , Shyy John Y.-J. , Zhu Yi
Published: May 2007

Epoxyeicosatrienoic acids (EETs), as metabolites of arachidonic acid, may function as antihypertensive and antiatherosclerotic mediators for vasculature. EETs are degraded by soluble epoxide hydrolase (sEH). Pharmacological inhibition and genetic ablation of sEH have been shown to increase the level of EETs, and treating angiotensin II (Ang II)-infused hypertension rats with sEH-selective inhibitors increased the levels of EETs, with attendant decrease in systolic blood pressure. To elucidate the mechanisms by which Ang II regulates sEH expression, we treated human umbilical vein endothelial cells (ECs) and bovine aortic ECs with Ang II and found increased sEH expression at both the mRNA and protein levels. Transient transfection assays showed that the activity of the human sEH promoter was increased in ECs in response to Ang II. Further analysis of the promoter region of the sEH gene demonstrated that treatment with Ang II, like overexpression of c-Jun/c-Fos, activates the sEH promoter through an AP-1-binding motif. The binding of c-Jun to the AP-1 site of the sEH promoter was confirmed by chromatin immunoprecipitation assays. In contrast, adenovirus overexpression of the dominant-negative mutant of c-Jun significantly attenuated the effects of Ang II on sEH induction. An elevated level of sEH was found in the aortic intima of both spontaneously hypertensive rats and Ang II-infused Wistar rats. Blocking Ang II binding to Ang II receptor 1 by losartan abolished the sEH induction. Thus, AP-1 activation is involved in the transcriptional up-regulation of sEH by Ang II in ECs, which may contribute to Ang II-induced hypertension.