bluuebunny/crossref_metadata_2025 huggingface dataset:
3-dimensional time-resolved contrast-enhanced magnetic resonance angiography for evaluation late after the Mustard operation for transposition
Authors: Johansson Bengt , Babu-Narayan Sonya V. , Kilner Philip J. , Cannell Timothy M. , Mohiaddin Raad H.
Published: November 2009

Purpose

Cardiovascular magnetic resonance assessment of adults late after an atrial redirection operation for transposition is demanding and time consuming. We hypothesised that the relatively fast and standardised 3-dimensional time-resolved contrast-enhanced magnetic resonance angiography, or dynamic angiography, would be valuable in the periodic follow-up of these patients.

Methods

We investigated prospectively 36 adults with transposition using dynamic angiography, comparing our results against a comprehensive but non-contrast cardiovascular magnetic resonance protocol. We acquired 6 dynamic angiographic datasets after injection of contrast. The primary aim was to detect significant obstruction of the pathways for venous flow.

Results

In 4 patients (11%), we found evidence of moderate-to-severe, and thus clinically important, obstruction of systemic venous channels on standard cardiovascular magnetic resonance. All these patients were correctly identified by dynamic angiography. In 4 additional patients, we found mild and haemodynamically insignificant obstructions in the systemic venous channels. Of the 8 (22%) patients with any obstruction, 6 were detected by angiography. There were no false positives reported, giving sensitivity of 75% and specificity of 100%, a positive predictive value of 100%, and negative predictive value of 93%. In 1 patient, there was a moderate obstruction of the pulmonary venous compartment which was not readily seen by dynamic angiography.

Conclusions

3-dimensional dynamic angiography is a useful method for detecting anatomically moderate-to-severe, but not mild, obstructions in the systemic venous channels following Mustard repair for transposition. This technique can be used as a single imaging method and/or as complimentary to standard two dimensional cardiovascular magnetic resonance techniques for detection of clinically important obstructions in the systemic venous channels.
Northern Cascadia episodic tremor and slip: A decade of tremor observations from 1997 to 2007
Authors: Kao Honn , Shan Shao‐Ju , Dragert Herb , Rogers Garry
Published: November 2009

We analyze continuous seismic and GPS records collected in the last decade (1997–2007) to establish the most comprehensive observational basis for northern Cascadia episodic tremor and slip (ETS) events. A simple “ETS scale” system, using a combination of a letter and a digit, is proposed to quantitatively characterize the spatial and temporal dimensions of ETS events. Clear correlation between GPS and tremor signals is observed for all A/B class episodes, but the GPS signature is less obvious for minor ones. Regular ETS recurrence can be established only for A/B class episodes in southern Vancouver Island. Halting and jumping are very common in ETS migration patterns, and along‐strike migration can happen in both directions. A prominent tremor gap is observed in midisland around 49.5°N. This gap coincides with the epicenters of the only two large earthquakes beneath Vancouver Island. ETS tremors also tend to occur in places where the local seismicity is relatively sparse. The tremor depth distribution shows a peak in the 25–35 km range where strong seismic reflectors (i.e., the E layer) are documented. Detailed waveform analysis confirms the existence of shallow tremors above the currently interpreted plate interface. Our results suggest that a significant portion of the tremor activity and perhaps associated shearing are taking place along well‐developed structures such as the E layer, while fewer tremor bursts are generated elsewhere in response to the induced stress variation throughout the source volume.
Solar wind periodicity in energetic electrons at Saturn
Authors: Carbary J. F. , Roelof E. C. , Mitchell D. G. , Krimigis S. M. , Krupp N.
Published: November 2009

Fluxes of energetic electrons (110–365 keV) have been subjected to a long‐term Lomb periodogram analysis from the middle of 2004 to the middle of 2009. Fluxes within 20 RS and outside the magnetopause were excluded, so only fluxes within the magnetosphere were included in the analysis. The periodicity “box” was expanded from 5 hours to 50 days. In addition to the familiar rotational period near 10.8 hours, the electron fluxes exhibited a strong periodicity near 26 days (the solar wind period) and also a weaker periodicity near 13 days (half the solar wind period). A simulated periodogram using a “rotating anomaly” as it would be seen from the Cassini orbit does not display 26‐day and 13‐day periods, so the solar wind periodicity cannot result from a possible orbital resonance. The long‐term electron periodogram does not show any periods associated with the periods of Saturn's moons.
Observations of loss cone–shaped back streaming energetic protons upstream of the Earth's bow shock
Authors: Seki Y. , Nishino M. N. , Fujimoto M. , Miyashita Y. , Keika K. , Hasegawa H. , Okabe K. , Kasaba Y. , Terasawa T. , Yamamoto T. I. , Shinohara I. , Saito Y. , Mukai T.
Published: November 2009

Energetic ions are at times observed in the upstream region of the Earth's bow shock, and their origin is considered to be in the interaction with the shock front. While the energy of the solar wind ions is a few keV at most, the energy of the back streaming ions ranges from ∼5 keV to several MeV. In the present study we investigate back streaming energetic ions in the upstream of the Earth's bow shock observed by Geotail during two coronal mass ejection events. The observed local magnetic field rotated significantly during the events. Using the bow shock model and the observed magnetic field data, we found that the energetic ions appeared only when the upstream magnetic field was connected to the bow shock. The energetic ions showed two distinct distribution function characteristics, namely, the field‐aligned beam (FAB) and the loss cone–shaped distribution. While the former is occasionally detected, the latter having higher energies (30 keV to several hundred keV, compared to <18 keV for FAB) has not been reported before. Using a bow shock model, we can also estimate the shock angle at the point on the shock surface that the upstream field line is connected to and find that the distribution function shape transits from the FAB to the loss cone–shaped distribution as the shock angle becomes larger (transition at ΘBn = 70°–80°). We discuss the possible mechanisms responsible for the production of the newly found member of the energetic upstream ion family.
Innate inflammation and resolution in acute gout
Authors: Martin William John , Harper Jacquie L
Published: November 2009

Acute gout is an inflammatory arthritis that is controlled by the innate arm of the immune response. Although the causative feature of gout has long been recognized, it is surprising that the cellular activities that underpin the initiation and resolution of acute gout remain poorly described. This review article summarizes what are currently thought to be the key cellular mechanisms at play during an inflammatory episode of acute gout. The emerging role of mononuclear phagocytes is highlighted as having a central role in both the initiation and resolution of acute gout, and the interplay between monocytes and other elements of the innate immune response, including neutrophils, and complement protein activation are discussed.
Directed evolution of gold nanoparticle delivery to cells
Authors: Li Na , Larson Timothy , Nguyen Hong H. , Sokolov Konstantin V. , Ellington Andrew D.
Published: November 2009

A newly selected anti-receptor (anti-EGFR) aptamer was conjugated to gold nanoparticles via a facile hybridization method and was found to specifically direct the delivery of gold nanoparticles to cells expressing EGFR through receptor-mediated endocytosis.
Queuosine modification of tRNA: its divergent role in cellular machinery
Authors: Vinayak Manjula , Pathak Chandramani
Published: November 2009

tRNAs possess a high content of modified nucleosides, which display an incredible structural variety. These modified nucleosides are conserved in their sequence and have important roles in tRNA functions. Most often, hypermodified nucleosides are found in the wobble position of tRNAs, which play a direct role in maintaining translational efficiency and fidelity, codon recognition, etc. One of such hypermodified base is queuine, which is a base analogue of guanine, found in the first anticodon position of specific tRNAs (tyrosine, histidine, aspartate and asparagine tRNAs). These tRNAs of the ‘Q-family’ originally contain guanine in the first position of anticodon, which is post-transcriptionally modified with queuine by an irreversible insertion during maturation. Queuine is ubiquitously present throughout the living system from prokaryotes to eukaryotes, including plants. Prokaryotes can synthesize queuine de novo by a complex biosynthetic pathway, whereas eukaryotes are unable to synthesize either the precursor or queuine. They utilize salvage system and acquire queuine as a nutrient factor from their diet or from intestinal microflora. The tRNAs of the Q-family are completely modified in terminally differentiated somatic cells. However, hypomodification of Q-tRNA (queuosine-modified tRNA) is closely associated with cell proliferation and malignancy. The precise mechanisms of queuine- and Q-tRNA-mediated action are still a mystery. Direct or indirect evidence suggests that queuine or Q-tRNA participates in many cellular functions, such as inhibition of cell proliferation, control of aerobic and anaerobic metabolism, bacterial virulence, etc. The role of Q-tRNA modification in cellular machinery and the signalling pathways involved therein is the focus of this review.
Failure of thermocapillary-driven permanent nonwetting droplets
Authors: Nagy Peter T. , Neitzel G. Paul
Published: November 2009

A droplet may be prevented from molecular contact with a solid surface by providing a thin, lubricating film of surrounding fluid between the solid and liquid surfaces. In this study, we exploit thermocapillary convection, caused by a temperature difference maintained between the droplet and the unwetted surface, to provide this lubricating film. This state may be sustained indefinitely (permanent nonwetting) if the load applied to the droplet does not exceed a threshold. Failure of such systems may be categorized as either film or pinning failures, depending on whether the lubrication film is breached, resulting in a molecular contact between the droplet and the solid surface, or the droplet is forced from its support by losing its pinning contact line. In this work, loads that trigger film and pinning failures are quantified, and their mechanisms explained. Results show that larger loads can be sustained for systems with an elevated temperature difference and for droplets of higher viscosity.
Perturbative quantum field theory via vertex algebras
Authors: Hollands Stefan , Olbermann Heiner
Published: November 2009

In this paper, we explain how perturbative quantum field theory can be formulated in terms of (a version of) vertex algebras. Our starting point is the Wilson–Zimmermann operator product expansion (OPE). Following ideas of a previous paper (S. Hollands, e-print arXiv:0802.2198), we consider a consistency (essentially associativity) condition satisfied by the coefficients in this expansion. We observe that the information in the OPE coefficients can be repackaged straightforwardly into “vertex operators” and that the consistency condition then has essentially the same form as the key condition in the theory of vertex algebras. We develop a general theory of perturbations of the algebras that we encounter, similar in nature to the Hochschild cohomology describing the deformation theory of ordinary algebras. The main part of the paper is devoted to the question how one can calculate the perturbations corresponding to a given interaction Lagrangian (such as λφ4) in practice, using the consistency condition and the corresponding nonlinear field equation. We derive graphical rules, which display the vertex operators (i.e., OPE coefficients) in terms of certain multiple series of hypergeometric type.
Short- and long-range orders in Fe–Cr: A Monte Carlo study
Authors: Pareige C. , Domain C. , Olsson P.
Published: November 2009

Atomistic kinetic Monte Carlo simulations based on the two-band semiempirical cohesive model for Fe–Cr have revealed a body centered tetragonal Fe14Cr ordered compound at very low temperatures. Density functional theory calculations have shown that this structure is more stable than the Fe15Cr compound reported in literature. The study of short-range order, at higher temperatures, has shown that short-range order is not only characterized by the existence of Fe–Cr correlations in the two first neighbor shells but also by the existence of Cr–Cr correlations in the seventh and eighth neighbor shells corresponding to characteristic lengths of the ordered compound. The comparison of these results to neutron diffuse scattering experiments has shown that these characteristic lengths are observed in the experiments. Nevertheless, it appears that a larger spectrum of correlation lengths must exist in the experimental alloy. A Fourier transform of the atomic configuration has shown that the α phase is short-range ordered in the two-phase region.
Thermodynamics of the thermoelectric potential
Authors: Goupil Christophe
Published: November 2009

We derive the principal contributions to energy flux and entropy flux in a thermoelectric material using a force-flux description. Using the reduced current u=−J∕κ∇T of the coupled thermal and electrical flows, we introduce the so-called thermoelectric potential Tα+1∕u. We show that this approach gives a simple description of the thermodynamics of the thermoelectric process, including the heat and entropy production terms. The thermoelectric potential gives a precise estimate of the thermodynamical best working conditions leading to a direct measurement of the irreversible contribution for practical applications where the optimal thermoelectric potential value cannot be maintained.
A lower bound estimate of the gains stemming from quiescent period predictive control using conventional sea state statistics
Authors: Belmont M. R.
Published: November 2009

The principle of quiescent period prediction control (QPPC) is introduced in the context of sea wave energy capture (WEC) devices. The QPPC strategy is compared to approaches using statistical wave parameters for adaptive control of WECs and is shown to offer considerable increases in the average power captured. Assessing the quantitative benefits of QPPC would normally be based on wave by wave sea surface elevation data. Such data are not typically available from commercial wave sensors, and hence the present work describes a technique for assessing a lower bound estimate to QPPC benefits using conventional statistical sea state parameters. A case study is presented for a site off Southern Ireland where over a 12 month period QPPC can deliver more than 100% increase in the average power captured.
Variation of magnetoresistance in Ni2+xMn1−xGa with composition
Authors: Banik S. , Singh Sanjay , Rawat R. , Mukhopadhyay P. K. , Ahuja B. L. , Awasthi A. M. , Barman S. R. , Sampathkumaran E. V.
Published: November 2009

The magnetoresistance (MR) of Ni2+xMn1−xGa (−1≤x≤0.35) ferromagnetic shape memory alloy shows a large increase in magnitude at room temperature (RT) with increasing x. For Mn2NiGa (x=−1), MR at 8 T is −0.2%, while for Ni2.35Mn0.65Ga (x=0.35), it is −7.3%. Thus, MR of Ni2+xMn1−xGa can be varied over one order of magnitude by changing composition (x). Considering that the Curie temperature (TC) varies with x, the MR behavior in the austenitic phase is explained on the basis of the s−d scattering model. By fitting the MR at 8 T in the austenitic phase for different x and T, a (T/TC)6 power law dependence is obtained. In contrast to the monotonic MR variation with x, the magnetization at RT is highest for Ni2MnGa (x=0) and decreases for both Ni and Mn excess compositions.
Theory of fundamental microwave absorption in sapphire (α-Al2O3)
Authors: Shtin Nicolas A. , Romero José Mauricio Lopez , Prokhorov Eugene
Published: November 2009

An accurate model for intrinsic dielectric loss in sapphire (α-Al2O3) is presented. The proposed model is based on a theory of electromagnetic field absorption governed by multiphonon relaxation processes influenced by a finite lifetime of thermal phonons. Expressions for anisotropic sapphire dielectric loss tangent are derived utilizing sapphire dielectric function given in terms of the quasiharmonic approximation. The frequency-dependent two- and three-phonon damping constants of each fundamental transverse optical mode were determined numerically employing the accurate anharmonic coefficient computations based on sapphire lattice-dynamical data. The results of the dielectric loss tangent calculations in microwave and millimeter-wave regions are presented. The developed sapphire dielectric loss model offers excellent agreement between the experimental and calculated magnitudes of the tan δ components and also accurately reproduces their frequency and temperature dependencies.
Photoelectron spectroscopy study of systematically varied doping concentrations in an organic semiconductor layer using a molecular p-dopant
Authors: Olthof S. , Tress W. , Meerheim R. , Lüssem B. , Leo K.
Published: November 2009

We investigate the doping behavior of the strongly electron accepting molecule 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane coevaporated with the host molecule N,N,N′,N′-tetrakis(4-methoxyphenyl)-benzidine by photoemission spectroscopy and conductivity measurements. Using interface resolved measurements, we compare the alignment on different substrates and investigate the effects of varying doping concentrations on the Fermi level position. We find that at high doping concentrations the Fermi level gets pinned at the exponentially decaying tail of the highest occupied molecular orbital and compare these results with different dopants and host molecules. The measurement of the doping dependent space charge layer thickness yields information on the amount of free charge carriers and thereby the efficiency of the doping.
Effect of the anisotropy distribution on the coercive field and switching field distribution of bit patterned media
Authors: Krone P. , Makarov D. , Schrefl T. , Albrecht M.
Published: November 2009

We present a systematic study on the magnetization reversal in square arrays of magnetic nanostructures. To account for the unavoidable inhomogeneities of the magnetic properties due to, i.e., template preparation, a distribution of magnetic anisotropy values was taken into account. We show that the variation in magnetic anisotropy within an array of magnetic nanostructures and the influence of magnetic dipole-dipole interaction between the individual bits with separation distance is crucial for the performance of bit patterned media (BPM) concerning in particular the switching field distribution (SFD). Interestingly, a narrowing of the SFD was found with the angle between the direction of the external magnetic field and easy axis of magnetization, which is an important aspect for the usability of BPM with tilted anisotropy at ultrahigh storage densities beyond 1 Tbit/in.2.
Tunneling magnetoresistance in spin valves exchange biased with metallic antiferromagnet La0.45Sr0.55MnO3
Authors: Muduli P. K. , Budhani R. C.
Published: November 2009

We present a detailed study of tunnel magnetoresistance (TMR) in La0.45Sr0.55MnO3/La0.67Sr0.33MnO3/SrTiO3/Co spin valve structures. The nonlinear current-voltage (I-V) characteristics of the 25×25 μm2 junctions, when modeled in the framework of elastic tunneling through trapezoidal potential barrier, yield a barrier height in confirmation of SrTiO3 band gap and its thickness. The zero-bias value G(0) of the differential conductance measured directly is high at low temperatures and then drops monotonically with temperature till ≈215 K followed by a rise on increasing the temperature. We observe a lower junction resistance (negative TMR) when the magnetizations M⃗1 and M⃗2 of the two ferromagnetic layers are aligned antiparallel to each other, suggesting negative spin polarization. Moreover, the TMR shows a precipitous but asymmetric drop with bias voltage till it reaches ≈±200 mV suggesting role of inelastic excitations in reducing the TMR. The unique feature of this study is the robust exchange bias with exchange energy J≈0.13 erg cm−2 at the interface between antiferromagnetic La0.45Sr0.55MnO3 [LSMO(AF)] and ferromagnetic La0.67Sr0.33MnO3 (LSMO), which has been used to engineer coercivity contrast between the LSMO and cobalt films. The difference of coercivity (HC) between LSMO and Co increases as the temperature is lowered and manifests itself as a change in switching fields of resistance in tunnel junctions. We also show that the exchange bias shift can be engineered by different field cooling directions and by changing the relative thickness of La0.45Sr0.55MnO3 and La0.67Sr0.33MnO3.
Enhancement of phosphorus activation in vacancy engineered thin silicon-on-insulator substrates
Authors: Smith A. J. , Gwilliam R. M. , Stolojan V. , Knights A. P. , Coleman P. G. , Kallis A. , Yeong S. H.
Published: November 2009

The concentration of vacancy-type defects in a silicon-on-insulator substrate consisting of a 110 nm silicon overlayer and a 200 nm buried oxide has been quantified using variable energy positron annihilation spectroscopy following 300 keV Si+ ion implantation to a dose of 1.5×1015 cm−2 and subsequent annealing at temperatures ranging from 300 to 700 °C. The preferential creation of vacancies (relative to interstitials) in the silicon overlayer leads to a net vacancy-type defect concentration after annealing. Assuming that the defects have a structure close to that of the divacancy we determine the concentration to range from 1.7×1019 to 5×1018 cm−3 for annealing temperatures ranging from 300 to 700 °C. The measured defect concentration is in excellent agreement with that predicted via Monte Carlo simulation. The impact of this net vacancy population on the diffusion and activation of phosphorus introduced by a 2 keV implantation to a dose of 1×1015 cm−2 has been observed. For samples that combine both Si+ and P+ implantations, postimplantation phosphorus diffusion is markedly decreased relative to that for P+ implantation only. Further, a fourfold increase in the electrical activation of phosphorus after postimplantation annealing at 750 °C is observed when both implantations of Si+ and P+ are performed. We ascribe this affect to the reduction in phosphorus-interstitial clusters by the excess vacancy concentration beyond the amorphous/crystalline interface created by the P+ implantation.
Type I/type II band alignment transition in strained PbSe∕PbEuSeTe multiquantum wells
Authors: Simma M. , Fromherz T. , Bauer G. , Springholz G.
Published: November 2009

Investigation of the optical transitions in tensily strained PbSe∕PbEuSeTe multiquantum wells by differential transmission spectroscopy reveals a type I/type II band alignment transition due to strain-induced lowering of the band edge energies of the quantum wells. From the measured shifts of the optical transitions the optical deformation potentials of PbSe are obtained. This is crucial for realistic modeling of the electronic properties of strained PbSe heterostructures.
Effect of the change in the load resistance on the high voltage pulse transformer of the intense electron-beam accelerators
Authors: Cheng Xin-bing , Liu Jin-liang , Qian Bao-liang , Zhang Yu , Zhang Hong-bo
Published: November 2009

A high voltage pulse transformer (HVPT) is usually used as a charging device for the pulse forming line (PFL) of intense electron-beam accelerators (IEBAs). Insulation of the HVPT is one of the important factors that restrict the development of the HVPT. Until now, considerable effort has been focused on minimizing high field regions to avoid insulation breakdown between windings. Characteristics of the HVPT have been widely discussed to achieve these goals, but the effects of the PFL and load resistance on HVPT are usually neglected. In this paper, a HVPT is used as a charging device for the PFL of an IEBA and the effect of the change in the load resistance on the HVPT of the IEBA is presented. When the load resistance does not match the wave impedance of the PFL, a high-frequency bipolar oscillating voltage will occur, and the amplitude of the oscillating voltage will increase with the decrease in the load resistance. The load resistance approximates to zero and the amplitude of the oscillating voltage is much higher. This makes it easier for surface flashover along the insulation materials to form and decrease the lifetime of the HVPT.
Successive large perturbation method for the elimination of initial value dependence in I-V curve fitting
Authors: Cai Jinhua , Satoh Norifusa , Yanagida Masatoshi , Han Liyuan
Published: November 2009

A successive large perturbation method (SLPM) is proposed to resolve the problem of initial value dependence in the numerical least-square fitting for the extraction of I-V parameters in solar cells. In this method a large perturbation is applied onto certain a parameter before next turn of Newton-like iteration is proceeded and an improved result is usually obtained if the I-V parameters suffer from a latent initial value dependence problem. The numerical insensitivity of mean square of deviation to the variation of large shunt resistance is a critical factor to cause the initial value dependence. An application example for a dye-sensitized solar cell shows that about a 60% change of reverse saturation current I0 occurs after SLPM is applied to the result obtained by Newton-like method. Our result demonstrates that SLPM is a powerful tool to eliminate the initial value dependence in I-V curve fitting.
Vertically aligned ZnO nanostructures grown on graphene layers
Authors: Kim Yong-Jin , Lee Jae-Hyun , Yi Gyu-Chul
Published: November 2009

We report the vertical growth of ZnO nanostructures on graphene layers and their photoluminescence (PL) characteristics. ZnO nanostructures were grown vertically on the graphene layers using catalyst-free metal-organic vapor-phase epitaxy. The surface morphology of the ZnO nanostructures on the graphene layers depended strongly on the growth temperature. Further, interesting growth behavior leading to the formation of aligned ZnO nanoneedles in a row and vertically aligned nanowalls was also observed and explained in terms of enhanced nucleation on graphene step edges and kinks. Additionally, the optical characteristics and carbon incorporation into ZnO were investigated using variable-temperature PL spectroscopy.
A laser interferometer for measuring straightness and its position based on heterodyne interferometry
Authors: Chen Benyong , Zhang Enzheng , Yan Liping , Li Chaorong , Tang Wuhua , Feng Qibo
Published: November 2009

Not only the magnitude but also the position of straightness errors are of concern to users. However, current laser interferometers used for measuring straightness seldom give the relative position of the straightness error. To solve this problem, a laser interferometer for measuring straightness and its position based on heterodyne interferometry is proposed. The optical configuration of the interferometer is designed and the measurement principle is analyzed theoretically. Two experiments were carried out. The first experiment verifies the validity and repeatability of the interferometer by measuring a linear stage. Also, the second one for measuring a flexure-hinge stage demonstrates that the interferometer is capable of nanometer measurement accuracy. These results show that this interferometer has advantages of simultaneously measuring straightness error and the relative position with high precision, and a compact structure.
Carrier lifetime measurements in short-period InAs/GaSb strained-layer superlattice structures
Authors: Donetsky Dmitry , Svensson Stefan P. , Vorobjev Leonid E. , Belenky Gregory
Published: November 2009

Minority carrier lifetime and interband absorption in midinfrared range of spectra were measured in InAs/GaSb strained-layer superlattices (SLSs) grown by molecular beam epitaxy on GaSb substrates. The carrier lifetime in 200-period undoped 7 ML InAs/8 ML GaSb SLS with AlSb carrier confinement layers was determined by time-resolved photoluminescence (PL) and from analysis of PL response to sinwave-modulated excitation. Study of PL kinetics in frequency domain allowed for direct lifetime measurements with the excess carrier concentration level of 3.5×1015 cm−3. The minority carrier lifetime of 80 ns at T=77 K was obtained from dependence of the carrier lifetime on excitation power.
Three-dimensional patterns in the Lengyel–Rabai–Epstein model of the chlorine dioxide-iodine-malonic acid reaction
Authors: Moore Peter K. , Horsthemke Werner
Published: November 2009

We present computational solutions to the Lengyel–Rabai–Epstein model in three space dimensions. The results show that three-dimensional patterns exist and that they differ significantly from the two-dimensional patterns. Patterns occur at three locations in the reactor corresponding to peaks in the one-dimensional concentration of the starch tri-iodide concentration. Each pattern possesses its own intrinsic wavelength and is neither striped nor hexagonal, the two types that have been shown to exist in two dimensions. Computations suggest a bifurcation exists as a function of the reactor thickness. Solutions are computed using a high-order adaptive finite element method coupled with a multistep integrator in time. Linear systems generated in the multistep solver are solved using the iterative method GMRES with a Jacobi preconditioner. Matrix storage is reduced by incomplete assembly via thresholding. Preconditioner factorization and matrix-vector multiplication efficiency are enhanced by the use of OPENMP.
Flow in a channel with accelerating or decelerating wall velocity: A comparison between self-similar solutions and Navier–Stokes computations in finite domains
Authors: Espín Leonardo , Papageorgiou Demetrios T.
Published: November 2009

We investigate computationally whether a class of self-similar solutions of the Navier–Stokes equations in infinite channels driven by accelerating or decelerating walls, arises anywhere in a channel restricted to finite length. The self-similar solutions satisfy a nonlinear partial differential equation involving time and the vertical coordinate and have been studied previously. Admissible self-similar solutions include stable and unstable steady branches, time-periodic branches emerging from Hopf bifurcations, as well as chaotic solutions following a period-doubling Feigenbaum cascade. The objective here is to explore whether such solutions emerge when restricted to finite, although long, channels. The problem is addressed numerically using fast algorithms to solve the Navier–Stokes equations. It is established that all branches of the self-similar solutions (including time-periodic ones) can occur in finite channels provided the Reynolds numbers are not too high (approximately 500 for accelerating and 33 for decelerating wall flows, respectively). As the Reynolds number increases it becomes more difficult to recover the self-similar branches with general inflow conditions, and this has been overcome by utilizing the self-similar solutions as inflow Dirichlet conditions. At sufficiently high Reynolds numbers, the self-similar inflow conditions are incapable of producing the exact solution in the interior, but instead new steady or time-periodic states emerge which depend on the Reynolds number and the channel length. It is established numerically by solving the linearized Navier–Stokes equations that such phenomena are due to a spatial instability of the self-similar states to perturbations which are not of self-similar form. The results indicate that caution must be exercised in drawing conclusions from a stability theory restricted to self-similar perturbations and examples are given where such analysis is erroneous. In the case of decelerating wall flows the self-similar solutions are recovered on finite domains but for a much smaller range of Reynolds numbers as compared to accelerating wall flows. The results also show that time-periodic self-similar states are possible in finite channels (the Navier– Stokes equations are solved subject to the spatiotemporal self-similar solution at inflow) for accelerating wall flows but not for decelerating ones. Of special interest are computed aperiodic states of the Navier–Stokes equations in the case of accelerating walls and relatively high Reynolds numbers. These solutions behave intermittently and bounce between long-lived states that are congruent to the self-similar solutions to non-self-similar aperiodic ones. This is a complicated phenomenon due to the dimensionality and nonlinear nature of the system but the results indicate that the self-similar states can be strong attractors in some regions of the phase space.
Continuously tailored Taylor vortices
Authors: Sprague M. A. , Weidman P. D.
Published: November 2009

Modified axisymmetric, finite-length Taylor–Couette (TC) cells with stationary outer cylinder and rotating inner cylinder are designed in an effort to produce simultaneous onset of toroidal vortices of continuously varying wavelength along the gap. For a given axial variation in the inner radius, the axial variation in the outer radius can be chosen such that at every axial position, the criterion for the onset of Taylor vortices in a corresponding classical TC cell is met. In one scenario, a conical inner cylinder is chosen and the shape of the outer cylinder is then determined by locally satisfying the onset criterion. In another scenario, the inner and outer radii are chosen such that the onset criterion is locally satisfied and the axial rate of change in the classical onset wave number is held constant. In both cases, the modified cells possess a large-scale meridional circulation wrought by the finite Ekman (Bödewadt) pumping on the inner (outer) cylinder walls. Using direct numerical simulation, it is found that for sufficiently large aspect ratio, there exists a critical rotation rate for the simultaneous transition from the base flow to counter-rotating toroidal vortices throughout the varying-radius region. The vortices propagate in the direction of decreasing gap width with a phase speed that decreases with increasing aspect ratio.
Melanoma-associated fibroblasts modulate NK cell phenotype and antitumor cytotoxicity
Authors: Balsamo Mirna , Scordamaglia Francesca , Pietra Gabriella , Manzini Claudia , Cantoni Claudia , Boitano Monica , Queirolo Paola , Vermi William , Facchetti Fabio , Moretta Alessandro , Moretta Lorenzo , Mingari Maria Cristina , Vitale Massimo
Published: November 2009

Although the role of the tumor microenvironment in the process of cancer progression has been extensively investigated, the contribution of different stromal components to tumor growth and/or evasion from immune surveillance is still only partially defined. In this study we analyzed fibroblasts derived from metastatic melanomas and provide evidence for their strong immunosuppressive activity. In coculture experiments, melanoma-derived fibroblasts sharply interfered with NK cell functions including cytotoxicity and cytokine production. Thus, both the IL-2-induced up-regulation of the surface expression of NKp44, NKp30, and DNAM-1 triggering receptors and the acquisition of cytolytic granules were inhibited in NK cells. This resulted in an impairment of the NK cell-mediated killing of melanoma target cells. Transwell cocultures and the use of specific inhibitors suggested that cell-to-cell contact was required for inducing DNAM-1 modulation. In contrast, modulation of NKp44 and NKp30 was due to PGE2released by fibroblasts during coculture. Normal skin fibroblasts could also partially affect NK cell phenotype and function. However, the inhibitory effect of tumor-derived fibroblasts was far stronger and directly correlated with their ability to produce PGE2either constitutively or upon induction by NK cells.
Eye movement evidence that readers maintain and act on uncertainty about past linguistic input
Authors: Levy Roger , Bicknell Klinton , Slattery Tim , Rayner Keith
Published: November 2009

In prevailing approaches to human sentence comprehension, the outcome of the word recognition process is assumed to be a categorical representation with no residual uncertainty. Yet perception is inevitably uncertain, and a system making optimal use of available information might retain this uncertainty and interactively recruit grammatical analysis and subsequent perceptual input to help resolve it. To test for the possibility of such an interaction, we tracked readers' eye movements as they read sentences constructed to vary in (i) whether an early word had near neighbors of a different grammatical category, and (ii) how strongly another word further downstream cohered grammatically with these potential near neighbors. Eye movements indicated that readers maintain uncertain beliefs about previously read word identities, revise these beliefs on the basis of relative grammatical consistency with subsequent input, and use these changing beliefs to guide saccadic behavior in ways consistent with principles of rational probabilistic inference.
The time course of word retrieval revealed by event-related brain potentials during overt speech
Authors: Costa Albert , Strijkers Kristof , Martin Clara , Thierry Guillaume
Published: November 2009

Speech production is one of the most fundamental activities of humans. A core cognitive operation involved in this skill is the retrieval of words from long-term memory, that is, from the mental lexicon. In this article, we establish the time course of lexical access by recording the brain electrical activity of participants while they named pictures aloud. By manipulating the ordinal position of pictures belonging to the same semantic categories, the cumulative semantic interference effect, we were able to measure the exact time at which lexical access takes place. We found significant correlations between naming latencies, ordinal position of pictures, and event-related potential mean amplitudes starting 200 ms after picture presentation and lasting for 180 ms. The study reveals that the brain engages extremely fast in the retrieval of words one wishes to utter and offers a clear time frame of how long it takes for the competitive process of activating and selecting words in the course of speech to be resolved.
Hypersensitivity to DNA damage in plant stem cell niches
Authors: Fulcher Nick , Sablowski Robert
Published: November 2009

The growing apices of plants contain stem cells that continually produce tissues, which, in the shoot, include the germline. These stem cell populations remain active throughout the plant's life, which can last for centuries, and are particularly exposed to environmental hazards that cause DNA damage and mutations. It is not known whether plants have mechanisms to safeguard the genome specifically in these crucial cell populations. Here, we show that root and shoot stem cells and their early descendants are selectively killed by mild treatment with radiomimetic drugs, x-rays, or mutations that disrupt DNA repair by nonhomologous end-joining. Stem cell death required transduction of DNA damage signals by the ATAXIA-TELANGIECTASIA MUTATED (ATM) kinase and, specifically in the root, also the ATM/RAD3-RELATED (ATR) kinase. Consistent with the absence of p53 and the core apoptotic machinery in plants, death of the stem cells did not show apoptotic but autolytic features as seen in other cases of plant developmentally programmed cell death. We propose that plants have independently evolved selective death as a stringent mechanism to safeguard genome integrity in their stem cell populations.
The plurilingual tradition and the English language in South Asia
Authors: Canagarajah Suresh
Published: November 2009

There has been a plurilingual tradition of communication in South Asia since precolonial times. Local scholars consider pluringualism as ‘natural’ to the ecology of this region. In plurilingualism, proficiency in languages is not conceptualized individually, with separate competencies developed for each language. The different languages constitute an integrated system to constitute a repertoire. After distinguishing plurilingualism from other forms of multilingual communication, the article shows how English has been accommodated in this tradition. What I label Plurilingual English is not an identifiable code or a systematized variety of English. It is a highly fluid and variable form of language practice. Speakers negotiate their different Englishes for intelligibility and effective communication. The article goes on to define plurilingual competence. For communication to work across such radical differences, it is important that acquisition and use go hand and hand. Such a competence is always in a state of becoming and, therefore, acquisition is emergent. Plurilingual communication works because competence does not rely solely on a form of knowledge, but rather, encompasses interaction strategies. In the final section, the article discusses how learner strategy training and language awareness go some way toward facilitating such interactional strategies and repertoire development.
Not plain sailing
Authors: Hashim Azirah
Published: November 2009

This paper focusses on language and education issues in Malaysia as they have unfolded in the context of nation building, societal multilingualism and globalization from independence to the present day. The paper first examines the origin and nature of language and medium-of-instruction policies in Malaysia and the rationale for them. Secondly, it discusses the conflicts and controversies pertaining to language and education analyzing the domains of contestation. The next part of the paper reflects on the various shifts in language policy over the decades, from the early institutionalization of Malay to the growing importance of English amidst globalization trends, and finally the recent shift back to Malay, also examining the positioning of the Chinese and Tamil languages in the country. This is followed by a discussion of the emergence of an indigenized variety of English and English as a lingua franca in the region. The paper ends with a critical evaluation of the impact of the language and medium-of-instruction policies, and the constraints of alternative policies, with suggestions for a possible way forward.
Beyond fear and loathing in SG
Authors: Lim Lisa
Published: November 2009

This paper considers the real mother tongues of Singapore, namely the Chinese ‘dialects’ and Singlish, the linguistic varieties which, respectively, arrived with the original immigrants to the rapidly developing British colony, and evolved in the dynamic multilingual ecology over the decades. Curiously these mother tongues have been regarded with fear and treated with loathing in the official language policies and accompanying prestige planning that have been developed and executed in Singapore since independence, being actively denigrated and discouraged in official discourse, viewed as not having a place in the globalization goals of the nation. Looking beyond the official line and census figures, actual linguistic practices of the community of speakers testify to the vitality of these varieties, in spite of the official sanctions; moreover, in spite of itself, the government does in fact allow itself the use of these mother tongues when certain contexts call for it. This paper suggests that an enlightened consideration of native ‘dialects’ and nativized Singlish and the plurilingual practices in which they are used, as well as of the question of intelligibility, must point policy makers in directions where fears are assuaged and spaces made for the natural existence and evolution of such varieties in multilingual ecologies.
Centrosomal Aki1 and cohesin function in separase-regulated centriole disengagement
Authors: Nakamura Akito , Arai Hiroyuki , Fujita Naoya
Published: November 2009

Sister chromatid separation at anaphase is triggered by cleavage of the cohesin subunit Scc1, which is mediated by separase. Centriole disengagement also requires separase. This dual role of separase permits concurrent control of these events for accurate metaphase to anaphase transition. Although the molecular mechanism underlying sister chromatid cohesion has been clarified, that of centriole cohesion is poorly understood. In this study, we show that Akt kinase–interacting protein 1 (Aki1) localizes to centrosomes and regulates centriole cohesion. Aki1 depletion causes formation of multipolar spindles accompanied by centriole splitting, which is separase dependent. We also show that cohesin subunits localize to centrosomes and that centrosomal Scc1 is cleaved by separase coincidentally with chromatin Scc1, suggesting a role of Scc1 as a connector of centrioles as well as sister chromatids. Interestingly, Scc1 depletion strongly induces centriole splitting. Furthermore, Aki1 interacts with cohesin in centrosomes, and this interaction is required for centriole cohesion. We demonstrate that centrosome-associated Aki1 and cohesin play pivotal roles in preventing premature cleavage in centriole cohesion.
Eukaryotic systems broaden the scope of synthetic biology
Authors: Haynes Karmella A. , Silver Pamela A.
Published: November 2009

Synthetic biology aims to engineer novel cellular functions by assembling well-characterized molecular parts (i.e., nucleic acids and proteins) into biological “devices” that exhibit predictable behavior. Recently, efforts in eukaryotic synthetic biology have sprung from foundational work in bacteria. Designing synthetic circuits to operate reliably in the context of differentiating and morphologically complex cells presents unique challenges and opportunities for progress in the field. This review surveys recent advances in eukaryotic synthetic biology and describes how synthetic systems can be linked to natural cellular processes in order to manipulate cell behavior and to foster new discoveries in cell biology research.
GATA-3 is required for early T lineage progenitor development
Authors: Hosoya Tomonori , Kuroha Takashi , Moriguchi Takashi , Cummings Dustin , Maillard Ivan , Lim Kim-Chew , Engel James Douglas
Published: November 2009

Most T lymphocytes appear to arise from very rare early T lineage progenitors (ETPs) in the thymus, but the transcriptional programs that specify ETP generation are not completely known. The transcription factor GATA-3 is required for the development of T lymphocytes at multiple late differentiation steps as well as for the development of thymic natural killer cells. However, a role for GATA-3 before the double-negative (DN) 3 stage of T cell development has to date been obscured both by the developmental heterogeneity of DN1 thymocytes and the paucity of ETPs. We provide multiple lines of in vivo evidence through the analysis of T cell development in Gata3 hypomorphic mutant embryos, in irradiated mice reconstituted with Gata3 mutant hematopoietic cells, and in mice conditionally ablated for the Gata3 gene to show that GATA-3 is required for ETP generation. We further show that Gata3 loss does not affect hematopoietic stem cells or multipotent hematopoietic progenitors. Finally, we demonstrate that Gata3 mutant lymphoid progenitors exhibit neither increased apoptosis nor diminished cell-cycle progression. Thus, GATA-3 is required for the cell-autonomous development of the earliest characterized thymic T cell progenitors.