bluuebunny/crossref_metadata_2025 huggingface dataset:
On zonal jets in oceans
Authors: Nadiga Balasubramanya T.
Published: May 2006

We find that in parameter regimes relevant to the recently observed alternating zonal jets in oceans, the formation of these jets can be explained as due to an arrest of the turbulent inverse‐cascade of energy by free Rossby waves (as opposed to Rossby basin modes) and a subsequent redirection of that energy into zonal modes. This mechanism, originally studied in the context of alternating jets in Jovian atmospheres and two dimensional turbulence in zonally‐periodic configurations survives in spite of the presence of the meridional boundaries in the oceanic context.
Spontaneous rupture processes on a bending fault
Authors: Kase Y. , Day S. M.
Published: May 2006

We simulated spontaneous rupture processes on a vertical, bending strike slip fault in a three‐dimensional half space, using a finite‐difference method. Rupture area and overall slip distribution on the fault vary with the initial stress field, which depends on strike change at the bend. Rupture velocity and detailed slip distribution around the bend, on the other hand, are affected by time‐dependent normal stress change caused by rupture. This dynamic stress change plays an important role in the rupture process ahead of the bend, as well as in the resulting ground motion. The numerical simulation method demonstrated here in a simplified geometry is equally applicable to modeling strong ground motion from geometrically complex ruptures in realistic earth models.
Immediate and updated forecasting of aftershock hazard
Authors: Ogata Yosihiko , Katsura Koichi
Published: May 2006

It is well known that the detection rate of aftershocks is extremely low during the period immediately after a large earthquake due to the contamination of arriving seismic waves. This has led to considerable difficulties in obtaining estimates of the empirical laws of aftershock decay and magnitude frequency immediately after main shocks. This paper presents an estimation method for predicting the underlying occurrence rate of aftershocks of any magnitude range, based on a magnitude frequency model that combines the Gutenberg‐Richter law with the detection rate function. This procedure enables real‐time probability forecasting of aftershocks immediately after the mainshock, when the majority of large aftershocks are likely to occur.
Boreal ecosystems sequestered more carbon in warmer years
Authors: Chen Jing M. , Chen Baozhang , Higuchi Kaz , Liu Jane , Chan Douglas , Worthy Douglas , Tans Pieter , Black Andy
Published: May 2006

A 13‐year (1990–1996, 1999–2004), hourly air CO2 record measured on a 40 m tower in northern Canada is analyzed against interpolated marine boundary layer CO2 data representing the free troposphere above the tower. In warmer years, the planetary boundary layer was more depleted with CO2, suggesting that the land area (103–104 km2) upwind of the tower sequestered more carbon. After using a novel approach to derive the photosynthetic flux from the air CO2 diurnal variation pattern, it is confirmed that boreal ecosystem photosynthesis increased more than ecosystem respiration in warmer years.
Rock glacier dynamics: Stick‐slip motion coupled to hydrology
Authors: Jansen F. , Hergarten S.
Published: May 2006

We demonstrate an approach to simulate rock glacier dynamics based on a three‐dimensional stick‐slip model coupled to a simple model of melt water dispersion. Simulation results account for observed kinematic discontinuities and exhibit a distribution of slip event sizes that is characterized by large fluctuations following a power law. The model presents a feedback loop of dynamics and internal structure: (1) the evolution of shear horizons, which are correlated to melt water occurrence, can be seen; and (2) melt water distribution narrows to regions of maximum slip. Although this approach is promising, improvements in some details must be made. The solution for stress transfer accompanying slip has been taken from a model of a sheared body that is vertically constrained. In future models, the boundary conditions must be modified to that of a body confined only at its base. Additionally, a heuristic treatment of hydrology currently used must be further quantified.
24 × 7 @ Full Speed: Accelerated Time to Market
Authors: Custodio Miguel Gabriel , Thorogood Alan , Yetton Philip
Published: May 2006

‘It's only a web site. What could be so difficult about that?’ This quote is from the cafeteria of a start-up business funded by a North American retailer, after the disastrous ‘Black Friday’ of 2000, during which its web site experienced systemic failure. This case describes the dynamics, complexities and consequences of fast tracking an e-business start-up. This consumer electronics retailer created one of the most visited retail web sites, from concept to operation in 6 months. Market analysts were predicting a major increase in online sales while consumers were adopting the Internet at a rate faster than any previous technology. Meeting the multi-channel demands of the dynamic and competitive environment required operational balance, stability, innovative flexibility, organizational fit and the alignment of resource capabilities with technology. This case challenges the reader to comment on how a large company positioned itself and integrated the necessary competencies to compete successfully in a developing market by establishing a spin-off operation, separate from the main company.
Local Adaptations of Generic Application Systems: The Case of Veiling Holambra in Brazil
Authors: Pozzebon Marlei , van Heck Eric
Published: May 2006

This paper focuses on local adaptations, referring to the significant or subtle changes local firms make in their local business processes and rules in order to fit with a generic application system, and to the changes they make in the features of a generic application system. Local adaptations are therefore bidirectional in nature. Although several studies stress the importance of local adaptations for the overall success of information technologies (IT) used across locations, more research is needed regarding what kind of local adaptations are required for a particular generic application system to work well in particular localities. The nature and extent of local adaptations are still poorly understood. This paper provides a concrete illustration of a historically situated local adaptation: the case of Veiling Holambra. This Brazilian cooperative has imported a generic auction marketplace model from Holland and adapted it to local conditions, to succeed in a globalized and competitive flower market. Using concepts drawn from studies on globalization, cross-cultural implementations, and IT-based organizational change literature, we put forward three propositions that help to explain the success of local adaptations. The results of our case study indicate that the immigration of Dutch people was critical for bringing knowledge of cooperative structure and flower production to Holambra and led to a relatively small design-use gap. The ability to take local, contextual requirements into account without neglecting the ‘generic’ knowledge led to the successful implementation of the generic auction model. This mutual influence was particularly enabled by the Brazilian culture of improvization.
Information Technology and the Modalisation of Organisational Behaviour: A Theoretical Framework
Authors: Corea Stephen
Published: May 2006

Information technologies can transform an organisation's capacity to act effectively and achieve its performance aims. This theoretical paper presents a framework, adapted from the work of the semiotician A.J. Greimas, for qualitatively analysing this shaping of organisational behaviour and effectiveness around the use of IT. This framework permits various forms of capability or constraint in organisational action to be distinguished, in terms of the functional capacities of IT systems or key dimensions of social structure. A multi-faceted consideration of positive and negative outcomes of IT-based activities is thus supported. The use of this framework is demonstrated through brief case examples that illustrate its utility in providing a dynamic perspective on organisational performance and alignment in the use of IT. This theoretical framework equips IS interpretive studies to analyse the shaping of IT-based organisational activity from a standpoint of structures of behaviour or significance in a context of purposeful action.
A quantitative analysis of self-collimation effects in planar photonic crystals
Authors: Lombardet B. , Dunbar L. A. , Ferrini R. , Houdré R. , Robin F.
Published: May 2006

A self-collimated beam propagating inside a planar photonic crystal is investigated. By measuring the beam divergence with distance a quantitative measure of the self-collimation effect is obtained. The beam width is measured using an experimental technique that maps the electromagnetic field inside the photonic crystal structure by measuring the out-of-plane scattering at the air holes. The experimental results agree well with theoretical predictions based on equifrequency surface analysis.
Transport of single molecules along the periodic parallel lattices with coupling
Authors: Stukalin Evgeny B. , Kolomeisky Anatoly B.
Published: May 2006

General discrete one-dimensional stochastic models to describe the transport of single molecules along coupled parallel lattices with period N are developed. Theoretical analysis that allows to calculate explicitly the steady-state dynamic properties of single molecules, such as mean velocity V and dispersion D, is presented for N=1 and N=2 models. For the systems with N>2 exact analytic expressions for the large-time dynamic properties are obtained in the limit of strong coupling between the lattices that leads to dynamic equilibrium between two parallel kinetic pathways. It is shown that for all systems dispersion is maximal when the coupling between channels is weak.
Evolution of nonlinear dust-ion-acoustic waves in an inhomogeneous plasma
Authors: Xiao De-long , Ma J. X. , Li Yang-fang , Xia Yinhua , Yu M. Y.
Published: May 2006

The propagation of nonlinear dust-ion-acoustic waves in an inhomogeneous dusty plasma is studied. At small but finite amplitudes, the wave evolution is governed by a modified Korteweg–deVries Burgers equation, whose coefficients are space dependent. The properties of the evolution equation are analyzed and the behavior of the corresponding shock and soliton solutions is numerically studied. If dust-charge perturbation is neglected, there exists a zero-nonlinearity point where the coefficient of the nonlinear term changes from negative to positive. At that point the nonlinear wave also undergoes structural deformation. If the dust-charge perturbation is taken into account, the zero-nonlinearity point may not appear and the soliton or shock wave will retain its form during the propagation.
Periodic orientational motions of rigid liquid-crystalline polymers in shear flow
Authors: Tao Yu-Guo , den Otter W. K. , Briels W. J.
Published: May 2006

The collective periodic motions of liquid-crystalline polymers in a nematic phase in shear flow have, for the first time, been simulated at the particle level by Brownian dynamics simulations. A wide range of parameter space has been scanned by varying the aspect ratio L∕D between 10 and 60 at three different scaled volume fractions Lφ∕D and an extensive series of shear rates. The influence of the start configuration of the box on the final motion has also been studied. Depending on these parameters, the motion of the director is either characterized as tumbling, kayaking, log-rolling, wagging, or flow-aligning. The periods of kayaking and wagging motions are given by T=4.2(Lφ∕D)γ̇−1 for high aspect ratios. Our simulation results are in agreement with theoretical predictions and recent shear experiments on fd viruses in solution. These calculations of elongated rigid rods have become feasible with a newly developed event-driven Brownian dynamics algorithm.
Ab initio calculations of dispersion coefficients for nucleic acid base pairs
Authors: Haley Terence P. , Graybill Eric R. , Cybulski Slawomir M.
Published: May 2006

The results of ab initio calculations of two- and three-body dispersion coefficients for the four most important nucleic acid bases are reported. The isotropic as well as anisotropic coefficients were found by using the time-dependent Hartree-Fock approach and the aug-cc-pVDZ basis set. Single and double excitation coupled-cluster theory with noniterative treatment of triple excitations [CCSD(T)] was used to find the values of static polarizabilities which were subsequently used to estimate the values of the CCSD(T) dispersion coefficients. A comparison of these estimated CCSD(T) dispersion coefficients with coefficients found by using empirical approaches based on atomic contributions revealed that the latter are not reliable.
Smart photochromic gratings with switchable wettability realized by green-light interferometry
Authors: Mele Elisa , Pisignano Dario , Varda Maria , Farsari Maria , Filippidis George , Fotakis Costas , Athanassiou Athanassia , Cingolani Roberto
Published: May 2006

We demonstrate the enhancement of the wetting properties of smart photochromic surfaces by a specifically developed, gentle interferometric patterning employing green light. We realized photochromic gratings with 2.5–10.0μm period by a blend consisting of a green-curable matrix and spiropyran molecules. The structured surfaces exhibit photocontrolled and reversible wettability, and enhanced hydrophilicity with respect to the native substrates. The dynamics of liquid spreading onto the gratings was also investigated, and the wetting behavior analyzed according to Wenzel’s [Ind. Eng. Chem. 28, 988 (1936)] model for rough surfaces. These results indicate switchable gratings as promising functional components for microfluidics and modulation, and green-light interferometry as a reliable lithographic method for patterning organics without degradation or photochemical reactions.
Near-infrared Fourier transform photoluminescence spectrometer with tunable excitation for the study of single-walled carbon nanotubes
Authors: McDonald Timothy J. , Jones Marcus , Engtrakul Chaiwat , Ellingson Randy J. , Rumbles Garry , Heben Michael J.
Published: May 2006

A fast, sensitive, automated Fourier transform (FT) photoluminescence (PL) spectrometer with tunable excitation has been developed for analyzing carbon nanotube suspensions over a wide spectral range. A commercially available spectrometer was modified by the addition of a tunable excitation source, custom collection optics, and computer software to provide control and automated data collection. The apparatus enables excitation from 400to1100nm and detection from 825to1700nm, permitting the analysis of virtually all semiconducting single-walled nanotubes (SWNTs), including those produced by the high pressure carbon monoxide conversion and laser processes. The FT approach provides an excellent combination of high sensitivity and fast measurement. The speed advantage exists because the entire emission spectrum is collected simultaneously, while the sensitivity advantage stems from the high optical throughput. The high sensitivity is demonstrated in the measurement of very dilute SWNT suspensions and the observation of novel spectral features, and the speed is demonstrated by measuring the real-time changes in the SWNT PL during rebundling. This contribution describes the assembly of components, the methods for automating data collection, and the procedures for correcting the wavelength-dependent excitation intensity and the interferometer and detector responses.
Response of a delta-doped charge-coupled device to low energy protons and nitrogen ions
Authors: Lepri S. T. , Nikzad Shouleh , Jones T. , Blacksberg J. , Zurbuchen T. H.
Published: May 2006

We present the results of a study of the response of a delta-doped charge-coupled device (CCD) exposed to ions with energies less than 10keV. The study of ions in the solar wind, the majority having energies in the 1–5keV range, has proven to be vital in understanding the solar atmosphere and the near Earth space environment. Delta-doped CCD technology has essentially removed the dead layer of the silicon detector. Using the delta-doped detector, we are able to detect H+ and N+ ions with energies ranging from 1to10keV in the laboratory. This is a remarkable improvement in the low energy detection threshold over conventional solid-state detectors, such as those used in space sensors, one example being the solar wind ion composition spectrometer (SWICS) on the Advanced Composition Explorer spacecraft, which can only detect ions with energies greater than 30keV because of the solid-state detector’s minimum energy threshold. Because this threshold is much higher than the average energy of the solar wind ions, the SWICS instrument employs a bulky high voltage postacceleration stage that accelerates ions above the 30keV detection threshold. This stage is massive, exposes the instrument to hazardous high voltages, and is therefore problematic both in terms of price and its impact on spacecraft resources. Adaptation of delta-doping technology in future space missions may be successful in reducing the need for heavy postacceleration stages allowing for miniaturization of space-borne ion detectors.
Uniform attractors for nonautonomous incompressible non-Newtonian fluid with locally uniform integrable external forces
Authors: Zhao Caidi , Zhou Shengfan , Liao Xinyuan
Published: May 2006

This paper discusses the long time behavior of solutions for a two-dimensional (2D) nonautonomous incompressible non-Newtonian fluid in 2D bounded domains. When the external force g0(x,t) is locally uniform integrable (see Definition 1.1) in Lloc2(R;H), the authors obtain the existence and structure of uniform attractors in space V for the family of processes associated with the fluid. Moreover, when ∥g0∥Lb2 is properly small, they provide some interesting corollaries.
Study of fusion regimes in an inertial electrostatic confinement device using the new eclipse disk diagnostic
Authors: Murali S. Krupakar , Cipiti B. B. , Santarius J. F. , Kulcinski G. L.
Published: May 2006

New diagnostics are required to understand the physics operation of an inertial electrostatic confinement (IEC) device. In an attempt to understand the fusion source regimes within the IEC device, a new diagnostic called the eclipse disk has been introduced. This diagnostic was used to exploit the byproduct protons’ energy difference between the deuterium-deuterium (D–D) and deuterium—an isotope of helium with two protons and one neutron (D–He3) reactions to study the contributions of the protons generated from various source regimes. These source regimes are divided into five categories namely: converged core, embedded, beam background, volume, and wall-surface sources. The eclipse disk diagnostic has provided the first confirmed evidence that D–He3 reactions are predominantly embedded reactions. It has been observed that at the present operating power levels (6–10kW) most of the D–D reactions occur in the volume of the chamber caused by the charge exchanged neutrals, and the converged core contribution is significant only for D–D reactions. Since the branching ratio for the proton and neutron generation in a D–D fusion reaction is ∼50%, it is inferred that the proton to neutron count ratio is a better parameter to monitor than either proton or neutron counts measured alone while studying the source regimes. This parameter may also be used for studying the potential wells within the cathode grid.
Powder magnetoresistance of Co2Cr0.6Fe0.4Al∕Al2O3 powder compacts
Authors: Block T. , Wurmehl S. , Felser C. , Windeln J.
Published: May 2006

We report on the magnetotransport properties of Co2Cr0.6Fe0.4Al mixed with insulating Al2O3. The powder compacts show a maximum magnetoresistance of 88% at a saturation moment of 0.125T at 295K. Different explanations for the reversible mechanism will be discussed, such as tunneling between contiguous ferromagnetic grains, particle movement, and magnetostriction. The effect in Co2Cr0.6Fe0.4Al∕Al2O3 powder compacts is the largest room temperature magnetoresistance that has been measured until now.
Nonlinear effects on magnetic energy release by forced magnetic reconnection: Long wavelength perturbations
Authors: Jain Rekha , Browning Philippa , Kusano K.
Published: May 2006

Two-dimensional, nonlinear magnetohydrodynamic simulations in a compressible plasma to investigate magnetic energy release during the process of forced magnetic reconnection are carried out. This is in order to study the heating of the Sun's corona where it is believed that reconnection is induced by the photospheric motions. A sheared force-free field is perturbed by a transitory slow disturbance (pulse) at the boundary. This disturbance triggers the formation of a current sheet that subsequently releases stored magnetic energy through magnetic reconnection. Previously, it has been shown that for small boundary perturbations, the simulation results are consistent with the previous analytic theory based on a linear approach. For larger amplitude perturbations, or close to the threshold for tearing instability, the evolution shows nonlinear behavior. Solar coronal heating may arise due to a series of reconnection events, and a primary aim of this work is to study the interaction of such heating events. Thus, the perturbations are applied at the boundary by successive pulses. It is found that following the second driving pulse, the current sheet expands along the separatrix before relaxing to a reconnective equilibrium with magnetic islands and releasing even more magnetic energy for the same amplitude perturbation. Here, the previous work is extended to study long wavelength perturbations for which the system exhibits even stronger nonlinear aspects.
Levitation apparatus for neutron diffraction investigations on high temperature liquids
Authors: Hennet Louis , Pozdnyakova Irina , Bytchkov Aleksei , Cristiglio Viviana , Palleau Pierre , Fischer Henry E. , Cuello Gabriel J. , Johnson Mark , Melin Philippe , Zanghi Didier , Brassamin Séverine , Brun Jean-François , Price David L. , Saboungi Marie-Louise
Published: May 2006

We describe a new high temperature environment based on aerodynamic levitation and laser heating designed for neutron scattering experiments up to 3000°C. The sample is heated to the desired temperature with three CO2 lasers from different directions in order to obtain a homogeneous temperature distribution. The apparent temperature of the sample is measured with an optical pyrometer, and two video cameras are employed to monitor the sample behavior during heating. The levitation setup is enclosed in a vacuum-tight chamber, enabling a high degree of gas purity and a reproducible sample environment for structural investigations on both oxide and metallic melts. High-quality neutron diffraction data have been obtained on liquid Y3Al5O12 and ZrNi alloy for relatively short counting times (1.5h).
Direct tip-position control using magnetic actuation for achieving fast scanning in tapping mode atomic force microscopy
Authors: Jayanth G. R. , Jeong Younkoo , Menq Chia-Hsiang
Published: May 2006

This article presents the development of a faster control loop for oscillation amplitude regulation in tapping mode operation of atomic force microscopy. Two techniques in relation to actuation and measurement are developed, that together significantly increase the bandwidth of the control loop. Firstly, magnetic actuation is employed to directly control the tip position of the cantilever to improve both the speed and the dynamics of the positioning system. Secondly, the signal path for oscillation amplitude regulation is separated from that for topography estimation in order to eliminate measurement delay that degrades the performance of the feedback loop. As a result, the phase-crossover frequency and gain margin of the control system are both increased, leading to a faster and more stable system. Two experiments are performed, one in air and the other in aqueous solution, to compare the developed control system with a commercial one and demonstrate the improvement. The results verify that the combination of the two techniques along with other existing methods eliminates all limitations associated with the instrument for the purpose of oscillation amplitude regulation, which is therewith dictated by the bandwidth of the cantilever.
Dispersion properties of compressional electromagnetic waves in quantum dusty magnetoplasmas
Authors: Ali S. , Shukla P. K.
Published: May 2006

A new dispersion relation for low-frequency compressional electromagnetic waves is derived by employing quantum magnetohydrodynamic model and Maxwell equations in cold quantum dusty magnetoplasmas. The latter is composed of inertialess electrons, mobile ions, and immobile charged dust particulates. The dispersion relation for the low-frequency compressional electromagnetic modes is further analyzed for the waves propagating parallel, perpendicular, and oblique to the external magnetic field direction. It is found theoretically and numerically that the quantum parameter αq=(ni0∕ne0)ℏ2∕(4memi) affects the real angular frequencies and the phase speeds of the compressional electromagnetic modes. Here, ni0 (ne0) is the equilibrium number density of the ions (electrons), me (mi) is the electron (ion) mass, and ℏ is the Plank constant divided by 2π.
Adiabatic bistable evolution of dynamical systems governed by a Hamiltonian with separatrix crossing
Authors: Polomarov Oleg , Shvets Gennady
Published: May 2006

Adiabatic evolution of a nonlinear resonantly driven dynamical system generic to a variety of plasma physics problems is studied. The corresponding Hamiltonian, depending on the strength and frequency of the slowly varying driver, has a variable number of fixed points and the dynamical system can be bistable due to repeated separatrix crossing in the phase space. It is analytically shown that the oscillation periods along the “sister” trajectories corresponding to the same value of the Hamiltonian are equal and the sum of the corresponding areas under them does not depend on the driver amplitude. As a consequence of that, the Hamiltonian of a bistable system always follows the same trajectory for an adiabatically varying driver, regardless of whether the system is excited or left quiescent.
The evolution of the transverse centroid of asymmetric laser field in plasmas with various density distributions
Authors: Wang Wei-min , Zheng Chun-yang
Published: May 2006

The propagation of asymmetric relativistic intense laser beams in nonuniform and uniform underdense cold plasmas is studied. After simplifying the wave equation, we obtain the evolution equation of the transverse centroid of laser beams in terms of variational approaches. Theoretical analysis shows that in uniform plasmas a laser beam with an asymmetric initial phase has a constant centroid drift velocity, at which the centroid of the laser beam drifts away from the light axis in a fixed direction; the centroid drift velocity of a laser beam with symmetric initial phase, but either symmetric or asymmetric amplitude, is always zero, i.e., the symmetric features of the laser field is retained. Furthermore, the channel-like symmetric plasma plays a role like a restoring force to confine the laser centroid around the density channel axis so the centroid of the laser beam with asymmetric amplitude or phase is going to oscillate with damp around the channel axis. The nonlinear effect can symmetrize initially asymmetric laser beams and the steeper effective density gradient is more beneficial to the symmetrizing process. Finally, the analytic results are checked and confirmed by numerical simulations with finite difference to the wave equation and two-dimensional particle-in-cell code.
Bias induced strain in AlGaN∕GaN heterojunction field effect transistors and its implications
Authors: Anwar A. F. M. , Webster Richard T. , Smith Kurt V.
Published: May 2006

We report gate bias dependence of the charge due to piezoelectric polarization obtained by using a fully coupled formulation based upon the piezoelectric constitutive equations for stress and electric displacement. This formulation is significant because it fully accounts for electromechanical coupling under the constraint of global charge control. The coupled formulation results in lower charge due to piezoelectric polarization as compared to the uncoupled formulation for a given Al mole fraction. With increasing two dimensional electron gas concentration, that is, for gate biases greater than threshold, the compressive strain along the c axis in the barrier AlGaN layer increases with a concomitant increase of in-plane stress. Current collapse is correlated to the increase in source and drain resistances through their dependence upon surface charge. An alternate explanation of current collapse using local charge neutrality is also presented.
Model to explain the anisotropic phenomenon of effective mobility of organic field-effect transistors
Authors: Shang Liwei , Wang Congshun , Liu Ming
Published: May 2006

Recent research has revealed that the overall effective mobility of organic field-effect transistors depends on the anisotropy film. To account for this behavior, a modified model is proposed based on the previous grain boundary trap model. In this model, the degeneration factor, which is related to the maximal misorientation angle of grains, is introduced to describe the difference between aligned and nonaligned organic films. More explicit definitions of effective grain length and grain boundary are given concerning this anisotropic phenomenon. The simulation results are consistent with experimental data for aligned pentacene and copper phthalocyanine (CuPc).
Heating in single-electron pumps driven by surface acoustic waves
Authors: Utko Pawel , Lindelof Poul Erik , Gloos Kurt
Published: May 2006

We use a practical thermometer based on the resistance of the two-dimensional electron gas to characterize single-electron devices driven by surface acoustic waves. At the typical microwave powers (∼10dBm) required to observe the quantization of the acoustoelectric current in such structures, the electron-gas temperature increases from our base 1.8Kto5–6K. The power deposited by the surface acoustic wave itself can be clearly resolved. However, it is several times smaller than the overall rf heating, which occurs over a frequency range of few gigahertz.
Preparation of a superhydrophobic surface by mixed inorganic-organic coating
Authors: Ferrari Michele , Ravera Francesca , Liggieri Libero
Published: May 2006

In recent years, superhydrophobic surfaces, with a water-contact angle greater than 150°, have attracted great interest for both fundamental research and practical applications. Due to the small area these surfaces show when in contact with water, interactions with aqueous environment are usually strongly reduced. An original methodology based on a mixed inorganic-organic coating in a multistep procedure is described here allowing a superhydrophobic surface to be prepared starting with a mechanical treatment of a glass surface.
Analysis of boron strain compensation in silicon-germanium alloys by Raman spectroscopy
Authors: Chopra Saurabh , Ozturk Mehmet C. , Misra Veena , McGuire Kris , McNeil Laurie E.
Published: May 2006

The impact of heavy boron doping on the biaxial compressive strain in Si1−xGex layers grown on Si has been investigated using Raman spectroscopy and theoretical calculations. It is shown that one boron atom is sufficient to compensate the strain due to approximately 6.9 Ge atoms. This effect is appreciably large for boron concentrations as low as 1%, typical for applications, which employ heavily boron doped layers. Using strain compensation, the Ge content can be substantially increased without increasing the stored strain energy. This phenomenon can be useful in applications, which require low-resistivity p-type strained Si1−xGex layers with high Ge content.
Critical bifurcation of shallow microtidal landforms in tidal flats and salt marshes
Authors: Fagherazzi Sergio , Carniello Luca , D'Alpaos Luigi , Defina Andrea
Published: May 2006

Shallow tidal basins are characterized by extensive tidal flats and salt marshes that lie within specific ranges of elevation, whereas intermediate elevations are less frequent in intertidal landscapes. Here we show that this bimodal distribution of elevations stems from the characteristics of wave-induced sediment resuspension and, in particular, from the reduction of maximum wave height caused by dissipative processes in shallow waters. The conceptual model presented herein is applied to the Venice Lagoon, Italy, and demonstrates that areas at intermediate elevations are inherently unstable and tend to become either tidal flats or salt marshes.
Circadian rhythms in gene transcription imparted by chromosome compaction in the cyanobacterium
Synechococcus elongatus
Authors: Smith Rachelle M. , Williams Stanly B.
Published: May 2006

In the cyanobacterium
Synechococcus elongatus
(PCC 7942) the
kai
genes A, B, and C and the
sasA
gene encode the functional protein core of the timing mechanism essential for circadian clock regulation of global gene expression. The Kai proteins comprise the central timing mechanism, and the sensor kinase SasA is a primary transducer of temporal information. We demonstrate that the circadian clock also regulates a chromosome compaction rhythm. This chromosome compaction rhythm is both circadian clock-controlled and
kai
-dependent. Although
sasA
is required for global gene expression rhythmicity, it is not required for these chromosome compaction rhythms. We also demonstrate direct control by the Kai proteins on the rate at which the SasA protein autophosphorylates. Thus, to generate and maintain circadian rhythms in gene expression, the Kai proteins keep relative time, communicate temporal information to SasA, and may control access to promoter elements by imparting rhythmic chromosome compaction.
Regulation of insect steroid hormone biosynthesis by innervating peptidergic neurons
Authors: Yamanaka Naoki , Žitňan Dušan , Kim Young-Joon , Adams Michael E. , Hua Yue-Jin , Suzuki Yusuke , Suzuki Minoru , Suzuki Akemi , Satake Honoo , Mizoguchi Akira , Asaoka Kiyoshi , Tanaka Yoshiaki , Kataoka Hiroshi
Published: May 2006

In insects, steroid hormones named ecdysteroids elicit molting and metamorphosis. The prothoracic gland (PG) is a predominant source of ecdysteroids, where their biosynthesis (ecdysteroidogenesis) is regulated by several neuropeptides. Here, we report that FMRFamide-related peptides (FaRPs) regulate ecdysteroidogenesis through direct innervation of the PG in the silkworm
Bombyx mori
. We purified a previously uncharacterized
Bombyx
FaRP, DPSFIRFamide, and identified the corresponding
Bombyx
FMRFamide gene (
Bommo-FMRFamide
,
BRFa
), which encodes three additional FaRPs. All BRFa peptides suppressed ecdysteroidogenesis in the PG by reducing cAMP production by means of the receptor for Bommo-myosuppressin, another FaRP we have previously shown to act as a prothoracicostatic factor.
BRFa
is predominantly expressed in neurosecretory cells of thoracic ganglia, and the neurons in the prothoracic ganglion innervate the PG to supply all four peptides to the gland surface. Electrophysiological recordings during development confirmed the increased firing activity of BRFa neurons in stages with low PG activity and decreased ecdysteroid levels in the hemolymph. To our knowledge, this study provides the first report of peptides controlling ecdysteroidogenesis by direct innervation.
The delivery of copper for thylakoid import observed by NMR
Authors: Banci Lucia , Bertini Ivano , Ciofi-Baffoni Simone , Kandias Nikolaos G. , Robinson Nigel J. , Spyroulias Georgios A. , Su Xun-Cheng , Tottey Stephen , Vanarotti Murugendra
Published: May 2006

The thylakoid compartments of plant chloroplasts are a vital destination for copper. Copper is needed to form holo-plastocyanin, which must shuttle electrons between photosystems to convert light into biologically useful chemical energy. Copper can bind tightly to proteins, so it has been hypothesized that copper partitions onto ligand-exchange pathways to reach intracellular locations without inflicting damage en route. The copper metallochaperone Atx1 of chloroplast-related cyanobacteria (ScAtx1) engages in bacterial two-hybrid interactions with N-terminal domains of copper-transporting ATPases CtaA (cell import) and PacS (thylakoid import). Here we visualize copper delivery. The N-terminal domain PacS
N
has a ferredoxin-like fold that forms copper-dependent heterodimers with ScAtx1. Removal of copper, by the addition of the cuprous-ion chelator bathocuproine disulfonate, disrupts this heterodimer, as shown from a reduction of the overall tumbling rate of the protein mixture. The NMR spectral changes of the heterodimer versus the separate proteins reveal that loops 1, 3, and 5 (the carboxyl tail) of the ScAtx1 Cu(I) site switch to an apo-like configuration in the heterodimer. NMR data (
2
J
NH
couplings in the imidazole ring of
15
N ScAtx1 His-61) also show that His-61, bound to copper(I) in [Cu(I)ScAtx1]
2
, is not coordinated to copper in the heterodimer. A model for the PacS
N
/Cu(I)/ScAtx1 complex is presented. Contact with PacS
N
induces change to the ScAtx1 copper-coordination sphere that drives copper release for thylakoid import. These data also elaborate on the mechanism to keep copper(I) out of the ZiaA
N
ATPase zinc sites.
Flows driven by flagella of multicellular organisms enhance long-range molecular transport
Authors: Short Martin B. , Solari Cristian A. , Ganguly Sujoy , Powers Thomas R. , Kessler John O. , Goldstein Raymond E.
Published: May 2006

Evolution from unicellular organisms to larger multicellular ones requires matching their needs to the rate of exchange of molecular nutrients with the environment. This logistic problem poses a severe constraint on development. For organisms whose body plan is a spherical shell, such as the volvocine green algae, the current (molecules per second) of needed nutrients grows quadratically with radius, whereas the rate at which diffusion alone exchanges molecules grows linearly, leading to a bottleneck radius beyond which the diffusive current cannot meet metabolic demands. By usingVolvox carteri, we examine the role that advection of fluid by the coordinated beating of surface-mounted flagella plays in enhancing nutrient uptake and show that it generates a boundary layer of concentration of the diffusing solute. That concentration gradient produces an exchange rate that is quadratic in the radius, as required, thus circumventing the bottleneck and facilitating evolutionary transitions to multicellularity and germ–soma differentiation in the volvocalean green algae.
Evolution of hepatitis C viral quasispecies and hepatic injury in perinatally infected children followed prospectively
Authors: Farci Patrizia , Quinti Isabella , Farci Stefania , Alter Harvey J. , Strazzera Rita , Palomba Elvia , Coiana Alessandra , Cao Daniele , Casadei Anna Maria , Ledda Ritarella , Iorio Raffaele , Vegnente Angela , Diaz Giacomo , Tovo Pier-Angelo
Published: May 2006

Perinatal infection with hepatitis C virus (HCV) is characterized by a wide range of alanine aminotransferase (ALT) levels. The mechanisms responsible for this variability are unknown. We examined whether the evolution of the HCV quasispecies was associated with different ALT profiles in perinatally infected children. Sequences within HCV envelope 1 and 2 genes, inclusive of the hypervariable region 1, the viral load, and the nascent humoral immunity were analyzed in serial serum samples from 12 perinatally infected children prospectively followed for a median of 53 months. These patients were selected to represent two different ALT patterns during the first year of life: 6 had high levels (maximum values ranging from 4.2 to 30 times the normal upper limit), and 6 had normal or slightly elevated levels (<2 times the normal upper limit). Two patterns of viral evolution were identified according to the ALT profiles. Biochemical evidence of hepatic injury was invariably associated with a mono- or oligoclonal viral population, whereas mild or no liver damage correlated with the early emergence of a heterogeneous viral quasispecies. Consistent with selective immune pressure, amino acid changes occurred almost exclusively within the hypervariable region 1 and were temporally associated with antibody seroconversion; at this time, the difference in genetic diversity between the two groups was highly significant (P= 0.002). The two patterns of viral evolution persisted over time and did not correlate with viral load or genotype. Our study demonstrates that, in perinatally infected children, the evolution of HCV quasispecies correlates with hepatic injury.
Locating active-site hydrogen atoms in
d
-xylose isomerase: Time-of-flight neutron diffraction
Authors: Katz Amy K. , Li Xinmin , Carrell H. L. , Hanson B. Leif , Langan Paul , Coates Leighton , Schoenborn Benno P. , Glusker Jenny P. , Bunick Gerard J.
Published: May 2006

Time-of-flight neutron diffraction has been used to locate hydrogen atoms that define the ionization states of amino acids in crystals of
d
-xylose isomerase. This enzyme, from
Streptomyces rubiginosus
, is one of the largest enzymes studied to date at high resolution (1.8 Å) by this method. We have determined the position and orientation of a metal ion-bound water molecule that is located in the active site of the enzyme; this water has been thought to be involved in the isomerization step in which
d
-xylose is converted to
d
-xylulose or
d
-glucose to
d
-fructose. It is shown to be water (rather than a hydroxyl group) under the conditions of measurement (pH 8.0). Our analyses also reveal that one lysine probably has an −NH
2
-terminal group (rather than NH
3
+
). The ionization state of each histidine residue also was determined. High-resolution x-ray studies (at 0.94 Å) indicate disorder in some side chains when a truncated substrate is bound and suggest how some side chains might move during catalysis. This combination of time-of-flight neutron diffraction and x-ray diffraction can contribute greatly to the elucidation of enzyme mechanisms.
Oxysterols stimulate Sonic hedgehog signal transduction and proliferation of medulloblastoma cells
Authors: Corcoran Ryan B. , Scott Matthew P.
Published: May 2006

Sterol synthesis is required for Sonic hedgehog (Shh) signal transduction. Errors in Shh signal transduction play important roles in the formation of human tumors, including medulloblastoma (MB). It is not clear which products of sterol synthesis are necessary for Shh signal transduction or how they act. Here we show that cholesterol or specific oxysterols are the critical products of sterol synthesis required for Shh pathway signal transduction in MB cells. In MB cells, sterol synthesis inhibitors reduce Shh target gene transcription and block Shh pathway-dependent proliferation. These effects of sterol synthesis inhibitors can be reversed by exogenous cholesterol or specific oxysterols. We also show that certain oxysterols can maximally activate Shh target gene transcription through the Smoothened (Smo) protein as effectively as the known Smo full agonist, SAG. Thus, sterols are required and sufficient for Shh pathway activation. These results suggest that oxysterols may be critical regulators of Smo, and thereby Shh signal transduction. Inhibition of Shh signaling by sterol synthesis inhibitors may offer a novel approach to the treatment of MB and other Shh pathway-dependent human tumors.
New Labour and Community Protests: the Case of the Govanhill Swimming Pool Campaign, Glasgow
Authors: Mooney Gerry , Fyfe Nick
Published: May 2006

Taking the case study of a community based protest against the closure of a swimming pool in Glasgow, this paper seeks to raise important critical questions about some of the key ideas informing New Labour's urban policy agenda: social capital and active community. It argues that normative notions of active citizenship seriously conflict with bottom-up community protests, highlighting in the process issues of power and inequality. Against claims that New Labour is promoting government through community, here we claim that in the context of this community protest, there was government against community.
The Impact of a Business School on Regional Economic Development: a Case Study
Authors: Cox Sue , Taylor Jim
Published: May 2006

This paper investigates the impact of a major extension to Lancaster University's Management School on the North West regional economy. It differs from earlier university impact studies since the estimated impact is not confined to backward linkage effects but focuses specifically on the forward linkage effects that will occur as a result of greater engagement with firms in the region's SME sector. The paper demonstrates that the expansion of the university sector can have far greater beneficial effects on their regional economies than is indicated by conventional impact studies. Specifically, the provision of business advice to SMEs can be a significant factor in increasing their sales volume.
Local Rural Labour Markets: Enterprising or Constraining?
Authors: Jarvis David , Dunham Philip , Ilbery Brian
Published: May 2006

This paper examines SMEs' experiences of labour markets and their adoption of technology, including ICTs, in two rural areas: South Warwickshire and North Devon. Findings are assessed within the context of existing theories of rural industrial growth, which have tended to stereotype firms on the basis of location, and have underplayed the role of ‘non-local’ factors such as supply chains in influencing both the behaviour and ‘success’ of individual SMEs. In contrast, this paper contends that understanding the true complexity of the SME sector is essential if efforts to foster and support enterprise in rural areas are to be successful.
Dilemmas in Regional University—Industry Research Collaboration
Authors: Gunasekara Chrys
Published: May 2006

Although it is now well recognised that universities perform an important role in knowledge creation and diffusion in regions, the extent of regional research collaboration is limited. This article analyses the local collaborative research performance of three Australian regional universities and raises several dilemmas: the indeterminacy of regional engagement policies; weak demand drivers; the scale of the region; the challenge of balancing regional research work, national/international work, competition and collaboration; and the appropriate role of government. The experience of academics and managers in these universities may resonate with others, particularly in European countries, who face similar challenges.
Promoting ‘Strategic’ Working within Area-based and Thematic Social Inclusion Partnerships in Scotland
Authors: Macpherson Suzi
Published: May 2006

Fundamental to the historical development of partnership working as an approach to managing neighbourhood regeneration has been a concern to promote ‘strategic’ working practices. However, there has been a distinct lack of conceptual clarity within both policy and practice over the meaning of ‘strategic’ working within local partnerships. This paper outlines three broad conceptual approaches to understanding ‘strategic’ working as: a plan of action, as changing organisational practices, and as multi-level organisational collaboration. Drawing on data from Social Inclusion Partnerships in Scotland the paper explores the relevance of these three approaches to strategic working to the practices of these Partnerships. The paper highlights that, contrary to a policy rhetoric promoting organisational change and collaboration, a relatively limited outputs focus has dominated regeneration practice. With pressure on SIPs to spend time-limited budgets and fill gaps in services, a tension emerges between the goals of delivering services and co-ordinating the activities of partner agencies. It is argued here that it is challenging for these localised Partnerships to try to take on both of these goals simultaneously. It is recommended that a more realistic approach is taken with regard to the potential role played by local regeneration partnerships in being ‘strategic’.