bluuebunny/crossref_metadata_2025 huggingface dataset:
Marginally turbulent flow in a square duct
Authors: UHLMANN MARKUS , PINELLI ALFREDO , KAWAHARA GENTA , SEKIMOTO ATSUSHI
Published: March 2008

A direct numerical simulation of turbulent flow in a straight square duct was performed in order to determine the minimal requirements for self-sustaining turbulence. It was found that turbulence can be maintained for values of the bulk Reynolds number above approximately 1100, corresponding to a friction-velocity-based Reynolds number of 80. The minimum value for the streamwise period of the computational domain is around 190 wall units, roughly independently of the Reynolds number. We present a characterization of the flow state at marginal Reynolds numbers which substantially differs from the fully turbulent one: the marginal state exhibits a four-vortex secondary flow structure alternating in time whereas the fully turbulent one presents the usual eight-vortex pattern. It is shown that in the regime of marginal Reynolds numbers buffer-layer coherent structures play a crucial role in the appearance of secondary flow of Prandtl's second kind.
The trailing-edge problem for mixed-convection flow past a horizontal plate
Authors: SAVIĆ LJUBOMIR , STEINRÜCK HERBERT
Published: March 2008

The flow near the trailing edge of a horizontal plate in a uniform parallel stream under a small angle of attack in the limit of large Reynolds number and large Grashof number is considered. Applying the concept of interacting boundary layers, a triple-deck problem taking the hydrostatic pressure perturbation into account can be formulated. However, it turns out that the interaction pressure is discontinuous at the trailing edge and thus new sublayers to resolve the discontinuity are introduced.
The efficiency of a turbine in a tidal channel
Authors: GARRETT CHRIS , CUMMINS PATRICK
Published: March 2008

There is an upper bound to the amount of power that can be generated by turbines in tidal channels as too many turbines merely block the flow. One condition for achievement of the upper bound is that the turbines are deployed uniformly across the channel, with all the flow through them, but this may interfere with other uses of the channel. An isolated turbine is more effective in a channel than in an unbounded flow, but the current downstream is non-uniform between the wake of the turbines and the free stream. Hence some energy is lost when these streams merge, as may occur in a long channel. We show here, for ideal turbine models, that the fractional power loss increases from 1/3 to 2/3 as the fraction of the channel cross-section spanned by the turbines increases from 0 to close to 1. In another scenario, possibly appropriate for a short channel, the speed of the free stream outside the turbine wake is controlled by separation at the channel exit. In this case, the maximum power obtainable is slightly less than proportional to the fraction of the channel cross-section occupied by turbines.
Violent conflicts and governance challenges in West Africa: the case of the Mano River basin area
Authors: Sawyer Amos
Published: March 2008

The Mano River basin area has become a conflict zone, in which state failure and violence in Liberia has spread to Sierra Leone and the forest region of Guinea. This article traces the origins of the conflicts to governance failures in all three states, and analyses their incorporation into a single conflict system, orchestrated especially through the entrepreneurial abilities and ambitions of Charles Taylor. Peace settlements negotiated to end the violence in Liberia and Sierra Leone failed, both because of the misconceived power-sharing formula that they embodied, and because they failed to take account of the complex linkages between conflicts across the basin area. The way forward lies in a multilevel basin-wide approach, which seeks to move beyond the failed formula of attempting to reconstitute state power, in favour of constructing institutions of accountable democratic governance at multiple levels from the local level to the regional level and beyond.
Phonological memory and lexical, narrative, and grammatical skills in second language oral production by adult learners
Authors: O'BRIEN IRENA , SEGALOWITZ NORMAN , COLLENTINE JOE , FREED BARBARA
Published: March 2008

This study investigated the role of phonological memory (PM) in second language (L2) speech production by English-speaking adults who were learning Spanish. PM, operationalized as serial nonword recognition, and L2 lexical, narrative, and grammatical abilities from speech samples were assessed 13 weeks apart. After controlling for the amount of speech output, PM contributed significantly to the development of L2 narrative skills for less proficient participants (17.5% of variance explained) and to gains in correct use of function words for more proficient participants (15.7% of variance explained). These findings suggest that PM plays an important role in narrative development at earlier stages of L2 learning and in the acquisition of grammatical competence at later stages.
Atoms in Electromagnetic Fields
Authors: HORA HEINRICH
Published: March 2008

Atoms in Electromagnetic Fields, Second Edition, by C.
Cohen-Tannoudji, World Scientific Publishing Company, Singapore, 752
pages, US $128.00, ISBN: 9812389423

The publisher has the merit to convince the author first against his
reluctance to prepare this compendium of reprints but it is a rare case
where this was so successful that a second extended edition was necessary.
It contains the most outstanding work which led to the Nobel Price for the
author who started from the work of one of the pioneers on spectroscopy
for the laser, Nobel Lauerate Alfred Kastler.
Fast ignition integrated interconnecting code project for
cone-guided targets
Authors: SAKAGAMI H. , JOHZAKI T. , NAGATOMO H. , MIMA K.
Published: March 2008

It was reported that the fuel core was heated up to ∼0.8 keV in
the fast ignition experiments with cone-guided targets, but they could not
theoretically explain heating mechanisms and achievement of such high
temperature. Thus simulations should play an important role in estimating
the scheme performance, and we must simulate each phenomenon with
individual codes and integrate them under the fast ignition integrated
interconnecting code project. In the previous integrated simulations, fast
electrons generated by the laser-plasma interaction were too hot to
efficiently heat the core and we got only 0.096 keV rise of temperature.
Including the density gap at the contact surface between the cone tip and
the imploded plasma, the period of core heating became longer and the core
was heated by 0.162 keV, ∼ 69% higher increment compared with ignoring
the density gap effect.
Nonlinear absorption of ultra short laser pulses by clusters
Authors: KANAPATHIPILLAI M.
Published: March 2008

Very good absorption of ultra short laser pulses by clusters is a well established fact. Efficient collisional absorption occurs only in the initial phase of the pulse. However, experiments and numerical simulations show that even after collisional absorption becomes inefficient subsequent to heating of the electrons, strong absorption continues. There have been a few attempts to model this phenomenon in terms of driven “linear” oscillator models with time dependent eigen-frequencies. Here we propose a nonlinear oscillator model and show that nonlinear resonance is the leading mechanism responsible for the collisionless absorption. Further it is demonstrated, on the basis of Lyapunov spectra, that laser-cluster interaction, under certain conditions, exhibits chaotic behavior.
Analytical description of rippling effect and ion acceleration in
plasma produced by a short laser pulse
Authors: GLOWACZ S. , HORA H. , BADZIAK J. , JABLONSKI S. , CANG YU , OSMAN F.
Published: March 2008

In this paper we present the analytical description of two processes
dealing with the skin-layer ponderomotive acceleration method of fast ion
generation by a short laser pulse: ion density rippling in the underdense
plasma region and generation of ion beams by trapped electromagnetic field
in plasma. Some numerical examples of hydrodynamic simulation illustrating
these processes are shown. The effect of using the laser pulse consisting
of different frequency components on the ion density rippling and on
phenomena connected with trapped electromagnetic field is analyzed.
Between two stream and filamentation instabilities: Temperature and
collisions effects
Authors: BRET ANTOINE , FIRPO MARIE-CHRISTINE , DEUTSCH CLAUDE
Published: March 2008

We will consider relativistic electron beam interacting with plasma
and study the electromagnetic instabilities obtained for arbitrarily
oriented wave vectors ranging from two-stream to filamentation
instabilities. For these unstable modes, we will study every temperature
effects, namely beam and plasma normal, and parallel temperatures.
Temperatures are supposed to be non-relativistic and modeled through water
bag distributions. It is found that only normal beam temperature and
parallel plasma temperature have a significative influence over the growth
rates for wave vector making an angle with the beam larger than a critical
angle θc which is determined exactly. The largest
growth rate being reached for a wave vector making an angle with the beam
smaller than θc, it is not damped by any kind of
temperatures. We finally explore collisions effects and show they can
reduce the largest growth rate.
Observation of strongly collimated proton beam from Tantalum targets
irradiated with circular polarized laser pulses
Authors: KADO MASATAKA , DAIDO HIROYUKI , FUKUMI ATSUSHI , LI ZHONG , ORIMO SATOSHI , HAYASHI YUKIO , NISHIUCHI MAMIKO , SAGISAKA AKITO , OGURA KOICHI , MORI MICHIAKI , NAKAMURA SHU , NODA AKIRA , IWASHITA YOSHIHISA , SHIRAI TOSHIYUKI , TONGU HIROMU , TAKEUCHI TAKESHI , YAMAZAKI ATSUSHI , ITOH HIROYUKI , SOUDA HIKARU , NEMOTO KOSHICHI , OISHI YUJI , NAYUKI TAKUYA , KIRIYAMA HIROMITSU , KANAZAWA SHUHEI , AOYAMA MAKOTO , AKAHANE YUTAKA , INOUE NORIHIRO , TSUJI KOICHI , NAKAI YOSHIKI , YAMAMOTO YOICHI , KOTAKI HIDEYUKI , KONDO SHUJI , BULANOV SERGEI , ESIRKEPOV TIMUR , UTSUMI TAKAYUKI , NAGASHIMA AKIRA , KIMURA TOYOAKI , YAMAKAWA KOICHI
Published: March 2008

High-energy protons are generated by focusing an ultrashort pulsed
high intensity laser at the Advanced Photon Research Center, JAERI-Kansai
onto thin (thickness <10 μm) Tantalum targets. The laser
intensities are about 4 × 1018 W/cm2. The
prepulse level of the laser pulse is measured with combination of a PIN
photo diode and a cross correlator and is less than 10−6.
A quarter-wave plate is installed into the laser beam line to create
circularly polarized pulses. Collimated high energy protons are observed
with CH coated Tantalum targets irradiated with the circularly polarized
laser pulses. The beam divergence of the generated proton beam is measured
with a CR-39 track detector and is about 6 mrad.
On generation of collimated high-power gamma beams
Authors: CHYLA W.T.
Published: March 2008

We consider spontaneous thermalization of free photon field (in a vacuum) due to self-interaction, mediated by the virtual e−e+field at ultra-high concentrations of the electromagnetic energy. That nonlinear, attractive, short-range interaction between photons triggers spontaneous evolution of the initial, low-frequency spectrum toward the maximum-entropy spectral distribution peaking in the gamma range of frequencies. Collimation and the total power of the photon beam (pulse) are hardly affected by the process of spontaneous thermalization. We estimate the threshold intensity that triggers spectral evolution of the photon field, the necessary power of the laser beam, the minimum size of the interaction region, parameters of the fully thermalized photon field, and discuss the near-threshold behavior of the electromagnetic field. Possible applications of thermalized photon beams are suggested, for example, they can serve as the pump field to attain gamma-lasing or facilitate ignition in the fusion pellet.
Enhancement of laser induced shock pressure in multilayer solid
targets
Authors: PANT H.C. , SHUKLA M. , PANDEY H.D. , KASHYAP YOGESH , SARKAR P.S. , SINHA A. , SENECHAM V.K. , GODWAL B.K.
Published: March 2008

The impedance mismatch technique was used for shock pressure
amplification in two layered planar foil targets. Numerical simulation
results using one-dimensional (1D) radiation hydrocode MULTI in two layer
target consisting of polyethylene (CH2)n-aluminium
(Al) and polyethylene (CH2)n-gold (Au), show a
pressure enhancement of 12 and 18 Mbar, respectively (or a pressure jump
of 1.64 and 2.54, respectively), from initial pressure of 7 Mbar in the
reference material (polyethylene) using laser intensity of 5 ×
1013 Watts/cm2 at 1.064 μm. The simulation
data was also corroborated by experiments in our laboratory. Results of
laser driven shock wave experiments for pressure enhancement studies in
CH2-Al and CH2-Au targets are also presented. A
Nd:YAG laser chain (2 J, 1.064 μm wavelength, 200 ps pulse duration
FWHM) is used for generating shocks in the planar CH2 foils of
thickness varying from 4 to10 μm, and in two layered CH2-Al
(or CH2-Au) targets with 8 μm CH2 and 1.5 μm
Al or Au .
A bilateral teleoperation controller considering the transition between the free space motion and the constrained motion
Authors: Wang Heng , Low K. H. , Wang Michael Yu
Published: March 2008

A two-channel bilateral controller is proposed for teleoperation systems. The controller takes into account both the free space motion and the constrained motion. Specifically, the force-position (F-P) architecture is applied during the constrained motion, while the position-position (P-P) architecture is applied during the free space motion. Theoretically, perfect transparency can be achieved. In addition, it does not need to switch the control modes of the master and the slave controllers during the transition between the free space motion and the constrained motion. Experiments are conducted to validate the analysis, and to demonstrate the effectiveness of the proposed bilateral controller. The limitations of the proposed controller are also discussed.
Dynamic context management for pervasive applications
Authors: EUZENAT JÉRÔME , PIERSON JÉRÔME , RAMPARANY FANO
Published: March 2008

Pervasive computing aims at providing services for human beings that interact with their environment (encompassing objects and people who reside in it). Pervasive computing applications must be able to take into account the context in which users evolve, for example, physical location, social or hierarchical position, current tasks as well as related information. These applications have to deal with the dynamic integration in the environment of new, and sometimes unexpected, elements (users or devices). In turn, the environment has to provide context information to newly designed applications. This requires a framework which is open, dynamic and minimal. We describe an architecture in which context information is distributed in the environment and context managers use semantic Web technologies in order to identify and characterize available resources. The components in the environment maintain their own context expressed in RDF (Resource Description Framework) and described through OWL ontologies. They may communicate this information to other components, obeying a simple protocol for identifying them and determining the information they can provide. We show how this architecture allows introducing new devices and new applications without interrupting what is working. In particular, the openness of ontology description languages makes possible the extension of context descriptions and ontology matching helps dealing with independently developed ontologies.
Personalized information retrieval based on context and ontological knowledge
Authors: MYLONAS PH. , VALLET D. , CASTELLS P. , FERNÁNDEZ M. , AVRITHIS Y.
Published: March 2008

Context modeling has long been acknowledged as a key aspect in a wide variety of problem domains. In this paper we focus on the combination of contextualization and personalization methods to improve the performance of personalized information retrieval. The key aspects in our proposed approach are (1) the explicit distinction between historic user context and live user context, (2) the use of ontology-driven representations of the domain of discourse, as a common, enriched representational ground for content meaning, user interests, and contextual conditions, enabling the definition of effective means to relate the three of them, and (3) the introduction of fuzzy representations as an instrument to properly handle the uncertainty and imprecision involved in the automatic interpretation of meanings, user attention, and user wishes. Based on a formal grounding at the representational level, we propose methods for the automatic extraction of persistent semantic user preferences, and live, ad-hoc user interests, which are combined in order to improve the accuracy and reliability of personalization for retrieval.
Situational reasoning for task-oriented mobile service recommendation
Authors: LUTHER MARKO , FUKAZAWA YUSUKE , WAGNER MATTHIAS , KURAKAKE SHOJI
Published: March 2008

We study the case of integrating situational reasoning into a mobile service recommendation system. Since mobile Internet services are rapidly proliferating, finding and using appropriate services require profound service descriptions. As a consequence, for average mobile users it is nowadays virtually impossible to find the most appropriate service among the many offered. To overcome these difficulties, task navigation systems have been proposed to guide users towards best-fitting services. Our goal is to improve the user experience of such task navigation systems making them context-aware (i.e. to optimize service navigation by taking the user's situation into account). We propose the integration of a situational reasoning engine that applies classification-based inference to qualitative context elements, gathered from multiple sources and represented using ontologies. The extended task navigator enables the delivery of situation-aware recommendations in a proactive way. Initial experiments with the extended system indicate a considerable improvement of the navigator's usability.
The Norm of Tradition: Gender Subordination and Women's Exclusion in International Relations
Authors: Sjoberg Laura
Published: March 2008

The survey data in “Women in International Relations” explains that women are underrepresented in international relations as a whole, and that this underrepresentation only grows at the higher ranks of our profession. In observing the “gender gap” in IR, the essay offers an interesting and important overview of the possible reasons for women's underrepresentation and points out some meaningful differences between women and men in terms of perspective in the discipline, publication productivity, and teaching style, among other things. Near the beginning of the essay, the authors set up alternative explanations for women's marginal position in the discipline. They note that while feminist scholars relate women's marginalization to gender subordination, “other scholars suggest that the content of women's scholarship contributes to their marginalization” (see p. 122). I would argue that women's differences and gender subordination might not be competing explanations for women's marginalization. Instead, it might be that gender subordination can explain both women's differences and women's underrepresentation in the field.
Kinematics and flow patterns in deep mantle and upper mantle subduction models: Influence of the mantle depth and slab to mantle viscosity ratio
Authors: Schellart W. P.
Published: March 2008

Three‐dimensional fluid dynamic laboratory simulations are presented that investigate the subduction process in two mantle models, an upper mantle model and a deep mantle model, and for various subducting plate/mantle viscosity ratios (ηSP/ηM = 59–1375). The models investigate the mantle flow field, geometrical evolution of the slab, sinking kinematics, and relative contributions of subducting plate motion and trench migration to the total rate of subduction. All models show that the subducting plate is always moving trenchward resulting from slab pull. Furthermore, all deep mantle models show trench retreat, as do upper mantle models in the initial stage of subduction before slab tip‐transition zone interaction. Upper mantle models with a low ηSP/ηM (66, 217) continue to show trench retreat after interaction. Upper mantle models with a high ηSP/ηM (378, 709) show a period of trench advance after interaction followed by trench retreat. Upper mantle models with a very high ηSP/ηM (1375) show continued trench advance after interaction. The difference in trench migration behavior and associated slab geometries is attributed to both ηSP/ηM and the mantle depth to plate thickness ratio TM/TSP, which both affect the slab bending radius to mantle thickness ratio rB/TM. Four subduction regimes can be defined: Regime I with rB/TM ≤ ∼0.3, trench retreat, slab draping, and a concave trench; Regime II with ∼0.3 < rB/TM < ∼0.5, episodic trench migration, slab folding, and a concave trench; Regime III with rB/TM ≈ 0.5, trench advance, slab rollover geometries, and minor trench curvature; and Regime IV with rB/TM ≥ ∼0.8, trench retreat, slab draping, and a rectilinear trench. In all models, slab‐parallel downdip motion induces poloidal mantle flow structures. In addition, trench retreat and rollback motion of the slab induce quasi‐toroidal return flow around the lateral slab edges toward the mantle wedge. Rollback‐induced poloidal flow around the slab tip is not observed in any of the experiments. Finally, comparison between the slab geometries observed in the upper mantle models and slab geometries observed in nature imply that the effective viscosity ratio between slab and ambient upper mantle in nature is less than 103 and of the order 1–7 × 102, with a best estimate of 1–3 × 102.
Texture and composition of pumices and scoriae from the Campi Flegrei caldera (Italy): Implications on the dynamics of explosive eruptions
Authors: Piochi M. , Polacci M. , De Astis G. , Zanetti A. , Mangiacapra A. , Vannucci R. , Giordano D.
Published: March 2008

The Campi Flegrei (CF) caldera is one of the most dangerous quiescent volcanic systems in the world. Its activity mostly resulted in low‐magnitude explosive eruptions, such as that of the Monte Nuovo tuff cone that represents the last eruptive event within the caldera (A.D. 1538). However, there have been more energetic Plinian events, e.g., the Agnano Monte Spina eruption (4.1 ka), and very highly explosive, caldera‐forming eruptions, e.g., the Campanian Ignimbrite eruption (39 ka). Here, we integrate new and literature data on the groundmass texture and composition of pyroclastic products from the three above eruptions with the aim of unraveling how volatiles content, degassing mechanisms, and crystallization processes influence magma explosivity and eruption dynamics at CF. Previous studies indicate that the investigated rocks share similar major element bulk and phenocryst chemistry; also similar is the water content of their trapped melt inclusions. These observations suggest that the magmas feeding these eruptions had comparable physicochemical properties during storage in the shallow crust. However, our investigations indicate that the studied rocks differ in texture and composition of the groundmass and viscosity of the related magmas. We ascribe such differences to the variable style of volatile exsolution and outgassing from the melt, primarily in response to changes of the rate of magma ascent to the surface. We conclude that the magma ascent rate was the key parameter in driving explosive eruptions at CF, and we suggest that this parameter may be influenced by magma‐water interaction and/or magma chamber geometry and replenishment.
Strong sensitivity of late 21st century climate to projected changes in short‐lived air pollutants
Authors: Levy Hiram , Schwarzkopf M. Daniel , Horowitz Larry , Ramaswamy V. , Findell K. L.
Published: March 2008

This study examines the impact of projected changes (A1B “marker” scenario) in emissions of four short‐lived air pollutants (ozone, black carbon, organic carbon, and sulfate) on future climate. Through year 2030, simulated climate is only weakly dependent on the projected levels of short‐lived air pollutants, primarily the result of a near cancellation of their global net radiative forcing. However, by year 2100, the projected decrease in sulfate aerosol (driven by a 65% reduction in global sulfur dioxide emissions) and the projected increase in black carbon aerosol (driven by a 100% increase in its global emissions) contribute a significant portion of the simulated A1B surface air warming relative to the year 2000: 0.2°C (Southern Hemisphere), 0.4°C globally, 0.6°C (Northern Hemisphere), 1.5–3°C (wintertime Arctic), and 1.5–2°C (∼40% of the total) in the summertime United States. These projected changes are also responsible for a significant decrease in central United States late summer root zone soil water and precipitation. By year 2100, changes in short‐lived air pollutants produce a global average increase in radiative forcing of ∼1 W/m2; over east Asia it exceeds 5 W/m2. However, the resulting regional patterns of surface temperature warming do not follow the regional patterns of changes in short‐lived species emissions, tropospheric loadings, or radiative forcing (global pattern correlation coefficient of −0.172). Rather, the regional patterns of warming from short‐lived species are similar to the patterns for well‐mixed greenhouse gases (global pattern correlation coefficient of 0.8) with the strongest warming occurring over the summer continental United States, Mediterranean Sea, and southern Europe and over the winter Arctic.
Red Sea during the Last Glacial Maximum: Implications for sea level reconstruction
Authors: Biton E. , Gildor H. , Peltier W. R.
Published: March 2008

The Red Sea is connected to the Indian Ocean via a narrow and shallow strait and exhibits a high sensitivity to atmospheric changes and a reduced sea level. We used an ocean general circulation model to investigate the hydrography and circulation in the Red Sea in response to reduced sea level and modified atmospheric conditions occurring during the Last Glacial Maximum (LGM). The model salinity shows high sensitivity to sea level reduction together with a mild atmospheric impact. Sea level reduction affects the stratification and alters the circulation pattern at the Strait of Bab el Mandab, which experiences a transition from a submaximal flow to a maximal flow. The best correlation to reconstructed conditions during LGM exists when the water depth of the Hanish Sill (the shallowest part in the Strait of Bab el Mandab) is 33 ± 10.75 m, which would be affected by a sea level lowering of approximately 105 m. Our results support the reconstructed maximum salinity of around 57 practical salinity units because of a simple model (that takes into account mixing processes along the strait) and comparison of the surface salinity gradient to reconstructions based on isotopic records from sedimentary cores. The salinity and δ18O are sensitive to the mixing process at the strait, and the sensitivity increases as the sea level is further reduced. A local relative sea level reduction of approximately 105 m is also in close agreement with the inference of the LGM low stand of the sea at the location of the sill based on the ICE‐5G (VM2) model.
Experimental evidence for mantle drag in the Mediterranean
Authors: Barba Salvatore , Carafa Michele M. C. , Boschi Enzo
Published: March 2008

What forces control active deformation in the Central Mediterranean? Slab‐pull has long been debated, but no other hypothesis has been generally accepted. Here we analyze the role of shear basal tractions. By using a thin‐shell modeling technique, we generated a large number of models that span different sets of boundary conditions from the literature; we then explored acceptable ranges of model parameters. We computed residuals between model predictions and several datasets of stress directions, GPS measurements and tectonic stress regimes that have been produced in recent studies, and then compared the best models obtained in the presence of tractions with those obtained in the absence of tractions. For all tested boundary conditions and all considered datasets, our results show that the only successful models are those with significant basal shear traction exerted by eastward mantle flow.
Dendritic cells: driving the differentiation programme of T cells in viral infections
Authors: Masson Frederick , Mount Adele M , Wilson Nicholas S , Belz Gabrielle T
Published: March 2008

Protective immunity against viral pathogens depends on the generation and maintenance of a small population of memory CD8+ T cells. Successful memory cell generation begins with early interactions between naïve T cell and dendritic cells (DCs) within the inflammatory milieu of the secondary lymphoid tissues. Recent insights into the role of different populations of DCs, and kinetics of antigen presentation, during viral infections have helped to understand how DCs can shape the immune response. Here, we review the recent progress that has been made towards defining how specific DC subsets drive effector CD8+ T‐cell expansion and differentiation into memory cells. Further, we endeavour to examine how the molecular signals imparted by DCs coordinate to generate protective CD8+ T‐cell immunity.
The Situatedness of Work Practices and Organizational Culture: Implications for Information Systems Innovation Uptake
Authors: Igira Faraja Teddy
Published: March 2008

This paper addresses work practices and organizational culture as situated actions and the implications for information systems innovation uptake. It reports research being conducted in Tanzania that brings an ethnographic research approach to understanding relations between local health care practices and health information systems development, by asking how health workers’ practices and everyday actions are influenced by the context of their specific situation. The research is being conducted in the context of a globally distributed open source software project to introduce and enhance health information systems in developing countries. Drawing on cultural historical activity theory, the study highlights the need for understanding each information system user's and each organization's specific and detailed work processes, and how situational and organizational factors may come together with the health information systems innovation processes in meeting the challenges discussed. In order to establish fully the potential of activity theory to innovation processes, situatedness of work practices focusing on the organization context is emphasized.
Surface modification of Co-doped ZnO nanocrystals and its effects on the magnetic properties
Authors: Pereira A. S. , Ankiewicz A. O. , Gehlhoff W. , Hoffmann A. , Pereira S. , Trindade T. , Grundmann M. , Carmo M. C. , Sobolev N. A.
Published: March 2008

A series of chemically prepared Co2+-doped ZnO colloids has been surface modified either by growing shells of ZnSe or by the in situ encapsulation in poly(styrene). The surface modification effects using these two distinct chemical strategies on the magnetic properties of the nanocrystals were probed by electron paramagnetic resonance (EPR). Structural characterization by means of x-ray diffraction and transmission electron microscopy gave no evidence of second phase formation within the detection limits of the used equipment. The EPR analysis was carried out by simulations of the powderlike EPR spectra. The results confirm that in the core of these nanocrystals Co was incorporated as Co2+, occupying the Zn2+ sites in the wurtzite structure of ZnO. Additionally we identify two Co signals stemming from the nanocrystals’ shell. The performed surface modifications clearly change the relative intensity of the EPR spectrum components, revealing the core and shell signals.
Direct imaging of current-induced domain wall motion in CoFeB structures
Authors: Heyne L. , Kläui M. , Backes D. , Möhrke P. , Moore T. A. , Kimling J. G. , Boulle O. , Rüdiger U. , Heyderman L. J. , Rodríguez A. Fraile , Nolting F. , Kirsch K. , Mattheis R.
Published: March 2008

By direct x-ray photoemission electron microscopy imaging, we probe current-induced domain wall motion in 20nm thick CoFeB wires. We observe transverse walls for all wire widths up to 1500nm as a consequence of the small saturation magnetization of the material. High critical current densities above 1×1012A∕m2 for wall displacement due to the spin transfer torque effect are found. The critical current densities jc increase further with decreasing wire width indicating that jc is governed by extrinsic pinning due to edge defects. In addition to wall displacements, we observe wall transformations to energetically favorable wall types due to heating. Owing to the high Curie temperature though, the sample temperature stays below the Curie temperature even for the highest current densities where structural damage sets in.
Nonanalyticity of magnetization curve for Dzialoshinsky–Moriya antiferromagnet: LaMnO3 as a model magnet
Authors: Bolzoni F. , Cabassi R.
Published: March 2008

An extensive study of the energy expression for an antiferromagnetic system with antisymmetric Dzialoshinsky–Moriya (DM) interaction and uniaxial magnetocrystalline anisotropy is presented and the main features are shown as a function of magnetic field H applied along the different crystallographic directions. The spin-flop transition is analyzed, showing that for the DM coupling constant D>Dcrit the transition changes from first to second order. Analytical results are followed by numerical computer simulations, both for single-crystal and for polycrystal with isotropic easy axis distribution. The first and second derivatives of the average magnetization with respect to H are analyzed as well, for their insight potentiality: the first derivative is found to be useful for a direct measurement of the spin-flop transition field in polycrystalline samples, while the shape of the second derivative allows us to distinguish the case D≠0 from the case D=0. The obtained results are then applied to the manganite perovskite LaMnO3, attaining satisfactory interpretation of experimental data and suggestions for further investigation techniques.
Room temperature visible photoluminescence of silicon nanocrystallites embedded in amorphous silicon carbide matrix
Authors: Coscia U. , Ambrosone G. , Basa D. K.
Published: March 2008

The nanocrystalline silicon embedded in amorphous silicon carbide matrix was prepared by varying rf power in high vacuum plasma enhanced chemical vapor deposition system using silane methane gas mixture highly diluted in hydrogen. In this paper, we have studied the evolution of the structural, optical, and electrical properties of this material as a function of rf power. We have observed visible photoluminescence at room temperature and also have discussed the role played by the Si nanocrystallites and the amorphous silicon carbide matrix. The decrease of the nanocrystalline size, responsible for quantum confinement effect, facilitated by the amorphous silicon carbide matrix, is shown to be the primary cause for the increase in the PL intensity, blueshift of the PL peak position, decrease of the PL width (full width at half maximum) as well as the increase of the optical band gap and the decrease of the dark conductivity.
Room-temperature microstructural evolution of electroplated Cu studied by focused ion beam and positron annihilation lifetime spectroscopy
Authors: Yin K. B. , Xia Y. D. , Zhang W. Q. , Wang Q. J. , Zhao X. N. , Li A. D. , Liu Z. G. , Hao X. P. , Wei L. , Chan C. Y. , Cheung K. L. , Bayes M. W. , Yee K. W.
Published: March 2008

Focused ion beam (FIB) microscopy was used to obtain the time dependent transformation fraction and positron annihilation lifetime spectroscopy (PALS) was employed to analyze the vacancy-type defects in electroplated copper (Cu) during room-temperature microstructrual evolution. It was found that PALS is more sensitive than FIB to show the room-temperature microstructual evolution of electroplated Cu at the first stage of self-annealing. The majority of defects in electroplated Cu are dislocation-bound vacancies and vacancy clusters. Both the size and the concentration of the defects are similar for the two samples at the completion of electroplating. During the incubation time, the mean size of vacancy-type defects increases. After the onset of visible grain growth, the size of vacancy-type defects decreases. The detail evolutions of defects differ with the two samples. The role of the evolution of codeposited species was also discussed.
Simple finite field nuclear relaxation method for calculating vibrational contribution to degenerate four-wave mixing
Authors: Kirtman Bernard , Luis Josep M.
Published: March 2008

A simple extended finite field nuclear relaxation procedure for calculating vibrational contributions to degenerate four-wave mixing (also known as the intensity-dependent refractive index) is presented. As a by-product one also obtains the static vibrationally averaged linear polarizability, as well as the first and second hyperpolarizability. The methodology is validated by illustrative calculations on the water molecule. Further possible extensions are suggested.
Fluctuations of statistics among subregions of a turbulence velocity field
Authors: Mouri Hideaki , Hori Akihiro , Takaoka Masanori
Published: March 2008

To study subregions of a turbulence velocity field, a long record of velocity data of grid turbulence is divided into smaller segments. For each segment, we calculate statistics such as the mean rate of energy dissipation and the mean energy at each scale. Their values significantly fluctuate, in lognormal distributions at least as a good approximation. Each segment is not under equilibrium between the mean rate of energy dissipation and the mean rate of energy transfer that determines the mean energy. These two rates still correlate among segments when their length exceeds the correlation length. Also between the mean rate of energy dissipation and the mean total energy, there is a correlation characterized by the Reynolds number for the whole record, implying that the large-scale flow affects each of the segments.
Silicon-oxide-nitride-oxide-silicon-type flash memory with a high-k NdTiO3 charge trapping layer
Authors: Pan Tung-Ming , Yu Te-Yi
Published: March 2008

In this letter, we demonstrate the silicon-oxide-nitride-oxide-silicon-type flash memory using a high-k NdTiO3 charge trapping layer. The structural and electrical properties of a high-k NdTiO3 memory were explored by x-ray diffraction, x-ray photoelectron spectroscopy, capacitance-voltage curves, and data retention. We found that the NdTiO3 charge trapping layer annealed at 800°C exhibited a large flatband voltage shift of 2.8V (programed at Vg=9V under 1ms) and a low charge loss of 3% (measured at room temperature) due to the higher probability of trapping the charge carriers, and they are trapped in the deep trap level of NdTiO3, indicative of the formation of a well-crystallized NdTiO3 structure and the reduction of the interfacial layer.
Microwave dielectric loss at single photon energies and millikelvin temperatures
Authors: O’Connell Aaron D. , Ansmann M. , Bialczak R. C. , Hofheinz M. , Katz N. , Lucero Erik , McKenney C. , Neeley M. , Wang H. , Weig E. M. , Cleland A. N. , Martinis J. M.
Published: March 2008

The microwave performance of amorphous dielectric materials at very low temperatures and very low excitation strengths displays significant excess loss. Here, we present the loss tangents of some common amorphous and crystalline dielectrics, measured at low temperatures (T<100mK) with near single-photon excitation energies, E∕ℏω0∼1, using both coplanar waveguide and lumped LC resonators. The loss can be understood using a two-level state defect model. A circuit analysis of the half-wavelength resonators we used is outlined, and the energy dissipation of such a resonator on a multilayered dielectric substrate is theoretically considered.
1.55
μ
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InAs quantum dots grown on a GaAs substrate using a GaAsSb metamorphic buffer layer
Authors: Liu H. Y. , Qiu Y. , Jin C. Y. , Walther T. , Cullis A. G.
Published: March 2008

The use of a GaAsSb metamorphic buffer layer (MBL) is demonstrated to significantly enhance the room-temperature photoluminescence intensity for 1.55μm metamorphic InAs∕GaAs quantum dots (QDs) in comparison with a conventional InGaAs MBL. A dramatic reduction of QD photoluminescence emission efficiency above 1.5μm has been observed at room temperature when the indium composition in the InxGa1−xAs MBL is increased over x=0.25. By using a GaAsSb buffer instead of InGaAs, we demonstrate a strong enhancement of photoluminescence intensity of InAs∕GaAs QDs. The effects of the GaAsSb MBL can be understood in terms of smoothing the surface morphology of the buffer layer and, hence, suppressing the formation of dislocations in the QD region. These results suggest an alternative approach to developing GaAs-based light sources in the telecommunication-wavelength range near 1.55μm.
Computing plasma focus pinch current from total current measurement
Authors: Lee S. , Saw S. H. , Lee P. C. K. , Rawat R. S. , Schmidt H.
Published: March 2008

The total current Itotal waveform in a plasma focus discharge is the most commonly measured quantity, contrasting with the difficult measurement of Ipinch. However, yield laws should be scaled to focus pinch current Ipinch rather than the peak Itotal. This paper describes how Ipinch may be computed from the Itotal trace by fitting a computed current trace to the measured current trace using the Lee model. The method is applied to an experiment in which both the Itotal trace and the plasma sheath current trace were measured. The result shows good agreement between the values of computed and measured Ipinch.
Use of gamma emission computed tomography to study the effect of electrolyte concentration on regions of preferred flow and hydraulic conductivity in deep regolith materials
Authors: Turner M. L. , Greene R. S. B. , Knackstedt M. , Senden T. J. , Sakellariou A. , White I.
Published: March 2008

Understanding fluid flow, displacement, and mixing processes in natural porous media is fundamentally dependent upon the accurate characterisation of complex 3-dimensional structures. This current study delineated the distribution of conducting regions within a suite of regolith materials as they interacted with electrolyte solutions of different concentrations. Previous studies on the effects of electrolyte concentration on clay swelling and dispersion and the concomitant changes in pore structure, and hence soil permeability, have mainly been carried out on repacked samples of disturbed surface soils. This study used unconsolidated materials recovered as undisturbed cores from a saline aquifer from the deeper regolith (8.0–55.8 m). Progressive dilution of the electrolyte concentration of the percolating fluid (while maintaining a constant sodium adsorption ratio) was used to alter the pore structure of these saturated regolith materials. The electrolyte concentration was reduced from an initial value of 383 m.e./L (the original electrolyte concentration of the saline aquifer) to below the threshold concentration, and finally the cores were rinsed with deionised water. The corresponding changes to the regions conducting fluid and therefore pore structure, and the major fluid pathways followed during the percolation process, were imaged using gamma emission computed tomography.
Five experimental core samples from depths of 8, 28, 30 (×2), and 55 m were used in the experiments. The average hydraulic conductivity was measured and found to decrease as a function of electrolyte concentration. The regions containing the major fluid pathways were found to decrease in volume as a function of electrolyte concentration. Clay mineralogy, sodium adsorption ratio, and grain size characteristics were found to be positively correlated with reductions in the average hydraulic conductivity. This method has the potential to aid in our understanding of the fundamental processes that govern the dynamics of pore structure changes and hence fluid flow in porous regolith materials, particularly in relation to changes in the electrolyte concentration and sodium adsorption ratio of the pore fluid. Such data will add significantly to our understanding of factors that affect the hydraulic properties of regolith materials under saline/sodic conditions.
Chemical transmission between dopaminergic neuron pairs
Authors: Vandecasteele Marie , Glowinski Jacques , Deniau Jean-Michel , Venance Laurent
Published: March 2008

Midbrain dopaminergic (DAergic) neurons play a major regulatory role in in goal-directed behavior and reinforcement learning. DAergic neuron activity, and therefore spatiotemporal properties of dopamine release, precisely encodes reward signals. Neuronal activity is shaped both by external afferences and local interactions (chemical and electrical transmissions). Numerous hints suggest the existence of chemical interactions between DAergic neurons, but direct evidence and characterization are still lacking. Here, we show, using dual patch-clamp recordings in rat brain slices, a widespread bidirectional chemical transmission between DAergic neuron pairs. Hyperpolarizing postsynaptic potentials were partially mediated by D2-like receptors, and entirely resulted from the inhibition of the hyperpolarization-activated depolarizing current (Ih). These results constitute the first evidence in paired recordings of a chemical transmission relying on conductance decrease in mammals. In addition, we show that chemical transmission and electrical synapses frequently coexist within the same neuron pair and dynamically interact to shape DAergic neuron activity.
Tug-of-war as a cooperative mechanism for bidirectional cargo transport by molecular motors
Authors: Müller Melanie J. I. , Klumpp Stefan , Lipowsky Reinhard
Published: March 2008

Intracellular transport is based on molecular motors that pull cargos along cytoskeletal filaments. One motor species always moves in one direction, e.g., conventional kinesin moves to the microtubule plus end, whereas cytoplasmic dynein moves to the microtubule minus end. However, many cellular cargoes are observed to move bidirectionally, involving both plus- and minus-end-directed motors. The presumably simplest mechanism for such bidirectional transport is provided by a tug-of-war between the two motor species. This mechanism is studied theoretically using the load-dependent transport properties of individual motors as measured in single-molecule experiments. In contrast to previous expectations, such a tug-of-war is found to be highly cooperative and to exhibit seven different motility regimes depending on the precise values of the single motor parameters. The sensitivity of the transport process to small parameter changes can be used by the cell to regulate its cargo traffic.