bluuebunny/crossref_metadata_2025 huggingface dataset:
Preliminary observations of tag shedding, tag reporting, tag wounds, and tag biofouling for raggedtooth sharks (Carcharias taurus) tagged off the east coast of South Africa
Authors: Dicken M.L. , Booth A.J. , Smale M.J.
Published: October 2006

A double-tagging experiment and integrated on-site questionnaire and telephone survey were used to investigate aspects of tag shedding, tag reporting, tag wounds, and tag biofouling for the raggedtooth shark (Carcharias taurus), tagged off the east coast of South Africa. Between 2002 and 2004, 84 juvenile (<1.8 m total length, TL), and 24 adult (>1.8 m TL) C. taurus were double-tagged. Of these, 11 juvenile and six adult double-tagged sharks were recaptured. Significantly, more tags were shed from adult than from juvenile sharks, and there was also a significant difference between the number of anterior and posterior tags shed. Rates of tag reporting were estimated from a survey of 477 randomly selected shore-anglers, and they varied both temporally and spatially from 27% to 100%. In all, 93 tag recaptures were reported in the survey, most (75.3%) with some biofouling. Tag-inflicted damage was reported in 35.5% of recaptured sharks, and the incidence of tag-inflicted damage was greater for disk (77.8%) than for dart tags (25.3%).
Cerclage-Wiring-Assisted Fixation of Difficult Hand Fractures
Authors: TEOH L. C. , TAN P. L. , TAN S. H. , CHEONG E. C.
Published: September 2006

Difficult hand fractures with multiple butterfly fragments, multiple cortical splits or intraarticular extension continue to pose a challenge for optimal stable fixation that allows early postoperative mobilisation. In this study, we describe the use of cerclage-wire-assisted fixation of 17 difficult hand fractures in 16 patients. The cerclage wires helped to maintain the reduction, so providing sufficient initial stability for placement of a plate and screws. Stable fixation of the fracture was then accomplished without losing the reduction. One to three cerclages of stainless-steel wires were used for the preliminary fixation. Stable fixation was then accomplished by a bridging or neutralising plate technique. Postoperatively, the fixation was sufficiently stable to allow immediate mobilisation. With an average follow up of 44.5 months, all 17 fractures united without loss of reduction. At final follow-up, the average total active range of motion was 247° (range 220–260°).
The Anatomical Site of Constriction of the Median Nerve in Patients with Severe Idiopathic Carpal Tunnel Syndrome
Authors: AL-QATTAN M. M
Published: September 2006

During open carpal tunnel release in patients with severe idiopathic carpal tunnel syndrome, an area of constriction in the substance of the median nerve is frequently noted. In a prospective study of 30 patients, the central point of the constricted part of the nerve was determined intraoperatively and found to be, on average, 2.5 (range 2.2–2.8) cm from the distal wrist crease. This point always corresponded to the location of the hook of the hamate bone. These intraoperative findings were compared with the “narrowest” point of the carpal canal as determined by anatomical and radiological studies in the literature.
I The Orator in Roman Society
Authors: Steel Catherine
Published: October 2006

Roman oratory consists of two distinct phenomena. One is the occasions when men – and, very seldom, women – spoke in public. The other is the body of written texts of speeches which survive from antiquity. These are distinct objects of study: not all speeches were written down, not all those which were written down have survived; and even if we had all the speeches ever delivered, the written text can only convey a part of the experience of hearing an orator, in a particular place and time and with all the non-verbal aspects of rhetoric which contributed to an oratorical performance. In this first chapter, I consider the various occasions on which individuals spoke at Rome, reserving until the second chapter the processes by which spoken performances were transferred into written texts.
FEMALE AUTONOMY AS A CONTRIBUTING FACTOR TO WOMEN’S HIV-RELATED KNOWLEDGE AND BEHAVIOUR IN THREE CULTURALLY CONTRASTING STATES IN INDIA
Authors: BLOOM SHELAH S. , GRIFFITHS PAULA L.
Published: October 2006

Factors contributing to India’s vulnerability to the AIDS epidemic include pervasive poverty, low levels of education and high gender stratification. This study uses data collected in the 1998–99 National Family Health Survey-2 (NFHS-2) to investigate the relationship between aspects of women’s autonomy and four measures of HIV-related knowledge and behaviour – awareness and knowledge of HIV/AIDS, condom awareness and condom use – in three culturally contrasting states in India: Kerala (n=2884), Karnataka (n=4357) and Uttar Pradesh (n=8981). The NFHS-2 is a nationally representative survey of India, with a sampling scheme that was designed such that each state sample can be generalized back to represent ever-married women aged 15–49 living in the state. Kerala scores highest in the four health outcome measures, followed by Karnataka and then Uttar Pradesh, but condom use is lowest in Karnataka. Kerala also leads in the four dimensions of autonomy examined and in socio-demographic status, followed again by Karnataka and Uttar Pradesh. Despite these observed differences, in all three states, women with greater autonomy as measured by this study were more likely to be knowledgeable about AIDS and condoms and to use condoms, after controlling for socio-demographic factors. These results concur with other studies focusing on women’s autonomy and health outcomes around the world, and point to the importance of incorporating a gender-based approach to AIDS prevention programmes in India.
Regulation of host cell survival by intracellularPlasmodiumandTheileriaparasites
Authors: HEUSSLER V. , STURM A. , LANGSLEY G.
Published: October 2006

PlasmodiumandTheileriaparasites are obligate intracellular protozoa of the phylum Apicomplexa.Theileriainfection of bovine leukocytes induces transformation of host cells and infected leukocytes can be kept indefinitely in culture.Theileria-dependent host cell transformation has been the subject of interest for many years and the molecular basis of this unique phenomenon is quite well understood. The equivalent life cycle stage ofPlasmodiumis the infection of mammalian hepatocytes, where parasites reside for 2–7 days depending on the species. Some of the molecular details of parasite-host interactions inP. berghei-infected hepatocytes have emerged only very recently. Similar to what has been shown forTheileria-infected leukocytes these data suggest that malaria parasites within hepatocytes also protect their host cell from programmed cell death. However, the strategies employed to inhibit host cell apoptotic pathways appear to be different to those used byTheileria. This review discusses similarities and differences at the molecular level ofPlasmodium- andTheileria-induced regulation of the host cell survival machinery.
Pro- and anti-apoptotic activities of protozoan parasites
Authors: SCHAUMBURG F. , HIPPE D. , VUTOVA P. , LÜDER C. G. K.
Published: October 2006

During infection, programmed cell death, i.e. apoptosis, is an important effector mechanism of innate and adaptive host responses to parasites. In addition, it fulfils essential functions in regulating host immunity and tissue homeostasis. Not surprisingly, however, adaptation of parasitic protozoa to their hosts also involves modulation or even exploitation of cell death in order to facilitate parasite survival in a hostile environment. During recent years, considerable progress has been made in our understanding of apoptosis during parasitic infections and there is now convincing evidence that apoptosis and its modulation by protozoan parasites has a major impact on the parasite-host interaction and on the pathogenesis of disease. This review updates our current knowledge on the diverse functions apoptosis may fulfil during infections with diverse protozoan parasites including apicomplexans, kinetoplastids and amoebae. Furthermore, we also summarize common mechanistic themes of the pro- and anti-apoptotic activities of protozoan parasites. The diverse and complex effects which parasitic protozoa exert on apoptotic cell death within the host highlight fascinating interactions of parasites and their hosts. Importantly, they also stress the importance of further investigations before the modulation of host cell apoptosis can be exploited to combat parasitic infections.
Determination and interpretation of surface and atmospheric Miniature Thermal Emission Spectrometer spectral end‐members at the Meridiani Planum landing site
Authors: Glotch Timothy D. , Bandfield Joshua L.
Published: October 2006

Factor analysis and target transformation techniques have been applied to Miniature Thermal Emission Spectrometer (Mini‐TES) spectra to isolate the end‐member surface and atmospheric component spectral shapes at Meridiani Planum. The surface spectral shapes recovered from the Mini‐TES data set include coarse, gray hematite, surface dust, basaltic sand, and the silica/sulfate‐rich outcrop. In addition, two atmospheric spectral shapes are identified, indicating the variable nature of the atmosphere over the course of the MER rover missions. Linear deconvolution of the basaltic spectral shape indicates that it is high in plagioclase and pyroxene, including pigeonite, with smaller amounts of glass/phyllosilicate and olivine. Linear deconvolution of the outcrop spectral shape indicates that it is composed primarily of amorphous silica/glass/phyllosilicates and Mg‐, Ca‐, and Fe‐bearing sulfates, with smaller amounts of plagioclase.
F region drift observations from Athens Digisonde
Authors: Belehaki Anna , Tsagouri Ioanna , Michalareas George , Herekakis Themistocles
Published: October 2006

Ionospheric drift measurements are of significant importance in the monitoring of the upper atmosphere dynamics and an important contributor toward the deeper understanding of the ionospheric electrodynamics. An interesting perspective for operational ionospheric drift measurements comes from the HF radars, such as the Digisondes. Nevertheless, when interpreting velocity measurements obtained from the Digisonde drift analysis method, care must be taken in relating the motion to the effects of photoionization, recombination, gravity waves, and plasma motion. In this paper we investigate the effect of all different mechanisms contributing to the apparent velocity measured by the Athens Digisonde. As a first step, the daily drift pattern over Athens under quiet magnetospheric conditions is preliminarily determined for the equinox months. Moreover, the substorm effect on the extracted pattern is also investigated. Our results provide some evidence for the direct effect of traveling atmospheric disturbances in the vertical component, while in the horizontal plane, the disturbance could be attributed to other substorm‐related mechanisms.
Incipient axial collapse of the Main Cordillera and strain partitioning gradient between the central and Patagonian Andes, Lago Laja, Chile
Authors: Melnick Daniel , Charlet François , Echtler Helmut P. , De Batist Marc
Published: October 2006

Lago Laja is a late Quaternary volcanic‐dammed lake located near the drainage divide of the south central Andes. Field observations, lake reflection seismic profiles, bathymetry, and remote sensing data reveal an active fault system that runs parallel to the volcanic arc along the axis of the Main Cordillera, the Lago Laja fault system (LLFS). Normal faults of this extensional system cut late Pleistocene volcanics, <7.1 ka still water lacustrine sediments, 6.3 ka pyroclastic deposits, and Holocene alluvial fans. We divide the LLFS in three segments on the basis of fault geometry, width, and slip magnitude. The underwater faults of the central segment in the lake's deepest part have the maximum Holocene vertical slip rate of >2.7 mm/yr. Since 7.1 ka, the LLFS accounts for ∼0.7% of arc‐normal extension at an average minimum rate of 1.2 mm/yr and strain rate of ∼10−14s−1. Seismites and surface ruptures evidence M>6 paleoearthquakes. The Main Cordillera at ∼37°S is a large‐scale pop‐up structure uplifted by thrusting along its foothills. In this light, we interpret extension in the axial and highest part of the Andes as incipient synorogenic gravitational collapse in response to uplift and crustal thickening. Thermal weakening due to elevated heat flow and postglacial lithospheric rebound and unbending have probably contributed to the arc‐limited collapse and Holocene acceleration of deformation rates. The lack of significant strike‐slip offsets along the LLFS as well as along both foothills‐thrust systems at 37°S contrasts with the intra‐arc dextral fault zone south of 38°S. Regional structural data indicates that north of 38°S, diffusely distributed strain reflects low partitioning of oblique subduction, while to the south deformation is localized in a discrete strike‐slip fault zone along the volcanic arc, reflecting a higher degree of partitioning. We relate this strain partitioning gradient to favorable fault orientations in the fore arc north of the Arauco Peninsula, a major seismotectonic boundary.
Stratospheric Joule heating by lightning continuing current inferred from radio remote sensing
Authors: Füllekrug Martin , Ignaccolo Massimiliano , Kuvshinov Alexei
Published: October 2006

The mean lightning current waveform of particularly intense lightning discharges is inferred from 52,510 radio wave recordings in the frequency range 1–200 Hz. The current waveform decays initially with a time constant of ∼2 ms, and the current lowers ∼60 C from cloud to ground within the first ∼10 ms of the discharge. The subsequent continuing current exhibits a decay time constant of ∼40 ms and lowers ∼170 C from cloud to ground within the next ∼100 ms of the discharge. The total charge transfer ∼230 C from cloud to ground deposits electrical energy into the stratosphere resulting from quasi‐static (Joule) heating. The energy deposition is dominated by the lightning continuing current, and it is ∼10−5 J/m3 at 30 km height. It is speculated that the initiation of blue jets and gigantic jets in the stratosphere may result from lightning continuing current ≳100 ms which can be observed with radio waves at frequencies ≲10 Hz.
Pharmacological blockade of CCR1 ameliorates murine arthritis and alters cytokine networksin vivo
Authors: Amat M , Benjamim C F , Williams L M , Prats N , Terricabras E , Beleta J , Kunkel S L , Godessart N
Published: October 2006

Background and purpose:

The chemokine receptor CCR1 is a potential target for the treatment of rheumatoid arthritis. To explore the impact of CCR1 blockade in experimental arthritis and the underlying mechanisms, we used J‐113863, a non‐peptide antagonist of the mouse receptor.

Experimental approach:

Compound J‐113863 was tested in collagen‐induced arthritis (CIA) and three models of acute inflammation;Staphylococcusenterotoxin B (SEB)‐induced interleukin‐2 (IL‐2), delayed‐type hypersensitivity (DTH) response, and lipopolysaccharide (LPS)‐induced tumour necrosis factorα (TNFα) production. In the LPS model, CCR1 knockout, adrenalectomised, or IL‐10‐depleted mice were also used. Production of TNFα by mouse macrophages and human synovial membrane samples in vitro were also studied.

Key results:

Treatment of arthritic mice with J‐113863 improved paw inflammation and joint damage, and dramatically decreased cell infiltration into joints. The compound did not inhibit IL‐2 or DTH, but reduced plasma TNFα levels in LPS‐treated mice. Surprisingly, CCR1 knockout mice produced more TNFα than controls in response to LPS, and J‐113863 decreased TNFα also in CCR1 null mice, indicating that its effect was unrelated to CCR1. Adrenalectomy or neutralisation of IL‐10 did not prevent inhibition of TNFα production by J‐113863. The compound did not inhibit mouse TNFα in vitro, but did induce a trend towards increased TNFα release in cells from synovial membranes of rheumatoid arthritis patients.

Conclusions and implications:

CCR1 blockade improves the development of CIA, probably via inhibition of inflammatory cell recruitment. However, results from both CCR1‐deficient mice and human synovial membranes suggest that, in some experimental settings, blocking CCR1 could enhance TNF production.

British Journal of Pharmacology(2006)149, 666–675. doi:10.1038/sj.bjp.0706912
Reciprocal regulation of human soluble and particulate guanylate cyclasesin vivo
Authors: Madhani M , Okorie M , Hobbs A J , MacAllister R J
Published: October 2006

Background & purpose:

We demonstrated previously that reciprocal regulation of soluble (sGC) and particulate (pGC) guanylate cyclases by NO and natriuretic peptides coordinates cyclic cGMP‐mediated vasodilatationin vitro. Herein, we investigated whether such an interaction contributes to vascular homeostasis in mice and humansin vivo.

Experimental approach:

Mean arterial blood pressure (MABP) changes in anaesthetized mice were monitored in response to i.v. administration of cGMP‐ and cAMP‐dependent vasodilators in wild‐type (WT), endothelial NO synthase (eNOS) and natriuretic peptide receptor (NPR)‐A knockout mice. Forearm blood flow (FBF) in response to intra‐brachial infusion of ANP (25, 50, 100, 200 pmol min‐1) in the absence and presence of the NOS inhibitor NG‐methyl‐L‐arginine (L‐NMA; 4 μmol min‐1) and the control constrictor noradrenaline (240 pmol min‐1) was assessed in healthy volunteers.

Key results:

Sodium nitroprusside (SNP; NO‐donor) and atrial natriuretic peptide (ANP) produced dose‐dependent reductions in MABP in WT animals that were significantly enhanced in eNOS KO mice. In NPR‐A K mice, SNP produced a dose‐dependent reduction in MABP that was significantly greater than that in WT mice. Responsiveness to the cAMP‐dependent vasodilator epoprostenol was similar in WT, eNOS KO and NPR‐A KO animals. ANP caused vasodilatation of the forearm resistance vasculature that was significantly greater in individuals lacking endothelium‐derived NO (i.e. L‐NMA treated).

Conclusions & implications:

These data demonstrate that crosstalk occurs between the NO‐sGC and ANP‐pGC pathways to regulate cGMP‐dependent vasodilatationin vivoin both mice and humans. These findings have implications for understanding the link between natriuretic peptide activity and cardiovascular risk.

British Journal of Pharmacology(2006)149, 797–801. doi:10.1038/sj.bjp.0706920
Sensitivity of glycogen phosphorylase isoforms to indole site inhibitors is markedly dependent on the activation state of the enzyme
Authors: Freeman S , Bartlett J B , Convey G , Hardern I , Teague J L , Loxham S J G , Allen J M , Poucher S M , Charles A D
Published: October 2006

Background and purpose:

Inhibition of hepatic glycogen phosphorylase is a potential treatment for glycaemic control in type 2 diabetes. Selective inhibition of the liver phosphorylase isoform could minimize adverse effects in other tissues. We investigated the potential selectivity of two indole site phosphorylase inhibitors, GPi688 and GPi819.

Experimental approach:

The activity of glycogen phosphorylase was modulated using the allosteric effectors glucose or caffeine to promote the less active T state, and AMP to promote the more active R state. In vitro potency of indole site inhibitors against liver and muscle glycogen phosphorylase a was examined at different effector concentrations using purified recombinant enzymes. The potency of GPi819 was compared with its in vivo efficacy at raising glycogen concentrations in liver and muscle of Zucker (fa/fa) rats.

Key results:

In vitro potency of indole site inhibitors depended upon the activity state of phosphorylase a. Both inhibitors showed selectivity for liver phosphorylase a when the isoform specific activities were equal. After 5 days dosing of GPi819 (37.5 μmol kg−1), where free compound levels in plasma and tissue were at steady state, glycogen elevation was 1.5‐fold greater in soleus muscle than in liver (P<0.05).

Conclusions and implications:

The in vivo selectivity of GPi819 did not match that seen in vitro when the specific activities of phosphorylase a isoforms are equal. This suggests T state promoters may be important physiological regulators in skeletal muscle. The greater efficacy of indole site inhibitors in skeletal muscle has implications for the overall safety profile of such drugs.

British Journal of Pharmacology (2006) 149, 775–785. doi:10.1038/sj.bjp.0706925
Time-resolved study of solvent-induced recombination in photodissociated IBr−(CO2)n clusters
Authors: Dribinski Vladimir , Barbera Jack , Martin Joshua P. , Svendsen Annette , Thompson Matthew A. , Parson Robert , Lineberger W. Carl
Published: October 2006

We report the time-resolved recombination of photodissociated IBr−(CO2)n (n=5–10) clusters following excitation to the dissociative IBr−A′Π1∕22 state of the chromophore via a 180fs, 795nm laser pulse. Dissociation from the A′ state of the bare anion results in I− and Br products. Upon solvation with CO2, the IBr− chromophore regains near-IR absorption only after recombination and vibrational relaxation on the ground electronic state. The recombination time was determined by using a delayed femtosecond probe laser, at the same wavelength as the pump, and detecting ionic photoproducts of the recombined IBr− cluster ions. In sharp contrast to previous studies involving solvated I2−, the observed recombination times for IBr−(CO2)n increase dramatically with increasing cluster size, from 12ps for n=5to900ps for n=8,10. The nanosecond recombination times are especially surprising in that the overall recombination probability for these cluster ions is unity. Over the range of 5–10 solvent molecules, calculations show that the solvent is very asymmetrically distributed, localized around the Br end of the IBr− chromophore. It is proposed that this asymmetric solvation delays the recombination of the dissociating IBr−, in part through a solvent-induced well in the A′ state that (for n=8,10) traps the evolving complex. Extensive electronic structure calculations and nonadiabatic molecular dynamics simulations provide a framework to understand this unexpected behavior.
A mixing-length formulation for the turbulent Prandtl number in wall-bounded flows with bed roughness and elevated scalar sources
Authors: Crimaldi John P. , Koseff Jeffrey R. , Monismith Stephen G.
Published: October 2006

Turbulent Prandtl number distributions are measured in a laboratory boundary layer flow with bed roughness, active blowing and sucking, and scalar injection near the bed. The distributions are significantly larger than unity, even at large distances from the wall, in apparent conflict with the Reynolds analogy. An analytical model is developed for the turbulent Prandtl number, formulated as the ratio of momentum and scalar mixing length distributions. The model is successful at predicting the measured turbulent Prandtl number behavior. Large deviations from unity are shown in this case to be consistent with measurable differences in the origins of the momentum and scalar mixing length distributions. Furthermore, these deviations are shown to be consistent with the Reynolds analogy when the definition of the turbulent Prandtl number is modified to include the effect of separate mixing length origin locations. The results indicate that the turbulent Prandtl number for flows over complex boundaries can be modeled based on simple knowledge of the geometric and kinematic nature of the momentum and scalar boundary conditions.
Near-field thermophotovoltaic energy conversion
Authors: Laroche M. , Carminati R. , Greffet J.-J.
Published: October 2006

We report a quantitative model of a near-field thermophotovoltaic (TPV) device consisting in a thermal source located in the near field of a TPV cell. The enhanced radiative transfer at short distance leads to an increase of the photogeneration current. We analyze quantitatively other potential near-field effects, in particular, on the dark current. We also study the influence of the modification of the spectrum of the sources in the near field, comparing the case of a tungsten source with the case of a quasimonochromatic source. Our model leads to a quantitative evaluation of the near-field TPV device output electric power and efficiency.
Resonant photonic band gap structures realized from molecular-beam-epitaxially grown InGaAs∕GaAs Bragg-spaced quantum wells
Authors: Prineas J. P. , Cao C. , Yildirim M. , Johnston W. , Reddy M.
Published: October 2006

We present a comprehensive study of the growth and fabrication of Bragg-spaced quantum wells, a type of resonant photonic band gap structure. To begin, we considered the impact of disorder and drift in the periodicity of the quantum wells on the formation of the resonant photonic band gap. We found that steady decrease in the periodicity greater than a few percent leads to collapse of the resonant photonic band gap, while random disorder in the quantum well periodicity of several percent leads to extra peaks in the resonant photonic band gap due to coupling to “intermediate band” states. Next, we optimized the growth of low x (x⩽0.06) InxGa1−xAs∕GaAs quantum wells, the building block of Bragg-spaced quantum well structures. Growth parameters optimized include growth rate, modulation of substrate temperature for barrier/quantum well, and V/III flux ratio. Fast growth of quantum wells was achieved with some of the narrowest heavy-hole exciton linewidths (0.37meV) reported to date for quantum wells of these widths. Using the optimized InGaAs∕GaAs quantum wells as a building block, we grew near-ideal N=210 Bragg-spaced quantum well structures. By monitoring growth rates during growth with reflection high energy electron diffraction and correcting drift by adjusting cell temperature, drift and disorder in periodicity were kept to less than 1%. We see no fundamental barriers to growing much longer structures such as N=1000 periods or longer.
A localized orbital analysis of the thermochemical errors in hybrid density functional theory: Achieving chemical accuracy via a simple empirical correction scheme
Authors: Friesner Richard A. , Knoll Eric H. , Cao Yixiang
Published: October 2006

This paper describes an empirical localized orbital correction model which improves the accuracy of density functional theory (DFT) methods for the prediction of thermochemical properties for molecules of first and second row elements. The B3LYP localized orbital correction version of the model improves B3LYP DFT atomization energy calculations on the G3 data set of 222molecules from a mean absolute deviation (MAD) from experiment of 4.8to0.8kcal∕mol. The almost complete elimination of large outliers and the substantial reduction in MAD yield overall results comparable to the G3 wave-function-based method; furthermore, the new model has zero additional computational cost beyond standard DFT calculations. The following four classes of correction parameters are applied to a molecule based on standard valence bond assignments: corrections to atoms, corrections to individual bonds, corrections for neighboring bonds of a given bond, and radical environmental corrections. Although the model is heuristic and is based on a 22 parameter multiple linear regression to experimental errors, each of the parameters is justified on physical grounds, and each provides insight into the fundamental limitations of DFT, most importantly the failure of current DFT methods to accurately account for nondynamical electron correlation.
Molecular alignment in a shock wave
Authors: Schlamp Stefan , Hathorn Bryan C.
Published: October 2006

Molecular dynamics simulations of dense nitrogen show that nonspherical molecules have a weak tendency to align their molecular axis such that it lies parallel to the plane of a shock wave front. As a consequence, there is also an even weaker tendency for the molecular rotation axis to align perpendicular to the shock front. The underlying mechanism is discussed and it is argued that this phenomenon can only be observed for dense fluids and only when considering realistic molecular interactions. A single relevant nondimensional parameter is proposed.
Two dimensional fall of granular columns controlled by slow horizontal withdrawal of a retaining wall
Authors: Mériaux Catherine
Published: October 2006

This paper describes a series of experiments designed to investigate the fall of granular columns in a quasi-static regime. Columns made of alternatively green and red sand layers were initially laid out in a box and then released when a retaining wall was set in slow motion with constant speed. The dependence of the dynamics of the fall on the initial aspect ratio of the columns, the velocity of the wall, and the material properties was investigated within the quasi-static regime. A change in the behavior of the columns was identified to be a function of the aspect ratio (height/length) of the initial sand column. Columns of high aspect ratio first subsided before sliding along failure planes, while columns of small aspect ratio were only observed to slide along failure planes. The transition between these two characteristic falls occurred regardless of the material and the velocity of the wall in the context of the quasi-static regime. When the final height and length of the piles were analyzed, we found power-law relations of the ratio of initial to final height and final run-out to initial length with the aspect ratio of the column. The dissipation of energy is also shown to increase with the run-out length of the pile until it reaches a plateau. Finally, we find that the structure of the slip planes that develop in our experiments are not well described by the failure of Coulomb’s wedges for twin retaining rough walls.
Applied reaction dynamics: Efficient synthesis gas production via single collision partial oxidation of methane to CO on Rh(111)
Authors: Gibson K. D. , Viste M. , Sibener S. J.
Published: October 2006

Supersonic molecular beams have been used to determine the yield of CO from the partial oxidation of CH4 on a Rh(111) catalytic substrate, CH4+(1∕2)O2→CO+2H2, as a function of beam kinetic energy. These experiments were done under ultrahigh vacuum conditions with concurrent molecular beams of O2 and CH4, ensuring that there was only a single collision for the CH4 to react with the surface. The fraction of CH4 converted is strongly dependent on the normal component of the incident beam’s translational energy, and approaches unity for energies greater than ∼1.3eV. Comparison with a simplified model of the methane-Rh(111) reactive potential gives insight into the barrier for methane dissociation. These results demonstrate the efficient conversion of methane to synthesis gas, CO+2H2, are of interest in hydrogen generation, and have the optimal stoichiometry for subsequent utilization in synthetic fuel production (Fischer-Tropsch or methanol synthesis). Moreover, under the reaction conditions explored, no CO2 was detected, i.e., the reaction proceeded with the production of very little, if any, unwanted greenhouse gas by-products. These findings demonstrate the efficacy of overcoming the limitations of purely thermal reaction mechanisms by coupling nonthermal mechanistic steps, leading to efficient C–H bond activation with subsequent thermal heterogeneous reactions.
Radial spreading of a viscous drop between parallel-plane surfaces
Authors: Ward Thomas
Published: October 2006

The radial spreading dynamics of a thin film of viscous Newtonian fluid squeezed between parallel plane walls at gap spacings much smaller than the capillary length is examined both experimentally and theoretically. Using a squeezing flow model, analogous to the classical solution derived by Stefan [K. Akad. Wiss. (Mathem-Naturwiss. Kl) 69, 713 (1874)], the effects of surface tension and viscosity on dynamic spreading of squeezed droplets are analyzed. The interaction between squeezing and surface tension is parameterized by a single dimensionless variable, F, which is the ratio of the constant external squeezing force, supplied by gravity acting on the top wall, to surface tension acting on a spreading droplets circumference. An analytical solution relating the gap height and time elapsed is derived in the limit of small Reynolds and negligible capillary numbers. Also, asymptotic solutions are derived for the change in gap height as a function of time, in the limit of either vanishingly small surface tension or external force. Experiments are performed using three fluids with different viscosity and surface tension for gap spacings O(10–100μm). There is excellent agreement between theory and the experimental results for the dynamic change in gap spacing.
Infrared studies of ionic clusters: The influence of Yuan T. Lee
Authors: Lisy James M.
Published: October 2006

Beginning in the mid-1980s, a number of innovative experimental studies on ionic clusters emerged from the laboratory of Yuan T. Lee combining infrared laser spectroscopy and tandem mass spectrometry. Coupled with modern electronic structure calculations, this research explored many facets of ionic clusters including solvation, structure, and dynamics. These efforts spawned a resurgence in gas-phase cluster spectroscopy. This paper will focus on the major areas of research initiated by the Lee group and how these studies stimulated and influenced others in what is currently a vibrant and growing field.
Spectroscopy and femtosecond dynamics of the ring opening reaction of 1,3-cyclohexadiene
Authors: Kuthirummal Narayanan , Rudakov Fedor M. , Evans Conor L. , Weber Peter M.
Published: October 2006

The early stages of the ring opening reaction of 1,3-cyclohexadiene to form its isomer 1,3,5-hexatriene, upon excitation to the ultrashort-lived 1B21 state, were explored. A series of one-color two-photon ionization/photoelectron spectra reveal a prominent vibrational progression with a frequency of 1350cm−1, which is interpreted in a dynamical picture as resulting from the ultrafast wave packet dynamics associated with the ring opening reaction. Photoionization in two-color three-photon and one-color four-photon ionization schemes show an ionization pathway via the same ultrashort-lived 1B21 state, and in addition, a series of Rydberg states with quantum defects of 0.93, 0.76, and 0.15, respectively. Using those Rydberg states as probes for the reaction dynamics in a time-resolved pump-probe experiment provides a direct observation of the elusive 2A11 state that has been implicated as an intermediate step between the initially excited 1B21 state and the ground electronic state. The rise and decay times for the 2A11 state were found to be 55 and 84fs, respectively.
Influence of miscut Y2O3-stabilized ZrO2 substrates on the azimuthal domain structure and ferroelectric properties of epitaxial La-substituted Bi4Ti3O12 films
Authors: Lee Sung Kyun , Hesse Dietrich , Gösele Ulrich , Lee Ho Nyung
Published: October 2006

We have investigated the influence of both miscut angle and miscut direction of Y2O3-stabilized ZrO2 (YSZ) (100) single crystal substrates on the azimuthal domain structure of SrRuO3 electrode layers as well as of La-substituted Bi4Ti3O12 (BLT) ferroelectric thin films, both grown on these substrates by pulsed laser deposition. X-ray diffraction ϕ scan and pole figure characterizations revealed that the YSZ[011] miscut direction is more effective to uniformly reduce the number of azimuthal domain variants in the films than the YSZ[001] miscut direction. The BLT films on YSZ(100) substrates with miscut angle of 5° and [011] miscut direction involve only half the number of azimuthal domains, compared to the BLT films on exactly cut YSZ(100) substrates. Atomic force microscopy and plan-view transmission electron microscopy also confirmed that almost all BLT grains on these miscut YSZ(100) substrates are arranged along only two (out of four) specific azimuthal directions. The BLT films on YSZ(100) substrates with 5° miscut towards YSZ[011] showed an about 1.3 times higher remanent polarization (Pr=12.5μC∕cm2) than the BLT films on exactly cut YSZ(100) substrates (Pr=9.5μC∕cm2), due most probably to a lower areal density of azimuthal domain boundaries. It thus appears that reducing the structural domains can be an effective way to further enhance the ferroelectric properties of multiply twinned, epitaxial ferroelectric films.
Dependence of microelastic-plastic nonlinearity of martensitic stainless steel on fatigue damage accumulation
Authors: Cantrell John H.
Published: October 2006

Self-organized substructural arrangements of dislocations formed during cyclic stress-induced fatigue of metals produce substantial changes in the material microelastic-plastic nonlinearity, a quantitative measure of which is the nonlinearity parameter β extracted from acoustic harmonic generation measurements. The contributions to β from the substructural evolution of dislocations and crack growth for fatigued martensitic 410Cb stainless steel are calculated from the Cantrell model [Proc. R. Soc. London, Ser. A 460, 757 (2004)] as a function of percent full fatigue life to fracture. A wave interaction factor fWI is introduced into the model to account experimentally for the relative volume of fatigue damage included in the total volume of material swept out by an interrogating acoustic wave. For cyclic stress-controlled loading at 551MPa and fWI=0.013 the model predicts a monotonic increase in β from dislocation substructures of almost 100% from the virgin state to roughly 95% full life. Negligible contributions from cracks are predicted in this range of fatigue life. However, during the last 5% of fatigue life the model predicts a rapid monotonic increase of β by several thousand percent that is dominated by crack growth. The theoretical predictions are in good agreement with experimental measurements of 410Cb stainless steel samples fatigued in uniaxial, stress-controlled cyclic loading at 551MPa from zero to full tensile load with a measured fWI of 0.013.
Thermodynamic scaling of the viscosity of van der Waals, H-bonded, and ionic liquids
Authors: Roland C. M. , Bair S. , Casalini R.
Published: October 2006

Viscosities η and their temperature T and volume V dependences are reported for seven molecular liquids and polymers. In combination with literature viscosity data for five other liquids, we show that the superpositioning of relaxation times for various glass-forming materials when expressed as a function of TVγ, where the exponent γ is a material constant, can be extended to the viscosity. The latter is usually measured to higher temperatures than the corresponding relaxation times, demonstrating the validity of the thermodynamic scaling throughout the supercooled and higher T regimes. The value of γ for a given liquid principally reflects the magnitude of the intermolecular forces (e.g., steepness of the repulsive potential); thus, we find decreasing γ in going from van der Waals fluids to ionic liquids. For some strongly H-bonded materials, such as low molecular weight polypropylene glycol and water, the superpositioning fails, due to the nontrivial change of chemical structure (degree of H bonding) with thermodynamic conditions.
Increase of water viscosity under the influence of magnetic field
Authors: Ghauri S. A. , Ansari M. S.
Published: October 2006

Effect of applied magnetic field on the water viscosity between 298 and 323K has been investigated. A higher absolute viscosity has been observed in the presence of applied magnetic field compared to no field which has been explained on the basis of stronger hydrogen bonds. The measurement is found to increase consistently at higher temperatures. The relative increase in viscosity Δη∕η0 is of the order of 10−3 in a 7.5kG transverse magnetic field where Δη is the viscosity change compared to the no-field viscosity η0 at a given temperature.
Near-field imaging in the megahertz range by strongly coupled magnetoinductive surfaces: Experiment and ab initio analysis
Authors: Freire Manuel J. , Marques Ricardo
Published: October 2006

In this work, the previously reported near-field imaging by two strongly coupled arrays of planar magnetic resonators is further studied. Experiments are performed to clarify the physical mechanisms underlying such an effect. The specific aim of these experiments is to clarify both the role played by magnetoinductive surface waves (MISWs) and the presence in the device of evanescent Fourier harmonics amplification. In addition to the experimental work, an ab initio theoretical analysis is developed to obtain a first approximation of the above effects. This model assumes that MISWs play the same role as plasmon-polaritons in negative refractive slabs, thus producing amplification of evanescent Fourier harmonics in the device. It also predicts that imaging occurs close to the resonators’ resonant frequency, between the passbands for the two MISW branches that can be excited in the lens. Both predictions from the theoretical model are in qualitative agreement with the experimental results. Quantitative agreement can also be obtained if some appropriate additional hypotheses, taking into account the discrete nature of the present device, are included in the model. The reported results suggest the possibility of using this kind of device for imaging in the megahertz range such as in nuclear magnetic resonance imaging.
Pulsed radio frequency plasma deposition of a-SiNx:H alloys: Film properties, growth mechanism, and applications
Authors: Vernhes R. , Zabeida O. , Klemberg-Sapieha J. E. , Martinu L.
Published: October 2006

In this work, we propose a fabrication process of a-SiNx:H alloys by pulsing the radio frequency (rf) signal in a low pressure plasma-enhanced chemical vapor deposition (PECVD) system. The characteristics of the films can be controlled simply by adjusting the duty cycle of the pulsed rf power, while keeping the N2∕SiH4 gas mixture constant. Spectroscopic ellipsometry analysis in the ultraviolet-visible-near infrared and far infrared ranges, atomic force microscopy, and elastic recoil detection reveal strong variations in the optical properties (1.88⩽n⩽2.75, 10−4⩽k⩽5×10−2 at 550nm), optical gap (4.01eV⩽Eg⩽1.95eV), microstructural characteristics (1.3nm⩽surfaceroughness⩽8.3nm), and chemical composition (0.47⩽x⩽1.35) of the coatings as a function of duty cycle. This behavior is interpreted in terms of radical concentration changes in the gas phase, as well as variation in the average ion bombardment energy at the film surface, leading to modifications of both chemical and physical mechanisms that sustain the film growth. Using the control of duty cycle, we fabricated two types of a-SiNx:H-based thin film devices, namely, (i) a model Fabry-Perot optical filter deposited on plastic substrate and (ii) a superlattice structure displaying a photoluminescence signal four times higher than the reference single layer. These two examples of applications point out the main advantages of this pulsed rf PECVD process, in particular, low deposition temperature, reproducibility, versatility, and ease of use.
Effects of wafer impedance on the monitoring and control of ion energy in plasma reactors
Authors: Sobolewski Mark A.
Published: October 2006

Ion kinetic energy in plasma reactors is controlled by applying radio-frequency (rf) substrate bias, but the efficiency and reproducibility of such control will be affected if the wafer being processed has a significant electrical impedance. Here, the effects of wafer impedance were studied by modeling and electrical measurements. Models of wafer impedance were proposed and tested by comparing model predictions to measured electrical wave forms. The tests were performed in an inductively coupled plasma reactor in 50% Ar, 50% CF4 gas at a pressure of 1.33Pa (10mTorr), rf bias frequencies of 0.1–10MHz, rf bias amplitudes of 20–300V, and inductive source powers of 100–500W. At high bias frequencies, the dominant contribution to the wafer impedance was the capacitance of the gap between the wafer and its chuck. At low bias frequencies, however, a resistance associated with the contact between the wafer and the chuck became significant. Electrical wave forms and ion energy distributions were most sensitive to wafer impedance at low bias frequencies and low bias amplitudes. At low bias frequencies, model predictions indicate that the wafer impedance produces an undesirable variation in surface potential, sheath voltage, and ion energy across the wafer surface. Because it neglects wafer impedance effects, a technique that analyzes electrical wave forms to determine ion currents, sheath voltages, and ion energy distributions was found to suffer significant errors at low bias frequencies and amplitudes. Nevertheless, the technique provided accurate results at moderate to high bias frequency and amplitude.
On the stability of the boundary layer subject to a wall-parallel Lorentz force
Authors: Albrecht Thomas , Grundmann Roger , Mutschke Gerd , Gerbeth Gunter
Published: October 2006

The stability of a transitional boundary layer influenced by a wall-parallel, streamwise oriented Lorentz force is investigated by means of direct numerical simulation. Damping of Tollmien-Schlichting waves is observed already at weak force amplitudes. For a particular amplitude, similar to homogeneous suction, the initial Blasius layer evolves towards an exponential velocity profile of strongly enhanced stability. Here, intermediate velocity profiles are found to have linear stability properties superior to that of the asymptotic exponential profile. Additional three-dimensional simulations support the two-dimensional results as Lorentz forcing clearly damps the coherent structures of the transitional flow.
Space qualification and environmental testing of quasicontinuous wave laser diode arrays
Authors: Troupaki Elisavet , Vasilyev Aleksey A. , Kashem Nasir B. , Allan Graham R. , Stephen Mark A.
Published: October 2006

NASA’s mission requirements for spaceborne laser diode arrays lead to a set of tests peculiar to space flight. The goal of these tests is to determine if vibration, radiation, or vacuum will impair the operation or lifetime of nominally 100W quasicontinuous wave 808nm laser diode arrays. To simulate the stresses expected during a mission, terrestrial tests involve mechanical vibration, simulating the acceleration of launch, exposure to the equivalent doses of ionizing radiation, and operation in a vacuum. Three sets of devices were tested: one set with random vibration up to 20 g root-mean-square (grms) applied along three axes, a second set of devices was irradiated with γ radiation (1.17 and 1.33MeV) at 744rad(Si)∕min up to 200krad(Si), and the third set was exposed to a flux of 5×1011 or 1012p∕cm2 of 200MeV protons up to 60krad total dose. Only the proton irradiated devices showed any effect attributable to the test: a slight rise in lasing threshold, which recovered over time with self-annealing. A selection of the devices were then operated in vacuum for a further 1400h accumulating 500×106 pulses without any signs of degradation. Similar results were obtained in a parallel test, conducted in air, accumulating over 109 pulses on a selection of the remaining devices.
Twin defect modes in one-dimensional photonic crystals with a single-negative material defect
Authors: Chen Y. H. , Dong J. W. , Wang H. Z.
Published: October 2006

Twin defect modes are found in one-dimensional photonic crystals stacking with single- negative-permittivity and single-negative-permeability media layers and a single-negative defect. The frequency interval of the two defect modes can be changed by varying the thickness of the defect layer or the thickness ratio of the two stacking layers. Conditions for the emergence of such twin defect modes only relate to the phase thicknesses of the defect layer and the two stacking layers. In addition, the electric fields at the frequencies of the defect modes are strongly localized at the interfaces between the defect layer and its adjacent layers.