bluuebunny/crossref_metadata_2025 huggingface dataset:
Investigating vortex streets behind real and virtual bluff bodies
Authors: Afanasyev Y. D. , Deacon C. G.
Published: February 2006

This paper describes a laboratory experiment designed to study regular arrays of vortices occurring behind an object in a stream of fluid. This phenomenon is observed in industrial flows, flows in the ocean, and in the atmosphere. In the first part of the experiment we consider the flow behind a circular cylinder. In the second part of the experiment the effect of a body on the fluid is imitated by using an appropriate force field, with no real body present in the fluid. The force field (virtual body) is created by a permanent magnet located above the surface of water in combination with an electric current applied in the horizontal direction. The apparatus required for the experiment is inexpensive and easy to construct.
Inexpensive fabrication of silicon Hall devices
Authors: Brody Jed , Dong Zhiyong , Dennen Tristan
Published: February 2006

Semiconductor Hall devices are typically prefabricated for instructional laboratories, but students may gain more understanding by fabricating their own devices. Semiconductor device fabrication usually involves photolithography, vacuum evaporators, and very high-temperature tube furnaces. This paper presents an inexpensive procedure to fabricate silicon Hall devices using only a hot plate and indium. van der Pauw resistivity measurements of p-type and n-type samples thus fabricated yielded results well within the manufacturer’s specifications. Hall measurements of these samples consistently indicated the correct carrier type in both cases. For both p-type and n-type samples, the carrier concentrations obtained from the Hall measurements were within 4% of the expected values.
Two-photon spectroscopy of rubidium using a grating-feedback diode laser
Authors: Olson Abraham J. , Carlson Evan J. , Mayer Shannon K.
Published: February 2006

We describe an experiment for investigating the 5S1∕2→5D5∕2 two-photon transition in rubidium using a single grating-feedback diode laser operating at 778.1nm (385THz). Continuous tuning of the laser frequency over 4GHz allows for the clear resolution of the Doppler-free spectral features and allows accurate measurement of the hyperfine ground-state splitting. A direct comparison between Doppler-broadened and Doppler-free spectral features is possible because both are distinctly evident in the two-photon spectra. By independently modifying the polarization state of the two laser fields, the impact of electric dipole selection rules on the two-photon transition spectra is investigated. This experiment is a valuable addition to the advanced undergraduate laboratory because it uses much of the same equipment as the single-photon saturated absorption spectroscopy experiment performed on the 5S1∕2→5P3∕2 transition in rubidium (λ=780.24nm) and provides students with an opportunity to investigate characteristics of atomic spectra not evident in the single-photon experiment.
SEMI-FERMIONIC REPRESENTATION FOR SPIN SYSTEMS UNDER EQUILIBRIUM AND NON-EQUILIBRIUM CONDITIONS
Authors: KISELEV M. N.
Published: February 2006

We present a general derivation of semi-fermionic representation for spin operators in terms of a bilinear combination of fermions in real and imaginary time formalisms. The constraint on fermionic occupation numbers is fulfilled by means of imaginary Lagrange multipliers resulting in special shape of quasiparticle distribution functions. We show how Schwinger–Keldysh technique for spin operators is constructed with the help of semi-fermions. We demonstrate how the idea of semi-fermionic representation might be extended to the groups possessing dynamic symmetries. We illustrate the application of semi-fermionic representations for various problems of strongly correlated and mesoscopic physics.
SPECTRUM INDUCED CHANGE IN THE DIFFRACTION OF VECTORIAL NONPARAXIAL PULSED BEAM
Authors: LU D. Q. , HU W. , ZHENG Y. Z. , YANG Z. J.
Published: February 2006

A vectorial nonparaxial correction to an arbitrary scalar paraxial solution of ultrashort pulsed beam is obtained by application of the Fourier transform and angular spectrum presentation methods. In general, the vectorial and nonparaxial property of pulsed beam depends on the pulse shape and its spectrum distribution. As the pulse duration decreases, changes of vectorial and nonparaxial correction depend on the pulse spectrum. Results of three typical pulse shapes are studied for comparison to show the spectrum-induced changes in vectorial nonparaxial propagation of ultrashort pulsed beam.
EXCITATION SPECTRUM AT THE YANG–LEE EDGE SINGULARITY OF THE 2D ISING MODEL
Authors: MCCABE JOHN F. , WYDRO TOMASZ
Published: February 2006

This paper studies the Yang–Lee edge singularity of 2-dimensional (2D) Ising model through a quantum spin chain. In particular, finite-size scaling measurements on the quantum spin chain are used to determine the low-lying excitation spectrum and central charge at the Yang–Lee edge singularity. The measured values are consistent with predictions for the (A4, A1) minimal conformal field theory.
INTERACTING DARK ENERGY AND COSMOLOGICAL EQUATIONS OF STATE
Authors: ZIMDAHL WINFRIED
Published: February 2006

Interactions within the cosmic medium modify its equation of state. We discuss implications of interacting dark energy models both for the spatially homogenous background and for the perturbation dynamics.
HOW RED IS A QUANTUM BLACK HOLE?
Authors: HUSAIN VIQAR , WINKLER OLIVER
Published: February 2006

Radiating black holes pose a number of puzzles for semiclassical and quantum gravity. These include the transplanckian problem — the nearly infinite energies of Hawking particles created near the horizon, and the final state of evaporation. A definitive resolution of these questions likely requires robust inputs from quantum gravity. We argue that one such input is a mechanism for a quantum bound on curvature. We show how the same method leads to an upper limit on the redshift of a Hawking emitted particle, to a maximum temperature for a black hole, and to the prediction of a Planck scale remnant.
A NEW PERSPECTIVE ON GRAVITY AND DYNAMICS OF SPACE–TIME
Authors: PADMANABHAN T.
Published: February 2006

The Einstein–Hilbert action has a bulk term and a surface term (which arises from integrating a four divergence). I show that one can obtain Einstein's equations from the surface term alone. This leads to: (i) a novel, completely self-contained, perspective on gravity and (ii) a concrete mathematical framework in which the description of space–time dynamics by Einstein's equations is similar to the description of a continuum solid in the thermodynamic limit.
METASTABLE MASSIVE GRAVITONS FROM AN INFINITE EXTRA DIMENSION
Authors: SEAHRA SANJEEV S.
Published: February 2006

Motivated by stringy considerations, Randall and Sundrum have proposed a model where all the fields and particles of physics, save gravity, are confined on a four-dimensional brane embedded in five-dimensional anti-de Sitter space. Their scenario features a stable bound state of bulk gravity waves and the brane that reproduces standard general relativity. We demonstrate that in addition to this zero-mode, there is also a discrete set of metastable bound states that behave like massive four-dimensional gravitons which decay by tunneling into the bulk. These are resonances of the bulk-brane system akin to black hole quasinormal modes — as such, they give rise to the dominant corrections to four-dimensional gravity. The phenomenology of braneworld perturbations is greatly simplified when these resonant modes are taken into account, which is illustrated by considering gravitational radiation emitted from nearby sources and early universe physics.
THE COSMOLOGICAL CONSTANT PROBLEM: A STRING THEORY APPROACH
Authors: MAHARANA JNANADEVA
Published: February 2006

We propose that stringy symmetries play a crucial role in the resolution of the cosmological constant problem. In the presence of constant fluxes along compact directions, it is possible to construct potentials for the moduli. For suitable choice of fluxes, they admit minima with non-zero cosmological constant and such solutions break duality symmetry. The corresponding duality symmetric solutions have vanishing cosmological constant. The naturalness hypothesis of 't Hooft may be invoked to argue that the cosmological constant must remain small since symmetry preserving solutions correspond to vanishing cosmological constant.
CLASSICAL AND QUANTUM GENERAL RELATIVITY: A NEW PARADIGM
Authors: GAMBINI RODOLFO , PULLIN JORGE
Published: February 2006

We argue that recent developments in discretizations of classical and quantum gravity imply a new paradigm for doing research in these areas. The paradigm consists in discretizing the theory in such a way that the resulting discrete theory has no constraints. This solves many of the hard conceptual problems of quantum gravity. It also appears as a useful tool in some numerical simulations of interest in classical relativity. We outline some of the salient aspects and results of this new framework.
BUILDING A CASE FOR A PLANCK-SCALE-DEFORMED BOOST ACTION: THE PLANCK-SCALE PARTICLE-LOCALIZATION LIMIT
Authors: AMELINO-CAMELIA GIOVANNI
Published: February 2006

"Doubly-special relativity" (DSR), the idea of a Planck-scale Minkowski limit that is still a relativistic theory, but with both the Planck scale and the speed-of-light scale as nontrivial relativistic invariants, was proposed as a physics intuition for several scenarios which may arise in the study of the quantum-gravity problem, but most DSR studies focused exclusively on the search of formalisms for the description of a specific example of such a Minkowski limit. A novel contribution to the DSR physics intuition came from a recent paper by Smolin suggesting that the emergence of the Planck scale as a second nontrivial relativistic invariant might be inevitable in quantum gravity, relying only on some rather robust expectations concerning the semiclassical approximation of quantum gravity. Here, we attempt to strengthen Smolin's argument by observing that an analysis of some independently-proposed Planck-scale particle-localization limits, such as the "Generalized Uncertainty Principle" often attributed to string theory in the literature, also suggests that the emergence of a DSR Minkowski limit might be inevitable. We discuss a possible link between this observation and recent results on logarithmic corrections to the entropy-area black-hole formula, and observe that both the analysis reported here and Smolin's analysis appear to suggest that the examples of DSR Minkowski limits for which a formalism has been sought in the literature might not be sufficiently general. We also stress that, as we now contemplate the hypothesis of a DSR Minkowski limit, there is an additional challenge for those in the quantum-gravity community attributing to the Planck length the role of "fundamental length scale."
MINIMUM LENGTH FROM FIRST PRINCIPLES
Authors: CALMET XAVIER , GRAESSER MICHAEL L. , HSU STEPHEN D. H.
Published: February 2006

We show that no device or gedanken experiment is capable of measuring a distance less than the Planck length. By "measuring a distance less than the Planck length" we mean, technically, resolve the eigenvalues of the position operator to within that accuracy. The only assumptions in our argument are causality, the uncertainty principle from quantum mechanics and a dynamical criteria for gravitational collapse from classical general relativity called the hoop conjecture. The inability of any gedanken experiment to measure a sub-Planckian distance suggests the existence of a minimal length.
DOES INFLATION PROVIDE NATURAL INITIAL CONDITIONS FOR THE UNIVERSE?
Authors: CARROLL SEAN M. , CHEN JENNIFER
Published: February 2006

If our universe underwent inflation, its entropy during the inflationary phase would have been substantially lower than it is today. Because a low-entropy state is less likely to be chosen randomly than a high-entropy one, inflation is unlikely to arise through randomly-chosen initial conditions. To resolve this puzzle, we examine the notion of a natural state for the universe, and argue that it is a nearly-empty space–time. If empty space has a small vacuum energy, however, inflation can begin spontaneously in this background. This scenario explains why a universe like ours is likely to have begun via a period of inflation, and also provides an origin for the cosmological arrow of time.
THE LENSE–THIRRING EFFECT IN THE JOVIAN SYSTEM OF THE GALILEAN SATELLITES AND ITS MEASURABILITY
Authors: IORIO LORENZO , LAINEY VALÉRY
Published: February 2006

We investigate the possibility of measuring the post-Newtonian general relativistic gravitomagnetic Lense–Thirring effect in the Jovian system of its Galilean satellites Io, Europa, Ganymede and Callisto in view of recent developments in processing and modeling their optical observations spanning a large time interval (125 years). The present day best observations have an accuracy between several kilometers to few tens of kilometers, which is just the order of magnitude of the Lense–Thirring shifts of the orbits of the Galilean satellites over almost a century. From a comparison between analytical development and numerical integration it turns out that, unfortunately, most of the secular component of the gravitomagnetic signature is removed in the process of fitting the initial conditions. Indeed, an estimation of the magnitude of the Lense–Thirring effect in the ephemerides residuals is given; the resulting residuals have a maximum magnitude of 20 meters only (over 125 years).
Expression of TPO and ThOXs in human thyrocytes is downregulated by IL-1α/IFN-γ, an effect partially mediated by nitric oxide
Authors: Gérard Anne-Catherine , Boucquey Marie , van den Hove Marie-France , Colin Ides M.
Published: February 2006

Morphological and functional alterations in Hashimoto's thyroiditis (HT) are predominantly mediated by Th1 cytokines through apoptotic cell death. This ultimate step could be preceded by functional injuries in thyroid hormone synthesis. The action of two Th1 cytokines (IL-1α/IFN-γ) on thyroperoxidase (TPO) and thyroid oxidase (ThOXs) expression was tested in human thyrocytes isolated from normal tissues, Graves' disease (GD) tissues, and autonomous toxic nodules. There was no evidence of cell death. Nitric oxide (NO) release was induced by cytokines but was absent when NG-nitro-l-arginine methyl ester (l-NAME) was coincubated. When thyrotropin (TSH)-incubated normal and GD thyrocytes were treated with IL-1α/IFN-γ, TPO and ThOXs protein and mRNA expression dropped, a decrease partially prevented by l-NAME, suggesting that NO acts as a mediator of Th1 effects. In thyrocytes from autonomous toxic nodules, the high level of TPO and ThOXs protein expression was not influenced by TSH or by cytokines, a finding partially reproduced when normal thyrocytes were treated with increasing concentrations of TSH. In conclusion, incubation of normal or GD thyrocytes with Th1 cytokines induces a significant reduction in TSH-increased expression of both TPO and ThOXs, an effect partially mediated by NO. The thyroid cell function can therefore be severely affected in HT, even when cells remain viable. In autonomous toxic nodules, cells become partially insensitive to exogenous Th1 cytokines.
Liver steatosis coexists with myocardial insulin resistance and coronary dysfunction in patients with type 2 diabetes
Authors: Lautamäki Riikka , Borra Ronald , Iozzo Patricia , Komu Markku , Lehtimäki Terho , Salmi Marko , Jalkanen Sirpa , Airaksinen K. E. Juhani , Knuuti Juhani , Parkkola Riitta , Nuutila Pirjo
Published: February 2006

Nonalcoholic fatty liver (NAFL) is a common comorbidity in patients with type 2 diabetes and links to the risk of coronary syndromes. The aim was to determine the manifestations of metabolic syndrome in different organs in patients with liver steatosis. We studied 55 type 2 diabetic patients with coronary artery disease using positron emission tomography. Myocardial perfusion was measured with [15O]H2O and myocardial and skeletal muscle glucose uptake with 2-deoxy-2-[18F]fluoro-d-glucose during hyperinsulinemic euglycemia. Liver fat content was determined by magnetic resonance proton spectroscopy. Patients were divided on the basis of their median (8%) into two groups with low (4.6 ± 2.0%) and high (17.4 ± 8.0%) liver fat content. The groups were well matched for age, BMI, and fasting plasma glucose. In addition to insulin resistance at the whole body level ( P = 0.012) and muscle ( P = 0.002), the high liver fat group had lower insulin-stimulated myocardial glucose uptake ( P = 0.040) and glucose extraction rate ( P = 0.0006) compared with the low liver fat group. In multiple regression analysis, liver fat content was the most significant explanatory variable for myocardial insulin resistance. In addition, the high liver fat group had increased concentrations of high sensitivity C-reactive protein, soluble forms of E-selectin, vascular adhesion protein-1, and intercellular adhesion molecule-1 ( P < 0.05) and lower coronary flow reserve ( P = 0.02) compared with the low liver fat group. In conclusion, in patients with type 2 diabetes and coronary artery disease, liver fat content is a novel independent indicator of myocardial insulin resistance and reduced coronary functional capacity. Further studies will reveal the effect of hepatic fat reduction on myocardial metabolism and coronary function.
The Presence of Lys27 Instead of Asn27 in Human Phospholamban Promotes Sarcoplasmic Reticulum Ca
2+
-ATPase Superinhibition and Cardiac Remodeling
Authors: Zhao Wen , Yuan Qunying , Qian Jiang , Waggoner Jason R. , Pathak Anand , Chu Guoxiang , Mitton Bryan , Sun Xiaoyin , Jin Jay , Braz Julian C. , Hahn Harvey S. , Marreez Yehia , Syed Faisal , Pollesello Piero , Annila Arto , Wang Hong-Sheng , Schultz Jo El J. , Molkentin Jeffery D. , Liggett Stephen B. , Dorn Gerald W. , Kranias Evangelia G.
Published: February 2006

Background—

Phospholamban (PLN) is an inhibitor of the Ca
2+
affinity of sarcoplasmic reticulum (SR) Ca
2+
-ATPase (SERCA2). The amino acid sequence of PLN is highly conserved, and although all species contain asparagine (Asn), human PLN is unique in containing lysine (Lys) at amino acid 27.

Methods and Results—

Human PLN was introduced in the null background. Expression of human PLN, at similar levels to mouse wild-type PLN, resulted in significant decreases in the affinity of SERCA2 for Ca
2+
, attributed to unique spatial conformation of this PLN form and increases in its monomeric active unit compared with mouse PLN. The increased inhibition by human PLN was associated with attenuated cardiac contractility in the intact-animal, organ, and cardiomyocyte levels and with depressed calcium kinetics. These inhibitory effects could not be fully reversed even on maximal isoproterenol stimulation. There were no alterations in the expression levels of SERCA2, calsequestrin, ryanodine receptor, and FKBP12, although the sodium/calcium exchanger and the L-type Ca
2+
channel expression levels were upregulated. The depressed function resulted in increased heart/body weight ratios and phosphorylation levels of Akt, p38, and Erk1/2.

Conclusions—

Human PLN may play a more inhibitory role than that of other species in Ca
2+
cycling. Expression of human PLN in the mouse is compensated by alterations in Ca
2+
-handling proteins and cardiac remodeling in an effort to normalize cardiac contractility. Thus, the unique amino acid sequence of human PLN may be critical in maintaining a high cardiac reserve, which is of paramount importance in the regulation of human cardiac function.
Dual-Doppler Analysis in a Single Plane from an Airborne Platform
Authors: Leon D. , Vali G. , Lothon M.
Published: February 2006

A modified dual-Doppler analysis technique for use with airborne Doppler radars utilizing two fixed beams is presented. Although the data collected by such a system would ideally lie in the plane defined by the radar beam orientations and the aircraft velocity vector, variations in the aircraft attitude and drift angles lead to displacements between the radar observations and the idealized observation plane. These variations motivated the development of a formal framework in which an a priori velocity estimate is used in conjunction with the two Doppler velocity measurements to form a three-dimensional velocity estimate. Two velocity components, lying within or close to the observation plane, and therefore containing only a small contribution from the a priori velocity estimate, are then extracted from the three-dimensional velocity estimate. Advantages of using the three-dimensional framework include improved accuracy (when an a priori velocity estimate is available) and a framework for assessing the effects of cross-plane contamination on the retrieved velocity components.

The velocity fields retrieved using the modified dual-Doppler analysis are affected by errors in the platform motion correction to the Doppler velocities, random noise in the mean Doppler velocity estimates, displacements between the radar beams (and between the radar beams and the idealized observation plane), and meteorological velocity variations about the a priori velocity estimate. Errors in the platform motion correction remain poorly characterized but are believed to be the largest source of error in many cases. However, these errors result primarily in biases (or low-frequency errors) in the retrieved velocity fields and therefore do not interfere with the ability to resolve actual velocity variations. Random noise in the mean Doppler velocity estimates increases dramatically with decreasing signal-to-noise ratio (SNR) (for SNR < 5 dB) and effectively limits the use of the single-plane dual-Doppler (SPDD) analysis to SNR > 0 dB. Displacements between the volumes sampled by the nadir and slanted beams can also be a significant source of error, especially at larger displacements from the aircraft. Errors resulting from meteorological velocity variations about the a priori velocity estimate tend to be small compared to the velocity variations of interest.

The dual-Doppler analysis presented in this paper has been applied to retrieve two-dimensional velocity fields with a resolution of ∼50 m using Doppler velocities collected using dual-beam configurations of the Wyoming Cloud Radar. Results are in horizontal and vertical planes for marine stratocumulus, cumulus congestus, and for the clear-air boundary layer.
Quantifying Global Uncertainties in a Simple Microwave Rainfall Algorithm
Authors: Kummerow Christian , Berg Wesley , Thomas-Stahle Jody , Masunaga Hirohiko
Published: February 2006

While a large number of methods exist in the literature for retrieving rainfall from passive microwave brightness temperatures, little has been written about the quantitative assessment of the expected uncertainties in these rainfall products at various time and space scales. The latter is the result of two factors: sparse validation sites over most of the world’s oceans, and algorithm sensitivities to rainfall regimes that cause inconsistencies against validation data collected at different locations. To make progress in this area, a simple probabilistic algorithm is developed. The algorithm uses an a priori database constructed from the Tropical Rainfall Measuring Mission (TRMM) radar data coupled with radiative transfer computations. Unlike efforts designed to improve rainfall products, this algorithm takes a step backward in order to focus on uncertainties. In addition to inversion uncertainties, the construction of the algorithm allows errors resulting from incorrect databases, incomplete databases, and time- and space-varying databases to be examined. These are quantified. Results show that the simple algorithm reduces errors introduced by imperfect knowledge of precipitation radar (PR) rain by a factor of 4 relative to an algorithm that is tuned to the PR rainfall. Database completeness does not introduce any additional uncertainty at the global scale, while climatologically distinct space/time domains add approximately 25% uncertainty that cannot be detected by a radiometer alone. Of this value, 20% is attributed to changes in cloud morphology and microphysics, while 5% is a result of changes in the rain/no-rain thresholds. All but 2%–3% of this variability can be accounted for by considering the implicit assumptions in the algorithm. Additional uncertainties introduced by the details of the algorithm formulation are not quantified in this study because of the need for independent measurements that are beyond the scope of this paper. A validation strategy for these errors is outlined.
Adequacy of the In Situ Observing System in the Satellite Era for Climate SST
Authors: Zhang Huai-Min , Reynolds Richard W. , Smith Thomas M.
Published: February 2006

A method is presented to evaluate the adequacy of the recent in situ network for climate sea surface temperature (SST) analyses using both in situ and satellite observations. Satellite observations provide superior spatiotemporal coverage, but with biases; in situ data are needed to correct the satellite biases. Recent NOAA/U.S. Navy operational Advanced Very High Resolution Radiometer (AVHRR) satellite SST biases were analyzed to extract typical bias patterns and scales. Occasional biases of 2°C were found during large volcano eruptions and near the end of the satellite instruments’ lifetime. Because future biases could not be predicted, the in situ network was designed to reduce the large biases that have occurred to a required accuracy. Simulations with different buoy density were used to examine their ability to correct the satellite biases and to define the residual bias as a potential satellite bias error (PSBE).

The PSBE and buoy density (BD) relationship was found to be nearly exponential, resulting in an optimal BD range of 2–3 per 10° × 10° box for efficient PSBE reduction. A BD of two buoys per 10° × 10° box reduces a 2°C maximum bias to below 0.5°C and reduces a 1°C maximum bias to about 0.3°C. The present in situ SST observing system was evaluated to define an equivalent buoy density (EBD), allowing ships to be used along with buoys according to their random errors. Seasonally averaged monthly EBD maps were computed to determine where additional buoys are needed for future deployments. Additionally, a PSBE was computed from the present EBD to assess the in situ system’s adequacy to remove potential future satellite biases.
An Integrated Approach to Error Correction for Real-Time Radar-Rainfall Estimation
Authors: Chumchean Siriluk , Sharma Ashish , Seed Alan
Published: February 2006

A procedure for estimating radar rainfall in real time consists of three main steps: 1) the measurement of reflectivity and removal of known sources of errors, 2) the conversion of the reflectivity to a rainfall rate (Z–R conversion), and 3) the adjustment of the mean field bias as assessed using a rain gauge network. Error correction is associated with the first two steps and incorporates removing erroneous measurements and correcting biases in the Z–R conversion. This paper investigates the relative importance of error correction and the mean field bias–adjustment processes. In addition to the correction for ground clutter, the bright band, and hail, the two error correction strategies considered here are 1) a scale transformation function to remove range-dependent bias in measured reflectivity resulting from an increase in observation volume with range, and 2) the classification of storm types to account for the variation in Z–R relationships for convective and stratiform rainfall. The mean field bias is removed using two alternatives: 1) estimation of the bias at each time step based on the sample of observations available, and 2) use of a Kalman filter to estimate the bias under assumptions of a Markovian dependence structure. A 7-month record of radar and rain gauge rainfall for Sydney, Australia, were used in this study. The results show a stepwise decrease in the root-mean-square error (rmse) of radar rainfall with added levels of error correction using either of the two mean field bias–adjustment methods considered in our study. It was found that although the effects of the two error correction strategies were small compared to bias adjustment, they do form an important step of radar-rainfall estimation.
Nonlinear Viscoelastic Creep Prediction of HDPE-Agro-fiber Composites
Authors: Pramanick A. , Sain M.
Published: February 2006

Agro-based plastic composites are being used as deck boards and other load-bearing materials. In these composites, both fibers and plastics contribute to creep when they carry loads. However, the existing literature concentrates on creep prediction and characterization of composites as a single-phase material. In our study, an attempt is made to develop a generic creep prediction model that describes the creep behavior of composites with the constituents’ creep behavior. The ‘theory of mixture’ for composites is extended to describe the creep behavior of this material, which is two phase. This model is validated for HDPE-rice husk composites with power-law-Boltzmann’s superposition principles. The model works well not only to describe creep, but also its nonlinearity. The model is generic enough for extending it to incorporate varying environmental conditions, such as time and temperature. This is the first model to describe creep for a two-phase bio-based composite. This study is a vanguard in correlating Schapery’s ‘single-phase’ model with a ‘two-phase’ model, where the same is validated for step-loading situations.
A Simple Fatigue Life Model for Three-dimensional Fiber-Polymer Composites
Authors: Mouritz A. P.
Published: February 2006

A simple model is proposed for predicting the fatigue life of three-dimensional (3D) fiber-polymer composite materials for certain cyclic load conditions. The fatigue life can be easily calculated using the model with three empirically determined constants: (i) the ultimate strength of the 3D composite, (ii) the ultimate strength of the two-dimensional (2D) laminate, which is identical in every respect to the 3D composite (e.g., same fiber layup pattern, fiber volume content) except for the through-thickness reinforcement, and (iii) the slope parameter (m) of the fatigue-life (S-log N) curve for the 2D laminate. It is shown that the S-log N curves for stitched composites under cyclic tension-tension and compression-compression loading and for z-pinned composites under cyclic bending loading can be accurately predicted using this model. This model can also approximate the tensile fatigue life of composite lap joints reinforced by stitches or z-pins. However, the model is not reliable in predicting the fatigue life of 3D composites in all cases. It is only accurate when the fatigue damage mechanisms and failure mode of the 3D composite are not altered significantly by the through-thickness reinforcement. Consequently, a limitation of the model is that a priori knowledge of the fatigue damage process of the 3D composite is needed before it can be used with confidence to predict fatigue life. This problem is exasperated by the paucity of information available on the fatigue mechanisms of many types of 3D composites. Until this problem is resolved, the model should only be applied to those types of 3D composites in which their fatigue processes have been determined.
Studies on Properties of Al-Sip Composites Fabricated by Vacuum Pressure Infiltration Method
Authors: Zhang Qiguo , Gu Mingyuan
Published: February 2006

High reinforcement content Al-Sip composites, free of porosity, have been fabricated by vacuum pressure infiltration technology. The properties and fracture behavior of the composites have been studied. Stress results in the brittle fracture of silicon particles. The cracks extend into the ductile matrix and lead to the final fracture of the composite. This explains the fracture behavior of the composite. The coefficient of thermal expansion (CTE) of the composites has been investigated by a high-precision thermomechanical analyzer. The CTEs were measured and compared with the predictions of three theoretical models and the experimental data agreed well with Turner’s model.
Risk and Governance in Water Recycling
Authors: Stenekes Nyree , Colebatch Hal K. , Waite T. David , Ashbolt Nick J.
Published: February 2006

Public acceptance is often seen as a key reason why water-recycling technology is (accepted or) rejected. A common assumption is that projects fail because the general public is unable to comprehend specialist information about risk and the belief that if the public were better informed, they would accept change more readily. This article suggests that rhetoric about acceptance is counterproductive in progressing sustainability as it does not address issues relating to institutional arrangements and reinforces a dichotomy between expert and lay groups. Instead, it is argued that institutional change is needed to build opportunities for constructive public engagement. The failure to implement sustainable water use through recycling can be understood as the result of several factors including present cost structures for water, institutional conservatism, administrative fragmentation, and inadequate involvement of communities in planning. Achieving sustainable water use through recycling may require better coordination between agencies and integrated government policies.
What Does It Take to Be Successful?
Authors: Hermanowicz Joseph C.
Published: February 2006

Physicists were asked the question, “What do you think are the most important qualities needed to be successful at the type of work you do?” The results demonstrate which qualities physicists value and how values vary among the qualities they identified. The results also show how physicists’ beliefs about success vary by the rank of their department, age, productivity, and gender. More generally, the findings cast light on the moral order of physics by eliciting how members of an occupation construe the structure of success in their line of work.
Precaution as an Approach to Technology Development
Authors: Welsh Rick , Ervin David E.
Published: February 2006

The commercialization of transgenic crops has engendered significant resistance from environmental groups and defensive responses from industry. A part of this struggle entails the politicization of science as groups gather evidence from the scholarly literature to defend a supportive or opposing position to transgenic crop commercialization. The authors argue that novel technology development and associated scientific uncertainty have led to two competing approaches to risk management: precaution and ex post trial and error. In this paper we use the controversies over currently commercialized transgenic crops to analyze the debate over these competing approaches. We also suggest a hybrid approach that incorporates a precautionary selection process, but also relies on ex post trial and error after commercialization. This approach is labeled precaution through experience since the development of a technology’s characteristics would ideally take into account previous experience with similar technologies, or rather technologies with similar applications. The authors argue that substantial public participation and dialogue is needed to identify socially desirable crop traits to guide research and development. Policy tools are also recommended that provide incentives to private-sector firms to engineer the identified traits into crops.
What’s Special about Basic Research?
Authors: Calvert Jane
Published: February 2006

“Basic research” is often used in science policy. It is commonly thought to refer to research that is directed solely toward acquiring new knowledge rather than any more practical objective. Recently, there has been considerable concern about the future of basic research because of purported changes in the nature of knowledge production and increasing pressures on scientists to demonstrate the social and economic benefits of their work. But is there really something special about basic research? The author argues here that “basic research” is a flexible and ambiguous concept that is drawn on by scientists to acquire prestige and resources. She shows that it is used for boundary work and gives examples of the work it does in different situations by drawing on interviews with scientists and policy makers on the category of basic research and the changes they have seen in it over time.
Duality and Paradox: Trust and Duplicity in Japanese Business Practice
Authors: Johnston Stewart , Selsky John W.
Published: February 2006

This paper extracts several dualistic constructs from the anthropological literature on Japan and interprets them in terms of recent understandings of paradox in organizational behaviour. Two historical and one contemporary illustration of these dualities within the Japanese business macroculture are offered. Each is interpreted using a normative, critical and paradox approach, and the different approaches are shown to constitute competing explanations of the phenomena. The findings are discussed in terms of how the dualities affect the dynamics of Japanese business conduct and how they reproduce a macroculture among the large business conglomerates. Insights are offered into how individual firm behaviour is shaped by dualistic features of the macroculture. Implications are drawn for how the conduct of cross-cultural business relationships and government policy may be informed by paradox.
Antecedents and Consequences of Organizational Change: ‘Institutionalizing’ the Behavioral Theory of the Firm
Authors: Wezel Filippo Carlo , Saka-Helmhout Ayse
Published: February 2006

In this paper, we highlight the conditions under which organizations initiate changes in two distinct institutional contexts. While the focus within behavioral research has been on aspiration-driven organizational change, the effect of institutional dynamics on the probability of change has been given limited attention. Pooled cross-sectional data covering the period 1920-2001 in the baseball industry are regressed to examine a set of hypotheses that predict the drivers of organizational change in periods of institutional stability and instability, as well as the impact of these changes on performance. Our findings show that the role of aspiration-driven organizational change diminishes in environments characterized by institutional instability. Rather, mimetic and cognitive pressures pave the ground for responses to institutional dynamics. We also shed light on how the relative stability/instability of the institutional environment heterogeneously influences the implications of behavioral changes for organizational performance.
From Brainwashing to Organizational Therapy: A Conceptual and Empirical Journey in Search of ‘Systemic’ Health and a General Model of Change Dynamics. A Drama in Five Acts
Authors: Schein Edgar H.
Published: February 2006

In this article Schein reviews his 50 years of work on culture, careers, coercive persuasion, and process consultation in the form of a drama with acts, scenes and commentary from the chorus. An attempt is made to show how the various concepts all inform the model of ‘change’ that underlies all of this work and how insights about the mechanisms of change already occurred early in the career.
The COX-2 Specific Inhibitor Valdecoxib versus Tramadol in Acute Ankle Sprain
Authors: Ekman Evan F. , Ruoff Gary , Kuehl Kerry , Ralph Lee , Hormbrey Philip , Fiechtner Justus , Berger Manuela F.
Published: February 2006

Background

The cyclooxygenase-2 specific inhibitor valdecoxib has not been approved in the United States for treatment of acute pain.

Hypothesis

Valdecoxib 20 mg twice daily or once daily (both with a 40-mg loading dose) is not clinically inferior to tramadol for treating the signs and symptoms of acute ankle pain.

Study Design

Randomized, controlled clinical trial; Level of evidence, 1.

Methods

Patients (N = 829) with acute firstor second-degree ankle sprain received 7 days’ treatment with valdecoxib 20 mg either twice daily or once daily (both with 40-mg loading dose), tramadol 50 mg 4 times daily, or placebo. The primary end point was Patient's Assessment of Ankle Pain visual analog scale on day 4; a test of noninferiority compared valdecoxib with tramadol.

Results

On day 4, both valdecoxib doses were significantly better versus placebo and were comparable with tramadol in relieving ankle pain. On day 7, valdecoxib, but not tramadol, significantly reduced pain versus placebo. On days 4 and 7, more patients resumed normal walking with valdecoxib (45%-47% and 73%-79%, respectively) than with placebo (35% and 64%, respectively) or tramadol (38% and 67%, respectively). In contrast to valdecoxib, the number of withdrawals due to adverse events was significantly higher in the tramadol group (12.2% vs 3.4%; P = .0005).

Conclusions

Valdecoxib was comparable with tramadol and was significantly better than placebo in treating acute ankle sprain, and it enabled more patients to resume normal walking on days 4 and 7. Both valdecoxib and tramadol were well tolerated.
A Comparison between Clinical Assessment and Magnetic Resonance Imaging of Acute Hamstring Injuries
Authors: Schneider-Kolsky Michal E. , Hoving Jan Lucas , Warren Price , Connell David A.
Published: February 2006

Background

Physicians evaluating hamstring strains in professional football players are increasingly turning to magnetic resonance imaging to support the clinical diagnosis and management of the injury. However, little information is available to assess how magnetic resonance imaging compares with the clinical evaluation in establishing the duration of rehabilitation required.

Hypothesis

Magnetic resonance imaging of hamstring strains can be useful in determining duration of rehabilitation.

Study Design

Cohort study (Diagnosis); Level of evidence, 1.

Methods

Fifty-eight professional football players with a diagnosis of hamstring injury made by the team physician were enrolled in the study. All players underwent magnetic resonance imaging and a clinical evaluation by an independent physical therapist within 3 days of the injury. Presence, type, and location of injury were recorded in each examination. The physical therapist estimated the time required until return to competition, and the radiologist used the length of the injury (coronal view) to establish rehabilitation duration. Both clinicians were blinded to the other modality.

Results

Clinical and magnetic resonance imaging assessments were in agreement in 38 of 58 cases (65.5%). In 18 cases (31.0%), a clinically positive diagnosis was made, but no abnormalities were evident on magnetic resonance imaging. In 2 cases (3.4%), magnetic resonance imaging detected an injury, whereas the clinical examination had negative or equivocal findings. Both clinical examination and magnetic resonance imaging findings were strongly correlated with the actual time required to return to competition (r = .69, P < .001 and r = .58, P < .001, respectively). The correlation coefficient between clinical predictions and magnetic resonance imaging findings was moderate (r = .36, P = .006).

Conclusion

This study shows that magnetic resonance imaging is not required for estimating the duration of rehabilitation of an acute minor or moderate hamstring injury in professional football players.
Weakness in End-Range Plantar Flexion after Achilles Tendon Repair
Authors: Mullaney Michael J. , McHugh Malachy P. , Tyler Timothy F. , Nicholas Stephen J. , Lee Steven J.
Published: February 2006

Background

Separation of tendon ends after Achilles tendon repair may affect the tendon repair process and lead to postoperative end-range plantarflexion weakness.

Hypothesis

Patients will have disproportionate end-range plantarflexion weakness after Achilles tendon repair.

Study Design

Descriptive laboratory study.

Methods

Four-strand core suture repairs of Achilles tendon were performed on 1 female and 19 male patients. Postoperatively, patients were nonweightbearing with the ankle immobilized for 4 weeks. Plantarflexion torque, dorsiflexion range of motion, passive joint stiffness, toe walking, and standing single-legged heel rise (on an incline, decline, and level surface) were assessed after surgery (mean, 1.8 years postoperative; range, 6 months-9 years). Maximum isometric plantarflexion torque was measured at 20° and 10° of dorsiflexion, neutral, and 10° and 20° of plantar flexion. Percentage strength deficit (relative to noninvolved leg) was computed at each angle. Passive dorsiflexion range of motion was measured goniometrically. Passive joint stiffness was computed from increase in passive torque between 10° and 20° of dorsiflexion, before isometric contractions.

Results

Significant plantarflexion weakness was evident on the involved side at 20° and 10° of plantar flexion (34% and 20% deficits, respectively; P < .001), with no torque deficits evident at other angles (6% at neutral, 3% at 10° of dorsiflexion, 0% at 20° of dorsiflexion). Dorsiflexion range of motion was not different between involved and noninvolved sides (P = .7). Passive joint stiffness was 34% lower on the involved side (P < .01). All patients could perform an incline heel rise; 14 patients could not perform a decline heel rise (P < .01).

Conclusion

Disproportionate weakness in end-range plantar flexion, decreased passive stiffness in dorsiflexion, and inability to perform a decline heel rise are evident after Achilles tendon repair. Possible causes include anatomical lengthening, increased tendon compliance, and insufficient rehabilitation after Achilles tendon repair.

Clinical Relevance

Impairments will have functional implications for activities (eg, descending stairs and landing from a jump). Weakness in end-range plantar flexion may be an unrecognized problem after Achilles tendon repair.
The Effect of a Balance Training Program on the Risk of Ankle Sprains in High School Athletes
Authors: McGuine Timothy A. , Keene James S.
Published: February 2006

Background

Ankle sprains are the most common musculoskeletal injuries that occur in athletes, and they have a profound impact on health care costs and resources.

Hypothesis

A balance training program can reduce the risk of ankle sprains in high school athletes.

Study Design

Randomized controlled clinical trial; Level of evidence, 1.

Methods

Seven hundred and sixty-five high school soccer and basketball players (523 girls and 242 boys) were randomly assigned to either an intervention group (27 teams, 373 subjects) that participated in a balance training program or to a control group (28 teams, 392 subjects) that performed only standard conditioning exercises. On-site athletic trainers recorded athlete exposures and sprains.

Results

The rate of ankle sprains was significantly lower for subjects in the intervention group (6.1%, 1.13 of 1000 exposures vs 9.9%, 1.87 of 1000 exposures; P = .04). Athletes with a history of an ankle sprain had a 2-fold increased risk of sustaining a sprain (risk ratio, 2.14), whereas athletes who performed the intervention program decreased their risk of a sprain by one half (risk ratio, 0.56). The ankle sprain rate for athletes without previous sprains was 4.3% in the intervention group and 7.7% in the control group, but this difference was not significant (P = .059).

Conclusion

A balance training program will significantly reduce the risk of ankle sprains in high school soccer and basketball players.