bluuebunny/crossref_metadata_2025 huggingface dataset:
A LONGITUDINAL MODEL OF SPONSORSHIP AND CAREER SUCCESS: A STUDY OF INDUSTRIAL‐ORGANIZATIONAL PSYCHOLOGISTS
Authors: JUDGE TIMOTHY A. , KAMMEYER‐MUELLER JOHN , BRETZ ROBERT D.
Published: July 2007

Drawing from research on the sociology of science, we hypothesized a model of academic career success in an effort to extend research on particularistic and universalistic influences on career success. Results, based on a sample of 154 members of the Society of Industrial and Organizational Psychology, provided support for the hypothesized model. Specifically, doctoral program prestige and publications as a PhD student influenced prestige of the first job. Furthermore, these 2 variables—along with chair publications—influenced career publications, prestige of the first job and career publications influenced extrinsic success (a composite variable comprised of rank, salary, longitudinal citation rates, prestige of current job, fellowships, and presence on editorial boards), and extrinsic success influenced intrinsic career success (career satisfaction). The results further suggest that individual performance has a stronger influence on the career success of industrial‐organizational psychologists than do social networks.
WORK VALUE CONGRUENCE AND INTRINSIC CAREER SUCCESS: THE COMPENSATORY ROLES OF LEADER‐MEMBER EXCHANGE AND PERCEIVED ORGANIZATIONAL SUPPORT
Authors: ERDOGAN BERRIN , KRAIMER MARIA L. , LIDEN ROBERT C.
Published: July 2007

We hypothesized that leader‐member exchange (LMX) and perceived organizational support (POS) would each interact with work value congruence in relation to intrinsic career success. In a sample of 520 teachers from 30 high schools in Turkey, we found that work value congruence was positively related to job and career satisfaction when POS was low but not related to job and career satisfaction when POS was high. Similarly, work value congruence was positively related to career satisfaction when LMX was low but not related when LMX was high. The results contribute to the POS, LMX, and person‐organization fit literatures by demonstrating the compensatory nature of LMX and POS for low value congruence in its relation to job and career satisfaction.
UNDERSTANDING SELF‐OTHER AGREEMENT: A LOOK AT RATER AND RATEE CHARACTERISTICS, CONTEXT, AND OUTCOMES
Authors: OSTROFF CHERI , ATWATER LEANNE E. , FEINBERG BARBARA J.
Published: July 2007

This study investigated (a) the relative importance of a number of biographic (e.g., age, race, gender) and contextual (e.g., span of control, functional area) variables and their interactions on self‐other agreement and (b) the relationship between self‐other agreement and outcome variables such as performance and compensation. Usable data were collected from 3,217 managers and their multi‐source raters in 527 organizations. Multivariate regression procedures (as opposed to categorization procedures) were used to determine the sources of rating disagreement. Results indicated that a significant portion of variance in self‐other ratings was accounted for by the set of background/context variables. Self‐other agreement was also related to performance, compensation, and organizational level, though rating patterns differed.
REMOTE CONTROL: PREDICTORS OF ELECTRONIC MONITORING INTENSITY AND SECRECY
Authors: ALGE BRADLEY J. , BALLINGER GARY A. , GREEN STEPHEN G.
Published: July 2007

Electronic monitoring research has focused predominantly on the reactions of monitored employees and less attention has been paid to the processes that trigger managers' decisions to electronically monitor subordinates. Employing a distributed virtual team simulation, this study examined the effects of dependence, future performance expectations, and propensity to trust on team leaders' decisions to electronically monitor their subordinates. Results indicate that team leaders electronically monitor subordinates more intensely when dependence on subordinates is high or future performance expectations are low. Moreover, team leaders are more likely to monitor in secret when dependence is high or propensity to trust is low. Although team leaders increased their level of electronic monitoring over time, this tendency was stronger when the leader had consistently low performance expectations.
MATCHING INDIVIDUALS TO OCCUPATIONS USING ABILITIES AND THE O*NET: ISSUES AND AN APPLICATION IN CAREER GUIDANCE
Authors: CONVERSE PATRICK D. , OSWALD FREDERICK L. , GILLESPIE MICHAEL A. , FIELD KEVIN A. , BIZOT ELIZABETH B.
Published: July 2007

The Occupational Information Network (O*NET) is a modern computerized occupational database with the potential to be an important resource for numerous work‐related applications. However, developing any O*NET‐based application requires working through conceptual, methodological, and practical issues. This article discusses a set of major issues in the context of using the O*NET for person‐occupation matching purposes, providing examples of how these issues were addressed in a systematic ability‐based matching application developed for career guidance. Specifically, we (a) describe the O*NET and its potential for career guidance, (b) explain person‐occupation fit and its positive consequences for individuals and organizations, (c) compare person‐occupation fit with person‐job fit, (d) discuss matching individuals to occupations empirically using abilities, (e) highlight issues faced in using the O*NJST in this process and give examples of how these issues were addressed in our matching application, and (f) evaluate the functioning of this example matching method.
Prediction of Solvation Sites at the Interface of Src SH2 Domain Complexes Using Molecular Dynamics Simulations
Authors: Geroult Sebastien , Hooda Manisha , Virdee Satpal , Waksman Gabriel
Published: July 2007

Src Homology 2 (SH2) domains are ∼100 amino acid domains that mediate recognition of tyrosine‐phosphorylated sites by signalling proteins. Structures of SH2 domains with bound ligands indicate a potentially important role of water in influencing the binding thermodynamics. In this study, we used molecular dynamics (MD) simulation methods to evaluate solvation sites at the binding interface of the Src SH2 domain. We designed a software, WaRP (Water Residency Potential), to compute the positions of hydration sites from coordinates data of MD simulations and studied the impact of the computed positions on the prediction of the thermodynamics of Src SH2 domain binding to phosphorylated peptides using a method based on accessible surface area buried upon association. Two dually phosphorylated ligands and one monophosphorylated ligand were studied. We showed that the software predicted between 70% and 85% of the crystallographic water molecules depending on complexes. Comparison of the predicted water structures of both the bound and unbound binding partners led to a thorough evaluation of water behaviour during the binding reaction. We also showed that the predicted water structures of all ligand‐SH2 domain structures investigated may be used to derive the entropy change provided that the heat capacity change is known. This study is the first to examine the dynamics of the water structure around the SH2 domain binding interface and contributes to our understanding of binding thermodynamics in SH2 domains.
Estimating and Optimising Analytical and Sampling Uncertainty in Environmental Investigations: Application and Evaluation
Authors: Boon Katy A. , Taylor Paul D. , Ramsey Michael H.
Published: July 2007

Measurements taken to characterise environmental contamination contain uncertainty, which is generated by both field sampling and chemical analyses. Recently devised techniques have been applied for the first time to estimate this uncertainty in the commercial monitoring and assessment of contaminated land. The uncertainty reduces the reliability of the classification of the land that is made following a site investigation. The possible misclassification of areas of land, as a result of measurement uncertainty, can lead to substantial financial penalties, resulting from litigation or unnecessary remediation. Previous studies have developed methods for the estimation and financial optimisation of measurement uncertainty. These methods have now been applied to a series of six contrasting site investigations, which were conducted by various commercial organisations. The previous uses of these sites included a gas works, a tin mine and railway sidings. The measurement uncertainty was successfully estimated for each of the six investigations, showing its applicability to a wide range of different sampling methods, such as trial pits, window sampling and augering. The measurement uncertainty ranged widely between sites from 25% to 158%, indicating that investigations can differ widely in their reliability. The field sampling tended to generate the largest component of the measurement uncertainty when compared to the contribution from the chemical analysis. The Optimised Contaminated Land Investigation (OCLI) method was applied to each site, with the initial aim of estimating the financial losses that could be incurred as a result of misclassifying the land, due to the uncertainty. It showed that the expectation of loss value per sampling location ranged from only £58 at one site to over £ 11 000 at another. The optimal level of uncertainty that produced the minimal financial loss was then calculated for each site. It provided a reduction in the expectation of loss for the whole site of over £ 10 000 at two of the sites and over £90 000 at two others. These findings demonstrate that implementing concepts of uncertainty can have practical benefits in environmental monitoring, and can enable improvements to be made in the quality of sampling and hence of measurements in general.
Precise Determination of Ultra‐Low (sub‐ng g‐1) Level Rare Earth Elements in Ultramafic Rocks by Quadrupole ICP‐MS
Authors: Nakamura Kentaro , Chang Qing
Published: July 2007

We present a new method that determines precisely and accurately rare earth elements (REE) at the sub‐ng g‐1 level in ultramafic rocks based on acid dissolution and quadrupole ICP‐MS with systematic interference corrections on each sample. The method is demonstrated by analyses of the international geochemical reference materials, PCC‐1 (peridotite), DTS‐1 (dunite) and DTS‐2 (dunite) provided by the United States Geological Survey (USGS), and JP‐1 (peridotite) issued by the Geological Survey of Japan (GSJ). Detection limits, as rock equivalent, were calculated to be 0.01‐0.08 ng g‐1 for our instrument, which is sufficiently low compared to the REE concentrations of ultramafic rocks. In addition, procedural blanks of the proposed method were 0.2‐5 pg, which is negligible even for the ultra‐low level REE determinations. Reproducibility obtained from separate dissolutions and measurements of USGS DTS‐2 and GSJ JP‐1 was 3‐6%, which corresponds to the high‐precision data obtained by ID‐TIMS or magnetic sector field ICP‐MS with a desolvating nebuliser. The REE data determined exhibit smooth chondrite‐normalised REE patterns for all of the tested geochemical reference materials, and the abundances are in good agreement with recently published data.
Large Eddy Simulations
of a Brine-Mixing Tank
Authors: Zamankhan Piroz , Huang Jun , Mousavi S.
Mohammad
Published: July 2007

Traditionally, solid–liquid mixing has always been regarded as an empirical technology with many aspects of mixing, dispersing, and contacting related to power draw. One important application of solid–liquid mixing is the preparation of brine from sodium formate. This material has been widely used as a drilling and completion fluid in challenging environments such as in the Barents Sea. In this paper large-eddy simulations, of a turbulent flow in a solid–liquid, baffled, cylindrical mixing vessel with a large number of solid particles, are performed to obtain insight into the fundamental aspects of a mixing tank. The impeller-induced flow at the blade tip radius is modeled by using the sliding mesh. The simulations are four-way coupled, which implies that both solid–liquid and solid–solid interactions are taken into account. By employing a soft particle approach the normal and tangential forces are calculated acting on a particle due to viscoelastic contacts with other neighboring particles. The results show that the granulated form of sodium formate may provide a mixture that allows faster and easier preparation of formate brine in a mixing tank. In addition it is found that exceeding a critical size for grains phenomena, such as caking, can be prevented. The obtained numerical results suggest that by choosing appropriate parameters a mixture can be produced that remains free-flowing no matter how long it is stored before use.
Three-Dimensional Numerical Simulations of Circular Cylinders Undergoing Two Degree-of-Freedom Vortex-Induced Vibrations
Authors: Pontaza Juan P. , Chen Hamn-Ching
Published: July 2007

In an effort to gain a better understanding of vortex-induced vibrations (VIV), we present three-dimensional numerical simulations of VIV of circular cylinders. We consider operating conditions that correspond to a Reynolds number of 105, low structural mass and damping (m*=1.0, ζ*=0.005), a reduced velocity of U*=6.0, and allow for two degree-of-freedom (X and Y) motion. The numerical implementation makes use of overset (Chimera) grids, in a multiple block environment where the workload associated with the blocks is distributed among multiple processors working in parallel. The three-dimensional grid around the cylinder is allowed to undergo arbitrary motions with respect to fixed background grids, eliminating the need for grid regeneration as the structure moves on the fluid mesh.
Motion Analysis of Pendulum Type Isolation Systems During Earthquakes (Probabilistic Study of Isolation Performance of Base Isolated Structure Considering Characteristic Dispersion of Pendulum Type Isolation Systems)
Authors: Okamura Shigeki , Fujita Satoshi
Published: July 2007

Most of the base isolated buildings or structures are built on laminated rubber bearings in order to give them certain natural periods. This situation, however, also encourages structural engineers to research and develop nonrubber-type isolation systems such as linear motion bearing isolators and friction pendulum systems. It is considered that the nonrubber-type isolation systems can be applied to important industrial facilities, such as LNG tanks, boiler facilities, and so on, to refine their seismic reliabilities. This device of a nonrubber-type isolation system uses the energy loss associated with sliding to reduce the deleterious effects of earthquakes. However, when using nonrubber-type isolation systems with sliding in the atmosphere, long term durability of the systems must be taken into account. It may be difficult to maintain the friction coefficient of the system. In this paper, a stochastic study of the effect on rotational motion and isolation performance of two structures subjected to an earthquake with a friction pendulum bearing is analyzed with a Monte Carlo method.
A mechano-acoustic model of the effect of superior canal dehiscence on hearing in chinchilla
Authors: Songer Jocelyn E. , Rosowski John J.
Published: July 2007

Superior canal dehiscence (SCD) is a pathological condition of the ear that can cause a conductive hearing loss. The effect of SCD (a hole in the bony wall of the superior semicircular canal) on chinchilla middle- and inner-ear mechanics is analyzed with a circuit model of the dehiscence. The model is used to predict the effect of dehiscence on auditory sensitivity and mechanics. These predictions are compared to previously published measurements of dehiscence related changes in chinchilla cochlear potential, middle-ear input admittance and stapes velocity. The comparisons show that the model predictions are both qualitatively and quantitatively similar to the physiological results for frequencies where physiologic data are available. The similarity supports the third-window hypothesis of the effect of superior canal dehiscence on auditory sensitivity and mechanics and provides the groundwork for the development of a model that predicts the effect of superior canal dehiscence syndrome on auditory sensitivity and mechanics in humans.
An investigation of transmission coefficients for finite and semi-infinite coupled plate structures
Authors: Skeen Michael B. , Kessissoglou Nicole J.
Published: July 2007

This paper introduces a method for determining the transmission coefficient for finite coupled plates using an analytical waveguide model combined with a scattering matrix. In the scattering matrix method, the amplitudes of the structural waves impinging on a junction are separated into incident, reflected, and transmitted components. The energy flow due to each of these waves is obtained using a wave impedance method, which is subsequently used to determine the transmission coefficient. Transmission coefficients for semi-infinite and finite L-shaped plates are investigated for single and multiple point force excitations, and for controlled incident wave sources. It is shown that the transmission coefficients can also be calculated from details of the modal transmission coefficients and the modal composition of the energy incident on the junction. Results show that the modal transmission coefficients are largely independent of whether the plates have finite or semi-infinite boundary conditions, and are only dependent on the details of the coupling. Finally, frequency averaged transmission coefficients are compared for semi-infinite and finite structures. In the cases considered, it is found that the semi-infinite system is a good approximation for finite systems after frequency averaging, especially if the system is excited with multiple point force excitation.
The influence of signal parameters on the sound source localization ability of a harbor porpoise (Phocoena phocoena)
Authors: Kastelein Ronald A. , de Haan Dick , Verboom Willem C.
Published: July 2007

It is unclear how well harbor porpoises can locate sound sources, and thus can locate acoustic alarms on gillnets. Therefore the ability of a porpoise to determine the location of a sound source was determined. The animal was trained to indicate the active one of 16 transducers in a 16-m-diam circle around a central listening station. The duration and received level of the narrowband frequency-modulated signals (center frequencies 16, 64 and 100kHz) were varied. The animal’s localization performance increased when the signal duration increased from 600to1000ms. The lower the received sound pressure level (SPL) of the signal, the harder the animal found it to localize the sound source. When pulse duration was long enough (≈1s) and the received SPLs of the sounds were high (34–50dB above basic hearing thresholds or 3–15dB above the theoretical masked detection threshold in the ambient noise condition of the present study), the animal could locate sounds of the three frequencies almost equally well. The porpoise was able to locate sound sources up to 124° to its left or right more easily than sounds from behind it.
Poroelastic modeling of seismic boundary conditions across a fracture
Authors: Nakagawa Seiji , Schoenberg Michael A.
Published: July 2007

Permeability of a fracture can affect how the fracture interacts with seismic waves. To examine this effect, a simple mathematical model that describes the poroelastic nature of wave-fracture interaction is useful. In this paper, a set of boundary conditions is presented which relate wave-induced particle velocity (or displacement) and stress including fluid pressure across a compliant, fluid-bearing fracture. These conditions are derived by modeling a fracture as a thin porous layer with increased compliance and finite permeability. Assuming a small layer thickness, the boundary conditions can be derived by integrating the governing equations of poroelastic wave propagation. A finite jump in the stress and velocity across a fracture is expressed as a function of the stress and velocity at the boundaries. Further simplification for a thin fracture yields a set of characteristic parameters that control the seismic response of single fractures with a wide range of mechanical and hydraulic properties. These boundary conditions have potential applications in simplifying numerical models such as finite-difference and finite-element methods to compute seismic wave scattering off nonplanar (e.g., curved and intersecting) fractures.
Sound propagation above a porous road surface with extended reaction by boundary element method
Authors: Anfosso-Lédée Fabienne , Dangla Patrick , Bérengier Michel
Published: July 2007

Acoustic impedance of an absorbing interface is easily introduced in boundary element codes provided that a local reaction is assumed. But this assumption is not valid in the case of porous road surface. A two-domain approach was developed for the prediction of sound propagation above a porous layer that takes into account the sound propagation inside the porous material. The porous material is modeled by a homogeneous dissipative fluid medium. An alternative to this time consuming two-domain approach is proposed by using the grazing incidence approximate impedance in the traditional single-domain boundary element method (BEM). It can be checked that this value is numerically consistent with the surface impedance calculated at the interface from the pressure and surface velocity solutions of the two-domain approach. The single-domain BEM introducing this grazing incidence impedance is compared in terms of sound attenuation with analytical solutions and two-domain BEM. The comparison is also performed with the single-domain BEM using the normal incidence impedance, and reveals a much better accuracy for the prediction of sound propagation above a porous interface.
Blue and fin whale call source levels and propagation range in the Southern Ocean
Authors: Širović Ana , Hildebrand John A. , Wiggins Sean M.
Published: July 2007

Blue (Balaenoptera musculus) and fin whales (B. physalus) produce high-intensity, low-frequency calls, which probably function for communication during mating and feeding. The source levels of blue and fin whale calls off the Western Antarctic Peninsula were calculated using recordings made with calibrated, bottom-moored hydrophones. Blue whales were located up to a range of 200km using hyperbolic localization and time difference of arrival. The distance to fin whales, estimated using multipath arrivals of their calls, was up to 56km. The error in range measurements was 3.8km using hyperbolic localization, and 3.4km using multipath arrivals. Both species produced high-intensity calls; the average blue whale call source level was 189±3dB re:1μPa-1m over 25–29Hz, and the average fin whale call source level was 189±4dB re:1μPa-1m over 15–28Hz. Blue and fin whale populations in the Southern Ocean have remained at low numbers for decades since they became protected; using source level and detection range from passive acoustic recordings can help in calculating the relative density of calling whales.
The bag-of-frames approach to audio pattern recognition: A sufficient model for urban soundscapes but not for polyphonic music
Authors: Aucouturier Jean-Julien , Defreville Boris , Pachet François
Published: July 2007

The “bag-of-frames” approach (BOF) to audio pattern recognition represents signals as the long-term statistical distribution of their local spectral features. This approach has proved nearly optimal for simulating the auditory perception of natural and human environments (or soundscapes), and is also the most predominent paradigm to extract high-level descriptions from music signals. However, recent studies show that, contrary to its application to soundscape signals, BOF only provides limited performance when applied to polyphonic music signals. This paper proposes to explicitly examine the difference between urban soundscapes and polyphonic music with respect to their modeling with the BOF approach. First, the application of the same measure of acoustic similarity on both soundscape and music data sets confirms that the BOF approach can model soundscapes to near-perfect precision, and exhibits none of the limitations observed in the music data set. Second, the modification of this measure by two custom homogeneity transforms reveals critical differences in the temporal and statistical structure of the typical frame distribution of each type of signal. Such differences may explain the uneven performance of BOF algorithms on soundscapes and music signals, and suggest that their human perception rely on cognitive processes of a different nature.
Intelligibility of speech in noise at high presentation levels: Effects of hearing loss and frequency region
Authors: Summers Van , Cord Mary T.
Published: July 2007

These experiments examined how high presentation levels influence speech recognition for high- and low-frequency stimuli in noise. Normally hearing (NH) and hearing-impaired (HI) listeners were tested. In Experiment 1, high- and low-frequency bandwidths yielding 70%-correct word recognition in quiet were determined at levels associated with broadband speech at 75dB SPL. In Experiment 2, broadband and band-limited sentences (based on passbands measured in Experiment 1) were presented at this level in speech-shaped noise filtered to the same frequency bandwidths as targets. Noise levels were adjusted to produce ∼30%-correct word recognition. Frequency bandwidths and signal-to-noise ratios supporting criterion performance in Experiment 2 were tested at 75, 87.5, and 100dB SPL in Experiment 3. Performance tended to decrease as levels increased. For NH listeners, this “rollover” effect was greater for high-frequency and broadband materials than for low-frequency stimuli. For HI listeners, the 75-to87.5-dB increase improved signal audibility for high-frequency stimuli and rollover was not observed. However, the 87.5-to100-dB increase produced qualitatively similar results for both groups: scores decreased most for high-frequency stimuli and least for low-frequency materials. Predictions of speech intelligibility by quantitative methods such as the Speech Intelligibility Index may be improved if rollover effects are modeled as frequency dependent.
Speech signal modification to increase intelligibility in noisy environments
Authors: Yoo Sungyub D. , Boston J. Robert , El-Jaroudi Amro , Li Ching-Chung , Durrant John D. , Kovacyk Kristie , Shaiman Susan
Published: July 2007

The role of transient speech components on speech intelligibility was investigated. Speech was decomposed into two components—quasi-steady-state (QSS) and transient—using a set of time-varying filters whose center frequencies and bandwidths were controlled to identify the strongest formant components in speech. The relative energy and intelligibility of the QSS and transient components were compared to original speech. Most of the speech energy was in the QSS component, but this component had low intelligibility. The transient component had much lower energy but was almost as intelligible as the original speech, suggesting that the transient component included speech elements important to speech perception. A modified version of speech was produced by amplifying the transient component and recombining it with the original speech. The intelligibility of the modified speech in background noise was compared to that of the original speech, using a psychoacoustic procedure based on the modified rhyme protocol. Word recognition rates for the modified speech were significantly higher at low signal-to-noise ratios (SNRs), with minimal effect on intelligibility at higher SNRs. These results suggest that amplification of transient information may improve the intelligibility of speech in noise and that this improvement is more effective in severe noise conditions.
Filament stretching and capillary breakup extensional rheometry measurements of viscoelastic wormlike micelle solutions
Authors: Bhardwaj Avinash , Miller Erik , Rothstein Jonathan P.
Published: July 2007

A filament stretching extensional rheometer and capillary breakup extensional rheometer are used to measure the extensional rheology of a series of wormlike micelle solutions experiencing a uniaxial elongational flow. The experiments are performed using a series of wormlike micelle solutions of both cetylpyridinium chloride and sodium salicylate (NaSal) in an aqueous sodium chloride solution and cetyltrimethylammonium bromide and NaSal in de-ionized water. The linear viscoelasticity of all the wormlike micelle solutions is well described by a Maxwell model with just one or two relaxation times while the steady shear measurements all demonstrate characteristics of shear banding at large shear rates. In transient homogeneous uniaxial extension imposed by a filament stretching rheometer, each of the wormlike micelle solutions demonstrate significant strain hardening. At large extension rates, the wormlike micelle solution filaments are all found to fail through a dramatic rupture near the axial midplane at a constant stress independent of imposed extension rate. The result is an extensional viscosity that decays linearly with increasing extension rate. This filament failure likely stems from the local scission of individual wormlike micelle chains. For the more concentrated solutions, as the imposed extension rate is reduced, a critical extension rate is found below which the filament does not rupture, but instead elastocapillary pinch off is recovered and the elastic tensile stresses achieved in the fluid filament grow far beyond the value observed at rupture. This dramatic upturn in the elastic tensile stress and the extensional viscosity at low extension rates is not intuitively expected and is most likely a result of structural changes to the entangled wormlike micelle solution. Strain hardening is also observed in capillary breakup rheometry experiments, however, when the results of filament stretching and capillary breakup rheometry measurements at nominally the same extension rate are superimposed, the results do not agree; the extensional viscosity measurements from filament stretching are in some instances more than an order of magnitude larger. This result calls into question the use of capillary breakup rheometry for quantitatively measuring the extensional viscosity of wormlike micelle solutions.
Temporary degradation and recovery of drag-reducing surfactant solutions
Authors: Gasljevic K. , Hoyer K. , Matthys E. F.
Published: July 2007

We have investigated the intentional temporary degradation and the subsequent recovery of the drag-reducing properties of surfactant solutions. Degradation was achieved by exposing the fluid to mechanical stresses after which it showed significantly reduced drag reduction capability. The recovery time varies from a fraction of second to several minutes, depending on the surfactant concentration, the counter-ion concentration and the temperature. The recovery process generally showed a linear increase of the drag reduction level with time, with the rate of recovery being essentially independent of the flow velocity and the initial level of degradation, though the recovery at rest is considerably slower than the recovery under turbulent flow conditions. The recovery time decreases sharply with increasing concentration and temperature, and with increasing counter-ion concentration for the cationic surfactant. The mechanical degradation apparently affects not only the shear-induced structure but also the rod-like micelles themselves.
Drop deformation in sheared polymer blends
Authors: Caserta S. , Reynaud S. , Simeone M. , Guido S.
Published: July 2007

Drop deformation in equiviscous polymer blends with dispersed phase volume fraction ranging from 0 to 10% has been investigated by video microscopy and image analysis in a parallel plate shear apparatus. Under steady external flow conditions the shape of individual drops, as measured by the three main axes, the orientation angle and the deformation parameter, showed marked time fluctuations around an average value depending on dispersed phase concentration and on drop capillary number. At small volume fractions the deformed shape was essentially coincident with the isolated drop case, whereas the higher the concentration, the larger the observed drop deformation at a given capillary number. Such deviations from the isolated drop case can be attributed to hydrodynamic interactions, mainly due to flow-induced collisions among drops. The experimental results can be conveniently described by a mean field approximation whereby the forces causing drop deformation are taken as proportional to blend viscosity rather than to continuous phase viscosity. By using this correction, i.e., by calculating the capillary number from blend viscosity, all the data collapsed to the isolated drop case, thus allowing one to exploit the small-deformation theoretical analyses available from the literature to predict the morphology of concentrated polymer blends.
Correlation between stresses and microstructure in concentrated suspensions of non-Brownian spheres subject to unsteady shear flows
Authors: Bricker Jonathan M. , Butler Jason E.
Published: July 2007

Stresses within unsteady simple shear flows of suspensions of non-Brownian spheres constrained to move in the velocity-gradient plane are calculated using Stokesian dynamics simulations. The unsteady flows considered include shear reversal and oscillatory flows of varying strain amplitude. The evolution of the stresses in time are reported along with the corresponding microstructural development for all flow conditions. For shear reversal, the shear stress rapidly decreases to a minimum before gradually returning to the steady state value reached in the previous direction, whereas the normal stress briefly changes sign upon reversal of shear before returning to the steady state value. For oscillatory shear flow, the shear stress increases with total strain before attaining a steady state that depends upon the applied strain amplitude, indicating irreversible behavior even at small strain amplitudes. The shear stresses show a nonmonotonic dependence on the applied strain amplitude that agrees with experimental results [Bricker and Butler, J. Rheol. 50, 711–728 (2006)]. The steady state normal stresses also depend on the strain amplitude and may change signs at low strain amplitudes.
2D Modeling of high-speed fiber spinning with flow-enhanced crystallization
Authors: Kohler William H. , McHugh Anthony J.
Published: July 2007

A two-dimensional (2D) analysis of fiber spinning is presented based on a modified version of the two-phase model [Shrikhande et al., J. Appl. Polym. Sci. 100, 3240–3254 (2006); Kohler et al., J. Macromol. Sci. Phys. 44, 185–202 (2005)] that accounts for flow-enhanced crystallization (FEC). The modified model employs the extended pom-pom (XPP) constitutive equation for the amorphous phase and the rigid rod equation for the semicrystalline phase. Calculations are carried out for the high-speed spinning of nylons, polyethylene terephthalate (PET), and pure poly(L-lactic acid) (PLLA), as well as racemic mixtures of the latter (rPLA). Radial variations in temperature and degree of crystalline transformation and microstructure for the PLLA, rPLA, and higher speed PET examples show significant patterns in the skin and core regions of the fiber that reflect the interplay between FEC and thermal-induced crystallization (TIC). Insight is gained into the relationship of TIC and FEC in determining radial birefringence profiles. Likewise, similar considerations for the particular Nylon and lower speed PET examples indicate their less pronounced radial effects are the result of the same interplay.
Multiplicity, bifurcation, stability and hysteresis in dynamic solutions of film blowing process
Authors: Shin Dong Myeong , Lee Joo Sung , Jung Hyun Wook , Hyun Jae Chun
Published: July 2007

The complicated nonlinear dynamics in film blowing process has been investigated focusing on the multiplicity, bifurcation, and stability in the dynamic solutions of the system using both the theoretical model simulation and experiments. A number of interesting findings have been revealed about the dynamics of the process including a fundamentally different behavior of the system with a maximum of three steady states for the nonisothermal operations in contrast to the isothermal approximation where only two steady states were predicted. These differences have been identified as stemming from the fact that multiple values of a bubble radius at the freezeline height can give the same value of the air pressure inside the bubble depending upon the process conditions and the values of the bifurcation parameters of the system. The stability of the three steady states also displays many different patterns dictated by the process conditions, including the hysteresis in the bifurcation diagrams. These stability results of the system are quite reminiscent of those in the well-known CSTR (continuous stirred tank reactor) cases found in the literature of chemical reaction engineering. The theoretical models of the film blowing system developed by this study produce quite accurate predictions of the bubble and film shape results both in the steady state and the transient solutions as compared with experiments. It is considered that the findings of this study can be readily utilized to enhance the stabilization and optimization of the film blowing operation.
Delayed flow in thermo-reversible colloidal gels
Authors: Gopalakrishnan V. , Zukoski C. F.
Published: July 2007

In this study we present a systematic investigation of the highly nonlinear creep behavior of thermo-reversible gels composed of octadecyl coated silica particles suspended in decalin. These suspensions display a gelation transition below a volume fraction dependent critical temperature. The mechanical response of the resulting gels is characterized by a time for the elastic modulus to recover after preshear that can take several hours. Once steady state is reached, upon application of a constant stress, σ, the compliance of the gel falls into two regimes. Below a critical stress, σcrit, the strain produced in the gel increases slowly with time where the rate of increase decreases with time. Above σcrit, at short times, the strain response is nearly identical to that observed when σ<σcrit. However, at a stress dependent characteristic time, τbreak, the gel yields under the shear stress and begins to flow similar to a liquid leading to a rapid increase in the strain by several orders in magnitude. τbreak decreases with increasing stress and above a certain stress falls below the measurable time windows and the gel appears to flow at the instant that the stress is applied. τbreak is also found to be a strong function of volume fraction and temperature. We develop a simplified model built on the hypothesis that the phenomenon is the result of a competition between the rate of stress-induced bond-breakage events and the rate at which these broken bonds are reformed. Below the critical stress, bond-reformation rates can match the rate at which bonds are broken thereby retaining connectivity within the gel network to support the applied stress and permitting a slow increase in compliance with time. However, above the critical stress, the bond-breakage rates overwhelm the rate at which the gel can heal itself thereby resulting in the eventual degradation of the gel structure and the generation of liquidlike behavior.
Rheology of multiwall carbon nanotube suspensions
Authors: Fan Zhihang , Advani Suresh G.
Published: July 2007

Carbon nanotubes have exhibited unusually large changes in selective physical and mechanical properties when added to polymers or polymer composites in small quantities. To understand their rheological behavior and processibility, we mixed multiwalled carbon nanotubes (MWNT) in epoxy and created suspensions of different dispersion qualities, MWNT aspect ratios, concentrations, suspension network structures, and MWNT orientation states. Their rheological properties were measured with a cone and plate rheometer. It was found that as MWNT dispersion quality improved or their network connections, the aspect ratio or concentration increased, the MWNTs interactions became stronger as indicated by a higher storage modulus G′, complex viscosity ∣η*∣, and steady shear viscosity η. It was found that suspensions which contained a mixture of separated MWNT along with small MWNT aggregates exhibited G′ that was independent of frequency suggesting solidlike behavior. This frequency sweep method could be used to characterize the network structure state for well dispersed nanotube suspensions. The steady shear viscosity η was found to be more sensitive to MWNT separation than G′ and ∣η*∣. All suspensions exhibited shear thinning behavior and nanotubes showed statistically significant alignment in the direction of the shear flow. Aligned MWNT suspensions not only displayed lower η than randomly orientated MWNT suspensions, but also had lower G′ and ∣η*∣ values. Transmission electron microscope (TEM) images of cured suspensions and a recently developed capillary method was used to validate the MWNTs suspension state and its microstructure.
Effects of compatibilizer on immiscible polymer blends near phase inversion
Authors: Martin Jeffrey D. , Velankar Sachin S.
Published: July 2007

We consider the effects of adding a PIB-PDMS diblock copolymer as a compatibilizer in model blends composed of polyisobutylene (PIB) and polydimethylsiloxane (PDMS). The ratio of PIB to PDMS was varied from 20:80 to 80:20 and, hence, these blends are dubbed “concentrated” blends. Most experiments were conducted on blends containing 0.01 or 0.1wt.% compatibilizer. All blends had a droplet-matrix morphology, with the minor phase being the drop phase; thus, phase inversion occured when PIB and PDMS were in a 50:50 ratio. Previously, we have studied effects of compatibilizer in “dilute” blends with PIB and PDMS in a 10:90 ratio. Much of the rheological behavior of the concentrated blends studied here is found to be qualitatively similar to that of dilute blends: compatibilizer increases the terminal complex viscosity, the terminal relaxation time, steady shear viscosity, and the ultimate recovery upon cessation of shear. However, there are two noteworthy differences. The first is that in blends in which PIB forms the continuous phase, the compatibilizer can suppress coalescence of the PDMS drops. Therefore, rheological properties that depend on drop size, e.g., relaxation time or ultimate recovery, are correspondingly affected. Second, the compatibilizer increases the viscosity, especially the terminal complex viscosity, of the concentrated blends far more than it does in dilute blends. This can be interpreted in terms of a partial immobilization of drop surfaces by the compatibilizer. Indeed, in blends with PIB as the continuous phase, the viscosity is only slightly lower than of a suspension of rigid spheres, suggesting that the compatibilizer immobilizes the interface almost completely.
Pharmacodynamic Assessment Based on Mutant Prevention Concentrations of Fluoroquinolones To Prevent the Emergence of Resistant Mutants of
Streptococcus pneumoniae
Authors: Homma Tomoyuki , Hori Toshihiko , Sugimori Giichi , Yamano Yoshinori
Published: July 2007

The objective of this study was to investigate the relationship between pharmacokinetic and pharmacodynamic parameters, on the basis of the mutant prevention concentration (MPC) concept, and the emergence of resistant mutants of
Streptococcus pneumoniae
to fluoroquinolone antibacterials. Some clinical isolates with various MIC and MPC values of moxifloxacin and levofloxacin were exposed under conditions simulating the time-concentration curves observed when moxifloxacin (400 or 80 mg, once a day) or levofloxacin (200 mg, twice a day) was orally administered by using an in vitro pharmacodynamic model. The decrease in susceptibility was evaluated by altering the population analysis profiles after moxifloxacin or levofloxacin treatment for 72 h. When the area under the concentration-time curve from 0 to 24 h (AUC
0-24
)/MPC and peak concentration (
C
max
)/MPC were above 13.41 and 1.20, respectively, complete eradication occurred and no decrease in susceptibility was observed. On the other hand, when AUC
0-24
/MPC and
C
max
/MPC were below 0.84 and 0.08, respectively, the susceptibility decreased. However, the time inside the mutant selective window and the time above the MPC did not show any correlation with the decrease in susceptibility. These results suggest that AUC
0-24
/MPC and
C
max
/MPC are important parameters for predicting the emergence of resistant mutants and that higher values indicate greater effectiveness.
Refuting the net risks test: a response to Wendler and Miller’s “Assessing research risks systematically”
Authors: Weijer C , Miller P B
Published: July 2007

Earlier in the pages of this journal (p481), Wendler and Miller offered the “net risks test” as an alternative approach to the ethical analysis of benefits and harms in research. They have been vocal critics of the dominant view of benefit–harm analysis in research ethics, which encompasses core concepts of duty of care, clinical equipoise and component analysis. They had been challenged to come up with a viable alternative to component analysis which meets five criteria. The alternative must (1) protect research subjects; (2) allow clinical research to proceed; (3) explain how physicians may offer trial enrolment to their patients; (4) address the challenges posed by research containing a mixture of interventions and (5) define ethical standards according to which the risks and potential benefits of research may be consistently evaluated. This response argues that the net risks test meets none of these criteria and concludes that it is not a viable alternative to component analysis.
The philosophical moment of the medical decision: revisiting emotions felt, to improve ethics of future decisions
Authors: Le Coz Pierr , Tassy Sebastien
Published: July 2007

The present investigation looks for a solution to the problem of the influence of feelings and emotions on our ethical decisions. This problem can be formulated in the following way. On the one hand, emotions (fear, pity and so on) can alter our sense of discrimination and lead us to make our wrong decisions. On the other hand, it is known that lack of sensitivity can alter our judgment and lead us to sacrifice basic ethical principles such as autonomy, beneficence, non-maleficence and justice. Only emotions can turn a decision into an ethical one, but they can also turn it into an unreasonable one. To avoid this contradiction, suggest integrating emotions with the decisional factors of the process of “retrospective thinking”. During this thinking, doctors usually try to identify the nature and impact of feelings on the decision they have just made. In this retrospective moment of analysis of the decision, doctors also question themselves on the feelings they did not experience. They do this to estimate the consequences of this lack of feeling on the way they behaved with the patient.