bluuebunny/crossref_metadata_2025 huggingface dataset:
Migration velocities of spherical solid particles near a vertical wall for Reynolds number from 0.1 to 5
Authors: Takemura Fumio
Published: December 2003

Migration velocities of spherical, solid particles suspended in silicon oil near a vertical wall were measured for Reynolds number, Re<5 (Re=2RU/ν, R is the particle radius, U is the sedimentation velocity, and ν is kinematic viscosity). The sedimentation velocity and the distance between the particle and the wall were measured as a function of time and the lateral migration velocity calculated. The migration velocity was also estimated by assuming that for the flow disturbance produced by the particle, the wall lies in either the Stokes or Oseen regions. The results indicate that as the particle migrates away from the wall, that the velocity components parallel to and normal to the wall transit from the Stokes to the Oseen regions. The results also show that the deviation of the calculated values from the measured values increases as Re increases. Empirical equations are proposed to estimate the velocities parallel to and normal to the wall for Re<5.
Laminar Craya–Curtet jets
Authors: Revuelta Antonio , Martı́nez-Bazán Carlos , Sánchez Antonio L. , Liñán Amable
Published: December 2003

This Brief Communication investigates laminar Craya–Curtet flows, formed when a jet with moderately large Reynolds number discharges into a coaxial ducted flow of much larger radius. It is seen that the Craya–Curtet number, C=(Jc/Jj)1/2, defined as the square root of the ratio of the momentum flux of the coflowing stream to that of the central jet, arises as the single governing parameter when the boundary-layer approximation is used to describe the resulting steady slender jet. The numerical integrations show that for C above a critical value Cc the resulting streamlines remain aligned with the axis, while for C<Cc the entrainment demands of the jet cannot be satisfied by the coflow, and a toroidal recirculation region forms. The critical Craya–Curtet number is determined for both uniform and parabolic coflow, yielding Cc=0.65 and Cc=0.77, respectively. The streamlines determined numerically are compared with those obtained experimentally by flow visualizations, yielding good agreement in the resulting flow structure and also in the value of Cc.
A nonlinear atomization model based on a boundary layer instability mechanism
Authors: Yoon Sam S. , Heister Stephen D.
Published: December 2003

An axisymmetric boundary element method has been used to simulate primary atomization of a liquid jet including the effects of the orifice passage geometry. A ring vortex is placed at the orifice exit plane; its strength and location are uniquely determined by the local boundary layer characteristics at this locale. Using this methodology, nonlinear simulations are performed that include hundreds of individual atomization events. A linear analysis due to Ponstein is used to estimate the number of droplets formed from individual rings of fluid which are pinched from the periphery of the jet. Numerous results have been obtained to assess the effects of fluid parameters and orifice design on droplet sizes and atomization characteristics. Predicted droplet sizes show agreement with some limited experimental data.
The hydrodynamics of an oscillating porous sphere
Authors: Looker Jason R. , Carnie Steven L.
Published: December 2003

We determine the hydrodynamics of a rigid, weakly permeable sphere undergoing translational oscillations in an incompressible Newtonian fluid. We check using homogenization and scaling arguments that the flow inside the sphere may be modeled by Darcy’s law and that the Beavers–Joseph–Saffman (BJS) boundary condition still applies for oscillatory flows, provided the frequency of oscillation is not too high. The BJS boundary condition introduces a slip velocity and to leading order in ε=k/a, where k is the particle permeability and a is the radius, the particle may be regarded as impermeable with a slip length independent of frequency. Under these circumstances we solve for the flow field, pressure distribution and drag explicitly and show their behavior for 0⩽ε⩽0.05 and frequencies relevant to electroacoustics (1–10 MHz). From the drag we find the leading order corrections due to particle permeability of the pseudo-steady drag, Basset force and added mass.
Equivalence of two different integral representations of droplet distribution moments in condensing flow
Authors: Hagmeijer Rob
Published: December 2003

It is proved that two different and independently derived integral representations of droplet size distribution moments encountered in the literature are equivalent and, moreover, consistent with the general dynamic equation that governs the droplet size distribution function. One of these representations consists of an integral over the droplet radius while the other representation consists of an integral over time. The proof is based on analytical solution of the general dynamic equation in the absence of coagulation but in the presence of both growth and nucleation. The solution derived is explicit in the droplet radius, which is in contrast with the literature where solutions are presented along characteristics. This difference is essential for the equivalence proof. Both the case of nonconvected vapor as well as the case of convected vapor are presented.
The effects of quadratic drag on the inverse cascade of two-dimensional turbulence
Authors: Grianik N. , Held I. M. , Smith K. S. , Vallis G. K.
Published: December 2003

We explore the effects of a quadratic drag, similar to that used in bulk aerodynamic formulas, on the inverse cascade of homogeneous two-dimensional turbulence. If a two-dimensional fluid is forced at a relatively small scale, then an inverse cascade of energy will be generated that may then be arrested by such a drag at large scales. Both scaling arguments and numerical experiments support the idea that in a statistically steady state the length scale of energy-containing eddies will not then depend on the energy input to the system; rather, the only external parameter that defines this scale is the quadratic drag coefficient itself. A universal form of the spectrum is suggested, and numerical experiments are in good agreement. Further, the turbulent transfer of a passive tracer in the presence of a uniform gradient is well predicted by scaling arguments based solely on the energy cascade rate and the nonlinear drag coefficient.
Two-phase Couette–Taylor flow: Arrangement of the dispersed phase and effects on the flow structures
Authors: Djeridi H. , Gabillet C. , Billard J. Y.
Published: December 2003

This study investigates the mutual interactions between a continuous and a dispersed phase (noncondensable or condensable) in the well-known Couette–Taylor flow between two concentric cylinders at low Reynolds numbers, where the outer cylinder is immobilized. In this experiment, the turbulent structures take place progressively. The noncondensable dispersed phase (air) is introduced either by ventilation, generated by agitation of a free surface situated at the top of the gap between the two cylinders. The condensable dispersed phase is generated by cavitation due to a drop in pressure. Comparisons are made between the single phase flow patterns and those observed in ventilated or cavitating flow. Two particular arrangements of the dispersed phase are experimentally evident, according to the Reynolds number of the flow. For low Reynolds numbers, bubbles are trapped in the core of the Taylor cells, whereas they migrate to the outflow regions near the inner cylinder for higher Reynolds numbers. Assessment of the forces applied to the bubbles and computation of their equilibrium position can act as a base in describing the bubble capture. When bubbles are located near the wall in the outflow region, it is found that the three first instabilities are strongly influenced by the dispersed phase. The cavitating flow is also characterized by an earlier appearance of the third instability.
Vapor flows condensing at incidence onto a plane condensed phase in the presence of a noncondensable gas. II. Supersonic condensation
Authors: Taguchi Satoshi , Aoki Kazuo , Takata Shigeru
Published: December 2003

This paper is the second part of the study of a steady flow of a vapor in a half space condensing onto a plane condensed phase of the vapor at incidence in the presence of a noncondensable gas near the condensed phase. The aim of the study is to clarify the behavior of the vapor and noncondensable gas on the basis of kinetic theory under the assumption that the molecules of the noncondensable gas are mechanically identical with those of the vapor. In the first part [S. Taguchi et al., Phys. Fluids 15, 689 (2003)], the case of subsonic condensation, where the Mach number corresponding to the flow-velocity component perpendicular to the condensed phase at infinity is less than unity, is considered. In the present second part, the case of supersonic condensation is investigated in detail on the same lines as the first part.
A new Eulerian–Lagrangian length-scale in turbulent flows
Authors: Khan M. A. I. , Vassilicos J. C.
Published: December 2003

We introduce a time-dependent Eulerian–Lagrangian length-scale and an inverse locality hypothesis which explain scalings of second order one-particle Lagrangian structure functions observed in kinematic simulations (KS) of homogeneous isotropic turbulence. Our KS results are consistent with the physical picture that particle trajectories are more/less autocorrelated if they are smoother/rougher as a result of encountering less/more straining stagnation points, thus leading to enhanced/reduced turbulent diffusion.
Effects of rotation on turbulent mixing: Nonpremixed passive scalars
Authors: Yeung P. K. , Xu Jia
Published: December 2003

We study by direct numerical simulations the effects of uniform solid-body rotation on passive scalar mixing in turbulent flow, with a focus on the unsteady problem of nonpremixed scalars in forced rotating turbulence with isotropic initial conditions in the velocity field. The expectation of reduced mixing as a result of reduced spectral transfer is readily verified in several aspects, including slower decay rates for the scalar variance, increased scalar mixing times, and slower relaxation of the probability density function from its initially bimodal form to a near-Gaussian shape. Spectral transfer in the scalar field is shown to be dominated by very low-wavenumber velocity modes, and strongly suppressed at higher wavenumbers in the scalar field. Considerable departure from local isotropy is observed in the scalar gradient fluctuations, which are smaller in the direction along the axis of rotation where there is less mixing than in the orthogonal plane. A partial explanation is given in terms of the influence of a modified turbulence velocity structure on directional characteristics of spectral transfer, which leads to anisotropy in the scalar gradient spectra as well as one-dimensional spectra of the scalar field. The observed anisotropy is stronger than that for the velocity field, especially for high rotation rates, and is more pronounced at Schmidt number 1 than at 1/8. A reduction in intermittency compared with nonrotating turbulence is also observed.
Miscible density fingering of chemical fronts in porous media: Nonlinear simulations
Authors: De Wit A.
Published: December 2003

Nonlinear interactions between chemical reactions and Rayleigh–Taylor type density fingering are studied in porous media or thin Hele-Shaw cells by direct numerical simulations of Darcy’s law coupled to the evolution equation for the concentration of a chemically reacting solute controlling the density of miscible solutions. In absence of flow, the reaction-diffusion system features stable planar fronts traveling with a given constant speed v and width w. When the reactant and product solutions have different densities, such fronts are buoyantly unstable if the heavier solution lies on top of the lighter one in the gravity field. Density fingering is then observed. We study the nonlinear dynamics of such fingering for a given model chemical system, the iodate-arsenious acid reaction. Chemical reactions profoundly affect the density fingering leading to changes in the characteristic wavelength of the pattern at early time and more rapid coarsening in the nonlinear regime. The nonlinear dynamics of the system is studied as a function of the three relevant parameters of the model, i.e., the dimensionless width of the system expressed as a Rayleigh number Ra, the Damköhler number Da, and a chemical parameter d which is a function of kinetic constants and chemical concentration, these two last parameters controlling the speed v and width w of the stable planar front. For small Ra, the asymptotic nonlinear dynamics of the fingering in the presence of chemical reactions is one single finger of stationary shape traveling with constant nonlinear speed V>v and mixing zone W>w. This is drastically different from pure density fingering for which fingers elongate monotonically in time. The asymptotic finger has axial and transverse averaged profiles that are self-similar in unit lengths scaled by Ra. Moreover, we find that W/Ra scales as Da−0.5. For larger Ra, tip splittings are observed.
On the role of vorticity in the microstructure of a passive scalar field
Authors: Gonzalez M. , Paranthoën P.
Published: December 2003

Analysis of experimental and modeling results on second-order moments of temperature derivatives downstream of a heated line source suggests a prevailing effect of vorticity in the destruction of anisotropy at this level. The influence of vorticity on small-scale anisotropy is also confirmed in the quite different case of a forced passive scalar in isotropic turbulence; assuming that vorticity promotes reorientation of large instantaneous scalar gradients through rotation of scalar fronts enables us to explain the trend of the scalar gradient skewness with increasing Schmidt number which is observed in recent numerical simulations.
Phase-resolved flow field produced by a vibrating cantilever plate between two endplates
Authors: Kim Yong-Hwan , Wereley Steven T. , Chun Chung-Hwan
Published: December 2003

The flow field created by a vibrating cantilever plate was studied using phase-resolved particle image velocimetry measurements as well as a smoke visualization technique. The cantilever is 38 mm wide, 31 mm long, and is actuated by a piezoelectric material. It is immersed in initially quiescent air, i.e., no free stream velocity is imposed on the system. The cantilever’s vibration frequency in these experiments is set to 180 Hz—the fundamental natural frequency of cantilever. The flow is quite complicated in nature. During each vibration cycle a pair of counter-rotating vortices is generated. A high velocity region is formed between these two counter-rotating vortices in which the maximum velocity is nearly four times the maximum speed of the free end of the plate. Front and rear walls are installed at the lateral edges of the cantilever initially with the thought of making the flow quasi-two-dimensional. While a two-dimensional flow field is indeed formed near the cantilever tip, the flow downstream of the tip is complex and three-dimensional. Phase-resolved velocity fields for five different amplitudes are acquired in detail. The corresponding Reynolds numbers Reh based on the cantilever tip vibration amplitude and the tip speed are 146, 126, 101, 72, and 43, respectively. The nondimensionalized velocity fields are almost identical and symmetric near the tip, but asymmetric flows are formed and the nondimensionalized velocity fields are no longer identical further downstream of the tip. The time dependent circulation of each vortex is calculated by applying the general theory of oscillating, deformable airfoils and compared to the experimental circulation.
Double diffusion natural convection in a rectangular enclosure filled with binary fluid saturated porous media: The effect of lateral aspect ratio
Authors: Mohamad A. A. , Bennacer R. , Azaiez J.
Published: December 2003

Three-dimensional, double diffusion, natural convection in a rectangular enclosure filled with binary fluid saturating porous media is investigated numerically. The effect of lateral aspect ratio on the heat, mass, and momentum transfer is systematically studied. For certain range of parameters, it is interesting to find that the flow patterns may duplicate themselves as the lateral aspect ratio increases by integer factors, which is similar to longitudinal roll formation in a Rayleigh–Bénard problem. For the mentioned range of parameters the change in the lateral aspect ratio has no influence on the rates of heat and mass transfer. However, for other ranges of parameters, the flow exhibits completely different patterns and the rates of heat and mass transfer are influenced drastically compared with that of cubic cavity. In general, the flow of three- and two-dimensional results are difficult to justify, especially if interest is on the flow structure.
Gaseous slip models based on the Langmuir adsorption isotherm
Authors: Myong R. S.
Published: December 2003

On the basis of Langmuir’s theory of adsorption of gases on solids, a robust gaseous slip model is presented. The concept of accommodation coefficient and the difference of gas particles are explained within the new framework. It turned out that the Langmuir model recovers the Maxwell model in the first-order approximation in the case of the microchannel gas flow. In order to validate the new approach, the model is applied to problems of technical interests: pressure-driven microchannel gas flow and low Reynolds number gas flow past a sphere. With the help of previous theoretical and experimental results it is shown that with an adjustable parameter the model in low-speed creeping regime with moderate Knudsen numbers yields a prediction in qualitative agreement with the data.
Compressibility effects on the Rayleigh–Taylor instability growth between immiscible fluids
Authors: Livescu D.
Published: December 2003

The linearized Navier–Stokes equations for a system of superposed immiscible compressible ideal fluids are analyzed. The results of the analysis reconcile the stabilizing and destabilizing effects of compressibility reported in the literature. It is shown that the growth rate n obtained for an inviscid, compressible flow in an infinite domain is bounded by the growth rates obtained for the corresponding incompressible flows with uniform and exponentially varying density. As the equilibrium pressure at the interface p∞ increases (less compressible flow), n increases towards the uniform density result, while as the ratio of specific heats γ increases (less compressible fluid), n decreases towards the exponentially varying density incompressible flow result. This remains valid in the presence of surface tension or for viscous fluids and the validity of the results is also discussed for finite size domains. The critical wavenumber imposed by the presence of surface tension is unaffected by compressibility. However, the results show that the surface tension modifies the sensitivity of the growth rate to a differential change in γ for the lower and upper fluids. For the viscous case, the linearized equations are solved numerically for different values of p∞ and γ. It is found that the largest differences compared with the incompressible cases are obtained at small Atwood numbers. The most unstable mode for the compressible case is also bounded by the most unstable modes corresponding to the two limiting incompressible cases.
Thermocapillary convection in the over-filled and partially filled cavities
Authors: El-Gammal M. , Furmanski P. , Floryan J. M.
Published: December 2003

Marangoni convection in a cavity with a non-planar free upper surface and differentially heated sidewalls is investigated. The results show the existence of limit points beyond which processes leading to the interface rupture set in. It is demonstrated that the cavity over-filling may delay the onset of the rupture.
A note on power-law scaling in a Taylor–Couette flow
Authors: Lim T. T. , Tan K. S.
Published: December 2003

Recent studies [Lathrop et al., Phys. Rev. A 46, 6390 (1992); Lewis et al., Phys. Rev. E 59, 5457 (1999)] on Taylor–Couette flow, where the inner cylinder is rotating and the outer one is at rest, show that, despite earlier predictions [Wendt, Ing. Arch. 4, 557 (1933); Tong et al., Phys. Rev. Lett. 65, 2780 (1990)], the non-dimensional torque (G=T/ρν2L) does not follow a fixed power-law scaling (i.e., G∼Reα, where α is a constant value) for 800<Re<1.23×106. Here, we perform simultaneous flow visualization and high precision torque measurements of the same flow configuration using a Haake RS-75 Rheometer to establish if this is also true in the lower Reynolds number range (Re<800). Results show that, although α varies with the Reynolds number, it can be approximated reasonably well with a constant value α=1 for Re/Rec<1 and α=1.5 for 1.5<Re/Rec<6.32. The latter finding is in good agreement with that of Wendt [Ing. Arch. 4, 557 (1933)]. A possible explanation for the differences with the results of earlier studies is provided in this paper.
Neural Substrates of Eyeblink Conditioning: Acquisition and Retention
Authors: Christian Kimberly M. , Thompson Richard F.
Published: December 2003

Classical conditioning of the eyeblink reflex to a neutral stimulus that predicts an aversive stimulus is a basic form of associative learning. Acquisition and retention of this learned response require the cerebellum and associated sensory and motor pathways and engage several other brain regions including the hippocampus, neocortex, neostriatum, septum, and amygdala. The cerebellum and its associated circuitry form the essential neural system for delay eyeblink conditioning. Trace eyeblink conditioning, a learning paradigm in which the conditioned and unconditioned stimuli are noncontiguous, requires both the cerebellum and the hippocampus and exhibits striking parallels to declarative memory formation in humans. Identification of the neural structures critical to the development and maintenance of the conditioned eyeblink response is an essential precursor to the investigation of the mechanisms responsible for the formation of these associative memories. In this review, we describe the evidence used to identify the neural substrates of classical eyeblink conditioning and potential mechanisms of memory formation in critical regions of the hippocampus and cerebellum. Addressing a central goal of behavioral neuroscience, exploitation of this simple yet robust model of learning and memory has yielded one of the most comprehensive descriptions to date of the physical basis of a learned behavior in mammals.
Spatial Learning in the 5-HT1B Receptor Knockout Mouse: Selective Facilitation/Impairment Depending on the Cognitive Demand
Authors: Buhot Marie-Christine , Wolff Mathieu , Benhassine Narimane , Costet Pierre , Hen René , Segu Louis
Published: December 2003

Age-related memory decline is associated with a combined dysfunction of the cholinergic and serotonergic systems in the hippocampus and frontal cortex, in particular. The 5-HT1B receptor occupies strategic cellular and subcellular locations in these structures, where it plays a role in the modulation of ACh release. In an attempt to characterize the contribution of this receptor to memory functions, 5-HT1B receptor knockout (KO) mice were submitted to various behavioral paradigms carried out in the same experimental context (water maze), which were aimed at exposing mice to various levels of memory demand. 5-HT1BKO mice exhibited a facilitation in the acquisition of a hippocampal-dependent spatial reference memory task in the Morris water maze. This facilitation was selective of task difficulty, showing thus that the genetic inactivation of the 5-HT1B receptor is associated with facilitation when the complexity of the task is increased, and reveals a protective effect on age-related hippocampal-dependent memory decline. Young-adult and aged KO and wild-type (WT) mice were equally able to learn a delayed spatial matching-to-sample working memory task in a radial-arm water maze with short (0 or 5 min) delays. However, 5-HT1BKO mice, only, exhibited a selective memory impairment at intermediate and long (15, 30, and 60 min) delays. Treatment by scopolamine induced the same pattern of performance in wild type as did the mutation for short (5 min, no impairment) and long (60 min, impairment) delays. Taken together, these studies revealed a beneficial effect of the mutation on the acquisition of a spatial reference memory task, but a deleterious effect on a working memory task for long delays. This 5-HT1BKO mouse story highlights the problem of the potential existence of “global memory enhancers.”
The Antimetabolite ara-CTP Blocks Long-Term Memory of Conditioned Taste Aversion
Authors: Wang Jianpeng , Ren Keqin , Pérez Javier , Silva Alcino J. , Peña de Ortiz Sandra
Published: December 2003

We examined the hypothesis that processes related to DNA recombination and
repair are involved in learning and memory. Rats received
intracerebroventricular (icv) infusions of the antimetabolite
1-beta-D-arabinofuranosylcytosine triphosphate (ara-CTP) or its precursor
cytosine arabinoside (ara-C) 30 min prior to conditioned taste aversion (CTA)
training. Both ara-CTP and ara-C caused significant impairments in long-term
memory (LTM) of CTA. Control experiments indicate that the effect of ara-CTP
on CTA memory is related to interference with learning. Furthermore, as it was
previously demonstrated for the protein synthesis inhibitor anisomycin,
ara-CTP had no effect on CTA memory when it was injected 1 h after training.
Importantly, although both ara-CTP and anisomycin significantly blocked LTM in
the task, short-term memory (STM) measured 1 h after training was not affected
by either of the drugs. Finally, ara-CTP had no effect on in vitro
transcription, but it did effectively block nonhomologous DNA end joining
(NHEJ) activity of brain protein extracts. We suggest that DNA ligase-mediated
DNA recombination and repair processes are necessary for the expression of LTM
in the brain.
Basolateral Amygdala Lesions Do Not Prevent Memory of Context-Footshock Training
Authors: Berlau Daniel J. , McGaugh James L.
Published: December 2003

The present studies examined the effects of basolateral amygdala (BLA)
lesions induced prior to or after context-footshock training on 48-h memory,
using several retention measures. In experiment 1, male Sprague-Dawley rats
with bilateral BLA lesions (NMDA, 12.5 mg/mL, 0.2 μL) were given footshock
training in one compartment of a two-compartment alley. Rats were habituated
to the alley and 24 h later were given two footshocks in the shock
compartment. Retention was tested 48 h later, using latency to enter the shock
compartment and time spent freezing as measures of memory. Two days later,
they were tested again and received a footshock on each re-entry of the shock
compartment prior to remaining in the safe compartment for 200 consecutive
seconds. The BLA lesions did not block retention as assessed by freezing or
number of re-entries of the shock compartment. In experiment 2, no prior
habituation was given, and only one footshock was used for the training. BLA
lesions did not block retention, as indicated by latencies to enter the shock
compartment on a 48-h test or by number of entries of the shock compartment.
Experiment 3 examined the effects of the GABAA agonist muscimol
infused into the BLA prior to the 48-h retention test. The muscimol infusions
decreased retention test entrance latencies but did not block retention as
assessed by the number of subsequent entries of the shock compartment. These
findings provide additional evidence that an intact BLA is not required for
the acquisition or retention of context-footshock training.
Long-Term Plasticity of Intrinsic Excitability: Learning Rules and Mechanisms
Authors: Daoudal Gaël , Debanne Dominique
Published: December 2003

Spatio-temporal configurations of distributed activity in the brain is thought to contribute to the coding of neuronal information and synaptic contacts between nerve cells could play a central role in the formation of privileged pathways of activity. Synaptic plasticity is not the exclusive mode of regulation of information processing in the brain, and persistent regulations of ionic conductances in some specialized neuronal areas such as the dendrites, the cell body, and the axon could also modulate, in the long-term, the propagation of neuronal information. Persistent changes in intrinsic excitability have been reported in several brain areas in which activity is elevated during a classical conditioning. The role of synaptic activity seems to be a determinant in the induction, but the learning rules and the underlying mechanisms remain to be defined. We discuss here the role of synaptic activity in the induction of intrinsic plasticity in cortical, hippocampal, and cerebellar neurons. Activation of glutamate receptors initiates a long-term modification in neuronal excitability that may represent a parallel, synergistic substrate for learning and memory. Similar to synaptic plasticity, long-lasting intrinsic plasticity appears to be bidirectional and to express a certain level of input or cell specificity. These nonsynaptic forms of plasticity affect the signal propagation in the axon, the dendrites, and the soma. They not only share common learning rules and induction pathways with the better-known synaptic plasticity such as NMDA receptor dependent LTP and LTD, but also contribute in synergy with these synaptic changes to the formation of a coherent engram.
Recognition Memory for Complex Visual Discriminations Is Influenced by Stimulus Interference in Rodents With Perirhinal Cortex Damage
Authors: Gilbert Paul E. , Kesner Raymond P.
Published: December 2003

Rats with perirhinal cortex (PRC), hippocampal, or sham lesions were
trained on a successive discrimination go/no-go task to examine recognition
memory for an array of visual objects with varying interference among the
objects in the array. Rats were trained to recognize a target array consisting
of four particular objects that could be presented in any one of four possible
configurations to cover baited food wells. If the four target objects were
presented, the rat should displace each object to receive food. However, if a
novel object replaced any one or more of the target objects, then the rat
should withhold its response. The number of novel objects presented on
nonrewarded trials varied from one to four. The fewer the number of novel
objects in the array, the more interference the array shared with the target
array, therefore increasing task difficulty. An increased number of novel
objects should result in less interference with the target array and decreased
task difficulty. Although accuracy was slightly lower in rats with hippocampal
lesions compared with controls, the learning of the groups was not
statistically different. In contrast, rats with PRC lesions were significantly
impaired in learning compared with both control and hippocampal-lesioned rats.
The results suggest that recognition memory for complex visual discriminations
is affected by stimulus interference in rodents with PRC damage.
Emergence of a Cue Strategy Preference on the Water Maze Task in Aged C57B6 × SJL F1 Hybrid Mice
Authors: Nicolle Michelle M. , Prescott Sonya , Bizon Jennifer L.
Published: December 2003

The effects of age on cue learning, spatial reference memory, and strategy preference were assessed in B6 × SJL F1 mice by using the Morris water maze. This mouse strain is of particular interest because it is the background strain for a common transgenic model of Alzheimer's disease, the Tg2576 mouse, which develops plaques and other neurobiological markers of pathology beginning at 8 mo and increasing in severity with advanced age. In the current study, 12- and 23-mo-old C57B6 × SJL F1 mice were serially trained in cue and place versions of the Morris water maze task. At the completion of training, mice received a strategy probe test in which place (hidden) and cue (visible) strategies were in competition. Cue and spatial learning ability was maintained between 12 and 23 mo of age; however, on the strategy preference probe test, the 23-mo-old mice exhibited a significant bias toward the selection of a cue strategy. There was no relationship between strategy preference in the probe test and spatial learning ability, but the 23-mo-old mice did exhibit a strong trend toward shorter latencies during visible platform training, possibly reflecting the enhanced function of striatal-based neural systems in aging. These data demonstrate that 23-mo-old C57B6 × SJL F1 mice are capable of effective place learning, but if a place strategy is pitted against the use of a cue strategy, the use of a cue strategy predominates in the aged mice. The strategy preference observed here may reflect an emergence of differential processing in underlying brain circuitry with age in the B6 × SJL F1 mouse strain.
In Vitro Analog of Classical Conditioning of Feeding Behavior in
Aplysia
Authors: Mozzachiodi Riccardo , Lechner Hilde A. , Baxter Douglas A. , Byrne John H.
Published: December 2003

The feeding behavior of Aplysia californica can be classically
conditioned using tactile stimulation of the lips as a conditioned stimulus
(CS) and food as an unconditioned stimulus (US). Moreover, several neural
correlates of classical conditioning have been identified. The present study
extended previous work by developing an in vitro analog of classical
conditioning and by investigating pairing-specific changes in neuronal and
synaptic properties. The preparation consisted of the isolated cerebral and
buccal ganglia. Electrical stimulation of a lip nerve (AT4) and a
branch of the esophageal nerve (En2) served as the CS and US,
respectively. Three protocols were used: paired, unpaired, and US alone. Only
the paired protocol produced a significant increase in CS-evoked fictive
feeding. At the cellular level, classical conditioning enhanced the magnitude
of the CS-evoked synaptic input to pattern-initiating neuron B31/32. In
addition, paired training enhanced both the magnitude of the CS-evoked
synaptic input and the CS-evoked spike activity in command-like neuron CBI-2.
The in vitro analog of classical conditioning reproduced all of the cellular
changes that previously were identified following behavioral conditioning and
has led to the identification of several new learning-related neural changes.
In addition, the pairing-specific enhancement of the CS response in CBI-2
indicates that some aspects of associative plasticity may occur at the level
of the cerebral sensory neurons.
Impaired Visual and Odor Recognition Memory Span in Patients With Hippocampal Lesions
Authors: Levy Daniel A. , Manns Joseph R. , Hopkins Ramona O. , Gold Jeffrey J. , Broadbent Nicola J. , Squire Larry R.
Published: December 2003

In a recent study, rats with hippocampal lesions performed as well as did
unoperated rats on an olfactory memory span task, performing ∼80% correct
even when the span length reached 24 odors. This finding seems potentially at
odds with demonstrations that memory-impaired patients typically fail tasks in
which large amounts of information must be retained. Accordingly, we have
assessed recognition memory span performance for line drawings of objects,
designs, and odors in amnesic patients with damage thought to be limited to
the hippocampal region. The patients were impaired on all three tasks. We
consider possible explanations for the difference between the findings for
humans and rats, including the fact that olfactory function is particularly
well-developed in rodents.
Histidine-Decarboxylase Knockout Mice Show Deficient Nonreinforced Episodic Object Memory, Improved Negatively Reinforced Water-Maze Performance, and Increased Neo- and Ventro-Striatal Dopamine Turnover
Authors: Dere Ekrem , De Souza-Silva Maria A. , Topic Bianca , Spieler Richard E. , Haas Helmut L. , Huston Joseph P.
Published: December 2003

The brain's histaminergic system has been implicated in hippocampal synaptic plasticity, learning, and memory, as well as brain reward and reinforcement. Our past pharmacological and lesion studies indicated that the brain's histamine system exerts inhibitory effects on the brain's reinforcement respective reward system reciprocal to mesolimbic dopamine systems, thereby modulating learning and memory performance. Given the close functional relationship between brain reinforcement and memory processes, the total disruption of brain histamine synthesis via genetic disruption of its synthesizing enzyme, histidine decarboxylase (HDC), in the mouse might have differential effects on learning dependent on the task-inherent reinforcement contingencies. Here, we investigated the effects of an HDC gene disruption in the mouse in a nonreinforced object exploration task and a negatively reinforced water-maze task as well as on neo- and ventro-striatal dopamine systems known to be involved in brain reward and reinforcement. Histidine decarboxylase knockout (HDC-KO) mice had higher dihydrophenylacetic acid concentrations and a higher dihydrophenylacetic acid/dopamine ratio in the neostriatum. In the ventral striatum, dihydrophenylacetic acid/dopamine and 3-methoxytyramine/dopamine ratios were higher in HDC-KO mice. Furthermore, the HDC-KO mice showed improved water-maze performance during both hidden and cued platform tasks, but deficient object discrimination based on temporal relationships. Our data imply that disruption of brain histamine synthesis can have both memory promoting and suppressive effects via distinct and independent mechanisms and further indicate that these opposed effects are related to the task-inherent reinforcement contingencies.
Introduction Personnel economics: theoretical perspectives and empirical evidence
Authors: Rullière Jean‐Louis , Villeval Marie‐Claire
Published: December 2003

Introduces the special issue on personnel economics and outlines the themes discussed in the papers contained within.
An investigation into the role of human capital competences and their pay‐off
Authors: Heijke Hans , Meng Christoph , Ramaekers Ger
Published: December 2003

In this paper, the role of three different types of competences in the labour market for higher education graduates is investigated. The article distinguishes discipline‐specific competences, general academic competences and management competences, the first being an example of competences acquired at school, which are of direct use in the labour market, the second being a type of competences also acquired in school, but which fulfil an indirect role by facilitating the acquisition of new competences after graduation from school, and the third, management competences, being an example of competences acquired mainly in a working context and, like discipline‐specific competences, being of direct use in that context. This paper shows that, first, the level of discipline‐specific competences obtained in higher education offers a comparative advantage for graduates working inside the own discipline‐specific domain, and therefore has a pay‐off for those graduates who are able to find a job in this domain; second, the management competences are valued in the labour market but seem to be more likely acquired in a working context than in higher education, and third, the general academic competences acquired in higher education do not pay off directly, but have a significant supportive role when learning competences that have a direct pay‐off in the labour market, like management competences, but are more likely acquired outside education.
Returns to tenure, firm‐specific human capital and worker heterogeneity
Authors: Bingley Paul , Westergaard‐Nielsen Niels
Published: December 2003

Workers with longer job tenure are paid more, on average, than those with shorter tenure. This paper re‐opens the debate about whether individual financial returns to tenure are due to firm‐specific human capital accumulation or sorting according to unobserved individual productivity heterogeneity. The paper constructs worker‐firm employment histories 1964‐1998 for all residents of Denmark and links this to wage and demographic information for all private sector workers 1980‐1998. All firm closures are observed, and following Kletzer we exploit these exogenous worker displacements from larger firms to distinguish between firm‐specific human capital and worker heterogeneity. Although the proportion of tenure returns due to firm‐specific human capital is smaller than that found in the USA, it has increased from 10 per cent in 1980 to 30 per cent in 1998 in Denmark. This change coincides with decentralisation of the wage bargaining process and may be explained by the increased freedom to write individual contracts.
Careers and wages within large firms: evidence from a matched employer‐employee data set
Authors: Lima Francisco , Telhado Pereira Pedro
Published: December 2003

The relationship between the workers' career and wages is studied using a longitudinal sample of firms. The analysis shows that the interactions of human capital attributes with the hierarchical levels are an important determinant of wages. The relationship between wage growth and several career events is characterized, namely, the effects of demotions and different types of promotions on wage paths. The wage‐career dynamics generates a U‐shape to the wage premiums for promotions over the hierarchical ladder. In the context of the model discussed, this shape suggests a stronger employer learning and/or human capital accumulation effect at the bottom of the hierarchy and a stronger job assignment effect at the top.
An analysis of the theory of biased contests in an organisational setting
Authors: Barmby Tim , Bridges Sarah
Published: December 2003

This paper uses personnel data gathered from a large financial sector firm to examine the idea of biased contests. The pattern of scores attained by individual workers in performance ratings is used to explain the probability of subsequent promotion within the organisation. Initial empirical evidence is presented, which gives some support for the theory.
Job assignment and bandit problems
Authors: Valsecchi Irene
Published: December 2003

The paper is concerned with dynamic job assignment when observed performance is an imperfect signal of the worker's type. When the rate of learning from past performance depends upon the particular job performed, promotion can be due to good performance only at a job for which the resulting probability of mistaking a low‐ability type for a high‐ability type is higher than for the job the worker is upgraded to. Income risk can be greater for old workers than for young workers. The length of the worker's active life is relevant for job mobility notwithstanding optimal myopic procedures for job assignment. The dynamic perspective induced by learning can generate new forms of opportunism.
Ostracism in work teams: a public good experiment
Authors: Masclet David
Published: December 2003

This paper provides an experimental examination of the effects of ostracism on cooperation. Ostracism is one of the most radical forms of peer pressure. More generally, ostracism is the exclusion of disapproved individuals from interaction with a social group. By performing a laboratory experiment involving a public good game with exclusion, the paper provides empirical evidence that threats of exclusion increase contributions. The results show that subjects exclude their peers for two reasons. Subjects are willing to punish unfair behaviors (non‐strategic reason) and expect changes in behavior in response to exclusions (strategic reason).
The role of socio‐cultural, political‐legal, economic, and educational dimensions in quality management
Authors: Prasad Sameer , Tata Jasmine
Published: December 2003

Quality management practices have recently flourished across the globe. In this research we review and integrate the literature by identifying and organizing significant research findings, and develop a conceptual model of the relationships between international environmental conditions (e.g. socio‐cultural, political‐legal, economic, and educational factors) and dimensions of quality management (e.g. strategic quality planning, customer focus and satisfaction, human resource development and management, information and analysis, management of process quality, and quality and operational results). The model developed here helps us move beyond examining the differences in quality practices across countries to an understanding of why such differences occur, and helps practitioners gain a better perspective on how quality management techniques can be adopted in different regions around the world.
Managing planned and emergent change within an operations management environment
Authors: Bamford David R. , Forrester Paul L.
Published: December 2003

Organisational change, as a general topic, has been extensively researched since the 1950s, as evidenced by the proliferation of papers in the last five decades. As a research topic within operations management, it offers fascinating insights into the way manufacturing organisations function and adapt in reality. This paper evaluates what has worked, and what has not been effective, within a UK‐based manufacturing company, tracking multiple change initiatives over several years across two company sites. The core research focused on the implementation of change initiatives based on common constructs, such as planned change, as defined by management writers and consultants. From the research it emerged that a realistic interpretation of the change process had to take into account multiple and varied forces, such as: customers and suppliers; the economic environment; national and international legislation; the history of the organisation; etc. The research underpinning this paper enabled an identification of the specific influences on changes in the organisation and the way these interacted over time. A model of organisational change, developed from the research, is presented. The contribution of this paper lies mainly in deepening operations managers’ understanding of organisational change. It also uncovers the underlying rationales that steer change initiatives (planned or emergent) and identifies the key influences on organisational change. It provides and renews the necessary vocabulary, allowing managers to understand better and act on the multiple dimensions of organisational change. Furthermore, the provision of key learning points through a number of management “guidelines”, provides specific advice on how to effect sustainable change within organisations.
The macroeconomics of the social chapter: minimum wages, human capital and labour productivity
Authors: Gazioglu Saziye , McCausland W. David
Published: December 2003

This paper integrates trade and macro theory to provide a two‐country, multi‐product framework, including debt servicing and profit repatriation in the current account, and foreign money, financial assets and shares in the capital account. We investigate the effects of minimum wage legislation on the domestic tradeables and inward foreign investment sectors. Our findings show that there are asymmetrical effects on international debt and competitiveness. Thus, policy makers must have a more detailed knowledge of the sectoral structure of the country they are concerned with, in order to make informed decisions as to the merits of minimum wage legislation.
Rethinking the East Asian Miracle
Authors: Naseem S.M.
Published: December 2003

This paper discusses Rethinking the East Asian Miracle, a collection of 13 essays on a wide spectrum of issues, ranging from the causes of the East Asian crisis and possibilities of recovery to the strengths and weaknesses in the technical, financial and governance structures of the East Asian economies.