bluuebunny/crossref_metadata_2025 huggingface dataset:
Multicellular natural convection in a vertical slot
Authors: Lee Yee , Korpela Seppo A.
Published: April 2006

In this article we present numerical solutions to multicellular natural convection in a vertical enclosure. The calculated streamlines faithfully represent what has been seen in the laboratory by smoke traces in air and particle traces in oils. The calculated isotherms for air correspond to reported interferometric patterns. Solutions exhibiting travelling waves for water were calculated near conditions where they should occur according to linear stability theory. Heat-transfer results for air are given and their dependence on the aspect ratio of the enclosure exhibited.
High-strain-rate free-surface boundary-layer flows
Authors: Bertschy J. R. , Chin R. W. , Abernathy F. H.
Published: April 2006

Two-dimensional boundary-layer flows of water down an inclined table were investigated in both the laminar and turbulent regimes. Mean, r.m.s. and skewness and velocity spectra were determined from streamwise velocity measurements. Two laser-Doppler anemometry methods were developed (for studying polymer-solution flows using this same water table) and compared with measurements obtained using hot-film anemometry. All three techniques obtained consistent results.

An analysis based on a von Mises transformation is presented which accurately predicts the mean-velocity profile and flow development in the laminar regime. High strain rates are achieved which can be varied independently of Reynolds number, and turbulent flows are easily generated by inserting a disturbance. These turbulent flows are surprisingly similar to more commonly investigated turbulent boundarylayer flows of much greater y+ extent. Turbulent water-table flows typically extend only to y+ = 100, yet mean velocity essentially follows the law of the wall, and intensity and skewness measurements are similar to those obtained in flows much less limited in y+.
Double-diffusive plumes in unconfined and confined environments
Authors: McDougall Trevor J.
Published: April 2006

We address two aspects of the influence of double diffusion on convection from point buoyancy sources (plumes). First we consider double-diffusive convection acting in conjunction with buoyancy from an isolated source in an unconfined environment, and we study the problem of when fluxes of properties occur in the opposite direction to that of the initial buoyancy. A simple dimensional analysis is in good agreement with the experimental data for these ‘counterbuoyant’ fluxes of properties. Secondly, we consider a double-diffusive plume discharging into a confined environment. The plume now does not always reach the bottom (or top) of the confined environment, but can spread out into the environment at intermediate depths. Double-diffusive interfaces form, and we describe their development and the evolution of the density profile in the confined environment. A quantitative measure of the importance of double-diffusive convection in relation to the normal filling-box mechanism is obtained in the experiments by using the measured density profile, and this correlates well with a theoretically derived parameter Bρ.
Fully developed periodic turbulent pipe flow. Part 1. Main experimental results and comparison with predictions
Authors: Tu S. W. , Ramaprian B. R.
Published: April 2006

The present paper is the first part of a two-part report on a detailed investigation of periodic turbulent pipe flow. In this investigation, experimental data on instantaneous velocity and wall shear stress were obtained at a mean Reynolds number of 50000 in a fully developed turbulent pipe flow in which the volumetric flow rate was varied sinusoidally with time around the mean. Two oscillation frequencies at significant levels of flow modulation were studied in detail. The higher of these frequencies was of the order of the turbulent bursting frequency in the flow, and the other can be regarded as an intermediate frequency at which the flow still departed significantly from quasi-steady behaviour. While a few similar experiments have been reported in the recent literature, the present study stands out from the others in respect of the flow regimes investigated, the magnitude of flow modulation, the detailed nature of the measurements and most importantly the identification of a relevant parameter to characterize unsteady shear flows. The present paper contains the main experimental results and comparisons of these results with the results of a numerical calculation procedure which employs a well-known quasi-steady turbulence closure model. The experimental data are used to study the manner in which the time-mean, the ensemble-averaged and the random flow properties are influenced by flow oscillation at moderate to high frequencies. In addition, the data are also used to bring out the capability and limitations of quasi-steady turbulence modelling in the prediction of unsteady shear flows. A further and more detailed analysis of the experimental data, results of some additional experiments and a discussion on the characterization of turbulent shear flows are provided in Part 2 (Ramaprian & Tu 1983).
The production of turbulent stress in a shear flow by irrotational fluctuations
Authors: Gartshore I. S. , Durbin P. A. , Hunt J. C. R.
Published: April 2006

This paper is a study of how external turbulence affects an initially turbulence-free region in which there is a mean-velocity gradient dU/dz. Rapid-distortion theory shows how external turbulence induces irrotational fluctuations in the sheared region, which interact with the shear to produce rotational velocity fluctuations and mean Reynolds stresses. These stresses extend into the sheared region over a distance of the order of the integral scale L∞. Since the actual front between the initial external turbulence and the shear flow is a randomly contorted surface, the turbulence of a fixed point near the front is intermittent. Intermittency is included in the present analysis by a simple statistical model.

Experiments were done in a wind tunnel with the flow divided by a plate extending from upstream to x = 0. Above the plate, turbulence was produced by a grid. Below the plate a low turbulence shear was produced by wire screens. The wake of the plate (x > 0) decayed downstream.

Turbulent shear stress was observed to grow from zero to significant values in the interaction region. The magnitude and extent of the observed stress agrees reasonably well with predictions. We conclude that turbulent stresses can be produced by irrotational fluctuations in a region of mean shear, and that this effect can be estimated using rapid-distortion theory.
Laminar condensation on a moving drop. Part 1. Singular perturbation technique
Authors: Chung J. N. , Ayyaswamy P. S. , Sadhal S. S.
Published: April 2006

In this paper, laminar condensation on a spherical drop in a forced flow is investigated. The drop experiences a strong, radial, condensation-induced velocity while undergoing slow translation. In view of the high condensation velocity, the flow field, although the drop experiences slow translation, is not in the Stokes-flow regime. The drop environment is assumed to consist of a mixture of saturated steam (condensable) and air (non-condensable). The study has been carried out in two different ways. In Part 1 the continuous phase is treated as quasi-steady and the governing equations for this phase are solved through a singular perturbation technique. The transient heat-up of the drop interior is solved by the series-truncation numerical method. The solution for the total problem is obtained by matching the results for the continuous and dispersed phases. In Part 2 both the phases are treated as fully transient and the entire set of coupled equations are solved by numerical means. Validity of the quasi-steady assumption of Part 1 is discussed. Effects due to the presence of the non-condensable component and of the drop surface temperature on transport processes are discussed in both parts. A significant contribution of the present study is the inclusion of the roles played by both the viscous and the inertial effects in the problem treatment.
Liquid-metal flow in a rectangular duct with a strong non-uniform magnetic field
Authors: Petrykowski John C. , Walker John S.
Published: April 2006

Liquid-metal flows in rectangular ducts having electrically insulating tops and bottoms and perfectly conducting sides and in the presence of strong, polar, transverse magnetic fields are examined. Solutions are presented for the boundary layers adjacent to the sides that are parallel to the magnetic field. Overshoots in the radial velocity profiles show that the side layers have zero displacement thickness and do not perturb the inviscid core. Very weak secondary flows involve four significant vortices, as reflected in the polar velocity profiles.
Oscillatory convection in vertical slots
Authors: Koster J. N. , MÜLler U.
Published: April 2006

Convective flow phenomena in slender vertical slots with larger vertical than horizontal dimension, i.e. Hele Shaw slots, heated from below and subject to specified lateral boundary conditions, are investigated experimentally. Temperature fields in the liquid were visualized by holographic interferometry. Power-density spectra of local time-dependent thermocouple signals are calculated.

In these slender slots different steady and time-dependent convection patterns develop with increasing Rayleigh number. The range of oscillatory convective flow exhibits periodic, quasiperiodic or non-periodic structures including possible frequency locking, subharmonics and intermittency. Quasiperiodic and periodic oscillations reappear at higher Rayleigh numbers, with non-periodic flows occurring in-between. These time-dependent flows appear to be caused by an instability of thermal boundary layers at the horizontal walls. Finally, at still higher Rayleigh numbers a reverse transition to a steady-state flow pattern is observed. The transitions between steady and non-steady flows are characterized by hysteresis.
A steady-unsteady visualization technique for wake-flow studies
Authors: Ilegbusi J. O. , Spalding D. B.
Published: April 2006

A description is given of the principle and a preliminary embodiment of a flow-visualization technique in which the test body is pulled through water.

Initially, dyed and undyed parts of the water are separated by a plane horizontal interface; as the body emerges from below this interface, it carries dyed fluid upwards in its wake. A succession of photographs reveals the nature of the flow.

In principle, the flow is steady in a frame fixed relative to the body, and unsteady in one relative to the tank and the initial interface. Interpretation of the experimental results must therefore proceed by way of an analysis in which the steady-state equations are solved for velocity and turbulence quantities but an unsteady-state equation is solved for the dye concentration.

Preliminary results are reported for the flows behind a wedge and behind a bar. They reveal that these particular flows are unsteady even in the body-fixed coordinate frame, being strongly oscillatory.
The Sears problem for a lifting airfoil revisited - new results
Authors: Atassi H. M.
Published: April 2006

It is shown that for a thin airfoil with small camber and small angle of attack moving in a periodic gust pattern, the unsteady lift caused by the gust can be constructed by linear superposition to the Sears lift of three independent components accounting separately for the effects of airfoil thickness, airfoil camber and non-zero angle of attack to the mean flow. This is true in spite of the nonlinear dependence of the unsteady flow on the mean potential flow of the airfoil. Specific lift formulas are derived and analysed to assess the importance of mean flow angle of attack and airfoil camber on the gust response.
Natural convection in an inclined square cavity in regions of density inversion of water
Authors: Inaba Hideo , Fukuda Takeyuki
Published: April 2006

The steady laminar natural convection of water in an inclined square cavity is investigated experimentally and analytically at temperatures in the neighbourhood of maximum density near 4°C. One hot wall of the square cavity is maintained at various uniform temperatures from 2 to 20°C and the opposing cold wall is kept at a uniform temperature of 0°C, while the other walls are thermally insulated. Photographs and analytical descriptions of the flow patterns, temperature profiles in the water layer and average heat-transfer coefficients are presented in this paper for various surface temperatures Th of the hot wall and inclination angles of the square cavity θ from 0° (heated from below) to 180° (heated from above) by 30° intervals. From this study it should be noted that the density inversion of water has a strong effect on the natural convection occurring in the inclined square cavity, and the average heat-transfer coefficient is a peculiar function of the surface temperature of the hot wall, unlike previous results for Boussinesq fluids without density inversion. Solutions of the governing equations for steady two-dimensional laminar natural convection are obtained numerically, and the results obtained agree reasonably well with the experimental ones in the ranges of 30° < θ ≤ 180° for Th > 8°C, 0° ≤ θ ≤ 120° for Th < 8°C, and 0° ≤ θ ≤ 180° for Th = 8°C.
Stokeslet arrays in a pipe and their application to ciliary transport
Authors: Liron N.
Published: April 2006

The problem of fluid transport by cilia in a circular cylinder is investigated. The discrete-cilia approach is used in building the model, using the Green function due to an infinite periodic Stokeslet array in a pipe. Two different expressions are obtained for the Green function, one via a residue method and the other using the Poisson summation formula each amenable for computation in a different region. Interaction of the Stokeslets is investigated to see how, as distance decreases, interaction changes from initially separated closed vortices to a continuous flow. The singular integral equations for the forces in this model are now replaced by non-singular equations, thus overcoming the numerical difficulties in earlier works. It is found that in the pipe core the flow is time-independent and varies between a plug flow and a negative parabolic profile, in the pumping range. These results are seen to be local results due to the near field. Streamlines in the sublayer show eddies near the cilia bases blending into a uniform flow near the cilia tips.
Oblique wave groups in deep water
Authors: Bryant P. J.
Published: April 2006

Oblique wave groups consist of waves whose straight parallel lines of constant phase are oblique to the straight parallel lines of constant group phase. Numerical solutions for periodic oblique wave groups with envelopes of permanent shape are calculated from the equations for irrotational three-dimensional deep-water motion with nonlinear upper free-surface conditions. Two distinct families of periodic wave groups are found, one in which the waves in each group are in phase with those in all other groups, and the other in which there is a phase difference of π between the waves in consecutive groups. It is shown that some analytical solutions for oblique wave groups calculated from the nonlinear Schrödinger equation are in error because they ignore the resonant forcing of certain harmonics in two dimensions. Particular attention is given to oblique wave groups whose group-to-wave angle is in the neighbourhood of the critical angle tan−1√½, corresponding to waves on the boundary wedge of the Kelvin ship-wave pattern.
Turbulent mixing in a pulsed plasma-jet exhaust
Authors: Topham D. R. , Clements R. M. , Smy P. R.
Published: April 2006

High-speed schlieren cinéphotography of the firing of a high-energy plasma-jet igniter reveal turbulent structures similar in appearance to laboratory models of thermals or turbulent puffs. Measurements of the growth rates of these features together with those of their impulse and thermal energy confirm this similarity. A simple model based on the entrainment assumption gives a good description of the motion of the element and also of the decay of the internal temperature.
Two-phase flow equations for a dilute dispersion of gas bubbles in liquid
Authors: Biesheuvel A. , Wijngaarden L. Van
Published: April 2006

Equations of motion correct to the first order of the gas concentration by volume are derived for a dispersion of gas bubbles in liquid through systematic averaging of the equations on the microlevel. First, by ensemble averaging, an expression for the average stress tensor is obtained, which is non-isotropic although the local stress tensors in the constituent phases are isotropic (viscosity is neglected). Next, by applying the same technique, the momentum-flux tensor of the entire mixture is obtained. An equation expressing the fact that the average force on a massless bubble is zero leads to a third relation. Complemented with mass-conservation equations for liquid and gas, these equations appear to constitute a completely hyperbolic system, unlike the systems with complex characteristics found previously. The characteristic speeds are calculated and shown to be related to the propagation speeds of acoustic waves and concentration waves.
The influence of the horizontal component of Earth's angular velocity on the instability of the Ekman layer
Authors: Leibovich S. , Lele S. K.
Published: April 2006

A systematic study is made of the effect of latitude on the linear, normal mode stability characteristics of the laminar barotropic Ekman layer. The outcome depends upon the direction of the geostrophic flow (in the case of flows modelling the atmospheric Ekman layer) or, alternatively, upon the direction of the applied stress (in the case of flows modelling the oceanic Ekman layer). The minimum critical Reynolds number Rc is a function of latitude. For the atmospheric Ekman layer Rc = 30.8 for all latitudes less than 26.2° and increases monotonically with latitude to 54.2. At a latitude of 45° N, Rc is 33.9 and arises for a geostrophic wind directed towards a compass heading 252° (clockwise from north), corresponding to rolls with axes pointing due west and having wavenumber k (with unit of length taken to be the Ekman layer depth) of 0.594. The minimum Rc for the oceanic boundary layer is 11.6 for latitudes less than 81.1°, and increases with latitude to 11.8. At 45° N latitude, the critical condition arises for a surface-current compass heading of 345.2°, roll axis of 351° and a wavenumber k = 0.33. The results for Rc are all symmetric about the equator, with roll axes and associated basic flow directions rotated by 180°. As the Reynolds number R increases, the effects of the perturbation Coriolis acceleration on the instability diminish, as has been previously shown, and the error caused by neglect of the horizontal component of angular velocity therefore decreases. The high Reynolds number limit is systematically explored. It is shown that the lower branch of the neutral curve is not inviscid as R → ∞; rather kR → constant. The upper branch is inviscid in the limit R → ∞, and corresponds to a regular or singular neutral mode depending on whether the angle ε between the outer geostrophic flow and the roll axis is greater or less than 15.93°. ‘Inflectional’ modes, thought to be relevant by some investigators, do not exist for ε < 15.93°. Lastly, the most unstable inviscid mode corresponding to zero phase speed, a condition to which certain well-known experiments are sensitive, occurs at ε = 11.8° with wavenumber k = 0.6. This is in good agreement with published experimental data.
The effect of contraction on a homogeneous turbulent shear flow
Authors: Sreenivasan K. R.
Published: April 2006

A homogeneous turbulent shear flow in its asymptotic stage of development was subjected to an additional (longitudinal) strain by passing the flow through gradual contraction in the direction perpendicular to that of the mean shear. Two contractions, of area ratio 1.4 and 2.6, were used. Mean velocity and turbulent stress (both normal and shear) distributions were measured at several streamwise locations in the contraction region. The mean velocity distributions agree quite well with calculations based on the (inviscid) Bernoulli equation. Until at least half-way down the contraction with the larger area ratio, the rapid-distortion calculations considering only the streamwise acceleration were found to be reasonably successful in predicting the turbulent intensities. For the smaller-area-ratio contraction, corrections for the ‘natural development’ of the shear flow become important nearly everywhere. Similar calculations considering the shear as the only straining mechanism are generally less successful, although the shear strain rate is at least as rapid as, or even more so than, the longitudinal one. The pressure-rate-of-strain covariance terms estimated from the approximate component energy balance were used to test the adequacy of three models with varying degrees of complexity. Although none of these models appears general enough, their performance is generally adequate for the lower-area-ratio contraction; perhaps not surprisingly, the more complex the model the better its performance.
Self-sustained radial oscillating flows between parallel disks
Authors: Mochizuki S. , Yang Wen-Jei
Published: April 2006

The flow-visualization methods of dye injection, hydrogen-bubble generation and paraffin mist are employed to investigate radial flow between parallel circular disks with a steady influx. Three distinct flow patterns are observed in the range of Re between 1.5 and 50. (1) Steady flow without boundary-layer separation and re-attachment, for Re < Rec. (2) A self-controlled flow oscillation which decays further downstream, in the range of Rec [les ] Re < Ret. (3) A self-sustained flow fluctuation which develops into a laminar-turbulent transition with a reverse transition further downstream, when Re [ges ] Ret. Rec and Ret are the critical and transition Reynolds number, respectively.

The oscillating flows are caused by a vortex street consisting of vortices (i.e. separating annular bubbles) that separate periodically and alternately from both disks. Finite-difference solutions of the unsteady vorticity transport equation broadly agree with certain experimental observations. The study concludes that the separation and reattachment of shear layers in the radial flow through parallel disks are unsteady phenomena and the sequence of nucleation, growth, migration and decay of the vortices is self-sustained.
Structure of large-scale vortices and unsteady reverse flow in the reattaching zone of a turbulent separation bubble
Authors: Kiya Masaru , Sasaki Kyuro
Published: April 2006

This paper describes experiments concerning the structure of large-scale vortices and the unsteady reverse-flow properties in the reattaching zone of a nominally two-dimensional separation bubble formed at the leading edge of a blunt flat plate with right-angled corners. The experiment was performed in a wind tunnel with a constant Reynolds number 2.6 × 104 (based on the main-flow velocity and the thickness of the plate). Split-film probes, being sensitive to instantaneous reversals of flow direction, were extensively employed. An important feature of this study is a judicious use of surface-pressure fluctuations as a conditioning signal to educe the structure of the large-scale vortices.

Distributions of fluctuating-velocity vectors and contour lines of high-frequency turbulent energy in a few space–time domains are presented and discussed. The most economical interpretation of these space-time distributions is that the large-scale vortices in the reattaching zone are hairpin vortices whose configuration is sketched in the text. The unsteady flow in the reattaching zone is mainly governed by two agents; the motion of the large-scale vortices and the low-frequency unsteadiness. The unsteady flow is clarified in terms of the motion (in a space–time domain) of zeros of the longitudinal velocity close to the surface of the plate; the effects of the two agents on this motion are presented separately. On the basis of these results, a mathematical model of the unsteady flow in the reattaching zone is suggested and found to yield good comparison with measured reverse-flow intermittency and frequency of local-flow reversals. It appears that the separation bubble experiences shrinkage and enlargement in connection with the low-frequency unsteadiness and that the speed of shrinkage is much greater than that of enlargement. The strength of the large-scale vortices in the reattaching zone seems to be dependent on the phase of the low-frequency unsteadiness.
The trapping and vertical focusing of internal waves in a pycnocline due to the horizontal inhomogeneities of density and currents
Authors: Badulin S. I. , Shrira V. I. , Tsimring L. Sh.
Published: April 2006

This paper studies the propagation of a wave packet in regions where the central packet frequency ω is close to the local maximum of the effective Väisälä frequency Nf(z) = N(z)/[1 − k·U(z)/ω], where k is the central wavevector of the packet and U is the mean current with a vertical velocity shear. The wave approaches the layer ω = Nfm asymptotically, i.e. trapping of the wave takes place. The trapping of guided internal waves is investigated within the framework of the linearized equations of motion of an incompressible stratified fluid in the WKB approximation, with viscosity, spectral bandwidth of the packet, vertical shear of the mean current and non-stationarity of the environment taken into account. As the packet approaches the layer of trapping, the growth of the wavenumber k is restricted only by possible wave-breaking and viscous dissipation. The growth of k is accompanied by the transformation of the vertical structure of internal-wave modes. The wave motion focuses at a certain depth determined by the maximum effective Väisälä frequency Nfm. The trapping of the wave packet results in power growth of the wave amplitude and steepness. At larger times the viscous dissipation becomes a dominating factor of evolution as a result of strong slowing down of the packet motion.

The role of trapping in the energy exchange of internal waves, currents and small-scale turbulence is discussed.
The language of the glosses in the Bornu quranic manuscripts
Authors: BONDAREV DMITRY
Published: April 2006

The Bornu quranic manuscripts with interlinear ajami glosses in a Kanuri dialect were discovered by A. D. H. Bivar in the late 1950s. The unique corpus of written evidence for the Kanuri language as spoken over 300 years ago has never been analysed in any depth. The first part of the paper contains a general description of the collection and a discussion of codicological and palaeographical characteristics of the manuscripts. The second part comprises a brief note on the Kanuri language and a description of the Bornu writing system used for quranic commentary in this language. The third part explores the phonological and morphological properties of selected examples of glosses. Finally, a preliminary view on the dialect affiliation of the language of the glosses is suggested.
Distribution of density along magnetospheric field lines
Authors: Denton R. E. , Takahashi K. , Galkin I. A. , Nsumei P. A. , Huang X. , Reinisch B. W. , Anderson R. R. , Sleeper M. K. , Hughes W. J.
Published: April 2006

This paper examines the field line distribution of magnetospheric electron density and mass density. The electron density distributions from IMAGE RPI active sounding are generally monotonic. The density increases with increasing MLAT slightly faster than the dependence found from the field line dependence model of Denton et al. (2002b); in general, a power law dependence ne = ne0 (LRE/R)α with α ∼ 1 appears to be appropriate within the plasmasphere, at least for geocentric radius R > 2 RE. Our comparison to RPI data included also one field line distribution at LT = 7.4, which we fit with α = 2.5, a value typical of the plasmatrough based on previous studies. We calculated the average electron density field line distribution at low MLAT using the CRRES plasma wave data and found that the density was relatively flat near the magnetic equator with no convincing evidence for an equatorial peak. Using the average values of toroidal Afven frequencies, we calculated the mass density field line distributions and found that they were roughly monotonic for LT < 6, with α = 2 appropriate for LT = 4–5 and α = 1 appropriate for LT = 5–6. At LT = 6–8, the distribution was nonmonotonic, with a local peak in mass density at the magnetic equator. Dividing the frequency data into different groups based on activity, we found that the inferred average mass density field line dependence was insensitive to geomagnetic activity at LT = 4–6 but that at LT = 6–8, the tendency for the mass density to be peaked at the magnetic equator increased with respect to larger Alfven wave amplitude and more negative Dst. The average frequency ratios at LT = 6–8 did not change if we limited the data to cases with MLT = 8–16, for which the assumed perfect conductor boundary condition was better justified. Taken together, these results imply that heavy ions are preferentially peaked at the magnetic equator for LT = 6–8, at least during more geomagnetically active periods.
Transition rate prefactors for systems of many degrees of freedom
Authors: Chen L. Y. , Horing N. J. M.
Published: April 2006

When a minimum on the potential energy surface is surrounded by multiple saddle points with similar energy barriers, the transition pathways with greater prefactors are more important than those that have similar energy barriers but smaller prefactors. In this paper, we present a theoretical formulation for the prefactors, computing the probabilities for transition paths from a minimum to its surrounding saddle points. We apply this formulation to a system of 2degrees of freedom and a system of 14degrees of freedom. The first is Brownian motion in a two-dimensional potential whose global anharmonicities play a dominant role in determining the transition rates. The second is a Lennard-Jones (LJ) cluster of seven particles in two dimensions. Low lying transition states of the LJ cluster, which can be reached directly from a minimum without passing through another minimum, are identified without any presumption of their characteristics nor of the product states they lead to. The probabilities are computed for paths going from an equilibrium ensemble of states near a given minimum to the surrounding transition states. These probabilities are directly related to the prefactors in the rate formula. This determination of the rate prefactors includes all anharmonicities, near or far from transition states, which are pertinent in the very sophisticated energy landscape of LJ clusters and in many other complex systems.
Investigation of excess adsorption, solvation force, and plate-fluid interfacial tension for Lennard-Jones fluid confined in slit pores
Authors: Fu Dong
Published: April 2006

The excess Helmholtz free energy functional is formulated in terms of a modified fundamental measure theory [Y. X. Yu and J. Z. Wu, J. Chem. Phys. 117, 10156 (2002)] for a short ranged repulsion and a first-order mean-spherical approximation theory [Y. P. Tang, J. Chem. Phys. 118, 4140 (2003)] for a long ranged attraction. Within the framework of the density functional theory, the density profile, excess adsorption, solvation force, and plate-fluid interfacial tension of a Lennard-Jones fluid confined in slit pores are predicted, and the results agree well with the simulation data. The phase equilibria inside the slit pores are determined according to the requirement that temperature, chemical potential, and grand potential in coexistence phases should be equal, and the plate-fluid interfacial tensions at equilibrium states are predicted consequently.
Effect of Auger recombination on the performance of p-doped quantum dot lasers
Authors: Mokkapati S. , Buda M. , Tan H. H. , Jagadish C.
Published: April 2006

Experimental results on spontaneous emission rates from InGaAs quantum dot lasers that can be explained theoretically by considering the influence of nonradiative mixed state recombinations in the quantum dot-wetting layer system are presented. Our model qualitatively explains the experimental results such as an increase in the threshold current density, temperature stability, and a narrower gain spectrum due to doping the quantum dot active region with the acceptors. Our model also predicts that moderate acceptor concentrations can improve the laser performance at higher carrier injection densities; but high acceptor concentrations deteriorate the laser performance due to the nonradiative Auger recombination that counteracts the benefits of increased spontaneous emission rates.
Derivatives of the local ballooning growth rate with respect to surface label, field line label, and ballooning parameter
Authors: Hudson S. R.
Published: April 2006

Expressions for the derivative of the local ballooning growth rate with respect to surface label, field line label, and ballooning-parameter are presented. Such expressions lead to increased computational efficiency for ballooning stability applications.
Loss management using parity-selective barriers for single-mode, single-cell photonic crystal resonators
Authors: Kim Sun-Kyung , Kim Guk-Hyun , Kim Se-Heon , Lee Yong-Hee , Kim Sung-Bock , Kim In
Published: April 2006

We propose and realize truly single-mode, single-cell photonic crystal resonators surrounded by six symmetric waveguides. The waveguides provide different parity-selective loss paths for different resonant cavity modes. We found symmetry conditions where only the hexapole mode is well confined while the other modes are severely leaky along the waveguides. Utilizing the parameters derived from this parity-mismatch principle, the hexapole-mode resonators were fabricated on InP–InGaAsP slabs. Through photopumping, we obtained the hexapole-mode laser operating in a single mode over a wide range of around 100nm.
Self-assembly of heterojunction quantum dots
Authors: Eyink K. G. , Tomich D. H. , Pitz J. J. , Grazulis L. , Mahalingam K. , Shank J. M.
Published: April 2006

The fabrication of a self-assembled heterojunction quantum dot structure composed of multiple materials is reported. This structure consists of a composite dot formed of an initial core of one material which results from normal self-assembly, followed by the epitaxy of a crown composed of a similarly strained material. Finally the entire dot structure is capped with a barrier material closely lattice matched to the substrate. In this demonstration, self-assembled InAs quantum dots were first formed on a GaAs substrate and subsequently crowned with GaSb. The entire structure was encapsulated with a GaAs cap layer. Atomic force microscopy shows that additional nucleation between the InAs layers has been minimized and cross-sectional transmission electron microscopy shows the formation of the composite structure.
Synthesis of nanowires in room temperature ambient: A focused ion beam approach
Authors: Lugstein A. , Bernardi Johannes , Tomastik Christian , Bertagnolli E.
Published: April 2006

We present a focused ion beam based technique for the synthesis of nanowires in room temperature ambient without using any additional material source. Based on the idea of a catalytic approach gallium antimonide and antimony nanowires were grown with diameters of about 20nm. We suppose that the intense focused ion beam exposure forms catalytic particles alloyed by the constituents of the growing nanowire in situ. In contrast to a broad class of techniques for nanowire growth neither heating of the sample nor any additional material source is required, thereby being compatible with on-chip microelectronics.
Sustainable grazing systems for the Central Tablelands of New South Wales. 5. A bioeconomic framework for assessing the long-term economic benefits of grazing management tactics and implications for sustainability
Authors: Jones R. E. , Dowling P. M. , Michalk D. L. , King W. McG.
Published: April 2006

There have been significant declines in the perennial grass (PG) content in native and sown pastures across temperate Australia. Not only has this reduced agricultural productivity, it has contributed to more serious degradation, such as loss of soil and biodiversity, decreasing water quality, and dryland salinity caused by rising watertables. Results from the Sustainable Grazing Systems Key Program (SGS) research undertaken at Carcoar on the Central Tablelands of New South Wales were reported by Michalk et al. (2003). This research indicated that grazing management tactics can be used to manipulate pasture composition, thereby changing animal production and water-use patterns. The main grazing tactic investigated was termed a summer grazing rest, where resting was imposed in late spring if PG composition was <50%. Reported in this present paper is an economic framework for valuing the long-term benefits of grazing management tactics. The framework involves the development of a bioeconomic modelling system that links a dynamic programming model with biophysical models for water and environmental processes, soil fertility, pasture growth, livestock energy requirements and the change in pasture species composition. The study concludes that long-term economic returns are improved by strategies, e.g. a summer rest, that lead to an increase in PG composition over time. The study also determined that environmental factors, such as deep drainage, runoff and soil loss, are reduced as perenniality is increased.
Interannual climatic variation mediates elevated CO2 and O3 effects on forest growth
Authors: KUBISKE MARK E. , QUINN VANESSA S. , HEILMAN WARREN E. , McDONALD EVAN P. , MARQUARDT PAULA E. , TECLAW RON M. , FRIEND ALEXANDER L. , KARNOSKY DAVID F.
Published: April 2006

We analyzed growth data from model aspen (Populus tremuloides Michx.) forest ecosystems grown in elevated atmospheric carbon dioxide ([CO2]; 518 μL L−1) and ozone concentrations ([O3]; 1.5 × background of 30–40 nL L−1 during daylight hours) for 7 years using free‐air CO2 enrichment technology to determine how interannual variability in present‐day climate might affect growth responses to either gas. We also tested whether growth effects of those gasses were sustained over time. Elevated [CO2] increased tree heights, diameters, and main stem volumes by 11%, 16%, and 20%, respectively, whereas elevated ozone [O3] decreased them by 11%, 8%, and 29%, respectively. Responses similar to these were found for stand volume and basal area. There were no growth responses to the combination of elevated [CO2+O3]. The elevated [CO2] growth stimulation was found to be decreasing, but relative growth rates varied considerably from year to year. Neither the variation in annual relative growth rates nor the apparent decline in CO2 growth response could be explained in terms of nitrogen or water limitations. Instead, growth responses to elevated [CO2] and [O3] interacted strongly with present‐day interannual variability in climatic conditions. The amount of photosynthetically active radiation and temperature during specific times of the year coinciding with growth phenology explained 20–63% of the annual variation in growth response to elevated [CO2] and [O3]. Years with higher photosynthetic photon flux (PPF) during the month of July resulted in more positive growth responses to elevated [CO2] and more negative growth responses to elevated [O3]. Mean daily temperatures during the month of October affected growth in a similar fashion the following year. These results indicate that a several‐year trend of increasingly cloudy summers and cool autumns were responsible for the decrease in CO2 growth response.
Extramammary Paget's disease—a proliferation of adnexal origin?
Authors: Regauer S
Published: April 2006

Aim : To investigate a possible follicular origin of extramammary Paget's disease (EPD). EPD is a predominantly intraepidermal tumour with extensive involvement of adnexal structures and high recurrence rates suggesting a follicular stem cell origin. Cytokeratin (CK) 15 and CK19 are considered markers for follicular stem cells located in the hair follicle bulge region.

Methods and results : Formalin‐fixed paraffin‐embedded tissues of 12 cases of primary EPD (three anal, nine vulvar) were studied immunohistochemically with antibodies to CK15 and CK19. All cases of EPD showed polygonal Paget cells in the interfollicular epidermis, hair follicles, sebaceous and apocrine glands distributed individually, in nests and in gland‐like areas. The polygonal Paget cells were intimately associated with small, flat, mitotically active, ‘compressed’ keratinocytes. The large Paget cells uniformly expressed CK19 in 12/12 EPD. The small ‘compressed’ keratinocytes showed strong cytoplasmic CK15 staining in 9/12 EPD with focal accentuation, while the polygonal Paget cells were negative.

Conclusions : These histological and immunohistochemical observations allow the following conclusions: (i) the small, flat, ‘compressed’ keratinocytes are an integral part of EPD; (ii) the dual cell population is reminiscent of sebaceous glands with mature sebocytes and germinative keratinocytes; (iii) since both cell types express cytokeratins typical for follicular differentiation, EPD may be a proliferation of adnexal stem cells residing in the infundibulo‐sebaceous unit of hair follicles and adnexal structures.
Trastuzumab/docetaxel‐induced nail dystrophy
Authors: Alexandrescu Doru T. , Vaillant Juan , Wiernik Peter H.
Published: April 2006

Combination of trastuzumab, an antibody directed against the Her‐2/neu receptor, with chemotherapy is increasingly used for the treatment of metastatic breast cancer, and currently is being explored in the adjuvant setting. We report the case of a 55‐year‐old woman with metastatic breast cancer, who developed nail dystrophic changes comprising Beau's lines, subungual hyperkeratosis, dyschromia and onycholysis early in the treatment with trastuzumab/docetaxel. Nail alterations advanced with the continuation of therapy. This combination of nail changes, and its progressive course, are extremely rarely encountered with the use of taxanes alone. The cellular mechanisms of action of trastuzumab and docetaxel are discussed in regards to their potential synergy, which may explain the particularities and severity of nail alterations in this patient.
An autonomous mobile agent‐based distributed learning architecture: a proposal and analytical analysis
Authors: Ahmed Iftikhar , Sadeq Muhammad Jafar
Published: April 2006

Current distance learning systems are increasingly packing highly data‐intensive contents on servers, resulting in the congestion of network and server resources at peak service times. A distributed learning system based on faded information field (FIF) architecture that employs mobile agents (MAs) has been proposed and simulated in this work. The learning contents are decentralised in the proposed system, and these are dynamically distributed around the main education site server on different nodes in response to network congestion and server overload. The system simulation results have been presented and analysed. The proposed system holds the potential to address the network congestion and server‐overload problems in distance learning systems.
Mechanisms of Autonomic Disturbance in the Face During and Between Attacks of Cluster Headache
Authors: Drummond PD
Published: April 2006

Lacrimation and nasal secretion during attacks of cluster headache appear to be due to massive trigeminal-parasympathetic discharge. In addition, the presence of oculo-sympathetic deficit and loss of thermoregulatory sweating and flushing on the symptomatic side of the forehead indicate that the cervical sympathetic pathway to the face is injured in a subgroup of cluster headache patients. In this review, it is argued that a peripheral rather than a central lesion produces signs of cervical sympathetic deficit, probably resulting from compression of the sympathetic plexus around the internal carotid artery. Although trigeminal-parasympathetic discharge appears to be the main trigger for vasodilation during attacks, supersensitivity to neurotransmitters such as vasoactive intestinal polypeptide, together with release of sympathetic vasoconstrictor tone, may boost facial blood flow in patients with cervical sympathetic deficit. In addition, parasympathetic neural discharge may provoke aberrant facial sweating during attacks in patients with cervical sympathetic deficit. Although neither trigeminal-parasympathetic discharge nor cervical sympathetic deficit appears to be the primary trigger for attacks of cluster headache, these autonomic disturbances could contribute to the rapid escalation of pain once the attack begins. For example, a pericarotid inflammatory process that excites trigeminal nociceptors might initiate neurogenic inflammation and trigeminal-parasympathetic vasodilation. To complete the loop, neurogenic inflammation and trigeminal-parasympathetic vasodilation could provoke the release of mast cell products, which aggravate inflammation and intensify trigeminal discharge.
Role of acetylcholine and polyspecific cation transporters in serotonin-induced bronchoconstriction in the mouse
Authors: Kummer Wolfgang , Wiegand Silke , Akinci Sibel , Wessler Ignatz , Schinkel Alfred H , Wess Jürgen , Koepsell Hermann , Haberberger Rainer V , Lips Katrin S
Published: April 2006

Background

It has been proposed that serotonin (5-HT)-mediated constriction of the murine trachea is largely dependent on acetylcholine (ACh) released from the epithelium. We recently demonstrated that ACh can be released from non-neuronal cells by corticosteroid-sensitive polyspecific organic cation transporters (OCTs), which are also expressed by airway epithelial cells. Hence, the hypothesis emerged that 5-HT evokes bronchoconstriction by inducing release of ACh from epithelial cells via OCTs.

Methods

We tested this hypothesis by analysing bronchoconstriction in precision-cut murine lung slices using OCT and muscarinic ACh receptor knockout mouse strains. Epithelial ACh content was measured by HPLC, and the tissue distribution of OCT isoforms was determined by immunohistochemistry.

Results

Epithelial ACh content was significantly higher in OCT1/2 double-knockout mice (42 ± 10 % of the content of the epithelium-denuded trachea, n = 9) than in wild-type mice (16.8 ± 3.6 %, n = 11). In wild-type mice, 5-HT (1 μM) caused a bronchoconstriction that slightly exceeded that evoked by muscarine (1 μM) in intact bronchi but amounted to only 66% of the response to muscarine after epithelium removal. 5-HT-induced bronchoconstriction was undiminished in M2/M3 muscarinic ACh receptor double-knockout mice which were entirely unresponsive to muscarine. Corticosterone (1 μM) significantly reduced 5-HT-induced bronchoconstriction in wild-type and OCT1/2 double-knockout mice, but not in OCT3 knockout mice. This effect persisted after removal of the bronchial epithelium. Immunohistochemistry localized OCT3 to the bronchial smooth muscle.

Conclusion

The doubling of airway epithelial ACh content in OCT1/2-/- mice is consistent with the concept that OCT1 and/or 2 mediate ACh release from the respiratory epithelium. This effect, however, does not contribute to 5-HT-induced constriction of murine intrapulmonary bronchi. Instead, this activity involves 1) a non-cholinergic epithelium-dependent component, and 2) direct stimulation of bronchial smooth muscle cells, a response which is partly sensitive to acutely administered corticosterone acting on OCT3. These data provide new insights into the mechanisms involved in 5-HT-induced bronchoconstriction, including novel information about non-genomic, acute effects of corticosteroids on bronchoconstriction.