bluuebunny/crossref_metadata_2025 huggingface dataset:
Quantitative dynamics and spatial profile of perisomatic GABAergic input during epileptiform synchronization in the CA1 hippocampus
Authors: Marchionni Ivan , Maccaferri Gianmaria
Published: October 2009

Perisomatic GABAergic input appears spared or even increased in intractable temporal lobe epilepsy, and has been suggested to contribute to the generation of pathological discharges. Nevertheless, its degree of functional activity during epileptiform synchronization has not been thoroughly investigated. Thus, it remains unclear how structural preservation or loss of domain‐specific GABAergic input may affect the network. Here, we have taken advantage of a model of epileptiform activityin vitroto quantify the charge transfer provided by perisomatic GABAAreceptor‐mediated input to CA1 pyramidal neurons during interictal‐like bursts. By recording both firing in GABAergic interneurons and the charge transfer generated by unitary postsynaptic currents to target pyramidal cells, we have estimated the charge transfer that would be dynamically generated by the recruitment of the entire pool of perisomatic‐targeting interneurons and the number of perisomatic‐targeting interneurons that would be required to generate the experimentally observed GABAergic input. In addition, we have recorded and compared the dynamics and charge density of GABAergic input recorded at different membrane compartments such as the somavs.the proximal dendrite. Our results suggest that GABAAreceptor‐mediated perisomatic input is massively activated during burst synchronization and that its kinetic properties and charge density are similar at the soma and proximal dendrite. These functional results match structural data published by other laboratories very well and strengthen the hypothesis that the potential preservation of perisomatic GABAergic input in intractable epilepsies may be a key factor in the generation of pathological network activity.
Local Heat Transfer Coefficients around Horizontal Tubes in Fluidized Beds
Authors: Chandran R. , Chen J. C. , Staub F. W.
Published: October 2009

The local characteristics of heat transfer from horizontal tubes immersed in fluidized beds were investigated experimentally. Steady-state heat transfer measurements were obtained in air-fluidized beds of glass beads, both for a single tube and a ten-row bare tube bundle. The test results indicated that local heat transfer coefficients are strongly influenced by angular position and gas flow rate, as well as by particle size and system pressure. The heat transfer coefficients, averaged around the circumference of the tube, exhibited a general tendency to increase with decreasing particle size and increasing system pressure. The heat transfer coefficients for a tube in an inner-row position within the bundle were found to be slightly higher than those for a tube in the bottom-row. Comparison of the average heat transfer coefficient data obtained in this study with some of the existing correlations for heat transfer from horizontal tubes showed that the correlations are unsatisfactory.
Thermal Conductivity of Methane at Atmospheric Pressure in the Temperature Range of 360-1275 K
Authors: Afshar R. , Cogley A. C. , Saxena S. C.
Published: October 2009

Thermal conductivity of a research grade pure methane sample is measured in a hot-wire column instrument in the temperature range 360–1275 K from heat transfer rate data taken in the continuum region. The results are correlated by a quadratic polynomial in temperature viz., k(T) = −23.35 + 0.1698T + 1.893 × 10−5T2. Here k is in m W/m-K and T in K. The experimental data are compared with the available conductivity values and with the predictions of kinetic theories of polyatomic gases in conjunction with realistic intermolecular potentials. The conductivity data are also employed to compute the diffusion coefficient for vibrational energy. The effect of gaseous radiative transfer on the measured thermal conductivity of methane is estimated by comparing the conductivity coefficients of a slab of gas with and without the presence of the absorption bands.
Vapor/Liquid Interaction and Entrainment in Falling Film Evaporators
Authors: Yung D. , Lorenz J. J. , Ganic´ E. N.
Published: October 2009

The problem of vapor/liquid interaction and entrainment in falling film evaporators is analyzed. Attention is focused primarily on horizontal tube falling film evaporators where liquid falls from one tube to the next in either a droplet or column mode. A criterion is presented for the onset of column formation, and equations are derived for the deflection of droplets and columns due to vapor crossflow. Based on an experimental study of drop detachment and breakup, a correlation is established for the resulting droplet sizes. For high vapor crossflow velocities, a criterion is presented for the inception of liquid entrainment by a process known as stripping. Based on the foregoing models, conditions are defined under which vapor/liquid interaction and entrainment are important for falling film evaporators.
A Parametric Analysis of the Performance of Internally Finned Tubes for Heat Exchanger Application
Authors: Webb R. L. , Scott M. J.
Published: October 2009

This paper presents a parametric analysis of the performance of internally finned tubes in turbulent forced convection for application to heat exchangers. The analysis compares the performance of an internally finned tube exchanger with that of an exchanger having internally smooth tubes. The calculations are performed for three important design cases. By variation of the internal fin geometric parameters, we define the performance benefits and the preferred geometrical parameters which allow use of minimum tube material. The best axial internal fins offer less than 10 percent material savings for equal pumping power and heat duty. However, the material savings are increased to 49 percent using internal fins having a 30 deg helix angle. The heat exchanger UA may be increased 35 to 40 percent for equal pumping power and total tubing length. Pumping power reduction of 42 percent is obtained using five fins 2 mm in height with zero helix angle. The majority of the calculations are performed for water (Pr = 3) and include the effect of fin efficiency. The paper also compares the performance of internally finned and internally roughened tubes.
Prediction of Void Fraction in Low Velocity Vertical Steam-Water Flow
Authors: Ardron K. H. , Hall P. C.
Published: October 2009

A new drift flux relation is derived for low speed vertical bubble flows by balancing the hydrostatic pressure with the liquid eddy stresses; the effective eddy viscosity is related to the energy dissipated by the gas flow. Comparisons with steam-water data show that the observed variation of void fraction with gas flux, and the effects of pipe diameter, are well predicted by the model. However, to represent the pressure effects it is found necessary to postulate that the eddy viscosity increase systematically with pressure. Further experimental data are required to test this hypothesis.
Heat Transfer and Pressure Drop Characteristics Induced by a Slat Blockage in a Circular Tube
Authors: Sparrow E. M. , Koram K. K. , Charmchi M.
Published: October 2009

Complementary heat transfer and fluid flow experiments were performed to determine transfer coefficients and pressure drops associated with the presence of a slat-like blockage in a tube. Water was the working fluid for the heat transfer studies (Pr = 4), while for the fluid flow experiments, which were performed under isothermal conditions, air was employed. The flow was turbulent in all cases, with the Reynolds number ranging from 10,000 to 60,000. Three blockage elements were used which respectively blocked 1/4, 1/2, and 3/4 of the tube cross-sectional area. Downstream of the blockage, heat transfer coefficients were measured around the circumference of the tube as well as along its length. The heat transfer coefficients in the region just downstream of the blockage were found to be several times as large as those for a corresponding conventional turbulent pipe flow. With increasing downstream distance, the coefficients diminish and thermal development is completed (to within five percent) at about 10, 15, and 18 diameters from the respective blockages. The blockage-induced circumferential variations of the heat transfer coefficient are dissipated by about five diameters. The pressure losses induced by the blockage are high, with values for the respective blockages that are 1.2, 5.2, and 33.2 times the velocity head in the pipe flow in which the blockage is situated. These losses are comparable to those for a gate valve.
A Turbine-Meter Evaluation Model for Two-Phase Transients
Authors: Kamath P. S. , Lahey R. T.
Published: October 2009

This work involves the development of an analytical model to calculate the transient two-phase mass flux in a conduit instrumented with a free-field turbind flow meter. The effects of rotor inertia, velocity and void profiles in the conduit, slip ratio, imperfect guidance of the flow by the rotor blades, bearing friction and windage losses have been incorporated into the model. The analytical Turbine-meter Evaluation Model for Two-Phase Transients (TEMPT) was programed and was used for numerical calculations. For a typical blowdown transient, the effects of velocity and void profiles, and rotor inertia were found to be the most significant parameters.
Unit Thermal Performance of Atmospheric Spray Cooling Systems
Authors: Porter R. W. , Jain M. , Chaturvedi S. K.
Published: October 2009

Thermal performance of an open atmospheric spray pond or canal depends on the direct-contact evaporative cooling of an individual spray unit (spray nozzle or module) and the interference caused by local heating and humidification. Droplet parameters may be combined into a dimensionless group, number of transfer units (NTU) or equivalent, whereas large-scale air-vapor dynamics determine interference through the local wet-bulb temperature. Quantity NTU were implied from field experiments for a floating module used in steam-condenser spray canals. Previous data were available for a fixed-pipe nozzle assembly used in spray ponds. Quantity NTU were also predicted using the Ranz-Marshall correlations with the Sauter-mean diameter used as the characteristic length. Good agreement with experiments was shown for diameters of 1–1.1 cm (module) and 1.9 mm (fixed-pipe nozzle).
Thermal Instability of Natural Convection Flow over a Horizontal Ice Cylinder Encompassing a Maximum Density Point
Authors: Saitoh T. , Hirose K.
Published: October 2009

The problem of three-dimensional thermal instability over a horizontal ice cylinder which occurs in a minimum heat transfer region has been solved. A fully numerical method was applied to the governing equations in the transverse and longitudinal planes, which were simplified to two-dimensional. The perturbation method was employed to obtain the wave number. The appearance of a convexo-concave melting front, which was predicted by a previous experiment, was clearly explained by the convection pattern along the cylinder. The transient process of onset of stable vortices around a cylinder was clarified by streamlines and isotherms. Comparing the wave numbers obtained by the numerical and the small perturbation methods, it is concluded that the perturbation method cannot be effectively applied to problems involving density inversion.
Analysis of Heat Transfer in Slightly Eccentric Annuli
Authors: Yao L. S.
Published: October 2009

The regular perturbation solution of heat transfer is developed for slightly eccentric annuli. The numerical results demonstrate that the heat transfer in slightly eccentric annuli can be predicted from the solution of concentric annuli by a simple radial coordinate transformation when the ratio of the radius of the inner cylinder and the characteristic gap width is not too small. The regular perturbation solution breaks down when this ratio approaches zero.
On the Minimum Film Boiling Conditions for Spherical Geometries
Authors: Gunnerson F. S. , Cronenberg A. W.
Published: October 2009

An analytical method is presented for predicting the minimum heater temperature and the minimum heat flux at the onset of film boiling for spherical and flat plate heaters in saturated and subcooled liquids. Consideration is given to a variety of factors known to affect the minimum film boiling point, including transient liquid-heater contact, interfacial wettability, heater geometry, and liquid subcooling. The theoretical correlations developed are the first known predictions for spherical geometries. A comparison of theory with experimental data indicates good agreement for the minimum heat flux and the minimum film boiling temperature. Results indicate that the minimum conditions may span a wide range depending upon the thermophysical nature of the heater surface and the boiling liquid.
Convective Heat Transfer Correlations for Planar, Supersonic, Separated Flows
Authors: Lamb J. P.
Published: October 2009

Correlations are developed for minimum heat transfer levels within the separated flow fields formed by a variety of planar geometries including backsteps, open cavities, and cylinders of arbitrary cross section. Proposed correlations include the independent effects of Mach number, unit Reynolds number, and the length scale of the separated region. Both laminar and turbulent regimes are considered.
A Study of the Heat Transfer Mechanisms in Horizontal Flame Propagation
Authors: Ray S. R. , Fernandez-Pello A. C. , Glassman I.
Published: October 2009

An experimental study is performed on the magnitude of the different mechanisms by which heat is transferred from the flaming region to the unburnt fuel ahead of the flame for flames propagating horizontally over the surface of a solid fuel. Measurements of the gas velocity field, temperature fields and radiant flux distribution in a particular case of laboratory scale flame spread over a thick fuel are used to determine the magnitude of the heat fluxes ahead of the flame. The results show that, for this particular case, although heat conduction through the solid is dominant, radiation from the flame contributes significantly to the heat transfer process. An analysis of the development of the fire indicates that there is a transition in the mechanisms of heat transfer as the fire grows. While in the early stages of the fire, heat conduction through the solid is dominant, radiation from the flame becomes of increased importance as the size of the fire increases.
An Experimental Study of the Rapid Depressurization of Hot Water
Authors: Alamgir Md. , Kan C. Y. , Lienhard J. H.
Published: October 2009

New measurements of the pressure history in 5.08 and 1.27 cm i.d. tubes during extremely rapid depressurization from BWR and PWR conditions are presented. The pressure to which the present system (as well as the systems of other investigators) returns, is successfully correlated using a suggestion by Stuhmiller. New pressure undershoot data are given here, but they are rationalized elsewhere. The rate of opening, and the rarefaction wave speed, in the present system are also presented and correlated. The present study suggests that scaled replications of the early process of depressurization are reliable.
Prediction of Horizontal Tubeside Condensation of Pure Components Using Flow Regime Criteria
Authors: Breber G. , Palen J. W. , Taborek J.
Published: October 2009

In order to select the appropriate correlations for prediction of horizontal tubeside condensation heat transfer coefficients, it is necessary to estimate what types of flow patterns exist at various points along the tube. The main criteria required are shown to be the ratio of shear to gravity forces on the condensate film and the ratio of vapor volume to liquid volume. A recently proposed prediction method by Taitel and Dukler is compared with observed flow regimes for condensation in horizontal tubes. The theoretically obtained parameters are shown to characterize the flow regimes well. Based on these parameters, a simplified procedure for prediction of local heat transfer coefficients for pure component condensation in horizontal tubes is proposed.
Lower Bound Estimate for Droplet Size in Two-Phase Dispersed Flow
Authors: Delale C. F.
Published: October 2009

A theoretical post-dryout heat transfer model is developed based on one-dimensional two-phase dispersed flow and is applied to calculate the wall temperatures in the post-CHF regime. The model is also applied to reason the existence of a lower bound for average droplet diameter in two-phase dispersed flow. Results obtained using data by Bennett, et al. show lower droplet sizes than the experimentally measured values.
Experimental Study of the Transition from Forced to Natural Circulation in EBR-II at Low Power and Flow
Authors: Gillette J. L. , Singer R. M. , Tokar J. V. , Sullivan J. E.
Published: October 2009

A series of tests was conducted in EBR-II which examined the dynamics of the transition from forced to natural circulation flow in a liquid-metal-cooled fast breeder reactor. Each test was initiated by abruptly tripping an electromagnetic pump which supplies 5–6 percent of the normal full operational primary flow rate. The ensuing flow coastdown reached a minimum value after which the flow increased as natural circulation was established. The effects of secondary system flow through the intermediate heat exchanger and reactor decay power level on the minimum in-core flow rates and maximum in-core temperatures were examined.
Directional Control of Radiation Heat Transfer by V-Groove Cavities—Collimation of Energy in Direction Normal to Cavity Opening
Authors: Masuda H.
Published: October 2009

To improve the V-groove cavity devised for directional control of radiation heat transfer, a new model with a black fin provided on the cavity base is proposed. The radiative characteristics of the new model are theoretically offered comparing two typical constitutional forms—symmetrical and asymmetrical. It is evident that the fin helps accelerate radiation heat transfer from the V-groove and promote its collimation. The effects can be further enhanced by carefully choosing the various geometrical parameters. The new V-groove cavity proposed would probably be evaluated as a favorable directional surface. The direction of energy collimation can be altered by using the asymmetrical groove cavity.
An Analytical Study of Natural Convective Heat Transfer within a Trapezoidal Enclosure
Authors: Iyican L. , Bayazitogˇlu Y. , Witte L. C.
Published: October 2009

The natural convection motion and the heat transfer within a trapezoidal enclosure with parallel cylindrical top and bottom walls at different temperatures and plane adiabatic sidewalls are studied. Two-dimensional natural convective fields for a range of Rayleigh numbers, up to 2.7 × 106, and enclosure tilt angles, 0 to 180 deg measured from vertical, are investigated. The Galerkin’s method of solution is applied to nonlinear form of the momentum and energy equations to determine the velocity and temperature fields. The average and local Nusselt numbers are also presented.
Instability of the Planar Freeze Front During Solidification of an Aqueous Binary Solution
Authors: O’Callaghan M. G. , Cravalho E. G. , Huggins C. E.
Published: October 2009

A model describing the heat transfer, solute redistribution, and interface stability during the planar solidification of an aqueous binary solution has been developed. The temperature field was calculated using a modified Ka´rma´n-Pohlhausen integral technique. With this technique, the averaged heat conduction equation was solved with the full set of boundary conditions using an assumed spatial variation of the temperature profile. The concentration field was solved for analytically. The stability of the planar freezing morphology was determined using the Mullins-Sekerka stability criterion, in which the time variation of a sinusoidal perturbation of the planar interface was calculated. Application of this criterion to the freezing of saline indicates that for any practical freezing rate the planar interface was unstable. This represents an indictment of the planar freezing model and indicates the tendency for aqueous solutions to freeze dendritically.
Heat and Mass Transfer in Fixed Beds at Low Reynolds Numbers
Authors: Glicksman L. R. , Joos F. M.
Published: October 2009

In a fixed or fluidized bed at low particle Reynolds numbers, the overall or effective Sherwood and Nusselt number has been found by many investigators to be much less than unity. The limiting value of the particle Sherwood or Nusselt number based on local concentration or temperature differences is shown to be equal to or greater than unity. An analytical model was established using realistic packed bed geometries to allow for diffusion in the flow direction, channeling due to nonuniformities in bed voidage and different particle sizes, and inaccuracies in the experimental measurements. The predicted values of the effective Sherwood and Nusselt numbers are found to agree closely with experimental measurements for gases and liquids. Diffusion is shown to be the primary mechanism for the fall-off in the effective bed characteristics.
Heat Conduction in Unsteady, Periodic, and Steady States in Laminated Composites
Authors: Huang S. C. , Chang Y. P.
Published: October 2009

This paper provides analytical solutions for heat conduction in composites of infinite, semi-infinite, and finite laminates in unsteady, periodic, and steady states. For compactness and generality, Green’s functions are used. The method of analysis applies for composites of any number of layers, but only solutions for two material composites are presented in this paper. Some calculated results of an example in steady and periodic states are shown and discussed.
Natural Convection From a Horizontal Cylinder—Turbulent Regime
Authors: Farouk B. , Gu¨c¸eri S. I.
Published: October 2009

A two-equation model has been adopted in obtaining numerical solutions of turbulent natural convection from an isothermal horizontal circular cylinder. The k-ε model employed in this study characterizes turbulence through the kinetic energy and its volumetric rate of dissipation. The transport equations for these two variables, along with those for time-averaged stream function, vorticity, and temperature, form a closed set of five coupled partial differential equations. These equations are solved for the entire flow domain, without boundary layer approximations. Buoyancy effects on the turbulence structure are also accounted for. Results are presented for a Rayleigh number range of 5×107 to 1010 and the average Nusselt numbers are compared with existing correlations and limited available experimental data.
Volumetric Heat-Transfer Coefficients for Direct-Contact Evaporation
Authors: Smith R. C. , Rohsenow W. M. , Kazimi M. S.
Published: October 2009

An analytical model has been developed for calculating volumetric heat-transfer coefficients for direct-contact evaporation. Heat transfer is modeled using single droplet correlations for the Nusselt number, while the fluid dynamics are described by a drift-flux model. The analysis is divided into a preagglomerative and a postagglomerative stage on the basis of an assumed maximum value for the dispersed phase volume fraction. The analytical results showed good agreement with data obtained from an experimental direct-contact evaporator using cyclopentane and water.
Hydrodynamics of a Subsonic Vapor Jet in Subcooled Liquid
Authors: Simpson M. E. , Chan C. K.
Published: October 2009

Small scale experiments were performed to investigate the condensation process and hydrodynamic pressure oscillations when steam was discharged into a subcooled water pool. The dynamic behavior of subsonic jets, differed from that of sonic jets. The interfacial motion of a subsonic jet was periodic, composed by three intervals: bubble growth, bubble translation, and bubble separation (necking). The condensation rate for each interval was governed by different processes. The pressure transient of the subsonic jet was marked by periodic impulses, originated by the necking process. Of the intensive parameters studied, pool subcooling exhibited the largest influence on dynamic behavior. The pulse frequency and intensity were found to be best fit by correlations involving the Jacob number and the Reynolds number.
Characteristics of Nucleate Pool Boiling From Porous Metallic Coatings
Authors: Bergles A. E. , Chyu M. C.
Published: October 2009

A study of pool boiling from a commercial porous metallic matrix surface is reported. The excellent steady boiling characteristics of this type of surface are confirmed; however, high wall superheats are required in most cases to initiate boiling. The resultant boiling curve hysteresis does not appear to have been previously reported in the literature. This effect is indicated in recent pilot plant tests. The present results generally confirm the speculated mechanism of boiling with these surfaces and suggest reasons whereby single-tube performance may be superior to tube bundle performance.
Effects of Pore Diameters and System Pressure on Saturated Pool Nucleate Boiling Heat Transfer From Porous Surfaces
Authors: Nakayama W. , Daikoku T. , Nakajima T.
Published: October 2009

The porous surface structure was manufactured with precision for the experimental study of nucleate boiling heat transfer in R-11. Boiling curves and the data of bubble formation were obtained with a variety of geometrical and operational parameters; the pore diameters were of 50, 100, 150 μm, there was a combination of pores of different sizes; and the system pressures were of 0.04, 0.1, 0.23 MPa. The boiling curves exhibit certain trends effected by the diameter and population density of pores. A combination of high system pressure and pore sizes of 100 or 150 μm dia enables boiling to persist even when the wall superheat is reduced to an extremely low level of 0.1 K. A noteworthy feature of porous surface boiling is that intense bubble formation does not necessarily yield a high heat-transfer performance. Examination of the data indicates that liquid suction and evaporation inside the cavities are a proable mechanism of boiling with small temperature differences.
Seepage and Heat Flow in Soil Freezing
Authors: Frivik P. E. , Comini G.
Published: October 2009

In this paper we describe a system of computer programs based on the finite element method, which can be used for the calculation of coupled velocity and temperature fields during freezing and thawing of soils in the presence of seepage flow. In the programs, the mass and energy conservation equations are solved simultaneously, without the use of too limiting assumptions. The results of the computations are compared with experimental measurements made on a laboratory model of a soil freezing system, and the agreement between measured and computed values is good.
Transient Conduction With Pyrolysis (Approximate Solutions for Charring of Wood Slabs)
Authors: Kanury A. M. , Holve D. J.
Published: October 2009

The rate of charring of a heated one-dimensional, wood-like solid slab is predicted by solving the transient conduction equation with a phase-change energy sink term. This solution procedure uses an integral method with spatially-linear-temperature profiles. Two types of front-face boundary conditions are considered—prescribed temperature and prescribed heat flux. The backface is insulated. The prescribed temperature condition leads to the conclusion that for all reasonable exposure temperatures, the slab would only partially char. The maximum char depth is most sensitive to the char conductivity and exposure temperature and less sensitive to the char specific heat and charring endothermicity. Results of the constant flux are in reasonable agreement with the available experimental data both qualitatively and quantitatively.
The Influence of a Laminar Boundary Layer and Laminar Injection on Film Cooling Performance
Authors: Goldstein R. J. , Yoshida T.
Published: October 2009

Measurements are reported of the film cooling effectiveness and heat transfer following injection of air into a mainstream of air. A single row of circular injection holes inclined at an angle of 35 deg is used with a lateral spacing between the holes of 3 dia. Low Reynolds number mainstream and injection flow permit studying the influence of a laminar approaching boundary layer and laminar film coolant flow. Measurements of the surface heat transfer taken with no injection indicate that the hole openings can effectively trip the laminar boundary layer into a turbulent flow. The type of the approaching boundary layer has relatively little influence on either the adiabatic effectiveness or the heat transfer with film cooling. The importance of the nature of the injected flow on film cooling performance can at least be qualitatively explained by the differences in the transport mechanisms and in the penetration of the injected air into the mainstream.
Radiation Configuration Factors Between Disks and a Class of Axisymmetric Bodies
Authors: Naraghi M. H. N. , Chung B. T. F.
Published: October 2009

A general formulation is developed for the radiation shape factors between a disk and a class of coaxial axisymmetric bodies such as cylinder, cone, ellipsoid, and paraboloid. In certain cases, the view factors can be derived analytically directly from the present technique, while in others, they can be generated from a single numerical integration. The analytical solutions for view factors from a disk to a coaxial cylinder based on the present approach are found to agree with those published earlier. The analytical formulae of view factors from disks or annular rings to circular cones, truncated cones, ellipsoid, paraboloids, and truncated praboloid are herein presented.
Heat Transfer From a Buoyant Plume to an Unconfined Ceiling
Authors: Cooper L. Y.
Published: October 2009

The heat transfer to ceilings during enclosure fires is related to the heat transfer to unconfined ceiling surfaces from buoyant plume driven ceiling jets. This paper briefly discusses this relationship, and then focuses attention on the unconfined ceiling problem. Previously published theoretical and experimental studies dealing with interactions of unheated free jets and solid surfaces, as well as literature which focuses directly on fire plume-unconfined ceiling interactions are brought to bear on the problem. A critical review of this literature results in easily applicable formulae for estimating the heat transfer in question.
Two-Dimensional Study of Heat Transfer and Fluid Flow in a Natural Convection Loop
Authors: Mertol A. , Greif R. , Zvirin Y.
Published: October 2009

A study has been made of the heat transfer and fluid flow in a natural convection loop. Previous studies of these systems have utilized a one-dimensional approach which requires a priori specifications of the friction and the heat-transfer coefficients. The present work carries out a two-dimensional analysis for the first time. The results yield the friction and the heat-transfer coefficients and give their variation along the loop with the Graetz number as a parameter. Comparison is also made with experimental data for the heat flux and good agreement is obtained.
Experimental Investigation of Natural Convection in Partitioned Enclosures
Authors: Bajorek S. M. , Lloyd J. R.
Published: October 2009

Natural convection heat transfer within a two-dimensional, partitioned enclosure of aspect ratio 1 was investigated experimentally using a Mach-Zehnder interferometer. The vertical walls were maintained isothermal at different temperatures, while the horizontal walls and the partitions were insulated. Local and average heat-transfer coefficients were determined for the air and carbon dioxide filled enclosures both with and without partitions for Grashof numbers between 1.7×105 and 3.0×106. Good agreement was found between the results in the present study for the nonpartitioned enclosure and those previously published. The partitions were found to significantly influence the convective heat transfer. Observations of the interferometric fringes indicated that the core region is unsteady, with the unsteadiness occasionally affecting the flow along the vertical isothermal walls, beginning at Grashof numbers as low as 5×105.
High Rayleigh Number Solutions to Problems of Latent Heat Thermal Energy Storage in a Horizontal Cylinder Capsule
Authors: Saitoh T. , Hirose K.
Published: October 2009

An analysis was made of the melting and solidification heat transfer inside a horizontal circular cylinder capsule in which n-octadecane or water was used as a phase change material. Special efforts were made to obtain solutions with high Rayleigh numbers (i.e., for large diameters). To this end, the following three tools had been adopted: (i) To save computation time, a high-accuracy, multipoint, explicit finite difference scheme was adopted; (ii) To eliminate complex moving boundaries, two-dimensional Landau transformation was adopted; (iii) To suppress the strong numerical instability, a smoothing technique using the least square method of the sixth order was devised. Transient aspects for natural convection flow, temperature profiles, and melting interfaces were clarified in detail. It is especially noted that entirely different results from those of Pannu et al. were obtained.
Teaching Special Relativity
Authors: Carr James J.
Published: October 2009

I was not one of those many AAPT members to whom Lawrence Ruby refers, that in 2007 received Elisha Huggins' booklet containing the first chapter of a physics textbook espousing the new educational philosophy of teaching special relativity first in elementary physics.
Inexpensive Strobe-like Photographs
Authors: Medeiros Emil L. , Tavares Odilon A. P. , Duarte Sérgio B.
Published: October 2009

This paper reports on a technique the authors have developed to produce and analyze, at very low cost, good quality strobe-like photographs like the one shown in Figs. 1(a) and 1(b). While the concept is similar to the one described by Graney and DiNoto,1 the strategy described here benefits from recent advances in the fields of digital photography and related software to significantly reduce the costs, simplify the production process, and enhance the final quality of photographs of this type, as well as to obtain greater accuracy in measurements made with them.
A Slide Show
Authors: Korsunsky Boris
Published: October 2009

A block is placed on a long and wide inclined plane that makes angle θ with the horizontal. The coefficient of kinetic friction between the block and the plane is μktan θ. After a quick push, the block acquires velocity v0 that makes angle α with the line of fastest descent. Find the time interval τ during which the block is in motion.
Molecular Correlates of High-Level Antifolate Resistance in Rwandan Children with
Plasmodium falciparum
Malaria
Authors: Karema Corine , Imwong Mallika , Fanello Caterina I. , Stepniewska Kasia , Uwimana Aline , Nakeesathit Supatchara , Dondorp Arjen , Day Nicholas P. , White Nicholas J.
Published: October 2009

Antifolate drugs have an important role in the treatment of malaria. Polymorphisms in the genes encoding the dihydrofolate reductase and dihydropteroate synthetase enzymes cause resistance to the antifol and sulfa drugs, respectively. Rwanda has the highest levels of antimalarial drug resistance in Africa. We correlated the efficacy of chlorproguanil-dapsone plus artesunate (CPG-DDS+A) and amodiaquine plus sulfadoxine-pyrimethamine (AQ+SP) in children with uncomplicated malaria caused by
Plasmodium falciparum
parasites with
p
fdhfr
and
p
fdhps
mutations, which are known to confer reduced drug susceptibility, in two areas of Rwanda. In the eastern province, where the cure rates were low, over 75% of isolates had three or more
p
fdhfr
mutations and two or three
p
fdhps
mutations and 11% had the
p
fdhfr
164-Leu polymorphism. In the western province, where the cure rates were significantly higher (
P
< 0.001), the prevalence of multiple resistance mutations was lower and the
p
fdhfr
I164L polymorphism was not found. The risk of treatment failure following the administration of AQ+SP more than doubled for each additional
p
fdhfr
resistance mutation (odds ratio [OR] = 2.4; 95% confidence interval [CI] = 1.01 to 5.55;
P
= 0.048) and each
p
fdhps
mutation (OR = 2.1; 95% CI = 1.21 to 3.54;
P
= 0.008). The risk of failure following CPG-DDS+A treatment was 2.2 times higher (95% CI = 1.34 to 3.7) for each additional
p
fdhfr
mutation, whereas there was no association with mutations in the
p
fdhps
gene (
P
= 0.13). The
p
fdhfr
164-Leu polymorphism is prevalent in eastern Rwanda. Antimalarial treatments with currently available antifol-sulfa combinations are no longer effective in Rwanda because of high-level resistance.
In VitroActivity of Thimerosal against Ocular Pathogenic Fungi
Authors: Xu Yan , Pang Guangren , Zhao Dongqing , Gao Chuanwen , Zhou Lutan , Sun Shengtao , Wang Bingliang
Published: October 2009

Thein vitroactivity of thimerosal versus those of amphotericin B and natamycin was assessed against 244 ocular fungal isolates. The activity of thimerosal againstFusariumspp.,Aspergillusspp., andAlternaria alternatawas 256 times, 512 times, and 128 times, respectively, greater than that of natamycin and 64 times, 32 times, and 32 times, respectively, greater than that of amphotericin B. Thimerosal's antifungal activity was significantly superior to those of amphotericin B and natamycin against ocular pathogenic fungiin vitro.
Attributable Hospital Cost and Length of Stay Associated with Health Care-Associated Infections Caused by Antibiotic-Resistant Gram-Negative Bacteria
Authors: Mauldin Patrick D. , Salgado Cassandra D. , Hansen Ida Solhøj , Durup Darshana T. , Bosso John A.
Published: October 2009

Determination of the attributable hospital cost and length of stay (LOS) are of critical importance for patients, providers, and payers who must make rational and informed decisions about patient care and the allocation of resources. The objective of the present study was to determine the additional total hospital cost and LOS attributable to health care-associated infections (HAIs) caused by antibiotic-resistant, gram-negative (GN) pathogens. A single-center, retrospective, observational comparative cohort study was performed. The study involved 662 patients admitted from 2000 to 2008 who developed HAIs caused by one of following pathogens:Acinetobacterspp.,Enterobacterspp.,Escherichia coli,Klebsiellaspp., orPseudomonasspp. The attributable total hospital cost and LOS for HAIs caused by antibiotic-resistant GN pathogens were determined by comparison with the hospital costs and LOS for a control group with HAIs due to antibiotic-susceptible GN pathogens. Statistical analyses were conducted by using univariate and multivariate analyses. Twenty-nine percent of the HAIs were caused by resistant GN pathogens, and almost 16% involved a multidrug-resistant GN pathogen. The additional total hospital cost and LOS attributable to antibiotic-resistant HAIs caused by GN pathogens were 29.3% (P< 0.0001; 95% confidence interval, 16.23 to 42.35) and 23.8% (P= 0.0003; 95% confidence interval, 11.01 to 36.56) higher than those attributable to HAIs caused by antibiotic-susceptible GN pathogens, respectively. Significant covariates in the multivariate analysis were age ≥12 years, pneumonia, intensive care unit stay, and neutropenia. HAIs caused by antibiotic-resistant GN pathogens were associated with significantly higher total hospital costs and increased LOSs compared to those caused by their susceptible counterparts. This information should be used to assess the potential cost-efficacy of interventions aimed at the prevention of such infections.
Absence of Inflammation and Pneumonia during Infection with Nonpigmented
Yersinia pestis
Reveals a New Role for the
pgm
Locus in Pathogenesis
Authors: Lee-Lewis Hanni , Anderson Deborah M.
Published: October 2009

Yersinia pestis
causes primary pneumonic plague in many mammalian species, including humans, mice, and rats. Virulent
Y. pestis
strains undergo frequent spontaneous deletion of a 102-kb chromosomal DNA fragment, known as the pigmentation (
pgm
) locus, when grown in laboratory media, yet this locus is present in every virulent isolate. The
pgm
locus encodes, within a high-pathogenicity island, siderophore biosynthesis genes that are required for growth in the mammalian host when inoculated by peripheral routes. Recently, higher challenge doses of nonpigmented
Y. pestis
were reported to cause fatal pneumonic plague in mice, suggesting a useful model for studies of virulence and immunity. In this work, we show that intranasal infection of BALB/c mice with nonpigmented
Yersinia pestis
does not result in pneumonic plague. Despite persistent bacterial colonization of the lungs and the eventual death of infected mice, pulmonary inflammation was generally absent, and there was no disease pathology characteristic of pneumonic plague. Iron given to mice at the time of challenge, previously shown to enhance the virulence of
pgm
-deficient strains, resulted in an accelerated disease course, with less time to bacteremia and lethality, but lung inflammation and pneumonia were still absent. We examined other rodent models and found differences in lung inflammatory responses, some of which led to clearance and survival even when high challenge doses were used. Together, the results suggest that the
Y. pestis pgm
locus encodes previously unappreciated virulence factors required for the induction of pneumonic plague that are independent of iron scavenging from the mammalian host.
CcpA and LacD.1 Affect Temporal Regulation ofStreptococcus pyogenesVirulence Genes
Authors: Kietzman Colin C. , Caparon Michael G.
Published: October 2009

Production of H2O2follows a growth phase-dependent pattern that mimics that of many virulence factors ofStreptococcus pyogenes. To gain greater insight into mechanisms coupling virulence factor expression to growth phase, we investigated the molecular basis for H2O2generation and its regulation. Deletion of the gene encoding lactate oxidase (lctO) or culture in the presence of glucose eliminated H2O2production, implicating carbohydrate regulation oflctOas a key element of growth phase control. In examining known carbohydrate-responsive regulators, deletion of the gene encoding CcpA but not that encoding LacD.1 resulted in both derepression and an uncoupling oflctOtranscription from its growth phase pattern. Expanding this analysis to additional virulence factors demonstrated both negative (cfa, encoding CAMP factor) and positive (speB, encoding a cysteine protease) regulation by CcpA and that CcpA mutants were highly cytotoxic for cultured macrophages. This latter property resulted from enhanced transcription of the streptolysin S biogenesis operon. Examination of CcpA-promoter interactions using a DNA pull-down assay mimicking physiological conditions showed direct binding to the promoters oflctOandspeBbut not those ofsagA. CcpA but not LacD.1 mutants were attenuated in a murine model of soft-tissue infection, and analysis of gene expression in infected tissue indicated that CcpA mutants had altered expression oflctO,cfa, andspeBbut not the indirectly regulatedsagAgene. Taken together, these data show that CcpA regulates virulence genes via at least three distinct mechanisms and that disruption of growth phase regulation alters transcriptional patterns in infected tissues.
Localization and Developmental Regulation of a Dispersed Gene Family 1 Protein in
Trypanosoma cruzi
Authors: Lander Noelia , Bernal Carolina , Diez Nardy , Añez Néstor , Docampo Roberto , Ramírez José Luis
Published: October 2009

The dispersed gene family 1 (
DGF-1
) is the fifth largest gene family in the
T
rypanosoma cruzi
genome, with over 500 members (11). Many of the predicted
DGF-1
protein products have several transmembrane domains and N
-
glycosylation and phosphorylation sites and were thought to localize in the plasma membrane. Here, we report that affinity-purified antibodies against a region of one of these proteins (DGF-1.2) localized it intracellularly in different stages of the parasite. DGF-1.2 is more abundant in the amastigote stage than in trypomastigotes and epimastigotes, as detected by immunofluorescence and Western blot analyses. The protein changed localization during intracellular or extracellular differentiation from the trypomastigote to the amastigote stage, where it finally localized to small bodies in close contact with the inner side of the amastigote plasma membrane. DGF-1.2 did not colocalize with markers of other subcellular organelles, such as acidocalcisomes, glycosomes, reservosomes, lipid droplets, or endocytic vesicles. During extracellular differentiation, the protein was detected in the culture medium from 0 to 22 h, peaking at 14 h. The presence of DGF-1.2 in the differentiation culture medium was confirmed by mass spectrometry analysis. Finally, when epimastigotes were subjected to starvation, there was a decrease in the labeling of the cells and, in Western blots, the appearance of bands of lower molecular mass, suggesting its cleavage. These results represent the first report of direct immunodetection and developmental expression and secretion of a DGF-1 protein.
Bicarbonate as a Potential Confounding Factor in Cladoceran Toxicity Assessments of Pore Water from Contaminated Sediments
Authors: Hoke Robert A. , Gala William R. , Drake James B. , Giesy John P. , Flegler Stan
Published: October 2009

Elevated alkalinity values measured in sediment pore water samples from the Grand Calumet River–Indiana Harbor Canal, an International joint Commission Area of Concern (AOC), caused concern over the potential effects of alkalinity on cladoceran test responses. Forty-eight-hour tests with NaHCO3and NaCl as reference toxicants indicated that NaHCO3toxicity to Daphnia magna and Ceriodaphnia dubia was due to both Na+and HCO3−, although greater HCO3−toxicity was observed to D. magna. Theoretical HCO3−concentrations in sediment pore waters from the AOC demonstrated sufficient HCO3−in several samples to produce acute toxicity, based on 48-h LC50s from the reference toxicant tests. X-ray microanalysis was conducted to qualitatively assess the effects on internal Cl−levels of D. magna after exposure to NaHCO3, to an AOC sediment pore water sample, and to NaSCN, a metabolic inhibitor of Cl−uptake. Based on these results the proposed mechanism of HCO3−toxicity to D. magna is the inhibition of the active uptake of Cl−from water. We suggest that pore water alkalinity should be considered when interpreting the results of sediment pore water and effluent toxicity tests with D. magna, other cladocerans, and, perhaps, other invertebrates and fish.
Food Consumption of Juvenile Coho (Oncorhynchus kisutch) and Chinook Salmon (O. tshawytscha) on the Continental Shelf off Washington and Oregon
Authors: Brodeur Richard D. , Francis Robert C. , Pearcy William G.
Published: October 2009

The overall food consumption by juvenile coho (Oncorhychus kisutch) and chinook salmon (O. tshawytscha) along the continental shelf off Washington and Oregon was estimated for the summer months of 1981–84 using both a direct field and indirect bioenergetic approach. Both models yielded similar estimates but the consumption estimated by the bioenergetic model was 14.8 and 3.2% higher for coho and chinook salmon, respectively. In a given year, overall consumption increased throughout the summer, despite decreasing abundances of both salmon species, but there were substantial differences among the four years within the same month. A preliminary comparison of the consumption estimates for important prey taxa early in the summer with estimated zooplankton biomass suggested that sufficient food levels may have been available for salmon during 1981. During the El Niño of 1983, however, several prey groups were consumed at high levels relative to their estimated availability and the biomass of these taxa may not have been sufficient to sustain the total population of salmon.