bluuebunny/crossref_metadata_2025 huggingface dataset:
Free Convection Effects on the Developing Laminar Flow in Vertical Concentric Annuli
Authors: El-Shaarawi M. A. I. , Sarhan A.
Published: October 2009

Coupled energy and momentum boundary layer equations have been numerically solved for the problem of combined forced-free laminar convection in the entrance region of vertical concentric annuli. Both upflow and downflow of a fluid with Pr = 0.7 are considered under the thermal conditions of one wall being isothermal and the other adiabatic. Results for the development of velocity profiles, axial distance at which the axial velocity gradient normal to the wall vanishes, pressure drop, and heat transfer characteristics are presented at various values of the parameter Gr/Re ranged from −700 to 1500.
Natural Convection in a Porous Layer under the Influence of an Exothermic Decomposition Reaction
Authors: Saatdjian E. , Caltagirone J. P.
Published: October 2009

A porous medium saturated with a gas is bounded by two impermeable planes. As the temperature of the lower side is increased, part of the porous matrix decomposes exothermically into gaseous products. A two dimensional model which couples the effects of this reaction to natural convection is solved numerically. At first, the reaction dominates the phenomena; the temperature and velocity components increase and a thermal front passes through the layer. As the reaction dies out due to a depletion of reactant, convective effects alone remain. Though this final state is well known, the density of the fluid is, here, allowed to vary and, furthermore, an ideal gas instead of an incompressible liquid is considered.
A Comparison of a Penalty Finite Element Model with the Stream Function-Vorticity Model of Natural Convection in Enclosures
Authors: Reddy J. N. , Satake Akio
Published: October 2009

This paper is concerned with a comparative study of the stream function-vorticity formulation and penalty function formulation of the two-dimensional equations governing natural connection in enclosures. The penalty function formulation presented herein is the only correct way of describing it for the problem at hand. The penalty-finite element model developed herein is novel with this work, and involves two velocities, temperature, and stream function as degrees of freedom at each node. The model includes, as a special case, the penalty-finite element model of natural convection in enclosures reported in the literature. Numerical results obtained using the two formulations are compared for several geometries, and boundary conditions, and the effects of Rayleigh number and Prandtl number on the flow and heat transfer are studied.
Effects of Natural Convection in the Melted Region Around a Heated Horizontal Cylinder
Authors: Yao L. S. , Chen F. F.
Published: October 2009

Two heat transfer modes are involved in the process of melting around a heated horizontal cylinder: conduction and convection. The magnitude of convection is proportional to the Rayleigh number based on the width of the melted region. The importance of natural convection increases with time. For a short period after the beginning of melting, heat transfer is dominated by conduction. A regular perturbation solution is presented to demonstrate the increasing effect of natural convection on the melting process.
Anisotropic Conduction and Surface Radiation around a Hollow Cylinder
Authors: Edwards D. K.
Published: October 2009

An analytical expression is developed for the temperature distribution in the wall of a hollow cylinder radiantly heated externally in a circumferentially nonuniform manner. The solution includes two-dimensional anisotropic conduction within the wall, external radiation absorption and emission, and internal radiation heat transfer. Sample results are presented for a graphite-reinforced boom exposed to solar heating in space.
Turbulent Transfer of Momentum and Heat in a Separated and Reattached Flow over a Blunt Flat Plate
Authors: Ota Terukazu , Kon Nobuhiko
Published: October 2009

Turbulent shear stress and heat flux were measured with a hot-wire anemometer in the separated, reattached, and redeveloped regions of a two-dimensional incompressible air flow over a flat plate of finite thickness having blunt leading edge. The characteristic features of the turbulent heat flux are found to be nearly equal to those of the turbulent shear stress in the separated and reattached flow regions. However, in the turbulent boundary layer downstream from the reattachment point, the development of turbulent heat flux appears to be much quicker than that of turbulent shear stress. Eddy diffusivities of momentum and heat are evaluated and then the turbulent Prandtl number is estimated in the thermal layer downstream of reattachment. These results are compared with the available previous data.
Analysis of Heat Transfer During Hydrair Cooling of Slab-Shaped Food Products—Part I: Theoretical Investigations
Authors: Abdul Majeed P. M.
Published: October 2009

Hydrair cooling of perishable food products is expected to incorporate the advantages of both air cooling and hydrocooling processes. This technique consists of passing cold air over a product which is continuously wetted by a spray of chilled water. In this paper, a mathematical model for the hydrair cooling of slab-shaped food products is proposed. The set of differential equations for heat transfer through the product and the wetting liquid are solved simultaneously, using finite difference method. It is observed that the process of hydrair cooling is advantageous at lower values of the film Reynolds number for higher Biot number values. The cooling speed and the governing parameters are correlated.
An Experimental Investigation of Merging Buoyant Jets in a Crossflow
Authors: Gregoric M. , Davis L. R. , Bushnell D. J.
Published: October 2009

Merging buoyant jets discharged in a crossflow were investigated experimentally using a unique visualization technique. Salt water jets were discharged from a constant head tank while being towed in an inverted position at desired rates through stagnant receiving water. Visualization of the jet cross section was produced by using fluorescent dye and a vertical slit light source. The results were photographed as a sequence of instantaneous cross sections taken by a motor-driven camera. Maximum heights, widths, and the vertical cross sections of the deflected jets were determined for different ratios of crossflow velocity to discharge velocity, number of discharge jets and discharge nozzle line orientation. Horseshoe shaped cross sections were observed in the cases of a single jet and multiple jets where the crossflow velocity was parallel to the line of discharge ports, but the horseshoe pattern was not clear when the cross flow was perpendicular to the line of multiple jets. The wake behind the multiple jets in the crossflow exhibited a distinct trailing vortex sheet.
Natural Convection in an Attic-Shaped Space Filled With Porous Material
Authors: Bejan A. , Poulikakos D.
Published: October 2009

This article reports an analytical study of natural convection in a wedge-shaped horizontal space filled with a fluid-saturated porous medium. The study focuses on the detrimental effect of natural convection on the insulation value of an attic-shaped porous layer in “winter” conditions (cold roof, warm ceiling). The study reveals the most basic features of the temperature field and flow pattern established in the porous layer. The study addresses two distinct flow regimes: (a) the shallow attic limit (H/L→0, RaH = finite, but fixed) and (b) the boundary layer regime which consists of a boundary layer driven by the sloped (roof) wall plus a core flow moving slowly along the horizontal (ceiling) wall. Heat-transfer results are developed for both flow regimes.
An Application of the Optical Correlation Computer to the Detection of the Malkus Transitions in Free Convection
Authors: Somerscales E. F. C. , Parsapour H. B.
Published: October 2009

This paper presents the results of an investigation concerned with measurements of the scale-size of the flow patterns near the so-called Malkus transitions. The flow patterns in a heated fluid layer were photographed at various Rayleigh numbers and these photographs subjected to quantitative analysis using an optical correlation computer. The results showed that the method provides a very sensitive technique for locating the transitions. Transitions reported by other investigators have been confirmed for Rayleigh numbers between 5.0 × 103 and 1.0 × 106, and an additional, previously unobserved, transition has been detected. Heat-transfer measurements were also made. This data demonstrated the limitations, compared to the optical method, of this approach to the detection of transitions.
Pool Boiling Heat Transfer From Enhanced Surfaces to Dielectric Fluids
Authors: Marto P. J. , Lepere V. J.
Published: October 2009

Pool boiling heat-transfer measurements were made using a 15.8 mm o.d. plain copper tube and three copper enhanced surfaces: a Union Carbide High Flux surface, a Hitachi Thermoexcel-E surface and a Wieland Gewa-T surface. The dielectric fluids were Freon-113 and Fluorinert FC-72, a perfluorinated organic compound manufactured to cool electronic equipment. Data were taken at atmospheric pressure, and at heat fluxes from 100 W/m2 to 200,000 W/m2. Prior to operation, each test surface was subjected to one of three aging procedures to observe the effect of surface past history upon boiling incipience. For Freon-113 the enhanced surfaces showed a two to tenfold increase in the heat-transfer coefficient when compared to a plain tube, whereas for FC-72 an increase of two to five was measured. The High Flux surface gave the best performance over the range of heat fluxes. The Gewa-T surface did not show as much of an enhancement at low fluxes as the other two surfaces, but at high fluxes its performance improved. In fact, it was the only surface tested which delayed the onset of film boiling with FC-72. The degree of superheat required to activate the enhanced surfaces was sensitive to both past history of the surface and to fluid properties.
A Theoretical Study of Ignition in the Laminar Mixing Layer
Authors: Law C. K. , Law H. K.
Published: October 2009

The structure of the weakly reactive states leading to ignition in the laminar mixing layer flow is studied both analytically and numerically. It is shown that the flow consists of a reactive region and a self-similar frozen region separated by a transitional, nonsimilar frozen region, that the reactive region is intrinsically nonsimilar because of its excessively slow diffusion rate, and that the ignition characteristics are primarily governed by the velocity of the hot stream and therefore minimally dependent on the velocity distribution. Fundamental functional groups are identified, and an explicit prescription is presented, for large activation energy reactions, for the evaluation of the minimum streamwise distance to achieved ignition.
The Galerkin Method for Solving Radiation Transfer in Plane-Parallel Participating Media
Authors: O¨zis¸ik M. N. , Yener Y.
Published: October 2009

The Galerkin method is applied to solve radiative heat transfer in an isotropically scattering, absorbing, and emitting plane-parallel medium with diffusely reflecting boundaries. In this approach, the integral form of the equation of radiative transfer is transformed into a set of algebraic equations for the determination of the expansion coefficients associated with the representation of the incident radiation in a power series in the space variable. The method is easy and straightforward to apply and requires relatively little computer time for the computations, since explicit analytical expressions are obtainable for the expansion coefficients.
Flow Induced Vibration in a Heat Exchanger With Seal Strips
Authors: Kissel J. H.
Published: October 2009

Flow induced vibration tests using water as the shell side medium were conducted on a shell and tube exchanger with single segmental baffles and various tube layouts. The heat exchanger was of the externally packed floating head type with seal strips that directed the water flow into the bundle to prevent by-passing of the fluid between the bundle and the shell. High localized velocities exist in the vicinity of the seal strips and contributed directly to the vibration problem. The tube natural frequency for various baffle spacings was measured at the vibration point and a gap velocity at the critical section of the bundle was estimated. A correlation was then made with these parameters and the fluidelastic excitation theory. A discussion of the velocity profile through the heat exchanger is included.
Optimal Finite Analytic Methods
Authors: Manohar R. , Stephenson J. W.
Published: October 2009

A new method is proposed for obtaining finite difference equations for the solution of linear partial differential equations. The method is based on representing the approximate solution locally on a mesh element by polynomials which satisfy the differential equation. Then, by collocation, the value of the approximate solution, and its derivatives at the center of the mesh element may be expressed as a linear combination of neighbouring values of the solution.
The Motion of Particles Inside a Droplet
Authors: Chung J. N.
Published: October 2009

Equations of motion for particles translating inside a droplet with internal circulation were developed. The forces experienced by these particles and their relative importance are also summarized. Sample calculations for coal particles in oil droplets show that for high-droplet Reynolds numbers, particles will accumulate near the droplet surface before substantial evaporation of the droplet, based on the results that the characteristic time of transport is two orders of magnitude smaller than the droplet lifetime. These accumulations of particles near the droplet surface will probably result in particle agglomeration. Fow low-droplet Reynolds numbers, the particles are making slow looping motions and the characteristic time of transport is comparable to the droplet lifetime. This results in a more even distribution of particles in the droplet with slightly higher particle density near the surface. This indicates a higher particle burning rate and the possibility of internal boiling and microexplosion due to heterogeneous nucleation initiated from those coal particles.
Laminar Wavy-Film Flow: Part I, Hydrodynamic Analysis
Authors: Hirshburg R. I. , Florschuetz L. W.
Published: October 2009

The hydrodynamic characteristics of thin, laminar, gravity-driven, wavy-film flow are considered. A theoretical model is developed to predict the hydrodynamic features of asymptotic, wavy-flow states. The mathematical closure question arising in asymptotic-state analyses is resolved by incorporating the results of a prior stability analysis of smooth-film flow. Calculated values for mean film thickness, trough-to-crest dimension, wave celerity, and wavelength are found to be consistent with published experimental data for these quantities.
Heat Transfer From Vertical/Inclined Boundaries of Heat-Generating Boiling Pools
Authors: Chawla T. C. , Chan S. H.
Published: October 2009

A model for heat transfer from the sides of a volume heated boiling pool is proposed. Because of the density difference caused by volume boiling and by thermal expansion due to the temperature difference between the bulk fluid and the fluid near the wall, the lighter liquid and vapor bubbles cause movement of the bulk fluid in the upward direction. The rising liquid between the bubbles finds a return path along the walls or sides of the pool and forms a boundary layer which may be laminar in its initial length followed by transition to turbulent depending, of course, on the conditions prevailing at the entry to the sides and in the bulk of the pool. The analysis for the laminar case provides the definition of equivalent Grashof number for the combined two-phase and thermal expansion driven natural convection along the sides of pool. The turbulent boundary layer is analyzed by assuming a two-layer model in which the inner layer is characterized by viscous and conduction terms and the outer by mean convection terms. The similarity analysis of the governing equations yields universal profiles for temperature and velocity and the scaling laws for the inner and outer layers. An asymptotic matching of the temperature profile in the overlap region leads to a heat transfer law which correlates the available experimental data on volume heated boiling pools exceedingly well.
Latent and Sensible Heat-Transfer Rates in the Boiling of Binary Mixtures
Authors: Thome J. R.
Published: October 2009

Nucleate pool boiling bubble departure data were obtained for the liquid nitrogen-argon cryogenic binary mixture system at 1.3 atmospheres absolute pressure. The latent and sensible heat transport rates at individual boiling sites were calculated from the data to deduce their effect on the degradation in the boiling heat-transfer coefficient in binary mixtures. The latent heat-transfer rate is a result of the bubble evaporation mechanism and the sensible heat-transport rate is due to cyclic thermal boundary layer stripping by departing bubbles. The latent and sensible heat-transport rates at individual boiling sites were found to decrease to a minimum at the maximum vapor-liquid mole fraction difference for both constant heat flux and wall superheating conditions. The large decrease in binary boiling heat-transfer coefficients was thus partially explained by the retardation of these two mechanisms and should be included in any model for predicting boiling heat-transfer coefficients in binary and multicomponent mixtures.
Free Convection Heat Transfer From Upward-Facing Isothermal Horizontal Surfaces
Authors: Yousef W. W. , Tarasuk J. D. , McKeen W. J.
Published: October 2009

Heat transfer by free convection in air from isothermal horizontal surfaces heated and facing upward has been experimentally studied by using a Mach-Zehnder interferometer. The local and the average heat-transfer coefficients and the temperature distributions were determined in the range of Gr Pr from 1.9 × 106 to 1.7 × 108. Measurements were compared with available experimental and theoretical results. Periodical flow instabilities caused random changes, which could reach +45 and −35 percent of mean values in the local Nusselt number and +23 and −15 percent of mean value in the average Nusselt number. The nature of the free convection flow over the heated surface and the separation of the boundary layer were inferred from these random changes in the local and average Nusselt numbers.
Experiments on Free Convection Between Vertical Plates With Symmetric Heating
Authors: Wirtz R. A. , Stutzman R. J.
Published: October 2009

Laboratory experiments on natural convection of air between vertical parallel plates with uniform and symmetric heat fluxes are reported. Data collection was through direct temperature measurement using thermocouples and through analysis of interferograms of the flow. Data were collected over a range of heat fluxes and geometric parameters where the flow was in the developing temperature field regime. A correlation is developed that allows for the calculation of the maximum temperature variation of the plates for a given input heat flux and plate geometry. The equation is expected to be accurate to ±5 percent.
Effect of Thermal Boundary Conditions on Natural Convection in Vertical and Inclined Air Layers
Authors: ElSherbiny S. M. , Hollands K. G. T. , Raithby G. D.
Published: October 2009

Measurements of the heat transfer by natural convection across vertical and inclined air layers are reported. The air layer is bounded by two parallel isothermal flat plates and around the edges by a low thermal conductivity wall of thickness B. A critical wall thickness Bc was determined by solving the two-dimensional conduction equation in the bounding wall region: for B>Bc the convective heat transfer should be insensitive to B. Measurements are reported for air layers with B>Bc and an aspect ratio of 5. They cover a range in Rayleigh number from 103 to 108, and a range in orientation from horizontal to vertical. The effect of the emissivity of the bounding wall on the heat transfer across the air layer was evaluated from measurements obtained respectively with a low and a high value of the wall emissivity. The paper proposes terminology required to define the thermal conditions, and discusses the impact of these boundary conditions on the total heat transfer.
Transient Natural Convection Experiments in Shallow Enclosures
Authors: Yewell R. , Poulikakos D. , Bejan A.
Published: October 2009

This paper reports experimental observations on transient natural convection in enclosures at high Rayleigh numbers (1.28×109, 1.49×109) and low aspect ratios (0.0625, 0.112). The phenomenon consists of the establishment of thin intrusion layers along the horizontal adiabatic surfaces; in time, the intrusion layers exchange heat with the isothermal core of the cavity, leading to the thermal stratification of the core. The approach to steady state is gradual, contrary to the theoretical prediction of Brunt-Vaisala wave motion (Patterson and Imberger [6]). The measured durations of the observed transients agree very well with theoretical estimates.
Heat Transfer Through a Double Pane Window
Authors: Korpela S. A. , Lee Yee , Drummond J. E.
Published: October 2009

By finite difference calculations the convective flow in a vertical enclosure heated from a side is investigated. The emphasis in the study is for the flow of air in a window cavity. Detailed plots of the stream patterns and isotherms in a multicellular flow are shown and vertically averaged Nusselt numbers as well as typical local values are given. The calculations compare favorably with the experiments of ElSherbiny, Raithby, and Hollands. A working formula for window spacings is suggested.
Patients with Long-Term Oral Carriage Harbor High-Persister Mutants of
Candida albicans
Authors: LaFleur Michael D. , Qi Qingguo , Lewis Kim
Published: October 2009

Fungal biofilms produce a small number of persister cells which can tolerate high concentrations of fungicidal agents. Persisters form upon attachment to a surface, an important step in the pathogenesis of
Candida
strains. The periodic application of antimicrobial agents may select for strains with increased levels of persister cells. In order to test this possibility, 150 isolates of
Candida albicans
and
C. glabrata
were obtained from cancer patients who were at high risk for the development of oral candidiasis and who had been treated with topical chlorhexidine once a day. Persister levels were measured by exposing biofilms growing in the wells of microtiter plates to high concentrations of amphotericin B and plating for survivors. The persister levels of the isolates varied from 0.2 to 9%, and strains isolated from patients with long-term carriage had high levels of persisters. High-persister strains were isolated from every patient with
Candida
carriage of more than 8 consecutive weeks but from no patients with transient carriage. All of the high-persister isolates had an amphotericin B MIC that was the same as that for the wild type, indicating that these strains were drug-tolerant rather than drug-resistant mutants. Biofilms of the majority of high-persister strains also showed an increased tolerance to chlorhexidine and had the same MIC for this antimicrobial as the wild type. This study suggests that persister cells are clinically relevant, and antimicrobial therapy selects for high-persister strains in vivo. The drug tolerance of persisters may be a critical but overlooked component responsible for antimicrobial drug failure and relapsing infections.
Continuous Clindamycin Infusion, an Innovative Approach to Treating Bone and Joint Infections
Authors: Zeller Valérie , Dzeing-Ella Arnaud , Kitzis Marie-Dominique , Ziza Jean-Marc , Mamoudy Patrick , Desplaces Nicole
Published: October 2009

The feasibility, safety, and efficacy of prolonged, continuous, intravenous clindamycin therapy were retrospectively evaluated for 70 patients treated for bone and joint infections, 40% of whom were treated as outpatients. The median treatment duration was 40 days, the median daily clindamycin dose was 2,400 mg, and three moderate-grade adverse events occurred. The median serum clindamycin concentrations on days 3 to 14 and days 8 to 28 were 5 and 6.2 mg/liter, respectively; the median concentration was significantly lower (
P
< 0.02) in patients treated with rifampin (5.3 mg/liter) than in those not treated with rifampin (8.9 mg/liter). Among 53 patients with a median follow-up of 30 months (range, 24 to 53 months), 49 (92%) were considered cured (1 patient had a relapse, and 3 patients had reinfections).
In Vitro Activity of Mirincamycin (U24729A) against
Plasmodium falciparum
Isolates from Gabon
Authors: Held Jana , Westerman Richard , Kremsner Peter G. , Mordmüller Benjamin
Published: October 2009

We assessed the in vitro activity of mirincamycin, a lincosamide antibiotic, against
Plasmodium falciparum
clinical isolates from Gabon. Growth was determined by HRP2 enzyme-linked immunosorbent assay using an adapted protocol with a prolonged incubation time (6 days) to account for antibiotic-induced delayed death. Mirincamycin's
cis
and
trans
isomers are more active (median 50% inhibitory concentrations [IC
50
s], 3.2 nM and 2.6 nM) than the comparator drugs clindamycin (IC
50
, 12 nM) and doxycycline (IC
50
, 720 nM), and therefore, further clinical development is promising.
Mouse Macrophages Are Permissive to MotileLegionellaSpecies That Fail To Trigger Pyroptosis
Authors: Whitfield Natalie N. , Byrne Brenda G. , Swanson Michele S.
Published: October 2009

Legionella pneumophila, a motile opportunistic pathogen of humans, is restricted from replicating in the lungs of C57BL/6 mice. Resistance of mouse macrophages toL. pneumophiladepends on recognition of cytosolic flagellin. Once detected by the NOD-like receptors Naip5 and Ipaf (Nlrc4), flagellin triggers pyroptosis, a proinflammatory cell death. In contrast, motile strains ofL. parisiensisandL. tucsonensisreplicate profusely within C57BL/6 macrophages, similar to flagellin-deficientL. pneumophila. To gain insight into how motile species escape innate defense mechanisms of mice, we compared their impacts on macrophages.L. parisiensisandL. tucsonensisdo not induce proinflammatory cell death, as measured by lactate dehydrogenase (LDH) release and interleukin-1β (IL-1β) secretion. However, flagellin isolated fromL. parisiensisandL. tucsonensistriggers cell death and IL-1β secretion when transfected into the cytosol of macrophages. Neither strain displays three characteristics of the canonicalL. pneumophilaDot/Icm type IV secretion system: sodium sensitivity, LAMP-1 evasion, and pore formation. Therefore, we postulate that whenL. parisiensisandL. tucsonensisinvade a mouse macrophage, flagellin is confined to the phagosome, protecting the bacteria from recognition by the cytosolic surveillance system and allowingLegionellato replicate. Despite their superior capacity to multiply in mouse macrophages,L. parisiensisandL. tucsonensishave been associated with only two cases of disease, both in renal transplant patients. These results point to the complexity of disease, a product of the pathogenic potential of the microbe, as defined in the laboratory, and the capacity of the host to mount a measured defense.
Mannose Receptor-Dependent Delay in Phagosome Maturation by
Mycobacterium avium
Glycopeptidolipids
Authors: Sweet Lindsay , Singh Prachi P. , Azad Abul K. , Rajaram Murugesan V. S. , Schlesinger Larry S. , Schorey Jeffrey S.
Published: October 2009

The ability of pathogenic mycobacteria to block phagosome-lysosome fusion is critical for its pathogenesis. The molecules expressed by mycobacteria that inhibit phagosome maturation and the mechanism of this inhibition have been extensively studied. Recent work has indicated that mannosylated lipoarabinomannan (ManLAM) isolated from
Mycobacterium tuberculosis
can function to delay phagosome-lysosome fusion and that this delay requires the interaction of ManLAM with the mannose receptor (MR). However, the molecules expressed by other pathogenic mycobacteria that function to inhibit phagosome maturation have not been well described. In the present study, we show that phagosomes containing silica beads coated with glycopeptidolipids (GPLs), a major surface component of
Mycobacterium avium
, showed limited acidification and delayed recruitment of late endosomal/lysosomal markers compared to those of phosphatidylcholine-coated beads. The carbohydrate component of the GPLs was required, as beads coated only with the lipopeptide core failed to delay phagosome-lysosome fusion. Moreover, the ability of GPLs to delay phagosome maturation was dependent on the macrophage expression of the MR. Using CHO cells expressing the MR, we confirmed that the GPLs bind this receptor. Finally, human monocyte-derived macrophages knocked down for MR expression showed increased
M. avium
phagosome-lysosome fusion relative to control cells. Together, the data indicate that GPLs can function to delay phagosome-lysosome fusion and suggest that GPLs, like ManLAM, work through the MR to mediate this activity.
Characterization of Novel β-Galactosidase Activity That Contributes to Glycoprotein Degradation and Virulence in
Streptococcus pneumoniae
Authors: Terra Vanessa S. , Homer Karen A. , Rao Susmitha G. , Andrew Peter W. , Yesilkaya Hasan
Published: October 2009

The pneumococcus obtains its energy from the metabolism of host glycosides. Therefore, efficient degradation of host glycoproteins is integral to pneumococcal virulence. In search of novel pneumococcal glycosidases, we characterized the
Streptococcus pneumoniae
strain D39 protein encoded by
SPD_0065
and found that this gene encodes a β-galactosidase. The SPD_0065 recombinant protein released galactose from desialylated fetuin, which was used here as a model of glycoproteins found
in vivo
. A pneumococcal mutant with a mutation in
SPD_0065
showed diminished β-galactosidase activity, exhibited an extended lag period in mucin-containing defined medium, and cleaved significantly less galactose than the parental strain during growth on mucin. As pneumococcal β-galactosidase activity had been previously attributed solely to
SPD_0562
(
bgaA
), we evaluated the contribution of
SPD_0065
and
SPD_0562
to total β-galactosidase activity. Mutation of either gene significantly reduced enzymatic activity, but β-galactosidase activity in the double mutant, although significantly less than that in either of the single mutants, was not completely abolished. The expression of
SPD_0065
in
S. pneumoniae
grown in mucin-containing medium or tissues harvested from infected animals was significantly upregulated compared to that in pneumococci from glucose-containing medium. The
SPD_0065
mutant strain was found to be attenuated in virulence in a manner specific to the host tissue.
The Presence of CD14 Overcomes Evasion of Innate Immune Responses by VirulentFrancisella tularensisin Human Dendritic Cells In Vitro and Pulmonary Cells In Vivo
Authors: Chase Jennifer C. , Bosio Catharine M.
Published: October 2009

Francisella tularensisis a Gram-negative bacterium that causes acute, lethal disease following inhalation. We have previously shown that viableF.tularensisfails to stimulate secretion of proinflammatory cytokines following infection of human dendritic cells (hDC) in vitro and pulmonary cells in vivo. Here we demonstrate that the presence of the CD14 receptor is critical for detection of virulentF.tularensisstrain SchuS4 by dendritic cells, monocytes, and pulmonary cells. Addition of soluble CD14 (sCD14) to hDC restored cytokine production following infection with strain SchuS4. In contrast, addition of anti-CD14 to monocyte cultures inhibited the ability of these cells to respond to strain SchuS4. Addition of CD14 or blocking CD14 following SchuS4 infection in dendritic cells and monocytes, respectively, was not due to alterations in phagocytosis or replication of the bacterium in these cells. Administration of sCD14 in vivo also restored cytokine production following infection with strain SchuS4, as assessed by increased concentrations of tumor necrosis factor alpha (TNF-α), interleukin-1β (IL-1β), IL-12p70, and IL-6 in the lungs of mice receiving sCD14 compared to mock-treated controls. In contrast to homogenous cultures of monocytes or dendritic cells infected in vitro, mice treated with sCD14 in vivo also exhibited controlled bacterial replication and dissemination compared to mock-treated controls. Interestingly, animals that lacked CD14 were not more susceptible or resistant to pulmonary infection with SchuS4. Together, these data support the hypothesis that the absence or low abundance of CD14 on hDC and in the lung contributes to evasion of innate immunity by virulentF.tularensis. However, CD14 is not required for development of inflammation during the last 24 to 48 h of SchuS4 infection. Thus, the presence of this receptor may aid in control of virulentF.tularensisinfections at early, but not late, stages of infection.
Helicobacter pylori
Promotes the Production of Thymic Stromal Lymphopoietin by Gastric Epithelial Cells and Induces Dendritic Cell-Mediated Inflammatory Th2 Responses
Authors: Kido Masahiro , Tanaka Junya , Aoki Nobuhiro , Iwamoto Satoru , Nishiura Hisayo , Chiba Tsutomu , Watanabe Norihiko
Published: October 2009

Helicobacter pylori
colonizes the stomach and induces strong, specific local and systemic humoral and cell-mediated immunity, resulting in the development of chronic gastritis in humans. Although
H. pylori
-induced chronic atrophic gastritis is characterized by marked infiltration of T helper type 1 (Th1) cytokine-producing CD4
+
T cells, almost all of the inflamed gastric mucosae also contain focal lymphoid aggregates with germinal centers. In addition, typical
H. pylori
-induced chronic gastritis in children, called follicular gastritis, is characterized by B-cell follicle formation in the gastric mucosa. The aim of this study was to examine whether thymic stromal lymphopoietin (TSLP), an epithelial-cell-derived cytokine inducing a dendritic cell (DC)-mediated inflammatory Th2 response, is involved in Th2 responses triggering B-cell activation in
H. pylori
-induced gastritis. Here, we show that
H. pylori
triggered human gastric epithelial cells to produce TSLP, together with the DC-attracting chemokine MIP-3α and the B-cell-activating factor BAFF. After DCs were incubated with supernatants from
H. pylori
-infected epithelial cells, the conditioned cells expressed high levels of costimulatory molecules, such as CD80, and triggered naïve CD4
+
T cells to produce high levels of the Th2 cytokines interleukin-4 and interleukin-13 and of the inflammatory cytokines tumor necrosis factor alpha and gamma interferon. In contrast, after incubation of the supernatants with the neutralizing antibodies to TSLP, the conditioned DCs did not prime T cells to produce high levels of Th2 cytokines. These results, together with the finding that TSLP was expressed by the epithelial cells of human follicular gastritis, suggest that
H. pylori
can directly trigger epithelial cells to produce TSLP. It also suggests that TSLP-mediated DC activation may be involved in Th2 responses triggering B-cell activation in
H. pylori
-induced gastritis.
Host Chemokine and Cytokine Response in the Endocervix within the First Developmental Cycle of
Chlamydia muridarum
Authors: Rank Roger G. , Lacy H. Marie , Goodwin Anna , Sikes James , Whittimore Judy , Wyrick Priscilla B. , Nagarajan Uma M.
Published: October 2009

The initial host response in a primary chlamydial infection is the onset of acute inflammation. However, we still know very little about the early temporal events in the induction of the acute inflammatory response and how these events relate to the initial chlamydial developmental cycle in an actual genital infection. Because it was critical to initiate a synchronous infection in the endocervix in the first 24 h to evaluate the sequential expression of the host response, we developed the surgical methodology of depositing
Chlamydia muridarum
directly on the endocervix. Cervical tissue was collected at 3, 12, and 24 h after inoculation and the expression array of chemokines, cytokines, and receptors was assessed to characterize the response during the initial developmental cycle. Polymorphonuclear leukocyte (PMN) infiltration was first observed at 12 h after inoculation, and a few PMNs could be seen in the epithelium at 24 h. Electron microscopic analysis at 24 h showed that virtually all inclusions were at the same stage of development, indicating a synchronous infection. Several chemokine and cytokine genes were expressed as early as 3 h after infection, but by 12 h, 41 genes were expressed. Thus, activation of the host response occurs both with the introduction of elementary bodies into the host and early replication of reticulate bodies. No significant response was observed when UV-inactivated organisms were inoculated into the cervix at any time interval. This model provides an ideal opportunity to investigate the mechanisms by which the early inflammatory response is induced in vivo.
Roles of Capsule and Lipopolysaccharide O Antigen in Interactions of Human Monocyte-Derived Dendritic Cells and
Klebsiella pneumoniae
Authors: Evrard B. , Balestrino D. , Dosgilbert A. , Bouya-Gachancard J.-L. J. , Charbonnel N. , Forestier C. , Tridon A.
Published: October 2009

In humans,
Klebsiella pneumoniae
is a saprophytic bacterium of the nasopharyngeal and intestinal mucosae that is also frequently responsible for severe nosocomial infections. Two major factors of virulence, capsular polysaccharide (CPS) and lipopolysaccharide (LPS) O antigen, are involved in mucosal colonization and the development of infections. These bacterial surface structures are likely to play major roles in interactions with the mucosal immune system, which are orchestrated by a network of surveillance based on dendritic cells (DCs). To determine the roles of
K. pneumoniae
CPS and LPS in the DC response, we investigated the response of immature human monocyte-derived DCs to bacterial challenge with a wild-type strain and its isogenic mutants deficient in CPS or LPS O-antigen production. As observed by flow cytometry and confocal laser microscopy, the rate of phagocytosis was inversely proportional to the amount of CPS on the bacterial cell surface, with LPS playing little or no role. The
K. pneumoniae
wild-type strain induced DC maturation with upregulation of CD83, CD86, and TLR4 and downregulation of CD14 and DC-SIGN. With CPS mutants, we observed a greater decrease in DC-SIGN, suggesting a superior maturation of DCs. In addition, incubation of DCs with CPS mutants, and to a lesser extent with LPS mutants, resulted in significantly higher Th1 cytokine production. Combined, our findings suggest that
K. pneumoniae
CPS, by hampering bacterial binding and internalization, induces a defective immunological host response, including maturation of DCs and pro-Th1 cytokine production, whereas the LPS O antigen seems to be involved essentially in DC activation.
Effect of MarA-Like Proteins on Antibiotic Resistance and Virulence in
Yersinia pestis
Authors: Lister Ida M. , Mecsas Joan , Levy Stuart B.
Published: October 2009

MarA, an AraC/XylS transcriptional regulator in
Escherichia coli
, affects drug susceptibility and virulence. Two MarA-like proteins have been found in
Yersinia pestis
: MarA47 and MarA48. Deletion or overexpression of these proteins in the attenuated KIM 1001 Δ
pgm
strain led to a change in multidrug susceptibility (including susceptibility to clinically relevant drugs). Additionally, lung colonization by the
marA47
or
marA48
deletion mutant was decreased about 10-fold in a pneumonic plague mouse model. Complementation of the deletions by replacing the deleted genes on the chromosome restored wild-type characteristics. These findings show that two MarA homologs in
Y. pestis
affect antibiotic susceptibility and virulence.
Biomass Spectra of Aquatic Ecosystems in Relation to Fisheries Yield
Authors: Boudreau P. R. , Dickie L. M.
Published: October 2009

The biomass density of aquatic ecosystems can be expressed as an allometric function of organism body size. The log–log plot of this relation, termed the biomass spectrum, is used to compare aquatic ecosystems in various parts of the world. We develop a standardized presentation for several example environments where detailed data on biomass density by body size in the trophic positions, phytoplankton, zooplankton, benthos, and fish, make it possible to establish overall or primary spectral slopes. The basic methodology is adapted for application to other ecosystems where less detailed data are available. Spectra from all the different environments exhibit a uniform low slope, but with different intercepts that appear to reflect ecosystem differences in nutrient circulation and availability. Detail on the secondary structuring at various positions in the trophic system appears to provide information useful for distinguishing between long-term changes in productivity and short-term perturbations in biomass or abundance.
Effect of Population Density on Gillnet Catchability in Four Allopatric Populations of Brown Trout (Salmo trutta)
Authors: Borgstrøm Reidar
Published: October 2009

The gillnet catchability of allopatric brown trout (Salmo trutta) populations was studied in four Norwegian high-mountain lakes, with large differences in population densities. The number of fish and the length composition of the populations were estimated by mark–recapture. The catchability coefficient and the catch per unit effort were described by power functions, and the catchability was inversely related to number of fish present. An important fisheries management implication is that brown trout populations with low densities are more vulnerable to gillnets than populations with high densities. Furthermore, the use of gillnet catches as an estimator of brown trout population density will be biased.
Optimizing Sampling from Trawl Catches: Contemporaneous Multistage Sampling for Age and Length structures
Authors: Horppila Jukka , Peltonen Heikki
Published: October 2009

The objective of this study was to find out the optimal sampling strategy for contemporaneous multistage sampling of age and length structures of trawl catches. Samples were taken from a roach (Rutilus rutilus) stock of Lake Vesijärvi, southern Finland. Two-stage sampling proved to be superior to three-stage sampling (i.e. subsamples from the trawl catches are unnecessary). Assuming that all the age and length groups are equally important, the optimal strategy is to sample 34 fish from each of 46 loads. Compared with the present scheme (500 fish from each of 10 loads), this design cuts down the total variance of the estimated proportions of different age and length groups to about one third. An age–length key was used when estimating the proportions of the age groups. The benefits of the applied age–length key were obvious. The estimates of the proportions of different age groups were more accurate than those obtained with age readings only. Increasing the fraction of age-determined fish increases the costs, diminishes the optimal number of samples, and consequently increases the variance of the estimated proportions of different groups.
Changes in Behaviour at Onset of Exogenous Feeding in Marine Fish Larvae
Authors: Skiftesvik Anne Berit
Published: October 2009

The activity and swimming speed of fed and starved larvae of Atlantic cod (Gadus morhua) and turbot (Scophthalmus maximus) were measured from hatching to metamorphosis. The results indicate changes in behaviour over time, as well as differences between starved and fed larvae. It is suggested that determining the point at which activity increases and swimming speed during active periods decreases may be relevant as an indicator of the time of first feeding in marine fish larvae.
Effectiveness of a Stock Enhancement Program Evaluated by a Two-Stage Sampling Survey of Commercial Landings
Authors: Kitada Syuiti , Taga Yasushi , Kishino Hirohisa
Published: October 2009

In this study, we evaluated the effectiveness of fish stock enhancement programs using a two-stage random sampling survey of commercial landings. Estimators for the total number of fish landed, the ratio of the number of fish released to the total number of fish landed, the recovery rate, and the amount of income were formulated. Variance formulas for these estimators were also derived. In a case study of the flounder fishery, we obtained the conservative estimate of 36 982 recoveries from 246 300 hatchery-reared fish over 3 yr after release. The ratio of the recovery rate to the number of fish released was 0.15. The total income and benefit estimate were $260 000 and $63 000 (U.S.), respectively. We found that the stock enhancement program was economically profitable. We also studied several sampling strategies. We recommend that as many markets as possible be surveyed for a minimum number of days because the variation in daily landings among markets was larger than that within markets. Stratification of markets should be conducted for accurate estimation.
Planktonic Sea Scallop Larvae (Placopecten magellanicus) in the Georges Bank Region: Broadscale Distribution in Relation to Physical Oceanography
Authors: Tremblay M. John , Sinclair Michael
Published: October 2009

During autumn surveys for sea scallop larvae (Placopecten magellanicus) from 1985 to 1987, the mean abundance of sea scallop larvae on the northeast part of Georges Bank (1201–20080∙m−2) was much greater than on the southern Scotian Shelf (5–240∙m−2). Few larvae were collected between these two areas, and exchange between Georges Bank and the Scotian Shelf appears very limited. Transects across the northern flank in 1988 revealed peaks in larval abundance when on-bank temperature stratification was high. Relative larval abundance on the transects was positively related to the speed of the along-front current, suggesting physical convergence of larvae. The on-bank retention of scallop larvae on Georges Bank appears to be due to physical processes alone, since scallop larvae undertake only limited diel vertical migration. Larval exhange among adult scallop aggregations on Georges Bank (the northeast peak, the southeast part, and the South Channel) is probable, but evidence from this study is limited. The autumn production of late-stage larvae on the northern flank and northeast peak of Georges Bank is estimated to range from 120 to 1500∙m−2, which is 10–100 times greater than the density of scallops aged 1–2 yr.
Linkage between Epilithic Algal Growth and Water Column Nutrients in Softwater Lakes
Authors: Fairchild G. Winfield , Sherman John W.
Published: October 2009

We examined the dependence of epilithic algal standing crop, production, and nutrient limitation upon water column nutrients in 12 softwater lakes of northeastern Pennsylvania. Elevated dissolved inorganic nitrogen accompanied low dissolved inorganic carbon in the more acidic lakes, while P varied little within the study area. The growth of epilithon on clay flower pot substrata diffusing combinations of N (NaNO3), P (Na2HPO4), and C (NaHCO3) was compared with growth on control substrata to evaluate which of the three nutrients limited growth in each lake. Standing crop accrual as chlorophyll a on control substrata averaged 0.8 μg/cm2, with little variation among lakes. Nutrient limitation of growth, however, was strongly related to lake alkalinity. Chlorophyll a was typically enhanced by N and/or P only in lakes with alkalinity greater than ~100 μeq/L and responded strongly to C enrichment in the two most acidic lakes. Combined addition of all three nutrients produced the largest chlorophyll a accrual in all 12 lakes. Invertebrate grazer biomass, dominated by chironomids in the more acidic lakes and by snails at higher alkalinity, was negatively related to chlorophyll a on these NPC substrata (r = −0.57, p = 0.05) and may have reduced algal standing crop well below nutrient-sustainable levels in some lakes.