bluuebunny/crossref_metadata_2025 huggingface dataset:
Periodic Discontinuities in the Acceleration of Spheres in Free Flight
Authors: Tyler A. L. , Salt D. L.
Published: October 2010

The trajectories of unrestrained spheres being accelerated from rest behind a normal shock wave in a shock tube have been recorded by high-speed stroboscopic photography, and precise measurements of the particle positions made with an optical comparator. Data of sufficient precision were obtained to permit the accurate determination of the second time derivative of the particle trajectories. The experiments were conducted in air with plastic spheres ranging in diameter from 0.7 to 2.4 mm and with specific gravities from 0.7 to 1.5. Particle Reynolds numbers from 1 × 104 to 5 × 104 were obtained, and absolute particle accelerations from 1 × 106 to 5 × 106 ± 0.16 × 106 cm/s2 were measured. The relative velocities were all subsonic; relative Mach numbers ranged from 0.3 to 0.6. The values of the particle acceleration, when plotted as a function of time, were found to contain periodic abrupt changes similar to a mathematical discontinuity. It is postulated that the associated abrupt changes in the forces exerted on the particles are caused by periodic detachment of low-pressure centers of vorticity which form behind the spheres. Values of the drag coefficients determined from the data similarly exhibit periodic abrupt changes. These changes appear, in the way they consistently increase during each cycle of the period and fall at the point of “discontinuity,” to be compatible with the postulate that the periodic behavior is caused by formation and abrupt detachment of low-pressure vortices in the wake. Values of the drag coefficients were found to vary from 10 percent to 30 percent above steady-state values at comparable Reynolds numbers—the range of the computed values of the drag coefficient being caused by the periodic nature of the quantity.
The Effect of Periodic Errors in Blade Setting on the Potential Incompressible Flow in Compressor Cascades
Authors: El-Taher R. M. M. , Shaalan M. R. A. , Rashed M. I.
Published: October 2010

An analysis is given for the potential incompressible flow through compressor cascades with periodic one-blade setting errors. The effects of three components of errors (chord-wise, cascadewise, and angular) on the cascade performance are predicted. It is shown that setting errors can produce substantial changes in the aerodynamic parameters of a given cascade. However, the cascade performance appears to be more sensitive to angular errors than it is to other types of error. The analysis, which is essentially a modified Schlichting approach, leads to “influence coefficients” that may be used to predict the effect of a periodic setting error in more than one blade on the loading of any of the cascade blades.
A Flow Study in Radial Inflow Turbine Scroll-Nozzle Assembly
Authors: Hamed A. , Baskharone E. , Tabakoff W.
Published: October 2010

The present analysis describes the flow behavior in the combined scroll-nozzle assembly of a radial inflow turbine. This model was chosen to provide a better understanding of the mutual interaction effects of these two components on the flow. The finite element method is used in the solution of the flow field in this multiply connected domain. The mass flow rates in the different nozzle channels is not presumed constant, but is determined from the solution.
An Evaluation of Mean Reynolds Stress Turbulence Models: The Triple Velocity Correlation
Authors: Cormack D. E. , Leal L. G. , Seinfeld J. H.
Published: October 2010

A four-parameter model is presented for the triple velocity correlation which appears in the mean Reynolds stress tensor equations of turbulence. A comparison with the closure models of Hanjalic and Launder [1], Daly and Harlow [2], Wyngaard, Cote´, and Rao [3], and Shir [4], in the context of existing experimental data, indicates that the proposed model is superior. It is also demonstrated that, of the one-parameter models, the Hanjalic-Launder model best approximates the data. Due to the complexity of the four-parameter representation, it is recommended that the Hanjalic-Launder model be used for computational purposes.
Predetermination of the Relative Error on the Flow Coefficient of Orifice Meters in Nonstandard Approach Conditions
Authors: Jaumotte A. L. , Nagel P. P.
Published: October 2010

This note summarizes the practical conclusions of a study of the influence of non-standard approach sections (swept bends, orifice plates …) on the relative error on the flow coefficient of orifice meters. On the basis of experimental curves of “error versus upstream distance” for a few studied pipe fittings, it is shown that a correlation can be defined and used for the predetermination of the almost complete curve of many other pipe fittings for which the error is only given by the standards for a limited number of upstream distances.
Experiments on the Dynamic Behavior of Cavitating Pumps
Authors: Ng S. L. , Brennen C.
Published: October 2010

This paper describes experiments performed to measure the dynamic transfer matrices for cavitating (and noncavitating) pumps. These transfer matrices describe the relationship between small linear oscillatory perturbations in the pressures and mass flow rates at inlet and discharge from the hydraulic machine. The matrices were deduced from direct measurements of these fluctuating quantities for different modes of excitation of the machine. Results for a cavitating inducer are presented as functions of frequency and mean operating state. Though some of the trends in the data are consistent with existing theoretical models of inducer dynamics, others are not, indicating a need for further theoretical investigation of the dynamic characteristics of such flows. The results exhibit increasingly complex dynamics with increasing cavitation; it appears that the hydraulic machine deviates from an essentially passive response without cavitation to an increasingly active response as the cavitation number is reduced.
A Procedure for Computation of Fully Stalled Flows in Two-Dimensional Passages
Authors: Woolley R. L. , Kline S. J.
Published: October 2010

A procedure is described for computation of incompressible, steady, two-dimensional flows in fully-stalled diffusers with plenum exit. The procedure is successful in predicting pressure distributions and patterns to the accuracy of the data. The procedure employs a zonal model; this maintains close connections between the modeling and the physics thereby providing insight into critical aspects of modeling separated flows. The procedure presented is also convenient for computing unstalled flows in passages with turbulent boundary layers for either direct or indirect design problems. Computing times are well within engineering feasibility. The concepts developed can be extended to other classes of separated flows; some of these extensions have already been completed and are referenced.
Reynolds Number Dependence of Skin Friction and Other Bulk Flow Variables in Two-Dimensional Rectangular Duct Flow
Authors: Dean R. B.
Published: October 2010

The Reynolds number dependence of Cf, Uo, H and other bulk flow parameters in “two dimensional” (high aspect ratio) rectangular duct flow is explored and the empirical relations Cf = 0.073 Re−1/4 and Uo/U¯ = 1.28 Re−0.0116 are presented. The values A = 2.12 and K = 0.41 for the log-law constants and Π = 0.14 for Coles’ wake parameter are derived and are shown to be independent of Re. The integration of Dean’s formula for the complete velocity profile provides close agreement with all parameters when these values of A, K and Π are used and is shown to coincide with the “optimum log-law” for skin friction (which contains Π).
Boundary Layer Calculation for Analysis and Design
Authors: Weber H. E.
Published: October 2010

A simple, semiempirical method for calculating the laminar, transition, and turbulent boundary layer with arbitrary free stream pressure gradient is developed. Good correlation is obtained with data on general two dimensional turbulent flows, diffuser flows, and the cylinder in cross-flow. However only for the diffuser has the boundary layer flow been coupled with the potential core so that only the inlet conditions and geometry are required. In other cases the free stream velocity distribution must be known or calculable. Skin friction coefficient, momentum thickness Reynolds number, and free stream pressure gradient parameter correlation employs a simple lag theory. With the integral momentum equation the complete boundary layer parameters are obtained as functions of the distance along a surface.
Flow Induced Vibrations of a Hydraulic Valve and Their Elimination
Authors: Weaver D. S. , Adubi F. A. , Kouwen N.
Published: October 2010

The flow induced vibrations of a check valve with a spring damper to prevent slamming have been studied experimentally. Both prototype and two-dimensional model experiments were conducted to develop an understanding of the mechanism of self-excitation. The phenomenon is shown to be caused by the high rate of change of discharge at small angles of valve opening and the hysteretic hydrodynamic loading resulting from fluid inertia. As the discharge-displacement characteristics of the valve are dependent on its geometry, modifications of this geometry were examined and one found which eliminated the vibrations entirely. The phenomenon studied is considered to be the same as that causing vibrations in numerous other flow control devices when operating at small openings.
Analytical and Experimental Studies of ASME Flow Nozzles
Authors: Benedict R. P. , Wyler J. S.
Published: October 2010

In this paper, we first present a state of the art review of the published work concerning theoretical nozzle discharge coefficients. Then, we develop a new nozzle discharge coefficient based on an axisymmetric boundary layer solution, which in turn is based on a new axisymmetric potential flow solution. These solutions apply to plenum inlet installations which offer major advantages over conventional ASME pipe inlet installations as to losses, and as to predictability of the discharge coefficient at the higher Reynolds numbers encountered in industry. Next, we present new correlations for static pressure tap errors and apply these to the theoretical (zero tap size) discharge coefficients. Finally, we present new experimental data showing how a laminar boundary layer is preserved and tap error is accordingly minimized for the case of a plenum inlet with ASME nozzle contour.
Tailoring the Waveform of a Periodic Flow With a Programmable Damper
Authors: Simpson R. L. , Sallas J. J. , Nasburg R. E.
Published: October 2010

Investigators of unsteady flows normally have little control over the waveform of the flow unsteadiness. This paper describes a programmable rotating blade damper system that is capable of producing a near sinusoidal velocity waveform without wind tunnel resonance. By varying the angular velocity of the rotating blades in a damper at various times in a cycle the desired waveform can be obtained. The amplitude and frequency of the flow oscillation are also adjustable. There is little variation of the period of the waveform and the results are highly repeatable.
Experimental Study of a Solid-Gas Jet Issuing Into a Transverse Stream
Authors: Salzman R. N. , Schwartz S. H.
Published: October 2010

The results of an experimental investigation of the trajectory and dispersion of a solid-gas (silicate-air) jet injected into a transverse stream are presented. The centerline and the spread of the jet were defined by the particulate distribution as sampled with an isokinetic probe. The jets of this study had a solid to air mass ratio on the order of 15:1. Correlation equations obtained for the trajectory are similar to those reported in the literature for single phase jets. Equations are also obtained for plume dispersion.
Vortex Sheet Analysis of the Giromill
Authors: Wilson R. E.
Published: October 2010

A two-dimensional analysis of the performance and flowfield of the Giromill is presented. The Giromill is a vertical-axis wind turbine with straight blades that are articulated to produce maximum energy extraction from the wind. It is found that the power coefficient and windwise force coefficient for the Giromill have the same limit as obtained for the horizontal-axis wind turbine. A cross-wind force is also obtained with this type of wind turbine. The cross-wind force is of second order and decreases with tip speed. Streamlines and velocity profiles are illustrated for several loading conditions.
An Improved
Thermoregulatory Model for Automatic Cooling Control Development in Liquid Cooling Garment
Systems
Authors: Westin Johan
K. , Kapat Jayanta S. , Chow Louis C.
Published: October 2010

Current state-of-the-art thermoregulatory models do not simulate body temperature responses with the accuracies that are required for the development of automatic cooling control in liquid cooling garment (LCG) systems. Automatic cooling control would be beneficial in a variety of space, aviation, military, and industrial environments. It would optimize cooling efficiency, aid in making LCGs as portable and practical as possible, alleviate the individual from manual cooling control, and improve thermal comfort and cognitive performance. In this study, we implement an available state-of-the-art thermoregulatory model in a LCG environment and compare the thermal model response with experimental data for a 700 W rectangular type metabolic rate schedule. We modify the blood flow dynamics of the thermoregulatory model and identify a new vasoconstriction signal, i.e., the rate of change of hypothalamus temperature weighted by the hypothalamus error signal, which governs the thermoregulatory response during conditions of simultaneously increasing core and decreasing skin temperatures. With this new vasoconstriction dependency, the thermoregulatory model simulates rectal and mean skin temperature responses with root mean square deviations of 0.10°C and 0.48°C, respectively, which results in 40% and 17% reductions in the mean and peak body heat storage errors, respectively. Although the new model’s mean body heat storage error is within the allowable by an 11% margin, the peak body heat storage error exceeds the allowable by 222%, indicating that further refinements are needed. With additional improvements to the set-point temperatures, the central blood pool formulation, and the LCG boundary condition, it seems possible to achieve the strict accuracy that is needed for the development of automatic cooling control in LCG systems.
Parametric Study of a Piezoceramic Patch Actuator for Proportional Velocity Feedback Control Loop
Authors: Aoki Y. , Gardonio P. , Gavagni M. , Galassi C. , Elliott S. J.
Published: October 2010

This paper presents a parametric study on the stability and control performance of proportional velocity feedback control with square piezoceramic patch actuators of various widths and thicknesses, used to suppress the vibration of a thin rectangular plate. A simple stability-performance formula has been derived, which, using the open loop sensor-actuator frequency response function, gives the maximum control performance that can be produced by such a feedback loop at resonance frequencies of the lower order modes of the plate. The parametric study has been carried out using simulated sensor-actuator frequency response functions. The results have been validated using measured frequency response functions on sets of rectangular panels with a square piezoceramic patch of various widths and thicknesses. The parametric study has shown that the control performance is significantly improved by increasing the width and reducing the thickness of the square actuator.
Axisymmetric Vibrations of a Piezoelectric Spherical Shell Submerged in a Compressible Viscous Fluid Medium
Authors: Hu Juxi , Qiu Zhiping , Su Tsung-Chow
Published: October 2010

Axisymmetric vibrations of a hollow piezoelectric sphere submerged in a compressible viscous fluid medium are investigated. The piezoelectric sphere is radially polarized. The differential equations governing the shell motion are obtained by the use of Hamilton’s principle. Based on the classical bending theory of shells, it is shown that all the piezoelectric contributions can be included in the in vacuo natural frequencies and their corresponding mode shapes. As such, the previous theory on elastic shell vibration becomes readily extendable. The flow field, determined by the boundary layer theory, is coupled to the shell motion through no-slip and no-penetrating conditions. It is found that the contribution of the piezoelectric parameters in the thin shell’s free vibration is of small order and is negligible. Natural frequencies and their associated vibration characteristics are numerically obtained and presented for a Polyvinglindene fluoride (PVDF) shell submerged in water. Dynamic responses of a submerged piezoelectric sherical shell, and the associated radiation of sound are investigated. The oscillations are harmonically driven by an axisymmetrically applied electric potential difference across the surface of the shell. The vibrational, fluid loading, and energy flow characteristics are derived and evaluated for a PVDF shell submerged in water. The essential feature of the modal response is determined by various critical frequencies, such as resonant frequencies and vibration-absorbing frequencies. Viscous effect is found noticeable in several cases.
Application and Comparison of High Breakdown-Point and Bounded-Influence Estimators to Rotor Balancing
Authors: Chatterton Steven , Ricci Roberto , Pennacchi Paolo
Published: October 2010

In the field of rotor balancing, the traditional influence coefficient method is often employed along with weighted least squares in order to reduce amplitude vibrations, typically at selected rotating speeds such as critical or operating ones. Usually, these weights are manually selected by the operator. In this paper, an automatic procedure for the balancing mass estimation based on robust regression methods is introduced. The analysis is focused on high breakdown-point and bounded-influence estimators. The effectiveness and robustness of the proposed balancing procedure are shown by means of simulations of a 180 MW gas turbo generator of a power plant.
Multiphysics Modeling and Experimental Validation of the Active Reduction of Structure-Borne Noise
Authors: Zielinski Tomasz G.
Published: October 2010

This paper presents a fully coupled multiphysics modeling and experimental validation of the problem of active reduction of noise generated by a thin plate under forced vibration. The plate is excited in order to generate a significant low-frequency noise, which is then reduced by actuators in the form of piezoelectric patches glued to the plate with epoxy resin in locations singled out earlier during finite element (FE) analyses. To this end, a fully coupled FE system relevant for the problem is derived. The modeling is very accurate: The piezoelectric patches are modeled according to the electromechanical theory of piezoelectricity, the layers of epoxy resin are thoroughly considered, and the acoustic-structure interaction involves modeling of a surrounding sphere of air with the nonreflective boundary conditions applied in order to simulate the conditions found in anechoic chamber. The FE simulation is compared with many experimental results. The sound pressure levels computed in points at different distances from the plate agree excellently with the noise measured in these points. Similarly, the computed voltage amplitudes of controlling signal turn out to be very good estimations.
Supervisory Control of Dynamical Systems With Uncertain Time Delays
Authors: Song Bo , Sun Jian-Qiao
Published: October 2010

A study of controlling dynamical systems with uncertain and varying time delays is presented in this paper. The uncertain time delay is assumed to fall in a range with known upper and lower bounds. We apply the supervisory control algorithm to deal with uncertainties in the time delay. An index is defined for each of the predetermined controls for a discrete set of time delays sampled from the range. Based on this index, a hysteretic switching rule selects a control from the predetermined controls with optimal feedback gains. Each predetermined control must be stable for any time delay in the range. Two control design methods are discussed, namely, the mapping method and a higher order approach. Examples of linear systems are used to demonstrate the theoretical work.
Advanced Techniques for Pressure Pulsations Modeling in Volumetric Compressor Manifolds
Authors: Cyklis Piotr
Published: October 2010

Pressure pulsations in volumetric compressor manifolds are one of the most important problems occurring in the compressor installations. They cause noise and vibrations, which may result in installation failures. In 2005 DOE USA (Advanced Reciprocating Compression Technology (ARCT), 2005, Final Report SwRI® Project No. 18.11052, DOE Award No. DE-FC26-04NT42269) published a report where pressure pulsations attenuation is named as one of the three most important problems in compressor plants design and operation. Three main approaches of modeling acoustic wave can be named here: one dimensional pipeline modeling with real domain solution and finite difference methods, Helmholtz theory based acoustic model, where complex Fourier transform is used, or finally full computational fluid dynamics (CFD) multidimensional approach. All of them have limited capabilities. With one dimensional model no real geometry of an oil separator or a damper can be introduced. In the Helmholtz approach apart from the length limit of a pipe, complex geometry requires transmission properties of the element. CFD is the most accurate but very time consuming in both computational time and data preparation for the CFD software. In the present paper, one of the coupling methods is shown with the introduction of transmittance characteristics. The resulting simulation using generalized Helmholtz model shows much better agreement with the experimental results than for the classic Helmholtz modeling.
Noise Reduction Analysis of an Underwater Decoupling Layer
Authors: Tao Meng , Tang Wei Lin , Hua Hong Xing
Published: October 2010

Based on the vibro-acoustic coupled model of an infinite bare plate, using the impedance transfer matrix, the analytical model predicting the noise reduction performance of a void decoupling layer covered on an infinite plate under mechanical excitation is presented. The void decoupling layer, especially containing periodically distributed cylindrical or conical holes, can be approximated as a homogenous material described by several parameters, including the effective density, the effective propagation constant, and the effective attenuation. Analysis shows that (1) the primary mechanism of noise reduction is the vibration attenuation of the decoupling layer from the “front” interface between the decoupling layer and the plate to the “back” interface between the decoupling layer and the water, rather than the plate vibration reduction, (2) the plate vibration is increased with the decoupling layer at low frequencies and the increased amount of plate vibration is more than the attenuated amount of the decoupling layer vibration, so the radiated pressure is increased at low frequencies, and (3) at high frequencies, the pressure insertion loss, which quantitatively describes the noise reduction performance of the decoupling layer is estimated by the general sound transmission loss through a simple expression. Finally, good agreement between analytical calculations and experimental results validates that the developed model is useful to predict the noise reduction performance of the void decoupling layer.
Design and Performance of a Constant Temperature and Humidity Air-Conditioning System Driven by a Ground Source Heat Pump in Summer
Authors: Yu X. , Zhai X. Q. , Wang R. Z.
Published: October 2010

A constant temperature and humidity air-conditioning system driven by a ground source heat pump was designed and constructed in an archives building in Shanghai. The system consists of a water-to-water heat pump and 280 boreholes with 80 m in depth. During the operation in summer, the heat extraction from the condenser of the heat pump was divided: Part was rejected to the soil, while another was used to reheat the air in air handling units (AHUs). According to the experimental results under a typical summer weather condition of Shanghai, the average coefficient of performance of the heat pump was 5.4. The average indoor temperature and relative humidity of the archives house were 22.8°C and 46.6%, respectively. Since part of the heat extraction from the condenser was used to reheat the air in AHUs, the heat rejected to the soil was reduced by 23%, which was helpful for the earth energy conservation. According to the theoretical analysis, the distance between two boreholes is suggested to be 4–5 m. The deepness of the boreholes is suggested to be 80–100 m in Shanghai.
Computational Investigation of Cold Flow in a Dump Combustor With Tapered Exit
Authors: Sailaja R. , Yadav N. P. , Kushari A.
Published: October 2010

This paper reports the results of a numerical study of the cold flow field in a dump combustor with a tapered exit. The numerical model was benchmarked against the data available in the literature. The flow field inside the combustor was investigated by numerical visualization of different regions in the flow field, and the effect of the combustor length was studied. It was seen that the presence of shear layer between the potential core and the recirculation region, as well as the pressure and velocity variation inside the combustor, alters the recirculation region and hence the flow field. It was also observed that the extent of the recirculation region increases, while the shear layer becomes thinner as the length of the chamber decreases. The effect of the variation in the flow Reynolds number and the inlet turbulence intensity on the flow field of a low aspect ratio (2.3) dump combustor was studied in detail. It was observed that the extent of recirculating flow increases with a decrease in the Reynolds number, and the increase in turbulence intensity results in higher turbulence energy generation in the shear layer. The pressure recovery was found less, but the recirculation was stronger in the low aspect ratio combustor. The results of this study can help optimize the combustor chamber to achieve better mixing of fuel with air and stabilization of the flame.
Different growth mechanisms of vertical carbon nanotubes by rf- or dc-plasma enhanced chemical vapor deposition at low temperature
Authors: Wang Huiyao , Moore John J.
Published: October 2010

Vertically aligned carbon nanotubes (CNTs) were synthesized using FeNi or Fe sputtered catalyst layers on glass substrates by radio frequency or direct current plasma enhanced chemical vapor deposition (rf- or dc-PECVD). This article compared the growth mechanisms of CNTs synthesized by rf- and dc-PECVD, based on gas flow rate, plasma power, and catalysts. Tip growth CNTs were produced at 180 °C, 10 SCCM (SCCM denotes cubic centimeter per minute at STP) CH4, and 30 W by rf-PECVD using 8 or 4 nm FeNi or 4 nm Fe island films sputtered onto glass substrates. CNTs could not grow using dc-PECVD under the same deposition conditions; tip growth of CNTs occurred at 180 °C, 15 SCCM CH4, and 50 W using dc-PECVD with sputtered FeNi island catalysts on increasing the plasma power and CH4 flow rate. This article explained why rf-PECVD provided more efficient decomposition of gas molecules than dc-PECVD by plasma theory. The major difference between rf- and dc-PECVD was the higher concentration of reactive radicals in the former. However, in dc-PECVD, the CNT growth was well aligned vertically. FeNi thin film catalysts exhibited higher activity and better wetting ability than the Fe island thin film catalysts.
The Role of Discharge Variation in Scaling of Drainage Area and Food Chain Length in Rivers
Authors: Sabo John L. , Finlay Jacques C. , Kennedy Theodore , Post David M.
Published: October 2010

River Food Chains

Food chain length, or the number of organisms involved in any eat-or-be-eaten relationship, is a key property of aquatic habitats that regulates nutrient cycling, energy flow, and carbon exchange between aquatic ecosystems and the atmosphere. Investigating river food webs in North American watersheds,

Sabo
et al.

(p.
965
, published online 14 October) found discharge variation governed the link between ecosystem size (watershed area) and food chain length. River-drying truncated food chain length because intermittent streams have much higher discharge variation than perennial rivers. These results could be important for the management of rivers as drought and climate change may increase the frequency of river drying and discharge variability.
Oscillator Fine-Tuning
Authors: Ray L. Bryan
Published: October 2010

Individual control of amplitude, frequency, and damping of a biological oscillator is demonstrated in cultured cells.
Signal Transduction in Child Health: Closing the Gap Between Clinical and Basic ResearchA report on the third NICHe Conference, “New Inroads to Child Health—Child Health and Signal Transduction,” Varberg, Sweden, 21 to 23 May 2010
Authors: Chan Li , Albertsson-Wikland Kerstin , Camacho-Hübner Cecilia , Hochberg Ze'ev
Published: October 2010

The New Inroads to Child Health Conference focused on plasma membrane receptor-mediated pathways involved in endocrine signaling.
Mode-of-Action Studies of the Novel Bisquaternary Bisnaphthalimide MT02 against
Staphylococcus aureus
Authors: Menzel Thomas M. , Tischer Maximilian , François Patrice , Nickel Joachim , Schrenzel Jacques , Bruhn Heike , Albrecht Annette , Lehmann Leane , Holzgrabe Ulrike , Ohlsen Knut
Published: October 2010

Screening of various bisquaternary bisnaphthalimides against a variety of human pathogens revealed one compound, designated MT02, with strong inhibitory effects against Gram-positive bacteria. The MICs ranged from 0.31 μg/ml against community-acquired methicillin-resistant
Staphylococcus aureus
(MRSA) lineage USA300 to 20 μg/ml against
Streptococcus pneumoniae
. Radioactive whole-cell labeling experiments indicated a strong impact of MT02 on bacterial DNA replication. DNA microarray studies generated a transcriptional signature characterized by stronger expression of genes involved in DNA metabolism, DNA replication, SOS response, and transport of positively charged compounds. Furthermore, surface plasmon resonance and gel retardation experiments demonstrated direct binding of MT02 to DNA in a concentration-dependent, reversible, and non-sequence-specific manner. The data presented suggest that the bisquaternary bisnaphthalimide MT02 exerts anti-Gram-positive activity by binding to DNA and thereby preventing appropriate DNA replication.
Novel Compounds Containing Multiple Guanide Groups That Bind the HIV Coreceptor CXCR4
Authors: Wilkinson Royce A. , Pincus Seth H. , Shepard Joyce B. , Walton Sarah K. , Bergin Edward P. , Labib Mohamed , Teintze Martin
Published: October 2010

The G-protein-coupled receptor CXCR4 acts as a coreceptor for human immunodeficiency virus type 1 (HIV-1) infection, as well as being involved in signaling cell migration and proliferation. Compounds that block CXCR4 interactions have potential uses as HIV entry inhibitors to complement drugs such as maraviroc that block the alternate coreceptor CCR5 or in cancer therapy. The peptide T140, which contains five arginine residues, is the most potent antagonist of CXCR4 developed to date. In a search for nonpeptide CXCR4 ligands that could inhibit HIV entry, three series of compounds were synthesized from 12 linear and branched polyamines with 2, 3, 4, 6, or 8 amino groups, which were substituted to produce the corresponding guanidines, biguanides, or phenylguanides. The resulting compounds were tested for their ability to compete with T140 for binding to the human CXCR4 receptor expressed on mammalian cells. The most effective compounds bound CXCR4 with a 50% inhibitory concentration of 200 nM, and all of the compounds had very low cytotoxicity. Two series of compounds were then tested for their ability to inhibit the infection of TZM-bl cells with X4 and R5 strains of HIV-1. Spermine phenylguanide and spermidine phenylguanide inhibited infection by X4 strains, but not by R5 strains, at low micromolar concentrations. These results support further investigation and development of these compounds as HIV entry inhibitors.
PA-824 Exhibits Time-Dependent Activity in a Murine Model of Tuberculosis
Authors: Ahmad Zahoor , Peloquin Charles A. , Singh Rajendra P. , Derendorf Hartmut , Tyagi Sandeep , Ginsberg Ann , Grosset Jacques H. , Nuermberger Eric L.
Published: October 2010

PA-824 is one of two nitroimidazoles in phase II clinical trials to treat tuberculosis. In mice, it has dose-dependent early bactericidal and sterilizing activity. In humans with tuberculosis, PA-824 demonstrated early bactericidal activity (EBA) at doses ranging from 200 to 1,200 mg per day, but no dose-response effect was observed. To better understand the relationship between drug exposure and effect, we performed a dose fractionation study in mice. Dose-ranging pharmacokinetic data were used to simulate drug exposure profiles. Beginning 2 weeks after aerosol infection with
Mycobacterium tuberculosis
, total PA-824 doses from 144 to 4,608 mg/kg were administered as 3, 4, 8, 12, 24, or 48 divided doses over 24 days. Lung CFU counts after treatment were strongly correlated with the free drug
T
>MIC
(
R
2
= 0.87) and correlated with the free drug AUC/MIC (
R
2
= 0.60), but not with the free drug
C
max
/MIC (
R
2
= 0.17), where
T
>MIC
is the cumulative percentage of the dosing interval that the drug concentration exceeds the MIC under steady-state pharmacokinetic conditions and AUC is the area under the concentration-time curve. When the data set was limited to regimens with dosing intervals of ≤72 h, both the
T
>MIC
and the AUC/MIC values fit the data well. Free drug
T
>MIC
of 22, 48, and 77% were associated with bacteriostasis, a 1-log kill, and a 1.59-log kill (or 80% of the maximum observed effect), respectively. Human pharmacodynamic simulations based on phase I data predict 200 mg/day produces free drug
T
>MIC
values near the target for maximal observed bactericidal effect. The results support the recently demonstrated an EBA of 200 mg/day and the lack of a dose-response between 200 and 1,200 mg/day.
T
>MIC
, in conjunction with AUC/MIC, is the parameter on which dose optimization of PA-824 should be based.
Activities of TMC207, Rifampin, and Pyrazinamide against
Mycobacterium tuberculosis
Infection in Guinea Pigs
Authors: Shang Shaobin , Shanley Crystal A. , Caraway Megan L. , Orme Eileen A. , Henao-Tamayo Marcela , Hascall-Dove Laurel , Ackart David , Lenaerts Anne J. , Basaraba Randall J. , Orme Ian M. , Ordway Diane J.
Published: October 2010

The experimental compound TMC207 is showing promise against infections caused by
Mycobacterium tuberculosis
both in a variety of animal studies and in the field. In this study, we used the guinea pig model, a species that shows several similarities to human tuberculosis, including the hallmark of primary granuloma necrosis, to determine the efficacy of a combination regimen combining TMC207 with rifampin and pyrazinamide. This drug regimen rapidly reduced the bacterial load in the lungs to undetectable levels by 8 weeks of treatment. This reduction was associated with a substantial improvement in lung pathology, but despite this effect areas of residual necrosis still remained. In the draining lymph nodes, however, tissue damage was rapid and not significantly reversed by the drug treatment. Approximately 10 to 11 months after the treatment had ended, the animals began to trigger a Karnovsky scale indicating bacterial regrowth and potential relapse, an event confirmed by the new development of both pulmonary and extrapulmonary granulomatous lesions. Interestingly, a similar rate of relapse was also seen in animals receiving 24 weeks of rifampin, pyrazinamide, and isoniazid standard chemotherapy. These data indicate that TMC207 could be a useful addition to current treatment regimens for tuberculosis.
Structural and Biochemical Analysis of the Pentapeptide Repeat Protein
Efs
Qnr, a Potent DNA Gyrase Inhibitor
Authors: Hegde Subray S. , Vetting Matthew W. , Mitchenall Lesley A. , Maxwell Anthony , Blanchard John S.
Published: October 2010

The chromosomally encoded Qnr homolog protein from
Enterococcus faecalis
(
Efs
Qnr), when expressed, confers to its host a decreased susceptibility to quinolones and consists mainly of tandem repeats, which is consistent with belonging to the pentapeptide repeat family of proteins (PRPs).
Efs
Qnr was cloned with an N-terminal 6× His tag and purified to homogeneity.
Efs
Qnr partially protected DNA gyrase from fluoroquinolone inhibition at concentrations as low as 20 nM.
Efs
Qnr inhibited the ATP-dependent supercoiling activity of DNA gyrase with a 50% inhibitory concentration (IC
50
) of 1.2 μM, while no significant inhibition of ATP-independent relaxation activity was observed.
Efs
Qnr was cytotoxic when overexpressed in
Escherichia coli
, resulting in the clumping of cells and a loss of viability. The X-ray crystal structure of
Efs
Qnr was determined to 1.6-Å resolution.
Efs
Qnr exhibits the right-handed quadrilateral beta-helical fold typical of PRPs, with features more analogous to MfpA (mycobacterium fluoroquinolone resistance pentapeptide) than to the PRPs commonly found in cyanobacteria.
Domains of the
Shigella flexneri
Type III Secretion System IpaB Protein Involved in Secretion Regulation
Authors: Shen Da-Kang , Saurya Saroj , Wagner Carolin , Nishioka Hiroaki , Blocker Ariel J.
Published: October 2010

Type III secretion systems (T3SSs) are key determinants of virulence in many Gram-negative bacterial pathogens. Upon cell contact, they inject effector proteins directly into eukaryotic cells through a needle protruding from the bacterial surface. Host cell sensing occurs through a distal needle “tip complex,” but how this occurs is not understood. The tip complex of quiescent needles is composed of IpaD, which is topped by IpaB. Physical contact with host cells initiates secretion and leads to assembly of a pore, formed by IpaB and IpaC, in the host cell membrane, through which other virulence effector proteins may be translocated. IpaB is required for regulation of secretion and may be the host cell sensor. It binds needles via its extreme C-terminal coiled coil, thereby likely positioning a large domain containing its hydrophobic regions at the distal tips of needles. In this study, we used short deletion mutants within this domain to search for regions of IpaB involved in secretion regulation. This identified two regions, amino acids 227 to 236 and 297 to 306, the presence of which are required for maintenance of IpaB at the needle tip, secretion regulation, and normal pore formation but not invasion. We therefore propose that removal of either of these regions leads to an inability to block secretion prior to reception of the activation signal and/or a defect in host cell sensing.
Human Airway Epithelial Cell Responses to
Neisseria lactamica
and Purified Porin via Toll-Like Receptor 2-Dependent Signaling
Authors: Liu Xiuping , Wetzler Lee M. , Oliveira Nascimento Laura , Massari Paola
Published: October 2010

The human airway epithelium is constantly exposed to microbial products from colonizing organisms. Regulation of Toll-like receptor (TLR) expression and specific interactions with bacterial ligands is thought to mitigate exacerbation of inflammatory processes induced by the commensal flora in these cells. The genus
Neisseria
comprises pathogenic and commensal organisms that colonize the human nasopharynx.
Neisseria lactamica
is not associated with disease, but
N. meningitidis
occasionally invades the host, causing meningococcal disease and septicemia. Upon colonization of the airway epithelium, specific host cell receptors interact with numerous
Neisseria
components, including the PorB porin, at the immediate bacterial-host cell interface. This major outer membrane protein is expressed by all
Neisseria
strains, regardless of pathogenicity, but its amino acid sequence varies among strains, particularly in the surface-exposed regions. The interaction of
Neisseria
PorB with TLR2 is essential for driving TLR2/TLR1-dependent cellular responses and is thought to occur via the porin's surface-exposed loop regions. Our studies show that
N. lactamica
PorB is a TLR2 ligand but its binding specificity for TLR2 is different from that of meningococcal PorB. Furthermore,
N. lactamica
PorB is a poor inducer of proinflammatory mediators and of TLR2 expression in human airway epithelial cells. These effects are reproduced by whole
N. lactamica
organisms. Since the responsiveness of human airway epithelial cells to colonizing bacteria is in part regulated via TLR2 expression and signaling, commensal organisms such as
N. lactamica
would benefit from expressing a product that induces low TLR2-dependent local inflammation, likely delaying or avoiding clearance by the host.
Endovascular treatment of intracranial aneurysms: review of current practice
Authors: Currie Stuart , Mankad Kshitij , Goddard Anthony
Published: October 2010

Subarachnoid haemorrhage remains a major cause of morbidity and mortality throughout the world. Of those suffering the condition, 15% are known to die before they reach hospital and half of all patients die within 1 month of presentation. Of those patients who survive the initial 30 days, just under half are believed to remain dependent for their normal activities of daily living. In the vast majority of cases, SAH results from the rupture of an intracranial aneurysm. After patient stabilisation, primary treatment is focused on the prevention of re-bleeding. Until recently, this exclusively involved the surgical clipping of the ruptured aneurysm via a craniotomy. The early 1990s, with the introduction of aneurysmal coiling via endovascular intervention, heralded the dawn of a new treatment option. Presently, endovascular therapy largely supersedes surgical intervention in the management of intracranial aneurysms in the developed world. Moreover, with the emergence of new technologies and approaches for the treatment of aneurysms, the field of neurovascular intervention is only likely to expand further. However, due to its relative infancy, unanswered questions regarding long term endovascular outcome remain. This is particularly pertinent to newer techniques of embolisation for which data on complete aneurysmal occlusion rates are limited. Thus, to understand fully the capability and limitations of this treatment, further well constructed randomised controlled trials are a necessity.
ON EUCLIDEAN G-MANIFOLDS WHICH HAVE TWO DIMENSIONAL ORBIT SPACES
Authors: MIRZAIE R.
Published: October 2010

We show that the orbit space of Euclidean space, under the action of a closed and connected Lie group of isometries is homeomorphic to a plane or closed half-plane, if the action is of cohomogeneity two.
ON THE TOPOLOGY OF POLYNOMIAL MAPPINGS FROM ℂn TO ℂn-1
Authors: VUI HA HUY , THANG NGUYEN TAT
Published: October 2010

We consider a polynomial map from ℂn to ℂn-1 and prove that if there exists a so-called very good projection with respect to the value t0, then this value is an atypical value for the map if and only if the Euler characteristic of the fibers are not constant. We describe some topology of the fibers and prove that there is no extension of the characterization of the atypical value via the Lojasiewicz number as in the case n = 2.
ON THE SO(N) AND Sp(N) FREE ENERGY OF A RATIONAL HOMOLOGY THREE-SPHERE
Authors: TAKATA TOSHIE
Published: October 2010

We give an explicit presentation of the SO(N) and Sp(N) free energy of lens spaces and show that the genus g terms of it are analytic in a neighborhood at zero, where we can choose the neighborhood independently of g. Moreover, we prove that for any rational homology three-sphere M and any g, the genus g terms of SO(N) and Sp(N) free energy of M agree up to sign. We also observe new weight systems related to the free energy.
BIMEROMORPHIC GEOMETRY OF RIGID ANALYTIC SURFACES
Authors: MITSUI KENTARO
Published: October 2010

We show that any proper rigid analytic surface admits a relatively minimal regular model. Further, we give a criterion for relative minimality of proper regular rigid analytic surfaces.
PARASITIC INFESTATION AND CHOICE OF REPRODUCTIVE REGIMES
Authors: SOUSA A. O. , de OLIVEIRA S. MOSS , Sá MARTINS J. S.
Published: October 2010

The Penna model is used to simulate the competition between an asexual parthenogenetic and asexual population inhabiting the same environment represented by a square lattice. With a small probability, a newborn from the sexual population mutates into an asexual one and vice versa. Then, the asexual population rapidly dominates the sexual one, which all but disappears. However, when an infestation by mutating genetically coupled parasites, that mimic trematodes that feed on gonads, is introduced, the outcome may be one in which both populations coevolve or one in which one of the populations overcomes the other, depending on the density of parasites on the lattice.
CONSTRUCTING 2N-SOLITON PERIODIC WAVE SOLUTIONS FOR GENERALIZED DERIVATIVE NONLINEAR SCHRÖDINGER EQUATION
Authors: TIAN SHOU-FU , ZHANG HONG-QING
Published: October 2010

In this paper, three new kinds of N-fold Darboux transformations with multi-parameters for spectral problem associated with generalized Derivative Nonlinear Schrödinger equation (GDNS) are structured with the help of different gauge transformations. With these transformations, some new 2N-soliton periodic wave solutions for the GDNS equation are obtained by taking position spectral (λ > 0), negaton spectral (λ < 0) and complexiton spectral. When N = 1 we obtained two-soliton periodic wave solutions. In particular, when N = 2 we obtained some four-soliton periodic wave solutions. By using mathematical software, we show their profiles. In this method, we can give a Darboux transformation for a very systematic system of even-dimensional and odd-dimensional Lax integrable systems. This method can also be applied to other nonlinear evolution equations.
SPREAD OF EPIDEMIC ON COMPLEX NETWORKS UNDER VOLUNTARY VACCINATION MECHANISM
Authors: XUE SHENGJUN , RUAN FENG , YIN CHUANYANG , ZHANG HAIFENG , WANG BINGHONG
Published: October 2010

Under the assumption that the decision of vaccination is a voluntary behavior, in this paper, we use two forms of risk functions to characterize how susceptible individuals estimate the perceived risk of infection. One is uniform case, where each susceptible individual estimates the perceived risk of infection only based on the density of infection at each time step, so the risk function is only a function of the density of infection; another is preferential case, where each susceptible individual estimates the perceived risk of infection not only based on the density of infection but only related to its own activities/immediate neighbors (in network terminology, the activity or the number of immediate neighbors is the degree of node), so the risk function is a function of the density of infection and the degree of individuals. By investigating two different ways of estimating the risk of infection for susceptible individuals on complex network, we find that, for the preferential case, the spread of epidemic can be effectively controlled; yet, for the uniform case, voluntary vaccination mechanism is almost invalid in controlling the spread of epidemic on networks. Furthermore, given the temporality of some vaccines, the waves of epidemic for two cases are also different. Therefore, our work insight that the way of estimating the perceived risk of infection determines the decision on vaccination options, and then determines the success or failure of control strategy.