bluuebunny/crossref_metadata_2025 huggingface dataset:
Characteristics of Centrifugal Pump Rotor System Under Exciting Forces Generated by Shroud Leakage Flows
Authors: Liu Quan-zhong , Gong Ru-zhi , Wang Hong-jie , Yao Yang
Published: March 2011

In order to investigate the flow-induced vibration in the impeller clearance of centrifugal pump, and make the rotordynamic prediction of the centrifugal pump rotor system, a rotordynamic force model is established which is indispensable to the impeller-rotor system dynamics analysis. The coefficient in the dynamic force model is solved by quasi-steady CFD solution. Multiple quasi-steady solutions of an eccentric three-dimensional model at a series of relative spin velocity yield the rotordynamic forces at different whirl frequency ratios, and a second-order least-square fitting of the rotordynamic forces generates the skew-symmetric stiffness, damping, and mass matrices. Based on the work, the finite element method is applied to establish the model of turbo pump impeller-rotor system. The phenomenon of the fluid oscillation and some typical features are explained from the perspective of oscillation fluid mechanics. The results show complicated frequency characteristics presents in the turbo pump rotor vibration due to the exciting forces generated by shroud leakage flows.
Pressure Pulsations in a Drum Excited by a Centrifugal Compressor Connected to a Piping System
Authors: Hayashi Itsuro , Kaneko Shigehiko
Published: March 2011

The characteristics of the pressure pulsations in a drum connected to a piping system excited by a centrifugal compressor or a blower operated at blade-passing frequencies were investigated. In this study, the equivalent resistance of a compressor and that of a piping system were introduced and linked to the three dimensional calculation model, so that the non-linear damping proportional to velocity squared in the system is properly incorporated. The experiment was performed in order to validate the proposed simulation model. As a result, the three dimensional pressure response in the drum as well as the pipe can be well evaluated by this model. Furthermore, the effect of the acoustic dynamic absorber on the pressure pulsations in the pipe and drum is evaluated. When the resonant frequency of the pipe coincides with that of the drum, two peaks appear in the frequency response curve around the resonant frequency of the pipe, because the drum acts as an acoustic dynamic absorber. It is shown that the maximum pressure amplitude in the drum is obtained when the resonant frequency of the pipe is slightly shifted from the resonant frequency of the drum under the small damping conditions. The effect of the damping in the drum and the mode shape of the drum on the maximum pressure amplitude in the drum is discussed in detail.
Coupled Fluid-Structure Model for Duckbill Valve Flow
Authors: Wang J. , Weaver D. S. , Tullis S.
Published: March 2011

DuckBill Valves (DBV) are non-return axial water flow valves made of a fabric reinforced layered rubber material, and are widely used for large pipe diameter flows with low back pressures. Fluid-Structure Interaction (FSI) is directly involved in the opening process of the DBV, with the opening depending on the pressure differential across the valve. This paper presents an FSI simulation of the DBV opening process by using a Finite Element Method (FEM). The valve is modeled as a laminated thick shell structure with some simplifications to the boundary conditions. The pressure load acting on the shell surface of DBV is a function of the variable valve cross-section area and determined, for preliminary analysis purposes, by using a simple potential flow model for the fluid mechanics. The hyperelasticity of the rubber and orthotropy of the fiber reinforcement, as well as large deflections of DBV, are considered in the simulation. The valve is modeled as being closed when the upstream pressure is applied and the transient opening process is tracked until a steady state opening is achieved. A static case of viscous flow passing through the deformed valve structure has also been carried out to compare the pressure and velocity fields of fluid flow with the corresponding pressure and velocity distribution predicted by the potential flow FSI model in order to evaluate the influence of fully viscous flow in the FSI model in future work. More realistic modeling of the edges of the valve where thick shell elements are considered inappropriate is also discussed.
Numerical Simulation of Internal Cavities Acoustic Trapped Modes With Mean Flow
Authors: Aly Kareem , Ziada Samir
Published: March 2011

Flow-excited acoustic resonance of trapped modes in ducts has been reported in different engineering applications. The excitation mechanism of these modes results from the interaction between the hydrodynamic flow field and the acoustic particle velocity, and is therefore dependent on the mode shape of the resonant acoustic field, including the amplitude and phase distributions of the acoustic particle velocity. For a cavity-duct system, the aerodynamic excitation of the trapped modes can generate strong pressure pulsations at moderate Mach numbers (M>0.1). This paper investigates numerically the effect of mean flow on the characteristics of the acoustic trapped modes for a cavity-duct system. Numerical simulations are performed for a two-dimensional planar configuration and different flow Mach numbers up to 0.3. A two-step numerical scheme is adopted in the investigation. A linearized acoustic perturbation equation is used to predict the acoustic field. The results show that as the Mach number is increased, the acoustic pressure distribution develops an axial phase gradient, but the shape of the amplitude distribution remains the same. Moreover, the amplitude and phase distributions of the acoustic particle velocity are found to change significantly near the cavity shear layer with the increase of the mean flow Mach number. These results demonstrate the importance of considering the effects of the mean flow on the flow-sound interaction mechanism.
A Mechanical Fish Emulates the C-Shape Fast-Start Mechanism
Authors: Modarres-Sadeghi Yahya , Watts Matthew , Conte Joe , Hover Franz , Triantafyllou Michael S.
Published: March 2011

We have built a simple mechanical system to emulate the fast-start performance of fish. The system consists of a thin metal beam covered by a urethane rubber, the fish body, and an appropriately shaped tail. The body form of the mechanical fish was modeled after a pike species, selected because it is a widely studied fast-start specialist. The mechanical fish was held in curvature and hung in water by two restraining lines, which were simultaneously released by a pneumatic cutting mechanism. The potential energy in the beam was transferred into the fluid, thereby accelerating the fish. We measured the resulting acceleration, and calculated the efficiency of propulsion for the mechanical fish model, defined as the ratio of the final kinetic energy of the fish and the initially stored potential energy in the body beam. We also ran a series of flow visualizaiton tests to observe the resulting flow patterns. The maximum start-up acceleration was measured around 40 ms−2, with the maximum final velocity around 1.2 ms−1. The form of the measured acceleration signal as function of time is quite similar to that of Type I fast-start motions studied by Harper and Blake. The hydrodynamic efficiency of the fish was found to be around 10%. Flow visualization of the mechanical fast-start wake was also analyzed, showing that the acceleration peaks are associated with the shedding of two vortex rings in near-lateral directions.
Aerothermoelastic Stability of Functionally Graded Circular Cylindrical Shells
Authors: Sabri Farhad , Lakis Aouni A.
Published: March 2011

In this work, a hybrid finite element formulation is presented to predict the flutter boundaries of circular cylindrical shells made of functionally graded materials. The development is based on the combination of linear Sanders thin shell theory and classic finite element method. Material properties are temperature dependent, and graded in the shell thickness direction according to a simple power law distribution in terms of volume fractions of constituents. The temperature field is assumed to be uniform over the shell surface and along the shell thickness. First order piston theory is applied to account for supersonic aerodynamic pressure. The effects of temperature rise and shell internal pressure on the flutter boundaries of FG circular cylindrical shell for different values of power law index are investigated. The present study shows efficient and reliable results that can be applied to the aeroelastic design and analysis of shells of revolution in aerospace vehicles.
Flow-Structure Interaction Problem of a Pitched Baseball Without Spin (Knuckleball)
Authors: Higuchi Hiroshi , Kiura Toshiro
Published: March 2011

The “knuckleball” effect is believed to be caused by asymmetric flow separation over the baseball, but little is known about its flow physics. The baseball is gripped with the knuckles in a certain position and is pitched in a way that introduces nearly no rotation, resulting in erratic flight paths which confuse batters. In the experiment described in this paper, the flow near the seams of the baseball is visualized thoroughly and the velocity vector fields near the surface and in the wake are obtained with Digital Particle Image Velocimetry. Depending on its position, the seam is found to trigger the boundary layer transition thus delaying the separation, or to cause separation itself. Three-dimensional wake patterns associated with specific ball orientations are identified and related to the force variations on the ball.
Active Control of Vortex Induced Vibration by Plasma Actuation
Authors: Sari Gh. , Mureithi N. W.
Published: March 2011

In this paper, the results of experiments on the elimination of vortex induced vibration (VIV) of a cylinder in cross-flow by using a simple active control method are reported. Motivated by new research, a Single Dielectric Barrier Discharge (SDBD) plasma actuator is used and the effect of steady and unsteady actuation demonstrated. The feasibility of the model parameters estimation was also studied in simulations by investigating the Fisher Information Matrix and the nonlinear numerical curve fitting methods applied to estimate identifiable parameters from experimental data. The efficiency of the control methods was found to be acceptable and simulation outcomes supported the experimental results.
Experimental Study of Single Mode Panel Flutter
Authors: Vedeneev Vasily V. , Guvernyuk Sergey V. , Zubkov Alexander F. , Kolotnikov Mikhail E.
Published: March 2011

Single mode flutter is a type of panel flutter, which cannot be analyzed theoretically using conventional piston theory, and for this reason it is studied very little. In this paper a plate, designed such that it cannot experience “classical” coupled-type flutter, but can experience single mode flutter, is tested. Analysis of the tested data clearly indicates the occurrence of single mode panel flutter.
Flow Induced Cylinder Oscillation and Its Control With High Order Spectral Difference Method on Deformable Mesh
Authors: Ou Kui , Jameson Antony
Published: March 2011

In the recent work by the authors, high order spectral difference (SD) method has been formulated in a framework with dynamic deformable meshes, and been demonstrated to preserve the design accuracy of the underlying high order temporal and spatial discretization methods. In this study, the current SD method has been extended to solve fluid structure interaction problems on deforming meshes. The SD method with collocated solution and flux points is used as the spatial discretization method, while the explicit fourth order five-stage Runge-Kutta is used to advance the flow in time. The solid structure, which is the cylinder, is modelled as a spring-mass system. The movement of the solid cylinder is handled with a dynamic deforming mesh using an algebraic high order blending polynomial. The present work has focused on flow induced cylinder oscillation, bluff body wake and cylinder interaction, and control of flow induced oscillation through mechanism of counter-rotating cylinders. Numerical experiment for flow over counter-rotating cylinder pair shows that significant drag reduction and wake suppression can be obtained. Numerical calculation for a free-stream flow over a free-floating cylinder shows that the wake symmetry of a cylinder can not be maintained. The resultant wake instability propels the cylinder in the cross-flow direction, but the cylinder was found to eventually locked in a flow induced self-oscillation at an equilibrium position. Active control of the cylinder vibration through the mechanism of counter-rotation of solid bodies is finally investigated.
Numerical Simulation of Rivulet Dynamics Associated With Rain-Wind Induced Vibration
Authors: Taylor Ian J. , Robertson Andrew C.
Published: March 2011

On wet and windy days, the inclined cables of cable-stayed bridges can experience large amplitude, potentially damaging oscillations known as Rain-Wind Induced Vibration (RWIV). The phenomenon is believed to be the result of a complicated nonlinear interaction between rivulets of rain water that run down the cables and the wind loading on the cables due to the unsteady aerodynamic flow field. A numerical method has been developed at the University of Strathclyde, to simulate aspects of RWIV, the results of which can be used to assess the importance of the water rivulets on the instability. This combines a Discrete Vortex Method solver to determine the external flow field and unsteady aerodynamic loading and a pseudo-spectral solver based on lubrication theory to model the water on the surface of the body and which is used to determine the evolution and growth of the water rivulets under external loading. These two models are coupled to simulate the interaction between the aerodynamic field and the thin liquid film on a horizontal circular cylinder. The results illustrate the effects of various loading combinations, and importantly demonstrate rivulet formation in the range of angles previous research has indicated that these may suppress the Karman vortex and lead to a galloping instability. These rivulets are found to be of self limiting thickness in all cases.
Rotating Microsensors With Non-Linear Feedback
Authors: Sloboda Andrew R. , Epureanu Bogdan I.
Published: March 2011

The need for instruments that detect and quantify small amounts of chemical and biological agents has spurred the development of micro-scale and nano-scale resonators. Most of these sensors are variations of vibrating cantilever beams and rely on resonant frequency shifts to quantify added mass. While very sensitive in vacuum or low viscosity environments, these types of sensors suffer performance degradation in viscous fluids, where damping is significantly increased. This paper presents a unique sensor architecture consisting of an immersed micro-plate designed to vibrate rotationally about an axis as fluid flows past it in a micro-channel. The idea behind this design is that some of the energy in the incoming flow can be harvested due to fluid-structure interaction, thereby reducing the effective damping. Only a small outside energy input is then required to obtain sustained, large amplitude vibrations. We show how sensitivity vector techniques applied to such a device can provide an alternate means of effectively detecting small mass variations. A method of optimizing the feedback control in order to maximize sensitivity using a spline-based force surface spanning the state space is also presented.
An Experimental Study of Boundary-Layer Transition Induced Vibrations on a Hydrofoil
Authors: Ducoin Antoine , Astolfi Jacques Andre´ , Gobert Marie-Laure
Published: March 2011

In this paper, we investigate through an experimental approach the laminar to turbulent transition in the boundary-layer flow along a hydrofoil at a Reynolds number of 7.5 × 105, together with the vibrations of the hydrofoil induced by the transition. The latter is caused by a Laminar Separation Bubble (LSB) resulting from a laminar separation of the boundary-layer. The experiments, conducted in the hydrodynamic tunnel of the Research Institute of the French Naval Academy, are based on wall pressure and flow velocity measurements along a rigid hydrofoil, which enable a characterization of the Laminar Separation Bubble and the identification of a vortex shedding at a given frequency. Vibrations measurements are then carried out on a flexible hydrofoil in the same operating conditions. The results indicate that the boundary-layer transition induces important vibrations, whose characteristics in terms of frequency and amplitude depend on the vortex shedding frequency, and can be coupled with natural frequencies.
Flutter Instability of a Fluid-Conveying, Fluid-Immersed Pipe Affixed to a Rigid Body
Authors: Hellum Aren M. , Mukherjee Ranjan , Hull Andrew J.
Published: March 2011

Studies of fluid-conveying pipes typically consider systems with an anchor at one or more boundaries, such as pinning or clamping. These types of conditions are satisfactory in the study of many common engineering applications, such as pipelines or heat exhangers. However, a small, fish-like submersible propelled by a fluttering fluid-conveying pipe requires boundary conditions which account for the relative freedom at both ends of the pipe. A submersible of this type achieves its propulsion by a combination of jet action and thrust produced by the fluttering pipe. A simple model of this type of vehicle was devised, consisting of a rigid body affixed to a fluid-conveying pipe. The applicable linearized boundary conditions were derived, and this rigid-free case can be shown to be a generalization of both the free-free and cantilever conditions. The equation of motion of this rigid-free system approaches that of the cantilever and free-free systems for appropriately large and small rigid body masses, respectively. “Intermediate” values of (non-dimensional) rigid body mass, in the range corresponding to a proposed physical realization of the system, were investigated. Consistent with prior work, it was found that, with the addition of external flow generated by the forward motion of the submersible through still water, the onset of flutter instability can be achieved for lower values of conveyed (internal) velocity than would be required in the absence of external flow. Furthermore, the onset of flutter for certain rigid body masses can be achieved at a lower internal velocity than the cantilever case at the same external speed. This point is critical; since it is the internal velocity which must be “paid for”, by powering the system’s prime mover, reduction of the required velocity to achieve flutter has the potential to improve the submersible’s efficiency.
Dynamics of Pipes Conveying Fluid With Non-Uniform Turbulent and Laminar Velocity Profiles
Authors: Hellum Aren M. , Mukherjee Ranjan , Hull Andrew J.
Published: March 2011

Previous analytical work on stability of fluid-conveying pipes assumed a uniform velocity profile for the conveyed fluid. In real fluid flows, the presence of viscosity leads to a sheared region near the wall. Earlier studies correctly note that viscous forces do not affect the dynamics of the system since these forces are balanced by pressure drop in the conveyed fluid. Although viscous shear has not been ignored in these studies, a uniform velocity profile assumes that the sheared region is infinitely thin. Prior analysis was extended to account for a fully developed nonuniform profile such as would be encountered in real fluid flows. A modified, highly tractable equation of motion was derived, which includes a single additional parameter to account for the true momentum of the fluid. This empirical parameter was determined by numerical analysis over the Reynolds number range of interest. The stability of cantilever pipes conveying fluid with two types of non-uniform velocity profile was assessed. In the first case, the profile was a function of Reynolds number and transition to turbulence occurred before the onset of flutter instability. This case had stability properties similar to the uniform velocity case except in specific narrow regions of the parameter space. The second case required that the Reynolds number be such that the flow was always laminar. For this case, lower fluid velocity was required to achieve instability, and the oscillation frequency at instability was considerably lower over much of the parameter space, compared to the uniform case.
Experimental Study of Self-Excited Vibration in a Thin Film Wrapped Around an Air-Turn Bar
Authors: Hara Kensuke , Watanabe Masahiro
Published: March 2011

This paper describes an experimental study for a self-excited vibration in the thin film wrapped around an air-turn bar. The characteristics of a self-excited vibration are investigated by obtaining time histories of the film deflection and distributions of a steady pressure and a pressure fluctuation at a surface of the airturn bar. The experimental results show that this system has two different types of vibration modes. One is a low-frequency mode which the film vibrates radially with respect to the the air-turn bar. The other is a high-frequency mode which the film flaps in the out-of-plane direction of the film. Moreover, a stability diagram of the self-excited vibration is obtained by changing the flow rate and the tensile force acting on the film. It is shown that the low-frequency vibration mode occurs when the flow rate and the tensile force are large, and the high-frequency vibration mode occurs at any flow rate and tensile force in this experiment.
Experimental Study of Dynamic Interaction Between a Steam Generator Tube and an Anti-Vibration Bar
Authors: Lalonde V. , Ross A. , Pettigrew M. J. , Nowlan I.
Published: March 2011

A first experimental work was previously carried out to study the dynamic behavior of a tube simply supported at both ends in interaction with an anti-vibration bar at mid-span. This paper presents modifications to the previous setup with the aim of improving the accuracy of the results. A comparison of the dynamic behavior of the tube is made between both setups. The objective of this experimental study is to characterize the vibration behavior of U-tubes found in steam generators of nuclear power plants. Indeed, two-phase cross-flow in the U-tubes section of steam generators can cause many problems related to vibration. In fact, flow-induced vibration of the U-tubes can cause impacts or rubbing of the tubes against their flat bar supports. Variation of the clearance between the AVB and the U-tubes may lead to ineffective supports. The resulting in-plane and out-of-plane motions of the tubes are causing fretting-wear and impact abrasion. In this study, the clearance between the tube and the AVB, as well as the amplitude, form and frequency of the excitation force are controlled parameters. The first two modes of the tube are studied. The modifications made to the setup lead to significant improvements in the results. The natural frequencies of both setups are compared to theoretical values. The difference between experimental and theoretical frequencies confirms that the new setup better represents the theoretical model of a simply supported tube. The damping of both setups is also compared to values found in literature. The results show that the new setup is more representative of realistic steam generator situations. Compared to the first setup, the displacements of the new setup clearly indicate that the movement of the tube is mostly parallel to the flat bar and in the same direction as the excitation force. The whirling motion of the tube is prevented in the new setup. The accuracy of the contact force as a function of clearance was also improved. The use of more sensitive force sensors helped to reduce the noise level of the contact force. Finally, the dynamic interaction between the tube and the AVB, defined by the fretting wear work-rate, presents a more consistent behavior. The maximum work-rate occurs when the tube is excited around the second mode for clearance between −0.10 and 0.00 mm. Such clearance between the tube and the AVB should then be avoided to minimize fretting damage.
Experimental and Numerical Characterization of Flow-Induced Vibration of Multi-Span U-Tubes
Authors: Mohany Atef , Janzen Victor P. , Feenstra Paul , King Shari
Published: March 2011

This paper describes a test program that was developed to measure the dynamic response of a bundle of steam generator U-tubes with Anti-Vibration Bar (AVB) supports, subjected to Freon two-phase cross-flow. The tube bundle geometry is similar to the geometry used in preliminary designs for future CANDU® steam generators. This test program is one of the initiatives that Atomic Energy of Canada Limited (AECL) is undertaking to demonstrate that the tube support design for future CANDU steam generators meets the stringent requirements associated with a 60-year lifetime. In particular, the tests will address issues related to in- and out-of-plane fluidelastic instability and random turbulent excitation of a U-tube bundle with Anti-Vibration Bar (AVB) supports. Therefore, the measurements include tube vibration amplitudes and frequencies, work-rate due to impacting and sliding motion of the tubes against their supports, bulk process conditions and local two-phase flow properties. Details of the test rig set-up and the measurement techniques are described in the paper. Moreover, a numerical prediction of the U-tube vibration response to flow was performed with AECL’s PIPO-FE code. A summary of the numerical results is presented.
Sloshing in a Vertical Circular Cylindrical Container With a Vertical Baffle
Authors: Askari E. , Daneshmand F. , Amabili M.
Published: March 2011

The linear problem of liquid sloshing in a cylindrical container with a vertical baffle is considered in the present paper. In this study, a theoretical oriented approach is developed for calculating the natural frequencies of liquid. The baffle is a thin-walled and open-ended cylindrical shell that is concentrically placed and partially submerged inside the container. The free surface of liquid is assumed to be perpendicular to axis of the container and is divided into two parts by the baffle. The method also captures the singular asymptotic behavior of the velocity potential at the sharp baffle edge. The liquid is assumed to be incompressible and inviscid and the method uses matched eigenfunction expansions and Galerkin expansions to derive unknown coefficients presented in the velocity potential series. A finite element analysis is also used to check the validity of the proposed method. The effects of some important parameters of system are also considered on the sloshing frequencies.
Ubiquitin on Ras: Warden or Partner in Crime?
Authors: Pfleger Cathie M.
Published: March 2011

Ubiquitination of different Ras isoforms has distinct effects on abundance, activity, and access to effectors.
Dual Mode of Oncogenesis
Authors: Gough Nancy R.
Published: March 2011

Oncogenic Ras mutants stimulate the first kinase in the MAPK pathway (Raf) and prevent SUMOylation-mediated inhibition of the second kinase, MEK.
Sizing Signals
Authors: Hurtley Stella M.
Published: March 2011

Mitosis starts when morphogen signaling levels have increased by half since the beginning of the cell cycle.
Improving Old Memories
Authors: Stern Peter R.
Published: March 2011

In rats, overexpression of a persistently active protein kinase C isoform enhances memories long after they have been formed.
Fluoroquinolone and Quinazolinedione Activities against Wild-Type and Gyrase Mutant Strains of Mycobacterium smegmatis
Authors: Malik Muhammad , Marks Kevin R. , Mustaev Arkady , Zhao Xilin , Chavda Kalyan , Kerns Robert J. , Drlica Karl
Published: March 2011

Quinazolinediones (diones) are fluoroquinolone-like inhibitors of bacterial gyrase and DNA topoisomerase IV. To assess activity against mycobacteria, C-8-methoxy dione derivatives were compared with cognate fluoroquinolones by using cultured
Mycobacterium smegmatis
. Diones exhibited higher MIC values than fluoroquinolones; however, MICs for fluoroquinolone-resistant
gyrA
mutants, normalized to the MIC for wild-type cells, were lower. Addition of a 3-amino group to the 2,4-dione core increased relative activity against mutants, while alteration of the 8-methoxy group to a methyl or of the 2,4-dione core to a 1,3-dione core lowered activity against mutants. A GyrA G89C bacterial variant was strikingly susceptible to most of the diones tested; in contrast, low susceptibility to fluoroquinolones was observed. Many of the bacteriostatic differences between diones and fluoroquinolones were explained by interactions at the N terminus of GyrA helix IV revealed by recently published X-ray structures of drug-topoisomerase-DNA complexes. When lethal activity was normalized to the MIC in order to minimize the effects of drug uptake, efflux, and ternary complex formation, a 3-amino-2,4-dione exhibited killing activity comparable to that of a cognate fluoroquinolone. Surprisingly, the lethal activity of the dione was inhibited less by chloramphenicol than that of the cognate fluoroquinolone. This observation adds the 2,4-dione structural motif to the list of structural features known to impart lethality to fluoroquinolone-like compounds in the absence of protein synthesis, a phenomenon that is not explained by X-ray structures of drug-enzyme-DNA complexes.
Clonal Spread of Levofloxacin-Resistant Streptococcus pneumoniae Invasive Isolates in Madrid, Spain, 2007 to 2009
Authors: Rodríguez-Avial Iciar , Ramos Belén , Ríos Esther , Cercenado Emilia , Ordobás María , Sanz Juan Carlos
Published: March 2011

Among 1,349
Streptococcus pneumoniae
invasive isolates, 45 (3.3%) were levofloxacin resistant. Serotype distribution was as follows: 8 (
n
= 32 isolates), 19A (
n
= 4 isolates), 7F (
n
= 3 isolates), 9V (
n
= 2 isolates), 10A (
n
= 1 isolate), 19F (
n
= 1 isolate), 6B (
n
= 1 isolate), and nontypeable (
n
= 1 isolate). Levofloxacin-resistant isolates had dual mutations in the
gyrA
and
parC
genes. Serotype 8 strains corresponded to a capsular switching of the Sweden
15A
-25 clone. Levofloxacin resistance was also detected among multiresistant (ST276
19A
, Spain
9V
-ST156, ST88
19F
, and ST1542
6B
) and among usually antibiotic-susceptible (Netherlands
7F
-ST191, ST1201
19A
, and ST2639
10A
) clones.
Effect of Nutritional Status on Response to Treatment with Artemisinin-Based Combination Therapy in Young Ugandan Children with Malaria
Authors: Verret Wendy J. , Arinaitwe Emmanuel , Wanzira Humphrey , Bigira Victor , Kakuru Abel , Kamya Moses , Tappero Jordan W. , Sandison Taylor , Dorsey Grant
Published: March 2011

The relationship between malnutrition and malaria in young children is under debate, and no studies evaluating the association between malnutrition and response to artemisinin-based combination therapies (ACTs) have been published. We evaluated the association between malnutrition and response to antimalarial therapy in Ugandan children treated with ACTs for repeated episodes of malaria. Children aged 4 to 12 months diagnosed with uncomplicated malaria were randomized to dihydroartemisinin-piperaquine (DP) or artemether-lumefantrine (AL) and followed for up to 2 years. All HIV-exposed and HIV-infected children received trimethoprim-sulfamethoxazole prophylaxis (TS). The primary exposure variables included height-for-age and weight-for-age
z
scores. Outcomes included parasite clearance at days 2 and 3 and risk of recurrent parasitemia after 42 days of follow-up. Two hundred ninety-two children were randomized to DP or AL, resulting in 2,013 malaria treatments. Fewer than 1% of patients had a positive blood smear by day 3 (DP, 0.2%; AL, 0.6% [
P
= 0.18]). There was no significant association between height-for-age or weight-for-age
z
scores and a positive blood smear 2 days following treatment. For children treated with DP but not on TS, decreasing height-for-age
z
scores of <−1 were associated with a higher risk of recurrent parasitemia than a height-for-age
z
score of >0 (hazard ratio [HR] for height-for-age
z
score of <−1 and ≥−2 = 2.89 [
P
= 0.039]; HR for height-for-age
z
score of <−2 = 3.18 [
P
= 0.022]). DP and AL are effective antimalarial therapies in chronically malnourished children in a high-transmission setting. However, children with mild to moderate chronic malnutrition not taking TS are at higher risk for recurrent parasitemia and may be considered a target for chemoprevention.
Interaction and flexibility of molecules in hydrocarbon aggregates, torsional potential in a group of hexanes
Authors: Gajdoš Ján , Bleha Tomáš
Published: March 2011

The molecular-mechanics method has been used for calculation of the torsional potential V(φ) of internal rotation around central C-C bond in hexane with one or two other hexane molecules in the neighbourhood and with full optimization of external and internal degrees of freedom. The optimum energy arrangement of the hydrocarbon molecules has been determined for various values of the φ angle as well as the optimum intramolecular geometry parameters. The adjacent molecules with all-trans conformation accommodate to the shape variation of the rotating molecule by means of translation motion. The adjacent molecules can change substantially the form of V(φ) potential as compared with the isolated molecule, and they increase rigidity of the hydrocarbon chain. For some types of mutual arrangement, however, it has been found that the other molecule in the vicinity decrease the conformational energies and barriers of transitions between the rotation isomers as compared with the isolated molecule. Thus the inter-chain forces can induce also an effective coiling of the chain. Implications of these findings have been discussed with respect to structural properties of various real hydrocarbon aggregates in solution and in solid state.
Organic semiconductors: Simple and complex salts of 1-methyl-3-alkylimidazolium 7,7,8,8-tetracyano-p-quinodimethane
Authors: Šorm Miloslav , Nešpůrek Stanislav , Procházka Miloslav , Koropecký Igor
Published: March 2011

By metathesis between lithium salts of 7,7,8,8-tetracyano-p-quinodimethane and 1-methyl-3-alkylimidazolium bromides, simple radical salts were prepared whose specific electrical conductivity values are c. 10-7-10-3, Ω-1 m-1, according to the donor structure. Combining these salts with neutral 7,7,8,8-tetracyano-p-quinodimethane (TCNQ°) gave complex salts with an electrical conductivity higher by 7-3 orders of magnitude which increase monotonically with increasing volume of the alkyl group. The compounds are stable in anhydrous conditions also in presence of oxygen, and if irradiated by daylight. The rate constant of hydrolysis of these salts is proportional to the water content in solution and inversely proportional to the content of neutral TCNQ° in the simple radical salt. The hydrolysis is predominantly activated by light absorbed by the decomposition products.
5,5-Disubstituted barbituric acids and their analogues
Authors: Kotva Rudolf , Křepelka Jiří , Semonský Miroslav
Published: March 2011

Condensation of 2-substituted triethyl esters of 2-carboxy-1,7-heptanedioic acids XIV - XIX with urea afforded 5-substituted 5-(4-carboxybutyl)barbituric acids I - VI. Similarly, thiourea and the triethyl esters XIV and/or XVI gave the analogous 5-substituted 5-(4-carboxybutyl)-2-thiobarbituric acids, VII and VIII respectively. Condensation of guanidine with triethyl esters XIX - XXI produced 5-substituted derivatives of 5-(4-carboxybutyl)-2-amino-1,4,5,6-tetrahydro-4,6-dioxopyrimidine, IX -XI. Reactions of the acids II and IV with glycine ethyl ester, using the method of mixed anhydrides, gave rise to ethoxycarbonylmethylamides, XII and XIII respectively. Some of the compounds prepared exhibited enhancing effects on 5-fluorouracil in curing leukemic mice, and antineoplastic activity, manifesting itself by reducing the size of transplanted tumours in experimental animals.
N-(Aminoacyl) and N-(aminoalkyl) derivatives of 4-cyclopentylaniline and N-ethyl-4-cyclopentylaniline; Synthesis and pharmacological screening
Authors: Vejdělek Zdeněk , Bartošová Marie , Protiva Miroslav
Published: March 2011

Acylation of 4-cyclopentylaniline (I) with chloracetyl chloride, 3-chloropropionyl chloride, 4-chlorobutyryl chloride and 2-bromo-4-methylvaleryl bromide gave the halogenoacyl derivatives IV - VII out of which the first two were subjected to substitution reactions with diethylamine and piperidine. The N-(aminoacyl) derivatives VIII - XI obtained were reduced with lithium aluminium hydride to the N-(aminoalkyl) derivatives XII and XV. N-Ethyl-4-cyclopentylaniline (XVI), prepared by reduction of N-(4-cyclopentylphenyl)acetamide (II), was similarly transformed via the chloroacetyl derivative XVII to the amide XVIII and the diamine XIX. Salts of the compounds prepared (amino amides and diamines) bring about in higher doses central excitation which is apparently in close connection with the found discoordinating effect of a part of products (VIII - XI, XIII) in the rotarod test, further with the antireserpine effects in the tests of antagonization of reserpine ptosis and hypothermia (VIII, X, XII, XIII) and finally with the anorectic effect of compound X. All substances showed a mild spasmolytic effect of the anticholinergic type. On the other hand, the expected local anaesthetic effect was found only with compounds VIII, XVIII, XIX.
Excess entropy of the systems of molecules differing in size and shape
Authors: Boublík Tomáš
Published: March 2011

The excess entropy of mixing of mixtures of hard spheres and spherocylinders is determined from an equation of state of hard convex bodies. The obtained dependence of excess entropy on composition was used to find the accuracy of determining ΔSE from relations employed for the correlation and prediction of vapour-liquid equilibrium. Simple rules were proposed for establishing the mean parameter of nonsphericity for mixtures of hard bodies of different shapes allowing to describe the P-V-T behaviour of solutions in terms of the equation of state fo pure substance. The determination of ΔSE by means of these rules is discussed.
Photolytic and thermal annealing of radical anions in gamma-irradiated ammonium salts of carboxylic acids
Authors: Mach Karel , Vacek Karel
Published: March 2011

The γ-radiolysis of simple ammonium carboxylates at 77 K generates radical anions in yields comparable with those found in parent carboxylic acids. The structure of radical anions as derived from their ESR spectra and their behaviour on thermal annealing and photobleaching is mostly analogous to that found in carboxylic acids. The fast photobleaching of radical anions allowed to estimate the amount of radical anions in the sum of all paramagnetic products after γ-radiolysis. These amounts ranged usually 50% only in ammonium acetate the unexplainable 75% of radical anions were found. Very efficient photolytic and thermal transformations of radicals RCHCOO ⇄ RCH2 were observed in ammonium acetate (R = H) while in the propionate (R = CH3) both radicals decayed during photolysis.
Synthesis and structure of iso-C4B18H22
Authors: Janoušek Zbyněk , Plešek Jaromír , Štíbr Bohumil , Heřmánek Stanislav
Published: March 2011

Iso-C4B18H22 isolated earlier as a minor by-product in the H2CrO4 oxidation of the C2B9H12(-) anion was prepared in 10% yield by thermolysis of 7,8-C2B9H13. The originally suggested structure, 3-(8'-nido-5,6-C2B8H11)-1,2-C2B10H11, is confirmed by the 11B NMR spectra.
Stretching vibrations of the V(O2) group and structure of vanadium(V) peroxo complexes
Authors: Schwendt Peter
Published: March 2011

The infrared spectra of some vanadium(V) peroxo complexes were measured and supplemented with published data ( a total of 33 complexes) to seek for relations between the stretching vibrations of the V(O2) group and the structure of the complexes. While no such relation could be established in the region of 9.10 - 800 cm-1, in the 660 - 490 cm-1 range the spectral patterns were found sensitive to the composition and structure of the coordination polyhedron, thus making it possible to discriminate between complexes of different types.
(E-Z) Isomerism of vinyl sulfides and ethers
Authors: Procházka Miloš , Vondrák Tomáš , Poláková Jana
Published: March 2011

Enthalpic data for the (E-Z) isomerisation of 1-methoxy-1-propene, 1-methylthio-1-propene, 1-methoxy-2-methylthioethene and 1,2-bis(methylthio)ethene were analyzed on the basis of calculated (CNDO/2) energy differences between the isomers.
Substituted ω-(4-oxo-3,4-dihydro-5-pyrimidinyl) alkanoic acids, their derivatives and analogues
Authors: Beran Miloš , Černý Antonín , Křepelka Jiří , Vachek Jaroslav
Published: March 2011

Condensation of guanidine with diethyl 2-formylbutanedioate (XI), diethyl 2-cyanobutanedioate (XII), diethyl 2-cyanoheptanedioate (XIII), ethyl 6,6-dicyanohexanoate (XIV), or diethyl 6,6-dicyanoundecanedioate (XV), followed by hydrolysis of the esters formed, afforded the respective substituted ω-(2-amino-5-pyrimidinyl)alkanoic acids (II, V, VI, IX and X). Analogously, condensation of the ester XIII with urea or thiourea gave acids VII and VIII. The acid II was converted into its ethyl and butyl ester (III and IV, respectively). The compounds prepared showed no significant antineoplastic effects in mice with experimental tumours.
8-Substitution derivatives of D-6-methylergoline-I
Authors: Křepelka Jiří , Vlčková Drahuše , Holubek Jiří , Roubík Jiří
Published: March 2011

Reactions of esters I and II with methylsulphinylmethylsodium in dimethyl sulphoxide afforded β-keto sulphoxides III and IV, which were converted either into compounds V and VI under the conditions of the Pummerer rearrangement, or into ketones VII and VIII by the action of aluminium amalgam in 1,2-dimethoxyethane. Reduction of the compounds III and V with sodium borohydride produced β-hydroxy sulphoxide IX and dihydroxy derivative X respectively; the latter was characterised in the form of derivatives XI and XII. Condensation of the compound III with 1,2-diaminobenzene in acetic acid gave quinoxaline derivative XIII. The compounds prepared had no marked antilactation or antinidation activity.
Electrochemical reduction of 2,2'-dinitrophenyl ether and 2,2'-dinitrodiphenylamine at mercury cathodes
Authors: Hlavatý Jaromír , Volke Jiří , Bakos Viktor
Published: March 2011

2,2'-Dinitrophenyl ether (I) is reduced at less negative potentials than 2,2'-dinitrodiphenylamine (II); the respective mechanism of their reduction differ essentially. (I) is electrolytically reduced in a single wave with an uptake of eight electrons per molecule, giving rise to a bishydroxylamine intermediate which undergoes an intramolecular disproportionation. The resulting 2-nitroso-2'-amino-diphenyl ether undergoes a chemical follow-up reaction leading on the one hand to dibenzo-(b,e)-(1,4,5)-oxadiazepine, on the other hand to a diphenylamine product (resulting by a chemical rearrangement) which reacts with reductants present in the solution and yields dihydrophenazine. It is merely by chance that in the electrolytical reduction of II dihydrophenazine also results in addition to other products. 2,2'-dinitrodiphenylamine (II) enables here, however, a partial electrolytical reduction in which 2-amino-2'-nitrophenylamine is formed in a single 6-electron wave. In the following, more negative wave, is clearly separated only in alkaline media, the other nitro group reduces with an uptake of 4 electrons to an intermediate which eliminates the hydroxylamine group with the corresponding electron pair. The subsequent chemical reaction leads to dihydrophenazine. This substance is the reduced form of an chemicaly and electrochemically reversible system, this system participates in the chemical reactions of reaction intermediates. Its regeneration readily proceeds at potentials more positive than the reduction potential of II. Phenazine is oxidized in the catholyte by the hydroxylamine set free to phenazine N-oxide. Nitrogen is thus eliminated in its elemental form via hydroxylamine from the substrate molecule.
Spontaneous penetration of hydrogen and oxygen through semihydrophobic fuel cell electrodes
Authors: Smrček Karel , Marholová Olga , Micka Karel
Published: March 2011

Spontaneous penetration of hydrogen or oxygen through porous Teflon membranes into water or KOH solution was studied by a new method based on the measurement of the minimum gas overpressure necessary for the penetration at various temperatures. The results were compared with measurements on hydrogen-oxygen fuel cells and are in qualitative agreement with theoretical studies. The penetration of gases into the electrolyte can be prevented by their humidification before introducing them into the cells.
Hydrodynamic characteristics of flow in systems with turbine impellers
Authors: Obeid Ahmed , Fořt Ivan , Bertrand Joël
Published: March 2011

The study deals with a phenomenological description of a flow leaving the blades of different types of turbine impellers, which are always placed in a cylindrical vessel with radial baffles under turbulent regime of liquid flow. The flow description is determined by three basic characteristics of the proposed model: i.e. the diameter of a cylindrical tangential jet a, the width parameter of a cylindrical tangential jet σ and the parameter of the intensity of momentum flux in the flow leaving the turbine A. All these parameters were calculated from the measured profiles of mean velocity for different types of turbines (standard, closed and with profiled blades) in systems of various dimensions. From the results follows that for geometrically similar agitated systems the model parameters have the same values; they vary with the type of turbine used and are independent on the relative size and position of the impeller in the system.
N-alkylation of Hantzsch 1,4-dihydropyridines with esters of halogenocarboxylic acids
Authors: Paleček Jaroslav , Pavlík Manfred , Kuthan Josef
Published: March 2011

1,4-Dihydropyridine derivatives IIIa,b,d,e and IVa,b,e were prepared from the corresponding Hantzsch dihydropyridines I and II by alkylation with ethyl halogenocarboxylates after deprotonation of the starting compounds with sodium hydride in dimethylformamide. Attempts to prepare compounds IIIc and IVc,d by this method failed. Spectral characteristics of the products and their fragmentation on electron impact are discussed.
Stability of dicyclohexylcarbodiimide in an aqueous medium. The effect of mitochondrial phospholipids
Authors: Kopecký Jan , Pavelka Stanislav , Dědina Jiří , Siglerová Věra , Vereš Karel
Published: March 2011

The stability of N,N'-dicyclohexylcarbodiimide (DCCD) was analyzed with respect to the use of DCCD as a specific chemical modifier of membrane-bound enzymes. The disappearance of DCCD from the sucrose-Tris medium obeyes the pseudo-first-order kinetics the rate constant (kd) of which is pH-dependent (kd = 12.0 . 10-3 min-1 at pH 6.0, and kd = 1.6 . 10-3 min-1 at pH 9.0, respectively). However, the rate of the total [14C]DCCD binding to mitochondrial membrane proteins is not markedly influenced by the change of pH (6.0-9.0). The rate of DCCD disappearance is enhanced in the presence of mitochondrial phospholipids. It is concluded that the rapid equilibration of DCCD between the phospholipid and water phase, the reactivity of DCCD with phospholipids, H+-stimulated hydration of DCCD to dicyclohexylurea and the sorption of DCCD to the test tube must be considered when studying the interaction of DCCD with membrane-bound enzymes.
Effect of the pretreatment conditions on the activity of an industrial Co-Mo/Al2O3 catalyst
Authors: Petrov Lachezar , Vladov Chavdar , Shopov Dimitar , Friebová Věnceslava , Beránek Ludvík
Published: March 2011

The processes of reduction and sulphidation of an industrial Co-Mo/Al2O3 catalyst have been studied by means of gravimetric and kinetic methods at atmospheric pressure. The effect of the pretreatment temperature on the catalytic activity for ethylene hydrogenation and thiophene hydrodesulphurization has been studied. Two types of active centres, for hydrogenation and for hydrodesulphurization, have been characterized on the basis of their different properties.