bluuebunny/crossref_metadata_2025 huggingface dataset:
Forces on Bends and T-Joints due to Multiphase Flow
Authors: Belfroid S. P. C. , Cargnelutti M. F. , Schiferli W. , van Osch Marlies
Published: March 2011

To be able to assess the mechanical integrity of piping structures for loading to multiphase flow conditions, air-water experiments were carried out in a horizontal 1″ pipe system. Forces and accelerations were measured on a number of bends and T-joint configurations for a wide range of operating conditions. Five different configurations were measured: a baseline case consisting of a straight pipe only, a sharp edged bend, a large radius bend, a symmetric T-joint and a T-joint with one of the arms closed off. The gas flow was varied from a superficial velocity of 0.1 to 30 m/s and the liquid flow was varied from 0.05 to 2 m/s. This operating range ensures that the experiment encompasses all possible flow regimes. The magnitude of the measured forces was found to vary over a wide range depending on the flow regime. For slug flow conditions very high force levels were measured, up to 4 orders of magnitude higher than in single phase flow for comparable velocities. The annular flow regime resulted in the (relative) lowest forces, although the absolute amplitude is of the same order as in the case of slug flow. In case of slug flow, the measured results can be described assuming a simple slug unit model. For both the frequency and amplitude the available models can be used in assessments. In annular and stratified flow a different model is required, since no slug unit is present. Instead, the amplitude of the excitation force can be estimated using mixture properties. To predict the main frequency for the annular flow and stratified flow additional experiments are required.
Experimental Investigation of the Vortex Shedding in the Wake of Oblique and Blunt Trailing Edge Hydrofoils Using PIV-POD Method
Authors: Zobeiri Amirreza , Ausoni Philippe , Avellan Franc¸ois , Farhat Mohamed
Published: March 2011

This paper presents an experimental investigation of the vortex shedding in the wake of blunt and oblique trailing edge hydrofoils at high Reynolds number, Re = 5 105 − 2.9 106. The velocity field in the wake is surveyed with the help of Particle-Image-Velocimetry, PIV, using Proper-Orthogonal-Decomposition, POD. Besides, flow induced vibration measurements and high-speed visualization are performed. The high-speed visualization clearly shows that the oblique trailing edge leads to a spatial phase shift of the upper and lower vortices at their generation stage, resulting their partial cancellation. For the oblique trailing edge geometry and in comparison with the blunt one, the vortex-induced vibrations are significantly reduced. Moreover, PIV data reveals a lower vorticity for the oblique trailing edge. The phase shift between upper and lower vortices, introduced by the oblique truncation of the trailing edge, is found to vanish in the far wake, where alternate shedding is recovered as observed with the blunt trailing edge. The phase shift generated by the oblique trailing edge and the resulting partial cancellation of the vortices is believed to be the main reason of the vibration reduction.
Time Domain Models for Damping-Controlled Fluidelastic Instability Forces in Multi-Span Tubes With Loose Supports
Authors: Hassan Marwan , Rogers Robert , Gerber Andrew
Published: March 2011

This paper presents simulations of a loosely supported multi-span tube subjected to turbulence and fluidelastic instability forces. Several time-domain fluid force models simulating the damping controlled fluidelastic instability mechanism in tube arrays are presented. These models include the negative damping model based on the Connors equation, fluid force coefficient-based models (Chen; Tanaka and Takahara), and two semi-analytical models (Price and Pai¨doussis; and Lever and Weaver). Time domain modelling challenges for each of these theories are discussed. The implemented models are validated against available experimental data. The linear simulations show that the Connors-equation based model exhibits the most conservative prediction of the critical flow velocity when the recommended design values for the Connors equation are used. The models are then utilized to simulate the nonlinear response of a three-span cantilever tube in a lattice bar support subjected to air crossflow. The tube is subjected to a single-phase flow passing over one of the tubes spans and the flow velocity and the support clearance are varied. Special attention is paid to the tube/support interaction parameters that affect wear, such as impact forces, contact ratio, and normal work rate. As was seen for the linear cases, the reduced flow velocity at the instability threshold differs for the fluid force models considered. The investigated models do, however, exhibit similar response characteristics for the impact force, tip lift response, and work rate, except for the Connors-based model that overestimates the response and the tube/support interaction parameters for the loose support case, especially at large clearances.
The Dynamics of a Cantilevered Pipe Aspirating Fluid Studied by Experimental, Numerical and Analytical Methods
Authors: Giacobbi Dana , Rinaldi Stephanie , Semler Christian , Pai¨doussis Michael P.
Published: March 2011

This paper investigates the dynamics of a slender, flexible, aspirating cantilevered pipe, ingesting fluid at its free end and conveying it towards its clamped end. The problem is interesting not only from a fundamental perspective, but also because applications exist, notably in ocean mining [1]. First, the need for the present work is demonstrated through a review of previous research into the topic — spanning many years and yielding often contradictory results — most recently concluding that the system loses stability by flutter at relatively low flow velocities [2]. In the current paper, that conclusion is refined and expanded upon by exploring the problem in three ways: experimentally, numerically and analytically. First, air-flow experiments, in which the flow velocity of the fluid was varied and the frequency and amplitude of oscillation of the pipe were measured, were conducted using different elastomer pipes and intake shapes. Second, a fully-coupled Computational Fluid Dynamics (CFD) and Computational Structural Mechanics (CSM) model was developed in ANSYS in order to simulate experiments and corroborate experimental results. Finally, using an analytical approach, the existing linear equation of motion describing the system was significantly improved upon, and then solved via the Galerkin method in order to determine its stability characteristics. Heavily influenced by a CFD analysis, the proposed analytical model is different from previous ones, most notably because of the inclusion of a two-part fluid depressurization at the intake. In general, both the actual and numerical experiments suggest a first-mode loss of stability by flutter at relatively low flow velocities, which agrees with the results from the new analytical model.
Heat Transfer and Wake Interaction Dynamics for Low Mass-Damping Cylinder Undergoing Flow-Induced Vibration at High Reynolds Number
Authors: Elbanhawy Amr , Turan Ali
Published: March 2011

The current open literature carries numerous publications about the dynamics of single structures freely oscillating in response to flow-induced forces of a cross-stream. Influence of controlled oscillations on heat transfer for relatively low Reynolds number cross-flow has been looked at previously, nonetheless, high Reynolds number measurements are difficult to obtain. Studies on the flow field in the vicinity of bodies with Flow-Induced Vibration (FIV) and its interaction with surface heat flux are what the current literature needs to enhance realization of such phenomenon and advance equipment design. The present study aims firstly at investigating the influence of cylinder’s heat flux on (FIV) response and vice versa. Secondly, it explores the influence of high Reynolds number (140,000) both on the cylinder’s response and on heat transfer. An unsteady numerical framework is employed for the simulations, incorporating an Arbitrary Lagrangian Eulerian method for the associated grid deformation to simulate the coupled motion of the low mass-damping circular cylinder with a single degree of freedom in the initial regime. Attention is paid towards resolving the large scales of the fluid motion and the inherent coupling of the cylinder’s motion towards the associated evolution of the time averaged flow field. The cylinder is assumed to have a constant heat flux while Large Eddy Simulation is used to solve for the turbulent flow field. Predictions show that significant changes occur to cylinder hydrodynamics and Reynolds stresses due to FIV. Wake mixing is enhanced and kinetic energy production field is qualitatively altered. Heat flux results in a noticeable increase in response amplitude for FIV cases while surface temperature and heat transfer coefficient undergo qualitative modifications in FIV scenario as opposed to a static cylinder. The variance of Nusselt number increases at parts of the cylinder’s circumference due to FIV.
Finite Element-Boundary Element Mesh Generation Technique for Fluid Structure Problems
Authors: Sharifi Hamid
Published: March 2011

In this article an approach for fully automatic mesh generation for two dimensional fluid structure problems that respect the integrity of the geometrical boundaries is presented. This approach is based on the modified Quadtree method. First, interior quadrants of the solid structure are created as the original Quadtree method. Boundary quadrants of the solid structure are created between the boundary curves and the interior quadrants using a simple projection algorithm. As a result, the problem of cut quadrants of the original modified Quadtree method is eliminated here. Boundary elements of the fluid region are created on the boundary curves using calculated projection points. The use of closed non uniform composite B-spline curves, for a unified representation of boundaries curves, simplifies the projection algorithm. On the other hand using this type of boundaries representation reduces geometrical incompatibilities of the generated mesh and produces a perfect compatibility between boundary elements and finite elements. This method can be extended to problems of three dimensional mesh generation and eliminate all cases of cut octants. An object-oriented prototype program in C++ has been written and application example is presented in this paper. Several algorithms of this method are suitable for an implementation on parallel computers.
Bluff-Body Simulation by SPH Method With Relatively High Reynolds Number in Laminar Flow Regime
Authors: Shadloo Mostafa Safdari , Zainali Amir , Yildiz Mehmet
Published: March 2011

In this work, we present solutions for flow over an airfoil and square obstacle using Weakly Compressible Smoothed Particle Hydrodynamics (WCSPH) method. For the solution of these two problems, we present an improved WCSPH algorithm that can handle complex geometries with the usage of multiple tangent solid boundary method, and eliminate particle clustering induced instabilities with the implementation of particle fracture repair procedure as well as the corrected SPH discretization scheme. We have shown that the improved WCSPH method can be effectively used for flow simulations over bluff-bodies with Reynolds numbers as high as 1400, which is not achievable with standard WCSPH formulations. Our simulation results are validated with a Finite Element mesh-dependent Method (FEM), and excellent agreements among the results were observed. We illustrated that the improved WCSPH method is able to capture the complex physics of bluff-body flows naturally such as flow separation, detachment of separated flow, wake formation at the trailing edge, and vortex shedding without any extra effort to increase the particle resolution in some specific areas of interest.
Fluid-Structure Interaction Simulation by Smoothed Particle Hydrodynamics
Authors: Shadloo Mostafa Safdari , Zainali Amir , Yildiz Mehmet
Published: March 2011

In this article, a modified SPH algorithm is proposed to solve Fluid-Structure Interaction (FSI) problems including fluid flow in interaction with compatible structures under a large deformation. To validate the current algorithm against available data in literature, we consider two important benchmark cases; namely, an oscillating elastic beam and dam breaking problems. The proposed algorithm is based on the elimination of the intermediate data transfer steps between the fluid and the solid structures, whereby resulting in an easy and time-saving simulation method. With the test application studied, we were able to prove the ability of the modified SPH method for solving of fluid and solid domains monolithically without the need to define an interfacial boundary condition or any additional steps to simulate the deformation of an elastic dam. Numerical results suggest that upon choosing correct SPH parameters such as smoothing function, and lengths, as well as coefficients for artificial viscosity and artificial stress, one can obtain results in satisfactorily agreement with numerical findings of earlier works.
Fluid Structure Interaction With Mean Flow: Over-Scattering and Unstable Resonance Growth
Authors: Arzoumanian Sevag , Peake Nigel
Published: March 2011

It is known theoretically [1–3] that infinitely long fluid loaded plates in mean flow exhibit a range of unusual phenomena in the ‘long time’ limit. These include convective instability, absolute instability and negative energy waves which are destabilized by dissipation. However, structures are necessarily of finite length and may have discontinuities. Moreover, linear instability waves can only grow over a limited number of cycles before non-linear effects become dominant. We have undertaken an analytical and computational study to investigate the response of finite, discontinuous plates to ascertain if these unusual effects might be realized in practice. Analytically, we take a “wave scattering” [2,4] — as opposed to a “modal superposition” [5] — view of the fluttering plate problem. First, we solve for the scattering coefficients of localized plate discontinuities and identify a range of parameter space, well outside the convective instability regime, where over-scattering or amplified reflection/transmission occurs. These are scattering processes that draw energy from the mean flow into the plate. Next, we use the Wiener-Hopf technique to solve for the scattering coefficients from the leading and trailing edges of a baffled plate. Finally, we construct the response of a finite, baffled plate by a superposition of infinite plate propagating waves continuously scattering off the plate ends and solve for the unstable resonance frequencies and temporal growth rates for long plates. We present a comparison between our computational results and the infinite plate theory. In particular, the resonance response of a moderately sized plate is shown to be in excellent agreement with our long plate analytical predictions.
Piezo-Actuated Valveless Micropumps for Micro-Total Analysis Systems
Authors: Chandrasekaran Arvind , Packirisamy Muthukumaran
Published: March 2011

In this work, a Piezo actuated Valveless micropump is proposed for applications in Micro-Total Analysis Systems (μTAS) and Lab-on-a-Chip. Flow rectification in the micropump has been brought about with the use of a diffuser element. The device is fabricated on PDMS-Glass substrate with the glass acting as the diaphragm. A PZT disc is integrated with the setup for actuation. The micropump has been characterized for its dynamic behavior, flow characteristics, and pressure. It was found that the maximum flow rate for the micropump was obtained at low frequency which makes it usable for practical μTAS applications.
Improved Oxacillin Treatment Outcomes in Experimental Skin and Lung Infection by a Methicillin-Resistant Staphylococcus aureus Isolate with a
vraSR
Operon Deletion
Authors: Jo Dae Sun , Montgomery Christopher P. , Yin Shaohui , Boyle-Vavra Susan , Daum Robert S.
Published: March 2011

Methicillin-resistant
Staphylococcus aureus
(MRSA) strains are major pathogens causing infections of the skin and soft tissues and more serious, life-threatening diseases, including sepsis and necrotizing pneumonia. The
vraSR
operon encodes the key regulatory system that modulates the stress response of
S. aureus
elicited upon exposure to cell wall antibiotics. Mutation of
vraS
and
vraR
results in decreased oxacillin resistance
in vitro
. We investigated the effect of oxacillin treatment in experimental models employing a clinical USA300 MRSA strain (strain 923) and an isogenic
vraSR
deletion mutant (strain 923-M23). In a murine model of
S. aureus
necrotizing pneumonia, animals were treated with oxacillin, beginning 15 min after inoculation. Among mice infected with mutant strain 923-M23, oxacillin treatment significantly improved survival compared with saline treatment, whereas oxacillin treatment had no effect in mice infected with strain 923. Similarly, treatment with oxacillin decreased the bacterial burden among animals infected with strain 923-M23 but not among animals infected with strain 923. In a murine skin infection model, oxacillin eliminated the development of dermonecrosis among 923-M23-infected mice and decreased the bacterial burden in the lesions, but not among strain 923-infected mice. We conclude that deletion of the
vraSR
operon allowed an oxacillin regimen to be effective in murine models of MRSA pneumonia and skin infection. These findings provide proof-of-principle for development of a new antibiotic that could restore the usefulness of oxacillin against MRSA by inhibiting VraS or VraR.
Legionella pneumophila Type II Secretion Dampens the Cytokine Response of Infected Macrophages and Epithelia
Authors: McCoy-Simandle Kessler , Stewart Catherine R. , Dao Jenny , DebRoy Sruti , Rossier Ombeline , Bryce Paul J. , Cianciotto Nicholas P.
Published: March 2011

The type II secretion (T2S) system ofLegionella pneumophilais required for the ability of the bacterium to grow within the lungs of A/J mice. By utilizing mutants lacking T2S (lsp), we now document that T2S promotes the intracellular infection of both multiple types of macrophages and lung epithelia. Following infection of macrophages,lspmutants (but not a complemented mutant) elicited significantly higher levels of interleukin 6 (IL-6), tumor necrosis factor alpha (TNF-α), IL-10, IL-8, IL-1β, and MCP-1 within tissue culture supernatants. A similar result was obtained with infected lung epithelial cell lines and the lungs of infected A/J mice. Infection with a mutant specifically lacking the T2S-dependent ProA protease (but not a complementedproAmutant) resulted in partial elevation of cytokine levels. These data demonstrate that the T2S system ofL. pneumophiladampens the cytokine/chemokine output of infected host cells. Upon quantitative reverse transcription (RT)-PCR analysis of infected host cells, anlspFmutant, but not theproAmutant, produced significantly higher levels of cytokine transcripts, implying that some T2S-dependent effectors dampen signal transduction and transcription but that others, such as ProA, act at a posttranscriptional step in cytokine expression. In summary, the impact of T2S on lung infection is a combination of at least three factors: the promotion of growth in macrophages, the facilitation of growth in epithelia, and the dampening of the chemokine and cytokine output from infected host cells. To our knowledge, these data are the first to identify a link between a T2S system and the modulation of immune factors following intracellular infection.
Interpretation of a molecular wave function in terms of individual structures
Authors: Ponec Robert
Published: March 2011

A general method is presented suitable for the decomposition of a MO wave function into a set of non-orthogonal structures. Applying this method provides evidence that the generally accepted idea of the weight of a structure has no physical meaning and cannot therefore be used for interpreting the problems of structure and reactivity.
Extraction of hexavalent uranium from citrate medium by the toluene solution of trilaurylamine
Authors: Vaňura Petr , Kuča Libor
Published: March 2011

Complexes of the type (UO2HA)p(TLA)q(H3A)r are formed in the extraction of uranyl by the toluene solutions of trilaurylamine (TLA) from the isomolar aqueous phase formed by 1M-(H, Na,(UO2)0.5)3A, where H3A is citric acid. The extraction was studied at pH 1.62 with the equilibrium concentration of uranium in the aqueous phase in the range 10-4 -10-1 mol l-1 and with TLA concentration in the organic phase ranging from 0.0305 to 0.308 mol l-1. Complexes with q=5 and p+r=3 predominate in the extraction by TLA solutions of lower concentrations (c(TLA) = 0.0305 mol l-1). The fraction of more associated complexes (q=8-9, q - (p+r=0-2) increase with the increase of TLA concentration.
Spectrophotometric study of the complexation equilibria of cadmium ions with 5-bromo and 5-chloro derivatives of 2-(2-pyridylazo)-5-diethylaminophenol (BrPADAP, ClPADAP)
Authors: Kubáň Vlastimil , Macka Miroslav
Published: March 2011

The composition, optical characteristics, molar absorption coefficients and equilibrium constants of the reactions of formation of the ML and ML2 complexes of both reagents with cadmium(II) ions were determined by graphical analysis and numerical interpretation of the absorbance-pH curves by the modified SQUAD-G program. Optimal conditions were proposed for the spectrophotometric determination of Cd in 10% v/v ethanol medium in the presence of 0.1% w/v Triton X-100 or 1% w/v Brij 35. BrPADAP and ClPADAP are the most sensitive spectrophotometric reagents for the determination of cadmium(II) ions (ε = 1.28-1.44 . 105 mmol-1 cm2 at 560 nm and pH 8.0-9.5) with a high colour contrast in the reaction (Δλmax ~117 nm) and a selectivity similar to that of other N-heterocyclic azodyes (PAR, PAN, etc.).
Alkaline solvolysis of diaminophosphates
Authors: Mollin Jiří , Láznička Jiří , Kašpárek František
Published: March 2011

Mechanism of alkaline solvolysis of phenyl diaminophosphates is discussed on the basis of its selectivity, activation entropy and steric effects. All methods used show that the reaction proceeds by SN2 mechanism via an intermediate, containing a pentavalent phosphorus.
Spectrophotometric determination of zinc with 5-methyl-1,3,4-thiadiazolyl-(2-azo-1)-2-naphthol
Authors: Cacho Juan , Nerin Cristina
Published: March 2011

The reaction of Zn(II) with 5-methyl-1,3,4-thiadiazolyl-(2-azo-1)-2-naphthol (MTDAN) and extraction of the complex formed in chloroform is studied. The optimum pH range for the extraction and formation of the complex is 10-11.2 and Beer's law is obeyed in the interval of 0-2 ppm of Zn(II) in the organic phase. The molar absorptivity is 5.9 . 104 l mol-1 cm-1 at 568 nm. The stoichiometry of the complex corresponds to the type ML2. Some interferences are studied and an easy way is given to eliminate them. The results are compared with those corresponding to TAN. The reaction is applied to the analysis of synthetic samples of bronzes with satisfactory results.
Cyclization kinetics and mechanism of N-benzoyl-N'-(1,2-dimethyl-3-oxo-1-butenyl)thiourea
Authors: Kaválek Jaromír , Potěšil Tomáš , Štěrba Vojeslav
Published: March 2011

Cyclization kinetics of N-benzoyl-N'-(1,2-dimethyl-3-oxo-1-butenyl)thiourea have been studied in aqueous and methanolic solutions of acids and bases. In all cases the cyclization product is 4,5,6-trimethyl-2,5-dihydro-2-thioxopyrimidine or its protonated or deprotonated forms. In dilute methanolic and aqueous hydrochloric acid the substrate reacts in its monoprotonated form. The cyclization in basic media is catalyzed by methoxide or hydroxyl ion and also by primary and secondary amines at such pH values where the catalysis by lyate ion is practically insignificant. Tertiary amines and acetate ion do not catalyze the cyclization.
Temperature control in chemical reactors with slow response of the cooling system; Definition of coefficients of control safety
Authors: Horák Josef , Jiráček František
Published: March 2011

Coefficients of static, dynamic and information safety are defined. They cold be used for consideration of how difficult is the feedback of temperature control in a chemical reactor with exothermic reaction. An analysis is made for a batch reactor which should be kept in a pseudostationary state which is unstable at the open control loop. Control is based on measurement of the reaction mixture temperature and on evaluation of temperature derivative with time. The action quantity is flow rate of the carrier in the cooling system. The result of an analysis is the highest operating temperature of the mixture at which the safety of the reactor operation is still secured and further the trajectory on which it is possible to reach in the shortest time the given operating temperature at preserving safety of the reactor operating.
The use of the theory of statistical moments for a description and evaluation of noble gase breakthrough in carbon adsorbent beds
Authors: Wilhelmová Ludmila , Cejnar František , Dvořák Zdeněk
Published: March 2011

The values of the first-fourth statistical moments have been determined of the argon, krypton and xenon breakthrough curves, which were measured on the active carbon Supersorbon HS and the carbon adsorbent Jado LD 1191 beds, at temperatures 298-473 K, by means of elution gas chromatography. The application of the Gram-Charlier series - including the first-fourth statistical moments - enabled to describe satisfactorily the breakthrough curves over the whole range of outlet concentrations of the studied gases. On the basis of the theory of statistical moments, selected parameters, characterizing the dynamic adsorption in the studied systems were determined. The obtained parameters allowed to compare and evaluate the properties of the adsorption beds of both adsorbents - especially with respect to their possible use as a packing in the delaying line units of radioactive noble gases.
Effect of liquid viscosity on liquid side mass transfer coefficient at vertical film flow on expanded metal sheets
Authors: Brož Zdeněk , Endršt Mirko
Published: March 2011

Experimental results are presented on the effect of liquid viscosity on absorption rate of carbon dioxide into a liquid film flowing downward the vertical surface of expanded metal sheets. On basis of these results the conclusion has been reached that the Highbie model does not enable to predict the effect of kinematic viscosity on liquid side mass transfer coefficient k1. The film-penetration model has been proposed where the existence of non-mixed region is assumed at the interface with the thickness ϑ and to it periodically incoming disturbances with the length scale of disturbance λ and characteristic Reynolds number of disturbance equal to one. On basis of experimental data were evaluated the dimensionless thicknesses of the film and penetration regions ϑ+ = 0.04 and λ+ = 10.6. A good agreement of the measured and calculated values of the mass transfer coefficient k1 were obtained for three types of expanded metal sheets of vertical pitch diagonal 10, 16 and 28 mm and nine liquids with kinematic viscosities within the range from 0.6 to 15.1 μm2s-1.
Conformation around several equivalent bonds. Polymethoxy derivatives of benzene
Authors: Exner Otto , Jehlička Václav
Published: March 2011

Dipole moments of benzene methoxy derivatives I-IX were measured in benzene solution and discussed in terms of the conformation around the Car-O bonds, exploiting the method of graphical comparison and systematic introduction of substituents. In the case of 1,2-dimethoxybenzene several explanations are in accord with the dipole moment data. However, considering all available evidence, most probable seems to be the presence of two conformers, one of which is non-planar with two non-equivalent methoxy groups (IC). The conformation of 1,2,3-trimethoxybenzene is similar to that found for many derivatives in the crystalline phase (VC), only the outer methoxy groups are probably slightly deviating from the coplanar position.
Crowns in alkali alkoxide-conjugate acid solutions: A remarkably low propensity to complex formation
Authors: Pechanec Václav , Kocián Oldřich , Závada Jiří
Published: March 2011

Complexing ability of the macrocyclic polyethers 18-crown-6, 15-crown-5 and 12-crown-4 has been investigated ebulliometrically in the homologous series of 0.6 molal ROM-ROH solutions (M = K, Na, Li; R = H, CH3, C2H5, n-C3H7, i-C3H7, t-C4H9). The values of complexation constants have been estimated in all the 54 crown-ROM combinations and the effects of cation, crown-cavity size and solvent have been examined. Two intriguing facts emerged from a comparison of the new results with the pertinent literature data. Firstly, it was found that the cation-crown cavity-complex stability variation in the ROM-ROH series disagrees with the well-known principle of steric match, the propensity of crowns to complexation decreasing in most instances in the order 15-crown-5 > 12-crown-4 > 18-crown-6 for the potassium and 12-crown-4 > 15-crown-5 > 18-crown-6 for the sodium alkoxide. An energetical preference of 2 : 1 over 1 : 1 crown-ROM complexes is presumably the responsible factor. Secondly, and even more importantly, it was found that complexation constants obtained in this study are strikingly small, the values for complexation of potassium and sodium alkoxides with 18-crown-6 being smaller by 3-7 power of ten than those which were previously obtained for the alkali ions, at lower concentrations. Evidence is provided that the difference does not originate from ion-pairing but from the operation of some effect which so far escaped notice.
Alkaline hydrolysis of monomethyl esters of maleic and fumaric acids
Authors: Komadel Petr , Holba Vladislav , Truchlik Štefan
Published: March 2011

The kinetics of alkaline hydrolysis of maleic and fumaric acids monomethyl esters were studied as function of the temperature, ionic strength, and relative permittivity of the reaction medium. Electrostatic and nonelectrostatic contributions of the interaction energies of reacting species were calculated from the measured data and compared with the experimental activation energy values. The dependence of the rate constant on the temperature brings an evidence for the mutual compensation of the electrostatic and nonelectrostatic effects.
5'-O-diphosphorylphosphonylmethylribonucleosides - A new group of DNA-dependent RNA polymerase inhibitors
Authors: Horská Květa , Rosenberg Ivan , Holý Antonín , Šebesta Karel
Published: March 2011

The effect of 5'-O-diphosphorylphosphonylmethylribonucleosides I on the transcription reaction catalyzed by DNA-dependent RNA polymerase from Escherichia coli was studied. These analogues of ribonucleoside 5'-triphosphates are not enzyme substrates but inhibit the transcription reaction, competing specifically with the natural substrates. According to the inhibition constants, the pyrimidine derivatives Ia,b are more potent inhibitors than the purine derivatives Ic,d.
Determination of rate constants of redox reactions of second order from current-less potential-time curves by a simplified graphical-numerical method
Authors: Tockstein Antonín , Skopal František
Published: March 2011

A method for constructing curves is proposed that are linear in a wide region and from whose slopes it is possible to determine the rate constant, if a parameter, θ, is calculated numerically from a rapidly converging recurrent formula or from its explicit form. The values of rate constants and parameter θ thus simply found are compared with those found by an optimization algorithm on a computer; the deviations do not exceed ±10%.
Isothermal dynamics of adsorption in diluted sorbent layers; The adsorber with an infinite sorption layer
Authors: Stárek Jindřich , Kočiřík Milan , Zukal Arnošt
Published: March 2011

The phenomenological model of the adsorbate transport in isothermal adsorber with a constant diameter was solved for an infinite, static and statistically homogeneous and isotropic sorption layer of constant composition. The layer was formed by a mixture of the adsorbent and the inert material grains with identical form and size. The model applies the linear adsorption isotherm and accounts for contributions of the convection, axial dispersion, external and internal diffusion and rate of adsorption. The obtained Laplace's image of the solution was used for calculation of the statistical moments up to the fourth order. The analysis of the effect of dilution on the separation efficiency (characterized by a number of theoretical plates) has led to the conclusion that for equal amounts of the adsorbent, the more diluted layer will have higher efficiency, or, for equal separation efficiencies, the amount of the adsorbent in the more diluted layer will be lower than in the less diluted layer. It has been shown that the contribution of axial dispersion has a positive, primary effect on the separation efficiency.
Quantum-chemical interpretation of electronic absorption spectra of the Hantzsch 1,4-dihydropyridines
Authors: Kurfürst Antonín , Kuthan Josef
Published: March 2011

Electronic absorption spectra of 1,4-dihydropyridines I-XII have been interpreted by means of the SCF-PPP method. Possibility of interpretation of the said spectra of 4-substituted derivatives V-XII as superposition of two independent chromophoric systems is discussed.
Calculation of the density of aqueous solutions of strong electrolytes from individual ionic parameters
Authors: Čeleda Jiří
Published: March 2011

Based on a hypothesis verified earlier, according to which the concentration dependence of apparent molar volumes of ions in aqueous solutions is caused by their dehydration due to the decrease of the volume concentration of water, a method for the calculation of the density of concentrated aqueous electrolytes from individual ionic constants is proposed. The theory is verified by comparing with experimental data from the literature (420 solutions of 57 electrolytes).
Glass transition temperatures in the system calcium chloride-water-dimethylsulphoxide
Authors: Malá Jarmila , Sláma Ivo
Published: March 2011

The glass-forming composition region of the CaCl2-H2O-DMSO system has been established, and the glass transition temperatures of the mixtures have been determined as a function of the CaCl2 content at a constant DMSO mole fraction in the mixed solvent. The dependence of the glass transition temperature on the CaCl2 mole fraction at a constant mole fraction of DMSO in the mixed solvent can be described by a linear relationship.
Formation of sulphur compounds in hydrodenitrogenation of quinoline, 1,2,3,4-tetrahydroquinoline, pyridine, piperidine and 1-pent-4-enylamine on a nickel-tungsten catalyst in the presence of hydrogen sulphide
Authors: Černý Mirko , Trka Antonín
Published: March 2011

Hydrodenitrogenation (HDN) of quinoline and 1,2,3,4-tetrahydroquinoline on a sulphided nickel-tungsten catalyst in the presence of hydrogen and of its mixture with hydrogen sulphide has been studied in an autoclave at 350 °C. The results show that hydrogen sulphide exhibits rate-accelerating effect on HDN of the above compounds by formation of sulphur compounds. It was found that neutral portion of the reaction mixture contains octahydro-2H-1-benzothiopyran, octahydro-1H-2-benzothiopyran, octahydro-2-methylbenzo(b)thiophene and other sulphur compounds. The reaction scheme for HDN of quinoline that accounts for favourable effect of hydrogen sulphide is proposed. In the neutral portion of the reaction mixture from HDN of piperidine and 1-pent-4-enylamine in the presence of hydrogen sulphide further sulphur-containing compounds were identified.
Donor activity of 5'-O-phosphonylmethyl analogues of ATP and GTP in the phosphorylation of uridine catalyzed by uridine kinase from mouse leukemic cells
Authors: Veselý Jiří , Rosenberg Ivan , Holý Antonín
Published: March 2011

The phosphonate analogues of ATP and GTP can function as phosphate donors in uridine kinase reaction. The Km constants for ATP and its analogue ATPc (I) are identical, the Vmax value for ATP is five times higher than that for ATPc. Also the Vmax constants with respect to uridine follow the same pattern (250 nmol for ATP, 35.7 nmol for ATPc). The optimum Mg2+ concentration for the phosphonate is 3 times higher compared with ATP.
Production of biomass from sulphite liquors in tower fermentor with forced circulation
Authors: Zahradník Jindřich , Rychtera Mojmír , Kratochvíl Jan , Havlíčková Ludmila , Čermák Jan
Published: March 2011

Cultivation of the yeast Candida utilis on sulphite liquors was studied in a tower fermentor with ejector-type gas distributor and additional bubble bed showering. The aim of the work was to test the fermentor applicability for the cultivation process studied and to obtain data characterizing the fermentation in the tested unit. The effect of medium composition and dilution rate on selected cultivation parameters was determined in the fermentor with active volume 0.1 m3 and the hydrodynamic and energy characteristics of the apparatus were evaluated. The experimental results proved the fermentor to be suitable for the cultivation process studied. Favourable effect of the optimized fermentation medium was observed both on the values of characteristic cultivation parameters and on the efficiency of the utilization of energy supplied to the system.
Carbon gas diffusion electrodes promoted with silver and operating on air or oxygen in alkaline medium. Physical parameters of electrodes and their components
Authors: Smrček Karel , Wedell Martin , Mrha Jiří , Musilová Miroslava
Published: March 2011

From the ratio of hydrophobic to hydrophilic pore volumes determined after a long-term exposure of the gas or active layer to water, the strong hydrophobic nature of the teflonized carbon black contained in carbon-based gas diffusion electrodes was confirmed. This material proves better than Teflon in Teflon-bonded active carbon electrodes, whose hydrophobicity is adversely affected on heating and the mechanical strength of the layer decreases. Measurement of the penetration of water and rate of flow of oxygen revealed that the teflonized carbon black ensures two essential functions of the gas diffusion electrode: feeding the active layer with oxygen and prevention of flooding of the gas pores.
Effect of ionizing radiation on supported catalysts of Ni-ZnO type in maleic acid hydrogenation
Authors: Kudláček Rostislav , Solařová Hana
Published: March 2011

A silica supported nickel-zinc oxide mixed catalyst was modified in different stages of its preparation by preliminary treatment with 60Co gamma rays. The investigation was performed aimed to find such a composition and preparation procedure which would guarantee a satisfactory catalyst activity in the maleic acid hydrogenation. Possible explanation is offered for the change in activity observed after the irradiation of the catalyst. The precipitation step and the activation of the catalyst with hydrogen which is carried out after the reduction of the mixed oxide, have been found to be the stages determining the activity of the catalyst.
The effect of sulphidation on the nature of active sites on nickel-molybdenum-alumina hydrorefining catalysts
Authors: López Rafael
Published: March 2011

A strong influence of sulphidation on the hydrogenation and hydrogenolytic activity of Mo-Al2O3 and Ni-Mo-Al2O3 hydrotreating catalysts has been found. Two kinds of active sites are distinguished, the first consisting of surface molybdenum atoms and serving mostly for hydrogenation, the second type formed by interaction of Mo with Ni atoms and being active in sulphided form for direct hydrogenolysis of the C-S bonds.
Polarographic reduction of 1-(p-substituted benzyl)-3-cyanopyridinium chlorides
Authors: Pavlíková-Raclová Františka , Kuthan Josef
Published: March 2011

Reduction of 3-cyanopyridinium salts has been studied on the mercury dropping electrode. Solvent and substituent effects and pH of the medium have been shown to modify in a certain extent differently the polarographic characteristics as compared with analogous 3-carbamoyl derivatives, which is due to higher electronegativity of the studied cations.
Kinetics and mechanism of oxidation of tartaric acid by bromate ions and an heterogeneous oscillation reaction of tartaric acid
Authors: Adamčíková Ľubica , Knappová Olga
Published: March 2011

The kinetics and mechanism of oxidation of tartaric acid by bromate ions in sulphuric acid solutions have been studied. As the relation between the concentration of H3O+ ions and the reaction rate constant indicates, the species involved in the reaction are protonized bromate ions (HBrO3) and tartaric acid molecules. Their interaction is of dipole-dipole nature, as borne out by measurements of the rate constant in dependence on the dielectric constant and on the ionic strength. The activation parameters and the stoichiometry of the reaction have been evaluated. An oscilation behaviour is observed in the presence of a Mn(II) catalyst if bromine is removed from the system constantly. The concentration ranges in which the oscillations occur have been established. Bromine is shown to play a major part in the heterogeneous oscillation system.
The structure of a new sesquiterpene - Siol acetate from Sium latifolium L.
Authors: Casinovi Carlo Giulio , Cerrini Silvio , Motl Otakar , Fardella Giuseppe , Fedeli Walter , Gavuzzo Enrico , Lamba Doriano
Published: March 2011

A new sesquiterpenic ester, a carotane derivative, aws isolated from fruits of Sium latifolium (Umbelliferae). Its structure (I) was elucidated by spectroscopic and X-ray analysis.
Possibility of predicting the existence of a complex compound in the NaF-Na2SO4 system
Authors: Malinovský Milan , Vrbenská Jaroslava
Published: March 2011

A method of thermodynamic prediction of the existence of a complex compound in the NaF-Na2SO4 binary system is described. On the basis of the knowledge of a part of liquids drawn in the vicinity of NaF melting point and coordinates of eutectic point, the conclusion was made that there exists the complex compound Na3FSO4 in the system. Its true and hypothetic melting points and the degree of its thermal dissociation were calculated. Further, the probable coordinates of a eutectic point in the Na3FSO4-Na2SO4 subsystem were found out. The calculated results were confronted with experimental determination; the agreement is very good. The method described can be useful for experimental studies of binary phase diagrams.
Isothermal and isobaric vapour-liquid equilibrium data in the tetrachloromethane-sec-butyl alcohol system
Authors: Linek Jan
Published: March 2011

Isothermal vapour-liquid equilibrium data at 65, 73 and 80 °C and isobaric ones at 101.3 kPa were measured in the tetrachloromethane-sec-butyl alcohol system. A modified circulation still of the Gillespie type was used for the measurements. Under the conditions of measurement, the system exhibits positive deviations from Raoult's law and minimum boiling-point azeotropes. The experimental data were fitted to a number of correlation equations, the most suitable being the Wilson equation.
Kinetics of the radical copolymerization of styrene and 2-methoxyethyl methacrylate
Authors: Stejskal Jaroslav , Straková Dagmar , Procházka Ondřej , Kratochvíl Pavel
Published: March 2011

Twenty low-conversion statistical copolymers of styrene and 2-methoxyethyl methacrylate with various composition were prepared. The dependence of the copolymer composition, molecular weight, initiation efficiency and other parameters on the composition of the monomer mixture is discussed. Kinetic data are correlated by means of various models of the copolymerization kinetics. The best fit with experimental data is provided by a diffusion-controlled termination model, especially its dyad variant suggested in this study.
Vapour-liquid equilibrium at low pressures from the back equation of state
Authors: Boublík Tomáš
Published: March 2011

The BACK semiempirical equation of state was employed to determine the excess thermodynamic functions of five binary mixtures composed of benzene with cyclohexane, n-pentane, n-hexane, n-heptane, and n-octane at 298.15 K. Two sets of mixing rules are discussed and values of the excess thermodynamic functions of equimolar solutions, calculated on their basis, are compared with experimental data. The calculated and experimental equilibrium data are compared in the x-y diagrams.
Hydrogen peroxide photolysis. Mechanism of photocatalytic effect of transition metals
Authors: Luňák Stanislav , Vepřek-Šiška Josef
Published: March 2011

The photochemical decomposition of hydrogen peroxide depends on the presence of transition metal ions in the reaction system. Photochemical reduction of the poorly catalytically active ions with higher oxidation states produces catalytically active ions of lower oxidation states which catalyze the thermal reaction. The quantum yield of hydrogen peroxide photolysis is proportional to the number of catalytic cycles occurring on the photochemically generated catalyst.
13C and 15N NMR study of azo-hydrazone tautomerism in azo dyes containing amino or acetamido groups
Authors: Lyčka Antonín
Published: March 2011

13C and 15N NMR spectra of ten model azo dyes containing NH2 or NHCOCH3 group in ortho- or para-position to the phenylazo group on benzene, naphthalene and anthracene skeleton were measured. A negligible content of the hydrazone form in these compounds follows from the 13C and 15N chemical shifts and from a slight temperature dependence of the 15N chemical shifts and 1J(15N15N) coupling constants. The 15N isotope effect Δδ (15N) = 0.1 ppm was observed and the values of 1J(15N15N) = 15.6 ± 0.3 Hz were found with compounds double labelled by 15N.
Endothermic crystallization of inorganic substances from aqueous solutions
Authors: Vacek Václav
Published: March 2011

An account is given of common inorganic substances that crystallize from aqueous solutions by an endothermic process. The relation between the thermodynamic characteristics of the substances and the heat effect of crystallization is briefly discussed.
Theoretical study of the rate determining proton transfer at the mechanism of serine proteases action
Authors: Baňacký Pavol
Published: March 2011

The proton transfer step at the breakdown of the tetrahedral intermediate of chymotryptic catalysis was studied using the simple quantum-statistical theory of unimolecular proton transfer reactions. The physical basis of the enzymatic high catalytic efficiency is discussed from the view-point of experimental and theoretically obtained kinetic parameters. The experiment is suggested to test the possible importance of vibrational excited states at the enzyme action.
New synthesis of 2-amino-4-oxopyrido[3,2-e]-1,3-thiazines and 1-alkyl(aryl)pyrido[3,2-e]-2-thiouracils
Authors: Koščík Dušan , Kristian Pavol , Gonda Jozef , Dandárová Emília
Published: March 2011

Addition reactions of 2-chloronicotinoyl isothiocyanate with primary and secondary amines and subsequent cyclization of intermediate thioureas represent new synthesis of pyrido[3,2-e]thiouracil and pyrido[3,2-e]-thiazine derivatives. 2-Amino-4-oxopyrido[3,2-e]-1,3-thiazines are formed upon heating the reaction components in ethanol, whereas 1-alkyl(aryl)pyrido[3,2-e]-2-thiouracils are products of alkali-catalyzed reaction. In reaction with primary amines the corresponding thioureas were isolated as intermediates, whereas secondary amines reacted directly to give the pyridothiazine derivatives. Structure of the synthesized compounds was confirmed by their 13C NMR and mass spectra; also the IR and 1H NMR spectra are in accord with the suggested formulae.