bluuebunny/crossref_metadata_2025 huggingface dataset:
Acute shifts in baroreflex control of renal sympathetic nerve activity induced by REM sleep and grooming in rats
Authors: Nagura Satsuki , Sakagami Tamaki , Kakiichi Ai , Yoshimoto Misa , Miki Kenju
Published: June 2004

The present study aimed to determine the impact of  REM sleep and grooming on the baroreflex stimulus–response curve for renal sympathetic nerve activity (RSNA). At least 3 days before study, Wistar female rats (n= 12) were chronically implanted with catheters to measure systemic arterial pressure (Pa) and to intravenously infuse vasoactive drugs. In addition, electrodes were placed for measurements of RSNA, electroencephalogram, trapezius electromyogram and electrocardiogram. The baroreflex curve for RSNA was determined by changingPausing rapid intravenous infusions of phenylephrine and nitroprusside and then fitted to an inverse sigmoid function curve. REM sleep induced a vertical suppression of thePa–RSNA baroreflex curve, which was characterized by significant decreases in the maximum response (by 72.0%,P< 0.05) and the maximum gain (by 4.02% mmHg−1,P< 0.05) compared with NREM sleep level. Grooming shifted thePa–RSNA baroreflex curve upward and to the right, which was associated with increases in the maximum response (by 45.2%,P< 0.05), the minimum response (by 20.7%,P< 0.05) and the pressure at the centring point (by 11.1 mmHg,P< 0.05). These data suggest that thePa–RSNA baroreflex curve was shifted acutely and differently in a state‐dependent manner during natural sleep and wake cycle in rats.
Electrotonic coupling between stratum oriens interneurones in the intact in vitro mouse juvenile hippocampus
Authors: Zhang Xiao‐Lei , Zhang Liang , Carlen Peter L.
Published: June 2004

Using the isolated juvenile (7–14 days) mouse whole hippocampus preparation, which contains intact complex local circuitry, 145 dual whole cell recordings were made from stratum oriens (s.o.) interneurones under infrared microscopy. In 11.7% of paired recordings, evidence for direct electrotonic coupling between the s.o. interneurones was obtained from the response of one interneurone to a long (400–600 ms) constant current pulse passed into the coupled interneurone. When specifically orienting the dual recordings in the transectional plane of the hippocampus, 18.5% of paired recordings showed electrotonic coupling. The coupling coefficient, estimated from averaged data, was 6.9 ± 4.7%, ranging from 1.3 to 17.6%. The time constant of the electrotonically transmitted hyperpolarization was inversely related to the coupling coefficient between the two neurones. The electrotonic responses of one neurone to constant current pulses injected into the other coupled neurone were intermittent. Spikes in one of the coupled neurones were associated with small electrotonic EPSPs (spikelets) in the other coupled neurone, in those neuronal pairs with coupling coefficients greater than 10%. Failure of spikelet production following a spike in the coupled cell occurred 5–10% of the time. Electrotonic coupling and spikelets persisted in the presence of chemical synaptic transmission blockade by CNQX, APV and bicuculline, or in zero Ca2+ perfusate, but were abolished by carbenoxolone (100 μm), a gap junctional blocker. These data confirm the existence of electrotonic coupling between s.o. interneurones, presumably via gap junctions located in dendrites.
Effect of extracellular acid–base disturbances on the intracellular pH of neurones cultured from rat medullary raphe or hippocampus
Authors: Bouyer Patrice , Bradley Stefania Risso , Zhao Jinhua , Wang Wengang , Richerson George B. , Boron Walter F.
Published: June 2004

Previous reports suggest that an important characteristic of chemosensitive neurones is an unusually large change of steady‐state intracellular pH in response to a change in extracellular pH (ΔpHi/ΔpHo). To determine whether such a correlation exists between neurones from the medullary raphe (a chemosensitive brain region) and hippocampus (a non‐chemosensitive region), we used BCECF to monitor pHi in cultured neurones subjected to extracellular acid–base disturbances. In medullary raphe neurones, respiratory acidosis (5%→ 9% CO2) caused a rapid fall in pHi (ΔpHi∼0.2) with no recovery and a large ΔpHi/ΔpHo of 0.71. Hippocampal neurones had a similar response, but with a slightly lower ΔpHi/ΔpHo (0.59). We further investigated a possible link between pHi regulation and chemosensitivity by following the pHi measurements on medullary raphe neurones with an immunocytochemistry for tryptophan hydroxylase (a marker of serotonergic neurones). We found that the ΔpHi/ΔpHo of 0.69 for serotonergic neurones (which are stimulated by acidosis) was not different from either the ΔpHi/ΔpHo of 0.75 for non‐serotonergic neurones (most of which are not chemosensitive), or from the ΔpHi/ΔpHo of hippocampal neurones. For both respiratory alkalosis (5%→ 3% CO2) and metabolic alkalosis (22 mm→ 35 mm HCO3−), ΔpHi/ΔpHo was 0.42–0.53 for all groups of neurones studied. The only notable difference between medullary raphe and hippocampal neurones was in response to metabolic acidosis (22 mm→ 14 mm HCO3−), which caused a large pHi decrease in ∼80% of medullary raphe neurones (ΔpHi/ΔpHo= 0.71), but relatively little pHi decrease in 70% of the hippocampal neurones (ΔpHi/ΔpHo= 0.09). Our comparison of medullary raphe and hippocampal neurones indicates that, except in response to metabolic acidosis, the neurones from the chemosensitive region do not have a uniquely high ΔpHi/ΔpHo. Moreover, regardless of whether neurones were cultured from the chemosensitive or the non‐chemosensitive region, pHi did not recover during any of the acid–base stresses.
Electrophysiological characterization of a recombinant human Na+‐coupled nucleoside transporter (hCNT1) produced in Xenopus oocytes
Authors: Smith Kyla M. , Ng Amy M. L. , Yao Sylvia Y. M. , Labedz Kathy A. , Knaus Edward E. , Wiebe Leonard I. , Cass Carol E. , Baldwin Stephen A. , Chen Xing‐Zhen , Karpinski Edward , Young James D.
Published: June 2004

Human concentrative nucleoside transporter 1 (hCNT1) mediates active transport of nucleosides and anticancer and antiviral nucleoside drugs across cell membranes by coupling influx to the movement of Na+ down its electrochemical gradient. The two‐microelectrode voltage‐clamp technique was used to measure steady‐state and presteady‐state currents of recombinant hCNT1 produced in Xenopus oocytes. Transport was electrogenic, phloridzin sensitive and specific for pyrimidine nucleosides and adenosine. Nucleoside analogues that induced inwardly directed Na+ currents included the anticancer drugs 5‐fluorouridine, 5‐fluoro‐2′‐deoxyuridine, cladribine and cytarabine, the antiviral drugs zidovudine and zalcitabine, and the novel thymidine mimics 1‐(2‐deoxy‐β‐d‐ribofuranosyl)‐2,4‐difluoro‐5‐methylbenzene and 1‐(2‐deoxy‐β‐d‐ribofuranosyl)‐2,4‐difluoro‐5‐iodobenzene. Apparent Km values for 5‐fluorouridine, 5‐fluoro‐2′‐deoxyuridine and zidovudine were 18, 15 and 450 μm, respectively. hCNT1 was Na+ specific, and the kinetics of steady‐state uridine‐evoked Na+ currents were consistent with an ordered simultaneous transport model in which Na+ binds first followed by uridine. Membrane potential influenced both ion binding and carrier translocation. The Na+–nucleoside coupling stoichiometry, determined directly by comparing the uridine‐induced inward charge movement to [14C]uridine uptake was 1: 1. hCNT1 presteady‐state currents were used to determine the fraction of the membrane field sensed by Na+ (61%), the valency of the movable charge (−0.81) and the average number of transporters present in the oocyte plasma membrane (6.8 × 1010 per cell). The hCNT1 turnover rate at −50 mV was 9.6 molecules of uridine transported per second.
Experimental and Numerical Investigation of Trailing Edge Film Cooling by Circular Coolant Wall Jets Ejected From a Slot With Internal Rib Arrays
Authors: Martini P. , Schulz A.
Published: June 2004

The present study concentrates on the experimental and computational investigation of a cooled trailing edge in a modern turbine blade. The trailing edge features a pressure side cutback and a slot, stiffened by two rows of evenly spaced ribs in an inline configuration. Cooling air is ejected through the slot and forms a cooling film on the trailing edge cutback region. In the present configuration the lateral spacing of the ribs equals two times their width. The height of the ribs, i.e., the height of the slot equals their width. Since the ribs are provided with fillet radii of half the slot height in size, circular coolant jets are exiting the slot tangentially to the trailing edge cutback. The adiabatic wall temperature mappings on the trailing edge cutback indicate that strong three-dimensional flow interaction between the coolant jets and the hot main flow takes place in such a way that two or more coolant jets coalesce depending on the blowing ratio. Experimental and numerical data to be presented in the present study include adiabatic film cooling effectiveness on the trailing edge cutback, the pressure distribution along the internal ribbed passage as well as slot discharge coefficients for different blowing ratios ranging from M=0.35 to 1.1.
The Influence of Leading-Edge Geometry on Secondary Losses in a Turbine Cascade at the Design Incidence
Authors: Benner M. W. , Sjolander S. A. , Moustapha S. H.
Published: June 2004

The paper presents detailed experimental results of the secondary flows from two large-scale, low-speed linear turbine cascades. The aerofoils for the two cascades were designed for the same inlet and outlet conditions and differ mainly in their leading-edge geometries. Detailed flow field measurements were made upstream and downstream of the cascades using three and seven-hole pressure probes and static pressure distributions were measured on the aerofoil surfaces. All measurements were made exclusively at the design incidence. The results from this experiment suggest that the strength of the passage vortex plays an important role in the downstream flow field and loss behavior. It was concluded that the aerofoil loading distribution has a significant influence on the strength of this vortex. In contrast, the leading-edge geometry appears to have only a minor influence on the secondary flow field, at least for the design incidence.
Investigation of Stator-Rotor Interaction in a Transonic Turbine Stage Using Laser Doppler Velocimetry and Pneumatic Probes
Authors: Go¨ttlich E. , Neumayer F. , Woisetschla¨ger J. , Sanz W. , Heitmeir F.
Published: June 2004

The current paper presents steady and unsteady flow data of a transonic test turbine stage operating under flow conditions similar to modern highly loaded gas turbines. Measurements were performed between stator and rotor as well as downstream of the rotor in planes perpendicular to the rotor axis. Time-resolved axial and tangential velocities were measured by a two-component laser doppler velocimeter (LDV) to investigate unsteady phenomena, while time-averaged flow properties were measured by means of a pneumatic seven-hole probe for all three spatial directions. The time-resolved investigation done by LDV allows to present velocity fields, flow angles and turbulence data at different stator-rotor positions during one blade passing period. Averaging these results enabled comparison with the pneumatic multihole probe measurement. LDV data and stage geometry can be obtained per email request and used for computational fluid dynamics (CFD) code verification.
Study on Crack Propagation Tendencies of Non-Repaired and Repaired Nozzles
Authors: Fujii Tomoharu , Takahashi Takeshi
Published: June 2004

A system designed to control and predict the length of cracks that generate in the first-stage nozzles of E and F class gas turbines was developed. This system consists of three programs for (1) inputting cracks, (2) displaying cracks, and (3) predicting cracks, and a database consisting of approximately 350,000 cracks generated in first-stage nozzles taken from past repair records of five power plants operating in Japan. The database also contains data on operating time and number of starts of gas turbines. The distinctive features of this system are described below. (1) The crack data can be entered on the nozzle drawing as a picture by using the mouse. (2) The accumulated data allows the sections of nozzles in which cracks have generated most frequently to be identified. (3) The correlation formula of cracks and operating time or number of starts can be obtained simply. (4) By entering the scheduled operating time or number of start-ups to the time of the next scheduled inspection in the correlation formula, the length of cracks in optional sections and propagating in optional directions can be predicted. Using this system, the statuses of cracks generated in non-repaired and repaired nozzles of E class gas turbines were compared. The comparison focused on 11 patterns with comparatively long cracks selected from the cracks propagating together with the increase in operating time or number of starts. The propagation of cracks covering a period of approximately two years, which corresponds to the inspection interval of power plants in Japan, was also compared. The results showed that the extent of crack propagation tends to increase with the increase in the number of repairs. Furthermore, the propagation of cracks in repair nozzles is about two times greater than that in non-repair nozzles. It was also found that the system could identify the sections in which the longest cracks are generated.
Mechanics of electroelastic bodies under biasing fields
Authors: Yang Jiashi , Hu Yuantai
Published: June 2004

This is a review article on the mechanics of small-amplitude motions superposed on finite biasing or initial fields in an electroelastic body. It begins with a summary of the nonlinear theory of electroelasticity, which is the theoretical foundation for the theory of small fields superposed on a bias. This theory, obtained by different approaches, and the development of structural theories for electroelastic beams, plates, and shells under biasing fields are discussed. Applications of these theories for small fields superposed on biasing fields in the buckling of thin electroelastic structures, frequency stability of piezoelectric resonators for time-keeping and telecommunication, acoustic wave sensors based on frequency shifts due to biasing fields, characterization of nonlinear electroelastic materials by propagation of small-amplitude waves in electroelastic bodies under biasing fields, and electrostrictive ceramics which operate under a biasing electric field are reviewed. A summary of some current and possible future research topics in this field is given. The article contains 166 references.
Interaction of Film Cooling Rows: Effects of Hole Geometry and Row Spacing on the Cooling Performance Downstream of the Second Row of Holes
Authors: Saumweber Christian
Published: June 2004

A comprehensive set of generic experiments is conducted to investigate the interaction of film cooling rows. Five different film cooling configurations are considered on a large-scale basis each consisting of two rows of film cooling holes in staggered arrangement. The hole pitch to diameter ratio within each row is kept constant at P/D=4. The spacing between the rows is either x/D=10, 20, or 30. Fan-shaped holes or simple cylindrical holes with an inclination angle of 30 deg and a hole length of 6-hole diameters are used. With a hot gas Mach number of Mam=0.3, an engine like density ratio of ρc/ρm=1.75, and a freestream turbulence intensity of Tu=5.1% are established. Operating conditions are varied in terms of blowing ratio for the upstream and, independently, the downstream row in the range 0.5<M<2.0. The results illustrate the importance of considering ejection into an already film-cooled boundary layer. Adiabatic film cooling effectiveness and heat transfer coefficients are significantly increased. The decay of effectiveness with streamwise distance is much less pronounced downstream of the second row primarily due to pre-cooling of the boundary layer by the first row of holes. Additionally, a comparison of measured effectiveness data with predictions according to the widely used superposition model of Sellers is given for two rows of fanshaped holes.
Design of Industrial Axial Compressor Blade Sections for Optimal Range and Performance
Authors: Sieverding Frank , Ribi Beat , Casey Michael , Meyer Michael
Published: June 2004

Background: The blade sections of industrial axial flow compressors require a wider range from surge to choke than typical gas turbine compressors in order to meet the high volume flow range requirements of the plant in which they operate. While in the past conventional blade profiles (NACA65 or C4 profiles) at moderate Mach number have mostly been used, recent well-documented experience in axial compressor design for gas turbines suggests that peak efficiency improvements and considerable enlargement of volume flow range can be achieved by the use of so-called prescribed velocity distribution (PVD) or controlled diffusion (CD) airfoils. Method of approach: The method combines a parametric geometry definition method, a powerful blade-to-blade flow solver and an optimization technique (breeder genetic algorithm) with an appropriate fitness function. Particular effort has been devoted to the design of the fitness function for this application which includes non-dimensional terms related to the required performance at design and off-design operating points. It has been found that essential aspects of the design (such as the required flow turning, or mechanical constraints) should not be part of the fitness function, but need to be treated as so-called “killer” criteria in the genetic algorithm. Finally, it has been found worthwhile to examine the effect of the weighting factors of the fitness function to identify how these affect the performance of the sections. Results: The system has been tested on the design of a repeating stage for the middle stages of an industrial axial compressor. The resulting profiles show an increased operating range compared to an earlier design using NACA65 profiles. Conclusions: A design system for the blade sections of industrial axial compressors has been developed. Three-dimensional CFD simulations and experimental measurements demonstrate the effectiveness of the new profiles with respect to the operating range.
Real Gas Effects in Turbomachinery Flows: A Computational Fluid Dynamics Model for Fast Computations
Authors: Boncinelli Paolo , Rubechini Filippo , Arnone Andrea , Cecconi Massimiliano , Cortese Carlo
Published: June 2004

A numerical model was included in a three-dimensional viscous solver to account for real gas effects in the compressible Reynolds averaged Navier-Stokes (RANS) equations. The behavior of real gases is reproduced by using gas property tables. The method consists of a local fitting of gas data to provide the thermodynamic property required by the solver in each solution step. This approach presents several characteristics which make it attractive as a design tool for industrial applications. First of all, the implementation of the method in the solver is simple and straightforward, since it does not require relevant changes in the solver structure. Moreover, it is based on a low-computational-cost algorithm, which prevents a considerable increase in the overall computational time. Finally, the approach is completely general, since it allows one to handle any type of gas, gas mixture or steam over a wide operative range. In this work a detailed description of the model is provided. In addition, some examples are presented in which the model is applied to the thermo-fluid-dynamic analysis of industrial turbomachines.
A Numerical Method for Turbomachinery Aeroelasticity
Authors: Cinnella P. , De Palma P. , Pascazio G. , Napolitano M.
Published: June 2004

This work provides an accurate and efficient numerical method for turbomachinery flutter. The unsteady Euler or Reynolds-averaged Navier-Stokes equations are solved in integral form, the blade passages being discretised using a background fixed C-grid and a body-fitted C-grid moving with the blade. In the overlapping region data are exchanged between the two grids at every time step, using bilinear interpolation. The method employs Roe’s second-order-accurate flux difference splitting scheme for the inviscid fluxes, a standard second-order discretisation of the viscous terms, and a three-level backward difference formula for the time derivatives. The dual-time-stepping technique is used to evaluate the nonlinear residual at each time step. The state-of-the-art second-order accuracy of unsteady transonic flow solvers is thus carried over to flutter computations. The code is proven to be accurate and efficient by computing the 4th Aeroelastic Standard Configuration, namely, the subsonic flow through a turbine cascade with flutter instability in the first bending mode, where viscous effect are found practically negligible. Then, for the very severe 11th Aeroelastic Standard Configuration, namely, transonic flow through a turbine cascade at off-design conditions, benchmark solutions are provided for various values of the inter-blade phase angle.
A Technique for Processing Transient Heat Transfer, Liquid Crystal Experiments in the Presence of Lateral Conduction
Authors: Ling John P. C. W. , Ireland Peter T. , Turner Lynne
Published: June 2004

New techniques for processing transient liquid crystal heat transfer experiment have been developed. The methods are able to measure detailed local heat transfer coefficient and adiabatic wall temperature in a three temperature system from a single transient test using the full intensity history recorded. Transient liquid crystal processing methods invariably assume that lateral conduction is negligible and so the heat conduction process can be considered one-dimensional into the substrate. However, in regions with high temperature variation such as immediately downstream of a film-cooling hole, it is found that lateral conduction can become significant. For this reason, a procedure which allows for conduction in three dimensions was developed by the authors. The paper is the first report of a means of correcting data from the transient heat transfer liquid crystal experiments for the effects of significant lateral conduction. The technique was applied to a film cooling system as an example and a detailed uncertainty analysis performed.
Long-Lived
Drosophila
with Overexpressed dFOXO in Adult Fat Body
Authors: Giannakou Maria E. , Goss Martin , Jünger Martin A. , Hafen Ernst , Leevers Sally J. , Partridge Linda
Published: June 2004

Reduced activity of the insulin/insulin-like growth factor signaling (IIS) pathway increases life-span in diverse organisms. We investigated the timing of the effect of reduced IIS on life-span and the role of a potential target tissue, the fat body. We overexpressed dFOXO, a downstream effector of IIS, in the adult
Drosophila
fat body, which increased life-span and reduced fecundity of females but had no effect on male life-span. The role of FOXO transcription factors and the adipose tissue are therefore evolutionarily conserved in the regulation of aging, and reduction of IIS in the adult is sufficient to mediate its effects on life-span and fecundity.
Force Microscopy with Light-Atom Probes
Authors: Hembacher Stefan , Giessibl Franz J. , Mannhart Jochen
Published: June 2004

The charge distribution in atoms with closed electron shells is spherically symmetric, whereas atoms with partially filled shells can form covalent bonds with pointed lobes of increased charge density. Covalent bonding in the bulk can also affect surface atoms, leading to four tiny humps spaced by less than 100 picometers in the charge density of adatoms on a (001) tungsten surface. We imaged these charge distributions by means of atomic force microscopy with the use of a light-atom probe (a graphite atom), which directly measured high-order force derivatives of its interaction with a tungsten tip. This process revealed features with a lateral distance of only 77 picometers.
Photochemistry of Free-Base Porphyrin Linked to Methyl Viologen
Authors: Guindy N. M. , Elzawawy F. M. , Sabry D. Y.
Published: June 2004

The photochemistry of free-base meso-tetraphenylporphyrin linked to methyl viologen via an alkoxy chain (n = 3) at the ortho, meta or para-position of one meso-phenyl group, in Triton X-100 micellar aqueous solutions is reported. The appended viologen does not quench the porphyrin fluorescence nor its triplet excited state due to the different solubilization of both parts of the molecule in the medium where the porphyrin ring resides in the hydrophobic phase and the alkoxy linker protrudes into the rather diffuse outer phase of detergent oxyethylene units, while the viologen moiety penetrates into the aqueous layer. However, laser flash photolysis measurements show that in the presence of nicotinamide dinucleotide, NADH, the porphyrin ring is reduced to phlorin due to the penetration of NADH into the organic phase. For porphyrin-tetraviologen in which a viologen molecule is linked to each of the porphyrin meso-position via alkoxy chain, fluorescence quenching could be achieved. The values of the quenching efficiency are high (94% in acetonitrile) compared to intramolecular quenching and are dependent upon the solvent viscosity.
Thermal Dehydrochlorination of Poly(vinyl chloride) in Syndiotactic Systems
Authors: Burda Jaroslav , Lukáš Rudolf
Published: June 2004

The thermal dehydrochlorination of syndiotactic poly(vinyl chloride) sequences has been studied theoretically on low-molecular weight models ranging from vinyl chloride dimer to pentamer using the semiempirical quantum chemical MNDO method. Parameters obtained with saturated systems and their change caused by the proceeding elimination of hydrogen chloride accompanied by the formation of the corresponding unsaturated structures are discussed with respect to the repeated chloroallyl or α-chloropolyene activation of the dehydrochlorination process. The study of the assumed radical and ionic intermediates is used in discussing the reaction mechanism of dehydrochlorination, and the radical or ionic mechanism is supposed to be operative depending on the reaction conditions.
Geodesic Formulation of the Least Motion Principle in Chemical Reactivity
Authors: Strnad Martin , Ponec Robert
Published: June 2004

In this study an attempt is presented at the quantitative formulation of the old intuitive criterion for the characterization of chemical reactivity known as the principle of the least motion. The proposed formulation originates from the abstract mathematical model, within the framework of which the criterion of minimal structural changes is realized by the requirement of minimal changes of the state vectors in the Hilbert space of electron states. The presented approach is demonstrated on the practical example of pericyclic reactions for which its results correctly reproduce the conclusions of Woodward-Hoffmann rules.
An Alternative Synthesis of Ψ(CH2O) Pseudodipeptides
Authors: Hlaváček Jan , Král Vladimír
Published: June 2004

An alternative route to obtain Ψ(CH2O) pseudodipeptide unit based on insertion of carbens in hydroxylic bond of alcohols mediated by catalyst rhodium(II) acetate is described. In that way, N-protected derivatives of alaninol, valinol, isoleucinol leucinol and phenylalaninol were converted, upon a treatment with methyl or ethyl diazoacetate, to corresponding fully protected pseudodipeptides with methyleneoxy isostere bond which can be further used in peptide synthesis.
Melanin Concentrating Hormone Analogs: Contraction of the Cyclic Structure. III. CD Spectroscopic Study
Authors: Frič Ivo , Lebl Michal , Hruby Victor J.
Published: June 2004

A comparison of the CD spectra of MCH analogs differing in length but containing a heterodetic ring of the same size (compounds I, IV and VII or III, VI and IX) reveals that a conformational change occurs upon elongating the peptide chain from thirteen to seventeen amino-acid residues. The 5-17 fragments appear to prefer a β-turn conformation, whereas the 1-17 full-sequence peptides prefer α-helical conformation. Peptides containing seventeen-membered ring exhibit greater conformational adaptability (the incorporation of their cyclic moiety into an ordered conformation being easier) than those containing a twenty-six-membered ring. Spectral properties of the twenty-three-membered heterodetic ring in peptides II and V indicate that they do not possess highly ordered conformation.
Metabolism of 1-(S)-(3-Hydroxy-2-phosphonomethoxypropyl)cytosine (HPMPC) in Human Embryonic Lung Cells
Authors: Cihlar Tomas , Votruba Ivan , Horská Květoslava , Liboska Radek , Rosenberg Ivan , Holý Antonín
Published: June 2004

The acyclic nucleotide analogue HPMPC is in human embryonic lung cells, cultured in vitro, transformed to its mono- and diphosphates (HPMPCp and HPMPCpp) and HPMPCp-choline; the synthesis of HPMPCp is catalysed by pyrimidine nucleoside monophosphate kinase (EC 2.7.4.14); HPMPCp-choline (analogue of CDP-choline) is formed from HPMPCpp and choline phosphate in the presence of CTP:phosphorylcholine cytidylyltransferase (EC 2.7.7.15). These metabolites persist for a long time in the cellular pool even after HPMPC has been removed from the medium; on the other hand, they efflux to the medium. Neither HPMPC, nor any of its metabolites interfere with intracellular CDP-choline level.
Catalytic Properties of Fluorine Modified SmNa-Y Zeolites
Authors: Kowalak Stanisłav , Pawłowska Maria , Balkus Kenneth J.
Published: June 2004

It is known that mild fluorination of zeolites, including those modified with polyvalent cations, increases their activity for acid catalyzed reactions. In this study we report the reactivity of fluorine modified Sm(III) exchanged zeolite NaY. Mild fluorination of SmNaY reduces the activity of strong protonic acid sites and increases the contribution of weak aprotic acid centres. Results for cumene cracking and toluene disproportionation as well as for 1-hexene isomerization are reported.
Transformation of 1-Butene over Synthetic Zeolites
Authors: Ferino Italo , Monaci Roberto , Solinas Vincenzo , Forni Lucio , Rivoldini Antonio , Sanseverino Luigi
Published: June 2004

The behaviour of several zeolites as catalysts for the title reaction has been investigated by means of a continuous flow microreactor. Runs performed at atmospheric pressure indicated that at 423 K the completely protonic forms of the zeolites catalyze just the isomerization reaction. In the case of Y zeolites, oligomerization occurs only over the partially decationated samples, in the temperature range between 373 and 423 K and W/F between 0.2 and 22 gcath/g1-but, to an extent which depends on the reaction conditions. Most of the catalysts were tested also under pressure (4.05 MPa) at 423 K. The protonic forms of Y and ZSM-5 zeolites seem promising catalysts in terms of both conversion and selectivity to oligomers. The 1-olefins account for 30% of the entire olefinic mixture. The octenes, which account for 70% of the liquid mixture, are mostly formed of dimethylhexenes. Trimers are also formed during the reaction and, in the very particular case of H[B]ZSM-5, tetramers are produced.
Hydroconversion of Heptane Catalyzed by Sulfided NiMo/HY Zeolites
Authors: Leglise Jacques , El Qotbi Mohammed , Cornet Daniel
Published: June 2004

A series of catalysts made of Ni, Mo and NiMo sulfide encaged in HY zeolites (Si/Al = 3 to 17) were tested for the hydroconversion of heptane. The reaction was carried out at P(H2) = 8 MPa and with a constant supply of H2S. Propane and isobutane were the main products, but bimolecular cracking processes occurred to some extent. The yield of heptane isomers was low, showing a deficient hydrogenation function. The influence of the Si/Al ratio upon catalytic activity and selectivity was examined.
Sorption Properties of Zeolite Y Modified by Controlled Deposition of Intracrystalline Coke
Authors: Rozwadowski Michał , Włoch Jerzy , Erdmann Krzysztof , Kornatowski Jan
Published: June 2004

The possibility of zeolite Y modification by controlled deposition of coke during the process of methanol conversion was studied. It was found, that coke deposits lower the sorption capacity of the zeolite, which yields the possibility to obtain modified zeolite of definite sorption properties. The process of coking was analysed using the results of kinetic measurements, XRD, IR, TGA, and sorption-isotherms determination. The Polanyi-Dubinin potential theory was applied to describe the water-vapor sorption isotherms.
The Role of Ion Exchange Method of Na-ZSM-5 Zeolite and Influence Hydrogenation Components on Properties and Activity of Dewaxing Catalysts
Authors: Grzechowiak Jolanta R. , Masalska Aleksandra , Romotowski Tadeusz , Komorek Jolanta
Published: June 2004

Hydrocracking of n-hexane and diesel oil fraction over presulfided NiMo, Mo and Ni catalysts has been carried out using a high pressure flow reactor system. The ion-exchanged form of ZSM-5 extrudates (50% alumina binder) was loaded with 2-20 wt.% of metals. The results indicate that, using Ni/H-ZSM-5 zeolite obtained by incorporation of nickel by ion exchange treatment of NH4-ZSM-5 from nickel nitrate solution, it is possible to obtain sufficiently active catalysts for low-temperature hydrocracking process. The catalysts containing Ni-ZSM-5 zeolites (Ni/H-ZSM-5 or Ni/Na-ZSM-5) were superior to catalyst prepared by using P/H-ZSM-5. It was found that nickel was an essential hydrogenation components of low temperature hydrocracking catalysts.
Study of the V2O5/Al2O3 Catalyst of the NO + NH3 Reaction
Authors: Stopka Pavel , Čížek Milan
Published: June 2004

During the reduction of the catalyst, the maximum intensity in the ESR spectrum does not correspond to the catalyst composition of V2O4/Al2O3. The feasible explanations of this fact are discussed in relation to the reduction of VV on the surface and in deeper layers of the catalyst.
Study of Spatial Distribution of Kinetic Energy of Turbulence in a Cylindrical System with Turbine Impellers and Radial Baffles
Authors: Fořt Ivan , Ettler Petr , Kolín František , Vanags Juris , Rikmanis Maris A.
Published: June 2004

The paper deals with the description and results of experimental investigation of spatial distribution of kinetic energy of turbulence in a cylindrical system with one or two standard turbine impellers on the same shaft and with radial bafflers at the vessel wall. The time-averaged specific kinetic energy of turbulence of agitated liquid is measured with a stirring-intensity-meter (SIM) consisting of mechanical-piezoelectric sensor and an auxiliary electronic device for processing the scanned fluctuation signal (the SIM calibration was carried out by means of a lasser-doppler anemometer). The measurements were performed in a model vessel of diameter D = 350 mm, in the range of values of Reynolds number for mixing ReM ∈ <1.2.103, 1.06.105> and relative size of impeller and vessel d/D = 0.286 in the single-phase and two-phase system (air was blown into the system through a sparger ring under the lower impeller). It follows from the measured and processed results that the spatial distribution of mean specific kinetic energy of turbulence in systems wit turbine impellers is considerably influenced by the amount of blown air: the mean specific kinetic energy of turbulence decreases with growing volumetric flow rate of air in the stream streaking from blades of rotating impeller, and, in the region outside this stream, it significantly increases.
Chemical Bonds and Their Transformations in the Course of Chemical Reactions
Authors: Ponec Robert , Strnad Martin
Published: June 2004

The Julg's concept of chemical bond as a region of small charge fluctuation was generalized by incorporating into the framework of recently proposed overlap determinant method. The resulting generalization allowing a simple theoretical description of structural transformation in terms close to classical picture of disappearing and newly formed chemical bonds was applied to the analysis of several selected pericyclic reactions both allowed and forbidden. The forbidden reactions were shown to be accompanied by deeper charge fluctuations than the allowed ones.
Analogs of Deamino Carba Oxytocin with Inhibitory Properties; Synthesis and Biological Activities
Authors: Procházka Zdenko , Slaninová Jiřina , Barth Tomislav , Stierandová Alena , Trojnar Jerzy , Melin Per , Lebl Michal
Published: June 2004

Solid phase methodology on polyamide-kieselguhr resin was used for the synthesis of six analogs of deamino carba-1 or carba-6 oxytocin with non-coded amino acids in position 2, threonine in position 4, ornithine in position 8 and without glycine in position 9. The following analogs were prepared: des-Gly9-[L-Phe(p-Et)2, Thr4, Orn8]deamino-carba-1-oxytocin (I), des-Gly9-[D-Phe(p-Et)2, Thr4, Orn8]deamino-carba-1-oxytocin (II), des-Gly9-[D-Tyr(Et)2, Thr4, Orn8]deamino-carba-1-oxytocin (III), des-Gly9-[L-Phe(p-Et)2, Thr4, Orn8]deamino-carba-6-oxytocin (IV), des-Gly9-[D-Phe(p-Et)2, Thr4, Orn8]deamino-carba-6-oxytocin (V), and des-Gly9-[D-Tyr(Et)2, Thr4, Orn8]deamino-carba-1-oxytocin (VI). All the analogs were found to be strong uterotonic and pressor inhibitors. The highest potency in the uterotonic inhibitory test was exhibited by analog II (pA2 = 8.3) and strongest pressor inhibitor was compound I (pA2 = 7.5).
Modelling of the Multiphase Behavior of Methane-Ethane-Nitrogen Mixture at Low Temperatures with an Equation of State
Authors: Stateva Roumiana P. , Tsvetkov Stefan G.
Published: June 2004

The paper discusses modelling of the multiphase behavior of the methane-ethane-nitrogen mixture, which is of a considerable interest for the natural gas and oil industries. The thermodynamic model is a modified Redlich-Kwong-Soave equation of state. The computer algorithm is based on a new approach to solving the isothermal multiphase flash problem, when the number and identity of the phases present at equilibrium are unknown in advance. The results demonstrate that Redlich-Kwong-Soave equation of state and the algorithm applied predict with reasonable accuracy the complicated phase behavior and the region of L1L2V equilibrium, observed in the experiment, of the methane-ethane-nitrogen system.
Phase Inversion in Two-Phase Liquid Systems
Authors: Weiss Jindřich
Published: June 2004

New data on critical holdups of dispersed phase were measured at which the phase inversion took place. The systems studied differed in the ratio of phase viscosities and interfacial tension. A weak dependence was found of critical holdups on the impeller revolutions and on the material contactor; on the contrary, a considerable effect of viscosity was found out as far as the viscosity of continuous phase exceeded that of dispersed phase.
Influence of the Thermophysical Properties Extrapolation, in the Course of Iterative Calculations, on the Convergence Characteristics of Higher Level Simulation Algorithms - A General Analysis
Authors: Tsvetkov Stefan G. , Stateva Roumiana P.
Published: June 2004

An extrapolating model provides values for thermophysical properties when infeasible specifications (either pressure or temperature) are recognized at a given iteration in process simulator, applying an EOS technique. The model has a considerable effect on the convergence characteristics, accuracy and robustness of a higher level simulation algorithm. The present paper outlines a strategy for evaluating and comparing the abilities of different extrapolating techniques: to promote the convergence of higher level algorithms; to ensure for them a solution, which will be of accuracy, not significantly inferior, to the actual one. The latter could have been obtained using for example a different thermodynamic model.
Synthesis of Isomeric N-(3-Fluoro-2-hydroxypropyl) and N-(2-Fluoro-3-hydroxypropyl) Derivatives of Purine and Pyrimidine Bases
Authors: Jindřich Jindřich , Dvořáková Hana , Holý Antonín
Published: June 2004

Reaction of fluoromethyloxirane (III) with heterocyclic bases in the presence of potassium carbonate afforded N-(3-fluoro-2-hydroxypropyl) derivatives of adenine (VI), 3-deazaadenine (VII), 2-amino-6-chloropurine (XII), 6-nitro-1-deazapurine (IX), 4-methoxy-2-pyrimidone (XVIII) and its 5-methyl derivative (XIX). Acid hydrolysis of compounds XII, XVIII, and XIX gave 9-(3-fluoro-2-hydroxypropyl)guanine (XIII), 1-(3-fluoro-2-hydroxypropyl)uracil (XX) and -thymine (XXI). The intermediates XVIII and XIX were ammonolyzed to give 1-(3-fluoro-2-hydroxypropyl)cytosine (XXII) and -5-methylcytosine (XXIII). Reaction of chloro derivative XII with sodium azide followed by hydrogenation of the formed 2-amino-6-azidopurine (XIV) led to 9-(3-fluoro-2-hydroxypropyl)-2,6-diaminopurine (XV). 9-(3-Fluoro-2-hydroxypropyl)-1-deazaadenine (X) was obtained by hydrogenation of compound IX. Benzyloxymethyloxirane (XXIV) was reacted with pyridine-hydrogen fluoride adduct to give 3-benzyloxy-2-fluoropropanol (XXV) whose tosylate XXVI on reaction with sodium salt of adenine and subsequent hydrogenolysis of the intermediate XXVII afforded 9-(2-fluoro-3-hydroxypropyl)adenine (XXVIII). The same compound was obtained by reaction of 3-benzyloxy-1-bromo-2-fluoropropanol (XXX) with sodium salt of adenine followed by methanolysis. Condensation of sodium salt of XI, XVI, and XVII with synthon XXX and subsequent acid deblocking gave 9-(2-fluoro-3-hydroxypropyl)guanine (XXXIII), 1-(2-fluoro-3-hydroxypropyl)uracil (XXXVI), and 1-(2-fluoro-3-hydroxypropyl)thymine (XXXVII). 1-(2-Fluoro-3-hydroxypropyl) derivatives of cytosine (XXXVIII) and 5-methylcytosine (XXXIX) were obtained by ammonolysis of the corresponding 4-methoxypyrimidine intermediates XXXIV and XXXV.
Spectrophotometric Study of the Interaction of Bromopyrogallol Red with Tensides and the Effect of NaNO3
Authors: Němcová Irena , Čermáková Ludmila
Published: June 2004

A study was carried out of the effect of a strong electrolyte (NaNO3) on the change in the electron spectra (in the visible region) of bromopyrogallol red in the presence of Septonex, sodium dodecyl sulfate and Triton X-100. It was confirmed that NaNO3 has a marked effect on the solubilization of the dissociated forms of the dye in Septonex, in contrast to solubilization by Triton X-100.
Catalytic Activity of Smectites on Dimerization of Oleic Acid
Authors: Číčel Blahoslav , Komadel Peter , Nigrin Miloš
Published: June 2004

A series of dimerization experiments were conducted to investigate the relationship between dimerization yield and crystallochemical composition of five smectite minerals used as catalysts. Effect of interlayer cations and acid treatement of one montmorillonite was also investigated. The maximum dimer yield was obtained with magnesium as interlayered cation. Aluminium and calcium varieties yielded lower amounts of dimers. Addition of sodium carbonate (natrification) was detrimental to dimer production. Dimer recovery was increased by the use of montmorillonite partially decomposed by hydrochloric acid. Variations in the crystallochemical composition of smectites had little effect on the amount of dimer produced. High iron content in the catalyst lowered the quality of the dimerization products.
Simulation of Primary Selectivity of Hydrocarbon Pyrolysis
Authors: Bělohlav Zdeněk , Horák Josef
Published: June 2004

The mathematical model is described for the determination of primary selectivity of hydrocarbon pyrolysis, i.e., the determination of proportion of single components in the first generation of products of pyrolysis. The model stems from the radical reaction mechanism. It is assumed that the main influence on the product composition has the chain propagation involving the hydrogen atom transfer, isomerization and breaking the hydrocarbon radical. To determine the rate constants, the kinetic data published in the literature and the data on bond enthalpies in hydrocarbon molecules were employed. The simulation results were compared with the experimental data taken from the literature and with the results of measurements obtained in pyrolysis of two types of naphthas in a pilot-plant reactor.
Long-Range 2D INADEQUATE in Structure Determination
Authors: Schraml Jan , Blechta Vratislav , Krahé Eduard
Published: June 2004

It is demonstrated that the 2D INADEQUATE experiment utilizing long-range 13C-13C spin-spin couplings is feasible and that it can solve structural assignment problems when one-bond connectivities do not provide sufficient clue for structure determination. In such cases, the long-range 2D INADEQUATE can be used instead of the standard 2D INADEQUATE since it also yields the one-bond connectivities in addition to the connectivities over more bonds. The two types of connectivities are easily distinguished according to satellite separations. Because of similar magnitudes of various long-range 13C-13C couplings, the method of J-resolved INADEQUATE suggested earlier for such purpose is unlikely to provide unambiguous results. The proposed method is utilized for complete assignment of 13C and 1H NMR spectra of dicyclohexylphenylphosphine.
Geometric Factor in Skeletal Reactions of 2-Methylpentane on Stepped Surfaces of Platinum Catalyst
Authors: Hejtmánek Vladimír
Published: June 2004

The role of geometric factor in the course of skeletal reactions (isomerization, hydrogenolysis) of 2-methylpentane on stepped (119), (557) and reconstructed R(557) surfaces of single crystals of platinum was evaluated with computer designed models. These calculations were compared with reported experimental data. It was found by analysis of geometric conditions that there are accessible active ensembles on double step of the reconstructed R(557) surface. In addition, these active sites are unsaturated in their coordination sphere and thus catalytically effective. This finding is consistent with published data, confirming higher catalytic activity of this surface. The various pathways of Bond Shift isomerization mechanism of 2-methylpentane from the point of view of steric demands of surface intermediates on differently located ensembles are discussed, too.
Feedback Reactor and Nonlinear Regression Methods
Authors: Dušek Václav , Skopal František
Published: June 2004

Linear and nonlinear regression methods are compared with respect to their application to the evaluation of chemico-kinetic measurements of a feedback reactor. Their assets and pitfalls are demonstrated.
Hydrogenation of Fatty Acid Esters. I. Nickel(II) Carboxylate-Sodium Dihydridobis(2-methoxyethoxo)aluminate Catalyst
Authors: Zavřel Pavel , Svoboda Petr , Hetflejš Jiří
Published: June 2004

Factors determining the catalytic activity of the title system, its selectivity and stability have been studied, using hydrogenation of low erucic rapeseed oil as a model reaction. It was found that catalytically active systems are formed already at substoichiometric Al:Ni molar ratios. By contrast to their efficiency, their stability is depended strongly on the way of their preparation, the catalysts obtained under solventless conditions being more stable. The selectivity of the above systems determined by a partial hydrogenation of the oil was insensitive to changes of preparation conditions, as demonstrated by similar relative composition of hydrogenated fatty acids as well as by the same level of trans-isomerization.
Structure of 2,3,4,5-Tetra-O-acetyl-6-amino-6-deoxy-D-allonolactam
Authors: Ondráček Jan , Havlíček Jaroslav , Kefurt Karel , Jarý Jiří , Novotný Jiří , Kratochvíl Bohumil
Published: June 2004

The crystal structure of 2,3,4,5-tetra-O-acetyl-6-amino-6-deoxy-D-allonolactam was solved by direct methods and refined anisotropically to R = 0.085 for 1345 unique observed reflections. The title compound crystallizes in A2 space group with the lattice parameters a = 11.756(4), b = 8.139(3), c = 23.713(11) Å, β = 116.71(4)°, V = 2027(2) Å3, Z = 4. The ring of 2,3,4,5-tetra-O-acetyl-6-amino-6-deoxy-D-allonolactam adopts the 4C1,N(D) conformation with the planar arrangement of the C(6)-NH-C(1)O-C(2) atoms. In the crystal structure the adjacent molecules of this lactam are bonded by one intermolecular hydrogen bond, forming a helical chain.