bluuebunny/crossref_metadata_2025 huggingface dataset:
Features of the sexual life during pregnancy
Authors: ISAJEVA Jelena , ŠILKŪNAS Mindaugas , DRĄSUTIENĖ Gražina  Stanislava , BARTKEVIČIENĖ Daiva
Published: July 2012

Background. The aim of our study was to evaluate Vilnius and Vilnius Region women’s knowledge about sexual intercourse during pregnancy.
Materials and methods. The study included 94 women who were in the Center Affiliate of VUH Santariskiu Clinics after delivery. The women were interviewed using a questionnaire. They were divided in three groups by levels of education.
Results. The study showed that 83% of pregnant women had sexual intercourse during pregnancy. 55.1% had coitus several times a month. The first trimester was the most frequent period of sexual intercourse (52.6%). 22.6% of pregnant women were at high risk of miscarriage and 61.9% of them have had sexual intercourse. The frequency of miscarriage in the sexually active group was 17.9% and in the non-active group it was 50% (p < 0.05). All women who reported frequent sexual intercourse were not at threat for miscarriage compared to incidence of miscarriage of those 13 (22%) women who reported infrequent intercourse (p = 0.019). 79.8% of pregnant women were concerned about the adverse effects of sexual intercourse on pregnancy outcomes. 20.2% of the women thought that intercourse during pregnancy was safe. 63.8% of pregnant women were not asked by doctors during pregnancy about their sexual life.
Conclusions. The majority (79.8%) of pregnant women were concerned about the adverse effects of sexual intercourse on pregnancy outcomes but even 83% of pregnant women had sexual intercourse during pregnancy. There were no statistical differences between women with different education level. Pregnant women were rarely asked by doctors about their sexual life.
Surface markers distinguishing mesenchymal stem cells from fibroblasts
Authors: KUNDROTAS Gabrielis
Published: July 2012

Human mesenchymal stem cells (MSCs) are widely used for treatment of various diseases. Clinical applications require large quantities of MSCs, therefore these cells must be expanded in the culture system. It is believed that contamination of MSC cultures with fibroblasts may lead to the decrease of the stem cell differentiation potential. Moreover, such stem cell preparations are potentially unsafe to use for clinical applications since a few fibroblasts can become tumorigenic. Therefore, there is a need to separate MSCs from fibroblasts. However, studies show that MSCs and fibroblasts have much in common. These two types of cells share such properties as identical spindle-like morphology, plastic adherence and the same expression of most surface antigens. The aim of this review article is to analyze the literature on the similarities and differences between the MSCs and fibroblasts, particularly in the expression of cell surface markers in order to determine which could be used for quick separating of MSCs from fibroblasts. Interestingly, the results of recent studies suggest that the use of CD10, CD26, CD106, CD146 and ITGA11 could be helpful for the discrimination of MSCs from fibroblasts. Identification and elimination of fibroblasts from MSC cultures could improve the MSC yield and differentiation potential and also prevent possible tumor formation after MSC transplantation.
Rare types of breast carcinoma
Authors: STEPONAVIČIENĖ Laura , GUDAVIČIENĖ Daiva , MEŠKAUSKAS Raimundas
Published: July 2012

Background. Breast cancer is a heterogeneous disease that encompasses several distinct entities with remarkably different characteristics. One of very important cancer characteristics is its histological type.
Materials and methods. We used Pubmed and Medscape databases and analyzed original articles and literature reviews about rare histological types of breast cancer.
Results and discussion. World Health Organization (WHO) presents a detailed classification of breast cancers. According to this classification, cancers are divided into epithelial, mesenchymal, fibroepithelial tumors. Malignant lymphoma, metastatic tumors can also be found in the breast. WHO also marks tumors of the nipple, male breast cancer and myoepithelial lesions. In this paper, only the invasive epithelial tumors are discussed. Most tumors are derived from mammary ductal epithelium, and up to 75% of the breast cancers are ductal carcinomas. The second most common epithelial tumor type is invasive lobular carcinoma which comprises 5–15% of the group. There are more than a dozen variants which are less common. They comprise less than 10% of breast tumors. Their clinical behavior can differ greatly. So, it is important to know their main characteristics in order to make the best treatment choice and to foresee prognosis. We shortly describe the epidemiology, diagnostics, clinical and immunophenotypic features, prognosis and predictive factors of rare epithelial breast tumors.
Crystal Growth and Photoelectrochemical Characterization of Cd4BSe6 (B = Si or Ge)
Authors: Manivannan A. , Fujishima A. , Aravamudan G. , Rao G. V. Subba
Published: July 2012

Single crystals of Cd4BSe6 (B = Si, Ge) (ARGYRODITES) were grown by CVT method using a three zone furnace. As‐grown crystals were of n‐type and they have been characterized by photoelectrochemical (PEC) measurements in aqueous electrolytes. The current‐potential curves, Mott‐Schottky plots and action spectra were examined. From the analysis of spectral response measurements the band gaps (indirect) for Cd4SiSe6 and Cd4GeSe6 were found to be 1.68 and 1.5 eV, respectively. The opencircuit photopotentials for these semiconductor electrodes were as high as 1.1 V vs. SCE in some of the electrolytes used.
Flow Properties and Shear‐induced Structural Changes in Fluids: A Case Study on the Interplay between Theory, Simulation, Experiment and Application
Authors: Hess Siegfried , Loose Werner
Published: July 2012

The interrelation between the flow properties of fluids and the shear‐induced changes of their structure is discussed and the methods for their study are reviewed. The fruitful interaction between (conventional) theory, simulation, experiment and application is emphasized. Results are presented for simple fluids where the distortion of the local (short range) order, as described by the pair‐correlation function or the static structure factor, is found to be in good agreement with kinetic theory predictions. Experimental data are compared with results of nonequilibrium molecular dynamics (NEMD) computer simulations which are also used to study the non‐newtonian flow behavior of simple fluids. The spectacular long range positional order found in NEMD simulations at high shear rates is reviewed and interpreted as a hydrodynamic instability.
Self and Collective Diffusion Coefficients of Hard Sphere Suspensions
Authors: Cichocki B. , Hinsen K.
Published: July 2012

We present the results of a computer simulation of the dynamics of a hard sphere suspension without hydrodynamic interactions that was performed using an algorithm recently developed by the authors. The dynamical structure factors and the mean‐square displacement have been calculated for various volume fractions between 0.1 and 0.5. Is is shown that the temporal behaviour of the time derivative of the mean‐square displacement is very well described by the stretched exponential function exp(‐const.√t). It is also shown that the results for the dynamical structure factors almost perfectly agree with those of a theory combining in the proper way the Enskog term with the mode‐mode coupling term.
MD Simulation Results on the Dynamics in a Liquid‐Vapour Interface
Authors: And Amal Lotfi , Fischer Johann
Published: July 2012

Molecular Dynamics simulations with vectorized codes on a CYBER 205 have been performed for the free liquid surface at three different temperatures. The particles passing through the Gibbs dividing surface and subsequently through a parallel control plane are counted which yields cumulative numbers for the particle trajectories of the following four types: evaporation, retention, condensation and reflection. It is observed that the particle fluxes leaving the Gibbs dividing surface are essentially due to either reflection or retention. This means that the particles can not so easily pass through the liquid‐vapour interface from one phase to the other.
Molecular Motion in Krypton Films Physisorbed on a Grooved Graphite Surface: A Computer Simulation Study
Authors: Bojan Mary J. , Steele William
Published: July 2012

Molecular dynamics simulations of monolayers of krypton adsorbed on a heterogeneous graphite surface are reported. The heterogeneity is introduced by modeling a surface with parallel, straight‐walled grooves of depth ≃ 7 Å. The dynamical processes simulated included diffusion parallel to the surface; transfer between first layer atoms and the small amount of second layer adsorption that occurs at the simulation temperatures of 90, 110 and 140 K; and transfers between step and groove. Also considered was the special role played by the edge atoms adsorbed at the ledge between step and groove. Diffusion constants and transfer rates are reported and the results are discussed.
Isotope Effects upon Translational Diffusion as a Probe for Translation‐Rotation Coupling in Molecular Liquids
Authors: Holz M. , Weinärtner H. , Sacco A.
Published: July 2012

Mass changes of molecules caused by isotopic substitution (e.g. H‐D substitution) can change the dynamic properties of a molecular liquid. Up to now, these dynamic isotope effects have been investigated only for a very small number of liquids. In the present paper we report on isotope effects upon self‐diffusion coefficients, upon limiting tracer diffusion coefficients and upon viscosities of methanol, dimethylsulphoxide, dimethylformamide and nitromethane at 25°C. It is shown that the square‐root of mass dependence, which follows from a first theoretical approach, cannot predict the observed dynamic isotope effects. The experimental data correlate much better with the square root of the moments of inertia. Thus we establish a strong coupling between translational and rotational motion in these liquids. These results demonstrate that the dynamic isotope effects may serve as a sensitive probe for translation‐rotation coupling in molecular liquids. The experimental finding of translation‐rotation coupling is in agreement with recent computer simulations and has far consequences for the correct interpretation of liquid‐state spectra as e.g. far‐infrared absorption spectra.
Corresponding States Concept for Simple Supercooled Liquids Identifying a Change of Diffusion Mechanism above the Glass Transition Temperature
Authors: Rössler Ernst
Published: July 2012

A corresponding states concept is applied to viscosity η and reorientational correlation times τ of simple supercooled liquids revealing a change of dynamics for a temperature Tc well above the glass transition temperature Tg. Reducing T by the minorly corrected Tg an improved master plot for the viscosity results. An universal behaviour is discovered above 103P whereas the viscosity follows individual curves below 103P. A power law, η = A (T — Tc), describes the individual curves with Tc = 1.18 Tg for all liquids. Above 103P several approaches are checked. For NMR correlation times plotted on such an improved scale the bifurcation of the correlation times for the β and α process appears at T/Tg = 1.18. The β process is an intrinsic feature of the universal viscous regime, only. The change of dynamics is also indicated by a breakdown of the Stokes‐Einstein relations. Comparing several supercooled liquids a discontinuity for τ/η and 1/(Dη) as a function of 1/T is found at T/Tg = 1.19–1.25. In addition, arguments are given which support a cease of anisotropic reorientation in the viscous regime. All together, these indications favour the concept of the recent mode coupling theory where a dynamical phase transition is predicted above Tg.
Correlation of Viscometric and Molecular Dynamics Behaviour for the Model Lubricant, 2‐Ethylhexyl Benzoate (EHB)
Authors: Whitley A. , Yarwood J. , Gardiner D. J.
Published: July 2012

Variations in shear viscosity and reorientational correlation times with temperature for EHB have been interpreted according to the hydrodynamic model of Kivelson et al. in order to extract effective molecular volumes or “torque” parameters. The data fall into high and low temperature regimes characterised by different (Arrhenius) activation energies for reorientation. The hydrodynamic model appears to point to a correlation between rotational times and the internal motions which lead to relatively low effective volumes and which reflect molecular flexibility. Evidence for a “transition” temperature for molecular flexibility is presented and discussed.
Influence of Electric Fields on the Heat Conductivity of Liquids Investigated by the Thermal Lensing Effect
Authors: Eden G. , Schröer W.
Published: July 2012

The energy absorbed in a liquid sample from a laser beam causes an inhomogenity in the temperature and in the refractive index. This makes the sample to behave as a concave lens. In an electric field this effect, which is known as the thermal lensing effect, is reduced. For various compounds (Benzene, Toluene, Trifluorotoluene, o‐Dichloro‐benzene, Nitrobenzene) the time dependence of the intensity at the centre of the laser beam is investigated as function of the applied field. The experiments are analysed assuming an anisotropic contribution to the heat conductivity tensor, determined by the electric field. The averaged heat conductivity is found to depend linearly on the voltage, which suggests to explain the enhancement of the heat transfer from the laser beam by a micro convection connected to the small ionic current.
Anomalous Thermal Conductivity in the Close Neighbourhood of a UCST
Authors: Maczek A. O. S. , Davies M. K.
Published: July 2012

Results of measurements of the temperature dependence of the thermal conductivity of the binary system perfluoromethylcyclohexane + methylcyclohexane are reported. These were obtained using a modified hot‐wire transient technique which allowed measurements to be made using very small temperature rises (<100 mK), with a precision of better than ± 0.5%. The results show a small but unmistakable anomalous rise in thermal conductivity on very close approach to the critical point. Analysis shows that this rise is compatible with a value for the critical exponent χλ= 0.572, in agreement with the theoretical predictions of dynamic renormalisation group theory. The anomaly is very small‐some five hundred times smaller in magnitude than the corresponding anomaly in thermal conductivity for a one component fluid near its gas‐liquid critical point.
Evidence for a Change in the Fluidity of DDAB Vesicular Membranes following γ‐Irradiation by Use of Lucigenin Chemiluminescent Reaction
Authors: Domazou A. S. , Mantaka‐Marketou A. E.
Published: July 2012

The fluidity changes of the Didodecyldimethylammonium Bromide (DDAB) vesicular bilayer, mimetic agent of biological membranes, following γ‐irradiation were investigated under conditions where mainly OH radicals existed. The chemiluminescence (CL) quantum yields of Lucigenin light reaction were found to be strongly depended upon the irradiation dose above 0.65 kGy. Quenching of N‐Methylacridone fluorescence, the primary emitter of the light reaction, after irradiation was not observed. Thus, the increase in fluidity of the vesicular bilayer structure seems to be the principal cause of the CL decrease.
Implications of the Soliton Model on a Novel Mode for Proton Transfer Catalysis in RNA
Authors: Fernández Ariel
Published: July 2012

We establish the identity of a novel mode of proton transfer catalysis for RNA in a regime remote from double‐stranded denaturation. This mode is activated by energy localization induced by a coherent wave excitation.
Increasing the Replicative Capacity of a Naturally‐Occurring RNA Template
Authors: Fernändez Ariel
Published: July 2012

We consider the template‐directed autocatalytic synthesis of RNA strands by Qβ‐replicase. We introduce a mutation on a naturally‐occurring template, MDV‐1RNA, for the replicase. The autocatalytic activity is improved over that of the original system. We demonstrate that this enhancement is not the result of an acceleration of the replica assembling process itself. Instead, the initiation step is enhanced as a consequence of the mutation which has the effect of destabilizing the folding structure of the internal recognition site.
Crystal Structure and Nuclear Quadrupole Resonance. The Bond Length C — Cl and 35Cl NQR
Authors: Brummer Stefanie , Weiss Alarich
Published: July 2012

The intramolecular distances dC—Cl for chlorine bound to sp2 carbon and to sp3 carbon, respectively, and the 35Cl NQR frequencies assigned to the corresponding Cl atoms correlate quite well according to the theory: v(35Cl) ∼ (dC—Cl)−3. The relation is v(35Cl) = (4 ± 6) MHz + (166 ± 31) · 106 · (dC—Cl)−3 · MHz · pm3 for {sp2‐C}‐Cl and v(35Cl) = (21 ± 5) MHz + (101 ± 25) · 106 · (dC—Cl)−3 · MHz · pm3 for {sp3‐C}‐Cl. — The crystal structures and chemical bonds of 1 (4‐methyl‐4‐trichloromethyl‐2,5‐cyclohexadiene‐1‐one), 2 (2‐chloro‐4,5‐dimethyl‐4‐trichloromethyl‐2,5‐cyclohexadiene‐1‐one), 3 (4,5‐dichloro‐1‐phenyl‐pyridazine‐6‐one), and 4 (2,2,4,5‐tetrachloro‐cyclo‐pentene‐1,3‐dione) were studied by single crystal X‐ray diffraction and 35Cl nuclear quadrupole resonance (NQR). 1 crystallizes with the space group D152h‐Pbca, Z = 8. The lattice constants are a = 1206.0(3) pm, b = 1341.3(3) pm, and c = 1178.8(3) pm. 2 crystallizes monoclinic, space group C52h‐P21/c, Z = 4, a = 696.3(3) pm, b = 1404.0(5) pm, c = 1151.4(5) pm, and β = 100.23(1)°. 3 crystallizes in the orthorhombic space group D4h‐P212121, Z = 4, a = 4303(1) pm, b = 586.8(2) pm, and c = 390.5(1) pm. 4 crystallizes cubic, space group T4h‐Fd3, with 48 molecules in the unit cell, a = 2181.5(5) pm. The 35Cl NQR spectra were observed for the two 2,5‐cyclohexadiene‐1‐ones, 1 and 2 in the temperature range 77 < T/K < melting point. For 3, the 35Cl NQR spectra was determined at T = 77 K and T = 295 K. No phase transition has been found for the three compounds in the temperature range in which the 35Cl NQR spectroscopy was performed.
Elementary Reactions of Ketene with Fluorine and Chlorine Atoms in the Gas Phase
Authors: Ebrecht J. , Hack W. , Gg. Wagner H.
Published: July 2012

The elementary reactions of F and Cl atoms with CH2CO were studied in an isothermal flow reactor with a mass spectrometric detection device. The atoms were produced in a microwave discharge of F2/He and Cl2/Ar mixtures respectively. — For the reactions of F and Cl atoms with CH2CO, applying pseudo first order conditions ([F]0 → [CH2CO]0 and [Cl]0 → [CH2CO]0 respectively, the second order rate constants magnified image were found. — The following mechanism was obtained for the F atom reaction: magnified image The abstraction channel to form HF and CHCO was calibrated to contribute 20% to the overall reaction. — For the Cl reaction the two main reaction pathways magnified image were determined.
Solution of Hydrogen in Cold‐Worked and Annealed Pd95Ag5 Alloys
Authors: Kishimoto Shozo , Yoshida Noritetsu , Arita Yoshitaka , Flanagan Ted B.
Published: July 2012

The effect of cold‐working and subsequent annealing on the hydrogen solubility of a Pd95Ag5 random substitutional alloy has been examined. For the first time a correlation of physical properties such as electrical resistance and hardness with hydrogen solubility has been made.
Form and Structure Factors of Water/AOT/Oil Microemulsions from Synchrotron SAXS
Authors: Hilfiker Rolf , Eicke Hans‐Friedrich , Sager Wiebke , Steeb Christian , Hofmeier Urs , Gehrke Rainer
Published: July 2012

Synchrotron small angle X‐ray scattering (SAXS) measurements were performed on water/AOT/n‐hexane w/o microemulsions with w0 ( = [H2O]/[AOT]) values ranging from about 0 to 100. The volume fraction of solute and the temperature were varied in a wide range. The scattering behaviour (form and structure factor) could be explained on the basis of a pseudo hard sphere model, where the spheres were allowed to be spheroidally deformed to a certain extent. We have shown that these deformations become larger as the lower consolute point of the mixture is approached. Furthermore, we have demonstrated that the radius of gyration is temperature independent, and that it depends linearly on w0. The w0‐dependence of the scattering intensity could be explained on the basis of the droplet model.
Magnetite (Fe3O4) in an Oxygen Potential Gradient: Chemical Diffusion, Tracer Diffusion, and Phase Boundary Reaction
Authors: Dorris S. , Martin M.
Published: July 2012

An analysis is given for chemical and tracer diffusion in magnetite exposed to an oxygen potential gradient. From a single experiment, the correlation factor and the self‐diffusion coefficient of the dominant defect can be determined. Results are provided for both the provided for both the vacancy and interstitial regimes. In addition, the rate constant is determined for the exchange of oxygen between magnetite and CO/CO2 mixtures.
A Thermodynamic Study of Adsorption of Cationic Surfactants from their Aqueous Solutions onto Oxide Surfaces: Theoretical Description of Adsorption Isotherms and Heats of Adsorption
Authors: Narkiewicz‐Michalek J.
Published: July 2012

Except for the region of very low surface coverages, the adsorption of cationic surfactants from their aqueous solutions onto negatively charged oxide surfaces is governed by the competition between monolayer‐like and bilayer‐like surfactant aggregates formed on the solid surface. That adsorption mechanism combines, thus, the features of both ion and polymer adsorption, and yet is influenced strongly by the energetic heterogeneity of the surfaces of the real oxides. — Starting from that adsorption model a theoretical approach is developed, making a quantitative description of experimental adsorption isotherms and heats of adsorption possible. Illustrative calculations are presented for DTAB adsorption on silica gel.
The Dynamical Structure Factor of Particles Diffusing in a Closed Volume
Authors: Stockmeyer Rolf
Published: July 2012

The dynamical structure factor of incoherently scattering nuclei, diffusing in a restricted volume of rectangular shape, is calculated and the result is compared with the corresponding curves for particles enclosed in a spherical shell. A program is written, running on a popular minicomputer with industry‐standard‐architecture, which quickly yields the parameters of the diffusion model to fit a given set of neutron scattering data.
Electrochemical Properties of a Molten Carbonate Fuel Cell
Authors: Landes H. , Luft G. , Mund K. , Rummel W.
Published: July 2012

The characteristics of electrodes of a fuel cell containing molten carbonate electrolyte were investigated in a small laboratory scale cell. The cell can be operated at 650°C and a current density of 150 mA/cm2 be derived at a voltage of 0.76 V. The analysis of impedance measurements revealed for both electrodes that the voltage drop in the electrolyte of the working layer determines the loading capacity. In addition to the charge transfer reaction, also the adsorption is rate determining for the anode. The diffusion of oxygen in the electrolyte of the working layer increases the polarization resistance of the cathode.
PEM‐Fuel Cells: State of the Art and Development Possibilities
Authors: Straßer K.
Published: July 2012

After conducting an analysis of fuel cell systems for comparison, the basic know how of the PEM‐fuel cell was transferred from GE to Siemens 1983/84 and in the following Siemens has started the development of FC‐modules as power source of an air‐independent propulsion system. The PEM‐FC‐system, which is characterized by its simple design, high power density and favourable longlife behaviour, is superior to other FC‐systems by the versatility of service. At a current density of 0.5 A/cm2 cells were operated during more than 20000 hours. A current density of 5 A/cm2 is possible. Cells with an active area of more than 1000 cm2 and 10 kW‐stacks, which contains 20 cells, were constructed. Test results and possibilities of improvements will be reported.
Ion Exchange Membranes as Electrolyte for Electrochemical Energy Conversion
Authors: Ledjeff K. , Ahn J. , Zylka D. , Heinzel A.
Published: July 2012

For solar energy systems long term energy storage with a high efficiency is required. Hydrogen is a suitable energy carrier, its generation by water electrolysis, the conversion into heat by (catalytic) combustion and into electrical energy by fuel cells is the present state of the art. Electrolyzer and fuel cell with a solid polymer electrolyte show several advantages compared to cells with liquid electrolyte. In compact modules high energy densities and high efficiencies are realized without a costly and complicated peripheral gas and electrolyte management system. The current work is concerned with the construction of a pressure electrolyzer, a hydrogen/oxygen fuel cell and the development of a “reversible” system which works as electrolyzer and fuel cell as well. The modification of the fuel cell for the use of methanol as a fuel is a promising goal. Methanol is an attractive fuel for a back up system in the case of exhausted hydrogen reverse. The electrochemical reactions of hydrogen, oxygen and methanol at membrane/electrode composites are investigated.
Long‐Term Poisoning of Methanol Anodes
Authors: Hamnett A. , Weeks S. A. , Kennedy B. J. , Troughton G. , Christensen P. A.
Published: July 2012

The evidence for oxide formation on dispersed platinum particles being the main cause for long‐term poisoning of methanol anodes in direct methanol fuel cells is reviewed. On the basis of in situ FTIR, XPS and current interrupt data, it is shown that poisoning by organic oxidation fragments is far less significant on such particles than on planar platinum. In addition, the mode of long‐term poisoning on Pt/Ru electrodes is also investigated; quite different behaviour from pure platinum is found, with conversion of an active hydrous oxide to the inactive rutile form of RuO2 being primarily responsible for the decline in activity with time.
Ions and Charged Soot Particles in Hydrocarbon Flames III. Negative Ions in Fuel‐rich Acetylene/Oxygen Flames
Authors: Gerhardt Ph. , Homann K. H.
Published: July 2012

Negative ions up to masses > 3 · 103 u in fuel‐rich and sooting premixed low‐pressure acetylene/oxygen flames have been analyzed by means of a time‐of‐flight mass spectrometer. This work deals with the quantitative analysis of ions up to masses of 200 u, but the larger polyhedral carbon ions, which were negative charge carriers in the soot forming zone, are not considered here. Concentration profiles of ca. 50 different ions and the dependence of maximum ion concentrations on the C/O ratio are reported. ‐ Ions in the preheating zone were anions of carbonic acids and diacids which contained oxo, keto and peroxy groups. With increasing height in the flame these anions decomposed by decarboxylation and dissociative electron detachment. At higher temperature in the oxidation zone, polyynides (C2nH−), linear polycarbon ions and higher ketenides (CmHO−) prevailed. The polyynides were in chemical equilibrium with acetylene and higher neutral polyynes. Enthalpies of formation (referenced to that of C2H−, 274 kJ/mol) were determined for C4H− (414), C6H− (603), C8H− (810) and C10H− (1025 kJ/mol). Possible reaction mechanisms for the formation of the acid anions and the ketenides are discussed. Negative polycyclic aromatic hydrocarbon ions were completely missing in acetylene flames, in contrast to their occurrence in benzene flames.
Pressure Effect on the Radiationless Deactivation of Singlet Oxygen in Solution
Authors: Schmidt R. , Seikel K. , Brauer H. D.
Published: July 2012

Lifetimes of 1Δg singlet oxygen (1O2) have been determined in 12 solvents in dependence of pressure and in part of temperature using time resolved phosphorescence techniques. Experimental activation volumes for the deactivation of 1O2 by solvent molecules vary between ‐11.9 (pentane) ≤ ΔV#obs ≤ ‐4.1 ml mol−1 (formamide) at 298 K. The increase of ΔV#obs with temperature was measured in toluene and CH3CN. The data are analyzed by means of a kinetic scheme assuming a preequilibrium of 1O2 and solvent molecule to form a singlet contact complex 1C. Deactivation of 1O2 occurs by energy transfer between the collision partners of C converting 1C to 3C, which subsequently splits into the deactivation products. A statistical model developed by Yoshimura and Nakahara is used to calculate the reaction volume ΔVc of the preequilibrium. It is revealed that the major part of ΔV#obs, consists of ΔVc. Activation volumes ΔV#E of the actual deactivation of 1O2 by oscillators X–Y of the solvent molecule depend neither on the polarities of solvent nor of X–Y. Independent of oscillator they are estimated to be ΔV#E ≈ −2 ml mol−1 if X–Y is C–H, C–CI, C–F, N–H or C=S.
Viscosity of the n‐Decane—Methane System in the Liquid Phase
Authors: Knapstad B. , Skjølsvik P. A. , Øye H. A.
Published: July 2012

The viscosity of liquid n‐decane and liquid mixtures of n‐decane—methane containing 31.2, 55.7, 69 and 84.7 mol% methane has been measured using an absolute oscillation vessel viscometer. The measurements have been performed in the temperature range 20–150°C, and at pressures up to 40 MPa.—The viscosities of the n‐decane and the liquid mixtures are described separately by an empirical correlation in terms of temperature and pressure. The standard deviation in fit are 0.14–0.2%. The estimated accuracy is ± 1% for n‐decane at 20°C deteriorating to ±4% at 150°C for the mixtures containing 84.7 mol% methane.—Applying a generalization of the Grundberg and Nissan equation, the experimental viscosities are expressed as a function of temperature, pressure and composition with an overall standard deviation in the fit of 0.6%.—Literature data deviate 0‐ +4% from the correlated n‐decane viscosities, and +10 to +40% from the mixture viscosities of the present investigation.
Study of Non‐Equilibrium States of a Homogeneous 2‐Butoxyethanol/Water Mixture of Critical Composition in the Vicinity of Its Lower Critical Point Using Fast Pressure Jumps
Authors: Sieber M. , Woermann D.
Published: July 2012

The pressure dependence of the critical temperature is used to bring a homogeneous 2‐butoxyethanol/ water mixture of critical composition (xc = 0.0598; mole fraction of 2‐butoxyethanol; critical temperature Tc (P = 1 bar) = 49.39°C) from a state away from its critical temperature to a state close to the critical temperature. This is accomplished by fast pressure jumps (expansions) with an amplitude in the range of −50 bar < ΔP < −5 bar (ΔP = (Pf‐Pi); Pf, hydrostatic pressure in the final state (Pf = 1 bar); Pi, hydrostatic pressure in the initial state) and a characteristic time constant of τp ≃ 0.3 ms. The coefficient characterizing the pressure dependence of the critical temperature has a value of (dTc/dP)c.l. = 43 mK bar−1. The delayed increase of the intensity of scattered light (“critical opalescence”) is measured as function of time at different scattering angles (10° ≤ θ ≤ 60°) and different temperature differences (Tc ‐ Tf) (Tc. critical temperature; Tf, final temperature after the pressure jump). The fast pressure jump leads to a small decrease of the temperature of the sample ((∂T/∂P)s = 6 mK bar−1). The measured relaxation curves are found to be single exponentials for times short compared with the relaxation time τT of the heat conduction process bringing the system back to its initial temperature Tf (τT is in the order of seconds). – For small values of the scaling variable (qζf) < 0.7 (q, absolute value of scattering wave vector; q = (4μñ/λ0) sin (0/2); 0, scattering angle; ñ, index of refraction; λ0, wavelength of incident light in vacuum; ζ, correlation length of local concentration fluctuations) the structure factor relaxes as expected on the basis of linear response (τhyd/τexp = 1; τhyd, hydrodynamic relaxation time calculated from independent dynamic and static light scattering experiments; τexp, experimental relaxation time). At larger values of (qζf) ((qζf) > 0.7) the structure factor relaxes more slowly than theoretically expected (i.e. τhyd/τexp < 1). This behaviour is similar to that of the systems 3‐methyl‐pentane/nitroethane and 2, 6‐dimethylpyridine/water.
The Debye‐Hückel Theory for Hydrated Ions III. The Square‐Cross Rule for the Gibbs Energy of Aqueous Solutions of Some 1:1 Electrolytes at 25°C
Authors: Schönert Hansjürgen
Published: July 2012

A recently formulated Debye‐Hückel theory for aqueous solutions of hydrated, singly charged ions is extended to solutions with reciprocal electrolyte pairs: MX, MY, NX and NY. The results are analyzed with respect to the square‐cross rule for the excess Gibbs energy of hydrogen and alkali halogenides. The parameters for the model are taken from a fit to the activity coefficients of the respective binary solutions. The DH 2 variation of the new model theory is in good agreement with the square‐cross rule.
The Role of Some Solvent Binaries in the Alkaline Decomposition of Tetraphenylphosphonium Bromide
Authors: Hanna M. T. , Khalil Fayez Y. , El‐Batouti M.
Published: July 2012

Comparative study of the role of solvent effects of aqueous methyl cellosolve and tetrahydrofuran solvent systems on the alkaline decomposition of tetraphenylphosphonium bromide was carried out. The reaction rate increases remarkably as the medium changes from purely aqueous to a water‐organic cosolvent reaction mixture. The relative changes in the solvation states of both reactants and transition state as the structural properties of the two solvent binaries change were shown to be the direct reasons for the difference in the effects on rate and activation energies.
Negative Thermal Expansion in One‐Dimensional Fluids
Authors: Yoshimura Y.
Published: July 2012

The molecular origin of the negative thermal expansion of fluids has been studied for the one‐dimensional system with nearest‐neighbor interactions. The PLT behavior accompanying the negative thermal expansion is demonstrated for two model potential functions: Added to the hard core repulsive force, Model I has a truncated power potential function and Model II has a step potential function. In Model II, the negative thermal expansion is accompanied by the positive thermal expansion in the lower temperature region, i. e. the length of the system has the maximum and the minimum with increasing the temperature at constant pressure in Model II. Peculiar thermodynamical behavior of Model II is ascribed to the thermal transition between two molecular states, which is simulated by the mixture model of fluids. – The negative thermal expansion is analyzed on the basis of the theory of thermal fluctuation: The thermal expansion of length is composed of two terms due to the correlation between the internal energy and the length and the autocorrelation of the length, respectively. The negative thermal expansion is brought about by the negative correlation between the internal energy and the length, and the system shows a large fluctuation within and around the region of the negative thermal expansion. Since the attractive interaction reduces the fluctuation of the length, the attractive interaction enlarges the region of the negative thermal expansion in cooperation with soft‐repulsive interactions. Present results on the one‐dimensional system reproduce the essential feature of the negative thermal expansion in the real systems such as water or liquid tellurium.
Shear Induced Micellar Structures
Authors: Hofmann S. , Rauscher A. , Hoffmann H.
Published: July 2012

Mixed solutions of the anionic surfactant Sodiumdodecylsulfate (SDS) and the zwitterionic Tetradecyldimethylaminoxid (TDMAO) were studied under shear in a Couette‐type apparatus. For shear rates exceeding a critical shear gradient γc the solutions show birefringence which approaches a constant value ΔnMAX with increasing shear rate. At the same time properties like the shear viscosity and the normal stress difference increase dramatically. A structural modification must thus have taken place for γ > γc: a shear‐induced structure (SIS) has developed. – The structure of the micelles in the solution at rest was determined by SANS‐, electric birefringence‐ and viscosity experiments for different mixing ratios, concentrations and ionic strength. The solutions under shear were studied by SANS, flow‐birefringence and rheological measurements. – At rest small, rodlike micelles which consist of mixed surfactants are present. The length of the micelles are smaller than their mean distance and the viscosity is low in this case. The dimensions of the micelles were determined from the positions of the correlation peaks in the SANS‐patterns which are due to repulsive forces between the charged aggregates. At a mixing ratio of 9:1 (TDMAO:SDS; C = 100 mM) the solutions are viscoelastic and no SIS is detected. The SIS is thus formed only in solutions with surfactant concentrations which are below the overlap concentration. At γc – at which the SIS is beginning to form – the product of γc and τROT, the rotational relaxation time of the rods, is much smaller than one. – As soon as a critical shear gradient is reached these former isotropic micellar solutions show birefringence, an extinction angle of zero degrees, normal stress difference and an increased viscosity. Former isotropic SANS‐patterns deform and peaks show the appearence of a highly ordered structure in equilibrium with unordered micelles. All micelles taking part in the SIS are completely aligned in the direction of flow. Formation of the SIS is highly dependent on concentration, mixing ratio and ionic strength. Finally, two proposals for the nature of SIS are presented: A shear induced phase transition into domains of (pseudo)nematic phases seems most likely to us and is consistent with our experimental results. But also a pearl‐string like array in domains of oriented micelles is conceivable.
Hopping of Quantum Particles on Crystals with Energy Disorder: Influence on Spin Resonance
Authors: Reineker P. , Köhler J.
Published: July 2012

For spin 1/2 quantum particles hopping on energetically disordered lattices paramagnetic lineshapes and free induction decay (FID) signals are calculated as a function of the hopping rate γ between nearest neighbours. The energy disorder is modeled by local magnetic fields chosen from a Gaussian or dichotomic distribution. For motion on a linear chain it is derived – using a continued fraction method – that the FID signal shows a cross over from an exp(–t3/2) law to an asymptotic exp(–t) behaviour. Preliminary investigations for 2‐ and 3‐dimensional lattices have been performed using algebraic multigrid methods.
Thermodynamic Study of the Gaseous Heterocomplexes NaSnCl3 and NaSnBr3
Authors: Hilpert K. , Miller M. , Venugopal V.
Published: July 2012

The NaCl – SnCl2 and NaBr – SnBr2 systems were investigated under equilibrium conditions in the temperature ranges between 713 to 963 K and 653 to 893 K, respectively, by using Knudsen effusion mass spectrometry with a two‐compartment Knudsen cell. The gaseous species NaX, (NaX)2, SnX2, and NaSnX3 (X = Cl, Br) are present in the vapour of the two systems. The enthalpy and entropy changes of the dissociation reactions

NaSnCl3(g) ⇄ NaCl(g) + SnCl2(g) (1)

and

NaSnBr3(g) ⇄ NaBr(g) + SnBr2(g) (2)

resulted as

ΔHo298(Eq. (1)) = 197 ± 6 kJ mol−1,

ΔSo298(Eq. (1)) = 153 ± 7 J mol−1 K−1,

ΔHo298,(Eq. (2)) = 190 ± 6 kJ mol−1, and

ΔHo298(Eq. (2)) = 160 ± 7 J mol−1 K−1.

The enthalpy and entropy changes of the reactions

SnX2(g) + (NaX)2(g) ⇄ NaSnX3(g) NaX(g), X = Cl, Br, (3)

are additionally evaluated as well as equilibrium constants for the reactions Eqs. (1) to (3). The results obtained are discussed.
The Dielectric Constant and Density of Benzene to 400 °C and 3000 bar
Authors: Deul R. , Rosenzweig S. , Franck E. U.
Published: July 2012

A high pressure apparatus is described to measure simultaneously within one cell the dielectric constant and the density of non‐polar supercritical fluids to 400 °C and 3000 bar. Thus relations between the dielectric constant and the fluid density at any given temperature can be discussed with particular reliability. The apparatus consists of a cylindrical autoclave, which encloses a stainless steel belows containing the sample. A cylindrical capacitor (ca. 60 pF) is mounted inside the bellows. A back‐up fluid of heptane is used to produce the pressure on the bellows. Measurements are made between 10 kHz and 1 MHz. Values of the dielectric constant ϵ are reported for 10 temperatures between 27.5 and 400 °C and for pressures between 1 bar and 3000 bar. At 27.5°C and 1 bar ϵ is 2.273. At 100°C it varies from 2.124 to 2.425 between 1 and 2800 bar. At 400°C and 3000 bar ϵ = 2.198. The probable error is below 0.2%. Density measurements cover the same range. The temperature dependence of ϵ at constant density is very small. The Clausius‐Mossotti‐function is presented for the whole region. In accordance with existing theories it can be described as a three‐term series in powers of density and a T−1‐term.
Enthalpy of Demixing of a Binary Liquid Mixture of Critical Composition: Study of the System Iso‐Butoxyethanol/Water
Authors: Zimmer H.‐J. , Woermann D.
Published: July 2012

A fast pressure jump technique is used to measure calorimetrically the temperature dependence of the enthalpy of demixing of an iso‐butoxyethanol(i‐C4E1)/water mixture of critical composition (xc(i‐C4E1) = 0.0664; Tc = 26.46 °C) in the vicinity of its lower critical point. It is found that the enthalpy of demixing has a positive sign as expected thermodynamically for a lower critical point. A linear relation is observed between the molar enthalpy of demixing ΔdemixHm(Xc) and the temperature difference (T – Tc) (Tc, critical temperature; T, temperature; (T > Tc) with a slope of (∂ ΔdemixHm(Xc)/∂T)p = (5.5 ± 0.3) J mol−1 K−1. The enthalpy of demixing ΔdemixHm(Xc) becomes zero at the critical temperature Tc. The value of (∂ ΔdemixHm(Xc)/∂T)p is of the same order of magnitude as the absolute value of (∂ ΔdemixHm(Xc)/∂T)p of the system isobutyric acid/water (upper critical point; (∂ ΔdemixHm(Xc)/∂T)p = −(5.2 ± 0.4) J mol−1 K−1) using the same technique.
Osmotic Properties of Crystalline Inorganic Precipitation Membranes: Study of Barium Sulfate Membranes
Authors: Milz M. , Forke R. , Woermann D. , Sunn U.
Published: July 2012

BaSO4 precipitation zones with membrane properties (“conditioned state”: characteristic values of membrane potential, non‐ohmic electric current‐voltage characteristic) are generated by interdiffusion of iso‐osmotic aqueous solutions of BaCl2 and Na2SO4 within cellophane skins. In the “conditioned state” they are found to be impermeable to glucose, sucrose, and raffinose. Osmotic differences of these substances between the bulk phases as well as osmotic differences of BaCl2 and Na2SO4 cause an osmotic volume flow across the precipitation zone from which the hydrodynamic permeability of the precipitation membrane imbedded within cellophane skin can be calculated. The hydrodynamic permeability of a cellophane skin containing a BaSO4 precipitation zone in its “conditioned state” is smaller by a factor of more than 10 compared with that of an untreated cellophane skin. A precipitation zone looses its characteristic properties (“deconditioned state”) if the ions forming the precipitate (Ba++, SO4–) are removed from the bulk phases. This triggers changes of the properties of the surface of the BaSO4 crystallites and Ostwald ripening processes set in. Such a precipitation zone becomes permeable to glucose, sucrose, and raffinose. In the “deconditioned state” the hydrodynamic permeability of precipitations zones approaches nearly the value of an untreated cellophane skin. Adding again Ba+ + and SO4– ions to the bulk phase regenerates the electrochemical and osmotic properties of the precipitation zone. Low angle scattering patterns of synchroton radiation of freeze dried cellulose skins containing a BaSO4 precipitation zone in its “conditioned state” are analyzed in terms of a random structure model. It is found that the correlation length of local electron density fluctuations has a value of about 6 nm. This reflects the tight packing of BaSO4 crystallites forming a precipitation zone with membrane properties.
The Frequency Dependence of the Dynamical Conductivity of Molten Alkali Nitrates in the Microwave and Millimetre Wave Range
Authors: Happ H. , Fend Th. , Yen S.
Published: July 2012

Measurements are reported of the dynamical conductivity of the alkali nitrates in the molten state near their melting points Tm (1 < T/Tm < 1.2) in the microwave and millimetre‐wave range. The conductivity of KNO3, RbNO3 and CsNO3 shows no dispersion up to the far‐infrared whereas in LiNO3 and NaNO3 it passes through a shallow minimum in the millimetre‐wave range. The temperature dependence of the conductivity indicates that it is due to activated processes up to the millimetre‐wave region. The shallow minimum in LiNO3 and NaNO3 indicates a high frequency limit of the diffusive response at about 50 GHz.
Formation and Reduction of Semiconductor‐Like Aggregates of Silver‐Carboxy‐Alkane‐Thiolates in Aqueous Solution
Authors: Fojtik Anton , Mulvaney Paul , Linnert Thomas , Giersig Michael , Henglein Arnim
Published: July 2012

In slightly acidic solutions of Ag+ and carboxy‐methane‐thiol (CMT) or carboxy‐ethane‐thiol (CET), aggregates are formed whose absorption spectrum is significantly different from that of the monomeric silver‐carboxy‐alkane‐thiols. The build‐up of the aggregates occurs slowly. They develop a band at 335 nm (AgCMT) or 355 nm (AgCET), and simultaneously, acquire fluorescence. Silver is produced upon the photolysis of the aggregates. A very small amount of silver atoms deposited on the aggregates is sufficient to quench the fluorescence substantially. Both the absorption and fluorescence bands are blue‐shifted as the aggregates become smaller during photolysis or dissolution in alkaline solution. The aggregates are proposed to have semiconductor‐like ionic planes separated from each other by the organic groups. Electron microscopy shows that the aggregates are partly crystalline and have a size of about 25 Å when they are freshly prepared. The crystallinity increases and the structure changes upon aging for several days.—When Ag+ is reduced by NaBH4 in the presence of carboxy‐alkane‐thiols, stable silver aggregates of different sizes are formed. The absorption bands and chemical behaviour of some of the aggregates resemble those of oligomeric silver clusters investigated previously. The stability of the clusters is explained in terms of “pre‐complexation” of silver surface atoms by the carboxy‐thiols.
Solvent and Acidity Function Effects in the Kinetics of the Acid Hydrolysis of Ditert‐Butylsuccinate in Aqueous Acetone
Authors: Hanna M. T. , Khalil Fayez Y. , Asaad Adel N.
Published: July 2012

The rates for the consecutive acid hydrolysis of ditert‐butylsuccinate were measured in a series of an aqueous dipolar aprotic solvent, namely, acetone. The observed rates of the two steps of the reaction were analysed into four separate terms due to the unimolecular (AAL1) and bimolecular (AAC2) mechanisms. These rates were correlated with the measured acidity function H0 of the medium, where linear relationships exist at lower acetone contents for the unimolecular rate constants (k′I1 & k′II1). The bimolecular rate constants (k′I2 & k′II2), however, follow a non‐linear trend indicating the operation of the AAC2 mechanism. The activation parameters and the rate‐acidity function relationships were computed and discussed as evidences of mechanistic pathway and solvation effects involved in the reaction.