bluuebunny/crossref_metadata_2025_split huggingface dataset:
Calorimetric Study of the Dipalmitoylphosphatidylcholine/Water Phase Diagram
Authors: Jürgens E. , Höhne G. , Sackmann E. 
Published: July 2012

AbstractThe dipalmitoylphosphatidylcholine (DPPC)/water‐system was studied by differential scanning calorimetry between 0.1 and 17 weight percent of water and from 22°C to 142°C. Main emphasis was directed towards the exact determination of the water content. This was achieved by a moisture meter based on the Karl‐Fischer method. – The scanning curves exhibit up to 6 transition lines altogether. In order to study the variation of transition temperatures with the water concentration, heating and cooling curves of one sample were run repeatedly up to 57 times. A small leakage of the sample capsule allowed for a very small water loss at each scanning cycle leading to a continuous decrease in water concent at each scanning run. The water content was thus changed from 5.5 to about 0.5 weight percent. A phase diagram of the DPPC/water‐system is established.
A Kinetic and Thermodynamic Study of the Reaction of Hydrogen and Deuterium with FeTi at Low Pressures
Authors: Pedersen Allan S. , Møller Preben J. , Sørensen O. Toft 
Published: July 2012

AbstractThe initial reaction of hydrogen and deuterium with clean surfaces of FeTi powder, following a five‐cycles activation procedure using hydrogen, were studied by volumetric and microgravimetric techniques. – It was concluded that within the 78 K to 88 K temperature range a non‐activated dissociative Temkin chemisorption process occurred upon a Ti surface layer, while at temperatures within the 300 K to 500 K range a dissolution process took place limited by diffusion in the α‐phase.
On the Orientational Structure and Dielectric Properties of Water. A Comparison of ST2 and MCY Potential
Authors: Steinhauser Othmar 
Published: July 2012

AbstractMolecular dynamics simulations involving 500 and 1000 molecules are reported for the ST2 [7] and MCY [8] potential. The thermodynamic state corresponds to a density of ρ = 1 gcm−3 and a temperature around T = 400 K. Although traditionally used, atom‐atom correlation functions are found to be inappropriate for a detailed discussion of the orientational structure. Therefore the complete analysis is based on the full angle‐dependent pair correlation function g(R, Ω1, Ω2, Ω12). In the case of MCY considerable distortion of the ideal tetrahedral picture is observed. Although a collective property, the Kirkwood g‐factor turns out to be a sensitive probe of the input potentials and differs by a factor of 3 as a consequence of the angle‐dependent short‐range forces of the MCY potential. The mutual consistence of local and asymptotic dielectric properties is carefully examined. Thus a unique dielectric constant of ϵMCY = 30 ± 5 is derived. Possible refinements of the MCY potential are discussed in order to bring the computed ϵMCY closer to the experimental value ϵexp = 51.
Rotational Diffusion in Liquid 1,4‐Cyclohexadiene
Authors: Pajak Z. , Latanowicz L. , Jurga K. 
Published: July 2012

AbstractThe small‐step Brownian diffusion model, applied to the analysis of selectively measured proton spin‐lattice relaxation times T1 for 1,4‐cyclohexadiene solutions in carbon tetrachloride at various temperatures, yields the rotational diffusion coefficients of the molecule treated as a symmetrical top. The evidenced anisotropy of motion is pronounced – for the neat liquid at room temperature D∥ = 15.1 · 1010s−1 and D⟂ = 8.1 · 1010s−1. The last value characterizing reorientation of the major symmetry axis is well corroborated by contour analysis of two totally symmetrical Raman scattering bands. The usefulness of various hydrodynamic models in the description of motional behaviour is discussed.
Quenching of the 2Eg State of Hexacyanochromate(III) in Dimethylformamide Solution
Authors: Buckels H.‐W. , Wasgestian F. 
Published: July 2012

AbstractThe quenching efficiency of mild organic oxidants and of iodine cyanide was found to correlate with the polarographic half wave potentials, indicating oxidative quenching. The quenching by ICN was compared with that by naphthacene, which quenches by energy transfer. Both compounds differ in quenching rate (3 · 104 and 3.5 · 107 M−1 s−1 (22°C)), activation energy (38 and 2.6 kJ mol−1), activation entropy (−48 and −102 J mol−1 K−1), and salt effect. – From the data it is concluded that for the oxidative quenching close contact between quencher and the excited [Cr(CN)6]3− is necessary, the rate determining step being the formation of an encounter complex. Energy transfer is supposed to proceed via a solvent or counter ion separated donor acceptor pair with the intrinsic transfer step as rate determining.
Kinetics of the Hydrogen Abstraction from Hydrogen Cyanide by Trifluoromethyl Radicals
Authors: Lane Silvia , Oexler Elena V. , Staricco Eduardo H. 
Published: July 2012

AbstractThe reaction of CF3 radicals with HCN in the gas phase has been studied in the temperature range 573–673 K using CF3 radicals generated by thermal decomposition of CF3I. Arrhenius parameters for the reaction:

relative to CF3 recombination:

are given by:

Rate parameters are compared with those for other reactions of CF3 with polar and non‐polar substrates.
Early Stages of the Decomposition of Alloys
Authors: Haasen P. 
Published: July 2012

AbstractField ion microscopy combined with mass spectroscopy, the atom probe, is applied to the analysis of nuclei in the decomposition of alloys. The interface of the particles shows the sharp concentration profile expected from Becker's theory. The time evolution of particle size, density and matrix supersaturation is measured for the first time during the nucleation stage of alloy decomposition. It is shown that Ostwald ripening must be taken into account already during this stage in agreement with a recent theory of Langer and Schwartz. The alternative spinodal decomposition mode can also be clearly recognized in the atom probe but a satisfactory non‐linear theory for this mode is still missing.
Kinetics of a Unidirectionally Inhomogeneous Ising Alloy
Authors: van Baal C. M. 
Published: July 2012

AbstractA new way of treating kinetic problems in crystalline systems, applied earlier to homogeneous systems, here is applied to the Hillert model of an alloy i.e. to a model in which it is assumed that inhomogeneities in composition only exist in one crystal direction. For this model the diffusion equations are derived and shown to lead to equilibrium. The equations are solved in linear approximation. The solutions are unstable inside the spinodal and have characteristics that are in very good agreement with the Cahn‐Hilliard theory of spinodal decomposition.
Phase Transitions and Incommensurability in Crystalline Model Bilayers
Authors: Kind R. 
Published: July 2012

AbstractCrystalline layer structure compounds containing aligned aliphatic chains show essentially the same phase transition behaviour as lipid bilayers in liquid systems. This is demonstrated on two representatives of the (CnH2n + 1NH3)2MCl4 family (n = 10, M = Cd and n = 3, M = Mn) and on one compound of the CnH2n + NH3Cl family (n = 10). Transitions from completely ordered closely packed structures to disordered states with “melted” chains, transitions from intercalated to nonintercalated structures, as well as modulated (“ripple”) phases can be observed in these model bilayers. A phenomenological description of these transitions is given in the framework of the Landau theory.
C. D. W. Phase Transition in NbSe3 and Related Compounds
Authors: Rouxel Jean , Meerschaut Alain , Gressier Pascal 
Published: July 2012

AbstractCharge Density Wave instabilities represent a particular type of phase transitions which can be well illustrated by the properties of niobium and tantalum trichalcogenides. Some basic features of CDW's instabilities are reminded. Then, NbSe3 and some related compounds such as monoclinic TaS3 and the (Fe ‐ Nb)Nb2Se10 series, are the basis of an experimental illustration of the concepts. NbSe3 exhibits two CDW's phase transitions at T1 (145 K) and T2 (59 K). The feature which makes NbSe3 unique is the non ohmicity observed at very low electric field (few tenths of mV‐cm−1) just below T1 and T2. It is now well established that this non linear effect results from the depinning of CDW, which carries a current. Conclusion is indicative of the role of the anion pairing in the triangular base of the trigonal prism, of the cation pairing along the chain and of the interchain coupling.
Ten Years of X‐Ray Diffuse Scattering Studies of One Dimensional Conductors and Superconductors
Authors: Comes R. 
Published: July 2012

AbstractCompeting effects in real one dimensional conductors have considerably enriched the original structural picture of the instability of a single metallic chain. Such effects include transverse as well as longitudinal polarizations of the Peierls distorsion, instabilities on different molecular chains, 2 and 4kF instabilities, and commensurability effects. In the more recent class of organic superconductors (TMTSF)2X, superconductivity is not only in competition with the Peierls instability but also with order‐disorder phase transitions involving the non centrosymmetric counter ions.
Phase Equilibria in the H2/C2H4System at Temperatures from 114.1 to 247.1 K and Pressures to 600 MPa
Authors: Heintz Andreas , Streett William B. 
Published: July 2012

AbstractExperimental data for liquid‐vapor phase compositions of Hydrogen + Ethylene are reported for 14 temperatures in the range 114.1 to 247.1 K and pressures up to 600 MPa. The data have been obtained using a vapor‐recirculating apparatus suitable for measurement up to 1000 MPa. The entire region of liquid‐vapor coexistence has been explored for the first time. The mixture critical line and the pressure temperature trace of the 3‐phase line solid‐liquid‐vapor have been located. These lines intersect at 153 K and 675 MPa to form an upper critical end point. Results obtained up to 52 MPa have been compared to published data. Calculations have been made to compare the experimental results with predictions of the Peng‐Robinson and Redlich‐Kwong equations of state.
Ostwald Ripening of Precipitates I. Numerical Solution for the Particle Size Distribution Function in Closed Systems
Authors: Venzl Gerd 
Published: July 2012

AbstractA numerical solution shows the existence of an asymptotic regime for the Ostwald ripening of precipitates in closed but infinite systems. The asymptotic time evolution is independent of the preparation (initial conditions) and in accord with the predictions of the Lifshitz‐Slyozov‐Wagner‐theory. Diffusion‐limited growth is considered as a representative example. The relation to Kahlweit's approach and the applicability to large but finite systems and more complicated growth laws are discussed.
A Broadband Submillimeter Wave Spectrometer System with On‐Line Microcomputer Data Analysis
Authors: Schäfer Eckhard , Winnewisser Manfred 
Published: July 2012

AbstractA submillimeter wave spectrometer operating in the frequency range 100 to 800 GHz has been constructed for the study of transient molecules in the gas phase. The instrument employs harmonic generation of millimeter wave frequencies and a He‐cooled InSb photoconducting detector. A high degree of flexibility is achieved using an exchangeable free‐space Pyrex absorption cell and a microcomputer for on‐line data analysis. The spectrometer can be operated in a free‐running video mode together with a fast signal averager or phase‐locked to a microwave reference with source modulation. It is shown that the reproducibility of line center frequency measurements up to 600 GHz is ± 10 kHz. Transitions with absorption coefficients of at least 3 · 10−8 cm−1 can be detected in the range from 150 to 250 GHz. Ground state rotational transitions of OCS between 200 and 690 GHz are reported and analysed together with previous data.
The Electrical Conductivity of Solid and Molten Cesium Hydroxide – A Contribution to Solid Proton Conductors
Authors: Haas K.‐H. , Schindewolf U. 
Published: July 2012

AbstractThe electrical conductivity of solid cesium hydroxide is by several powers of ten larger, its activation energy by a factor of two to three lower than those of normal solid salts. A steep tenfold increase of the conductivity is observed at the α‐β‐phase transition temperature of solid cesium hydroxide (220°C) above which the OH −‐ions can rotate freely (rotator phase). A further increase by three powers of ten occurs between 280°C and the melting point (335°C), above which the conductivity is that of a normal molten salt. The conductivity behaviour thus resembles that of potassium hydroxide (Stephen and Howe [10]), which also exhibits the pronounced breaks at the α‐β‐transition temperature (248°C) and at around 366°C. Since the second break in solid cesium hydroxide and potassium hydroxide coincides with the eutectic temperatures of the respective hydroxide‐carbonate systems (alkali hydroxides hardly can be obtained free of carbonate) it has to be assumed that it is caused by the increase of ionic charge carriers due to partial melting of the eutectic within the solid framework of the hydroxide. The relatively high conductivity of cesium hydroxide and potassium hydroxide below the eutectic temperatures is due to a “Grotthus”‐type proton conductivity mechanism (aided by CO‐ and H2O impurity defects) with OH−‐ion rotation.
Low‐Temperature Luminescence in Eu3+‐Doped Tungstates of the Perovskite Stacking‐Variant Type
Authors: Blasse G. , Kemmler‐Sack S. 
Published: July 2012

AbstractThe photoluminescence at low temperatures of Eu3+‐activated tungstates of the perovskite stacking‐variant type are reported. The main examples are Ba2La2‐xEuxMgW2□O12 (12 layer) and Ba2Y2‐xEuxW3□O18 (18 layer). The luminescence of 12 and 18 layer compounds are strikingly different. Not only are the emission and absorption spectra of the Eu3+ ions different, but also the energy transfer processes are not the same. These phenomena are discussed in terms of existing theories.
Photochemistry of the Di‐Deuterated Benzenes
Authors: Semeluk G. P. , Synnott J. A. , Unger I. 
Published: July 2012

AbstractThe photochemistry of the di‐deuterated benzenes has been examined in the vapour phase over the wavelength range of 245 to 270 nm. The sensitized emission of biacetyl technique was used to obtain the triplet yields. The sums of the singlet and triplet yields for all three molecules were found to be unity between 255 and 265 nm. – Phosphorescence lifetimes in EPA and methylcyclohexane glasses have been recorded and found to be non‐exponential. – Mechanisms consistent with the experimental observations are presented and various rate constants have been examined.
On the “Anomalous” Temperature Dependence of the FIR‐Absorption Band of Acetonitrile
Authors: Goslich R. , Chatzidimitriou‐Dreismann C. A. , Lippert E. 
Published: July 2012

AbstractAn anomalous red‐shift of the FIR‐absorption band of CH3CN in n‐heptane with increasing temperature had been reported in Ref. [1]. This result is experimentally confirmed. We also observed the same effect in some other solvents (CCl4, CS2, and cyclohexane). In the case of n‐heptane the temperature dependence of the overall absorption intensity attains a maximum within the temperature range under examination. The theoretical interpretation of the anomalous red‐shift as given in previous papers is mentioned.
Thermodynamische Untersuchungen an Menshutkin‐Komplexen V. Wärmekapazitäten fester Komplexe und flüssiger Mischungen
Authors: Sondern Ch R. , Perkampus H.‐H. 
Published: July 2012

AbstractThe influence of complex formation upon heat capacities was investigated for the systems SbCl3/benzene and SbCl3/mesitylene. While the cρ value of the solid complex 2SbCl3 · benzene was exactly the sum of the cρ‐values of the components, positive heat capacities were found in the liquid mixtures, which are due to the existence of dissolved charge transfer complexes. A simple model is able to describe these results on a semiquantitative level.
Thermodynamische Untersuchungen an Menshutkin‐Komplexen VI. Exzßenthalpien flüssiger SbCl3/Aromat‐Mischungen und Bildungsenthalpien fester Komplexe
Authors: Sondern Chr. , Perkampus H.‐H. 
Published: July 2012

AbstractThe mixing enthalpies of liquid mixtures of SbCl3/C3H6–nXn (X = CH3 for 1 ≤ n ≤ 6; X = Cl for 1 ≤ n ≤ 3) were measured at one composition and temperature (T > 350 K). The system SbCl3/mesitylene was investigated over the whole range of concentrations. With these and earlier measured data it was possible to calculate the formation enthalpies of the solid complexes. In one case it was also possible to evaluate the formation entropy by additional vapour pressure measurements. The dependency of the excess enthalpies upon the benzene substituents confirms our assumptions about the formation of dissolved change transfer complexes in the liquid mixtures of SbCl3 with aromatic compounds.
The Temperature Dependence of the Properties of Electrolyte Solutions. V. Determination of the Glass Transition Temperature and Comparison of the Temperature Coefficients of Electrolyte Conductance and Solvent Viscosity of Propylene Carbonate Solutions
Authors: Barthel J. , Gores H.‐J. , Carlier P. , Feuerlein F. , Utz M. 
Published: July 2012

AbstractViscosity measurements on pure propylene carbonate and conductance measurements on solutions of 13 salts in propylene carbonate from low to high concentrations were carried out in the temperature range −45°C ≤ θ ≤ +25°C. Data analysis based on the Vogel‐Fulcher‐Tammann equation yields equal values for the glass transition temperature of propylene carbonate, T0, from both conductance [T0 = (151.6 ± 0.9) K] and viscosity [T0 = (152.3 ± 1.6) K] measurements. The energies of activation of conductance at infinite dilution, E (m → 0, T) = (3350 ± 50) [T/(T‐T0)]2 J mol−1, of all the electrolyte solutions investigated are independent of the solute and equal to that of the viscosity of the solvent, E = (3420 ± 50) [T/(T‐T0)]2 J mol−1, at every temperature.
A Calorimetric Study on the Effect of Non‐Complementary Bases on the Stability of Helical Complexes with Poly U
Authors: Stulz J. , Ackermann Th. 
Published: July 2012

AbstractDouble and triple helical complexes of poly U with oligo‐ and polynucleotides containing complementary adenine residues and non‐complementary guanine residues are studied by calorimetry. The complexes are characterized by IR‐spectroscopy. The transition enthalpies of the polynucleotides are corrected using the stacking enthalpies of poly A and poly (A,G), which were determined independently. The enthalpy change for the formation of a GU‐base pair depends on the temperature. In spite of the relatively high value of 28 kJ/mol base pair for the enthalpy change, the change of free enthalpy is low and may reach slightly positive or negative values, depending on the temperature and the NaCl‐concentration. The formation of triple helical complexes with poly U leads to a comparatively constant value of enthalpy change for poly A, ApA and poly (A,G), whereas both stabilities and transition enthalpies are reduced in the analogous complexes of poly U with ApApG and ApGpA. A “phase diagram” of the system poly (A,G)/poly U shows reduced transition temperatures and an increased area of stability for the double helix in comparison with the analogous diagram of the system poly A/poly U.
Photochemistry of Colloidal Metal Sulfides. 4. Cathodic Dissolution of CdS and Excess Cd2+ Reduction
Authors: Gutiérrez M. , Henglein A. 
Published: July 2012

AbstractA highly reactive cadmium deposit is formed, when colloidal cadmium sulfide is illuminated in the presence of sulfite or dithionite anions (10−4−10−3M). It is oxidized by oxygen, nitrous oxide, hydrogen ions and methylviologen. The quantum yield amounts to 0.005 in the absence of excess cadmium ions. In the presence of 5 · 10−4 Cd2+ ions, the quantum yield is 0.053. The rate of cadmium formation was investigated as a function of the excess Cd2+ concentration, sulfite concentration and the pH. The effects are explained in terms of the formation of electrons and positive holes upon illumination, scavenging of the holes by adsorbed sulfite anions and reaction of the excess electrons with Cd2+ ions. The sulfite anions react mainly in an one‐hole oxidation process yielding SO radicals that form SO and S2O via the respective disproportionations and combinations. The deposition of cadmium metal was also observed in the illumination of CdS powder suspended in a 1 M sulfite solution. In the beginning of the illumination Cd was formed, later on hydrogen was generated. These effects are explained in terms of a large overpotential for the reduction of water by excess electrons in CdS and the catalytic action of a cadmium layer. — Cadmium metal is formed with practically 100% efficiency when colloidal CdS solutions are γ‐irradiated in the presence of suitable organic additives. This effect is attributed to the transfer of electrons from reducing organic radicals to the colloidal particles.
Effects of Temperature and Pressure on the Thermal Conductivity of Solid n‐Undecane
Authors: Forsman H. , Andersson P. 
Published: July 2012

AbstractWe have measured the thermal conductivity, λ, of n‐undecane, using the transient hot‐wire technique. At low pressures, n‐undecane has a plastic crystal phase αH. The increase in λ, going from the liquid to phase αH, was 35%. For a liquid → plastic crystal transition, this is a high value. It reflects that orientational disorder is mainly limited to rotation of the rod‐shaped molecule around its chain axis. The low temperature phase βO, was shown to exhibit a weak temperature dependence of λ at isochoric conditions. This suggests the presence of structural disorder, probably caused by reorientation of the chain‐end methyl groups. The volume dependence of λ in phase βO,g= ‐(∂ln λ/∂lnV)T, was found to be about 9.5. This result is discussed in terms of the anharmonicity of the weak interchain van der Waal's bonds. Some heat capacity results were also obtained.
Chemical Bonding and Electronic Structure of Small Homonuclear Clusters of Elements of Groups IA, IIA, IIIA and IVA
Authors: Pacchioni Gianfranco , Plavšić Dejan , Koutecký Jaroslav 
Published: July 2012

AbstractThe clusters Lik(k = 3–8), Na4, K4, Bex(x = 3–13), Mgy, Cay, Aly(y = 3–5) and Gez(z = 3–6) are investigated employing the ab initio CI method. — The bond in alkali metal clusters is due to the interaction of the outer s orbitals but p polarization functions are essential for a correct prediction of the electronic structure and stability of possible geometries of these clusters. In alkaline earth metal clusters the role of sp hybridization is crucial for the appearance of attractive interactions. The most relevant factor determining the stability of Al and Ge clusters is the bonding between p atomic orbitals. The spin properties of small clusters, which are important for their stability, are determined by their geometry and symmetry. — The most stable clusters of elements which crystallize in compact structures (bcc, fcc and hcp) are always sections of the corresponding crystal lattices. On the contrary, the Ge clusters exhibiting large stability are not parts of the diamond lattice and can be considered as deformed parts of more compact lattices. — The binding energy per atom of Li and Be clusters qualitatively converges to the cohesive energy of the metals with the growth of the cluster size. — In the largest clusters the existence of very small singlet‐triplet energy splittings indicates the development of a metallic character.