bluuebunny/crossref_metadata_2025_split huggingface dataset:
A Microscope‐Spectrometric Method for Determining Small Fe3+‐Concentrations Due to Fe3+‐Bearing Defects in Fayalite
Authors: Cemic L. , Grammenopoulou‐Bilal St. , Langer K. 
Published: July 2012

AbstractA microscope‐spectrometric method with areal resolution of 3 μm Ø is developed to determine the small Fe3+‐concentrations in fayalite, caused by the formation of (2Fe*M(1,2) + V″M(1,2)) and (Fe*M(1,2)Fe′Si) majority defects as a function fO2 and T. From polarized spectra E‖X(‖b), E‖Y(‖c), E‖‖Z(‖a) in the UV, i.e. in the range of O‐Fe2+ and O‐Fe3+ charge‐transfer transitions, on oriented fayalite crystals grown at 800°C/10 kb and at various fO2, calibration curves were obtained αX,26500 = 107191 · X + 647.0 (r = 0.999), αY,26500 = 69468 · X + 505.5 (r = 0.93), and αZ,28000 = 165804 · X + 640.6 (r = 0.993). Here, αX,Y,Z,ṽ are the linear absorption coefficients and X is the site fraction, X = [FeM(1,2)3+]+[Fe3+M(1,2)Fe3+Si], calculated according to Nakamura and Schmalzried [1] for the fO2 conditions applied. The applicability of the calibration is shown by determining, by microscopespectrometry, a Fe3+ ‐concentration profile along Y(‖c) in a fayalite single crystal grown at fO′2 (ca. 1200°C/4.0·10−9 atm O2, ca. FMQ) and reheated at another oxygen fugacity fO″2(895°C/9.7 · 10−18 atm O2, ca. WI).
Debye‐Hückel‐Type Relaxation Processes in Solid Electrolytes: Complex Conductivity Arcs and Broad Quasielastic Neutron Scattering
Authors: Funke K. 
Published: July 2012

AbstractCorrelated forward‐backward hopping processes are a common feature in solid electrolytes. A simple Debye‐Hückel‐type model is constructed to show how “trial‐and‐error” hops are being caused by the electrostatic interaction between the mobile charge carriers. The forward‐backward hopping processes are shown to be responsible for a number of well‐known experimental findings which have so far not been understood microscopically. These include the occurrence of almost circular arcs in the complex impedance and conductivity planes, with centers displaced below the real axes, and the power‐law behavior of the frequency dependent conductivity. Both effects have often been called “universal dielectric response”. The model also yields quasielastic contributions to the energy resolved neutron scattering spectra which are much broader than the quasielastic lines due to translational jump diffusion.
Diffusion Processes and Interphase Boundary Morphology in Ternary Metal‐Ceramic Systems
Authors: Backhaus‐Ricoult M. 
Published: July 2012

AbstractDiffusion processes, product formation, and interphase boundary morphology are discussed in terms of thermodynamics and linear transport theory for isothermal diffusion annealed ternary metal‐ceramic systems, which have not reached equilibrium. Some experimental results are presented for typical systems like Ni‐Al2O3, Ni‐MgO and Nb‐Al2O3 and compared with theoretical calculations. It is shown how the starting composition of the ceramic or that of the metal phase, as well as the oxygen activity can influence the chemical compositions at the interphase boundary.
Structural Collapse or Expansion of the Hydro‐Sodalite Series Na8[AlSiO4]6(OH)2·nH2O and Na6[AlSiO4]6·nH2O Upon Dehydratation
Authors: Felsche J. , Luger S. 
Published: July 2012

AbstractThe two end‐member series of hydro‐sodalites show different structural expansion characteristics during dehydratation at elevated temperatures (300–900 K). The anomalous expansion in cell volume which is observed for series Na6[AlSiO4]6 · nH2O upon loss of 0 < n ≤ 8 H2O is correlated to the destruction of the significant hydrogen bonding system between non‐framework and framework oxygen atoms of the corresponding sodalite structures. The contraction of the unit cell of the basic sodalites Na8[AlSiO4]6(OH)2 · nH2O upon loss of 0 < n ≤ 4 H2O, however, is well understood in terms of space filling of the non‐framework constituents and some special stereochemical features amongst sodium, oxygen and hydrogen atoms.
The Mineral Cordierite: Structure and Reactions in the Presence of Fluid Phases
Authors: Schreyer Werner 
Published: July 2012

AbstractThe complex framework silicate cordierite with a structure similar to that of beryl forms Al/Si‐ordered orthorhombic as well as disordered hexagonal polymorphs and varieties as a function of temperature and composition. Even in the stability range of the ordered cordierite initial crystallization leads to the disordered form that becomes gradually ordered via a modulated structure. A miscibility gap as a two‐phase loop exists between orthorhombic Mg‐cordierite of the composition Mg2[Al4Si5O18] and the new hexagonal, Bc‐bearing cordierite solid solutions formed by the substitutions Be[4]+Si for 2 Al[4]. (Na,K)‐bearing cordierites with the alkalies present in the structural channels are due to the substitution Alk+ + Al[4] for Si[4]. These metastable phases are hexagonal, probably because of the deviating Al/Si ratios that are not conducive to ordering. Neutral gas molecules and atoms like H2O, CO2, N2, and Ar can occupy the structural channels, H2O changing its dipole orientation depending on the presence or absence of Na in these channels. The pressure temperature stabilities of cordierite end members are mainly a function of the nature of their octahedrally coordinated atoms with PT‐ranges decreasing in the order Mg > Fe > Mn > Co; but there is also a stabilizing effect by gas channel occupants. Disordered cordierites form metastably at generally higher temperatures and lower pressures than their stable, ordered counterparts.
Transport of Ions Against their Concentration Gradient Across Cation Exchange Membranes
Authors: Schwahn P. , Woermann D. 
Published: July 2012

AbstractThe transport of mono‐ and bi‐valent cations against their concentration gradients across cation exchange membranes is studied experimentally under isothermal‐isobaric conditions. The driving forces of this transport are generated by a pH difference between the bulk phases of the membrane. A general theoretical analysis of the systems is given based on the model of the membrane with narrow pores. The extent of the observed stationary concentration increase of the ion species transported against its concentration gradient as well as the selectivity of the transport (if two ionic species are transported simultaneously) are in good agreement with theoretical predictions. Furthermore, results of electric transference experiments to separate two different kinds of mono‐valent counterion species are reported.
Selective Solvation of Some Silver(I) Salts in Water‐Pyridine Mixtures at 30°C
Authors: Palanivel A. , Rajendran G. , Kalidas C. 
Published: July 2012

AbstractThe selective solvation behaviour of silver(I) salts viz Ag2SO4, AgBrO3and AgIO3has been investigated in water‐pyridine (Py) mixtures at 30°C by solubility and emf measurements. It was observed that the solubilities of Ag2SO4, AgBrO3and AgIO3pass through a maximum near XPy= 0.5, XPy= 0.5 and XPy= 0.1 respectively and then decrease with further addition of Py. The Gibbs transfer energy of the silver ion, ΔG0t(Ag+) decreases continuously while that of the anions increases with the addition of Py. These results together with those concerning the solvent transport number Δ, are interpreted in terms of the heteroselective solvation of the salts, the silver ion being preferentially solvated by Pyand the anions by water.
Influence of Ionic Traces Upon the Electric Conductivity of an Electrolyte Solution. On the Possibility of Obtaining the Trace Mobility of an Ion Exclusively by Conductance Measurements
Authors: Raineri F. O. , Timmermann E. O. 
Published: July 2012

AbstractIn a detailed theoretical and experimental study it is shown that the initial slope for the dependence of the conductivity of an electrolyte solution with respect to the concentration of an added trace electrolyte is not only determined by the trace ionic conductivity of the non‐common ion added plus the ionic conductivity of the common ion at the concentration of the original (supporting) electrolyte, as has been proposed by H. G. Hertz et al. (J. Chim. Phys. 78, 68 (1981)). It is also determined in a non‐negligible amount by the variation of the equivalent conductivity of the pure supporting electrolyte with concentration as well as by the variation of this conductivity with the composition of the mixture at constant total concentration. The theoretical equations are verified with the complete electric transport data of the system HCl‐KCl‐H2O and careful conductivity measurements for the system NaCl‐KCl‐H2O. It is concluded that the trace ionic conductivity of an ion in a mixture cannot in general be obtained by conductivity measurements alone (transport number determinations are unavoidable) and the proposal due to Hertz et al. is shown to be inadequate. Only in the case of H+ as a trace ion the later two dependences mentioned above can be neglected within an error of 1% at relatively low concentrations of the supporting electrolyte.
The Low‐Pressure Pyrolysis of Butadiyne (C4H2)
Authors: Homann K. H. , Pidoll U. V. 
Published: July 2012

AbstractButadiyne (C4H2) mixed with helium (maximum 1:9) was pyrolyzed in a low‐pressure flow reactor at temperatures between 700 and 1000°C and total pressures of 3 to 13 mbar. The residence time (maximum 45 ms) was varied by a movable inlet lance for the C4H2. Samples were drawn through a molecular beam system and analyzed mass‐spectrometrically. The main products were C2H2, H2, polyyines (C6H2, C8H2), oligomers of the composition (C4H2)n, n = 2 to 5, polymer and coke. Most of the H2 and a smaller part of C2H2 and C6H2 were formed heterogeneously while the oligomers and C8H2 were generated in homogeneous reaction. The oligomers with n ≧ 3 are most probably aromatic compounds with C2H side groups. They are intermediates which repeatedly split off their C2H groups until the base hydrocarbons benzene, naphthalene, and phenanthrene or anthracene remain. Addition of C2H2 to the pyrolyzing C4H2 led to a mixed oligomerization while addition of H atoms had no measurable effect. A large part of the C4H2 decomposed heterogeneously with an apparent activation energy of 109 kJ mol−1. The activation energy for oligomer formation ranged from 145 to 168 kJ mol−1 increasing with higher degree of oligomerization. — A mechanism for the formation of polyynes and oligomers is discussed starting with an excited C4H2 which can add C4H2 to give either a linear or a branched dimer C8H2. The results are compared to the formation of polycyclic aromatic compounds in the burned gas of fuel‐rich flames that also contains C2H2 and C4H2.
Reaktormodelle für heterogen katalysierte Gasphasenreaktionen
Authors: Emig G. 
Published: July 2012

AbstractIn most chemical processes heterogeneously catalyzed gas‐phase reactions play an important role. Therefore, the modeling of the fixed bed reactors is increasingly important today. The aim of a model building procedure is to use information already available to predict the behavior of new catalysts, the optimization of process conditions, scale‐up, etc. The phenomena occuring in a reactor for heterogeneously catalyzed reactions vary greatly and are very complex, therefore, all models are only approximations with differing degrees of accuracies for the real system. In practice, however, it can be shown that relatively few simple model types can satisfactorily describe a large number of important cases. A priori criteria can aid in the decision when more complex models must be applied.
Reaction Sequences from Light Absorption to the Cleavage of Water in Photosynthesis—Routes, Rates and Intermediates
Authors: Witt H. T. , Schlodder E. , Brettel K. , Saygin Ö. 
Published: July 2012

AbstractThe reaction sequence between the primary electron acceptor, the oxidized Chlorophyll‐aII, and the terminal electron donor, the water splitting enzyme system S, is being described in the range from nanoseconds to milliseconds. For the cleavage of water Chlorophyll‐a+II extracts four electrons in four turnovers from the enzyme system S responsible for the water oxidation. For each extraction the electron is moved step by step along the chain that connects the Chlorophyll‐aII center with that of S. Beginning with the transfer from the immediate donor, D1 to Chl‐a+II, the subsequent transfer from D2 to D+I ends in the electron transfer from S to D2+. This final act establishes in S the oxidizing equivalent, probably in the form of oxidized manganese. Coupled with these acts is an intrinsic proton release and a surplus charge formation. After the generation of the 4th oxidizing equivalent in a concerted final action the evolution of O2 from water takes place. Correlations between the events are described quantitatively.
Nonlinear Phenomena in the Evolution of Satellite DNA
Authors: Stephan Wolfgang 
Published: July 2012

AbstractSatellite DNA forms long clusters of tandemly repeated sequences of 104 to 107 copies, and is found in the chromosomes of all higher organisms. In particular in mammals, satellites comprise anywhere from a few percent (human) to over 50% (kangaroo rat) of total DNA. But a function of these highly abundant, noncoding sequences has not been identified so far, though a great deal of structural information has been gathered in the past 25 years. This paper looks at the structure‐function debate for satellite DNA. The basic question addressed is why are highly repeated sequences of no (obvious) functional significance such as satellite sequences tolerable in millions of copies in the chromosomes of higher organisms. A model is proposed which shows that the accumulation of clustered, highly repeated DNA (HRDNA) can most readily be explained as a result of synergistic effects of the forces of amplification, unequal crossing over and natural selection. Accordingly, satellite DNA clusters may build up only in those regions of the chromosomes where the effectiveness of unequal crossing over—operating as a nonlinear control mechanism and, in doing so, supporting selection—is drastically reduced. This result conforms well to the experimental finding that satellite DNA is located only in the genetically inactive parts of the chromosomes such as centromeres and telomeres, in which recombination is in general severely suppressed.
Model Calculations About the Reduction of Atmospheric Ozone by Different Halogenated Hydrocarbons
Authors: Krüger B. C. , Fabian P. 
Published: July 2012

AbstractThe impact of halogen radicals released from various halocarbons on atmospheric ozone has been studied by means of a time‐dependent one‐dimensional model. Different scenarios for future emissions rates, up to the year 2020, were used. The impact of chlorine is different from that of bromine which can be explained by the differences in the chemistry of the respective halocarbons themselves as well as of the inorganic halogen compounds in the atmosphere.
A Rheological Switch: Shear Induced Phase Transitions in Aqueous Surfactant Solutions
Authors: Rehage H. , Hoffmann H. , Wunderlich I. 
Published: July 2012

AbstractAqueous solutions of cationic surfactants show the striking phenomenon of shear induced phase transitions. Two different processes can be distinguished: At very low surfactant concentrations we observe flow induced sol → gel transitions and at higher concentrations shear induced transitions occur from a clear gel state to a turbid phase. The surfactant solutions act as a rheological switch and they can be used as elements which are sensitive to shear forces.
Polyethyleneoxide‐Dynamics in Aqueous Solutions Studied by Nuclear Magnetic Relaxation
Authors: Breen J. , Duijn D. Van , Bleijser J. De , Leyte J. C. 
Published: July 2012

AbstractThe local polymer dynamics of polyethyleneoxide in aqueous solutions were studied by 1H‐ and 13C‐nuclear magnetic relaxation. The concentration dependence is caused by polymer‐polymer interactions, whereas in the concentration independent range the polymer dynamics is mainly determined intramolecularly and by water‐PEO interactions. The latter interaction is influenced by the presence of salts. MW‐dependence of the relaxation rates is not observed for DP > 100. From the dispersion of the 1H relaxation rates, for a PEO‐sample with DP = 360 at a concentration of 0.5 mol/kg, the polymer segment dynamics are evaluated in terms of an overall and an internal motion.
A Narrow Window for Observation of Spiral Lipid Crystals
Authors: Heckl W. M. , Möhwald H. 
Published: July 2012

AbstractThe growth of spiral solid domains in monolayers of dimyristoylphosphatidic acid containing 1 mol% cholesterol is observed by fluorescence microscopy at the air/water interface. Spiral or lamellar domains are encountered only at high pH (11) where the large head group charge induces a chain tilt. Spiral width is drastically reduced with decreasing temperature, is uniform and can be varied reversibly.—The findings can be understood considering repulsive and anisotropically attractive electrostatic forces that increase with decreasing temperature and edge tension being reduced by incorporation of cholesterol. The shape of the spirals can be numerically calculated using a crude model containing only three adjustable parameters.
Hydrogen Abstraction Reactions by NH2(X̃2B1)‐Radicals from Hydrocarbons in the Gas Phase
Authors: Hack W. , Kurzke H. , Rouveirolles P. , Wagner H. Gg. 
Published: July 2012

AbstractThe NH2(X̃2B1) radical reactions with saturated hydrocarbons, toluene and acetaldehyde were investigated in an isothermal discharge flow system over the given temperature ranges. The pressure was varied between 2.6 and 7.8 mbar. Helium was used as the main carrier gas. The temperature dependences of the rates are represented by the following Arrhenius expressions, with A in [cm3 mol−1 s−1 and EA in [kJ mol−1]:

A correlation between the Arrhenius activation energy and the energy of the broken CH bond is discussed.
Integral Carbon Mass Balance in Premixed Sooting Flames
Authors: Brei M. , Jander H. , Wagner H. Gg. 
Published: July 2012

AbstractIn sooting C2H4‐air, C6H6‐air and C2H2‐air flames the burned gases have been analyzed for different fuel‐air ratios and the fractions of carbon which end up as CO and CO2, as soot and as hydrocarbons have been determined. The amount of soot formed increases strongly with increasing fuel content beyond the threshold of soot formation, following approximately the same formal relation for the different fuels. At a given fuel concentration above the soot threshold the soot mass per cm3 rises from C2H2 to C2H4 and to C6H6‐air flames. The concentrations of hydrocarbons in the burned gases increase also with increasing fuel concentrations but in different ways for the different fuels. For benzene‐air flames the carbon present as soot exceeds that present as hydrocarbon already at fuel concentrations slightly above the soot threshold. The same happens in C2H4‐air flames only at C/O ratios close to one and not at all for the C2H2‐air flames.—There is no uniquely simple correlation between the soot mass per cm3 formed in these flames of various fuels and the concentrations of hydrocarbon in their burned gases.
Defects and Cation Diffusion in Magnetite (VIII): Migration Enthalpies for Iron and Impurity Cations
Authors: Dieckmann R. , Hilton M. R. , Mason T. O. 
Published: July 2012

AbstractRecent point defect formation and defect diffusion data in magnetite are used to analyze tracer diffusion data of Fe, Co, Cr and Al for motion enthalpies in vacancy and interstitial(cy) mechanisms. Correlations are made with ion properties such as radius, polarizability, and bond strength. The best correlation was made with the melting points of the end member ferrites containing the ions of interest. An explanation for the consistent minimum in diffusion coefficients is given.
A proton NMR study on the structure of water of hydration of aqueous micelles
Authors: El Seoud Monica I. , Farah João P. S. , El Seoud Omar A. 
Published: July 2012

AbstractThe chemical shift of water was measured as a function of concentration of the detergents cetyltrimethylammonium chloride. CTACl; 3‐N‐dodecyl‐N,N‐dimethylammonio‐1‐propanesulfonate, DDAPS; polyoxyethylene (9.5) octylphenyl ether, Triton X‐100, and the deuterium content of the solvent. The short chain compound butyltrimethylammonium bromide was also studied as a model for CTACl. Graphs of the chemical shifts vs. the mole fractions of the solubilizates were linear in all cases and the slopes were used to calculate the so called “fractionation factor, ϕ” which can be used as a measure of the degree of structure of the water of hydration of the appropriate species (relative to bulk water). The calculated ϕ values indicated that the butyltrimethylammonium ion does not perturb hydrogen bonding of the solvent (ϕ = 0.99), whereas the water in the Stern layer of CTACl is more organized than bulk water ( = 1.06). Zwitterionic DDAPS was found to enhance the structuring marginally (ϕ = 1.02) whereas the nonionic surfactant Triton X‐100 has a structure decreasing effect (ϕ = 0.95).
The molecular Zeeman effect of 2‐fluoropropane. A high resolution microwave fouriertransform study
Authors: Böttcher O. , Kleibömer B. , Sutter D. H. 
Published: July 2012

AbstractA microwave Fouriertransform spectrometer, developed for rotational Zeeman effect studies is described. Its high resolution capabilities are demonstrated by the analysis of the dense Zeeman multiplets of 2‐fluoropropane. The diagonal elements of the molecular g‐tensor as referred to the principal inertia axes system are obtained as gaa = −0.00794(13), gbb = +0.00722(08), and gcc = −0.01051(11). The two independent molecular magnetic susceptibility anisotropies are obtained as 2χaa ‐ χbb ‐χcc = −2.77(34) · 10−6 erg G−2 mol−1 and 2χbb ‐ χcc ‐ χaa = −5.40(20) · 10−6 erg G−2 mol−1. The observed magnetic susceptibilities are compared with those observed earlier for propane and are discussed successfully within the model of local atom susceptibilities.
UV resonance raman studies on the structure of polyriboadenylic acid and adenosine 5'‐monophosphate depending on the pH value
Authors: Gfrörer A. , Schnetter M. , Wolfrum J. , Greulich K. O. 
Published: July 2012

AbstractUV resonance Raman spectra of polyriboadenylic acid (poly(rA)) and adenosine‐5'‐monophosphate (AMP) were obtained with a Raman spectrometer based on an excimer/dye laser system. A pH‐induced structural transition between a single helical form and a double‐stranded structure of poly(rA) is documented by many characteristic spectral changes. We found a high degree of similarity for the spectral changes of AMP between pH 4.5 and pH 2.5 and poly(rA) between pH 7.0 and pH 4.5. The behaviour of the resonance Raman spectra of poly(rA) between pH 4.5 and pH 2.5 indicates a second structural change of poly(rA) which is different from the cooperative double‐strand formation at higher pH values.
The laser electron microscope (LEM)
Authors: Manuccia T. J. , Loda R. T. 
Published: July 2012

AbstractWe have developed a new SEM imaging mode which we refer to as laser electron microscopy (LEM). In this technique, a thin sample is mounted on a diamond substrate and overcoated with a phosphor having a highly temperature dependent cathodoluminescence (CL) emission intensity. The sample is held at low temperatures (T < 95 K) and is irradiated through the diamond substrate with a laser. Localized areas of the sample that absorb the laser radiation heat, and transfer this heat to the nearby phosphor coating, which is being simultaneously probed by the raster scanned electron beam. Thus, one detects a cathodoluminescence image of only those areas of the sample where the laser is absorbed. With IR irradiation, this interaction mechanism produces an image resembling that of a darkfield monochromatic infrared microscope but with the improved spatial resolution of electron beam imaging. One can then image the distribution of distinct molecular species.