A new advanced thermo-microbalance

The capabilities of the new NETZSCH thermo-microbalance TG 209 are illustrated by four applications from the polymer industry.     

Heat capacities and densities of mixtures of very polar substances. 3. Mixtures containing either trichloromethane or 1,4-dioxane or diisopropylether

Excess molar heat capacities C _P ^E at constant pressure and excess molar volumes V ^E have been determined, as a function of mole fraction x₁ at 25°C and atmospheric pressure, for 10 binary liquid mixtures containing either trichloromethane (series I) with C₆H₅CH₃, or C₆H₅Cl, or C₅H₅N, or CH₃COCH₃, or C₆H₅NO₂; 1,4-dioxane (series II) with (C₂H₅)₃N, or (CH₃)₂CHOCH(CH₃)₂, or (CH_{3 2}SO); or diisopropyl ether (di-1-methylethyl ether) (series III) with (C₂H₅)₃N, or CHCl₃. The dipole momentsp (10^–30C-m) of the substances range from nearly 0 to 14.1 for nitrobenzene. The C _P ^E of series I and III are all positive, with C _P ^E (x₁=0.5) (J-K^–1-mol^–1) ranging from 1.04 for {x₁CHCl₃+x₂C₆H₅Cl} to 16.66 for {x₁(CH₃)₂CHOCH(CH₃)₂+x₂CHCl₃}. In series II, the C _P ^E are positive and small for {x₁1,4-C₄H₈O₂+x₂(CH₃)₂CHOCH(CH₃)₂}, S-shaped and small for {x₁1,4-C₄H₈O₂+x₂(C₂H₅)₃N}, and negative and small for {x₁1,4-C₄H₈O₂+x₂(CH₃)₂SO}. The excess volumes are small and positive for {x₁CHCl₃+x₂C₆H₅CH₃}, S-shaped for {x₁CHCl₃+x₂CH₃COCH₃}, {x₁1,4-C₄H₈O₂+x₂(C₂H₅)₃N} and {x₁(CH₃)₂CHOCH(CH₃)₂+x₂(C₂H₅)₃N}, and negative for the other systems.Presented at the Symposium, 76^th CSC Congress, Sherbrooke, Quebec, May 30–June 3, 1993, honoring Professor Donald Patterson on the occasion of his 65^th birthday     

Models for μ+ depolarization in spin glasses reflecting dynamical processes

The muon spin depolarization function is calculated for different dynamical processes. Muon diffusion is shown to cause motional narrowing at high temperatures (TT_f=freezing temperature of the spin glass) as well as at low temperatures (Tf), where the static line is essentially lorentzian due to the randomness of the spin distribution of the dilute system. Different models for ⁺ depolarization reflecting the freezing process of the spin glass system above T_f consider single correlation times as well as wide distributions of correlation times. It will be shown that the SR depolarization investigated in transverse external fields does not enable us to distinguish between single correlation times and wide correlation time distributions. Therefore, an interpretation of the spin dynamics requires a comparison of TF-SR with results of different measuring methods.     

A new symmetrical micro-thermobalance

A new symmetrical micro-thermogravimetric analyzer has been developed. The symmetrical design of this instrument allows determination of very small mass changes over a wide range of temperatures. The utility of the instrument was demonstrated by studying the decomposition characteristics of CaC₂O₄·H₂O and the curing and decomposition kinetics of a glass filled polymer composite.

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Zusammenfassung Ein neuer symmetrische mikrothermogravimetrischer Analyser wurde entwickelt. Die symmetrische Gestaltung dieses Instruments ermöglicht die Bestimmung sehr geringer, sich über weite Temperaturbereiche hinziehender Massenveränderungen. Die Brauchbarkeit des Instruments wird demonstriert, in dem die Zersetzungscharakteristik von CaC₂O₄.H₂O und die Kinetik der Härtung und Zersetzung von glassverstärkten Polymerverbundstoffen untersucht wird.

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- . . ₂₄.₂, .

     

Excess heat capacities of binary mixtures of carbon tetrachloride with n-alkanes at 298.15 K

A Picker flow microcalorimeter was used to determine molar excess heat capacities C_P^E at 298.15 K for mixtures of carbon tetrachloride + n-heptane, n-nonane, and n-decane. The excess heat capacities are negative in all cases. The absolute value |C_P^E| increases with increasing chain length of the alkane. A formal interchange parameter, c_P12, is calculated and its dependence on n-alkane chain length is discussed briefly in terms of molecular orientations.     

Recent advantages in thermal analysis instrumentation

Curing and decomposition of a phenolic resin is studied by simultaneous thermal analysis (STA) and mass spectrometry (MS) to get quantitative and qualitative information on the reactions. The influence of the heating rate and the curing mass loss of the same material is measured with a symmetrical micro thermobalance. A high temperature DSC apparatus is used to determine the specific heat of a glass ceramic. Poco graphite is used for expansion calibration measurements with a new dilatometer up to 2000 °C.

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Zusammenfassung Mittels simultaner Thermoanalyse (STA) und Massenspektroskopie (MS) wurden Vernetzung und Zersetzung von Phenolharzen untersucht, um so quantitative und qualitative Erkenntnisse über die entsprechenden Reaktionen zu erlangen. Der Einfluß der Aufheizgeschwindigkeit und des Vernetzungsmassenverlustes desselben Stoffes wurde mit einer Mikrothermowaage gemessen. Zur Bestimmung der specifischen Wärme einer Glaskeramik wurde ein Hochtemperatur-DSC Gerät verwendet. Zu Ausdehnungskalibrationsmessungen bis zu 2000° mit einem neuen Dilatometer wurde Pocographit verwendet.

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- . . . 2000 .

     

Thermodynamics of liquid mixtures containing hydrocarbons and strongly polar substances:V E andC P E of {pyridine or piperidine+cyclohexane} at 298.15 K

Summary Excess molar volumesV ^E and excess molar heat capacitiesC _P ^E at constant pressure have been determined, as a function of mole fractionx ₁ at 298.15 K and atmospheric pressure, for the two liquid mixtures {pyridine or piperidine+cyclohexane}. The instruments used were a vibrating-tube densimeter and a Picker flow microcalorimeter, respectively. The two systems show positive excess volumes withV ^E(x ₁=0.5)=0.531 cm³·mol^–1 for {pyridine+cyclohexane} and 0.295 cm³·mol^–1 for {piperidine+cyclohexane}. The curveC _P ^E vs. x ₁ for {pyridine+cyclohexane} shows a rather complex S-shape:C _P ^E is negative at small mole fractionsx ₁ of pyridine and positive forx ₁>0.22, roughly.C _P ^E of the piperidine system is negative throughout and strongly asymmetric with the minimumC _P ^E (x _1,min)=–2.32J·K^–1·mol^–1 being situated at a mole fraction of piperidinex _1,min0.27.

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Zur Thermodynamik flüssiger Mischungen von Kohlenwasserstoffen und stark polaren Substanzen:V ^E undC _P ^E von {Pyridin oder Piperidin+Cyclohexan} bei 298.15 K

Zusammenfassung Für die beiden flüssigen Mischungen {Pyridin oder Piperidin+Cyclohexan} wurden molare ZusatzvoluminaV ^E und molare ZusatzwärmekapazitätenC _P ^E bei konstantem Druck als Funktion des Molenbruchsx ₁ bei 298.15K bestimmt. Die Messungen wurden mit einem Biegeschwinger-Dichtemeßgerät bzw. einem Strömungsmikrokalorimeter nach Picker durchgeführt. Die Zusatzmolvolumina beider Systeme sind positiv mitV ^E(x ₁=0.5)=0.531 cm³·mol^–1 für {Pyridin+Cyclohexan} und 0.295 cm³·mol^–1 für {Piperidin+Cyclohexan}. Die KurveC _P ^E vs. x ₁ des Systems {Pyridin+Cyclohexan} zeigt einen ungewöhnlichen S-förmigen Verlauf: bei kleinen Molenbrüchenx ₁ von Pyridin istC _P ^E negativ, fürx ₁>0.22 istC _P ^E positiv. Die molare Zusatzwärmekapazität des Piperidinsystems ist überall negativ und stark unsymmetrisch: im Minimum beix _1,min0.27 findet manC _P ^E (x _1,min)=–2.32J·K^–1·mol^–1.

     

Compound inversive congruential pseudorandom numbers: an average-case analysis

The present paper deals with the compound (or generalized) inversive congruential method for generating uniform pseudorandom numbers, which has been introduced recently. Equidistribution and statistical independence properties of the generated sequences over parts of the period are studied based on the discrepancy of certain point sets. The main result is an upper bound for the average value of these discrepancies. The method of proof is based on estimates for exponential sums.

     

Low Pre-Transplant Caveolin-1 Serum Concentrations Are Associated with Acute Cellular Tubulointerstitial Rejection in Kidney Transplantation

Acute and chronic transplant rejections due to alloreactivity are essential contributors to graft loss. However, the strength of alloreactivity is biased by non-immunological factors such as ischemia reperfusion injury (IRI). Accordingly, protection from IRI could be favorable in terms of limiting graft rejection. Caveolin-1 (Cav-1) is part of the cell membrane and an important regulator of intracellular signaling. Cav-1 has been demonstrated to limit IRI and to promote the survival of a variety of cell types including renal cells under stress conditions. Accordingly, Cav-1 could also play a role in limiting anti-graft immune responses. Here, we evaluated a possible association between pre-transplant serum concentrations of Cav-1 and the occurrence of rejection during follow-up in a pilot study. Therefore, Cav-1-serum concentrations were analyzed in 91 patients at the time of kidney transplantation and compared to the incidence of acute and chronic rejection. Higher Cav-1 levels were associated with lower occurrence of acute cellular tubulointerstitial rejection episodes.