Determination of cell asymmetry in temperature-modulated DSC

The quality of measurement of heat capacity by differential scanning calorimetry (DSC) is based on the symmetry of the twin calorimeters. This symmetry is of particular importance for the temperature-modulated DSC (TMDSC) since positive and negative deviations from symmetry cannot be distinguished in the most popular analysis methods. Three different DSC instruments capable of modulation have been calibrated for asymmetry using standard non-modulated measurements and a simple method is described that avoids potentially large errors when using the reversing heat capacity as the measured quantity. It consists of overcompensating the temperature-dependent asymmetry by increasing the mass of the sample pan.On leave from Toray Industries, Inc., Otsu, Shiga 520, JapanOn leave from Toray Research Center, Inc., Otsu, Shiga 520, JapanThis work was supported by the Division of Materials Research, National Science Foundation, Polymers Program, Grant # DMR 90-00520 and the Division of Materials Sciences, Office of Basic Energy Sciences, U. S. Department of Energy at Oak Ridge National Laboratory, managed by Lockheed Martin Energy Research Corp. for the U. S. Department of Energy, under contract number DE-AC0S-96OR22464. Support for instrumentation came from TA Instruments, Inc. and Mettler-Toledo, Research support was also given by ICI Painls, and Toray Industries, Inc.     

Single run heat capacity measurements

An outline for the data analysis of single-run heat capacity measurments by dual sample DSC is presented with the following features: 1. Heat flow correction by subtracting the contribution due to the sample pan, including correction for mismatched pan masses. 2. Heat flow and temperature correction with a nonlinear temperature calibration, temperature lag correction, and heating rate correction. 3. Calculation of the cell constants for both cell positions and evaluation of the asymmetry factor between cell positions A and B. 4. Heat capacity calibration and calculation with slope and asymmetry correction. 5. Calculation of heat capacity for multiple runs. 6. Data curve fitting for heat capacity.This work was supported by the Division of Materials Research, National Science Foundation, Polymers Program, Grant # DMR 8818412 and the Division of Materials Sciences, Office of Basic Energy Sciences, U.S. Department of Energy, under Contract DE-AC05-84OR21400 with Martin Marietta Energy Systems, Inc. Thanks are given to TA Instruments, Inc. (New Castle, DE) for providing the commercial heat capacity software and helping with the acquisition of the calorimeter.     

Melting of indium by temperature-modulated differential scanning calorimetry

The melting and crystallization of a sharply melting standard has been explored for the calibration of temperature-modulated differential scanning calorimetry, TMDSC. Modulated temperature and heat flow have been followed during melting and crystallization of indium. It is observed that indium does not supercool as long as crystal nuclei remain in the sample when analyzing quasi-isothermally with a small modulation amplitude. For standard differential scanning calorimetry, DSC, the melting and crystallization temperatures of indium are sufficiently different not to permit its use for calibration on cooling, unless special analysis modes are applied. For TMDSC with an underlying heating rate of 0.2 K min^–1 and a modulation amplitude of 0.5–1.5 K at periods of 30–90 s, the extrapolated onsets of melting and freezing were within 0.1 K of the known melting temperature of indium. Further work is needed to separate the effects originating from loss of steady state between sample and sensor on the one hand and from supercooling on the other.On leave from Toray Research Center, Inc., Otsu, Shiga 520, Japan.This work was supported by the Division of Materials Research, National Science Foundation, Polymers Program, Grant # DMR 90-00520 and the Division of Materials Sciences, Office of Basic Energy Sciences, U.S. Department of Energy at Oak Ridge National Laboratory, managed by Lockheed Martin Energy Research Corp. for the U.S. Department of Energy, under contract number DEACOS-960R22464. Support for instrumentation came from TA Instruments, Inc. and Mettler-Toledo Inc. Research support was also given by ICI Paints.     

Modulated differential scanning calorimetry in the glass transition region

Temperature-modulated calorimetry (TMC) allows the experimental evaluation of the kinetic parameters of the glass transition from quasi-isothermal experiments. In this paper, model calculations based on experimental data are presented for the total and reversing apparent heat capacities on heating and cooling through the glass transition region as a function of heating rate and modulation frequency for the modulated differential scanning calorimeter (MDSC). Amorphous poly(ethylene terephthalate) (PET) is used as the example polymer and a simple first-order kinetics is fitted to the data. The total heat flow carries the hysteresis information (enthalpy relaxation, thermal history) and indications of changes in modulation frequency due to the glass transition. The reversing heat flow permits the assessment of the first and higher harmonics of the apparent heat capacities. The computations are carried out by numerical integrations with up to 5000 steps. Comparisons of the calculations with experiments are possible. As one moves further from equilibrium, i.e. the liquid state, cooperative kinetics must be used to match model and experiment.On leave from Toray Industries, Inc., Otsu, Shiga 520, Japan.This work was supported by the Division of Materials Research, National Science Foundation, Polymers Program, Grant # DMR 90-00520 and the Division of Materials Sciences, Office of Basic Energy Sciences, U. S. Department of Energy at Oak Ridge National Laboratory, managed by Lockheed Martin Energy Research Corp. for the U. S. Department of Energy, under contract number DE-AC05-96OR22464. Support for instrumentation came from TA Instruments, Inc. Research support was also given by ICI Paints, and Toray Industries, Inc.     

Multiple melting peak analysis with gel-spun ultra-high molar mass polyethylene

The multiple melting peaks observed on differential scanning calorimetry (DSC) of ultrahigh molar-mass polyethylene fibers (UHMMPE) are analyzed as a function of sample mass. Using modern DSC capable of recognizing single fibers of microgram size, it is shown that the multiple peaks are in part or completely due to sample packing. Loosely packed fibers fill the entire volume of the pan with rather large thermal resistance to heat flow. On melting, the fibers contract and flow to collect ultimately at the bottom of the pan. This process seems to be able to cause an artifact of multistage melting dependent on the properties of the fibers. A method is proposed to greatly reduce, or even eliminate, errors of this type. The crucial elements of the analysis of melting behavior and melting temperature are decreasing the sample size and packing the individual fibers in a proper geometry, or to introduce inert media to enhance heat transport.This work was supported by the Division of Materials Research, National Science Foundation, Polymers Program, Grant # DMR 90-00520 and the Division of Materials Sciences, Office of Basic Energy Sciences, US Department of Energy at Oak Ridge National Laboratory, managed by Lockheed Martin Energy Research Corp. for the US Department of Energy, under contract number DE-ACOS-96OR22464. Support for instrumentation came from TA Instruments, Inc. and Mettler-Toledo, research support was also given by ICI Paints.     

A computation scheme to evaluate debye and tarasov equations for heat capacity computation without numerical integration

TheATHAS computation scheme of heat capacities of solid, linear macromolecules has been developed for an IBM-compatible microcomputer on a Lotus 1-2-3 based software. In this effort the Debye functions that can only be integrated numerically have been approximated by polynomials and logarithmic polynomials, which describe these functions to an accuracy of better than ±0.1%. Heat capacities can now be computed much faster and with greater ease.

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Zusammenfassung Für einen IBM-kompatiblen Mikrocomputer mit einer Softwarebasis Lotus 1-2-3 wurde unter der Namen ATHAS ein Rechenschema für Wärmekapazitäten von festen, linearen Makromolekülen entwickelt. In diesem Beitrag wurden die ausschlielich numerisch integrierbaren Debye-Funktionen durch Funktionen aus Polynomen und exponentiellen Polynomen genähert, die Funktionen mit einer Genauigkeit von mindestens ±0.1% wiedergeben. Wärmekapazitäten können nun somit schneller und einfacher errechnet werden.

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This research was sponsored by the Materials Division of the National Science Foundation of the U.S. Polymers Program, Grant # 8818412 and the Division of Materials Sciences, Office of Basic Energy Sciences, U.S. Department of Energy, under Contract DEAC05-840R21400 with Martin Marietta Energy Systems, Inc.     

Single run heat capacity measurements

A prior study of single-run differential scanning calorimetry that leads directly to heat capacity results is extended to low temperatures (180 K). The instrument considered was the duPont dual sample differential scanning calorimeter with auto sampler and liquid nitrogen cooling accessary-II. The major error is caused by the low temperature isotherm. After optimizing all parameters, heat capacities of selenium, aluminum, quartz, polystyrene, sodium chloride were measured between 180 to 370 K. The root mean square error of all measurements on comparison with well established adiabatic calorimetry is ±2.9%.

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Zusammenfassung In einer vorangehenden Untersuchung wurde single-run DSC zur direkten Ermittlung von WÄrmekapazitÄtswerten angewendet. Diese Methode wird hier auf den niedrigen Temperaturbereich (180 K) ausgedehnt. Das benutzte GerÄt war ein duPont Doppelproben-DSCalorimeter mit Auto-Sampler und einem Flüssigstickstoff-KühlerzusatzgerÄt-II. Der grö\te Fehler wird durch die Niedrigtemperaturisotherme verursacht. Nach Optimierung aller Parameter wurden im Temperaturbereich 180–370 K die WÄrmekapazitÄten von Selen, Aluminium, Quarz, Polystyrol und Natriumchlorid gemessen. Verglichen mit der gutuntersuchten adiabatischen Kalorimetrie betrÄgt der Standardfehler aller Messungen ±2.9 %.

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On leave from the Dept. of Material Science, Fudan University, Shanghai, China.

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This work was supported by the Division of Materials Sciences, National Science Foundation, Polymers Program, Grant # DMR 8818412 and the Division of Materials Sciences, Office of Basic Energy Sciences, U. S. Department of Energy, under Contract DE-AC05-84OR21400 with Martin Marietta Energy Systems, Inc. In addition, support by the duPont Company in acquisition of the instrumentation is acknowledged.     

Performance visualization for parallel programs

Summary We describe here a set of graphical performance visualization tools that have been developed at Argonne National Laboratory for increasing one's understanding of the behavior of parallel programsThis work was supported by the Applied Mathematical Sciences subprogram of the Office of Energy Research, U.S. Department of Energy, under contract W-31-109-Eng-38     

A parallel version of ARGOS: A distributed memory model for shared memory UNIX computers

Summary A distributed memory programming model was used in a fully parallel implementation of theab initio integral evaluation program ARGOS (R. Pitzer (1973)J. Chem. Phys. 58:3111), on shared memory UNIX computers. The method used is applicable to many similar problems, including derivative integral evaluation. Only a few lines of the existing sequential FORTRAN source required modification. Initial timings on several multi-processor computers are presented. A simplified version of the programming tool used is also presented, and general consideration is given to the parallel implementation of quantum chemistry algorithms.Work performed at Argonne National Laboratory under the auspices of the Division of Chemical Sciences, Office of Basic Energy Sciences, U.S. Department of Energy under contract W-31-109-Eng-38. Pacific Northwest Laboratory is operated for the U.S. Department of Energy by Battelle Memorial Institute under contract DE-AC06-76RLO 1830     

An efficient implementation of the direct-SCF algorithm on parallel computer architectures

Summary The development and implementation of a parallel direct self consistent field (SCF) Hartree-Fock algorithm, with gradients and random phase approximation solutions is presented. Important details of the structure of the parallel version of DISCO and preliminary results for calculations using the Concurrent Supercomputing Consortium Intel Touchstone Delta parallel computer system are reported. The data show that the algorithms are efficiently parallelized and that throughput of a one processor CRAY X-MP is reached with about 16 nodes on the Delta. The data also indicate sequential code which was not a bottleneck on traditional supercomputers, can become time critical on parallel computers.This work was performed under the auspices of the Office of Basic Energy Sciences, Division of Chemical Sciences, U.S. Department of Energy, under contract DE-AC06-76RLO 1830 for Pacific Northwest Laboratory which is operated by Battelle Memorial Institute for the U.S. Department of Energy.     

Stabilization of divalent californium in crystalline strontium tetraborate

The divalent oxidation state of californium (Cf) has been stabilized in crystalline SrB₄O₇. The ability to generate this less-stable oxidation state in an oxide matrix is significant. Factors promoting this stabilization have been determined. Access to this divalent state and those of many other lanthanide and actinide elements via a rather straightforward laboratory procedure now facilitates their study and characterization.Research sponsored by the Division of Chemical Sciences, Office of Basic Energy Sciences, U.S. Department of Energy under grant DE-FG05-88ER13865 to the University of Tennessee, Knoxville and contract DE-AC05-84OR21400 with Martin Marietta Energy Systems, Inc.     

Neural network inversion of the Tarasov function used for the computation of polymer heat capacities

The neural network method is trained using back propagation with a series of heat capacities (C _v) in the temperature range 10 to 200 K for the skeletal vibration of 36 linear macromolecules. The trained network could then accurately extract both parameters of the Tarasov function (₁ and ₃) from heat capacities of three computed test cases and a set of experimental measurements for polyethylene. The neural network method offers a major improvement in handling heat capacity data.

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Zusammenfassung Die Neural-Network Methode wird zur Bestimmung der Wärme kapacität (C _v) von 36 linearen Makromolekül-Gerüstschwingungen im Temperaturbereich 10–200 K angewendet. Das präparierte System ist dann in der Lage, bei drei rechnerischen Testfällen und einer Reihe von experimentellen Messungen an Polyethylen aus den Wärmekapazitäten beide Parameter der Tarasov-Funktion (₁ und ₂) genau zu ermitteln. Die Neural-Network Methode stellt eine wesentliche Verbesserung zur Handhabung von Wärmekapazitätsangaben dar.

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Research sponsored by the Division of Materials Sciences, Office of Basic Energy Sciences, U.S. Department of Energy, under contract DE-AC05-84 OR21400 with Martin Marietta Energy Systems, Inc. and the Materials Research Division of the National Science Foundation, Polymers Program Grant # DMR-88-18412     

Monte Carlo study of electron correlation functions for small molecules

A study is made of electron-electron correlation functions for use in trial wave functions for small molecules. New forms are proposed that have only a few variational parameters, and these parameters have physical meanings that are easily discerned. Total energies for H₂, LiH and Li₂ computed using these correlation functions are presented, and comparison is made with previous forms, including the Jastrow-Pade form often used in Monte Carlo studies. We further treat the possibility that correlation depends not only on the separation of a pair of electrons but also on the location of the electron pair relative to the nuclei — indicative of a density-dependent or many body correlation effect. Our results indicate that such a many-body correlation effect is weakly present.This work was supported by the Director, Office of Energy Research, Office of Basic Energy Sciences, Chemical Sciences Division of the U.S. Department of Energy under Contract No. DE-AC03-76SF00098     

On the use of computational neural networks for the prediction of polymer properties

A general purpose computational paradigm using neural networks is shown to be capable of efficiently predicting properties of polymeric compounds based on the structure and composition of the monomeric repeat unit. Results are discussed for the prediction of the heat capacity, glass transition temperature, melting temperature, change in the heat capacity at the glass transition temperature, degradation temperature, tensile strength and modulus, ultimate elongation, and compressive strength for 11 different families of polymers. The accuracies of the predictions range from 1–13% average absolute error. The worst results were obtained for the mechanical properties (tensile strength and modulus: 13%, 7% elongation: 12%, and compressive strength: 8%) and the best results for the thermal properties (heat capacity, glass transition temperature, and melting point: <4%). A simple modification to the overall method is devised to better take into account the fact that the mechanical properties are experimentally determined with a fairly large range (due to variability in measurement procedures and especially the sample). This modification treats the bounds on the range for the mechanical properties as complex numbers (complex, modular neural networks) and leads to more rapid optimization with a smaller average error (reduced by 3%).Dedicated to Professor Bernhard Wunderlich on the occasion of his 65th birthdayThis research was sponsored by the Division of Materials Sciences, Office of Basic Energy Sciences, U.S. Department of Energy, under Contract No. DE-AC05-84R21400 with Lockheed Martin Energy Systems, Inc. We would like to express our gratitude for the continued collaboration, support, and interest of Prof. Wunderlich in our research. We would also like to thank participants of the 1st DOE Workshop on Applications of Neural Networks in Materials Sciences for useful discussion on materials properties and neural networks.     

On the role of parallel architecture supercomputers in time-dependent approaches to quantum scattering

Summary Results of our initial study of the use of parallel architecture super-computers in solving time-dependent quantum scattering equations are reported. The specific equations solved are obtained from the time-dependent Lippmann-Schwinger integral equation by means of a quadrature approximation to the time integral. This leads to a modified Cayley transform algorithm in which the primary computational step is a matrix-vector multiplication. Implementation has been carried out both for the MasPar MP-1 and the NCUBE 6400 parallel machines. The codes are written in a modular form that greatly facilitates porting from one machine architecture to another. Both parallel machines prove to be more powerful for this application than the serial architecture VAX 8650. Specific analysis of machine performance is given.Ames Laboratory is operated for the U.S. Department of Energy by Iowa State University under Contract No. 2-7405-ENG-82. This research was supported by the Division of Chemical Sciences and Applied Mathematical Sciences, Office of Basic Energy SciencesR.A. Welch Predoctoral Fellow under R.A. Welch Foundation Grant E-608Supported in part under National Science Foundation Grant CHE89-07429     

Fabrication of 50-mg252Cf neutron sources for the FDA activation analysis facility

The Transuranium Processing Plant (TPP) at the Oak Ridge National Laboratory (ORNL) has been requested by the Food and Drug Administration (FDA) to furnish 200 mg of²⁵²Cf for use in their new activation analysis facility. This paper discusses the procedure to be employed in fabricating the californium into four neutron sources, each containing a nominal 50-mg of²⁵²Cf. The completed neutron sources will be assayed using a precision fast-neutron counter, decontaminated and loaded into a concreete-shielded shipping container weighing 10.7 Mg for shipment to the FDA facility located at Howard University in Washington, D. C.Research sponsored by the Office of Basic Energy Sciences, U. S. Department of Energy, under contract DE-AC05-840R21400 with Martin Marietta Energy Systems, Inc.     

Cyclotron isotopes and radiopharmaceuticals XXVI. A carrier-free separation of77Br from se

A silver chloride co-precipitation and ion exchange separation method is described for the carrier-free isolation of⁷⁷Br bromide from isotopically enriched⁷⁷Se targets following dissolution of the irradiated⁷⁷Se in nitric acid. A cation exchange procedure has been devised to remove the silver and yield a dilute hydrochloric acid solution containing ≈90% of the precipitated⁷⁷Br as bromide. The radiochemical and chemical composition of several preparations have been analyzed. A method for the quantitative recovery of the isotopically enriched selenium is described. Research carried out under contract with the U.S. Department of Energy and supported by its Division of Basic Energy Sciences. Supported in part by the Massachusetts Heart Association and by NIH Grant No. HL 18487-01. All inquiries should be directed to R. M. Lambrecht. For earlier papers in this series see Ref.¹²     

The enegry idea drought

Research sponsored by the Office of Energy Research, U.S. Department of Energy, under Contract DE-AC05-840R21400 with Martin Marietta Energy Systems, Inc.     

Fortieth Anniversary of the New Brunswick Laboratory

Research sponsored by the Office of Energy Research, U.S. Department of Energy, under Contract DE-AC05-84OR21400 with Martin Marietta Energy Systems, Inc.     

Non-NAA bomb Detection

Research sponsored by the Office of Energy Research, U.S. Department of Energy, under contract DE-AC05-840R21400 with Martin Marietta Energy Systems, Inc.