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Differential scanning calorimetry and thermogravimetric analysis combination for thermochemical kinetic measurements, matching analytical and experimental curves for data accuracy
Analysis of the differential kinetic energy per nucleon spectra of galactic cosmic-ray He, Li, Be, B, C, N, and O with the University of Chicago cosmic-ray telescope on board the IMP-5 satellite in 1969-1970. The ratios He/(C + N + O) and (Li + Be + B)/(C + N + O) obtained from these spectra are found, within errors of about 20%, to be energy-independent over the energy range 10-1000 MeV per nucleon, and equal to about 15 and about 0.25, respectively. These results are compared with discrepancies existing among other measurements of these ratios, and with predictions of a class of steady-state models of cosmic-ray propagation which assume that Li, Be, and B are absent in cosmic-ray sources. The best fits for the present measurements are obtained for models with a source spectrum in the form of a power law in total energy per nucleon, but even these fits are outside the error limits at energies below 100 MeV per nucleon. In the context of the propagation models examined, it is concluded that the observed behavior of these ratios requires an additional mechanism operative at low energies. This mechanism may be adiabatic deceleration of cosmic rays in the solar wind. In order for this mechanism to be adiabatic deceleration, the deceleration in 1969 must have been such that particles observed at 10 to 20 MeV per nucleon had energies greater than 100 to 150 MeV per nucleon in the local interstellar space.
Two dimensionality-reducing approximations, the j sub z-conserving coupled states (sometimes called the centrifugal decoupling) method and the effective potential method, were applied to collision calculations of He with CO and with HCl. The coupled states method was found to be sensitive to the interpretation of the centrifugal angular momentum quantum number in the body-fixed frame, but the choice leading to the original McGuire-Kouri expression for the scattering amplitude - and to the simplest formulas - proved to be quite successful in reproducing differential and gas kinetic cross sections. The computationally cheaper effective potential method was much less accurate.
The evolution of an initially totally molten magma ocean is constrained on the basis of analysis of various physical problems in the magma ocean. First of all an equilibrium thermodynamics of the magma ocean is developed in the melting temperature range. The equilibrium thermodynamical parameters are found as functions only of temperature and pressure and are used in the subsequent models of kinetics and convection. Kinematic processes determine the crystal size and also determine a non-equilibrium thermodynamics of the system. Rheology controls all dynamical regimes of the magma ocean. The thermal convection models for different rheological laws are developed for both the laminar convection and for turbulent convection in the case of equilibrium thermodynamics of the multiphase system. The evolution is estimated on the basis of all the above analysis.
A nuclear morphometric assay for preosteoblasts is introduced as a cell-kinetic technique, applicable to routine histological preparations of mineralized tissue. Because this method is a morphological marker for osteoblast precursor cell differentiation, it provides a new dimension for determining the mechanism of osteoblast histogenesis. Osteoblast precursors of the periodontal ligament are a mixed population of progenitors, kinetically separable into two distinct groups according to nuclear size. Preosteoblasts, the immediate proliferating precursors of osteoblasts, have large nuclei (greater than 170 micrometers3) and are derived from relatively undifferentiated fibroblastlike cells, which have smaller nuclei (less than 80 micrometers3). Increase in nuclear volume, during G1 phase of the cell cycle, is apparently a morphological manifestation of change in genomic expression. This key event in preosteoblast differentiation is related to mechanical stress/strain and may be an important rate-limiting step in osteoblast histogenesis.
The differential equations governing the transient response of a one-dimensional ablative thermal protection system undergoing stagnation ablation are derived. These equations are for thermal nonequilibrium effects between the pyrolysis gases and the char layer and kinetically controlled chemical reactions and mass transfer between the pyrolysis gases and the char layer. The boundary conditions are written for the particular case of stagnation heating with surface removal by oxidation or sublimation and pyrolysis of the uncharred layer occurring in a plane. The governing equations and boundary conditions are solved numerically using the modified implicit method (Crank-Nicolson method). Numerical results are compared with exact solutions for a number of simplified cases. The comparison is favorable in each instance.
Crystallization kinetics of a barium calcium aluminosilicate glass (BCAS), a sealant material for planar solid oxide fuel cells, have been investigated by differential thermal analysis (DTA). From variation of DTA peak maximum temperature with heating rate, the activation energy for glass crystallization was calculated to be 259 kJ/mol. Development of crystalline phases on thermal treatments of the glass at various temperatures has been followed by powder x-ray diffraction. Microstructure and chemical composition of the crystalline phases were investigated by scanning electron microscopy and energy dispersive spectroscopic (EDS) analysis. BaSiO3 and hexacelsian (BaAl2Si2O8) were the primary crystalline phases whereas monoclinic celsian (BaAl2Si2O8) and (Ba(x), Ca(y))SiO4 were also detected as minor phases. Needle-shaped BaSiO3 crystals are formed first, followed by the formation of other phases at longer times of heat treatments. The glass does not fully crystallize even after long term heat treatments at 750 to 900 C.
A study was made on the cure kinetics of an epoxy neat-resin (Narmco 5208) using Differential Scanning Calorimetry (DSC). Two interrelated analytical methods were applied to dynamic DSC data for evaluating the kinetic parameters, such as activation energy, E, the order of reaction, n, and the total heat of polymerization (or crosslinking), delta H sub t. The first method was proposed by Ellerstein (1968), and uses a thorough differential-integral analysis of a single DSC curve to evaluate the kinetic parameters. The second method was proposed by Kissinger (1957), and uses multiple DSC curves obtained at various heating rates to evaluate E regardless of n. Kinetic analysis of Narmco 5208 epoxy resin showed that the reaction order, n, is substantially affected by the rate of heating; i.e., n is approximately 2 at slow scan rates but is reduced to 1.5 at higher scan rates. The activation energy, E, is not affected by the scan rate, and the average value of E is 25.6 + or - 1.8 kcal/mole.
A rocket engine igniter has been created that uses a pneumatically driven hammer that, by specialized geometry, is induced into an oscillatory state that can be used to either repeatedly impact a piezoelectric crystal with sufficient force to generate a spark capable of initiating combustion, or can be used with any other system capable of generating a spark from direct oscillatory motion. This innovation uses the energy of flowing gaseous propellant, which by means of pressure differentials and kinetic motion, causes a hammer object to oscillate. The concept works by mass flows being induced through orifices on both sides of a cylindrical tube with one or more vent paths. As the mass flow enters the chamber, the pressure differential is caused because the hammer object is supplied with flow on one side and the other side is opened with access to the vent path. The object then crosses the vent opening and begins to slow because the pressure differential across the ball reverses due to the geometry in the tube. Eventually, the object stops because of the increasing pressure differential on the object until all of the kinetic energy has been transferred to the gas via compression. This is the point where the object reverses direction because of the pressure differential. This behavior excites a piezoelectric crystal via direct impact from the hammer object. The hammer strikes a piezoelectric crystal, then reverses direction, and the resultant high voltage created from the crystal is transferred via an electrode to a spark gap in the ignition zone, thereby providing a spark to ignite the engine. Magnets, or other retention methods, might be employed to favorably position the hammer object prior to start, but are not necessary to maintain the oscillatory behavior. Various manifestations of the igniter have been developed and tested to improve device efficiency, and some improved designs are capable of operation at gas flow rates of a fraction of a gram per second (0.001 lb/s) and pressure drops on the order of 30 to 50 kilopascal (a few psi). An analytical model has been created and tested in conjunction with a precisely calibrated reference model. The analytical model accurately captures the overall behavior of this innovation. The model is a simple "volume-orifice" concept, with each chamber considered a single temperature and pressure "node" connected to adjacent nodes, or to vent paths through flow control orifices. Mass and energy balances are applied to each node, with gas flow predicted using simple compressible flow equations.
The differential kinetic-energy spectra of cosmic-ray nuclei in the charge range from 4 to 28 are determined using data obtained from a high-altitude balloonborne detector. The data are derived from the response of an acrylic plastic Cerenkov counter and cover the kinetic-energy range from 400 to 2100 MeV/amu. A Cerenkov pulse-height histogram is obtained for each charge, and the kinetic-energy spectra are derived by means of a formal mathematical deconvolution of these histograms. Results of the deconvolution calculation extrapolated to the top of the atmosphere are presented for the most abundant nuclei; it is found that the spectra are not amenable to representation by spectral indices, so the relative spectra of the different elements are compared by evaluating the charge ratios as a function of energy. The results show that secondary/primary ratios decrease with increasing energy, while primary/primary ratios are constant for Z of 6 to 10 and 14 to 26 but vary for Z of 10 to 14. It is concluded that the data seem to indicate more than one cosmic-ray source region.
The one particle distribution function f on the scale of the bounce motion of particles in a magnetic field B is considered. The Vlasov equation is expanded through O(epsilon) in the adiabatic parameter which is the ratio of particle gyroradius to scale length of the magnetic field. Because f is directly proportional to particle flux differential in kinetic energy and solid angle, f is in principle measurable in space experiments, and the analysis is tailored to be explicitly applicable to space problems. To O(1), f is gyrotropic; its first velocity moment is (if non-vanishing) parallel to B, and hence macroscopic parallel flow is included in this term. The O(epsilon) contribution is non-gyrotropic and macroscopic flow parallel to B plus additional parallel flow results from these terms. The degree of non-gyrotropy and the amount of cross-field macroscopic flow depend on the perpendicular component of the electric field, on curvature and shear in the magnetic field, and on the spatial gradient, pitch angle derivative, and speed derivative of the lowest order distribution function.
Assuming time stationarity of the one-particle distribution function f on the scale of the bounce motion of particles in a magnetic field, the paper expands the Vlasov equation through O(epsilon) in the adiabatic parameter epsilon, which is the ratio of particle gyroradius to scale length of the magnetic field. Since f is directly proportional to particle flux differential in kinetic energy and solid angle, f is in principle measurable in space experiments, and the present analysis is tailored to be explicitly applicable to space problems. It is shown that the usual expression for the electric field which produces plasma corotation in an axisymmetric system such as a dipole also holds for any nonaxisymmetric but rigidly rotating magnetic field pattern, provided the observed magnetic field is used in place of the dipole field. The analysis is applied to the electric field in a rigidly corotating magnetosphere.
Annealing in nitrogen below the glass transition temperature T(g) is found to affect the matrix-dominated physical properties of postcured, (+ and -45)2s specimens of Thornel 300 carbon fiber/Fiberite 934 epoxy composite as well as neat Fiberite 934 epoxy resin. The damping behavior, stress-relaxation rate and enthalpic state of the matrix material are found to decrease as functions of annealing time. The time-dependent change in physical properties is explained on the basis of free-volume collapse related to the physical aging of the nonequilibrium glassy network of epoxy. Such physical aging in network epoxy has been demonstrated to be thermoreversible through the monitoring of its kinetics by differential scanning calorimetry, stress relaxation tests, and dynamic mechanical analysis.
Mechanically isolated mesophyll cells of Zinnia elegans L. cv Envy differentiate to tracheary elements when cultured in inductive medium containing 0.5 micromolar alpha-naphthaleneacetic acid and 0.5 micromolar benzyladenine. The cells do not differentiate when cultured in medium in which the concentration of auxin and/or cytokinin has been reduced to 0.005 micromolar. Cells require an initial 24-hour exposure to inductive cytokinin and 56-hour exposure to inductive auxin for differentiation at 72 hours of culture. Freshly isolated Zinnia cells can be maintained in medium having low concentrations of both auxin and cytokinin for only 1 day without significant loss of potential to differentiate upon transfer to inductive medium. Initial culture for up to 2 days in medium having high auxin and low cytokinin, or low auxin and high cytokinin, allows full differentiation on the third day after transfer to inductive medium and potentiates the early differentiation of some cells.
Conventional algorithms for the numerical integration of ordinary differential equations (ODEs) are based on the use of polynomial functions as interpolants. However, the exact solutions of stiff ODEs behave like decaying exponential functions, which are poorly approximated by polynomials. An obvious choice of interpolant are the exponential functions themselves, or their low-order diagonal Pade (rational function) approximants. A number of explicit, A-stable, integration algorithms were derived from the use of a three-parameter exponential function as interpolant, and their relationship to low-order, polynomial-based and rational-function-based implicit and explicit methods were shown by examining their low-order diagonal Pade approximants. A robust implicit formula was derived by exponential fitting the trapezoidal rule. Application of these algorithms to integration of the ODEs governing homogenous, gas-phase chemical kinetics was demonstrated in a developmental code CREK1D, which compares favorably with the Gear-Hindmarsh code LSODE in spite of the use of a primitive stepsize control strategy.
Error growth and stability analyzed for numerical integration of differential equations in chemical kinetics
The cascade of kinetic energy from macro- through mesoscales is studied on the basis of a nested grid system used to solve a set of nonlinear differential equations. The kinetic energy cascade and the concentration of vorticity through the hydrodynamic spectrum provide a means for predicting the location and intensity of severe weather from large-scale data sets. A mechanism described by the surface pressure tendency equation proves to be important in explaining how initial middle-tropospheric mass-momentum imbalances alter the low-level pressure field.
This research involves the manipulation of the root-zone water potential for the purposes of discriminating the rate limiting step in the inorganic nutrient uptake mechanism utilized by higher plants. This reaction sequence includes the pathways controlled by the root-zone conditions such as water tension and gradient concentrations. Furthermore, plant based control mechanisms dictated by various protein productions are differentiated as well. For the nutrients limited by the environmental availability, the kinetics were modeled using convection and diffusion equations. Alternatively, for the nutrients dependent upon enzyme manipulations, the uptakes are modeled using Michaelis-Menten kinetics. In order to differentiate between these various mechanistic steps, an experimental apparatus known as the Porous Ceramic Tube - Nutrient Delivery System (PCT-NDS) was used. Manipulation of the applied suction pressure circulating a nutrient solution through this system imposes a change in the matric component of the water potential. This compensates for the different osmotic components of water potential dictated by nutrient concentration. By maintaining this control over the root-zone conditions, the rate limiting steps in the uptake of the essential nutrients into tomato plants (Lycopersicon esculentum cv. Cherry Elite) were differentiated. Results showed that the uptake of some nutrients were mass transfer limited while others were limited by the enzyme kinetics. Each of these were adequately modeled with calculations and discussions of the parameter estimations provided.