Measurement of reaction kinetics by a pressure rise method

Decomposition of urea nitrate in an initially evacuated system gave sigmoidal pressurevs. time curves. The experimental kinetic data fit the growing nuclei model with a measured enthalpy of activation of 142±12.5 kJ/mole as compared to 115±11.3 kJ/mole obtained thermogravimetrically. This higher value ofH is explained on the basis of two factors: 1) the inhibitory effect of the product gases and 2) self heating, whose extent increasedH by about 12.5 kJ/mole.

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Zusammenfassung Die Zersetzung von Harnstoffnitrat in einem anfanglich evakuierten System ergab sigmoide Druck-Zeit Kurven. Die kinetischen Versuchsangaben können einem Kernwachstums-Modell einer gemessenen Aktivierungsenthalpie von 142±12,5 kJ/mol angepaßt werden, im Vergleich zu den auf thermogravimetrischen Weg ermittelten Wert von 115±11.3 kJ/Mol. Dieser hohe Wert vonH, wird auf Grund zweier Faktoren erklärt: 1) der Hemmungseffekt der Produktgase und 2) Selbsterhitzung, deren AusmaßH um etwa 12.5 kJ/Mol erhöhte.

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Résumé La décomposition du nitrate d'urée dans un système initialement mis sous vide, donne des courbes sigmoïdales de pression en fonction du temps. Les données cinétiques expérimentales peuvent être ajustées à un modèle de grossissement de germes, avec une enthalpie d'activation mesurée de 142±12.5 kJ/mole, comparée à 115±11.3 kJ/mole obtenue par thermogravimétrie. Cette valeur plus élevée deH s'explique sur la base de deux facteurs: 1) l' effet inhibiteur des gaz produits et 2) phénomène d'autoéchauffement qui augmente la valeur deH d'environ 12.5 kJ/mole.

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. , 142+-12.5 / 115 + 11.3 /, . H : 1) 2) , 12.5 /.

     

Determination of microtacticity of poly(vinylketones) and their derivatives by NMR spectroscopies of carbon-13 and proton

Sequence distribution of atactic poly(phenylvinylketone) (PPVK) has been determined by [¹³C]-[¹H]NMR spectroscopy. Quantitative analysis of the carbonyl pattern allows resolution into pentads with intensities fitting a first order Markov process. The carbonyl pattern of highly isotactic PPVK, initiated by diethylzinc, deviates strongly from Bernoullian statistics, as in the case of highly isotactic polymethylvinylketone (PMVK). For n-butyl-lithium initiated poly(isopropenylphenylvinylketone) (PIPK), the carbonyl pattern practically agrees with a Bernoullian distribution. Atactic PMVK, analyzed from the methylene and the carbonyl pattern in [¹³C] or [¹H]NMR, shows that the polymerization process is purely Bernoullian and quite different from that for poly(isopropenylmethylketone). Except for poly(methylallylalcohol) for which the tacticity can be determined, the resolution is too poor to allow a quantitative sequence distribution of poly(allylalcohols) or poly(allyltrifluoroacetates). [¹H] and [¹⁹F]NMR spectroscopies of these compounds do not give better results.     

On Nonexistence of type II blowup for a supercritical nonlinear heat equation

In this paper we study blowup of radially symmetric solutions of the nonlinear heat equation u_t = Δu + |u|^p?1u either on ?^N or on a finite ball under the Dirichlet boundary conditions. We assume that the exponent p is supercritical in the Sobolev sense, that is, We prove that if p_s < p < p^*, then blowup is always of type I, where p^* is a certain (explicitly given) positive number. More precisely, the rate of blowup in the L^∞ norm is always the same as that for the corresponding ODE dv/dt = |v|^p?1v. Because it is known that “type II” blowup (or, equivalently, “fast blowup”) can occur if p > p^*, the above range of exponent p is optimal. We will also derive various fundamental estimates for blowup that hold for any p > p_s and regardless of type of blowup. Among other things we classify local profiles of type I and type II blowups in the rescaled coordinates. We then establish useful estimates for the so‐called incomplete blowup, which reveal that incomplete blowup solutions belong to nice function spaces even after the blowup time. © 2004 Wiley Periodicals, Inc.     

On the 1/3–2/3 Conjecture

Let (P, ≤) be a finite poset (partially ordered set), where P has cardinality n. Consider linear extensions of P as permutations x₁x₂?x_n in one-line notation. For distinct elements x, y ∈ P, we define ?(x ? y) to be the proportion of linear extensions of P in which x comes before y. For \(0\leq \alpha \leq \frac {1}{2}\), we say (x, y) is an α-balanced pair if α ≤ ?(x ? y) ≤?1 ? α. The 1/3–2/3 Conjecture states that every finite partially ordered set which is not a chain has a 1/3-balanced pair. We make progress on this conjecture by showing that it holds for certain families of posets. These include lattices such as the Boolean, set partition, and subspace lattices; partial orders that arise from a Young diagram; and some partial orders of dimension 2. We also consider various posets which satisfy the stronger condition of having a 1/2-balanced pair. For example, this happens when the poset has an automorphism with a cycle of length 2. Various questions for future research are posed.     

Random laser action in bovine semen

Experiments using bovine semen reveal that the addition of a high-gain water soluble dye results in random laser action when excited by a Q-switched, frequency doubled, Nd:Yag laser. The data shows that the linewidth collapse of the emission is correlated to the sperm count of the individual samples, potentially making this a rapid, low sample volume approach to count determination.     

Beam-helicity asymmetry in photon and pion electroproduction in the Δ(1232)-resonance region at Q2 = 0.35(GeV/c)2

The beam-helicity asymmetry has been measured simultaneously for the reactions p→epγ and p→epπ ⁰ in the Δ(1232)-resonance region at Q ² = 0.35(GeV/c)². The experiment was performed at MAMI with a longitudinally polarized beam and an out-of-plane detection of the proton. The results are compared with calculations based on dispersion relations for virtual Compton scattering and with the MAID model for pion electroproduction. There is an overall good agreement between experiment and theoretical calculations. The remaining discrepancies may be ascribed to an imperfect parametrization of some γ ^(*) N→πN multipoles, mainly contributing to the non-resonant background. The beam-helicity asymmetry in both channels (γ and π ⁰) shows a good sensitivity to these multipoles and should allow future improvement in their parametrization.     

Radiative transmission of lepton flavor hierarchies

We discuss a one loop model for neutrino masses which leads to a seesaw-like formula with the difference that the charged lepton masses replace the unknown Dirac mass matrix present in the usual seesaw case. This is a considerable reduction of parameters in the neutrino sector and predicts a strong hierarchical pattern in the right handed neutrino mass matrix that is easily derived from a U(1)_H family symmetry. The model is based on the left–right gauge group with an additional Z₄ discrete symmetry which gives vanishing neutrino Dirac masses and finite Majorana masses arising at the one loop level. Furthermore, it is one of the few models that naturally allow for large (but not necessarily maximal) mixing angles in the lepton sector. A generalization of the model to the quark sector requires three iso-spin singlet vector-like down type quarks, as in E₆. The model predicts an inert doublet type scalar dark matter.     

Second-order time evolution of PN equations for radiation transport

Using polynomials to represent the angular variation of the radiation intensity is usually referred to as the P_N or spherical harmonics method. For infinite order, the representation is an exact solution of the radiation transport solution. For finite N, in some physical situations there are oscillations in the solution that can make the radiation energy density be negative. For small N, the oscillations may be large enough to force the material temperature to numerically have non-physical negative values. The second-order time evolution algorithm presented here allows for more accurate solutions with larger time steps; however, it also can resolve the negativities that first-order time solutions smear out. Therefore, artificial scattering is studied to see how it can be used to decrease the oscillations in low-order solutions and prevent negativities. Small amounts of arbitrary, non-physical scattering can significantly improve the accuracy of the solution to test problems. Flux-limited diffusion solutions can also be improved by including artificial scattering. One- and two-dimensional test results are presented.     

An Isserlis’ Theorem for Mixed Gaussian Variables: Application to the Auto-Bispectral Density

This work derives a version of Isserlis’ theorem for the specific case of four mixed-Gaussian random variables. The theorem is then used to derive an expression for the auto-bispectral density for quadratically nonlinear systems driven with mixed-Gaussian iid noise. C.C. Olson is a NRC Postdoctoral Research Associate.