Effect of X-rays on the surface composition of polyphosphazene: X-ray photoelectron spectroscopic study

X-ray photoelectron spectroscopy has been employed for in situ investigation of the effect of MgK _α X-rays with an energy of characteristic irradiation of 1253.6 eV on the composition of the surface of poly[bis(trifluoroethoxy)phosphazene]. An X-ray source is applied to simultaneously irradiate the surface and to generate photoelectrons. An increase in irradiation time and X-ray source power leads to a change in the surface elemental composition and causes the appearance of new states of carbon and nitrogen atoms.     

Thermal stability of alkylbiphenyls in the subcritical,critical, and supercritical states

The kinetics of gas-phase thermal transformations of 4-methyl-, 4,4′-dimethyl-, 4-tert-butyl-, and 4,4′-di-tert-butylbiphenyls was studied over the temperature ranges 813–848, 733–793, 703–763, and 703–763 K, respectively. Competition between cracking and alkyl substituent isomerization at aromatic nuclei of the initial substance and products formed was observed for tert-butylbiphenyls. The kinetic parameters of the overall transformation of alkylbiphenyls (ABPs) were determined. Recommendations for the determination of the critical temperatures of ABPs, their synthesis, processing, and use of articles with structural fragments in molecules identical to those studied in this work were given. It was found experimentally that 2-, 3-, and 4-methylbiphenyls and their mixtures with toluene were thermally unstable over the whole composition range at critical temperatures (600–780 K).     

Modified scattering for the critical nonlinear Schrödinger equation

We consider the nonlinear Schrödinger equation

$i{u}_t+\mathrm{\Delta }u=\lambda |u{|}^{\frac{2}{N}}u$

in all dimensions $N\ge 1$, where $\lambda \in \mathbb{C}$ and $?\lambda \le 0$. We construct a class of initial values for which the corresponding solution is global and decays as $t\to \infty$, like $t^{?\frac{N}{2}}$ if $?\lambda =0$ and like ${(t\log ?t)}^{?\frac{N}{2}}$ if $?\lambda <0$. Moreover, we give an asymptotic expansion of those solutions as $t\to \infty$. We construct solutions that do not vanish, so as to avoid any issue related to the lack of regularity of the nonlinearity at $u=0$. To study the asymptotic behavior, we apply the pseudo-conformal transformation and estimate the solutions by allowing a certain growth of the Sobolev norms which depends on the order of regularity through a cascade of exponents.     

Damped wave equation with a critical nonlinearity

We study large time asymptotics of small solutions to the Cauchy problem for nonlinear damped wave equations with a critical nonlinearity

where 0,$"> and space dimensions . Assume that the initial data

where \frac{n}{2},$"> weighted Sobolev spaces are

Also we suppose that

0,\int u_{0}\left( x\right) dx>0, \end{displaymath}">

where

Then we prove that there exists a positive such that the Cauchy problem above has a unique global solution satisfying the time decay property

for all 0,$"> where

     

The step-decay problem for the Korteweg-de Vries-Burgers equation

M. V. Lomonosov Moscow State University. Translated from Funktsional'nyi Analiz i Ego Prilozheniya, Vol. 25, No. 1, pp. 21–32, January–March, 1991.     

Organosilicon fluoro-containing polymer brushes based on epoxy matrix: XPS analysis

Russian Chemical Bulletin - Using the XPS method the possibility of the formation of fluoro-containing polymer brushes based on organofluorosilicon compounds and epoxy matrix has been investigated....     

Heat transfer in a flow of gas mixture with low Prandtl number in triangular channels

We investigated heat transfer in a channel with a triangular cross-section. The working medium is a helium–xenon mixture with a low Prandtl number. This channel configuration corresponds to one of possible cases of fuel cells layout in a gas-cooled nuclear reactor. New experimental data on heat transfer in helium–xenon mixtures were obtained. Results of numerical modeling were compared with the experimental data and the known empirical correlations.     

Photoinduced charge transfer reaction at surfaces. III. (HF)2...Na n/LiF(001)+hnu(640 nm)-->HFF-Na n +/LiF(001)+H(g)

A sub-monolayer of atomic sodium was deposited on a LiF(001) surface at 40 K. The adsorbed sodium exists at the surface as single atoms and clusters. The surface was dosed with 1 L of HF, to form adsorbed (HF)2...Na(n) (n=1,2,3,...) complexes, which were then irradiated by 640 nm laser light, to induce charge-transfer reaction. The reaction-product atomic H(g) was observed leaving the surface by two-color Rydberg-atom time-of-flight (TOF) spectroscopy. The TOF spectrum of the desorbed H atoms contained two components; a "fast" component with a maximum at approximately 0.85 eV, and a "slow" component with a maximum at 0.45 eV. These two components were attributed to photoreaction on adsorbed single atoms and clusters of sodium, respectively. The fast component exhibited a structure (48+/-17 meV spacing) near the high-energy end of spectrum. This structure was attributed to vibration of NaFHF photoproduct residing on the surface. The cross section of the harpooning event in the Na...(HF)2 adsorbed complex was determined as (9.1+/-2.0)x10(-19) cm(2). To interpret the experimental vibrational structure and the relative energies of the fast and slow components of the TOF spectrum, high-level ab initio calculations were performed for reactants Na(n)...(HF)(m) (n,m=1,2) and reaction products Na(n)F(m)H(m-1). The calculated NaF-HF and Na-Na(HF)(2) bond dissociation energies indicated that photoexcitation of the precursor complexes led not only to ejection of H atoms, but also to dissociation of the Na(n)...(HF)(2) (n=1,2) species through cleavage of the NaF-HF and Na-Na(HF)(2) bonds.