On the Existence of Focal Points near Closed Geodesics on Surfaces

We establish some criteria for the existence or nonexistence of focal points near closed geodesics on surfaces. These criteria are in terms of the curvature of the manifold along the closed geodesic and the average values of the partial derivatives of the curvature in the direction perpendicular to the geodesic. Our criteria lead to a new family of examples of surfaces with no focal points. We also show that if S is a compact surface with no focal points and an inequality relating the curvature of the surface to the curvature of the horocycles holds, then the horocycles (considered as curves in S) are uniformly C ^2+Lipschitz.     

A Raman technique applicable for the analysis of the working principle of promoters and inhibitors of gas hydrate formation

We report a Raman technique applicable for the in situ analysis of the development of hydrogen bonds in the liquid water‐rich phase just before the onset of gas hydrate formation. Herewith, the phase transition as well as the working principle of hydrate formation inhibitors and promoters can be analyzed. © 2015 The Authors. Journal of Raman Spectroscopy published by John Wiley & Sons Ltd.     

"Compression-only" behavior: a second-order nonlinear response of ultrasound contrast agent microbubbles

Oscillating phospholipid-coated ultrasound contrast agent microbubbles display a so-called "compression-only" behavior, where it is observed that the bubbles compress efficiently while their expansion is suppressed. Here, a theoretical understanding of the source of this nonlinear behavior is provided through a weakly nonlinear analysis of the shell buckling model proposed by Marmottant et al. [J. Acoust. Soc. Am. 118, 3499-3505 (2005)]. It is shown that the radial dynamics of the bubble can be considered as a superposition of a linear response at the fundamental driving frequency and a second-order nonlinear low-frequency response that describes the negative offset of the mean bubble radius. The analytical solution deduced from the weakly nonlinear analysis shows that the compression-only behavior results from a rapid change of the shell elasticity with bubble radius. In addition, the radial dynamics of single phospholipid-coated microbubbles was recorded as a function of both the amplitude and the frequency of the driving pressure pulse. The comparison between the experimental data and the theory shows that the magnitude of compression-only behavior is mainly determined by the initial phospholipids concentration on the bubble surface, which slightly varies from bubble to bubble.     

Beantwortung einer Frage von J. Arason und A. Pfister als Korollar eines Ergebnisses von L. Bröcker

Ohne Zusammenfassung     

Quantum calculation of ro-vibrational states: methodology and DOCl application results

An improved Lanczos eigenvalue analysis method has been developed to compute the bound ro-vibrational states for the DOCl system at a total angular momentum of J = 0 and J = 30. In this method, the error norm is used to identify all the true eigenvalues, using the Lanczos algorithm without re-orthogonalization. For ro-vibrational spectroscopy calculations, the comparisons among experimental results, the exact quantum mechanical calculations, and the widely used approximate adiabatic rotation method have been made for J = 30. For J = 0, the density of states (DOS) in both the bound and unimolecular dissociation regime have been computed, whereas for the J = 30 case, only the DOS in the lower portion of the bound spectrum has been reported, because of substantial computational tasks.     

State-to-state reaction probabilities for the H+O2(v,j)-->O+OH(v',j') reaction on three potential energy surfaces

We report state-to-state and total reaction probabilities for J=0 and total reaction probabilities for J=2 and 4 for the title reaction, both for ground-state and initially rovibrationally excited reactants. The results for three different potential energy surfaces are compared and contrasted. The potential energy surfaces employed are the DMBE IV surface by Pastrana et al. [J. Phys. Chem. 94, 8073 (1990)], the surface by Troe and Ushakov (TU) [J. Chem. Phys. 115, 3621 (2001)], and the new XXZLG ab initio surface by Xu et al. [J. Chem. Phys. 122, 244305 (2005)]. Our results show that the total reaction probabilities from both the TU and XXZLG surfaces are much smaller in magnitude for collision energies above 1.2 eV compared to the DMBE IV surface. The three surfaces also show different behavior with regards to the effect of initial state excitation. The reactivity is increased on the XXZLG and the TU surfaces and decreased on the DMBE IV surface. Vibrational and rotational product state distributions for the XXZLG and the DMBE IV surface show different behaviors for both types of distributions. Our results show that for energies above 1.25 eV the dynamics on the DMBE IV surface are not statistical. However, there is also evidence that the dynamics on the XXZLG surface are not purely statistical for energies above the onset of the first excited product vibrational state v'=1. The magnitude of the total reaction probability is decreased for J>0 for the DMBE IV and the XXZLG surfaces for ground-state reactants. However, for initially rovibrationally excited reactants, the total reaction probability does not decrease as expected for both surfaces. As a result the total cross section averaged over all Boltzmann accessible rotational states may well be larger than the cross section reported in the literature for j=1.     

Isolation and structure elucidation of two new cytotoxic metabolites from red yeast rice

In this study, 10 already described secondary metabolites and 2 unknown metabolites were identified in an extract of Monascus purpureus by high-performance liquid chromatography-diode array detection. The unknown metabolites were isolated and their chemical structures were elucidated. The new metabolites possess the molecular formulas C(21)H(27)NO(4) and C(23)H(31)NO(4). They were named monascopyridines E and F due to their pyridine backbone. The cytotoxicity of the new compounds was studied using immortalised human kidney epithelial cells displaying IC(50) values in the micromolar range.     

An accurate study of the dynamics of the C+OH reaction on the second excited 1(4)A" potential energy surface

The dynamics of the C((3)P)+OH(X(2)Π) → CO(a(3)Π)+H((2)S) on its second excited potential energy surface, 1(4)A", have been investigated in detail by means of an accurate quantum mechanical (QM) time-dependent wave packet (TDWP) approach. Reaction probabilities for values of the total angular momentum J up to 50 are calculated and integral cross sections for a collision energy range which extends up to 0.1 eV are shown. The comparison with quasi-classical trajectory (QCT) and statistical methods reveals the important role played by the double well structure existing in the potential energy surface. The TDWP differential cross sections exhibit a forward-backward symmetry which could be interpreted as indicative of a complex-forming mechanism governing the dynamics of the process. The QM statistical method employed in this study, however, is not capable to reproduce the main features of the possible insertion nature in the reactive collision. The ability to stop individual trajectories selectively at specific locations inside the potential energy surface makes the QCT version of the statistical approach a better option to understand the overall dynamics of the process.     

Acetylene chemistry. Part 25. Reactions of ethyl 4-hydroxy-3-quinolin-2(1H)-onecarboxylates with 3-bromoprop-1-yne

Ethyl 4-hydroxyquinolin-2(1H)-onecarboxylates 1a and 1b which are obtained conveniently by the condensation of isatoic anhydride and diethylmalonate [4], were reacted with 3-bromoprop-1-yne ( 2 ) to obtain monoand dialkylated derivatives.