Observation of radiative double electron capture for

Radiative double electron capture (RDEC), occurring when two electrons are captured to a projectile ion with the simultaneous emission of a single photon, has been investigated. RDEC can be considered as the time inverse process of double photoionization. Strong evidence for RDEC is found in F⁹⁺ + N₂ collisions and additionally for one-electron F⁸⁺ for which the probability for the process is expected to be considerably smaller. Preliminary values for the cross sections for RDEC have been determined. A significant advantage of the gas target is that multiple-collision effects seen for a solid target are avoided due to the single-collision conditions that prevail for gas targets.     

NONCOOPERATIVE MANAGEMENT OF THE NORTHEAST ATLANTIC COD FISHERY: A FIRST MOVER ADVANTAGE

The point of departure for this analysis is Bjørndal and Lindroos [2012], who developed an empirical bioeconomic model to analyze cooperative and noncooperative management of Northeast Atlantic cod. In their analysis, only constant strategies were analyzed for noncooperative games. In this paper, nonconstant strategies are considered. Moreover, the fishery in question is characterized by cooperative management. What may happen in the real world is that one nation breaks the cooperative agreement by fishing in excess of its quota. Often, it takes time for the other agent to detect this and respond. In this paper, we allow this kind of delayed response into a two‐agent noncooperative game so that, if country 2 exceeds its quota, there will be a time lag before this is detected by country 1; moreover, there may also be a delay until country 1 is able to respond. Results show that the outcome critically depends on the length of these two lags as well as initial conditions.     

Secondary flow in a parallel-disk viscometer

Summary A numerical solution of theNavier-Stokes equations is obtained for flow in a parallel-disk viscometer. The inertial secondary flow consists of a single eddy which is well represented away from the free surface by the approximate analytical solution for infinite disks.

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Zusammenfassung Für die Strömung in einem Parallelplatten-Viskosimeter wird eine numerische Lösung derNavier-Stokes-Gleichungen angegeben. Die trägheitsbehaftete Sekundärströmung besteht aus einem Einzelwirbel, der, außer an der freien Oberfläche, durch die analytische Näherungslösung für unendliche Platten gut darstellbar ist.

     

New Developments in the Eight Vertex Model

We demonstrate that the Q matrix introduced in Baxter's 1972 solution of the eight vertex model has some eigenvectors which are not eigenvectors of the spin reflection operator and conjecture a new functional equation for Q(v) which both contains the Bethe equation that gives the eigenvalues of the transfer matrix and computes the degeneracies of these eigenvalues.     

Finite Size Corrections for the Ising Model on Higher Genus Triangular Lattices

We study the topology dependence of the finite size corrections to the Ising model partition function by considering the model on a triangular lattice embedded on a genus two surface. At criticality we observe a universal shape dependent correction, expressible in terms of Riemann theta functions, that reproduces the modular invariant partition function of the corresponding conformal field theory. The period matrix characterizing the moduli parameters of the limiting Riemann surface is obtained by a numerical study of the lattice continuum limit. The same results are reproduced using a discrete holomorphic structure.     

A Bernstein property of solutions to a class of prescribed affine mean curvature equations

Let \(x: M \rightarrow A^{n+1}\) be a locally strongly convex hypersurface, given as the graph of a locally strongly convex function x _n+1 = z(x ₁, ..., x _n ). In this paper we prove a Bernstein property for hypersurfaces which are complete with respect to the metric \(G^{\sharp} = \sum \left( \frac{\partial^{2}z}{\partial x_{i} \partial x_{j}} \right) dx_{i} dx_{j}\) and which satisfy a certain Monge–Ampère type equation. This generalises in some sense the earlier result of Li and Jia for affine maximal hypersurfaces of dimension n = 2 and n = 3 (Li, A.-M., Jia, F.: A Bernstein property of affine maximal hypersurfaces. Ann. Glob. Anal. Geom. 23, 359–372 (2003)), related results (Li, A.-M., Jia, F.: Locally strongly convex hypersurfaces with constant affine mean curvature. Diff. Geom. Appl. 22(2), 199–214 (2005)) and results for n = 2 of Trudinger and Wang (Trudinger, N.S., Wang, X.-J.: Bernstein-Jörgens theorem for a fourth order partial differential equation. J. Partial Diff. Equ. 15(2), 78–88 (2002)).     

Novel porphyrin-incorporated hydrogels for photoactive intraocular lens biomaterials

Novel surface-modified hydrogel materials have been prepared by binding charged porphyrins TMPyP (tetrakis(4-N-methylpyridyl)porphyrin) and TPPS (tetrakis(4-sulfonatophenyl)porphyrin) to copolymers of HEMA (2-hydroxyethyl methacrylate) with either MAA (methacrylic acid) or DEAEMA (2-(diethylamino)ethyl methacrylate). The charged hydrogels display strong electrostatic interactions with the appropriate cationic or anionic porphyrins to give materials which are intended to be used to generate cytotoxic singlet oxygen (1O2) on photoexcitation and can therefore be used to reduce postoperative infection of the intraocular hydrogel-based replacement lenses that are used in cataract surgery. The UV/vis spectra of TMPyP in MAA:HEMA copolymers showed a small shift in the Soret band and a change from single exponential (161 micros) triplet decay lifetime in solution to a decay that could be fitted to a biexponential fit with two approximately equal components with tau = 350 and 1300 micros. O2 bubbling reduced the decay to a dominant (90%) component with a much reduced lifetime of 3 micros and a minor, longer lived (20 micros) component. With D2O solvent the 1O2 lifetime was measured by 1270 nm fluorescence as 35 micros in MAA:HEMA, compared to 67 mus in solution, although absorbance-matched samples showed similar yield of 1O2 in the polymers and in aqueous solution. In contrast to the minor perturbation in photophysical properties caused by binding TMPyP to MAA:HEMA, TPPS binding to DEAEMA:HEMA copolymers profoundly changed the 1O2 generating ability of the TPPS. In N2-bubbled samples, the polymer-bound TPPS behaved in a similar manner to TMPyP in its copolymer host; however, O2 bubbling had only a very small effect on the triplet lifetime and no 1O2 generation could be detected. The difference in behavior may be linked to differences in binding in the two systems. With TMPyP in MAA:HEMA, confocal fluorescence microscopy showed significant penetration of the porphyrin into the core of the polymer film samples (>150 microm). However, for TPPS in DEAEMA:HEMA copolymers, although the porphyrin bound much more readily to the polymer, it remained localized in the first 20 microm, even in heavily loaded samples. It is possible that the resulting high concentration of TPPS may have cross-linked the hydrogels to such an extent that it significantly reduced the solubility and/or diffusion rate of oxygen into the doped polymers. This effect is significant since it demonstrates that even simple electrostatic binding of charged porphyrins to hydrogels can have an unexpectedly large effect on the properties of the system as a whole. In this case it makes the apparently promising TPPS/DEAEMA:HEMA system a poor candidate for clinical application as a postoperative antibacterial treatment for intraocular lenses while the apparently equivalent cationic system TMPyP/MAA:HEMA displays all the required properties.     

Characterizing excited states of CH5+ with diffusion Monte Carlo

The spectroscopy and dynamics of protonated methane have been of long-standing interest due to the unusual and highly fluxional behavior of CH5+. This reflects the fact that the ground-state wave function for CH5+ has nearly equal amplitude at the 120 equivalent minima and at the saddle points that connect these minima. While low-resolution spectra of CH5+ have been assigned, the nature of the couplings between the CH stretches and the low-frequency modes is not as well characterized. An understanding of this will be important in the interpretation of rotationally resolved spectra. In this work, fixed-node diffusion Monte Carlo techniques are used to calculate energies and probability amplitudes for several excited states. The calculated energies are shown to be in good agreement with previously reported vibrational configuration interactions calculations. Analysis of the 12-dimensional probability amplitudes shows that there are strong couplings between the high-frequency CH stretch and HCH bend motions and the low-frequency modes that lead to isomerization CH5+.     

Quantum/classical studies of vibrationally mediated photodissociation of Ar x H2O

Results of multiple configuration quantum/classical simulations of the dynamics of Ar x H2O photodissociation are reported. In agreement with experimental studies of Nesbitt and co-workers [J. Chem. Phys. 2000, 112, 7449], we find that the OH products emerge rotationally excited, compared to the dissociation of bare H2O. The wavelength dependence of the total cross section and the energy transfer to the argon atom are also investigated. The trends are interpreted in terms of features in the Ar x H2O A state potential surface.     

Polarization studies of resonant forbidden reflections in liquid crystals

We report the results of resonant x-ray diffraction experiments performed on thick films of a biaxial liquid crystal made of achiral bent-core molecules. Polarization properties of forbidden reflections are observed as a function of the sample rotation angle phi about the scattering vector Q for the first time on a fluid material. The experimental data are successfully analyzed within a tensor structure factor model by taking the nonperfect alignment of the liquid crystal into account. The local structure of the B2 mesophase is hence determined to be SmC_{S}P_{A}.