Finite Mass Effect on Two Photon Processes in Hydrogenic Systems: Effective Scalar Photon Interaction

We consider a hydrogenic system with a nucleus of finite mass. The coupling of the radiation field to the center of mass motion gives rise to an effective scalar type coupling. This induced scalar photon interaction emerges as a correction in competition with the usual multipole interactions. This effect is particularly important in positronium where the electric quadrupole interaction is totally suppressed. We illustrate this effect with the two-photon decay of metastable hydrogenic systems.Comment: 12 pages, Latex, no figure. Version to appear in Phys. Lett.

Range-dependent flexibility in the acoustic field of view of echolocating porpoises (Phocoena phocoena)

Funding: Det Frie Forskningsrad (MJ)Toothed whales use sonar to detect, locate, and track prey. They adjust emitted sound intensity, auditory sensitivity and click rate to target range, and terminate prey pursuits with high-repetition-rate, low-intensity buzzes. However, their narrow acoustic field of view (FOV) is considered stable throughout target approach, which could facilitate prey escape at close-range. Here we show that, like some bats, harbour porpoises can broaden their biosonar beam during the terminal phase of attack but, unlike bats, maintain the ability to change beamwidth within this phase. Based on video, MRI, and acoustic-tag recordings, we propose this flexibility is modulated by the melon and implemented to accommodate dynamic spatial relationships with prey and acoustic complexity of surroundings. Despite independent evolution and different means of sound generation and transmission, whales and bats adaptively change their FOV, suggesting that beamwidth flexibility has been an important driver in the evolution of echolocation for prey tracking.Publisher PDFPeer reviewe

INCF Lithuanian Workshop on Neuroscience and Information Technology

The aim of this workshop was to give a current overview of neuroscience and informatics research in Lithuania, and to discuss the strategies for forming the Lithuanian Neuroinformatics Node and becoming a member of INCF. The workshop was organized by Dr. Aušra Saudargiene (Department of Informatics, Vytautas Magnus University, Kaunas, and Faculty of Natural Sciences, Vilnius University, Lithuania) and INCF.
The workshop was attended by 15 invited speakers, among them 4 guests and 11 Lithuanian neuroscientists, and over 20 participants. The workshop was organized into three main sessions: overview of the INCF activities including the Swedish and UK nodes of INCF; presentations on Neuroscience research carried out in Lithuania; discussion about the strategies for forming an INCF national node, and the benefits of having such a node in Lithuania (Appendix A: Program; Appendix B: Abstracts)

Perturbative Scattering Phase Shifts in One-Dimension: Closed-form Results

A simple closed form expression is obtained for the scattering phase shift perturbatively to any given order in effective one-dimensional problems. The result is a hierarchical scheme, expressible in quadratures, requiring only knowledge of the zeroth order solution and the perturbation potential.Comment: 10 pages in REVTe

Some Recent Results on Pair Correlation Functions and Susceptibilities in Exactly Solvable Models

Using detailed exact results on pair-correlation functions of Z-invariant Ising models, we can write and run algorithms of polynomial complexity to obtain wavevector-dependent susceptibilities for a variety of Ising systems. Reviewing recent work we compare various periodic and quasiperiodic models, where the couplings and/or the lattice may be aperiodic, and where the Ising couplings may be either ferromagnetic, or antiferromagnetic, or of mixed sign. We present some of our results on the square-lattice fully-frustrated Ising model. Finally, we make a few remarks on our recent works on the pentagrid Ising model and on overlapping unit cells in three dimensions and how these works can be utilized once more detailed results for pair correlations in, e.g., the eight-vertex model or the chiral Potts model or even three-dimensional Yang-Baxter integrable models become available.Comment: LaTeX2e using iopart.cls, 10 pages, 5 figures (5 eps files), Dunk Island conference in honor of 60th birthday of A.J. Guttman