Fermion confinement via Quantum Walks in 2D+1 and 3D+1 spacetime

We analyze the properties of a two and three dimensional quantum walk that are inspired by the idea of a brane-world model put forward by Rubakov and Shaposhnikov [1]. In that model, particles are dynamically confined on the brane due to the interaction with a scalar field. We translated this model into an alternate quantum walk with a coin that depends on the external field, with a dependence which mimics a domain wall solution. As in the original model, fermions (in our case, the walker), become localized in one of the dimensions, not from the action of a random noise on the lattice (as in the case of Anderson localization), but from a regular dependence in space. On the other hand, the resulting quantum walk can move freely along the "ordinary" dimension.Comment: 5 pages, 6 figure

Searching and fixating: scale-invariance vs. characteristic timescales in attentional processes

In an experiment involving semantic search, the visual movements of sample populations subjected to visual and aural input were tracked in a taskless paradigm. The probability distributions of saccades and fixations were obtained and analyzed. Scale-invariance was observed in the saccadic distributions, while the fixation distributions revealed the presence of a characteristic (attentional) time scale for literate subjects. A detailed analysis of our results suggests that saccadic eye motions are an example of Levy, rather than Brownian, dynamics.Comment: Accepted to Europhysics Letters (2011

Phylogeography of Stable Fly (Diptera: Muscidae) Estimated by Diversity at Ribosomal 16S and Cytochrome Oxidase I Mitochondrial Genes

The blood-feeding cosmopolitan stable fly, Stomoxys calcitrans L. (Diptera: Muscidae), is thought to disperse rapidly and widely, and earlier studies of allozyme variation were consistent with high vagility in this species. The geographic origins of New World populations are unknown. Diversity at mitochondrial loci r16S and cytochrome oxidase I was examined in 277 stable flies from 11 countries, including five zoogeographical regions. Of 809 nucleotides, 174 were polymorphic and 133 were parsimony informative. Seventy-six haplotypes were found in frequencies consistent with the Wright–Fisher infinite allele model. None were shared among four or more zoogeographical regions. The null hypothesis of mutation neutrality was not rejected, thereby validating the observed distribution. Fifty-nine haplotypes were singular, eight were private and confined to the Old World, and three of 76 haplotypes were shared between the Old and New World. Only 19 haplotypes were found in the New World, 14 of which were singletons. Haplotype and nucleotide diversities were heterogeneous among countries and regions. The most diversity was observed in sub-Saharan Africa. Regional differentiation indices were GRT = 0.26 and NRT = 0.31, indicating populations were highly structured macrogeographically. Palearctic and New World flies were the least differentiated from each other. There were strong genetic similarities among populations in the Nearctic, Neotropical, and Palearctic regions, and it is most likely that New World populations were derived from the Palearctic after 1492 CE, in the colonial era

Halo Cores and Phase Space Densities: Observational Constraints on Dark Matter Physics and Structure Formation

We explore observed dynamical trends in a wide range of dark matter dominated systems (about seven orders of magnitude in mass) to constrain hypothetical dark matter candidates and scenarios of structure formation. First, we argue that neither generic warm dark matter (collisionless or collisional) nor self-interacting dark matter can be responsible for the observed cores on all scales. Both scenarios predict smaller cores for higher mass systems, in conflict with observations; some cores must instead have a dynamical origin. Second, we show that the core phase space densities of dwarf spheroidals, rotating dwarf and low surface brightness galaxies, and clusters of galaxies decrease with increasing velocity dispersion like Q ~ sigma^-3 ~ M^-1, as predicted by a simple scaling argument based on merging equilibrium systems, over a range of about eight orders of magnitude in Q. We discuss the processes which set the overall normalization of the observed phase density hierarchy. As an aside, we note that the observed phase-space scaling behavior and density profiles of dark matter halos both resemble stellar components in elliptical galaxies, likely reflecting a similar collisionless, hierarchical origin. Thus, dark matter halos may suffer from the same systematic departures from homology as seen in ellipticals, possibly explaining the shallower density profiles observed in low mass halos. Finally, we use the maximum observed phase space density in dwarf spheroidal galaxies to fix a minimum mass for relativistically decoupled warm dark matter candidates of roughly 700 eV for thermal fermions, and 300 eV for degenerate fermions.Comment: Submitted to the Astrophysical Journal, LaTeX, 26 pages including 4 pages of figure

Consumer credit information systems: A critical review of the literature. Too little attention paid by lawyers?

This paper reviews the existing literature on consumer credit reporting, the most extensively used instrument to overcome information asymmetry and adverse selection problems in credit markets. Despite the copious literature in economics and some research in regulatory policy, the legal community has paid almost no attention to the legal framework of consumer credit information systems, especially within the context of the European Union. Studies on the topic, however, seem particularly relevant in view of the establishment of a single market for consumer credit. This article ultimately calls for further legal research to address consumer protection concerns and inform future legislation

Stomatin-like Protein 2 Links Mitochondria to T-Cell Receptor Signalosomes at the Immunological Synapse and Enhances T-Cell Activation

T cell activation through the antigen receptor (TCR) requires sustained signalling from microclusters in the peripheral region of the immunological synapse (IS). The bioenergetics of such prolonged signaling have been linked to the redistribution of mitochondria to the IS. Here, we report that stomatin-like protein-2 (SLP-2) plays an important role in this process by bridging polarized mitochondria to these signaling TCR microclusters or signalosomes in the IS in a polymerized actin-dependent manner. In this way, SLP-2 helps to sustain TCR-dependent signalling and enhances T cell activation

Thread-level information for comment classification in community question answering

Community Question Answering (cQA) is a new application of QA in social contexts (e.g., fora). It presents new interesting challenges and research directions, e.g., exploiting the dependencies between the different comments of a thread to select the best answer for a given question. In this paper, we explored two ways of modeling such dependencies: (i) by designing specific features looking globally at the thread; and (ii) by applying structure prediction models. We trained and evaluated our models on data from SemEval-2015 Task 3 on Answer Selection in cQA. Our experiments show that: (i) the thread-level features consistently improve the performance for a variety of machine learning models, yielding state-of-the-art results; and (ii) sequential dependencies between the answer labels captured by structured prediction models are not enough to improve the results, indicating that more information is needed in the joint model

Near-Infrared and Star-forming properties of Local Luminous Infrared Galaxies

We use HST NICMOS continuum and Pa-alpha observations to study the near-infrared and star-formation properties of a representative sample of 30 local (d ~ 35-75Mpc) luminous infrared galaxies (LIRGs, infrared 8-1000um luminosities of L_IR=11-11.9[Lsun]). The data provide spatial resolutions of 25-50pc and cover the central ~3.3-7.1kpc regions of these galaxies. About half of the LIRGs show compact (~1-2kpc) Pa-alpha emission with a high surface brightness in the form of nuclear emission, rings, and mini-spirals. The rest of the sample show Pa-alpha emission along the disk and the spiral arms extending over scales of 3-7kpc and larger. About half of the sample contains HII regions with H-alpha luminosities significantly higher than those observed in normal galaxies. There is a linear empirical relationship between the mid-IR 24um and hydrogen recombination (extinction-corrected Pa-alpha) luminosity for these LIRGs, and the HII regions in the central part of M51. This relation holds over more than four decades in luminosity suggesting that the mid-IR emission is a good tracer of the star formation rate (SFR). Analogous to the widely used relation between the SFR and total IR luminosity of Kennicutt (1998), we derive an empirical calibration of the SFR in terms of the monochromatic 24um luminosity that can be used for luminous, dusty galaxies.Comment: Accepted for publication in ApJ. Contact first author for high qualitity version of figure