Switching dynamics of spatial solitary wave pixels

Separatrices and scaling laws in the switching dynamics of spatial solitary wave pixels are investigated. We show that the dynamics in the full model are similar to those in the plane-wave limit. Switching features may be indicated and explained by the motion of the (complex) solitary wave amplitude in the phase plane. We report generalization, into the domain of transverse effects, of the pulse area theorem for the switching process and a logarithmic law for the transient dynamics. We also consider, for what is the first time to our knowledge, phase-encoded address of solitary pixels and find that a near-square-wave temporal switching pattern is permitted without (transverse) cross switching

A concise review of carbon nanotube's toxicology

Carbon nanotubes can be either single-walled or multi-walled, each of which is known to have a different electron arrangement and as a result have different properties. However, the shared unique properties of both types of carbon nanotubes (CNT) allow for their potential use in various biomedical devices and therapies. Some of the most common properties of these materials include the ability to absorb near-infra-red light and generate heat, the ability to deliver drugs in a cellular environment, their light weight, and chemical stability. These properties have encouraged scientists to further investigate CNTs as a tool for thermal treatment of cancer and drug delivery agents. Various promising data have so far been obtained about the usage of CNTs for cancer treatment; however, toxicity of pure CNTs represents a major challenge for clinical application. Various techniques both in vivo and in in vitro have been conducted by a number of different research groups to establish the factors which have a direct effect on CNT-mediated cytotoxicity. The main analysis techniques include using Alamar blue, MTT, and Trypan blue assays. Successful interpretation of these results is difficult because the CNTs can significantly disrupt the emission of the certain particles, which these assays detect. In contrast, in vivo studies allow for the measurement of toxicity and pathology caused by CNTs on an organismal level. Despite the drawbacks of in vitro studies, they have been invaluable in identifying important toxicity factors, such as size, shape, purity, and functionalisation, the latter of which can attenuate CNT toxicity

A simple integrated single-atom detector

We present a reliable and robust integrated fluorescence detector capable of detecting single atoms. The detector consists of a tapered lensed single-mode fiber for precise delivery of excitation light and a multimode fiber to collect the fluorescence. Both are mounted in lithographically defined SU-8 holding structures on an atom chip. Rb87 atoms propagating freely in a magnetic guide are detected with an efficiency of up to 66%, and a signal-to-noise ratio in excess of 100 is obtained for short integration times.Comment: 3 pages, 3 figure

High-energy Particle Acceleration and Production of Ultra-high-energy Cosmic Rays in the Giant Lobes of Centaurus A

‘The definitive version is available at www3.interscience.wiley.com '. Copyright Royal Astronomical Society. DOI: 10.1111/j.1365-2966.2008.14265.xThe nearby radio galaxy Centaurus A is poorly studied at high frequencies with conventional radio telescopes because of its very large angular size, but is one of a very few extragalactic objects to be detected and resolved by the Wilkinson Microwave Anisotropy Probe (WMAP).We have used the five-year WMAP data for Cen A to constrain the high-frequency radio spectra of the 10-degree giant lobes and to search for spectral changes as a function of position along the lobes. We show that the high-frequency radio spectra of the northern and southern giant lobes are significantly different: the spectrum of the southern lobe steepens monotonically (and is steeper further from the active nucleus) whereas the spectrum of the northern lobe remains consistent with a power law. The inferred differences in the northern and southern giant lobes may be the result of real differences in their high-energy particle acceleration histories, perhaps due to the influence of the northern middle lobe, an intermediate-scale feature which has no detectable southern counterpart. In light of these results, we discuss the prospects for Gamma-ray Large Area Space Telescope (GLAST) detections of inverse-Compton emission from the giant lobes and the lobes’ possible role in the production of the ultra-high energy cosmic rays (UHECR) detected by the Pierre Auger Observatory. We show that the possibility of a GLAST detection depends sensitively on the physical conditions in the giant lobes, with the northern lobe more likely to be detected, and that any emission observed by GLAST is likely to be restricted to the soft end of the GLAST energy band. On the other hand we argue that the estimated conditions in the giant lobes imply that UHECRs can be accelerated there, with a potentially detectable -ray signature at GeV-TeV energies.Peer reviewe

Symmetry Breaking and Order in the Age of Quasicrystals

The discovery of quasicrystals has changed our view of some of the most basic notions related to the condensed state of matter. Before the age of quasicrystals, it was believed that crystals break the continuous translation and rotation symmetries of the liquid-phase into a discrete lattice of translations, and a finite group of rotations. Quasicrystals, on the other hand, possess no such symmetries-there are no translations, nor, in general, are there any rotations, leaving them invariant. Does this imply that no symmetry is left, or that the meaning of symmetry should be revised? We review this and other questions related to the liquid-to-crystal symmetry-breaking transition using the notion of indistinguishability. We characterize the order-parameter space, describe the different elementary excitations, phonons and phasons, and discuss the nature of dislocations-keeping in mind that we are now living in the age of quasicrystals.Comment: To appear in a special issue on quasicrystals of The Israel Journal of Chemistry, in celebration of the 2011 Nobel Prize in Chemistr

Quantum projection filter for a highly nonlinear model in cavity QED

Both in classical and quantum stochastic control theory a major role is played by the filtering equation, which recursively updates the information state of the system under observation. Unfortunately, the theory is plagued by infinite-dimensionality of the information state which severely limits its practical applicability, except in a few select cases (e.g. the linear Gaussian case.) One solution proposed in classical filtering theory is that of the projection filter. In this scheme, the filter is constrained to evolve in a finite-dimensional family of densities through orthogonal projection on the tangent space with respect to the Fisher metric. Here we apply this approach to the simple but highly nonlinear quantum model of optical phase bistability of a stongly coupled two-level atom in an optical cavity. We observe near-optimal performance of the quantum projection filter, demonstrating the utility of such an approach.Comment: 19 pages, 6 figures. A version with high quality images can be found at http://minty.caltech.edu/papers.ph

Coherent spin relaxation in molecular magnets

Numerical modelling of coherent spin relaxation in nanomagnets, formed by magnetic molecules of high spins, is accomplished. Such a coherent spin dynamics can be realized in the presence of a resonant electric circuit coupled to the magnet. Computer simulations for a system of a large number of interacting spins is an efficient tool for studying the microscopic properties of such systems. Coherent spin relaxation is an ultrafast process, with the relaxation time that can be an order shorter than the transverse spin dephasing time. The influence of different system parameters on the relaxation process is analysed. The role of the sample geometry on the spin relaxation is investigated.Comment: Latex file, 22 pages, 7 figure

On the quasi-yield surface concept in plasticity theory

In this paper we provide deeper insights into the concept of the quasi-yield surface in plasticity theory. More specifically, in this work, unlike the traditional treatments of plasticity where special emphasis is placed on an unambiguous definition of a yield criterion and the corresponding loading-unloading conditions, we place emphasis on the study of a general rate equation which is able to enforce elastic-plastic behavior. By means of this equation we discuss the fundamental concepts of the elastic range and the elastic domain. The particular case in which the elastic domain degenerates into its boundary leads to the quasi-yield surface concept. We exploit this concept further by discussing several theoretical issues related to it and by introducing a simple material model. The ability of the model in predicting several patterns of the real behavior of metals is assessed by representative numerical examples