REDO RSVP: Efficient Signalling for Multimedia in the Internet

Alarming reports of performance and scalability problems associated with per-flow reservations, have led many to lose belief in RSVP and the Integrated Services Architecture that relies on it. Because we are convinced of the need for some form of resource reservation, to support multimedia communications in the Internet, we have set about trying to improve RSVP. By careful study of the protocol, we have identified areas for improvement, and propose REDO RSVP, a reduced overhead version that includes a fast establishment mechanism (FEM). In this paper we describe the rationale for REDO RSVP and present a detailed analysis of its features and operations. We also analyse REDO RSVP by means of simulations, and show that it offers improvements to the performance of RSVP

Proximal operators for multi-agent path planning

We address the problem of planning collision-free paths for multiple agents using optimization methods known as proximal algorithms. Recently this approach was explored in Bento et al. 2013, which demonstrated its ease of parallelization and decentralization, the speed with which the algorithms generate good quality solutions, and its ability to incorporate different proximal operators, each ensuring that paths satisfy a desired property. Unfortunately, the operators derived only apply to paths in 2D and require that any intermediate waypoints we might want agents to follow be preassigned to specific agents, limiting their range of applicability. In this paper we resolve these limitations. We introduce new operators to deal with agents moving in arbitrary dimensions that are faster to compute than their 2D predecessors and we introduce landmarks, space-time positions that are automatically assigned to the set of agents under different optimality criteria. Finally, we report the performance of the new operators in several numerical experiments.Comment: See movie at http://youtu.be/gRnsjd_ocx

GRIDKIT: Pluggable overlay networks for Grid computing

A `second generation' approach to the provision of Grid middleware is now emerging which is built on service-oriented architecture and web services standards and technologies. However, advanced Grid applications have significant demands that are not addressed by present-day web services platforms. As one prime example, current platforms do not support the rich diversity of communication `interaction types' that are demanded by advanced applications (e.g. publish-subscribe, media streaming, peer-to-peer interaction). In the paper we describe the Gridkit middleware which augments the basic service-oriented architecture to address this particular deficiency. We particularly focus on the communications infrastructure support required to support multiple interaction types in a unified, principled and extensible manner-which we present in terms of the novel concept of pluggable overlay networks

Ultrafast optical nonlinearity in quasi-one-dimensional Mott-insulator Sr2CuO3{\rm Sr_2CuO_3}

We report strong instantaneous photoinduced absorption (PA) in the quasi-one-dimensional Mott insulator ${\rm Sr_2CuO_3}$ in the IR spectral region. The observed PA is to an even-parity two-photon state that occurs immediately above the absorption edge. Theoretical calculations based on a two-band extended Hubbard model explains the experimental features and indicates that the strong two-photon absorption is due to a very large dipole-coupling between nearly degenerate one- and two-photon states. Room temperature picosecond recovery of the optical transparency suggests the strong potential of ${\rm Sr_2CuO_3}$ for all-optical switching.Comment: 10 pages, 4 figure

A 3-Month interdisciplinary Process Drama Program to Build Social Skills in Pre-Schoolers with ASD: A Feasibility Study

Objectives: To test the feasibility and effect of an interdisciplinary process drama program targeting social skill development in 3-5 year-old children with Autism Spectrum Disorder (ASD) characteristics To develop a paradigm for testing brain-behavior relationships related to social skills in these children using EEG and testing its ability to detect intervention-related changes. Background: Social skill deficits are a hallmark cause of disability in ASD. Such disability is of critical concern given the rising prevalence (1 in 54 Utah children) of ASD. [1] As children learn through social experiences, difficulty in social interactions can limit development and ability to succeed in school and eventually employment. One possible contributor to social interaction difficulties in ASD is a deficit in theory of mind (ToM), the ability to understand others\u27 perspectives, proposed to rely on memories of cognitive and emotional events that allow one to experience others\u27 situations as if they were one\u27s own. [2.3] Children with ASD have deficits in ToM [2,3] and show aberrant neural activation patterns in areas most typically activated during ToM tasks in healthy children. [4,5] An effective intervention fostering generalizable social skill development in children with ASD remains elusive. We propose to address this need with an interdisciplinary process drama intervention involving collaboration among occupational therapists (OT), theatre faculty/teachers, and speech language pathologists (SLP) to improve social interactions in preschoolers with ASD. Process drama may be an excellent medium for fostering social skill development due to the ability to create specific learning experiences in an autotelic manner [6] in which people experience the embodied cognition and emotions without conscious commitment to abstract social skill improvement goals. The scenes can emphasize social and emotional cues and explicit identification of scene-related feelings for the formation of social cognitive and emotional memories that can be recalled as the basis for later social functioning.[3] Process drama programs foster communication development in typically developing children [7] and a few studies have shown such programs enhance social skills of children aged 8-17 with ASD [8,9] However, targeting process drama intervention in preschool children may have the greatest potential for effect on ToM and subsequent social skill development. The overpruning hypothesis [10] proposes that ASD results from abnormal neural pruning in widespread neural networks, with weaker long-range connections being more vulnerable to major disruption. As neural connections strengthen through experience,[11] providing interventions targeting desired processing will strengthen associated connections making them less susceptible to pruning and resulting in preserved function. Peak synaptic density for auditory and prefrontal cortices, both involved in social skills, occurs between age 3-5 years [11], suggesting an optimal period for strengthening connections through intervention. Impact: The deficits in social skills of people with ASD significantly affect their ability to function in society. These deficits take a large toll on families and on independence and employability of the individual. Finding effective interventions to facilitate social skills would have a large impact on society by reducing disability in this prevalent population. Results: The primary goal of the proposed study is to gather preliminary data on potential utility of an interdisciplinary process drama intervention to improve social skills in children with ASD. We will address the following specific aims: 1) determine the feasibility of: a) the protocol for collecting neural activation data via EEG on preschoolers with ASD characteristics; b) conducting a 3 month, 3x/week process drama intervention program led by a collaborative team of theatre teachers, OTs and SLPs aimed at improving social skills. 2) Determine preliminary effects of this interdisciplinary intervention on: a) increasing positive social behaviors; b) changes in neural activation during social tasks

On Form Factors in nested Bethe Ansatz systems

We investigate form factors of local operators in the multi-component Quantum Non-linear Schr\"odinger model, a prototype theory solvable by the so-called nested Bethe Ansatz. We determine the analytic properties of the infinite volume form factors using the coordinate Bethe Ansatz solution and we establish a connection with the finite volume matrix elements. In the two-component models we derive a set of recursion relations for the "magnonic form factors", which are the matrix elements on the nested Bethe Ansatz states. In certain simple cases (involving states with only one spin-impurity) we obtain explicit solutions for the recursion relations.Comment: 34 pages, v2 (minor modifications

A theoretical investigation of the low lying electronic structure of poly(p-phenylene vinylene)

The two-state molecular orbital model of the one-dimensional phenyl-based semiconductors is applied to poly(p-phenylene vinylene). The energies of the low-lying excited states are calculated using the density matrix renormalization group method. Calculations of both the exciton size and the charge gap show that there are both Bu and Ag excitonic levels below the band threshold. The energy of the 1Bu exciton extrapolates to 2.60 eV in the limit of infinite polymers, while the energy of the 2Ag exciton extrapolates to 2.94 eV. The calculated binding energy of the 1Bu exciton is 0.9 eV for a 13 phenylene unit chain and 0.6 eV for an infinite polymer. This is expected to decrease due to solvation effects. The lowest triplet state is calculated to be at ca. 1.6 eV, with the triplet-triplet gap being ca. 1.6 eV. A comparison between theory, and two-photon absorption and electroabsorption is made, leading to a consistent picture of the essential states responsible for most of the third-order nonlinear optical properties. An interpretation of the experimental nonlinear optical spectroscopies suggests an energy difference of ca. 0.4 eV between the vertical energy and ca. 0.8 eV between the relaxed energy, of the 1Bu exciton and the band gap, respectively.Comment: LaTeX, 19 pages, 7 eps figures included using epsf. To appear in Physical Review B, 199

Quantum flutter of supersonic particles in one-dimensional quantum liquids

The non-equilibrium dynamics of strongly correlated many-body systems exhibits some of the most puzzling phenomena and challenging problems in condensed matter physics. Here we report on essentially exact results on the time evolution of an impurity injected at a finite velocity into a one-dimensional quantum liquid. We provide the first quantitative study of the formation of the correlation hole around a particle in a strongly coupled many-body quantum system, and find that the resulting correlated state does not come to a complete stop but reaches a steady state which propagates at a finite velocity. We also uncover a novel physical phenomenon when the impurity is injected at supersonic velocities: the correlation hole undergoes long-lived coherent oscillations around the impurity, an effect we call quantum flutter. We provide a detailed understanding and an intuitive physical picture of these intriguing discoveries, and propose an experimental setup where this physics can be realized and probed directly.Comment: 13 pages, 9 figure