2,175 research outputs found
Phase-slip avalanches in the superflow of He through arrays of nanopores
Recent experiments by Sato et al. [1] have explored the dynamics of He
superflow through an array of nanopores. These experiments have found that, as
the temperature is lowered, phase-slippage in the pores changes its character,
from synchronous to asynchronous. Inspired by these experiments, we construct a
model to address the characteristics of phase-slippage in superflow through
nanopore arrays. We focus on the low-temperature regime, in which the
current-phase relation for a single pore is linear, and thermal fluctuations
may be neglected. Our model incorporates two basic ingredients: (1) each pore
has its own random value of critical velocity (due, e.g., to atomic-scale
imperfections), and (2) an effective inter-pore coupling, mediated through the
bulk superfluid. The inter-pore coupling tends to cause neighbours of a pore
that has already phase-slipped also to phase-slip; this process may cascade,
creating an avalanche of synchronously slipping phases. As the temperature is
lowered, the distribution of critical velocities is expected to effectively
broaden, owing to the reduction in the superfluid healing length, leading to a
loss of synchronicity in phase-slippage. Furthermore, we find that competition
between the strength of the disorder in the critical velocities and the
strength of the inter-pore interaction leads to a phase transition between
non-avalanching and avalanching regimes of phase-slippage.
[1] Sato, Y., Hoskinson, E. Packard, R. E. cond-mat/0605660.Comment: 8 pages, 5 figure
Prototype of Fault Adaptive Embedded Software for Large-Scale Real-Time Systems
This paper describes a comprehensive prototype of large-scale fault adaptive
embedded software developed for the proposed Fermilab BTeV high energy physics
experiment. Lightweight self-optimizing agents embedded within Level 1 of the
prototype are responsible for proactive and reactive monitoring and mitigation
based on specified layers of competence. The agents are self-protecting,
detecting cascading failures using a distributed approach. Adaptive,
reconfigurable, and mobile objects for reliablility are designed to be
self-configuring to adapt automatically to dynamically changing environments.
These objects provide a self-healing layer with the ability to discover,
diagnose, and react to discontinuities in real-time processing. A generic
modeling environment was developed to facilitate design and implementation of
hardware resource specifications, application data flow, and failure mitigation
strategies. Level 1 of the planned BTeV trigger system alone will consist of
2500 DSPs, so the number of components and intractable fault scenarios involved
make it impossible to design an `expert system' that applies traditional
centralized mitigative strategies based on rules capturing every possible
system state. Instead, a distributed reactive approach is implemented using the
tools and methodologies developed by the Real-Time Embedded Systems group.Comment: 2nd Workshop on Engineering of Autonomic Systems (EASe), in the 12th
Annual IEEE International Conference and Workshop on the Engineering of
Computer Based Systems (ECBS), Washington, DC, April, 200
Immersive Composition for Sensory Rehabilitation: 3D Visualisation, Surround Sound, and Synthesised Music to Provoke Catharsis and Healing
There is a wide range of sensory therapies using sound, music and visual stimuli. Some focus on soothing or distracting stimuli such as natural sounds or classical music as analgesic, while other approaches emphasize the
active performance of producing music as therapy. This paper proposes an immersive
multi-sensory Exposure Therapy for people suffering from anxiety disorders, based on a rich, detailed surround-soundscape. This soundscape is composed to include the users’ own idiosyncratic anxiety triggers as a form of
habituation, and to provoke psychological catharsis, as a non-verbal, visceral and enveloping exposure. To accurately pinpoint the most effective sounds and to optimally compose the soundscape we will monitor the participants’ physiological responses such as electroencephalography, respiration, electromyography, and heart rate during exposure. We hypothesize that such physiologically optimized sensory landscapes will aid the development of future immersive therapies for various psychological conditions, Sound is a major trigger of anxiety, and auditory hypersensitivity is an extremely problematic symptom. Exposure to stress-inducing sounds can free anxiety sufferers from entrenched avoidance behaviors, teaching physiological coping strategies and encouraging resolution of the psychological issues agitated by the sound
Self-Healing Tile Sets
Biology provides the synthetic chemist with a tantalizing and frustrating challenge:
to create complex objects, defined from the molecular scale up to meters,
that construct themselves from elementary components, and perhaps
even reproduce themselves. This is the challenge of bottom-up fabrication.
The most compelling answer to this challenge was formulated in the early
1980s by Ned Seeman, who realized that the information carried by DNA
strands provides a means to program molecular self-assembly, with potential
applications including DNA scaffolds for crystallography [19] or for molecular
electronic circuits [15]. This insight opened the doors to engineering with the
rich set of phenomena available in nucleic acid chemistry [20]
Asynchronous neighborhood task synchronization
Faults are likely to occur in distributed systems. The motivation for designing self-stabilizing system is to be able to automatically recover from a faulty state. As per Dijkstra\u27s definition, a system is self-stabilizing if it converges to a desired state from an arbitrary state in a finite number of steps. The paradigm of self-stabilization is considered to be the most unified approach to designing fault-tolerant systems. Any type of faults, e.g., transient, process crashes and restart, link failures and recoveries, and byzantine faults, can be handled by a self-stabilizing system; Many applications in distributed systems involve multiple phases. Solving these applications require some degree of synchronization of phases. In this thesis research, we introduce a new problem, called asynchronous neighborhood task synchronization ( NTS ). In this problem, processes execute infinite instances of tasks, where a task consists of a set of steps. There are several requirements for this problem. Simultaneous execution of steps by the neighbors is allowed only if the steps are different. Every neighborhood is synchronized in the sense that all neighboring processes execute the same instance of a task. Although the NTS problem is applicable in nonfaulty environments, it is more challenging to solve this problem considering various types of faults. In this research, we will present a self-stabilizing solution to the NTS problem. The proposed solution is space optimal, fault containing, fully localized, and fully distributed. One of the most desirable properties of our algorithm is that it works under any (including unfair) daemon. We will discuss various applications of the NTS problem
Self-Healing Computation
In the problem of reliable multiparty computation (RC), there are
parties, each with an individual input, and the parties want to jointly compute
a function over inputs. The problem is complicated by the fact that an
omniscient adversary controls a hidden fraction of the parties.
We describe a self-healing algorithm for this problem. In particular, for a
fixed function , with parties and gates, we describe how to perform
RC repeatedly as the inputs to change. Our algorithm maintains the
following properties, even when an adversary controls up to parties, for any constant . First, our
algorithm performs each reliable computation with the following amortized
resource costs: messages, computational
operations, and latency, where is the depth of the circuit
that computes . Second, the expected total number of corruptions is , after which the adversarially controlled parties are
effectively quarantined so that they cause no more corruptions.Comment: 17 pages and 1 figure. It is submitted to SSS'1
Self-Healing Partial Reconfiguration of an FPGA
The goal of this project, sponsored by General Dynamics, is to create an FPGA-based system capable of detecting and gracefully recovering from errors without compromising system functionality. Previous research developed a prototype for partial reconfiguration, but a major limitation was the need for a PC to partially reprogram the FPGA. By implementing a method of self-reconfiguration and developing a system using triple module redundancy, the FPGA can locate errors and partially self-reconfigure the corrupted areas while maintaining valid system outputs
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