15,375 research outputs found
Magnetic behaviour of SO(5) superconductors
The distinction between type I and type II superconductivity is re-examined
in the context of the SO(5) model recently put forth by Zhang. Whereas in
conventional superconductivity only one parameter (the Ginzburg-Landau
parameter ) characterizes the model, in the SO(5) model there are two
essential parameters. These can be chosen to be and another parameter,
, related to the doping. There is a more complicated relation between
and the behaviour of a superconductor in a magnetic field. In
particular, one can find type I superconductivity even when is large,
for appropriate values of .Comment: 7 pages, 5 figures. Talk given at MRST Conference on High Energy
Physics (2002), Perimeter Institute, Waterloo, Ontari
Parity violation, anyon scattering and the mean field approximation
Some general features of the scattering of boson-based anyons with an added
non-statistical interaction are discussed. Periodicity requirements of the
phase shifts are derived, and used to illustrate the danger inherent in
separating these phase shifts into the well-known pure Aharanov-Bohm phase
shifts, and an additional set which arise due to the interaction. It is proven
that the added phase shifts, although due to the non-statistical interaction,
necessarily change as the statistical parameter is varied, keeping the
interaction fixed. A hard-disk interaction provides a concrete illustration of
these general ideas. In the latter part of the paper, scattering with an
additional hard-disk interaction is studied in detail, with an eye towards
providing a criterion for the validity of the mean-field approximation for
anyons, which is the first step in virtually any treatment of this system. We
find, consistent with previous work, that the approximation is justified if the
statistical interaction is weak, and that it must be more weak for boson-based
than for fermion-based anyons.Comment: 17 pages plus 3 encoded/compressed post-script figures,
UdeM-LPN-TH-94-18
Multi-physics simulation of friction stir welding process
Purpose: The Friction Stir Welding (FSW) process comprises of several highly coupled (and non-linear) physical phenomena: large plastic deformation, material flow transportation, mechanical stirring of the tool, tool-workpiece surface interaction, dynamic structural evolution, heat generation from friction and plastic deformation, etc. In this paper, an advanced Finite Element (FE) model encapsulating this complex behavior is presented and various aspects associated with the FE model such as contact modeling, material model and meshing techniques are discussed in detail. Methodology: The numerical model is continuum solid mechanics-based, fully thermomechanically coupled and has successfully simulated the friction stir welding process including plunging, dwelling and welding stages. Findings: The development of several field variables are quantified by the model: temperature, stress, strain, etc. Material movement is visualized by defining tracer particles at the locations of interest. The numerically computed material flow patterns are in very good agreement with the general findings from experiments. Value: The model is, to the best of the authors’ knowledge, the most advanced simulation of FSW published in the literature
A comprehensive study of the usability of multiple graphical passwords
Recognition-based graphical authentication systems (RBGSs) using
images as passwords have been proposed as one potential solution to the need
for more usable authentication. The rapid increase in the technologies requiring
user authentication has increased the number of passwords that users have to
remember. But nearly all prior work with RBGSs has studied the usability of a
single password. In this paper, we present the first published comparison of the
usability of multiple graphical passwords with four different image types:
Mikon, doodle, art and everyday objects (food, buildings, sports etc.). A longi-tudinal experiment was performed with 100 participants over a period of 8
weeks, to examine the usability performance of each of the image types. The re-sults of the study demonstrate that object images are most usable in the sense of
being more memorable and less time-consuming to employ, Mikon images are
close behind but doodle and art images are significantly inferior. The results of
our study complement cognitive literature on the picture superiority effect, vis-ual search process and nameability of visually complex images
An assessment of blockchain consensus protocols for the Internet of Things
In a few short years the Internet of Things has become an intrinsic part of everyday life, with connected devices included in products created for homes, cars and even medical equipment. But its rapid growth has created several security problems, with respect to the transmission and storage of vast amounts of customers data, across an insecure heterogeneous collection of networks. The Internet of Things is therefore creating a unique set of risk and problems that will affect most households. From breaches in confidentiality, which could allow users to be snooped on, through to failures in integrity, which could lead to consumer data being compromised; devices are presenting many security challenges to which consumers are ill equipped to protect themselves from. Moreover, when this is coupled with the heterogeneous nature of the industry, and the interoperable and scalability problems it becomes apparent that the Internet of Things has created an increased attack surface from which security vulnerabilities may be easily exploited. However, it has been conjectured that blockchain may provide a solution to the Internet of Things security and scalability problems. Because of blockchain’s immutability, integrity and scalability, it is possible that its architecture could be used for the storage and transfer of Internet of Things data. Within this paper a cross section of blockchain consensus protocols have been assessed against a requirement framework, to establish each consensus protocols strengths and weaknesses with respect to their potential implementation in an Internet of Things blockchain environment
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