7,972 research outputs found
Wide-Area Imaging of Ultrasonic Fields by Digital Phase-Stepping Shearography
Shearography, introduced in 1973 by both Hung & Taylor [1] and Leendertz & Butters [2], was developed from speckle pattern interferometry. Both methods are full- field optical techniques which generate interference patterns by combining a reference beam with the reflected light from a diffusive surface. However, a significant difference exists between the manner in which these two methods form their resulting interferograms. Shearography is a common path intereferometer; the reference beam is derived from the same beam as that used to probe the object. This distinction has a number of advantages including tolerance to rigid body motions, reduced laser coherence requirements, compact design, convenient sensitivity adjustment, and direct measurement of differential displacement. The advent of modern video cameras has allowed designers to build upon these intrinsic advantages producing a portable low-cost sensor. In this configuration, (electronic) shearography has gained acceptance as a nondestructive inspection technique [3–5], which is commonly used on aerospace structures and materials [6–10]
CAPTCHaStar! A novel CAPTCHA based on interactive shape discovery
Over the last years, most websites on which users can register (e.g., email
providers and social networks) adopted CAPTCHAs (Completely Automated Public
Turing test to tell Computers and Humans Apart) as a countermeasure against
automated attacks. The battle of wits between designers and attackers of
CAPTCHAs led to current ones being annoying and hard to solve for users, while
still being vulnerable to automated attacks.
In this paper, we propose CAPTCHaStar, a new image-based CAPTCHA that relies
on user interaction. This novel CAPTCHA leverages the innate human ability to
recognize shapes in a confused environment. We assess the effectiveness of our
proposal for the two key aspects for CAPTCHAs, i.e., usability, and resiliency
to automated attacks. In particular, we evaluated the usability, carrying out a
thorough user study, and we tested the resiliency of our proposal against
several types of automated attacks: traditional ones; designed ad-hoc for our
proposal; and based on machine learning. Compared to the state of the art, our
proposal is more user friendly (e.g., only some 35% of the users prefer current
solutions, such as text-based CAPTCHAs) and more resilient to automated
attacks.Comment: 15 page
Allelomimesis as universal clustering mechanism for complex adaptive systems
Animal and human clusters are complex adaptive systems and many are organized
in cluster sizes that obey the frequency-distribution . Exponent describes the relative abundance of the cluster
sizes in a given system. Data analyses have revealed that real-world clusters
exhibit a broad spectrum of -values, . We show that allelomimesis is a
fundamental mechanism for adaptation that accurately explains why a broad
spectrum of -values is observed in animate, human and inanimate cluster
systems. Previous mathematical models could not account for the phenomenon.
They are hampered by details and apply only to specific systems such as cities,
business firms or gene family sizes. Allelomimesis is the tendency of an
individual to imitate the actions of its neighbors and two cluster systems
yield different values if their component agents display different
allelomimetic tendencies. We demonstrate that allelomimetic adaptation are of
three general types: blind copying, information-use copying, and non-copying.
Allelomimetic adaptation also points to the existence of a stable cluster size
consisting of three interacting individuals.Comment: 8 pages, 5 figures, 2 table
Representations of the Canonical group, (the semi-direct product of the Unitary and Weyl-Heisenberg groups), acting as a dynamical group on noncommuting extended phase space
The unitary irreducible representations of the covering group of the Poincare
group P define the framework for much of particle physics on the physical
Minkowski space P/L, where L is the Lorentz group. While extraordinarily
successful, it does not provide a large enough group of symmetries to encompass
observed particles with a SU(3) classification. Born proposed the reciprocity
principle that states physics must be invariant under the reciprocity transform
that is heuristically {t,e,q,p}->{t,e,p,-q} where {t,e,q,p} are the time,
energy, position, and momentum degrees of freedom. This implies that there is
reciprocally conjugate relativity principle such that the rates of change of
momentum must be bounded by b, where b is a universal constant. The appropriate
group of dynamical symmetries that embodies this is the Canonical group C(1,3)
= U(1,3) *s H(1,3) and in this theory the non-commuting space Q= C(1,3)/
SU(1,3) is the physical quantum space endowed with a metric that is the second
Casimir invariant of the Canonical group, T^2 + E^2 - Q^2/c^2-P^2/b^2 +(2h
I/bc)(Y/bc -2) where {T,E,Q,P,I,Y} are the generators of the algebra of
Os(1,3). The idea is to study the representations of the Canonical dynamical
group using Mackey's theory to determine whether the representations can
encompass the spectrum of particle states. The unitary irreducible
representations of the Canonical group contain a direct product term that is a
representation of U(1,3) that Kalman has studied as a dynamical group for
hadrons. The U(1,3) representations contain discrete series that may be
decomposed into infinite ladders where the rungs are representations of U(3)
(finite dimensional) or C(2) (with degenerate U(1)* SU(2) finite dimensional
representations) corresponding to the rest or null frames.Comment: 25 pages; V2.3, PDF (Mathematica 4.1 source removed due to technical
problems); Submitted to J.Phys.
On the supranational spell of PISA in policy
BACKGROUND: PISA results appear to have a large impact upon government policy. The phenomenon is growing, with more countries taking part in PISA testing and politicians pointing to PISA results as reasons for their reforms.
PURPOSE: The aims of this research were to depict the policy reactions to PISA across a number of jurisdictions, to see whether they exhibited similar patterns and whether the same reforms were evident.
SOURCES OF EVIDENCE: We investigated policy and media reactions to the 2009 and 2012 PISA results in six cases: Canada, China (Shanghai), England, France, Norway and Switzerland. Cases were selected to contrast high-performing jurisdictions (Canada, China) with average performers (England, France, Norway and Switzerland). Countries that had already been well reported on in the literature were excluded (Finland, Germany).
DESIGN AND METHODS: Policy documents, media reports and academic articles in English, French, Mandarin and Norwegian relating to each of the cases were critically evaluated.
RESULTS: A policy reaction of ‘scandalisation’ was evident in four of the six cases; a technique used to motivate change. Five of the six cases showed ‘standards-based reforms’ and two had reforms in line with the ‘ideal-governance’ model. However, these are categorisations: the actual reforms had significant differences across countries. There are chronological problems with the notion that PISA results were causal with regard to policy in some instances. Countries with similar PISA results responded with different policies, reflecting their differing cultural and historical education system trajectories.
CONCLUSIONS: The connection between PISA results and policy is not always obvious. The supranational spell of PISA in policy is in the way that PISA results are used as a magic wand in political rhetoric, as though they conjure particular policy choices. This serves as a distraction from the ideological basis for reforms. The same PISA results could motivate a range of different policy solutions
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