6,021 research outputs found
Physical aspects of oracles for randomness, and Hadamard's conjecture
We analyze the physical aspects and origins of currently proposed oracles for
(absolute) randomness.Comment: 10 pages, 3 figures. arXiv admin note: substantial text overlap with
arXiv:1405.140
SUSApp: a mobile app for measuring and comparing questionnaire-based usability assessments
Usability questionnaires are one of the most used methods to
measure usability in terms of the user’s subjective satisfaction.
However, most of the usability questionnaires do not provide a
complete environment to store measurements and compare
different usability values of application categories and versions
over the long term, which makes it difficult to study the usability
of a software product or even the usability of different versions of
such products over time, hindering the facility to obtain
comparisons and thresholds in usability measurements for
different product lines. In this paper we present SUSApp, a tool
conceived for the analysis of usability through the SUS (System
Usability Scale) questionnaire, which is one of the most popular
ones. This tool was conceived for mobile platforms, and it is
intended to easily analyze usability by storing and recovering past
evaluations, and allowing to statistically compare usability
measurements among different software products and applications
categories. In addition, a user testing is presented. This has
provided acceptable usability results concerning SUSApp in an
experiment with real usersThis work has been partially supported by the funding projects
«eMadrid-CM», granted by the Madrid Research Council (project
code S2013/ICE-2715), and «Flexor» granted by the Spanish
Government (project code TIN2014-52129-R
A dark energy multiverse
We present cosmic solutions corresponding to universes filled with dark and
phantom energy, all having a negative cosmological constant. All such solutions
contain infinite singularities, successively and equally distributed along
time, which can be either big bang/crunchs or big rips singularities.
Classicaly these solutions can be regarded as associated with multiverse
scenarios, being those corresponding to phantom energy that may describe the
current accelerating universe
Fundamental limitations on "warp drive" spacetimes
"Warp drive" spacetimes are useful as "gedanken-experiments" that force us to
confront the foundations of general relativity, and among other things, to
precisely formulate the notion of "superluminal" communication. We verify the
non-perturbative violation of the classical energy conditions of the Alcubierre
and Natario warp drive spacetimes and apply linearized gravity to the
weak-field warp drive, testing the energy conditions to first and second order
of the non-relativistic warp-bubble velocity. We are primarily interested in a
secondary feature of the warp drive that has not previously been remarked upon,
if it could be built, the warp drive would be an example of a "reaction-less
drive". For both the Alcubierre and Natario warp drives we find that the
occurrence of significant energy condition violations is not just a high-speed
effect, but that the violations persist even at arbitrarily low speeds.
An interesting feature of this construction is that it is now meaningful to
place a finite mass spaceship at the center of the warp bubble, and compare the
warp field energy with the mass-energy of the spaceship. There is no hope of
doing this in Alcubierre's original version of the warp-field, since by
definition the point in the center of the warp bubble moves on a geodesic and
is "massless". That is, in Alcubierre's original formalism and in the Natario
formalism the spaceship is always treated as a test particle, while in the
linearized theory we can treat the spaceship as a finite mass object. For both
the Alcubierre and Natario warp drives we find that even at low speeds the net
(negative) energy stored in the warp fields must be a significant fraction of
the mass of the spaceship.Comment: 18 pages, Revtex4. V2: one reference added, some clarifying comments
and discussion, no physics changes, accepted for publication in Classical and
Quantum Gravit
Effect of adherend thickness and mixed mode loading on debond growth in adhesively bonded composite joints
Symmetric and unsymmetric double cantilever beam (DCB) specimens were tested and analyzed to assess the effect of: (1) adherend thickness, and (2) a predominantly mode I mixed mode loading on cyclic debond growth and static fracture toughness. The specimens were made of unidirectional composite (T300/5208) adherends bonded together with EC3445 structural adhesive. The thickness was 8, 16, or 24 plies. The experimental results indicated that the static fracture toughness increases and the cyclic debond growth rate decreases with increasing adherend thickness. This behavior was related to the length of the plastic zone ahead of the debond tip. For the symmetric DCB specimens, it was further found that displacement control tests resulted in higher debond growth rates than did load control tests. While the symmetric DCB tests always resulted in cohesive failures in the bondline, the unsymmetric DCB tests resulted in the debond growing into the thinner adherend and the damage progressing as delamination in that adherend. This behavior resulted in much lower fracture toughness and damage growth rates than found in the symmetric DCB tests
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