6,319 research outputs found
A Quantum-Gravity Perspective on Semiclassical vs. Strong-Quantum Duality
It has been argued that, underlying M-theoretic dualities, there should exist
a symmetry relating the semiclassical and the strong-quantum regimes of a given
action integral. On the other hand, a field-theoretic exchange between long and
short distances (similar in nature to the T-duality of strings) has been shown
to provide a starting point for quantum gravity, in that this exchange enforces
the existence of a fundamental length scale on spacetime. In this letter we
prove that the above semiclassical vs. strong-quantum symmetry is equivalent to
the exchange of long and short distances. Hence the former symmetry, as much as
the latter, also enforces the existence of a length scale. We apply these facts
in order to classify all possible duality groups of a given action integral on
spacetime, regardless of its specific nature and of its degrees of freedom.Comment: 10 page
Radicals and primes in incidence algebras
AbstractThe nil radicals of an incidence algebra are determined. The prime ideal structure of the algebra and the unboundedness of the underlying partial order are related, leading to a notion of topological end for ordered sets
Gravity from the extension of spatial diffeomorphisms
The possibility of the extension of spatial diffeomorphisms to a larger
family of symmetries in a class of classical field theories is studied. The
generator of the additional local symmetry contains a quadratic kinetic term
and a potential term which can be a general (not necessarily local) functional
of the metric. From the perspective of the foundation of Einstein's gravity our
results are positive: The extended constraint algebra is either that of
Einstein's gravity, or ultralocal gravity. If our goal is a simple modification
of Einstein's gravity that for example makes it perturbatively renormalizable,
as has recently been suggested, then our results show that there is no such
theory within this class.Comment: 34 page
Coupling between static friction force and torque
We show that the static friction force which must be overcome to render a
sticking contact sliding is reduced if an external torque is also exerted. As a
test system we study a planar disk lying on horizontal flat surface. We perform
experiments and compare with analytical results to find that the coupling
between static friction force and torque is nontrivial: It is not determined by
the Coulomb friction laws alone, instead it depends on the microscopic details
of friction. Hence, we conclude that the macroscopic experiment presented here
reveals details about the microscopic processes lying behind friction.Comment: 6 pages, 4 figures, revte
Nasal Morphology of the Chinese: Three-Dimensional Reference Values for Rhinoplasty
OBJECTIVE: To determine normative nasal measurements for Chinese young adults, conditioned on demographics.
STUDY DESIGN: A cross-sectional descriptive study.
SETTING: A university hospital.
SUBJECTS AND METHODS: Three-dimensional (3D) photographs were captured from 103 Chinese subjects between 18 and 35 years of age using a commercial stereophotographic system. Anthropometric landmarks were identified on these 3D surface images, and measurements suitable for nasal analysis were performed and contrasted against established Caucasian norms. Gender differences in anthropometric dimensions were also analyzed.
RESULTS: Normative data for these measurements are made available. Linear nasal measurements, except those for mid-columella length, were significantly larger in men than in women; further, the nasal tip angle and nasofrontal angle were significantly larger in Chinese women. Contrasts of these new data against published Caucasian norms revealed dimensions that differ for these 2 groups. The Chinese normative mean values for morphological nose width, nasal tip angle, nasofrontal angle, and alar slope angle exceeded those reported for North American Caucasians.
CONCLUSIONS: Gender-specific normative data for the Chinese nose were established in this study to provide a useful tool for surgeons in dealing with rhinoplasty. Moreover, the Chinese nasal anthropometric measurements in this study are broader and flatter than those reported for North American Caucasians.
© American Academy of Otolaryngology—Head and Neck Surgery Foundation 2014.postprin
Construction of equilibrium networks with an energy function
We construct equilibrium networks by introducing an energy function depending
on the degree of each node as well as the product of neighboring degrees. With
this topological energy function, networks constitute a canonical ensemble,
which follows the Boltzmann distribution for given temperature. It is observed
that the system undergoes a topological phase transition from a random network
to a star or a fully-connected network as the temperature is lowered. Both
mean-field analysis and numerical simulations reveal strong first-order phase
transitions at temperatures which decrease logarithmically with the system
size. Quantitative discrepancies of the simulation results from the mean-field
prediction are discussed in view of the strong first-order nature.Comment: To appear in J. Phys.
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Problematic Internet Use and Problematic Online Gaming Are Not the Same: Findings from a Large Nationally Representative Adolescent Sample
There is an ongoing debate in the literature whether problematic internet use (PIU) and problematic online gaming (POG) are two distinct conceptual and nosological entities or whether they are the same. The present study contributes to this question by examining the interrelationship and the overlap between PIU and POG in terms of gender, school achievement, time spent using the internet and/or online gaming, psychological wellbeing, and preferred online activities. Questionnaires assessing these variables were administered to a nationally representative sample of adolescent gamers (N=2,073; mean age 16.4 years, SD=0.87, 68.4% male). Data showed that internet use was a common activity among adolescents while online gaming was engaged in by a considerably smaller group. Similarly, more adolescents met the criteria for PIU than for POG and a small group of adolescents showed symptoms of both problem behaviors. The most notable difference between the two problem behaviors was in terms of gender. POG was much more strongly associated with being male. Self-esteem had low effect sizes on both behaviors, while depressive symptoms were associated with both PIU and POG, affecting PIU slightly more. In terms of preferred online activities, PIU was positively associated with online gaming, online chatting, and social networking while POG was only associated with online gaming. Based on our findings POG appears to be a conceptually different behavior than PIU and therefore data support the notion that Internet Addiction Disorder and Internet Gaming Disorder are separate nosological entities
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