14,358 research outputs found
Sound clocks and sonic relativity
Sound propagation within certain non-relativistic condensed matter models
obeys a relativistic wave equation despite such systems admitting entirely
non-relativistic descriptions. A natural question that arises upon
consideration of this is, "do devices exist that will experience the relativity
in these systems?" We describe a thought experiment in which 'acoustic
observers' possess devices called sound clocks that can be connected to form
chains. Careful investigation shows that appropriately constructed chains of
stationary and moving sound clocks are perceived by observers on the other
chain as undergoing the relativistic phenomena of length contraction and time
dilation by the Lorentz factor, with c the speed of sound. Sound clocks within
moving chains actually tick less frequently than stationary ones and must be
separated by a shorter distance than when stationary to satisfy simultaneity
conditions. Stationary sound clocks appear to be length contracted and time
dilated to moving observers due to their misunderstanding of their own state of
motion with respect to the laboratory. Observers restricted to using sound
clocks describe a universe kinematically consistent with the theory of special
relativity, despite the preferred frame of their universe in the laboratory.
Such devices show promise in further probing analogue relativity models, for
example in investigating phenomena that require careful consideration of the
proper time elapsed for observers.Comment: (v2) consistent with published version; (v1) 15 pages, 9 figure
A new PPN parameter to test Chern-Simons gravity
We study Chern-Simons (CS) gravity in the parameterized post-Newtonian (PPN)
framework through a weak-field solution of the modified field equations. We
find that CS gravity possesses the same PPN parameters as general relativity,
except for the inclusion of a new term, proportional to the CS coupling and the
curl of the PPN vector potential. This new term leads to a modification of
frame dragging and gyroscopic precession and we provide an estimate of its
size. This correction might be used in experiments, such as Gravity Probe B, to
bound CS gravity and test string theory.Comment: 4 pages, replaced with version accepted for publication in Phys. Rev.
Letters (December, 2007
Gap and channelled plasmons in tapered grooves: a review
Tapered metallic grooves have been shown to support plasmons --
electromagnetically coupled oscillations of free electrons at metal-dielectric
interfaces -- across a variety of configurations and V-like profiles. Such
plasmons may be divided into two categories: gap-surface plasmons (GSPs) that
are confined laterally between the tapered groove sidewalls and propagate
either along the groove axis or normal to the planar surface, and channelled
plasmon polaritons (CPPs) that occupy the tapered groove profile and propagate
exclusively along the groove axis. Both GSPs and CPPs exhibit an assortment of
unique properties that are highly suited to a broad range of cutting-edge
nanoplasmonic technologies, including ultracompact photonic circuits,
quantum-optics components, enhanced lab-on-a-chip devices, efficient
light-absorbing surfaces and advanced optical filters, while additionally
affording a niche platform to explore the fundamental science of plasmon
excitations and their interactions. In this Review, we provide a research
status update of plasmons in tapered grooves, starting with a presentation of
the theory and important features of GSPs and CPPs, and follow with an overview
of the broad range of applications they enable or improve. We cover the
techniques that can fabricate tapered groove structures, in particular
highlighting wafer-scale production methods, and outline the various photon-
and electron-based approaches that can be used to launch and study GSPs and
CPPs. We conclude with a discussion of the challenges that remain for further
developing plasmonic tapered-groove devices, and consider the future directions
offered by this select yet potentially far-reaching topic area.Comment: 32 pages, 34 figure
Expression of foraging and Gp-9 are associated with social organization in the fire ant Solenopsis invicta.
The aim of this study was to investigate levels of expression of two major genes, the odorant binding protein Gp-9 (general protein-9) and foraging, that have been shown to be associated with behavioural polymorphisms in ants. We analysed workers and young nonreproductive queens collected from nests of the monogyne (single reproductive queen per nest) and polygyne (multiple reproductive queens) social forms of Solenopsis invicta. In workers but not young queens, the level of foraging expression was significantly associated with social form and the task performed (ie localization in the nest or foraging area). The level of expression of Gp-9 was also associated with social form and worker localization. In addition there was a higher level of expression of the Gp-9(b) allele compared with the Gp-9(B) allele in the heterozygote workers and the young nonreproductive queens. Finally, in the polygyne colonies the level of expression of foraging was not significantly associated with the Gp-9 genotype for either workers or young nonreproductive queens, suggesting that both genes have independent non-epistatic effects on behaviour in S. invicta
Towards Intelligent Databases
This article is a presentation of the objectives and techniques
of deductive databases. The deductive approach to databases aims at extending
with intensional definitions other database paradigms that describe
applications extensionaUy. We first show how constructive specifications can
be expressed with deduction rules, and how normative conditions can be defined
using integrity constraints. We outline the principles of bottom-up and
top-down query answering procedures and present the techniques used for
integrity checking. We then argue that it is often desirable to manage with
a database system not only database applications, but also specifications of
system components. We present such meta-level specifications and discuss
their advantages over conventional approaches
The potential therapeutic effects of creatine supplementation on body composition and muscle function in cancer
Low muscle mass in individuals with cancer has a profound impact on quality of life and independence and is associated with greater treatment toxicity and poorer prognosis. Exercise interventions are regularly being investigated as a means to ameliorate treatment-related adverse effects, and nutritional/supplementation strategies to augment adaptations to exercise are highly valuable. Creatine (Cr) is a naturally-occurring substance in the human body that plays a critical role in energy provision during muscle contraction. Given the beneficial effects of Cr supplementation on lean body mass, strength, and physical function in a variety of clinical populations, there is therapeutic potential in individuals with cancer at heightened risk for muscle loss. Here, we provide an overview of Cr physiology, summarize the evidence on the use of Cr supplementation in various aging/clinical populations, explore mechanisms of action, and provide perspectives on the potential therapeutic role of Cr in the exercise oncology setting
Rotating superfluids in anharmonic traps: From vortex lattices to giant vortices
We study a superfluid in a rotating anharmonic trap and explicate a rigorous
proof of a transition from a vortex lattice to a giant vortex state as the
rotation is increased beyond a limiting speed determined by the interaction
strength. The transition is characterized by the disappearance of the vortices
from the annulus where the bulk of the superfluid is concentrated due to
centrifugal forces while a macroscopic phase circulation remains. The analysis
is carried out within two-dimensional Gross-Pitaevskii theory at large coupling
constant and reveals significant differences between 'soft' anharmonic traps
(like a quartic plus quadratic trapping potential) and traps with a fixed
boundary: In the latter case the transition takes place in a parameter regime
where the size of vortices is very small relative to the width of the annulus
whereas in 'soft' traps the vortex lattice persists until the width of the
annulus becomes comparable to the vortex cores. Moreover, the density profile
in the annulus where the bulk is concentrated is, in the 'soft' case,
approximately gaussian with long tails and not of the Thomas-Fermi type like in
a trap with a fixed boundary.Comment: Published version. Typos corrected, references adde
The most influential countries in market orientation: A bibliometric analysis between 1990 and 2016
© The Author(s) 2018. The purpose of this article is to analyze the most productive and influential countries engaging in market orientation (MO) research between 1990 and 2016. This article shows the general trajectories of these countries, the relationships among them, and their research in the area of MO by analyzing results on citations and publications. The article uses applied bibliometric techniques on available information found in the Web of Science. The results show that the 10 leading countries produce more than 70% of total publications, where the United States leads in all indicators, followed by the United Kingdom and China. Furthermore, although there has been a steady increase in overall number of publications, this trend is not shared evenly among different nations
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