1,180 research outputs found
Phi-four solitary waves in a parabolic potentia: existence, stability, and collisional dynamics
We explore a φ4 model with an added external parabolic potential term. This term dramatically alters the spectral properties of the system. We identify single and multiple kink solutions and examine their stability features; importantly, all of the stationary structures turn out to be unstable. We complement these with a dynamical study of the evolution of a single kink in the trap, as well as of the scattering of kink and anti-kink solutions of the model. We observe that some of the key characteristics of kink-antikink collisions, such as the critical velocity and the multi-bounce windows, are sensitively dependent on the trap strength parameter, as well as the initial displacement of the kink and antikink.Accepted manuscrip
An overview of Polaroid sun eyewear: Function, application and market
Patients are constantly looking for the newest technologies that will assist them in accomplishing the activities that they desire more comfortably and efficiently, in both their personal and professional lives. It is our responsibility as primary care practitioners to be current with the latest advancement in ophthalmic therapies, and effectively pass this knowledge on to our patients. This paper will encompass the properties of specialty protective sun eyewear, emphasizing polarized sunglasses, and how they can be incorporated into a private practice as a viable profit center. The intent is to provide the practitioner with a general overview of the basic properties of light and the history of polarized sunglasses and the functional benefits that they may offer consumers. This review will help to enable a practitioner to feel confident and more comfortable in prescribing and recommending these specialty performance lenses to their patients
On Witten's Instability and Winding Tachyons
We investigate, from a spacetime perspective, some aspects of Horowitz's
recent conjecture that black strings may catalyze the decay of Kaluza-Klein
spacetimes into a bubble of nothing. We identify classical configurations that
interpolate between flat space and the bubble, and discuss the energetics of
the transition. We investigate the effects of winding tachyons on the size and
shape of the barrier and find no evidence at large compactification radius that
tachyons enhance the tunneling rate. For the interesting radii, of order the
string scale, the question is difficult to answer due to the failure of the
expansion.Comment: 15 pages, 2 figures, Late
The Refractive Index of Curved Spacetime II: QED, Penrose Limits and Black Holes
This work considers the way that quantum loop effects modify the propagation
of light in curved space. The calculation of the refractive index for scalar
QED is reviewed and then extended for the first time to QED with spinor
particles in the loop. It is shown how, in both cases, the low frequency phase
velocity can be greater than c, as found originally by Drummond and Hathrell,
but causality is respected in the sense that retarded Green functions vanish
outside the lightcone. A "phenomenology" of the refractive index is then
presented for black holes, FRW universes and gravitational waves. In some
cases, some of the polarization states propagate with a refractive index having
a negative imaginary part indicating a potential breakdown of the optical
theorem in curved space and possible instabilities.Comment: 62 pages, 14 figures, some signs corrected in formulae and graph
Prepyramid-to-pyramid transition of SiGe islands on Si(001)
The morphology of the first three-dimensional islands appearing during
strained growth of SiGe alloys on Si(001) was investigated by scanning
tunneling microscopy. High resolution images of individual islands and a
statistical analysis of island shapes were used to reconstruct the evolution of
the island shape as a function of size. As they grow, islands undergo a
transition from completely unfacetted rough mounds (prepyramids) to partially
{105} facetted islands and then they gradually evolve to {105} facetted
pyramids. The results are in good agreement with the predictions of a recently
proposed theoretical model
Twin Paradox and the logical foundation of relativity theory
We study the foundation of space-time theory in the framework of first-order
logic (FOL). Since the foundation of mathematics has been successfully carried
through (via set theory) in FOL, it is not entirely impossible to do the same
for space-time theory (or relativity). First we recall a simple and streamlined
FOL-axiomatization SpecRel of special relativity from the literature. SpecRel
is complete with respect to questions about inertial motion. Then we ask
ourselves whether we can prove usual relativistic properties of accelerated
motion (e.g., clocks in acceleration) in SpecRel. As it turns out, this is
practically equivalent to asking whether SpecRel is strong enough to "handle"
(or treat) accelerated observers. We show that there is a mathematical
principle called induction (IND) coming from real analysis which needs to be
added to SpecRel in order to handle situations involving relativistic
acceleration. We present an extended version AccRel of SpecRel which is strong
enough to handle accelerated motion, in particular, accelerated observers.
Among others, we show that the Twin Paradox becomes provable in AccRel, but it
is not provable without IND.Comment: 24 pages, 6 figure
A comprehensive strategy to tackle arsenic contamination of drinking water in Uttar Pradesh in India
Exposure to naturally occurring arsenic through consumption of contaminated groundwater, food and soil is now widely
recognized as a new threat to public health in several countries in South and South-East Asia, including parts of India.
The realization that arsenic not only occurs in groundwater used for drinking in the Ganges-Brahmaputra delta of West
Bengal in India, but also further upstream in Bihar and Uttar Pradesh in the middle and upper Gangetic plains, has
necessitated the need to develop arsenic testing and mitigation strategies in these states. This paper outlines the strategy
evolved by the state government of Uttar Pradesh, with the support of UNICEF, to tackle the problem of arsenic in
groundwater used for drinking. The comprehensive approach includes testing, communication, mitigation and health
aspects, and novel strategies used to overcome technological issues are detailed. A similar approach has been used in
the neighbouring state of Bihar
Lodged in the throat: Internal infinities and AdS/CFT
In the context of AdS3/CFT2, we address spacetimes with a certain sort of
internal infinity as typified by the extreme BTZ black hole. The internal
infinity is a null circle lying at the end of the black hole's infinite throat.
We argue that such spacetimes may be described by a product CFT of the form
CFT-L * CFT-R, where CFT-R is associated with the asymptotically AdS boundary
while CFT-L is associated with the null circle. Our particular calculations
analyze the CFT dual of the extreme BTZ black hole in a linear toy model of
AdS3/CFT2. Since the BTZ black hole is a quotient of AdS3, the dual CFT state
is a corresponding quotient of the CFT vacuum state. This state turns out to
live in the aforementioned product CFT. We discuss this result in the context
of general issues of AdS/CFT duality and entanglement entropy.Comment: 11 pages, 2 figures; v2 - some typos corrected, minor revision
Superconducting p-branes and Extremal Black Holes
In Einstein-Maxwell theory, magnetic flux lines are `expelled' from a black
hole as extremality is approached, in the sense that the component of the field
strength normal to the horizon goes to zero. Thus, extremal black holes are
found to exhibit the sort of `Meissner effect' which is characteristic of
superconducting media. We review some of the evidence for this effect, and do
present new evidence for it using recently found black hole solutions in string
theory and Kaluza-Klein theory. We also present some new solutions, which arise
naturally in string theory, which are non-superconducting extremal black holes.
We present a nice geometrical interpretation of these effects derived by
looking carefully at the higher dimensional configurations from which the lower
dimensional black hole solutions are obtained. We show that other extremal
solitonic objects in string theory (such as p-branes) can also display
superconducting properties. In particular, we argue that the relativistic
London equation will hold on the worldvolume of `light' superconducting
p-branes (which are embedded in flat space), and that minimally coupled zero
modes will propagate in the adS factor of the near-horizon geometries of
`heavy', or gravitating, superconducting p-branes.Comment: 22 pages, 2 figure
Different Modes of Retrovirus Restriction by Human APOBEC3A and APOBEC3G In Vivo
The apolipoprotein B editing complex 3 (A3) cytidine deaminases are among the most highly evolutionarily selected retroviral restriction factors, both in terms of gene copy number and sequence diversity. Primate genomes encode seven A3 genes, and while A3F and 3G are widely recognized as important in the restriction of HIV, the role of the other genes, particularly A3A, is not as clear. Indeed, since human cells can express multiple A3 genes, and because of the lack of an experimentally tractable model, it is difficult to dissect the individual contribution of each gene to virus restriction in vivo. To overcome this problem, we generated human A3A and A3G transgenic mice on a mouse A3 knockout background. Using these mice, we demonstrate that both A3A and A3G restrict infection by murine retroviruses but by different mechanisms: A3G was packaged into virions and caused extensive deamination of the retrovirus genomes while A3A was not packaged and instead restricted infection when expressed in target cells. Additionally, we show that a murine leukemia virus engineered to express HIV Vif overcame the A3G-mediated restriction, thereby creating a novel model for studying the interaction between these proteins. We have thus developed an in vivo system for understanding how human A3 proteins use different modes of restriction, as well as a means for testing therapies that disrupt HIV Vif-A3G interactions
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