885 research outputs found
Graviton Propagation and Vacuum Polarization in Curved Space
The effects of vacuum polarization arising from loops of massive scalar
particles on graviton propagation in curved space are considered. Physically,
they are due to curvature induced tidal forces acting on the cloud of virtual
scalar particles surrounding the graviton. The effects are tractable in a WKB
and large mass limit and the results can be written as an effective refractive
index for the graviton modes with both a real and imaginary part. The imaginary
part of the refractive index is a curvature induced contribution to the
wavefunction renormalization of the graviton in real affine time and can have
the effect of dressing or un-dressing the graviton. The real part of the
refractive index increases logarithmically at high frequency as long as the
null energy condition is satisfied by the background.Comment: 21 pages, typos correcte
A Possible Geographic Origin of Endemic Hepatitis C Virus 6a in Hong Kong: Evidences for the Association with Vietnamese Immigration
BACKGROUND: Hepatitis C virus (HCV) 6a accounts for 23.6% of all HCV infections of the general population and 58.5% of intravenous drug users in Hong Kong. However, the geographical origin of this highly predominant HCV subgenotype is largely unknown. This study explores a hypothesis for one possible transmission route of HCV 6a to Hong Kong. METHODS: NS5A sequences derived from 26 HCV 6a samples were chosen from a five year period (1999-2004) from epidemiologically unrelated patients from Hong Kong. Partial-NS5A sequences (513-bp from nt 6728 to 7240) were adopted for Bayesian coalescent analysis to reconstruct the evolutionary history of HCV infections in Hong Kong using the BEAST v1.3 program. A rooted phylogenetic tree was drawn for these sequences by alignment with reference Vietnamese sequences. Demographic data were accessed from "The Statistic Yearbooks of Hong Kong". RESULTS: Bayesian coalescent analysis showed that the rapid increase in 6a infections, which had increased more than 90-fold in Hong Kong from 1986 to 1994 correlated to two peaks of Vietnamese immigration to Hong Kong from 1978 to 1997. The second peak, which occurred from 1987 through 1997, overlapped with the rapid increase of HCV 6a occurrence in Hong Kong. Phylogenetic analyses have further revealed that HCV 6a strains from Vietnam may be ancestral to Hong Kong counterparts. CONCLUSIONS: The high predominance of HCV 6a infections in Hong Kong was possibly associated with Vietnamese immigration during 1987-1997
Quantum to Classical Transition in a Single-Ion Laser
Stimulated emission of photons from a large number of atoms into the mode of
a strong light field is the principle mechanism for lasing in "classical"
lasers. The onset of lasing is marked by a threshold which can be characterised
by a sharp increase in photon flux as a function of external pumping strength.
The same is not necessarily true for the fundamental building block of a laser:
a single trapped atom interacting with a single optical radiation mode. It has
been shown that such a "quantum" laser can exhibit thresholdless lasing in the
regime of strong coupling between atom and radiation field. However, although
theoretically predicted, a threshold at the single-atom level could not be
experimentally observed so far. Here, we demonstrate and characterise a
single-atom laser with and without threshold behaviour by changing the strength
of atom-light field coupling. We observe the establishment of a laser threshold
through the accumulation of photons in the optical mode even for a mean photon
number substantially lower than for the classical case. Furthermore,
self-quenching occurs for very strong external pumping and constitutes an
intrinsic limitation of single-atom lasers. Moreover, we find that the
statistical properties of the emitted light can be adjusted for weak external
pumping, from the quantum to the classical domain. Our observations mark an
important step towards fundamental understanding of laser operation in the
few-atom limit including systems based on semiconductor quantum dots or
molecules.Comment: 19 pages, 4 figures, 10 pages supplement, accepted by Nature Physic
Conformal algebra: R-matrix and star-triangle relation
The main purpose of this paper is the construction of the R-operator which
acts in the tensor product of two infinite-dimensional representations of the
conformal algebra and solves Yang-Baxter equation. We build the R-operator as a
product of more elementary operators S_1, S_2 and S_3. Operators S_1 and S_3
are identified with intertwining operators of two irreducible representations
of the conformal algebra and the operator S_2 is obtained from the intertwining
operators S_1 and S_3 by a certain duality transformation. There are
star-triangle relations for the basic building blocks S_1, S_2 and S_3 which
produce all other relations for the general R-operators. In the case of the
conformal algebra of n-dimensional Euclidean space we construct the R-operator
for the scalar (spin part is equal to zero) representations and prove that the
star-triangle relation is a well known star-triangle relation for propagators
of scalar fields. In the special case of the conformal algebra of the
4-dimensional Euclidean space, the R-operator is obtained for more general
class of infinite-dimensional (differential) representations with nontrivial
spin parts. As a result, for the case of the 4-dimensional Euclidean space, we
generalize the scalar star-triangle relation to the most general star-triangle
relation for the propagators of particles with arbitrary spins.Comment: Added references and corrected typo
Chemical Basis of Prey Recognition in Thamnophiine Snakes: The Unexpected New Roles of Parvalbumins
Detecting and locating prey are key to predatory success within trophic chains. Predators use various signals through specialized visual, olfactory, auditory or tactile sensory systems to pinpoint their prey. Snakes chemically sense their prey through a highly developed auxiliary olfactory sense organ, the vomeronasal organ (VNO). In natricine snakes that are able to feed on land and water, the VNO plays a critical role in predatory behavior by detecting cues, known as vomodors, which are produced by their potential prey. However, the chemical nature of these cues remains unclear. Recently, we demonstrated that specific proteins–parvalbumins–present in the cutaneous mucus of the common frog (Rana temporaria) may be natural chemoattractive proteins for these snakes. Here, we show that parvalbumins and parvalbumin-like proteins, which are mainly intracellular, are physiologically present in the epidermal mucous cells and mucus of several frog and fish genera from both fresh and salt water. These proteins are located in many tissues and function as Ca2+ buffers. In addition, we clarified the intrinsic role of parvalbumins present in the cutaneous mucus of amphibians and fishes. We demonstrate that these Ca2+-binding proteins participate in innate bacterial defense mechanisms by means of calcium chelation. We show that these parvalbumins are chemoattractive for three different thamnophiine snakes, suggesting that these chemicals play a key role in their prey-recognition mechanism. Therefore, we suggest that recognition of parvalbumin-like proteins or other calcium-binding proteins by the VNO could be a generalized prey-recognition process in snakes. Detecting innate prey defense mechanism compounds may have driven the evolution of this predator-prey interaction
Causality violation, gravitational shockwaves and UV completion
The effective actions describing the low-energy dynamics of QFTs involving
gravity generically exhibit causality violations. These may take the form of
superluminal propagation or Shapiro time advances and allow the construction of
"time machines", i.e. spacetimes admitting closed non-spacelike curves. Here,
we discuss critically whether such causality violations may be used as a
criterion to identify unphysical effective actions or whether, and how,
causality problems may be resolved by embedding the action in a fundamental, UV
complete QFT. We study in detail the case of photon scattering in an
Aichelburg-Sexl gravitational shockwave background and calculate the phase
shifts in QED for all energies, demonstrating their smooth interpolation from
the causality-violating effective action values at low-energy to their
manifestly causal high-energy limits. At low energies, these phase shifts may
be interpreted as backwards-in-time coordinate jumps as the photon encounters
the shock wavefront, and we illustrate how the resulting causality problems
emerge and are resolved in a two-shockwave time machine scenario. The
implications of our results for ultra-high (Planck) energy scattering, in which
graviton exchange is modelled by the shockwave background, are highlighted.Comment: 42 pages, 15 figures, updated reference
Eliciting a predatory response in the eastern corn snake (Pantherophis guttatus) using live and inanimate sensory stimuli: implications for managing invasive populations
North America's Eastern corn snake (Pantherophis guttatus) has been introduced to several islands throughout the Caribbean and Australasia where it poses a significant threat to native wildlife. Invasive snake control programs often involve trapping with live bait, a practice that, as well as being costly and labour intensive, raises welfare and ethical concerns. This study assessed corn snake response to live and inanimate sensory stimuli in an attempt to inform possible future trapping of the species and the development of alternative trap lures. We exposed nine individuals to sensory cues in the form of odour, visual, vibration and combined stimuli and measured the response (rate of tongue-flick [RTF]). RTF was significantly higher in odour and combined cues treatments, and there was no significant difference in RTF between live and inanimate cues during odour treatments. Our findings suggest chemical cues are of primary importance in initiating predation and that an inanimate odour stimulus, absent of simultaneous visual and vibratory cues, is a potential low-cost alternative trap lure for the control of invasive corn snake populations
Estimating the long-term impact of a prophylactic human papillomavirus 16/18 vaccine on the burden of cervical cancer in the UK
To predict the public health impact on cervical disease by introducing human papillomavirus (HPV) vaccination in the United Kingdom, we developed a mathematical model that can be used to reflect the impact of vaccination in different countries with existing screening programmes. Its use is discussed in the context of the United Kingdom. The model was calibrated with published data. The impact of vaccination on cervical cancer and deaths, precancerous lesions and screening outcomes were estimated for a vaccinated cohort of 12-year-old girls, among which it is estimated that there would be a reduction of 66% in the prevalence of high-grade precancerous lesions and a 76% reduction in cervical cancer deaths. Estimates for various other measures of the population effects of vaccination are also presented. We concluded that it is feasible to forecast the potential effects of HPV vaccination in the context of an existing national screening programme. Results suggest a sizable reduction in the incidence of cervical cancer and related deaths. Areas for future research include investigation of the beneficial effects of HPV vaccination on infection transmission and epidemic dynamics, as well as HPV-related neoplasms in other sites
Phylogeography of Japanese encephalitis virus:genotype is associated with climate
The circulation of vector-borne zoonotic viruses is largely determined by the overlap in the geographical distributions of virus-competent vectors and reservoir hosts. What is less clear are the factors influencing the distribution of virus-specific lineages. Japanese encephalitis virus (JEV) is the most important etiologic agent of epidemic encephalitis worldwide, and is primarily maintained between vertebrate reservoir hosts (avian and swine) and culicine mosquitoes. There are five genotypes of JEV: GI-V. In recent years, GI has displaced GIII as the dominant JEV genotype and GV has re-emerged after almost 60 years of undetected virus circulation. JEV is found throughout most of Asia, extending from maritime Siberia in the north to Australia in the south, and as far as Pakistan to the west and Saipan to the east. Transmission of JEV in temperate zones is epidemic with the majority of cases occurring in summer months, while transmission in tropical zones is endemic and occurs year-round at lower rates. To test the hypothesis that viruses circulating in these two geographical zones are genetically distinct, we applied Bayesian phylogeographic, categorical data analysis and phylogeny-trait association test techniques to the largest JEV dataset compiled to date, representing the envelope (E) gene of 487 isolates collected from 12 countries over 75 years. We demonstrated that GIII and the recently emerged GI-b are temperate genotypes likely maintained year-round in northern latitudes, while GI-a and GII are tropical genotypes likely maintained primarily through mosquito-avian and mosquito-swine transmission cycles. This study represents a new paradigm directly linking viral molecular evolution and climate
The Evolution of Bat Vestibular Systems in the Face of Potential Antagonistic Selection Pressures for Flight and Echolocation
PMCID: PMC3634842This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited
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