28,338 research outputs found
Property of the spectrum of large-scale magnetic fields from inflation
The property of the spectrum of large-scale magnetic fields generated due to
the breaking of the conformal invariance of the Maxwell theory through some
mechanism in inflationary cosmology is studied. It is shown that the spectrum
of the generated magnetic fields should not be perfectly scale-invariant but be
slightly red so that the amplitude of large-scale magnetic fields can be
stronger than G at the present time. This analysis is performed
by assuming the absence of amplification due to the late-time action of some
dynamo (or similar) mechanism.Comment: 8 pages, no figure; references correcte
Relation Between Einstein And Quantum Field Equations
We show that there exists a choice of scalar field modes, such that the
evolution of the quantum field in the zero-mass and large-mass limits is
consistent with the Einstein equations for the background geometry. This choice
of modes is also consistent with zero production of these particles and thus
corresponds to a preferred vacuum state preserved by the evolution. In the
zero-mass limit, we find that the quantum field equation implies the Einstein
equation for the scale factor of a radiation-dominated universe; in the
large-mass case, it implies the corresponding Einstein equation for a
matter-dominated universe. Conversely, if the classical radiation-dominated or
matter-dominated Einstein equations hold, there is no production of scalar
particles in the zero and large mass limits, respectively. The suppression of
particle production in the large mass limit is over and above the expected
suppression at large mass. Our results hold for a certain class of conformally
ultrastatic background geometries and therefore generalize previous results by
one of us for spatially flat Robertson-Walker background geometries. In these
geometries, we find that the temporal part of the graviton equations reduces to
the temporal equation for a massless minimally coupled scalar field, and
therefore the results for massless particle production hold also for gravitons.
Within the class of modes we study, we also find that the requirement of zero
production of massless scalar particles is not consistent with a non-zero
cosmological constant. Possible implications are discussed.Comment: Latex, 24 pages. Minor changes in text from original versio
Seasonal predictability of the winter North Atlantic Oscillation from a jet stream perspective
The winter North Atlantic Oscillation (NAO) has varied on interannual and decadal
timescales over the last century, associated with variations in the speed and latitude of the eddy-driven jet
stream. This paper uses hindcasts from two operational seasonal forecast systems (the European Centre for
Medium-range Weather Forecasts's seasonal forecast system, and the U.K. Met Office global seasonal
forecast system) and a century-long atmosphere-only experiment (using the European Centre for
Medium-range Weather Forecasts's Integrated Forecasting System model) to relate seasonal prediction
skill in the NAO to these aspects of jet variability. This shows that the NAO skill realized so far arises from
interannual variations in the jet, largely associated with its latitude rather than speed. There likely remains
further potential for predictability on longer, decadal timescales. In the small sample of models analyzed
here, improved representation of the structure of jet variability does not translate to enhanced seasonal
forecast skill
Detection of solvents using a distributed fibre optic sensor
A fibre optic sensor that is capable of distributed detection of liquid solvents is presented. Sensor interrogation using optical time domain reflectometry (OTDR) provides the capability of locating solvent spills to a precision of ±2 m over a total sensor length that may extend to 20 km
Polymorphism of Eimerian Oocysts: A Dilemma Posed by Working with Some Naturally Infected Hosts
Morphological variation of sporulated oocysts within individual eimerian species is well documented (Joyner, 1982. In Biology of the Coccidia, P. L. Long (ed.). University Park Press, Baltimore, pp. 35-62). In some cases, oocysts of a single eimerian species are known to vary in size by as much as 40% during patency (Duszynski, 1971, Journal of Parasitology 57: 948-952). During a survey to determine the prevalence of coccidiosis in sandhill cranes (Grus canadensis) wintering in New Mexico (Parker and Duszynski, 1986, Journal of Wildlife Diseases 21: 25-35), marked polymorphism was observed among sporulated oocysts of Eimeria reichenowi. Oocysts were obtained from intestinal contents of cranes necropsied in the field and processed for study by routine sporulation and flotation techniques (Duszynski et al., 1982, Journal of Parasitology 68: 1,146-1,148). Initially, oocysts were categorized into 5 groups based on obvious qualitative/quantitative features including oocyst wall texture, appearance of the sporocyst residuum, and the number of polar bodies. Fifty-seven of 118 (48%) fecal samples with E. reichenowi contained 2 or more morphological types of oocysts. Oocysts were measured under oil immersion (100 x Neofluar objective, Zeiss Universal Photomicroscope) and differences between the 5 oocyst groups were tested for significance (P \u3c0.05) using the Student-Newman-Keuls procedure
Vanishing of Gravitational Particle Production in the Formation of Cosmic Strings
We consider the gravitationally induced particle production from the quantum
vacuum which is defined by a free, massless and minimally coupled scalar field
during the formation of a gauge cosmic string. Previous discussions of this
topic estimate the power output per unit length along the string to be of the
order of ergs/sec/cm in the s-channel. We find that this production
may be completely suppressed. A similar result is also expected to hold for the
number of produced photons.Comment: 10 pages, Plain LaTex. Minor improvements. To appear in PR
Invasive Pneumococcal Serotype 3 Disease Despite Pneumococcal Polysaccharide Vaccine-23
Pneumococcal disease has a high global morbidity and mortality. We report a case of a 63-year old female with a history of vaccination with pneumococcal polysaccharide vaccine-23 (PPSV-23) who was transferred to a tertiary care facility with fever and seizures due to an unknown etiology. The diagnosis of invasive pneumococcal disease (IPD) was based the identification of Streptococcus pneumoniae in the blood (culture; serogroup 3) and cerebrospinal fluid (antigen), and the finding of purulence under pressure at craniotomy. The pneumococcal vaccine should provide protection from IPD. The findings reported here display that IPD can overcome immunity proffered by the pneumococcal vaccine especially in patients with multiple comorbidities. This patient represents those who are under-vaccinated despite national recommendations for pneumococcal vaccination
Anisotropic and long-range vortex interactions in two-dimensional dipolar Bose gases
We perform a theoretical study into how dipole-dipole interactions modify the
properties of superfluid vortices within the context of a two-dimensional
atomic Bose gas of co-oriented dipoles. The reduced density at a vortex acts
like a giant anti-dipole, changing the density profile and generating an
effective dipolar potential centred at the vortex core whose most slowly
decaying terms go as and . These effects modify
the vortex-vortex interaction which, in particular, becomes anisotropic for
dipoles polarized in the plane. Striking modifications to vortex-vortex
dynamics are demonstrated, i.e. anisotropic co-rotation dynamics and the
suppression of vortex annihilation.Comment: PRL accepted, 6 pages, 5 figure
Solar Flare Intermittency and the Earth's Temperature Anomalies
We argue that earth's short-term temperature anomalies and the solar flare
intermittency are linked. The analysis is based upon the study of the scaling
of both the spreading and the entropy of the diffusion generated by the
fluctuations of the temperature time series. The joint use of these two methods
evidences the presence of a L\'{e}vy component in the temporal persistence of
the temperature data sets that corresponds to the one that would be induced by
the solar flare intermittency. The mean monthly temperature datasets cover the
period from 1856 to 2002.Comment: 4 pages, 5 figure
Alkali oxide-tantalum, niobium and antimony oxide ionic conductors
The phase equilibrium relations of four systems were investigated in detail. These consisted of sodium and potassium antimonates with antimony oxide and tantalum and niobium oxide with rubidium oxide as far as the ratio 4Rb2O:llB2O5 (B=Nb, Ta). The ternary system NaSbO3-Sb2O4-NaF was investigated extensively to determine the actual composition of the body centered cubic sodium antimonate. Various other binary and ternary oxide systems involving alkali oxides were examined in lesser detail. The phases synthesized were screened by ion exchange methods to determine mobility of the mobility of the alkali ion within the niobium, tantalum or antimony oxide (fluoride) structural framework. Five structure types warranted further investigation; these structure types are (1) hexagonal tungsten bronze (HTB), (2) pyrochlore, (3) the hybrid HTB-pyrochlore hexagonal ordered phases, (4) body centered cubic antimonates and (5) 2K2O:3Nb2O5. Although all of these phases exhibit good ion exchange properties only the pyrochlore was prepared with Na(+) ions as an equilibrium phase and as a low porosity ceramic. Sb(+3) in the channel interferes with ionic conductivity in this case, although relatively good ionic conductivity was found for the metastable Na(+) ion exchanged analogs of RbTa2O5F and KTaWO6 pyrochlore phases
- …