931 research outputs found
Magnetic relaxation of a system of superparamagnetic particles weakly coupled by dipole-dipole interactions
The effect of long range dipole-dipole interactions on the thermal
fluctuations of the magnetization of an assembly of single-domain ferromagnetic
particles is considered. If orientational correlations between the particles
are neglected, the evolution of the magnetization orientations may be described
by a nonlinear Fokker-Planck equation (FPE) reducing to the usual linear one in
the limit of infinite dilution [W.F. Brown Jr, Phys. Rev. 130, 1677 (1963)].
The thermally activated relaxation time scale of the assembly is estimated,
leading to a simple modification of the axially symmetric asymptotes for the
superparamagnetic relaxation time.Comment: 31 pages, 3 figures, regular articl
A Bayesian framework for verification and recalibration of ensemble forecasts: How uncertain is NAO predictability?
Predictability estimates of ensemble prediction systems are uncertain due to
limited numbers of past forecasts and observations. To account for such
uncertainty, this paper proposes a Bayesian inferential framework that provides
a simple 6-parameter representation of ensemble forecasting systems and the
corresponding observations. The framework is probabilistic, and thus allows for
quantifying uncertainty in predictability measures such as correlation skill
and signal-to-noise ratios. It also provides a natural way to produce
recalibrated probabilistic predictions from uncalibrated ensembles forecasts.
The framework is used to address important questions concerning the skill of
winter hindcasts of the North Atlantic Oscillation for 1992-2011 issued by the
Met Office GloSea5 climate prediction system. Although there is much
uncertainty in the correlation between ensemble mean and observations, there is
strong evidence of skill: the 95% credible interval of the correlation
coefficient of [0.19,0.68] does not overlap zero. There is also strong evidence
that the forecasts are not exchangeable with the observations: With over 99%
certainty, the signal-to-noise ratio of the forecasts is smaller than the
signal-to-noise ratio of the observations, which suggests that raw forecasts
should not be taken as representative scenarios of the observations. Forecast
recalibration is thus required, which can be coherently addressed within the
proposed framework.Comment: 36 pages, 10 figure
Investigating the source of Planck-detected AME: high resolution observations at 15 GHz
The Planck 28.5 GHz maps were searched for potential Anomalous Microwave
Emission (AME) regions on the scale of or smaller, and several
new regions of interest were selected. Ancillary data at both lower and higher
frequencies were used to construct spectral energy distributions (SEDs), which
seem to confirm an excess consistent with spinning dust models. Here we present
higher resolution observations of two of these new regions with the Arcminute
Microkelvin Imager Small Array (AMI SA) between 14 and 18 GHz to test for the
presence of a compact (10 arcmin or smaller) component. For
AME-G107.1+5.2, dominated by the {\sc Hii} region S140, we find evidence for
the characteristic rising spectrum associated with the either the spinning dust
mechanism for AME or an ultra/hyper-compact \textsc{Hii} region across the AMI
frequency band, however for AME-G173.6+2.8 we find no evidence for AME on
scales of arcmin.Comment: 13 pages, 8 figures, 4 tables. Submitted to Advances in Astronomy AME
Special Issu
Optical nonlinearity enhancement of graded metallic films
The effective linear and third-order nonlinear susceptibility of graded
metallic films with weak nonlinearity have been investigated. Due to the simple
geometry, we were able to derive exactly the local field inside the graded
structures having a Drude dielectric gradation profile. We calculated the
effective linear dielectric constant and third-order nonlinear susceptibility.
We investigated the surface plasmon resonant effect on the optical absorption,
optical nonlinearity enhancement, and figure of merit of graded metallic films.
It is found that the presence of gradation in metallic films yields a broad
resonant plasmon band in the optical region, resulting in a large enhancement
of the optical nonlinearity and hence a large figure of merit. We suggest
experiments be done to check our theoretical predictions, because graded
metallic films can be fabricated more easily than graded particles.Comment: 11 pages, 2 eps figures, submitted to Applied Physics Letter
Solvated dissipative electro-elastic network model of hydrated proteins
Elastic netwok models coarse grain proteins into a network of residue beads
connected by springs. We add dissipative dynamics to this mechanical system by
applying overdamped Langevin equations of motion to normal-mode vibrations of
the network. In addition, the network is made heterogeneous and softened at the
protein surface by accounting for hydration of the ionized residues. Solvation
changes the network Hessian in two ways. Diagonal solvation terms soften the
spring constants and off-diagonal dipole-dipole terms correlate displacements
of the ionized residues. The model is used to formulate the response functions
of the electrostatic potential and electric field appearing in theories of
redox reactions and spectroscopy. We also formulate the dielectric response of
the protein and find that solvation of the surface ionized residues leads to a
slow relaxation peak in the dielectric loss spectrum, about two orders of
magnitude slower than the main peak of protein relaxation. Finally, the
solvated network is used to formulate the allosteric response of the protein to
ion binding. The global thermodynamics of ion binding is not strongly affected
by the network solvation, but it dramatically enhances conformational changes
in response to placing a charge at the active site of the protein
A rhoptry antigen of Plasmodium falciparum is protective in Saimiri monkeys
A non-polymorphic antigen associated with the rhoptry organelles of Plasmodium falciparum has been purified by immuno-affinity chromatography. The antigen, RAP-1 (rhoptry associated protein-1). which is defined by monoclonal antibodies which inhibit parasite growth in vitro, is a multi-component antigen consisting of four major proteins of 80, 65, 42 and 40 kDa and two minor proteins of 77 and 70 kDa. These proteins were electro-eluted from preparative sodium dodecyl sulphate polyacrylamide gels and protected Saimiri sciureus monkeys from a lethal blood-stage infection of P. falciparum malaria. Sera from the protected animals recognized only proteins of the RAP-1 antigen when used to probe a Western blot of total parasite protein extract, confirming that RAP-1 is responsible for eliciting the protective immune respons
Intraseasonal effects of El Niño-Southern Oscillation on North Atlantic climate
This is the final version. Available from American Meteorological Society via the DOI in this record.It is well established that El Niño-Southern Oscillation (ENSO) impacts the North Atlantic-European (NAE) climate, with the strongest influence in winter. In late winter, the ENSO signal travels via both tropospheric and stratospheric pathways to the NAE sector and often projects onto the North Atlantic Oscillation. However, this signal does not strengthen gradually during winter, and some studies have suggested that the ENSO signal is different between early and late winter and that the teleconnections involved in the early winter subperiod are not well understood. In this study, we investigate the ENSO teleconnection to NAE in early winter (November-December) and characterize the possible mechanisms involved in that teleconnection. To do so, observations, reanalysis data and the output of different types of model simulations have been used. We show that the intraseasonal winter shift of the NAE response to ENSO is detected for both El Niño and La Niña and is significant in both observations and initialized predictions, but it is not reproduced by free-running Coupled Model Intercomparison Project phase 5 (CMIP5) models. The teleconnection is established through the troposphere in early winter and is related to ENSO effects over the Gulf of Mexico and Caribbean Sea that appear in rainfall and reach the NAE region. CMIP5 model biases in equatorial Pacific ENSO sea surface temperature patterns and strength appear to explain the lack of signal in the Gulf of Mexico and Caribbean Sea and, hence, their inability to reproduce the intraseasonal shift of the ENSO signal over Europe.European CommissionEuropean CommissionNatural Environment Research Council (NERC
Optical nonlinearity enhancement of graded metal-dielectric composite films
We have derived the local electric field inside graded metal-dielectric
composite films with weak nonlinearity analytically, which further yields the
effective linear dielectric constant and third-order nonlinear susceptibility
of the graded structures. As a result, the composition-dependent gradation can
produce a broad resonant plasmon band in the optical region, resulting in a
large enhancement of the optical nonlinearity and hence a large figure of
merit.Comment: 11 pages, 2 figures. To be published in Europhysics Letter
Tooling materials compatible with carbon fibre composites in a microwave environment
Although metals are the most commonly used tooling materials to cure composites, they do not provide optimal results in a microwave environment. Following a selection process based on the properties of the materials, an alternative tooling material in carbon fibre reinforced plastic (CFRP) was successfully utilised to cure CFRP panels in laboratory and industrial microwaves. The conductive carbon fibres in the tool facilitated the fast heat transfer across the part. Other tooling materials including a glass fibre cyanate ester prepreg and tooling board were trialled, although the latter exhibited damage during cure. These advantages demonstrate that the CFRP tool is a compatible material that can be used when microwave curing composites
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