21,640 research outputs found
Comment on Higgs Inflation and Naturalness
We rebut the recent claim (arXiv:0912.5463) that Einstein-frame scattering in
the Higgs inflation model is unitary above the cut-off energy Lambda ~ Mp/xi.
We show explicitly how unitarity problems arise in both the Einstein and Jordan
frames of the theory. In a covariant gauge they arise from non-minimal Higgs
self-couplings, which cannot be removed by field redefinitions because the
target space is not flat. In unitary gauge, where there is only a single scalar
which can be redefined to achieve canonical kinetic terms, the unitarity
problems arise through non-minimal Higgs-gauge couplings.Comment: 5 pages, 1 figure V3: Journal Versio
Effects of different combinations of Hoaglandâs solution and Azolla filiculoides on photosynthesis and chlorophyll content in Beta vulgaris subsp. Cycla âfordhook giantâ grown in hydroponic cultures
The assessments of photosynthetic rate, stomatal conductance, evapotranspiration, intercellular CO2 concentration and chlorophyll content in Beta vulgaris subsp. cycla âFordhook Giantâ grown in hydroponic cultures containing different compositions of hydroponic solutions were evaluated in this study. The aim of the study was to quantify the effects of different combinations of Hoaglandâs solution and Azolla filiculoides on photosynthesis processes and chlorophyll content in B. vulgaris grown in hydroponic cultures. The following treatments were evaluated in four replications: (1) Control (Hoaglandâs solution minus N solution excluding Azolla; (2) Hoaglandâs minus N solution including Azolla; (3) full Hoaglandâs solution plus Azolla; and (4) full Hoaglandâs solution excluding Azolla. Results show that photosynthetic rate, evapotranspiration, intercellular CO2 concentration and chlorophyll were generally higher in full Hoaglandâs solution. This was closely followed by full Hoaglandâs solution plus Azolla, and Hoaglandâs minus N solution plus Azolla treatments. The lowest photosynthetic rates and chlorophyll contents were found in the control (Hoaglandâs minus N solution) treatment.Keywords: Photosynthetic rate, stomatal conductance, evapotranspiration, intercellular CO2 concentration, chlorophyll a, chlorophyll bAfrican Journal of Biotechnology Vol. 12(16), pp. 2006-201
Development of a novel forward dynamic programming method for weather routing
This paper presents a novel forward dynamic programming method for weather routing to minimise ship fuel consumption during a voyage. Compared with traditional weather routing methods which only optimise the ship's heading, while the engine power or propeller rotation speed is set as a constant throughout the voyage, this new method considers both the ship power settings and heading controls. A float state technique is used to reduce the iterations required during optimisation and thus save computation time. This new method could lead to quasiglobal optimal routing in comparison with the traditional weather routing methods
Bulk Axions, Brane Back-reaction and Fluxes
Extra-dimensional models can involve bulk pseudo-Goldstone bosons (pGBs)
whose shift symmetry is explicitly broken only by physics localized on branes.
Reliable calculation of their low-energy potential is often difficult because
it requires details of the stabilization of the extra dimensions. In rugby ball
solutions, for which two compact extra dimensions are stabilized in the
presence of only positive-tension brane sources, the effects of brane
back-reaction can be computed explicitly. This allows the calculation of the
shape of the low-energy pGB potential and response of the extra dimensional
geometry as a function of the perturbing brane properties. If the
pGB-dependence is a small part of the total brane tension a very general
analysis is possible, permitting an exploration of how the system responds to
frustration when the two branes disagree on what the proper scalar vacuum
should be. We show how the low-energy potential is given by the sum of brane
tensions (in agreement with common lore) when only the brane tensions couple to
the pGB. We also show how a direct brane coupling to the flux stabilizing the
extra dimensions corrects this result in a way that does not simply amount to
the contribution of the flux to the brane tensions. We calculate the mass of
the would-be zero mode, and briefly describe several potential applications,
including a brane realization of `natural inflation,' and a dynamical mechanism
for suppressing the couplings of the pGB to matter localized on the branes.
Since the scalar can be light enough to be relevant to precision tests of
gravity (in a technically natural way) this mechanism can be relevant to
evading phenomenological bounds.Comment: 36 pages, JHEP styl
Asymptotic Dynamics of High Dynamic Range Stratified Turbulence.
Direct numerical simulations of homogeneous sheared and stably stratified turbulence are considered to probe the asymptotic high dynamic range regime suggested by Gargett et al. J. Fluid Mech. 144, 231 (1984)10.1017/S0022112084001592 and Shih et al. J. Fluid Mech. 525, 193 (1999)10.1017/S0022112004002587. We consider statistically stationary configurations of the flow that span three decades in dynamic range defined by the separation between the Ozmidov length scale L_{O}=sqrt[Δ/N^{3}] and the Kolmogorov length scale L_{K}=(Îœ^{3}/Δ)^{1/4}, up to Re_{b}âĄ(L_{O}/L_{K})^{4/3}=Δ/(ÎœN^{2})âŒO(1000), where Δ is the mean turbulent kinetic energy dissipation rate, Îœ is the kinematic viscosity, and N is the buoyancy frequency. We isolate the effects of Re_{b}, particularly on irreversible mixing, from the effects of other flow parameters of stratified and sheared turbulence. Specifically, we evaluate the influence of dynamic range independent of initial conditions. We present evidence that the flow approaches an asymptotic state for Re_{b}âȘ300, characterized both by an asymptotic partitioning between the potential and kinetic energies and by the approach of components of the dissipation rate to their expected values under the assumption of isotropy. As Re_{b} increases above 100, there is a slight decrease in the turbulent flux coefficient Î=Ï/Δ, where Ï is the dissipation rate of buoyancy variance, but, for this flow, there is no evidence of the commonly suggested ÎâRe_{b}^{-1/2} dependence when 100â€Re_{b}â€1000.This work was funded by the U.S. Office of Naval Research via grant N00014-15-1-2248. High performance computing resources were provided through the U.S. Department of Defense High Performance Computing Modernization Program by the Army Engineer Research and Development Center, the Army Research Laboratory and the Navy DSRC under Frontier Project FP-CFD-FY14- 007. The research activity of C.P.C. is supported by EPSRC Programme Grant EP/K034529/1 entitled `Mathematical Underpinnings of Stratified Turbulence'
Smooth tensionful higher-codimensional brane worlds with bulk and brane form fields
Completely regular tensionful codimension-n brane world solutions are
discussed, where the core of the brane is chosen to be a thin codimension-(n-1)
shell in an infinite volume flat bulk, and an Einstein-Hilbert term localized
on the brane is included (Dvali-Gabadadze-Porrati models). In order to support
such localized sources we enrich the vacuum structure of the brane by the
inclusion of localized form fields. We find that phenomenological constraints
on the size of the internal core seem to impose an upper bound to the brane
tension. Finite transverse-volume smooth solutions are also discussed.Comment: 1+14 pages, 2 figures; section 2.3 improved, typos corrected and
references added. Published versio
Robust Inflation from fibrous strings
Successful inflationary models should (i) describe the data well; (ii) arise generically from sensible UV completions; (iii) be insensitive to detailed fine-tunings of parameters and (iv) make interesting new predictions. We argue that a class of models with these properties is characterized by relatively simple potentials with a constant term and negative exponentials. We here continue earlier work exploring UV completions for these modelsâincluding the key (though often ignored) issue of modulus stabilisationâto assess the robustness of their predictions. We show that string models where the inflaton is a fibration modulus seem to be robust due to an effective rescaling symmetry, and fairly generic since most known Calabi-Yau manifolds are fibrations. This class of models is characterized by a generic relation between the tensor-to-scalar ratio r and the spectral index ns of the form r â (nsâ1)2 where the proportionality constant depends on the nature of the effects used to develop the inflationary potential and the topology of the internal space. In particular we find that the largest values of the tensor-to-scalar ratio that can be obtained by generalizing the original set-up are of order r lesssim 0.01. We contrast this general picture with specific popular models, such as the Starobinsky scenario and α-attractors. Finally, we argue the self consistency of large-field inflationary models can strongly constrain non-supersymmetric inflationary mechanisms
Iodine-131 in Household waste - a pilot study
Werknemers in de thuis- en verpleegzorg en vuilnisophalers komen soms zonder dat te weten in aanraking met de radioactieve stof jodium-131. Toch is het niet aannemelijk dat zij aan een te hoge stralingsdosis blootstaan. Voorwaarde is, dat ze de normale hygienische voorschriften naleven. Dit blijkt uit verkennend onderzoek van het RIVM. Aanleiding is een tiental stralingsmeldingen bij een afvalverbrandingsinstallatie voor huishoudelijk afval in Dordrecht tussen april 2008 en april 2009. De straling was afkomstig van jodium-131 in incontinentiemateriaal en ander afval van patienten die met deze radioactieve stof zijn behandeld wegens een schildklierafwijking. Voor het onderzoek zijn vijf ziekenhuizen bezocht en zijn gegevens van de VROM-Inspectie gebruikt. Op basis hiervan heeft het RIVM scenario's opgesteld waarmee dosisschattingen voor werknemers zijn gemaakt. Deze schattingen zijn gebaseerd op de veronderstelling dat de hoeveelheid jodium-131 in incontinentiemateriaal niet groter is dan tot nu toe in het huishoudelijk afval is waargenomen. Er zijn twee mogelijke verklaringen voor de aanwezigheid van jodium-131 in het incontinentiemateriaal. Incontinente patienten mogen in Nederland niet poliklinisch met jodium-131 worden behandeld, maar in de praktijk gebeurt dat toch. De eerste 24 uur na de behandeling bevat de urine van deze patienten relatief veel van deze radioactieve stof. Een tweede verklaring zou kunnen zijn dat patienten die met een hoge dosering zijn behandeld, in sommige ziekenhuizen vaker vervroegd worden ontslagen. In Duitsland is poliklinische behandeling met jodium-131 niet toegestaan. Gezien de beperkte risico's lijkt een dergelijk totaalverbod in Nederland niet te rechtvaardigen. Om de risico's voor derden laag te houden, zou men bij incontinente patienten terughoudend moeten zijn met poliklinische behandeling en vervroegd ontslag.Workers in homecare and nursing homes are occasionally exposed to the radioactive drug iodine-131. Still, it is unlikely that dose limits are exceeded, provided that sanitary procedures are followed. This is shown in a pilot study by RIVM carried out after a number of radiation alerts at the household waste incinerator in Dordrecht between April 2008 and April 2009. The radiation originated from iodine-131 in diapers and similar waste from patients that had been treated for thyroid disorders. For this pilot study, five hospitals have been visited, and data were obtained from the environmental inspectorate. Based on this, scenarios were drawn up and dose estimates were made for workers. Two explanations are given for the unexpected presence of iodine-131 in household waste. First iodine-131 therapy is not allowed for outpatients if they are incontinent, but it is still done. Second, early release of patients treated with high doses may occur more often in some hospitals. In Germany, iodine therapy of outpatients is not allowed at all. In view of the limited risks, such a total ban seems unjustifiable in the Netherlands. To keep the risks for others to a minimum, hospitals should exercise restraint on sending incontinent patients home early.VRO
New Constraints (and Motivations) for Abelian Gauge Bosons in the MeV-TeV Mass Range
We survey the phenomenological constraints on abelian gauge bosons having
masses in the MeV to multi-GeV mass range (using precision electroweak
measurements, neutrino-electron and neutrino-nucleon scattering, electron and
muon anomalous magnetic moments, upsilon decay, beam dump experiments, atomic
parity violation, low-energy neutron scattering and primordial
nucleosynthesis). We compute their implications for the three parameters that
in general describe the low-energy properties of such bosons: their mass and
their two possible types of dimensionless couplings (direct couplings to
ordinary fermions and kinetic mixing with Standard Model hypercharge). We argue
that gauge bosons with very small couplings to ordinary fermions in this mass
range are natural in string compactifications and are likely to be generic in
theories for which the gravity scale is systematically smaller than the Planck
mass - such as in extra-dimensional models - because of the necessity to
suppress proton decay. Furthermore, because its couplings are weak, in the
low-energy theory relevant to experiments at and below TeV scales the charge
gauged by the new boson can appear to be broken, both by classical effects and
by anomalies. In particular, if the new gauge charge appears to be anomalous,
anomaly cancellation does not also require the introduction of new light
fermions in the low-energy theory. Furthermore, the charge can appear to be
conserved in the low-energy theory, despite the corresponding gauge boson
having a mass. Our results reduce to those of other authors in the special
cases where there is no kinetic mixing or there is no direct coupling to
ordinary fermions, such as for recently proposed dark-matter scenarios.Comment: 49 pages + appendix, 21 figures. This is the final version which
appears in JHE
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Testing the assumptions underlying ocean mixing methodologies using direct numerical simulations
AbstractDirect numerical simulations of stratified turbulence are used to test several fundamental assumptions involved in the Osborn, OsbornâCox, and Thorpe methods commonly used to estimate the turbulent diffusivity from field measurements. The forced simulations in an idealized triply periodic computational domain exhibit characteristic features of stratified turbulence including intermittency and layer formation. When calculated using the volume-averaged dissipation rates from the simulations, the vertical diffusivities inferred from the Osborn and OsbornâCox methods are within 40% of the value diagnosed using the volume-averaged buoyancy flux for all cases, while the Thorpe-scale method performs similarly well in the simulation with a relatively large buoyancy Reynolds number (Reb â 240) but significantly overestimates the vertical diffusivity in simulations with Reb < 60. The methods are also tested using a limited number of vertical profiles randomly selected from the computational volume. The Osborn, OsbornâCox, and Thorpe-scale methods converge to their respective estimates based on volume-averaged statistics faster than the vertical diffusivity calculated directly from the buoyancy flux, which is contaminated with reversible contributions from internal waves. When applied to a small number of vertical profiles, several assumptions underlying the Osborn and OsbornâCox methods are not well supported by the simulation data. However, the vertical diffusivity inferred from these methods compares reasonably well to the exact value from the simulations and outperforms the assumptions underlying these methods in terms of the relative error. Motivated by a recent theoretical development, it is speculated that the Osborn method might provide a reasonable approximation to the diffusivity associated with the irreversible buoyancy flux.</jats:p
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