3,535 research outputs found
A multi-layer extension of the stochastic heat equation
Motivated by recent developments on solvable directed polymer models, we
define a 'multi-layer' extension of the stochastic heat equation involving
non-intersecting Brownian motions.Comment: v4: substantially extended and revised versio
Stochastic B\"acklund transformations
How does one introduce randomness into a classical dynamical system in order
to produce something which is related to the `corresponding' quantum system? We
consider this question from a probabilistic point of view, in the context of
some integrable Hamiltonian systems
Drivers of intrapopulation variation in resource use in a generalist predator, the macaroni penguin
Intrapopulation variation in resource use occurs in many populations of generalist predators with important community and evolutionary implications. One of the hypothesised mechanisms for such widespread variation is ecological opportunity, i.e. resource availability determined by intrinsic constraints and extrinsic conditions. We combined tracking data and stable isotope analysis to examine how breeding constraints and prey conditions influenced intrapopulation variation in resource use among macaroni penguins Eudyptes chrysolophus. Isotopic variation was also examined as a function of breeding success, individual traits and individual specialisation. Variation in isotope ratios was greatest across multiple tissue types when birds were able to undertake mid-range foraging trips (i.e. during incubation and pre-moult). This variation was highly consistent between years that spanned a 3-fold difference in local krill Euphausia superba density and was also highly consistent at the individual level between 2 years that had similar krill densities. However, by comparing our results with previous work on the same population, it appeared that a decrease in local prey availability can increase intrapopulation variation in resource use during periods with more restricted foraging ranges (i.e. during brood-guard and crèche). This study highlights the importance of considering ecological interactions that operate on multiple spatio-temporal scales when examining the drivers of resource use in populations of generalist predators
Signatures of the Youngest Starbursts: Optically-thick Thermal Bremsstrahlung Radio Sources in Henize 2-10
VLA radio continuum imaging reveals compact (<8 pc) ~1 mJy radio sources in
the central 5" starburst region of the blue compact galaxy Henize 2-10. We
interpret these radio knots as extremely young, ultra-dense HII regions. We
model their luminosities and spectral energy distributions, finding that they
are consistent with unusually dense HII regions having electron densities, 1500
cm^-3 < n_e < 5000 cm^-3, and sizes of 3-8 pc. Since these H II regions are not
visible in optical images, we propose that the radio data preferentially reveal
the youngest, densest, and most highly obscured starforming events. Energy
considerations imply that each of the five \HII regions contains ~750 O7V
equivalent stars, greater than the number found in 30 Doradus in the LMC. The
high densities imply an over-pressure compared to the typical interstellar
medium so that such objects must be short-lived (<0.5 Myr expansion
timescales). We conclude that the radio continuum maps reveal the very young
(<0.5 Myr) precursors of ``super starclusters'' or ``proto globular clusters''
which are prominent at optical and UV wavelengths in He 2-10. If the
ultra-dense HII regions are typical of those which we predict will be found in
other starbursting systems, then super starclusters spend 15% of their lifetime
in heavily-obscured environments, similar to Galactic ultra-compact HII
regions. This body of work leads us to propose that massive extragalactic star
clusters (i.e. proto globular clusters) with ages <10^6 yr may be most easily
identified by finding compact radio sources with optically-thick thermal
bremsstrahlung spectral signatures.Comment: AASTeX, 8 figures 2 included with psfig in text; other 6 in jpeg
format; Postscript versions of figures may be found at
http://zem.ucolick.org/chip/Research/young_clusters.html -- Accepted for
publication in the Astrophysical Journa
Transformed Dissipation in Superconducting Quantum Circuits
Superconducting quantum circuits must be designed carefully to avoid
dissipation from coupling to external control circuitry. Here we introduce the
concept of current transformation to quantify coupling to the environment. We
test this theory with an experimentally-determined impedance transformation of
and find quantitative agreement better than a factor of 2 between
this transformation and the reduced lifetime of a phase qubit coupled to a
tunable transformer. Higher-order corrections from quantum fluctuations are
also calculated with this theory, but found not to limit the qubit lifetime. We
also illustrate how this simple connection between current and impedance
transformation can be used to rule out dissipation sources in experimental
qubit systems.Comment: 4 pages, 4 figure
Production of Enhanced Beam Halos via Collective Modes and Colored Noise
We investigate how collective modes and colored noise conspire to produce a
beam halo with much larger amplitude than could be generated by either
phenomenon separately. The collective modes are lowest-order radial eigenmodes
calculated self-consistently for a configuration corresponding to a
direct-current, cylindrically symmetric, warm-fluid Kapchinskij-Vladimirskij
equilibrium. The colored noise arises from unavoidable machine errors and
influences the internal space-charge force. Its presence quickly launches
statistically rare particles to ever-growing amplitudes by continually kicking
them back into phase with the collective-mode oscillations. The halo amplitude
is essentially the same for purely radial orbits as for orbits that are
initially purely azimuthal; orbital angular momentum has no statistically
significant impact. Factors that do have an impact include the amplitudes of
the collective modes and the strength and autocorrelation time of the colored
noise. The underlying dynamics ensues because the noise breaks the
Kolmogorov-Arnol'd-Moser tori that otherwise would confine the beam. These tori
are fragile; even very weak noise will eventually break them, though the time
scale for their disintegration depends on the noise strength. Both collective
modes and noise are therefore centrally important to the dynamics of halo
formation in real beams.Comment: For full resolution pictures please go to
http://www.nicadd.niu.edu/research/beams
Continuum-particle hybrid coupling for mass, momentum and energy transfers in unsteady fluid flow
The aim of hybrid methods in simulations is to communicate regions with
disparate time and length scales. Here, a fluid described at the atomistic
level within an inner region P is coupled to an outer region C described by
continuum fluid dynamics. The matching of both descriptions of matter is made
across an overlapping region and, in general, consists of a two-way coupling
scheme (C->P and P->C) which conveys mass, momentum and energy fluxes. The
contribution of the hybrid scheme hereby presented is two-fold: first it treats
unsteady flows and, more importantly, it handles energy exchange between both C
and P regions. The implementation of the C->P coupling is tested here using
steady and unsteady flows with different rates of mass, momentum and energy
exchange. In particular, relaxing flows described by linear hydrodynamics
(transversal and longitudinal waves) are most enlightening as they comprise the
whole set of hydrodynamic modes. Applying the hybrid coupling scheme after the
onset of an initial perturbation, the cell-averaged Fourier components of the
flow variables in the P region (velocity, density, internal energy, temperature
and pressure) evolve in excellent agreement with the hydrodynamic trends. It is
also shown that the scheme preserves the correct rate of entropy production. We
discuss some general requirements on the coarse-grained length and time scales
arising from both the characteristic microscopic and hydrodynamic scales.Comment: LaTex, 12 pages, 9 figure
The steady state load of five firefighting tasks
Purpose. Physiologic demands of five common tasks in firefighting have been examined. Methods. Eight male volunteers, being dressed up as smoke divers (+21 kg extra load), carried out the following tasks at constant pace for 5 min: Walking at 1.4 m·s–1, walking (all walks at the same speed) while carrying a 10 kg ladder, walking carrying two hose packs of 16 kg together, walking carrying a 32 kg spreader tool, finally climbing up and down a ladder at preset pace. A 5 min break separated each exercise. Heart rate, O2-uptake and ventilation were measured continuously, and blood lactate con-centration was recorded after each task. Results. The end-exercise heart rate rose from 108 to 180 bpm from first to last task, blood lactate concentration rose from 1 to 7 mmol·L–1, O2-uptake rose from 19 to 48 ml·kg–1·min–1, and ventilation rose from 38 to 124 L·min–1. Discussion. Walking was an easy task even when dressed up as a smoke diver. Adding loads increased demands; ladder climbing taxed >90% of the subjects’ aerobic power. Conclusions. The physiologic demands varied considera-bly between different tasks.acceptedVersio
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The relationship between healthy lifestyle behaviours and outcomes for people living with and beyond cancer: an overview of Systematic Reviews
There are an extensive number of published evidence reviews examining the influence of lifestyle behaviours on cancer outcomes. Healthy lifestyles are a significant topic of debate in oncology and in policy and practice organisations that support people living with and beyond cancer. Such reviews vary in quality, address different relationships, outcomes and cancers, and there is often more than one review on important topics. This makes it difficult for policy and practice professionals to make decisions about the prescription and promotion of lifestyle behaviours for cancer populations. An overview of systematic reviews provides a single, overarching summary of evidence from published systematic reviews and compares and contrasts the findings of systematic reviews, providing healthcare professionals with the evidence needed for more effective decision making (Smith et al. 2011). This overview of systematic reviews synthesises evidence from systematic reviews on smoking, physical activity, dietary behaviours and alcohol consumption to present a summary of evidence about the relationships between these lifestyle behaviours and outcomes for people living with and beyond cancer
Intertwinings for general β Laguerre and Jacobi processes
We show that, for β≥1, the semigroups of β-Laguerre and β-Jacobi processes of different dimensions are intertwined in analogy to a similar result for β-Dyson Brownian motion recently obtained in Ramanan and Shkolnikov (Intertwinings of β-Dyson Brownian motions of different dimensions, 2016. arXiv:1608.01597). These intertwining relations generalize to arbitrary β≥1 the ones obtained for β=2 in Assiotis et al. (Interlacing diffusions, 2016. arXiv:1607.07182) between h-transformed Karlin–McGregor semigroups. Moreover, they form the key step toward constructing a multilevel process in a Gelfand–Tsetlin pattern leaving certain Gibbs measures invariant. Finally, as a by-product, we obtain a relation between general β-Jacobi ensembles of different dimensions
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