1,653 research outputs found
ANL/RBC: A computer code for the analysis of Rankine bottoming cycles, including system cost evaluation and off-design performance
This report describes, and is a User's Manual for, a computer code (ANL/RBC) which calculates cycle performance for Rankine bottoming cycles extracting heat from a specified source gas stream. The code calculates cycle power and efficiency and the sizes for the heat exchangers, using tabular input of the properties of the cycle working fluid. An option is provided to calculate the costs of system components from user defined input cost functions. These cost functions may be defined in equation form or by numerical tabular data. A variety of functional forms have been included for these functions and they may be combined to create very general cost functions. An optional calculation mode can be used to determine the off-design performance of a system when operated away from the design-point, using the heat exchanger areas calculated for the design-point
Chapman-Enskog expansion about nonequilibrium states: the sheared granular fluid
The Chapman-Enskog method of solution of kinetic equations, such as the
Boltzmann equation, is based on an expansion in gradients of the deviations fo
the hydrodynamic fields from a uniform reference state (e.g., local
equilibrium). This paper presents an extension of the method so as to allow for
expansions about \emph{arbitrary}, far-from equilibrium reference states. The
primary result is a set of hydrodynamic equations for studying variations from
the arbitrary reference state which, unlike the usual Navier-Stokes
hydrodynamics, does not restrict the reference state in any way. The method is
illustrated by application to a sheared granular gas which cannot be studied
using the usual Navier-Stokes hydrodynamics.Comment: 23 pages, no figures. Submited to PRE Replaced to correct misc.
errors Replaced to correct misc. errors, make notation more consistant,
extend discussio
Segregation of an intruder in a heated granular dense gas
A recent segregation criterion [V. Garz\'o, Phys. Rev. E \textbf{78},
020301(R) (2008)] based on the thermal diffusion factor of an
intruder in a heated granular gas described by the inelastic Enskog equation is
revisited. The sign of provides a criterion for the transition
between the Brazil-nut effect (BNE) and the reverse Brazil-nut effect (RBNE).
The present theory incorporates two extra ingredients not accounted for by the
previous theoretical attempt. First, the theory is based upon the second Sonine
approximation to the transport coefficients of the mass flux of intruder.
Second, the dependence of the temperature ratio (intruder temperature over that
of the host granular gas) on the solid volume fraction is taken into account in
the first and second Sonine approximations. In order to check the accuracy of
the Sonine approximation considered, the Enskog equation is also numerically
solved by means of the direct simulation Monte Carlo (DSMC) method to get the
kinetic diffusion coefficient . The comparison between theory and
simulation shows that the second Sonine approximation to yields an
improvement over the first Sonine approximation when the intruder is lighter
than the gas particles in the range of large inelasticity. With respect to the
form of the phase diagrams for the BNE/RBNE transition, the kinetic theory
results for the factor indicate that while the form of these diagrams
depends sensitively on the order of the Sonine approximation considered when
gravity is absent, no significant differences between both Sonine solutions
appear in the opposite limit (gravity dominates the thermal gradient). In the
former case (no gravity), the first Sonine approximation overestimates both the
RBNE region and the influence of dissipation on thermal diffusion segregation.Comment: 9 figures; to be published in Phys. Rev.
A note on the violation of the Einstein relation in a driven moderately dense granular gas
The Einstein relation for a driven moderately dense granular gas in
-dimensions is analyzed in the context of the Enskog kinetic equation. The
Enskog equation neglects velocity correlations but retains spatial correlations
arising from volume exclusion effects. As expected, there is a breakdown of the
Einstein relation relating diffusion and
mobility , being the temperature of the impurity. The kinetic theory
results also show that the violation of the Einstein relation is only due to
the strong non-Maxwellian behavior of the reference state of the impurity
particles. The deviation of from unity becomes more significant as
the solid volume fraction and the inelasticity increase, especially when the
system is driven by the action of a Gaussian thermostat. This conclusion
qualitatively agrees with some recent simulations of dense gases [Puglisi {\em
et al.}, 2007 {\em J. Stat. Mech.} P08016], although the deviations observed in
computer simulations are more important than those obtained here from the
Enskog kinetic theory. Possible reasons for the quantitative discrepancies
between theory and simulations are discussed.Comment: 6 figure
Integration through transients for Brownian particles under steady shear
Starting from the microscopic Smoluchowski equation for interacting Brownian
particles under stationary shearing, exact expressions for shear-dependent
steady-state averages, correlation and structure functions, and
susceptibilities are obtained, which take the form of generalized Green-Kubo
relations. They require integration of transient dynamics. Equations of motion
with memory effects for transient density fluctuation functions are derived
from the same microscopic starting point. We argue that the derived formal
expressions provide useful starting points for approximations in order to
describe the stationary non-equilibrium state of steadily sheared dense
colloidal dispersions.Comment: 17 pages, Submitted to J. Phys.: Condens. Matter; revised version
with minor correction
True blue: Temporal and spatial stability of pelagic wildlife at a submarine canyon
Funding: This research was funded through the Ian Potter Foundation and the First author.In coastal systems, marine-protected areas (MPAs) have been shown to increase the diversity, abundance, and biomass of wildlife assemblages as well as their resilience to climate change. The effectiveness of pelagic MPAs is less clear, with arguments against their establishment typically based on the highly mobile nature of pelagic taxa. We used mid-water stereo-baited remote underwater video systems (stereo-BRUVS) and spatial predictive models to characterize the pelagic wildlife assemblage at the head of the Perth Canyon, one of the largest submarine canyons in Australia, over a 7-yr period (2013â2019). The total number of unique taxa and mean values of taxonomic richness, abundance, fork length, and biomass demonstrated strong interannual stability, although mean taxonomic richness and abundance were significantly lower in 2018 relative to other years. Seasonal variability was absent in 2016, but in 2018, taxonomic richness and abundance were three times greater in the Austral spring than in the autumn. Some mobile megafauna were only recorded at the Perth Canyon Marine Park (PCMP) in the autumn, suggesting a seasonal component to their occurrence. The fine-scale distribution of pelagic taxa at the canyon head was largely stable over time, with many areas of higher relative probability of presence located outside protected zones. Despite a degree of variability that may relate to the effect of the El Niño Southern Oscillation on the Leeuwin Current, the PCMP assemblage demonstrates a relatively high degree of spatiotemporal stability. Stronger protection of the PCMP (IUCN II or higher) would potentially improve conservation outcomes for many species of pelagic wildlife.Publisher PDFPeer reviewe
COVID-19 contact tracing apps: UK public perceptions
In order to combat the COVID-19 pandemic, policymakers around the globe have increasingly invested in digital health technologies to support the âtest, track and traceâ approach of containing the spread of the novel coronavirus. These technologies include mobile âcontact tracingâ applications (apps), which can trace individuals likely to have come into contact with those who have reported symptoms or tested positive for the virus and request that they self-isolate. This paper takes a critical public health perspective that advocates for âgenuine participationâ in public health interventions and emphasises the need to take citizenâs knowledge into account during public health decision-making. In doing so, it presents and discusses the findings of a UK interview study that explored public views on the possibility of using a COVID-19 contact-tracing app public health intervention at the time the United Kingdom (UK) Government announced their decision to develop such a technology. Findings illustrated intervieweesâ range and degree of understandings, misconceptions, and concerns about the possibility of using an app. In particular, concerns about privacy and surveillance predominated. Interviewees associated these concerns much more broadly than health by identifying with pre-existent British national narratives associated with individual liberty and autonomy. In extending and contributing to ongoing sociological research with public health, we argue that understanding and responding to these matters is vital, and that our findings demonstrate the need for a forward-looking, anticipatory strategy for public engagement as part of the responsible innovation of the COVID-19 contact-tracing app in the UK
Nonequilibrium Microscopic Distribution of Thermal Current in Particle Systems
A nonequilibrium distribution function of microscopic thermal current is
studied by a direct numerical simulation in a thermal conducting steady state
of particle systems. Two characteristic temperatures of the thermal current are
investigated on the basis of the distribution. It is confirmed that the
temperature depends on the current direction; Parallel temperature to the
heat-flux is higher than antiparallel one. The difference between the parallel
temperature and the antiparallel one is proportional to a macroscopic
temperature gradient.Comment: 4 page
Nonequilibrium fluctuation dissipation relations of interacting Brownian particles driven by shear
We present a detailed analysis of the fluctuation dissipation theorem (FDT)
close to the glass transition in colloidal suspensions under steady shear using
mode coupling approximations. Starting point is the many-particle Smoluchowski
equation. Under shear, detailed balance is broken and the response functions in
the stationary state are smaller at long times than estimated from the
equilibrium FDT. An asymptotically constant relation connects response and
fluctuations during the shear driven decay, restoring the form of the FDT with,
however, a ratio different from the equilibrium one. At short times, the
equilibrium FDT holds. We follow two independent approaches whose results are
in qualitative agreement. To discuss the derived fluctuation dissipation
ratios, we show an exact reformulation of the susceptibility which contains not
the full Smoluchowski operator as in equilibrium, but only its well defined
Hermitian part. This Hermitian part can be interpreted as governing the
dynamics in the frame comoving with the probability current. We present a
simple toy model which illustrates the FDT violation in the sheared colloidal
system.Comment: 21 pages, 13 figures, submitted to Phys. Rev.
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