4,690 research outputs found
First principles predictions of thermophysical properties of refrigerant mixtures
We present pair potentials for fluorinated methanes and their dimers with CO2 based on ab initio potential energy surfaces. These potentials reproduce the experimental second virial coefficients of the pure fluorinated methanes and their mixtures with CO2 without adjustment. Ab initio calculations on trimers are used to model the effects of nonadditive dispersion and induction. Simulations using these potentials reproduce the experimental phase-coexistence properties of CH3F within 10% over a wide range of temperatures. The phase coexistence curve of the mixture of CH2F2 and CO2 is reproduced with an error in the mole fractions of both phases of less than 0.1. The potentials described here are based entirely on ab initio calculations, with no empirical fits to improve the agreement with experiment
Global perspectives on the energy landscapes of liquids, supercooled liquids, and glassy systems: The potential energy landscape ensemble
In principle, all of the dynamical complexities of many-body systems are
encapsulated in the potential energy landscapes on which the atoms move - an
observation that suggests that the essentials of the dynamics ought to be
determined by the geometry of those landscapes. But what are the principal
geometric features that control the long-time dynamics? We suggest that the key
lies not in the local minima and saddles of the landscape, but in a more global
property of the surface: its accessible pathways. In order to make this notion
more precise we introduce two ideas: (1) a switch to a new ensemble that
removes the concept of potential barriers from the problem, and (2) a way of
finding optimum pathways within this new ensemble. The potential energy
landscape ensemble, which we describe in the current paper, regards the maximum
accessible potential energy, rather than the temperature, as a control
variable. We show here that while this approach is thermodynamically equivalent
to the canonical ensemble, it not only sidesteps the idea of barriers, it
allows us to be quantitative about the connectivity of a landscape. We
illustrate these ideas with calculations on a simple atomic liquid and on the
Kob-Andersen model of a glass-forming liquid, showing, in the process, that the
landscape of the Kob-Anderson model appears to have a connectivity transition
at the landscape energy associated with its mode-coupling transition. We turn
to the problem of finding the most efficient pathways through potential energy
landscapes in our companion paper.Comment: 43 pages, 7 figure
Paternal diet programs offspring health through sperm- and seminal plasma-specific pathways in mice
Parental health and diet at the time of conception determine the development and life-long disease risk of their offspring. While the association between poor maternal diet and offspring health is well established, the underlying mechanisms linking paternal diet with offspring health are poorly defined. Possible programming pathways include changes in testicular and sperm epigenetic regulation and status, seminal plasma composition, and maternal reproductive tract responses regulating early embryo development. In this study, we demonstrate that paternal low-protein diet induces sperm-DNA hypomethylation in conjunction with blunted female reproductive tract embryotrophic, immunological, and vascular remodeling responses. Furthermore, we identify sperm- and seminal plasma-specific programming effects of paternal diet with elevated offspring adiposity, metabolic dysfunction, and altered gut microbiota
Report of the panel on geopotential fields: Gravity field, section 8
The objective of the Geopotential Panel was to develop a program of data acquisition and model development for the Earth's gravity and magnetic fields that meet the basic science requirements of the solid Earth and ocean studies. Presented here are the requirements for gravity information and models through the end of the century, the present status of our knowledge, data acquisition techniques, and an outline of a program to meet the requirements
Convicts and coolies : rethinking indentured labour in the nineteenth century
This article seeks to shift the frame of analysis within which discussions of Indian indentured migration take place. It argues that colonial discourses and practices of indenture are best understood not with regard to the common historiographical framework of whether it was 'a new system of slavery', but in the context of colonial innovations in incarceration and confinement. The article shows how Indian experiences of and knowledge about transportation overseas to penal settlements informed in important ways both their own understandings and representations of migration and the colonial practices associated with the recruitment of indentured labour. In detailing the connections between two supposedly different labour regimes, it thus brings a further layer of complexity to debates around their supposed distinctions
Point Sources from a Spitzer IRAC Survey of the Galactic Center
We have obtained Spitzer/IRAC observations of the central 2.0 x 1.4 degrees
(~280 x 200 pc) of the Galaxy at 3.6-8.0 microns. A point source catalog of
1,065,565 objects is presented. The catalog includes magnitudes for the point
sources at 3.6, 4.5, 5.8, and 8.0 microns, as well as JHK photometry from
2MASS. The point source catalog is confusion limited with average limits of
12.4, 12.1, 11.7, and 11.2 magnitudes for [3.6], [4.5], [5.8], and [8.0],
respectively. We find that the confusion limits are spatially variable because
of stellar surface density, background surface brightness level, and extinction
variations across the survey region. The overall distribution of point source
density with Galactic latitude and longitude is essentially constant, but
structure does appear when sources of different magnitude ranges are selected.
Bright stars show a steep decreasing gradient with Galactic latitude, and a
slow decreasing gradient with Galactic longitude, with a peak at the position
of the Galactic center. From IRAC color-magnitude and color-color diagrams, we
conclude that most of the point sources in our catalog have IRAC magnitudes and
colors characteristic of red giant and AGB stars.Comment: 44 pages, 13 figures, ApJS in pres
Does wage rank affect employees' well-being?
How do workers make wage comparisons? Both an experimental study and an analysis of 16,000 British employees are reported. Satisfaction and well-being levels are shown to depend on more than simple relative pay. They depend upon the ordinal rank of an individual's wage within a comparison group. âRankâ itself thus seems to matter to human beings. Moreover, consistent with psychological theory, quits in a workplace are correlated with pay distribution skewness
CBR Anisotropy from Primordial Gravitational Waves in Two-Component Inflationary Cosmology
We examine stochastic temperature fluctuations of the cosmic background
radiation (CBR) arising via the Sachs-Wolfe effect from gravitational wave
perturbations produced in the early universe. We consider spatially flat,
perturbed FRW models that begin with an inflationary phase, followed by a mixed
phase containing both radiation and dust. The scale factor during the mixed
phase takes the form , where are
constants. During the mixed phase the universe smoothly transforms from being
radiation to dust dominated. We find analytic expressions for the graviton mode
function during the mixed phase in terms of spheroidal wave functions. This
mode function is used to find an analytic expression for the multipole moments
of the two-point angular correlation function
for the CBR anisotropy. The analytic expression for the multipole
moments is written in terms of two integrals, which are evaluated numerically.
The results are compared to multipoles calculated for models that are {\it
completely} dust dominated at last-scattering. We find that the multipoles
of the CBR temperature perturbations for are
significantly larger for a universe that contains both radiation and dust at
last-scattering. We compare our results with recent, similar numerical work and
find good agreement. The spheroidal wave functions may have applications to
other problems of cosmological interest.Comment: 28 pgs + 6 postscript figures, RevTe
Cosmological parameter estimation using Very Small Array data out to l=1500
We estimate cosmological parameters using data obtained by the Very Small
Array (VSA) in its extended configuration, in conjunction with a variety of
other CMB data and external priors. Within the flat CDM model, we find
that the inclusion of high resolution data from the VSA modifies the limits on
the cosmological parameters as compared to those suggested by WMAP alone, while
still remaining compatible with their estimates. We find that , , , , and
for WMAP and VSA when no external prior is
included.On extending the model to include a running spectral index of density
fluctuations, we find that the inclusion of VSA data leads to a negative
running at a level of more than 95% confidence (),
something which is not significantly changed by the inclusion of a stringent
prior on the Hubble constant. Inclusion of prior information from the 2dF
galaxy redshift survey reduces the significance of the result by constraining
the value of . We discuss the veracity of this result in the
context of various systematic effects and also a broken spectral index model.
We also constrain the fraction of neutrinos and find that at
95% confidence which corresponds to when all neutrino
masses are the equal. Finally, we consider the global best fit within a general
cosmological model with 12 parameters and find consistency with other analyses
available in the literature. The evidence for is only marginal
within this model
Large carnivore science: non-experimental studies are useful, but experiments are better
1. Response to Bruskotter and colleagues
We recently described the following six interrelated issues that justify questioning some of the discourse about the reliability of the literature on the ecological roles of large carnivores (Allen et al., in press):
1. The overall paucity of available data,
2. The reliability of carnivore population sampling techniques,
3. The general disregard for alternative hypotheses to top-down forcing,
4. The lack of applied science studies,
5. The frequent use of logical fallacies,
6. The generalisation of results from relatively pristine systems to those substantially altered by humans.
We thank Bruskotter et al. (2017) for responding to our concerns and engaging with this important issue. We agree completely that nonexperimental studies can and do often have great value, and we recognize that in many (most) cases these types of studies may provide the only data that are available. We acknowledge the many challenges of working on large, cryptic, dangerous, and highly-mobile animals in the wild. However, the absence of more robust data and the reality of these challenges do not excuse weak inference or overstating conclusions â a practice apparent in many studies (and communication of those studies) adopting only observational or correlative methods to infer the roles of large carnivores (reviewed in Allen et al., in press)
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