1,087 research outputs found
LES, DNS, and RANS for the Analysis of High-Speed Turbulent Reacting Flows
A filtered density function (FDF) method suitable for chemically reactive flows is developed in the context of large eddy simulation. The advantage of the FDF methodology is its inherent ability to resolve subgrid scales (SGS) scalar correlations that otherwise have to be modeled. Because of the lack of robust models to accurately predict these correlations in turbulent reactive flows, simulations involving turbulent combustion are often met with a degree of skepticism. The FDF methodology avoids the closure problem associated with these terms and treats the reaction in an exact manner. The scalar FDF approach is particularly attractive since it can be coupled with existing hydrodynamic computational fluid dynamics (CFD) codes
Star Clusters in M 31. IV. A Comparative Analysis of Absorption Line Indices in Old M 31 and Milky Way Clusters
We present absorption line indices measured in the integrated spectra of
globular clusters both from the Galaxy and from M 31. Our samples include 41
Galactic globular clusters, and more than 300 clusters in M 31. The conversion
of instrumental equivalent widths into the Lick system is described, and
zero-point uncertainties are provided. Comparison of line indices of old M 31
clusters and Galactic globular clusters suggests an absence of important
differences in chemical composition between the two cluster systems. In
particular, CN indices in the spectra of M 31 and Galactic clusters are
essentially consistent with each other, in disagreement with several previous
works. We reanalyze some of the previous data, and conclude that reported CN
differences between M 31 and Galactic clusters were mostly due to data
calibration uncertainties. Our data support the conclusion that the chemical
compositions of Milky Way and M 31 globular clusters are not substantially
different, and that there is no need to resort to enhanced nitrogen abundances
to account for the optical spectra of M 31 globular clusters.Comment: 72 pages, including 15 figures and 14 tables. Published by the
Astronomical Journa
Infrared High-Resolution Integrated Light Spectral Analyses of M31 Globular Clusters From Apogee
Chemical abundances are presented for 25 M31 globular clusters (GCs), based on moderately high resolution (R = 22,500) H-band integrated light (IL) spectra from the Apache Point Observatory Galactic Evolution Experiment (APOGEE). Infrared (IR) spectra offer lines from new elements, lines of different strengths, and lines at higher excitation potentials compared to the optical. Integrated abundances of C, N, and O are derived from CO, CN, and OH molecular features, while Fe, Na, Mg, Al, Si, K, Ca, and Ti abundances are derived from atomic features. These abundances are compared to previous results from the optical, demonstrating the validity and value of IR IL analyses. The CNO abundances are consistent with typical tip of the red giant branch stellar abundances but are systematically offset from optical Lick index abundances. With a few exceptions, the other abundances agree between the optical and the IR within the 1σ uncertainties. The first integrated K abundances are also presented and demonstrate that K tracks the α elements. The combination of IR and optical abundances allows better determinations of GC properties and enables probes of the multiple populations in extragalactic GCs. In particular, the integrated effects of the Na/O anticorrelation can be directly examined for the first time
Applications and Benefits of Catalytic Converter Thermal Management
A catalytic converter thermal management system (TMS) using variable-conductance vacuum insulation and phase-change thermal storage can maintain the converter temperature above its operating temperature for many hours, allowing most trips to begin with minimal ``cold-start`` emissions. The latest converter TMS prototype was tested on a Ford Taurus (3.0 liter flex-fuel engine) at Southwest Research Institute. Following a 24-hour soak, the FTP-75 emissions were 0.031, 0.13, and 0.066 g/mile for NMHC, CO, and NOx, respectively. Tests were also run using 85% ethanol (E85), resulting in values of 0.005, 0.124, and 0.044 g/mile, and 0.005 g/mile NMOG. Compared to the baseline FTP levels, these values represent reductions of 84% to 96% for NMHC, NMOG, and CO
Permafrost conditions in the Mediterranean region since the Last Glaciation.
Cold-climate geomorphological processes today in the Mediterranean region are only distributed in the highest mountain environments. However, climate condition prevailing during the Late Pleistocene and Holocene have conditioned significant spatio-temporal variations of the glacial and periglacial domain in these mountains, including permafrost. In this communication we examine permafrost condition in the Mediterranean region taking into account five periods: Last Glaciation, deglaciation, Holocene, Little Ice Age (LIA) and present-day. The distribution of currently inactive permafrost-derived landforms and sedimentary records indicates that the permafrost elevation during the Last Glaciation was ca. 1000 m lower than present. Permafrost was also widespread in non-glaciated slopes above the snowline forming rock glaciers and block streams, as well as in relatively flat summit areas where meter-sized stone circles developed. As in most areas of the Northern Hemisphere, the deglaciation in the Mediterranean region started ca. 19-20 ka. The exposed terrain by retreating glaciers was affected by paraglacial dynamics and intense periglacial processes, mostly associated with permafrost condition. Many rock glaciers, protalus lobes and block streams formed in these recently deglaciated environments, becoming gradually inactive as temperatures rose during the Bølling-Allerød. Following the Younger Dryas glacial advance, the last massive deglaciation in Mediterranean mountains took place during the Early Holocene together with a progressive shift of the periglacial belt to higher elevations. It is unlikely that widespread permafrost have existed in Mediterranean mountains during the Holocene, except in the highest massifs exceeding 2500-3000 m. The colder climate prevailing during the LIA favoured a minor glacial advance and the spatial expansion of permafrost, with the development of new protalus lobes and rock glaciers in the highest massifs. Finally, the warming started during the second half of the 19th century has led to glacial retreat and/or complete melting, increased paraglacial activity, migration of periglacial processes to the highest lands and degradation of alpine permafrost along with geoecological changes
Atrial myxoma presenting with orthostatic hypotension in an 84-year-old Hispanic man: a case report
This is an Open Access article distributed under the terms of the Creative Commons Attribution Licens
A non-hybrid method for the PDF equations of turbulent flows on unstructured grids
In probability density function (PDF) methods of turbulent flows, the joint
PDF of several flow variables is computed by numerically integrating a system
of stochastic differential equations for Lagrangian particles. A set of
parallel algorithms is proposed to provide an efficient solution of the PDF
transport equation, modeling the joint PDF of turbulent velocity, frequency and
concentration of a passive scalar in geometrically complex configurations. An
unstructured Eulerian grid is employed to extract Eulerian statistics, to solve
for quantities represented at fixed locations of the domain (e.g. the mean
pressure) and to track particles. All three aspects regarding the grid make use
of the finite element method (FEM) employing the simplest linear FEM shape
functions. To model the small-scale mixing of the transported scalar, the
interaction by exchange with the conditional mean model is adopted. An adaptive
algorithm that computes the velocity-conditioned scalar mean is proposed that
homogenizes the statistical error over the sample space with no assumption on
the shape of the underlying velocity PDF. Compared to other hybrid
particle-in-cell approaches for the PDF equations, the current methodology is
consistent without the need for consistency conditions. The algorithm is tested
by computing the dispersion of passive scalars released from concentrated
sources in two different turbulent flows: the fully developed turbulent channel
flow and a street canyon (or cavity) flow. Algorithmic details on estimating
conditional and unconditional statistics, particle tracking and particle-number
control are presented in detail. Relevant aspects of performance and
parallelism on cache-based shared memory machines are discussed.Comment: Accepted in Journal of Computational Physics, Feb. 20, 200
Does engaging in action research support trainee teachers in forming and reflecting on values?
A monitoring campaign (2013-2020) of ESA's Mars Express to study interplanetary plasma scintillation
The radio signal transmitted by the Mars Express (MEX) spacecraft was
observed regularly between the years 2013-2020 at X-band (8.42 GHz) using the
European Very Long Baseline Interferometry (EVN) network and University of
Tasmania's telescopes. We present a method to describe the solar wind
parameters by quantifying the effects of plasma on our radio signal. In doing
so, we identify all the uncompensated effects on the radio signal and see which
coronal processes drive them. From a technical standpoint, quantifying the
effect of the plasma on the radio signal helps phase referencing for precision
spacecraft tracking. The phase fluctuation of the signal was determined for
Mars' orbit for solar elongation angles from 0 - 180 deg. The calculated phase
residuals allow determination of the phase power spectrum. The total electron
content (TEC) of the solar plasma along the line of sight is calculated by
removing effects from mechanical and ionospheric noises. The spectral index was
determined as which is in agreement with Kolomogorov's
turbulence. The theoretical models are consistent with observations at lower
solar elongations however at higher solar elongation (160 deg) we see the
observed values to be higher. This can be caused when the uplink and downlink
signals are positively correlated as a result of passing through identical
plasma sheets.Comment: The paper has 13 figures and one table. It has been accepted for
publication in PASA and the article will receive its DOI in a week's tim
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