214 research outputs found
Large eddy simulations and direct numerical simulations of high speed turbulent reacting flows
This research is involved with the implementations of advanced computational schemes based on large eddy simulations (LES) and direct numerical simulations (DNS) to study the phenomenon of mixing and its coupling with chemical reactions in compressible turbulent flows. In the efforts related to LES, a research program was initiated to extend the present capabilities of this method for the treatment of chemically reacting flows, whereas in the DNS efforts, focus was on detailed investigations of the effects of compressibility, heat release, and nonequilibrium kinetics modeling in high speed reacting flows. The efforts to date were primarily focussed on simulations of simple flows, namely, homogeneous compressible flows and temporally developing hign speed mixing layers. A summary of the accomplishments is provided
IMAGE DATA CLASSIFICATION BY NFES-MODEL
In this paper, we propose an identification method of the land cover from remote sensing data with combining neuro-fuzzy and expert system. This combining then is called by Neuro-Fuzzy Expert System Model (NFES-Model). A Neural network (NN) is a part from neuro-fuzzy has the ability to recognize complex patterns, and classifies them into many desired classes. However, the neural network might produce misclassification. By adding fuzzy expert system into NN using geographic knowledge based, then misclassification can be decreased, with the result that improvement of classification result, compared with a neural network approximation
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
Safety Recommendations for Evaluation and Surgery of the Head and Neck During the COVID-19 Pandemic
Importance The rapidly expanding novel coronavirus disease 2019 (COVID-19) pandemic, caused by severe acute respiratory syndrome coronavirus 2, has challenged the medical community to an unprecedented degree. Physicians and health care workers are at added risk of exposure and infection during the course of patient care. Because of the rapid spread of this disease through respiratory droplets, health care workers who come in close contact with the upper aerodigestive tract during diagnostic and therapeutic procedures, such as otolaryngologists–head and neck surgeons, are particularly at risk. A set of safety recommendations was created based on a review of the literature and communications with physicians with firsthand knowledge of safety procedures during the COVID-19 pandemic.
Observations A high number of health care workers were infected during the first phase of the pandemic in the city of Wuhan, China. Subsequently, by adopting strict safety precautions, other regions were able to achieve high levels of safety for health care workers without jeopardizing the care of patients. The most common procedures related to the examination and treatment of upper aerodigestive tract diseases were reviewed. Each category was reviewed based on the potential risk imposed to health care workers. Specific recommendations were made based on the literature, when available, or consensus best practices. Specific safety recommendations were made for performing tracheostomy in patients with COVID-19.
Conclusions and Relevance Preserving a highly skilled health care workforce is a top priority for any community and health care system. Based on the experience of health care systems in Asia and Europe, by following strict safety guidelines, the risk of exposure and infection of health care workers could be greatly reduced while providing high levels of care. The provided recommendations, which may evolve over time, could be used as broad guidance for all health care workers who are involved in the care of patients with COVID-19
Experimental Study on Vibration-Assisted Magnetic Abrasive Finishing for Internal Surface of Aluminum Tubes
In this research, a new apparatus is designed and set to polish the internal surface of aluminum tube in the presence of axial vibration (AV) for the poles. Several parameters influence the quality of polished surface during magnetic abrasive finishing. The effect of such parameters has been the subject of researches to achieve the best finished surface with desired characteristics. This paper has a statistical approach to investigate the effects of four parameters, i.e., mesh size of the abrasives, the weight of the abrasive powders, the number of cycles and especially vibration frequency of the poles on surface roughness and material removal weight in finishing process. Design of experiments (DOE) methods and analysis of variance are applied to determine the significant factors. Microscopic view of the working surface is also presented for better understanding the parameters effect on the finished surface
Development of Methods to Predict the Effects of Test Media in Ground-Based Propulsion Testing
This report discusses work that began in mid-2004 sponsored by the Office of the Secretary of Defense (OSD) Test & Evaluation/Science & Technology (T&E/S&T) Program. The work was undertaken to improve the state of the art of CFD capabilities for predicting the effects of the test media on the flameholding characteristics in scramjet engines. The program had several components including the development of advanced algorithms and models for simulating engine flowpaths as well as a fundamental experimental and diagnostic development effort to support the formulation and validation of the mathematical models. This report provides details of the completed work, involving the development of phenomenological models for Reynolds averaged Navier-Stokes codes, large-eddy simulation techniques and reduced-kinetics models. Experiments that provided data for the modeling efforts are also described, along with with the associated nonintrusive diagnostics used to collect the data
Probing the Inner Jet of the Quasar PKS 1510-089 with Multi-waveband Monitoring during Strong Gamma-ray Activity
We present results from monitoring the multi-waveband flux, linear
polarization, and parsec-scale structure of the quasar PKS 1510-089,
concentrating on eight major gamma-ray flares that occurred during the interval
2009.0-2009.5. The gamma-ray peaks were essentially simultaneous with maxima at
optical wavelengths, although the flux ratio of the two wavebands varied by an
order of magnitude. The optical polarization vector rotated by 720 degrees
during a 5-day period encompassing six of these flares. This culminated in a
very bright, roughly 1 day, optical and gamma-ray flare as a bright knot of
emission passed through the highest-intensity, stationary feature (the "core")
seen in 43 GHz Very Long Baseline Array images. The knot continued to propagate
down the jet at an apparent speed of 22c and emit strongly at gamma-ray
energies as a months-long X-ray/radio outburst intensified. We interpret these
events as the result of the knot following a spiral path through a mainly
toroidal magnetic field pattern in the acceleration and collimation zone of the
jet, after which it passes through a standing shock in the 43 GHz core and then
continues downstream. In this picture, the rapid gamma-ray flares result from
scattering of infrared seed photons from a relatively slow sheath of the jet as
well as from optical synchrotron radiation in the faster spine. The 2006-2009.7
radio and X-ray flux variations are correlated at very high significance; we
conclude that the X-rays are mainly from inverse Compton scattering of infrared
seed photons by 20-40 MeV electrons.Comment: 10 pages of text + 5 figures, to be published in Astrophysical
Journal Letters in 201
On the Location of the Gamma-ray Emission in the 2008 Outburst in the BL Lacertae Object AO 0235+164 through Observations across the Electromagnetic Spectrum
We present observations of a major outburst at centimeter, millimeter,
optical, X-ray, and gamma-ray wavelengths of the BL Lacertae object AO
0235+164. We analyze the timing of multi-waveband variations in the flux and
linear polarization, as well as changes in Very Long Baseline Array (VLBA)
images at 7mm with 0.15 milliarcsecond resolution. The association of the
events at different wavebands is confirmed at high statistical significance by
probability arguments and Monte-Carlo simulations. A series of sharp peaks in
optical linear polarization, as well as a pronounced maximum in the 7 mm
polarization of a superluminal jet knot, indicate rapid fluctuations in the
degree of ordering of the magnetic field. These results lead us to conclude
that the outburst occurred in the jet both in the quasi-stationary "core" and
in the superluminal knot, both parsecs downstream of the supermassive black
hole. We interpret the outburst as a consequence of the propagation of a
disturbance, elongated along the line of sight by light-travel time delays,
that passes through a standing recollimation shock in the core and propagates
down the jet to create the superluminal knot. The multi-wavelength light curves
vary together on long time-scales (months/years), but the correspondence is
poorer on shorter time-scales. This, as well as the variability of the
polarization and the dual location of the outburst, agrees with the
expectations of a multi-zone emission model in which turbulence plays a major
role in modulating the synchrotron and inverse Compton fluxes.Comment: Accepted for Publication in the Astrophysical Journal Letters. 7
pages (including 5 figures). Minor corrections with regard to previous
version, as proposed by the refere
Flaring Behavior of the Quasar 3C~454.3 across the Electromagnetic Spectrum
We analyze the behavior of the parsec-scale jet of the quasar 3C~454.3 during
pronounced flaring activity in 2005-2008. Three major disturbances propagated
down the jet along different trajectories with Lorentz factors 10. The
disturbances show a clear connection with millimeter-wave outbursts, in 2005
May/June, 2007 July, and 2007 December. High-amplitude optical events in the
-band light curve precede peaks of the millimeter-wave outbursts by 15-50
days. Each optical outburst is accompanied by an increase in X-ray activity. We
associate the optical outbursts with propagation of the superluminal knots and
derive the location of sites of energy dissipation in the form of radiation.
The most prominent and long-lasting of these, in 2005 May, occurred closer to
the black hole, while the outbursts with a shorter duration in 2005 Autumn and
in 2007 might be connected with the passage of a disturbance through the
millimeter-wave core of the jet. The optical outbursts, which coincide with the
passage of superluminal radio knots through the core, are accompanied by
systematic rotation of the position angle of optical linear polarization. Such
rotation appears to be a common feature during the early stages of flares in
blazars. We find correlations between optical variations and those at X-ray and
-ray energies. We conclude that the emergence of a superluminal knot
from the core yields a series of optical and high-energy outbursts, and that
the mm-wave core lies at the end of the jet's acceleration and collimation
zone.Comment: 57 pages, 23 figures, 8 tables (submitted to ApJ
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