50,740 research outputs found
The Thermal Evolution of the Donors in AM CVn Binaries
(Abridged) We calculate the full stellar-structural evolution of donors in AM
CVn systems formed through the WD channel coupled to the binary's evolution.
Contrary to assumptions made in prior modelling, these donors are not fully
convective over much of the AM CVn phase and do not evolve adiabatically under
mass loss indefinitely. Instead, we identify three distinct phases of
evolution: a mass transfer turn-on phase (during which the orbital period
continues to decrease even after contact, the donor contracts, and the mass
transfer rate accelerates to its maximum), a phase in which the donor expands
adiabatically in response to mass loss, and a cooling phase beginning at
orbital periods of approximately 45--55 minutes during which the donor
contracts. The physics that determines the behaviour in the first and third
phases, both of which are new outcomes of this study, are discussed in some
detail. We find the overall duration of the turn-on phase to be between - yrs, significantly longer than prior estimates. We predict the
donor's luminosity and effective temperature. During the adiabatic expansion
phase (ignoring irradiation effects), the luminosity is approximately
-- and the effective temperature is approximately
1000--1800 K. However, the flux generated in the accretion flow dominates the
donor's intrinsic light at all times. The impact of irradiation on the donor
extends the phase of adiabatic expansion to longer orbital periods and alters
the donor's observational characteristics. Irradiated donors during the
adiabatic phase can attain a surface luminosity of up to . We argue that the turn-on and cooling phases both will leave
significant imprints on the AM CVn population's orbital period distribution.Comment: (20 pages, 20 figures, accepted to the Monthly Notices of the Royal
Astronomical Society
Fluid-induced Rotordynamic Forces and Instabilities
In the late 1970s, the authors began a collaboration with our colleague Tom Caughey that helped define a new set of fluid-structure interaction phenomena in turbomachines, namely fluid-induced rotordynamic forces and instabilities. That collaboration and the 31 joint ABC papers it produced epitomized Tom Caughey's genius and we reprise it here in his honor.
The design of the space shuttle main engine (SSME) pushed beyond the boundaries of many known technologies. In particular, the rotating speeds and operating conditions of the high speed liquid oxygen and liquid hydrogen turbopumps were extreme and early testing revealed a whirl instability whose magnitude exceeded expectations and allowable limits. It was suspected and later proven that fluid-induced rotordynamic effects were a contributing factor and yet very little was known of such phenomena. As one of the efforts seeking understanding, we constructed a facility to measure fluid-induced rotordynamic forces. This was subsequently used in a broad range of investigations. Initially, the effort was directed to understanding the source and parametric variations of destabilizing fluid forces. Later various components of the flow in a high speed turbopump were investigated. And finally, some ameliorative measures and their effectiveness were examined. This paper reviews this body of knowledge and the lessons learnt along the way
Sensitivity Analysis of Computations of the Vapor-Liquid Equilibria of Methane + Methanol or Glycols at Gas Hydrate Formation Conditions
The Soave-Redlich-Kwong (SRK-EOS) and Peng-Robinson (PR-EOS) equations of state are used often to describe the behavior of pure substances and mixtures despite difficulties in handling substances, like water, with high polarity and hydrogen bonding. They were employed in studying the binary vapor-liquid equilibria (VLE) of methane + methanol, monoethylene glycol (MEG), and triethylene glycol (TEG). These liquids are used to inhibit the formation of gas hydrates. The investigation focused on the conditions at which methane-water clathrates can form 283.89 K to 323.56 K and 5.01 MPa to 18.48 MPa. The pressure of methane in methanol is overestimated by a factor of two by either the SRK-EOS or the PR-EOS. In the methane + MEG system, the predicted pressures for both equations of state are generally less than experimental pressure except for the highest concentration of methane in MEG calculated by the SRK-EOS. In the methane + TEG system, the predictions of both models are close and trend similarly. Because of the comparative lack of extensive experimental methane + TEG data, the similarity of the methane + TEG computed results can be used as a basis for further study of this system experimentally
Dusty Exoplanetary Debris Disks in the Single-Temperature Blackbody Plane
The 21st European Workshop on White Dwarfs was held in Austin, TX from July 23rd to 27th of 2018We present a bulk sample analysis of the metal
polluted white dwarfs which also host infrared
bright dusty debris disks, known to be direct signatures
of an active exoplanetary accretion source.
We explore the relative positions of these systems
in a “single-temperature blackbody plane”, defined
as the temperature and radius of a single temperature
blackbody as fitted to the infrared
excess. We find that the handful of dust systems
which also host gaseous debris in emission
congregate along the high temperature boundary
of the dust disk region in the single-temperature
blackbody plane. We discuss interpretations of
this boundary and propose the single-temperature
blackbody plane selection technique for use in future
targeted searches of gaseous emission.Astronom
Characterization of a Human Powered Nebulizer Compressor for Resource Poor Settings
Background
Respiratory disease accounts for three of the ten leading causes of death worldwide. Many of these diseases can be treated and diagnosed using a nebulizer. Nebulizers can also be used to safely and efficiently deliver vaccines. Unfortunately, commercially available nebulizers are not designed for use in regions of the world where lung disease is most prevalent: they are electricity-dependent, cost-prohibitive, and not built to be reliable in harsh operating conditions or under frequent use.
To overcome these limitations, the Human Powered Nebulizer compressor (HPN) was developed. The HPN does not require electricity; instead airflow is generated manually through a hand-crank or bicycle-style pedal system. A health care worker or other trained individual operates the device while the patient receives treatment.
This study demonstrates functional specifications of the HPN in comparison with a standard commercially available electric jet nebulizer compressor, the DeVilbiss Pulmo-Aide 5650D (Pulmo-Aide). Methods
Pressure and flow characteristics were measured with a rotameter and pressure transducer, respectively. Volume nebulized by each compressor was determined by mass, and particle size distribution was determined via laser diffraction. The Hudson RCI Micro Mist nebulizer mouthpiece was used with both compressors. Results
The pressure and flow generated by the HPN and Pulmo-Aide were: 15.17 psi and 10.5 L/min; and 14.65 psi and 11.2 L/min, respectively. The volume of liquid delivered by each was equivalent, 1.097 ± 0.107 mL (mean ± s.e.m., n = 13) for the HPN and 1.092 ± 0.116 mL for the Pulmo-Aide. The average particle size was also equivalent, 5.38 ± 0.040 micrometers (mean ± s.e.m., n = 7) and 5.40 ± 0.025 micrometers, respectively. Conclusions
Based on these characteristics, the HPN’s performance is equivalent to a popular commercially available electric nebulizer compressor. The findings presented in this paper, combined with the results of two published clinical studies, suggest that the HPN could serve as an important diagnostic and therapeutic tool in the fight against global respiratory health challenges including: tuberculosis, chronic obstructive pulmonary disease, asthma, and lower respiratory infections
Informed baseline subtraction of proteomic mass spectrometry data aided by a novel sliding window algorithm
Proteomic matrix-assisted laser desorption/ionisation (MALDI) linear
time-of-flight (TOF) mass spectrometry (MS) may be used to produce protein
profiles from biological samples with the aim of discovering biomarkers for
disease. However, the raw protein profiles suffer from several sources of bias
or systematic variation which need to be removed via pre-processing before
meaningful downstream analysis of the data can be undertaken. Baseline
subtraction, an early pre-processing step that removes the non-peptide signal
from the spectra, is complicated by the following: (i) each spectrum has, on
average, wider peaks for peptides with higher mass-to-charge ratios (m/z), and
(ii) the time-consuming and error-prone trial-and-error process for optimising
the baseline subtraction input arguments. With reference to the aforementioned
complications, we present an automated pipeline that includes (i) a novel
`continuous' line segment algorithm that efficiently operates over data with a
transformed m/z-axis to remove the relationship between peptide mass and peak
width, and (ii) an input-free algorithm to estimate peak widths on the
transformed m/z scale. The automated baseline subtraction method was deployed
on six publicly available proteomic MS datasets using six different m/z-axis
transformations. Optimality of the automated baseline subtraction pipeline was
assessed quantitatively using the mean absolute scaled error (MASE) when
compared to a gold-standard baseline subtracted signal. Near-optimal baseline
subtraction was achieved using the automated pipeline. The advantages of the
proposed pipeline include informed and data specific input arguments for
baseline subtraction methods, the avoidance of time-intensive and subjective
piecewise baseline subtraction, and the ability to automate baseline
subtraction completely. Moreover, individual steps can be adopted as
stand-alone routines.Comment: 50 pages, 19 figure
Jet A Explosion Experiments: Laboratory Testing
This report describes a series of experiments and analyses on the flammability of Jet A (aviation kerosene) in air. This is a progress report on ongoing work. The emphasis so far has been on measuring basic explosion parameters as a function of fuel amount and temperature. These parameters include vapor pressure, flammability limits, peak explosion
pressure and pressure as a function of time during the explosion. These measurements were undertaken in order to clear up some fundamental issues with the existing data.
The report is organized as follows: First, we give some background with data from previous studies and discuss the fuel weathering issues. Second, we describe the facility used to do combustion experiments, the combustion test procedures and the results of the combustion experiments. Third, we give estimates of peak pressure, review the standard analysis of pressure histories and discuss the application to the present data. Fourth, we review the standard approach to flammability limits and the issues in determining Jet A flammability. Fifth, we discuss the problems associated with measuring vapor pressure and describe our results for Jet A. Sixth, we present a model for Jet A which illustrates the issues in analyzing multicomponent fuels. Finally, we apply these results to TWA 800 and summarize our conclusions to date
Spark Ignition Energy Measurements in Jet A
Experiments have been carried out to measure the spark ignition energy of Jet A vapor in air. A range of ignition energies from 1 mJ to 100 J was examined in these tests. The test method was validated by first measuring ignition energies for lean mixtures of the fuels hexane (C6H6) and propane (C3H8) in air at normal temperature (295 K) and pressure (1 atm). These results agree with existing data and provide new results for compositions between the lean flame limit and stoichiometric mixtures. Jet A (from LAX, flashpoint 45–48 [degress] C) vapor mixtures with air have been tested at temperatures between 30 and 60 [degrees] C at two fuel mass loadings, 3 and 200 kg/m3, in an explosion test vessel with a volume of 1.8 liter. Tests at 40, 50, and 60 [degrees] C have been performed at a mass loading of 3 kg/m3 in an 1180-liter vessel. Experiments with Jet A have
been carried out with initial conditions of 0.585 bar pressure to simulate altitude conditions appropriate to the TWA 800 explosion.
Ignition energies and peak pressures vary strongly as a function of initial temperature, but are a weak function of mass loading. The minimum ignition energy varies from less than 1 mJ at 60 [degrees] C to over 100 J at 30 [degrees] C. At temperatures less than 30 [degrees] C, ignition was not possible with 100 J or even a neon sign transformer (continuous discharge). The peak pressure between 40 and 55 [degrees] C was approximately 4 bar. Peak pressures in the 1180-liter vessel were slightly lower and the ignition energy was higher than in the 1.8-liter vessel.
The following conclusions were reached relative to the TWA 800 crash: (a) spark ignition sources with energies between 5 mJ and 1 J are sufficient to ignite Jet A vapor, resulting in a propagating flame; (b) the peak pressure rise was between 1.5 and 4 bar (20 and 60 psi). (c) a thermal ignition source consisting of a hot filament created by discharging electrical energy into a metal wire is also sufficient to ignite Jet A vapor, resulting in a propagating flame; (d) laminar burning speeds are between 15 and 45 cm/s; and (e) the limited amount of fuel available in the CWT (about 50 gal) did not significantly increase the flammability limit.
The rapid decrease in spark ignition energy with increasing temperature demonstrates that hot fuel tanks are significantly more hazardous than cool ones with respect to spark ignition sources. A systematic effort is now needed in order to utilize these results and apply spark ignition energy measurements to future analyses of fuel tank flammability. Some key issues that need to be addressed in future testing are: (a) effect of flashpoint on the ignition energy-temperature relationship; (b) ignition energy vs. temperature as a function of altitude; (c) effect of fuel weathering on ignition energy; and (d) the effect of ignition source type on ignition limits
Does Drinking Really Decrease in Bad Times?
This paper investigates the relationship between macroeconomic conditions, alcohol use, and drinking problems using individual-level data from the 1987-1999 years of the Behavioral Risk Factor Surveillance System. We confirm the procyclical variation in overall drinking identified in previous research using aggregate sales data and show that this largely results from changes in consumption among existing drinkers, rather than movements into or out of drinking. Moreover, the decrease in alcohol use occurring during bad economic times is concentrated among heavy consumers, with light drinking actually increasing in these periods. We find no evidence that the decline in overall drinking masks a rise in alcohol use for persons becoming unemployed during contractions, suggesting that any stress-induced increases in consumption are more than offset by reductions resulting from changes in economic factors such as lower incomes.
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