5,526 research outputs found
Greenhouse gas emissions from domestic hot water: heat pumps compared to most commonly used systems
We estimate the emissions of the two most important greenhouse gasses (GHG), carbon dioxide (CO2) and methane (CH4), from the use of modern high-efficiency heat pump water heaters compared to the most commonly used domestic hot water systems: natural gas storage tanks, tankless natural gas demand heaters, electric resistance storage tanks, and tankless electric resistance heaters. We considered both natural gas-powered electric plants and coal-powered plants as the source of the electricity for the heat pumps, the thermal electric storage tanks, and the tankless electric demand heaters. The time-integrated radiative forcing associated with using a heat pump water heater was always smaller than any other means of heating water considered in this study across all time frames including at 20 and 100 years. The estimated amount of CH4 lost during its lifecycle was the most critical factor determining the relative magnitude of the climatic impact. The greatest net climatic benefit within the 20-year time frame was predicted to be achieved when a storage natural gas water heater (the most common system for domestic hot water in the United States) fueled by shale gas was replaced with a high efficiency heat pump water heater powered by coal-generated electricity; the heat pump system powered by renewable electricity would have had an even greater climatic benefit, but was not explicitly modeled in this study. Our analysis provides the first assessment of the GHG footprint associated with using a heat pump water heater, which we demonstrate to be an effective and economically viable way of reducing emissions of GHGs.This study was funded by the Wallace Global Fund, the Park Foundation, and Cornell University
Amplitude variability in satellite photometry of the non-radially pulsating O9.5V star zeta Oph
We report a time-series analysis of satellite photometry of the non-radially
pulsating Oe star zeta Oph, principally using data from SMEI obtained
2003--2008, but augmented with MOST and WIRE results. Amplitudes of the
strongest photometric signals, at 5.18, 2.96, and 2.67/d, each vary
independently over the 6-year monitoring period (from ca. 30 to <2 mmag at
5.18/d), on timescales of hundreds of days. Signals at 7.19/d and 5.18/d have
persisted (or recurred) for around two decades. Supplementary spectroscopic
observations show an H-alpha emission episode in 2006; this coincided with
small increases in amplitudes of the three strongest photometric signals.Comment: MNRAS, in pres
The Influence of Stellar Wind Variability on Measurements of Interstellar O VI Along Sightlines to Early-Type Stars
A primary goal of the FUSE mission is to understand the origin of the O VI
ion in the interstellar medium of the Galaxy and the Magellanic Clouds. Along
sightlines to OB-type stars, these interstellar components are usually blended
with O VI stellar wind profiles, which frequently vary in shape. In order to
assess the effects of this time-dependent blending on measurements of the
interstellar O VI lines, we have undertaken a mini-survey of repeated
observations toward OB-type stars in the Galaxy and the Large Magellanic Cloud.
These sparse time series, which consist of 2-3 observations separated by
intervals ranging from a few days to several months, show that wind variability
occurs commonly in O VI (about 60% of a sample of 50 stars), as indeed it does
in other resonance lines. However, in the interstellar O VI 1032
region, the O VI 1038 wind varies only in 30% of the cases. By
examining cases exhibiting large amplitude variations, we conclude that
stellar-wind variability {\em generally} introduces negligible uncertainty for
single interstellar O VI components along Galactic lines of sight, but can
result in substantial errors in measurements of broader components or blends of
components like those typically observed toward stars in the Large Magellanic
Cloud. Due to possible contamination by discrete absorption components in the
stellar O VI line, stars with terminal velocities greater than or equal to the
doublet separation (1654 km/s) should be treated with care.Comment: Accepted for publication in the Astrophysical Journal Lette
Automotive Stirling engine development program
This is the ninth Semiannual Technical Progress Report prepared under the Automotive Stirling Engine Development Program. It covers the twenty-eighth and twenty-ninth quarters of activity after award of the contract. Quarterly Technical Progress Reports related program activities from the first through the thirteenth quarters; thereafter, reporting was changed to a Semiannual format. This report summarizes the study of higher-power kinematic Stirling engines for transportation use, development testing of Mod I Stirling engines, and component development activities. Component development testing included successful conical fuel nozzle testing and functional checkout of Mod II controls and auxiliaries on Mod I engine test beds. Overall program philosophy is outlined and data and test results are presented
Automotive Stirling engine development program
The major accomplishments were the completion of the Basic Stirling Engine (BSE) and the Stirling Engine System (SES) designs on schedule, the approval and acceptance of those designs by NASA, and the initiation of manufacture of BSE components. The performance predictions indicate the Mod II engine design will meet or exceed the original program goals of 30% improvement in fuel economy over a conventional Internal Combustion (IC) powered vehicle, while providing acceptable emissions. This was accomplished while simultaneously reducing Mod II engine weight to a level comparable with IC engine power density, and packaging the Mod II in a 1985 Celebrity with no external sheet metal changes. The projected mileage of the Mod II Celebrity for the combined urban and highway CVS cycle is 40.9 mpg which is a 32% improvement over the IC Celebrity. If additional potential improvements are verified and incorporated in the Mod II, the mileage could increase to 42.7 mpg
Forty eclipsing binaries in the Small Magellanic Cloud: fundamental parameters and Cloud distance
We have conducted a programme to determine the fundamental parameters of a
substantial number of eclipsing binaries of spectral types O and B in the Small
Magellanic Cloud. New spectroscopic data, obtained with the two-degree-field
multi-object spectrograph on the 3.9-m Anglo-Australian Telescope, have been
used in conjunction with photometry from the Optical Gravitational Lens
Experiment (OGLE-II) database of SMC eclipsing binaries. Previously we reported
results for 10 systems; in this second and concluding paper we present spectral
types, masses, radii, temperatures, surface gravities and luminosities for the
components of a further 40 binaries. The full sample of 50 OB-type eclipsing
systems is the largest single set of fundamental parameters determined for
high-mass binaries in any galaxy. We find that 21 of the systems studied are in
detached configurations, 28 are in semi-detached post-mass-transfer states, and
one is a contact binary.
Each system provides a primary distance indicator. We find a mean distance
modulus to the SMC of 18.91+/-0.03+/-0.1 (internal and external uncertainties;
D=60.6+/-1.0 kpc). This value represents one of the most precise available
determinations of the distance to the SMC.Comment: paper accepted on 22 November 2004 for publication by MNRAS; 26
pages, 6 tables, 12 figure
Automotive Stirling Engine Development Program
Development test activities on Mod I engines directed toward evaluating technologies for potential inclusion in the Mod II engine are summarized. Activities covered include: test of a 12-tube combustion gas recirculation combustor; manufacture and flow-distribution test of a two-manifold annular heater head; piston rod/piston base joint; single-solid piston rings; and a digital air/fuel concept. Also summarized are results of a formal assessment of candidate technologies for the Mod II engine, and preliminary design work for the Mod II. The overall program philosophy weight is outlined, and data and test results are presented
Studies in the Lake Ontario Basin using ERTS-1 and high altitude data
Studies in the Lake Ontario Basin are designed to provide input for models of river basin discharge and macro-scale features of lake circulation. Lake studies appear to require high altitude imagery to record the dynamic features of Lake Ontario so that ERTS-1 data may be interpreted. Land area studies require input of soil moisture, land use and soil-sediment-geomorphology measurements some of which appear to be available, on a regional scale from ERTS-1 products
Fundamental stellar parameters of zeta Pup and gamma^2 Vel from HIPPARCOS data
We report parallax measurements by the HIPPARCOS satellite of zeta Puppis and
gamma^2 Velorum. The distance of zeta Pup is d=429 (+120/ -77) pc, in agreement
with the commonly adopted value to Vela OB2. However, a significantly smaller
distance is found for the gamma^2 Vel system: d=258 (+41/-31) pc. The total
mass of gamma^2 Vel derived from its parallax, the angular size of the
semi-major axis as measured with intensity interferometry, and the period is
M(WR+O)=29.5 (+/-15.9) Msun. This result favors the orbital solution of Pike et
al. (1983) over that of Moffat et al. (1986). The stellar parameters for the O
star companion derived from line blanketed non-LTE atmosphere models are:
Teff=34000 (+/-1500) K, log L/Lsun=5.3 (+/-0.15) from which an evolutionary
mass of M=29 (+/-4) Msun and an age of 4.0 (+0.8/-0.5) Myr is obtained from
single star evolutionary models. With non-LTE model calculations including He
and C we derive a luminosity log L/Lsun~4.7 (+/-0.2) for the WR star. The
mass-luminosity relation of hydrogen-free WR stars implies a mass of M(WR)~5
(+/-1.5) Msun. From our data we favor an age of ~10 Myr for the bulk of the
Vela OB2 stars. Evolutionary scenarios for zeta Pup and gamma^2 Vel are
discussed in the light of our results.Comment: Submitted to ApJ Letters (misprints corrected
Massive stars and the energy balance of the interstellar medium. II. The 35 solar mass star and a solution to the "missing wind problem"
We continue our numerical analysis of the morphological and energetic
influence of massive stars on their ambient interstellar medium for a 35 solar
mass star that evolves from the main sequence through red supergiant and
Wolf-Rayet phases, until it ultimately explodes as a supernova. We find that
structure formation in the circumstellar gas during the early main-sequence
evolution occurs as in the 60 solar mass case but is much less pronounced
because of the lower mechanical wind luminosity of the star. Since on the other
hand the shell-like structure of the HII region is largely preserved, effects
that rely on this symmetry become more important. At the end of the stellar
lifetime 1% of the energy released as Lyman continuum radiation and stellar
wind has been transferred to the circumstellar gas. From this fraction 10% is
kinetic energy of bulk motion, 36% is thermal energy, and the remaining 54% is
ionization energy of hydrogen. The sweeping up of the slow red supergiant wind
by the fast Wolf-Rayet wind produces remarkable morphological structures and
emission signatures, which are compared with existing observations of the
Wolf-Rayet bubble S308. Our model reproduces the correct order of magnitude of
observed X-ray luminosity, the temperature of the emitting plasma as well as
the limb brightening of the intensity profile. This is remarkable, because
current analytical and numerical models of Wolf-Rayet bubbles fail to
consistently explain these features. A key result is that almost the entire
X-ray emission in this stage comes from the shell of red supergiant wind swept
up by the shocked Wolf-Rayet wind rather than from the shocked Wolf-Rayet wind
itself as hitherto assumed and modeled. This offers a possible solution to what
is called the ``missing wind problem'' of Wolf-Rayet bubbles.Comment: 52 pages, 20 figures, 2 tables, accepted for publication in the
Astrophysical Journa
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