1,147 research outputs found
Energy From Biochemical Sources
As available energy reserves decline, renewable sources must be utilized. Organic matter, grown agriculturally, represents a renewable energy source, which is readily available. This paper reviews the methods by which organic matter can be converted to energy sources by biochemical processes. The economics of conversion of agricultural crops and byproducts to alcohols by fermentation and conversion of these agricultural materials to methane by anaerobic digestion are examined. Projections of the potential of this energy source are quite promising
Optimization of design and beam test of microstrip gas chambers
We describe recent experimental and theoretical work aimed at optimizing the geometry and the operation of micro-strip gas chambers in order to improve their performance and reliability. With the help of a simulation program, we have studied the mechanism of signal propagation and analyzed the effects on signal shape and size of resistivity of strips, grouping of biased strips and presence of a back-plane. Several detectors manufactured according to the results of the study and equipped with fast amplifiers have been installed in a test beam to study general operating characteristics, efficiency and localization accuracy; preliminary results of the data analysis are discussed
Ram pressure stripping of the cool core of the Ophiuchus Cluster
(abridged) We report results from a Chandra study of the central regions of
the nearby, X-ray bright, Ophiuchus Cluster (z = 0.03), the second-brightest
cluster in the sky. Our study reveals a dramatic, close-up view of the
stripping and potential destruction of a cool core within a rich cluster. The
X-ray emission from the Ophiuchus Cluster core exhibits a comet-like morphology
extending to the north, driven by merging activity, indicative of ram-pressure
stripping caused by rapid motion through the ambient cluster gas. A cold front
at the southern edge implies a velocity of 1000200 km/s (M~0.6). The X-ray
emission from the cluster core is sharply peaked. As previously noted, the peak
is offset by 4 arcsec (~2 kpc) from the optical center of the associated cD
galaxy, indicating that ram pressure has slowed the core, allowing the
relatively collisionless stars and dark matter to carry on ahead. The cluster
exhibits the strongest central temperature gradient of any massive cluster
observed to date: the temperature rises from 0.7 keV within 1 kpc of the
brightness peak, to 10 keV by 30 kpc. A strong metallicity gradient is also
observed within the same region. This supports a picture in which the outer
parts of the cool core have been stripped by ram-pressure due to its rapid
motion. The cooling time of the innermost gas is very short, ~5
yrs. Within the central 10 kpc radius, multiple small-scale fronts and a
complex thermodynamic structure are observed, indicating significant motions.
Beyond the central 50 kpc, and out to a radius ~150 kpc, the cluster appears
relatively isothermal and has near constant metallicity. The exception is a
large, coherent ridge of enhanced metallicity observed to trail the cool core,
and which is likely to have been stripped from it.Comment: Accepted to MNRAS. 11 pages, 9 figure
Extending Optical Flare Models to the UV: Results from Comparing of TESS and GALEX Flare Observations For M Dwarfs
The ultraviolet (UV) emission of stellar flares may have a pivotal role in
the habitability of rocky exoplanets around low-mass stars. Previous studies
have used white-light observations to calibrate empirical models which describe
the optical and UV flare emission. However, the accuracy of the UV predictions
of models have previously not been tested. We combined TESS optical and GALEX
UV observations to test the UV predictions of empirical flare models calibrated
using optical flare rates of M stars. We find that the canonical 9000 K
blackbody model used by flare studies underestimates the GALEX NUV energies of
field age M stars by up to a factor of 6.50.7 and the GALEX FUV energies
of fully convective field age M stars by 30.610.0. We calculated energy
correction factors that can be used to bring the UV predictions of flare models
closer in line with observations. We calculated pseudo-continuum flare
temperatures that describe both the white-light and GALEX NUV emission. We
measured a temperature of 10,700 K for flares from fully convective M stars
after accounting for the contribution from UV line emission. We also applied
our correction factors to the results of previous studies of the role of flares
in abiogenesis. Our results show that M stars do not need to be as active as
previously thought in order to provide the NUV flux required for prebiotic
chemistry, however we note that flares will also provide more FUV flux than
previously modelled.Comment: 20 pages, 9 figures, 4 tables. Accepted for publication in the
Monthly Notices of the Royal Astronomical Societ
Feedback under the microscope II: heating, gas uplift, and mixing in the nearest cluster core
Using a combination of deep 574ks Chandra data, XMM-Newton high-resolution
spectra, and optical Halpha+NII images, we study the nature and spatial
distribution of the multiphase plasma in M87. Our results provide direct
observational evidence of `radio mode' AGN feedback in action, stripping the
central galaxy of its lowest entropy gas and preventing star-formation. This
low entropy gas was entrained with and uplifted by the buoyantly rising
relativistic plasma, forming long "arms". These arms are likely oriented within
15-30 degrees of our line-of-sight. The mass of the uplifted gas in the arms is
comparable to the gas mass in the approximately spherically symmetric 3.8 kpc
core, demonstrating that the AGN has a profound effect on its immediate
surroundings. The coolest X-ray emitting gas in M87 has a temperature of ~0.5
keV and is spatially coincident with Halpha+NII nebulae, forming a multiphase
medium where the cooler gas phases are arranged in magnetized filaments. We
place strong upper limits of 0.06 Msun/yr on the amount of plasma cooling
radiatively from 0.5 keV and show that a uniform, volume-averaged heating
mechanism could not be preventing the cool gas from further cooling. All of the
bright Halpha filaments appear in the downstream region of the <3 Myr old shock
front, at smaller radii than ~0.6'. We suggest that shocks induce shearing
around the filaments, thereby promoting mixing of the cold gas with the ambient
hot ICM via instabilities. By bringing hot thermal particles into contact with
the cool, line-emitting gas, mixing can supply the power and ionizing particles
needed to explain the observed optical spectra. Mixing of the coolest X-ray
emitting plasma with the cold optical line emitting filamentary gas promotes
efficient conduction between the two phases, allowing non-radiative cooling
which could explain the lack of X-ray gas with temperatures under 0.5 keV.Comment: to appear in MNRA
New observations with the gas electron multiplier (GEM)
We describe recent measurements realized with the Gas Electron Multiplier (GEM) mesh added as pre-amplification element to a multiwire and a micro-strip chamber. Large, stable combined gains are obtained, with good uniformity and energy resolution, in a wide range of filling gases including non-flammable mixtures; coupled to a micro-strip plate, the pre-amplification element allows to maintain the high rate capability and resolution at considerably lower operating voltages, completely eliminating discharge problems. Charge gains are large enough to allow detection of signals in the ionization mode on the last element, permitting the use of a simple printed circuit as read-out electrode; two-dimensional read-out can then be easily implemented. The absence of charge multiplication in the last stage avoids charge build-up on the substrate and prevents ageing phenomena. A new generation of simple, reliable and cheap fast position sensitive detectors seems at hand
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