22,605 research outputs found
Use of co-solvents in hydrothermal liquefaction (HTL) of microalgae
This study reviewed and summarized the literature regarding the use of alcohols during hydrothermal liquefaction (HTL) of algal biomass feedstocks. The use of both pure alcohols and alcohol-water co-solvents were considered. Based upon this review, laboratory experiments were conducted to investigate the impacts of different alcohol co-solvents (ethanol, isopropanol, ethylene glycol, and glycerol) on the HTL treatment of a specific saltwater microalga (Tetraselmis sp.) at two temperatures: 300 ?C and 350 ?C. Based on their performance, two co-solvents, isopropanol and ethylene glycol, were selected to explore the effects of varying solvent concentrations and reaction temperatures on product yields and biocrude properties. The type and amount of added alcohol did not significantly affect the biocrude yield or composition. Biocrude yields were in the range of 30-35%, while a nearly constant yield of 21% insoluble products was observed, largely resulting from ash constituents within the algal feedstock. The benefits of using alcohol co-solvents (especially isopropanol) were the reduced viscosity of the biocrude products and reduced rates of viscosity increase with biocrude aging. These effects were attributed mainly to the physical properties of the co-solvent mixtures (solubility, polarity, density, etc.) rather than chemical processes. Under the reaction conditions used, there was no evidence that the co-solvents participated in biocrude production by means of hydrogen donation or other chemical processes. Recovery and recycling of the co-solvent present various challenges, depending upon the type and amount of the co-solvent that is used. For example, glycol solvents are recovered nearly completely within the aqueous product stream, whereas simple alcohols are partitioned between the biocrude and aqueous product streams. In commercial applications, the slight benefits provided by the use of co-solvents must be balanced by the challenges of co-solvent recovery and recycling. - 2019 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).This research received funding from the Qatar National Priorities Research Program (NPRP grant, grant number 8-646-4-727 from the Qatar National Research Fund).Scopu
SPEAR Far Ultraviolet Spectral Images of the Cygnus Loop
We present far-ultraviolet (FUV) spectral images, measured at C IV 1550, He
II 1640, Si IV+O IV] 1400, and O III] 1664, of the entire Cygnus Loop, observed
with the Spectroscopy of Plasma Evolution from Astrophysical Radiation (SPEAR)
instrument, also known as FIMS. The spatial distribution of FUV emission
generally corresponds with a limb-brightened shell, and is similar to optical,
radio and X-ray images. The features found in the present work include a
``carrot'', diffuse interior, and breakout features, which have not been seen
in previous FUV studies. Shock velocities of 140-160 km/s is found from a line
ratio of O IV] to O III], which is insensitive not only to resonance scattering
but also to elemental abundance. The estimated velocity indicates that the fast
shocks are widespread across the remnant. By comparing various line ratios with
steady-state shock models, it is also shown that the resonance scattering is
widespread.Comment: 13 pages, 3 figures, 1 table, accepted for publication in ApJ
Amplitude Zeros in Production
We demonstrate that the Standard Model amplitude for at the Born-level exhibits an approximate zero located at
at
high energies, where the () are the left-handed couplings
of the -boson to fermions and is the center of mass scattering
angle of the -boson. The approximate zero is the combined result of an exact
zero in the dominant helicity amplitudes and strong gauge
cancelations in the remaining amplitudes. For non-standard couplings
these cancelations no longer occur and the approximate amplitude zero is
eliminated.Comment: 11 pages, 4 figures submitted separately as uuencoded tar-ed
postscript files, FSU-HEP-940307, UCD-94-
An origin for small neutrino masses in the NMSSM
We consider the Next to Minimal Supersymmetric Standard Model (NMSSM) which
provides a natural solution to the so-called mu problem by introducing a new
gauge-singlet superfield S. We realize that a new mechanism of neutrino mass
suppression, based on the R-parity violating bilinear terms mu_i L_i H_u mixing
neutrinos and higgsinos, arises within the NMSSM, offering thus an original
solution to the neutrino mass problem (connected to the solution for the mu
problem). We generate realistic (Majorana) neutrino mass values without
requiring any strong hierarchy amongst the fundamental parameters, in contrast
with the alternative models. In particular, the ratio |mu_i/mu| can reach about
10^-1, unlike in the MSSM where it has to be much smaller than unity. We check
that the obtained parameters also satisfy the collider constraints and internal
consistencies of the NMSSM. The price to pay for this new cancellation-type
mechanism of neutrino mass reduction is a certain fine tuning, which get
significantly improved in some regions of parameter space. Besides, we discuss
the feasibility of our scenario when the R-parity violating bilinear terms have
a common origin with the mu term, namely when those are generated via a VEV of
the S scalar component from the couplings lambda_i S L_i H_u. Finally, we make
comments on some specific phenomenology of the NMSSM in the presence of
R-parity violating bilinear terms.Comment: 21 pages, 5 figures, Latex fil
The Turn-On of Mass Transfer in AM CVn Binaries: Implications for RX J0806+1527 and RX J1914+2456
We report on evolutionary calculations of the onset of mass transfer in AM
CVn binaries, treating the donor's evolution in detail. We show that during the
early contact phase, while the mass transfer rate, \Mdot, is increasing,
gravity wave (GW) emission continues to drive the binary to shorter orbital
period, \Porb. We argue that the phase where \Mdot > 0 and \nudot > 0
(\nu = 1/\Porb) can last between and yrs, significantly longer
than previously estimated. These results are applied to RX J0806+1527 (\Porb =
321 s) and RX J914+2456 (\Porb=569 s), both of which have measured \nudot >
0. \emph{Thus, a \nudot > 0 does not select between the unipolar inductor
and accretion driven models proposed as the source of X-rays in these systems}.
For the accretion model, we predict for RX J0806 that \ddot{\nu} \approx
\ee{1.0-1.5}{-28} Hz s and argue that timing observations can probe
at this level with a total yr baseline. We also place
constraints on each system's initial parameters given current observational
data.Comment: 5 pages, 3 figures, accepted to ApJ
An update on vector boson pair production at hadron colliders
We present numerical results (including full one-loop QCD corrections) for
the processes p p-bar and pp -> W+ W-, W+/- Z/gamma* and Z/gamma* Z/gamma*
followed by the decay of the massive vector bosons into leptons. In addition to
their intrinsic importance as tests of the standard model, these processes are
also backgrounds to conjectured non-standard model processes. Because of the
small cross sections at the Tevatron, full experimental control of these
backgrounds will be hard to achieve. This accentuates the need for up-to-date
theoretical information. A comparison is made with earlier work and cross
section results are presented for p p-bar collisions at sqrt{s}=2 TeV and pp
collisions at sqrt{s}=14 TeV. Practical examples of the use of our calculations
are presented.Comment: 18 pages, 5 embedded figures, included extra reference [7
The fastest unbound star in our Galaxy ejected by a thermonuclear supernova
Hypervelocity stars (HVS) travel with velocities so high, that they exceed
the escape velocity of the Galaxy. Several acceleration mechanisms have been
discussed. Only one HVS (US 708, HVS 2) is a compact helium star. Here we
present a spectroscopic and kinematic analysis of US\,708. Travelling with a
velocity of , it is the fastest unbound star in our
Galaxy. In reconstructing its trajectory, the Galactic center becomes very
unlikely as an origin, which is hardly consistent with the most favored
ejection mechanism for the other HVS. Furthermore, we discovered US\,708 to be
a fast rotator. According to our binary evolution model it was spun-up by tidal
interaction in a close binary and is likely to be the ejected donor remnant of
a thermonuclear supernova.Comment: 16 pages report, 20 pages supplementary material
Hot Subdwarfs in Resolved Binaries
In the last decade or so, there have been numerous searches for hot subdwarfs
in close binaries. There has been little to no attention paid to wide binaries
however. The advantages of understanding these systems can be many. The stars
can be assumed to be coeval, which means they have common properties. The
distance and metallicity, for example, are both unknown for the subdwarf
component, but may be determinable for the secondary, allowing other properties
of the subdwarf to be estimated. With this in mind, we have started a search
for common proper motion pairs containing a hot subdwarf component. We have
uncovered several promising candidate systems, which are presented here.Comment: 6 pages, 4 figures. Proceedings of The Fourth Meeting on Hot Subdwarf
Stars and Related Objects held in China, 20-24 July 2009. Accepted for
publication in Astrophysics and Space Scienc
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