739 research outputs found
Thermodynamics, strange quark matter, and strange stars
Because of the mass density-dependence, an extra term should be added to the
expression of pressure. However, it should not appear in that of energy
according to both the general ensemble theory and basic thermodynamic
principle. We give a detail derivation of the thermodynamics with
density-dependent particle masses. With our recently determined quark mass
scaling, we study strange quark matter in this new thermodynamic treatment,
which still indicates a possible absolute stability as previously found.
However, the density behavior of the sound velocity is opposite to the previous
finding, but consistent with one of our recent publication. We have also
studied the structure of strange stars using the obtained equation of state.Comment: 6 pages, 6 PS figures, REVTeX styl
Low levels of nestmate discrimination despite high genetic differentiation in the invasive pharaoh ant
<p>Abstract</p> <p>Background</p> <p>Ants typically distinguish nestmates from non-nestmates based on the perception of colony-specific chemicals, particularly cuticular hydrocarbons present on the surface of the ants' exoskeleton. These recognition cues are believed to play an important role in the formation of vast so-called supercolonies that have been described for some invasive ant species, but general conclusions about the role of these cues are hampered by only few species being studied. Here we use data on cuticular hydrocarbons, aggression and microsatellite genetic markers to investigate the interdependence of chemical recognition cues, genetic distance and nestmate discrimination in the pharaoh ant (<it>Monomorium pharaonis</it>), a widespread pest species, and ask whether introduced populations of this species are genetically differentiated and exhibit intraspecific aggression.</p> <p>Results</p> <p>Microsatellite analyses of a total of 35 colonies from four continents revealed extremely high levels of genetic differentiation between almost all colonies (<it>F</it><sub>ST </sub>= 0.751 ± 0.006 SE) and very low within-colony diversity. This implies that at least 34 and likely hundreds more independent lineages of this ant have spread worldwide. Aggression tests involving workers from 14 different colonies showed only low levels of aggression, even between colonies that were geographically and/or genetically very distant. Chemical analyses of groups of worker ants showed that all colonies had the same cuticular compounds, which varied only quantitatively among colonies. There was a positive correlation between geographical and genetic distance, but no other significant relationships were detected between aggression, chemical profile, genetic distance and geographical distance.</p> <p>Conclusions</p> <p>The pharaoh ant has a global invasion history of numerous independent introductions resulting in genetically highly differentiated colonies typically displaying surprisingly low levels of intraspecific aggression, a behaviour that may have evolved in the native range or by lineage selection in the introduced range.</p
Does the quark-gluon plasma contain stable hadronic bubbles?
We calculate the thermodynamic potential of bubbles of hadrons embedded in
quark-gluon plasma, and of droplets of quark-gluon plasma embedded in hadron
phase. This is a generalization of our previous results to the case of non-zero
chemical potentials. As in the zero chemical potential case, we find that a
quark-gluon plasma in thermodynamic equilibrium may contain stable bubbles of
hadrons of radius fm. The calculations are performed within the
MIT Bag model, using an improved multiple reflection expansion. The results are
of relevance for neutron star phenomenology and for ultrarelativistic heavy ion
collisions.Comment: 12 pages including 8 figures. To appear in Phys. Rev.
Clusters, phason elasticity, and entropic stabilisation: a theory perspective
Personal comments are made about the title subjects, including: the relation
of Friedel oscillations to Hume-Rothery stabilisation; how calculations may
resolve the random-tiling versus ideal pictures of quasicrystals; and the role
of entropies apart from tile-configurational.Comment: IOP macros; 8pp, 1 figure. In press, Phil. Mag. A (Proc. Intl. Conf.
on Quasicrystals 9, Ames Iowa, May 2005
Protostellar accretion traced with chemistry. High resolution C18O and continuum observations towards deeply embedded protostars in Perseus
Context: Understanding how accretion proceeds is a key question of star
formation, with important implications for both the physical and chemical
evolution of young stellar objects. In particular, very little is known about
the accretion variability in the earliest stages of star formation.
Aims: To characterise protostellar accretion histories towards individual
sources by utilising sublimation and freeze-out chemistry of CO.
Methods: A sample of 24 embedded protostars are observed with the
Submillimeter Array (SMA) in context of the large program "Mass Assembly of
Stellar Systems and their Evolution with the SMA" (MASSES). The size of the
CO emitting region, where CO has sublimated into the gas-phase, is
measured towards each source and compared to the expected size of the region
given the current luminosity. The SMA observations also include 1.3 mm
continuum data, which are used to investigate whether a link can be established
between accretion bursts and massive circumstellar disks.
Results: Depending on the adopted sublimation temperature of the CO ice,
between 20% and 50% of the sources in the sample show extended CO
emission indicating that the gas was warm enough in the past that CO sublimated
and is currently in the process of refreezing; something which we attribute to
a recent accretion burst. Given the fraction of sources with extended CO
emission, we estimate an average interval between bursts of 20000-50000 yr,
which is consistent with previous estimates. No clear link can be established
between the presence of circumstellar disks and accretion bursts, however the
three closest known binaries in the sample (projected separations <20 AU) all
show evidence of a past accretion burst, indicating that close binary
interactions may also play a role in inducing accretion variability.Comment: Accepted for publication in A&A, 21 pages, 13 figure
The rotating molecular core and precessing outflow of the young stellar object Barnard 1c
We investigate the structure of the core surrounding the recently identified
deeply embedded young stellar object Barnard 1c which has an unusual
polarization pattern as traced in submillimeter dust emission. Barnard 1c lies
within the Perseus molecular cloud at a distance of 250 pc. It is a deeply
embedded core of 2.4 solar masses (Kirk et al.) and a luminosity of 4 +/- 2
solar luminosities. Observations of CO, 13CO, C18O, HCO+ and N2H+ were obtained
with the BIMA array, together with the continuum at 3.3 mm and 2.7 mm.
Single-dish measurements of N2H+ and HCO+ with FCRAO reveal the larger scale
emission in these lines, The CO and HCO+ emission traces the outflow, which
coincides in detail with the S-shaped jet recently found in Spitzer IRAC
imaging. The N2H+ emission, which anticorrelates spatially with the C18O
emission, originates from a rotating envelope with effective radius ~ 2400 AU
and mass 2.1 - 2.9 solar masses. N2H+ emission is absent from a 600 AU diameter
region around the young star. The remaining N2H+ emission may lie in a coherent
torus of dense material. With its outflow and rotating envelope, B1c closely
resembles the previously studied object L483-mm, and we conclude that it is a
protostar in an early stage of evolution. We hypothesize that heating by the
outflow and star has desorbed CO from grains which has destroyed N2H+ in the
inner region and surmise that the presence of grains without ice mantles in
this warm inner region can explain the unusual polarization signature from B1c.Comment: 17 pages, 17 figures (9 colour). Accepted to The Astrophysical
Journal. For higher resolution images, see
http://astrowww.phys.uvic.ca/~brenda/preprints.htm
Dimethyl ether in its ground state, v=0, and lowest two torsionally excited states, v11=1 and v15=1, in the high-mass star-forming region G327.3-0.6
The goal of this paper is to determine the respective importance of solid
state vs. gas phase reactions for the formation of dimethyl ether. This is done
by a detailed analysis of the excitation properties of the ground state and the
torsionally excited states, v11=1 and v15=1, toward the high-mass star-forming
region G327.3-0.6. With the Atacama Pathfinder EXperiment 12 m submillimeter
telescope, we performed a spectral line survey. The observed spectrum is
modeled assuming local thermal equilibrium. CH3OCH3 has been detected in the
ground state, and in the torsionally excited states v11=1 and v15=1, for which
lines have been detected here for the first time. The emission is modeled with
an isothermal source structure as well as with a non-uniform spherical
structure. For non-uniform source models one abundance jump for dimethyl ether
is sufficient to fit the emission, but two components are needed for the
isothermal models. This suggests that dimethyl ether is present in an extended
region of the envelope and traces a non-uniform density and temperature
structure. Both types of models furthermore suggest that most dimethyl ether is
present in gas that is warmer than 100 K, but a smaller fraction of 5%-28% is
present at temperatures between 70 and 100 K. The dimethyl ether present in
this cooler gas is likely formed in the solid state, while gas phase formation
probably is dominant above 100 K. Finally, the v11=1 and v15=1 torsionally
excited states are easily excited under the density and temperature conditions
in G327.3-0.6 and will thus very likely be detectable in other hot cores as
well.Comment: 12 pages (excluding appendices), 8 figures, A&A in pres
Removal of pharmaceuticals in WWTP effluents by ozone and hydrogen peroxide
Ozonation to achieve removal of pharmaceuticals from wastewater effluents, with pH values in the upper and lower regions of the typical range for Swedish wastewater, was investigated. The main aim was to study the effects of varying pH values (6.0 and 8.0), and if small additions of H2O2 prior to ozone treatment could improve the removal and lower the reaction time. The effluents studied differed in their chemical characteristics, particularly in terms of alkalinity (65.3-427 mg center dot l(-1) HCO3-), COD (18.2-41.8 mg center dot l(-1)), DOC (6.9-12.5 mg center dot l(-1)), ammonium content (0.02-3.6 mg center dot l(-1)) and specific UV absorbance (1.78-2.76 l center dot mg(-1)center dot m(-1)). As expected, lower ozone decomposition rates were observed in the effluents at pH 6.0 compared to pH 8.0. When pH 8.0 effluents were ozonated, a higher degree of pharmaceutical removal occurred in the effluent with low specific UV absorbance. For pH 6.0 effluents, the removal of pharmaceuticals was most efficient in the effluent with the lowest organic content. The addition of H2O2 had no significant effect on the quantitative removal of pharmaceuticals but enhanced the ozone decomposition rate. Thus, H2O2 addition increased the reaction rate. In practice, this will mean that the reactor volume needed for the ozonation of wastewater effluents can be reduced
Nucleation of quark matter bubbles in neutron stars
The thermal nucleation of quark matter bubbles inside neutron stars is
examined for various temperatures which the star may realistically encounter
during its lifetime. It is found that for a bag constant less than a critical
value, a very large part of the star will be converted into the quark phase
within a fraction of a second. Depending on the equation of state for neutron
star matter and strange quark matter, all or some of the outer parts of the
star may subsequently be converted by a slower burning or a detonation.Comment: 13 pages, REVTeX, Phys.Rev.D (in press), IFA 93-32. 5 figures (not
included) available upon request from [email protected]
Network Meta-Analysis of Tofacitinib, Biologic Disease-Modifying Antirheumatic Drugs, and Apremilast for the Treatment of Psoriatic Arthritis
Background: Tofacitinib and other new treatments approved for use in psoriatic arthritis have only recently been included in psoriatic arthritis treatment guidelines, and studies evaluating the relative efficacy of available therapies are important to inform treatment decisions by healthcare professionals. Objective: To perform a network meta-analysis to evaluate the efficacy and safety profiles of tofacitinib, biologic disease-modifying antirheumatic drugs (bDMARDs), and apremilast in patients with psoriatic arthritis naive to tumor necrosis factor inhibitor therapy (TNFi-naive) or with an inadequate response (TNFi-IR). Methods: A systematic literature review used searches of MEDLINE, Embase, and The Cochrane Library on October 9, 2017. Randomized controlled trials including adult patients with psoriatic arthritis receiving treatment administered as monotherapy or with conventional synthetic DMARDs were selected. Efficacy outcomes included American College of Rheumatology 20 response, change from baseline in Health Assessment Questionnaire-Disability Index, >/=75% improvement in Psoriasis Area and Severity Index, and change from baseline in Dactylitis Severity Score and Leeds Enthesitis Index. Treatment effects were evaluated during placebo-controlled phases, using a binomial logit model for binary outcomes and a normal identify link model for other outcomes. Discontinuations due to adverse events and serious infection events were assessed as safety outcomes. Results: The network meta-analysis included 24 published randomized controlled trials, of which 13 enrolled TNFi-naive patients only, 3 enrolled TNFi-IR patients only, and 8 enrolled both TNFi-naive and TNFi-IR patients. Placebo-controlled treatment durations ranged from 12 to 24 weeks. Indirect comparisons showed tofacitinib 5 and 10 mg BID to have similar efficacy compared with most bDMARDs and apremilast in improving joint symptoms (based on American College of Rheumatology 20 response), and with some bDMARDs in improving skin symptoms (based on Psoriasis Area and Severity Index) (tofacitinib 10 mg BID only in TNFi-IR) in patients with psoriatic arthritis who were TNFi-naive or TNFi-IR. Results also showed that, compared with placebo, the improvement in physical functioning (based on Health Assessment Questionnaire-Disability Index) with tofacitinib 5 and 10 mg BID was similar to that observed with most bDMARDs and apremilast in TNFi-naive patients, and similar to that observed with all bDMARDs with available data in the TNFi-IR population. Improvements in Dactylitis Severity Score and Leeds Enthesitis Index scores were comparable between treatments. Tofacitinib 5 and 10 mg BID were median-ranked 8 and 15, respectively, for discontinuation due to any adverse events, and 5 and 16, respectively, for a serious infection event out of a total of 20 treatments in the network (lower numbers are more favorable). Conclusions: Tofacitinib provides an additional treatment option for patients with psoriatic arthritis, both in patients naive to TNFi and in those with TNFi-IR. (Curr Ther Res Clin Exp. 2020; 81:XXX-XXX)
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