692 research outputs found
Haloferax volcanii for biotechnology applications: challenges, current state and perspectives
© 2019, The Author(s). Haloferax volcanii is an obligate halophilic archaeon with its origin in the Dead Sea. Simple laboratory culture conditions and a wide range of genetic tools have made it a model organism for studying haloarchaeal cell biology. Halophilic enzymes of potential interest to biotechnology have opened up the application of this organism in biocatalysis, bioremediation, nanobiotechnology, bioplastics and the biofuel industry. Functionally active halophilic proteins can be easily expressed in a halophilic environment, and an extensive genetic toolkit with options for regulated protein overexpression has allowed the purification of biotechnologically important enzymes from different halophiles in H. volcanii. However, corrosion mediated damage caused to stainless-steel bioreactors by high salt concentrations and a tendency to form biofilms when cultured in high volume are some of the challenges of applying H. volcanii in biotechnology. The ability to employ expressed active proteins in immobilized cells within a porous biocompatible matrix offers new avenues for exploiting H. volcanii in biotechnology. This review critically evaluates the various application potentials, challenges and toolkits available for using this extreme halophilic organism in biotechnology
Reduced antimicrobial prescribing during autogenous staphylococcal bacterin therapy: a retrospective study in dogs with pyoderma
Autogenous staphylococcal bacterins are commonly mentioned as treatment for canine recurrent pyoderma but little is known about their efficacy. This retrospective study describes use and assesses efficacy of an autogenous Staphylococcus (pseud)intermedius bacterin in dogs with pyoderma. Frequency and duration of systemic antimicrobial therapy were compared 12 months before and after starting bacterin (Wilcoxon signed-rank test) with data extracted from general practice medical histories
Pyroelectric and photovoltaic properties of Nb doped PZT thin films
Nb-doped lead zirconate titanate (PZT) films with up to 12 at. % of Nb were co-sputtered from oxide PZT and metallic Nb targets at a substrate temperature of 600 °C. Up to 4 at. % of Nb was doped into the perovskite structure with the formation of B-site cation vacancies for charge compensation. The preferential (111) PZT orientation decreased with Nb-doping within the solid solution region. The ferroelectric response of the films was affected by the large values of the internal field present in the samples (e.g., −84.3 kV cm−1 in 12 at. % Nd doped films). As-deposited unpoled films showed large values of the pyroelectric coefficient due to self-poling. The pyroelectric coefficient increased with Nb-doping and showed a complex dependence on the applied bias. The photovoltaic effect was observed in the films. The value of the photocurrent increased with the A/B ratio. The combined photovoltaic–pyroelectric effect increased the values of the measured current by up to 47% upon light illumination
Near-infrared Linear Polarization of Ultracool Dwarfs
We report on near-infrared J- and H-band linear polarimetric photometry of
eight ultracool dwarfs (two late-M, five L0-L7.5, and one T2.5) with known
evidence for photometric variability due to dust clouds, anomalous red infrared
colors, or low-gravity atmospheres. The polarimetric data were acquired with
the LIRIS instrument on the William Herschel Telescope. We also provide
mid-infrared photometry in the interval 3.4-24 micron for some targets obtained
with Spitzer and WISE, which has allowed us to confirm the peculiar red colors
of five sources in the sample. We can impose modest upper limits of 0.9% and
1.8% on the linear polarization degree for seven targets with a confidence of
99%. Only one source, 2MAS, J02411151-0326587 (L0), appears to be strongly
polarized (P ~ 3%) in the J-band with a significance level of P/sigma_P ~ 10.
The likely origin of its linearly polarized light and rather red infrared
colors may reside in a surrounding disk with an asymmetric distribution of
grains. Given its proximity (66 +/- 8 pc), this object becomes an excellent
target for the direct detection of the disk.Comment: Accepted for publication in Ap
Infrared and kinematic properties of the substellar object G 196-3B
We report unusual near- and mid-infrared photometric properties of G 196-3 B,
the young substellar companion at 16 arcsec from the active M2.5-type star G
196-3 A, using data taken with the IRAC and MIPS instruments onboard Spitzer. G
196-3 B shows markedly redder colors at all wavelengths from 1.6 up to 24
micron than expected for its spectral type, which is determined at L3 from
optical and near-infrared spectra. We discuss various physical scenarios to
account for its reddish nature, and conclude that a low-gravity atmosphere with
enshrouded upper atmospheric layers and/or a warm dusty disk/envelope provides
the most likely explanations, the two of them consistent with an age in the
interval 20-300 Myr. We also present new and accurate separate proper motion
measurements for G 196-3 A and B confirming that both objects are
gravitationally linked and share the same motion within a few mas/yr. After
integration of the combined spectrophotometric spectral energy distributions,
we obtain that the difference in the bolometric magnitudes of G 196-3 A and B
is 6.15 +/- 0.10 mag. Kinematic consideration of the Galactic space motions of
the system for distances in the interval 15-30 pc suggests that the pair is a
likely member of the Local Association, and that it lay near the past positions
of young star clusters like alpha Persei less than 85 Myr ago, where the binary
might have originated. At these young ages, the mass of G 196-3 B would be in
the range 12-25 Mjup, close to the frontier between planets and brown dwarfs.Comment: Accepted for publication in ApJ
THE HAWAII INFRARED PARALLAX PROGRAM. II. YOUNG ULTRACOOL FIELD DWARFS
(Abridged) We present a large, uniform analysis of young (~10-150 Myr)
ultracool dwarfs, based on new high-precision IR parallaxes for 68 objects. We
find that low-gravity (VL-G) late-M and L dwarfs form a continuous sequence in
IR color-magnitude diagrams, separate from field objects and current
theoretical models. VL-G objects also appear distinct from young substellar
(brown dwarf and exoplanet) companions, suggesting the two populations have a
different range of physical properties. In contrast, at the L/T transition,
young, old, and peculiar objects all span a narrow range in near-IR absolute
magnitudes. At a given spectral type, the IR absolute magnitudes of young
objects can be offset from ordinary field dwarfs, with the largest offsets
occurring in the Y and J bands for late-M dwarfs (brighter than the field) and
mid/late-L dwarfs (fainter than the field). Overall, low-gravity (VL-G) objects
have the most uniform photometric behavior while intermediate-gravity (INT-G)
objects are more diverse, suggesting a third governing parameter beyond
spectral type and gravity class. We examine the moving group memberships for
all young ultracool dwarfs with parallaxes, changing/refuting the status of 23
objects and fortifying the status of another 28 objects. We use our resulting
age-calibrated sample to establish empirical young isochrones and find a
declining frequency of VL-G objects relative to INT-G objects with increasing
age. Notable objects in our sample include high-velocity INT-G objects; very
red, late-L dwarfs with high surface gravities; candidate disk-bearing members
of the MBM20 cloud and beta Pic moving group; and very young distant
interlopers. Finally, we provide a comprehensive summary of the absolute
magnitudes and spectral classifications of 102 young ultracool dwarfs, found in
the field and as substellar companions to young stars.Comment: ApJ, in press, 138 pages including 33 figures and 15 tables.
Compilation of young ultracool dwarfs and young substellar (brown dwarf and
exoplanet) companions available at the Database of Ultracool Parallaxes (see
http://www.as.utexas.edu/~tdupuy/plx
Two Transiting Earth-size Planets Near Resonance Orbiting a Nearby Cool Star
Discoveries from the prime Kepler mission demonstrated that small planets (<
3 Earth-radii) are common outcomes of planet formation. While Kepler detected
many such planets, all but a handful orbit faint, distant stars and are not
amenable to precise follow up measurements. Here, we report the discovery of
two small planets transiting K2-21, a bright (K = 9.4) M0 dwarf located
656 pc from Earth. We detected the transiting planets in photometry
collected during Campaign 3 of NASA's K2 mission. Analysis of transit light
curves reveals that the planets have small radii compared to their host star,
2.60 0.14% and 3.15 0.20%, respectively. We obtained follow up NIR
spectroscopy of K2-21 to constrain host star properties, which imply planet
sizes of 1.59 0.43 Earth-radii and 1.92 0.53 Earth-radii,
respectively, straddling the boundary between high-density, rocky planets and
low-density planets with thick gaseous envelopes. The planets have orbital
periods of 9.32414 days and 15.50120 days, respectively, and have a period
ratio of 1.6624, very near to the 5:3 mean motion resonance, which may be a
record of the system's formation history. Transit timing variations (TTVs) due
to gravitational interactions between the planets may be detectable using
ground-based telescopes. Finally, this system offers a convenient laboratory
for studying the bulk composition and atmospheric properties of small planets
with low equilibrium temperatures.Comment: Updated to ApJ accepted version; photometry available alongside LaTeX
source; 10 pages, 7 figure
The Age, Stellar Content and Star Formation Timescale of the B59 Dense Core
We have used moderate resolution, near-infrared spectra from the SpeX
spectrograph on the NASA Infrared Telescope facility to characterize the
stellar content of Barnard 59 (B59), the most active star-forming core in the
Pipe Nebula. Measuring luminosity and temperature sensitive features in the
spectra of 20 candidate YSOs, we identified likely background giant stars and
measured each star's spectral type, extinction, and NIR continuum excess. We
find that B59 is composed of late type (K4-M6) low-mass (0.9--0.1 M_sun) YSOs
whose median stellar age is comparable to, if not slightly older than, that of
YSOs within the Rho Oph, Taurus, and Chameleon star forming regions. Deriving
absolute age estimates from pre-main sequence models computed by D'Antona et
al., and accounting only for statistical uncertainties, we measure B59's median
stellar age to be 2.6+/-0.8 Myrs. Including potential systematic effects
increases the error budget for B59's median (DM98) stellar age to 2.6+4.1/-2.6
Myrs. We also find that the relative age orderings implied by pre-main sequence
evolutionary tracks depend on the range of stellar masses sampled, as model
isochrones possess significantly different mass dependencies. The maximum
likelihood median stellar age we measure for B59, and the region's observed gas
properties, suggest that the B59 dense core has been stable against global
collapse for roughly 6 dynamical timescales, and is actively forming stars with
a star formation efficiency per dynamical time of ~6%. This maximum likelihood
value agrees well with recent star formation simulations that incorporate
various forms of support against collapse, such as sub-critical magnetic
fields, outflows, and radiative feedback from protostellar heating. [abridged]Comment: 20 pages, 12 figures, accepted for publication in the Astrophysical
Journal; updated to amend acknowledgment
Political institutions and debt crises
This paper shows that political institutions matter in explaining defaults on external and domestic debt obligations. We explore a large number of political and macroeconomic variables using a non-parametric technique to predict safety from default. The advantage of this technique is that it is able to identify patterns in the data that are not captured in standard probit analysis. We find that political factors matter, and do so in different ways for democratic and non-democratic regimes, and for domestic and external debt. In democracies, a parliamentary system or sufficient checks and balances almost guarantee the absence of default on external debt when economic fundamentals or liquidity are sufficiently strong. In dictatorships, high stability and tenure play a similar role for default on domestic debt
Flibanserin and 8‐OH‐DPAT Implicate Serotonin in Association between Female Marmoset Monkey Sexual Behavior and Changes in Pair‐Bond Quality
Introduction. Psychopathological origins of personally distressing, hypoactive sexual desire disorder (HSDD) in women are unknown, but are generally attributed to an inhibitory neural regulator, serotonin (5‐HT). Flibanserin, a 5‐HT 1A agonist and 5‐HT 2A antagonist, shows promise as a treatment for HSDD. Aim. To test the hypothesis that female marmoset sexual behavior is enhanced by flibanserin and diminished by 8‐OH‐DPAT, in order to evaluate the efficacy of serotonergic modulation of female sexual behavior in a pairmate social setting comparable to humans. Methods. Sexual and social behavior were examined in eight female marmoset monkeys receiving daily flibanserin (15 mg/kg), 8‐OH‐DPAT (0.1 mg/kg), or corresponding vehicle for 15–16 weeks in a counterbalanced, within‐subject design, while housed in long‐term, stable male–female pairs. Main Outcome Measures. Marmoset pairmate interactions, including sexual and social behavior, were scored during weeks 5–6 of daily flibanserin, 8‐OH‐DPAT or vehicle treatment. 24‐hour pharmacokinetic profiles of the drugs and their metabolites, as well as drug‐induced acute symptoms of the 5‐HT behavioral syndrome were also assessed. Results. Two‐way analysis of variance reveals that flibanserin‐treated females attract more male sexual interest ( P = 0.020) and trigger increased grooming ( P = 0.001) between partners. In contrast, 8‐OH‐DPAT‐treated females show increased rejection of male sexual advances ( P = 0.024), a tendency for decreased male sexual interest ( P = 0.080), and increased aggression with their male pairmates ( P = 0.049). Conclusions. While 8‐OH‐DPAT‐treated female marmosets display decreased sexual receptivity and increased aggressive interactions with their male pairmates, flibanserin‐treated female marmosets demonstrate increased affiliative behavior with their male pairmates. Such pro‐affiliation attributes may underlie flibanserin's effectiveness in treating HSDD in women. Aubert Y, Gustison ML, Gardner LA, Bohl MA, Lange JR, Allers KA, Sommer B, Datson NA, and Abbott DH. Flibanserin and 8‐OH‐DPAT implicate serotonin in association between female marmoset monkey sexual behavior and changes in pair‐bond quality. J Sex Med 2012;9:694–707.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/90344/1/j.1743-6109.2011.02616.x.pd
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