138 research outputs found
The frequency and infrared brightness of circumstellar discs at white dwarfs
White dwarfs whose atmospheres are polluted by terrestrial-like planetary
debris have become a powerful and unique tool to study evolved planetary
systems. This paper presents results for an unbiased Spitzer IRAC search for
circumstellar dust orbiting a homogeneous and well-defined sample of 134 single
white dwarfs. The stars were selected without regard to atmospheric metal
content but were chosen to have 1) hydrogen rich atmospheres, 2) 17 000 K <
T_eff < 25 000 K and correspondingly young post main-sequence ages of
15-270Myr, and 3) sufficient far-ultraviolet brightness for a corresponding
Hubble Space Telescope COS Snapshot. Five white dwarfs were found to host an
infrared bright dust disc, three previously known, and two reported here for
the first time, yielding a nominal 3.7% of white dwarfs in this post-main
sequence age range with detectable circumstellar dust. Remarkably,
complementary HST observations indicate that a fraction of 27% show metals in
their photosphere that can only be explained with ongoing accretion from
circumstellar material, indicating that nearly 90% of discs escape detection in
the infrared, likely due to small emitting surface area. This paper also
presents the distribution of disc fractional luminosity as a function of
cooling age for all known dusty white dwarfs, suggesting possible disc
evolution scenarios and indicating an undetected population of circumstellar
discs.Comment: 17 pages, 5 figures and 4 tables. Accepted for publication in MNRA
Uniqueness and Non-uniqueness in the Einstein Constraints
The conformal thin sandwich (CTS) equations are a set of four of the Einstein
equations, which generalize the Laplace-Poisson equation of Newton's theory. We
examine numerically solutions of the CTS equations describing perturbed
Minkowski space, and find only one solution. However, we find {\em two}
distinct solutions, one even containing a black hole, when the lapse is
determined by a fifth elliptic equation through specification of the mean
curvature. While the relationship of the two systems and their solutions is a
fundamental property of general relativity, this fairly simple example of an
elliptic system with non-unique solutions is also of broader interest.Comment: 4 pages, 4 figures; abstract and introduction rewritte
Inhibition of protein crystallization by evolutionary negative design
In this perspective we address the question: why are proteins seemingly so
hard to crystallize? We suggest that this is because of evolutionary negative
design, i.e. proteins have evolved not to crystallize, because crystallization,
as with any type of protein aggregation, compromises the viability of the cell.
There is much evidence in the literature that supports this hypothesis,
including the effect of mutations on the crystallizability of a protein, the
correlations found in the properties of crystal contacts in bioinformatics
databases, and the positive use of protein crystallization by bacteria and
viruses.Comment: 5 page
Synthesis and evaluation of β-substituted fosmidomycin analogues as inhibitors of 1-deoxy-D-xylulose 5-phosphate reductoisomerase
Blocking the MEP pathway for isoprenoid biosynthesis offers interesting prospects for inhibiting Plasmodia growth. Fosmidomycin (1) and its homologue FR900098 (2) potently inhibit 1-deoxy-D-xylulose-5-phosphate reductoisomerase (Dxr), a key enzyme in this pathway. Although fosmidomycin is a remarkably safe antimalarial agent, low oral absorption, short serum half-life and malaria recrudescence preclude its use in monotherapy. The development of more lipophilic Dxr inhibitors able to passively permeate into cells with improved pharmacokinetic properties could lead to more efficacious agents.
Previously, we discovered that analogue 4, featuring a 3,4-dichlorophenyl substituent in α-position of the phosphonate, surpasses fosmidomycin’s potency in inhibiting P. falciparum growth. Here we explored the introduction of aryl or aralkyl substituents at the β-position of the known hydroxamate analogue 3.
We studied the effect of introducing substituents in β-position of the hydroxamate analogue 3. While direct addition of a β-aryl moiety resulted in poor P. falciparum Dxr inhibition, longer linkers between the carbon backbone and the phenyl ring were generally associated with better binding to the enzyme. X-ray structures of the parasite Dxr-inhibitor complexes show that the “longer” compounds generate a substantially different flap structure, in which a key tryptophan residue is displaced, and the aromatic group of the ligand lies between the tryptophan and the hydroxamate’s methyl group. Several analogues emerged as highly potent inhibitors of Plasmodium falciparum in vitro growth. In some cases (e.g. for compounds 7b and 7f) good Dxr inhibitory activity failed to translate in good in vitro activity against the parasite, which may be due to inefficient uptake. Compounds 5a-e likewise failed to inhibit EcDxr and MtbDxr while 6c was optimal for inhibition of these enzymes
Метод проектів у процесі музично-виконавської підготовки майбутнього вчителя музики
(uk) У статті визначається сутність інтегрованого методу художньо-творчих проектів, розкривається його специфіка у процесі музично-виконавської підготовки майбутніх учителів музики.(ru) В статье определяется сущность интегрированного метода художественно-творческих проэктов, раскрывается его специфика в процессе музыкально-исполнительской подготовки будущих учителей музыки
VLT/NACO astrometry of the HR8799 planetary system. L'-band observations of the three outer planets
HR8799 is so far the only directly imaged multiple exoplanet system. The
orbital configuration would, if better known, provide valuable insight into the
formation and dynamical evolution of wide-orbit planetary systems. We present
L'-band observations of the HR8799 system obtained with NACO at VLT, adding to
the astrometric monitoring of the planets HR8799b, c and d. We investigate how
well the two simple cases of (i) a circular orbit and (ii) a face-on orbit fit
the astrometric data for HR8799d over a total time baseline of ~2 years. The
results indicate that the orbit of HR8799d is inclined with respect to our line
of sight, and suggest that the orbit is slightly eccentric or non-coplanar with
the outer planets and debris disk.Comment: 5 pages, 4 figures, 1 table, accepted for publication in A\&A.
Updated version includes minor changes made in the proof
Characterization of the Benchmark Binary NLTT 33370
We report the confirmation of the binary nature of the nearby, very low-mass
system NLTT 33370 with adaptive optics imaging and present resolved
near-infrared photometry and integrated light optical and near-infrared
spectroscopy to characterize the system. VLT-NaCo and LBTI-LMIRCam images show
significant orbital motion between 2013 February and 2013 April. Optical
spectra reveal weak, gravity sensitive alkali lines and strong lithium 6708
Angstrom absorption that indicate the system is younger than field age.
VLT-SINFONI near-IR spectra also show weak, gravity sensitive features and
spectral morphology that is consistent with other young, very low-mass dwarfs.
We combine the constraints from all age diagnostics to estimate a system age of
~30-200 Myr. The 1.2-4.7 micron spectral energy distribution of the components
point toward T_eff=3200 +/- 500 K and T_eff=3100 +/- 500 K for NLTT 33370 A and
B, respectively. The observed spectra, derived temperatures, and estimated age
combine to constrain the component spectral types to the range M6-M8.
Evolutionary models predict masses of 113 +/- 8 M_Jup and 106 +/- 7 M_Jup from
the estimated luminosities of the components. KPNO-Phoenix spectra allow us to
estimate the systemic radial velocity of the binary. The Galactic kinematics of
NLTT 33370AB are broadly consistent with other young stars in the Solar
neighborhood. However, definitive membership in a young, kinematic group cannot
be assigned at this time and further follow-up observations are necessary to
fully constrain the system's kinematics. The proximity, age, and late-spectral
type of this binary make it very novel and an ideal target for rapid, complete
orbit determination. The system is one of only a few model calibration
benchmarks at young ages and very low-masses.Comment: 25 pages, 3 tables, 13 figures, accepted for publication in The
Astrophysical Journa
Binarity of Transit Host Stars - Implications on Planetary Parameters
Straight-forward derivation of planetary parameters can only be achieved in
transiting planetary systems. However, planetary attributes such as radius and
mass strongly depend on stellar host parameters. Discovering a transit host
star to be multiple leads to a necessary revision of the derived stellar and
planetary parameters. Based on our observations of 14 transiting exoplanet
hosts, we derive parameters of the individual components of three transit host
stars (WASP-2, TrES-2, and TrES-4) which we detected to be binaries. Two of
these have not been known to be multiple before. Parameters of the
corresponding exoplanets are revised. High-resolution "Lucky Imaging" with
AstraLux at the 2.2m Calar Alto telescope provided near diffraction limited
images in i' and z' passbands. These results have been combined with existing
planetary data in order to recalibrate planetary attributes. Despite the
faintness (delta mag ~ 4) of the discovered stellar companions to TrES-2,
TrES-4, and WASP-2, light-curve deduced parameters change by up to more than
1sigma. We discuss a possible relation between binary separation and planetary
properties, which - if confirmed - could hint at the influence of binarity on
the planet formation process.Comment: 9 pages, 3 Figures. Accepted by A&
Heat Treatment Process Energy Efficient Design and Optimisation
AbstractEnergy efficiency optimization ICT (Information and Communication Technology) solutions are currently being developed for energy saving in buildings and, to some ex-tent, also for the manufacturing domain. This paper describes an approach and ICT tool developed for manufacturing process energy efficiency optimization, in particular focused on the heat treatment process of steel casting parts. Traditionally this manufacturing process is designed based on experts experience selecting a predefined temperature-time curve provided customer specifications for the resulting steel parts. However this curve can actually be optimised in terms of energy consumption while keeping required mechanical properties. This improved design is what the tool here described provides, using knowledge based approach for process design and multivariate optimisation and simulation techniques for process optimisation
Lucky Imaging survey for southern M dwarf binaries
While M dwarfs are the most abundant stars in the Milky Way, there is still
large uncertainty about their basic physical properties (mass, luminosity,
radius, etc.) as well as their formation environment. Precise knowledge of
multiplicity characteristics and how they change in this transitional mass
region, between Sun-like stars on the one side and very low mass stars and
brown dwarfs on the other, provide constraints on low mass star and brown dwarf
formation. In the largest M dwarf binary survey to date, we search for
companions to active, and thus preferentially young, M dwarfs in the solar
neighbourhood. We study their binary/multiple properties, such as the
multiplicity frequency and distributions of mass ratio and separation, and
identify short period visual binaries, for which orbital parameters and hence
dynamical mass estimates can be derived in the near future. The observations
are carried out in the SDSS i' and z' band using the Lucky Imaging camera
AstraLux Sur at the ESO 3.5 m New Technology Telescope. In the first part of
the survey, we observed 124 M dwarfs of integrated spectral types M0-M6 and
identified 34 new and 17 previously known companions to 44 stars. We derived
relative astrometry and component photometry for these systems. More than half
of the binaries have separations smaller than 1 arcsec and would have been
missed in a simply seeing-limited survey. Correcting our sample for selection
effects yields a multiplicity fraction of 32+/-6% for 108 M dwarfs within 52 pc
and with angular separations of 0.1-6.0 arcsec, corresponding to projected
separation 3-180 AU at median distance 30 pc. Compared to early-type M dwarfs
(M>0.3M_Sun), later type (and hence lower mass) M dwarf binaries appear to have
closer separations, and more similar masses.Comment: 18 pages, 9 figures. Minor corrections and changes. Revised to match
accepted A&A versio
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