1,253 research outputs found
Atomic Size Mismatch Strain Induced Surface Reconstructions
The effects of lattice mismatch strain and atomic size mismatch strain on surface reconstructions are analyzed using density functional theory. These calculations demonstrate the importance of an explicit treatment of alloying when calculating the energies of alloyed surface reconstructions. Lattice mismatch strain has little impact on surface dimer ordering for the α2(2×4) reconstruction of GaAs alloyed with In. However, atomic size mismatch strain induces the surface In atoms to preferentially alternate position, which, in turn, induces an alternating configuration of the surface anion dimers. These results agree well with experimental data for α2(2×4) domains in InGaAs∕GaAs surfaces
The pattern of interleukin-1ß (IL-1ß) and its modulating agents IL-1 receptor antagonist and IL-1 soluble receptor type II in acute meningococcal infections
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4930.pdf (publisher's version ) (Open Access
Q-Curves with Complex Multiplication
The Hecke character of an abelian variety A/F is an isogeny invariant and the Galois action is such that A is isogenous to its Galois conjugate A^σ if and only if the corresponding Hecke character is fixed by σ. The quadratic twist of A by an extension L/F corresponds to multiplication of the associated Hecke characters. This leads us to investigate the Galois groups of families of quadratic extensions L/F with restricted ramification which are normal over a given subfield k of F. Our most detailed results are given for the case where k is the field of rational numbers and F is a field of definition for an elliptic curve with complex multiplication by K. In this case the groups which occur as Gal(L/K) are closely related to the 4-torsion of the class group of K. We analyze the structure of the local unit groups of quadratic fields to find conditions for the existence of curves with good reduction everywhere. After discussing the question of finding models for curves of a given Hecke character, we use twists by 3-torsion points to give an algorithm for constructing models of curves with known Hecke character and good reduction outside 3. The endomorphism algebra of the Weil restriction of an abelian variety A may be determined from the Grössencharacter of A. We describe the computation of these algebras and give examples in which A has dimension 1 or 2 and its Weil restriction has simple abelian subvarieties of dimension ranging between 2 and 24
Space Motions of the Dwarf Spheroidal Galaxies Draco and Sculptor based on HST Proper Motions with ~10-year Time Baseline
We present new proper motion (PM) measurements of the dwarf spheroidal
galaxies (dSphs) Draco and Sculptor using multi-epoch images obtained with the
Hubble Space Telescope ACS/WFC. Our PM results have uncertainties far lower
than previous measurements, even made with the same instrument. The PM results
for Draco and Sculptor are (mu_W,mu_N)_Dra =
(-0.0562+/-0.0099,-0.1765+/-0.0100) mas/yr and (mu_W,mu_N)_Scl =
(-0.0296+/-0.0209,-0.1358 +/-0.0214) mas/yr. The implied Galactocentric
velocity vectors for Draco and Sculptor have radial and tangential components:
(V_rad,V_tan)_Dra = (-88.6,161.4) +/- (4.4,5.6) km/s; and (V_rad,V_tan)_Scl =
(72.6,200.2) +/- (1.3,10.8) km/s. We study the detailed orbital history of both
Draco and Sculptor via numerical orbit integrations. Orbital periods of Draco
and Sculptor are found to be 1-2 and 2-5 Gyrs, respectively, accounting for
uncertainties in the MW mass. We also study the influence of the Large
Magellanic Cloud (LMC) on the orbits of Draco and Sculptor. Overall, the
inclusion of the LMC increases the scatter in the orbital results. Based on our
calculations, Draco shows a rather wide range of orbital parameters depending
on the MW mass and inclusion/exclusion of the LMC, but Sculptor's orbit is very
well constrained with its most recent pericentric approach to the MW being
0.3-0.4 Gyr ago. Our new PMs imply that the orbital trajectories of both Draco
and Sculptor are confined within the Disk of Satellites (DoS), better so than
implied by earlier PM measurements, and likely rule out the possibility that
these two galaxies were accreted together as part of a tightly bound group.Comment: 17 pages, 8 figures, 6 tables. Accepted for publication in Ap
Recovering the intrinsic shape of early-type galaxies
We investigate how well the intrinsic shape of early-type galaxies can be
recovered when both photometric and two-dimensional stellar kinematic
observations are available. We simulate these observations with galaxy models
that are representative of observed oblate fast-rotator to triaxial
slow-rotator early-type galaxies. By fitting realistic triaxial dynamical
models to these simulated observations, we recover the intrinsic shape (and
mass-to-light ratio), without making additional (ad-hoc) assumptions on the
orientation.
For (near) axisymmetric galaxies the dynamical modelling can strongly exclude
triaxiality, but the regular kinematics do not further tighten the constraint
on the intrinsic flattening significantly, so that the inclination is nearly
unconstrained above the photometric lower limit even with two-dimensional
stellar kinematics. Triaxial galaxies can have additional complexity in both
the observed photometry and kinematics, such as twists and (central)
kinematically decoupled components, which allows the intrinsic shape to be
accurately recovered. For galaxies that are very round or show no significant
rotation, recovery of the shape is degenerate, unless additional constraints
such as from a thin disk are available.Comment: 12 pages, 7 figures, PDFLaTeX, accepted to MNRAS, minor revision
State of the art of the Fontan strategy for treatment of univentricular heart disease [version 1; referees: 2 approved]
In patients with a functionally univentricular heart, the Fontan strategy achieves separation of the systemic and pulmonary circulation and reduction of ventricular volume overload. Contemporary modifications of surgical techniques have significantly improved survival. However, the resulting Fontan physiology is associated with high morbidity. In this review, we discuss the state of the art of the Fontan strategy by assessing survival and risk factors for mortality. Complications of the Fontan circulation, such as cardiac arrhythmia, thromboembolism, and protein-losing enteropathy, are discussed. Common surgical and catheter-based interventions following Fontan completion are outlined. We describe functional status measurements such as quality of life and developmental outcomes in the contemporary Fontan patient. The current role of drug therapy in the Fontan patient is explored. Furthermore, we assess the current use and outcomes of mechanical circulatory support in the Fontan circulation and novel surgical innovations. Despite large improvements in outcomes for contemporary Fontan patients, a large burden of disease exists in this patient population. Continued efforts to improve outcomes are warranted. Several remaining challenges in the Fontan field are outlined
Estimating Black Hole Masses in Triaxial Galaxies
Most of the super massive black hole mass estimates based on stellar
kinematics use the assumption that galaxies are axisymmetric oblate spheroids
or spherical. Here we use fully general triaxial orbit-based models to explore
the effect of relaxing the axisymmetric assumption on the previously studied
galaxies M32 and NGC 3379. We find that M32 can only be modeled accurately
using an axisymmetric shape viewed nearly edge-on and our black hole mass
estimate is identical to previous studies. When the observed 5 degrees
kinematical twist is included in our model of NGC 3379, the best shape is
mildly triaxial and we find that our best-fitting black hole mass estimate
doubles with respect to the axisymmetric model. This particular black hole mass
estimate is still within the errors of that of the axisymmetric model and
consistent with the M-sigma relationship. However, this effect may have a
pronounced impact on black hole demography, since roughly a third of the most
massive galaxies are strongly triaxial.Comment: Accepted for publication in MNRAS. 11 pages, 9 figures. PDFlate
The effect of unresolved binaries on globular cluster proper-motion dispersion profiles
High-precision kinematic studies of globular clusters require an accurate knowledge of all possible sources of contamination. Amongst other sources, binary stars can introduce systematic biases in the kinematics. Using a set of Monte Carlo cluster simulations with different concentrations and binary fractions, we investigate the effect of unresolved binaries on proper-motion dispersion profiles, treating the simulations like HST propermotion samples. Since globular clusters evolve towards a state of partial energy equipartition, more massive stars lose energy and decrease their velocity dispersion. As a consequence, on average, binaries have a lower velocity dispersion, since they are more massive kinematic tracers. We show that, in the case of clusters with high binary fraction (initial binary fraction of 50%) and high concentration (i.e., closer to energy equipartition), unresolved binaries introduce a color-dependent bias in the velocity dispersion of main-sequence stars of the order of 0.1-0.3 km s^-1 (corresponding to 1 − 6% of the velocity dispersion), with the reddest stars having a lower velocity dispersion, due to the higher fraction of contaminating binaries. This bias depends on the ability to distinguish binaries from single stars, on the details of the color-magnitude diagram and the photometric errors. We apply our analysis to the HSTPROMO data set of NGC 7078 (M15) and show that no effect ascribable to binaries is observed, consistent with the low binary fraction of the cluster. Our work indicates that binaries do not significantly bias proper-motion velocity-dispersion profiles, but should be taken into account in the error budget of kinematic analyses
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