5,766 research outputs found
Connecting substellar and stellar formation. The role of the host star's metallicity
Most of our current understanding of the planet formation mechanism is based
on the planet metallicity correlation derived mostly from solar-type stars
harbouring gas-giant planets. To achieve a far more reaching grasp on the
substellar formation process we aim to analyse in terms of their metallicity a
diverse sample of stars (in terms of mass and spectral type) covering the whole
range of possible outcomes of the planet formation process (from planetesimals
to brown dwarfs and low-mass binaries). Our methodology is based on the use of
high-precision stellar parameters derived by our own group in previous works
from high-resolution spectra by using the iron ionisation and equilibrium
conditions. All values are derived in an homogeneous way, except for the M
dwarfs where a methodology based on the use of pseudo equivalent widths of
spectral features was used. Our results show that as the mass of the substellar
companion increases the metallicity of the host star tendency is to lower
values. The same trend is maintained when analysing stars with low-mass stellar
companions and a tendency towards a wide range of host star's metallicity is
found for systems with low mass planets. We also confirm that more massive
planets tend to orbit around more massive stars. The core-accretion formation
mechanism for planet formation achieves its maximum efficiency for planets with
masses in the range 0.2 and 2 M. Substellar objects with higher
masses have higher probabilities of being formed as stars. Low-mass planets and
planetesimals might be formed by core-accretion even around low-metallicity
stars.Comment: Accepted by A&
Tunnel spectroscopy in ac-driven quantum dot nanoresonators
Electronic transport in a triple quantum dot shuttle device in the presence
of an ac field is analyzed within a fully quantum mechanical framework. A
generalized density matrix formalism is used to describe the time evolution for
electronic state occupations in a dissipative phonon bath. In the presence of
an ac gate voltage, the electronic states are dressed by photons and the
interplay between photon and vibrational sidebands produces current
characteristics that obey selection rules. Varying the ac parameters allows to
tune the tunneling current features. In particular, we show that coherent
destruction of tunneling can be achieved in our device
Development and test of advanced composite components. Center Directors discretionary fund program
This report describes the design, analysis, fabrication, and test of a complex bathtub fitting. Graphite fibers in an epoxy matrix were utilized in manufacturing of 11 components representing four different design and layup concepts. Design allowables were developed for use in the final stress analysis. Strain gage measurements were taken throughout the static load test and correlation of test and analysis data were performed, yielding good understanding of the material behavior and instrumentation requirements for future applications
Tunneling spectroscopy of the superconducting state of URu2Si2
We present measurements of the superconducting gap of URuSi made with
scanning tunneling microscopy (STM) using a superconducting tip of Al. We find
tunneling conductance curves with a finite value at the Fermi level. The
density of states is V shaped at low energies, and the quasiparticle peaks are
located at values close to the expected superconducting gap from weak coupling
BCS theory. Our results point to rather opened gap structures and gap nodes on
the Fermi surface
Radiative decay Z_H-> \gamma A_H in the little Higgs model with T-parity
In the little Higgs model with T-parity (LHTM), the only tree-level
kinematically allowed two-body decay of the Z_H boson is Z_H-> A_H H and thus
one-loop induced two-body decays may have a significant rate. We study the
Z_H-> \gamma A_H decay, which is induced at the one-loop level by a fermion
triangle and is interesting as it depends on the mechanism of anomaly
cancellation of the model. All the relevant two- and three-body decays of the
Z_H gauge boson arising at the tree-level are also calculated. We consider a
small region of the parameter space where the scale of the symmetry breaking f
is still allowed to be as low as 500 GeV by electroweak precision data. We
first analyze the scenario of a Higgs boson with a mass of 120 GeV. We found
that the Z_H->\gamma A_H branching ratio can be of the order of a tree-level
three-body decay and may be at the reach of detection at the LHC for f close to
500 GeV, but it may be difficult to detect for f=1 TeV. There is also an
scenario where the Higgs boson has an intermediate mass such that the Z_H-> A_H
H decay is closed, the Z_H-> \gamma A_H gets considerably enhanced and the
chances of detection get a large boost.Comment: 19 pages, 9 figures, 2 table
Tracking Advanced Planetary Systems (TAPAS) with HARPS-N. V.: A Massive Jupiter orbiting the very low metallicity giant star BD+03 2562 and a possible planet around HD~103485
We present two evolved stars from the TAPAS (Tracking Advanced PlAnetary
Systems) with HARPS-N project devoted to RV precision measurements of
identified candidates within the PennState - Torun Centre for Astronomy Planet
Search. Evolved stars with planets are crucial to understand the dependency of
the planet formation mechanism on the mass and metallicity of the parent star
and to study star-planet interactions. The paper is based on precise radial
velocity (RV) measurements, for HD 103485 we collected 57 epochs over 3317 days
with the Hobby-Eberly Telescope and its High Resolution Spectrograph and 18
ultra-precise HARPS-N data over 919 days. For BD+03 2562 we collected 46 epochs
of HET data over 3380 days and 19 epochs of HARPS-N data over 919 days. We
present the analysis of the data and the search for correlations between the RV
signal and stellar activity, stellar rotation and photometric variability.
Based on the available data, we interpret the RV variations measured in both
stars as Keplerian motion. Both stars have masses close to Solar (1.11 and
1.14), very low metallicities ([Fe/H]=-0.50 and -0.71), and, both have Jupiter
planetary mass companions (m sin i=7 and 6.4 Mj), in close to terrestrial
orbits (1.4 and 1.3~au), with moderate eccentricities (e=0.34 and 0.2).
However, we cannot totally exclude that the signal in the case of HD~103485 is
due to rotational modulation of active regions. Based on the current data, we
conclude that BD+03 2562 has a bona fide planetary companion while for HD
103485 we cannot totally exclude that the best explanation for the RV signal
modulations is not the existence of a planet but stellar activity. If, the
interpretation remains that both stars have planetary companions they represent
systems orbiting very evolved stars with very low metallicities, a challenge to
the conditions required for the formation of massive giant gas planets.Comment: Acepted A&A 12 pages, 11 figure
Dose Modeling Evaluations and Technical Support Document For the Authorized Limits Request for the DOE-Owned Property Outside the Limited Area, Paducah Gaseous Diffusion Plant Paducah, Kentucky
Environmental assessments and remediation activities are being conducted by the U.S. Department of Energy (DOE) at the Paducah Gaseous Diffusion Plant (PGDP), Paducah, Kentucky. The Oak Ridge Institute for Science and Education (ORISE), a DOE prime contractor, was contracted by the DOE Portsmouth/Paducah Project Office (DOE-PPPO) to conduct radiation dose modeling analyses and derive single radionuclide soil guidelines (soil guidelines) in support of the derivation of Authorized Limits (ALs) for 'DOE-Owned Property Outside the Limited Area' ('Property') at the PGDP. The ORISE evaluation specifically included the area identified by DOE restricted area postings (public use access restrictions) and areas licensed by DOE to the West Kentucky Wildlife Management Area (WKWMA). The licensed areas are available without restriction to the general public for a variety of (primarily) recreational uses. Relevant receptors impacting current and reasonably anticipated future use activities were evaluated. In support of soil guideline derivation, a Conceptual Site Model (CSM) was developed. The CSM listed radiation and contamination sources, release mechanisms, transport media, representative exposure pathways from residual radioactivity, and a total of three receptors (under present and future use scenarios). Plausible receptors included a Resident Farmer, Recreational User, and Wildlife Worker. single radionuclide soil guidelines (outputs specified by the software modeling code) were generated for three receptors and thirteen targeted radionuclides. These soil guidelines were based on satisfying the project dose constraints. For comparison, soil guidelines applicable to the basic radiation public dose limit of 100 mrem/yr were generated. Single radionuclide soil guidelines from the most limiting (restrictive) receptor based on a target dose constraint of 25 mrem/yr were then rounded and identified as the derived soil guidelines. An additional evaluation using the derived soil guidelines as inputs into the code was also performed to determine the maximum (peak) dose for all receptors. This report contains the technical basis in support of the DOE?s derivation of ALs for the 'Property.' A complete description of the methodology, including an assessment of the input parameters, model inputs, and results is provided in this report. This report also provides initial recommendations on applying the derived soil guidelines
Quasienergy spectrum and tunneling current in ac-driven triple quantum dot shuttles
The dynamics of electrons in ac driven double quantum dots have been
extensively analyzed by means of Floquet theory. In these systems, coherent
destruction of tunneling has been shown to occur for certain ac field
parameters. In the present work we analyze, by means of Floquet theory, the
electron dynamics of a triple quantum dot in series attached to electric
contacts, where the central dot position oscillates. In particular, we analyze
the quasienergy spectrum of this ac driven nanoelectromechanical system, as a
function of the intensity and frequency of the ac field and of external dc
voltages. For strong driving fields, we derive, by means of perturbation
theory, analytical expressions for the quasienergies of the driven oscillator
system. From this analysis we discuss the conditions for coherent destruction
of tunneling (CDT) to occur as a function of detuning and field parameters. For
zero detuning, and from the invariance of the Floquet Hamiltonian under a
generalized parity transformation, we find analytical expressions describing
the symmetry properties of the Fourier components of the Floquet states under
such transformation. By using these expressions, we show that in the vicinity
of the CDT condition, the quasienergy spectrum exhibits exact crossings which
can be characterized by the parity properties of the corresponding
eigenvectors
Return to Sport and Athletic Function in an Active Population After Primary Arthroscopic Labral Reconstruction of the Hip
Background: Labral reconstruction has been advocated as an alternative to debridement for the treatment of irreparable labral tears, showing favorable short-term results. However, literature is scarce regarding outcomes and return to sport in the nonelite athletic population.
Purpose: To report minimum 1-year clinical outcomes and the rate of return to sport in athletic patients who underwent primary hip arthroscopy with labral reconstruction in the setting of femoroacetabular impingement syndrome and irreparable labral tears.
Study Design: Case series; Level of evidence, 4.
Methods: Data were prospectively collected and retrospectively analyzed for patients who underwent an arthroscopic labral reconstruction between August 2012 and December 2017. Patients were included if they identified as an athlete (high school, college, recreational, or amateur); had follow-up on the following patient-reported outcomes (PROs): modified Harris Hip Score (mHHS), Nonarthritic Hip Score (NAHS), Hip Outcome Score–Sport Specific Subscale (HOS-SSS), and visual analog scale (VAS); and completed a return-to-sport survey at 1 year postoperatively. Patients were excluded if they underwent any previous ipsilateral hip surgery, had dysplasia, or had prior hip conditions. The proportions of patients who achieved the minimal clinically important difference (MCID) and patient acceptable symptomatic state (PASS) for mHHS and HOS-SSS were calculated. Statistical significance was set at P =.05.
Results: There were 32 (14 females) athletes who underwent primary arthroscopic labral reconstruction during the study period. The mean age and body mass index of the group were 40.3 years (range, 15.5-58.7 years) and 27.9 kg/m2 (range, 19.6-40.1 kg/m2), respectively. The mean follow-up was 26.4 months (range, 12-64.2 months). All patients demonstrated significant improvement in mHHS, NAHS, HOS-SSS, and VAS (P \u3c.001) at latest follow-up. Additionally, 84.4% achieved MCID and 81.3% achieved PASS for mHHS, and 87.5% achieved MCID and 75% achieved PASS for HOS-SSS. VAS pain scores decreased from 4.4 to 1.8, and the satisfaction with surgery was 7.9 out of 10. The rate of return to sport was 78%.
Conclusion: At minimum 1-year follow-up, primary arthroscopic labral reconstruction, in the setting of femoroacetabular impingement syndrome and irreparable labral tears, was associated with significant improvement in PROs in athletic populations. Return to sport within 1 year of surgery was 78%
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