957 research outputs found
Heavy Meson Masses in the \epsilon-Regime of HM\chi PT
The pseudoscalar and vector heavy meson masses are calculated in the
\epsilon-regime of Heavy Meson Chiral Perturbation Theory to order \epsilon^4.
The results of this calculation will allow the determination of low-energy
coefficients (LECs) directly from Lattice QCD calculations of the heavy mesons
masses for lattices that satisfy the \epsilon-regime criteria. In particular,
the LECs that parametrize the NLO volume dependance of the heavy meson masses
are necessary for evaluating the light pseudoscalar meson (\pi, K, \eta) and
heavy meson ({D^0, D^+, D^+_s}, {B^-,\bar{B}^0,\bar{B}^0_s}) scattering phase
shifts.Comment: 16 pages, 6 figure
Nuclear Reactions from Lattice QCD
One of the overarching goals of nuclear physics is to rigorously compute
properties of hadronic systems directly from the fundamental theory of strong
interactions, Quantum Chromodynamics (QCD). In particular, the hope is to
perform reliable calculations of nuclear reactions which will impact our
understanding of environments that occur during big bang nucleosynthesis, the
evolution of stars and supernovae, and within nuclear reactors and high
energy/density facilities. Such calculations, being truly ab initio, would
include all two-nucleon and three- nucleon (and higher) interactions in a
consistent manner. Currently, lattice QCD provides the only reliable option for
performing calculations of some of the low- energy hadronic observables. With
the aim of bridging the gap between lattice QCD and nuclear many-body physics,
the Institute for Nuclear Theory held a workshop on Nuclear Reactions from
Lattice QCD on March 2013. In this review article, we report on the topics
discussed in this workshop and the path planned to move forward in the upcoming
years.Comment: 35 pages, 13 figures, 1 table, review article for the "Nuclear
Reactions from Lattice QCD" workshop hosted by the Institute for Nuclear
Theory on March 2013; version 2 includes updated references and extended
discussion of previous wor
Moving Multi-Channel Systems in a Finite Volume with Application to Proton-Proton Fusion
The spectrum of a system with multiple channels composed of two hadrons with
nonzero total momentum is determined in a finite cubic volume with periodic
boundary conditions using effective field theory methods. The results presented
are accurate up to exponentially suppressed corrections in the volume due to
the finite range of hadronic interactions. The formalism allows one to
determine the phase shifts and mixing parameters of pipi-KK isosinglet coupled
channels directly from Lattice Quantum Chromodynamics. We show that the
extension to more than two channels is straightforward and present the result
for three channels. From the energy quantization condition, the volume
dependence of electroweak matrix elements of two-hadron processes is extracted.
In the non-relativistic case, we pay close attention to processes that mix the
1S0-3S1 two-nucleon states, e.g. proton-proton fusion (pp -> d+ e^+ + nu_e),
and show how to determine the transition amplitude of such processes directly
from lattice QCD.Comment: 20 pages, 3 figure
First Large-scale HerbigâHaro Jet Driven by a Proto-brown Dwarf
We report the discovery of a new HerbigâHaro jet, HH 1165, in SOAR narrow-band imaging of the vicinity of the Ï Orionis cluster. HH 1165 shows a spectacular extended and collimated spatial structure, with a projected length of 0.26 pc, a bent C-shaped morphology, multiple knots, and fragmented bow shocks at the apparent ends of the flow. The Hα image shows a bright halo with a clumpy distribution of material seen around the driving source, and curved reflection nebulosity tracing the outflow cavities. The driving source of HH 1165 is a Class I proto-brown dwarf, Mayrit 1701117 (M1701117), with a total (dust+gas) mass of ~36 M Jup and a bolometric luminosity of ~0.1 L â. High-resolution VLT/UVES spectra of M1701117 show a wealth of emission lines indicative of strong outflow and accretion activity. SOAR/Goodman low-resolution spectra along the jet axis show an asymmetrical morphology for HH 1165. We find a puzzling picture wherein the northwest part exhibits a classical HH jet running into a pre-dominantly neutral medium, while the southern part resembles an externally irradiated jet. The C-shaped bending in HH 1165 may be produced by the combined effects from the massive stars in the ionization front to the east, the Ï Orionis core to the west, and the close proximity to the B2-type star HR 1950. HH 1165 shows all of the signatures to be considered as a scaled-down version of parsec-length HH jets, and can be termed as the first sub-stellar analog of a protostellar HH jet system
Decentralizing UNIX abstractions in the exokernel architecture
Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1997.Includes bibliographical references (p. 49-51).by Héctor Manuel Briceño Pulido.M.Eng
Elemental abundances of low-mass stars in the young clusters 25 Ori and lambda Ori
Aims. We aim to derive the chemical pattern of the young clusters 25 Orionis
and lambda Orionis through homogeneous and accurate measurements of elemental
abundances. Methods. We present FLAMES/UVES observations of a sample of 14
K-type targets in the 25 Ori and lambda Ori clusters; we measure their radial
velocities, in order to confirm cluster membership. We derive stellar
parameters and abundances of Fe, Na, Al, Si, Ca, Ti, and Ni using the code
MOOG. Results. All the 25 Ori stars are confirmed cluster members without
evidence of binarity; in lambda Ori we identify one non-member and one
candidate single-lined binary star. We find an average metallicity
[Fe/H]=-0.05+/-0.05 for 25 Ori, where the error is the 1sigma standard
deviation from the average. lambda Ori members have a mean iron abundance value
of 0.01+/-0.01. The other elements show close-to-solar ratios and no
star-to-star dispersion. Conclusions. Our results, along with previous
metallicity determinations in the Orion complex, evidence a small but
detectable dispersion in the [Fe/H] distribution of the complex. This appears
to be compatible with large-scale star formation episodes and initial
non-uniformity in the pre-cloud medium. We show that, as expected, the
abundance distribution of star forming regions is consistent with the chemical
pattern of the Galactic thin disk.Comment: Accepted by Astronomy and Astrophysics. 14 pages, 10 figures, 7
table
17 new very low-mass members in Taurus. The brown dwarf deficit revisited
Recent studies of the substellar population in the Taurus cloud have revealed
a deficit of brown dwarfs (BD) compared to the Trapezium cluster population
(Briceno et al 1998; Luhman 2000; Luhman et al 2003a; Luhman 2004). However,
these works have concentrated on the highest stellar density regions of the
Taurus cloud. We have performed a large scale optical survey of this region,
covering a total area of 30 deg^2, and encompassing the densest part of the
cloud as well as their surroundings, down to a mass detection limits of 15
Jupiter Masses (MJ). In this paper, we present the optical spectroscopic
follow-up observations of 97 photometrically selected potential new low-mass
Taurus members, of which 27 are strong late-M (SpT < M4V) candidates. These
observations reveal 5 new very low mass (VLM) Taurus members and 12 new BDs.
Combining our observations with previously published results, we derive an
updated substellar to stellar ratio in Taurus of Rss =0.23 +/- 0.05. This ratio
now appears consistent with the value previously derived in the Trapezium
cluster under similar assumptions of 0.26 +/- 0.04. We find strong indication
that the relative numbers of BDs with respect to stars is decreased by a factor
2 in the central regions of the aggregates with respect to the more distributed
population. Our findings are best explained in the context of the
embryo-ejection model where brown dwarfs originate from dynamical interactions
in small N unstable multiple systems.Comment: 20 pages, 15 figure
Conocimiento didĂĄctico de los profesores de tecnologĂa antecedentes de la investigaciĂłn
This article is part of the doctoral thesis âDidactic Knowledge of the content of technology teachers involved in the learning network REDOTICâ, teaching based on knowledge of content, virtual networks for teaching and learning and technological knowledge. The text socializes the academic background of the research conducted in the field of teaching the content knowledge, understanding it as an organizing construct of a cognitive system of knowledge, beliefs, skills, abilities and capabilities. The research aims to characterize the teaching of content knowledge of technology teachers that are part of REDOTIC, from three categories, which are considered as structural: The knowledge of the contents of the object or fieldof education, it means the disciplinary content knowledge, students ideas and the teaching strategies applied through virtual learning network.El presente artĂculo se enmarca en la tesis doctoral âConocimiento didĂĄctico del contenido de los profesores de tecnologĂa que participan en la red de aprendizaje REDOTICâ, fundamentada en el conocimiento didĂĄctico del contenido, las redes virtuales de enseñanza y aprendizaje y el conocimiento tecnolĂłgico. En el texto se socializan los antecedentes en relaciĂłn con las investigaciones realizadas en el campo del conocimiento didĂĄctico del contenido, entendiĂ©ndolo como un constructo organizador de un sistema cognitivo de saberes, creencias, destrezas, habilidades y capacidades. La investigaciĂłn pretende caracterizar el conocimiento didĂĄctico del contenido de los profesores de tecnologĂa que hacen parte de REDOTIC, a partir de tres de las categorĂas que se consideran estructurales y son: el conocimiento de los contenidos del objeto o materia de enseñanza, es decir, el conocimiento del contenido disciplinar; las ideas de los estudiantes y las estrategias metodolĂłgicas para enseñar a travĂ©s de la red virtual de aprendizaje
Optical spectra of selected Chamaeleon I young stellar objects
We present optical spectra of eight candidate brown dwarfs and a previously
known T Tauri star (Sz 33) of the Chamaeleon I dark cloud. We derived spectral
types based on the strength of the TiO or VO absorption bands present in the
spectra of these objects as well as on the PC3 index of Martin et al. (1999).
Photometric data from the literature are used to estimate the bolometric
luminosities for these sources. We apply D'Antona & Mazzitelli (1997) pre-main
sequence evolutionary tracks and isochrones to derive masses and ages. Based on
the presence of Halpha in emission, we confirm that most of the candidates are
young objects. Our sample however includes two sources for which we can only
provide upper limits for the emission in Halpha; whereas these two objects are
most likely foreground/background stars, higher resolution spectra are required
to confirm their true nature. Among the likely cloud members, we detect one new
sub-stellar object and three transition stellar/sub-stellar sources.Comment: 22 pages - manuscript forma
- âŠ