604 research outputs found
A precise determination of the charm quark's mass in quenched QCD
We present a lattice determination of the charm quark's mass, using the mass
of the D_s meson as experimental input. All errors are under control with the
exception of the quenched approximation. Setting the scale with F_K=160 MeV,
our final result for the renormalization group invariant (RGI) quark mass is
M_c = 1.654(45) GeV, which translates to m_c(m_c) =1.301(34) GeV for the
running mass in the MSbar scheme. A 6 percent increase of the RGI quark mass is
observed when the scale is set by the nucleon mass. This is a typical quenched
scale ambiguity, which is reduced to about 3 percent for m_c(m_c), and to 4
percent for the mass ratio M_c/M_s. In contrast, the mass splitting
m(Dstar_s)-m(D_s) changes from 117(11) MeV to 94(11) MeV, which is
significantly smaller than the experimental value of 144 MeV.Comment: 27 pages, 5 figure
From participation to dropout
The academic e-learning practice has to deal with various participation patterns and types of online learners with different support needs. The online instructors are challenged to recognize these and react accordingly. Among the participation patterns, special attention is requested by dropouts, which can perturbate online collaboration. Therefore we are in search of a method of early identification of participation patterns and prediction of dropouts. To do this, we use a quantitative view of participation that takes into account only observable variables. On this background we identify in a field study the participation indicators that are relevant for the course completion, i.e. produce significant differences between the completion and dropout sub-groups. Further we identify through cluster analysis four participation patterns with different support needs. One of them is the dropout cluster that could be predicted with an accuracy of nearly 80%. As a practical consequence, this study recommends a simple, easy-to-implement prediction method for dropouts, which can improve online teaching. As a theoretical consequence, we underline the role of the course didactics for the definition of participation, and call for refining previous attrition models
Radiative Heavy Meson Transitions
We evaluate the radiative and hadronic decay rates of the mesons using
the Heavy Quark Effective Theory and the Vector Meson Dominance hypothesis. We
also estimate the width of the electromagnetic transitions and the
radiative decays of positive parity charmed mesons.Comment: 12 pages, LaTex, BARI-TH/93-14
Form factors for decay in a model constrained by chiral symmetry and quark model
The form factors for the transition are evaluated in the entire
momentum transfer range by using the constraints obtained in the framework
combining the heavy quark expansion and chiral symmetry for light quarks and
the quark model. In particular, we calculate the valence quark contributions
and show that it together with the equal time commutator contribution simulate
a B-meson pole q^2-dependence of form factors in addition to the usual vector
meson B^{*}-pole diagram for in the above framework. We
discuss the predictions in our model, which provide an estimate of |V_{ub}|^2.Comment: 7 pages, Revtex, 5 figure, fig 3 is replaced and some text is adde
A cross-sectional study of differences in 6-min walk distance in healthy adults residing at high altitude versus sea level
BACKGROUND: We sought to determine if adult residents living at high altitude have developed sufficient adaptation to a hypoxic environment to match the functional capacity of a similar population at sea level. To test this hypothesis, we compared the 6-min walk test distance (6MWD) in 334 residents living at sea level vs. at high altitude. METHODS: We enrolled 168 healthy adults aged ≥35 years residing at sea level in Lima and 166 individuals residing at 3,825 m above sea level in Puno, Peru. Participants completed a 6-min walk test, answered a sociodemographics and clinical questionnaire, underwent spirometry, and a blood test. RESULTS: Average age was 54.0 vs. 53.8 years, 48% vs. 43% were male, average height was 155 vs. 158 cm, average blood oxygen saturation was 98% vs. 90%, and average resting heart rate was 67 vs. 72 beats/min in Lima vs. Puno. In multivariable regression, participants in Puno walked 47.6 m less (95% CI -81.7 to -13.6 m; p < 0.01) than those in Lima. Other variables besides age and height that were associated with 6MWD include change in heart rate (4.0 m per beats/min increase above resting heart rate; p < 0.001) and percent body fat (-1.4 m per % increase; p = 0.02). CONCLUSIONS: The 6-min walk test predicted a lowered functional capacity among Andean high altitude vs. sea level natives at their altitude of residence, which could be explained by an incomplete adaptation or a protective mechanism favoring neuro- and cardioprotection over psychomotor activity
Remarks on Semileptonic B and D Decays into Orbitally Excited Mesons
We have obtained the differential decay rate and calculated the branching
ratios of the exclusive semileptonic decays , where is a
p-wave meson, using the nonrelativistic ISGW quark model. Our results are
compared with the predictions of the ISGW2 model. We have computed some
branching ratios that were not reported or were reported with 0.00 in this
model. For example, we find that , and , which seems to be
at the reach of forthcoming experiments. Furthermore, we have classified the
decays in two groups and compared the semileptonic and
nonleptonic decays including a tensor meson in the final state.Comment: 11 pages, LaTe
Semi-empirical dissipation source functions for ocean waves: Part I, definition, calibration and validation
New parameterizations for the spectra dissipation of wind-generated waves are
proposed. The rates of dissipation have no predetermined spectral shapes and
are functions of the wave spectrum and wind speed and direction, in a way
consistent with observation of wave breaking and swell dissipation properties.
Namely, the swell dissipation is nonlinear and proportional to the swell
steepness, and dissipation due to wave breaking is non-zero only when a
non-dimensional spectrum exceeds the threshold at which waves are observed to
start breaking. An additional source of short wave dissipation due to long wave
breaking is introduced to represent the dissipation of short waves due to
longer breaking waves. Several degrees of freedom are introduced in the wave
breaking and the wind-wave generation term of Janssen (J. Phys. Oceanogr.
1991). These parameterizations are combined and calibrated with the Discrete
Interaction Approximation of Hasselmann et al. (J. Phys. Oceangr. 1985) for the
nonlinear interactions. Parameters are adjusted to reproduce observed shapes of
directional wave spectra, and the variability of spectral moments with wind
speed and wave height. The wave energy balance is verified in a wide range of
conditions and scales, from gentle swells to major hurricanes, from the global
ocean to coastal settings. Wave height, peak and mean periods, and spectral
data are validated using in situ and remote sensing data. Some systematic
defects are still present, but the parameterizations yield the best overall
results to date. Perspectives for further improvement are also given.Comment: revised version for Journal of Physical Oceanograph
<i>Spitzer</i> microlens measurement of a massive remnant in a well-separated binary
We report the detection and mass measurement of a binary lens OGLE-2015-BLG-1285La,b, with the more massive component having M1 > 1.35 M⊙ (80% probability). A main-sequence star in this mass range is ruled out by limits on blue light, meaning that a primary in this mass range must be a neutron star (NS) or black hole (BH). The system has a projected separation r⊥ = 6.1 ± 0.4 AU and lies in the Galactic bulge. These measurements are based on the "microlens parallax" effect, i.e., comparing the microlensing light curve as seen from Spitzer, which lay at 1.25 AU projected from Earth, to the light curves from four ground-based surveys, three in the optical and one in the near-infrared. Future adaptive optics imaging of the companion by 30 m class telescopes will yield a much more accurate measurement of the primary mass. This discovery both opens the path and defines the challenges to detecting and characterizing BHs and NSs in wide binaries, with either dark or luminous companions. In particular, we discuss lessons that can be applied to future Spitzer and Kepler K2 microlensing parallax observations
Light meson mass dependence of the positive parity heavy-strange mesons
We calculate the masses of the resonances D_{s0}^*(2317) and D_{s1}(2460) as
well as their bottom partners as bound states of a kaon and a D^*- and
B^*-meson, respectively, in unitarized chiral perturbation theory at
next-to-leading order. After fixing the parameters in the D_{s0}^*(2317)
channel, the calculated mass for the D_{s1}(2460) is found in excellent
agreement with experiment. The masses for the analogous states with a bottom
quark are predicted to be M_{B^*_{s0}}=(5696\pm 40) MeV and M_{B_{s1}}=(5742\pm
40) MeV in reasonable agreement with previous analyses. In particular, we
predict M_{B_{s1}}-M_{B_{s0}^*}=46\pm 1 MeV. We also explore the dependence of
the states on the pion and kaon masses. We argue that the kaon mass dependence
of a kaonic bound state should be almost linear with slope about unity. Such a
dependence is specific to the assumed molecular nature of the states. We
suggest to extract the kaon mass dependence of these states from lattice QCD
calculations.Comment: 10 page
Planet Sensitivity from Combined Ground- and Space-based Microlensing Observations
To move one step forward toward a Galactic distribution of planets, we
present the first planet sensitivity analysis for microlensing events with
simultaneous observations from space and the ground. We present this analysis
for two such events, OGLE-2014-BLG-0939 and OGLE-2014-BLG-0124, which both show
substantial planet sensitivity even though neither of them reached high
magnification. This suggests that an ensemble of low to moderate magnification
events can also yield significant planet sensitivity and therefore probability
to detect planets. The implications of our results to the ongoing and future
space-based microlensing experiments to measure the Galactic distribution of
planets are discussed.Comment: 10 pages, 5 figures, 1 table; ApJ in pres
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