6,246 research outputs found
Dirichlet L-series with real and complex characters and their application to solving double sums
A description of the properties of \L with complex characters is given. By
using these, together with the more familiar \L with real characters, it is
shown how certain two dimensional lattice sums, which previously could not be
put into closed form, may now be expressed in this way.Comment: 21 pages, 1 tabl
It is time to improve the quality of medical information distributed to students across social media
The ubiquitous nature of social media has meant that its effects on fields outside of social communication have begun to be felt. The generation undergoing medical education are of the generation referred to as âdigital nativesâ, and as such routinely incorporate social media into their education. Social mediaâs incorporation into medical education includes its use as a platform to distribute information to the public (âdistributive educationâ) and as a platform to provide information to a specific audience (âpush educationâ). These functions have proved beneficial in many regards, such as enabling constant access to the subject matter, other learners, and educators. However, the usefulness of using social media as part of medical education is limited by the vast quantities of poor quality information and the time required to find information of sufficient quality and relevance, a problem confounded by many studentâs preoccupation with âefficientâ learning. In this Perspective, the authors discuss whether social media has proved useful as a tool for medical education. The current growth in the use of social media as a tool for medical education seems to be principally supported by studentsâ desire for efficient learning rather than by the efficacy of social media as a resource for medical education. Therefore, improvements in the quality of information required to maximize the impact of social media as a tool for medical education are required. Suggested improvements include an increase in the amount of educational content distributed on social media produced by academic institutions, such as universities and journals
Analysis of The Hipparcos Measurements of HD10697 - A Mass Determination of a Brown-Dwarf Secondary
HD10697 is a nearby main-sequence star around which a planet candidate has
recently been discovered by means of radial-velocity measurements (Vogt et al.
1999, submitted to ApJ). The stellar orbit has a period of about three years,
the secondary minimum mass is 6.35 Jupiter masses and the minimum semi-major
axis is 0.36 milli-arc-sec (mas). Using the Hipparcos data of HD10697 together
with the spectroscopic elements of Vogt et al. (1999) we found a semi-major
axis of 2.1 +/- 0.7 mas, implying a mass of 38 +/- 13 Jupiter masses for the
unseen companion. We therefore suggest that the secondary of HD10697 is
probably a brown dwarf, orbiting around its parent star at a distance of 2 AU.Comment: 6 pages, 2 figures, LaTex, aastex, accepted for publication by ApJ
Letter
On the Adromeda to Milky Way mass-ratio
We have explored the hypothesis that the total mass-ratio of the two main
galaxies of the Local Group: Andromeda Galaxy(M31) and the Milky Way (MW) can
be constrained measuring the tidal force induced by the surrounding mass
distribution, M31 included, on the MW. We argue that the total mass-ratio
between the two groups can be approximated, at least qualitatively, finding the
tidal radius where the internal binding force of the MW balances the external
tidal force acting on it. Since M31 is the massive tidal perturber of the local
environment, we have used a wide range of M31 to MW mass-ratio combinations to
compute the corresponding tidal radii. Of them, only few match the distance of
the zero-tidal shell i.e. the shell identified observationally by the outermost
dwarf galaxies which do not show any sign of tidal effects. This is the key to
constrain the best mass-ratio interval of the two galaxies. Our results favour
a solution where the mass-ratio ranges from 2 to 3 implying a massive
predominance of M31.Comment: 8 pages, 2 figures, Accepted for publication in Mon. Not. of Royal
Astron. So
A Keck/DEIMOS spectroscopic survey of faint Galactic satellites: searching for the least massive dwarf galaxies
[abridged] We present the results of a spectroscopic survey of the recently
discovered faint Milky Way satellites Boo, UMaI, UMaII and Wil1. Using the
DEIMOS spectrograph on Keck, we have obtained samples that contain from 15 to
85 probable members of these satellites for which we derive radial velocities
precise to a few km/s down to i~21-22. About half of these stars are observed
with a high enough S/N to estimate their metallicity to within \pm0.2 dex. From
this dataset, we show that UMaII is the only object that does not show a clear
radial velocity peak. However, the measured systemic radial velocity
(v_r=115\pm5 km/s) is in good agreement with recent simulations in which this
object is the progenitor of the recently discovered Orphan Stream. The three
other satellites show velocity dispersions that make them highly dark-matter
dominated systems. In particular the Willman 1 object is not a globular cluster
given its metallicity scatter over -2.0<[Fe/H]<-1.0 and is therefore almost
certainly a dwarf galaxy or dwarf galaxy remnant. We measure a radial velocity
dispersion of only 4.3_{-1.3}^{+2.3} km/s around a systemic velocity of
-12.3\pm2.3 km/s which implies a mass-to-light ratio of ~700 and a total mass
of ~5x10^5 Msun for this satellite, making it the least massive satellite
galaxy known to date. Such a low mass could mean that the 10^7 Msun limit that
had until now never been crossed for Milky Way and Andromeda satellite galaxies
may only be an observational limit and that fainter, less massive systems exist
within the Local Group. However, more modeling and an extended search for
potential extra-tidal stars are required to rule out the possibility that these
systems have not been significantly heated by tidal interaction.Comment: 24 pages, 11 figures, MNRAS accepte
Hodge numbers for the cohomology of Calabi-Yau type local systems
We use Higgs cohomology to determine the Hodge numbers of the first
intersection cohomology group of a local system V arising from the third direct
image of a family of Calabi-Yau 3-folds over a smooth, quasi-projective curve.
We give applications to Rhode's families of Calabi-Yau 3-folds without MUM.Comment: Some signs corrected. This article draws heavily from arXiv:0911.027
The Parent Populations of 6 groups identified from Chemical Tagging in the Solar neighborhood
We estimate the size and distribution of the parent populations for the 6
largest (at least 20 stars in the Solar neighborhood) chemical groups
identified in the Chemical Tagging experiment by Mitschang et al.~2014. Stars
in the abundance groups tend to lie near a boundary in angular momentum versus
eccentricity space where the probability is highest for a star to be found in
the Solar neighborhood and where orbits have apocenter approximately equal to
the Sun's galactocentric radius. Assuming that the parent populations are
uniformly distributed at all azimuthal angles in the Galaxy, we estimate that
the parent populations of these abundance groups contain at least 200,000
members. The spread in angular momentum of the groups implies that the
assumption of a uniform azimuthal distribution only fails for the two youngest
groups and only for the highest angular momentum stars in them. The parent
populations of three thin disk groups have narrow angular momentum
distributions, but tails in the eccentricity and angular momentum distributions
suggest that only a small fraction of stars have migrated and increased in
eccentricity. In contrast, the parent populations of the thick disk groups
exhibit both wide angular momentum and eccentricity distributions implying that
both heating and radial migration has taken place.Comment: accepted for publication in MNRA
Leo V: A Companion of a Companion of the Milky Way Galaxy
We report the discovery of a new Milky Way dwarf spheroidal galaxy in the
constellation of Leo identified in data from the Sloan Digital Sky Survey. Leo
V lies at a distance of about 180 kpc, and is separated by about 3 degrees from
another recent discovery, Leo IV. We present follow-up imaging from the Isaac
Newton Telescope and spectroscopy from the Hectochelle fiber spectrograph at
the Multiple Mirror Telescope. Leo V's heliocentric velocity is 173.4 km/s,
which is offset by about 40 km/s from that of Leo IV. A simple interpretation
of the kinematic data is that both objects may lie on the same stream, though
the implied orbit is only modestly eccentric (e = 0.2)Comment: Submitted to ApJ (Letters
Stability of the Higgs mass in theories with extra dimensions
We analyze the ultraviolet stability of the Higgs mass in recently proposed
Kaluza-Klein models compactified on S_1/Z_2 or S_1/(Z_2\times Z_2'), both at
the field theory and string theory level. Fayet-Iliopoulos terms of U(1)
hypercharge are shown to be of vital importance for this discussion. Models
with a single Higgs doublet seem to be generically affected by quadratic
divergences.Comment: Contribution to the Proceedings of Durham IPPP meeting May 2001.(12
pages, LaTeX
WISE circumstellar discs in the young Sco-Cen association
We present an analysis of the WISE photometric data for 829 stars in the Sco-Cen OB2 association, using thelatest high-mass membership probabilities. We detect infrared excesses associated with 135 BAF-type stars, 99 ofwhich are secure Sco-Cen members. There is a clear increase in excess fraction with membership probability, which can be fitted linearly.We infer that 41 ± 5 per cent of Sco-Cen OB2 BAF stars have excesses, while the field star excess fraction is consistent with zero. This is the first time that the probability of non-membership has been used in the calculation of excess fractions for young stars. We do not observe any significant change in excess fraction between the three subgroups.Within our sample, we have observed that B-type association members have a significantly smaller excess fraction than Aand F-type association members
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