563 research outputs found
Simultaneity as an Invariant Equivalence Relation
This paper deals with the concept of simultaneity in classical and
relativistic physics as construed in terms of group-invariant equivalence
relations. A full examination of Newton, Galilei and Poincar\'e invariant
equivalence relations in is presented, which provides alternative
proofs, additions and occasionally corrections of results in the literature,
including Malament's theorem and some of its variants. It is argued that the
interpretation of simultaneity as an invariant equivalence relation, although
interesting for its own sake, does not cut in the debate concerning the
conventionality of simultaneity in special relativity.Comment: Some corrections, mostly of misprints. Keywords: special relativity,
simultaneity, invariant equivalence relations, Malament's theore
Philosophy and updating of the asteroid photometric catalogue
The Asteroid Photometric Catalogue now contains photometric lightcurves for 584 asteroids. We discuss some of the guiding principles behind it. This concerns both observers who offer input to it and users of the product
Potentials for hyper-Kahler metrics with torsion
We prove that locally any hyper-K\"ahler metric with torsion admits an HKT
potential.Comment: 9 page
Planetary Science Virtual Observatory architecture
In the framework of the Europlanet-RI program, a prototype of Virtual
Observatory dedicated to Planetary Science was defined. Most of the activity
was dedicated to the elaboration of standards to retrieve and visualize data in
this field, and to provide light procedures to teams who wish to contribute
with on-line data services. The architecture of this VO system and selected
solutions are presented here, together with existing demonstrators
The activity of Main Belt comets
Main Belt comets represent a recently discovered class of objects. They are
quite intriguing because, while having a Tisserand invariant value higher than
3, are showing cometary activity. We study the activity of the Main Belt comets
making the assumption that they are icy-bodies and that the activity has been
triggered by an impact. We determine the characteristics of this activity and
if the nowadays impact rate in the Main Asteroid Belt is compatible with the
hypothesis of an activity triggered by a recent impact. Due to the fact that
the Main Belt comets can be considered as a kind of comets, we apply a thermal
evolution model developed for icy bodies in order to simulate their activity.
We also apply a model to derive the impact rate, with respect to the size of
the impactor, in the Main Belt. We demonstrate that a stable activity can
result from a recent impact, able to expose ice-rich layers, and that the
impact rate in the Main Belt is compatible with this explanation.Comment: 9 pages, 7 figure
Locality hypothesis and the speed of light
The locality hypothesis is generally considered necessary for the study of
the kinematics of non-inertial systems in special relativity. In this paper we
discuss this hypothesis, showing the necessity of an improvement, in order to
get a more clear understanding of the various concepts involved, like
coordinate velocity and standard velocity of light. Concrete examples are
shown, where these concepts are discussed.Comment: 23 page
Intersecting brane geometries
We present a survey of the calibrated geometries arising in the study of the
local singularity structure of supersymmetric fivebranes in M-theory. We pay
particular attention to the geometries of 4-planes in eight dimensions, for
which we present some new results as well as many details of the computations.
We also analyse the possible generalised self-dualities which these geometries
can afford.Comment: 29 pages. (v2: Two new sections have been added. Paper is now more
than 50% longer. A guided tour of the eight-dimensional geometries is
presented along with the computational details. We have also included a
discussion of the possible generalised self-dualities afforded by these
geometries.
A review of current induction strategies and emerging prognostic factors in the management of children and adolescents with acute lymphoblastic leukemia
Introduction: Acute lymphoblastic leukemia is the most frequent hematologic malignancy in children.
Almost 95% of children potentially achieve a complete remission after the induction treatment, but over
the last years, new insights in the genomic disease profile and in minimal residual disease detection
techniques have led to an improvement in the prognostic stratification, identifying selected patientsâ
subgroups with peculiar therapeutic needs.
Areas covered: According to a comprehensive search of peer-review literature performed in Pubmed, in
this review we summarize the recent evidences on the induction treatment strategies comprised in the
children acute lymphoblastic leukemia scenario, focusing on the role of key drugs such as corticosteroids
and asparaginase and discussing the crucial significance of the genomic characterization at baseline which
may drive the proper induction treatment choice.
Expert opinion: Current induction strategies already produce durable remissions in a significant proportion
of standard-risk children with acute lymphoblastic leukemia. A broader knowledge of the biologic features
related to acute lymphoblastic leukemia subtypes with worse prognosis, and an optimization of targeted
drugs now available, might lead to the achievement of long-term molecular remissions in this setting
Water in Comet 2/2003 K4 (LINEAR) with Spitzer
We present sensitive 5.5 to 7.6 micron spectra of comet C/2003 K4 (LINEAR)
obtained on 16 July 2004 (r_{h} = 1.760 AU, Delta_{Spitzer} = 1.409 AU, phase
angle 35.4 degrees) with the Spitzer Space Telescope. The nu_{2} vibrational
band of water is detected with a high signal-to-noise ratio (> 50). Model
fitting to the best spectrum yields a water ortho-to-para ratio of 2.47 +/-
0.27, which corresponds to a spin temperature of 28.5^{+6.5}_{-3.5} K. Spectra
acquired at different offset positions show that the rotational temperature
decreases with increasing distance from the nucleus, which is consistent with
evolution from thermal to fluorescence equilibrium. The inferred water
production rate is (2.43 +/- 0.25) \times 10^{29} molec. s^{-1}. The spectra do
not show any evidence for emission from PAHs and carbonate minerals, in
contrast to results reported for comets 9P/Tempel 1 and C/1995 O1 (Hale-Bopp).
However, residual emission is observed near 7.3 micron the origin of which
remains unidentified.Comment: 33 pages, including 11 figures, 2 tables, ApJ 2007 accepte
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