11,353 research outputs found
Nonrenormalization theorems for N=2 Super Yang-Mills
The BRST algebraic proofs of the the nonrenormalization theorems for the beta
functions of N=2 and N=4 Super Yang-Mills theories are reviewed.Comment: 3 pages, contribution to SUSY 2000 Encyclopedi
Lithium Depletion Boundary in a Pre-Main Sequence Binary System
A lithium depletion boundary is detected in HIP 112312 (GJ 871.1 A and B), a
\~12 Myr old pre-main sequence binary system. A strong (EW 300 mA) Li 6708 A
absorption feature is seen at the secondary (~M4.5) while no Li 6708 A feature
is detected from the primary (~M4). The physical companionship of the two stars
is confirmed from common proper motions. Current theoretical pre-main sequence
evolutionary models cannot simultaneously match the observed colors,
brightnesses, and Li depletion patterns of this binary system. At the age upper
limit of 20 Myr, contemporary theoretical evolutionary models predict too slow
Li depletion. If true Li depletion is a faster process than predicted by
theoretical models, ages of open clusters (Pleiades, alpha Persei, and IC 2391)
estimated from the Li depletion boundary method are all overestimated. Because
of the importance of the open cluster age scale, development of self-consistent
theoretical models to match the HIP 112312 data is desirable.Comment: Accepted in ApJL. 5 pages total (3 tables, 3 figures
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Dynamic interpersonal therapy for moderate to severe depression: A pilot randomized controlled and feasibility trial
Background: Improving Access to Psychological Therapies (IAPT) services treat most patients in England who present to primary care with major depression. Psychodynamic psychotherapy is one of the psychotherapies offered. Dynamic Interpersonal Therapy (DIT) is a psychodynamic and mentalization-based treatment for depression. 16 sessions are delivered over approximately 5 months. Neither DIT's effectiveness relative to low-intensity treatment (LIT), nor the feasibility of randomizing patients to psychodynamic or cognitive-behavioural treatments (CBT) in an IAPT setting has been demonstrated.
Methods: 147 patients were randomized in a 3:2:1 ratio to DIT (n = 73), LIT (control intervention; n = 54) or CBT (n = 20) in four IAPT treatment services in a combined superiority and feasibility design. Patients meeting criteria for major depressive disorder were assessed at baseline, mid-treatment (3 months) and post-treatment (6 months) using the Hamilton Rating Scale for Depression (HRSD-17), Beck Depression Inventory-II (BDI-II) and other self-rated questionnaire measures. Patients receiving DIT were also followed up 6 months post-completion.
Results: The DIT arm showed significantly lower HRSD-17 scores at the 6-month primary end-point compared with LIT (d = 0.70). Significantly more DIT patients (51%) showed clinically significant change on the HRSD-17 compared with LIT (9%). The DIT and CBT arms showed equivalence on most outcomes. Results were similar with the BDI-II. DIT showed benefit across a range of secondary outcomes.ConclusionsDIT delivered in a primary care setting is superior to LIT and can be appropriately compared with CBT in future RCTs
Topological mass mechanism and exact fields mapping
We present a class of mappings between models with topological mass mechanism
and purely topological models in arbitrary dimensions. These mappings are
established by directly mapping the fields of one model in terms of the fields
of the other model in closed expressions. These expressions provide the
mappings of their actions as well as the mappings of their propagators. For a
general class of models in which the topological model becomes the BF model the
mappings present arbitrary functions which otherwise are absent for
Chern-Simons like actions. This work generalizes the results of [1] for
arbitrary dimensions.Comment: 11 page
Studying the evolution of AGB stars in the Gaia epoch
We present asymptotic giant branch (AGB) models of solar metallicity, to
allow the interpretation of observations of Galactic AGB stars, whose distances
should be soon available after the first release of the Gaia catalogue. We find
an abrupt change in the AGB physical and chemical properties, occurring at the
threshold mass to ignite hot bottom burning,i.e. . Stars with
mass below reach the C-star stage and eject into the
interstellar medium gas enriched in carbon , nitrogen and . The higher
mass counterparts evolve at large luminosities, between and . The mass expelled from the massive AGB stars
shows the imprinting of proton-capture nucleosynthesis, with considerable
production of nitrogen and sodium and destruction of and . The
comparison with the most recent results from other research groups are
discussed, to evaluate the robustness of the present findings. Finally, we
compare the models with recent observations of galactic AGB stars, outlining
the possibility offered by Gaia to shed new light on the evolution properties
of this class of objects.Comment: 21 pages, 11 figure, 3 tables, accepted for publication in MNRAS
(2016 July 11
The early evolution of Globular Clusters: the case of NGC 2808
Enhancement and spread of helium among globular cluster stars have been
recently suggested as a way to explain the horizontal branch blue tails, in
those clusters which show a primordial spread in the abundances of CNO and
other elements involved in advanced CNO burning (D'Antona et al. 2002). In this
paper we examine the implications of the hypothesis that, in many globular
clusters, stars were born in two separate events: an initial burst (first
generation), which gives origin to probably all high and intermediate mass
stars and to a fraction of the cluster stars observed today, and a second,
prolonged star formation phase (second generation) in which stars form directly
from the ejecta of the intermediate mass stars of the first generation. In
particular, we consider in detail the morphology of the horizontal branch in
NGC 2808 and argue that it unveils the early cluster evolution, from the birth
of the first star generation to the end of the second phase of star formation.
This framework provides a feasible interpretation for the still unexplained
dichotomy of NGC 2808 horizontal branch, attributing the lack of stars in the
RR Lyr region to the gap in the helium content between the red clump, whose
stars are considered to belong to the first stellar generation and have
primordial helium, and the blue side of the horizontal branch, whose minimum
helium content reflects the helium abundance in the smallest mass
(~4Msun)contributing to the second stellar generation. This scenario provides
constraints on the required Initial Mass Function, in a way that a great deal
of remnant neutron stars and stellar mass black holes might have been produced.Comment: 23 pages, 7 figures, in press on The Astrophysical Journa
The investigation of time dependent flame structure by ionization probes
Ionization probes were used to measure mean ionization current and frequency spectra, auto-correlations and cross-correlations in jet flames with variation in the initial Reynolds numbers and equivalence ratios. Special attention was paid to the transitional region between the burner exit plane and the plane of onset of turbulence
Self-Enrichment in Globular Clusters: Is There a Role for the Super-Asymptotic Giant Branch Stars?
In four globular clusters (GCs) a non negligible fraction of stars can be
interpreted only as a very helium rich population. The evidence comes from the
presence of a "blue" main sequence in Cen and NGC 2808, and from the
the very peculiar horizontal branch morphology in NGC 6441 and NGC 6388.
Although a general consensus is emerging on the fact that self--enrichment is a
common feature among GCs, the helium content required for these stars is
Y\simgt0.35, and it is difficult to understand how it can be produced without
any --or, for Cen, without a considerable--associated metal
enhancement. We examine the possible role of super--AGB stars, and show that
they may provide the required high helium. However, the ejecta of the most
massive super--AGBs show a global CNO enrichment by a factor of 4, due
to the dredge--out process occurring at the second dredge up stage. If these
clusters show no evidence for this CNO enrichment, we can rule out that at
least the most massive super--AGBs evolve into O--Ne white dwarfs and take part
in the formation of the second generation stars. This latter hypothesis may
help to explain the high number of neutron stars present in GCs. The most
massive super--AGBs would in fact evolve into electron--capture supernovae.
Their envelopes would be easily ejected out of the cluster, but the remnant
neutron stars remain into the clusters, thanks to their small supernova natal
kicks.Comment: version accepted for publication in The Astrophysical Journal Letter
Dust from AGBs: relevant factors and modelling uncertainties
The dust formation process in the winds of Asymptotic Giant Branch stars is
discussed, based on full evolutionary models of stars with mass in the range
MMM, and metallicities .
Dust grains are assumed to form in an isotropically expanding wind, by growth
of pre--existing seed nuclei. Convection, for what concerns the treatment of
convective borders and the efficiency of the schematization adopted, turns out
to be the physical ingredient used to calculate the evolutionary sequences with
the highest impact on the results obtained. Low--mass stars with MM produce carbon type dust with also traces of silicon carbide. The
mass of solid carbon formed, fairly independently of metallicity, ranges from a
few M, for stars of initial mass M, to
M for MM; the size of dust
particles is in the range mm. On the contrary,
the production of silicon carbide (SiC) depends on metallicity. For the size of SiC grains varies in the range m, while the mass of SiC formed is
. Models of
higher mass experience Hot Bottom Burning, which prevents the formation of
carbon stars, and favours the formation of silicates and corundum. In this case
the results scale with metallicity, owing to the larger silicon and aluminium
contained in higher--Z models. At Z= we find that the most
massive stars produce dust masses M, whereas models of
smaller mass produce a dust mass ten times smaller. The main component of dust
are silicates, although corundum is also formed, in not negligible quantities
().Comment: Paper accepted for publication in Monthly Notices of the Royal
Astronomical Society Main Journal (2014 January 4
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