20,093 research outputs found
The variation of tidal dissipation in the convective envelope of low-mass stars along their evolution
Since 1995, more than 1500 exoplanets have been discovered around a large
diversity of host stars (from M- to A-type stars). Tidal dissipation in stellar
convective envelopes is a key actor that shapes the orbital architecture of
short-period systems. Our objective is to understand and evaluate how tidal
dissipation in the convective envelope of low-mass stars (from M to F types)
depends on their mass, evolutionary stage and rotation. Using a simplified
two-layer assumption, we compute analytically the frequency-averaged tidal
dissipation in their convective envelope. This dissipation is due to the
conversion into heat of the kinetic energy of tidal non wave-like/equilibrium
flow and inertial waves because of the viscous friction applied by turbulent
convection. Using grids of stellar models allows us to study the variation of
the dissipation as a function of stellar mass and age on the Pre-Main-Sequence
and on the Main-Sequence for stars with masses spanning from to
. As shown by observations, tidal dissipation in stars varies
over several orders of magnitude as a function of stellar mass, age and
rotation. During their Pre-Main-Sequence, all low-mass stars have an increase
of the frequency-averaged tidal dissipation for a fixed angular velocity in
their convective envelope until they reach a critical aspect and mass ratios.
Next, the dissipation evolves on the Main Sequence to an asymptotic value that
becomes maximum for K-type stars and that decreases by several
orders of magnitude with increasing stellar mass. Finally, the rotational
evolution of low-mass stars strengthens the importance of tidal dissipation
during the Pre-Main-Sequence for star-planet and multiple star systems.Comment: 5 pages, 4 figures, accepted for publication as a Letter in Astronomy
& Astrophysic
Study of the d/d resolution of a GEM Readout Chamber prototype for the upgrade of the ALICE TPC
The ALICE Collaboration is planning a major upgrade of its central barrel
detectors to be able to cope with the increased LHC luminosity beyond 2020. For
the TPC, this implies a replacement of the currently used gated MWPCs
(Multi-Wire Proportional Chamber) by GEM (Gas Electron Multiplier) based
readout chambers. In order to prove, that the present particle identification
capabilities via measurement of the specific energy loss are retained after the
upgrade, a prototype of the ALICE IROC (Inner Readout Chamber) has been
evaluated in a test beam campaign at the CERN PS. The d/d resolution of
the prototype has been proven to be fully compatible with the current MWPCs.Comment: 4 pages, 5 figures, Proceedings of "4th Conference on Micro-Pattern
Gaseous Detectors
Corporate social responsibility in the UK, the Netherlands and Germany: theory and forerunners
The results in this paper should help connect theoretical concepts with CSR practices in the current business world. This paper will present the findings of a survey sent to businesses in the UK, the Netherlands, and Germany. The empirical data indicate some interesting tendencies. CSR as perceived within the business community is strongly related to environmental management and has a longer history than might have been expected. External factors, such as legal requirements, general external pressure (NGOs, globalization), and media coverage and campaigning have triggered changes in the business world in favor of CSR, but when CSR policies and schemes are initially under discussion, internal forces, such as the board of directors and the middle management, take over and lead the process. Furthermore, the results of the questionnaire show that external forces, such as government, NGOs, and communities, are not relevant with respect to driving CSR development forward
New Horizons in Psychiatry
Psychiatrists have long held that there should be more psychiatry in general medicine, and the nonpsychiatric physicians have said that there should be much more medicine in psychiatry. Both groups have been perfectly correct and are being told by the consuming population that there must be more sociology in each of them. The future psychiatrist must and will work with his colleagues in medicine, not to achieve a utopia, but at least to approach this desirable situation in some degree
The New England Narrative
Though equally successful, noteworthy, inspiring, and crucial as the contributions to American Independence made by New England women patriots, the contributions made by North Carolinian women patriots are excluded from the history of America’s founding as a direct result of sectional nationalism
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The "Common Core" Standards Initiative: An Effective Reform Tool?
Very little evidence supports the contention that establishing national academic standards for K-12 schools will improve the quality of American public education, and the standards push may distract attention from other vital school reforms, concludes a new policy brief, The "Common Core" Standards Initiative: An Effective Reform Tool? The brief, authored by William J. Mathis, was released today by the Great Lakes Center for Education Research and Practice. "Without addressing both the in-school and out-of-school influences on test scores, common core standards are not likely to improve the quality and equity of America's public schools," Mathis explains. The Obama administration has embraced "common core" standards and has pressured states to adopt them by stating that federal Title I aid will be withheld from states that do not adopt standards such as those being developed by the National Governors Association and the Council of Chief State School Officers. In addition, states that adopt the standards have a major advantage on their Race to the Top applications. Standards advocates argue that common standards are necessary for keeping the nation competitive in a global economy. But Mathis points out that research does not support this oft-expressed rationale. No studies support a true causal relationship between national standards and economic competitiveness, and at the most superficial level we know that nations with centralized standards generally tend to perform no better (or worse) on international tests than those without. Further, research shows that national economic competitiveness is influenced far more by economic decisions than by test scores. Mathis also raises questions about the rapid development of the common-core standards, the lack of field testing, and the overarching need for any high-stakes consequences to be "valid," pursuant to established professional guidelines. Given these concerns, he says that the prospect of positive effects on educational quality or equality "seems improbable.
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