1,051 research outputs found
Near-infrared Spectral Features in Single-aged Stellar Populations
Synthetic spectra for single-aged stellar populations of metallicities [M/H]
= -0.5, 0.0 and +0.5, ages = 3 to 17 Gyrs, and initial mass function exponents
x = 0.1 to 2.0 were built in the wavelength range 6000-10200 Angstrons. For
such we have employed the grid of synthetic spectra described in Schiavon &
Barbuy (1999), computed for the stellar parameters 2500 <= Teff <= 6000 K, -0.5
<= log g <= 5.0, [M/H] = -0.5, 0.0 and +0.5, and [alpha/Fe] = 0.0, together
with the isochrones by Bertelli et al. (1994) and Baraffe et al. (1998). The
behavior of the features NaI8190, CaII8662, TiO6600 and FeH9900 in the
integrated spectra of single stellar populations were studied in terms of
metallicity, initial mass function and age variations. The main conclusions are
that the NaI doublet is an IMF-sensitive feature, which is however sensitive
also to metallicity and age, whereas TiO, CaII and FeH are very sensitive to
metallicity and essentially insensitive to IMF and age.Comment: 13 pages + 7 figures, ApJ accepte
The Thermodynamic Uncertainty Theorem
Thermodynamic uncertainty relations (TURs) express a fundamental tradeoff
between the precision (inverse scaled variance) of any thermodynamic current by
functionals of the average entropy production. Relying on purely variational
arguments, we significantly extend these inequalities by incorporating and
analyzing the impact of higher statistical cumulants of entropy production
within a general framework of time-symmetrically controlled computation. This
allows us to derive an exact expression for the current that achieves the
minimum scaled variance, for which the TUR bound tightens to an equality that
we name Thermodynamic Uncertainty Theorem (TUT). Importantly, both the minimum
scaled variance current and the TUT are functionals of the stochastic entropy
production, thus retaining the impact of its higher moments. In particular, our
results show that, beyond the average, the entropy production distribution's
higher moments have a significant effect on any current's precision. This is
made explicit via a thorough numerical analysis of swap and reset computations
that quantitatively compares the TUT against previous generalized TURs. Our
results demonstrate how to interpolate between previously-established bounds
and how to identify the most relevant TUR bounds in different nonequilibrium
regimes
Solution of the Fokker-Planck equation with a logarithmic potential and mixed eigenvalue spectrum
Motivated by a problem in climate dynamics, we investigate the solution of a
Bessel-like process with negative constant drift, described by a Fokker-Planck
equation with a potential V(x) = - [b \ln(x) + a\, x], for b>0 and a<0. The
problem belongs to a family of Fokker-Planck equations with logarithmic
potentials closely related to the Bessel process, that has been extensively
studied for its applications in physics, biology and finance. The Bessel-like
process we consider can be solved by seeking solutions through an expansion
into a complete set of eigenfunctions. The associated imaginary-time
Schroedinger equation exhibits a mix of discrete and continuous eigenvalue
spectra, corresponding to the quantum Coulomb potential describing the bound
states of the hydrogen atom. We present a technique to evaluate the
normalization factor of the continuous spectrum of eigenfunctions that relies
solely upon their asymptotic behavior. We demonstrate the technique by solving
the Brownian motion problem and the Bessel process both with a negative
constant drift. We conclude with a comparison with other analytical methods and
with numerical solutions.Comment: 21 pages, 8 figure
DESIGNING BY STUDENTS FOR STUDENTS: AN EDUCATIONAL ROADMAP IN THE DESIGN OF UNIVERSITY CAMPUSES
The increased emphasis on the environments contributing to people's well-being has prompted a more profound contemplation within university settings. Prioritising both physical and mental well-being has compelled universities to take decisive actions to ensure the welfare of students and all staff members.
The Laboratorio di Sintesi Finale (LSF) of section I1 is explicitly predicated on this premise. This course, the final design laboratory of Politecnico di Milano's three-year Interior Design degree program, gives the 57 enrolled students the chance to work on a project that will serve as the focus of their thesis. Students are expected to design spaces on Politecnico's three campuses in Milan to maximise the user experience of events and services. The intention is to engage students in working on permanent or temporary locations, as well as dedicated and interstitial spaces, both indoor and outdoor.
The faculty team is multidisciplinary and includes professors and specialists from architecture, interior design, product design, and materials expertise due to the diversity and scope of the work. Giving students the assistance they require to effectively present their research and projects is crucial. Consequently, the LSF aims to give students practical tools for analysing design problems in the larger framework of cultural, social, and technological changes (discoveries, new lifestyles, and new technological scenarios). Students have to develop an interior design project that narrates and represents their ideation process using a range of methodologies and digital and non-digital media. During the research phase, the students must design printed layouts, videos and presentations to represent their project; at the same time, they collect case studies on preset boards that summarise the analysed projects and artefacts.
The expected results are an in-depth representation of the research analysis and a description of the concept phase. The final documents must include technical and analytical aspects, mainly in hard copy, and emotional and conceptual elements, represented through videos. The case studies have been explored in depth in several course steps and are a reference throughout the design phase. The rules provided for the layout and organisation of the material make it possible to obtain coherent papers in proportions and format for the final exam.
Upon completing the course, students have comprehensively understood interior design, material selection, and practical guidance on crafting and editing a thesis. This has equipped them with a method for effectively representing and communicating their projects
Nonlinear Alfvén waves, discontinuities, proton perpendicular acceleration, and magnetic holes/decreases in interplanetary space and the magnetosphere: intermediate shocks?
International audienceAlfvén waves, discontinuities, proton perpendicular acceleration and magnetic decreases (MDs) in interplanetary space are shown to be interrelated. Discontinuities are the phase-steepened edges of Alfvén waves. Magnetic decreases are caused by a diamagnetic effect from perpendicularly accelerated (to the magnetic field) protons. The ion acceleration is associated with the dissipation of phase-steepened Alfvén waves, presumably through the Ponderomotive Force. Proton perpendicular heating, through instabilities, lead to the generation of both proton cyclotron waves and mirror mode structures. Electromagnetic and electrostatic electron waves are detected as well. The Alfvén waves are thus found to be both dispersive and dissipative, conditions indicting that they may be intermediate shocks. The resultant "turbulence" created by the Alfvén wave dissipation is quite complex. There are both propagating (waves) and nonpropagating (mirror mode structures and MDs) byproducts. Arguments are presented to indicate that similar processes associated with Alfvén waves are occurring in the magnetosphere. In the magnetosphere, the "turbulence" is even further complicated by the damping of obliquely propagating proton cyclotron waves and the formation of electron holes, a form of solitary waves. Interplanetary Alfvén waves are shown to rapidly phase-steepen at a distance of 1AU from the Sun. A steepening rate of ~35 times per wavelength is indicated by Cluster-ACE measurements. Interplanetary (reverse) shock compression of Alfvén waves is noted to cause the rapid formation of MDs on the sunward side of corotating interaction regions (CIRs). Although much has been learned about the Alfvén wave phase-steepening processfrom space plasma observations, many facets are still not understood. Several of these topics are discussed for the interested researcher. Computer simulations and theoretical developments will be particularly useful in making further progress in this exciting new area
High resolution infrared spectra of bulge globular clusters: Liller~1 and NGC 6553
Using the NIRSPEC spectrograph at Keck II, we have obtained echelle spectra
covering the range 1.5-1.8um for 2 of the brightest giants in Liller 1 and NGC
6553, old metal rich globular clusters in the Galactic bulge. We use spectrum
synthesis for the abundance analysis, and find [Fe/H]=-0.3 +/- 0.2 and
[O/H]=+0.3 +/- 0.2 dex. The composition of the clusters is similar to that of
field stars in the bulge and is consistent with a sceanrio in which the
clusters formed early, with rapid enrichment. We have dificulty achieveing a
good fit to the spectrum of NGC 6553 using either the low or the high values
recently reported in the literature, unless unusually large, or no
alpha-element enhancements are adopted, respectively.Comment: To appear in the Astronomical Journal, March 200
The Temperature Scale of Metal-Rich M Giants Based on TiO Bands: Population Synthesis in the Near Infrared
We have computed a grid of high resolution synthetic spectra for cool stars
(2500<Teff<6000 K) in the wavelength range 6000 -- 10200A, by employing an
updated line list of atomic and molecular lines, together with state-of-the-art
model atmospheres.
As a by-product, by fitting TiO bandheads in spectra of well-known M giants,
we have derived the electronic oscillator strengths of the TiO gamma prime,
delta, epsilon and phi systems. The derived oscillator strenghts for the gamma
prime, epsilon and phi systems differ from the laboratory and ab initio values
found in the literature, but are consistent with the model atmospheres and line
lists employed, resulting in a good match to the observed spectra of M giants
of known parameters.
The behavior of TiO bands as a function of the stellar parameters Teff, log g
and [Fe/H] is presented and the use of TiO spectral indices in stellar
population studies is discussed.Comment: ApJ accepted, 27 pages + 11 figures, AASLatex v4.
- …