20,249 research outputs found
The Library and Remedial/Developmental/Compensatory Education: A Case Study
published or submitted for publicatio
Modelling of the fast rotating delta Scuti star Altair
We present an asteroseismic study of the fast rotating star HD187642
(Altair), recently discovered to be a delta Scuti pulsator. We have computed
models taking into account rotation for increasing rotational velocities. We
investigate the relation between the fundamental radial mode and the first
overtone in the framework of Petersen diagrams. The effects of rotation on such
diagrams, which become important at rotational velocities above 150 km/s, as
well as the domain of validity of our seismic tools are discussed. We also
investigate the radial and non-radial modes in order to constrain models
fitting the five most dominant observed oscillation modes.Comment: Accepted for publication in A&A (11 pages, 6 figures, 4 tables
The role of rotation on Petersen Diagrams. The period ratios
The present work explores the theoretical effects of rotation in calculating
the period ratios of double-mode radial pulsating stars with special emphasis
on high-amplitude delta Scuti stars (HADS). Diagrams showing these period
ratios vs. periods of the fundamental radial mode have been employed as a good
tracer of non-solar metallicities and are known as Petersen diagrams (PD).In
this paper we consider the effect of moderate rotation on both evolutionary
models and oscillation frequencies and we show that such effects cannot be
completely neglected as it has been done until now. In particular it is found
that even for low-to-moderate rotational velocities (15-50 km/s), differences
in period ratios of some hundredths can be found. The main consequence is
therefore the confusion scenario generated when trying to fit the metallicity
of a given star using this diagram without a previous knowledge of its
rotational velocity.Comment: A&A in pres
Student Conceptual Difficulties in Hydrodynamics
We describe a study on the conceptual difficulties faced by college students
in understanding hydrodynamics of ideal fluids. This study was based on
responses obtained in hundreds of written exams and oral interviews, which were
held with first-year Engineering and Science university students. Their
responses allowed us to identify a series of misconceptions unreported in the
literature so far. The study findings demonstrate that the most important
difficulties arise from the students' inability to establish a link between the
kinematics and dynamics of moving fluids, and from a lack of understanding
regarding how different regions of a system interact.Comment: 12 pages, 10 figures (small corrections
Recent high resolution laboratory determinations of line broadening and intensity parameters: PH3, CH3D, and CO2
Recent unpublished laboratory work on rovibrational line strengths and broadening coefficients which is of interest in the study of planetary atmospheres was reviewed. The molecules discussed are PH3, CH3D and CO2
Toroidal Carbon Nanotubes with Encapsulated Atomic Metal Loops
Toroidal carbon nanotubes can serve as hosts for encapsulated loops of atomic
metal wires. Such composite structures have been analyzed using density
functional theory for a semiconducting C torus encapsulating chains of
Fe, Au and Cu atoms. The sheathed metal necklaces form a zigzag structure and
drops the HOMO/LUMO bandgap to less than 0.1 eV. The iron composite is
ferromagnetic with a magnetic moment essentially the same as that of bcc iron.
The azimuthal symmetry of these toroidal composites suggests that they may
offer novel elecromagnetic properties not associated with straight,
metal-encapsulated carbon nanotubes.Comment: 6 pages, 9 figure
Local-global neural networks: a new approach for nonlinear time series modelling
In this paper, the Local Global Neural Networks model is proposed within the context of time series models. This formulation encompasses some already existing nonlinear models and also admits the Mixture of Experts approach. We place emphasis on the linear expert case and extensively discuss the theoretical aspects of the model: stationarity conditions, existence, consistency and asymptotic normality of the parameter estimates, and model identifiability. A model building strategy is also considered and the whole procedure is illustrated with two real time-series.neural networks, nonlinear models, time-series, model identifiability, parameter estimation, model building, sunspot number.
MODELING FARM AND OFF-FARM ECONOMIC LINKAGES TO ANALYZE THE IMPACTS OF AN AREA-WIDE INSECT MANAGEMENT PROGRAM ON A REGIONAL ECONOMY
This study evaluated the impacts of the boll weevil eradication program at the farm level and on the west Tennessee region. Budgets, an acreage response model, and an input-output model were used to evaluate direct and indirect program impacts. The program generates small but positive economic benefits for the region.Crop Production/Industries,
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