4,047 research outputs found
Utilizing the Contextual Learning Model at the Plattsburgh State Art Museum
Inspired by the work of John Falk and Lynn Dierking, this article examines the characteristics of contextual learning at the Plattsburgh State Museum. It investigates the museum visitors\u27 experiences and process of learning through the lens of the Contextual Learning Model.
The purpose of this thesis is twofold: 1) to suggest a method for understanding the museum visitor experience, 2) and to demonstrate that visitor learning is fundamentally a meaning-making activity that involves a constant negotiation between the stories given by museums and those brought by visitors. As such, it is emphasized that museums can be effective educators if they recognize and honor the process of meaning-making
Analytical investigation of the effects of blade flexibility, unsteady aerodynamics, and variable inflow on helicopter rotor stall characteristics
Analytical investigation of effects of blade flexibility, unsteady aerodynamics, and variable inflow on helicopter rotor stall characteristic
Experimental investigation of model variable-geometry and ogee tip rotors
An experimental investigation was conducted to systematically explore the effects of inter-blade spatial relationships and pitch variations on rotor performance and wake geometry. Variable-geometry rotors consisting of various combinations of blade length, axial spacing, azimuth spacing, and collective pitch were tested at model scale in hover and forward flight. In addition, a hover test of a model rotor with an ogee blade tip design was conducted to determine its performance and wake characteristics. The results of this investigation indicate that properly selected variable geometry rotor configurations can offer substantial improvements in hover performance without adversely affecting forward flight performance. Axial spacing of alternate blades was found to provide the greatest performance benefit, and further improvements were achieved by combining azimuth spacing with axial spacing. The performance benefit appears to be related to the relief of local adverse aerodynamic phenomena produced by vortex interference. The ogee tip design was found to substantially reduce the concentrated core intensity of the tip vortex, and could thus prove beneficial for the relief of blade-vortex interaction problems. However, the ogee tip was found to reduce hover performance at model scale
Studies on the Occurrence and Elemental Composition of Bacteria in Freshwater Plankton
The occurrence and cation content of bacteria in a eutrophic freshwater lake (Rostherne Mere, Cheshire, UK) were investigated over a one year sampling period in relation to cation changes in the lake surface water and phytoplankton.
Scanning electron microscope examination of trawl-net and filtered samples demonstrated bacterial association with Anabaena, Aphanizomenon and diatoms. Direct counts of associated and unassociated bacteria showed that increases in bacterial population relate to population decline of major algal constituents.
Spectrophotometric determination of selected cation levels in the lake water demonstrated wide fluctuations throughout the sampling period, with elevated levels of transition metals before and at the end of Summer stratification. Zn and Pb also showed increased levels in relation to episodic events.
Mass fractions of spectrophotometrically-determined selected cations (Fe, Cu, Zn and Pb) in phytoplankton also varied considerably during the sampling period, with major increases apparently following peaks in water level.
X-ray microanalysis of whole, unassociated bacterial eel ls demonstrated high levels of soluble and bound cations, including K, Ca, Fe, Cu, Ni, Zn and Pb. Changes in the cation levels of bacteria did not follow a similar pattern to the general phytoplankton - probably due to differences in uptake or adsorption or to cycling of bacterial cells in the water column
Improved asteroseismic inversions for red-giant surface rotation rates
Asteroseismic observations of internal stellar rotation have indicated a
substantial lack of angular momentum transport in theoretical models of
subgiant and red-giant stars. Accurate core and surface rotation rate
measurements are therefore needed to constrain internal transport processes
included in the models. We eliminate substantial systematic errors of
asteroseismic surface rotation rates found in previous studies. We propose a
new objective function for the Optimally Localized Averages method of
rotational inversions for red-giant stars, which results in more accurate
envelope rotation rate estimates obtained from the same data. We use synthetic
observations from stellar models across a range of evolutionary stages and
masses to demonstrate the improvement. We find that our new inversion technique
allows us to obtain estimates of the surface rotation rate that are independent
of the core rotation. For a star at the base of the red-giant branch, we reduce
the systematic error from about 20% to a value close to 0, assuming constant
envelope rotation. We also show the equivalence between this method and the
method of linearised rotational splittings. Our new rotational inversion method
substantially reduces the systematic errors of red-giant surface rotation
rates. In combination with independent measures of the surface rotation rate,
this will allow better constraints to be set on the internal rotation profile.
This will be a very important probe to further constrain the internal angular
momentum transport along the lower part of the red-giant branch.Comment: 17 pages, 22 figures, accepted for publication in Astronomy and
Astrophysic
Variability of Blue Supergiants in the LMC with TESS
The blue supergiant problem, namely the overabundance of blue supergiants
(BSGs) inconsistent with classical stellar evolution theory, remains an open
question in stellar astrophysics. Several theoretical explanations have been
proposed, which may be tested by their predictions for the characteristic time
variability. In this work, we analyze the light curves of a sample of 20 BSGs
obtained from the Transiting Exoplanet Survey Satellite (TESS) mission. We
report a characteristic signal in the low-frequency
() range for all our targets. The power spectra
has a peak frequency at , and we are able to fit it
by a modified Lorentzian profile. The signal itself shows strong stochasticity
across different TESS sectors, suggesting its driving mechanism happens on
short () timescales. Our signals resemble those
obtained for a limited sample of hotter OB stars and yellow supergiants,
suggesting their possible common origins. We discuss three possible physical
explanations: stellar winds launched by rotation, convection motions that reach
the stellar surface, and waves from the deep stellar interior. The peak
frequency of the signal favors processes related to convection caused by the
iron opacity peak, and the shape of the spectra might be explained by the
propagation of high-order, damped gravity waves. We discuss the uncertainties
and limitations of all these scenarios.Comment: submitted to ApJ, comments welcom
Observational predictions for Thorne-\.Zytkow objects
Thorne-ytkow objects (TO) are potential end products of the merger
of a neutron star with a non-degenerate star. In this work, we have computed
the first grid of evolutionary models of TOs with the MESA stellar
evolution code. With these models, we predict several observational properties
of TOs, including their surface temperatures and luminosities, pulsation
periods, and nucleosynthetic products. We expand the range of possible TO
solutions to cover and
. Due to the much
higher densities our TOs reach compared to previous models, if TOs
form we expect them to be stable over a larger mass range than previously
predicted, without exhibiting a gap in their mass distribution. Using the GYRE
stellar pulsation code we show that TOs should have fundamental pulsation
periods of 1000--2000 days, and period ratios of 0.2--0.3. Models
computed with a large 399 isotope fully-coupled nuclear network show a
nucleosynthetic signal that is different to previously predicted. We propose a
new nucleosynthetic signal to determine a star's status as a TO: the
isotopologues and , which will
have a shift in their spectral features as compared to stable
titanium-containing molecules. We find that in the local Universe (~SMC
metallicities and above) TOs show little heavy metal enrichment,
potentially explaining the difficulty in finding TOs to-date.Comment: 17 pages, 16 figures, 3 Tables, Sumbitedd to MNRAS, Zenodo data
available https://doi.org/10.5281/zenodo.453442
Asteroseismic sensitivity to internal rotation along the red-giant branch
Transport of angular momentum in stellar interiors is currently not well
understood. Asteroseismology can provide us with estimates of internal rotation
of stars and thereby advances our understanding of angular momentum transport.
We can measure core-rotation rates in red-giant stars and we can place upper
bounds on surface-rotation rates using measurements of dipole () modes.
Here, we aim to determine the theoretical sensitivity of modes of different
spherical degree towards the surface rotation. Additionally, we aim to identify
modes that can potentially add sensitivity at intermediate radii. We used
asteroseismic rotational inversions to probe the internal stellar rotation
profiles in red-giant models from the base of the red-giant branch up to the
luminosity bump. We used the inversion method of multiplicative optimally
localised averages (MOLA) to assess how well internal and surface rotation
rates can be recovered from different mode sets and different synthetic
rotation profiles. We confirm that dipole mixed modes are sufficient to set
constraints on the average core-rotation rates in red giants. However,
surface-rotation rates estimated with only dipole mixed modes are contaminated
by the core rotation. We show that the sensitivity to the surface rotation
decreases from the base of the red-giant branch until it reaches a minimum at
0.6-0.8 due to a glitch in the buoyancy frequency. Thereafter a
narrow range of increased surface sensitivity just below the bump luminosity
exists. Quadrupole and octopole modes have more sensitivity in the outer parts
of the star. If observed, quadrupole and octopole modes enable us to
distinguish between differential and solid body rotation in the convection
zone. To obtain accurate estimates of rotation rates at intermediate radii,
acoustic oscillation modes with a spherical degree of are needed.Comment: accepted for publication in Astronomy and Astrophysics, revised
manuscript after language editin
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