15,650 research outputs found
Reference list for stability theory in ordinary differential equations
Reference list for stability and control theory in ordinary differential equation
Determination of Chilling Requirement of Arkansas Thornless Blackberry Cultivars
Little research has been done to determine the chilling requirement for blackberry cultivars. However, field observations from areas where fewer hours of chilling occur indicate that āNavahoā requires more hours of chilling than does āArapahoā. The objective of our study was to determine a method for measuring the chilling requirement using whole plants of two blackberry cultivars, Arapaho and Navaho. One-year old, bare-root plants were field-dug on 26 October 1999 and placed in a cold chamber at 3ĀŗC. Ten single-plant replications of each cultivar were removed at 100-hour intervals up to 1000 hours. The plants were potted and placed in a greenhouse (daily minimum temperature 15ĀŗC), and plants were arranged on benches in a completely randomized design. Budbreak was recorded on a weekly basis. Data for budbreak were analyzed as a two-factor factorial (2 cultivars and 10 chilling treatments) by SAS and means were separated by least significant difference (P = 0.05). Data indicated that the chilling requirement for Arapaho is between 400 and 500 hours. For Navaho, the data indicated the chilling requirement was between 800 and 900 hours. These data support previous observations and indicate that the method used was successful in determining the chilling requirement for blackberries
Bare quark stars or naked neutron stars? The case of RX J1856.5-3754
In a cool neutron star (T less than or similar to 10(6) K) endowed with a rather highmagnetic field (B greater than or similar to 10(13) G), a phase transition may occur in the outermost layers. As a consequence, the neutron star becomes "bare,'' i.e., no gaseous atmosphere sits on the top of the crust. The surface of a cooling, bare neutron star does not necessarily emit a blackbody spectrum because the emissivity is strongly suppressed at energies below the electron plasma frequency, omega(p). Since omega(p) approximate to 1 keV under the conditions typical of the dense electron gas in the condensate, the emission from a T similar to 100 eV bare neutron star will be substantially depressed with respect to that of a perfect Planckian radiator atmost energies. Here we present a detailed analysis of the emission properties of a bare neutron star. In particular, we derive the surface emissivity for an Fe composition in a range of magnetic fields and temperatures representative of cooling isolated neutron stars, like RX J1856.5 - 3754. We find that the emitted spectrum is strongly dependent on the electron conductivity in the solid surface layers. In the cold electron gas approximation ( no electron-lattice interactions), the spectrum turns out to be a featureless depressed blackbody in the 0.1 - 2 keV band with a steeper low-energy distribution. When damping effects due to collisions between electrons and the ion lattice ( mainly due to electron-phonon interactions) are accounted for, the spectrum is more depressed at low energies and spectral features may be present, depending on the magnetic field strength. Details of the emitted spectrum are found, however, to be strongly dependent on the assumed treatment of the transition from the external vacuum to the metallic surface. The implications of our results for RX J1856.5 - 3754 and other isolated neutron stars are discussed
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Inverse Geometry for Stereolithographic Manufacturing
As parts produced by stereolithography form and cure, they warp and shrink
to produce Pitrts that are not quite the san~ ~ as those originally specified. This
research attempts to solve the inverse geomptry problem, that is, what shape
should be specified initially so that the she pe produced is the desired one.
Assuming that 'the process is repeatable, we ~neasure the difference between the
ideal and actua). part dimensions. A finite-element based model is built which
mirrors the distortion from the ideal geometry. A "pre-deformed" geometry is
then built so that it deforms to the ideal geometry under the conditions imposed
on the finite element model. This pre-warped geometry is the geometry we seek.Mechanical Engineerin
An Information-Theoretic Approach to Optimize JWST Observations and Retrievals of Transiting Exoplanet Atmospheres
We provide an example of an analysis to explore the optimization of
observations of transiting hot jupiters with JWST to characterize their
atmospheres, based on a simple three-parameter forward model. We construct
expansive forward model sets for eleven hot jupiters, ten of which are
relatively well-characterized, exploring a range of parameters such as
equilibrium temperature and metallicity, as well as considering host stars over
a wide range in brightness. We compute posterior distributions of our model
parameters for each planet with all of the available JWST spectroscopic modes
and several programs of combined observations and compute their effectiveness
using the metric of estimated mutual information per degree of freedom. From
these simulations, clear trends emerge that provide guidelines for designing a
JWST observing program. We demonstrate that these guidelines apply over a wide
range of planet parameters and target brightnesses for our simple forward
model.Comment: Accepted to ApJ, 25 pages, 14 figures, 8 table
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