54,284 research outputs found
About the chemical composition of delta Scuti - the prototype of the class of pulsating variables
We present chemical abundances in the photosphere of Scuti -- the
prototype of the class of pulsating variables -- determined from the analysis
of a spectrum obtained at Terskol observatory 2 meter telescope with resolution
, signal to noise ratio 250. VLT and IUE spectra were used also .
Abundance pattern of \dsct consists of 49 chemical elements. The abundances of
Be, P, Ge, Nb, Mo, Ru, Er, Tb, Dy, Tm, Yb, Lu, Hf, Ta, Os, Pt, Th were not
investigated previously. The lines of third spectra of Pr and Nd also are
investigated for the first time. The abundances of heavy elements show the
overabundances with respect to the Sun up to 1 dex. The abundance pattern of
\dsct is similar to that of Am-Fm stars.Comment: 8 pages, 2 figures, subm. to Proc. of IAU Symp. 22
Linear multistep methods for integrating reversible differential equations
This paper studies multistep methods for the integration of reversible
dynamical systems, with particular emphasis on the planar Kepler problem. It
has previously been shown by Cano & Sanz-Serna that reversible linear
multisteps for first-order differential equations are generally unstable. Here,
we report on a subset of these methods -- the zero-growth methods -- that evade
these instabilities. We provide an algorithm for identifying these rare
methods. We find and study all zero-growth, reversible multisteps with six or
fewer steps. This select group includes two well-known second-order multisteps
(the trapezoidal and explicit midpoint methods), as well as three new
fourth-order multisteps -- one of which is explicit. Variable timesteps can be
readily implemented without spoiling the reversibility. Tests on Keplerian
orbits show that these new reversible multisteps work well on orbits with low
or moderate eccentricity, although at least 100 steps/radian are required for
stability.Comment: 31 pages, 9 figures, in press at The Astronomical Journa
Anxiety and Learning in Dynamic and Static Clock Game Experiments
In clock games, agents receive differently-timed private signals when an asset value is above its fundamental. The price crashes to
the fundamental when K of N agents have decided to sell. If selling decisions are private, bubbles can be sustained because people
delay selling, after receiving signals, knowing that others will delay too. Our results replicate the main features of the one previous
experimental study of clock game (in two subject pools): Selling delays are shorter than predicted, but converge toward equilibrium
predictions over repeated trials. We also find that delays are shorter in a dynamic game in which selling decisions unfold over time,
compared to a static equivalent in which subjects precommit to selling decisions. A model of learning with growing anxiety after
signal arrival can reproduce the empirical observations of shorter-than-predicted delay, smaller delay after later signal arrival, and
shorter delays in dynamic games
Analysis of edge impact stresses in composite plates
The in-plane edge impact of composite plates, with or without a protection strip, is investigated. A computational analysis based on the Fast Fourier Transform technique is presented. The particular application of the present method is in the understanding of the foreign object damage problem of composite fan blades. The method is completely general and may be applied to the study of other stress wave propagation problems in a half space. Results indicate that for the protective strip to be effective in reducing impact stresses in the composite the thickness must be equal or greater than the impact contact dimension. Large interface shear stresses at the strip - composite boundary can be induced under impact
An experimental study of coupling between combustor pressure, fuel/air mixing, and the flame
Fuel-air mixing behavior under the influence of imposed acoustic oscillations has been studied by investigating the response of the fuel mixture fraction field. The distribution of local fuel mixture fraction inside the mixing zone, which is expected to evolve into the local equivalence ratio in the flame zone, is closely coupled to unstable and oscillatory flame behavior. The Experiment was performed with an aerodynamically-stabilized non-premixed burner. In this study, acoustic oscillations were imposed at 22, 27, 32, 37, and 55Hz. Phase-resolved acetone PLIF was used to image the flow field of both isothermal and reacting flow cases and this data along with the derived quantities of temporal and spatial unmixedness were employed for analysis. The behavior of the unmixedness factor is compared with the previous measurements of oscillations in the flame zone. This comparison shows that local oscillations (of order millimeters or smaller) in fuel/air mixing are closely related to the oscillatory behavior of the flame. For each driving frequency, the mixture fraction oscillates at that frequency but with a slight phase difference between it and the pressure field/flame intensity, indicating that the fuel mixture fraction oscillation are likely the major reason for oscillatory behaviors of this category of flames and combustor geometry
Neutrino Oscillations and Lepton Flavor Mixing
In view of the recent announcement on non-zero neutrino mass from
Super-Kamiokande experiment, it would be very timely to investigate all the
possible scenarios on masses and mixings of light neutrinos. Recently suggested
mass matrix texture for the quark CKM mixing, which can be originated from the
family permutation symmetry and its suitable breakings, is assumed for the
neutrino mass matrix and determined by the four combinations of solar,
atmospheric and LSND neutrino data and cosmological hot dark matter bound as
input constraints. The charged-lepton mass matrix is assumed to be diagonal so
that the neutrino mixing matrix can be identified directly as the lepton flavor
mixing matrix and no CP invariance violation originates from the leptonic
sector. The results favor hierarchical patterns for the neutrino masses, which
follow from the case when either solar-atmospheric data or solar-HDM
constraints are used.Comment: Latex, 9 page
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