12,502 research outputs found
Demand for Multimedia in the Classroom: Do Students and Faculty Really Want it All?
Teaching/Communication/Extension/Profession,
Demand for Multimedia in the Classroom
This study elicits preferences for multimedia in the classroom for students and faculty members in agricultural economics. Employing an Internet-based conjoint ranking survey, the results show that students prefer multimedia instructional tools over a traditional chalkboard/whiteboard lecture format while faculty members do not. Neither students nor faculty members are enthusiastic about electronic textbooks, and students will accept them only if they save $80. Finally, preferences for multimedia are shown to differ with students who self-report differing note-taking abilities, preferences for chalkboard lectures, and the need for an engaging class. Successful multimedia adoption requires appropriate use and lowering costs for students.conjoint ranking, instruction, microeconomics, multimedia instruction, valuation, Demand and Price Analysis, Financial Economics, Institutional and Behavioral Economics, Research and Development/Tech Change/Emerging Technologies, Teaching/Communication/Extension/Profession, A22, Q19,
Improving Quantum Query Complexity of Boolean Matrix Multiplication Using Graph Collision
The quantum query complexity of Boolean matrix multiplication is typically
studied as a function of the matrix dimension, n, as well as the number of 1s
in the output, \ell. We prove an upper bound of O (n\sqrt{\ell}) for all values
of \ell. This is an improvement over previous algorithms for all values of
\ell. On the other hand, we show that for any \eps < 1 and any \ell <= \eps
n^2, there is an \Omega(n\sqrt{\ell}) lower bound for this problem, showing
that our algorithm is essentially tight.
We first reduce Boolean matrix multiplication to several instances of graph
collision. We then provide an algorithm that takes advantage of the fact that
the underlying graph in all of our instances is very dense to find all graph
collisions efficiently
Evolved stars in the Local Group galaxies. I. AGB evolution and dust production in IC 1613
We used models of thermally-pulsing asymptotic giant branch (AGB) stars, that
also describe the dust-formation process in the wind, to interpret the
combination of near- and mid-infrared photometric data of the dwarf galaxy IC
1613. This is the first time that this approach is extended to an environment
different from the Milky Way and the Magellanic Clouds (MCs). Our analysis,
based on synthetic population techniques, shows a nice agreement between the
observations and the expected distribution of stars in the colour-magnitude
diagrams obtained with JHK and Spitzer bands. This allows a characterization of
the individual stars in the AGB sample in terms of mass, chemical composition,
and formation epoch of the progenitors. We identify the stars exhibiting the
largest degree of obscuration as carbon stars evolving through the final AGB
phases, descending from 1-1.25Msun objects of metallicity Z=0.001 and from
1.5-2.5Msun stars with Z=0.002. Oxygen-rich stars constitute the majority of
the sample (65%), mainly low mass stars (<2Msun) that produce a negligible
amount of dust (<10^{-7}Msun/yr). We predict the overall dust-production rate
from IC 1613, mostly determined by carbon stars, to be 6x10^{-7}Msun/yr with an
uncertainty of 30%. The capability of the current generation of models to
interpret the AGB population in an environment different from the MCs opens the
possibility to extend this kind of analysis to other Local Group galaxies.Comment: 14 pages, 6 figures, accepted for publication on MNRA
Some Heuristic Semiclassical Derivations of the Planck Length, the Hawking Effect and the Unruh Effect
The formulae for Planck length, Hawking temperature and Unruh-Davies
temperature are derived by using only laws of classical physics together with
the Heisenberg principle. Besides, it is shown how the Hawking relation can be
deduced from the Unruh relation by means of the principle of equivalence; the
deep link between Hawking effect and Unruh effect is in this way clarified.Comment: LaTex file, 6 pages, no figure
Hydrodynamic reductions of the heavenly equation
We demonstrate that Pleba\'nski's first heavenly equation decouples in
infinitely many ways into a triple of commuting (1+1)-dimensional systems of
hydrodynamic type which satisfy the Egorov property. Solving these systems by
the generalized hodograph method, one can construct exact solutions of the
heavenly equation parametrized by arbitrary functions of a single variable. We
discuss explicit examples of hydrodynamic reductions associated with the
equations of one-dimensional nonlinear elasticity, linearly degenerate systems
and the equations of associativity.Comment: 14 page
Generating anisotropic fluids from vacuum Ernst equations
Starting with any stationary axisymmetric vacuum metric, we build anisotropic
fluids. With the help of the Ernst method, the basic equations are derived
together with the expression for the energy-momentum tensor and with the
equation of state compatible with the field equations. The method is presented
by using different coordinate systems: the cylindrical coordinates
and the oblate spheroidal ones. A class of interior solutions matching with
stationary axisymmetric asymptotically flat vacuum solutions is found in oblate
spheroidal coordinates. The solutions presented satisfy the three energy
conditions.Comment: Version published on IJMPD, title changed by the revie
On the nature of the most obscured C-rich AGB stars in the Magellanic Clouds
The stars in the Magellanic Clouds with the largest degree of obscuration are
used to probe the highly uncertain physics of stars in the asymptotic giant
branch (AGB) phase of evolution. Carbon stars in particular, provide key
information on the amount of third dredge-up (TDU) and mass loss. We use two
independent stellar evolution codes to test how a different treatment of the
physics affects the evolution on the AGB. The output from the two codes are
used to determine the rates of dust formation in the circumstellar envelope,
where the method used to determine the dust is the same for each case. The
stars with the largest degree of obscuration in the LMC and SMC are identified
as the progeny of objects of initial mass and , respectively. This difference in mass is motivated by the
difference in the star formation histories of the two galaxies, and offers a
simple explanation of the redder infrared colours of C-stars in the LMC
compared to their counterparts in the SMC. The comparison with the Spitzer
colours of C-rich AGB stars in the SMC shows that a minimum surface carbon mass
fraction must have been reached by stars of initial
mass around . Our results confirm the necessity of adopting
low-temperature opacities in stellar evolutionary models of AGB stars. These
opacities allow the stars to obtain mass-loss rates high enough () to produce the amount of dust needed to reproduce the
Spitzer coloursComment: 14 pages, 5 figures, 1 table; accepted for publication in MNRAS Main
Journa
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