6,871 research outputs found
Tracking Transfer of Reform Methodology from Science and Math College Courses to the Teaching Style of Beginning Teachers of Grades 5-12
The purpose of this study was to determine if reformed science and math courses at community colleges and the university were impacting education majors as they began a teaching career. The reformed courses, in contrast to typical lecture classes, implemented inquiry-based methods that emphasized deep understanding of fundamental science and math concepts. Trained evaluators, utilizing the Reformed Teaching Observation Protocol (RTOP) gathered a total of 86 classroom observations to gauge the level of reform that beginning teachers (one to three yearsâ teaching experience) were implementing in grades 5-12. The pre-service experience of the beginning teachers varied from having had zero to four reform courses. Results indicated that teachers who had completed reform college courses instructed in a signiïŹcantly more reformed manner. Furthermore, analysis of years of teaching experience revealed that, while both control and experimental groups achieved higher RTOP scores as they progressed from year to year, the experimental group significantly outpaced their counterparts
Hydrodynamic Simulations of Counterrotating Accretion Disks
Hydrodynamic simulations have been used to study accretion disks consisting
of counterrotating components with an intervening shear layer(s).
Configurations of this type can arise from the accretion of newly supplied
counterrotating matter onto an existing corotating disk. The grid-dependent
numerical viscosity of our hydro code is used to simulate the influence of a
turbulent viscosity of the disk. Firstly, we consider the case where the gas
well above the disk midplane rotates with angular rate +\Omega(r) and that well
below has the same properties but rotates with rate -\Omega(r). We find that
there is angular momentum annihilation in a narrow equatorial boundary layer in
which matter accretes supersonically with a velocity which approaches the
free-fall velocity and the average accretion speed of the disk can be
enormously larger than that for a conventional \alpha-disk rotating in one
direction. Secondly, we consider the case of a corotating accretion disk for
rr_t. In this case we observed, that
matter from the annihilation layer lost its stability and propagated inward
pushing matter of inner regions of the disk to accrete. Thirdly, we
investigated the case where counterrotating matter inflowing from large radial
distances encounters an existing corotating disk. Friction between the
inflowing matter and the existing disk is found to lead to fast boundary layer
accretion along the disk surfaces and to enhanced accretion in the main disk.
These models are pertinent to the formation of counterrotating disks in
galaxies and possibly in Active Galactic Nuclei and in X-ray pulsars in binary
systems.Comment: LaTeX, 18 pages, to appear in Ap
Effect of in-plane magnetic field on magnetic phase transitions in nu=2 bilayer quantum Hall systems
By using the effective bosonic spin theory, which is recently proposed by
Demler and Das Sarma [ Phys. Rev. Lett. 82, 3895 (1999) ], we analyze the
effect of an external in-plane magnetic field on the magnetic phase transitions
of the bilayer quantum Hall system at filling factor nu=2. It is found that the
quantum phase diagram is modified by the in-plane magnetic field. Therefore,
quantum phase transitions can be induced simply by tilting the magnetic field.
The general behavior of the critical tilted angle for different layer
separations and interlayer tunneling amplitudes is shown. We find that the
critical tilted angles being calculated agree very well with the reported
values. Moreover, a universal critical exponent for the transition from the
canted antiferromagnetic phase to the ferromagnetic phase is found to be equal
to 1/2 within the present effective theory.Comment: RevTeX, 4 pages with 3 EPS figures include
Doubly Enhanced Skyrmions in Bilayer Quantum Hall States
By tilting the samples in the magnetic field, we measured and compared the
Skyrmion excitations in the bilayer quantum Hall (QH) state at the Landau-level
filling factor and in the monolayer QH state at . The observed
number of flipped spins is in the bilayer system with a large
tunneling gap, and in the bilayer system with a small tunneling gap,
while it is in the monolayer system. The difference is interpreted due
to the interlayer exchange interaction. Moreover, we have observed seemingly
preferred numbers for the flipped spins by tilting bilayer
samples.Comment: 4 pages, 4 figure
Finite-temperature phase transitions in bilayer quantum Hall systems
In this paper, the influence of an in-plane magnetic field B_\parallel on the
finite-temperature phase transitions in nu=2 bilayer quantum Hall systems are
examined. It is found that there can exist two types of finite-temperature
phase transitions. The first is the Kosterlitz-Thouless (KT) transitions, which
can have an unusual non-monotonic dependence on B_\parallel; the second type
originates from the crossing of energy levels and always increases with
B_\parallel. Based on these results, we point out that the threshold
temperature observed in the inelastic light scattering experiments cannot be
the KT transition temperature, because the latter shows a totally different
B_\parallel-dependence as compared with the experimental observation. Instead,
it should be the level-crossing temperature, which we found agrees with the
B_\parallel-dependence observed. Moreover, combining the knowledge of these two
transition temperatures, a complete finite-temperature phase diagram is
presented.Comment: RevTeX, 5 pages with 3 EPS figures include
First-Principles Computation of YVO3; Combining Path-Integral Renormalization Group with Density-Functional Approach
We investigate the electronic structure of the transition-metal oxide YVO3 by
a hybrid first-principles scheme. The density-functional theory with the
local-density-approximation by using the local muffin-tin orbital basis is
applied to derive the whole band structure. The electron degrees of freedom far
from the Fermi level are eliminated by a downfolding procedure leaving only the
V 3d t2g Wannier band as the low-energy degrees of freedom, for which a
low-energy effective model is constructed. This low-energy effective
Hamiltonian is solved exactly by the path-integral renormalization group
method. It is shown that the ground state has the G-type spin and the C-type
orbital ordering in agreement with experimental indications. The indirect
charge gap is estimated to be around 0.7 eV, which prominently improves the
previous estimates by other conventional methods
Spin mapping, phase diagram, and collective modes in double layer quantum Hall systems at
An exact spin mapping is identified to simplify the recently proposed
hard-core boson description (Demler and Das Sarma, Phys. Rev. Lett., to be
published) of the bilayer quantum Hall system at filling factor 2. The
effective spin model describes an easy-plane ferromagnet subject to an external
Zeeman field. The phase diagram of this effective model is determined exactly
and found to agree with the approximate calculation of Demler and Das Sarma,
while the Goldstone-mode spectrum, order parameter stiffness and
Kosterlitz-Thouless temperature in the canted antiferromagnetic phase are
computed approximately.Comment: 4 pages with 2 figures include
Interferometric 12CO(J=2-1) image of the Nuclear Region of Seyfert 1 Galaxy NGC 1097
We have mapped the central region of the Seyfert 1 galaxy NGC 1097 in
12CO(J=2-1) with the Submillieter Array (SMA). The 12CO(J=2-1) map shows a
central concentration and a surrounding ring, which coincide respectively with
the Seyfert nucleus and a starburst ring. The line intensity peaks at the
nucleus, whereas in a previously published 12CO(J=1-0) map the intensity peaks
at the starburst ring. The molecular ring has an azimuthally averaged
12CO(J=2-1)/(J=1-0) intensity ratio (R21) of about unity, which is similar to
those in nearby active star forming galaxies, suggesting that most of the
molecular mass in the ring is involved in fueling the starburst. The molecular
gas can last for only about 1.2\times10^8 years without further replenishment
assuming a constant star formation rate and a perfect conversion of gas to
stars. The velocity map shows that the central molecular gas is rotating with
the molecular ring in the same direction, while its velocity gradient is much
steeper than that of the ring. This velocity gradient of the central gas is
similar to what is usually observed in some Seyfert 2 galaxies. To view the
active nucleus directly in the optical, the central molecular gas structure can
either be a low-inclined disk or torus but not too low to be less massive than
the mass of the host galaxy itself, be a highly-inclined thin disk or clumpy
and thick torus, or be an inner part of the galactic disk. The R21 value of
~1.9 of the central molecular gas component, which is significantly higher than
the value found at the molecular gas ring, indicates that the activity of the
Seyfert nucleus may have a significant influence on the conditions of the
molecular gas in the central component.Comment: 22 pages, 4 figures, accepted by Ap
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