7,165 research outputs found
A case study of effective practice in mathematics teaching and learning informed by Valsinerâs zone theory
The characteristics that typify an effective teacher of mathematics and the environments that support effective teaching practices have been a long-term focus of educational research. In this article we report on an aspect of a larger study that investigated âbest practiceâ in mathematics teaching and learning across all Australian states and territories. A case study from one Australian state was developed from data collected via classroom observations and semi-structured interviews with school leaders and teachers and analysed using Valsinerâs zone theory. A finding of the study is that âsuccessfulâ practice is strongly tied to school context and the cultural practices that have been developed by school leaders and teachers to optimise student learning opportunities. We illustrate such an alignment of school culture and practice through a vignette based on a case of one âsuccessfulâ school
Flash of photons from the early stage of heavy-ion collisions
The dynamics of partonic cascades may be an important aspect for particle
production in relativistic collisions of nuclei at CERN SPS and BNL RHIC
energies. Within the Parton-Cascade Model, we estimate the production of single
photons from such cascades due to scattering of quarks and gluons q g -> q
gamma, quark-antiquark annihilation q qbar -> g gamma, or gamma gamma, and from
electromagnetic brems-strahlung of quarks q -> q gamma. We find that the latter
QED branching process plays the dominant role for photon production, similarly
as the QCD branchings q -> q g and g -> g g play a crucial role for parton
multiplication. We conclude therefore that photons accompanying the parton
cascade evolution during the early stage of heavy-ion collisions shed light on
the formation of a partonic plasma.Comment: 4 pages including 3 postscript figure
Space station integrated wall design and penetration damage control. Task 3: Theoretical analysis of penetration mechanics
The efforts to provide a penetration code called PEN4 version 10 is documented for calculation of projectile and target states for the impact of 2024-T3 aluminum, R sub B 90 1018 steel projectiles and icy meteoroids onto 2024-T3 aluminum plates at impact velocities from 0 to 16 km/s. PEN4 determines whether a plate is perforated by calculating the state of fragmentation of projectile and first plate. Depth of penetration into the second to n sup th plate by fragments resulting from first plate perforation is determined by multiple cratering. The results from applications are given
Out of Equilibrium Non-perturbative Quantum Field Dynamics in Homogeneous External Fields
The quantum dynamics of the symmetry broken lambda (Phi^2)^2 scalar field
theory in the presence of an homogeneous external field is investigated in the
large N limit. We choose as initial state the ground state for a constant
external field J .The sign of the external field is suddenly flipped from
J to - J at a given time and the subsequent quantum dynamics calculated.
Spinodal instabilities and parametric resonances produce large quantum
fluctuations in the field components transverse to the external field. This
allows the order parameter to turn around the maximum of the potential for
intermediate times. Subsequently, the order parameter starts to oscillate near
the global minimum for external field - J, entering a novel quasi-periodic
regime.Comment: LaTex, 30 pages, 12 .ps figures, improved version to appear in Phys
Rev
Parton cascade description of relativistic heavy-ion collisions at CERN SPS energies ?
We examine Pb+Pb collisions at CERN SPS energy 158 A GeV, by employing the
earlier developed and recently refined parton-cascade/cluster-hadronization
model and its Monte Carlo implementation. This space-time model involves the
dynamical interplay of perturbative QCD parton production and evolution, with
non-perturbative parton-cluster formation and hadron production through cluster
decays. Using computer simulations, we are able to follow the entwined
time-evolution of parton and hadron degrees of freedom in both position and
momentum space, from the instant of nuclear overlap to the final yield of
particles. We present and discuss results for the multiplicity distributions,
which agree well with the measured data from the CERN SPS, including those for
K mesons. The transverse momentum distributions of the produced hadrons are
also found to be in good agreement with the preliminary data measured by the
NA49 and the WA98 collaboration for the collision of lead nuclei at the CERN
SPS. The analysis of the time evolution of transverse energy deposited in the
collision zone and the energy density suggests an existence of partonic matter
for a time of more than 5 fm.Comment: 16 pages including 7 postscript figure
Non-equilibrium dynamics in quantum field theory at high density: the tsunami
The dynamics of a dense relativistic quantum fluid out of thermodynamic
equilibrium is studied in the framework of the Phi^4 scalar field theory in the
large N limit. The time evolution of a particle distribution in momentum space
(the tsunami) is computed. The effective mass felt by the particles in such a
high density medium equals the tree level mass plus the expectation value of
the squared field. The case of negative tree level squared mass is particularly
interesting. In such case dynamical symmetry restoration as well as dynamical
symmetry breaking can happen. Furthermore, the symmetry may stay broken with
vanishing asymptotic squared mass showing the presence of out of equilibrium
Goldstone bosons. We study these phenomena and identify the set of initial
conditions that lead to each case. We compute the equation of state which turns
to depend on the initial state. Although the system does not thermalize, the
equation of state for asymptotically broken symmetry is of radiation type. We
compute the correlation functions at equal times. The two point correlator for
late times is the sum of different terms. One stems from the initial particle
distribution. Another term accounts for the out of equilibrium Goldstone bosons
created by spinodal unstabilities when the symmetry is asymptotically
broken.Both terms are of the order of the inverse of the coupling for distances
where causal signals can connect the two points. The contribution of the out of
equilibrium Goldstones exhibits scaling behaviour in a generalized sense.Comment: LaTex, 49 pages, 15 .ps figure
Inclusive Particle Spectra at RHIC
A simulation is performed of the recently reported data from PHOBOS at
energies of 56 and 130 A GeV using the relativistic heavy ion cascade LUCIFER
which had previously given a good description of the NA49 inclusive spectra at
E=17.2 A GeV. The results compare well with these early measurements at RHIC.Comment: 4 pages, 2 figure
Hydrogen-like Atoms from Ultrarelativistic Nuclear Collisions
The number of hydrogen-like atoms produced when heavy nuclei collide is
estimated for central collisions at the Relativistic Heavy Ion Collider using
the sudden approximation of Baym et al. As first suggested by Schwartz, a
simultaneous measurement of the hydrogen and hadron spectra will allow an
inference of the electron or muon spectra at low momentum where a direct
experimental measurement is not feasible.Comment: 6 pages, 4 figure
Multi-State Image Restoration by Transmission of Bit-Decomposed Data
We report on the restoration of gray-scale image when it is decomposed into a
binary form before transmission. We assume that a gray-scale image expressed by
a set of Q-Ising spins is first decomposed into an expression using Ising
(binary) spins by means of the threshold division, namely, we produce (Q-1)
binary Ising spins from a Q-Ising spin by the function F(\sigma_i - m) = 1 if
the input data \sigma_i \in {0,.....,Q-1} is \sigma_i \geq m and 0 otherwise,
where m \in {1,....,Q-1} is the threshold value. The effects of noise are
different from the case where the raw Q-Ising values are sent. We investigate
which is more effective to use the binary data for transmission or to send the
raw Q-Ising values. By using the mean-field model, we first analyze the
performance of our method quantitatively. Then we obtain the static and
dynamical properties of restoration using the bit-decomposed data. In order to
investigate what kind of original picture is efficiently restored by our
method, the standard image in two dimensions is simulated by the mean-field
annealing, and we compare the performance of our method with that using the
Q-Ising form. We show that our method is more efficient than the one using the
Q-Ising form when the original picture has large parts in which the nearest
neighboring pixels take close values.Comment: latex 24 pages using REVTEX, 10 figures, 4 table
Effect of baryon density on parton production, chemical equilibration and thermal photon emission from quark gluon plasma
The effect of baryon density on parton production processes of
and is studied
using full phase space distribution function and also with inclusion of quantum
statistics i.e. Pauli blocking and Bose enhancement factors, in the case of
both saturated and unsaturated quark gluon plasma. The rate for the process is found to be much less as compared to the most
commonly used factorized result obtained on the basis of classical
approximation. This discrepancy, which is found both at zero as well as at
finite baryon densities, however, is not due to the lack of quantum statistics
in the classical approximation, rather due to the use of Fermi-Dirac and
Bose-Einstein distribution functions for partons instead of Boltzmann
distribution which is appropriate under such approximation. Interestingly, the
rates of parton production are found to be insensitive to the baryo-chemical
potential particularly when the plasma is unsaturated although the process of
chemical equilibration strongly depends on it. The thermal photon yields, have
been calculated specifically from unsaturated plasma at finite baryon density.
The exact results obtained numerically are found to be in close agreement with
the analytic expression derived using factorized distribution functions
appropriate for unsaturated plasma. Further, it is shown that in the case of
unsaturated plasma, the thermal photon production is enhanced with increasing
baryon density both at fixed temperature and fixed energy density of the quark
gluon plasma.Comment: Latex, 24 pages, 6 postscript figures. Submitted to Phys. Rev.
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