285 research outputs found
Impact of the Algebra I End of Course Examination on African American Students Obtaining a Standard High School Diploma
The state of Florida requires all students complete Algebra I and pass the End of Course Examination (EOCE) to graduate with a standard high school diploma. Algebra I EOCE results indicate that many African American students do not pass the examination. This research sought to determine if there is a relationship between African American students’ failure to pass the Algebra I EOCE and graduate with a standard diploma. Four hypotheses, null and alternative were tested. Two ninth-grade cohorts, 2013-2014 and 2014-2015 comprised the sample. Data were analyzed using t test and one-way analyses of variance (ANOVA). Results indicate a significant relationship between African American students’ failure to pass the Algebra I EOCE and graduation with a standard high school diploma
Bianchi type II models in the presence of perfect fluid and anisotropic dark energy
Spatially homogeneous but totally anisotropic and non-flat Bianchi type II
cosmological model has been studied in general relativity in the presence of
two minimally interacting fluids; a perfect fluid as the matter fluid and a
hypothetical anisotropic fluid as the dark energy fluid. The Einstein's field
equations have been solved by applying two kinematical ans\"{a}tze: we have
assumed the variation law for the mean Hubble parameter that yields a constant
value of deceleration parameter, and one of the components of the shear tensor
has been considered proportional to the mean Hubble parameter. We have
particularly dwelled on the accelerating models with non-divergent expansion
anisotropy as the Universe evolves. Yielding anisotropic pressure, the fluid we
consider in the context of dark energy, can produce results that can be
produced in the presence of isotropic fluid in accordance with the \Lambda CDM
cosmology. However, the derived model gives additional opportunities by being
able to allow kinematics that cannot be produced in the presence of fluids that
yield only isotropic pressure. We have obtained well behaving cases where the
anisotropy of the expansion and the anisotropy of the fluid converge to finite
values (include zero) in the late Universe. We have also showed that although
the metric we consider is totally anisotropic, the anisotropy of the dark
energy is constrained to be axially symmetric, as long as the overall energy
momentum tensor possesses zero shear stress.Comment: 15 pages; 5 figures; matches the version published in The European
Physical Journal Plu
Towards a formalism for mapping the spacetimes of massive compact objects: Bumpy black holes and their orbits
Observations have established that extremely compact, massive objects are
common in the universe. It is generally accepted that these objects are black
holes. As observations improve, it becomes possible to test this hypothesis in
ever greater detail. In particular, it is or will be possible to measure the
properties of orbits deep in the strong field of a black hole candidate (using
x-ray timing or with gravitational-waves) and to test whether they have the
characteristics of black hole orbits in general relativity. Such measurements
can be used to map the spacetime of a massive compact object, testing whether
the object's multipoles satisfy the strict constraints of the black hole
hypothesis. Such a test requires that we compare against objects with the
``wrong'' multipole structure. In this paper, we present tools for constructing
bumpy black holes: objects that are almost black holes, but that have some
multipoles with the wrong value. The spacetimes which we present are good deep
into the strong field of the object -- we do not use a large r expansion,
except to make contact with weak field intuition. Also, our spacetimes reduce
to the black hole spacetimes of general relativity when the ``bumpiness'' is
set to zero. We propose bumpy black holes as the foundation for a null
experiment: if black hole candidates are the black holes of general relativity,
their bumpiness should be zero. By comparing orbits in a bumpy spacetime with
those of an astrophysical source, observations should be able to test this
hypothesis, stringently testing whether they are the black holes of general
relativity. (Abridged)Comment: 16 pages + 2 appendices + 3 figures. Submitted to PR
Strings in Homogeneous Background Spacetimes
The string equations of motion for some homogeneous (Kantowski-Sachs, Bianchi
I and Bianchi IX) background spacetimes are given, and solved explicitly in
some simple cases. This is motivated by the recent developments in string
cosmology, where it has been shown that, under certain circumstances, such
spacetimes appear as string-vacua.
Both tensile and null strings are considered. Generally, it is much simpler
to solve for the null strings since then we deal with the null geodesic
equations of General Relativity plus some additional constraints.
We consider in detail an ansatz corresponding to circular strings, and we
discuss the possibility of using an elliptic-shape string ansatz in the case of
homogeneous (but anisotropic) backgrounds.Comment: 25 pages, REVTE
Two-Loop Helicity Amplitudes for Quark-Quark Scattering in QCD and Gluino-Gluino Scattering in Supersymmetric Yang-Mills Theory
We present the two-loop QCD helicity amplitudes for quark-quark and
quark-antiquark scattering. These amplitudes are relevant for
next-to-next-to-leading order corrections to (polarized) jet production at
hadron colliders. We give the results in the `t Hooft-Veltman and
four-dimensional helicity (FDH) variants of dimensional regularization and
present the scheme dependence of the results. We verify that the finite
remainder, after subtracting the divergences using Catani's formula, are in
agreement with previous results. We also provide the amplitudes for
gluino-gluino scattering in pure N=1 supersymmetric Yang-Mills theory. We
describe ambiguities in continuing the Dirac algebra to D dimensions, including
ones which violate fermion helicity conservation. The finite remainders after
subtracting the divergences using Catani's formula, which enter into physical
quantities, are free of these ambiguities. We show that in the FDH scheme, for
gluino-gluino scattering, the finite remainders satisfy the expected
supersymmetry Ward identities.Comment: arXiv admin note: substantial text overlap with arXiv:hep-ph/030416
Two-Loop Helicity Amplitudes for Quark-Gluon Scattering in QCD and Gluino-Gluon Scattering in Supersymmetric Yang-Mills Theory
We present the two-loop QCD helicity amplitudes for quark-gluon scattering,
and for quark-antiquark annihilation into two gluons. These amplitudes are
relevant for next-to-next-to-leading order corrections to (polarized) jet
production at hadron colliders. We give the results in the `t Hooft-Veltman and
four-dimensional helicity (FDH) variants of dimensional regularization. The
transition rules for converting the amplitudes between the different variants
are much more intricate than for the previously discussed case of gluon-gluon
scattering. Summing our two-loop expressions over helicities and colors, and
converting to conventional dimensional regularization, gives results in
complete agreement with those of Anastasiou, Glover, Oleari and Tejeda-Yeomans.
We describe the amplitudes for 2 to 2 scattering in pure N=1 supersymmetric
Yang-Mills theory, obtained from the QCD amplitudes by modifying the color
representation and multiplicities, and verify supersymmetry Ward identities in
the FDH scheme.Comment: 77 pages. v2: corrected errors in eqs. (3.7) and (3.8) for one-loop
assembly; remaining results unaffecte
Supermassive Binaries and Extragalactic Jets
Some quasars show Doppler shifted broad emission line peaks. I give new
statistics of the occurrence of these peaks and show that, while the most
spectacular cases are in quasars with strong radio jets inclined to the line of
sight, they are also almost as common in radio-quiet quasars. Theories of the
origin of the peaks are reviewed and it is argued that the displaced peaks are
most likely produced by the supermassive binary model. The separations of the
peaks in the 3C 390.3-type objects are consistent with orientation-dependent
"unified models" of quasar activity. If the supermassive binary model is
correct, all members of "the jet set" (astrophysical objects showing jets)
could be binaries.Comment: 31 pages, PostScript, missing figure is in ApJ 464, L105 (see
http://www.aas.org/ApJ/v464n2/5736/5736.html
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