795 research outputs found
Scaffolding Discourse in Asynchronous Learning Networks
Discourse, a form of collaborative learning, is fundamentally a communications process. This in-progress study adapts Clark and Brennan’s grounding in communications principles to investigate how to “scaffold” asynchronous discourse. Scaffolding is defined as providing support for the learner at his or her level until the support is no longer needed. This paper presents early results from an experimental study measuring learning effectiveness. In the experiment, content and process scaffolding are manipulated based on pedagogic principles. A major contribution of the study is building and testing a technologymediated, discourse-centered, teaching and learning model called the Asynchronous Learning Networks Cognitive Discourse Model (ALNCDM). As discourse is one of the most widely used online methods of teaching and learning, the results of the study are expected to add to the body of knowledge on how to structure asynchronous online discourse assignments for more effective student learning
Wilson Loops in N=2 Super-Yang-Mills from Matrix Model
We compute the expectation value of the circular Wilson loop in N=2
supersymmetric Yang-Mills theory with N_f=2N hypermultiplets. Our results
indicate that the string tension in the dual string theory scales as the
logarithm of the 't Hooft coupling.Comment: 37 pages, 9 figures; v2: Numerical factors corrected, simple
derivation of Wilson loop and discussion of continuation to complex lambda
added; v3: instanton partition function re-analyzed in order to take into
account a contribution of the hypermultiplet
AGT on the S-duality Wall
Three-dimensional gauge theory T[G] arises on a domain wall between
four-dimensional N=4 SYM theories with the gauge groups G and its S-dual G^L.
We argue that the N=2^* mass deformation of the bulk theory induces a
mass-deformation of the theory T[G] on the wall. The partition functions of the
theory T[SU(2)] and its mass-deformation on the three-sphere are shown to
coincide with the transformation coefficient of Liouville one-point conformal
block on torus under the S-duality.Comment: 14 pages, 3 figures. v2: Revised the analysis in sections 3.3 and 4.
Notes and references added. Version to appear in JHE
Signal-to-noise measurements utilizing a novel dual-energy multimedia detector
Dual-energy measurements are presented utilizing a novel slot-scan digital radiographic imaging detector, operating on gaseous solid state ionization principles. The novel multimedia detector has two basic functional components: a noble gas-filled detector volume operating on gas microstrip principles, and a solid state detector volume. The purpose of this study is to investigate the potential use of this multimedia detector for enhanced dual-energy imaging. The experimental results indicate that the multimedia detector exhibits a large subtracted signal-to-noise ratio. Although the intrinsic merit of this device is being explored for medical imaging, potential applications of the multimedia detector technology in other industrial areas, such as aerospace imaging, aviation security, and surveillance, are also very promising
Nickel oxalate dihydrate nanorods attached to reduced graphene oxide sheets as a high-capacity anode for rechargeable lithium batteries
In the search for high-capacity anode materials, a facile hydrothermal route has been developed to synthesize phase-pure NiC2O4·2H2O nanorods, which were crystallized into the orthorhombic structure without using templates. To ensure the electrical conductivity of the nanorods, the produced NiC2O4·2H2O nanorods were attached to reduced graphene oxide (rGO) sheets via self-assembly layer-by-layer processes that utilize the electrostatic adsorption that occurs in a poly(diallyldimethylammonium chloride) solution. The high electrical conductivity aided by the presence of rGO significantly improved the electrochemical properties: 933 mAh g−1 for the charge capacity (oxidation), which showed 87.5% efficiency at the first cycle with a retention of approximately 85% for 100 cycles, and 586 mAh g−1 at 10 C-rates (10 A g−1) for the NiC2O4·2H2O/rGO electrode. The lithium storage processes were involved in the conversion reaction, which were fairly reversible via a transformation to Ni metal accompanied by the formation of a lithium oxalate compound upon discharge (reduction) and restoration to the original NiC2O4·2H2O upon charging (oxidation); this was confirmed via X-ray diffraction, transmission electron microscopy, X-ray photoelectron microscopy and time-of-flight secondary ion mass spectroscopy. We believe that the high rate capacity and rechargeability upon cycling are the result of the unique features of the highly crystalline NiC2O4·2H2O nanorods assisted by conducting rGOs
A note on perturbation series in supersymmetric gauge theories
Exact results in supersymmetric Chern-Simons and N=2 Yang-Mills theories can
be used to examine the quantum behavior of observables and the structure of the
perturbative series. For the U(2) x U(2) ABJM model, we determine the
asymptotic behavior of the perturbative series for the partition function and
write it as a Borel transform. Similar results are obtained for N=2 SU(2) super
Yang-Mills theory with four fundamental flavors and in N=2* super Yang-Mills
theory, for the partition function as well as for the expectation values for
Wilson loop and 't Hooft loop operators (in the 0 and 1 instanton sectors). In
all examples, one has an alternate perturbation series where the coefficient of
the nth term increases as n!, and the perturbation series are Borel summable.
We also calculate the expectation value for a Wilson loop operator in the N=2*
SU(N) theory at large N in different regimes of the 't Hooft gauge coupling and
mass parameter. For large masses, the calculation reproduces the running gauge
coupling for the pure N=2 SYM theory.Comment: 28 pages. V2: minor additions and reference adde
TRIS I: Absolute Measurements of the Sky Brightness Temperature at 0.6, 0.82 and 2.5 GHz
At frequencies close to 1 GHz the sky diffuse radiation is a superposition of
radiation of Galactic origin, the 3 K Relic or Cosmic Microwave Background
Radiation, and the signal produced by unresolved extragalactic sources. Because
of their different origin and space distribution the relative importance of the
three components varies with frequency and depends on the direction of
observation. With the aim of disentangling the components we built TRIS, a
system of three radiometers, and studied the temperature of the sky at , and GHz using geometrically scaled antennas
with identical beams (HPBW = ). Observations
included drift scans along a circle at constant declination
which provided the dependence of the sky signal on the
Right Ascension, and absolute measurement of the sky temperature at selected
points along the same scan circle. TRIS was installed at Campo Imperatore (lat.
= N, long.= , elevation = 2000 m a.s.l.) in
Central Italy, close to the Gran Sasso Laboratory.Comment: Accepted for publication in The Astrophysical Journa
Affine sl(N) conformal blocks from N=2 SU(N) gauge theories
Recently Alday and Tachikawa proposed a relation between conformal blocks in
a two-dimensional theory with affine sl(2) symmetry and instanton partition
functions in four-dimensional conformal N=2 SU(2) quiver gauge theories in the
presence of a certain surface operator. In this paper we extend this proposal
to a relation between conformal blocks in theories with affine sl(N) symmetry
and instanton partition functions in conformal N=2 SU(N) quiver gauge theories
in the presence of a surface operator. We also discuss the extension to
non-conformal N=2 SU(N) theories.Comment: 40 pages. v2: minor changes and clarification
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