3,251 research outputs found
ELF: The electronic learning facilitator
As the world‐wide computer network becomes ubiquitous, new tools have been developed, such as the World Wide Web (WWW), for the delivery of multimedia hypertext‐based documents. Similarly, there has been an explosion in the amount of email, bulletin boards, and Usenet News available. This has led to a major problem of information overload: we are slowly but surely being overwhelmed by the amount of information available to us
Feed system design and experimental results in the uhf model study for the proposed Urbana phased array
The effects of atmospheric turbulence and the basis for the coherent scatter radar techniques are discussed. The reasons are given for upgrading the Radar system to a larger steerable array. Phase array theory pertinent to the system design is reviewed, along with approximations for maximum directive gain and blind angles due to mutual coupling. The methods and construction techniques employed in the UHF model study are explained. The antenna range is described, with a block diagram for the mode of operation used
Proton Stability and Dark Matter in a Realistic String MSSM
We demonstrate the existence of an extra nonanomalous U(1) gauge symmetry in
a three-generation Pati-Salam model constructed with intersecting D6-branes in
Type IIA string theory on a T^6/(Z_2 \times Z_2) orientifold. This extra U(1)
forbids all dimension-4, 5, and 6 operators which mediate proton decay in the
MSSM. Moreover, this results in the effective promotion of baryon and lepton
number to local gauge symmetries, which can potentially result in leptophobic
and leptophilic bosons observable at the LHC. Furthermore, it is not
necessary to invoke R-parity to forbid the dimension-4 operators which allow
rapid proton decay. However, R-parity may arise naturally from a spontaneously
broken U(1)_{B-L}. Assuming the presence of R-parity, we then study the direct
detection cross-sections for neutralino dark matter, including the latest
constraints from the XENON100 experiment. We find that these limits are now
within required range necessary to begin testing the model.Comment: Expanded discussion of Z' boson phenomenology. Accepted for
publication to Physical Review D. arXiv admin note: text overlap with
arXiv:1103.603
Exact 1-D Model for Coherent Synchrotron Radiation with Shielding and Bunch Compression
Coherent Synchrotron Radiation has been studied effectively using a
1-dimensional model for the charge distribution in the realm of small angle
approximations and high energies. Here we use Jefimenko's form of Maxwell's
equations, without such approximations, to calculate the exact wake-fields due
to this effect in multiple bends and drifts. It has been shown before that the
influence of a drift can propagate well into a subsequent bend. We show, for
reasonable parameters, that the influence of a previous bend can also propagate
well into a subsequent bend, and that this is especially important at the
beginning of a bend. Shielding by conducting parallel plates is simulated using
the image charge method. We extend the formalism to situations with compressing
and decompressing distributions, and conclude that simpler approximations to
bunch compression usually overestimates the effect. Additionally, an exact
formula for the coherent power radiated by a Gaussian bunch is derived by
considering the coherent synchrotron radiation spectrum, and is used to check
the accuracy of wake-field calculations
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Memory in Autistic Spectrum Disorder
Behavioral evidence concerning memory in high-functioning forms of autism (HFA) and in moderately low-functioning autism (M-LFA) is reviewed and compared. Findings on M-LFA are sparse. However, it is provisionally concluded that memory profiles in HFA and M-LFA (relative to ability-matched controls) are similar, but that declarative memory impairments are more extensive in M-LFA than in HFA. Specifically, both groups have diminished memory for emotion- or person-related stimuli. Regarding memory for non-social stimuli, both groups probably have mental-age appropriate nondeclarative memory; and within declarative memory, both groups have mental-age appropriate immediate free recall of within-span or supra-span lists of unrelated items, as well as cued recall and paired associate learning. By contrast, recognition is largely unimpaired in HFA but moderately impaired in M-LFA; and free recall of meaningful or structured stimuli is moderately impaired in HFA but more severely impaired in M-LFA. Theoretical explanations of data on declarative memory in HFA identify problems in the integrative processing, or the consolidation and storage, of complex stimuli; or a specific problem of recollection. Proposed neural substrates include the following: disconnectivity of primary sensory and association areas; dysfunctions of medial prefrontal cortex, hippocampus or posterior parietal lobe; or combinations of these associated with neural disconnectivity. Hypothetically, perirhinal dysfunction might explain the more extensive declarative memory impairments in M-LFA. Foreseeable consequences of uneven memory abilities in HFA and M-LFA are outlined, including possible effects on language and learning in M-LFA. Finally, priorities for future research are identified, highlighting the urgent need for research on memory in lower-functioning individuals
Supergravity and Superstring Signatures of the One-Parameter Model at LHC
Many string constructions have a classical no-scale structure, resulting in a
one-parameter model (OPM) for the supersymmetry breaking soft terms. As a
highly constrained subset of mSUGRA, the OPM has the potential to be
predictive. Conversely, if the observed superpartner spectrum at LHC is a
subset of the OPM parameter space, then this may provide a clue to the
underlying theory at high energies. We investigate the allowed supersymmetry
parameter space for a generic one-parameter model taking into account the most
recent experimental constraints. We find that in the strict moduli scenario,
there are no regions of the parameter space which may satisfy all constraints.
However, for the dilaton scenario, there are small regions of the parameter
space where all constraints may be satisfied and for which the observed dark
matter density may be generated. We also survey the possible signatures which
may be observable at the Large Hadron Collider (LHC). Finally, we compare
collider signatures of OPM to those from a model with non-universal soft terms,
in particular those of an intersecting D6-brane model. We find that it may be
possible to distinguish between these diverse scenarios at LHC.Comment: 25 pages, 10 figures, accepted for publication in PR
Are infestations of Cymomelanodactylus killing Acropora cytherea in the Chagos archipelago?
Associations between branching corals and infaunal crabs are well
known, mostly due to the beneficial effects of Trapezia and Tetralia
crabs in protecting host corals from crown-of-thorns starfish (e.g.,
Pratchett et al. 2000) and/or sedimentation (Stewart et al. 2006).
These crabs are obligate associates of live corals and highly prevalent
across suitable coral hosts, with 1–2 individuals per colony
(Patton 1994). Cymo melanodactylus (Fig. 1) are also prevalent in
branching corals, mostly Acropora, and are known to feed on live
coral tissue, but are generally found in low abundance (<3 per
colony) and do not significantly affect their host corals (e.g., Patton
1994). In the Chagos archipelago, however, infestations of Cymo
melanodactylus were found on recently dead and dying colonies of
Acropora cytherea
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