774 research outputs found
Anticipatory eye movements evoked after active following versus passive observation of a predictable motion stimulus.
We used passive and active following of a predictable smooth pursuit stimulus in order to establish if predictive eye movement responses are equivalent under both passive and active conditions. The smooth pursuit stimulus was presented in pairs that were either âpredictableâ in which both presentations were matched in timing and velocity, or ârandomizedâ in which each presentation in the pair was varied in both timing and velocity. A visual cue signaled the type of response required from the subject; a green cue indicated the subject should follow both the target presentations (Go-Go), a pink cue indicated that the subject should passively observe the 1st target and follow the 2nd target (NoGo-Go), and finally a green cue with a black cross revealed a randomized (Rnd) trial in which the subject should follow both presentations. The results revealed better prediction in the Go-Go trials than in the NoGo-Go trials, as indicated by higher anticipatory velocity and earlier eye movement onset (latency). We conclude that velocity and timing information stored from passive observation of a moving target is diminished when compared to active following of the target. This study has significant consequences for understanding how visuomotor memory is generated, stored and subsequently released from short-term memory
Supersymmetric Unification Without Low Energy Supersymmetry And Signatures for Fine-Tuning at the LHC
The cosmological constant problem is a failure of naturalness and suggests
that a fine-tuning mechanism is at work, which may also address the hierarchy
problem. An example -- supported by Weinberg's successful prediction of the
cosmological constant -- is the potentially vast landscape of vacua in string
theory, where the existence of galaxies and atoms is promoted to a vacuum
selection criterion. Then, low energy SUSY becomes unnecessary, and
supersymmetry -- if present in the fundamental theory -- can be broken near the
unification scale. All the scalars of the supersymmetric standard model become
ultraheavy, except for a single finely tuned Higgs. Yet, the fermions of the
supersymmetric standard model can remain light, protected by chiral symmetry,
and account for the successful unification of gauge couplings. This framework
removes all the difficulties of the SSM: the absence of a light Higgs and
sparticles, dimension five proton decay, SUSY flavor and CP problems, and the
cosmological gravitino and moduli problems. High-scale SUSY breaking raises the
mass of the light Higgs to about 120-150 GeV. The gluino is strikingly long
lived, and a measurement of its lifetime can determine the ultraheavy scalar
mass scale. Measuring the four Yukawa couplings of the Higgs to the gauginos
and higgsinos precisely tests for high-scale SUSY. These ideas, if confirmed,
will demonstrate that supersymmetry is present but irrelevant for the hierarchy
problem -- just as it has been irrelevant for the cosmological constant problem
-- strongly suggesting the existence of a fine-tuning mechanism in nature.Comment: Typos and equations fixed, references adde
Surveying Standard Model Flux Vacua on
We consider the SU(2)LxSU(2)R Standard Model brane embedding in an
orientifold of T6/Z2xZ2. Within defined limits, we construct all such Standard
Model brane embeddings and determine the relative number of flux vacua for each
construction. Supersymmetry preserving brane recombination in the hidden sector
enables us to identify many solutions with high flux. We discuss in detail the
phenomenology of one model which is likely to dominate the counting of vacua.
While Kahler moduli stabilization remains to be fully understood, we define the
criteria necessary for generic constructions to have fixed moduli.Comment: 30 pages, LaTeX, v2: added reference
Embedding Flipped SU(5) into SO(10)
We embed the flipped SU(5) models into the SO(10) models. After the SO(10)
gauge symmetry is broken down to the flipped SU(5) \times U(1)_X gauge
symmetry, we can split the five/one-plets and ten-plets in the spinor
\mathbf{16} and \mathbf{\bar{16}} Higgs fields via the stable sliding singlet
mechanism. As in the flipped SU(5) models, these ten-plet Higgs fields can
break the flipped SU(5) gauge symmetry down to the Standard Model gauge
symmetry. The doublet-triplet splitting problem can be solved naturally by the
missing partner mechanism, and the Higgsino-exchange mediated proton decay can
be suppressed elegantly. Moreover, we show that there exists one pair of the
light Higgs doublets for the electroweak gauge symmetry breaking. Because there
exist two pairs of additional vector-like particles with similar
intermediate-scale masses, the SU(5) and U(1)_X gauge couplings can be unified
at the GUT scale which is reasonably (about one or two orders) higher than the
SU(2)_L \times SU(3)_C unification scale. Furthermore, we briefly discuss the
simplest SO(10) model with flipped SU(5) embedding, and point out that it can
not work without fine-tuning.Comment: RevTex4, 28 pages, 3 figures, typos correcte
Electron momentum distribution in underdoped cuprates
We investigate the electron momentum distribution function (EMD) in a weakly
doped two-dimensional quantum antiferromagnet (AFM) as described by the t-J
model. Our analytical results for a single hole in an AFM based on the
self-consistent Born approximation (SCBA) indicate an anomalous momentum
dependence of EMD showing 'hole pockets' coexisting with a signature of an
emerging large Fermi surface. The position of the incipient Fermi surface and
the structure of the EMD is determined by the momentum of the ground state. Our
analysis shows that this result remains robust in the presence of next-nearest
neighbor hopping terms in the model. Exact diagonalization results for small
clusters are with the SCBA reproduced quantitatively.Comment: 5 pages, submitted to PR
Ageârelated changes in the biophysical and morphological characteristics of mouse cochlear outer hair cells
Outer hair cells (OHCs) are electromotile sensory receptors that provide sound amplification within the mammalian cochlea. Although OHCs appear susceptible to ageing, the progression of the pathophysiological changes in these cells is still poorly understood. By using mouse strains with a different progression of hearing loss (C57BL/6J, C57BL/6NTac, C57BL/6NTacCdh23+ , C3H/HeJ), we have identified morphological, physiological and molecular changes in ageing OHCs (9â12 kHz cochlear region). We show that by 6 months of age, OHCs from all strains underwent a reduction in surface area, which was not a sign of degeneration. Although the ageing OHCs retained a normal basolateral membrane protein profile, they showed a reduction in the size of the K+ current and nonâlinear capacitance, a readout of prestinâdependent electromotility. Despite these changes, OHCs have a normal V m and retain the ability to amplify sound, as distortion product otoacoustic emission thresholds were not affected in aged, goodâhearing mice (C3H/HeJ, C57BL/6NTacCdh23+ ). The loss of afferent synapses was present in all strains at 15 months. The number of efferent synapses per OHCs, defined as postsynaptic SK2 puncta, was reduced in aged OHCs of all strains apart from C3H mice. Several of the identified changes occurred in aged OHCs from all mouse strains, thus representing a general trait in the pathophysiological progression of ageârelated hearing loss, possibly aimed at preserving functionality. We have also shown that the mechanoelectrical transduction (MET) current from OHCs of mice harbouring the Cdh23ahl allele is reduced with age, highlighting the possibility that changes in the MET apparatus could play a role in cochlear ageing
TomograPy: A Fast, Instrument-Independent, Solar Tomography Software
Solar tomography has progressed rapidly in recent years thanks to the
development of robust algorithms and the availability of more powerful
computers. It can today provide crucial insights in solving issues related to
the line-of-sight integration present in the data of solar imagers and
coronagraphs. However, there remain challenges such as the increase of the
available volume of data, the handling of the temporal evolution of the
observed structures, and the heterogeneity of the data in multi-spacecraft
studies.
We present a generic software package that can perform fast tomographic
inversions that scales linearly with the number of measurements, linearly with
the length of the reconstruction cube (and not the number of voxels) and
linearly with the number of cores and can use data from different sources and
with a variety of physical models: TomograPy
(http://nbarbey.github.com/TomograPy/), an open-source software freely
available on the Python Package Index. For performance, TomograPy uses a
parallelized-projection algorithm. It relies on the World Coordinate System
standard to manage various data sources. A variety of inversion algorithms are
provided to perform the tomographic-map estimation. A test suite is provided
along with the code to ensure software quality. Since it makes use of the
Siddon algorithm it is restricted to rectangular parallelepiped voxels but the
spherical geometry of the corona can be handled through proper use of priors.
We describe the main features of the code and show three practical examples
of multi-spacecraft tomographic inversions using STEREO/EUVI and STEREO/COR1
data. Static and smoothly varying temporal evolution models are presented.Comment: 21 pages, 6 figures, 5 table
Nucleon-deuteron elastic scattering as a tool to probe properties of three-nucleon forces
Faddeev equations for elastic Nd scattering have been solved using modern NN
forces combined with the Tucson-Melbourne two-pion exchange three-nucleon
force, with a modification thereof closer to chiral symmetry and the Urbana IX
three-nucleon force. Theoretical predictions for the differential cross section
and several spin observables using NN forces only and NN forces combined with
three-nucleon force models are compared to each other and to the existing data.
A wide range of energies from 3 to 200 MeV is covered. Especially at the higher
energies striking three-nucleon force effects are found, some of which are
supported by the still rare set of data, some are in conflict with data and
thus very likely point to defects in those three-nucleon force models.Comment: 30 pages, 14 Postscript figures; now minor changes in figures and
reference
in NonCommutative Standard Model
We study the top quark decay to b quark and W boson in the NonCommutative
Standard Model (NCSM). The lowest contribution to the decay comes from the
terms quadratic in the matrix describing the noncommutative (NC) effects while
the linear term is seen to identically vanish because of symmetry. The NC
effects are found to be significant only for low values of the NC
characteristic scale.Comment: 11 page Latex file containing 2 eps figures (redrawn). More
discussion included. To appear in PR
Spectral functions, Fermi surface and pseudogap in the t-J model
Spectral functions within the generalized t-J model as relevant to cuprates
are analyzed using the method of equations of motion for projected fermion
operators. In the evaluation of the self energy the decoupling of spin and
single-particle fluctuations is performed. It is shown that in an undoped
antiferromagnet (AFM) the method reproduces the selfconsistent Born
approximation. For finite doping with short range AFM order the approximation
evolves into a paramagnon contribution which retains large incoherent
contribution in the hole part of the spectral function as well as the
hole-pocket-like Fermi surface at low doping. On the other hand, the
contribution of (longitudinal) spin fluctuations, with the coupling mostly
determined predominantly by J and next-neighbor hopping t', is essential for
the emergence of the pseudogap. The latter shows at low doping in the effective
truncation of the large Fermi surface, reduced electron density of states and
at the same time quasiparticle density of states at the Fermi level.Comment: RevTex, 13 pages, 11 figures (5 color
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