1,991 research outputs found
Can the Tajmar effect be explained using a modification of inertia?
The Tajmar effect is an unexplained acceleration observed by accelerometers
and laser gyroscopes close to rotating supercooled rings. The observed ratio
between the gyroscope and ring accelerations was 3+/-1.2x10^-8. Here, a new
model for inertia which has been tested quite successfully on the Pioneer and
flyby anomalies is applied to this problem. The model assumes that the inertia
of the gyroscope is caused by Unruh radiation that appears as the ring and the
fixed stars accelerate relative to it, and that this radiation is subject to a
Hubble-scale Casimir effect. The model predicts that the sudden acceleration of
the nearby ring causes a slight increase in the inertial mass of the gyroscope,
and, to conserve momentum in the reference frame of the spinning Earth, the
gyroscope rotates clockwise with an acceleration ratio of 1.8+/-0.25x10^-8 in
agreement with the observed ratio. However, this model does not explain the
parity violation seen in some of the gyroscope data. To test these ideas the
Tajmar experiment (setup B) could be exactly reproduced in the southern
hemisphere, since the model predicts that the anomalous acceleration should
then be anticlockwise.Comment: 9 pages, 1 figure. Accepted by EPL on the 4th December, 200
Preservice mathematics teachers’ professional noticing of students’ mathematical thinking with technology
The purpose of this study is to examine the ways in which preservice secondary mathematics teachers (PSMT) professionally notice middle school students’ mathematical thinking on a technology enhanced mathematical task. The middle school students’ work was captured as a videocase for PSMTs to examine. Findings show that every PSMT included a discussion of the middle school students’ interaction with the technology in their noticing prompts, demonstrating that PSMTs recognized that the middle school students’ mathematical understanding was tied to their interactions with the technology. Additionally, results from PSMTs’ justifications for their predictions of middle school students’ responses to the task, incorporated the middle school students language and described how the middle school students would interact with the technology
Neurophysiology
Contains reports on eight research projects.Bell Telephone Laboratories, Inc.Teagle Foundation, Inc.National Science Foundation (Grant GP-2495)National Institutes of Health (Grants MH-04737-04)National Institutes of Health (NB-04985-01)U. S. Air Force. Aeronautical Systems Division (Contract AF 33(615)-1747)U. S. Air Force. Cambridge Research Laboratories (Contract AF19(628)-3807)U. S. Air Force. Electronic Systems Division (Contract AF19(628)-4147)National Aeronautics and Space Administration (Grant NsG-496
Application of the Density Matrix Renormalization Group in momentum space
We investigate the application of the Density Matrix Renormalization Group
(DMRG) to the Hubbard model in momentum-space. We treat the one-dimensional
models with dispersion relations corresponding to nearest-neighbor hopping and
hopping and the two-dimensional model with isotropic nearest-neighbor
hopping. By comparing with the exact solutions for both one-dimensional models
and with exact diagonalization in two dimensions, we first investigate the
convergence of the ground-state energy. We find variational convergence of the
energy with the number of states kept for all models and parameter sets. In
contrast to the real-space algorithm, the accuracy becomes rapidly worse with
increasing interaction and is not significantly better at half filling. We
compare the results for different dispersion relations at fixed interaction
strength over bandwidth and find that extending the range of the hopping in one
dimension has little effect, but that changing the dimensionality from one to
two leads to lower accuracy at weak to moderate interaction strength. In the
one-dimensional models at half-filling, we also investigate the behavior of the
single-particle gap, the dispersion of spinon excitations, and the momentum
distribution function. For the single-particle gap, we find that proper
extrapolation in the number of states kept is important. For the spinon
dispersion, we find that good agreement with the exact forms can be achieved at
weak coupling if the large momentum-dependent finite-size effects are taken
into account for nearest-neighbor hopping. For the momentum distribution, we
compare with various weak-coupling and strong-coupling approximations and
discuss the importance of finite-size effects as well as the accuracy of the
DMRG.Comment: 15 pages, 11 eps figures, revtex
Nuclear safety policy working group recommendations on nuclear propulsion safety for the space exploration initiative
An interagency Nuclear Safety Working Group (NSPWG) was chartered to recommend nuclear safety policy, requirements, and guidelines for the Space Exploration Initiative (SEI) nuclear propulsion program. These recommendations, which are contained in this report, should facilitate the implementation of mission planning and conceptual design studies. The NSPWG has recommended a top-level policy to provide the guiding principles for the development and implementation of the SEI nuclear propulsion safety program. In addition, the NSPWG has reviewed safety issues for nuclear propulsion and recommended top-level safety requirements and guidelines to address these issues. These recommendations should be useful for the development of the program's top-level requirements for safety functions (referred to as Safety Functional Requirements). The safety requirements and guidelines address the following topics: reactor start-up, inadvertent criticality, radiological release and exposure, disposal, entry, safeguards, risk/reliability, operational safety, ground testing, and other considerations
Quantitative assessment of renal structural and functional changes in chronic kidney disease using multi-parametric magnetic resonance imaging
BACKGROUND:Multi-parametric magnetic resonance imaging (MRI) provides the potential for a more comprehensive non-invasive assessment of organ structure and function than individual MRI measures, but has not previously been comprehensively evaluated in chronic kidney disease (CKD).METHODS:We performed multi-parametric renal MRI in persons with CKD (n = 22, 61 ± 24 years) who had a renal biopsy and measured glomerular filtration rate (mGFR), and matched healthy volunteers (HV) (n = 22, 61 ± 25 years). Longitudinal relaxation time (T1), diffusion-weighted imaging, renal blood flow (phase contrast MRI), cortical perfusion (arterial spin labelling) and blood-oxygen-level-dependent relaxation rate (R2*) were evaluated.RESULTS:MRI evidenced excellent reproducibility in CKD (coefficient of variation
Beyond Hebb: Exclusive-OR and Biological Learning
A learning algorithm for multilayer neural networks based on biologically
plausible mechanisms is studied. Motivated by findings in experimental
neurobiology, we consider synaptic averaging in the induction of plasticity
changes, which happen on a slower time scale than firing dynamics. This
mechanism is shown to enable learning of the exclusive-OR (XOR) problem without
the aid of error back-propagation, as well as to increase robustness of
learning in the presence of noise.Comment: 4 pages RevTeX, 2 figures PostScript, revised versio
The Road to Servomechanisms: The Influence of Cybernetics on Hayek from the Sensory Order to the Social Order
Multiscale Computations on Neural Networks: From the Individual Neuron Interactions to the Macroscopic-Level Analysis
We show how the Equation-Free approach for multi-scale computations can be
exploited to systematically study the dynamics of neural interactions on a
random regular connected graph under a pairwise representation perspective.
Using an individual-based microscopic simulator as a black box coarse-grained
timestepper and with the aid of simulated annealing we compute the
coarse-grained equilibrium bifurcation diagram and analyze the stability of the
stationary states sidestepping the necessity of obtaining explicit closures at
the macroscopic level. We also exploit the scheme to perform a rare-events
analysis by estimating an effective Fokker-Planck describing the evolving
probability density function of the corresponding coarse-grained observables
Interactions among mitochondrial proteins altered in glioblastoma
Mitochondrial dysfunction is putatively central to glioblastoma (GBM) pathophysiology but there has been no systematic analysis in GBM of the proteins which are integral to mitochondrial function. Alterations in proteins in mitochondrial enriched fractions from patients with GBM were defined with label-free liquid chromatography mass spectrometry. 256 mitochondrially-associated proteins were identified in mitochondrial enriched fractions and 117 of these mitochondrial proteins were markedly (fold-change ≥2) and significantly altered in GBM (p ≤ 0.05). Proteins associated with oxidative damage (including catalase, superoxide dismutase 2, peroxiredoxin 1 and peroxiredoxin 4) were increased in GBM. Protein–protein interaction analysis highlighted a reduction in multiple proteins coupled to energy metabolism (in particular respiratory chain proteins, including 23 complex-I proteins). Qualitative ultrastructural analysis in GBM with electron microscopy showed a notably higher prevalence of mitochondria with cristolysis in GBM. This study highlights the complex mitochondrial proteomic adjustments which occur in GBM pathophysiology
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