4,084 research outputs found
Universal Behavior in Large-scale Aggregation of Independent Noisy Observations
Aggregation of noisy observations involves a difficult tradeoff between
observation quality, which can be increased by increasing the number of
observations, and aggregation quality which decreases if the number of
observations is too large. We clarify this behavior for a protypical system in
which arbitrarily large numbers of observations exceeding the system capacity
can be aggregated using lossy data compression. We show the existence of a
scaling relation between the collective error and the system capacity, and show
that large scale lossy aggregation can outperform lossless aggregation above a
critical level of observation noise. Further, we show that universal results
for scaling and critical value of noise which are independent of system
capacity can be obtained by considering asymptotic behavior when the system
capacity increases toward infinity.Comment: 10 pages, 3 figure
A Geometrical Relationship between Broad-Line Clouds and an Accretion Disk around Active Galactic Nuclei
Recent hard X-ray spectroscopy of active galactic nuclei has strongly
suggested that double-peaked, very broad Fe K emission arises from an accretion
disk around the central engine. Model fitting of the observed Fe K emission
line profile makes it possible to estimate a probable inclination angle of the
accretion disk. In order to study the geometrical relationship between the
accretion disk and broad emission-line regions (BLRs), we investigate the
correlation between the inclination angle of the accretion disk and the
velocity width of BLRs for 18 type-1 Seyfert galaxies. We found that there may
be a negative correlation between them, i.e., Seyfert nuclei with a more
face-on accretion disk tend to have larger BLR velocity widths, suggesting that
the BLRs are not coplanar with respect to the accretion disk. The most probable
interpretation may be that the BLRs arise from outer parts ({\it r} 0.01
pc) of a warped accretion disk illuminated by the central engine.Comment: 11 pages, 3 figures; accepted for Publications of the Astronomical
Society of Japa
Magnetic Field Generation from Self-Consistent Collective Neutrino-Plasma Interactions
A new Lagrangian formalism for self-consistent collective neutrino-plasma
interactions is presented in which each neutrino species is described as a
classical ideal fluid. The neutrino-plasma fluid equations are derived from a
covariant relativistic variational principle in which finite-temperature
effects are retained. This new formalism is then used to investigate the
generation of magnetic fields and the production of magnetic helicity as a
result of collective neutrino-plasma interactions.Comment: 23 page
Field Quantization in 5D Space-Time with Z-parity and Position/Momentum Propagator
Field quantization in 5D flat and warped space-times with Z-parity is
comparatively examined. We carefully and closely derive 5D
position/momentum(P/M) propagators. Their characteristic behaviours depend on
the 4D (real world) momentum in relation to the boundary parameter () and
the bulk curvature (\om). They also depend on whether the 4D momentum is
space-like or time-like. Their behaviours are graphically presented and the
Z symmetry, the "brane" formation and the singularities are examined. It is
shown that the use of absolute functions is important for properly treating the
singular behaviour. The extra coordinate appears as a {\it directed} one like
the temperature. The problem, which is an important consistency
check of the bulk-boundary system, is solved {\it without} the use of
KK-expansion. The relation between P/M propagator (a closed expression which
takes into account {\it all} KK-modes) and the KK-expansion-series propagator
is clarified. In this process of comparison, two views on the extra space
naturally come up: orbifold picture and interval (boundary) picture.
Sturm-Liouville expansion (a generalized Fourier expansion) is essential there.
Both 5D flat and warped quantum systems are formulated by the Dirac's bra and
ket vector formalism, which shows the warped model can be regarded as a {\it
deformation} of the flat one with the {\it deformation parameter} \om. We
examine the meaning of the position-dependent cut-off proposed by
Randall-Schwartz.Comment: 44 figures, 22(fig.)+41 pages, to be published in Phys.Rev.D, Fig.4
is improve
Quark mass uncertainties revive KSVZ axion dark matter
The Kaplan-Manohar ambiguity in light quark masses allows for a larger
uncertainty in the ratio of up to down quark masses than naive estimates from
the chiral Lagrangian would indicate. We show that it allows for a relaxation
of experimental bounds on the QCD axion, specifically KSVZ axions in the eV mass range composing 100% of the galactic dark matter halo can evade the
experimental limits placed by the ADMX collaboration.Comment: 9 pages, 5 figure
Low-frequency local field potentials and spikes in primary visual cortex convey independent visual information
Local field potentials (LFPs) reflect subthreshold integrative processes that complement spike train measures. However, little is yet known about the differences between how LFPs and spikes encode rich naturalistic sensory stimuli. We addressed this question by recording LFPs and spikes from the primary visual cortex of anesthetized macaques while presenting a color movie.Wethen determined
how the power of LFPs and spikes at different frequencies represents the visual features in the movie.Wefound that the most informative LFP frequency ranges were 1– 8 and 60 –100 Hz. LFPs in the range of 12– 40 Hz carried little information about the stimulus, and may primarily reflect neuromodulatory inputs. Spike power was informative only at frequencies <12 Hz. We further quantified “signal
correlations” (correlations in the trial-averaged power response to different stimuli) and “noise correlations” (trial-by-trial correlations in the fluctuations around the average) of LFPs and spikes recorded from the same electrode. We found positive signal correlation between high-gamma LFPs (60 –100 Hz) and spikes, as well as strong positive signal correlation within high-gamma LFPs, suggesting that high-gamma LFPs and spikes are generated within the same network. LFPs<24 Hz shared strong positive noise correlations, indicating that they are influenced by a common source, such as a diffuse neuromodulatory input. LFPs<40 Hz showed very little signal and noise correlations with LFPs>40Hzand with spikes, suggesting that low-frequency LFPs reflect neural processes that in natural conditions are fully decoupled from those giving rise to spikes and to high-gamma LFPs
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Modeling reciprocal effects in medical research: critical discussion on the current practices and potential alternative models
Longitudinal designs provide a strong inferential basis for uncovering reciprocal effects or causality between variables. For this analytic purpose, a cross-lagged panel model (CLPM) has been widely used in medical research, but the use of the CLPM has recently been criticized in methodological literature because parameter estimates in the CLPM conflate between-person and within-person processes. The aim of this study is to present some alternative models of the CLPM that can be used to examine reciprocal effects, and to illustrate potential consequences of ignoring the issue. A literature search, case studies, and simulation studies are used for this purpose. We examined more than 300 medical papers published since 2009 that applied cross-lagged longitudinal models, finding that in all studies only a single model (typically the CLPM) was performed and potential alternative models were not considered to test reciprocal effects. In 49% of the studies, only two time points were used, which makes it impossible to test alternative models. Case studies and simulation studies showed that the CLPM and alternative models often produce different (or even inconsistent) parameter estimates for reciprocal effects, suggesting that research that relies only on the CLPM may draw erroneous conclusions about the presence, predominance, and sign of reciprocal effects. Simulation studies also showed that alternative models are sometimes susceptible to improper solutions, even when reseachers do not misspecify the model
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