2,148 research outputs found
Active Learning for Undirected Graphical Model Selection
This paper studies graphical model selection, i.e., the problem of estimating
a graph of statistical relationships among a collection of random variables.
Conventional graphical model selection algorithms are passive, i.e., they
require all the measurements to have been collected before processing begins.
We propose an active learning algorithm that uses junction tree representations
to adapt future measurements based on the information gathered from prior
measurements. We prove that, under certain conditions, our active learning
algorithm requires fewer scalar measurements than any passive algorithm to
reliably estimate a graph. A range of numerical results validate our theory and
demonstrates the benefits of active learning.Comment: AISTATS 201
A towing system for a sensing package: Experiences and plans
The development of a technique for towing standard oceanographic sensors (pressure, temperature, conductivity, and sound velocity) at intermediate depths of less than 1000 m is described. Data show the depth characteristics of the tow and the comparative output from each of the sensors...
On the existence of stationary states during granular compaction
When submitted to gentle mechanical taps a granular packing slowly compacts
until it reaches a stationary state that depends on the tap characteristics.
The properties of such stationary states are experimentally investigated. The
influence of the initial state, taps properties and tapping protocol are
studied. The compactivity of the packings is determinated. Our results strongly
support the idea that the stationary states are genuine thermodynamic states.Comment: to be published in EPJE. The original publication will be available
at www.europhysj.or
Analysis by x-ray microtomography of a granular packing undergoing compaction
Several acquisitions of X-ray microtomography have been performed on a beads
packing while it compacts under vertical vibrations. An image analysis allows
to study the evolution of the packing structure during its progressive
densification. In particular, the volume distribution of the pores reveals a
large tail, compatible to an exponential law, which slowly reduces as the
system gets more compact. This is quite consistent, for large pores, with the
free volume theory. These results are also in very good agreement with those
obtained by a previous numerical model of granular compaction.Comment: 4 pages, 4 figures. Latex (revtex4). to be published in Phys. Rev.
Outcomes of coronary artery bypass graft surgery
This review article summarizes the major studies that have investigated the outcomes of coronary artery bypass graft surgery (CABG). The article includes a review of the literature in the areas of: history of CABG; indications for CABG; and measurement of quality of life following CABG, including prolongation of life, physical functioning (ie, relief from angina and dyspnea, physical activity, as well as complications of surgery and re-hospitalization), psychological functioning, and social functioning. Overall, the literature demonstrates that the outcomes of CABG have historically been measured in terms of mortality and morbidity; however, it has now been well recognized that adjustment to CABG is a multidimensional phenomenon that is not fully explained by medical factors. Therefore, in addition to studying mortality and morbidity outcomes following CABG, many recent studies have identified that it is important to investigate various physical, psychological, and social variables that have a significant impact on post-operative adjustment to CABG
Quenching of the radio jet during the X-ray high state of GX 339-4
We have observed the black hole candidate X-ray binary GX 339-4 at radio
wavelengths before, during and after the 1998 high/soft X-ray state transition.
We find that the radio emission from the system is strongly correlated with the
hard X-ray emission and is reduced by a factor > 25 during the high/soft state
compared to the more usual low/hard state. At the points of state transition we
note brief periods of unusually optically-thin radio emission which may
correspond to discrete ejection events. We propose that in the low/hard state
black hole X-ray binaries produce a quasi-continuous outflow, in the high/soft
state this outflow is suppressed, and that state transitions often result in
one or more discrete ejection events. Future models for low/hard states, such
as ADAF/ADIOS solutions, need to take into account strong outflow of
relativistic electrons from the system. We propose that the inferred
Comptonising corona and the base of the jet-like outflow are the same thing,
based upon the strong correlation between radio and hard X-ray emission in GX
339-4 and other X-ray binaries, and the similarity in inferred location and
composition of these two components.Comment: Accepted for publication in ApJ Letter
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