37,599 research outputs found
Learning When Training Data are Costly: The Effect of Class Distribution on Tree Induction
For large, real-world inductive learning problems, the number of training
examples often must be limited due to the costs associated with procuring,
preparing, and storing the training examples and/or the computational costs
associated with learning from them. In such circumstances, one question of
practical importance is: if only n training examples can be selected, in what
proportion should the classes be represented? In this article we help to answer
this question by analyzing, for a fixed training-set size, the relationship
between the class distribution of the training data and the performance of
classification trees induced from these data. We study twenty-six data sets
and, for each, determine the best class distribution for learning. The
naturally occurring class distribution is shown to generally perform well when
classifier performance is evaluated using undifferentiated error rate (0/1
loss). However, when the area under the ROC curve is used to evaluate
classifier performance, a balanced distribution is shown to perform well. Since
neither of these choices for class distribution always generates the
best-performing classifier, we introduce a budget-sensitive progressive
sampling algorithm for selecting training examples based on the class
associated with each example. An empirical analysis of this algorithm shows
that the class distribution of the resulting training set yields classifiers
with good (nearly-optimal) classification performance
Through the Eye of the Beholder: Multiple Perspectives on Quality in Women\u27s Health Care
Quality is an illusive concept with different meanings to different people. Providers often define quality in terms of patient outcomes, professional standards of practice, predetermined criteria used to measure quality, and even subjective opinion. Patients describe quality in terms of the interpersonal aspects of care, how well they were treated, and the responsiveness of the provider to their needs. This qualitative study using a semi-structured interview defined quality from the perspectives of patients, physicians, nurses, and payers associated with a hospital-based women\u27s service line, and how the attributes of quality varied among the multiple groups. The study also described how stakeholders become aware of quality and how they determined a hospital\u27s quality. From the findings of the study, a conceptual framework of quality in women\u27s health was developed
Improved electro-optical tracking system
Electro-optical tracking system employs a laser beam illuminating source, an electronic laser beam deflector, and an image dissector photomultiplier. An electronic scanning transmitter and receiver follows rapid movements or accelerations of the target
Modelling CO emission from hydrodynamic simulations of nearby spirals, starbursting mergers, and high-redshift galaxies
We model the intensity of emission lines from the CO molecule, based on
hydrodynamic simulations of spirals, mergers, and high-redshift galaxies with
very high resolutions (3pc and 10^3 Msun) and detailed models for the
phase-space structure of the interstellar gas including shock heating, stellar
feedback processes and galactic winds. The simulations are analyzed with a
Large Velocity Gradient (LVG) model to compute the local emission in various
molecular lines in each resolution element, radiation transfer and opacity
effects, and the intensity emerging from galaxies, to generate synthetic
spectra for various transitions of the CO molecule. This model reproduces the
known properties of CO spectra and CO-to-H2 conversion factors in nearby
spirals and starbursting major mergers. The high excitation of CO lines in
mergers is dominated by an excess of high-density gas, and the high turbulent
velocities and compression that create this dense gas excess result in broad
linewidths and low CO intensity-to-H2 mass ratios. When applied to
high-redshift gas-rich disks galaxies, the same model predicts that their
CO-to-H2 conversion factor is almost as high as in nearby spirals, and much
higher than in starbursting mergers. High-redshift disk galaxies contain giant
star-forming clumps that host a high-excitation component associated to gas
warmed by the spatially-concentrated stellar feedback sources, although CO(1-0)
to CO(3-2) emission is overall dominated by low-excitation gas around the
densest clumps. These results overall highlight a strong dependence of CO
excitation and the CO-to-H2 conversion factor on galaxy type, even at similar
star formation rates or densities. The underlying processes are driven by the
interstellar medium structure and turbulence and its response to stellar
feedback, which depend on global galaxy structure and in turn impact the CO
emission properties.Comment: A&A in pres
Meteorite cloudy zone formation as a quantitative indicator of paleomagnetic field intensities and cooling rates on planetesimals
Metallic microstructures in slowly-cooled iron-rich meteorites reflect the
thermal and magnetic histories of their parent planetesimals. Of particular
interest is the cloudy zone, a nanoscale intergrowth of Ni-rich islands within
a Ni-poor matrix that forms below 350{\deg}C by spinodal decomposition. The
sizes of the islands have long been recognized as reflecting the
low-temperature cooling rates of meteorite parent bodies. However, a model
capable of providing quantitative cooling rate estimates from island sizes has
been lacking. Moreover, these islands are also capable of preserving a record
of the ambient magnetic field as they grew, but some of the key physical
parameters required for recovering reliable paleointensity estimates from
magnetic measurements of these islands have been poorly constrained. To address
both of these issues, we present a numerical model of the structural and
compositional evolution of the cloudy zone as a function of cooling rate and
local composition. Our model produces island sizes that are consistent with
present-day measured sizes. This model enables a substantial improvement in the
calibration of paleointensity estimates and associated uncertainties. In
particular, we can now accurately quantify the statistical uncertainty
associated with the finite number of islands and the uncertainty on their size
at the time of the record. We use this new understanding to revisit
paleointensities from previous pioneering paleomagnetic studies of cloudy
zones. We show that these could have been overestimated but nevertheless still
require substantial magnetic fields to have been present on their parent
bodies. Our model also allows us to estimate absolute cooling rates for
meteorites that cooled slower than 10000{\deg}C My-1. We demonstrate how these
cooling rate estimates can uniquely constrain the low-temperature thermal
history of meteorite parent bodies.Comment: Manuscript resubmitted after revision
Evaluation of the micro-carburetor
A prototype sonic, variable-venturi automotive carburetor was evaluated for its effects on vehicle performance, fuel economy, and exhaust emissions. A 350 CID Chevrolet Impala vehicle was tested on a chassis dynamometer over the 1975 Federal Test Procedure, urban driving cycle. The Micro-carburetor was tested and compared with stock and modified-stock engine configurations. Subsequently, the test vehicle's performance characteristics were examined with the stock carburetor and again with the Micro-carburetor in a series of on-road driveability tests. The test engine was then removed from the vehicle and installed on an engine dynamometer. Engine tests were conducted to compare the fuel economy, thermal efficiency, and cylinder-to-cylinder mixture distribution of the Micro-carburetor to that of the stock configuration. Test results show increases in thermal efficiency and improvements in fuel economy at all test conditions. Improve fuel/air mixture preparation is implied from the information presented. Further improvements in fuel economy and exhaust emissions are possible through a detailed recalibration of the Micro-carburetor
Thermodynamics of a subensemble of a canonical ensemble
Two approaches to describe the thermodynamics of a subsystem that interacts
with a thermal bath are considered. Within the first approach, the mean system
energy is identified with the expectation value of the system
Hamiltonian, which is evaluated with respect to the overall (system+bath)
equilibrium distribution. Within the second approach, the system partition
function is considered as the fundamental quantity, which is postulated
to be the ratio of the overall (system+bath) and the bath partition functions,
and the standard thermodynamic relation is used to
obtain the mean system energy. % (, is the
Boltzmann constant, %and is the temperature). Employing both classical and
quantum mechanical treatments, the advantages and shortcomings of the two
approaches are analyzed in detail for various different systems. It is shown
that already within classical mechanics both approaches predict significantly
different results for thermodynamic quantities provided the system-bath
interaction is not bilinear or the system of interest consists of more than a
single particle. Based on the results, it is concluded that the first approach
is superior
Paraunitary oversampled filter bank design for channel coding
Oversampled filter banks (OSFBs) have been considered for channel coding, since their redundancy can be utilised to permit the detection and correction of channel errors. In this paper, we propose an OSFB-based channel coder for a correlated additive Gaussian noise channel, of which the noise covariance matrix is assumed to be known. Based on a suitable factorisation of this matrix, we develop a design for the decoder's synthesis filter bank in order to minimise the noise power in the decoded signal, subject to admitting perfect reconstruction through paraunitarity of the filter bank. We demonstrate that this approach can lead to a significant reduction of the noise interference by exploiting both the correlation of the channel and the redundancy of the filter banks. Simulation results providing some insight into these mechanisms are provided
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