3,379 research outputs found
Americans' Access to Prescription Drugs Stabilizes, 2007-2010
Examines trends in the percentage of Americans reporting difficulty affording prescription drugs by insurance status, age group, income, and health status. Considers contributing factors such as changes in the uninsured population and fewer doctor visits
Solar-like oscillations in the metal-poor subgiant nu Indi: II. Acoustic spectrum and mode lifetime
Convection in stars excites resonant acoustic waves which depend on the sound
speed inside the star, which in turn depends on properties of the stellar
interior. Therefore, asteroseismology is an unrivaled method to probe the
internal structure of a star. We made a seismic study of the metal-poor
subgiant star nu Indi with the goal of constraining its interior structure. Our
study is based on a time series of 1201 radial velocity measurements spread
over 14 nights obtained from two sites, Siding Spring Observatory in Australia
and ESO La Silla Observatory in Chile. The power spectrum of the high precision
velocity time series clearly presents several identifiable peaks between 200
and 500 uHz showing regularity with a large and small spacing of 25.14 +- 0.09
uHz and 2.96 +- 0.22 uHz at 330 uHz. Thirteen individual modes have been
identified with amplitudes in the range 53 to 173 cm/s. The mode damping time
is estimated to be about 16 days (1-sigma range between 9 and 50 days),
substantially longer than in other stars like the Sun, the alpha Cen system or
the giant xi Hya.Comment: 5 pages, 7 figures, A&A accepte
Recommending Learning Algorithms and Their Associated Hyperparameters
The success of machine learning on a given task dependson, among other
things, which learning algorithm is selected and its associated
hyperparameters. Selecting an appropriate learning algorithm and setting its
hyperparameters for a given data set can be a challenging task, especially for
users who are not experts in machine learning. Previous work has examined using
meta-features to predict which learning algorithm and hyperparameters should be
used. However, choosing a set of meta-features that are predictive of algorithm
performance is difficult. Here, we propose to apply collaborative filtering
techniques to learning algorithm and hyperparameter selection, and find that
doing so avoids determining which meta-features to use and outperforms
traditional meta-learning approaches in many cases.Comment: Short paper--2 pages, 2 table
An Easy to Use Repository for Comparing and Improving Machine Learning Algorithm Usage
The results from most machine learning experiments are used for a specific
purpose and then discarded. This results in a significant loss of information
and requires rerunning experiments to compare learning algorithms. This also
requires implementation of another algorithm for comparison, that may not
always be correctly implemented. By storing the results from previous
experiments, machine learning algorithms can be compared easily and the
knowledge gained from them can be used to improve their performance. The
purpose of this work is to provide easy access to previous experimental results
for learning and comparison. These stored results are comprehensive -- storing
the prediction for each test instance as well as the learning algorithm,
hyperparameters, and training set that were used. Previous results are
particularly important for meta-learning, which, in a broad sense, is the
process of learning from previous machine learning results such that the
learning process is improved. While other experiment databases do exist, one of
our focuses is on easy access to the data. We provide meta-learning data sets
that are ready to be downloaded for meta-learning experiments. In addition,
queries to the underlying database can be made if specific information is
desired. We also differ from previous experiment databases in that our
databases is designed at the instance level, where an instance is an example in
a data set. We store the predictions of a learning algorithm trained on a
specific training set for each instance in the test set. Data set level
information can then be obtained by aggregating the results from the instances.
The instance level information can be used for many tasks such as determining
the diversity of a classifier or algorithmically determining the optimal subset
of training instances for a learning algorithm.Comment: 7 pages, 1 figure, 6 table
Functional tradeoffs in specialization for fighting versus running
Journal ArticleBoth locomotion and fighting are critical to survival and reproductive fitness in many vertebrate species. Yet, characters that make an individual good at fighting may, in many cases, limit locomotor performance and vice versa. Here I describe tests of three functional tradeoffs in the limb muscles of two breeds of domestic dogs that have undergone intense artificial selection for running (Greyhound) or fighting performance (Pit Bull). We found that Greyhounds differ from Pit Bulls in having relatively less muscle mass distally in their limbs, weaker muscles in their forelimbs than their hindlimbs, and a much greater capacity for elastic storage in the in-series tendons of the extensor muscles of their anlde joints. These observations are consistent with the hypothesis that specialization for rapid or economical running can limit fighting performance and vice versa. Variation in body form among dog breeds has been suggested to be largely a consequence of selection on the ontogenetic variation present in individual wolf-like dogs (Wayne, 1986a,b). This, plus recent work on the genetics of the caned skeleton, raise the possibility that pit bulls are a breed that has evolved by the retention of juvenile shape (i.e., neoteny) and greyhounds may represent an acceleration of shape ontogeny. Finally, functional tradeoffs that prevent simultaneous evolution of optimal performance in both locomotor and fighting abilities appear to be widespread taxonomically and may have been particularly important in the evolution of hominid anatomy and physiology
Switchgrass storage effects on the recovery of carbohydrates after liquid hot water pretreatment and enzymatic hydrolysis
Perennial grasses that would be used for bioenergy and bioproducts production will need to be stored for various periods of time to ensure a continual feedstock supply to a bioprocessing facility. The effects of storage practices on grass composition and the response of grasses to subsequent bioprocesses such as pretreatment and enzymatic hydrolysis needs to be understood to develop the most efficient storage protocols. This study examined the effect of outdoor storage of round switchgrass bales on composition before and after liquid hot water pretreatment (LHW) and enzymatic hydrolysis. This study also examined the effect of washing LHW pretreated biomass prior to enzymatic hydrolysis. It was determined that switchgrass composition after baling was stable. As expected, glucan and lignin contents increased after LHW due to decreases in xylan and galactan. Washing biomass prior to enzymatic hydrolysis reduced saccharification, especially in samples from the interior of the bale, by at least 5%
The effect of foot posture on capacity to apply free moments to the ground: implications for fighting performance in great apes
In contrast to most other primates, great apes have feet in which the heel supports body weight during standing, walking and running. One possible advantage of this plantigrade foot posture is that it may enhance fighting performance by increasing the ability to apply free moments (i.e. force couples) to the ground. We tested this possibility by measuring performance of human subjects when performing from plantigrade and digitigrade (standing on the ball of the foot and toes) postures. We found that plantigrade posture substantially increased the capacity to apply free moments to the ground and to perform a variety of behaviors that are likely to be important to fighting performance in great apes. As predicted, performance in maximal effort lateral striking and pushing was strongly correlated with free moment magnitude. All else being equal, these results suggest species that can adopt plantigrade posture will be able to apply larger free moments to the ground than species restricted to digitigrade or unguligrade foot posture. Additionally, these results are consistent with the suggestion that selection for physical competition may have been one of the factors that led to the evolution of the derived plantigrade foot posture of great apes
Spatial Multiplexing of QPSK Signals with a Single Radio: Antenna Design and Over-the-Air Experiments
The paper describes the implementation and performance analysis of the first
fully-operational beam-space MIMO antenna for the spatial multiplexing of two
QPSK streams. The antenna is composed of a planar three-port radiator with two
varactor diodes terminating the passive ports. Pattern reconfiguration is used
to encode the MIMO information onto orthogonal virtual basis patterns in the
far-field. A measurement campaign was conducted to compare the performance of
the beam-space MIMO system with a conventional 2-by-?2 MIMO system under
realistic propagation conditions. Propagation measurements were conducted for
both systems and the mutual information and symbol error rates were estimated
from Monte-Carlo simulations over the measured channel matrices. The results
show the beam-space MIMO system and the conventional MIMO system exhibit
similar finite-constellation capacity and error performance in NLOS scenarios
when there is sufficient scattering in the channel. In comparison, in LOS
channels, the capacity performance is observed to depend on the relative
polarization of the receiving antennas.Comment: 31 pages, 23 figure
Human flight and exercise in microgravity
Journal ArticleEarly experimenters in human flight learned, sometimes with fatal consequences, that the human body lacks the muscular power to fly (1). Indeed, the power demands are so great that only relatively small animals (less than 12 kg) are able to fly actively due to the interplay of morphologic scaling (muscle mass, wing area, power output) and organism weight (2). But this might not be true in a space station. Could humans fly in air when subject to microgravity? How demanding would such flight be
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