2,641 research outputs found
Gait Recognition By Walking and Running: A Model-Based Approach
Gait is an emerging biometric for which some techniques, mainly holistic, have been developed to recognise people by their walking patterns. However, the possibility of recognising people by the way they run remains largely unexplored. The new analytical model presented in this paper is based on the biomechanics of walking and running, and will serve as the foundation of an automatic person recognition system that is invariant to these distinct gaits. A bilateral and dynamically coupled oscillator is the key concept underlying this work. Analysis shows that this new model can be used to automatically describe walking and running subjects without parameter selection. Temporal template matching that takes into account the whole sequence of a gait cycle is applied to extract the angles of thigh and lower leg rotation. The phase-weighted magnitudes of the lower order Fourier components of these rotations form the gait signature. Classification of walking and running subjects is performed using the k-nearest-neighbour classifier. Recognition rates are similar to that achieved by other techniques with a similarly sized database. Future work will investigate feature set selection to improve the recognition rate and will determine the invariance attributes, for inter- and intra- class, of both walking and running
Validity and practical utility of accelerometry for the measurement of in-hand physical activity in horses
Background:
Accelerometers are valid, practical and reliable tools for the measurement of habitual physical activity (PA). Quantification of PA in horses is desirable for use in research and clinical settings. The objective of this study was to evaluate a triaxial accelerometer for objective measurement of PA in the horse by assessment of their practical utility and validity.
Horses were recruited to establish both the optimal site of accelerometer attachment and questionnaire designed to explore owner acceptance. Validity and cut-off values were obtained by assessing PA at various gaits. Validation study- 20 horses wore the accelerometer while being filmed for 10 min each of rest, walking and trotting and 5 mins of canter work. Practical utility study- five horses wore accelerometers on polls and withers for 18 h; compliance and relative data losses were quantified.
Results:
Accelerometry output differed significantly between the four PA levels (P <0•001) for both wither and poll placement. For withers placement, ROC analyses found optimal sensitivity and specificity at a cut-off of <47 counts per minute (cpm) for rest (sensitivity 99.5 %, specificity 100 %), 967–2424 cpm for trotting (sensitivity 96.7 %, specificity 100 %) and ≥2425 cpm for cantering (sensitivity 96.0 %, specificity 97.0 %). Attachment at the poll resulted in optimal sensitivity and specificity at a cut-off of <707 counts per minute (cpm) for rest (sensitivity 97.5 %, specificity 99.6 %), 1546–2609 cpm for trotting (sensitivity 90.33 %, specificity 79.25 %) and ≥2610 cpm for cantering (sensitivity 100 %, specificity 100 %) In terms of practical utility, accelerometry was well tolerated and owner acceptance high.
Conclusion:
Accelerometry data correlated well with varying levels of in-hand equine activity. The use of accelerometers is a valid method for objective measurement of controlled PA in the horse
A Very Large Array Search for 5 GHz Radio Transients and Variables at Low Galactic Latitudes
We present the results of a 5 GHz survey with the Very Large Array (VLA) and the expanded VLA, designed to search for short-lived (≾1 day) transients and to characterize the variability of radio sources at milli-Jansky levels. A total sky area of 2.66 deg^2, spread over 141 fields at low Galactic latitudes (b≅6-8 deg), was observed 16 times with a cadence that was chosen to sample timescales of days, months, and years. Most of the data were reduced, analyzed, and searched for transients in near real-time. Interesting candidates were followed up using visible light telescopes (typical delays of 1-2 hr) and the X-ray Telescope on board the Swift satellite. The final processing of the data revealed a single possible transient with a peak flux density of f_ν≅2.4 mJy. This implies a transient's sky surface density of κ(f_ν > 1.8 mJy) = 0.039^(+0.13 +0.18)_(–0.032,–0.038) deg^(–2) (1σ, 2σ confidence errors). This areal density is roughly consistent with the sky surface density of transients from the Bower et al. survey extrapolated to 1.8 mJy. Our observed transient areal density is consistent with a neutron star's origin for these events. Furthermore, we use the data to measure the source variability on timescales of days to years, and we present the variability structure function of 5 GHz sources. The mean structure function shows a fast increase on ≈1 day timescale, followed by a slower increase on timescales of up to 10 days. On timescales between 10 and 60 days, the structure function is roughly constant. We find that ≳30% of the unresolved sources brighter than 1.8 mJy are variables at the >4σ confidence level, presumably mainly due to refractive scintillation
Interacting Supernovae: Types IIn and Ibn
Supernovae (SNe) that show evidence of strong shock interaction between their
ejecta and pre-existing, slower circumstellar material (CSM) constitute an
interesting, diverse, and still poorly understood category of explosive
transients. The chief reason that they are extremely interesting is because
they tell us that in a subset of stellar deaths, the progenitor star may become
wildly unstable in the years, decades, or centuries before explosion. This is
something that has not been included in standard stellar evolution models, but
may significantly change the end product and yield of that evolution, and
complicates our attempts to map SNe to their progenitors. Another reason they
are interesting is because CSM interaction is an efficient engine for making
bright transients, allowing super-luminous transients to arise from normal SN
explosion energies, and allowing transients of normal SN luminosities to arise
from sub-energetic explosions or low radioactivity yield. CSM interaction
shrouds the fast ejecta in bright shock emission, obscuring our normal view of
the underlying explosion, and the radiation hydrodynamics of the interaction is
challenging to model. The CSM interaction may also be highly non-spherical,
perhaps linked to binary interaction in the progenitor system. In some cases,
these complications make it difficult to definitively tell the difference
between a core-collapse or thermonuclear explosion, or to discern between a
non-terminal eruption, failed SN, or weak SN. Efforts to uncover the physical
parameters of individual events and connections to possible progenitor stars
make this a rapidly evolving topic that continues to challenge paradigms of
stellar evolution.Comment: Final draft of a chapter in the "SN Handbook". Accepted. 25 pages, 3
fig
On the Progenitors of Core-Collapse Supernovae
Theory holds that a star born with an initial mass between about 8 and 140
times the mass of the Sun will end its life through the catastrophic
gravitational collapse of its iron core to a neutron star or black hole. This
core collapse process is thought to usually be accompanied by the ejection of
the star's envelope as a supernova. This established theory is now being tested
observationally, with over three dozen core-collapse supernovae having had the
properties of their progenitor stars directly measured through the examination
of high-resolution images taken prior to the explosion. Here I review what has
been learned from these studies and briefly examine the potential impact on
stellar evolution theory, the existence of "failed supernovae", and our
understanding of the core-collapse explosion mechanism.Comment: 7 Pages, invited review accepted for publication by Astrophysics and
Space Science (special HEDLA 2010 issue
Far-Ultraviolet to Near-Infrared Spectroscopy of A Nearby Hydrogen Poor Superluminous Supernova Gaia16apd
We report the first maximum-light far-Ultraviolet to near-infrared spectra
(1000A - 1.62um, rest) of a H-poor superluminous supernova, Gaia16apd. At
z=0.1018, it is one of the closest and the UV brightest such events, with 17.4
(AB) magnitude in Swift UV band (1928A) at -11days pre-maximum. Assuming an
exponential form, we derived the rise time of 33days and the peak bolometric
luminosity of 3x10^{44}ergs^-1. At maximum light, the estimated photospheric
temperature and velocity are 17,000K and 14,000kms^-1 respectively. The
inferred radiative and kinetic energy are roughly 1x10^{51} and 2x10^{52}erg.
Gaia16apd is extremely UV luminous, emitting 50% of its total luminosity at
1000 - 2500A. Compared to the UV spectra (normalized at 3100A) of well studied
SN1992A (Ia), SN2011fe(Ia), SN1999em (IIP) and SN1993J (IIb), it has orders of
magnitude more far-UV emission. This excess is interpreted primarily as a
result of weaker metal line blanketing due to much lower abundance of
iron-group elements in the outer ejecta. Because these elements originate
either from the natal metallicity of the star, or have been newly produced, our
observation provides direct evidence that little of these freshly synthesized
material, including 56Ni, was mixed into the outer ejecta, and the progenitor
metallicity is likely sub-solar. This disfavors Pair-Instability Supernova
(PISN) models with Helium core masses >=90Msun, where substantial 56Ni material
is produced. Higher photospheric temperature of Gaia16apd than that of normal
SNe may also contribute to the observed far-UV excess. We find some indication
that UV luminous SLSNe-I like Gaia16apd could be common. Using the UV spectra,
we show that WFIRST could detect SLSNe-I out to redshift of 8.Comment: 19 pages. Match with the version accepted in Ap
Quantitative errors in the Cochrane review on "Physical interventions to interrupt or reduce the spread of respiratory viruses"
The COVID-19 pandemic has heightened the urgency to understand and prevent
pathogen transmission, specifically regarding infectious airborne particles.
Extensive studies validate the understanding of larger (droplets) and smaller
(aerosols) particles in disease transmission. Similarly, N95 respirators, and
other forms of respiratory protection, have proven efficacy in reducing the
risk of infection across various environments. Even though multiple studies
confirm their protective effect when adopted in healthcare and public settings
for infection prevention, studies on their adoption over the last several
decades in both clinical trials and observational studies have not provided as
clear an understanding. Here we show that the standard analytical equations
used in the analysis of these studies do not accurately represent the random
variables impacting study results. By correcting these equations, it is
demonstrated that conclusions drawn from these studies are heavily biased and
uncertain, providing little useful information. Despite these limitations, we
show that when outcome measures are properly analyzed, existing results
consistently point to the benefit of N95 respirators over medical masks, and
masking over its absence. Correcting errors in widely reported meta-analyses
also yields statistically significant estimates. These findings have important
implications for study design and using existing evidence for infection control
policy guidelines.Comment: 23 pages, 8 figure
The supernova rate in local galaxy clusters
We report a measurement of the supernova (SN) rates (Ia and core-collapse) in
galaxy clusters based on the 136 SNe of the sample described in Cappellaro et
al. (1999) and Mannucci et al. (2005).
Early-type cluster galaxies show a type Ia SN rate (0.066 SNuM) similar to
that obtained by Sharon et al. (2007) and more than 3 times larger than that in
field early-type galaxies (0.019 SNuM). This difference has a 98% statistical
confidence level. We examine many possible observational biases which could
affect the rate determination, and conclude that none of them is likely to
significantly alter the results. We investigate how the rate is related to
several properties of the parent galaxies, and find that cluster membership,
morphology and radio power all affect the SN rate, while galaxy mass has no
measurable effect. The increased rate may be due to galaxy interactions in
clusters, inducing either the formation of young stars or a different evolution
of the progenitor binary systems.
We present the first measurement of the core-collapse SN rate in cluster
late-type galaxies, which turns out to be comparable to the rate in field
galaxies. This suggests that no large systematic difference in the initial mass
function exists between the two environments.Comment: MNRAS, revised version after referee's comment
Frequency-domain multiscale quantum mechanics/electromagnetics simulation method
A frequency-domain quantum mechanics and electromagnetics (QM∕EM) method is developed. Compared with the time-domain QM/EM method [Meng et al., J. Chem. Theory Comput. 8, 1190-1199 (2012)], the newly developed frequency-domain QM∕EM method could effectively capture the dynamic properties of electronic devices over a broader range of operating frequencies. The system is divided into QM and EM regions and solved in a self-consistent manner via updating the boundary conditions at the QM and EM interface. The calculated potential distributions and current densities at the interface are taken as the boundary conditions for the QM and EM calculations, respectively, which facilitate the information exchange between the QM and EM calculations and ensure that the potential, charge, and current distributions are continuous across the QM/EM interface. Via Fourier transformation, the dynamic admittance calculated from the time-domain and frequency-domain QM/EM methods is compared for a carbon nanotube based molecular device.published_or_final_versio
Towards a Robuster Interpretive Parsing
The input data to grammar learning algorithms often consist of overt forms that do not contain full structural descriptions. This lack of information may contribute to the failure of learning. Past work on Optimality Theory introduced Robust Interpretive Parsing (RIP) as a partial solution to this problem. We generalize RIP and suggest replacing the winner candidate with a weighted mean violation of the potential winner candidates. A Boltzmann distribution is introduced on the winner set, and the distribution’s parameter is gradually decreased. Finally, we show that GRIP, the Generalized Robust Interpretive Parsing Algorithm significantly improves the learning success rate in a model with standard constraints for metrical stress assignment
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