783 research outputs found
A statistical multiresolution approach for face recognition using structural hidden Markov models
This paper introduces a novel methodology that combines the multiresolution feature of the discrete wavelet transform (DWT) with the local interactions of the facial structures expressed through the structural hidden Markov model (SHMM). A range of wavelet filters such as Haar, biorthogonal 9/7, and Coiflet, as well as Gabor, have been implemented in order to search for the best performance. SHMMs perform a thorough probabilistic analysis of any sequential pattern by revealing both its inner and outer structures simultaneously. Unlike traditional HMMs, the SHMMs do not perform the state conditional independence of the visible observation sequence assumption. This is achieved via the concept of local structures introduced by the SHMMs. Therefore, the long-range dependency problem inherent to traditional HMMs has been drastically reduced. SHMMs have not previously been applied to the problem of face identification. The results reported in this application have shown that SHMM outperforms the traditional hidden Markov model with a 73% increase in accuracy
Epsilon Expansion for Multicritical Fixed Points and Exact Renormalisation Group Equations
The Polchinski version of the exact renormalisation group equations is
applied to multicritical fixed points, which are present for dimensions between
two and four, for scalar theories using both the local potential approximation
and its extension, the derivative expansion. The results are compared with the
epsilon expansion by showing that the non linear differential equations may be
linearised at each multicritical point and the epsilon expansion treated as a
perturbative expansion. The results for critical exponents are compared with
corresponding epsilon expansion results from standard perturbation theory. The
results provide a test for the validity of the local potential approximation
and also the derivative expansion. An alternative truncation of the exact RG
equation leads to equations which are similar to those found in the derivative
expansion but which gives correct results for critical exponents to order
and also for the field anomalous dimension to order . An
exact marginal operator for the full RG equations is also constructed.Comment: 40 pages, 12 figures version2: small corrections, extra references,
final appendix rewritten, version3: some corrections to perturbative
calculation
Higher breakfast glycaemic load is associated with increased metabolic syndrome risk, including lower HDL-cholesterol concentrations and increased TAG concentrations, in adolescent girls
Almost all previous studies examining the associations between glycaemic load (GL) and metabolic syndrome risk have used a daily GL value. The daily value does not distinguish between peaks of GL intake over the day, which may be more closely associated with the risk of the metabolic syndrome. The aim of the present study was to investigate the cross-sectional associations between daily and mealtime measures of GL and metabolic syndrome risk, including metabolic syndrome components, in adolescents. Adolescents participating in the 14-year follow-up of the Western Australian Pregnancy Cohort (Raine) Study completed 3 d food records and metabolic assessments. Breakfast GL, lunch GL, dinner GL and a score representing meal GL peaks over the day were determined in 516 adolescents. Logistic regression models were used to investigate whether GL variables were independent predictors of the metabolic syndrome in this population-based cohort (3·5 % prevalence of the metabolic syndrome). Breakfast GL was found to be predictive of the metabolic syndrome in girls (OR 1·15, 95 % CI 1·04, 1·27;
Historical geography II: traces remain
The second report in this series turns to focus on the trace in relation to life-writing and biography in historical geography and beyond. Through attention to tracing journeys, located moments and listening to the presence of ghosts (Ogborn, 2005), this report seeks to highlight the range of different ways in which historical geographers have explored lives, deaths, and their transient traces through varied biographical terrains. Continuing to draw attention in historical geography to the darkest of histories, this piece will pivot on moments of discovering the dead to showcase the nuanced ways in which historical geography is opening doors into uncharted lives and unspoken histories
The Electromagnetic Counterpart of the Binary Neutron Star Merger LIGO/VIRGO GW170817. V. Rising X-ray Emission from an Off-Axis Jet
We report the discovery of rising X-ray emission from the binary neutron star
(BNS) merger event GW170817. This is the first detection of X-ray emission from
a gravitational-wave source. Observations acquired with the Chandra X-ray
Observatory (CXO) at t~2.3 days post merger reveal no significant emission,
with L_x<=3.2x10^38 erg/s (isotropic-equivalent). Continued monitoring revealed
the presence of an X-ray source that brightened with time, reaching L_x\sim
9x10^39 erg/s at ~15.1 days post merger. We interpret these findings in the
context of isotropic and collimated relativistic outflows (both on- and
off-axis). We find that the broad-band X-ray to radio observations are
consistent with emission from a relativistic jet with kinetic energy
E_k~10^49-10^50 erg, viewed off-axis with theta_obs~ 20-40 deg. Our models
favor a circumbinary density n~ 0.0001-0.01 cm-3, depending on the value of the
microphysical parameter epsilon_B=10^{-4}-10^{-2}. A central-engine origin of
the X-ray emission is unlikely. Future X-ray observations at
days, when the target will be observable again with the CXO, will provide
additional constraints to solve the model degeneracies and test our
predictions. Our inferences on theta_obs are testable with gravitational wave
information on GW170817 from Advanced LIGO/Virgo on the binary inclination.Comment: 7 Pages, 4 Figures, ApJL, In Press. Keywords: GW170817, LV
The Electromagnetic Counterpart of the Binary Neutron Star Merger LIGO/VIRGO GW170817. VI. Radio Constraints on a Relativistic Jet and Predictions for Late-Time Emission from the Kilonova Ejecta
We present Very Large Array (VLA) and Atacama Large Millimeter/sub-millimeter
Array ALMA radio observations of GW\,170817, the first Laser Interferometer
Gravitational-wave Observatory (LIGO)/Virgo gravitational wave (GW) event from
a binary neutron star merger and the first GW event with an electromagnetic
(EM) counterpart. Our data include the first observations following the
discovery of the optical transient at both the centimeter ( hours post
merger) and millimeter ( days post merger) bands. We detect faint
emission at 6 GHz at 19.47 and 39.23 days after the merger, but not in an
earlier observation at 2.46 d. We do not detect cm/mm emission at the position
of the optical counterpart at frequencies of 10-97.5 GHz at times ranging from
0.6 to 30 days post merger, ruling out an on-axis short gamma-ray burst (SGRB)
for energies erg. For fiducial SGRB parameters, our limits
require an observer viewer angle of . The radio and X-ray
data can be jointly explained as the afterglow emission from an SGRB with a jet
energy of erg that exploded in a uniform density
environment with cm, viewed at an angle of from the jet axis. Using the results of our light curve
and spectral modeling, in conjunction with the inference of the circumbinary
density, we predict the emergence of late-time radio emission from the
deceleration of the kilonova (KN) ejecta on a timescale of years
that will remain detectable for decades with next-generation radio facilities,
making GW\,170817 a compelling target for long-term radio monitoring.Comment: 8 pages, 4 figures, 1 table. ApJL, in press. Keywords: GW170817, LV
The multiple sclerosis risk sharing scheme monitoring study - early results and lessons for the future
Background: Risk sharing schemes represent an innovative and important approach to the problems of rationing and achieving cost-effectiveness in high cost or controversial health interventions. This study aimed to assess the feasibility of risk sharing schemes, looking at long term clinical outcomes, to determine the price at which high cost treatments would be acceptable to the NHS.
Methods: This case study of the first NHS risk sharing scheme, a long term prospective cohort study of beta interferon and glatiramer acetate in multiple sclerosis ( MS) patients in 71 specialist MS centres in UK NHS hospitals, recruited adults with relapsing forms of MS, meeting Association of British Neurologists (ABN) criteria for disease modifying therapy. Outcome measures were: success of recruitment and follow up over the first three years, analysis of baseline and initial follow up data and the prospect of estimating the long term cost-effectiveness of these treatments.
Results: Centres consented 5560 patients. Of the 4240 patients who had been in the study for a least one year, annual review data were available for 3730 (88.0%). Of the patients who had been in the study for at least two years and three years, subsequent annual review data were available for 2055 (78.5%) and 265 (71.8%) patients respectively. Baseline characteristics and a small but statistically significant progression of disease were similar to those reported in previous pivotal studies.
Conclusion: Successful recruitment, follow up and early data analysis suggest that risk sharing schemes should be able to deliver their objectives. However, important issues of analysis, and political and commercial conflicts of interest still need to be addressed
The Electromagnetic Counterpart of the Binary Neutron Star Merger LIGO/VIRGO GW170817. VII. Properties of the Host Galaxy and Constraints on the Merger Timescale
We present the properties of NGC 4993, the host galaxy of GW170817, the first
gravitational wave (GW) event from the merger of a binary neutron star (BNS)
system and the first with an electromagnetic (EM) counterpart. We use both
archival photometry and new optical/near-IR imaging and spectroscopy, together
with stellar population synthesis models to infer the global properties of the
host galaxy. We infer a star formation history peaked at Gyr ago,
with subsequent exponential decline leading to a low current star formation
rate of 0.01 M yr, which we convert into a binary merger
timescale probability distribution. We find a median merger timescale of
Gyr, with a 90% confidence range of Gyr. This
in turn indicates an initial binary separation of R,
comparable to the inferred values for Galactic BNS systems. We also use new and
archival images to measure a projected offset of
the optical counterpart of kpc (0.64) from the center of NGC 4993
and to place a limit of mag on any pre-existing emission,
which rules out the brighter half of the globular cluster luminosity function.
Finally, the age and offset of the system indicates it experienced a modest
natal kick with an upper limit of km s. Future GWEM
observations of BNS mergers will enable measurement of their population delay
time distribution, which will directly inform their viability as the dominant
source of -process enrichment in the Universe.Comment: 9 Pages, 3 Figures, 2 Tables, ApJL, In Press. Keywords: GW170817, LV
A comprehensive evaluation of colonic mucosal isolates of Sutterella wadsworthensis from inflammatory bowel disease
Peer reviewedPublisher PD
Rapid Generation of Kilonova Light Curves Using Conditional Variational Autoencoder
The discovery of the optical counterpart, along with the gravitational waves
from GW170817, of the first binary neutron star merger, opened up a new era for
multi-messenger astrophysics. Combining the GW data with the optical
counterpart, also known as AT2017gfo, classified as a kilonova, has revealed
the nature of compact binary merging systems by extracting enriched information
about the total binary mass, the mass ratio, the system geometry, and the
equation of state. Even though the detection of kilonova brought about a
revolution in the domain of multi-messenger astronomy, since there has been
only one kilonova from a gravitational wave detected binary neutron star merger
event so far, this limits the exact understanding of the origin and propagation
of the kilonova. Here, we use a conditional variational autoencoder trained on
light curve data from two kilonova models having different temporal lengths,
and consequently, generate kilonova light curves rapidly based on physical
parameters of our choice with good accuracy. Once trained, the time scale for
light curve generation is of the order of a few milliseconds, thus speeding up
generating light curves by times compared to the simulation. The mean
squared error between the generated and original light curves is typically
with a maximum of for each set of considered physical parameter;
while having a maximum of error across the whole parameter space.
Hence, implementing this technique provides fast and reliably accurate results.Comment: 19 pages, 7 figures (3 additional figures in appendix), accepted to
Ap
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