1,166 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
The GRB-SLSN Connection: mis-aligned magnetars, weak jet emergence, and observational signatures
Multiple observational lines of evidence support a connection between
hydrogen-poor superluminous supernovae (SLSNe) and long duration gamma-ray
bursts (GRBs). Both events require a powerful central energy source, usually
attributed to a millisecond magnetar or an accreting black hole. The GRB-SLSN
link raises several theoretical questions: What distinguishes the engines
responsible for these different phenomena? Can a single engine power both a GRB
and a luminous SN in the same event? We propose a new unifying model for
magnetar thermalization and jet formation: misalignment between the rotation
() and magnetic dipole () axes thermalizes a fraction
of the spindown power by reconnection in the striped equatorial wind, providing
a guaranteed source of "thermal" emission to power the supernova. The remaining
un-thermalized power energizes a relativistic jet. In this picture, the
GRB-SLSN dichotomy is directly linked to . We extend
earlier work to show that even weak relativistic jets of luminosity
erg s can escape the expanding SN ejecta hours after the
explosion, implying that escaping relativistic jets may accompany many SLSNe.
We calculate the observational signature of these jets. We show that they may
produce transient UV cocoon emission lasting a few hours when the jet breaks
out of the ejecta surface. A longer-lived optical/UV signal may originate from
a mildly-relativistic wind driven from the interface between the jet and the
ejecta walls. This provides a new explanation for the secondary early-time
maximum observed in some SLSNe light curves, such as LSQ14bdq. This scenario
also predicts a population of GRB from on-axis jets with extremely long
durations, potentially similar to the population of "jetted tidal disruption
events", in coincidence with a small subset of SLSNe.Comment: 17 pages, 7 figures, submitted to MNRA
Unveiling the Engines of Fast Radio Bursts, Super-Luminous Supernovae, and Gamma-Ray Bursts
Young, rapidly spinning magnetars are invoked as central engines behind a
diverse set of transient astrophysical phenomena, including gamma-ray bursts
(GRB), super-luminous supernovae (SLSNe), fast radio bursts (FRB), and binary
neutron star (NS) mergers. However, a barrier to direct confirmation of the
magnetar hypothesis is the challenge of directly observing non-thermal emission
from the central engine at early times (when it is most powerful and thus
detectable) due to the dense surrounding ejecta. We present CLOUDY calculations
of the time-dependent evolution of the temperature and ionization structure of
expanding supernova or merger ejecta due to photo-ionization by a magnetar
engine, in order to study the escape of X-rays (absorbed by neutral gas) and
radio waves (absorbed by ionized gas), as well as to assess the evolution of
the local dispersion measure due to photo-ionization. We find that ionization
breakout does not occur if the engine's ionizing luminosity decays rapidly, and
that X-rays typically escape the oxygen-rich ejecta of SLSNe only on timescales, consistent with current X-ray non-detections. We apply
these results to constrain engine-driven models for the binary NS merger
GW170817 and the luminous transient ASASSN-15lh. In terms of radio transparency
and dispersion measure constraints, the repeating FRB 121102 is consistent with
originating from a young, , magnetar similar to
those inferred to power SLSNe. We further show that its high rotation measure
can be produced within the same nebula that is proposed to power the quiescent
radio source observed co-located with FRB 121102. Our results strengthen
previous work suggesting that at least some FRBs may be produced by young
magnetars, and motivate further study of engine powered transients.Comment: submitted to MNRAS; comments welcom
An ultraviolet excess in the superluminous supernova Gaia16apd reveals a powerful central engine
Since the discovery of superluminous supernovae (SLSNe) in the last decade,
it has been known that these events exhibit bluer spectral energy distributions
than other supernova subtypes, with significant output in the ultraviolet.
However, the event Gaia16apd seems to outshine even the other SLSNe at
rest-frame wavelengths below \AA. Yan et al (2016) have recently
presented HST UV spectra and attributed the UV flux to low metallicity and
hence reduced line blanketing. Here we present UV and optical light curves over
a longer baseline in time, revealing a rapid decline at UV wavelengths despite
a typical optical evolution. Combining the published UV spectra with our own
optical data, we demonstrate that Gaia16apd has a much hotter continuum than
virtually any SLSN at maximum light, but it cools rapidly thereafter and is
indistinguishable from the others by -15 days after peak. Comparing
the equivalent widths of UV absorption lines with those of other events, we
show that the excess UV continuum is a result of a more powerful central power
source, rather than a lack of UV absorption relative to other SLSNe or an
additional component from interaction with the surrounding medium. These
findings strongly support the central-engine hypothesis for hydrogen-poor
SLSNe. An explosion ejecting M, where
is the opacity in cmg, and forming a magnetar with spin
period ms, and G (lower than other SLSNe with
comparable rise-times) can consistently explain the light curve evolution and
high temperature at peak. The host metallicity, Z, is
comparable to other SLSNe.Comment: Updated to match accepted version (ApJL
A Hydrogen-Poor Superluminous Supernova with Enhanced Iron-Group Absorption: A New Link Between SLSNe and Broad-Lined Type Ic SNe
We present optical observations of the Type I superluminous supernova
(SLSN-I) SN2017dwh at , which reached
mag at peak. Spectra taken a few days after peak show an unusual and strong
absorption line centered near 3200\AA\ that we identify with Co II, suggesting
a high fraction of synthesized Ni in the ejecta. By month
after peak, SN2017dwh became much redder than other SLSNe-I, instead strongly
resembling broad-lined Type Ic supernovae (Ic-BL SNe) with clear suppression of
the flux redward of \AA, providing further evidence for a large
mass of Fe-group elements. Late-time upper limits indicate a Ni mass of
M, leaving open the possibility that SN2017dwh produced
a Ni mass comparable to SN1998bw ( M). Fitting the
light curve with a combined magnetar and Ni model using ,
we find that the light curve can easily accommodate such masses without
affecting the inferred magnetar parameters. We also find that SN2017dwh
occurred in the least-luminous detected host galaxy to date for a SLSN-I, with
mag and an implied metallicity of .
The spectral properties of SN2017dwh provide new evidence linking SLSNe-I with
Type Ic-BL SNe, and in particular the high Fe-group abundance may be due to
enhanced Ni production or mixing due to asphericity. Finally, we find
that SN2017dwh represents the most extreme end of a correlation between
continuum shape and Co II absorption strength in the near-peak spectra of
SLSNe-I, indicating that Fe-group abundance likely accounts for some of the
variation in their spectral shapes.Comment: 16 pages, 7 figures, Submitted to Ap
Risk factors and mortality associated with multimorbidity in people with stroke or transient ischaemic attack: a study of 8,751 UK Biobank participants
Background: Multimorbidity is common in stroke, but the risk factors and effects on mortality remain poorly understood. Objective: To examine multimorbidity and its associations with sociodemographic/lifestyle risk factors and all-cause mortality in UK Biobank participants with stroke or transient ischaemic attack (TIA). Design: Data were obtained from an anonymized community cohort aged 40–72 years. Overall, 42 comorbidities were self-reported by those with stroke or TIA. Relative risk ratios demonstrated associations between participant characteristics and number of comorbidities. Hazard ratios demonstrated associations between the number and type of comorbidities and all-cause mortality. Results were adjusted for age, sex, socioeconomic status, smoking, and alcohol intake. Data were linked to national mortality data. Median follow-up was 7 years. Results: Of 8,751 participants (mean age 60.9±6.7 years) with stroke or TIA, the all-cause mortality rate over 7 years was 8.4%. Over 85% reported ≥1 comorbidities. Age, socioeconomic deprivation, smoking and less frequent alcohol intake were associated with higher levels of multimorbidity. Increasing multimorbidity was associated with higher all-cause mortality. Mortality risk was double for those with ≥5 comorbidities compared to those with none. Having cancer, coronary heart disease, diabetes, or chronic obstructive pulmonary disease significantly increased mortality risk. Presence of any cardiometabolic comorbidity significantly increased mortality risk, as did any non-cardiometabolic comorbidity. Conclusions: In stroke survivors, the number of comorbidities may be a more helpful predictor of mortality than type of condition. Stroke guidelines should take greater account of comorbidities, and interventions are needed that improve outcomes for people with multimorbidity and stroke
Empirical constraints on the origin of fast radio bursts: volumetric rates and host galaxy demographics as a test of millisecond magnetar connection
The localization of the repeating FRB 121102 to a low-metallicity dwarf
galaxy at , and its association with a quiescent radio source,
suggests the possibility that FRBs originate from magnetars, formed by the
unusual supernovae in such galaxies. We investigate this via a comparison of
magnetar birth rates, the FRB volumetric rate, and host galaxy demographics. We
calculate average volumetric rates of possible millisecond magnetar production
channels such as superluminous supernovae (SLSNe), long and short gamma-ray
bursts (GRBs), and general magnetar production via core-collapse supernovae.
For each channel we also explore the expected host galaxy demographics using
their known properties. We determine for the first time the number density of
FRB emitters (the product of their volumetric birthrate and lifetime), Gpc, assuming that FRBs are predominantly emitted
from repetitive sources similar to FRB 121102 and adopting a beaming factor of
0.1. By comparing rates we find that production via rare channels (SLSNe, GRBs)
implies a typical FRB lifetime of 30-300 yr, in good agreement with
other lines of argument. The total energy emitted over this time is consistent
with the available energy stored in the magnetic field. On the other hand, any
relation to magnetars produced via normal core-collapse supernovae leads to a
very short lifetime of 0.5yr, in conflict with both theory and
observation. We demonstrate that due to the diverse host galaxy distributions
of the different progenitor channels, many possible sources of FRB birth can be
ruled out with host galaxy identifications. Conversely, targeted
searches of galaxies that have previously hosted decades-old SLSNe and GRBs may
be a fruitful strategy for discovering new FRBs and related quiescent radio
sources, and determining the nature of their progenitors
Risk assessment and predicting outcomes in patients with depressive symptoms: a review of potential role of peripheral blood based biomarkers
Depression is one of the major global health challenges and a leading contributor of health related disability and costs. Depression is a heterogeneous disorder and current methods for assessing its severity in clinical practice rely on symptom count, however this approach is unreliable and inconsistent. The clinical evaluation of depressive symptoms is particularly challenging in primary care, where the majority of patients with depression are managed, due to the presence of co-morbidities. Current methods for risk assessment of depression do not accurately predict treatment response or clinical outcomes. Several biological pathways have been implicated in the pathophysiology of depression; however, accurate and predictive biomarkers remain elusive. We conducted a systematic review of the published evidence supporting the use of peripheral biomarkers to predict outcomes in depression, using Medline and Embase. Peripheral biomarkers in depression were found to be statistically significant predictors of mental health outcomes such as treatment response, poor outcome and symptom remission; and physical health outcomes such as increased incidence of cardiovascular events and deaths, and all-cause mortality. However, the available evidence has multiple methodological limitations which must be overcome to make any real clinical progress. Despite extensive research on the relationship of depression with peripheral biomarkers, its translational application in practice remains uncertain. In future, peripheral biomarkers identified with novel techniques and combining multiple biomarkers may have a potential role in depression risk assessment but further research is needed in this area
PS16dtm: A Tidal Disruption Event in a Narrow-line Seyfert 1 Galaxy
[Abridged] We present observations of PS16dtm, a luminous transient that
occurred at the nucleus of a known Narrow-line Seyfert 1 galaxy hosting a
10 M black hole. The transient was previously claimed to be a Type
IIn SLSN due to its luminosity and hydrogen emission lines. The light curve
shows that PS16dtm brightened by about two magnitudes in ~50 days relative to
the archival host brightness and then exhibited a plateau phase for about 100
days followed by the onset of fading in the UV. During the plateau PS16dtm
showed no color evolution, maintained a blackbody temperature of 1.7 x 10
K, and radiated at approximately of the SMBH. The spectra exhibit
multi-component hydrogen emission lines and strong FeII emission, show little
evolution with time, and closely resemble the spectra of NLS1s while being
distinct from those of Type IIn SNe. Moreover, PS16dtm is undetected in the
X-rays to a limit an order of magnitude below an archival X-ray detection of
its host galaxy. These observations strongly link PS16dtm to activity
associated with the SMBH and are difficult to reconcile with a SN origin or any
known form of AGN variability, and therefore we argue that it is a TDE in which
the accretion of the stellar debris powers the rise in the continuum and
excitation of the pre-existing broad line region, while providing material that
obscures the X-ray emitting region of the pre-existing AGN accretion disk. A
detailed TDE model fit to the light curve indicates that PS16dtm will remain
bright for several years; we further predict that the X-ray emission will
reappear on a similar timescale as the accretion rate declines. Finally, we
place PS16dtm in the context of other TDEs and find that TDEs in AGN galaxies
are an order of magnitude more efficient and reach Eddington luminosities,
likely due to interaction of the stellar debris with the pre-existing accretion
disk.Comment: 19 pages, 17 figures, Submitted to Ap
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