DWT/PCA face recognition using automatic coefficient selection

In PCA-based face recognition, there is often a trade-off between selecting the most relevant parts of a face image for recognition and not discarding information which may be useful. The work presented in this paper proposes a method to automatically determine the most discriminative coefficients in a DWT/PCA-based face recognition system, based on their inter-class and intra-class standard deviations. In addition, the eigenfaces used for recognition are generally chosen based on the value of their associated eigenvalues. However, the variance indicated by the eigenvalues may be due to factors such as variation in illumination levels between training set faces, rather than differences that are useful for identification. The work presented proposes a method to automatically determine the most discriminative eigenfaces, based on the inter-class and intra-class standard deviations of the training set eigenface weight vectors. The results obtained using the AT&T database show an improvement over existing DWT/PCA coefficient selection techniques

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

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 $\sim 3000$ \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 $\sim 10$-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 $M_{\rm ej} = 4 (0.2/\kappa)$ M$_\odot$, where $\kappa$ is the opacity in cm$^2$g$^{-1}$, and forming a magnetar with spin period $P=2$ ms, and $B=2\times10^{14}$ G (lower than other SLSNe with comparable rise-times) can consistently explain the light curve evolution and high temperature at peak. The host metallicity, $Z=0.18$ Z$_\odot$, 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 $z\!\approx\!0.13$, which reached $M_{i}\!\approx\!-21$ 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 $^{56}$Ni in the ejecta. By $\sim\!1$ 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 $\sim\!5000$ \AA, providing further evidence for a large mass of Fe-group elements. Late-time upper limits indicate a $^{56}$Ni mass of $\lesssim 0.6$ M$_\odot$, leaving open the possibility that SN2017dwh produced a $^{56}$Ni mass comparable to SN1998bw ($\approx\!0.4$ M$_\odot$). Fitting the light curve with a combined magnetar and $^{56}$Ni model using ${\tt MOSFiT}$, 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 $M_{B} = -13.5$ mag and an implied metallicity of $Z\!\sim\!0.08$ $Z_\odot$. 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 $^{56}$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

Mechanisms for high spin in black-hole neutron-star binaries and kilonova emission: inheritance and accretion

Black-hole neutron-star binary mergers, whose existence has been confirmed by gravitational-wave detectors, can lead to an electromagnetic counterpart called a kilonova if the neutron star is disrupted prior to merger. The observability of a kilonova depends crucially on the amount of neutron star ejecta, which is sensitive to the aligned component of the black hole spin. These binaries likely originate from the evolution of isolated stellar binaries. We explore the dependence of the ejected mass on two main mechanisms that provide high black hole spin. When the black hole inherits a high spin from a Wolf-Rayet star that was born with least $\sim 10\%$ of its breakup spin under weak stellar core-envelope coupling, which is relevant for all formation pathways, the median of the ejected mass is $\gtrsim 10^{-2}$ M$_{\odot}$. Though only possible for certain formation pathways, similarly large ejected mass results when the black hole accretes $\gtrsim 20\%$ of its companion's envelope to gain a high spin, and a more massive stellar progenitor provides smaller ejected mass compared to when the black hole inherits high spin. Together, these signatures suggest that a population analysis of black hole masses and spins in black-hole neutron-star binary mergers may help distinguish between mechanisms for spin and possible formation pathways. Using a novel kilonova light curve model we show that current capabilities are unlikely to observe a counterpart, however future facilities such as the Vera Rubin Observatory will likely detect counterparts even if the aligned dimensionless spin of the disrupting black hole is as low as $\sim 0.2$. Our model predicts kilonovae as bright as $M_i \sim -14.5$ for an aligned black hole spin of $\sim 0.9$

A re-examination of the anatomy and systematics of the tomistomine crocodylians from the Miocene of Italy and Malta

Once a much more globally widespread crocodylian clade, Tomistominae is today represented by just one species, Tomistoma schlegelii (the false gharial), restricted to south-east Asia. Although tomistomine fossil occurrences are recognized from the early Eocene (∼55 Ma) onwards, their remains are often incomplete, making appropriate taxonomic classification within the group problematic. This is especially pertinent to several taxa from the Miocene of Europe, which were historically erected from fragmentary remains. Here we re-examine and describe four approximately contemporaneous taxa from Malta and Italy to determine their taxonomy and phylogenetic affinities: Melitosaurus champsoides, Tomistoma calaritanum, Tomistoma gaudense and Tomistoma lyceense. We place them into a phylogenetic analysis for the first time, comprising 70 taxa scored for 244 characters, several of which are revised or novel, and apply a number of character weighting strategies. Whereas ‘Tomistoma lyceense’ is deemed to be an indeterminate tomistomine, a unique combination of features confirms Melitosaurus champsoides, Tomistoma calaritanum and Tomistoma gaudense as three distinct species. These three taxa are recovered as derived tomistomines, with characters such as a posterior maxillary process between the lacrimal and nasal, large supratemporal fenestrae that are wider than long, and the posteromedial alignment of the last three premaxillary teeth, suggesting a close relationship with the approximately contemporaneous European taxa, Tomistoma lusitanica and Gavialosuchus eggenburgensis. It is unlikely that any of these species belong to Tomistoma, with the possibility that they can all be classified under Melitosaurus and Gavialosuchus. However, we retain them in open nomenclature pending reassessment of the remaining European Miocene tomistomines. Our taxonomic and phylogenetic revision helps to elucidate past tomistomine diversity in the Miocene of the Mediterranean region, prior to the group’s extirpation, and is an important first step in resolving the complicated history of European tomistomine systematics

Impact of the urgent care telephone service NHS 111 pilot sites: a controlled before and after study

Objectives To measure the impact of the urgent care telephone service NHS 111 on the emergency and urgent care system. Design Controlled before and after study using routine data. Setting Four pilot sites and three control sites covering a total population of 3.6 million in England, UK. Participants and data Routine data on 36 months of use of emergency ambulance service calls and incidents, emergency department attendances, urgent care contacts (general practice (GP) out of hours, walk in and urgent care centres) and calls to the telephone triage service NHS direct. Intervention NHS 111, a new 24 h 7 day a week telephone service for non-emergency health problems, operated by trained non-clinical call handlers with clinical support from nurse advisors, using NHS Pathways software to triage calls to different services and home care. Main outcomes Changes in use of emergency and urgent care services. Results NHS 111 triaged 277 163 calls in the first year of operation for a population of 1.8 million. There was no change overall in emergency ambulance calls, emergency department attendances or urgent care use. There was a 19.3% reduction in calls to NHS Direct (95% CI −24.6% to −14.0%) and a 2.9% increase in emergency ambulance incidents (95% CI 1.0% to 4.8%). There was an increase in activity overall in the emergency and urgent care system in each site ranging 4.7–12%/month and this remained when assuming that NHS 111 will eventually take all NHS Direct and GP out of hours calls. Conclusions In its first year of operation in four pilot sites NHS 111 did not deliver the expected system benefits of reducing calls to the 999 ambulance service or shifting patients to urgent rather than emergency care. There is potential that this type of service increases overall demand for urgent care

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 $z=0.193$, 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), $R_{\rm FRB}\tau\approx 10^4$Gpc$^{-3}$, 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 $\approx$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 $\approx$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 $\lesssim 10$ 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