46 research outputs found
A semi-free weighting matrices approach for neutral-type delayed neural networks
AbstractIn this paper, a new approach is proposed for stability issues of neutral-type neural networks (DNNs) with constant delay. First, the semi-free weighting matrices are proposed and used instead of the known free weighting matrices to express the relationship between the terms in the Leibniz–Newton formula to simplify the system synthesis and to obtain less computation demand. Second, global exponential stability conditions which are less conservative and restrictive than the known results are derived. At the same time, based on the above approach, fewer variable matrices are introduced in the construction of the Lyapunov functional and augmented Lyapunov functional. Two examples are given to show their effectiveness and advantages over others
Slicing-free Inverse Regression in High-dimensional Sufficient Dimension Reduction
Sliced inverse regression (SIR, Li 1991) is a pioneering work and the most
recognized method in sufficient dimension reduction. While promising progress
has been made in theory and methods of high-dimensional SIR, two remaining
challenges are still nagging high-dimensional multivariate applications. First,
choosing the number of slices in SIR is a difficult problem, and it depends on
the sample size, the distribution of variables, and other practical
considerations. Second, the extension of SIR from univariate response to
multivariate is not trivial. Targeting at the same dimension reduction subspace
as SIR, we propose a new slicing-free method that provides a unified solution
to sufficient dimension reduction with high-dimensional covariates and
univariate or multivariate response. We achieve this by adopting the recently
developed martingale difference divergence matrix (MDDM, Lee & Shao 2018) and
penalized eigen-decomposition algorithms. To establish the consistency of our
method with a high-dimensional predictor and a multivariate response, we
develop a new concentration inequality for sample MDDM around its population
counterpart using theories for U-statistics, which may be of independent
interest. Simulations and real data analysis demonstrate the favorable finite
sample performance of the proposed method
VLBI Astrometry of Radio Stars to Link Radio and Optical Celestial Reference Frames. I. HD 199178 AR Lacertae
To accurately link the radio and optical Celestial Reference Frames (CRFs) at
optical bright end, i.e., with Gaia G band magnitude < 13, increasing number
and improving sky distribution of radio stars with accurate astrometric
parameters from both Very Long Baseline Interferometry (VLBI) and Gaia
measurements are mandatory. We selected two radio stars HD 199178 and AR
Lacertae as the target for a pilot program for the frame link, using the Very
Long Baseline Array (VLBA) at 15 GHz at six epochs spanning about 1 year, to
measure their astrometric parameters. The measured parallax of HD 199178 is
mas and the proper motion is , , while the parallax of
AR Lac is mas and the proper motion is , . Our
VLBI measured astrometric parameters have accuracies about 4-5 times better
than the corresponding historic VLBI measurements and comparable accuracies
with those from Gaia, validating the feasibility of frame link using radio
stars. With the updated astrometric parameters for these two stars, there is a
25% reduction of the uncertainties on the Y axis for both orientation and spin
parameters.Comment: 11 pages, accepted by MNRAS on 2023 April 2
A centi-pc-scale compact radio core in the nearby galaxy M60
M60, an elliptical galaxy located 16.5~Mpc away, has an active nucleus with a
very low luminosity and an extremely low accretion rate. Its central
supermassive black hole has a mass of and a Schwarzschild radii corresponding to . To investigate the nature of its innermost radio
nucleus, data from the Very Long Baseline Array (VLBA) at 4.4 and 7.6~GHz were
reduced. The VLBA images reveal a compact component with total flux densities
of 20~mJy at both frequencies, a size of 0.27~mas (99.7
confidence level), about 0.022~pc () at 7.6~GHz, and a
brightness temperature of ~K. This suggests that the
observed centi-parsec-scale compact core could be attributed to a nonthermal
jet base or an advection-dominated accretion flow (ADAF) with nonthermal
electrons. The extremely compact structure also supports the presence of an
SMBH in the center. Our results indicate that M60 is a promising target for
broad-band VLBI observations at millimeter wavelengths to probe ADAF scenarios
and tightly constrain the potential photon ring (about 28\,as) around its
SMBH.Comment: 15 pages, 5 figures, 3 tables, accepted for publication in
Astrophysical Journa
The parallax and 3D kinematics of water masers in the massive star-forming region G034.43+0.24
We report a trigonometric parallax measurement of 22 GHz water masers in the
massive star-forming region G034.43+0.24 as part of the Bar and Spiral
Structure Legacy (BeSSeL) Survey using the Very Long Baseline Array. The
parallax is 0.33050.018 mas, corresponding to a distance of
kpc. This locates G034.43+0.24 near the inner edge of
the Sagittarius spiral arm and at one end of a linear distribution of massive
young stars which cross nearly the full width of the arm. The measured
3-dimensional motion of G034.43+0.24 indicates a near-circular Galactic orbit.
The water masers display arc-like distributions, possibly bow shocks,
associated with winds from one or more massive young stars
The ALMA-QUARKS survey: -- I. Survey description and data reduction
This paper presents an overview of the QUARKS survey, which stands for
`Querying Underlying mechanisms of massive star formation with ALMA-Resolved
gas Kinematics and Structures'. The QUARKS survey is observing 139 massive
clumps covered by 156 pointings at ALMA Band 6 ( 1.3 mm). In
conjunction with data obtained from the ALMA-ATOMS survey at Band 3
( 3 mm), QUARKS aims to carry out an unbiased statistical
investigation of massive star formation process within protoclusters down to a
scale of 1000 au. This overview paper describes the observations and data
reduction of the QUARKS survey, and gives a first look at an exemplar source,
the mini-starburst Sgr B2(M). The wide-bandwidth (7.5 GHz) and
high-angular-resolution (~0.3 arcsec) observations of the QUARKS survey allow
to resolve much more compact cores than could be done by the ATOMS survey, and
to detect previously unrevealed fainter filamentary structures. The spectral
windows cover transitions of species including CO, SO, ND, SiO,
H, HCO, CHCN and many other complex organic molecules,
tracing gas components with different temperatures and spatial extents. QUARKS
aims to deepen our understanding of several scientific topics of massive star
formation, such as the mass transport within protoclusters by (hub-)filamentary
structures, the existence of massive starless cores, the physical and chemical
properties of dense cores within protoclusters, and the feedback from already
formed high-mass young protostars.Comment: 9 figures, 4 tables, accepted by RA
The ALMA Survey of Star Formation and Evolution in Massive Protoclusters with Blue Profiles (ASSEMBLE): Core Growth, Cluster Contraction, and Primordial Mass Segregation
The ALMA Survey of Star Formation and Evolution in Massive Protoclusters with
Blue Profiles (ASSEMBLE) aims to investigate the process of mass assembly and
its connection to high-mass star formation theories in protoclusters in a
dynamic view. We observed 11 massive (Mclump>1000 Msun), luminous (Lbol>10,000
Lsun), and blue-profile (infall signature) clumps by ALMA with resolution of
2200-5500 au at 350 GHz (870 um) in continuum and line emission. 248 dense
cores were identified, including 106 cores showing protostellar signatures and
142 prestellar core candidates. Compared to early-stage infrared dark clouds
(IRDCs) by ASHES, the core mass and surface density within the ASSEMBLE clumps
exhibited significant increment, suggesting concurrent core accretion during
the evolution of the clumps. The maximum mass of prestellar cores was found to
be 2 times larger than that in IRDCs, indicating evolved protoclusters have the
potential to harbor massive prestellar cores. The mass relation between clumps
and their most massive core (MMCs) is observed in ASSEMBLE but not in IRDCs,
which is suggested to be regulated by multiscale mass accretion. The mass
correlation between the core clusters and their MMCs has a steeper slope
compared to that observed in stellar clusters, which can be due to
fragmentation of the MMC and stellar multiplicity. We observe a decrease in
core separation and an increase in central concentration as protoclusters
evolve. We confirm primordial mass segregation in the ASSEMBLE protoclusters,
possibly resulting from gravitational concentration and/or gas accretion.Comment: 37 pages, 13 figures, 5 tables; accepted for publication in ApJ
Amplicon-Based Detection and Sequencing of SARS-CoV-2 in Nasopharyngeal Swabs from Patients With COVID-19 and Identification of Deletions in the Viral Genome That Encode Proteins Involved in Interferon Antagonism
Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the causative agent of coronavirus disease 2019 (COVID-19). Sequencing the viral genome as the outbreak progresses is important, particularly in the identification of emerging isolates with different pathogenic potential and to identify whether nucleotide changes in the genome will impair clinical diagnostic tools such as real-time PCR assays. Although single nucleotide polymorphisms and point mutations occur during the replication of coronaviruses, one of the biggest drivers in genetic change is recombination. This can manifest itself in insertions and/or deletions in the viral genome. Therefore, sequencing strategies that underpin molecular epidemiology and inform virus biology in patients should take these factors into account. A long amplicon/read length-based RT-PCR sequencing approach focused on the Oxford Nanopore MinION/GridION platforms was developed to identify and sequence the SARS-CoV-2 genome in samples from patients with or suspected of COVID-19. The protocol, termed Rapid Sequencing Long Amplicons (RSLAs) used random primers to generate cDNA from RNA purified from a sample from a patient, followed by single or multiplex PCRs to generate longer amplicons of the viral genome. The base protocol was used to identify SARS-CoV-2 in a variety of clinical samples and proved sensitive in identifying viral RNA in samples from patients that had been declared negative using other nucleic acid-based assays (false negative). Sequencing the amplicons revealed that a number of patients had a proportion of viral genomes with deletions
Global, regional, and national disability-adjusted life-years (DALYs) for 359 diseases and injuries and healthy life expectancy (HALE) for 195 countries and territories, 1990-2017: a systematic analysis for the Global Burden of Disease Study 2017.
How long one lives, how many years of life are spent in good and poor health, and how the population's state of health and leading causes of disability change over time all have implications for policy, planning, and provision of services. We comparatively assessed the patterns and trends of healthy life expectancy (HALE), which quantifies the number of years of life expected to be lived in good health, and the complementary measure of disability-adjusted life-years (DALYs), a composite measure of disease burden capturing both premature mortality and prevalence and severity of ill health, for 359 diseases and injuries for 195 countries and territories over the past 28 years. Methods We used data for age-specific mortality rates, years of life lost (YLLs) due to premature mortality, and years lived with disability (YLDs) from the Global Burden of Diseases, Injuries, and Risk Factors Study (GBD) 2017 to calculate HALE and DALYs from 1990 to 2017. We calculated HALE using age-specific mortality rates and YLDs per capita for each location, age, sex, and year. We calculated DALYs for 359 causes as the sum of YLLs and YLDs. We assessed how observed HALE and DALYs differed by country and sex from expected trends based on Socio-demographic Index (SDI). We also analysed HALE by decomposing years of life gained into years spent in good health and in poor health, between 1990 and 2017, and extra years lived by females compared with males. Findings Globally, from 1990 to 2017, life expectancy at birth increased by 7·4 years (95% uncertainty interval 7·1-7·8), from 65·6 years (65·3-65·8) in 1990 to 73·0 years (72·7-73·3) in 2017. The increase in years of life varied from 5·1 years (5·0-5·3) in high SDI countries to 12·0 years (11·3-12·8) in low SDI countries. Of the additional years of life expected at birth, 26·3% (20·1-33·1) were expected to be spent in poor health in high SDI countries compared with 11·7% (8·8-15·1) in low-middle SDI countries. HALE at birth increased by 6·3 years (5·9-6·7), from 57·0 years (54·6-59·1) in 1990 to 63·3 years (60·5-65·7) in 2017. The increase varied from 3·8 years (3·4-4·1) in high SDI countries to 10·5 years (9·8-11·2) in low SDI countries. Even larger variations in HALE than these were observed between countries, ranging from 1·0 year (0·4-1·7) in Saint Vincent and the Grenadines (62·4 years [59·9-64·7] in 1990 to 63·5 years [60·9-65·8] in 2017) to 23·7 years (21·9-25·6) in Eritrea (30·7 years [28·9-32·2] in 1990 to 54·4 years [51·5-57·1] in 2017). In most countries, the increase in HALE was smaller than the increase in overall life expectancy, indicating more years lived in poor health. In 180 of 195 countries and territories, females were expected to live longer than males in 2017, with extra years lived varying from 1·4 years (0·6-2·3) in Algeria to 11·9 years (10·9-12·9) in Ukraine. Of the extra years gained, the proportion spent in poor health varied largely across countries, with less than 20% of additional years spent in poor health in Bosnia and Herzegovina, Burundi, and Slovakia, whereas in Bahrain all the extra years were spent in poor health. In 2017, the highest estimate of HALE at birth was in Singapore for both females (75·8 years [72·4-78·7]) and males (72·6 years [69·8-75·0]) and the lowest estimates were in Central African Republic (47·0 years [43·7-50·2] for females and 42·8 years [40·1-45·6] for males). Globally, in 2017, the five leading causes of DALYs were neonatal disorders, ischaemic heart disease, stroke, lower respiratory infections, and chronic obstructive pulmonary disease. Between 1990 and 2017, age-standardised DALY rates decreased by 41·3% (38·8-43·5) for communicable diseases and by 49·8% (47·9-51·6) for neonatal disorders. For non-communicable diseases, global DALYs increased by 40·1% (36·8-43·0), although age-standardised DALY rates decreased by 18·1% (16·0-20·2)
Erratum: Global, regional, and national comparative risk assessment of 84 behavioural, environmental and occupational, and metabolic risks or clusters of risks for 195 countries and territories, 1990–2017: a systematic analysis for the Global Burden of Disease Study 2017
Interpretation: By quantifying levels and trends in exposures to risk factors and the resulting disease burden, this assessment offers insight into where past policy and programme efforts might have been successful and highlights current priorities for public health action. Decreases in behavioural, environmental, and occupational risks have largely offset the effects of population growth and ageing, in relation to trends in absolute burden. Conversely, the combination of increasing metabolic risks and population ageing will probably continue to drive the increasing trends in non-communicable diseases at the global level, which presents both a public health challenge and opportunity. We see considerable spatiotemporal heterogeneity in levels of risk exposure and risk-attributable burden. Although levels of development underlie some of this heterogeneity, O/E ratios show risks for which countries are overperforming or underperforming relative to their level of development. As such, these ratios provide a benchmarking tool to help to focus local decision making. Our findings reinforce the importance of both risk exposure monitoring and epidemiological research to assess causal connections between risks and health outcomes, and they highlight the usefulness of the GBD study in synthesising data to draw comprehensive and robust conclusions that help to inform good policy and strategic health planning