629 research outputs found
Intensity Inhomogeneity Correction of SD-OCT Data Using Macular Flatspace
Images of the retina acquired using optical coherence tomography (OCT) often suffer from intensity inhomogeneity problems that degrade both the quality of the images and the performance of automated algorithms utilized to measure structural changes. This intensity variation has many causes, including off-axis acquisition, signal attenuation, multi-frame averaging, and vignetting, making it difficult to correct the data in a fundamental way. This paper presents a method for inhomogeneity correction by acting to reduce the variability of intensities within each layer. In particular, the N3 algorithm, which is popular in neuroimage analysis, is adapted to work for OCT data. N3 works by sharpening the intensity histogram, which reduces the variation of intensities within different classes. To apply it here, the data are first converted to a standardized space called macular flat space (MFS). MFS allows the intensities within each layer to be more easily normalized by removing the natural curvature of the retina. N3 is then run on the MFS data using a modified smoothing model, which improves the efficiency of the original algorithm. We show that our method more accurately corrects gain fields on synthetic OCT data when compared to running N3 on non-flattened data. It also reduces the overall variability of the intensities within each layer, without sacrificing contrast between layers, and improves the performance of registration between OCT images
The Zwicky Transient Facility: Surveys and Scheduler
We present a novel algorithm for scheduling the observations of time-domain
imaging surveys. Our Integer Linear Programming approach optimizes an observing
plan for an entire night by assigning targets to temporal blocks, enabling
strict control of the number of exposures obtained per field and minimizing
filter changes. A subsequent optimization step minimizes slew times between
each observation. Our optimization metric self-consistently weights
contributions from time-varying airmass, seeing, and sky brightness to maximize
the transient discovery rate. We describe the implementation of this algorithm
on the surveys of the Zwicky Transient Facility and present its on-sky
performance.Comment: Published in PASP Focus Issue on the Zwicky Transient Facility
(https://dx.doi.org/10.1088/1538-3873/ab0c2a). 13 Pages, 11 Figure
Assessment of water supply and sanitation of some coastal communities of the Niger Delta
A series of separate surveys were carried out on six coastal communities within a span of three years. The
study focused on the assessment of water supply and sanitation facilities in the selected communities. Water
samples were collected at various sources (boreholes, rivers, wells, streams and springs). Physico-chemical
and Microbiological characteristics of the various water samples from the study areas show that all the
water sources in the study areas were not fit for human consumption or for any reasonable use. The quality
of sanitation facilities in these communities were grossly inadequate. Therefore, there is a need to develop
deliberate specific programmes that are fit for purpose to address the total lack of adequate water supply
and sanitation in the coastal communities of the Niger Delta. The study makes recommendations for the
development of a ‘Framework for Intervention Programmes on Water Supply and Sanitation for Coastal
Communities in the region’
A journey without maps—Understanding the costs of caring for dependent older people in Nigeria, China, Mexico and Peru
Purpose of the study: Populations in Latin America, Asia and sub-Saharan Africa are rapidly ageing. The extent to which traditional systems of family support and security can manage the care of increased numbers of older people with chronic health problems is unclear. Our aim was to explore the social and economic effects of caring for an older dependent person, including insight into pathways to economic vulnerability. Design & methods: We carried out a series of household case studies across urban and rural sites in Peru, Mexico, China and Nigeria (n = 24), as part of a cross-sectional study, nested within the 10/66 Dementia Research Group cohort. Case studies consisted of in-depth narrative style interviews (n = 60) with multiple family members, including the older dependent person. Results: Governments were largely uninvolved in the care and support of older dependent people, leaving families to negotiate a ‘journey without maps’. Women were de facto caregivers but the traditional role of female relative as caregiver was beginning to be contested. Household composition was flexible and responsive to changing needs of multiple generations but family finances were stretched. Implications: Governments are lagging behind sociodemographic and social change. There is an urgent need for policy frameworks to support and supplement inputs from families. These should include community-based and residential care services, disability benefits and carers allowances. Further enhancement of health insurance schemes and scale-up of social pensions are an important component of bolstering the security of dependent older people and supporting their continued social and economic participation
Grazing incidence optics designs for future gamma-ray missions
Sensitive nuclear line spectroscopy for observations of prompt emission from supernovae, as well as mapping of remnants has been a primary goal of gamma-ray astrophysics since its inception. A number of key lines lie in the energy band from 10 - 600 keV. In this region of the spectrum, observations have to-date been limited by high background and poor angular resolution. In this paper, we present several designs capable of extending the sensitivity of grazing incidence optics into this energy range. In particular, we discuss a 15 m focal length design for NASA's High-Sensitivity Spectroscopic Imaging Mission concept, as well as a 50 m focal length design which can extend ESA's XEUS mission into this band. We demonstrate that an unprecedented line sensitivity of 10^(-7) cm^(-2) s^(-1) can be achieved for the most important lines in this energy band
Rapid Brain Meninges Surface Reconstruction with Layer Topology Guarantee
The meninges, located between the skull and brain, are composed of three
membrane layers: the pia, the arachnoid, and the dura. Reconstruction of these
layers can aid in studying volume differences between patients with
neurodegenerative diseases and normal aging subjects. In this work, we use
convolutional neural networks (CNNs) to reconstruct surfaces representing
meningeal layer boundaries from magnetic resonance (MR) images. We first use
the CNNs to predict the signed distance functions (SDFs) representing these
surfaces while preserving their anatomical ordering. The marching cubes
algorithm is then used to generate continuous surface representations; both the
subarachnoid space (SAS) and the intracranial volume (ICV) are computed from
these surfaces. The proposed method is compared to a state-of-the-art
deformable model-based reconstruction method, and we show that our method can
reconstruct smoother and more accurate surfaces using less computation time.
Finally, we conduct experiments with volumetric analysis on both subjects with
multiple sclerosis and healthy controls. For healthy and MS subjects, ICVs and
SAS volumes are found to be significantly correlated to sex (p<0.01) and age
(p<0.03) changes, respectively.Comment: ISBI 2023 Ora
Flexibility within the Heads of Muscle Myosin-2 Molecules
We show that negative-stain electron microscopy and image processing of nucleotide-free (apo) striated muscle myosin-2 subfragment-1 (S1), possessing one light chain or both light chains, is capable of resolving significant amounts of structural detail. The overall appearance of the motor and the lever is similar in rabbit, scallop and chicken S1. Projection matching of class averages of the different S1 types to projection views of two different crystal structures of apo S1 shows that all types most commonly closely resemble the appearance of the scallop S1 structure rather than the methylated chicken S1 structure. Methylation of chicken S1 has no effect on the structure of the molecule at this resolution: it too resembles the scallop S1 crystal structure. The lever is found to vary in its angle of attachment to the motor domain, with a hinge point located in the so-called pliant region between the converter and the essential light chain. The chicken S1 crystal structure lies near one end of the range of flexion observed. The Gaussian spread of angles of flexion suggests that flexibility is driven thermally, from which a torsional spring constant of ~ 23 pN·nm/rad2 is estimated on average for all S1 types, similar to myosin-5. This translates to apparent cantilever-type stiffness at the tip of the lever of 0.37 pN/nm. Because this stiffness is lower than recent estimates from myosin-2 heads attached to actin, we suggest that binding to actin leads to an allosteric stiffening of the motor–lever junction
R Coronae Borealis Stars in M31 from the Palomar Transient Factory
We report the discovery of R Coronae Borealis (RCB) stars in the Andromeda galaxy (M31) using the Palomar Transient Factory (PTF). RCB stars are rare hydrogen-deficient, carbon-rich supergiant variables, most likely the merger products of two white dwarfs. These new RCBs, including two confirmed ones and two candidates, are the first to be found beyond the Milky Way and the Magellanic Clouds. All of M31 RCBs showed >1.5 mag irregular declines over timescales of weeks to months. Due to the limiting magnitude of our data (R ≈ 21-22 mag), these RCB stars have R ≈ 19.5-20.5 mag at maximum light, corresponding to M_R = –4 to –5, making them some of the most luminous RCBs known. Spectra of two objects show that they are warm RCBs, similar to the Milky Way RCBs RY Sgr and V854 Cen. We consider these results, derived from a pilot study of M31 variables, as an important proof-of-concept for the study of rare bright variables in nearby galaxies with the PTF or other synoptic surveys
HACA3: A Unified Approach for Multi-site MR Image Harmonization
The lack of standardization is a prominent issue in magnetic resonance (MR)
imaging. This often causes undesired contrast variations due to differences in
hardware and acquisition parameters. In recent years, MR harmonization using
image synthesis with disentanglement has been proposed to compensate for the
undesired contrast variations. Despite the success of existing methods, we
argue that three major improvements can be made. First, most existing methods
are built upon the assumption that multi-contrast MR images of the same subject
share the same anatomy. This assumption is questionable since different MR
contrasts are specialized to highlight different anatomical features. Second,
these methods often require a fixed set of MR contrasts for training (e.g.,
both Tw-weighted and T2-weighted images must be available), which limits their
applicability. Third, existing methods generally are sensitive to imaging
artifacts. In this paper, we present a novel approach, Harmonization with
Attention-based Contrast, Anatomy, and Artifact Awareness (HACA3), to address
these three issues. We first propose an anatomy fusion module that enables
HACA3 to respect the anatomical differences between MR contrasts. HACA3 is also
robust to imaging artifacts and can be trained and applied to any set of MR
contrasts. Experiments show that HACA3 achieves state-of-the-art performance
under multiple image quality metrics. We also demonstrate the applicability of
HACA3 on downstream tasks with diverse MR datasets acquired from 21 sites with
different field strengths, scanner platforms, and acquisition protocols
A Pulsar Survey of 18 Supernova Remnants
We have performed a pulsar search of 18 known or probable supernova remnants with the Arecibo 305 m radio telescope at 430 and 1420 MHz. The remnants were selected to have angular sizes less than or of order a few telescope beam diameters (˜10' at 430 MHz and ˜3' at 1420 MHz). In some cases, larger remnants with centrally brightened cores of this scale were also included. The observations were sensitive to pulsars with periods ≳1 ms and flux densities as low as ˜0.2 mJy. The targets included two probable plerionic objects and several shell-type remnants with centrally brightened X-ray profiles. No new pulsars were discovered in the survey, and we discuss some of the selection effects that make the interpretation of pulsar surveys of supernova remnants problematic. Effects of high pulsar velocities, uncertain distances, and high remnant brightness temperatures make it difficult to exclude the presence of a pulsar in most remnants
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