arXiv subjects

Robert Chapman

Publications and source records attributed to Robert Chapman.

9 recordsLinked to original sources

arXiv2026

Association of Progressive PPFE and Mortality in Lung Cancer Screening Cohorts

Background: Pleuroparenchymal fibroelastosis (PPFE) is an upper lobe predominant fibrotic lung abnormality associated with increased mortality in established interstitial lung disease. However, the clinical significance of radiologic PPFE progression in lung cancer screening (LCS) populations remains unclear. Methods: We analysed longitudinal low-dose CT scans and clinical data from two LCS studies: National Lung Screening Trial (NLST; n=7,980); SUMMIT study (n=8,561). An automated algorithm quantified PPFE volume on baseline and follow-up scans. Annualised change in PPFE was derived and dichotomised using a distribution-based threshold to define progressive PPFE. Associations between progressive PPFE and mortality were evaluated using Cox proportional hazards models adjusted for demographic and clinical variables. In SUMMIT cohort, associations between progressive PPFE and clinical outcomes were assessed using incidence rate ratios (IRR) and odds ratios (OR). Findings: Progressive PPFE independently associated with mortality in both LCS cohorts (NLST: Hazard Ratio (HR)=1.25, 95% Confidence Interval (CI): 1.01--1.56, p=0.042; SUMMIT: HR=3.14, 95% CI: 1.66--5.97, p<0.001). Within SUMMIT, progressive PPFE was strongly associated with higher respiratory admissions (IRR=2.79, p<0.001), increased antibiotic and steroid use (IRR=1.55, p=0.010), and showed a trend towards higher modified medical research council scores (OR=1.40, p=0.055). Interpretation: Radiologic PPFE progression independently associates with mortality across two large LCS cohorts, and associates with adverse clinical outcomes. Quantitative assessment of PPFE progression may provide a clinically relevant imaging biomarker to identify individuals at increased risk of respiratory morbidity within LCS programmes.

q-bio.QM↗

arXiv2023

Interpolation-Split: a data-centric deep learning approach with big interpolated data to boost airway segmentation performance

The morphology and distribution of airway tree abnormalities enables diagnosis and disease characterisation across a variety of chronic respiratory conditions. In this regard, airway segmentation plays a critical role in the production of the outline of the entire airway tree to enable estimation of disease extent and severity. In this study, we propose a data-centric deep learning technique to segment the airway tree. The proposed technique utilises interpolation and image split to improve data usefulness and quality. Then, an ensemble learning strategy is implemented to aggregate the segmented airway trees at different scales. In terms of segmentation performance (dice similarity coefficient), our method outperforms the baseline model by 2.5% on average when a combined loss is used. Further, our proposed technique has a low GPU usage and high flexibility enabling it to be deployed on any 2D deep learning model.

eess.IV↗

arXiv2022

Child Care Provider Survival Analysis

The aggregate ability of child care providers to meet local demand for child care is linked to employment rates in many sectors of the economy. Amid growing concern regarding child care provider sustainability due to the COVID-19 pandemic, state and local governments have received large amounts of new funding to better support provider stability. In response to this new funding aimed at bolstering the child care market in Florida, this study was devised as an exploratory investigation into features of child care providers that lead to business longevity. In this study we used optimal survival trees, a machine learning technique designed to better understand which providers are expected to remain operational for longer periods of time, supporting stabilization of the child care market. This tree-based survival analysis detects and describes complex interactions between provider characteristics that lead to differences in expected business survival rates. Results show that small providers who are religiously affiliated, and all providers who are serving children in Florida's universal Prekindergarten program and/or children using child care subsidy, are likely to have the longest expected survival rates.

econ.GN↗

arXiv2015

All-optical thermometry and the thermal properties of the optically detected spin resonances of the NV center in nano-diamond

The negatively-charged nitrogen-vacancy (NV) center in diamond is at the frontier of quantum nano-metrology and bio-sensing. Recent attention has focused on the application of high-sensitivity thermometry using the spin resonances of NV centers in nano-diamond to sub-cellular biological and biomedical research. Here, we report a comprehensive investigation of the thermal properties of the center's spin resonances and demonstrate an alternate all-optical NV thermometry technique that exploits the temperature dependence of the center's optical Debye-Waller factor.

quant-ph↗

arXiv2011

Optically Induced Polarization and Depolarization of an Electron Spin in a Nitrogen-Vacancy Center of Diamond Nano-crystals

Pulsed laser excitation causes the luminescence of Nitrogen Vacancy centers in diamond to unexpectedly decrease with increasing pulse energy. This decrease is observed in both the negatively charged and neutral centers and is caused by shortening of the luminescence lifetimes of the centers of both types. In darkness, the luminescence does not show any recovery on a time scale of 10 microseconds but as little as three low-intensity pulses can return the luminescence to its previous, brighter state. An external magnetic field reduces the magnitude of the effect. A possible mechanism for these phenomena based on optical polarisation and depolarisation of an electronic spin is proposed.

cond-mat.mes-hall↗

arXiv2009

Short gamma-ray bursts from SGR giant flares and neutron star mergers: two populations are better than one

There is increasing evidence of a local population of short duration Gamma-ray Bursts (sGRB), but it remains to be seen whether this is a separate population to higher redshift bursts. Here we choose plausible Luminosity Functions (LF) for both neutron star binary mergers and giant flares from Soft Gamma Repeaters (SGR), and combined with theoretical and observed Galactic intrinsic rates we examine whether a single progenitor model can reproduce both the overall BATSE sGRB number counts and a local population, or whether a dual progenitor population is required. Though there are large uncertainties in the intrinsic rates, we find that at least a bimodal LF consisting of lower and higher luminosity populations is required to reproduce both the overall BATSE sGRB number counts and a local burst distribution. Furthermore, the best fit parameters of the lower luminosity population agree well with the known properties of SGR giant flares, and the predicted numbers are sufficient to account for previous estimates of the local sGRB population.

astro-ph↗

arXiv2007

Two populations are better than one: Short gamma-ray bursts from SGR giant flares and NS-NS mergers

With a peak luminosity of ~10^47 erg/s, the December 27th 2004 giant flare from SGR1806-20 would have been visible by BATSE (the Burst and Transient Source Experiment) out to ~50 Mpc. It is thus plausible that some fraction of the short duration Gamma-Ray Bursts (sGRBs) in the BATSE catalogue were due to extragalactic magnetar giant flares. According to the most widely accepted current models, the remaining BATSE sGRBs were most likely produced by compact object (neutron star-neutron star or neutron star-black hole) mergers with intrinsically higher luminosities. Previously, by examining correlations on the sky between BATSE sGRBs and galaxies within 155 Mpc, we placed limits on the proportion of nearby sGRBs. Here, we examine the redshift distribution of sGRBs produced by assuming both one and two populations of progenitor with separate Luminosity Functions (LFs). Using the local Galactic SGR giant flare rate and theoretical NS-NS merger rates evolved according to well-known Star Formation Rate parameterisations, we constrain the predicted distributions by BATSE sGRB overall number counts. We show that only a dual population consisting of both SGR giant flares and NS-NS mergers can reproduce the likely local distribution of sGRBs as well as the overall number counts. In addition, the best fit LF parameters of both sub-populations are in good agreement with observed luminosities.

astro-ph↗

arXiv2007

How common are long Gamma-Ray Bursts in the Local Universe?

The two closest Gamma-Ray Bursts so far detected (GRBs 980425 & 060218) were both under-luminous, spectrally soft, long duration bursts with smooth, single-peaked light curves. Only of the order of 100 GRBs have measured redshifts, and there are, for example, 2704 GRBs in the BATSE catalogue alone. It is therefore plausible that other nearby GRBs have been observed but not identified as relatively nearby. Here we search for statistical correlations between BATSE long duration GRBs and galaxy samples with recession velocities v <= 11,000 km/s (z = 0.0367, ~ 155 Mpc) selected from two catalogues of nearby galaxies. We also examine the correlations using burst sub-samples restricted to those with properties similar to the two known nearby bursts. Our results show correlation of the entire long GRB sample to remain consistent with zero out to the highest radii considered whereas a sub-sample selected to be low fluence, spectrally soft, with smooth single-peaked light curves (177 bursts) demonstrates increased correlation with galaxies within ~ 155 Mpc. The measured correlation (28% +/- 16% of the sample) suggests that BATSE observed between 2 and 9 long duration GRBs per year similar to, and from within similar distances to GRBs 980425 and 060218. This implies an observed local rate density (to BATSE limits) of 700 +/- 360 Gpc^{-3}yr^{-1} within 155 Mpc.

astro-ph↗

arXiv2006

Short GRBs in old populations: Magnetars from WD-WD mergers

Recent progress on the nature of short duration gamma-ray bursts has shown that a fraction of them originate in the local universe. These systems may well be the result of giant flares from soft gamma-repeaters (highly magnetized neutron stars commonly known as magnetars). However, if these neutron stars are formed via the core collapse of massive stars then it would be expected that the bursts should originate from predominantly young stellar populations, while correlating the positions of BATSE short bursts with structure in the local universe reveals a correlation with all galaxy types, including those with little or no ongoing star formation. This is a natural outcome if, in addition to magnetars formed via the core collapse of massive stars they also form via Accretion Induced Collapse following the merger of two white dwarfs, one of which is magnetic. We investigate this possibility and find that the rate of magnetar production via WD-WD mergers in the Milky Way is comparable to the rate of production via core-collapse. However, while the rate of production of magnetars by core collapse is proportional to the star formation rate, the rate of production via WD-WD mergers (which have long lifetimes) is proportional to the stellar mass density, which is concentrated in early-type systems. Therefore magnetars produced via WD-WD mergers may produce SGR giant flares which can be identified with early type galaxies. We also comment on the possibility that this mechanism could produce a fraction of the observed short duration burst population at higher redshift.

astro-ph↗