ORCID Profile
0000-0002-5471-7635
Current Organisations
Natural History Museum of Los Angeles County
,
University of Western Australia
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Publisher: Springer Science and Business Media LLC
Date: 1998
Publisher: American Astronomical Society
Date: 20-11-2008
DOI: 10.1086/592076
Publisher: Informa UK Limited
Date: 11-2001
Publisher: Springer Science and Business Media LLC
Date: 14-07-2022
Publisher: Springer Science and Business Media LLC
Date: 31-10-2022
DOI: 10.1038/S41598-022-22027-0
Abstract: Free-space optical communications are poised to alleviate the data-flow bottleneck experienced by spacecraft as traditional radio frequencies reach their practical limit. While enabling orders-of-magnitude gains in data rates, optical signals impose much stricter pointing requirements and are strongly affected by atmospheric turbulence. Coherent detection methods, which capitalize fully on the available degrees of freedom to maximize data capacity, have the added complication of needing to couple the received signal into single-mode fiber. In this paper we present results from a coherent 1550 nm link across turbulent atmosphere between a deployable optical terminal and a drone-mounted retroreflector. Through 10 Hz machine vision optical tracking with nested 200 Hz tip/tilt adaptive optics stabilisation, we corrected for pointing errors and atmospheric turbulence to maintain robust single mode fiber coupling, resulting in an uninterrupted 100 Gbps optical data link while tracking at angular rates of up to 1.5 deg/s, equivalent to that of spacecraft in low earth orbit. With the greater data capacity of coherent communications and compatibility with extant fiber-based technologies being demonstrated across static links, ground-to-low earth orbit links of Terabits per second can ultimately be achieved with capable ground stations.
Publisher: Optica Publishing Group
Date: 04-04-2022
DOI: 10.1364/OL.453869
Abstract: Corner cube retroreflectors are commonly used as cooperative targets in free-space laser applications. The previous literature suggests that due to path reciprocity, a retroreflected beam is self-corrected across a turbulent atmosphere and should show no angle-of-arrival variability in the near field. This is at odds with recent experiments that rely on angle-of-arrival measurements in retroreflected beams for effective tip/tilt correction. In this Letter we investigate the mechanism behind observed angle-of-arrival variability using numerical field propagation to model various transceiver and retroreflector geometries. We determine that asymmetric truncation of a curved wavefront at the retroreflector, transceiver, or both, results in a difference in tip/tilt between the transmitted and reflected wavefronts. This difference propagates as angle-of-arrival variation at the transceiver despite reciprocity, providing the error signal necessary for adaptive optics tip/tilt correction without a remote beacon.
Publisher: Geological Society of London
Date: 03-1999
Publisher: Springer Netherlands
Date: 2008
Publisher: Elsevier BV
Date: 10-2013
DOI: 10.1016/J.HUMPATH.2013.05.015
Abstract: Prostatic adenocarcinomas arising within the transition zone (Tz) are distinct from peripheral zone (Pz) tumors as regards biological aggression and mechanism of extraprostatic extension. Reliable biopsy identification of Tz tumors would allow targeted surgical approaches more likely to preserve erectile function without compromising surgical margins. Previous studies have demonstrated the presence of eosinophilic cytoplasmic granules (prostate secretory granules, or PSGs) after glutaraldehye fixation, with apparent depletion in neoplasia. We investigated PSG content, columnar cells, pale cytoplasm, and luminal secretions of both Pz and Tz tumors in 44 radical prostatectomies (RPs) and 135 biopsies fixed with gluteraldehyde-based fixative. Retention of PSG is characteristic of Tz carcinoma and infrequently seen in Pz tumors, and a combination of PSG greater than 30% with either columnar cells, pale cells, or secretions in biopsies is a reliable marker for Tz origin. When these criteria were prospectively applied to 3929 cases with follow-up RP, 510 Tz tumors were correctly identified on biopsy (sensitivity, 21.4% specificity, 97.4%). Biopsy-identified Tz tumors had higher volumes (mean, 3.48 versus 1.81 cm(3) P < .001) and higher rates of margin positivity (22.5% versus 17.5% P = .008) than did Tz tumors not identified preoperatively. Mean Tz tumor length in biopsies was 2.0 mm, with no correlation between tumor volume at RP and tumor length on biopsy. Tz tumors are reliably identified on biopsy, based on a combination of PSG retention with either columnar cells, pale cells, or secretion. Biopsy-identified Tz tumors may not be suitable for active surveillance because of an associated high probability of large tumor volume and increased risk of positive margins at RP.
Publisher: Cold Spring Harbor Laboratory
Date: 13-07-2021
DOI: 10.1101/2021.07.12.452083
Abstract: Spiny-rayed fishes (Acanthomorpha) dominate modern marine habitats and comprise more than a quarter of all living vertebrate species 1–3 . It is believed that this dominance resulted from explosive lineage and phenotypic ersification coincident with the Cretaceous-Paleogene (K-Pg) mass-extinction event 4 . It remains unclear, however, if living acanthomorph ersity is the result of a punctuated burst or gradual accumulation of ersity following the K-Pg. We assess these hypotheses with a time-calibrated phylogeny inferred using ultraconserved elements from a s ling of species that represent over 91% of all acanthomorph families, as well as an extensive body shape dataset of extant species. Our results indicate that several million years after the end-Cretaceous, acanthomorphs underwent a prolonged and significant expansion of morphological disparity primarily driven by changes in body elongation, and that acanthomorph lineages containing the bulk of the living species ersity originated throughout the Cenozoic. These acanthomorph lineages radiated into distinct regions of morphospace and retained their iconic phenotypes, including a large group of laterally compressed reef fishes, fast-swimming open-ocean predators, bottom-dwelling flatfishes, seahorses, and pufferfishes. The evolutionary success of spiny-rayed fishes is the culmination of a post K-Pg adaptive radiation in which rates of lineage ersification were decoupled from periods of high phenotypic disparity.
Publisher: Elsevier
Date: 1995
Publisher: Optica Publishing Group
Date: 21-04-2023
DOI: 10.1364/OE.483767
Abstract: Geopotential and orthometric height differences between distant points can be measured via timescale comparisons between atomic clocks. Modern optical atomic clocks achieve statistical uncertainties on the order of 10 −18 , allowing height differences of around 1 cm to be measured. Frequency transfer via free-space optical links will be needed for measurements where linking the clocks via optical fiber is not possible, but requires line of sight between the clock locations, which is not always practical due to local terrain or over long distances. We present an active optical terminal, phase stabilization system, and phase compensation processing method robust enough to enable optical frequency transfer via a flying drone, greatly increasing the flexibility of free-space optical clock comparisons. We demonstrate a statistical uncertainty of 2.5×10 −18 after 3 s of integration, corresponding to a height difference of 2.3 cm, suitable for applications in geodesy, geology, and fundamental physics experiments.
Publisher: American Physical Society (APS)
Date: 04-05-2023
Publisher: American Astronomical Society
Date: 16-08-2011
Publisher: CERN
Date: 2019
Publisher: Wiley
Date: 27-07-2015
DOI: 10.1111/BJU.13173
Abstract: To assess the influence of tumour zonality on biochemical recurrence (BCR) after radical prostatectomy (RP) with a histologically confirmed positive surgical margin (PSM). Data from 382 patients that underwent RP with either transition zone (TZ) or peripheral zone (PZ) tumours involving PSMs between 1998 and 2010 were retrieved from the Abbott West Australian Prostatectomy Database. Statistical analysis was used to evaluate the relationship of various tumour clinicopathological parameters, e.g. zonal origin of tumour, tumour volume, Gleason score, and stage to the development of BCR RESULTS: There were 51 TZ and 331 PZ tumours with PSMs identified. The TZ tumours compared with PZ tumours were larger (median 5.67 vs 3.64 mL, P < 0.001), more frequently lower grade (Gleason score 6 33% vs 5%, P < 0.01), organ confined (51% vs 35.6%, P = 0.073), and preferentially involved the bladder neck (49% vs 6%, P < 0.001). Tumour zonality was not associated with BCR for the entire cohort. TZ and PZ tumours had similar 5-year BCR-free survival rates (58% vs 63%, P = 0.691) and comparable time to development of BCR (14.4 vs 19.2 months, P = 0.346). On univariate analysis, preoperative PSA level, PSM at the bladder neck, tumour volume, Gleason score (P < 0.001) and tumour stage were independent predictors of BCR for the entire cohort. On multivariate analysis tumour volume and Gleason score retained significance as independent predictors of BCR. Tumour zonality was not directly associated with BCR. Of the patients who received adjuvant therapy, the incidence of BCR was similar for TZ and PZ tumours (58% vs 67%, P = 0.077), although TZ tumours failed significantly earlier (mean 4.4 vs 16.4 months, P = 0.037). PSA recurrence in patients with histologically confirmed PSMs after RP is independent of the zonal location of the index tumour. However, tumour zonal origin may have an indirect influence on PSA relapse, as TZ tumours tend to be of large volume and more likely involve the bladder neck margin, both risk factors for BCR. Bladder neck margin involvement is associated with higher rates of BCR than other sites of PSMs. The preoperative identification of TZ tumours might aid surgical planning with appropriate alteration of RP technique to incorporate wider surgical margins at the bladder neck. Adjuvant radiotherapy appears to be associated with adverse outcome for TZ tumours, a novel finding which warrants further investigation.
Publisher: American Astronomical Society
Date: 19-11-2019
Abstract: We report near simultaneous imaging using LMIRCam on the LBTI of the quadruply imaged lensed quasar HS 0810+2554 at wavelengths of 2.16, 3.7, and 4.78 μ m with a full width at half maximum spatial resolution of 0.″13, 0.″12, and 0.″15 respectively, comparable to Hubble Space Telescope optical imaging. In the z = 1.5 rest frame of the quasar, the observed wavelengths correspond to 0.86, 1.48, and 1.91 μ m respectively. The two brightest images in the quad, A and B, are clearly resolved from each other with a separation of 0.″187. The flux ratio of these two images (A/B) trends from 1.79 to 1.23 at wavelengths from 2.16 to 4.78 μ m. The trend in flux ratio is consistent with the 2.16 μ m flux originating from a small sized accretion disk in the quasar that experiences only microlensing. The excess flux above the contribution from the accretion disk at the two longer wavelengths originates from a larger sized region that experiences no microlensing. A simple model employing multiplicative factors for image B due to stellar microlensing ( m ) and substructure millilensing ( M ) is presented. The result is tightly constrained to the product m × M = 1.79. Given the observational errors, the 60% probability contour for this product stretches from m = 2.6, M = 0.69 to m = 1.79, M = 1.0, where the later is consistent with microlensing only.
Publisher: SPIE
Date: 08-08-2016
DOI: 10.1117/12.2232990
Publisher: American Astronomical Society
Date: 30-04-2013
Publisher: Liverpool University Press
Date: 2006
Publisher: MDPI AG
Date: 26-11-2021
DOI: 10.3390/S21237904
Abstract: Satellite-mediated quantum key distribution (QKD) is set to become a critical technology for quantum-secure communication over long distances. While satellite QKD cannot be effectively eavesdropped, we show it can be disrupted (or ‘jammed’) with relatively simple and readily available equipment. We developed an atmospheric attenuation and satellite optical scattering model to estimate the rate of excess noise photons that can be injected into a satellite QKD channel by an off-axis laser, and calculated the effect this added noise has on the quantum bit error rate. We show that a ground-based laser on the order of 1 kW can significantly disrupt modern satellite QKD systems due to photons scattering off the satellite being detected by the QKD receiver on the ground. This class of laser can be purchased commercially, meaning such a method of disruption could be a serious threat to effectively securing high-value communications via satellite QKD in the future. We also discuss these results in relation to likely future developments in satellite-mediated QKD systems, and countermeasures that can be taken against this, and related methods, of disruption.
Publisher: American Astronomical Society
Date: 23-11-2011
Publisher: Optica Publishing Group
Date: 02-02-2023
DOI: 10.1364/OL.482550
Abstract: Adaptive optics pre-compensation of free-space optical communications uplink from ground to space is complicated by the “point ahead angle” due to spacecraft velocity and the finite speed of light, as well as anisoplanatism of the uplink beam and the wavefront beacon. This Letter explores how pre-compensation varies with the number of spatial modes applied and how it varies with a beacon at the point-ahead angle versus a downlink beacon. Using a w 0 = 16 cm Gaussian beam propagating through a modified Hufnagel–Valley model as an ex le, we find pre-compensation performance plateaus beyond ∼100 applied modes regardless of integrated turbulence strength, and that a point ahead beacon provides a 1–4 dB gain in median received power and an order-of-magnitude reduction in scintillation over a downlink beacon at wavelengths typical of optical communications. Modeling tailored to specific scenarios should be conducted to determine whether implementing a resource-intensive point ahead beacon is the optimum path to meeting link requirements.
Publisher: American Astronomical Society
Date: 30-05-2007
DOI: 10.1086/519684
Publisher: University of Arizona Libraries
Date: 1999
Publisher: Geological Society of London
Date: 03-1999
Publisher: SPIE
Date: 10-07-2018
DOI: 10.1117/12.2313678
Publisher: American Astronomical Society
Date: 19-12-2009
Publisher: Springer Science and Business Media LLC
Date: 04-12-2008
Publisher: Wiley
Date: 08-1999
DOI: 10.1002/(SICI)1099-1417(199908)14:5<437::AID-JQS458>3.0.CO;2-Z
Publisher: SPIE
Date: 13-12-2020
DOI: 10.1117/12.2569987
Publisher: MDPI AG
Date: 31-01-2023
Abstract: Free-space optical (FSO) communication promises to bring fibre-like speeds to data transmissions between ground, sky and space. This is becoming more important in light of the increasing volume of data collected by aircraft and spacecraft. The University of Western Australia (UWA) is commissioning optical ground stations to support FSO communications payloads. We propose retroreflected laser links to drones as a useful step towards further ground-to-sky and ground-to-space FSO communications demonstrations. In this paper, we describe the operation of a hardware testbed for a high photon efficiency optical communication physical layer. This testbed was deployed over a slanted free space link to a drone to verify sub-systems required in communication between the ground station and a spacecraft in cis-Lunar space. Accomplishing this verification of the telescope pointing systems and communications systems would have otherwise been much harder or impossible without using a retroreflected drone link.
Publisher: Geological Society of London
Date: 07-1997
Location: United States of America
Location: United States of America
No related grants have been discovered for Shane Walsh.