Sparse-matrix wavefront reconstruction: simulations and experiments

Adaptive optics systems with Shack-Hartmann wavefront sensors require reconstruction of the atmospheric phase error from subaperture slope measurements, with every sensor in the array being used in the computation of each actuator command. This fully populated reconstruction matrix can result in a significant computational burden for adaptive optics systems with large numbers of actuators. A method for generating sparse wavefront reconstruction matrices for adaptive optics is proposed. The method exploits the relevance of nearby subaperture slope measurements for control of an individual actuator, and relies upon the limited extent of the influence function for a zonal deformable mirror. Relying only on nearby sensor information can significantly reduce the calculation time for wavefront reconstruction. In addition, a hierarchic controller is proposed to recover some of the global wavefront information. The performance of these sparse wavefront reconstruction matrices was evaluated in simulation, and tested on the Palomar Adaptive Optics System. This paper presents some initial results from the simulations and experiments

Optical characterization of the PALM-3000 3388-actuator deformable mirror

We describe the lab characterization of the new 3,388-actuator deformable mirror (DM3388) produced by Xinetics, Inc. for the PALM-3000 adaptive optics (AO) system1 under development by Jet Propulsion Laboratory and Caltech Optical Observatories. This square grid 66-by-66 actuator mirror has the largest number of actuators of any deformable mirror currently available and will enable high-contrast imaging for direct exoplanet imaging science at the Palomar 200" diameter Hale Telescope. We present optical measurements of the powered and unpowered mirror surface, influence functions, linearity of the actuators, and creep of the actuators. We also quantify the effect of changes in humidity

Patients' experiences of deep brain stimulation for Parkinson's disease: a qualitative systematic review and synthesis.

Published onlineJournal ArticleThis is the final version of the article. Available from BMJ Publishing Group via the DOI in this record.OBJECTIVE: To review and synthesise qualitative research studies that have explored patients' experience of deep brain stimulation (DBS) in advanced Parkinson's disease (PD). DESIGN: Systematic review and meta-synthesis of 7 original papers, using metaethnography. SETTING: Studies conducted in Denmark, France and Sweden. PARTICIPANTS: 116 patients who had undergone DBS and 9 spouses of patients. RESULTS: Prior to surgery, the experience of advancing PD is one of considerable loss and a feeling of loss of control. There are significant hopes for what DBS can bring. Following surgery, a sense of euphoria is described by many, although this does not persist and there is a need for significant transitions following this. We suggest that normality as a concept is core to the experience of DBS and that a sense of control may be a key condition for normality. Experience of DBS for patients and spouses, and of the transitions that they must undertake, is influenced by their hopes of what surgery will enable them to achieve, or regain (ie, a new normality). CONCLUSIONS: There is a need for further qualitative research to understand the nature of these transitions to inform how best patients and their spouses can be supported by healthcare professionals before, during and after DBS. In assessing the outcomes of DBS and other treatments in advanced PD, we should consider how to capture holistic concepts such as normality and control. Studies that examine the outcomes of DBS require longer term follow-up.This work was part funded by the Medical Research Council Midland Hub for Trials Methodology Research (Grant Number: G0800808). RG is partially supported by the National Institute for Health Research (NIHR) Collaboration for Leadership in Applied Health Research and Care (CLAHRC) for the South West Peninsula (PenCLAHRC)

Adaptive optics imaging of a stellar occultation by Titan

We present resolved images of the occultation of a binary star by Titan, recorded with the Palomar Observatory adaptive optics system on 20 December 2001 UT. These constitute the first resolved observations of a stellar occultation by a small body, and demonstrate several unique capabilities of diffraction-limited imaging systems for the study of planetary atmospheres. Two refracted stellar images are visible on Titan's limb throughout both events, displaying scintillations due to local density variations. Precise relative astrometry of the refracted stellar images with respect to the unnocculted component of the binary allows us to directly measure their altitude in Titan's atmosphere. Their changing positions also lead to simple demonstration of the finite oblateness of surfaces of constant pressure in Titan's mid-latitude stratosphere, consistent with the only previous measurement of Titan's zonal wind field

The Black Identity, Hair Product Use, and Breast Cancer Scale

Introduction Across the African Diaspora, hair is synonymous with identity. As such, Black women use a variety of hair products, which often contain more endocrine-disrupting chemicals than products used by women of other races. An emerging body of research is linking chemicals in hair products to breast cancer, but there is no validated instrument that measures constructs related to hair, identity, and breast health. The objective of this study was to develop and validate the Black Identity, Hair Product Use, and Breast Cancer Scale (BHBS) in a diverse sample of Black women to measure the social and cultural constructs associated with Black women’s hair product use and perceived breast cancer risk. Methods Participants completed a 27-item scale that queried perceptions of identity, hair products, and breast cancer risk. Principal Component Analyses (PCA) were conducted to establish the underlying component structures, and confirmatory factor analysis (CFA) was used to determine model fit. Results Participants (n = 185) were African American (73%), African, and Caribbean Black women (27%) aged 29 to 64. PCA yielded two components that accounted for 61% of total variance. Five items measuring sociocultural perspectives about hair and identity loaded on subscale 1 and accounted for 32% of total variance (α = 0.82; 95% CI = 0.77–0.86). Six items assessing perceived breast cancer risk related to hair product use loaded on subscale 2 and accounted for 29% of total variance (α = 0.82 (95% CI = 0.74–0.86). CFA confirmed the two-component structure (Root Mean Square Error of Approximation = 0.03; Comparative Fit Index = 0.91; Tucker Lewis Index = 0.88). Conclusions The BHBS is a valid measure of social and cultural constructs associated with Black women’s hair product use and perceived breast cancer risk. This scale is useful for studies that assess cultural norms in the context of breast cancer risk for Black women

Real-time wavefront control for the PALM-3000 high order adaptive optics system

We present a cost-effective scalable real-time wavefront control architecture based on off-the-shelf graphics processing units hosted in an ultra-low latency, high-bandwidth interconnect PC cluster environment composed of modules written in the component-oriented language of nesC. We demonstrate the architecture is capable of supporting the most computation and memory intensive wavefront reconstruction method (vector-matrix-multiply) at frame rates up to 2 KHz with latency under 250 &mgr;s for the PALM-3000 adaptive optics systems, a state-of-the-art upgrade on the 5.1 meter Hale Telescope that consists of a 64x64 subaperture Shack-Hartmann wavefront sensor and a 3368 active actuator high order deformable mirror in series with a 349 actuator "woofer" DM. This architecture can easily scale up to support larger AO systems at higher rates and lower latency

Sparse-matrix wavefront reconstruction: simulations and experiments

Adaptive optics systems with Shack-Hartmann wavefront sensors require reconstruction of the atmospheric phase error from subaperture slope measurements, with every sensor in the array being used in the computation of each actuator command. This fully populated reconstruction matrix can result in a significant computational burden for adaptive optics systems with large numbers of actuators. A method for generating sparse wavefront reconstruction matrices for adaptive optics is proposed. The method exploits the relevance of nearby subaperture slope measurements for control of an individual actuator, and relies upon the limited extent of the influence function for a zonal deformable mirror. Relying only on nearby sensor information can significantly reduce the calculation time for wavefront reconstruction. In addition, a hierarchic controller is proposed to recover some of the global wavefront information. The performance of these sparse wavefront reconstruction matrices was evaluated in simulation, and tested on the Palomar Adaptive Optics System. This paper presents some initial results from the simulations and experiments

A Close Companion Search Around L Dwarfs Using Aperture Masking Interferometry and Palomar Laser Guide Star Adaptive Optics

We present a close companion search around 16 known early L dwarfs using aperture masking interferometry with Palomar laser guide star adaptive optics (LGS AO). The use of aperture masking allows the detection of close binaries, corresponding to projected physical separations of 0.6-10.0 AU for the targets of our survey. This survey achieved median contrast limits of ΔK ~ 2.3 for separations between 1.2λ/D-4λ/D and ΔK ~ 1.4 at 2/3λ/D. We present four candidate binaries detected with moderate-to-high confidence (90%-98%). Two have projected physical separations less than 1.5 AU. This may indicate that tight-separation binaries contribute more significantly to the binary fraction than currently assumed, consistent with spectroscopic and photometric overluminosity studies. Ten targets of this survey have previously been observed with the Hubble Space Telescope as part of companion searches. We use the increased resolution of aperture masking to search for close or dim companions that would be obscured by full aperture imaging, finding two candidate binaries. This survey is the first application of aperture masking with LGS AO at Palomar. Several new techniques for the analysis of aperture masking data in the low signal-to-noise regime are explored

Adaptive optics imaging of a stellar occultation by Titan

We present resolved images of the occultation of a binary star by Titan, recorded with the Palomar Observatory adaptive optics system on 20 December 2001 UT. These constitute the first resolved observations of a stellar occultation by a small body, and demonstrate several unique capabilities of diffraction-limited imaging systems for the study of planetary atmospheres. Two refracted stellar images are visible on Titan's limb throughout both events, displaying scintillations due to local density variations. Precise relative astrometry of the refracted stellar images with respect to the unnocculted component of the binary allows us to directly measure their altitude in Titan's atmosphere. Their changing positions also lead to simple demonstration of the finite oblateness of surfaces of constant pressure in Titan's mid-latitude stratosphere, consistent with the only previous measurement of Titan's zonal wind field

Status of the PALM-3000 high-order adaptive optics system

The PALM-3000 upgrade to the Palomar Adaptive Optics system on the 5.1 meter Hale telescope will deliver extreme adaptive optics correction in near-infrared wavelengths and diffraction-limited images in visible wavelengths. PALM-3000 will use a 3388-actuator tweeter and a 241-actuator woofer deformable mirror, a Shack-Hartmann wavefront sensor with selectable pupil sampling, and an innovative wavefront control computer based on a cluster of 17 graphics processing units to correct wavefront aberrations at scales as fine as 8.1 cm at the telescope pupil using natural guide stars. The system is currently undergoing integration and testing, with deployment at Palomar Observatory planned in early 2011. We present the detailed design of key aspects of the adaptive optics system, and the current status of the deformable mirror characterization, wavefront sensor performance, and testbed activities