In X‐ray imaging, anti‐scatter grids are used to reduce scatter radiation reaching image receptors, hence improving image quality. Optimization of grid performance is essential for improving image ...diagnostic quality and minimizing radiation doses to patients. This work investigated the performance of a series of grid designs modeled from the design of typically focused grid with grid ratio 8:1 (r8) and strip height 1.7 mm (h1.7) for high‐energy radiographic applications. Monte Carlo simulation was used to evaluate designs (r8h1.7) which had the strip thickness changed from 6 to 150 μm in 2 μm increments and the interspace distance fixed at 214 μm. The transmissions of radiation in grid materials were modeled by using a regression with radial‐basis‐function‐networks (RBFNS). KSNR was then determined from RBFNS models of radiation transmissions. The optimal strip‐thickness was obtained at the maximum signal‐to‐noise ratio (SNR) improvement factor (KSNR). For high‐energy applications at 100 peak‐kilo‐voltage (kVp) and 30 cm PMMA thickness, the optimal lead‐strip‐thickness was found approximately 74 μm resulting in a strip‐frequency approximately 35 per cm (N35). Using the optimal thickness for imaging condition at 100 kVp and 30 cm thickness, the KSNR would increase by approximately 5.3%. This work showed the existence of optimal strip‐thickness for a series of grids with a given grid‐ratio, strip‐height, strip‐, and interspace materials. The findings are useful and provide guidance to improve grid designs for better performance that will essentially lead to better image quality and better radiation protection for patients.
ABSTRACT
In 1829 James Dunlop published the first southern double star catalogue of some 253 double stars. The accuracy of this catalogue has been determined by using Aladin to cross-match them with ...Gaia DR2 and estimate their positional (right ascension, declination, position angle, and separation) and magnitude accuracy. Seven per cent could not be identified using Aladin and 14 were single stars. We found 13 double stars (5 per cent) not currently listed in the Washington Double Star Catalog. The catalogue equinox was determined as B1826.0. Overall, 1σ uncertainties in right ascension were within 1 sidereal minute and declinations within 10 arcmin. We also identified and corrected a number of Quadrant errors in the position angles and quantified the separations. Apparent visual magnitude estimates were generally within 1 mag. Dunlop’s overall uncertainties were larger than those of his contemporaries, nevertheless the little known catalogue remains valuable as the earliest source of over 200 double star astrometric and visual magnitude estimates.
Abstract
We present light curves and flares from a 7 day, multiwavelength observational campaign of AU Mic, a young and active dM1e star with exoplanets and a debris disk. We report on 73 unique ...flares between the X-ray to optical data. We use high-time-resolution near-UV (NUV) photometry and soft X-ray (SXR) data from the X-ray Multi-Mirror Mission to study the empirical Neupert effect, which correlates the gradual and impulsive phase flaring emissions. We find that 65% (30 of 46) flares do not follow the Neupert effect, which is 3 times more excursions than seen in solar flares, and propose a four-part Neupert effect classification (Neupert, quasi-Neupert, non-Neupert types I and II) to explain the multiwavelength responses. While the SXR emission generally lags behind the NUV as expected from the chromospheric evaporation flare models, the Neupert effect is more prevalent in larger, more impulsive flares. Preliminary flaring rate analysis with X-ray and
U
-band data suggests that previously estimated energy ratios hold for a collection of flares observed over the same time period, but not necessarily for an individual, multiwavelength flare. These results imply that one model cannot explain all stellar flares and care should be taken when extrapolating between wavelength regimes. Future work will expand wavelength coverage using radio data to constrain the nonthermal empirical and theoretical Neupert effects to better refine models and bridge the gap between stellar and solar flare physics.
Antiscatter grids are used in biomedical X‐ray imaging to improve image quality by reducing scatter radiation reaching the image receptor. However, this comes at the cost of increasing radiation ...exposure. Grid performance can be improved by optimizing strip‐thickness, which reduces radiation exposure, leading to greater benefits achieved by the grid. Evidence has shown that strip height may also affect grid performance. This work investigates optimization of grid performance by varying both the strip thickness and height for a constant grid‐ratio of 15:1 (r15). A series of grid designs using lead strips and carbon‐fiber‐interspace materials for grids for high‐energy use was evaluated. The performance of these designs was determined by adopting a Monte Carlo simulation. For each grid design, the signal‐to‐noise ratio improvement factor (KSNR) was determined. A maximum value of KSNR (1.895) was found among these designs at a strip height of 6.8 mm and a thickness of 66.8 μm. The best performance of the r15‐series grids is 6% greater than that of a grid design with a grid ratio of 15:1 and a strip frequency of 44 cm−1 (found in the literature); consequently, the transmission of scatter radiation is reduced by 40%. The results show that grid designs can be optimized by both the strip height and thickness. If the optimization of the strip height and thickness cannot be done simultaneously, the recommendation is to optimize the strip height for better radiation protection without compromising the grid performance. The findings provide useful guidance for designing high‐performance antiscatter grids to reduce radiation exposure of patients.
The relative Rectilinear motion of optical double stars provides an important clue to the relationship of the components. We provide an objective method of confirming the optical status of double ...stars, and of obtaining unbiased rectilinear elements solely on data obtained from the HIPPARCOS and Gaia DR2 space missions. We apply this technique to determine the rectilinear elements of 14 optical double stars from the southern double star catalogue of James Dunlop. The resultant uncertainties are, on average, an order of magnitude smaller than the method currently used.
Binary double stars are those whose binding energies are less than zero. Obtaining binary star orbits from short arcs has been a long‐standing problem in astrophysics. A method is presented and ...tested here, which addresses the problem by using space‐based astrometry, photometry, and astrophysical data, together with historic measures, to generate and constrain a range of possible first‐order Grade 5 orbits. After testing the method on an established binary star, we apply the method to eight double stars from the first published catalog of southern double stars, that of Dunlop (1829) and generate orbits for five. The mean orbital period is ∼81,000 years, and the mean semi‐major axis is ∼76″ with a typical uncertainty of the Orbital Elements of ∼37%. Their Orbital Elements and associated plots are also presented.
Using a global network of small telescopes, we have obtained light curves of Proxima Centauri at 329 observation epochs from 2006 to 2017. The planet Proxima b discovered by Anglada-Escudé et al. ...with an orbital period of 11.186 days has an a priori transit probability of ∼1.5%; if it transits, the predicted transit depth is about 5 mmag. In Blank et al., we analyzed 96 of our light curves that overlapped with predicted transit ephemerides from previously published tentative transit detections and found no evidence in our data that would corroborate claims of transits with a period of 11.186 days. Here we broaden our analysis, using 262 high-quality light curves from our data set to search for any periodic transit-like events over a range of periods from 1 to 30 days. We also inject a series of simulated planet transits and find that our data are sufficiently sensitive to have detected transits of 5 mmag depth, with recoverability ranging from ∼100% for an orbital period of 1 day to ∼20% for an orbital period of 20 days for the parameter spaces tested. Specifically, at the 11.186-day period and 5 mmag transit depth, we rule out transits in our data with high confidence. We are able to rule out virtually all transits of other planets at periods shorter than 5 days and depths greater than 3 mmag; however, we cannot confidently rule out transits at the period of Proxima b due to incomplete orbital phase coverage and a lack of sensitivity to transits shallower than 4 mmag.
Proxima Centauri has become the subject of intense study since the radial-velocity (RV) discovery by Anglada-Escudé et al. of a planet orbiting this nearby M dwarf every ∼11.2 days. If Proxima ...Centauri b transits its host star, independent confirmation of its existence is possible, and its mass and radius can be measured in units of the stellar host mass and radius. To date, there have been three independent claims of possible transit-like event detections in light curve observations obtained by the MOST satellite (in 2014-15), the Bright Star Survey Telescope telescope in Antarctica (in 2016), and the Las Campanas Observatory (in 2016). The claimed possible detections are tentative, due in part to the variability intrinsic to the host star, and in the case of the ground-based observations, also due to the limited duration of the light curve observations. Here, we present preliminary results from an extensive photometric monitoring campaign of Proxima Centauri, using telescopes around the globe and spanning from 2006 to 2017, comprising a total of 329 observations. Considering our data that coincide directly and/or phased with the previously published tentative transit detections, we are unable to independently verify those claims. We do, however, verify the previously reported ubiquitous and complex variability of the host star. We discuss possible interpretations of the data in light of the previous claims, and we discuss future analyses of these data that could more definitively verify or refute the presence of transits associated with the RV-discovered planet.
AMPK (AMP-dependant protein kinase)-mTORC1 (mechanistic target of rapamycin in complex 1)-p70S6K1 (ribosomal protein S6 kinase 1 of 70 kDa) signaling plays a crucial role in muscle protein synthesis ...(MPS). Understanding this pathway has been advanced by the application of the Western blot (WB) technique. However, because many components of the mTORC1 pathway undergo numerous, multisite posttranslational modifications, solely studying the phosphorylation changes of mTORC1 and its substrates may not adequately represent the true metabolic signaling processes. The aim of this study was to develop and apply a quantitative in vitro γ-(32)P ATP kinase assay (KA) for p70S6K1 to assess kinase activity in human skeletal muscle to resistance exercise (RE) and protein feeding. In an initial series of experiments the assay was validated in tissue culture and in p70S6K1-knockout tissues. Following these experiments, the methodology was applied to assess p70S6K1 signaling responses to a physiologically relevant stimulus. Six men performed unilateral RE followed by the consumption of 20 g of protein. Muscle biopsies were obtained at pre-RE, and 1 and 3 h post-RE. In response to RE and protein consumption, p70S6K1 activity as assessed by the KA was significantly increased from pre-RE at 1 and 3 h post-RE. However, phosphorylated p70S6K1(thr389) was not significantly elevated. AMPK activity was suppressed from pre-RE at 3 h post-RE, whereas phosphorylated ACC(ser79) was unchanged. Total protein kinase B activity also was unchanged after RE from pre-RE levels. Of the other markers we assessed by WB, 4EBP1(thr37/46) phosphorylation was the only significant responder, being elevated at 3 h post-RE from pre-RE. These data highlight the utility of the KA to study skeletal muscle plasticity.
To detect objects that vary in brightness or spatial coordinates over time, C. Alard and R. H. Lupton in 1998 proposed an “optimal image subtraction” (OIS) method that constructs a convolution kernel ...from a set of matching stars distributed across the two images to be subtracted. Using multivariable least squares, the kernel is derived and can be designed to vary by pixel coordinates across the convolved image. Local effects in the optics, including aberrations or other spatially sensitive perturbations to a perfect image, can be mitigated. This paper presents the specific systems of equations that originate from the OIS method. Also included is a complete description of the Gaussian components basis vectors used by Alard & Lupton to construct the convolution kernel. An alternative set of basis vectors, called the delta function basis, is also described. Important issues are addressed, including the selection of the matching stars, differential background correction, constant photometric flux, contaminated pixel masking, and alignment at the subpixel level. Computer algorithms for the OIS method were developed, written using the Interactive Data Language (IDL), and applications demonstrating these algorithms are presented.
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![Application of the [γ-32P] ...](http://api.summon.serialssolutions.com/2.0.0/image/issn/XR4PS5YY4K/8750-7587_1522-1601/small "Application of the [γ-32P] ATP kinase assay to study anabolic signaling in human skeletal muscle")
