251 research outputs found

    Quantitative optical mapping of two-dimensional materials

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    The pace of two-dimensional materials (2DM) research has been greatly accelerated by the ability to identify exfoliated thicknesses down to a monolayer from their optical contrast. Since this process requires time-consuming and error-prone manual assignment to avoid false-positives from image features with similar contrast, efforts towards fast and reliable automated assignments schemes is essential. We show that by modelling the expected 2DM contrast in digitally captured images, we can automatically identify candidate regions of 2DM. More importantly, we show a computationally-light machine vision strategy for eliminating false-positives from this set of 2DM candidates through the combined use of binary thresholding, opening and closing filters, and shape-analysis from edge detection. Calculation of data pyramids for arbitrarily high-resolution optical coverage maps of two-dimensional materials produced in this way allows the real-time presentation and processing of this image data in a zoomable interface, enabling large datasets to be explored and analysed with ease. The result is that a standard optical microscope with CCD camera can be used as an analysis tool able to accurately determine the coverage, residue/contamination concentration, and layer number for a wide range of presented 2DMs

    Stellar multiplicity: an interdisciplinary nexus

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    Our uncertainties about binary star systems (and triples and so on) limit our capabilities in literally every single one of the Thematic Areas identified for Astro2020. We need to understand the population statistics of stellar multiplicity and their variations with stellar type, chemistry, and dynamical environment: Correct interpretation of any exoplanet experiment depends on proper treatment of resolved and unresolved binaries; stellar multiplicity is a direct outcome of star and companion formation; the most precise constraints on stellar structure come from well-characterized binary systems; stellar populations heavily rely on stellar and binary evolution modeling; high-redshift galaxy radiation and reionization is controlled by binary-dependent stellar physics; compact objects are the outcomes of binary evolution; the interpretation of multi-messenger astronomy from gravitational waves, light, and neutrinos relies on understanding the products of binary star evolution; near-Universe constraints on the Hubble constant with Type Ia supernovae and gravitational-wave mergers are subject to systematics related to their binary star progenitors; local measures of dark-matter substructure masses are distorted by binary populations. In order to realize the scientific goals in each of these themes over the next decade, we therefore need to understand how binary stars and stellar multiplets are formed and distributed in the space of masses, composition, age, and orbital properties, and how the distribution evolves with time. This white paper emphasizes the interdisciplinary importance of binary-star science and advocates that coordinated investment from all astrophysical communities will benefit almost all branches of astrophysics.Comment: Submitted to the Astro2020 Decadal Survey White Paper cal

    No Massive Companion to the Coherent Radio-Emitting M Dwarf GJ 1151

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    The recent detection of circularly polarized, long-duration (>8 hr) low-frequency (~150 MHz) radio emission from the M4.5 dwarf GJ 1151 has been interpreted as arising from a star-planet interaction via the electron cyclotron maser instability. The existence or parameters of the proposed planets have not been determined. Using 20 new HARPS-N observations, we put 99th-percentile upper limits on the mass of any close companion to GJ 1151 at Msini < 5.6 M earth. With no stellar, brown dwarf, or giant planet companion likely in a close orbit, our data are consistent with detected radio emission emerging from a magnetic interaction between a short-period terrestrial-mass planet and GJ 1151

    Competing risks of death in women treated with adjuvant aromatase inhibitors for early breast cancer on NCIC CTG MA.27

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    Baseline patient and tumor characteristics differentially affected type of death in the MA.17 placebo-controlled letrozole trial where cardiovascular death was not separately identified. The MA.27 trial allowed competing risks analysis of breast cancer (BC), cardiovascular, and other type (OT) of death. MA.27 was a phase III adjuvant breast cancer trial of exemestane versus anastrozole. Effects of baseline patient and tumor characteristics were tested for whether factors were associated with (1) all cause mortality and (2) cause-specific mortality. We also fit step-wise forward cause-specific-adjusted models. 7576 women (median age 64 years; 5417 (72 %) < 70 years and 2159 (28 %) ≥ 70 years) were enrolled and followed for median 4.1 years. The 432 deaths comprised 187 (43 %) BC, 66 (15 %) cardiovascular, and 179 (41 %) OT. Five baseline factors were differentially associated with type of death. Older patients had greater BC (p = 0.03), cardiovascular (p < 0.001), and other types (p < 0.001) of mortality. Patients with pre-existing cardiovascular history had worse cardiovascular mortality (p < 0.001); those with worse ECOG performance status had worse OT mortality (p < 0.001). Patients with T1 tumors (p < 0.001) and progesterone receptor positive had less BC mortality (p < 0.001). Fewer BC deaths occurred with node-negative disease (p < 0.001), estrogen receptor-positive tumors (p = 0.001), and without adjuvant chemotherapy (p = 0.005); worse cardiovascular mortality (p = 0.01), with trastuzumab; worse OT mortality, for non-whites (p = 0.03) and without adjuvant radiotherapy (p = 0.003). Overall, 57 % of deaths in MA.27 AI-treated patients were non-breast cancer related. Baseline patient and tumor characteristics differentially affected type of death with women 70 or older experiencing more non-breast cancer death
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