The Great Recession, institutional dysfunction, a growing divide between urban and rural prospects, and failed efforts to effectively address immigration have paved the way for a populist backlash ...that disrupts the postwar bargain between political elites and citizens. Whether today's populism represents a corrective to unfair and obsolete policies or a threat to liberal democracy itself remains up for debate. Yet this much is clear: these challenges indict the triumphalism that accompanied liberal democratic consolidation after the collapse of the Soviet Union. To respond to today's crisis, good leaders must strive for inclusive economic growth while addressing fraught social and cultural issues, including demographic anxiety, with frank attention. Although reforms may stem the populist tide, liberal democratic life will always leave some citizens unsatisfied. This is a permanent source of vulnerability, but liberal democracy will endure so long as citizens believe it is worth fighting for.
We observed the newly discovered hyperbolic minor planet 1I/'Oumuamua (2017 U1) on 2017 October 30 with Lowell Observatory's 4.3 m Discovery Channel Telescope. From these observations, we derived a ...partial lightcurve with a peak-to-trough amplitude of at least 1.2 mag. This lightcurve segment rules out rotation periods less than 3 hr and suggests that the period is at least 5 hr. On the assumption that the variability is due to a changing cross-section, the axial ratio is at least 3:1. We saw no evidence for a coma or tail in either individual images or in a stacked image having an equivalent exposure time of 9000 s.
'Oumuamua (1I/2017 U1) is the first object of interstellar origin observed in the solar system. Recently, Micheli et al. reported that 'Oumuamua showed deviations from a Keplerian orbit at a high ...statistical significance. The observed trajectory is best explained by an excess radial acceleration Δa ∝ r−2, where r is the distance of 'Oumuamua from the Sun. Such an acceleration is naturally expected for comets, driven by the evaporating material. However, recent observational and theoretical studies imply that 'Oumuamua is not an active comet. We explore the possibility that the excess acceleration results from solar radiation pressure. The required mass-to-area ratio is (m/A) 0.1 g cm−2. For a thin sheet this requires a thickness of 0.3-0.9 mm. We find that although extremely thin, such an object would survive interstellar travel over Galactic distances of ∼5 kpc, withstanding collisions with gas and dust grains as well as stresses from rotation and tidal forces. We discuss the possible origins of such an object. Our general results apply to any light probes designed for interstellar travel.
Background
The Liver Imaging Reporting and Data System (LI‐RADS) is being adapted by many clinical practices. To support continuation of its use, LI‐RADS (LR) is in need of multicenter validation ...studies of recent LI‐RADS iterations. Furthermore, while both gadoxetate and extracellular agents have been incorporated into LI‐RADS, comparison of the diagnostic performance between the two has yet to be determined.
Purpose/Hypothesis
To evaluate the rate, diagnostic performance, and interreader reliability (IRR) of LI‐RADS 2017 for hepatocellular carcinoma, including LR major and ancillary features, with both gadoxetate and extracellular agent‐enhanced MRI against a reference standard of histopathology or imaging follow‐up.
Study Type
Retrospective.
Population
In all, 114 patients with 144 observations were included who met LR 2017 criteria for at risk and had at least one hepatic observation on liver MRI performed with either gadoxetate (n = 52) or an extracellular agent (n = 92) between 2010–2016, with histopathology (n = 103) or follow‐up imaging (n = 41).
Field Strength/Sequence
1.5 and 3.0T/T1‐T2WI, diffusion‐weighted imaging.
Assessment
Three radiologists independently assessed major/ancillary features and assigned overall LI‐RADS category for every observation.
Statistical Tests
Diagnostic performance of LR5/TIV+LR5 for identifying hepatocellular carcinoma (HCC) was compared between contrast agents with a generalized estimating equation. Weighted kappa was performed for interrater reliability.
Results
The frequency of HCCs among LR1, LR2, LR3, L4, LR5, LRTIV+LR5, and LRM observations were: 0% (all readers), 0–12.5%, 11.4–26.9%, 50–76%, 83.0–95.1%, 83.3–100.0%, and 45.0–65.0%, respectively. Sensitivity of LR5/LRTIV+LR5 for HCC was 59.7–71.4% and specificity 85.0–96.8%. LI‐RADS specificity and positive predictive value for observations imaged with gadoxetate was higher than extracellular agent for the most inexperienced reader (R3) (P = 0.009–0.034). IRR for LI‐RADS categorization was substantial (k = 0.661).
Data Conclusion
Increasing numerical LI‐RADS 2017 categories demonstrate a greater percentage of HCCs. LR5/TIV+LR5 demonstrates excellent specificity and fair sensitivity for HCC. MRI with gadoxetate in liver transplant candidates may be beneficial for less experienced readers, although further large‐scale prospective studies are needed.
Level of Evidence: 4
Technical Efficacy: Stage 3
J. Magn. Reson. Imaging 2019;49:e205–e215.
We report on g-, r-, and i-band observations of the Interstellar Object 1I/'Oumuamua (1I) taken on 2017 October 29 from 04:28 to 08:40 UTC by the Apache Point Observatory (APO) 3.5 m telescope's ...ARCTIC camera. We find that 1I's colors are and , consistent with visible spectra and most comparable to the population of solar system C/D asteroids, Trojans, or comets. We find no evidence of any cometary activity at a heliocentric distance of 1.46 au, approximately 1.5 months after 1I's closest approach distance to the Sun. Significant brightness variability was seen in the r observations, with the object becoming notably brighter toward the end of the run. By combining our APO photometric time series data with the Discovery Channel Telescope data of Knight et al., taken 20 hr later on 2017 October 30, we construct an almost complete lightcurve with a most probable single-peaked lightcurve period of . Our results imply a double-peaked rotation period of 8.1 0.02 hr, with a peak-to-trough amplitude of 1.5-2.1 mag. Assuming that 1I's shape can be approximated by an ellipsoid, the amplitude constraint implies that 1I has an axial ratio of 3.5-10.3, which is strikingly elongated. Assuming that 1I is rotating above its critical break up limit, our results are compatible with 1I having modest cohesive strength and may have obtained its elongated shape during a tidal distortion event before being ejected from its home system.
The recent discovery by Pan-STARRS1 of 1I/2017 U1 ('Oumuamua), on an unbound and hyperbolic orbit, offers a rare opportunity to explore the planetary formation processes of other stars and the effect ...of the interstellar environment on a planetesimal surface. 1I/'Oumuamua's close encounter with the inner solar system in 2017 October was a unique chance to make observations matching those used to characterize the small-body populations of our own solar system. We present near-simultaneous g′, r′, and J photometry and colors of 1I/'Oumuamua from the 8.1 m Frederick C. Gillett Gemini-North Telescope and gri photometry from the 4.2 m William Herschel Telescope. Our g′r′J observations are directly comparable to those from the high-precision Colours of the Outer Solar System Origins Survey (Col-OSSOS), which offer unique diagnostic information for distinguishing between outer solar system surfaces. The J-band data also provide the highest signal-to-noise measurements made of 1I/'Oumuamua in the near-infrared. Substantial, correlated near-infrared and optical variability is present, with the same trend in both near-infrared and optical. Our observations are consistent with 1I/'Oumuamua rotating with a double-peaked period of 8.10 0.42 hr and being a highly elongated body with an axial ratio of at least 5.3:1, implying that it has significant internal cohesion. The color of the first interstellar planetesimal is at the neutral end of the range of solar system g − r and r − J solar-reflectance colors: it is like that of some dynamically excited objects in the Kuiper Belt and the less-red Jupiter Trojans.
We present observations of the interstellar interloper 1I/2017 U1 ('Oumuamua) taken during its 2017 October flyby of Earth. The optical colors B - V = 0.70 0.06, V - R = 0.45 0.05, overlap those of ...the D-type Jovian Trojan asteroids and are incompatible with the ultrared objects that are abundant in the Kuiper Belt. With a mean absolute magnitude HV = 22.95 and assuming a geometric albedo pV = 0.1, we find an average radius of 55 m. No coma is apparent; we deduce a limit to the dust mass production rate of only ∼2 × 10−4 kg s−1, ruling out the existence of exposed ice covering more than a few m2 of the surface. Volatiles in this body, if they exist, must lie beneath an involatile surface mantle 0.5 m thick, perhaps a product of prolonged cosmic-ray processing in the interstellar medium. The light curve range is unusually large at ∼2.0 0.2 mag. Interpreted as a rotational light curve the body has axis ratio :1 and semi-axes ∼230 m × 35 m. A 6:1 axis ratio is extreme relative to most small solar system asteroids and suggests that albedo variations may additionally contribute to the variability. The light curve is consistent with a two-peaked period ∼8.26 hr, but the period is non-unique as a result of aliasing in the data. Except for its unusually elongated shape, 1I/2017 U1 is a physically unremarkable, sub-kilometer, slightly red, rotating object from another planetary system. The steady-state population of similar, ∼100 m scale interstellar objects inside the orbit of Neptune is ∼104, each with a residence time of ∼10 years.
1I/2017 U1 ('Oumuamua), a recently discovered asteroid in a hyperbolic orbit, is likely the first macroscopic object of extrasolar origin identified in the solar system. Here, we present imaging and ...spectroscopic observations of 'Oumuamua using the Palomar Hale Telescope as well as a search of meteor activity potentially linked to this object using the Canadian Meteor Orbit Radar. We find that 'Oumuamua exhibits a moderate spectral gradient of , a value significantly lower than that of outer solar system bodies, indicative of a formation and/or previous residence in a warmer environment. Imaging observation and spectral line analysis show no evidence that 'Oumuamua is presently active. Negative meteor observation is as expected, since ejection driven by sublimation of commonly known cometary species such as CO requires an extreme ejection speed of ∼40 m s−1 at ∼100 au in order to reach the Earth. No obvious candidate stars are proposed as the point of origin for 'Oumuamua. Given a mean free path of ∼109 ly in the solar neighborhood, 'Oumuamua has likely spent a very long time in interstellar space before encountering the solar system.
Reviewers for 2017 Krausman, Paul R.; Knipps, Anna C. S.; Cox, Allison S.
The Journal of wildlife management,
April 2018, Letnik:
82, Številka:
3
Journal Article
The recently discovered minor body 1I/2017 U1 ('Oumuamua) is the first known object in our solar system that is not bound by the Sun's gravity. Its hyperbolic orbit (eccentricity greater than unity) ...strongly suggests that it originated outside our solar system; its red color is consistent with substantial space weathering experienced over a long interstellar journey. We carry out a simple calculation of the probability of detecting such an object. We find that the observed detection rate of 1I-like objects can be satisfied if the average mass of ejected material from nearby stars during the process of planetary formation is ∼20 Earth masses, similar to the expected value for our solar system. The current detection rate of such interstellar interlopers is estimated to be 0.2 yr−1, and the expected number of detections over the past few years is almost exactly one. When the Large Synoptic Survey Telescope begins its wide, fast, deep all-sky survey, the detection rate will increase to 1 yr−1. Those expected detections will provide further constraints on nearby planetary system formation through a better estimate of the number and properties of interstellar objects.
PDF
