The paper presents an analysis of the rheological properties of a selected viscoelastic material, which is dedicated to the reduction of vibrations in structures subjected to dynamic loads. A ...four-parameter, fractional Zener model was used to describe the dynamic behavior of the tested material. The model parameters were identified on the basis of laboratory tests performed at different temperatures and for different vibration frequencies. After proving that the material is thermoreologically simple, the so-called master curves were created using a horizontal shift factor. The Williams–Landel–Ferry formula was applied to create graphs of the master curves, the constants of which were determined for the selected temperature. The resulting storage and loss module functions spanned several decades in the frequency domain. The parameters of the fractional Zener model were identified by fitting the entire range of the master curves with the gradientless method (i.e., Particle Swarm Optimization), consisting in searching for the best-fitted solution in a set of feasible solutions. The parametric analysis of the obtained solutions allowed for the formulation of conclusions regarding the effectiveness of the applied rheological model.
In this paper, a non-contact method that allows to determine the carrier concentration in CdSe crystals is presented. The method relies on the measurement of the effective infrared absorption ...coefficient by means of the photothermal infrared radiometry (PTR). In order to obtain the effective infrared absorption coefficient and thermal diffusivity, the frequency characteristics of the PTR signal were analyzed in the frame of a one-dimensional heat transport model for infrared semitransparent crystals. The carrier concentrations were estimated using a theory introduced by Ruda and a recently proposed normalization procedure for the PTR signal. The deduced carrier concentrations of the investigated CdSe crystals are in reasonable agreement with those obtained using Hall measurements and infrared spectroscopy. The method presented in this paper can also be applied to other semiconductors with the carrier concentration in the range of 10
14
–10
17
cm
−3
.
Abstract
The All-Sky Automated Survey for Supernovae (ASAS-SN) is the first optical survey to routinely monitor the whole sky with a cadence of ∼2–3 d down to V ≲ 17 mag. ASAS-SN has monitored the ...whole sky since 2014, collecting ∼100–500 epochs of observations per field. The V-band light curves for candidate variables identified during the search for supernovae are classified using a random forest classifier and visually verified. We present a catalogue of 66 179 bright, new variable stars discovered during our search for supernovae, including 27 479 periodic variables and 38 700 irregular variables. V-band light curves for the ASAS-SN variables are available through the ASAS-SN variable stars data base
(https://asas-sn.osu.edu/variables). The data base will begin to include the light curves of known variable stars in the near future along with the results for a systematic, all-sky variability survey.
We report the discovery of a giant planet in the OGLE-2017-BLG-1522 microlensing event. The planetary perturbations were clearly identified by high-cadence survey experiments despite the relatively ...short event timescale of tE ∼ 7.5 days. The Einstein radius is unusually small, θE = 0.065 mas, implying that the lens system either has very low mass or lies much closer to the microlensed source than the Sun, or both. A Bayesian analysis yields component masses and source-lens distance , implying that this is a brown-dwarf/Jupiter system that probably lies in the Galactic bulge, a location that is also consistent with the relatively low lens-source relative proper motion = 3.2 0.5 mas yr−1. The projected companion-host separation is , indicating that the planet is placed beyond the snow line of the host, i.e., asl ∼ 0.12 au. Planet formation scenarios combined with the small companion-host mass ratio q ∼ 0.016 and separation suggest that the companion could be the first discovery of a giant planet that formed in a protoplanetary disk around a brown-dwarf host.
Abstract
We report discovery of the lowest mass ratio exoplanet to be found by the microlensing method in the light curve of the event OGLE 2016–BLG–1195. This planet revealed itself as a small ...deviation from a microlensing single lens profile from an examination of the survey data. The duration of the planetary signal is ∼2.5 h. The measured ratio of the planet mass to its host star is q = 4.2 ± 0.7 × 10−5. We further estimate that the lens system is likely to comprise a cold ∼3 Earth mass planet in an ∼2 au wide orbit around a 0.2 Solar mass star at an overall distance of 7.1 kpc.
Current microlensing surveys are sensitive to free-floating planets down to Earth-mass objects. All published microlensing events attributed to unbound planets were identified based on their short ...timescale (below two days), but lacked an angular Einstein radius measurement (and hence lacked a significant constraint on the lens mass). Here, we present the discovery of a Neptune-mass free-floating planet candidate in the ultrashort (tE = 0.320 0.003 days) microlensing event OGLE-2016-BLG-1540. The event exhibited strong finite-source effects, which allowed us to measure its angular Einstein radius of θE = 9.2 0.5 as. There remains, however, a degeneracy between the lens mass and distance. The combination of the source proper motion and source-lens relative proper motion measurements favors a Neptune-mass lens located in the Galactic disk. However, we cannot rule out that the lens is a Saturn-mass object belonging to the bulge population. We exclude stellar companions up to ∼15 au.
Although coronavirus disease 2019 (COVID-19) has affected endoscopy services globally, the impact on trainees has not been evaluated. We aimed to assess the impact of COVID-19 on procedural volumes ...and on the emotional well-being of endoscopy trainees worldwide.
An international survey was disseminated over a 3-week period in April 2020. The primary outcome was the percentage reduction in monthly procedure volume before and during COVID-19. Secondary outcomes included potential variation of COVID-19 impact between different continents and rates and predictors of anxiety and burnout among trainees.
Across 770 trainees from 63 countries, 93.8% reported a reduction in endoscopy case volume. The median percentage reduction in total procedures was 99% (interquartile range, 85%-100%), which varied internationally (P < .001) and was greatest for colonoscopy procedures. Restrictions in case volume and trainee activity were common barriers. A total of 71.9% were concerned that the COVID-19 pandemic could prolonged training. Anxiety was reported in 52.4% of respondents and burnout in 18.8%. Anxiety was independently associated with female gender (odds ratio OR, 2.15; P < .001), adequacy of personal protective equipment (OR, 1.75; P = .005), lack of institutional support for emotional health (OR, 1.67; P = .008), and concerns regarding prolongation of training (OR, 1.60; P = .013). Modifying existing national guidelines to support adequate endoscopy training during the pandemic was supported by 68.9%.
The COVID-19 pandemic has led to restrictions in endoscopic volumes and endoscopy training, with high rates of anxiety and burnout among endoscopy trainees worldwide. Targeted measures by training programs to address these key issues are warranted to improve trainee well-being and support trainee education.
PDF
