The sheared-flow stabilized Z pinch has demonstrated long-lived plasmas with fusion-relevant parameters. We present the first experimental results demonstrating sustained, quasi-steady-state neutron ...production from the fusion Z-pinch experiment, operated with a mixture of 20% deuterium/80% hydrogen by pressure. Neutron emissions lasting approximately 5 μs are reproducibly observed with pinch currents of approximately 200 kA during an approximately 16 μs period of plasma quiescence. The average neutron yield is estimated to be (1.25±0.45)×10^{5} neutrons/pulse and scales with the square of the deuterium concentration. Coincident with the neutron signal, plasma temperatures of 1-2 keV and densities of approximately 10^{17} cm^{-3} with 0.3 cm pinch radii are measured with fully integrated diagnostics.
Be stars exhibit variability for a great number of observables. Putting the pieces of the disk dynamics together is not an easy task and requires arduous modeling before achieving a good fit to the ...observational data. In order to guide the modeling process and make it more efficient, it is very instructive to investigate reference dynamical cases. This paper focuses on continuum polarimetric quantities and is the second of a series that aims to demonsttate the capacity of deriving the dynamical history and fundamental parameters of a classical Be star through follow-up of various observables. After a detailed study of the different opacities at play in the formation of polarized spectra, we investigate predictions of polarimetric observables in the continuum for different dynamical scenarios. Our models are based on a coupling of a hydrodynamic viscous decretion simulations in a disk and a three-dimensional non-LTE radiative transfer code. Through introduction of the polarization color diagram (PCD), we show that certain combinations of polarimettic observables exhibit features that are characteristic of a mass-loss history. This diagram also enables estimates of fundamental parameters such as the inclination angle, disk density scale, and the alpha viscous diffusion parameter. We present the PCD as a powerful diagnosis tool to ttack the dynamical phases of a Be star, such as disk build-up, dissipation, periodic, and episodic outbursts. Finally, we confront our models with observations of four Be stars that exhibited long-term polarimetric activity.
Lambda Boo stars are predominately A-type stars with solar abundant C, N, O, and S, but up to 2 dex underabundances of refractory elements. The stars’ unusual surface abundances could be due to a ...selective accretion of volatile gas over dust. It has been proposed that there is a correlation between the Lambda Boo phenomenon and IR excesses which are the result of a debris disc or interstellar medium (ISM) interaction providing the accreting material. We observe 70 or 100 and 160-μm excess emission around nine confirmed Lambda Boo stars with the Herschel Space Observatory, to differentiate whether the dust emission is from a debris disc or an ISM bow wave. We find that 3/9 stars observed host well-resolved debris discs. While the remaining 6/9 are not resolved; they are inconsistent with an ISM bow wave based on the dust emission being more compact for its temperature and predicted bow-wave models produce hotter emission than what is observed. We find the incidence of bright IR excesses around Lambda Boo stars is higher than normal A-stars. To explain this, given our observations, we explore Poynting–Robertson drag as a mechanism of accretion from a debris disc but find it insufficient. As an alternative, we propose the correlation is due to higher dynamical activity in the discs currently underway. Large impacts of planetesimals or a higher influx of comets could provide enough volatile gas for accretion. Further study on the transport of circumstellar material in relation to the abundance anomalies are required to explain the phenomenon through external accretion.
ABSTRACT
Spatially resolved images of debris discs are necessary to determine disc morphological properties and the scattering phase function (SPF) thatantifies the brightness of scattered light as a ...function of phase angle. Current high-contrast imaging instruments have successfully resolved several dozens of debris discs around other stars, but few studies have investigated trends in the scattered-light, resolved population of debris discs in a uniform and consistent manner. We have combined Karhunen-Loeve Image Projection (KLIP) with radiative-transfer disc forward modelling in order to obtain the highest-quality image reductions and constrain disc morphological properties of eight debris discs imaged by the Gemini Planet Imager at H-band with a consistent and uniformly applied approach. In describing the scattering properties of our models, we assume a common SPF informed from solar system dust scattering measurements and apply it to all systems. We identify a diverse range of dust density properties among the sample, including critical radius, radial width, and vertical width. We also identify radially narrow and vertically extended discs that may have resulted from substellar companion perturbations, along with a tentative positive trend in disc eccentricity with relative disc width. We also find that using a common SPF can achieve reasonable model fits for discs that are axisymmetric and asymmetric when fitting models to each side of the disc independently, suggesting that scattering behaviour from debris discs may be similar to Solar system dust.
Directly detecting thermal emission from young extrasolar planets allows measurement of their atmospheric compositions and luminosities, which are influenced by their formation mechanisms. Using the ...Gemini Planet Imager, we discovered a planet orbiting the ∼20-million-year-old star 51 Eridani at a projected separation of 13 astronomical units. Near-infrared observations show a spectrum with strong methane and water-vapor absorption. Modeling of the spectra and photometry yields a luminosity (normalized by the luminosity of the Sun) of 1.6 to 4.0 × 10–6 and an effective temperature of 600 to 750 kelvin. For this age and luminosity, "hot-start" formation models indicate a mass twice that of Jupiter. This planet also has a sufficiently low luminosity to be consistent with the "cold-start" core-accretion process that may have formed Jupiter.
Wellbeing has become an increasingly important priority worldwide. In the United Arab Emirates (UAE), much research and financial investment are being committed to increasing wellbeing. However, how ...the pursuit of happiness, as a driver of wellbeing, is not commonly investigated. In particular, fear of happiness and beliefs in its fragility challenge dominant Western views that happiness is desirable and actively pursued by all. How these lay beliefs of happiness are associated with individual levels of wellbeing and related behaviours have not been well explored. Accordingly, we sought to identify wellbeing profiles by examining mental health functioning, positive emotion, flourishing, cultural beliefs in the fear of happiness and fragility of happiness, physical activity and levels of reported sleep as well as demographics such as age and gender. Using a sample of 834 Emirati university students in the UAE, fear and fragility of happiness were used to develop wellbeing profiles. We found three profiles: ‘unstable’ moderate wellbeing,’ ‘fearful, moderate wellbeing,’ and ‘stable, high wellbeing.’ This is one of few studies to show that beliefs in the fear and fragility of happiness are related to lower subjective wellbeing and cluster with other behavioural factors, such that physical health indicators like physical activity and sleep were associated with greater subjective wellbeing and more stable wellbeing profiles. In sum, lay beliefs of happiness not only appear to influence wellbeing itself, but concomitant behaviours as well.
The sheared-flow stabilized Z pinch has demonstrated long-lived plasmas with fusion-relevant parameters. Here we present the first experimental results demonstrating sustained, quasi-steady-state ...neutron production from the fusion Z -pinch experiment, operated with a mixture of 20% deuterium/80% hydrogen by pressure. Neutron emissions lasting approximately 5 μs are reproducibly observed with pinch currents of approximately 200 kA during an approximately 16 μs period of plasma quiescence. The average neutron yield is estimated to be ( 1.25 ± 0.45 ) x 105 neutrons / pulse and scales with the square of the deuterium concentration. Coincident with the neutron signal, plasma temperatures of 1–2 keV and densities of approximately 1017 cm-3 with 0.3 cm pinch radii are measured with fully integrated diagnostics.
The sheared-flow stabilized \(Z\)-pinch has demonstrated long-lived plasmas with fusion-relevant parameters. This Letter presents the first experimental results demonstrating sustained, ...quasi-steady-state neutron production from the Fusion \(Z\)-pinch Experiment (FuZE), operated with a mixture of 20% deuterium/80% hydrogen by volume. Neutron emissions lasting approximately \(5~\mu\)s are reproducibly observed with pinch currents of approximately \(200\) kA during an approximately \(16~\mu\)s period of plasma quiescence. The average neutron yield is estimated to be \(\left ( 1.25\pm 0.45 \right )\times 10^{5}\) neutrons/pulse and scales with the square of the deuterium concentration. Coincident with the neutron signal, plasma temperatures of \(1-2\) keV, and densities of approximately \(10^{17}\) cm\(^{-3}\) with \(0.3\) cm pinch radii are measured with fully-integrated diagnostics.
Directly detecting thermal emission from young extrasolar planets allows measurement of their atmospheric composition and luminosity, which is influenced by their formation mechanism. Using the ...Gemini Planet Imager, we discovered a planet orbiting the \$sim$20 Myr-old star 51 Eridani at a projected separation of 13 astronomical units. Near-infrared observations show a spectrum with strong methane and water vapor absorption. Modeling of the spectra and photometry yields a luminosity of L/LS=1.6-4.0 x 10-6 and an effective temperature of 600-750 K. For this age and luminosity, "hot-start" formation models indicate a mass twice that of Jupiter. This planet also has a sufficiently low luminosity to be consistent with the "cold- start" core accretion process that may have formed Jupiter.
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