13 research outputs found
Screening current effects in Josephson junction arrays
The purpose of this work is to compare the dynamics of arrays of Josephson
junctions in presence of magnetic field in two different frameworks: the so
called XY frustrated model with no self inductance and an approach that takes
into account the screening currents (considering self inductances only). We
show that while for a range of parameters the simpler model is sufficiently
accurate, in a region of the parameter space solutions arise that are not
contained in the XY model equations.Comment: Figures available from the author
MUSCAT: The Mexico-UK Sub-Millimetre Camera for AsTronomy
The Mexico-UK Sub-millimetre Camera for AsTronomy (MUSCAT) is a large-format,
millimetre-wave camera consisting of 1,500 background-limited lumped-element
kinetic inductance detectors (LEKIDs) scheduled for deployment on the Large
Millimeter Telescope (Volc\'an Sierra Negra, Mexico) in 2018. MUSCAT is
designed for observing at 1.1 mm and will utilise the full 40' field of view of
the LMTs upgraded 50-m primary mirror. In its primary role, MUSCAT is designed
for high-resolution follow-up surveys of both galactic and extra-galactic
sub-mm sources identified by Herschel. MUSCAT is also designed to be a
technology demonstrator that will provide the first on-sky demonstrations of
novel design concepts such as horn-coupled LEKID arrays and closed continuous
cycle miniature dilution refrigeration.
Here we describe some of the key design elements of the MUSCAT instrument
such as the novel use of continuous sorption refrigerators and a miniature
dilutor for continuous 100-mK cooling of the focal plane, broadband optical
coupling to Aluminium LEKID arrays using waveguide chokes and anti-reflection
coating materials as well as with the general mechanical and optical design of
MUSCAT. We explain how MUSCAT is designed to be simple to upgrade and the
possibilities for changing the focal plane unit that allows MUSCAT to act as a
demonstrator for other novel technologies such as multi-chroic polarisation
sensitive pixels and on-chip spectrometry in the future. Finally, we will
report on the current status of MUSCAT's commissioning.Comment: Presented at SPIE Astronomical Telescopes + Instrumentation, 2018,
Austin, Texas, United State
Use of Native Plants for the Remediation of Abandoned Mine Sites in Mediterranean Semiarid Environments
A large oxygen-dominated core from the seismic cartography of a pulsating white dwarf
White-dwarf stars are the end product of stellar evolution for most stars in the Universe1. Their interiors bear the imprint of fundamental mechanisms that occur during stellar evolution2,3. Moreover, they are important chronometers for dating galactic stellar populations, and their mergers with other white dwarfs now appear to be responsible for producing the type Ia supernovae that are used as standard cosmological candles4. However, the internal structure of white-dwarf stars—in particular their oxygen content and the stratification of their cores—is still poorly known, because of remaining uncertainties in the physics involved in stellar modelling codes5,6. Here we report a measurement of the radial chemical stratification (of oxygen, carbon and helium) in the hydrogen- deficient white-dwarf star KIC08626021 (J192904.6+444708), independently of stellar-evolution calculations. We use archival data7,8 coupled with asteroseismic sounding techniques9,10 to determine the internal constitution of this star. We find that the oxygen content and extent of its core exceed the predictions of existing models of stellar evolution. The central homogeneous core has a mass of 0.45 solar masses, and is composed of about 86 per cent oxygen by mass. These values are respectively 40 per cent and 15 per cent greater than those expected from typical white-dwarf models. These findings challenge present theories of stellar evolution and their constitutive physics, and open up an avenue for calibrating white-dwarf cosmochronology11