1,652 research outputs found
Two-dimensional arrays of low capacitance tunnel junctions: general properties, phase transitions and Hall effect
We describe transport properties of two-dimensional arrays of low capacitance
tunnel junctions, such as the current voltage characteristic and its dependence
on external magnetic field and temperature. We discuss several experiments in
which the small capacitance of the junctions plays an important role. In arrays
where the junctions have a relatively large charging energy, (i.e. when they
have a low capacitance) and a high normal state resistance, the low bias
resistance increases with decreasing temperature and eventually at very low
temperature the array becomes insulating even though the electrodes in the
array are superconducting. This transition to the insulating state can be
described by thermal activation. In an intermediate region where the junction
resistance is of the order of the quantum resistance and the charging energy is
of the order of the Josephson coupling energy, the arrays can be tuned between
a superconducting and an insulating state with a magnetic field. We describe
measurements of this magnetic-field-tuned superconductor insulator transition,
and we show that the resistance data can be scaled over several orders of
magnitude. Four arrays follow the same universal function. At the transition
the transverse (Hall) resistance is found to be very small in comparison with
the longitudinal resistance. However, for magnetic field values larger than the
critical value.we observe a substantial Hall resistance. The Hall resistance of
these arrays oscillates with the applied magnetic field. features in the
magnetic field dependence of the Hall resistance can qualitatively be
correlated to features in the derivative of the longitudinal resistance,
similar to what is found in the quantum Hall effect.Comment: 29 pages, 16 eps figures, uses aipproc.sty and epsfig.sty,
contribution to Euroschool on "Superconductivity in Networks and Mesoscopic
Systems", held in Siena, Italy (8-20 september 1997
No Evidence for More Earth-sized Planets in the Habitable Zone of Kepler's M versus FGK Stars
Reliable detections of Earth-sized planets in the habitable zone remain
elusive in the Kepler sample, even for M dwarfs. The Kepler sample was once
thought to contain a considerable number of M dwarf stars ( K), which hosted enough Earth-sized ( R) planets to
estimate their occurrence rate () in the habitable zone. However,
updated stellar properties from Gaia have shifted many Kepler stars to earlier
spectral type classifications, with most stars (and their planets) now measured
to be larger and hotter than previously believed. Today, only one
partially-reliable Earth-sized candidate remains in the optimistic habitable
zone, and zero in the conservative zone. Here we performed a new investigation
of Kepler's Earth-sized planets orbiting M dwarf stars, using occurrence rate
models with considerations of updated parameters and candidate reliability.
Extrapolating our models to low instellations, we found an occurrence rate of
for the conservative habitable zone
(and for the optimistic), consistent with
previous works when considering the large uncertainties. Comparing these
estimates to those from similarly comprehensive studies of Sun-like stars, we
found that the current Kepler sample does not offer evidence to support an
increase in from FGK to M stars. While the Kepler sample is too
sparse to resolve an occurrence trend between early and mid-to-late M dwarfs
for Earth-sized planets, studies including larger planets and/or data from the
K2 and TESS missions are well-suited to this task.Comment: 22 pages, 11 figures, 2 tables; Accepted for publication in A
Glucose metabolism and oscillatory behavior of pancreatic islets
A variety of oscillations are observed in pancreatic islets.We establish a
model, incorporating two oscillatory systems of different time scales: One is
the well-known bursting model in pancreatic beta-cells and the other is the
glucose-insulin feedback model which considers direct and indirect feedback of
secreted insulin. These two are coupled to interact with each other in the
combined model, and two basic assumptions are made on the basis of biological
observations: The conductance g_{K(ATP)} for the ATP-dependent potassium
current is a decreasing function of the glucose concentration whereas the
insulin secretion rate is given by a function of the intracellular calcium
concentration. Obtained via extensive numerical simulations are complex
oscillations including clusters of bursts, slow and fast calcium oscillations,
and so on. We also consider how the intracellular glucose concentration depends
upon the extracellular glucose concentration, and examine the inhibitory
effects of insulin.Comment: 11 pages, 16 figure
Effect of floor type on the performance, physiological and behavioural responses of finishing beef steers
peer-reviewedBackground:The study objective was to investigate the effect of bare concrete slats (Control), two types of mats [(Easyfix mats (mat 1) and Irish Custom Extruder mats (mat 2)] fitted on top of concrete slats, and wood-chip to simulate deep bedding (wood-chip placed on top of a plastic membrane overlying the concrete slats) on performance, physiological and behavioral responses of finishing beef steers. One-hundred and forty-four finishing steers (503 kg; standard deviation 51.8 kg) were randomly assigned according to their breed (124 Continental cross and 20 Holstein–Friesian) and body weight to one of four treatments for 148 days. All steers were subjected to the same weighing, blood sampling (jugular venipuncture), dirt and hoof scoring pre study (day 0) and on days 23, 45, 65, 86, 107, 128 and 148 of the study. Cameras were fitted over each pen for 72 h recording over five periods and subsequent 10 min sampling scans were analysed.
Results: Live weight gain and carcass characteristics were similar among treatments. The number of lesions on the hooves of the animals was greater (P < 0.05) on mats 1 and 2 and wood-chip treatments compared with the animals on the slats. Dirt scores were similar for the mat and slat treatments while the wood-chip treatment had greater dirt scores. Animals housed on either slats or wood-chip had similar lying times. The percent of animals lying was greater for animals housed on mat 1 and mat 2 compared with those housed on concrete slats and wood chips. Physiological variables showed no significant difference among treatments.
Conclusions:
In this exploratory study, the performance or welfare of steers was not adversely affected by slats, differing mat types or wood-chip as underfoot material
Phylogeny of Diving Beetles Reveals a Coevolutionary Arms Race between the Sexes
BACKGROUND: Darwin illustrated his sexual selection theory with male and female morphology of diving beetles, but maintained a cooperative view of their interaction. Present theory suggests that instead sexual conflict should be a widespread evolutionary force driving both intersexual coevolutionary arms races and speciation. METHODOLOGY/PRINCIPAL FINDINGS: We combined Bayesian phylogenetics, complete taxon sampling and a multi-gene approach to test the arms race scenario on a robust diving beetle phylogeny. As predicted, suction cups in males and modified dorsal surfaces in females showed a pronounced coevolutionary pattern. The female dorsal modifications impair the attachment ability of male suction cups, but each antagonistic novelty in females corresponds to counter-differentiation of suction cups in males. CONCLUSIONS: A recently diverged sibling species pair in Japan is possibly one consequence of this arms race and we suggest that future studies on hypoxia might reveal the key to the extraordinary selection for female counter-adaptations in diving beetles
Primary thermometry in the intermediate Coulomb blockade regime
We investigate Coulomb blockade thermometers (CBT) in an intermediate
temperature regime, where measurements with enhanced accuracy are possible due
to the increased magnitude of the differential conductance dip. Previous
theoretical results show that corrections to the half width and to the depth of
the measured conductance dip of a sensor are needed, when leaving the regime of
weak Coulomb blockade towards lower temperatures. In the present work, we
demonstrate experimentally that the temperature range of a CBT sensor can be
extended by employing these corrections without compromising the primary nature
or the accuracy of the thermometer.Comment: 8 pages, 4 figure
Practising Mathematics Teacher Education: Expanding The Realm of Possibilities
It is often said that student teachers’ underlying beliefs of what mathematics consists of and how it should be taught are restricted in two ways. On the one hand, future elementary teachers in general use only weak mathematical conceptions, which often do not help them to realise their educational ambitions. On a general educational level, many of these students advocate discovery learning and collective problem solving, but when it comes down to the mathematical activities that have to be prepared, their experience of “traditional” school mathematics is of little help. On the other hand, future (higher) secondary teachers mostly are very well prepared with respect to formal academic mathematics when entering mathematics education programmes, either because they have already passed a mathematical formation at university or because their teacher education programmes emphasise the study of academic mathematics and not of educational or didactical modules
Scaling K2 VII: Evidence for a high occurrence rate of hot sub-Neptunes at intermediate ages
The NASA K2 mission obtained high precision time-series photometry for four
young clusters, including the near-twin 600-800 Myr-old Praesepe and Hyades
clusters. Hot sub-Neptunes are highly prone to mass-loss mechanisms, given
their proximity to the the host star and the weakly bound gaseous envelopes,
and analyzing this population at young ages can provide strong constraints on
planetary evolution models. Using our automated transit detection pipeline, we
recover 15 planet candidates across the two clusters, including 10 previously
confirmed planets. We find a hot sub-Neptune occurrence rate of 79-107% for GKM
stars in the Praesepe cluster. This is 2.5-3.5 sigma higher than the occurrence
rate of 16.54+1.00-0.98% for the same planets orbiting the ~3-9 Gyr-old GKM
field stars observed by K2, even after accounting for the slightly super-solar
metallicity ([Fe/H]~0.2 dex) of the Praesepe cluster. We examine the effect of
adding ~100 targets from the Hyades cluster, and extending the planet parameter
space under examination, and find similarly high occurrence rates in both
cases. The high occurrence rate of young, hot sub-Neptunes could indicate
either that these planets are undergoing atmospheric evolution as they age, or
that planetary systems that formed when the Galaxy was much younger are
substantially different than from today. Under the assumption of the
atmospheric mass-loss scenario, a significantly higher occurrence rate of these
planets at the intermediate ages of Praesepe and Hyades appears more consistent
with the core-powered mass loss scenario sculpting the hot sub-Neptune
population, compared to the photoevaporation scenario.Comment: 14 pages, 6 figures, published in A
Using Photometrically-Derived Properties of Young Stars to Refine TESS's Transiting Young Planet Survey Completeness
The demographics of young exoplanets can shed light onto their formation and
evolution processes. Exoplanet properties are derived from the properties of
their host stars. As such, it is important to accurately characterize the host
stars since any systematic biases in their derivation can negatively impact the
derivation of planetary properties. Here, we present a uniform catalog of
photometrically-derived stellar effective temperatures, luminosities, radii,
and masses for 4,865 young (<1 Gyr) stars in 31 nearby clusters and moving
groups within 200 pc. We compared our photometrically-derived properties to a
subset of those derived from spectra, and found them to be in good agreement.
We also investigated the effect of stellar properties on the detection
efficiency of transiting short-period young planets with TESS as calculated in
Fernandes et al. 2022, and found an overall increase in the detection
efficiency when the new photometrically derived properties were taken into
account. Most notably, there is a 1.5 times increase in the detection
efficiencies for sub-Neptunes/Neptunes (1.8-6 Re) implying that, for our sample
of young stars, better characterization of host star properties can lead to the
recovery of more small transiting planets. Our homogeneously derived catalog of
updated stellar properties, along with a larger unbiased stellar sample and
more detections of young planets, will be a crucial input to the accurate
estimation of the occurrence rates of young short-period planets.Comment: 16 pages, 5 Figures, 3 Tables. Revised and resubmitted to AJ after a
favorable referee report. Co-First Author
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