880 research outputs found
On the zero set of G-equivariant maps
Let be a finite group acting on vector spaces and and consider a
smooth -equivariant mapping . This paper addresses the question of
the zero set near a zero of with isotropy subgroup . It is known
from results of Bierstone and Field on -transversality theory that the zero
set in a neighborhood of is a stratified set. The purpose of this paper is
to partially determine the structure of the stratified set near using only
information from the representations and . We define an index
for isotropy subgroups of which is the difference of
the dimension of the fixed point subspace of in and . Our main
result states that if contains a subspace -isomorphic to , then for
every maximal isotropy subgroup satisfying , the zero
set of near contains a smooth manifold of zeros with isotropy subgroup
of dimension . We also present a systematic method to study
the zero sets for group representations and which do not satisfy the
conditions of our main theorem. The paper contains many examples and raises
several questions concerning the computation of zero sets of equivariant maps.
These results have application to the bifurcation theory of -reversible
equivariant vector fields
Evaluation of biasing and protection circuitry components for cryogenic MMIC low-noise amplifiers
Millimeter-wave integrated circuits with gate lengths as short as 35 nm are demonstrating extremely
low-noise performance, especially when cooled to cryogenic temperatures. These operate at low voltages
and are susceptible to damage from electrostatic discharge and improper biasing, as well as being
sensitive to low-level interference. Designing a protection circuit for low voltages and temperatures is
challenging because there is very little data available on components that may be suitable. Extensive
testing at low temperatures yielded a set of components and a circuit topology that demonstrates the
required level of protection for critical MMICs and similar devices. We present a circuit that provides
robust protection for low voltage devices from room temperature down to 4 K
Effective Use of Case Studies in the MIS Capstone Course through Semi-Formal Collaborative Teaching
This paper provides the theoretical grounding for the development of an instrument to assess the effectiveness of the case study approach in teaching the higher-level concepts associated with the MIS capstone course. The instrument was administered to students in the capstone class over three semesters. The resulting findings from the survey, combined with an understanding of each instructor’s approach to teaching case studies are then used collaboratively by the instructors as a means to identify strengths and areas for improvement. Items in the survey were developed from applicable prior research on teaching and learning and collaborative teaching. Responses to the survey items were subjected to an exploratory factor analysis, resulting in two dimensions of interest – teaching substance and teaching technique. The results of the survey indicate widespread satisfaction by students with the case study approach
Dense, Parsec-Scale Clumps Near the Great Annihilator
We report on Combined Array for Research in Millimeter-Wave Astronomy and James Clerk Maxwell Telescope observations toward the Einstein source 1E 1740.7–2942, a low-mass X-ray binary commonly known as the "Great Annihilator." The Great Annihilator is known to be near a small, bright molecular cloud in a region largely devoid of emission in ^(12)CO surveys of the Galactic center. This region is of interest because it is interior to the dust lanes which may be the shock zones where atomic gas from the HI nuclear disk is converted into molecular gas. We find that the region is populated with a large number of dense (n ~ 10^5 cm^(–3)) regions of excited gas with small filling factors. The gas appears to have turbulent support and may be the result of sprays of material from collisions in the shock zone. We estimate that ~(1-3) × 10^5 M⊙ of shocked gas resides in our r ~ 3', Δv_(LSR) = 100 km s^(–1) field. If this gas has recently shocked and is interior to the inner Lindblad resonance of the dominant bar, it is in transit to the x_2 disk, suggesting that a significant amount of mass may be transported to the disk by a low filling factor population of molecular clouds with low surface brightness in larger surveys
Decreasing landslide erosion on steeper slopes in soil‐mantled landscapes
Slope‐stability models predict that steeper hillslopes require smaller hydrological triggers for shallow landslides to occur due to the added downslope pull of gravity, which should result in more frequent landslides and faster erosion. However, field observations indicate that landslide frequency does not consistently increase on steeper hillslopes. Here, we use measurements of 1,096 soil landslides in California and Switzerland, and a compilation of landslide geometries, to show that steeper hillslopes typically have thinner soils and that thin soils inhibit landslides due to enhanced roles of cohesion and boundary stresses. We find that the landscape‐averaged landslide erosion depth peaks near the threshold slope for instability, and it drops to half that value on hillslopes that are just 5° to 10° steeper. We propose that faster rates of soil creep on steeper slopes cause thin and more stable soils, which in turn reduces landslide erosion, despite the added pull of gravity
Dense, Parsec-Scale Clumps near the Great Annihilator
We report on Combined Array for Research in Millimeter-Wave Astronomy (CARMA)
and James Clerk Maxwell Telescope (JCMT) observations toward the Einstein
source 1E 1740.7-2942, a LMXB commonly known as the "Great Annihilator." The
Great Annihilator is known to be near a small, bright molecular cloud on the
sky in a region largely devoid of emission in 12-CO surveys of the Galactic
Center. The region is of interest because it is interior to the dust lanes
which may be the shock zones where atomic gas from HI nuclear disk is converted
into molecular gas. We find that the region is populated with a number of dense
(n ~ 10^5 cm^-3) regions of excited gas with small filling factors, and
estimate that up to 1-3 x 10^5 solar masses of gas can be seen in our maps. The
detection suggests that a significant amount of mass is transported from the
shock zones to the GC star-forming regions in the form of small, dense bundles.Comment: 26 pages, 7 figures, accepted for publication by the Astrophysical
Journal, abstract abridge
An Integrated Literature Review of Time-on-Task Effects With a Pragmatic Framework for Understanding and Improving Decision-Making in Multidisciplinary Oncology Team Meetings
Multidisciplinary oncology team meetings (MDMs) or tumor boards, like other MDMs in healthcare, facilitate the incorporation of diverse clinical expertise into treatment planning for patients. Decision-making (DM) in relation to treatment planning in MDMs is carried out repeatedly until all patients put forward for discussion have been reviewed. Despite continuing financial pressure and staff shortages, the workload of cancer MDMs, and therefore meeting duration continue to increase (up to 5 h) with patients often receiving less than 2 min of team input. This begs the question as to whether the current set-up is conducive to achieve optimal DM, which these multi-specialty teams were set out to achieve in the first place. Much of what it is known, however, about the effects of prolonged cognitive activity comes from various subfields of science, leaving a gap in applied knowledge relating to complex healthcare environments. The objective of this review was thus to synthesize theory, evidence and clinical practice in order to bring the current understanding of prolonged, repeated DM into the context of cancer MDMs. We explore how and why time spent on a task affects performance in such settings, and what strategies can be employed by cancer teams to counteract negative effects and improve quality and safety. In the process, we propose a pragmatic framework of repeated DM that encompasses the strength, the process and the cost-benefit models of self-control as applied to real-world contexts of cancer MDMs. We also highlight promising research avenues for closing the research-to-practice gap. Theoretical and empirical evidence reviewed in this paper suggests that over prolonged time spent on a task, repeated DM is cognitively taxing, leading to performance detriments. This deterioration is associated with various cognitive-behavioral pitfalls, including decreased attentional capacity and reduced ability to effectively evaluate choices, as well as less analytical DM and increased reliance on heuristics. As a short to medium term improvement for ensuring safety, consistently high quality of care for all patients, and the clinician wellbeing, future research and interventions in cancer MDMs should address time-on-task effects with a combination of evidence-based cognitive strategies. We propose in this review multiple measures that range from food intake, short breaks, rewards, and mental exercises. As a long term imperative, however, capacity within cancer services needs to be reviewed as well as how best to plan workforce development and service delivery models to achieve population coverage whilst maintaining safety and quality of care. Hence the performance detriments that arise in healthcare workers as a result of the intensity (time spent on a task) and complexity of the workload require not only more research, but also wider regulatory focus and recognition
Spontaneous Initiation of Detonations in White Dwarf Environments: Determination of Critical Sizes
Some explosion models for Type Ia supernovae (SN Ia), such as the
gravitationally confined detonation (GCD) or the double detonation
sub-Chandrasekhar (DDSC) models, rely on the spontaneous initiation of a
detonation in the degenerate C/O material of a white dwarf. The length scales
pertinent to the initiation of the detonation are notoriously unresolved in
multi-dimensional stellar simulations, prompting the use of results of 1D
simulations at higher resolution, such as the ones performed for this work, as
guidelines for deciding whether or not conditions reached in the higher
dimensional full star simulations successfully would lead to the onset of a
detonation. Spontaneous initiation relies on the existence of a suitable
gradient in self-ignition (induction) times of the fuel, which we set up with a
spatially localized non-uniformity of temperature -- a hot spot. We determine
the critical (smallest) sizes of such hot spots that still marginally result in
a detonation in white dwarf matter by integrating the reactive Euler equations
with the hydrodynamics code FLASH. We quantify the dependences of the critical
sizes of such hot spots on composition, background temperature, peak
temperature, geometry, and functional form of the temperature disturbance, many
of which were hitherto largely unexplored in the literature. We discuss the
implications of our results in the context of modeling of SNe Ia.Comment: 43 pages, 12 figures, 12 table
Initiation of the detonation in the gravitationally confined detonation model of Type Ia supernovae
We study the initiation of the detonation in the gravitationally confined
detonation (GCD) model of Type Ia supernovae (SNe Ia). Initiation of the
detonation occurs spontaneously in a region where the length scale of the
temperature gradient extending from a flow (in which carbon burning is already
occurring) into unburned fuel is commensurate to the range of critical length
scales which have been derived from 1D simulations that resolve the initiation
of a detonation. By increasing the maximum resolution in a truncated cone that
encompasses this region, beginning somewhat before initiation of the detonation
occurs, we successfully simulate in situ the first gradient-initiated
detonation in a whole-star simulation. The detonation emerges when a
compression wave overruns a pocket of fuel situated in a Kelvin-Helmholtz cusp
at the leading edge of the inwardly directed jet of burning carbon. The
compression wave pre-conditions the temperature in the fuel in such a way that
the Zel'dovich gradient mechanism can operate and a detonation ensues. We
explore the dependence of the length scale of the temperature gradient on
spatial resolution and discuss the implications for the robustness of this
detonation mechanism. We find that the time and the location at which
initiation of the detonation occurs varies with resolution. In particular,
initiation of a detonation had not yet occurred in our highest resolution
simulation by the time we ended the simulation because of the computational
demand it required. We suggest that the turbulent shear layer surrounding the
inwardly directed jet provides the most favorable physical conditions, and
therefore the most likely location, for initiation of a detonation in the GCD
model.Comment: 28 pages, 12 figures, 1 table, accepted to Ap
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