947 research outputs found
From solar-like to anti-solar differential rotation in cool stars
Stellar differential rotation can be separated into two main regimes:
solar-like when the equator rotates faster than the poles and anti-solar when
the polar regions rotate faster than the equator. We investigate the transition
between these two regimes with 3-D numerical simulations of rotating spherical
shells. We conduct a systematic parameter study which also includes models from
different research groups. We find that the direction of the differential
rotation is governed by the contribution of the Coriolis force in the force
balance, independently of the model setup (presence of a magnetic field,
thickness of the convective layer, density stratification). Rapidly-rotating
cases with a small Rossby number yield solar-like differential rotation, while
weakly-rotating models sustain anti-solar differential rotation. Close to the
transition, the two kinds of differential rotation are two possible bistable
states. This study provides theoretical support for the existence of anti-solar
differential rotation in cool stars with large Rossby numbers.Comment: 5 pages, 6 figures, accepted for publication in MNRA
What controls the large-scale magnetic fields of M dwarfs?
Observations of active M dwarfs show a broad variety of large-scale magnetic
fields encompassing dipole-dominated and multipolar geometries. We detail the
analogy between some anelastic dynamo simulations and spectropolarimetric
observations of 23 M stars. In numerical models, the relative contribution of
inertia and Coriolis force in the global force balance -estimated by the
so-called local Rossby number- is known to have a strong impact on the magnetic
field geometry. We discuss the relevance of this parameter in setting the
large-scale magnetic field of M dwarfs.Comment: 4 pages, 3 figures, conference proceeding, IAUS 302 'Magnetic Fields
Throughout the Stellar Evolution', (26-30 Aug 2013, Biarritz, France
What controls the magnetic geometry of M dwarfs?
Context: observations of rapidly rotating M dwarfs show a broad variety of
large-scale magnetic fields encompassing dipole-dominated and multipolar
geometries. In dynamo models, the relative importance of inertia in the force
balance -- quantified by the local Rossby number -- is known to have a strong
impact on the magnetic field geometry. Aims: we aim to assess the relevance of
the local Rossby number in controlling the large-scale magnetic field geometry
of M dwarfs. Methods: we explore the similarities between anelastic dynamo
models in spherical shells and observations of active M-dwarfs, focusing on
field geometries derived from spectropolarimetric studies. To do so, we
construct observation-based quantities aimed to reflect the diagnostic
parameters employed in numerical models. Results: the transition between
dipole-dominated and multipolar large-scale fields in early to mid M dwarfs is
tentatively attributed to a Rossby number threshold. We interpret late M dwarfs
magnetism to result from a dynamo bistability occurring at low Rossby number.
By analogy with numerical models, we expect different amplitudes of
differential rotation on the two dynamo branches.Comment: 4 pages, 4 figures, accepted for publication in A&
Design Perspective on the Role of Advanced Bots for Self-Guided Learning
Virtual worlds are rapidly gaining acceptance in educational settings; with bots play an important role in these environments to help learners. Authentic learning can be significantly supported by bots to help self-guided learning in authentic tasks. in this paper, we investigate what is stopping educators from making more use of bots as a valuable resource and how these barriers can be overcome. This exploratory research uses interviews with six educators, who use educational bots. We show that while the experts have 'big plans' for bot use, the current educational implementations are 'low-level' and restrictive in their application. There is further confusion about appropriate pedagogical models and how to use them effectively as more than 'prompters' or 'extras'. While creation- and control-technologies are advancing, allowing use of bots as a 'hard technology' to guide learners through routine procedures; there is a lack of resources for automation as intelligence technologies are slower to develop and may required future partnerships with external parties before they are available useable by general educators
Solving mazes with memristors: a massively-parallel approach
Solving mazes is not just a fun pastime. Mazes are prototype models in graph theory, topology, robotics, traffic optimization, psychology, and in many other areas of science and technology. However, when maze complexity increases their solution becomes cumbersome and very time consuming. Here, we show that a network of memristors - resistors with memory - can solve such a non-trivial problem quite easily. In particular, maze solving by the network of memristors occurs in a massively parallel fashion since all memristors in the network participate simultaneously in the calculation. The result of the calculation is then recorded into the memristors’ states, and can be used and/or recovered at a later time. Furthermore, the network of memristors finds all possible solutions in multiple-solution mazes, and sorts out the solution paths according to their length. Our results demonstrate not only the first application of memristive networks to the field of massively-parallel computing, but also a novel algorithm to solve mazes which could find applications in different research fields
New Landscapes and New Eyes: The Role of Virtual World Design for Supply Chain Education
With the common availability of advanced educational technology, we are able to increase the emphasis on the design of learning experiences and benefit from the given flexibility and variety of opportunities to create learning spaces. As instructional design models become more commonplace we examine their role vis-Ă -vis with the fidelity of the experience while learning. High-fidelity experiences are known to be valuable in learning as they provide authenticity in learning and motivation; yet, high fidelity comes at the cost of greater investment. In this paper, we outline our experiments with two setups of differing levels of fidelity: using Second Life and the consumer-focused Oculus Rift Head-Mounted Display (HMD). We show qualitatively interpreted comments and user responses to demonstrate importance of the level of fidelity, uncover important elements, and relate back the fidelity to the learning experience. High-fidelity experiences can be supported by software and hardware that are now readily available but present the seductive opportunity to greatly improve participant engagement in the virtual environments presented
Extremely low longâterm erosion rates around the Gamburtsev Mountains in interior East Antarctica
The high elevation and rugged relief (>3 km) of the Gamburtsev Subglacial Mountains (GSM) have long been considered enigmatic. Orogenesis normally occurs near plate boundaries, not cratonic interiors, and largeâscale tectonic activity last occurred in East Antarctica during the PanâAfrican (480â600 Ma). We sampled detrital apatite from Eocene sands in Prydz Bay at the terminus of the Lambert Graben, which drained a large preâglacial basin including the northern Gamburtsev Mountains. Apatite fissionâtrack and (UâTh)/He cooling ages constrain bedrock erosion rates throughout the catchment. We doubleâdated apatites to resolve individual cooling histories. Erosion was very slow, averaging 0.01â0.02 km/Myr for >250 Myr, supporting the preservation of high elevation in interior East Antarctica since at least the cessation of Permian rifting. Longâterm topographic preservation lends credence to postulated highâelevation mountain ice caps in East Antarctica since at least the Cretaceous and to the idea that coldâbased glaciation can preserve tectonically inactive topography
Improved orbital solution and masses for the very low-mass multiple system LHS 1070
We present a refined orbital solution for the components A, B, and C of the
nearby late-M type multiple system LHS 1070. By combining astrometric
datapoints from NACO/VLT, CIAO/SUBARU, and PUEO/CFHT, as well as a radial
velocity measurement from the newly commissioned near infrared high-resolution
spectrograph CRIRES/VLT, we achieve a very precise orbital solution for the B
and C components and a first realistic constraint on the much longer orbit of
the A-BC system. Both orbits appear to be co-planar. Masses for the B and C
components calculated from the new orbital solution (M_(B+C) = 0.157 +/- 0.009
M_sun) are in excellent agreement with theoretical models, but do not match
empirical mass-luminosity tracks. The preliminary orbit of the A-BC system
reveals no mass excess for the A component, giving no indication for a
previously proposed fourth (D) component in LHS 1070.Comment: published in A&A, 2008, 484, 429; added CFHT acknowledgemen
Periodic Radio and H-alpha Emission from the L Dwarf Binary 2MASSW J0746425+200032: Exploring the Magnetic Field Topology and Radius of an L Dwarf
[Abridged] We present an 8.5-hour simultaneous radio, X-ray, UV, and optical
observation of the L dwarf binary 2MASSW J0746+20. We detect strong radio
emission, dominated by short-duration periodic pulses at 4.86 GHz with
P=124.32+/-0.11 min. The stability of the pulse profiles and arrival times
demonstrates that they are due to the rotational modulation of a B~1.7 kG
magnetic field. A quiescent non-variable component is also detected, likely due
to emission from a uniform large-scale field. The H-alpha emission exhibits
identical periodicity, but unlike the radio pulses it varies sinusoidally and
is offset by exactly 1/4 of a phase. The sinusoidal variations require
chromospheric emission from a large-scale field structure, with the radio
pulses likely emanating from the magnetic poles. While both light curves can be
explained by a rotating mis-aligned magnetic field, the 1/4 phase lag rules out
a symmetric dipole topology since it would result in a phase lag of 1/2
(poloidal field) or zero (toroidal field). We therefore conclude that either
(i) the field is dominated by a quadrupole configuration, which can naturally
explain the 1/4 phase lag; or (ii) the H-alpha and/or radio emission regions
are not trivially aligned with the field. Regardless of the field topology, we
use the measured period along with the known rotation velocity (vsini=27 km/s),
and the binary orbital inclination (i=142 deg), to derive a radius for the
primary star of 0.078+/-0.010 R_sun. This is the first measurement of the
radius of an L dwarf, and along with a mass of 0.085+/-0.010 M_sun it provides
a constraint on the mass-radius relation below 0.1 M_sun. We find that the
radius is about 30% smaller than expected from theoretical models, even for an
age of a few Gyr.Comment: Submitted to Ap
Experimental study on consumer-technology supported authentic immersion in virtual worlds for education and vocational training
Despite significant and rapid technology improvements, educators have frequently failed to make use of the new opportunities to create more authentic learning scenarios. Virtual worlds offer an attractive proposition to create 3D representations of real business environments to provide an authentic learning activity for higher education students to take part in. However, the controls and displays are still clunky and unnatural, reducing the opportunity for students to immerse themselves in the event and focus on experiential learning. To overcome this challenge we examine the role of using a headset display that allows the user to change perspective with a flick of the head, improving their ability to âfeelâ part of the environment, and thus increase their immersion in the activities that they are engaged in through more realistic control and improved perspective in the virtual environment. A series of experiments are conducted comparing the technology to established technologies and the level of control exerted by the learner (e.g., they either âcontrolâ or they âpassively observeâ as someone else controls). These experiments provide evidence that consumer-technology can improve immersion and equip educators with an affordable instrument to present classes that learners âtake more seriouslyâ
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