7,417 research outputs found
Evidence of photospheric vortex flows at supergranular junctions observed by FG/SOT (Hinode)
Twisting motions of different nature are observed in several layers of the
solar atmosphere. Chromospheric sunspot whorls and rotation of sunspots or even
higher up in the lower corona sigmoids are examples of the large scale twisted
topology of many solar features. Nevertheless, their occurrence at large scale
in the quiet photosphere has not been investigated. The present study reveals
the existence of vortex flows located at the supergranular junctions of the
quiet Sun. We use a 1-hour and a 5-hour time series of the granulation in Blue
continuum and G-band images from FG/SOT to derive the photospheric flows. A
feature tracking technique called Balltracking is performed to track the
granules and reveal the underlying flow fields. In both time series we identify
long-lasting vortex flow located at supergranular junctions. The first vortex
flow lasts at least 1 hour and is ~20-arcsec-wide (~15.5 Mm). The second vortex
flow lasts more than 2 hours and is ~27-arcsec-wide (~21 Mm).Comment: 4 pages, 10 figure
An anti-symmetric exclusion process for two particles on an infinite 1D lattice
A system of two biased, mutually exclusive random walkers on an infinite 1D
lattice is studied whereby the intrinsic bias of one particle is equal and
opposite to that of the other. The propogator for this system is solved exactly
and expressions for the mean displacement and mean square displacement (MSD)
are found. Depending on the nature of the intrinsic bias, the system's
behaviour displays two regimes, characterised by (i) the particles moving
towards each other and (ii) away from each other, both qualitatively different
from the case of no bias. The continuous-space limit of the propogator is found
and is shown to solve a Fokker-Planck equation for two biased, mutually
exclusive Brownian particles with equal and opposite drift velocity.Comment: 19 pages, 5 figure
Recursive Neural Networks Can Learn Logical Semantics
Tree-structured recursive neural networks (TreeRNNs) for sentence meaning
have been successful for many applications, but it remains an open question
whether the fixed-length representations that they learn can support tasks as
demanding as logical deduction. We pursue this question by evaluating whether
two such models---plain TreeRNNs and tree-structured neural tensor networks
(TreeRNTNs)---can correctly learn to identify logical relationships such as
entailment and contradiction using these representations. In our first set of
experiments, we generate artificial data from a logical grammar and use it to
evaluate the models' ability to learn to handle basic relational reasoning,
recursive structures, and quantification. We then evaluate the models on the
more natural SICK challenge data. Both models perform competitively on the SICK
data and generalize well in all three experiments on simulated data, suggesting
that they can learn suitable representations for logical inference in natural
language
Synthesising and utilising complex evidence to inform policy in education and health.
Oslo, Norway, May 19 to 21, 200
Improved head-controlled TV system produces high-quality remote image
Manipulator operator uses an improved resolution tv camera/monitor positioning system to view the remote handling and processing of reactive, flammable, explosive, or contaminated materials. The pan and tilt motions of the camera and monitor are slaved to follow the corresponding motions of the operators head
Chemistry and Apparent Quality of Surface Water and Ground Water Associated with Coal Basins
Personnel of the Arkansas Mining and Mineral Resources Research Institute conducted preliminary investigations on the chemistry and quality of surface and ground water associated with 12 coal-bearing sub-basins in the Arkansas Valley coal field. The coal field is approximately 60 miles long and 33 miles wide but only in 12 areas coal is thick enough and has proper quality to be termed commercial. Both surface and underground sample sites were established in each of the sub-basins with some minor variations in four areas where not all types of sites could be located. Water was collected from 19 surface points and 19 underground points in the established areas. Both field and laboratory analyses were made and elemental contents are reported herein. In the main, the chemistry and water quality suggests that all water is suitable for agricultural and industrial uses. To obtain potable water, treatment must be made to reduce calcium, magnesium, sodium sulfate and iron. The mineral content of the water is due to its contact with coal-bearing zones and, as such, reflects the mineral content of the coal. However, it is recommended that additional studies on the petrography and geochemistry of the coal, overburden and underburden is in order. Also, it is recommended that at least one detailed study be made of one of the coal sub-basins where geologic parameters can be completely established with regard to hydrogeology. This report is an important first step in determining the character and quality of Arkansas coal which must be fully understood to fully utilize this important mineral resource
New critical frontiers for the Potts and percolation models
We obtain the critical threshold for a host of Potts and percolation models
on lattices having a structure which permits a duality consideration. The
consideration generalizes the recently obtained thresholds of Scullard and Ziff
for bond and site percolation on the martini and related lattices to the Potts
model and to other lattices.Comment: 9 pages, 5 figure
Validation of the aerodynamic loading on basic flying disc geometries derived from CFD simulations
The present study in spin stabilised disc aerodynamics builds on previous experimental wind tunnel work to broaden the knowledge base through CFD simulation without the necessity for high facility or time cost. The current experimental database from previous studies is extensive enough for sufficient validation to be conducted on known geometries. From there, the limitations of CFD studies for this application on such complex highly separated bluff body flows can be understood. All of the results are for non-spinning discs to reduce computational time, this step is justifiable as the spinning case has previously been shown to have minimal effect on the aerodynamic loads at typical throw release spin rates. The work builds CFD simulation cases carefully and systematically starting with cylindrical discs with thickness to chord (diameter) ratio of 0.01 and 0.1, then to introduce a cavity to one flat side analogous to the Frisbee disc, before moving to look at a generic discus geometry from field athletics. The aerodynamic loading results compare very well to experimental data for the low angle of attack range, however, at higher angles of attack the CFD curves are divergent. It is possible that the generated mesh, for each geometry, does not capture the wake with enough resolution at high angles of attack, note that for sports disc applications the high angle of attack range is very important towards the end of the flight from a human throw. Therefore, further investigations are required to extend this initial study to a modified meshing regime with further refinement, prior to moving forward with any parametric design studies. Keyword - Spin-stabilised; sports disc; discwing; gyroscopic; aerodynamics; cf
Animal movements in the Kenya Rift and evidence for the earliest ambush hunting by hominins
Animal movements in the Kenya Rift Valley today are influenced by a combination of topography and trace nutrient distribution. These patterns would have been the same in the past when hominins inhabited the area. We use this approach to create a landscape reconstruction of Olorgesailie, a key site in the East African Rift with abundant evidence of large-mammal butchery between ~1.2 and ~0.5 Ma BP. The site location in relation to limited animal routes through the area show that hominins were aware of animal movements and used the location for ambush hunting during the Lower to Middle Pleistocene. These features explain the importance of Olorgesailie as a preferred location of repeated hominin activity through multiple changes in climate and local environmental conditions, and provide insights into the cognitive and hunting abilities of Homo erectus while indicating that their activities at the site were aimed at hunting, rather than scavenging
A large annotated corpus for learning natural language inference
Understanding entailment and contradiction is fundamental to understanding
natural language, and inference about entailment and contradiction is a
valuable testing ground for the development of semantic representations.
However, machine learning research in this area has been dramatically limited
by the lack of large-scale resources. To address this, we introduce the
Stanford Natural Language Inference corpus, a new, freely available collection
of labeled sentence pairs, written by humans doing a novel grounded task based
on image captioning. At 570K pairs, it is two orders of magnitude larger than
all other resources of its type. This increase in scale allows lexicalized
classifiers to outperform some sophisticated existing entailment models, and it
allows a neural network-based model to perform competitively on natural
language inference benchmarks for the first time.Comment: To appear at EMNLP 2015. The data will be posted shortly before the
conference (the week of 14 Sep) at http://nlp.stanford.edu/projects/snli
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