1,466 research outputs found
Existence and uniqueness for Legendre curves
We give a moving frame of a Legendre curve (or, a frontal) in the unite tangent bundle and define a pair of smooth functions of a Legendre curve like as the curvature of a regular plane curve. The existence and uniqueness for Legendre curves are holded like as regular plane curves. It is quite useful to analyse the Legendre curves. As applications, we consider contact between Legendre curves and the arc-length parameter of Legendre immersions in the unite tangent bundle.
Ewald methods for polarizable surfaces with application to hydroxylation and hydrogen bonding on the (012) and (001) surfaces of alpha-Fe2O3
We present a clear and rigorous derivation of the Ewald-like method for
calculation of the electrostatic energy of the systems infinitely periodic in
two-dimensions and of finite size in the third dimension (slabs) which is
significantly faster than existing methods. Molecular dynamics simulations
using the transferable/polarizable model by Rustad et al. were applied to study
the surface relaxation of the nonhydroxylated, hydroxylated, and solvated
surfaces of alpha-Fe2O3 (hematite). We find that our nonhydroxylated structures
and energies are in good agreement with previous LDA calculations on
alpha-alumina by Manassidis et al. [Surf. Sci. Lett. 285, L517, 1993]. Using
the results of molecular dynamics simulations of solvated interfaces, we define
end-member hydroxylated-hydrated states for the surfaces which are used in
energy minimization calculations. We find that hydration has a small effect on
the surface structure, but that hydroxylation has a significant effect. Our
calculations, both for gas-phase and solution-phase adsorption, predict a
greater amount of hydroxylation for the (012) surface than for the (001)
surface. Our simulations also indicate the presence of four-fold coordinated
iron ions on the (001) surface.Comment: 23 pages, REVTeX (LaTeX), 8 figures not included, e-mail to
[email protected], paper accepted in Surface Scienc
On the structure and evolution of a polar crown prominence/filament system
Polar crown prominences are made of chromospheric plasma partially circling
the Suns poles between 60 and 70 degree latitude. We aim to diagnose the 3D
dynamics of a polar crown prominence using high cadence EUV images from the
Solar Dynamics Observatory (SDO)/AIA at 304 and 171A and the Ahead spacecraft
of the Solar Terrestrial Relations Observatory (STEREO-A)/EUVI at 195A. Using
time series across specific structures we compare flows across the disk in 195A
with the prominence dynamics seen on the limb. The densest prominence material
forms vertical columns which are separated by many tens of Mm and connected by
dynamic bridges of plasma that are clearly visible in 304/171A two-color
images. We also observe intermittent but repetitious flows with velocity 15
km/s in the prominence that appear to be associated with EUV bright points on
the solar disk. The boundary between the prominence and the overlying cavity
appears as a sharp edge. We discuss the structure of the coronal cavity seen
both above and around the prominence. SDO/HMI and GONG magnetograms are used to
infer the underlying magnetic topology. The evolution and structure of the
prominence with respect to the magnetic field seems to agree with the filament
linkage model.Comment: 24 pages, 14 figures, Accepted for publication in Solar Physics
Journal, Movies can be found at http://www2.mps.mpg.de/data/outgoing/panesar
Triggering an eruptive flare by emerging flux in a solar active-region complex
A flare and fast coronal mass ejection originated between solar active
regions NOAA 11514 and 11515 on July 1, 2012 in response to flux emergence in
front of the leading sunspot of the trailing region 11515. Analyzing the
evolution of the photospheric magnetic flux and the coronal structure, we find
that the flux emergence triggered the eruption by interaction with overlying
flux in a non-standard way. The new flux neither had the opposite orientation
nor a location near the polarity inversion line, which are favorable for strong
reconnection with the arcade flux under which it emerged. Moreover, its flux
content remained significantly smaller than that of the arcade (approximately
40 %). However, a loop system rooted in the trailing active region ran in part
under the arcade between the active regions, passing over the site of flux
emergence. The reconnection with the emerging flux, leading to a series of jet
emissions into the loop system, caused a strong but confined rise of the loop
system. This lifted the arcade between the two active regions, weakening its
downward tension force and thus destabilizing the considerably sheared flux
under the arcade. The complex event was also associated with supporting
precursor activity in an enhanced network near the active regions, acting on
the large-scale overlying flux, and with two simultaneous confined flares
within the active regions.Comment: Accepted for publication in Topical Issue of Solar Physics: Solar and
Stellar Flares. 25 pages, 12 figure
The Role of Human-Automation Consensus in Multiple Unmanned Vehicle Scheduling
Objective: This study examined the impact of increasing automation replanning rates on operator performance and workload when supervising a decentralized network of heterogeneous unmanned vehicles. Background: Futuristic unmanned vehicles systems will invert the operator-to-vehicle ratio so that one operator can control multiple dissimilar vehicles connected through a decentralized network. Significant human-automation collaboration will be needed because of automation brittleness, but such collaboration could cause high workload. Method: Three increasing levels of replanning were tested on an existing multiple unmanned vehicle simulation environment that leverages decentralized algorithms for vehicle routing and task allocation in conjunction with human supervision. Results: Rapid replanning can cause high operator workload, ultimately resulting in poorer overall system performance. Poor performance was associated with a lack of operator consensus for when to accept the automation’s suggested prompts for new plan consideration as well as negative attitudes toward unmanned aerial vehicles in general. Participants with video game experience tended to collaborate more with the automation, which resulted in better performance. Conclusion: In decentralized unmanned vehicle networks, operators who ignore the automation’s requests for new plan consideration and impose rapid replans both increase their own workload and reduce the ability of the vehicle network to operate at its maximum capacity. Application: These findings have implications for personnel selection and training for futuristic systems involving human collaboration with decentralized algorithms embedded in networks of autonomous systems.Aurora Flight Sciences Corp.United States. Office of Naval Researc
Genetic diversity among farmer-preferred cassava landraces in Uganda
Understanding of genetic diversity among a breeding population is an
important requirement for crop improvement as it allows for the
selection of diverse parental combinations and formation of heterotic
pools for genetic gain. This study was carried out to determine genetic
diversity within and among 51 farmer-preferred cassava ( Manihot
esculenta ) landraces and 15 elite accessions grown in Uganda. Twenty
six simple sequence repeat (SSR) markers used for genetic diversity
assessment in this study revealed a total of 154 alleles, of which 24%
were unique alleles present only in landraces. The genetic diversity
and observed herozygosity in landraces were slightly higher than in
elite accessions. Elite accessions clustered with some of the landraces
indicating that there were some alleles in common. However, 58.8% of
the landraces fell into 3 different clusters independent of the elite
accessions. Including these landraces with unique alleles in cassava
breeding schemes will increase the chances of producing farmer
preferred adapted elite cultivars. The study also revealed genetic
differentiation among accessions from different regions providing an
opportunity for establishment of heterotic pools within a breeding
programme.La compr\ue9hension de la diversit\ue9 g\ue9n\ue9tique est une
condition importante dans la s\ue9lection de diverses combinaisons
parentales et la formation des groupes h\ue9terotiques
d\u2019int\ue9r\ueat g\ue9n\ue9tique pour
l\u2019am\ue9lioration des cultures. Cette \ue9tude \ue9tait
conduite pour d\ue9terminer la diversit\ue9 g\ue9n\ue9tique
parmi 51 vari\ue9t\ue9s locales de manioc ( Manihot esculenta )
pr\ue9f\ue9r\ue9es des fermiers et 15 accessions \ue9lites
cultiv\ue9es en Ouganda. Vingt six marqueurs simples \ue0 sequence
r\ue9p\ue9t\ue9e (SSR) utilis\ue9s pour l\u2019\ue9valuation
de la diversit\ue9 g\ue9n\ue9tique ont r\ue9v\ue9l\ue9 un
total de 154 all\ue8les, parmi lesquelles 24% \ue9taient des
all\ue8les uniques pr\ue9sentes dans les races locales seulement.
La diversit\ue9 g\ue9n\ue9tique et
l\u2019h\ue9terozygosit\ue9 observ\ue9es dans les races locales
\ue9taient l\ue9g\ue8rement sup\ue9rieures que dans les
accessions \ue9lites. Celles-ci s\u2019\ue9taient regroup\ue9es
avec quelques vari\ue9t\ue9s locales indiquant donc qu\u2019elles
avaient quelques all\ue8les en commun. Par ailleurs, 58.8% des races
locales ont form\ue9 trois diff\ue9rents groupes
ind\ue9pendamment des accessions \ue9lites. Inclure ces races
locales \ue0 all\ue8les uniques dans les syst\ue8mes
d\u2019am\ue9lioration du manioc permettra d\u2019augmenter les
chances de produire des cultivars \ue9lites pr\ue9f\ue9r\ue9s
des fermiers. L\u2019\ue9tude montre aussi que la
diff\ue9renciation g\ue9n\ue9tique trouv\ue9e parmi les
accessions de diff\ue9rentes r\ue9gions est une opportunit\ue9
offerte pour l\u2019\ue9tablissement des groupes h\ue9terotiques
dans le programme d\u2019am\ue9lioration
The Williams Scale of Attitude toward Paganism: development and application among British Pagans
This article builds on the tradition of attitudinal measures of religiosity established by Leslie Francis and colleagues with the Francis Scale of Attitude toward Christianity (and reflected in the Sahin-Francis Scale of Attitude toward Islam, the Katz-Francis Scale of Attitude toward Judaism, and the Santosh-Francis Scale of Attitude toward Hinduism) by introducing a new measure to assess the attitudinal disposition of Pagans. A battery of items was completed by 75 members of a Pagan Summer Camp. These items were reduced to produce a 21-item scale that measured aspects of Paganism concerned with: the God/Goddess, worshipping, prayer, and coven. The scale recorded an alpha coefficient of 0.93. Construct validity of the Williams Scale of Attitude toward Paganism was demonstrated by the clear association with measures of participation in private rituals
The impact of music festival attendance on young people's psychological and social well being
Although the social, emotional, physical and cognitive benefits of engagement in music are well known, little research has been conducted on the psychological benefits of music in the context of music festivals. This article draws on theoretical constructs from the field of positive psychology to interpret the impact of music festival attendance on participants' psychological and social well-being. Qualitative and quantitative data were collected from a focus group and questionnaire survey with young festival-goers aged 18-29 years. Four facets of the music festival experience were identified that were associated with well-being outcomes. These are explored and discussed with reference both to participants' focus group comments and statistical analysis of questionnaire responses. A conceptual model is presented in order to guide further research in this area, and enable both festival organizers and attendees to take optimal advantage of the potential of music festivals to impact positively on young adults' psychological and social well-being
Origins of the Ambient Solar Wind: Implications for Space Weather
The Sun's outer atmosphere is heated to temperatures of millions of degrees,
and solar plasma flows out into interplanetary space at supersonic speeds. This
paper reviews our current understanding of these interrelated problems: coronal
heating and the acceleration of the ambient solar wind. We also discuss where
the community stands in its ability to forecast how variations in the solar
wind (i.e., fast and slow wind streams) impact the Earth. Although the last few
decades have seen significant progress in observations and modeling, we still
do not have a complete understanding of the relevant physical processes, nor do
we have a quantitatively precise census of which coronal structures contribute
to specific types of solar wind. Fast streams are known to be connected to the
central regions of large coronal holes. Slow streams, however, appear to come
from a wide range of sources, including streamers, pseudostreamers, coronal
loops, active regions, and coronal hole boundaries. Complicating our
understanding even more is the fact that processes such as turbulence,
stream-stream interactions, and Coulomb collisions can make it difficult to
unambiguously map a parcel measured at 1 AU back down to its coronal source. We
also review recent progress -- in theoretical modeling, observational data
analysis, and forecasting techniques that sit at the interface between data and
theory -- that gives us hope that the above problems are indeed solvable.Comment: Accepted for publication in Space Science Reviews. Special issue
connected with a 2016 ISSI workshop on "The Scientific Foundations of Space
Weather." 44 pages, 9 figure
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