1,402 research outputs found
Weak and strong fillability of higher dimensional contact manifolds
For contact manifolds in dimension three, the notions of weak and strong
symplectic fillability and tightness are all known to be inequivalent. We
extend these facts to higher dimensions: in particular, we define a natural
generalization of weak fillings and prove that it is indeed weaker (at least in
dimension five),while also being obstructed by all known manifestations of
"overtwistedness". We also find the first examples of contact manifolds in all
dimensions that are not symplectically fillable but also cannot be called
overtwisted in any reasonable sense. These depend on a higher-dimensional
analogue of Giroux torsion, which we define via the existence in all dimensions
of exact symplectic manifolds with disconnected contact boundary.Comment: 68 pages, 5 figures. v2: Some attributions clarified, and other minor
edits. v3: exposition improved using referee's comments. Published by Invent.
Mat
Contact orderability up to conjugation
We study in this paper the remnants of the contact partial order on the
orbits of the adjoint action of contactomorphism groups on their Lie algebras.
Our main interest is a class of non-compact contact manifolds, called convex at
infinity.Comment: 28 pages, 1 figur
Tight Beltrami fields with symmetry
Let be a compact orientable Seifered fibered 3-manifold without a
boundary, and an -invariant contact form on . In a suitable
adapted Riemannian metric to , we provide a bound for the volume
and the curvature, which implies the universal tightness of the
contact structure .Comment: 26 page
Design and User Satisfaction of Interactive Maps for Visually Impaired People
Multimodal interactive maps are a solution for presenting spatial information
to visually impaired people. In this paper, we present an interactive
multimodal map prototype that is based on a tactile paper map, a multi-touch
screen and audio output. We first describe the different steps for designing an
interactive map: drawing and printing the tactile paper map, choice of
multi-touch technology, interaction technologies and the software architecture.
Then we describe the method used to assess user satisfaction. We provide data
showing that an interactive map - although based on a unique, elementary,
double tap interaction - has been met with a high level of user satisfaction.
Interestingly, satisfaction is independent of a user's age, previous visual
experience or Braille experience. This prototype will be used as a platform to
design advanced interactions for spatial learning
Right-veering diffeomorphisms of compact surfaces with boundary II
We continue our study of the monoid of right-veering diffeomorphisms on a
compact oriented surface with nonempty boundary, introduced in [HKM2]. We
conduct a detailed study of the case when the surface is a punctured torus; in
particular, we exhibit the difference between the monoid of right-veering
diffeomorphisms and the monoid of products of positive Dehn twists, with the
help of the Rademacher function. We then generalize to the braid group B_n on n
strands by relating the signature and the Maslov index. Finally, we discuss the
symplectic fillability in the pseudo-Anosov case by comparing with the work of
Roberts [Ro1,Ro2].Comment: 25 pages, 5 figure
Tightness in contact metric 3-manifolds
This paper begins the study of relations between Riemannian geometry and
global properties of contact structures on 3-manifolds. In particular we prove
an analog of the sphere theorem from Riemannian geometry in the setting of
contact geometry. Specifically, if a given three dimensional contact manifold
(M,\xi) admits a complete compatible Riemannian metric of positive 4/9-pinched
curvature then the underlying contact structure \xi is tight; in particular,
the contact structure pulled back to the universal cover is the standard
contact structure on S^3. We also describe geometric conditions in dimension
three for \xi to be universally tight in the nonpositive curvature setting.Comment: 29 pages. Added the sphere theorem, removed high dimensional material
and an alternate approach to the three dimensional tightness radius estimate
A comparison of two keyboarding instruction methods over 2 years for elementary students.
Background: As computer and digital device use continues to grow in prevalence for school and work tasks, it is important for elementary-aged students to develop efficient keyboarding skills to support future academic and vocational success.
Method: A quasi-experimental pre-test and post-test study design was used to compare the effect of two different keyboarding instructional approaches on elementary students over a consecutive 2-year period. One group used Keyboarding Without Tears (KWT; N = 592) both years while the other group used free web-based activities the first year and Keyboarding Without Tears the second year (mixed methods; N = 714). Keyboarding speed, accuracy, and technique were measured at the beginning and end of the 2-year period.
Results: The results showed significant improvements in keyboarding speed and accuracy in both groups for all grades favoring the KWT in second, third, and fourth grade. Improvements in keyboarding technique were also noted for both schools in all grades favoring the KWT group in all grades.
Conclusion: Although improvements were noted with both approaches, this study suggests stronger outcomes from those using KWT over 2 consecutive years, especially beginning in first grade and ending in fourth grade.ECU Open Access Publishing Support Fun
A Web-based Adaptive and Intelligent Tutor by Expert Systems
Todays, Intelligent and web-based E-learning is one of regarded topics. So
researchers are trying to optimize and expand its application in the field of
education. The aim of this paper is developing of E-learning software which is
customizable, dynamic, intelligent and adaptive with Pedagogy view for learners
in intelligent schools. This system is an integration of adaptive web-based
E-learning with expert systems as well. Learning process in this system is as
follows. First intelligent tutor determines learning style and characteristics
of learner by a questionnaire and then makes his model. After that the expert
system simulator plans a pre-test and then calculates his score. If the learner
gets the required score, the concept will be trained. Finally the learner will
be evaluated by a post-test. The proposed system can improves the education
efficiency highly as well as de-creases the costs and problems of an expert
tutor. As a result, every time and eve-rywhere (ETEW) learning would be
provided via web in this system. Moreover the learners can enjoy a cheap remote
learning even at home in a virtual simulated physical class. So they can learn
thousands courses very simple and fast.Comment: 10 pages, 3 figures, The Second International Conference on Advances
in Computing and Information Technology (ACITY 2012). arXiv admin note:
substantial text overlap with arXiv:1304.404
Numerical simulations of the cosmic star formation history
The cosmic star formation history in Cold Dark Matter dominated cosmological
scenarios is studied by means of hydrodynamical numerical simulations. In
particular, we explore a low density model with a Lambda-term and two high
density models with different power spectra, all of them being spatially flat.
Our simulations employ a fully nonlinear N-body and Eulerian hydrodynamics
algorithm with a model for star formation and supernovae feedback that depends
on two phenomenological parameters determined in agreement with previous
papers. We find a nearly constant star formation rate beyond z=1, and we
discuss which facts may determine the decrease in the SFR from z=1 to the
present epoch. The Lambda-term cosmology with realistic parameters for star
formation and feedback best reproduces the observed star formation history.Comment: 10 pages, 5 figures. Accepted for publication in A&
Past dynamics of HIV transmission among men who have sex with men in Montréal, Canada: a mathematical modeling study
BACKGROUND: Gay, bisexual, and other men who have sex with men (gbMSM) experience disproportionate risks of HIV acquisition and transmission. In 2017, Montréal became the first Canadian Fast-Track City, setting the 2030 goal of zero new HIV infections. To inform local elimination efforts, we estimate the evolving role of prevention and sexual behaviours on HIV transmission dynamics among gbMSM in Montréal between 1975 and 2019. METHODS: Data from local bio-behavioural surveys were analyzed to develop, parameterize, and calibrate an agent-based model of sexual HIV transmission. Partnership dynamics, HIV's natural history, and treatment and prevention strategies were considered. The model simulations were analyzed to estimate the fraction of HIV acquisitions and transmissions attributable to specific groups, with a focus on age, sexual partnering level, and gaps in the HIV care-continuum. RESULTS: The model-estimated HIV incidence peaked in 1985 (2.3 per 100 person years (PY); 90% CrI: 1.4-2.9 per 100 PY) and decreased to 0.1 per 100 PY (90% CrI: 0.04-0.3 per 100 PY) in 2019. Between 2000-2017, the majority of HIV acquisitions and transmissions occurred among men aged 25-44 years, and men aged 35-44 thereafter. The unmet prevention needs of men with > 10 annual anal sex partners contributed 90-93% of transmissions and 67-73% of acquisitions annually. The primary stage of HIV played an increasing role over time, contributing to 11-22% of annual transmissions over 2000-2019. In 2019, approximately 70% of transmission events occurred from men who had discontinued, or never initiated antiretroviral therapy. CONCLUSIONS: The evolving HIV landscape has contributed to the declining HIV incidence among gbMSM in Montréal. The shifting dynamics identified in this study highlight the need for continued population-level surveillance to identify gaps in the HIV care continuum and core groups on which to prioritize elimination efforts
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