702 research outputs found
The de Rham homotopy theory and differential graded category
This paper is a generalization of arXiv:0810.0808. We develop the de Rham
homotopy theory of not necessarily nilpotent spaces, using closed dg-categories
and equivariant dg-algebras. We see these two algebraic objects correspond in a
certain way. We prove an equivalence between the homotopy category of schematic
homotopy types and a homotopy category of closed dg-categories. We give a
description of homotopy invariants of spaces in terms of minimal models. The
minimal model in this context behaves much like the Sullivan's minimal model.
We also provide some examples. We prove an equivalence between fiberwise
rationalizations and closed dg-categories with subsidiary data.Comment: 47 pages. final version. The final publication is available at
http://www.springerlink.co
Detecting the neutral top-pion at colliders
We investigate some processes of the associated production of a neutral
top-pion with a pair of fermions() in the context of top-color-assisted technicolor(TC2)
theory at future colliders.
The studies show that the largest cross sections of the processes
could only reach the
level of 0.01fb, we can hardly detect a neutral top-pion through these
processes. For the processes ,
and ,
the cross sections of these processes are at the level of a few fb for the
favorable parameters and a few tens, even hundreds, of neutral top-pion events
can be produced at future colliders each year through these
processes. With the clean background of the flavor-changing channel,
the top-pion events can possibly be detected at the planned high luminosity
colliders. Therefore, such neutral top-pion production processes
provide a useful way to detect a neutral top-pion and test the TC2 model
directly.Comment: 13 pages, 4 figure
Investigating how faculty social networks and peer influence relate to knowledge and use of evidence-based teaching practices
Background: Calls for science education reform have been made for decades in the USA. The recent call to produce one million new science, technology, engineering, and math (STEM) graduates over 10 years highlights the need to employ evidence-based instructional practices (EBIPs) in undergraduate STEM classes to create engaging and effective learning environments. EBIPs are teaching strategies that have been empirically demonstrated to positively impact student learning, attitudes, and achievement in STEM disciplines. However, the mechanisms and processes by which faculty learn about and choose to implement EBIPs remain unclear. To explore this problem area, we used social network analysis to examine how an instructorâs knowledge and use of EBIPs may be influenced by their peers within a STEM department. We investigated teaching discussion networks in biology and chemistry departments at three public universities.
Results: We report that tie strength and tie diversity vary between departments, but that mean indegree is not correlated with organizational rank or tenure status. We also describe that teaching discussion ties can often be characterized as strong ties based on two measures of tie strength. Further, we compare peer influence models and find consistent evidence that peer influence in these departments follows a network disturbances model.
Conclusions: Our findings with respect to tie strength and tie diversity indicate that the social network structures in these departments vary in how conducive they might be to change. The correlation in teaching practice between discussion partner and peer influence models suggest that change agents should consider local social network characteristics when developing change strategies. In particular, change agents can expect that faculty may serve as opinion leaders regardless of their academic rank and that faculty can increase their use of EBIPs even if those they speak to about teaching use EBIPs comparatively less
Top quark associated production of the neutral top-pion at high energy colliders
In the context of topcolor-assisted technicolor (TC2) models, we calculate
the associated production of the neutral top-pion with a pair of
top quarks via the process . We
find that the production cross section is larger than that of the process both in the standard model (SM) and in the
minimal supersymmetric SM. With reasonable values of the parameters in TC2
models, the cross section can reach . The neutral top-pion
may be direct observed via this process.Comment: Latex files, 10 pages and 3 figure
The productions of the top-pions and top-Higgs associated with the charm quark at the hadron colliders
In the topcolor-assistant technicolor (TC2) model, the typical physical
particles, top-pions and top-Higgs, are predicted and the existence of these
particles could be regarded as the robust evidence of the model. These
particles are accessible at the Tevatron and LHC, and furthermore the
flavor-changing(FC) feature of the TC2 model can provide us a unique chance to
probe them. In this paper, we study some interesting FC production processes of
top-pions and top-Higgs at the Tevatron and LHC, i.e., and
productions. We find that the light charged top-pions
are not favorable by the Tevatron experiments and the Tevatron has a little
capability to probe neutral top-pion and top-Higgs via these FC production
processes. At the LHC, however, the cross section can reach the level of
pb for production and fb for
production. So one can expect that enough signals could be
produced at the LHC experiments. Furthermore, the SM background should be clean
due to the FC feature of the processes and the FC decay modes can provide us the typical signal to
detect the top-pions and top-Higgs. Therefore, it is hopeful to find the signal
of top-pions and top-Higgs with the running of the LHC via these FC processes.Comment: 12 pages, 6 figure
On ordinal utility, cardinal utility, and random utility Â
Though the Random Utility Model (RUM) was conceivedÂ
entirely in terms of ordinal utility, the apparatus throughwhich it is widely practised exhibits properties ofÂ
cardinal utility.  The adoption of cardinal utility as aÂ
working operation of ordinal is perfectly valid, providedÂ
interpretations drawn from that operation remain faithfulÂ
to ordinal utility.  The paper considers whether the latterrequirement holds true for several measurements commonlyÂ
derived from RUM.  In particular it is found thatÂ
measurements of consumer surplus change may depart fromÂ
ordinal utility, and exploit the cardinality inherent inÂ
the practical apparatus.
Laboratory observations of enhanced entrainment in dense overflows in the presence of submarine canyons and ridges
Author Posting. © Elsevier B.V., 2008. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Deep Sea Research Part I: Oceanographic Research Papers 55 (2008): 737-750, doi:10.1016/j.dsr.2008.02.007.The continental slopes in the oceans are often covered by small-scale topographic
features such as submarine canyons and ridges. When dense plumes, flowing
geostrophically along the slope, encounter such features they may be steered downslope
inside and alongside the topography. A set of laboratory experiments was conducted at
the rotating Coriolis platform to investigate the effect of small-scale topography on plume
mixing. A dense water source was placed on top of a slope, and experiments were
repeated with three topographies: a smooth slope, a slope with a ridge, and a slope with a
canyon. Three flow regimes were studied: laminar, waves, and eddies. When a ridge or a
canyon were present on the slope, the dense plume was steered downslope and
instabilities developed along the ridge and canyon wall. This happened regardless of the
flow characteristics on the smooth slope. Froude and Reynolds numbers were estimated,
and were found to be higher for the topographically steered flow than for flow on smooth
topography. The stratification in the collecting basin was monitored and the mixing
inferred. The total mixing and the entrainment rate increased when a ridge or a canyon
were present. The difference in mixing levels between the regimes was smaller when
topography was present, indicating that it was the small-scale topography and not the
large-scale characteristics of the flow that determined the properties of the product water.AW was funded by the Swedish Research Council and ED in part by Meltzer
Stiftelsen, for which we are grateful. CC was supported by an NSF grant OCE-0085089.
The work described in this publication was supported by the European Community's
Sixth Framework Programme through the grant to the budget of the Integrated
Infrastructure Initiative HYDRALAB III, Contract no. 022441 (RII3)
Equivariant cohomology over Lie groupoids and Lie-Rinehart algebras
Using the language and terminology of relative homological algebra, in
particular that of derived functors, we introduce equivariant cohomology over a
general Lie-Rinehart algebra and equivariant de Rham cohomology over a locally
trivial Lie groupoid in terms of suitably defined monads (also known as
triples) and the associated standard constructions. This extends a
characterization of equivariant de Rham cohomology in terms of derived functors
developed earlier for the special case where the Lie groupoid is an ordinary
Lie group, viewed as a Lie groupoid with a single object; in that theory over a
Lie group, the ordinary Bott-Dupont-Shulman-Stasheff complex arises as an a
posteriori object. We prove that, given a locally trivial Lie groupoid G and a
smooth G-manifold f over the space B of objects of G, the resulting
G-equivariant de Rham theory of f boils down to the ordinary equivariant de
Rham theory of a vertex manifold relative to the corresponding vertex group,
for any vertex in the space B of objects of G; this implies that the
equivariant de Rham cohomology introduced here coincides with the stack de Rham
cohomology of the associated transformation groupoid whence this stack de Rham
cohomology can be characterized as a relative derived functor. We introduce a
notion of cone on a Lie-Rinehart algebra and in particular that of cone on a
Lie algebroid. This cone is an indispensable tool for the description of the
requisite monads.Comment: 47 page
Tuning the valley and chiral quantum state of Dirac electrons in van der Waals heterostructures
Chirality is a fundamental property of electrons with the relativistic spectrum found in graphene and topological insulators. It plays a crucial role in relativistic phenomena, such as Klein tunneling, but it is difficult to visualize directly. Here we report the direct observation and manipulation of chirality and pseudospin polarization in the tunneling of electrons between two almost perfectly aligned graphene crystals. We use a strong in-plane magnetic field as a tool to resolve the contributions of the chiral electronic states that have a phase difference between the two components of their vector wavefunction. Our experiments not only shed light on chirality, but also demonstrate a technique for preparing grapheneâs Dirac electrons in a particular quantum chiral state in a selected valley
Chromomagnetic Dipole Moment of the Top Quark Revisited
We study the complete one-loop contributions to the chromagnetic dipole
moment of the top quark in the Standard Model, two Higgs doublet
models, topcolor assited technicolor models (TC2), 331 models and extended
models with a single extra dimension. We find that the SM predicts
and that the predictions of the other models are also
consitent with the constraints imposed on by low-energy
precision measurements.Comment: 20 pages, 5 figures, Updat
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