34,331 research outputs found
ICT as learning media and research instrument: What eResearch can offer for those who research eLearning?
Students‘ interactions in digital learning environments are distributed over time and space, and many aspects of eLearning phenomenon cannot be investigated using traditional research approaches. At the same time, the possibility to collect digital data about students‘ online interactions and learning opens a range of new opportunities to use ICT as research tool and apply new research approaches. This symposium brings together some of the recent advancements in the area of ICT-enhanced research and aims to discuss future directions for methodological innovation in this area. The session will include four presentations that will explore different directions of ICT use for eLearning research
Doped Mott insulators are insulators: hole localization in the cuprates
We demonstrate that a Mott insulator lightly doped with holes is still an
insulator at low temperature even without disorder. Hole localization obtains
because the chemical potential lies in a pseudogap which has a vanishing
density of states at zero temperature. The energy scale for the pseudogap is
set by the nearest-neighbour singlet-triplet splitting. As this energy scale
vanishes if transitions, virtual or otherwise, to the upper Hubbard band are
not permitted, the fundamental length scale in the pseudogap regime is the
average distance between doubly occupied sites. Consequently, the pseudogap is
tied to the non-commutativity of the two limits ( the on-site
Coulomb repulsion) and (the system size).Comment: 4 pages, 3 .eps file
Nonlinear Transport Near a Quantum Phase Transition in Two Dimensions
The problem of non-linear transport near a quantum phase transition is solved
within the Landau theory for the dissipative insulator-superconductor phase
transition in two dimensions. Using the non-equilibrium Schwinger round-trip
Green function formalism, we obtain the scaling function for the non-linear
conductivity in the quantum disordered regime. We find that the conductivity
scales as at low field but crosses over at large fields to a universal
constant on the order of . The crossover between these two regimes
obtains when the length scale for the quantum fluctuations becomes comparable
to that of the electric field within logarithmic accuracy.Comment: 4.15 pages, no figure
Creation of entangled states in coupled quantum dots via adiabatic rapid passage
Quantum state preparation through external control is fundamental to
established methods in quantum information processing and in studies of
dynamics. In this respect, excitons in semiconductor quantum dots (QDs) are of
particular interest since their coupling to light allows them to be driven into
a specified state using the coherent interaction with a tuned optical field
such as an external laser pulse. We propose a protocol, based on adiabatic
rapid passage, for the creation of entangled states in an ensemble of pairwise
coupled two-level systems, such as an ensemble of QD molecules. We show by
quantitative analysis using realistic parameters for semiconductor QDs that
this method is feasible where other approaches are unavailable. Furthermore,
this scheme can be generically transferred to some other physical systems
including circuit QED, nuclear and electron spins in solid-state environments,
and photonic coupled cavities.Comment: 10 pages, 2 figures. Added reference, minor changes. Discussion,
results and conclusions unchange
Stereociliary Myosin-1c Receptors Are Sensitive to Calcium Chelation and Absent from Cadherin 23 Mutant Mice
The identities of some of the constituents of the hair-cell transduction apparatus have been elucidated only recently. The molecular motor myosin-1c (Myo1c) functions in adaptation of the hair-cell response to sustained mechanical stimuli and is therefore an integral part of the transduction complex. Recent data indicate that Myo1c interacts in vitro with two other molecules proposed to be important for transduction: cadherin 23 (Cdh23), a candidate for the stereociliary tip link, and phosphatidylinositol 4,5-bisphosphate (PIP2), which is abundant in the membranes of hair-cell stereocilia. It is not known, however, whether these interactions occur in hair cells. Using an in situ binding assay on saccular hair cells, we demonstrated previously that Myo1c interacts with molecules at stereociliary tips, the site of transduction, through sequences contained within its calmodulin (CaM)-binding neck domain, which can bind up to four CaM molecules. In the current study, we identify the second CaM-binding IQ domain as a region of Myo1c that mediates CaM-sensitive binding to stereociliary tips and to PIP2 immobilized on a solid support. Binding of Myo1c to stereociliary tips of cochlear and vestibular hair cells is disrupted by treatments that break tip links. In addition, Myo1c does not bind to stereocilia from mice whose hair cells lack Cdh23 protein despite the presence of PIP2 in the stereociliary membranes. Collectively, our data suggest that Myo1c and Cdh23 interact at the tips of hair-cell stereocilia and that this interaction is modulated by CaM
A Survey of the Galactic Plane for 6.7-GHz Methanol Masers I: l = 325.0 - 335.0 ; b = -0.53 - 0.53
We report the results of the first complete survey of an area of the Galactic
Plane for maser emission from the 6.7-GHz transition of methanol. The survey
covers a 10.6-square-degree region of the Galactic Plane in the longitude range
325-335 degrees and latitude range -0.53-0.53 degrees. The survey is sensitive
to masers with a peak flux density greater than approximately 2.6 Jy. The
weakest maser detected has a peak flux density of 2.3 Jy and the strongest a
peak flux density of 425 Jy. We detected a total of 50 distinct masers, 26 of
which are new detections. We show that many 6.7-GHz methanol masers are not
associated with IRAS sources, and that some are associated with sources that
have colours differing from those of a typical ultra-compact HII region
(UCHII). We estimate that the number of UCHII regions in the Galaxy is
significantly more than suggested by IRAS-based estimates, possibly by more
than a factor of two.Comment: 19 pages including 4 figures, using LaTeX formatted with mn.sty,
accepted for publication in MNRA
Krylov-Bogoliubov-Mitropolsky Averaging Used to Construct Effective Hamiltonians in the Theory of Strongly Correlated Electron Systems
We show that the Krylov-Bogoliubov-Mitropolsky averaging in the canonical
formulation can be used as a method for constructing effective Hamiltonians in
the theory of strongly correlated electron systems. As an example, we consider
the transition from the Hamiltonians of the Hubbard and Anderson models to the
respective Hamiltonians of the t-J and Kondo models. This is a very general
method, has several advantages over other methods, and can be used to solve a
wide range of problems in the physics of correlated systems.Comment: 9 page
Subtractive renormalization of the NN interaction in chiral effective theory up to next-to-next-to-leading order: S waves
We extend our subtractive-renormalization method in order to evaluate the 1S0
and 3S1-3D1 NN scattering phase shifts up to next-to-next-to-leading order
(NNLO) in chiral effective theory. We show that, if energy-dependent contact
terms are employed in the NN potential, the 1S0 phase shift can be obtained by
carrying out two subtractions on the Lippmann-Schwinger equation. These
subtractions use knowledge of the the scattering length and the 1S0 phase shift
at a specific energy to eliminate the low-energy constants in the contact
interaction from the scattering equation. For the J=1 coupled channel, a
similar renormalization can be achieved by three subtractions that employ
knowledge of the 3S1 scattering length, the 3S1 phase shift at a specific
energy and the 3S1-3D1 generalized scattering length. In both channels a
similar method can be applied to a potential with momentum-dependent contact
terms, except that in that case one of the subtractions must be replaced by a
fit to one piece of experimental data.
This method allows the use of arbitrarily high cutoffs in the
Lippmann-Schwinger equation. We examine the NNLO S-wave phase shifts for
cutoffs as large as 5 GeV and show that the presence of linear energy
dependence in the NN potential creates spurious poles in the scattering
amplitude. In consequence the results are in conflict with empirical data over
appreciable portions of the considered cutoff range. We also identify problems
with the use of cutoffs greater than 1 GeV when momentum-dependent contact
interactions are employed. These problems are ameliorated, but not eliminated,
by the use of spectral-function regularization for the two-pion exchange part
of the NN potentialComment: 40 pages, 21 figure
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