7,250 research outputs found
On possible interactions between upper and lower atmosphere
Geomagnetic data was compared with data on tropospheric and stratospheric circulation characteristics; a statistically significant shrinking was found in areal extent of the stratospheric vortex from the third to the eighth day following a 'geomagnetic storm' The meridionality of the 30 640-m contour line at 10 millibars increases markedly from 5 to 8 days after the storm. During the contraction of the polar vortex edge, the mean height of the vortex central contour decreases only slightly. This indicates that a stratospheric warming event is associated with a steepening of the contour gradient rather than a warming over the entire area of the stratospheric polar vortex. The troposphere reacts to these weak, but significant, stratospheric warming events by a shrinkage of the area of the 500-millibar cold air pool. This shrinkage commences about 3 days after the stratospheric warming. The investigation indicates that the energy input into the stratosphere that is received in conjunction with the geomagnetic disturbance has to come at a propitious time, when the stratospheric-tropospheric circulation system is not already undergoing a major readjustment because of an inherent dynamic instability
A model for melting of confined DNA
When DNA molecules are heated they denature. This occurs locally so that
loops of molten single DNA strands form, connected by intact double-stranded
DNA pieces. The properties of this "melting" transition have been intensively
investigated. Recently there has been a surge of interest in this question,
caused by experiments determining the properties of partially bound DNA
confined to nanochannels. But how does such confinement affect the melting
transition? To answer this question we introduce, and solve a model predicting
how confinement affects the melting transition for a simple model system by
first disregarding the effect of self-avoidance. We find that the transition is
smoother for narrower channels. By means of Monte-Carlo simulations we then
show that a model incorporating self-avoidance shows qualitatively the same
behaviour and that the effect of confinement is stronger than in the ideal
case.Comment: 5 pages, 4 figures, supplementary materia
Quantum Fluctuations of a Single Trapped Atom: Transient Rabi Oscillations and Magnetic Bistability
Isolation of a single atomic particle and monitoring its resonance
fluorescence is a powerful tool for studies of quantum effects in
radiation-matter interaction. Here we present observations of quantum dynamics
of an isolated neutral atom stored in a magneto-optical trap. By means of
photon correlations in the atom's resonance fluorescence we demonstrate the
well-known phenomenon of photon antibunching which corresponds to transient
Rabi oscillations in the atom. Through polarization-sensitive photon
correlations we show a novel example of resolved quantum fluctuations:
spontaneous magnetic orientation of an atom. These effects can only be observed
with a single atom.Comment: LaTeX 2e, 14 pages, 7 Postscript figure
Negative quantum capacitance in graphene nanoribbons with lateral gates
We present numerical simulations of the capacitive coupling between graphene
nanoribbons of various widths and gate electrodes in different configurations.
We compare the influence of lateral metallic or graphene side gate structures
on the overall back gate capacitive coupling. Most interestingly, we find a
complex interplay between quantum capacitance effects in the graphene
nanoribbon and the lateral graphene side gates, giving rise to an
unconventional negative quantum capacitance. The emerging non-linear capacitive
couplings are investigated in detail. The experimentally relevant relative
lever arm, the ratio between the coupling of the different gate structures, is
discussed.Comment: 8 pages, 6 figure
Graded Differential Geometry of Graded Matrix Algebras
We study the graded derivation-based noncommutative differential geometry of
the -graded algebra of complex -matrices
with the ``usual block matrix grading'' (for ). Beside the
(infinite-dimensional) algebra of graded forms the graded Cartan calculus,
graded symplectic structure, graded vector bundles, graded connections and
curvature are introduced and investigated. In particular we prove the
universality of the graded derivation-based first-order differential calculus
and show, that is a ``noncommutative graded manifold'' in a
stricter sense: There is a natural body map and the cohomologies of and its body coincide (as in the case of ordinary graded manifolds).Comment: 21 pages, LATE
Synthetic sequence generator for recommender systems - memory biased random walk on sequence multilayer network
Personalized recommender systems rely on each user's personal usage data in
the system, in order to assist in decision making. However, privacy policies
protecting users' rights prevent these highly personal data from being publicly
available to a wider researcher audience. In this work, we propose a memory
biased random walk model on multilayer sequence network, as a generator of
synthetic sequential data for recommender systems. We demonstrate the
applicability of the synthetic data in training recommender system models for
cases when privacy policies restrict clickstream publishing.Comment: The new updated version of the pape
Effects of Solution Elicitation Aids and Need for Cognition on the Generation of Solutions to Ill-Structured Problems
Numerous techniques have been proposed to assist problem solvers in the solution generation process. We empirically examined the effectiveness of a solution elicitation technique based on the presentation of problem objectives and also examined whether the technique was effective across individual differences in need for cognition (NC). We found that when two conflicting objectives were presented successively, more solutions, more categories of solutions, and more effective solutions were generated than when the same two objectives were presented simultaneously or not at all. However, the results indicated that effective solutions may be more efficiently generated by considering objectives simultaneously. Need for cognition was positively related to measures of divergent thinking, and the presentation of objectives was particularly effective as a solution elicitation aid for individuals with low NC. Implications for creative problem-solving research and practice are discussed
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