15,800 research outputs found
Characterizing the Hofstadter butterfly's outline with Chern numbers
In this work, we report original properties inherent to independent particles
subjected to a magnetic field by emphasizing the existence of regular
structures in the energy spectrum's outline. We show that this fractal curve,
the well-known Hofstadter butterfly's outline, is associated to a specific
sequence of Chern numbers that correspond to the quantized transverse
conductivity. Indeed the topological invariant that characterizes the
fundamental energy band depicts successive stairways as the magnetic flux
varies. Moreover each stairway is shown to be labeled by another Chern number
which measures the charge transported under displacement of the periodic
potential. We put forward the universal character of these properties by
comparing the results obtained for the square and the honeycomb geometries.Comment: Accepted for publication in J. Phys. B (Jan 2009
Flight Flutter Testing of the P6M
On the P6M the shake behavior, i.e., the response to random excitation at subcritical speeds of lowly damped airplane modes, is as important as the actual flutter speed. The approach is to first study the problem by means of analyses and wind-tunnel tests. These predictions are compared with flight test data obtained by spectral analysis of tape recordings of the airplane vibration responses to random aerodynamic turbulence. A similar spectrum analysis approach was used in high speed wind-tunnel tests. A resonance excitation technique was developed for low speed wind-tunnel testing, and well defined V-g curves were obtained. The effect of various parameters on both shake and flutter of T-tails with and without dihedral were studied. Preliminary flight tests yielded good correlation; they also yielded interesting information concerning a low frequency transonic snaking mode, and excitation by shed vortices
On the Frequency of Potential Venus Analogs from Kepler Data
The field of exoplanetary science has seen a dramatic improvement in
sensitivity to terrestrial planets over recent years. Such discoveries have
been a key feature of results from the {\it Kepler} mission which utilizes the
transit method to determine the size of the planet. These discoveries have
resulted in a corresponding interest in the topic of the Habitable Zone (HZ)
and the search for potential Earth analogs. Within the Solar System, there is a
clear dichotomy between Venus and Earth in terms of atmospheric evolution,
likely the result of the large difference ( factor of two) in incident
flux from the Sun. Since Venus is 95\% of the Earth's radius in size, it is
impossible to distinguish between these two planets based only on size. In this
paper we discuss planetary insolation in the context of atmospheric erosion and
runaway greenhouse limits for planets similar to Venus. We define a ``Venus
Zone'' (VZ) in which the planet is more likely to be a Venus analog rather than
an Earth analog. We identify 43 potential Venus analogs with an occurrence rate
(\eta_{\venus}) of and for M
dwarfs and GK dwarfs respectively.Comment: 6 pages, 3 figures, 2 tables. Accepted for publication in the
Astrophysical Journal Letters. More information and graphics can be found at
the Habitable Zone Gallery (http://hzgallery.org
Evaluation of the cardiovascular system during various circulatory stresses Progress report, 1 Sep. 1968 - 1 May 1969
Cardiac response to chemotherapy after myocardial infraction and diagnostic methods of heart disease in man and animal
Possible Implications of Asymmetric Fermionic Dark Matter for Neutron Stars
We consider the implications of fermionic asymmetric dark matter for a "mixed
neutron star" composed of ordinary baryons and dark fermions. We find examples,
where for a certain range of dark fermion mass -- when it is less than that of
ordinary baryons -- such systems can reach higher masses than the maximal
values allowed for ordinary ("pure") neutron stars. This is shown both within a
simplified, heuristic Newtonian analytic framework with non-interacting
particles and via a general relativistic numerical calculation, under certain
assumptions for the dark matter equation of state. Our work applies to various
dark fermion models such as mirror matter models and to other models where the
dark fermions have self interactions.Comment: 20 pages, 6 figure
Effective One-Dimensional Coupling in the Highly-Frustrated Square-Lattice Itinerant Magnet CaCoAs
Inelastic neutron scattering measurements on the itinerant antiferromagnet
(AFM) CaCoAs at a temperature of 8 K reveal two
orthogonal planes of scattering perpendicular to the Co square lattice in
reciprocal space, demonstrating the presence of effective one-dimensional spin
interactions. These results are shown to arise from near-perfect bond
frustration within the - Heisenberg model on a square lattice with
ferromagnetic , and hence indicate that the extensive previous
experimental and theoretical study of the - Heisenberg model on
local-moment square spin lattices should be expanded to include itinerant spin
systems
Supporting Pluralism by Artificial Intelligence: Conceptualizing Epistemic Disagreements as Digital Artifacts
A crucial concept in philosophy and social sciences, epistemic disagreement, has not yet been adequately reflected in the Web. In this paper, we call for development of intelligent tools dealing with epistemic disagreements on the Web to support pluralism. As a first step, we present Polyphony, an ontology for representing and annotating epistemic disagreements
Charmed Mesons Have No Discernable Color-Coulomb Attraction
Starting with a confining linear Lorentz scalar potential V_s and a Lorentz
vector potential V_v which is also linear but has in addition a color-Coulomb
attraction piece, -alpha_s/r, we solve the Dirac equation for the ground-state
c- and u-quark wave functions. Then, convolving V_v with the u-quark density,
we find that the Coulomb attraction mostly disappears, making an essentially
linear barV_v for the c-quark. A similar convolution using the c-quark density
also leads to an essentially linear tildeV_v for the u-quark. For bound cbar-c
charmonia, where one must solve using a reduced mass for the c-quarks, we also
find an essentially linear widehatV_v. Thus, the relativistic quark model
describes how the charmed-meson mass spectrum avoids the need for a
color-Coulomb attraction.Comment: 9 pages, 5 PDF figure
A scoping review characterising the activities and landscape around implementing NICE guidance
Clinical, public health and social care guidance provide evidence-based recommendations on how professionals and commissioners working within these fields should care for patients, service users and the wider public. Evidence-based clinical guidance aims to reduce variation in practice and improve levels of patient and service user care, while at the same time allowing clinical freedom for individual practitioners. The guidance produced by the National Institute for Health and Care Excellence (NICE) are not mandatory, although NICE does set out a business case in terms of the clinical and cost-effectiveness for implementation. Implementation in this sense signifies the active planned processes that take place to enable guidance-based best practice to become routinely embedded within day-to-day activity. There is growing recognition that getting evidence to influence and change practice is a complex undertaking. Despite a growth in the evidence base in this area, there remain gaps in understanding which types of implementation strategies are most effective for which types of guidance, for which audiences and in which circumstances. This review sought to investigate the strategies used to implement NICE guidance in routine practice, and particularly to examine the impact of implementation strategies operationalised by national level organisations and networks
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