368 research outputs found
Steady States of a Microwave Irradiated Quantum Hall Gas
We consider effects of a long-wavelength disorder potential on the Zero
Conductance State (ZCS) of the microwave-irradiated 2D electron gas. Assuming a
uniform Hall conductivity, we construct a Lyapunov functional and derive
stability conditions on the domain structure of the photo-generated fields. We
solve the resulting equations for a general one-dimensional and certain
two-dimensional disorder potentials, and find non-zero conductances,
photo-voltages, and circulating dissipative currents. In contrast, weak white
noise disorder does not destroy the ZCS, but induces mesoscopic current
fluctuations.Comment: 4 pages, 2 colour figure
Training-induced inversion of spontaneous exchange bias field on La1.5Ca0.5CoMnO6
In this work we report the synthesis and structural, electronic and magnetic
properties of La1.5Ca0.5CoMnO6 double-perovskite. This is a re-entrant spin
cluster material which exhibits a non-negligible negative exchange bias effect
when it is cooled in zero magnetic field from an unmagnetized state down to low
temperature. X-ray powder diffraction, X-ray photoelectron spectroscopy and
magnetometry results indicate mixed valence state at Co site, leading to
competing magnetic phases and uncompensated spins at the magnetic interfaces.
We compare the results for this Ca-doped material with those reported for the
resemblant compound La1.5Sr0.5CoMnO6, and discuss the much smaller spontaneous
exchange bias effect observed for the former in terms of its structural and
magnetic particularities. For La1.5Ca0.5CoMnO6, when successive magnetization
loops are carried, the spontaneous exchange bias field inverts its sign from
negative to positive from the first to the second measurement. We discuss this
behavior based on the disorder at the magnetic interfaces, related to the
presence of a glassy phase. This compound also exhibits a large conventional
exchange bias, for which there is no sign inversion of the exchange bias field
for consecutive cycles
Global Ethics and Nanotechnology: A Comparison of the Nanoethics Environments of the EU and China
The following article offers a brief overview of current nanotechnology policy, regulation and ethics in Europe and The People’s Republic of China with the intent of noting (dis)similarities in approach, before focusing on the involvement of the public in science and technology policy (i.e. participatory Technology Assessment). The conclusions of this article are, that (a) in terms of nanosafety as expressed through policy and regulation, China PR and the EU have similar approaches towards, and concerns about, nanotoxicity—the official debate on benefits and risks is not markedly different in the two regions; (b) that there is a similar economic drive behind both regions’ approach to nanodevelopment, the difference being the degree of public concern admitted; and (c) participation in decision-making is fundamentally different in the two regions. Thus in China PR, the focus is on the responsibility of the scientist; in the EU, it is about government accountability to the public. The formulation of a Code of Conduct for scientists in both regions (China PR’s predicted for 2012) reveals both similarity and difference in approach to nanotechnology development. This may change, since individual responsibility alone cannot guide S&T development, and as public participation is increasingly seen globally as integral to governmental decision-making
Escape from the vicinity of fractal basin boundaries of a star cluster
The dissolution process of star clusters is rather intricate for theory. We
investigate it in the context of chaotic dynamics. We use the simple Plummer
model for the gravitational field of a star cluster and treat the tidal field
of the Galaxy within the tidal approximation. That is, a linear approximation
of tidal forces from the Galaxy based on epicyclic theory in a rotating
reference frame. The Poincar\'e surfaces of section reveal the effect of a
Coriolis asymmetry. The system is non-hyperbolic which has important
consequences for the dynamics. We calculated the basins of escape with respect
to the Lagrangian points and . The longest escape times have been
measured for initial conditions in the vicinity of the fractal basin
boundaries. Furthermore, we computed the chaotic saddle for the system and its
stable and unstable manifolds. The chaotic saddle is a fractal structure in
phase space which has the form of a Cantor set and introduces chaos into the
system.Comment: Accepted by MNRAS, Figures have lower qualit
A dimensão ética da formação profissional em saúde: estudo de caso com cursos de graduação em odontologia
Probing the order parameter symmetry in the cuprate high temperature superconductors by SQUID microscopy
The orbital component of the order parameter in the cuprate high-Tc cuprate
superconductors is now well established, in large part because of phase
sensitive tests. Although it would be desirable to use such tests on other
unconventional superconductors, there are a number of favorable factors
associated with the properties of the cuprates, and a number of technical
advances, that were required for these tests to be successful. In this review I
will describe the development of phase sensitive pairing symmetry tests using
SQUID microscopy, underlining the factors favoring these experiments in the
cuprates and the technical advances that had to be made.Comment: 12 pages, 7 figure, invited review to be published in Comptes Rendus
de l'Academie des Sciences (Comptes Rendus Physique
Case study on the efficacy of a lanthanum-enriched clay (Phoslock®) in controlling eutrophication in Lake Het Groene Eiland (The Netherlands)
Lake Het Groene Eiland was created in the beginning of 2008 by construction of dikes for isolating it from the surrounding 220-ha water body. This so-called claustrum of 5 ha was treated using lanthanum-modified clay (Phoslock®) to control eutrophication and mitigate cyanobacterial nuisance. Cyanobacteria chlorophyll-a were significantly lower in the claustrum than those in the reference water body, where a massive bloom developed in summer, 2008. However, PO4-P and TP did not statistically differ in these two waters. TN and NO3-N were significantly lower in the claustrum, where dense submerged macrophytes beds developed. Lanthanum concentrations were elevated after the applications of the modified clay in the claustrum, but filterable lanthanum dropped rapidly below the Dutch standard of 10.1 μg l−1. During winter, dozens of Canada geese resided at the claustrum. Geese droppings contained an average of 2 mg PO4-P g−1 dry weight and 12 mg NH3-N g−1 dry weight and might present a growing source of nutrients to the water. Constructing the claustrum enabled unrestricted bathing in subsequent three summers, as no swimming bans had to be issued due to cyanobacteria blooms. However, the role of the modified clay in this positive outcome remains unclear, and longevity of the measures questionable.
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