34,720 research outputs found
Microwave photoresistance of a high-mobility two-dimensional electron gas in a triangular antidot lattice
The microwave (MW) photoresistance has been measured on a high-mobility
two-dimensional electron gas patterned with a shallow triangular antidot
lattice, where both the MW-induced resistance oscillations (MIRO) and
magnetoplasmon (MP) resonance are observed superposing on sharp commensurate
geometrical resonance (GR). Analysis shows that the MIRO, MP, and GR are
decoupled from each other in these experiments.Comment: 5 pages, 4 figures, paper accepted by PR
Spatial oscillations in the spontaneous emission rate of an atom inside a metallic wedge
A method of images is applied to study the spontaneous emission of an atom
inside a metallic wedge with an opening angle of , where N is an
arbitrary positive integer. We show the method of images gives a rate formula
consistent with that from Quantum Electrodynamics. Using the method of images,
we show the correspondence between the oscillations in the spontaneous emission
rate and the closed-orbits of emitted photon going away and returning to the
atom inside the wedge. The closed-orbits can be readily constructed using the
method of images and they are also extracted from the spontaneous emission
rate.Comment: 8 figure
Nonclassical paths in the recurrence spectrum of diamagnetic atoms
Using time-independent scattering matrices, we study how the effects of
nonclassical paths on the recurrence spectra of diamagnetic atoms can be
extracted from purely quantal calculations. This study reveals an intimate
relationship between two types of nonclassical paths: exotic ghost orbits and
diffractive orbits. This relationship proves to be a previously unrecognized
reason for the success of semiclassical theories, like closed-orbit theory, and
permits a comprehensive reformulation of the semiclassical theory that
elucidates its convergence properties.Comment: 5 pages, 4 figure
Magnetization-controlled spin transport in DyAs/GaAs layers
Electrical transport properties of DyAs epitaxial layers grown on GaAs have
been investigated at various temperatures and magnetic fields up to 12T. The
measured longitudinal resistances show two distinct peaks at fields around 0.2
and 2.5T which are believed to be related to the strong spin-disorder
scattering occurring at the phase transition boundaries induced by external
magnetic field. An empirical magnetic phase diagram is deduced from the
temperature dependent experiment, and the anisotropic transport properties are
also presented for various magnetic field directions with respect to the
current flow.Comment: 3 pages with 3 figure
Origin of the high piezoelectric response in PbZr(1-x)TixO3
High resolution x-ray powder diffraction measurements on poled PbZr(1-x)TixO3
(PZT) ceramic samples close to the rhombohedral-tetragonal phase boundary (the
so-called morphotropic phase boundary, MPB) have shown that for both
rhombohedral and tetragonal compositions, the piezoelectric elongation of the
unit cell does not occur along the polar directions but along those directions
associated with the monoclinic distortion. This work provides the first direct
evidence for the origin of the very high piezoelectricity in PZT.Comment: 4 pages, 4 EPS figures embedded. More specific title and abstract. To
appear in Phys. Rev. Let
Magnetic Reversal Time in Open Long Range Systems
Topological phase space disconnection has been recently found to be a general
phenomenon in isolated anisotropic spin systems. It sets a general framework to
understand the emergence of ferromagnetism in finite magnetic systems starting
from microscopic models without phenomenological on-site barriers. Here we
study its relevance for finite systems with long range interacting potential in
contact with a thermal bath. We show that, even in this case, the induced
magnetic reversal time is exponentially large in the number of spins, thus
determining {\it stable} (to any experimental observation time) ferromagnetic
behavior. Moreover, the explicit temperature dependence of the magnetic
reversal time obtained from the microcanonical results, is found to be in good
agreement with numerical simulations. Also, a simple and suggestive expression,
indicating the Topological Energy Threshold at which the disconnection occurs,
as a real energy barrier for many body systems, is obtained analytically for
low temperature
Evidence for a New Dissipationless Regime in 2D Electronic Transport
In an ultra-clean 2D electron system (2DES) subjected to crossed
millimeterwave (30--150 GHz) and weak (B < 2 kG) magnetic fields, a series of
apparently dissipationless states emerges as the system is detuned from
cyclotron resonances. Such states are characterized by an exponentially
vanishing low-temperature longitudinal resistance and a classical Hall
resistance. The activation energies associated with such states exceeds the
Landau level spacing by an order of magnitude. Our findings are likely
indicative of a collective ground state previously unknown for 2DES.Comment: 4 pages, 2 figure
Malolactic Fermentation: The ABC’s of MLF
There are two main fermentations associated with the winemaking process. Alcoholic fermentation is conducted bythe yeast culture and malolactic fermentation takes place as a result of the metabolic activity of lactic acid bacteria,specifically from the genera Oenococcus, Lactobacillus, Pediococcus and Leuconostoc. Malolactic fermentation isdefined as the conversion of malic acid to lactic acid and CO2 and besides deacidification also contributes to microbialstability and modification of the aroma profile. This paper aims to provide a comprehensive review discussing all themain aspects and factors related to malolactic fermentation, including practical considerations for monitoring andensuring a successful fermentation
Photometric stability analysis of the Exoplanet Characterisation Observatory
Photometric stability is a key requirement for time-resolved spectroscopic
observations of transiting extrasolar planets. In the context of the Exoplanet
Characterisation Observatory (EChO) mission design, we here present and
investigate means of translating spacecraft pointing instabilities as well as
temperature fluctuation of its optical chain into an overall error budget of
the exoplanetary spectrum to be retrieved. Given the instrument specifications
as of date, we investigate the magnitudes of these photometric instabilities in
the context of simulated observations of the exoplanet HD189733b secondary
eclipse.Comment: submitted to MNRA
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