12,194 research outputs found
Waveguiding properties of surface states in photonic crystals
We propose and analyze novel surface-state-based waveguides in bandgap
photonic crystals. We discuss surface mode band structure, field localization
and effect of imperfections on the waveguiding properties of the surface modes.
We demonstrate that surface-state-based waveguides can be used to achieve
directional emission out of the waveguide. We also discuss the application of
the surface-state waveguides as efficient light couplers for conventional
photonic crystal waveguides.Comment: 4 pages 5 figure
Comparative study of mycotoxin occurrence in Andean and cereal grains cultivated in South America and North Europe
The consumption of high-quality Andean grains (a.k.a. pseudocereals) is increasing worldwide, and yet very little is known about the susceptibility of these crops to mycotoxin contamination. In this survey study, a multi-analyte liquid chromatographyâtandem mass spectrometry (LCâMS/MS) method was utilised to determine mycotoxin and fungal metabolite levels in Andean grains (quinoa and kañiwa) in comparison to cereal grains (barley, oats and wheat), cultivated in both South American (Bolivia and Peru) and North European (Denmark, Finland and Latvia) countries. A total of 101 analytes were detected at varying levels, primarily produced by Penicillium spp., Fusarium spp. and Aspergillus spp., depending on the type of crop, geographical location and agricultural practices used. Generally, Andean grains from South America showed lower mycotoxin contamination (concentration and assortment) than those from North Europe, while the opposite occurred with cereal grains. Mycotoxin contamination profiles exhibited marked differences between Andean and cereal grains, even when harvested from the same regions, highlighting the need for crop-specific approaches for mycotoxin risk mitigation. Lastly, the efficacy of grain cleaning in respect to total mycotoxin content was assessed, which resulted in significantly lower levels (overall reduction approx. 50%) in cleaned samples for the majority of contaminants.Peer reviewe
Crossover of thermal to shot noise in chaotic cavities
We study the crossover between thermal and shot-noise power in a chaotic
quantum dot in the presence of non-ideal contacts at finite temperature. The
result explicitly demonstrates that the temperature affect the
suppression-amplification effect present in the main quantum noise. In
particular, the weak localization contribution to the noise has an anomalous
thermal behavior when one let the barriers vary, indicating the presence of a
critical point related to specific value of the tunneling barriers. We also
show how to get to the opaque limit of the quantum dot at finite temperature.Comment: 6 pages, 5 figures. To be published in Europhysics Letter
On the nature of the phase transition in the three-dimensional random field Ising model
A brief survey of the theoretical, numerical and experimental studies of the
random field Ising model during last three decades is given. Nature of the
phase transition in the three-dimensional RFIM with Gaussian random fields is
discussed. Using simple scaling arguments it is shown that if the strength of
the random fields is not too small (bigger than a certain threshold value) the
finite temperature phase transition in this system is equivalent to the
low-temperature order-disorder transition which takes place at variations of
the strength of the random fields. Detailed study of the zero-temperature phase
transition in terms of simple probabilistic arguments and modified mean-field
approach (which take into account nearest-neighbors spin-spin correlations) is
given. It is shown that if all thermally activated processes are suppressed the
ferromagnetic order parameter m(h) as the function of the strength of the
random fields becomes history dependent. In particular, the behavior of the
magnetization curves m(h) for increasing and for decreasing reveals the
hysteresis loop.Comment: 22 pages, 12 figure
ALMA resolves the torus of NGC 1068: continuum and molecular line emission
We have used the Atacama Large Millimeter Array (ALMA) to map the emission of
the CO(6-5) molecular line and the 432 {\mu}m continuum emission from the 300
pc-sized circumnuclear disk (CND) of the nearby Seyfert 2 galaxy NGC 1068 with
a spatial resolution of ~4 pc. These observations spatially resolve the CND
and, for the first time, image the dust emission, the molecular gas
distribution, and the kinematics from a 7-10 pc-diameter disk that represents
the submillimeter counterpart of the putative torus of NGC 1068. We fitted the
nuclear spectral energy distribution of the torus using ALMA and near and
mid-infrared (NIR/MIR) data with CLUMPY models. The mass and radius of the
best-fit solution for the torus are both consistent with the values derived
from the ALMA data alone: Mgas_torus=(1+-0.3)x10^5 Msun and Rtorus=3.5+-0.5 pc.
The dynamics of the molecular gas in the torus show non-circular motions and
enhanced turbulence superposed on the rotating pattern of the disk. The
kinematic major axis of the CO torus is tilted relative to its morphological
major axis. By contrast with the nearly edge-on orientation of the H2O
megamaser disk, we have found evidence suggesting that the molecular torus is
less inclined (i=34deg-66deg) at larger radii. The lopsided morphology and
complex kinematics of the torus could be the signature of the
Papaloizou-Pringle instability, long predicted to likely drive the dynamical
evolution of active galactic nuclei (AGN) tori.Comment: Final version accepted by the Astrophysical Journal Letters
(ApJLetters) on April 27th 2016, 6 pages, 5 figure
Strangeness at SIS energies
In this contribution we discuss the physics of strange hadrons in low energy
() heavy ion collision. In this energy range the relevant
strange particle are the kaons and anti-kaons. The most interesting aspect
concerning these particles are so called in-medium modifications. We will
attempt to review the current status of understanding of these in medium
modifications. In addition we will briefly discuss other issues related with
kaon production, such as the nuclear equation of state and chemical
equilibrium.Comment: Proceedings Strange Quark Matter 2003, Atlantic Beach, NC, USA, March
200
Ultrasonic evidence of an uncorrelated cluster formation temperature in manganites with first-order magnetic transition at T_C
Ultrasonic attenuation and phase velocity measurements have been carried out
in the ferromagnetic perovskites La_{2/3}Ca_{1/3}MnO_3 and
La_{2/3}Sr_{1/3}MnO_3. Data show that the transition at the Curie temperature,
T_C, changes from first- to second-order as Sr replaces Ca in the perovskite.
The compound with first-order transition shows also another transition at a
temperature T* > T_C. We interpret the temperature window T_C < T < T* as a
region of coexistence of a phase separated regime of metallic and insulating
regions, in the line of recent theoretical proposals.Comment: 4 pages, 2 figure
Beyond the required LISA free-fall performance: new LISA pathfinder results down to 20ââÎŒHz
In the months since the publication of the first results, the noise performance of LISA Pathfinder has improved because of reduced Brownian noise due to the continued decrease in pressure around the test masses, from a better correction of noninertial effects, and from a better calibration of the electrostatic force actuation. In addition, the availability of numerous long noise measurement runs, during which no perturbation is purposely applied to the test masses, has allowed the measurement of noise with good statistics down to 20ââÎŒHz. The Letter presents the measured differential acceleration noise figure, which is at (1.74±0.05)ââfmâs^{-2}/sqrt[Hz] above 2 mHz and (6±1)Ă10ââfmâs^{-2}/sqrt[Hz] at 20ââÎŒHz, and discusses the physical sources for the measured noise. This performance provides an experimental benchmark demonstrating the ability to realize the low-frequency science potential of the LISA mission, recently selected by the European Space Agency
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