906 research outputs found
Coherent electronic and nuclear dynamics in a rhodamine heterodimer-DNA supramolecular complex
Elucidating the role of quantum coherences in energy migration within biological and artificial multichromophoric antenna systems is the subject of an intense debate. It is also a practical matter because of the decisive implications for understanding the biological processes and engineering artificial materials for solar energy harvesting. A supramolecular rhodamine heterodimer on a DNA scaffold was suitably engineered to mimic the basic donor-acceptor unit of light-harvesting antennas. Ultrafast 2D electronic spectroscopic measurements allowed identifying clear features attributable to a coherent superposition of dimer electronic and vibrational states contributing to the coherent electronic charge beating between the donor and the acceptor. The frequency of electronic charge beating is found to be 970 cm-1 (34 fs) and can be observed for 150 fs. Through the support of high level ab initio TD-DFT computations of the entire dimer, we established that the vibrational modes preferentially optically accessed do not drive subsequent coupling between the electronic states on the 600 fs of the experiment. It was thereby possible to characterize the time scales of the early time femtosecond dynamics of the electronic coherence built by the optical excitation in a large rigid supramolecular system at a room temperature in solution. © 2017 the Owner Societies.Multi valued and parallel molecular logi
P-Fuzzy Diffusion Equation Using Rules Base
We propose a fuzzy system that simulates dispersion of individuals whose movements are described by diffusion. We will use only the position of the population as an input variable for describing the process. We emphasize that the classical diffusion equation along with its analytical solution in no time was used for obtaining our solution
Bi-directional Alfv\'en Cyclotron Instabilities in the Mega-Amp Spherical Tokamak
Alfv\'en cyclotron instabilities excited by velocity gradients of energetic
beam ions were investigated in MAST experiments with super-Alfv\'enic NBI over
a wide range of toroidal magnetic fields from ~0.34 T to ~0.585 T. In MAST
discharges with high magnetic field, a discrete spectrum of modes in the
sub-cyclotron frequency range is excited toroidally propagating counter to the
beam and plasma current (toroidal mode numbers n < 0).Comment: 28 pages, 13 figures. This article has been submitted to Physics of
Plasmas. After it is published, it will be found at
http://scitation.aip.org/content/aip/journal/pop/brows
Investigating fusion plasma instabilities in the Mega Amp Spherical Tokamak using mega electron volt proton emissions (invited)a)
The proton detector (PD) measures 3 MeV proton yield distributions from deuterium-deuterium fusion reactions within the Mega Amp Spherical Tokamak (MAST). The PD's compact four-channel system of collimated and individually oriented silicon detectors probes different regions of the plasma, detecting protons (with gyro radii large enough to be unconfined) leaving the plasma on curved trajectories during neutral beam injection. From first PD data obtained during plasma operation in 2013, proton production rates (up to several hundred kHz and 1 ms time resolution) during sawtooth events were compared to the corresponding MAST neutron camera data. Fitted proton emission profiles in the poloidal plane demonstrate the capabilities of this new system
Minority and mode conversion heating in (3He)-H JET plasma
Radio frequency (RF) heating experiments have recently been conducted in JET (He-3)-H plasmas. This type of plasmas will be used in ITER's non-activated operation phase. Whereas a companion paper in this same PPCF issue will discuss the RF heating scenario's at half the nominal magnetic field, this paper documents the heating performance in (He-3)-H plasmas at full field, with fundamental cyclotron heating of He-3 as the only possible ion heating scheme in view of the foreseen ITER antenna frequency bandwidth. Dominant electron heating with global heating efficiencies between 30% and 70% depending on the He-3 concentration were observed and mode conversion (MC) heating proved to be as efficient as He-3 minority heating. The unwanted presence of both He-4 and D in the discharges gave rise to 2 MC layers rather than a single one. This together with the fact that the location of the high-field side fast wave (FW) cutoff is a sensitive function of the parallel wave number and that one of the locations of the wave confluences critically depends on the He-3 concentration made the interpretation of the results, although more complex, very interesting: three regimes could be distinguished as a function of X[He-3]: (i) a regime at low concentration (X[He-3] < 1.8%) at which ion cyclotron resonance frequency (ICRF) heating is efficient, (ii) a regime at intermediate concentrations (1.8 < X[He-3] < 5%) in which the RF performance is degrading and ultimately becoming very poor, and finally (iii) a good heating regime at He-3 concentrations beyond 6%. In this latter regime, the heating efficiency did not critically depend on the actual concentration while at lower concentrations (X[He-3] < 4%) a bigger excursion in heating efficiency is observed and the estimates differ somewhat from shot to shot, also depending on whether local or global signals are chosen for the analysis. The different dynamics at the various concentrations can be traced back to the presence of 2 MC layers and their associated FW cutoffs residing inside the plasma at low He-3 concentration. One of these layers is approaching and crossing the low-field side plasma edge when 1.8 < X[He-3] < 5%. Adopting a minimization procedure to correlate the MC positions with the plasma composition reveals that the different behaviors observed are due to contamination of the plasma. Wave modeling not only supports this interpretation but also shows that moderate concentrations of D-like species significantly alter the overall wave behavior in He-3-H plasmas. Whereas numerical modeling yields quantitative information on the heating efficiency, analytical work gives a good description of the dominant underlying wave interaction physics
Classification of compact radio sources in the Galactic plane with supervised machine learning
Generation of science-ready data from processed data products is one of the
major challenges in next-generation radio continuum surveys with the Square
Kilometre Array (SKA) and its precursors, due to the expected data volume and
the need to achieve a high degree of automated processing. Source extraction,
characterization, and classification are the major stages involved in this
process. In this work we focus on the classification of compact radio sources
in the Galactic plane using both radio and infrared images as inputs. To this
aim, we produced a curated dataset of ~20,000 images of compact sources of
different astronomical classes, obtained from past radio and infrared surveys,
and novel radio data from pilot surveys carried out with the Australian SKA
Pathfinder (ASKAP). Radio spectral index information was also obtained for a
subset of the data. We then trained two different classifiers on the produced
dataset. The first model uses gradient-boosted decision trees and is trained on
a set of pre-computed features derived from the data, which include
radio-infrared colour indices and the radio spectral index. The second model is
trained directly on multi-channel images, employing convolutional neural
networks. Using a completely supervised procedure, we obtained a high
classification accuracy (F1-score>90%) for separating Galactic objects from the
extragalactic background. Individual class discrimination performances, ranging
from 60% to 75%, increased by 10% when adding far-infrared and spectral index
information, with extragalactic objects, PNe and HII regions identified with
higher accuracies. The implemented tools and trained models were publicly
released, and made available to the radioastronomical community for future
application on new radio data.Comment: 27 pages, 15 figures, 9 table
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