7,387 research outputs found
Continuous-Wave Multiphoton Photoemission from Plasmonic Nanostars
Highly nonlinear optical processes, such as multiphoton photoemission,
require high intensities, typically achieved with ultrashort laser pulses and,
hence, were first observed with the advent of picosecond laser technology. An
alternative approach for reaching the required field intensities is offered by
localized optical resonances such as plasmons. Here, we demonstrate localized
multiphoton photoemission from plasmonic nanostructures under continuous-wave
illumination. We use synthesized plasmonic gold nanostars, which exhibit sharp
tips with structural features smaller than 5 nm, leading to
near-field-intensity enhancements exceeding 1000. This large enhancement
facilitates 3-photon photoemission driven by a simple continuous-wave laser
diode. We characterize the intensity and polarization dependencies of the
photoemission yield from both individual nanostars and ensembles. Numerical
simulations of the plasmonic enhancement, the near-field distributions, and the
photoemission intensities are in good agreement with experiment. Our results
open a new avenue for the design of nanoscale electron sources
Virtues and Flaws of the Pauli Potential
Quantum simulations of complex fermionic systems suffer from a variety of
challenging problems. In an effort to circumvent these challenges, simpler
``semi-classical'' approaches have been used to mimic fermionic correlations
through a fictitious ``Pauli potential''. In this contribution we examine two
issues. First, we address some of the inherent difficulties in a widely used
version of the Pauli potential. Second, we refine such a potential in a manner
consistent with the most basic properties of a cold Fermi gas, such as its
momentum distribution and its two-body correlation function.Comment: 16 pages, 6 figure
Decontamination of Diesel particles from air by using the Counterfog (R) system
The existence of particles with diameter under 10m in air is strongly correlated with respiratory diseases. These particles are profusely produced by heating systems, traffic, and Diesel engines creating a serious problem to modern cities. Natural mechanisms removing particles from the atmosphere are too slow to deal with the huge amount of particles daily released by human activity. The objective of this work is to measure the effectiveness of a new technology called Counterfog (R) to eliminate airborne particles. The results show that Counterfog (R) is able to wash out PM10, PM5, and PM2.5 Diesel-generated airborne particles quite efficiently.This work has been funded by the FP7-SEC-2012-1 program of the EU Commission under grant number 312804
Quantum kinetic Ising models
We introduce a quantum generalization of classical kinetic Ising models,
described by a certain class of quantum many body master equations. Similarly
to kinetic Ising models with detailed balance that are equivalent to certain
Hamiltonian systems, our models reduce to a set of Hamiltonian systems
determining the dynamics of the elements of the many body density matrix. The
ground states of these Hamiltonians are well described by matrix product, or
pair entangled projected states. We discuss critical properties of such
Hamiltonians, as well as entanglement properties of their low energy states.Comment: 20 pages, 4 figures, minor improvements, accepted in New Journal of
Physic
Adjoint fermion zero-modes for SU(N) calorons
We derive analytic formulas for the zero-modes of the Dirac equation in the
adjoint representation in the background field of Q=1 SU(N) calorons. Solutions
with various boundary conditions are obtained, including the physically most
relevant cases of periodic and antiperiodic ones. The latter are essential
ingredients in a semiclassical treatment of finite temperature supersymmetric
Yang-Mills theory. A detailed discussion of adjoint zero-modes in several other
contexts is also presented.Comment: 40 latex pages and 5 eps figure
Decoherence and relaxation in the interacting quantum dot system
In this paper we study the low temperature kinetics of the electrons in the
system composed of a quantum dot connected to two leads by solving the equation
of motion. The decoherence and the relaxation of the system caused by the gate
voltage noise and electron-phonon scattering are investigated. In order to take
account of the strong correlation of the electrons in this system, the
quasi-exact wave functions are calculated using an improved matrix product
states algorithm. This algorithm enables us to calculate the wave functions of
the ground state and the low lying excited states with satisfied accuracy and
thus enables us to study the kinetics of the system more effectively. It is
found that although both of these two mechanisms are proportional to the
electron number operator in the dot, the kinetics are quite different. The
noise induced decoherence is much more effective than the energy relaxation,
while the energy relaxation and decoherence time are of the same order for the
electron-phonon scattering. Moreover, the noise induced decoherence increases
with the lowering of the dot level, but the relaxation and decoherence due to
the electron-phonon scattering decrease.Comment: Minor revision. Add journal referenc
Graphene Synthesis Using a CVD Reactor and a Discontinuous Feed of Gas Precursor at Atmospheric Pressure
The present work shows a new method in order to cost-effectively achieve the synthesis of graphene by Chemical Vapor Deposition (CVD). Unlike most usual processes, where precursors such as argon, H2, CH4, and high purity copper foil are used, the proposed method has replaced the previous ones by N2, N2 (90%) : H2 (10%), C2H2, and electrolytic copper (technical grade) since the use of industrialized precursors helps reduce production costs. On the other hand, the process was modified from a continuous flow system with vacuum to a discontinuous one at atmospheric pressure, eliminating the use of vacuum pump. In addition, this modification optimized the consumption of gases, which reduced the waste and the emission of pollutant gases into the atmosphere. Graphene films were grown under different gas flowrates and temperatures. Then, the obtained material was characterized by TEM, Raman spectroscopy, and AFM, confirming the presence of few graphene layers. In brief, the growth time was reduced to six minutes with acetylene as a carbon precursor at 1000°C and at atmospheric pressure, with a flow rate of 30 sccm. Finally, the reported conditions can be used for the synthesis of good quality graphene films in industrial applications
Grapevine leaf uptake of mineral elements influenced by sugar foam amendment of an acidic soil
The use of sugar foam (industrial waste from sugar beet extraction) as an acidic soil (raña) liming agent has been studied in a singular winegrowing region. The contents of the major elements (Al, Ca, Fe, K, Na, Mg, S, Si) and trace elements (As, Ba, Ce, Co, Cr, Cs, Cu, Ga, Hf, La, Mo, Nb, Nd, Ni, Pb, Rb, Sc, Sn, Sr, Ta, Th, U, V, W, Y, Zn, Zr) in the original soil, the amended soil and in grapevine leaves has been measured by X-ray fluorescence. The addition of sugar foam modified the agronomic properties of the original soil. The amendment caused a slight increase in major elements (Ca, 10.4 g·kg-1; Mg, 1.9 g·kg-1 and K, 12.9 g·kg-1) and decreased Al (from 62 to 57.8 g·kg-1) and Fe (from 41.2 to 26.5 g·kg-1) content. Regarding trace elements, there was an increase in levels of Ba, Rb and Sr in the amended soil in comparison to the original soil. The major elements that accumulated in the vine leaf were Ca, Mg and S (Biological Absorption Coefficient, BAC, greater than 1). As for trace elements in leaf, Ba and Sr had a "medium" BAC (0.27 and 0.8, respectively) whereas Rb had a "slight"value (0.08). It is worth noting that the bioaccumulation rate of Zn was greater than 1. The use of sugar foam as a liming agent did not have a negative effect on the absorption of major and trace elements in vine leaves and led to improved BAC values for essential elements in the grapevine. The treatment did not increase the amount of trace elements in the soil above the reference levels for the region.
Synthesis, structural characterization and electrocatalytic properties of cobalt phosphides and pyrophosphates derived from glyphosine
Póster presentado en el XXX Simposio del GE3CMetal phosphonates (MPs), a subclass of coordination polymers, result from the bonding of phosphonic acids (RPO32-) with metal ions, giving rise to an uniformly dispersion of the metal sites at the atomic scale. This characteristic allows the preparation of metal-phosphorous-based nano-carbon composites by a simple one-step pyrolysis, what makes them very attractive precursors of Non-Precious Metal Catalysts (NPMCs).
Herein, we report the synthesis, characterization and electrochemical properties of three cobalt(II) coordination polymers derived from the glycine-N,N-bis(methylenenphosphonic acid) (BPMGLY), with formula [Co(C4H9O8NP2(H2O)2]·nH2O (n=0, 2). In contrast with the zero-dimensional structure of [Co(C4H9O8NP2(H2O)2]·2H2O (Co-BPMGLY-I), the two new polymorphs synthesized, Co(C4H9O8NP2(H2O)2 (Co-BPMGLY-II and Co-BPMGLY-III), whose structures have been solved from powder diffraction data, show two-dimensional frameworks with different connectivity between the Co2+ ions and the ligand within the sheets.
These MPs were used as precursors of NPMCs by pyrolyzing them under 5%-H2/Ar at different temperatures. The electrochemical behavior of the resulting compounds, mainly crystalline cobalt pyrophosphates and/or phosphides, is fully studied regarding to the Oxygen Evolution and Reduction Reactions (OER and ORR, respectively) as well as Hydrogen Evolution Reaction (HER). Cobalt phosphide (CoP) derived from Co-BPMGLY-I displayed the best results, showing an overpotential of 156 mV for HER.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech.
Proyectos nacionales MAT2016-77648-R y PID2019-110249RB-I0
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