Lifetime measurements in neutral and singly ionized vanadium

Radiative lifetimes of ten odd-parity levels of V I belonging to the 3d(3)4s4p and 3d(4)4p configurations and of 11 odd-parity levels of V II belonging to the 3d(3)4p configuration are reported. The lifetimes were measured with use of single-step excitation and time-resolved fluorescence spectroscopy. The neutral and singly ionized vanadium atoms were produced in a laser-induced vanadium plasma. (c) 2006 Optical Society of America

NAIS: Neural Attentive Item Similarity Model for Recommendation

Item-to-item collaborative filtering (aka. item-based CF) has been long used for building recommender systems in industrial settings, owing to its interpretability and efficiency in real-time personalization. It builds a user's profile as her historically interacted items, recommending new items that are similar to the user's profile. As such, the key to an item-based CF method is in the estimation of item similarities. Early approaches use statistical measures such as cosine similarity and Pearson coefficient to estimate item similarities, which are less accurate since they lack tailored optimization for the recommendation task. In recent years, several works attempt to learn item similarities from data, by expressing the similarity as an underlying model and estimating model parameters by optimizing a recommendation-aware objective function. While extensive efforts have been made to use shallow linear models for learning item similarities, there has been relatively less work exploring nonlinear neural network models for item-based CF. In this work, we propose a neural network model named Neural Attentive Item Similarity model (NAIS) for item-based CF. The key to our design of NAIS is an attention network, which is capable of distinguishing which historical items in a user profile are more important for a prediction. Compared to the state-of-the-art item-based CF method Factored Item Similarity Model (FISM), our NAIS has stronger representation power with only a few additional parameters brought by the attention network. Extensive experiments on two public benchmarks demonstrate the effectiveness of NAIS. This work is the first attempt that designs neural network models for item-based CF, opening up new research possibilities for future developments of neural recommender systems

Determination of radiative lifetimes of excited states in neutral gold using time-resolved vacuum-ultraviolet laser spectroscopy

Natural radiative lifetimes of the states in the highly perturbed 5d10np 2P sequence in neutral gold, Au i, for n=69, as well as of four of the perturbing 5d96s6p 2P states, have been measured. This was done by direct excitation from the ground state with short-pulse vacuum-ultraviolet laser light and time-resolved detection of the laser-induced fluorescence. We found the lifetimes to be (6p 2P1/2)=6.2(2) ns, (6p 2P3/2)=4.7(2) ns, (7p 2P1/2)=6.4(7) ns, (7p 2P3/2)=5.3(7) ns, (8p 2P1/2)=63(3) ns, (8p 2P3/2)=24(2) ns, (9p 2P1/2)=28(2) ns, and (9p 2P3/2)=75(4) ns. For the perturbing states (two states of each term have been observed) we found (2P1/2, 60 983.05 cm-1)=17.5(10) ns, (2P1/2, 62 540.65 cm-1)=6.7(7) ns, (2P3/2, 58 826.30 cm-1)=2.1(15) ns, and (2P3/2, 63 005.62 cm-1)=2.7(15) ns. Furthermore, we have investigated the hyperfine structure of the 6p 2P3/2 state. © 1994 The American Physical Society

Spectroscopic characterization of aluminum plasma using laser-induced breakdown spectroscopy

A detailed investigation of aluminum plasma induced by a 1064 nm Nd:YAG laser in air was performed. The emission of spectral lines arising from Al I transition at 396.07 nm, Al II transition at 358.46 nm, Al Ill transition at 360.72 nm and Al IV transition at 363.05 nm were well-resolved. The plasma parameters including electron temperature and electron density were determined through the Boltzmann plot method using the emission line intensities of the same ionized stages of aluminum atoms and the Stark-broadening profiles of Al II emission line, respectively. The temporal evolutions of the spectral lines belonging to atomic and ionic aluminum elements and the plasma parameters were investigated at three different laser pulse energies. Moreover, the validity of local thermodynamic equilibrium was elucidated in our experimental condition. (c) 2014 Elsevier GmbH. All rights reserved

Optical emission enhancement of laser-produced copper plasma under a steady magnetic field

From a copper target, laser-ablated plasma was investigated by spectral- and temporal-resolved emission spectroscopy. With the presence of a 0.8T steady magnetic field, the emission of the expanding plasma showed significant enhancements of the spectral lines for all neutral, singly, and doubly ionized species. The relative enhancements for different species have been studied with temporal-resolved measurement by comparing the spectra obtained with and without the magnetic field. The enhanced emission from the plasma plume is attributed to an increase of the radiative recombination rate in the plasma due to magnetic confinement. The temporal evolution of the plasma parameters, including electron temperature and electron density, was deduced and discussed for the cases with and without a magnetic field. (C) 2008 Optical Society of Americ