265 research outputs found
Computational and experimental studies of the wide bandgap semiconductors NH<sub>4</sub>TiOF<sub>3</sub> and (NH<sub>4</sub>)<sub>2</sub>TiOF<sub>4</sub>
Second order gradient ascent pulse engineering
We report some improvements to the gradient ascent pulse engineering (GRAPE)
algorithm for optimal control of quantum systems. These include more accurate
gradients, convergence acceleration using the BFGS quasi-Newton algorithm as
well as faster control derivative calculation algorithms. In all test systems,
the wall clock time and the convergence rates show a considerable improvement
over the approximate gradient ascent.Comment: Submitted for publicatio
Precursor engineering of hydrotalcite-derived redox sorbents for reversible and stable thermochemical oxygen storage
Chemical looping processes based on multiple-step reduction and oxidation of metal oxides hold great promise for a variety of energy applications, such as CO2 capture and conversion, gas separation, energy storage, and redox catalytic processes. Copper-based mixed oxides are one of the most promising candidate materials with a high oxygen storage capacity. However, the structural deterioration and sintering at high temperatures is one key scientific challenge. Herein, we report a precursor engineering approach to prepare durable copper-based redox sorbents for use in thermochemical looping processes for combustion and gas purification. Calcination of the CuMgAl hydrotalcite precursors formed mixed metal oxides consisting of CuO nanoparticles dispersed in the Mg-Al oxide support which inhibited the formation of copper aluminates during redox cycling. The copper-based redox sorbents demonstrated enhanced reaction rates, stable O2 storage capacity over 500 redox cycles at 900 °C, and efficient gas purification over a broad temperature range. We expect that our materials design strategy has broad implications on synthesis and engineering of mixed metal oxides for a range of thermochemical processes and redox catalytic applications
What Drives Fitness Apps Usage? An Empirical Evaluation
Part 3: Creating Value through ApplicationsInternational audienceThe increased health problems associated with lack of physical activity is of great concern around the world. Mobile phone based fitness applications appear to be a cost effective promising solution for this problem. The aim of this study is to develop a research model that can broaden understanding of the factors that influence the user acceptance of mobile fitness apps. Drawing from Unified Theory of Acceptance and Use of Technology (UTAUT) and Elaboration Likelihood Model (ELM), we conceptualize the antecedents and moderating factors of fitness app use. We validate our model using field survey. Implications for research and practice are discussed
Gravity, Twistors and the MHV Formalism
We give a self-contained derivation of the MHV amplitudes for gravity and use
the associated twistor generating function to define a twistor action for the
MHV diagram approach to gravity. Starting from a background field calculation
on a spacetime with anti self-dual curvature, we obtain a simple spacetime
formula for the scattering of a single, positive helicity linearized graviton
into one of negative helicity. Re-expressing our integral in terms of twistor
data allows us to consider a spacetime that is asymptotic to a superposition of
plane waves. Expanding these out perturbatively yields the gravitational MHV
amplitudes of Berends, Giele & Kuijf. We go on to take the twistor generating
function off-shell at the perturbative level. Combining this with a twistor
action for the anti self-dual background, we obtain a twistor action for the
MHV diagram approach to perturbative gravity. We finish by extending these
results to supergravity, in particular N=4 and N=8.Comment: 39 pages, 3 figures. Minor typos corrected, some clarification adde
Superstripes and complexity in high-temperature superconductors
While for many years the lattice, electronic and magnetic complexity of
high-temperature superconductors (HTS) has been considered responsible for
hindering the search of the mechanism of HTS now the complexity of HTS is
proposed to be essential for the quantum mechanism raising the superconducting
critical temperature. The complexity is shown by the lattice heterogeneous
architecture: a) heterostructures at atomic limit; b) electronic heterogeneity:
multiple components in the normal phase; c) superconducting heterogeneity:
multiple superconducting gaps in different points of the real space and of the
momentum space. The complex phase separation forms an unconventional granular
superconductor in a landscape of nanoscale superconducting striped droplets
which is called the "superstripes" scenario. The interplay and competition
between magnetic orbital charge and lattice fluctuations seems to be essential
for the quantum mechanism that suppresses thermal decoherence effects at an
optimum inhomogeneity.Comment: 20 pages, 3 figures; J. Supercon. Nov. Mag. 201
Use of SMS texts for facilitating access to online alcohol interventions: a feasibility study
A41 Use of SMS texts for facilitating access to online alcohol interventions: a feasibility study
In: Addiction Science & Clinical Practice 2017, 12(Suppl 1): A4
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