1,085 research outputs found
Formulation of gradient multiaxial fatigue criteria
International audienceA formulation of gradient fatigue criteria is proposed in the context of multiaxial high-cycle fatigue (HCF) of metallic materials. The notable dependence of fatigue limit on some common factors not taken into account in classical fatigue criteria, is analyzed and modeled. Three interconnected factors, the size, stress gradient and loading effects, are here investigated. A new class of fatigue criteria extended from classical ones with stress gradient terms introduced not only in the normal stress but also in the shear stress components, is formulated. Such a formulation allows to capture gradient effects and related “size” effects, as well as to cover a wide range of loading mode, then can model both phenomena “Smaller is Stronger” and “Higher Gradient is Stronger”. Gradient versions of some classical fatigue criteria such as Crossland and Dang Van are provided as illustrations
Dark exciton energy splitting in monolayer WSe2: insights from time-dependent density-functional theory
We present here a formalism based on time-dependent density-functional theory
(TDDFT) to describe characteristics of both intra- and inter-valley excitons in
semiconductors, the latter of which had remained a challenge. Through the usage
of an appropriate exchange-correlation kernel (nanoquanta), we trace the energy
difference between the intra- and inter-valley dark excitons in monolayer (1L)
WSe2 to the domination of the exchange part in the exchange-correlation
energies of these states. Furthermore, our calculated transition contribution
maps establish the momentum resolved weights of the electron-hole excitations
in both bright and dark excitons thereby providing a comprehensive
understanding of excitonic properties of 1L WSe2. We find that the states
consist of hybridized excitations around the corresponding valleys which leads
to brightening of the dark excitons, i.e., significantly decreasing their
lifetime which is reflected in the PL spectrum. Using many-body perturbation
theory, we calculate the phonon contribution to the energy bandgap and the
linewidths of the excited electrons, holes and (bright) exciton to find that as
the temperature increases the bandgap significantly decreases, while the
linewidths increase. Our work paves for describing the ultrafast charge
dynamics of transition metal dichalcogenide within an ab initio framework
General Derivative-Free Optimization Methods under Global and Local Lipschitz Continuity of Gradients
This paper addresses the study of derivative-free smooth optimization
problems, where the gradient information on the objective function is
unavailable. Two novel general derivative-free methods are proposed and
developed for minimizing such functions with either global or local Lipschitz
continuous gradients. The newly developed methods use gradient approximations
based on finite differences, where finite difference intervals are
automatically adapted to the magnitude of the exact gradients without knowing
them exactly. The suggested algorithms achieve fundamental convergence results,
including stationarity of accumulation points in general settings as well as
global convergence with constructive convergence rates when the Kurdyka-\L
ojasiewicz property is imposed. The local convergence of the proposed
algorithms to nonisolated local minimizers, along with their local convergence
rates, is also analyzed under this property. Numerical experiences involving
various convex, nonconvex, noiseless, and noisy functions demonstrate that the
new methods exhibit essential advantages over other state-of-the-art methods in
derivative-free optimization.Comment: 30 pages, 49 figure
Inexact reduced gradient methods in smooth nonconvex optimization
This paper proposes and develops new line search methods with inexact
gradient information for finding stationary points of nonconvex continuously
differentiable functions on finite-dimensional spaces. Some abstract
convergence results for a broad class of line search methods are reviewed and
extended. A general scheme for inexact reduced gradient (IRG) methods with
different stepsize selections are proposed to construct sequences of iterates
with stationary accumulation points. Convergence results with convergence rates
for the developed IRG methods are established under the Kurdyka-Lojasiewicz
property. The conducted numerical experiments confirm the efficiency of the
proposed algorithms
Sex modulates the ApoE ε4 effect on brain tau deposition measured by 18F-AV-1451 PET in individuals with mild cognitive impairment
Proximity to bank headquarters and branch efficiency : evidence from mortgage lending
We use the staggered introduction of new flight routes to identify reductions in travel time between banks’ headquarters and branches to examine their effects on branch outputs and efficiency. Reductions in headquarters-branch travel time increases branch-level mortgage origination volume, and these loans exhibit higher ex-post performance. Further analyses suggest these effects are due to branch employees working harder and more efficiently in seeking new customers, and screening applications. Overall, our results suggest that geographic proximity enables bank headquarters to monitor branches more effectively and mitigate distance-related agency costs.Peer reviewe
Electromyography (EMG) based Classification of Neuromuscular Disorders using Multi-Layer Perceptron
Electromyography (EMG) signals are the measure of activity in the muscles. The aim of this study is to identify the neuromuscular disease based on EMG signals by means of classification. The neuromuscular diseases that have been identified are myopathy and neuropathy. The classification was carried out using Artificial Neural Network (ANN). There are five feature extraction techniques that were used to extract the signals such as Autoregressive (AR), Root Mean Square (RMS), Zero Crossing (ZC), Waveform length (WL) and Mean Absolute Value (MAV). A comparative analysis of these different techniques were carried out based on the results. The Multilayer Perceptron (MLP) was used for carrying out the classification
High Efficiency Water Splitting using Ultrasound Coupled to a BaTiO 3 Nanofluid
To date, a number of studies have reported the use of vibrations coupled to ferroelectric materials for water splitting. However, producing a stable particle suspension for high efficiency and long-term stability remains a challenge. Here, the first report of the production of a nanofluidic BaTiO3 suspension containing a mixture of cubic and tetragonal phases that splits water under ultrasound is provided. The BaTiO3 particle size reduces from approximately 400 nm to approximately 150 nm during the application of ultrasound and the fine-scale nature of the particulates leads to the formation of a stable nanofluid consisting of BaTiO3 particles suspended as a nanofluid. Long-term testing demonstrates repeatable H2 evolution over 4 days with a continuous 24 h period of stable catalysis. A maximum rate of H2 evolution is found to be 270 mmol h–1 g–1 for a loading of 5 mg l–1 of BaTiO3 in 10% MeOH/H2O. This work indicates the potential of harnessing vibrations for water splitting in functional materials and is the first demonstration of exploiting a ferroelectric nanofluid for stable water splitting, which leads to the highest efficiency of piezoelectrically driven water splitting reported to date
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