Finite-temperature properties of non-magnetic transition metals: Comparison of the performance of constraint-based semi and nonlocal functionals

We assess the performance of nonempirical, truly nonlocal and semi-local functionals with regard to structural and thermal properties of $3d$, $4d$, and $5d$ non-magnetic transition metals. We focus on constraint-based functionals and consider the new consistent-exchange van der Waals density functional version vdW-DF-cx [Phys. Rev. B 89, 035412 (2014)], the semi-local PBE [Phys. Rev. Lett. 77, 3865 (1996)] and PBEsol functionals [Phys. Rev. Lett. 100, 136406 (2008)] as well as the AM05 meta-functional [Phys. Rev. B 72, 085108 (2005)]. Using the quasi-harmonic approximation structural parameters, elastic response, and thermal expansion at finite temperatures are computed and compared to experimental data. We also compute cohesive energies explicitly including zero-point vibrations. It is shown that overall vdW-DF-cx provides an accurate description of thermal properties and retains a level of transferability and accuracy that is comparable to or better than some of the best constraint-based semi-local functionals. Especially, with regard to the cohesive energies the consistent inclusion of spin polarization effects in the atoms turns out to be crucial and it is important to use the rigorous spin-vdW-DF-cx formulation [Phys. Rev. Lett. 115, 136402 (2015)]. This demonstrates that vdW-DF-cx has general-purpose character and can be used to study systems that have both sparse and dense electron distributions.Comment: 10 pages, 5 figure

Mechanism of Re precipitation in irradiated W-Re alloys from kinetic Monte Carlo simulations

High-temperature, high-dose, neutron irradiation of W results in the formation of Re-rich clusters at concentrations one order of magnitude lower than the thermodynamic solubility limit. These clusters may eventually transform into brittle W-Re intermetallic phases, which can lead to high levels of hardening and thermal conductivity losses. Standard theories of radiation enhanced diffusion and precipitation cannot explain the formation of these precipitates and so understanding the mechanism by which nonequilibrium clusters form under irradiation is crucial to predict materials degradation and devise mitigation strategies. Here we carry out a thermodynamic study of W-Re alloys and conduct kinetic Monte Carlo simulations of Re cluster formation in irradiated W-2Re alloys using a generalized Hamiltonian for crystals containing point defects parameterized entirely with electronic structure calculations. Our model incorporates recently-gained mechanistic information of mixed-interstitial solute transport, which is seen to control cluster nucleation and growth by forming quasi-spherical nuclei after an average incubation time of 20 s at 1800 K. These nuclei are seen to grow by attracting more mixed interstitials bringing solute atoms, which in turns attracts vacancies leading to recombination and solute agglomeration. The clusters grow to a maximum size of approximately 4-nm radius, and are not fully dense with Re, containing 50% or less near the center. Our simulations are in reasonable agreement with recent atom probe examinations of ion irradiated W-2Re systems at 773 K

The role of interstitial binding in radiation induced segregation in W-Re alloys

Due to their high strength and advantageous high-temperature properties, tungsten-based alloys are being considered as plasma-facing candidate materials in fusion devices. Under neutron irradiation, rhenium, which is produced by nuclear transmutation, has been found to precipitate in elongated precipitates forming thermodynamic intermetallic phases at concentrations well below the solubility limit. Recent measurements have shown that Re precipitation can lead to substantial hardening, which may have a detrimental effect on the fracture toughness of W alloys. This puzzle of sub-solubility precipitation points to the role played by irradiation induced defects, specifically mixed solute-W interstitials. Here, using first-principles calculations based on density functional theory, we study the energetics of mixed interstitial defects in W-Re, W-V, and W-Ti alloys, as well as the heat of mixing for each substitutional solute. We find that mixed interstitials in all systems are strongly attracted to each other with binding energies of -2.4 to -3.2 eV and form interstitial pairs that are aligned along parallel first-neighbor strings. Low barriers for defect translation and rotation enable defect agglomeration and alignment even at moderate temperatures. We propose that these elongated agglomerates of mixed-interstitials may act as precursors for the formation of needle-shaped intermetallic precipitates. This interstitial-based mechanism is not limited to radiation induced segregation and precipitation in W-Re alloys but is also applicable to other body-centered cubic alloys.Comment: 8 pages, 7 figure

Optical absorption spectrum in disordered semiconductor multilayers

The effects of chemical disorder on the electronic and optical properties of semiconductor alloy multilayers are studied based on the tight-binding theory and single-site coherent potential approximation. Due to the quantum confinement of the system, the electronic spectrum breaks into a set of subbands and the electronic density of states and hence the optical absorption spectrum become layer-dependent. We find that, the values of absorption depend on the alloy concentration, the strength of disorder, and the layer number. The absorption spectrum in all layers is broadened because of the influence of disorder and in the case of strong disorder regime, two optical absorption bands appear. In the process of absorption, most of the photon energy is absorbed by the interior layers of the system. The results may be useful for the development of optoelectronic nanodevices.Comment: 6 pages, 6 EPS figures, revised versio

Machine Learning Challenges of Biological Factors in Insect Image Data

The BIOSCAN project, led by the International Barcode of Life Consortium, seeks to study changes in biodiversity on a global scale. One component of the project is focused on studying the species interaction and dynamics of all insects. In addition to genetically barcoding insects, over 1.5 million images per year will be collected, each needing taxonomic classification. With the immense volume of incoming images, relying solely on expert taxonomists to label the images would be impossible; however, artificial intelligence and computer vision technology may offer a viable high-throughput solution. Additional tasks including manually weighing individual insects to determine biomass, remain tedious and costly. Here again, computer vision may offer an efficient and compelling alternative. While the use of computer vision methods is appealing for addressing these problems, significant challenges resulting from biological factors present themselves. These challenges are formulated in the context of machine learning in this paper.Comment: 4 pages, 3 figures. Submitted to the Journal of Computational Vision and Imaging System

Acceptance and commitment therapy, selective serotonin reuptake inhibitors, and their combination in the improvement of obsessive-compulsive symptoms and experiential avoidance in patients with obsessive-compulsive disorder

Background: Selective serotonin reuptake inhibitors (SSRIs) and exposure with response prevention for treatment of obsessive-compulsive disorder (OCD) have demonstrated empirical support; however, a substantial number of patients remain with clinically significant OCD symptoms after such treatments. Objectives: The aim of this study was to compare the effectiveness of acceptance and commitment therapy (ACT), selective serotonin reuptake inhibitors (SSRIs) and combination of ACT and SSRIs in the treatment of adults with obsessive-compulsive disorder (OCD). Patients and Methods: Thirty-two outpatients meeting Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, Text Revision criteria for OCD were randomly assigned to one of the three treatment conditions: ACT, SSRIs and combined treatment. The Yale-Brown Obsessive-Compulsive Scale and Acceptance and Action Questionnaire were administered at pre-treatment and post-treatment. Twenty-seven patients completed the study. Data was analyzed using one-way analysis of variance (ANOVA) and one-way analysis of covariance (ANCOVA), clinically significant change (CSC) and complete remission status. Results: ANCOVA revealed that patients treated with ACT and combined treatment experienced a significantly greater improvement in obsessive-compulsive (OC) symptoms and experiential avoidance (EA) at post-treatment compared to those treated with SSRIs alone. However, there were no significant differences between ACT and combined treatment on OC symptoms and EA. CSC and complete remission status results showed that unlike SSRI, ACT and combined treatment led to more improvement in OC symptoms. Conclusions: ACT and combined treatment are more effective than SSRIs alone in treating OC symptoms and EA. However, it appears that adding SSRIs to ACT does not increase the effectiveness of ACT in the treatment of adults with OCD in the short-term. © 2015, Mazandaran University of Medical Sciences

Adaptive Energy Aware Cooperation Strategy in Heterogeneous Multi-domain Sensor Networks

AbstractIn some applications of sensor networks, multi-domain exists and cooperation among domains could lead to longer lifetime. In this paper, we consider heterogeneous multi-domain sensor networks. It means that different networks belong to different domains and sensors are deployed at the same physical location and their topology is heterogonous. Apparently, domains life time can be increased by means of cooperation in packet forwarding; however selfishness is inevitable from rational perspective. We investigate this problem to find out cooperation of authorities while their sensors are energy aware. When sensors are energy aware, spontaneous cooperation cannot take place. Therefore we presented the Adaptive Energy Aware strategy, a novel algorithm that is based on TIT-FOR-TAT, starts with generosity and ends up with conservative behaviour. Our simulation results showed that this algorithm could prolong its network lifetime in competition with other networks