2,193 research outputs found
Avoiding Overconfidence in Predictions of Residential Energy Demand through Identification of the Persistence Forecast Effect
EPR identification of defects responsible for thermoluminescence in Cu-doped lithium tetraborate (Li2B4O7) crystals
Electron paramagnetic resonance (EPR) is used to identify the electron and hole traps responsible for thermoluminescence (TL) peaks occurring near 100 and 200 ◦C in copper-doped lithium tetraborate (Li2B4O7) crystals. As-grown crystals have Cu+ and Cu2+ ions substituting for lithium and have Cu+ ions at interstitial sites. All of the substitutional Cu2+ ions in the as-grown crystals have an adjacent lithium vacancy and give rise to a distinct EPR spectrum. Exposure to ionizing radiation at room temperature produces a second and different Cu2+ EPR spectrum when a hole is trapped by substitutional Cu+ ions that have no nearby defects. These two Cu2+ trapped-hole centers are referred to as Cu2+-VLi and Cu2+active, respectively. Also during the irradiation, two trapped-electron centers in the form of interstitial Cu0 atoms are produced when interstitial Cu+ ions trap electrons. They are observed with EPR and are labeled Cu0A and Cu0B. When an irradiated crystal is warmed from 25 to 150 ◦C, the Cu2+active centers have a partial decay step that correlates with the TL peak near 100 ◦C. The concentrations of Cu0A and Cu0B centers, however, increase as the crystal is heated through this range. As the crystal is futher warmed between 150 and 250 ◦C, the EPR signals from the Cu2+active hole centers and Cu0A and Cu0B electron centers decay simultaneously. This decay step correlates with the intense TL peak near 200 ◦C
Discrete solvent effects on the effective interaction between charged colloids
Using computer simulations of two charged colloidal spheres with their
counterions in a hard sphere solvent, we show that the granular nature of the
solvent significantly influences the effective colloidal interaction. For
divalent counterions, the total effective force can become attractive generated
by counterion hydration, while for monovalent counterions the forces are
repulsive and well-described by a solvent-induced colloidal charge
renormalization. Both effects are not contained in the traditional "primitive"
approaches but can be accounted for in a solvent-averaged primitive model.Comment: 4 pages, 3 figure
Structural Polymorphism of the Cytoskeleton: A Model of Linker-Assisted Filament Aggregation
The phase behavior of charged rods in the presence of inter-rod linkers is
studied theoretically as a model for the equilibrium behavior underlying the
organization of actin filaments by linker proteins in the cytoskeleton. The
presence of linkers in the solution modifies the effective inter-rod
interaction and can lead to inter-filament attraction. Depending on the
system's composition and physical properties such as linker binding energies,
filaments will either orient perpendicular or parallel to each other, leading
to network-like or bundled structures. We show that such a system can have one
of three generic phase diagrams, one dominated by bundles, another by networks,
and the third containing both bundle and network-like phases. The first two
diagrams can be found over a wide range of interaction energies, while the
third occurs only for a narrow range. These results provide theoretical
understanding of the classification of linker proteins as bundling proteins or
crosslinking proteins. In addition, they suggest possible mechanisms by which
the cell may control cytoskeletal morphology.Comment: 17 pages, 3 figure
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Light-Induced Currents at Domain Walls in Multiferroic BiFeO3.
Multiferroic BiFeO3 (BFO) films with spontaneously formed periodic stripe domains can generate above-gap open circuit voltages under visible light illumination; nevertheless the underlying mechanism behind this intriguing optoelectronic response has not been understood to date. Here, we make contact-free measurements of light-induced currents in epitaxial BFO films via detecting terahertz radiation emanated by these currents, enabling a direct probe of the intrinsic charge separation mechanisms along with quantitative measurements of the current amplitudes and their directions. In the periodic stripe samples, we find that the net photocurrent is dominated by the charge separation across the domain walls, whereas in the monodomain samples the photovoltaic response arises from a bulk shift current associated with the non-centrosymmetry of the crystal. The peak current amplitude driven by the charge separation at the domain walls is found to be 2 orders of magnitude higher than the bulk shift current response, indicating the prominent role of domain walls acting as nanoscale junctions to efficiently separate photogenerated charges in the stripe domain BFO films. These findings show that domain-wall-engineered BFO thin films offer exciting prospects for ferroelectric-based optoelectronics, as well as bias-free strong terahertz emitters
Estimated probabilities of positive, vs. negative, events show separable correlations with covid-19 preventive behaviours
Research has associated optimism with better health-protective behaviours, but few studies have measured optimism or pessimism directly, by asking participants to estimate probabilities of events. We used these probability estimates to examine how optimism and/or pessimism relate to protecting oneself from COVID-19. When COVID-19 first reached Turkey, we asked a snowball sample of 494 Istanbul adults how much they engaged in various COVID-protective behaviours. They also estimated the probabilities of their catching COVID-19, and of other positive and negative events happening to them. Estimated probability of general positive events (optimism) correlated positively with officially-recommended helpful behaviours (e.g. wearing masks), but not with less-helpful behaviours (e.g. sharing ‘alternative’ COVID-related information online). Estimated probabilities of general negative events (pessimism), or of catching COVID, did not correlate significantly with helpful COVID-related behaviours; but they did correlate with psychopathological symptoms, as did less-helpful COVID-related behaviours. This shows important nuances can be revealed by measuring optimism and pessimism, as separate variables, using probability estimates.WOS:000766608100006Scopus - Affiliation ID: 60105072PMID: 35228768Social Sciences Citation IndexQ2ArticleUluslararası işbirliği ile yapılan - EVETMarch2022YÖK - 2021-22Hazira
On the Properties of Two Pulses Propagating Simultaneously in Different Dispersion Regimes in a Nonlinear Planar Waveguide
Properties of two pulses propagating simultaneously in different dispersion
regimes, anomalous and normal, in a Kerr-type planar waveguide are studied in
the framework of the nonlinear Schroedinger equation. Catastrophic
self-focusing and spatio-temporal splitting of the pulses is investigated. For
the limiting case when the dispersive term of the pulse propagating in the
normal dispersion regime can be neglected an indication of a possibility of a
stable self-trapped propagation of both pulses is obtained.Comment: 18 pages (including 15 eps figures
Origin of magnetic interactions and their influence on the structural properties of Ni2MnGa and related compounds
In this work, we perform first principles DFT calculations to investigate the
interplay between magnetic and structural properties in Ni2MnGa. We demonstrate
that the relative stability of austenite (cubic) and non-modulated martensite
(tetragonal) phases depends critically on the magnetic interactions between Mn
atoms. While standard approximate DFT functionals stabilize the latter phase, a
more accurate treatment of electronic localization and magnetism, obtained with
DFT+U, suppresses the non-modulated tetragonal structure for the stoichiometric
compound, in better agreement with the experiments. We show that the Anderson
impurity model, with Mn atoms treated as magnetic impurities, can explain this
observation and that the fine balance between super-exchange RKKY type
interactions mediated by Ni d and Ga p orbitals determines the equilibrium
structure of the crystal. The Anderson model is also demonstrated to capture
the effect of the number of valence electrons per unit cell on the structural
properties, often used as an empirical parameter to tune the behavior of
Ni2MnGa based alloys. Finally, we show that off-stoichiometric compositions
with excess Mn promote transitions to a non-modulated tetragonal structure, in
agreement with experiments.Comment: 16 pages, 25 figure
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