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The maximum a posteriori probability rule for atom column detection from HAADF STEM images
摘要： Recently, the maximum a posteriori (MAP) probability rule has been proposed as an objective and quantitative method to detect atom columns and even single atoms from high-resolution high-angle annular dark-field (HAADF) scanning transmission electron microscopy (STEM) images. The method combines statistical parameter estimation and model-order selection using a Bayesian framework and has been shown to be especially useful for the analysis of the structure of beam-sensitive nanomaterials. In order to avoid beam damage, images of such materials are usually acquired using a limited incoming electron dose resulting in a low contrast-to-noise ratio (CNR) which makes visual inspection unreliable. This creates a need for an objective and quantitative approach. The present paper describes the methodology of the MAP probability rule, gives its step-by-step derivation and discusses its algorithmic implementation for atom column detection. In addition, simulation results are presented showing that the performance of the MAP probability rule to detect the correct number of atomic columns from HAADF STEM images is superior to that of other model-order selection criteria, including the Akaike Information Criterion (AIC) and the Bayesian Information Criterion (BIC). Moreover, the MAP probability rule is used as a tool to evaluate the relation between STEM image quality measures and atom detectability resulting in the introduction of the so-called integrated CNR (ICNR) as a new image quality measure that better correlates with atom detectability than conventional measures such as signal-to-noise ratio (SNR) and CNR.
关键词： Atom detection,Scanning transmission electron microscopy (STEM),Atom detectability,Model selection
更新于2025-09-19 17:15:36
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[IEEE 2018 11th Global Symposium on Millimeter Waves (GSMM) - Boulder, CO, USA (2018.5.22-2018.5.24)] 2018 11th Global Symposium on Millimeter Waves (GSMM) - High-Resolution Antenna Near-Field Imaging and Sub-THz Measurements with a Small Atomic Vapor-Cell Sensing Element
摘要： Atomic sensing and measurement of millimeter-wave (mmW) and THz electric fields using quantum-optical EIT spectroscopy of Rydberg states in atomic vapors has garnered significant interest in recent years towards the development of atomic electric-field standards and sensor technologies. Here we describe recent work employing small atomic vapor cell sensing elements for near-field imaging of the radiation pattern of a Ku-band horn antenna at 13.49 GHz. We image fields at a spatial resolution of λ/10 and measure over a 72 to 240 V/m field range using off-resonance AC-Stark shifts of a Rydberg resonance. The same atomic sensing element is used to measure sub-THz electric fields at 255 GHz, an increase in mmW-frequency by more than one order of magnitude. The sub-THz field is measured over a continuous ±100 MHz frequency band using a near-resonant mmW atomic transition.
关键词： atom,microwave,electric field,metrology,quantum sensing,millimeter-wave,THz,antenna,mmW,Rydberg,terahertz,Atomic sensors,antenna characterization
更新于2025-09-19 17:15:36
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Photoinduced atom transfer radical polymerization of methyl methacrylate with conducting polymer nanostructures as photocatalyst
摘要： Light-mediated control/living radical polymerization (CLRP) provides a convenient method to synthesize polymers with controlled molecular weight and narrow molecular weight distribution. However, high-energy wavelengths (such as UV light) and blue light are needed to initiate the polymerization, leading to unwanted side reactions. To overcome these defects, the use of long-wavelength light for light-mediated CLRP is highly desirable. In this work, photoinduced atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) was successfully carried out for the synthesis of polyMMA (PMMA) with predictable molecular weights (Mn,GPC) and narrow molecular weight distribution (Mw/Mn). This was achieved using one-dimensional nanopoly(diphenyl butadiyne) (nanoPDPB) as photocatalyst, which activated the dormant alkyl bromides initiator to reversibly produce propagating radicals at ambient temperature. Initiation and termination of polymerization were regulated by periods of light. The polymerization of MMA was accomplished by the radicals generated in the redox reaction of nanoPDPB with EBP. Both 1H nuclear magnetic resonance (1H NMR) spectroscopy and chain-end extension polymerization show highly preserved bromine chain-end functionality in the synthesized PMMA. nanoPDPB displays remarkable photophysical properties in the visible light region. The polymerization of MMA followed the first-order kinetics and the evolution of the Mn,GPC versus monomer conversion and Mw/Mn demonstrated the well-controlled polymerization process. The living character of heterogeneous photomediated ATRP with nanoPDPB as photocatalyst was successfully confirmed.
关键词： Poly(diphenyl butadiyne),Control/living radical polymerization,Living radical polymerization,Photocatalyst,Atom transfer radical polymerization
更新于2025-09-19 17:15:36
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Evolution of Statistical Properties of Hybrid System Starting from Binary Field States Constructed in Experiments
摘要： In quantum optics, researchers usually study evolution of states starting from traditional ones: coherent, squeezed, Fock, and their superpositions. In a recent work (Ferreira et al. Int. J. Mod. Phys. B, 1850222, 2018), we discussed an example of experiment involving 'atom'-field interaction allowing us to construct a list of field states inside a high-Q microwave cavity. The procedure employed a dispersive Hamiltonian ensuring both sub-systems to remain with only two Fock state components for all times of their evolution. The aim was to use this sequence of states having pre-selected properties as initial states in other investigations. Here, we use an updated platform and a variety of states at our disposal in the mentioned list to study the evolution of a hybrid system under the action of the Jaynes-Cummings Hamiltonian. Interesting results are obtained, e.g., when we examine how the 'atomic' population inversion and field statistics evolve in time from initial field states with different degrees of super- and sub-Poissonian effects. The experimental feasibility of the proposal was also discussed.
关键词： Jaynes-Cummings Hamiltonian,High-Q microwave cavity,Atom-field interaction
更新于2025-09-19 17:15:36
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Mean-Force Scattering Potential for Calculating Optical Properties of Dense Plasmas
摘要： We assess the relative importance of ionic structure on the opacity of dense plasmas by using the potential of mean force as a scattering potential within the Kubo-Greenwood formalism. We compare results from the potential of mean force, which includes realistic ionic structure, to results using an average atom potential, which includes only a crude treatment of ionic structure. Comparisons with less approximate but more expensive DFT-MD simulations for aluminum plasma reveal that the mean force generally improves agreement for DC conductivity. We also see improvement when applying the mean force to free-free transitions, whereas for bound-bound and bound-free transitions the mean force leads to poorer agreement on transition energies. Further, we assess the impact of accounting for correlations within the plasma at the temperature and density conditions relevant to iron opacity measurements at Sandia's Z machine facility [Bailey et al., Nature 517:56-59, 2015] and find that these correlations do not account for the discrepancy between the measurements and leading opacity calculations.
关键词： Warm Dense Matter,Radiative Properties,Ion Correlations,Average Atom
更新于2025-09-19 17:15:36
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Photoredox catalyzed generation of acetonyl radical in flow: theoretical investigation and synthetic applications
摘要： A Hydrogen Atom Transfer (HAT) step from acetone allowed the smooth generation of acetonyl radical, that was then exploited as synthon in the mild formation of C–C bonds under flow conditions. The process was promoted by aryl radicals photocatalytically generated via Single Electron Transfer (SET) reduction of arenediazonium salts. The mechanism has been investigated by a combined experimental and computational approach and further supported by deuterium labelling experiments.
关键词： Arenediazonium salts,Hydrogen Atom Transfer (HAT),Acetonyl radical,Photocatalysis,Aryl radicals
更新于2025-09-19 17:15:36
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Theory of two atoms in a chiral waveguide
摘要： A theory is presented that describes the atom and field dynamics for two atoms in a chiral waveguide. A source-field approach is used that enables one to identify the various physical processes contributing to these dynamics. Each atom is prepared in an arbitrary state at t = 0 and the field intensity and correlation functions are calculated, fully accounting for retardation. When the atoms are prepared in identical superposition states, the effects of constructive and destructive interference play a significant role on both the field intensity and second-order correlation function. It is also shown that the results can be taken over to provide a solution for the related problem of a single-photon pulse incident on an atom prepared in an arbitrary initial state.
关键词： chiral waveguide,second-order correlation function,source-field approach,atom-field dynamics,interference,retardation
更新于2025-09-19 17:13:59
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Influence of the polarization of a multielectron atom in a strong laser field on high-order harmonic generation
摘要： We study the ionization and high-order harmonic generation (HHG) in argon by short linearly polarized laser pulses. We compare the populations of atomic orbitals and HHG spectra in a wide range of laser-pulse parameters, taking into account the dynamics of all orbitals based on the time-dependent density-functional theory (TDDFT) and only the most active orbital within the single-active electron (SAE) approximation. At high intensities of laser pulses, the atom polarization leads to suppression in the bound-state depletion due to the screening of the external field. The significant increase in the HHG yield is observed for the TDDFT calculations in comparison with the SAE calculations. The contribution of different orbitals in the TDDFT calculations of HHG spectra is discussed.
关键词： ionization,high-order harmonic generation,atom polarization,argon,TDDFT,laser pulses,SAE approximation
更新于2025-09-19 17:13:59
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Specifications of Photovoltaic Pumping Systems in Agriculture || Photovoltaic Energy: Basic Principles
摘要： The sun is a star which provides nearly 95% of its energy to generate nearly all the energy available on the earth. In fact, the earth energy is a direct or indirect conversion form of the sun’s lights. For instance, the solar heat ensures the plants evaporation-transpiration by converting the sunlight energy into storable chemical form through the photosynthesis process, which allows the fauna and flora to be maintained in the earth. Moreover, the sunlight is the source of generating wind and wave energies, by causing temperature difference in the atmosphere. Additionally, sunlight generates the photothermal and photovoltaic energies, which are used to provide electrical and heat energies. Consequently, sun means life.
关键词： P-N junction,Silicon atom,Solar radiation,Photovoltaic energy,Solar cell efficiency
更新于2025-09-19 17:13:59
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Mechanisms of extrinsic alkali incorporation in CIGS solar cells on flexible polyimide elucidated by nanoscale and quantitative analyses
摘要： In this work, Cu(In,Ga)Se2 (CIGS) solar cells on polyimide (PI) substrates were fabricated using a low-temperature three-stage co-evaporation process. To enhance device performance, the CIGS films were extrinsically doped with alkali (Na and K) using an in-situ post deposition treatment (PDT). To account for mechanisms of extrinsic alkali incorporation in CIGS solar cells on flexible polyimide, the alkali dopant concentrations in the film bulk (intragrain and grain boundary) and the surface chemistries/band structures were quantitatively investigated with various advanced characterization methods. In addition, the effects of the PDT sequences on the resulting device performance were studied with a particular emphasis on the characteristics of CIGS surfaces. By controlling the alkali incorporation into the CIGS absorber films, flexible lightweight CIGS thin-film solar cells with an efficiency of approximately 19% were obtained.
关键词： Flexible,CIGS,Atom probe tomography,Solar cells,Polyimide
更新于2025-09-19 17:13:59