Excitation Strength Research Articles

Modified HSE06 functional applied to anatase TiO2: influence of exchange fraction on the quasiparticle electronic structure and optical response

The influence of non-interacting Kohn–Sham Hamiltonian on the non-self consistent GW(G 0 W 0) quasiparticle gap and Bethe–Salpeter-equation (BSE) optical spectra of anatase TiO2 is systematically evaluated. G 0 W 0 and BSE calculations are carried out starting with HSE06 (Heyd–Scuseria–Ernzerhof) type functionals containing 20%, 25% and 30% exact Hartree–Fock exchange. The results are also compared against G 0 W 0 + BSE calculations starting from semi-local (PBE) functionals. Our results indicate that the G 0 W 0 and BSE calculations of anatase TiO2 depend critically on the mean-field starting point, wherein its dependence is mainly introduced through the dielectric screening evaluated at the intermediate G 0 W 0. We find that the band dispersion, density of states, and consequently the oscillator strengths of optical excitation and spatial localization of excitons are insensitive to the starting points while the quasiparticle gap, optical gap and exciton binding energies are strongly affected. G 0 W 0 quasiparticle gap of anatase TiO2 computed over hybrid functional starting points is typically overestimated compared to measured values. However, by varying the amount of exact exchange, the dielectric screening can be tuned, and thus the quasiparticle gap. Exciton binding energy is shown to increase in proportion to the increase of the amount of exact exchange. A simple extrapolation of the calculated data leads to the exact match with the recently measured value with 13% of the exact exchange. Systematic analysis of G 0 W 0 + BSE calculation starting from screened hybrid functionals provided in this study forms a reference for all such future calculations of pristine anatase TiO2 and its derivatives.

Theoretical Model and Experimental Research on Determining Aquifer Permeability Coefficients by Slug Test under the Influence of Positive Well-Skin Effect

In the process of slug test in the field, mud and debris may infiltrate into the aquifer during the formation of the test well, and a poorly permeable annulus area appears around the test well wall. This is called the positive well-skin effect, which can have a significant impact on the results of slug tests due to the characteristics of a slug test. Therefore, to carry out the research on the determination of aquifer permeability coefficients by slug test under the influence of positive well-skin effect, a mathematical model of a slug test considering the positive well-skin effect was constructed. The Laplace transform method and the AWG algorithm were used to solve for a series of standard curves, and specific steps were given for calculating aquifer permeability coefficients by slug test under the influence of positive well-skin effect. Meanwhile, an indoor test model with positive well-skin effect was constructed, then several sets of slug tests and pumping tests with different excitation strengths were carried out. Based on this study, the presence of positive well-skin layer had a great impact on the aquifer permeability coefficient determined from both the pumping test and Kipp model of slug test, resulting in smaller results. The HWS model overcomes the influence of positive well-skin effect. This will further improve the theory of slug test, increase the accuracy of slug test in determining the permeability coefficient, and promote the application scope of slug test. It is therefore possible to discern the well-skin factor and determine the aquifer permeability coefficient by fitting the slug test data to a standard curve.

A Novel Slug Heat Test Theoretical and Indoor Model Research for Determining Thermal Property Parameters of Aquifers and Rock-Soil Skeletons

As important parameters for characterizing heat transfer, thermal property parameters of aquifers and rock-soil skeletons have important research significance in the development and utilization of geothermal resources. The slug heat test is inspired by the slug test, and the heat is instantaneously excited in the test well so as to change the temperature of test section in the test well instantaneously. Based on the thermal radial convection-dispersion theory and the principle of heat conservation, the theoretical model of the slug heat test is established, and the model is solved by Laplace transform and inverse transform to obtain multiple sets of standard curves under different conditions. The slug heat tests were conducted in the indoor model, the slug heat test data under different hydrodynamic conditions were fitted with the standard curves and the thermal property parameters, including effective thermal conductivity, stagnant thermal conductivity, thermal mechanical dispersion coefficient, thermal dispersive degree, thermal diffusivity, heat capacity of aquifer, heat capacity and thermal conductivity of rock-soil skeletons, were accurately obtained. The test results are in good agreement with the empirical values. Meanwhile, the effective thermal conductivity of the aquifer also clearly increases with the increase of flow rate. The excitation temperature difference had little effect on the effective thermal conductivity of the aquifer. At the same time, numerical simulation methods are used to establish a numerical model consistent with the indoor test model, and the numerical model is assigned with the thermal property parameters obtained from the indoor slug heat test, and the measured values of temperature changes in the test well during the slug heat test under different hydrodynamic and excitation strength conditions are compared with the simulated values for verification. The research results show that the slug heat test has the characteristics of high applicability, simple operation and rapid testing, and can effectively determine the thermal properties parameters of aquifers and rock-soil skeletons.

High-Speed Inspection of Rails by Passive Ultrasonic Monitoring

Abstract This paper presents a high-speed noncontact rail inspection technique that has the potential of detecting internal rail defects at regular (revenue) train speeds. The technique utilizes an array of capacitive air-coupled ultrasonic transducers in continuous recording mode to extract a reconstructed transfer function for a rail segment in a passive manner. The passive approach utilizes the ambient excitation of the rail induced by the wheels of the test car and eliminates the need for a controlled source. A normalized cross-correlation operator with modified Welch's periodogram technique is used to extract the transfer function in a manner that is independent of the uncontrolled excitation source (rolling wheels). Discontinuities in the rail (e.g., joints, welds, and defects) alter the reconstructed transfer function which is statistically tracked using an outlier analysis for detection robustness and sensitivity. Field tests were carried out with a prototype at the Transportation Technology Center Inc. (TTCI) in Pueblo, CO at testing speeds of up to 80 mph. The performance of the system in detecting rail discontinuities was assessed via receiver operating characteristic curves for a range of varying operational parameters such as excitation strength, baseline distribution length, testing speed, and multiple runs.

Probability density analysis of nonlinear stochastic dynamics of horizontal axis wind turbine blades

Wind turbine blades with horizontal axis are frequently subjected to cyclic and random loads during operation, which may decrease blade stability and impair power generation efficiency. In this paper, the finite element method (FEM) is mainly used to investigate the nonlinear stochastic dynamics of turbine blades and assess blade operation stability. The harmonic excitation and Gaussian white noise are combined to represent the external stimulation of the Mathieu-Duffing equation describing blade vibration, the Fokker-Planck (FP) equation is formulated and numerically solved using the FEM and the Crank Nicholson method to obtain the transient joint probability density function (PDF) and marginal PDF. The findings show that the blade's PDF exhibits an unstable split phenomenon in one vibration cycle, meaning that the blade's motion may jump randomly and has some uncertainty, potentially affecting blade operating stability and power generation efficiency. Furthermore, the sensitivity of blade stability to excitation strength is examined. The form and position of the PDF vary when the intensity of the harmonic excitation or noise is strong, increasing the random jump probability of blade vibration and compounding the instability and uncertainty of blade motion. Under severe circumstances, the blades may lose stability or even damage, endangering the safety and efficacy of blade operation. The current study might be used to evaluate blade stability and the overall safety of turbines.

Generalized oscillator strength of the core-excited states of molecular nitrogen studied by nonresonant inelastic x-ray scattering

Fast electron impact was used to study the generalized oscillator strengths of the inner-shell excitations in atoms and molecules previously. In this work, a nonresonant inelastic x-ray scattering technique is extended to determine the generalized oscillator strengths of $(1{\ensuremath{\sigma}}_{g}\ensuremath{\rightarrow}1{\ensuremath{\pi}}_{g})+(1{\ensuremath{\sigma}}_{u}\ensuremath{\rightarrow}1{\ensuremath{\pi}}_{g})$ inner-shell excitations of molecular nitrogen in the squared momentum transfer range of 0.86 to 14.40 a.u. at a photon energy of about 10 keV and an energy resolution of about 1.3 eV. The present generalized oscillator strength strictly follows the first Born approximation and thus provides a rigorous test to the previously calculated results and the experimental ones measured by the electron energy loss spectroscopy. The presently extrapolated optical oscillator strength at zero momentum transfer is in accord with most experimental results and the theoretical data with the correlation effect considered carefully. This work indicates that the nonresonant inelastic x-ray scattering technique is a powerful tool to study the core excitation mechanism in atoms and molecules.

Ultrafast energy exchange between two single Rydberg atoms on a nanosecond timescale

Rydberg atoms, with their enormous electronic orbitals, exhibit dipole–dipole interactions reaching the gigahertz range at a distance of a micrometre, making them a prominent contender for realizing ultrafast quantum operations. However, such strong interactions between two single atoms have so far never been harnessed due to the stringent requirements on the fluctuation of the atom positions and the necessary excitation strength. Here we introduce novel techniques to explore this regime. First, we trap and cool atoms to the motional quantum ground state of holographic optical tweezers, which allows control of the inter-atomic distance down to 1.5 μm with a quantum-limited precision of 30 nm. We then use ultrashort laser pulses to excite a pair of these nearby atoms to a Rydberg state simultaneously, far beyond the Rydberg blockade regime, and perform Ramsey interferometry with attosecond precision. This allows us to induce and track an ultrafast interaction-driven energy exchange completed on nanosecond timescales—two orders of magnitude faster than in any other Rydberg experiments in the tweezers platform so far. This ultrafast coherent dynamics gives rise to a conditional phase, which is the key resource for a quantum gate, opening the path for quantum simulation and computation operating at the speed limit set by dipole–dipole interactions with this ultrafast Rydberg platform.

Magnetoplasmonic coupling in graphene nanodisk dimers: An extended coupled-dipole model for circularly polarized states

Plasmonic coupling is one of the most important effects in compact plasmonic systems, and it has been studied intensively. In contrast, magnetoplasmonic coupling (MPC) is rarely mentioned, even in graphene nanostructures supporting the strong magneto-optic effect. Here, we theoretically investigate MPC in graphene nanodisk dimers in the presence of either parallel (case I) or antiparallel (case II) magnetic fields. We find the hybridized modes always appear for two states with same chirality, while their excitations depend on incident polarization. Moreover, two antisymmetric modes are dark in case I, but all four modes are bright in case II. To provide better insight, an extended coupled-dipole model is presented, in which the fundamental circularly polarized magnetoplasmons are decomposed into two linear and orthogonal dipoles, with a $\ensuremath{\pi}/2$ phase difference, and then the coupling is described by two linear dipoles along the two orthogonal directions separately. The parameters for the magneto-optic effect and coupling strengths are independent and can be easily extracted from their individual simulations. The eigenvalues and wave functions obtained from the model can describe well the resonance frequency and excitation strength of each hybridized mode. We finally discuss MPC in touching graphene nanodisks, where the charge transfer plasmon is immune to the magneto-optic effect, and in case II, a circular resonance state will be replaced by a linear one with the incident electric field along the touching direction. In this paper, we provide a general framework for investigating mode coupling of two circular states and pave the way to magneto-optic and plasmonic applications.

Relating a Spiking Neural Network Model and the Diffusion Model of Decision-Making.

Many models of decision making assume accumulation of evidence to threshold as a core mechanism to predict response probabilities and response times. A spiking neural network model (Wang, 2002) instantiates these mechanisms at the level of biophysically-plausible pools of neurons with excitatory and inhibitory connections, and has numerous model parameters tuned by physiological measures. The diffusion model (Ratcliff, 1978) is a cognitive model that can be fitted to a range of behaviors and conditions. We investigated how parameters of the cognitive-level diffusion model relate to the parameters of a neural-level spiking model. In each simulated "experiment", we generated "data" from the spiking neural network by factorially combining a manipulation of choice difficulty (via the input to the spiking model) and a manipulation of one of the core parameters of the spiking model. We then fitted the diffusion model to these simulated data to observe how manipulation of each core spiking model parameter mapped on to fitted drift rate, response threshold, and non-decision time. Manipulations of parameters in the spiking model related to input sensitivity, threshold, and stimulus processing time mapped on to their conceptual analogues in the diffusion model, namely drift rate, threshold, and non-decision time. Manipulations of parameters in the spiking model with no direct analogue to the diffusion model, non-stimulus-specific background input, strength of recurrent excitation, and receptor conductances, mapped on to threshold in the diffusion model. We discuss implications of these results for interpretations of fits of the diffusion model to behavioral data.

Valence-shell electronic excitations of CF4 studied by fast electron scattering

Oscillator strengths and cross sections of the valence-shell excitations in CF4 are of crucial importance in modeling the etching plasma and monitoring the greenhouse effect. In this work, generalized oscillator strengths of the valence-shell excitations in CF4 were measured by using an angle-resolved electron energy loss spectrometer, operating at an incident electron energy of 1.5 keV and a high energy resolution of 80 meV. The experimental GOSs are analytically fitted with the well-known Lassettre formula, and, thus, the optical oscillator strengths are determined at the limit of squared momentum transfer K2=0. The analytical GOS also enables an integration over K2, determining the Born cross sections with respect to the incident electron energy from the excitation threshold to 5000 eV. The BE-scaled integral cross sections for dipole-allowed transitions are obtained by adopting the BE-scaling method. Oscillator strengths and cross sections of the valence-shell excitations in CF4 provide an independent cross-check to the previous experimental and theoretical works. Moreover, the cross-checked data supplement and benchmark the molecular database for use in plasma models.

Applying Random Forest classification to diagnose autism using acoustical voice-quality parameters during lexical tone production

Atypical voice quality has been reported among children with autism spectrum disorder (ASD). Yet, it is unclear which acoustic parameters played a crucial role in discriminating the voice of children with ASD from that of their typically developing (TD) peers, especially those who speak a tone language. The current study carried out a preliminary investigation of voice quality in Mandarin-speaking children with ASD using multidimensional acoustic parameters, in an effort to seek the most robust cues using the Random Forest classification. Twenty Mandarin-speaking children with ASD and twenty age-matched TD children participated in the lexical tone production using a picture-naming task. Acoustic parameters included in this study were time-domain parameters: fundamental frequency (F0), the range of F0, the strength of excitation; spectral parameters: H1*-H2*, H2*-H4*, H1*-A1*, H1*-A2*, H1*-A3*; and signal aperiodicity parameters: cepstral peak prominence, harmonic-to-noise ratio, subharmonic-to-harmonic ratio, jitter, and shimmer. Results showed that except for HNR and F0 range, group differences (ASD vs. TD) were found in the other 11 parameters. Additionally, a 78.5% accuracy rate was obtained for classification analysis between voice-quality features of children with and without ASD, with shimmer and jitter as robust parameters. These results indicated that Mandarin-speaking children with ASD tended to overexert and overstrained their voices. Especially for Tone 3 production, they notably exhibited a higher F0 with a less creaky voice, losing the typical voice-quality feature of T3. Although no voice disorders were detected among Mandarin-speaking children with ASD, voice quality has the potential and supplementary value for diagnosing ASD.

Research on wave suppression mechanism of porous baffle based on vortex dynamics

The exciting force generated by the violent sloshing of the fluid in the tank will damage the tank structure and even affect the attitude stability of a vehicle. Hence, this study constructs a numerical model and horizontal excitation experimental platform. Taking the porous baffle in the tank of a specific type of tanker as an example, the current study analyses the impact pressure response law at different frequencies. On the basis of vortex dynamics, this work explores the evolution mechanism of the vortex flow structure under different excitation amplitudes and frequencies. The exploration reveals the law of dimensionless vortex intensity and energy change. In addition, the relationship between vortex intensity and wall pressure is determined. Studies have shown that the non-linear violent sloshing causes the resonance frequency of the tank to deviate from the natural frequency. When the excitation amplitude intensifies, the range and strength of the vortex structure and the distance from the vortex core to the baffle increase. In such circumstance, the accumulation and dissipation of energy are more evident. In addition, when the excitation frequency is closer to the resonance frequency, the distance between the vortex core and the baffle widens. Moreover, the energy intensity around the baffle increases as the frequency increases. The time history of wall pressure P and vortex intensity Q shows a certain regularity, and the ratio of Pmax to Qmax decreases with the increase of the excitation frequency.

An efficient optical properties of Sn doped ZnO/CdS based solar light driven nanocomposites for enhanced photocatalytic degradation applications

Metal sulfide - semiconductor nanocomposites synthesized with well-defined tin metal, exhibited the wide bandgap, the absorptions are limited to the UV–vis region for reduction of Reactive Blue 160 (RB 160) under solar light irradiation. The prepared samples were characterized using optoelectronic techniques. Conveniently, a wider range of wavelengths and physical properties can be enabled by doping these metal oxide nanoparticles. Whereas the photoreduction of RB 160 is unambiguously associated within charge separation and transmission progression from the excited Sn doped ZnO/CdS. Furthermore, Photocatalytic degradation efficiency for the Sn doped ZnO/CdS composites still reliant on the excitation strength, indicating the several electrons and protons were precise as a result of charge separation and transmission in prepared catalyst. Sn doped ZnO/CdS composites shows 94% Photocatalytic degradation efficiency within 120 min under sunlight irradiation. This photocatalytic nanocomposites may find capable applications in solar cells to power stretchable and also in wearable electronics.

Quantum Mollow Quadruplet in Nonlinear Cavity QED.

We develop an exact analytical approach to the optical response of a two-level system coupled to a microcavity for arbitrary excitation strengths. The response is determined in terms of the complex amplitudes of transitions between the rungs of the Jaynes-Cummings ladder, explicitly isolating nonlinearities of different orders. Increasing the pulse area of the excitation field, we demonstrate the formation of a quantum Mollow quadruplet (QMQ), quantizing the semiclassical Mollow triplet into a coherent superposition of a large number of transitions between rungs of the ladder, with inner and outer doublets of the QMQ formed by densely lying inner and outer quantum transitions between the split rungs. Remarkably, a closed-form analytic approximation for the QMQ of any order of nonlinearity is found in the high-field low-damping limit.

TM polarization preferentially implemented in the next generation of high-intensity laser systems based on multilayer dielectric gratings

The laser-induced damage (LID) response of multilayer dielectric gratings (MDGs) to transverse magnetic (TM) and transverse electric polarization was investigated based on polarized-independent MDGs. It was found that TM-polarized MDGs have the superiority of a high LID threshold, low sensitivity to laser excitation strength, low response to damaged structure, and reduced LID growth speed and dynamics. These results provide a strong motive to preferentially develop and mount TM-polarized MDGs in the next generation of high-intensity picosecond-petawatt laser systems.

Border of the island of inversion: Unbound states in Ne29

The nucleus $^{29}$Ne is situated at the border of the island of inversion. Despite significant efforts, no bound low-lying intruder $f_{7/2}$-state, which would place $^{29}$Ne firmly inside the island of inversion, has yet been observed. Here, the first investigation of unbound states of $^{29}$Ne is reported. The states were populated in $^{30}\mathrm{Ne}(p,pn)$ and $^{30}\mathrm{Na}(p,2p)$ reactions at a beam energy of around $230$ MeV/nucleon, and analyzed in terms of their resonance properties, partial cross sections and momentum distributions. The momentum distributions are compared to calculations using the eikonal, direct reaction model, allowing $\ell$-assignments for the observed states. The lowest-lying resonance at an excitation energy of 1.48(4) MeV shows clear signs of a significant $\ell$=3-component, giving first evidence for $f_{7/2}$ single particle strength in $^{29}$Ne. The excitation energies and strengths of the observed states are compared to shell-model calculations using the sdpf-u-mix interaction

Substituent effects on the UV-visible spectrum and excited electronic states of dithiocarboxylates.

The absorption spectra of a series of dithiocarboxylates were investigated in the ultraviolet-visible region. Two questions that this study aimed to address were as follows: (1) What transitions give rise to the features in the electronic spectra? And (2) what are the long- and short-range substituent effects on the absorption spectra? A series of 11 dithiocarboxylates were prepared as organic soluble salts. Time-dependent density functional theory (TDDFT) was used to calculate excited state energies and oscillator strengths of electronic transitions. TDDFT at the CAM-B3LYP/def2-TZVPD level of theory predicts two low-energy n → π* transitions and two π → π* transitions at higher energy, consistent with the experimental spectra. This state ordering and density is in contrast to the better studied thiocarbonyls for which only two transitions within the singlet manifold appear in the UV-visible region. For derivatives of dithiobenzoate, the energy of the three lowest energy states are insensitive to changes to substituents para to the dithiocarboxylate group. In contrast, the energy of the highest ππ* state varies by 0.78eV. This work shows that the results of TDDFT calculations can be used to predict the electronic absorption spectra of dithiocarboxylates, providing a useful tool for designing dithiocarboxylate light absorbers.

Normalization, orthogonality, and completeness of quasinormal modes of open systems: the case of electromagnetism [Invited

The scattering of electromagnetic waves by resonant systems is determined by the excitation of the quasinormal modes (QNMs), i.e. the eigenmodes, of the system. This Review addresses three fundamental concepts in relation to the representation of the scattered field as a superposition of the excited QNMs: normalization, orthogonality, and completeness. Orthogonality and normalization enable a straightforward assessment of the QNM excitation strength for any incident wave. Completeness guarantees that the scattered field can be faithfully expanded into the complete QNM basis. These concepts are not trivial for non-conservative (non-Hermitian) systems and have driven many theoretical developments since initial studies in the 70's. Yet, they are not easy to grasp from the extensive and scattered literature, especially for newcomers in the field. After recalling fundamental results obtained in initial studies on the completeness of the QNM basis for simple resonant systems, we review recent achievements and the debate on the normalization, clarify under which circumstances the QNM basis is complete, and highlight the concept of QNM regularization with complex coordinate transforms.

Generalized Oscillator Strengths for the Valence Shell Excitations in Carbon Tetrachloride Studied by Fast Electron Impact.

A joint experimental and theoretical investigation of the valence shell excitations of carbon tetrachloride has been performed by fast electron scattering and time dependent density functional theory calculations. At a collision energy of 1.5 keV and an energy resolution of about 70 meV, the dipole-forbidden transition of a1σ* ← 2t1 has been clearly observed at large momentum transfers, and its excitation energy of 6.15 eV and line width of 0.72 eV have been determined. Two new features are also recognized at 9.97 and 10.26 eV. The generalized oscillator strengths of the excited states at 5-11.3 eV have been determined from the measured spectra. The calculated generalized oscillator strength of the a1σ* ← 2t1 transition with the vibronic effect shows better agreement with the experiment, and the vibronic effect also accounts for its nonzero intensity at zero squared momentum transfer. The optical oscillator strengths of the valence shell excitations have also been obtained by extrapolating the generalized oscillator strengths to the limit of zero squared momentum transfer. The integral cross sections have been systematically determined from the threshold to 5000 eV by means of the BE-scaling method. The present oscillator strengths and cross sections provide the fundamental data of carbon tetrachloride and have important applications in photochemical modeling for atmospheric physics.

Single-Particle and Collective Structures in Neutron-Rich Sr Isotopes

Neutron-rich Sr nuclei around N=60 exhibit a sudden shape transition from a spherical ground state to strongly prolate-deformed. Recently, much new insight into the structure of Sr isotopes in this region has been gained through experimental studies of the excited levels, transition strengths, and spectroscopic factors. In this work, a “classic” shell model description of strontium isotopes from N=50 to N=58 is provided, using a natural valence space outside the 78Ni core. Both even–even and even–odd isotopes are addressed. In particular, spectroscopic factors are computed to shed more light on the structure of low-energy excitations and their evolution along the Sr chain. The origin of deformation at N=60 is mentioned in the context of the present and previous shell model and Monte Carlo shell model calculations.