Excitation Strength Research Articles

Rydberg Series Excitation of a Single Trapped ^{40}Ca^{+} Ion for Precision Measurements and Principal Quantum Number Scalings.

A complete set of spectroscopic data is indispensable when using Rydberg states of trapped ions for quantum information processing. We carried out Rydberg series spectroscopy for nS_{1/2} states with 38≤n≤65 and for nD_{5/2} states with 37≤n≤50 on a single trapped ^{40}Ca^{+} ion. We determined the ionization energy of 2 870 575.582(15)GHz, 60 times more accurately as compared to the accepted value and contradicting it by 7.5 standard deviations. We confirm quantum defect values of δ_{S_{1/2}}=1.802 995(5) and δ_{D_{5/2}}=0.626 888(9) for nS_{1/2} and nD_{5/2} states, respectively, which allow for unambiguous addressing of Rydberg levels of Ca^{+} ions. Our measurements confirm Rydberg ion scaling properties, e.g., for blackbody induced ionization, linewidths and excitation strengths.

Revisiting the oscillator strengths and cross sections of atomic neon by fast electron scattering

The generalized oscillator strengths of the valence-shell excitations from the ground state to the 2p5(3s, 3s′, 3p, 3p′, 4s, 4s′) states of atomic neon have been determined by means of fast electron scattering, with an incident electron energy of 1500 eV and an energy resolution of about 80 meV. The adopted relative flow technique improved accuracy of the experimental measurements prominently. The validity condition of the first Born approximation is clarified by comparing the present measured data with previous experimental and theoretical results. We found that the first Born approximation is not applicable for the monopolar transition in the whole momentum transfer region even at the incident electron energy of 1500 eV. However, the high-order Born terms are found dominating only at the minimum for the dipolar transitions. The good agreement of the present extrapolated optical oscillator strengths with previous available data confirms the reliability of the measurement. With the cross-checked generalized oscillator strengths, the state-resolved integral cross sections in a wide collision energy range have been obtained by adopting the BE-scaling method. The analysis of the feasibility of the BE-scaling method demonstrates that the scaling law applies for the typical dipole-allowed transitions while it would overestimate the cross sections for the dipolar transitions with significant dipole-forbidden components. Present data compilation constitutes a benchmark for developing and testing the theoretical methods or computational codes.

Mass design of nonlinear energy sinks

Nonlinear energy sink (NES) is attracting more attention because of its promising in the control of engineering structure vibration. This paper thoroughly reviews the selection of NES mass ratios in existing studies and finds the big difference. So there is still a lack of a unified and profound understanding of the mass design of the NES. To achieve decent vibration mitigation and reduce costs, the mass design of the NES is essential. This paper pioneers the optimal mass design of NESs. The non-dominated sorting differential evolution algorithm and parameter sensitivity analysis are adopted. The relations between the optimal mass and the vibration mitigation effects are discussed in different damping and harmonic excitation strength. The results show that different from the monostable NES, the bistable NES with a small mass ratio (no more than 0.7%) and small damping can reduce 30% of the resonance peak of the primary system in most situations. However, both these two NESs with large damping need larger mass ratios to achieve decent vibration mitigation. Smaller damping of the primary system will contribute to wider effective ranges of the mass ratio of the two NESs, while larger excitation will contribute to those of the monostable NES. To ensure the vibration mitigation effects in small mass ratio, the monostable and bistable NESs with small damping need large and small cubic stiffness, respectively. Besides, the bistable NES with small damping prefers small negative linear stiffness. In summary, this paper presents a detailed study of the mass design of the nonlinear energy sink. It will help researchers and engineers find the suitable mass and design NES in the vibration reduction of engineering structures.

On the steerability of phased array EMATs: The dipole element

Shear wave phased array EMATs have a range of properties that make them a desirable solution compared to their piezoelectric counterparts: They do not require direct contact with the specimen and they can operate at elevated temperatures. Shear wave phased array EMATs do not need a Perspex wedge or couplant, making them easy to deploy across industrial applications even at elevated temperatures. Nonetheless, they are not commonly used because of concerns over the strength of signal excitation and lack of knowledge about potential changes in the emitted wavefields as a result of changes in the magnetic properties of the inspected material. In this work, a shear wave phased array EMAT designed to induce shear waves into paramagnetic, diamagnetic, ferromagnetic and ferromagnetic and magnetostrictive metals without compromising its angle coverage or steerability is proposed. The phased array EMAT was designed based on a dipole element wave generation source. The proposed dipole element source is formed by the interaction of the bias magnetic field of the PA EMAT and the electromagnetic field induced by the race-track coils of the PA EMAT. For each race-track coil this results in a combined source that consists of two parallel and slightly separated shear line sources of opposite polarity. A detailed study of the wave generation based on the surface loads induced by the dipole element is presented. The surface loads of the three excitation mechanisms involved in the EMAT transduction -Lorentz force, magnetisation force and magnetostriction force-were estimated in a 2D finite element model. The waves generated by the induced surface loads were estimated in a second 2D finite element model. A shear wave steerability analysis of the phased array EMAT on different metallic materials based on the 2D finite element results is presented in combination with an experimental evaluation on Aluminium 6082 (diamagnetic), mild steel EN1A (ferromagnetic), stainless steel 316 (paramagnetic), stainless steel 304 (paramagnetic) and nickel 201 (ferromagnetic and magnetostrictive). The experimental results showed good agreement with the simulation study. The simulation and experimental results concluded that the angle coverage of the phased array EMAT is almost insensitive to the inspected metallic material.

Analysis and classification of speech sounds of children with autism spectrum disorder using acoustic features

Children with autism spectrum disorder (ASD) produce speech sounds different from that of Normal or non-ASD children. Hence, analyzing acoustic features can help characterizing the ASD speech signals. In this study, the distinguishing characteristics of speech production are examined for ASD affected children, with comparison to Normal children’s speech. Acoustic features are analyzed first and then classification of ASD vs Normal speech is attempted using different machine learning techniques. Two speech sound databases are recorded for this study: the speech database of children with ASD and the speech database of Normal children. English speech utterances are recorded for children of Indian regional (Tamil and Telugu) nativity. The changes due to autism effect are examined in context of 5 English vowel sounds (/a/, /e/, /i/, /o/, and /u/). Changes in the speech production characteristics of children are explored using three sets of features. Firstly, changes in the excitation source features are examined using strength of excitation (SoE) and instantaneous fundamental frequency (F0). Secondly, changes in the vocal tract (VT) filter features are examined using dominant frequencies (FD1, FD2) and formant frequencies (F1 to F5). Thirdly, changes in the source-filter combined features are examined using signal energy (E), zero-crossing rate (ZCR), linear prediction cepstrum coefficients (LPCC), and Mel-frequency cepstral coefficients (MFCC). Then, various combinations of the acoustic features are classified utilizing machine learning methods such as probabilistic neural network (PNN), multilayer perceptron (MLP), support vector machine (SVM), and K-nearest neighbors (KNN). Analyses of acoustic features shows significant differences between the speech of children with ASD and the Normal children. Results up to 98.17% accuracy are obtained for classification between acoustic features of the speech sounds of children with ASD and the Normal children. The observations and this study results may be useful as acoustic biomarkers to identify autism and its progression/cure among children. This study may also be valuable towards developing a system for ASD diagnosis from children’s speech sounds, in the future.

Structure of high-lying levels populated in the 96Y →96Zr β decay

The nature of the high-lying final levels of the 96Ygsβ decay, one of the three most important contributors to the high-energy reactor antineutrino spectrum, has been investigated in high-resolution γ-ray spectroscopy following the β decay as well as in a campaign of inelastic photon scattering experiments. The comprehensive approach establishes 1− levels associated with the Pygmy Dipole Resonance as high-lying final levels in the β decay. Branching ratios extracted from β decay complement photon scattering and allow the absolute E1 excitation strength to be determined for levels populated in both reactions. The combined data represents a comprehensive approach to the wavefunction of the 1− levels below the Qβ value, which are investigated in the Quasiparticle Phonon Model. The calculations reveal that the components populated in β decay contribute only with small amplitudes to the complex wavefunction of these 1− levels. A comparison of the β decay results to data from total absorption γ-ray spectroscopy demonstrates a good agreement between both measurements.

Cell assembly formation and structure in a piriform cortex model.

The piriform cortex is rich in recurrent excitatory synaptic connections between pyramidal neurons. We asked how such connections could shape cortical responses to olfactory lateral olfactory tract (LOT) inputs. For this, we constructed a computational network model of anterior piriform cortex with 2000 multicompartment, multiconductance neurons (500 semilunar, 1000 layer 2 and 500 layer 3 pyramids; 200 superficial interneurons of two types; 500 deep interneurons of three types; 500 LOT afferents), incorporating published and unpublished data. With a given distribution of LOT firing patterns, and increasing the strength of recurrent excitation, a small number of firing patterns were observed in pyramidal cell networks: first, sparse firings; then temporally and spatially concentrated epochs of action potentials, wherein each neuron fires one or two spikes; then more synchronized events, associated with bursts of action potentials in some pyramidal neurons. We suggest that one function of anterior piriform cortex is to transform ongoing streams of input spikes into temporally focused spike patterns, called here "cell assemblies", that are salient for downstream projection areas.

Quenching of Isovector and Isoscalar Spin-M1 Excitation Strengths in N = Z Nuclei

Spin-M1 excitations of nuclei are important for describing neutrino reactions in supernovae or in neutrino detectors since they are allowed transitions mediated by neutral current neutrino interactions. The spin-M1 excitation strength distributions in self-conjugate N=Z nuclei were studied by proton inelastic scattering at forward angles for each of isovector and isoscalar excitations as reported in H. Matsubara et al., Phys. Rev. Lett. 115, 102501 (2015). The experiment was carried out at the Research Center for Nuclear Physics, Osaka University, employing a proton beam at 295 MeV and the high-resolution spectrometer Grand Raiden. The measured cross-section of each excited state was converted to the squared nuclear matrix elements of spin-M1 transitions by applying a unit cross-section method. Comparison with predictions by a shell-model has revealed that isoscalar spin-M1 strengths are not quenched from the prediction although isovector spin-M1 strengths are quenched similarly with Gamow-Teller strengths in charged-current reactions. This finding hints at an important origin of the quenching of the strength relevant to neutrino scattering, that is, the proton-neutron spin-spin correlation in the ground state of the target nucleus. In this manuscript we present the details of the unit cross-section method used in the data analysis and discuss the consistency between the quenching of the isoscalar magnetic moments and that of the isoscalar spin-M1 strengths.

Dynamic responses of a two-degree-of-freedom bistable electromagnetic energy harvester under filtered band-limited stochastic excitation

This study investigates the dynamic responses of a two-degree-of-freedom (2DOF) nonlinear bistable electromagnetic energy harvester under filtered band-limited stochastic excitation. The mathematical model of the 2DOF bistable energy harvester is derived, and its fidelity is experimentally verified. A comprehensive numerical investigation is conducted under filtered band-limited stochastic excitation (which is the white Gaussian noise filtered by a second-order filter). Comparative studies are performed between the 2DOF bistable energy harvester, the 2DOF equivalent linear energy harvester, and the single-degree-of-freedom (SDOF) linear energy harvester when subjected to white Gaussian noise and the exampled band-limited stochastic excitation. The comparative results show that the 2DOF bistable energy harvester can significantly improve the average power compared to the equivalent 2DOF and SDOF linear energy harvesters. The study reveals the insights of the excitation strength, bandwidth, and center frequency into the system performance. Finally, structural parametric studies demonstrate that the bigger frame mass and the larger spring stiffness coefficient will increase the oscillation velocity which has great significance for energy harvester.

Coherence of resonant light-matter interaction in the strong-coupling limit

We explore the role of quantum fluctuations in the strong-coupling limit of the dissipative Jaynes–Cummings oscillator driven on resonance. For weak excitation, we derive analytical expressions for the spectrum and the intensity correlation function for the photons scattered by the two-state atom coupled to the coherently driven cavity mode. We do so by writing down a birth–death process adding the higher orders in the excitation strength needed to go beyond the pure-state factorization, following the method introduced in Carmichael (2008). Our results for the first and second-order correlation functions are complemented by the numerical investigation of the waiting-time distribution for the photon emissions directed sideways, and the comparison with ordinary resonance fluorescence. To close out our discussion, we increase the driving field amplitude and approach the critical point organizing a second-order dissipative quantum phase transition by depicting the excitation pathways in the intracavity field distribution for a finite system size.

Photoinduced phase transition and associated timescales in the excitonic insulator Ta2NiSe5

We investigate the non-equilibrium electronic structure and characteristic time scales in a candidate excitonic insulator, Ta$_2$NiSe$_5$, using time- and angle-resolved photoemission spectroscopy with a temporal resolution of 50 fs. Following a strong photoexcitation, the band gap closes transiently within 100 fs, i.e., on a time scale faster than the typical lattice vibrational period. Furthermore, we find that the characteristic time associated with the rise of the photoemission intensity above the Fermi energy decreases with increasing excitation strength, while the relaxation time of the electron population towards equilibrium shows an opposite behaviour. We argue that these experimental observations can be consistently explained by an excitonic origin of the band gap in the material. The excitonic picture is supported by microscopic calculations based on the non-equilibrium Green's function formalism for an interacting two-band system. We interpret the speedup of the rise time with fluence in terms of an enhanced scattering probability between photo-excited electrons and excitons, leading to an initially faster decay of the order parameter. We show that the inclusion of electron-phonon coupling at a semi-classical level changes only the quantitative aspects of the proposed dynamics, while the qualitative features remain the same. The experimental observations and microscopic calculations allow us to develop a simple and intuitive phenomenological model that captures the main dynamics after photoexcitation in Ta$_2$NiSe$_5$.

High-frequency vibrational control of principal parametric resonance of a nonlinear cantilever beam: Theory and experiment

The effects of high-frequency parametric excitation on the principal parametric resonance of a nonlinear beam are studied both theoretically and experimentally. Only the first mode of vibration under simultaneous slow-fast parametric excitation is considered for investigation. The method of direct partition of motion yields slow dynamics of the system which is further analyzed by multiple time scale method to obtain the amplitude and phase response of the system. It is observed that the effective damping and stiffness of the system is significantly modified by the high frequency parametric excitation. The analysis reveals that the parametric resonance curve shifts towards the higher range of slow parametric excitation frequency due to high-frequency excitation. The peak resonant response decreases with the increasing value of the strength of the high frequency excitation and also beyond a critical value of the strength of the high-frequency excitation, the jump resonance is eliminated. Overall, it is found that the principal Parametric resonance can be effectively controlled and suppressed by high frequency excitation. Analytical results are validated by direct numerical simulations and experiments. For some parameter values, vibrational resonance is also observed in theory and experiment. The parametric vibrational resonance of a cantilever beam is not previously observed experimentally and thus, it is a new finding of the present study. The vibrational resonance is believed to be utilized in amplifying the response of parametrically driven microcantilever beams found in many microsystems applications.

Functional brain network dynamics based on the Hindmarsh–Rose model

In order to reveal the dynamics of brain network, we proposed a new research method based on the Hindmarsh–Rose model. In the method, a neural network model was developed by constructing a functional brain network topology based on functional magnetic resonance imaging resting-state data and using Hindmarsh–Rose neurons as nodes in place of the brain regions belonging to the functional brain network. The dynamics of the functional brain network were investigated using the dynamics model. The simulation results showed that the dynamic behaviors of the brain regions in the functional brain network could be divided into three types: stable, chaotic, and periodical bursts. A state space was introduced to analyze the dynamic behavior of the brain regions in the network. We find that increasing excitation and mutual connection strength among brain regions enhanced network communication capabilities in the state space. Both the periodic and stable modes exhibited stronger communication capabilities than the chaotic mode. Despite individual differences in the dynamics of brain regions among subjects, brain regions in the periodic mode were highly consistent and corresponded to key regions of the default mode network in the resting state.

Oscillator strengths and integral cross-sections of the valence-shell excitations of CH3Cl studied by fast electron scattering

The generalized oscillator strengths (GOSs) of the valence-shell excitations of CH3Cl have been determined at an incident electron energy of 1500 eV and an energy resolution of about 70 meV. The momentum transfer dependence behaviors of the GOSs of the valence-shell excitations have been carefully analyzed, and the A band shows a strong dipole-forbidden characteristic. By extrapolating the GOSs to the limit of a zero squared momentum transfer, the optical oscillator strengths have been obtained, which provide an independent cross-check for the previous experimental and theoretical results. The BE-scaled integral cross sections (where B is the binding energy and E is the excitation energy) of the valence-shell excitations of CH3Cl have been derived systematically from the threshold to 5000 eV with the aid of a BE-scaling method. The results provide the fundamental spectroscopic data of CH3Cl and have important applications in photochemical modeling for atmospheric physics.

Nonlinear dynamics of a RLC series circuit modeled by a generalized Van der Pol oscillator

Abstract In this paper, nonlinear dynamics study of a RLC series circuit modeled by a generalized Van der Pol oscillator is investigated. After establishing a new general class of nonlinear ordinary differential equation, a forced Van der Pol oscillator subjected to an inertial nonlinearity is derived. According to the external excitation strength, harmonic, subharmonic and superharmonic oscillatory states are obtained using the multiple time scales method. Bifurcation diagrams displayed by the model for each system parameter are performed numerically through the fourth-order Runge–Kutta algorithm.

Resonant and random excitations on the proton beam in the Large Hadron Collider for active halo control with pulsed hollow electron lenses

We present the results of numerical simulations and experimental studies about the effects of resonant and random excitations on proton losses, emittances, and beam distributions in the Large Hadron Collider (LHC). In addition to shedding light on complex nonlinear effects, these studies are applied to the design of hollow electron lenses for active beam halo control. In the High-Luminosity Large Hadron Collider (HL-LHC), a considerable amount of energy will be stored in the beam tails. To control and clean the beam halo, the installation of two hollow electron lenses, one per beam, is being considered. In standard electron-lens operation, a proton bunch sees the same electron current at every revolution. Pulsed electron beam operation (i.e., different currents for different turns) is also considered, because it can widen the range of achievable halo removal rates. For an axially symmetric electron beam, only protons in the halo are excited. If a residual field is present at the location of the beam core, these particles are exposed to time-dependent transverse kicks and to noise. We discuss the numerical simulations and the experiments conducted in 2016 and 2017 at injection energy in the LHC. The excitation patterns were generated by the transverse feedback and damping system, which acted as a flexible source of dipole kicks. Proton beam losses, emittances, and transverse distributions were recorded as a function of excitation patterns and strengths. The resonant excitations induced rich dynamical effects and nontrivial changes of the beam distributions, which, to our knowledge, have not previously been observed and studied in this detail. We conclude with a discussion of the tolerable and achievable residual fields and proposals for further studies.

Chemically heterogeneous carbon dots enhanced cholesterol detection by MALDI TOF mass spectrometry

A binary system composed of carbon dots (CDs) and N-doped CDs (N-CDs) embedded in an organic matrix was used for the analysis of cholesterol by MALDI (matrix-assisted laser desorption and ionization time-of-flight) mass spectrometry, as a model for detection of small, biologically relevant molecules. The results showed that both CDs are sensitive to the cholesterol and can be used either alone or in a binary system with 2,5-dihydroxybenzoic acid (DHB) to enhance the detection process. It was found that both COOH and NH2 groups on CDs surface contributed to the enhancement in the cholesterol detection by MALDI mass spectrometry in the presence of inorganic cations. Nevertheless, in the presence of NaCl, N-CDs led to a better reproducibility of results. It was due to the coexistence of positive and negative charge on N-CDs surface that led to a homogeneous analyte/substrate distribution, which is an important detection parameter. The enhancing effect of carbon dots was linked to a negative Gibbs energy of the complex formation between CDs, Na+, cholesterol and DHB, and it was supported by theoretical calculations. Moreover, upon the addition of CDs/N-CDs, such features as a low ionization potential, vertical excitation, dipole moment and oscillator strength positively affected the cholesterol detection by MALDI in the presence of Na+.

Neuromorphic Implementation of a Continuous Attractor Neural Network With Various Synaptic Dynamics

A continuous attractor neural network (CANN) configured with various synaptic dynamics can implement many brain cognitive functions. Corresponding neuromorphic implementation can be beneficial to carry out these cognitive computations in real-time. Herein, we present a neuromorphic implementation of the CANN of spiking neurons on the field-programmable gate array (FPGA), in which the synaptic strength of local excitation and global inhibition can be configured to achieve winner-take-all (WTA) competition. In contrast to previously reported neuromorphic CANN, in addition to fast-linear synapses, recurrent connections can also be implemented with slow-nonlinear synapses. This endows the proposed CANN on the FPGA with the capability of performing neural computations that require slow and nonlinear temporal dynamics, such as decision making and working memory. Circuit simulations on the hardware reproduced gradually ramping neural activities observed in decision-making experiments and multiple sustained activities observed during the delay in working memory experiments, especially the fade-out and merging of activity bumps in the latter task. Theoretical analysis illuminated the underlying mechanisms of decision making and working memory on the FPGA. The unstable two-bump steady state of the CANN is responsible for the two-alternative decision making, similar to the saddle-node structure in the reduced two-variable decision model. Meanwhile, the stable uniformly distributed N-bump steady states account for the multiple-item working memory, similar to the multistability in previous mean-field models. Furthermore, the asymmetrical N-bump unstable steady states exhibit attractor dynamics underlying the fade-out and merging of activity bumps. The consistency between simulations on the hardware and the theoretical analysis demonstrated that the neuromorphic CANN is endowed with attractor dynamics relating to slow and nonlinear neural computations and has the potential to implement sophisticated cognitive functions by configuring various synaptic dynamics. This implementation shows promise for integrating the cognitive platform due to its characteristics of various dynamics and flexible configurations.

The Study of the Low-Lying Valence-Shell Excitations of Hydrogen Sulfide by Fast Electron Impact.

The valence-shell excitations of hydrogen sulfide have been studied by fast electron impact at a collision energy of 1.5 keV and an energy resolution of about 70 meV. By analyzing the variations of intensity and shape of the feature in the range of 5.0-7.5 eV at different scattering angles, the excitation energy of 5.85 ± 0.01 eV and the line width of 0.80 ± 0.01 eV of the 3b21A2 state have been determined. The generalized oscillator strengths of the valence-shell excitations in the energy range of 5.0-9.2 eV of hydrogen sulfide have been determined from the measured spectra. The corresponding optical oscillator strengths have been obtained by extrapolating the generalized oscillator strengths to the limit of zero squared momentum transfer. The integral cross sections have also been systematically determined from the threshold to 5000 eV by means of the BE-scaling method. The presently obtained oscillator strengths and integral cross sections have significant applications in the studies of planetary atmospheres and interstellar gases.

Disorder-induced spin-liquid-like behavior in kagome-lattice compounds

Quantum spin liquids (QSLs) are an exotic state of matter that is subject to extensive research. However, the relationship between the ubiquitous disorder and the QSL behaviors is still unclear. Here, by performing comparative experimental studies on two kagom\'{e}-lattice QSL candidates, Tm$_3$Sb$_3$Zn$_2$O$_{14}$ and Tm$_3$Sb$_3$Mg$_2$O$_{14}$, which are isostructural to each other but with strong and weak structural disorder, respectively, we show unambiguously that the disorder can induce spin-liquid-like features. In particular, both compounds show dominant antiferromagnetic interactions with a Curie-Weiss temperature of -17.4 and -28.7 K for Tm$_3$Sb$_3$Zn$_2$O$_{14}$ and Tm$_3$Sb$_3$Mg$_2$O$_{14}$, respectively, but remain disordered down to about 0.05 K. Specific heat results suggest the presence of gapless magnetic excitations characterized by a residual linear term. Magnetic excitation spectra obtained by inelastic neutron scattering (INS) at low temperatures display broad continua. All these observations are consistent with those of a QSL. However, we find in Tm$_3$Sb$_3$Zn$_2$O$_{14}$ which has strong disorder resulting from the random mixing of the magnetic Tm$^{3+}$ and nonmagnetic Zn$^{2+}$, that the low-energy magnetic excitations observed in the specific heat and INS measurements are substantially enhanced, compared to those of Tm$_3$Sb$_3$Mg$_2$O$_{14}$ which has much less disorder. We believe that the effective spins of the Tm$^{3+}$ ions in the Zn$^{2+}$/Mg$^{2+}$ sites give rise to the low-energy magnetic excitations, and the amount of the random occupancy determines the excitation strength. These results provide direct evidence of the mimicry of a QSL caused by disorder.