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A facile NMR method is reported for analysis of ammonia from the electrochemical reduction of nitrogen, which compares a calibrated colorimetric method, a calibrated 1H NMR method and two 1H NMR direct measurements using external reference materials. Unlike spectrophotometric methods, 1H NMR requires less bench time and does not require separation of ammonia from the electrolyte. A novel approach to the problem of radiation damping in NMR measurements considered the specific role of hardware tuning. Radiation damping is suppressed improving signal‐to‐noise ratio and detection limit (1.5 µg L−1). The method is demonstrated to be effective for the analysis of ammonia from direct electrochemical nitrogen reduction in KOH, and from lithium‐mediated nitrogen reduction in a non‐aqueous solution. An uncertainty budget is prepared for the measurement of ammonia. [ABSTRACT FROM AUTHOR]

Natural modes characterized by amplification diagrams with extremely narrow peaks are frequently observed in harbor oscillations, referred to as extreme modes. This study presents a detailed numerical investigation into extreme modes. A new definition of extreme modes is established based on the modal structure instead of solely relying on the frequency–response diagram. Extreme modes arise when they primarily oscillate between the harbor walls, and one or more nodal lines intersect the harbor entrance. Subsequently, the variations exhibited by the extreme mode in response to varying geometry and wave parameters are explored, with specific consideration given to the influences of wave direction, partial reflection, and topography. The creation of an extra entrance in the oscillatory direction of the extreme mode may cause it to disappear. Moreover, the extreme mode can be significantly mitigated by slightly reducing the wave reflection between harbor walls. Changing the entrance position can adjust the modal structure and prevent nodal lines from crossing the entrance, thereby averting excessively high amplification factors. Under symmetrical conditions, extreme modes may not be activated, but slight asymmetries in wave direction, topography, or harbor layout can trigger them. The extreme modes exhibit heightened sensitivity to variations in entrance width and length compared to ordinary modes. A reduction in entrance width or an extension of the entrance length can notably intensify the extreme mode. [ABSTRACT FROM AUTHOR]

Purpose: In any MR experiment, the bulk magnetization acts on itself, caused by the induced current in the RF receiver circuit that generates an oscillating damping field. This effect, known as "radiation damping" (RD), is usually weak and, therefore, unconsidered in MRI, but can affect quantitative studies performed with dedicated coils that provide a high SNR. The current work examined RD in a setup for investigations of small tissue specimens including a quantitative characterization of the spin‐coil system. Theory and Methods: A custom‐made Helmholtz coil (radius and spacing 16 mm) was interfaced to a transmit‐receive (Tx/Rx) switch with integrated passive feedback for modulation or suppression of RD similar to preamplifier decoupling. Pulse sequences included pulse‐width arrays to demonstrate the absence/ presence of RD and difference techniques employing gradient pulses or composite RF pulses to quantify RD effects during free precession and transmission, respectively. Experiments were performed at 3T in small samples of MnCl2 solution. Results: Significant RD effects may impact RF pulse application and evolution periods. Effective damping time constants were comparable to typical T2* times or echo spacings in multi‐echo sequences. Measurements of the phase relation showed that deviations from the commonly assumed 90° angle between the damping field and the transverse magnetization may occur. Conclusion: Radiation damping may affect the accuracy of quantitative MR measurements performed with dedicated RF coils. Efficient mitigation can be achieved hardware‐based or by appropriate consideration in the pulse sequence. [ABSTRACT FROM AUTHOR]

Understanding the physical mechanisms which link fluid injection with triggered earthquakes is critical in minimizing hazard in subsurface fluid‐injection operations. Currently, injection‐induced changes in effective stress on faults are considered as the main criterion in triggering seismic fault slip. However, rate of change in effective stress, together with inertial effects, are also be implicated in this criterion. We present a modified critical stiffness criterion to investigate the relative likelihood of triggering earthquakes during injection for different injection rate schedules (constant‐vs‐cycled‐vs‐increasing). A stability analysis of fault stress is used to define a critical stiffness as a function of magnitudes and rate of change in effective stresses. The relative potential for triggering earthquakes due to fluid injection is investigated using a coupled fluid‐flow‐deformation model. Polarities of change in critical stiffness are employed as an index to define the tendency for a transition from aseismic to seismic reactivation. During constant rate injection and self‐equilibration stages, the absolute magnitude of effective stress controls the transition. Conversely, the rate of change in effective stress dominates this transition when injection suddenly starts or stops, and inertial effects suppress the transformation to seismic slip. Cycling injection rates into a given fault is the most stable, followed by constant injection, with linear injection the least stable for the same total volume injected. High permeability reservoirs and strike‐slip faulting regimes reduce the potential of inducing seismicity. This work provides both new insights into assessing the seismic risks associated with injection and guidance for mitigation. Plain Language Summary: During subsurface operations, fluid injections can lower fault strength and trigger slip on pre‐existing faults. This slip may be aseismic (no earthquake) or seismic (earthquake), being controlled by the fault critical stiffness ‐ determined from fault frictional characteristics and stress state. The stiffness change can be quantified in terms of the absolute fault stress magnitude and its rate of change, induced by the fluid injection. This change may be used to determine the tendency of reactivation as either aseismic or seismic. From our analysis, the rate of change in effective stress dominates the likelihood of triggering earthquakes as injection rates suddenly change. Suddenly stopping injection readily triggers earthquakes and inertial effects helpfully restrain the transition from aseismic and seismic slip‐on faults. Cycled injection and high permeability reservoirs are the most effective factors in minimizing seismicity. This study provides a new insight to understand and mitigate earthquake occurrence during subsurface fluid injection. Key Points: The rate of change in effective stress on a fault determines the likelihood of triggering seismicity when injection suddenly starts or stopsInertial effects restrain the transition between aseismic and seismic reactivation over the injection periodStress transfer can increase effective stress during constant injection and drive seismic slip [ABSTRACT FROM AUTHOR]

Seismic loads on a 3MW offshore wind turbine supported by a monopile are investigated by a one-dimensional Winkler model (1D model) with multi-soil springs and dashpots and are compared with those by a three-dimensional thin layer method (3D TLM). Firstly, the Winkler springs by Francis’s formula and dashpots by the simplified method are evaluated and compared with those obtained by the TLM. It is found that the predicted stiffness is close to that by the TLM, while the predicted damping is considerably smaller than that by the TLM. The seismic loads by the 1D models with the evaluated springs and dashpots are then compared with those by the 3D TLM. It is found that the seismic loads evaluated by the 1D model are close to those by the 3D TLM when the springs and dashpots are evaluated by the TLM, while the 1D model with the Winkler springs and dashpots obtained from Francis’s formula and the simplified method overestimates the seismic loads on the tower and monopile. [ABSTRACT FROM AUTHOR]

Radio amplification using stimulated emission of radiation (RASER) effects in the NMR can increase NMR signals over time due to a feedback loop between the sample magnetization and the probe coil coupled with radiation damping (RD). Previously, RD rates had been directly observed only for the 1H, 3He, 17O and 129Xe nuclei. We report that experimental direct measurements of an NMR RASER to determine RD time constants for the three heteronuclei (133Cs (I = 7/2), 7Li (I = 3/2) and 31P (I = 1/2)) in a highly concentrated solution from the NMR RASER emissions using a conventional NMR probe. Under conditions where the RD rate exceeds the transverse relaxation rate (i.e., the NMR RASER condition is fulfilled), we recorded both the transverse NMR RASER response to imperfect inversion and the recovery of longitudinal magnetization. The data were directly evaluated based on the well-known Bloom model as estimated RD rate constants of 8.0, 1.8 and 25 Hz for 133Cs, 7Li and 31P, respectively. The proposed method can be applied to observe RD rate constants for the other nuclei as well. [ABSTRACT FROM AUTHOR]

In this article, we study the asymptotic behavior of classical solutions to three‐dimensional Vlasov–Poisson system with radiation damping arising in plasma physics. For smooth solutions with compact support in phase space, the growth estimate of the largest velocity of plasma particles is improved to O((t+1)2/15ln8/15(t+2))$$ O\left({\left(t+1\right)}^{2/15}{\ln}^{8/15}\left(t+2\right)\right) $$. As a consequence, some better estimates of the charge density and electrostatic field are obtained. [ABSTRACT FROM AUTHOR]

Despite its critical role in the study of earthquake processes, numerical simulation of the entire stages of fault rupture remains a formidable task. The main challenges in simulating a fault rupture process include the complex evolution of fault geometry, frictional contact, and off‐fault damage over a wide range of spatial and temporal scales. Here, we develop a phase‐field model for quasi‐dynamic fault nucleation, growth, and propagation, which features two standout advantages: (i) it does not require any sophisticated algorithms to represent fault geometry and its evolution; and (ii) it allows for modeling fault nucleation, propagation, and off‐fault damage processes with a single formulation. Built on a recently developed phase‐field framework for shear fractures with frictional contact, the proposed formulation incorporates rate‐ and state‐dependent friction, radiation damping, and their impacts on fault mechanics and off‐fault damage. We show that the numerical results of the phase‐field model are consistent with those obtained from well‐verified approaches that model the fault as a surface of discontinuity, without suffering from the mesh convergence issue in the existing continuous approaches to fault rupture (e.g., the stress glut method). Further, through numerical examples of fault propagation in various settings, we demonstrate that the phase‐field approach may open new opportunities for investigating complex earthquake processes that have remained overly challenging for the existing numerical methods. [ABSTRACT FROM AUTHOR]

Radio amplification using stimulated emission of radiation (RASER) effects in the NMR can increase NMR signals over time due to a feedback loop between the sample magnetization and the probe coil coupled with radiation damping (RD). Previously, RD rates had been directly observed only for the 1H, 3He, 17O and 129Xe nuclei. We report that experimental direct measurements of an NMR RASER to determine RD time constants for the three heteronuclei (133Cs (I = 7/2), 7Li (I = 3/2) and 31P (I = 1/2)) in a highly concentrated solution from the NMR RASER emissions using a conventional NMR probe. Under conditions where the RD rate exceeds the transverse relaxation rate (i.e., the NMR RASER condition is fulfilled), we recorded both the transverse NMR RASER response to imperfect inversion and the recovery of longitudinal magnetization. The data were directly evaluated based on the well-known Bloom model as estimated RD rate constants of 8.0, 1.8 and 25 Hz for 133Cs, 7Li and 31P, respectively. The proposed method can be applied to observe RD rate constants for the other nuclei as well.

Silicon Nitride (Si 3 N 4) possesses large refractive index and transparent behaviour in a broad spectral range from ultraviolet to infrared. These properties of Si 3 N 4 facilitate an efficient light-matter interaction leading to enhanced light confinement. In this work, we have investigated Si 3 N 4 -based plasmonic sensor for pathogenic colorectal tissues detection at a wavelength of 1000 nm. The sensor structure consists of fused silica prism and Ag–Si 3 N 4 heterojunction. The figure-of-merit (FOM) of the sensor is optimized by judiciously coordinating the thickness of Ag layer (d M) and Si 3 N 4 layer (d A) under optimum radiation damping (ORD). An optimized FOM as high as 6011 RIU−1 (at d M = 47.3 nm) has been achieved corresponding to d A = 8.6 nm under ORD. At ORD, the corresponding power loss ratio (PLR) is as high as 2.773, and the normalized electric field enhancement factor (FEF) is about 1.06. The magnitude of combined performance factor (CPF), which is the product of FOM, PLR and FEF, of the proposed sensor is as large as 17668.61 RIU−1. The proposed application of Si 3 N 4 in plasmonic sensor in combination with ORD condition leads to substantially enhanced sensing performance and has been explored for the first time to the best of our knowledge. • Silicon Nitride (Si 3 N 4) possesses large refractive index and transparent behaviour in a broad spectral range from ultraviolet to infrared. • We have investigated Si 3 N 4 -based plasmonic sensor for pathogenic colorectal tissues detection at a wavelength of 1000 nm. • The figure-of-merit (FOM) of the sensor is optimized by judiciously coordinating the thickness of Ag \ (d M) and Si 3 N 4 (d A) under optimum radiation damping (ORD). • An optimized FOM as high as 6011 RIU−1 (at d M = 47.3 nm) has been achieved corresponding to d A = 8.6 nm under ORD. • The magnitude of combined performance factor (CPF) is as large as 17668.61 RIU−1. [ABSTRACT FROM AUTHOR]

• Integration of Explainable Artificial Intelligence (XAI) models on fiber optic SPR sensors. • Insights into the intricate patterns and features learned by the model are attained. • A comparative analysis of XAI models, namely SHAP and LIME is carried out. • LIME and SHAP methods jointly find that metal layer thickness has considerably greater influence than wavelength on sensing performance. • This finding is consistent with the concept of radiation damping related to fiber optic SPR sensor. In recent years, there has been a significant surge in interest surrounding the utilization of machine learning techniques to optimize the performance of fiber optic sensors. This paper delves into the integration of machine learning methodologies, with a specific focus on Explainable Artificial Intelligence (XAI) models, within the domain of fiber optic surface plasmon resonance (SPR) sensors. We implement XAI techniques into a previously-trained Gaussian Process Regression (GPR) model to gain insights into the intricate patterns and features learned by the model, thereby providing valuable insights into its decision-making process. Furthermore, we present a comparative analysis of XAI models, namely SHAP and LIME , to elucidate the individual impact of light wavelength (λ) and metal layer thickness (d m) on the enhancement of sensor's figure of merit (FOM). The results obtained from both LIME and SHAP methods lead to a common finding that compared to λ, it is the value of d m that possesses a significantly greater influence on achieving maximum FOM. Furthermore, this finding is in complete agreement with the concept of radiation damping related to fiber optic SPR sensor structures. This study has the potential to contribute to the refinement of design and fabrication processes related to fiber optic SPR sensor for a wide variety of applications. [ABSTRACT FROM AUTHOR]

The site fundamental period plays a key role in the characterization of site conditions to construct design spectrum models. For layered soil profiles on bedrock, it is generally believed that radiation damping caused by energy leaking into the bedrock does not change the fundamental period. This study finds that radiation damping can significantly affect the fundamental period. The effect of radiation damping on the site fundamental period is systematically studied, and a simple method for the fundamental period of linear soil profiles considering radiation damping is proposed. The validity of the proposed method is demonstrated using many actual soil profiles. [ABSTRACT FROM AUTHOR]

A facile NMR method is reported for analysis of ammonia from the electrochemical reduction of nitrogen, which compares a calibrated colorimetric method, a calibrated 1 H NMR method and two 1 H NMR direct measurements using external reference materials. Unlike spectrophotometric methods, 1 H NMR requires less bench time and does not require separation of ammonia from the electrolyte. A novel approach to the problem of radiation damping in NMR measurements considered the specific role of hardware tuning. Radiation damping is suppressed improving signal-to-noise ratio and detection limit (1.5 µg L -1 ). The method is demonstrated to be effective for the analysis of ammonia from direct electrochemical nitrogen reduction in KOH, and from lithium-mediated nitrogen reduction in a non-aqueous solution. An uncertainty budget is prepared for the measurement of ammonia., (© 2024 The Authors. Small Methods published by Wiley‐VCH GmbH.)

In the present study, surface gravity wave scattering and radiation by a freely floating rectangular buoy placed near a partially reflecting seawall and in the presence of an array of caisson blocks are analyzed. Various hydrodynamic parameters related to the wave scattering and radiation, such as the added mass and radiation damping coefficients, correspond to sway, heave, and roll motions of the floating buoy, horizontal force, vertical force, and moment acting on the floating structure, and horizontal wave force acting on the partially reflecting seawall, are studied for a variety of wave and structural parameters. The study reveals that the resonating pattern in various hydrodynamic coefficients occurs for moderate values of the wavenumber. Furthermore, when the distance between the floater and the sidewall is an integral time of half wavelength, the resonating behavior in the sway, heave, and roll added masses, and associated damping coefficients appears, and the aforementioned hydrodynamic coefficients change rapidly around this zone. These resonance phenomena can be diminished significantly with appropriate positioning of the floater with respect to the sidewall and in the presence of partially reflecting seawall. [ABSTRACT FROM AUTHOR]

High-frequency surface acoustic waves(SAWs) in the gigahertz range can be generated using absorption from an ultrafast laser in a patterned metallic grating on a substrate. Reducing the attenuation at these frequencies can yield better sensors as well as enable them to better probe phonon and electron-phonon interactions near surfaces. It is not clear from existing experiments which mechanisms dominate damping at high frequencies. We calculate damping times of SAWs due to various mechanisms in the 1-100 GHz range to find that mechanical loading of the grating on the substrate dominates dissipation by radiating energy from the surface into the bulk. To overcome this and enable future measurements to probe intrinsic damping, we propose incorporating distributed acoustic Bragg reflectors in the experimental structure. Layers of alternating materials with contrasting acoustic impedances embedded a wavelength away from the surface serve to reflect energy back to the surface. Using numerical simulations, we show that a single Bragg reflector is sufficient to increase the energy density at the surface by more than five times. We quantify the resulting damping time to find that it is longer than the intrinsic damping time. The proposed structure can enable future measurements of intrinsic damping in SAWs at ~100 GHz. [ABSTRACT FROM AUTHOR]

We show to which extent the signal to noise ratio per unit time of a spin 1/2 particle can be maximized. We consider a cyclic repetition of experiments made of a measurement followed by a radio-frequency magnetic field excitation of the system, in the case of unbounded amplitude. In the periodic regime, the objective of the control problem is to design the initial state of the system and the pulse sequence which leads to the best signal to noise performance. We focus on two specific issues relevant in nuclear magnetic resonance, the crusher gradient and the radiation damping cases. Optimal control techniques are used to solve this non-standard control problem. We discuss the optimality of the Ernst angle solution, which is commonly applied in spectroscopic and medical imaging applications. In the radiation damping situation, we show that in some cases, the optimal solution differs from the Ernst one. [ABSTRACT FROM AUTHOR]

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Seismic modeling of massive structures requires special caution, as wave propagation effects significantly affect the responses. This becomes more crucial when the path-dependent behavior of the material is considered. The coexistence of these conditions renders numerical earthquake analysis of concrete dams challenging. Herein, a finite element model for a comprehensive nonlinear seismic simulation of concrete gravity dams, including realistic soil-structure interactions, is introduced. A semi-infinite medium is formulated based on the domain reduction method in conjunction with standard viscous boundaries. Accurate representation of radiation damping in a half-space medium and wave propagation effects in a massed foundation are verified using an analytical solution of vertically propagating shear waves in a viscoelastic half-space domain. A rigorous nonlinear finite element model requires a precise description of the material response. Hence, a microplane-based anisotropic damage-plastic model of concrete is formulated to reproduce irreversible deformations and tensorial degeneration of concrete in a coupled and rate-dependent manner. Finally, the Koyna concrete gravity dam is analyzed based on different assumptions of foundation, concrete response, and reservoir conditions. Comparison between responses obtained based on conventional assumptions with the results of the presented comprehensive model indicates the significance of considering radiation damping and employing a rigorous constitutive material model, which is pursued for the presented model. [ABSTRACT FROM AUTHOR]

• A novel scaled boundary transformation of the geometry is proposed. • An improved scaled boundary element method for layered half-space is developed. • The radiation damping at infinity is satisfied strictly. • The horizontal layered and discontinuous layered half-space are analyzed. In this paper, a modified scaled boundary finite element method is proposed to deal with the dynamic analysis of a discontinuous layered half-space. In order to describe the geometry of discontinuous layered half-space exactly, splicing lines, rather than a point, are chosen as the scaling center. Based on the modified scaled boundary transformation of the geometry, the Galerkin's weighted residual technique is applied to obtain the corresponding scaled boundary finite element equations in displacement. Then a modified version of dimensionless frequency is defined, and the governing first-order partial differential equations in dynamic stiffness with respect to the excitation frequency are obtained. The global stiffness is obtained by adding the dynamic stiffness of the interior domain calculated by a standard finite element method, and the dynamic stiffness of far field is calculated by the proposed method. The comparison of two existing solutions for a horizontal layered half-space confirms the accuracy and efficiency of the proposed approach. Finally, the dynamic response of a discontinuous layered half-space due to vertical uniform strip loadings is investigated. [ABSTRACT FROM AUTHOR]

We propose experiments on the collision of high intensity electromagnetic pulses with electron bunches and on the collision of multiple electromagnetic pulses for studying extreme field limits in the nonlinear interaction of electromagnetic waves. The effects of nonlinear QED will be revealed in these laser plasma experiments. © 2012 American Institute of Physics.

The scientific literature contains reports of external magnetic fields affecting the fundamental properties and structure of water, including a report of the rotational motion of water molecules being slowed due to increased hydrogen bonding resulting from magnetic treatment. To investigate such a change in molecular motion, 1H spin-lattice relaxation times of water were measured at increasing magnetic field strengths. Strong radiation damping was observed at each magnetic field strength when using inversion-recovery experiments. To measure the relaxation times in the presence of radiation damping, several experimental methods of saturation recovery to measure spin-lattice relaxation were applied to a 90% H2O sample to obtain results as a function of field strength for proton frequencies from 300 to 800 MHz.

A number of vertical array records during eight destructive earthquakes in Japan are utilized, after discussing criteria for desirable requirements of vertical arrays, to formulate seismic amplification between ground surface and outcrop base for seismic zonation. A correlation between peak spectrum amplification and Vs (S-wave velocity) ratio (base Vs/surface Vs) was found to clearly improve by using Vs in an equivalent surface layer wherein predominant frequency or first peak is exerted, though the currently used average Vs in top 30 m is also meaningful, correlating positively with the amplification. We also found that soil nonlinearity during strong earthquakes has only a marginal effect even in soft soil sites on the amplification between surface and outcrop base except for ultimate soil liquefaction failure, while strong nonlinearity clearly appears in the vertical array amplification between surface and downhole base. Its theoretical basis has been explained by a simple study on a two-layered system in terms of radiation damping and strain-dependent equivalent nonlinearity.

We study the dynamics of many charges interacting with the Maxwell field. The particles are modeled by means of nonnegative distribution functions f + and f - representing two species of charged matter with positive and negative charge, respectively. If their initial velocities are small compared to the speed of light, c , then in lowest order, the Newtonian or classical limit, their motion is governed by the Vlasov–Poisson system. We investigate higher-order corrections with an explicit control on the error terms. The Darwin order correction, order | v ¯ / c | 2 , has been proved previously. In this contribution, we obtain the dissipative corrections due to radiation damping, which are of order | v ¯ / c | 3 relative to the Newtonian limit. If all particles have the same charge-to-mass ratio, the dissipation would vanish at that order. [ABSTRACT FROM AUTHOR]

The dynamic nature of radiation damping is exploited in a fluoride fiber–based plasmonic sensor in terms of variable temperature (T) and Ag layer thickness (dm) at certain near-infrared wavelengths. The optimum point of radiation damping, which is stimulated by the presence of a graphene monolayer and its dynamic dispersive and thermo-optic properties as per Kubo formulation, causes extremely huge enhancement in sensor's performance (analyzed in terms of its figure of merit, i.e., FOM). The simulation indicates that at λ = 1550 nm, the optimum radiation damping is achieved at dm = 35 nm and T = 322.7 K leading to a peak FOM value of 27,086 RIU−1. At λ = 1310 nm, the peak FOM is 16,736.65 RIU−1 for dm = 35.4 nm and T = 315.6 K. The above peak FOM values are significantly greater than those presently available with plasmonic sensors. [ABSTRACT FROM AUTHOR]

The performance of multiple variants of fluoride fiber plasmonic sensor is simulated and analyzed under optimum radiation damping (ORD) in terms of coordinated tuning of Ag layer thickness ($\text{d}_{\mathbf {Ag}}$) and near infrared (NIR) wavelength ($\lambda $). The sensor variants are in terms of number of monolayers (N: 1 – 5) of graphene and MoS2. The dispersion relations of all constituent layers along with the transfer matrix method are utilized for sensor simulation. The sensor’s performance is evaluated in terms of figure of merit (FOM) that takes into account the shift and width of fiber power loss resonance curves originating under the plasmonic modulation. Further totality is added to performance evaluation by combining the FOM with signal scattering and power loss ratio factors. The simulation results and their comprehensive analysis indicate that a combination of $\lambda =925.3$ nm, $\text{d}_{\mathbf {Ag}} =48.4$ nm, and MoS2 monolayer can provide considerably enhanced performance in terms of maximum FOM, small light signal scattering (and analyte photodamage), and large power loss ratio (with respect to the reference resonance curve). The FOM achievable with this sensor is 4.5 times better than the previously reported chalcogenide fiber plasmonic sensor under its corresponding ORD. A deeper analysis of the proposed fluoride sensor predicts that even smaller signal scattering (and photodamage) along with nearly identical power loss ratio and FOM can be achieved with the sensor variant based on MoS2 bilayer. [ABSTRACT FROM AUTHOR]

The kinetic approach is applied to calculate oscillations of a surface plasmon linewidth in a spheroidal metal nanoparticle embedded in any dielectric media. The principal attention is focused on the case, when the free electron path is much greater than the particle size. The linewidth of the plasmon resonance as a function of the particle radius, shape, dielectric constant of the surrounding medium, and the light frequency is studied in detail. It is found that the resonance plasmon linewidth oscillates with increasing both the particle size and the dielectric constant of surrounding medium. The main attention is paid to the electron surface-scattering contribution to the plasmon decay. All calculations of the plasmon resonance linewidth are illustrated by the example of the Na nanoparticles with different radii. The results obtained in the kinetic approach are compared with the known ones from other models. The role of the radiative damping is discussed as well. [ABSTRACT FROM AUTHOR]

We consider the time-optimal control of an ensemble of uncoupled spin 1/2 particles in the presence of relaxation and radiation damping effects, whose dynamics is governed by nonlinear equations generalizing the standard linear Bloch equations. For a single spin, the optimal control strategy can be fully characterized analytically. However, in order to take into account the inhomogeneity of the static magnetic field, an ensemble of isochromats at different frequencies must be considered. For this case, numerically optimized pulse sequences are computed and the dynamics under the corresponding optimal field is experimentally demonstrated using nuclear magnetic resonance techniques. [ABSTRACT FROM AUTHOR]

Mechanical anomalies (damping peaks sharper than Debye peaks, in contrast to a broad relaxation peak) were observed in tetragonal barium titanate ceramic via broadband viscoelastic spectroscopy at low frequencies (<10 Hz) at ambient temperature after aging at 90 °C for 15 h. The sharp peaks disappear after aging above the Curie point (150 °C for 10 h). Mechanical anomalies are tentatively attributed to negative stiffness heterogeneity, the mechanism of which is proposed based upon the theory of symmetry-conforming short-range order property of point defects. [ABSTRACT FROM AUTHOR]

The two-pulse COSY revamped by asymmetric Z-gradient echo detection (CRAZED) NMR experiment has the basic form 90°-Gδ-trec-β-nGδ-trec-FID, with a phase-encoding gradient pulse G of length δ applied during the evolution time τ for transverse magnetization, readout pulse β, rephasing gradient nGδ, and recovery time trec prior to acquisition of the free-induction decay. Based on the classical treatment of the spatially modulated dipolar demagnetizing field and without invoking intermolecular multiple-quantum coherence, a new formulation of the first-order approximation for the theoretical solution of the nonlinear Bloch equations has been developed. The nth-order CRAZED signal can be expressed as a simple product of a scaling function Cn(β,τ) and a signal amplitude function An(t), where the domain t begins immediately after the β pulse. Using a single-quantum coherence model, a generalized rf phase shift function has also been developed, which explains all known phase behavior, including nth-order echo selection by phase cycling. Details of the derivations are provided in two appendices as supplementary material. For n>1, An(t) increases from zero to a maximum value at t=tmax before decaying and can be expressed as a series of n exponential decays with antisymmetric binomial coefficients. Fourier transform gives an antisymmetric binomial series of Lorentzians, where the composite lineshape exhibits negative wings, zero integral, and a linewidth that decreases with n. Analytical functions are presented for tmax and An(tmax) and for estimating the maximal percent error incurred for An(tmax) when using the first-order model. The preacquisition delay Δ=δ+trec results in the loss of the data points for t=0 to Δ. Conventional Fourier transformation produces time-zero truncation artifacts (reduced negative wing amplitude, nonzero integral, and reduced effective T2 *), which can be avoided by time-domain fitting after right shifting the data by Δ. A doped water sample (9.93 mM NiSO4, 10 mm sample tube) was used to study the behavior of the CRAZED signal for n=1–4 with β=90° at 7 T (300 MHz 1H frequency) as a function of Δ, with and without radiation damping. Pulse-acquire experiments were used to determine the relaxation times (T1=61.8 ms and T2 *=29.7 ms), and the radiation damping time constant Trd=18.5 ms. When experimental CRAZED data sets were right shifted by Δ, excellent least-squares fits to the first-order model function were obtained for all n using a minimal set of free variables. Without radiation damping the fitted T2 *values (29.7–30.2 ms) agreed with the reference value. With radiation damping the fitted effective T2 * values were 16.2 ms for a 90° pulse-acquire experiment and 18.8–20.2 ms for the CRAZED experiment with n=1–4 and signal amplitudes spanning a range of 105. [ABSTRACT FROM AUTHOR]

The sensitive detection of dilute solute spins is critical to biomolecular NMR. In this work, a spin amplifier for detecting dilute solute magnetization is developed using the radiation damping interaction in solution magnetic resonance. The evolution of the solvent magnetization, initially placed along the unstable -z⁁ direction, is triggered by the radiation damping field generated by the dilute solute magnetization. As long as the radiation damping field generated by the solute is larger than the corresponding thermal noise field generated by the sample coil, the solute magnetization can effectively trigger the evolution of the water magnetization under radiation damping. The coupling between the solute and solvent magnetizations via the radiation damping field can be further improved through a novel bipolar gradient scheme, which allows solute spins with chemical shift differences much greater than the effective radiation damping field strength to affect the solvent magnetizations more efficiently. Experiments performed on an aqueous acetone solution indicate that solute concentrations on the order of 10-5 that of the solvent concentration can be readily detected using this spin amplifier. [ABSTRACT FROM AUTHOR]

Energy exchange between pump and daughter waves during the stimulated Raman scattering process in a plasma is investigated, including the effect of a damping coefficient of electron-ion collision at different initial three-wave phases. To obey the energy and momentum conservations, the resonance conditions are satisfied at an optimal initial phase difference between the interacting waves. The amplitudes of the interacting waves exhibit behaviors such as a parametric oscillator. The variations in initial three-wave phase difference generate a phase mismatch, which enhances the rate of the amplitude variations of the interacting waves. The relativistic mass effect modifies the dispersion relations of the interacting waves, and consequently the energy exchange during the stimulated Raman scattering is affected. The collisional damping in the plasma is shown to have an important effect on the evolution of the interacting waves. [ABSTRACT FROM AUTHOR]

The dynamics under the joint action of radiation damping and the distant dipolar field in high-field solution magnetic resonance are investigated. Different dynamical regimes during the evolution are identified and their individual features are discussed. In the steady state, the dynamics can be associated with a strange attractor in phase space on which the motion is chaotic. The possibility of the observed chaotic motion being spatiotemporal is examined. [ABSTRACT FROM AUTHOR]

In the present work, the overall energy dissipation of a pile embedded in the soil, modeled as visco-elastic springs, is thoroughly investigated. The term dissipation is used to measure the rate of decay of amplitude of displacement response in the time domain. The estimation of dissipation in piles is necessary to understand how quickly a pile reaches its steady state or equilibrium under dynamic loads or in cases of free vibration, respectively. A higher level of dissipation indicates a shorter duration of transient vibration, which is a deserving trait for vibration mitigation in extreme events, such as earthquakes, storms, blasts, shocks, etc. The dispersion relation which is a function of wavenumber and free wave frequency is obtained for the pile embedded in the soil medium by implementing the generalized form of Bloch's theorem. The dispersion relationship is solved in the free-wave approach, in which a real wave number yields a set of complex frequencies. For predicting the overall dissipation of the system from the complex frequency values, an analytical closed-form expression is proposed in this paper. Further, the predicted dissipation is validated with a finite element-based numerical model of the soil–pile system. [ABSTRACT FROM AUTHOR]

The cost of Floating Offshore Wind (FOW) is driven by the foundation, thus it can be reduced by optimising the floater design from the early stage. Most of the numerical tools for the platform design integrate radiation–diffraction theory-based software, but it can make the whole process very time-consuming since the preliminary design phases usually imply the analysis of a large number of designs. In order to accelerate the first stages of design, and consequently, achieve the foundation cost reduction, this study proposes an efficient methodology for the hydrodynamic added mass, radiation damping, and excitation loads calculation. The method is implemented for a semi-submersible platform, and it is verified against the radiation–diffraction commercial software AQWA. The methodology is validated through a comparative analysis of the response of ten different platforms, and it has shown that the hydrodynamic coefficients derived from either radiation–diffraction analysis or from the proposed method lead to equivalent conclusions. The maximum values of the platform's pitch angle and the nacelle acceleration are assessed, achieving a maximum deviation among the most critical designs of 3% and 17%, respectively. This methodology has demonstrated to provide with reasonable accuracy the dynamic behaviour of the offshore wind substructures achieving a significant computational cost reduction compared to the state-of-the-art methods, which enables to accelerate the optimisation process and thus, resulting in a more accurate floater preliminary design. • Methodology for the estimation hydrodynamic coefficients on semisubmersible floaters. • Efficient method through interpolation and superposition of the hydrodynamic data. • Parametric study to analyse the cross-interaction effects between the columns. • Validation against radiation–diffraction commercial software. • Comparative analysis of different platforms to quantify the method's accuracy. [ABSTRACT FROM AUTHOR]

Although the theories and potential applications of intermolecular multiple-quantum coherences (iMQCs) have been under active investigations for over a decade, discussion of iMQC NMR signal formation was mainly confined in the time domain. In this paper, a full line-shape theory was developed to describe iMQC signals in the frequency domain. Relevant features of the line shape, such as peak height, linewidth, and phase, were investigated in detail. Predictions based on the theory agree well with experimental and simulated results. Since radiation-damping effects always couple with iMQCs in highly polarized liquid-state NMR systems, and strongly radiation-damped signals have many spectral characteristics similar to those of iMQCs, a detailed comparison was also made between them from different spectral aspects. With detailed comparison of peak height, linewidth, and phase, this work demonstrates that the iMQC and radiation-damping phenomena result from two completely different physical mechanisms despite that both present similar signal features and coexist in highly polarized liquid-state NMR systems. [ABSTRACT FROM AUTHOR]

The paper evaluates the radiation damping associated with shallow foundations sitting on linear or nonlinear soil medium. The study was motivated by the need to develop macroscopic foundation models that can realistically capture the nonlinear behaviour and energy dissipation mechanism of shallow foundations. Such model is essential to simulate the complex behaviour of structure components (e.g. shear walls, columns etc.) sitting on flexible foundations due to soil-structure interaction effects. In this study, the dynamic response of an infinitely long strip foundation resting on an elastic and inelastic half-space is investigated. The numerical analysis results presented here reveal that dynamic responses of shallow foundations strongly depend on amplitude and frequency of the input motion. In particular, the radiation damping of the system is affected by soil nonlinearity, foundation geometry and excitation frequency. The yielding of soil reduces the energy dissipation through the out going waves. As a result, the radiation damping of nonlinear soil medium is significantly lower than the elastic soil counterpart. The effects of initial elastic stiffness, yielding stress and excitation amplitude are incorporated in a nonlinearity indicator, which has shown strong correspondence to the radiation damping of the system.

This paper investigates the dynamic response of shallow foundations on linear and nonlinear soil medium using finite element method. The study was motivated by the need to develop macroscopic foundation models that can realistically capture the nonlinear behavior and energy dissipation mechanism of shallow foundations. An infinitely long strip foundation resting on soil half-space is analyzed in depth to evaluate the dependence of its dynamic responses on various parameters, e.g. foundation width, material properties, input motion amplitude and frequency etc. Special attentions are paid to choose appropriate domain scale, mesh size and boundary conditions so as to minimize the often observed numerical oscillations when the outgoing waves are contaminated by the reflecting waves at boundaries. Such judicious choice results in an excellent agreement between the finite element analysis and the analytical solution of strip foundation on linear soil half-space. Closed-form formulas are developed to describe the frequency-dependent linear dynamic stiffness of strip foundation along both horizontal and vertical directions. Various nonlinear constitutive models of soil, which exhibit the yielding and kinematic hardening behavior of soil, are implemented in this study to evaluate the dynamic stiffness of strip foundation sitting on nonlinear soil medium. The finite element analyses reveal the strong dependency of response on input motion amplitude, frequency and yielding of soil. A nonlinearity indicator is developed to incorporate the combined effects of initial elastic stiffness, yielding stress and excitation amplitude. The numerical analyses presented here provide improved understanding on the nonlinear behavior and energy dissipation mechanism of shallow foundations under dynamic loads.

The effect of plasmon and LO-phonon damping on the optical measurements of InN films is discussed. Phonon and plasmon damping dramatically modifies the spectral features of the optical spectra and destabilizes the coupled modes of the system. Phonon damping affects the optical properties in a qualitatively different way from plasmon damping. Increased phonon damping leads to a merging of the coupled modes for a certain range of carrier density. Plasmon damping broadens the spectral linewidths of both of the coupled modes when plasmon energies are of the order of LO-phonon energies. However, when plasmon energies are larger than LO-phonon energies, increasing plasmon damping makes the higher-energy mode completely degenerate with plasmon, and may even have lower energies than plasmon. In weakly damped situations, we also discuss the low-energy optical transmission region that forms in between the coupled modes. Finally, the effect of plasmon and LO-phonon coupling on the analyses of the experimental infrared reflection data of InN films (for different electron densities) is discussed. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

In this article we extend previous studies of the dynamical instabilities to incorporate the roles of the tipping angle, the overall shape of the sample, (optional) pulsed field gradients in various directions, and radiation damping. The linear stability for small perturbations is discussed analytically in detail, and numerical simulations are used to have a glimpse at the turbulent spin motion for large perturbations. [ABSTRACT FROM AUTHOR]

In this paper, the dynamics of a magnetization undergoing a radiation-damping based feedback radio-frequency field is investigated both theoretically and experimentally. It is shown that due to the presence of T[sub 1] relaxation the evolution equations predict the existence of self-sustained maser pulses. This phenomenon is a consequence of the competition between two different processes, namely, T[sub 1] relaxation and a precession about a magnetization-dependent radio-frequency field. Experiments show the existence of periodic revivals of the free induction decay over unusually long periods of time, on the order of tens of seconds. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A theory is presented for radiation damping (RD) in the toroid cavity nuclear magnetic resonance detector, a cylindrically symmetric inhomogeneous-rf field detector in which the magnitude of B[sub 1] is inversely proportional to the distance from the cylindrical symmetry axis. The equations of motion of the magnetization components are obtained and discussed. Numerical simulations of conventional- and composite-pulse experiments are presented, along with a discussion of the effects of RD on the evolution of magnetization. Preliminary simulations of RD in the presence of inhomogeneous line broadening are also presented. The signature effect of radiation damping in the TCD is the winding or unwinding of magnetization gratings that has recently been observed by other researchers. The observed magnitude of the effect is linked to the effective filling factor, which currently appears to be limited by the stray inductance of the detection circuit. The results are of interest in connection with recent findings regarding the interaction of RD with the dipolar demagnetizing field. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Interest in renewable and clean energy over the past decade has motivated immense research on wind energy. The main issues in design of offshore wind turbines in regions of recent development have been aero- and hydro-dynamic loads; however, earthquake is a design concern in seismic areas such as East Asia and Western United states. This paper reviews the state of practice in seismic design of offshore wind turbines. It is demonstrated that wind turbines are in particular vulnerable to vertical earthquake excitation due to their rather high natural frequencies in vertical direction; however, inclusion of the radiation damping could contribute considerably reduce the earthquake loads. Moreover, it is demonstrated how soil nonlinearity could lead to settlement and permanent tilting of offshore wind turbines on caisson foundations or tripods. Using these cases, the paper demonstrates that the design of offshore wind turbines for earthquake loading is driven by performance-based considerations. • Effect of combined environmental and earthquake loads on offshore wind turbines, highlighting the issue of permanent tilt. • Nonlinear foundation springs with reduced/controlled hysteretic damping for soil-structure interaction analysis. • Rigorous modelling of radiation damping and its role in reduction of vertical seismic response of wind turbines. • Harmonization of earthquake hazard requirements in design of wind turbines. • Review of key issues in earthquake design of offshore wind turbines. [ABSTRACT FROM AUTHOR]

Copyright of Engineering Mechanics / Gongcheng Lixue is the property of Engineering Mechanics Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Engineering for Thermal Energy & Power / Reneng Dongli Gongcheng is the property of Journal of Engineering for Thermal Energy & Power and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

A semi-analytic model based on linear potential theory is developed to solve wave radiation from an array of truncated cylinders with arbitrary cross sections, free to oscillate independently in water of finite depth. The radiated velocity potential in the interior region below each cylinder and the exterior region extending to infinity are expressed as a series of eigenfunctions in the local cylindrical coordinate system using the method of separation of variables. They are solved subsequently by imposing the continuity condition of the velocity and pressure at the wetted surfaces of the cylinders and the fluid interfaces between adjacent regions. In the process, the Fourier series expansion method is applied to the terms regarding the arbitrary cross sections. The model is successfully validated through a case study with two caissons – excellent agreement is obtained with a numerical model based on the boundary element method. The semi-analytic model is then applied to explore the influence of layout (angle and spacing between the two caissons) on the added-mass and radiation damping coefficients. It is found that the hydrodynamic interaction between the two caissons can increase or decrease the value of the coefficients depending on the wave frequency. • We develop a semi-analytic model of wave radiation by multiple cylinders. • The vertical truncated cylinders have arbitrary cross sections. • We validate the semi-analytic model vs. numerical results, with excellent agreement. • Model is applied to case study with two caissons representing mobile offshore bases. • We analyse the sensitivity of hydrodynamic coefficients to layout (angle, spacing). [ABSTRACT FROM AUTHOR]

The spring persistence barrier remains a critical challenge for the prediction of El Niño–Southern Oscillation (ENSO) because it severely limits the potential ability of ENSO forecast across the boreal spring. Our observational analysis shows that the spring persistence barrier exhibited a significant decadal modulation in the last half century. Further analysis shows that this decadal modulation is caused by the decadal variation in spring ENSO stability, which, in turn, is dominated by the thermal damping feedback of the sea surface temperature (SST) through latent heat flux and shortwave radiation flux. The change of the thermal damping feedback is associated with the background mean SST, with a cooler SST corresponding to a greater ENSO instability and a severer spring persistence barrier and vice versa. Plain Language Summary: Obtaining effective and correct El Niño–Southern Oscillation (ENSO) forecasts is always an inspiring and challenging task but requires additional research for optimization. One fundamental obstacle that must be faced is the so‐called boreal spring persistence barrier, which relates to the significant decrease in ENSO's prediction skill that always occurs during the boreal spring. Through investigating the spring persistence barrier issues by the observational analyses, our study proposes a mechanism for controlling its variability on the decadal time scale and highlights the significant effects of the interdecadal climate variability in the tropical Pacific. As the mean state of the tropical Pacific warms, more moisture is released into the atmosphere for the same magnitude of sea surface temperature warming, which further leads to the thermal damping over the tropical Pacific and induces more stable ENSO during the boreal spring. The more stable ENSO then weakens the spring persistence barrier, making ENSO easier to predict. This study will draw the scientific community's attention on understanding about ENSO and ENSO predictability; the decadal variations in spring persistence barrier intensity and its related physical processes should be adequately represented in climate models used for seasonal predictions and studies of climate variability, change, and projection. Key Points: The ENSO spring persistence barrier exhibited a significant decadal variability in the last half centuryThe decadal modulation of the barrier is caused by the decadal variation in spring ENSO stabilityThe ENSO's stability is further dominated by the nonlinear heat flux‐SST damping feedback [ABSTRACT FROM AUTHOR]

Abstract A series of analytic models are presented of a partially-submerged, straight circular cross-section pipe subjected to reciprocating flow, incorporating viscous and turbulent boundary-layer dissipation. This pipe is the most elementary paradigm for a fixed-type Oscillating Water Column (OWC), and its analysis more generally addresses one aspect of reciprocating pipe flow. The derivation of the dissipation terms in the momentum conservation equations from their origin in the Navier–Stokes equation are explicitly identified. The contribution of different damping sources to the overall energy loss is compared. The flow inside the pipe is assumed fully developed along the entire length, neglecting the effect of the flow development region. For relevance to engineering applications, a power take-off system is modelled assuming that the air compresses and expands isentropically in an air chamber at the top of the pipe. Existing theory is adapted into the current models for computing the hydrodynamic coefficients related to the scattered wave and radiation wave. A novel contribution of this paper is the inclusion of damping due to the wall shear stress, modelled for the reciprocating flow system inside the pipe. Comparison between the damping factors in relatively short OWCs confirms the findings in the literature that the major part of the damping is due to the radiation wave. However, it is found that with the increase of the draft length, the wall shear stress damping may also become an important factor in the resulting dynamics. [ABSTRACT FROM AUTHOR]

Through spin-exchange interactions, a precessing Xe nuclear spin (brown) drags Rb spin (grey) to precess around B 0 with identical frequency ω and a phase lag α, at the cost of fast relaxation and decreased precessing frequency. • The Rb spins give back action to the precessing nuclear spins in Rb-Xe comagnetometers. • The nuclear spins relax faster due to the "radiation damping" effect caused by polarized Rb spins. • The precessing frequency of the nuclear spins shifts due to the backaction of polarized Rb spins. We report a new kind of interaction between overlapping Rb-Xe spin ensembles polarized by spin-exchange optical pumping. The Rb acts as both a medium to optically polarize the Xe spins and as a magnetometer to probe the precession of Xe spins. When Xe spins precess, they result in the precession of Rb spins. Like the radiation damping effect caused by the coil in conventional NMR systems, the precessing Rb spins lead to damping and a frequency-shift for the precessing Xe spins. When Xe spins are operated in a free-induction decay mode, the transverse relaxation time and oscillating frequency of Xe spins change due to the "radiation damping" effect of Rb spins. When Xe spins are operated in the self-oscillating mode, its transverse relaxation time and oscillating frequency will also be changed. These effects will influence the accuracy of NMR probes, which are widely used in the search for CPT- and Lorentz-invariance violations, the fifth force, etc. If this problem is solved or compensated for, the limit of the aforementioned search may be improved. [ABSTRACT FROM AUTHOR]