Elastic Energy Loss Research Articles

The effect of latent plasticity on the shape recovery of a shape memory vitrimer

The utility of covalent crosslinkers as permanent netpoints has enabled robust shape memory behaviour in shape memory thermosets (SMTs). Having this permanent crosslinked structure, alternatively, challenges the reprogramming of permanent shapes. The introduction of vitrimeric type dynamic chemistry into SMTs allows for reconfiguration of crosslinked network and thus reprogramming of permanent shapes. However, adding this adaptability/plasticity to the network could potentially affect the shape memory behaviour, especially when the shape programming is conducted at a temperature that activates the network plasticity as well. Herein, to address the potential influence of network plasticity, we studied the shape memory behaviour of a shape memory vitrimer (SMV) that possesses a low network activation energy (Ea) of 33 kJ/mol, which indicates a relatively high plasticity index during shape programming. As we found, there is a dependence of shape recovery on the shape-programming time: a longer programming time leads to a poorer shape recovery. This negative correlation results from the dissipation of stored elastic energy at local strained regions associated with shape programming. We further related the loss of elastic energy to the stress-relaxation that results from chain exchanges. Accordingly, the dependence can be analyzed with an analog of stress-relaxation model. We reasoned that this latent plasticity associated with dynamic chain exchanges is ubiquitous in SMVs, and so one needs to carefully evaluate the reprogramming temperature and time when performing shape memory studies on SMVs.

Determining the Effect of Hot Electron Dissipation on Molecular Scattering Experiments at Metal Surfaces.

Nonadiabatic effects that arise from the concerted motion of electrons and atoms at comparable energy and time scales are omnipresent in thermal and light-driven chemistry at metal surfaces. Excited (hot) electrons can measurably affect molecule–metal reactions by contributing to state-dependent reaction probabilities. Vibrational state-to-state scattering of NO on Au(111) has been one of the most studied examples in this regard, providing a testing ground for developing various nonadiabatic theories. This system is often cited as the prime example for the failure of electronic friction theory, a very efficient model accounting for dissipative forces on metal-adsorbed molecules due to the creation of hot electrons in the metal. However, the exact failings compared to experiment and their origin from theory are not established for any system because dynamic properties are affected by many compounding simulation errors of which the quality of nonadiabatic treatment is just one. We use a high-dimensional machine learning representation of electronic structure theory to minimize errors that arise from quantum chemistry. This allows us to perform a comprehensive quantitative analysis of the performance of nonadiabatic molecular dynamics in describing vibrational state-to-state scattering of NO on Au(111) and compare directly to adiabatic results. We find that electronic friction theory accurately predicts elastic and single-quantum energy loss but underestimates multiquantum energy loss and overestimates molecular trapping at high vibrational excitation. Our analysis reveals that multiquantum energy loss can potentially be remedied within friction theory whereas the overestimation of trapping constitutes a genuine breakdown of electronic friction theory. Addressing this overestimation for dynamic processes in catalysis and surface chemistry will likely require more sophisticated theories

Impact of off-shell dynamics on the transport properties and the dynamical evolution of charm quarks at RHIC and LHC temperatures

We evaluate drag and diffusion transport coefficients comparing a quasi-particle approximation with on-shell constituents of the QGP medium and a dynamical quasi-particles model with off-shell bulk medium at finite temperature T. We study the effects of the width gamma of the particles of the bulk medium on the charm quark transport properties exploring the range where gamma < M_{q,g}. We find that off-shell effects are in general quite moderate and can induce a reduction of the drag coefficient at low momenta that disappear already at moderate momenta, p gtrsim 2–3 GeV. We also observe a moderate reduction of the breaking of the fluctuation–dissipation theorem (FDT) at finite momenta. Moreover, we have performed a first study of the dynamical evolution of HQ elastic energy loss in a bulk medium at fixed temperature extending the Boltzmann (BM) collision integral to include off-shell dynamics. A comparison among the Langevin dynamics, the BM collisional integral with on-shell and the BM extension to off-shell dynamics shows that the evolution of charm energy when off-shell effects are included remain quite similar to the case of the on-shell BM collision integral.

Intense ionizing irradiation-induced atomic movement toward recrystallization in 4H-SiC

An ultrafast thermal spike within a time interval of a few pico-seconds generated by intense ionizing energy deposited using 100 MeV Ag ions is utilized to study the atomistic details of damage recovery in 4H-SiC. Sequential single ion irradiations were performed using 300 keV Ar and 100 MeV Ag in ⟨0001⟩ 4H-SiC to invoke swift heavy ion (SHI) beam induced epitaxial recrystallization in samples with different degrees of pre-damaged conditions. SHI irradiation was carried out at both room temperature and a low temperature of ∼80K. Low-temperature irradiation was carried out to arrest thermal diffusion of defects and to isolate ionization-induced defect migration in 4H-SiC. Insights into the thermal spike generated by ionizing events in crystalline and amorphous regions at both the temperatures predict a SiC response to SHI. The results emphasize the role of different degrees of pre-damage induced physico-chemical conditions and irradiation temperatures against SHI-induced recrystallization as evaluated by Rutherford backscattering/channeling, Raman spectroscopy, and hard x-ray photoelectron spectroscopy. Understanding the dependence of ion-beam damage accumulation and their recovery on the inelastic to elastic energy loss ratio is important for the performance prediction of SiC intended for extreme environments such as space, defense, and nuclear radiation. We report substantial damage recovery even at a near liquid nitrogen temperature of ∼80K. The recovery gets impeded mainly by the formation of complex defects having homonuclear bonds. The results are explained in the framework of the inelastic thermal spike model, and the role of phonon in the damage recovery process is emphasized.

Charmed hadron chemistry in relativistic heavy-ion collisions

We develop for charmed hadron production in relativistic heavy-ion collisions a comprehensive coalescence model that includes an extensive set of s and p-wave hadronic states as well as the strict energy-momentum conservation, which ensures the boost invariance of the coalescence probability and the thermal limit of the produced hadron spectrum. By combining our hadronization scheme with an advanced Langevin-hydrodynamics model that incorporates both elastic and inelastic energy loss of heavy quarks inside the dynamical quark-gluon plasma, we obtain a successful description of the pT-integrated and differential Λc/D0 and Ds/D0 ratios measured at RHIC and the LHC. We find that including the effect of radial flow of the medium is essential for describing the enhanced Λc/D0 ratio observed in relativistic heavy-ion collisions. We also find that the puzzling larger Λc/D0 ratio observed in Au+Au collisions at RHIC than in Pb+Pb collisions at the LHC is due to the interplay between the effects of the QGP radial flow and the charm quark transverse momentum spectrum at hadronization. Our study further suggests that charmed hadrons have larger sizes in medium than in vacuum.

Comparison of dynamic mechanical properties of dentin between deciduous and permanent teeth

ABSTRACT Purpose: Even though differences between deciduous and permanent dentin have been widely studied, their dynamic mechanical behavior has never been compared. The objective of the present study was to quantify the differences between deciduous and permanent dentin under cyclic mechanical loading, which is similar to masticatory stress. Materials and Methods: Deciduous and permanent teeth, respectively from children (9 ~ 12 years old) and young people (18 ~ 25 years old), were wet-sectioned perpendicular to the longitudinal axis and the central specimens of coronal dentin were evaluated by nanoscopic dynamic mechanical analysis (nanoDMA). Results: The average storage, loss, and complex moduli, as well as the hardness of deciduous dentin were significantly (p < 0.05) lower than those of permanent dentin. Moreover, the tan δ value of permanent dentin was significantly (p < 0.05) lower than that of deciduous dentin across the loading frequency range, indicating that viscoelastic behavior and loss of elastic energy were significantly reduced in the stiffer permanent dentin. All the nanoDMA responses showed a significant influence of the dynamic loading frequency (p < 0.05): Both deciduous and permanent dentin showed reduced viscoelasticty with increased loading frequencies. Conclusions: Compared with deciduous dentin, permanent dentin exhibits higher stiffness with reduced energy loss during deformation, and therefore superior mechanical characteristics for the mastication process.

The structural evolution of light-ion implanted 6H-SiC single crystal: Comparison of the effect of helium and hydrogen

The microstructure evolution of hydrogen-implanted 6H-SiC at different temperatures and fluences is investigated by using various experimental techniques. In H-implanted samples with relatively low fluence at RT, dense blister cavities are observed after annealing at 1100 °C, while no visible blister cavities appear after annealing at 1100 °C in the sample implanted at RT with high fluence. The absence of blister cavities is due to the loss of elastic energy during the crystalline-to-amorphous transition. With a further increase of implantation temperature to 450 and 900 °C, amorphization did not occur and H-containing microcracks grew laterally below the surface. Thus, blisters appeared on the surface of the samples implanted at 900 °C even without annealing. The results are compared to the microstructural evolution of He-implanted 6H-SiC which was explored in our previous work. The behavior of hydrogen and helium ions in 6H-SiC lattice was rather different. For He implantation, regardless of the fluence and implantation temperature, blisters did not form. The mechanism of migration and coalescence of nanoscale bubbles that are responsible for blistering were studied via density functional theory calculations, which well-supported the presented results. We found that both mechanisms (migration and coalescence) are energetically cheaper in the case of H compared to He.

Distinct Expression of Nonmuscle Myosin IIB in Pulmonary Arteries of Patients With Aortic Stenosis vs Insufficiency Undergoing a Ross Procedure

BackgroundClinical studies have revealed a greater risk of pulmonary autograft dilation after the Ross procedure in patients with preoperative aortic insufficiency (AI). The present study examined whether the morphologic, biomechanical, and cellular properties of the pulmonary artery (PA) from patients with AI were phenotypically different compared with patients diagnosed with aortic stenosis (AS). MethodsPA segments were harvested from patients undergoing the Ross procedure for AS (n = 16) and AI (n = 6). Preoperative aortic annulus was significantly larger (P < 0.05) in patients with AI (28.5 ± 1.8 mm) vs AS (22.8 ± 1.2 mm). Morphologic, biomechanical, and cellular phenotypes of the PA were analyzed. ResultsCollagen and elastin content in the media of the PA wall were similar in patients with AS and AI. Elastic modulus and energy loss of the PA were not significantly different between the groups. In the media of the PA, expression of a panel of vascular smooth muscle cell–specific proteins were similar in patients with AS and AI. In contrast, nonmuscle myosin IIB protein levels in the PA of AS patients were significantly higher compared with AI patients, and immunofluorescence identified staining in α-smooth muscle actin–positive vascular smooth muscle cells. ConclusionsDespite similar morphological and biomechanical properties, the disparate expression of nonmuscle myosin IIB protein distinguishes the PA of patients with AI from patients with AS. The biological role in vascular smooth muscle cells and the potential contribution of nonmuscle myosin IIB to pulmonary autograft dilation in a subset of AI patients after the Ross procedure remain to be determined.

Revealing Low-Radiative Modes of Nanoresonators with Internal Raman Scattering

Revealing hidden non-radiative (dark) of resonant nanostructures using optical methods such as dark-field spectroscopy often becomes a sophisticated problem due to a weak coupling of these modes with a far-field radiation, whereas methods of dark-modes spectroscopy, e.g. cathodoluminescence or elastic energy losses, are not always convenient in use. Here, we suggest an approach for experimental determining the mode structure of a nanoresonator basing on utilizing intrinsic incoherent Raman scattering. We theoretically predict the efficiency of this approach and realize it experimentally for silicon nanoparticle resonators possessing strong Raman line at 520 cm^-1. With this method, we studied a silicon nanoparticle placed on a gold substrate and reveal the spectral position of a low-radiative magnetic quadrupole mode which is hardly observable with common dark-field optical spectroscopy.

DREENA-C framework: joint RAA and v2 predictions and implications to QGP tomography

In this paper, we presented our recently developed Dynamical Radiative and Elastic ENergy loss Approach (DREENA-C) framework, which is a fully optimized computational suppression procedure based on our state-of-the-art dynamical energy loss formalism in constant temperature finite size QCD medium. With this framework, we have generated, for the first time, joint RAA and v2 predictions within our dynamical energy loss formalism. The predictions are generated for both light and heavy flavor probes, and different centrality regions in Pb + Pb collisions at the LHC, and compared with the available experimental data. While RAA predictions agree with experimental data, v2 predictions qualitatively agree with, but are quantitatively visibly above, the experimental data (in disagreement with other models, which underestimate v2). Consistently with numerical predictions, through simple analytic analysis, we show that RAA is insensitive to medium evolution (though highly sensitive to energy loss mechanisms), while v2 is highly sensitive to the evolution. As a major consequence for precision quark-gluon plasma (QGP) tomography, this then leaves a possibility to calibrate energy loss models on RAA data, while using v2 to constrain QGP parameters that are in agreement with both high and low p⊥ data.

Global constraints from RHIC and LHC on transport properties of QCD fluids in CUJET/CIBJET framework * * Supported by the National Science Foundation (PHY-1352368), IOPP of CCNU Wuhan China, the computations in this study were performed on IU's Big Red II clusters, supported in part by the Lilly Endowment, Inc., through its support for the Indiana University Pervasive Technology Institute,

We report results of a comprehensive global analysis of nuclear collision data from RHIC (0.2 ATeV), LHC1 (2.76 ATeV), and recent LHC2 (5.02 ATeV) energies using the updated CUJET framework. The framework consistently combines viscous hydrodynamic fields predicted by VISHNU2+1 (validated with soft GeV bulk observables) and the DGLV theory of jet elastic and inelastic energy loss generalized to QGP fluids with an sQGMP color structure, including effective semi-QGP color electric quark and gluon as well as emergent color magnetic monopole degrees of freedom constrained by lattice QCD data. We vary the two control parameters of the model (the maximum value of the running QCD coupling, , and the ratio of color magnetic to electric screening scales) and calculate the global compared with available jet fragment observables ( ). A global minimum is found with and . Using CIBJET, the event-by-event (ebe) generalization of the CUJET framework, we show that ebe fluctuations in the initial conditions do not significantly alter our conclusions (except for ). An important theoretical advantage of the CUJET and CIBJET frameworks is not only its global consistency with jet fragment observables at RHIC and LHC and with non-perturbative lattice QCD data, but also its internal consistency of the constrained jet transport coefficient, , with the near-perfect fluid viscosity to entropy ratio ( ) property of QCD fluids near needed to account for the low GeV flow observables. Predictions for future tests at LHC with 5.44 ATeV Xe + Xe and 5.02 ATeV Pb + Pb are also presented.

Dynamical energy loss formalism: from describing suppression patterns to implications for future experiments

We overview our recently developed DREENA-C and DREENA-B frameworks, where DREENA (Dynamical Radiative and Elastic ENergy loss Approach) is a computational implementation of the dynamical energy loss formalism; C stands for constant temperature and B for the medium evolution modeled by Bjorken expansion. At constant temperature our predictions overestimate ν2, in contrast to other models, but consistent with simple analytical estimates. With Bjorken expansion, we obtain good agreement with both RAA and ν2 measurements. We find that introducing medium evolution has a larger effect on ν2 predictions, but for precision predictions it has to be taken into account in RAA predictions as well. We also propose a new observable, which we call path length sensitive suppression ratio, for which we argue that the path length dependence can be assessed in a straightforward manner. We also argue that Pb + Pb vs. Xe + Xe collisions make a good system to assess the path length dependence. As an outlook, we expect that introduction of more complex medium evolution (beyond Bjorken expansion) in the dynamical energy loss formalism can provide a basis for a state of the art QGP tomography tool – e.g. to jointly constrain the medium properties from the point of both high-p⊥ and low-p⊥ data.

Elastic Energy Losses and Orientation Effects during Interaction between Atomic Particles

Patterns of energy transfer and accumulation in elastic interactions between Nb+ ions (E0 = 0.1–3 keV) and atoms of a Nb single crystal are studied by means of molecular dynamics. Spatial distributions of the recoil energy in the bulk of the crystal are calculated. It is shown that recoil energy is accumulated in the region of the densest packing of atoms, mainly in the outermost (N = 1–3) monolayers of the crystal. The effect the orientation of the target with respect to the beam has on the recoil energy and its spatial distributions is determined.

Medium Recoils and background subtraction in JEWEL

Jewel is a fully dynamical event generator for jet evolution in a dense QCD medium, which has been validated for multiple jet and jet-like observables. Jet constituents (partons) undergo collisions with thermal partons from the medium, leading to both elastic and radiative energy loss. The recoiling medium scattering centers carry away energy and momentum from the jet. Keeping track of these recoils is essential for the description of intra-jet observables. Since the thermal component of the recoils is part of the soft background activity, comparison with data on jet observables requires the implementation of a background subtraction procedure. We will show two independent procedures through which background subtraction can be performed and discuss the impact of the medium recoil on jet shape observables and jet-background correlations. Keeping track of the medium recoil significantly improves the Jewel description of jet shape measurements.

Role of atomic-level defects and electronic energy loss on amorphization in LiNbO3 single crystals

Understanding complex non-equilibrium defect processes, where multiple irradiation mechanisms may take place simultaneously, is a long standing subject in material science. The separate and combined effects of elastic and inelastic energy loss are a very complicated and challenging topic. In this work, LiNbO3 has been irradiated with 0.9 MeV Si+ and 8 MeV O3+, which are representative of regimes where nuclear (Sn) and electronic (Se) energy loss are dominant, respectively. The evolution of damage has been investigated by Rutherford backscattering spectrometry (RBS) in channeling configuration. Pristine samples were irradiated with 0.9 MeV Si+ ions to create different pre-existing damage states. Below the threshold (Se,th = 5–6 keV nm−1) for amorphous track formation in this material, irradiation of the pristine samples with a highly ionizing beam of 8 MeV O3+ ions, with nearly constant Se of about 3 keV nm−1, induces a crystalline to amorphous phase transition at high ion fluences. In the pre-damaged samples, the electronic energy loss from the 8 MeV O3+ ions interacts synergistically with the pre-existing damage, resulting in a rapid, non-linear increase in damage production. There is a significant reduction in the incubation fluence for rapid amorphization with the increasing amount of pre-existing damage. These results highlight the important role of atomic-level defects on increasing the sensitivity of some oxides to amorphization induced by electronic energy loss. Controlling the nature and amount of pre-damage may provide a new approach to tuning optical properties for photonic device applications.

Medium response in JEWEL and its impact on jet shape observables in heavy ion collisions

Realistic modeling of medium-jet interactions in heavy ion collisions is becoming increasingly important to successfully predict jet structure and shape observables. In Jewel, all partons belonging to the parton showers initiated by hard scattered partons undergo collisions with thermal partons from the medium, leading to both elastic and radiative energy loss. The recoiling medium partons carry away energy and momentum from the jet. Since the thermal component of these recoils’ momenta is part of the soft background activity, comparison with data requires the implementation of a subtraction procedure. We present two independent procedures through which background subtraction can be performed and discuss the impact of the medium recoil on jet shape observables. Keeping track of the medium response significantly improves the Jewel description of jet shape measurements.

Analytical models for the impact of a solid sphere on a fluid-filled spherical shell incorporating the stress wave propagation effect and their applications to blunt head impacts

A new analytical (non-linear) model for the impact of a solid sphere on a fluid-filled spherical shell is developed by including the stress wave propagation effect in addition to the Hertzian contact deformations and the shell membrane and bending actions. The expressions for determining the maximum mutual approach and impact duration are analytically derived using the principle of energy conservation. A simplified (linearized) model incorporating the elastic energy loss due to the stress wave propagation is then formulated by using a linear force-deflection relation, which leads to a closed-form expression for the impact duration. It is shown that the new non-linear model reduces to that of Young (2003) and the linearized model recovers that of Mansoor–Baghaei and Sadegh (2011) when the stress wave propagation effect is not considered. By directly applying the newly obtained non-linear and linearized models, three representative problems simulating blunt head impacts are analyzed. The first problem characterizes the blunt impact of a human head on the ground or on an automobile, the second one simulates the blunt impact of a non-lethal projectile on a human head, and the third one represents two football players’ head collision. Numerical results for the maximum deflection, maximum impact force and impact duration are provided to quantitatively show their variations with the impact velocity and shell thickness. The values predicted by the current new models are also compared with those given by the two existing models and with available finite element simulation results, and a good agreement is observed.

Theoretical modeling insights into elastic wave attenuation mechanisms in marine sediments with pore‐filling methane hydrate

AbstractThe majority of presently exploitable marine methane hydrate reservoirs are likely to host hydrate in disseminated form in coarse grain sediments. For hydrate concentrations below 25–40%, disseminated or pore‐filling hydrate does not increase elastic frame moduli, thus making impotent traditional seismic velocity‐based methods. Here, we present a theoretical model to calculate frequency‐dependent P and S wave velocity and attenuation of an effective porous medium composed of solid mineral grains, methane hydrate, methane gas, and water. The model considers elastic wave energy losses caused by local viscous flow both (i) between fluid inclusions in hydrate and pores and (ii) between different aspect ratio pores (created when hydrate grows); the inertial motion of the frame with respect to the pore fluid (Biot's type fluid flow); and gas bubble damping. The sole presence of pore‐filling hydrate in the sediment reduces the available porosity and intrinsic permeability of the sediment affecting Biot's type attenuation at high frequencies. Our model shows that attenuation maxima due to fluid inclusions in hydrate are possible over the entire frequency range of interest to exploration seismology (1–106 Hz), depending on the aspect ratio of the inclusions, whereas maxima due to different aspect ratio pores occur only at sonic to ultrasound frequencies (104–106 Hz). This frequency response imposes further constraints on possible hydrate saturations able to reproduce broadband elastic measurements of velocity and attenuation. Our results provide a physical basis for detecting the presence and amount of pore‐filling hydrate in seafloor sediments using conventional seismic surveys.

Chemical–physical characterization of ancient paper with functionalized polyamidoamines (PAAs)

Hybrid inorganic–organic treatments, based on amide-amine polymers (PAAs), against thermal oxidation have been prepared on paper dating back to eighteenth century. The polymeric sols are obtained by step-growth Michael addition polymerization and functionalized with siloxane network by sol–gel method. Five types of samples have been prepared changing the molar ratios among the reagents and their concentration. The treated paper samples were subjected to morphological and structural characterization, by using Scanning Electron Microscopy and vibrational spectroscopies (FTIR and Raman), respectively. Static mechanical tests have been carried out on the samples for measuring elastic modulus, ultimate strength, ultimate deformation and energy loss, whereas dynamic-mechanical measurements have been recorded at increasing temperatures to evaluate E′, E″ and tan δ. Finally, Thermo-Gravimetry and Differential Scanning Calorimetry have been carried out in order to study the behaviour of treated samples in temperature with respect the plain paper. The main result is that the siloxane-modified PAA treatment can improve significantly both mechanical and dynamic-mechanical properties, as well as the thermal resistance, without altering the aspect and texture of the original material. In general, the thicker the impregnation, the better the performances of treated paper: the thickest treatment is able to prevent the combustion of paper samples until 500 °C. The treatment is very promising to preserve ancient manuscripts during accidental fire and against the embrittlement due to natural ageing.

Defect distribution and Schottky barrier at metal/Ge interfaces: Role of metal-induced gap states

The defect distribution and Schottky barrier at metal/Ge interfaces were studied using first-principles calculation. It was shown that the defect density markedly increases around the interface owing to the stabilization caused by the hybridization of defect electronic states with metal-induced gap states (MIGS) and by the associated small elastic energy loss around the interface. By comparing the formation energies of various defects at a variety of metal/substrate interfaces, we showed that MIGS not only control the Schottky barrier but also promote a defect-density increase at most metal/semiconductor interfaces. Moreover, we showed that interface oxide layers block MIGS penetration into the Ge substrate and promote the observed breakdown of Fermi-level pinning.