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This paper presents the effect of sintering temperature on the structural, electrical, and dielectric properties of polycrystalline Dy0.4Sm0.6FeO3 orthoferrite prepared via the sol–gel method, and sintered at 800°C, 1000°C, and 1200°C. Rietveld refinement of XRD confirmed that the samples sintered at 800°C and 1000°C exhibit a single phase, whereas the sample sintered at 1200°C shows a small amount of Dy3Fe5O12 impurity. Room temperature Raman spectra confirmed the active vibrational modes of Dy0.4Sm0.6FeO3 and the impurity phase. FESEM images illustrate an increase in grain size with increasing sintering temperature and sintering at 1000°C shows less porosity. P-E loop data reveal the deficient ferroelectric and leaky nature of the samples. The dielectric constant and dielectric loss increase with increasing sintering temperature, and the dielectric relaxation phenomena is shifted to the high temperature side with increasing sintering temperature. The dielectric loss and activation energy are lower for the sample sintered at 1000°C compared to the other samples. The findings of this paper establish that the sample sintered at 1000°C, Dy0.4Sm0.6FeO3 , optimizes the structural, electrical, and dielectric properties. Dy0.4Sm0.6FeO3 sample prepared through the sol–gel method and sintered at 800°C, 1000°C, and 1200°C, investigated for their structural, electrical, and dielectric properties. DSFO samples sintered at 800°C and 1000°C exhibit a single phase without any impurity. [ABSTRACT FROM AUTHOR]

This article investigates the behavior of thermoelastic damping in a micro/nano beam subjected to an external magnetic field and an elastic matrix via small-scale theory. The material properties of the beam, such as Young's modulus, thermal conductivity, specific heat capacity, and coefficient of thermal expansion, are considered to analyze the physical aspects of thermoelastic damping. Further, the critical magnetic field strength of the nanobeam, which affects magnetic properties, is studied in relation to temperature, magnetic material properties, modenumber, and boundary conditions, leading to important findings for magnetomechanical systems and materials design. [ABSTRACT FROM AUTHOR]

This primary goal of this analysis is to investigate how several slips affect the flow, heat, and mass performance of Darcy–Forchheimer unstable behavior beyond a stretching sheet using a numerical analysis of the Soret effect. The novel constitutive model Cattaneo–Christov is illustrated to analyze the features of thermal relaxation time. The Cattaneo–Christov method is used to predict heat and mass transport. A surface that slanders and has varying thicknesses propels the flow. Through the use of local similarity transformations, the governing nonlinear partial differential equations reduce to the coupled ordinary differential equations and include the momentum, energy, and concentration equations. The altered ODEs are calculated numerically using the Runge–Kutta Fehlberg scheme and an efficient shooting procedure. The physical properties of the temperature, concentration, and fluid velocity profiles are shown visually and shed light on the change of several governing parameters. For example, in comparison to the classical Fourier's heat model, our result suggests that the Cattaneo–Christov heat flux constitution has lower temperature and thermal boundary layer thickness. In the meantime, a high wall thickness parameter greatly upgrades the rate of heat transfer, and thermal relaxation has the opposite effect. Discussion is held regarding the effects of various miscellaneous variables on temperature, concentration, and velocity. [ABSTRACT FROM AUTHOR]

Porous materials have been extensively used in electronic communications, aerospace, bio-medicine and petrochemical, etc. due to their attractive attributes such as low relative density, thermal and acoustical insulation and good permeability. Ultrashort laser pulses have a series of unique advantages including high energy density, ultrashort interaction time and high accuracy, which are widely used in the fields of precision machining and microelectronic manufacture. For porous materials heated by an ultrashort laser pulse, revealing the interplay between deformation field and temperature field is crucial to guide their engineering application and optimization design. The present work devotes to investigating the transient response of a porous half-space heated by a non-Gaussian laser beam on its boundary surface based on the newly established linear thermoelastic theory with strain and thermal relaxations. The coupled governing equations are formulated and solved through the Laplace transform and its numerical inversion. The distributions of the non-dimensional temperature, displacement, stress as well as volume fraction field are obtained and illustrated graphically. In calculation, the effects of the thermal relaxation factor, the strain relaxation factor on the temperature field, volume fraction field, displacement field as well as stress field are examined and discussed in detail. [ABSTRACT FROM AUTHOR]

The photoexcitation dynamics of N3−‐bound ferric myoglobin (MbN3) were investigated after exciting MbN3 in D2O at 283 K with a 575 nm pulse by probing the anti‐symmetric stretching mode of the azide. Global fitting of the overall time‐resolved spectra revealed that thermal relaxation of two stretching bands proceeded with a time constant of 6 ps, and that a new absorption band formed and decayed with time constants of 0.6 and 23 ps, respectively. The new absorption near 2040 cm−1 was attributed to the high‐spin species 2.4 kJ/mol above the low‐spin species, as the excited low‐spin relaxes thermally via the high‐spin species. However, this absorption could also arise from deligated N3̄ remaining within the protein. The decay of this absorption can be interpreted as either spin transition of the high‐spin species into the low‐spin species or geminate recombination of the dissociated N3̄. The implications of both interpretations are discussed. [ABSTRACT FROM AUTHOR]

Significance: In the photoacoustic (PA) technique, the laser irradiation in the time domain (i.e., laser pulse duration) governs the characteristics of PA imaging--it plays a crucial role in the optical-acoustic interaction, the generation of PA signals, and the PA imaging performance. Aim: We aim to provide a comprehensive analysis of the impact of laser pulse duration on various aspects of PA imaging, encompassing the signal-to-noise ratio, the spatial resolution of PA imaging, the acoustic frequency spectrum of the acoustic wave, the initiation of specific physical phenomena, and the photothermal-PA (PT-PA) interaction/conversion. Approach: By surveying and reviewing the state-of-the-art investigations, we discuss the effects of laser pulse duration on the generation of PA signals in the context of biomedical PA imaging with respect to the aforementioned aspects. Results: First, we discuss the impact of laser pulse duration on the PA signal amplitude and its correlation with the lateral resolution of PA imaging. Subsequently, the relationship between the axial resolution of PA imaging and the laser pulse duration is analyzed with consideration of the acoustic frequency spectrum. Furthermore, we examine the manipulation of the pulse duration to trigger physical phenomena and its relevant applications. In addition, we elaborate on the tuning of the pulse duration to manipulate the conversion process and ratio from the PT to PA effect. Conclusions: We contribute to the understanding of the physical mechanisms governing pulse-width-dependent PA techniques. By gaining insight into the mechanism behind the influence of the laser pulse, we can trigger the pulse-with-dependent physical phenomena for specific PA applications, enhance PA imaging performance in biomedical imaging scenarios, and modulate PT-PA conversion by tuning the pulse duration precisely. [ABSTRACT FROM AUTHOR]

The phosphate‐coordination triple helicates A2L3 (A=anion) with azobenzene‐spaced bis‐bis(urea) ligands (L) have proven to undergo a rare in situ photoisomerization (without disassembly of the structure) rather than the typically known, stepwise "disassembly‐isomerization‐reassembly" process. This is enabled by the structural self‐adaptability of the "aniono" assembly arising from multiple relatively weak and flexible hydrogen bonds between the phosphate anion and bis(urea) units. Notably, the Z→E thermal relaxation rate of the isomerized azobenzene unit is significantly decreased (up to 20‐fold) for the triple helicates compared to the free ligands. Moreover, the binding of chiral guest cations inside the cavity of the Z‐isomerized triple helicate can induce optically pure diastereomers, thus demonstrating a new strategy for making light‐activated chiroptical materials. [ABSTRACT FROM AUTHOR]

The phosphate‐coordination triple helicates A2L3 (A=anion) with azobenzene‐spaced bis‐bis(urea) ligands (L) have proven to undergo a rare in situ photoisomerization (without disassembly of the structure) rather than the typically known, stepwise "disassembly‐isomerization‐reassembly" process. This is enabled by the structural self‐adaptability of the "aniono" assembly arising from multiple relatively weak and flexible hydrogen bonds between the phosphate anion and bis(urea) units. Notably, the Z→E thermal relaxation rate of the isomerized azobenzene unit is significantly decreased (up to 20‐fold) for the triple helicates compared to the free ligands. Moreover, the binding of chiral guest cations inside the cavity of the Z‐isomerized triple helicate can induce optically pure diastereomers, thus demonstrating a new strategy for making light‐activated chiroptical materials. [ABSTRACT FROM AUTHOR]

A theoretical exploration is presented for the obtaining a transfer matrix and using this technique with stiffness matrix for obtaining a solution for dispersion curves in heat conducting n–layered isotropic in the context of generalized theory of thermoelasticity This paper discusses transfer matrix technique and obtained stiffness matrix for heat conducting isotropic layered in generalized thermoelasticity with thermal relaxation. Some special cases have also been deduced and discussed from the obtained result. [ABSTRACT FROM AUTHOR]

The theory of wave propagation in non-isothermal porous rocks has been introduced in geophysics in recent years by combining the single-phase-lag (SPL) Lord-Shulman (LS) model of heat conduction with Biot's poroelasticity theory. However, the theory of SPL thermoporoelasticity is inadequate in describing the lagging behavior of thermal relaxation for wave dissipation due to fluid and heat flow effects. We address this problem by incorporating a dual-phase-lags (DPL) model of heat conduction into thermoporoelasticity, utilizing analytical solutions and numerical simulations. The DPL model involves two lagging times: the (macroscopic) heat-flux lagging time τq from the LS model and an additionally introduced lagging time τT of temperature gradient that characterizes the fluid phase. A plane-wave analysis predicts four propagation waves, namely, fast P, slow P, thermal (T), and shear (S). We calculate wavefield snapshots by using a finite-difference solver for the DPL thermoelastic equations and provide further insight into the physics of two lagging times for porous rocks. The simulations show that the DPL model induces higher thermal attenuation and larger velocity dispersion compared to the SPL model, especially at high frequencies. The influence of fluids is crucial for wave propagation within thermoporoelastic media. [ABSTRACT FROM AUTHOR]

Establishing the relationship between molecular structures and mechanical properties is of great significance for the structural design of vulcanised styrene-butadiene rubber (SBR). The molecular dynamics method was used to study the mechanical properties of cross-linked SBR with controlled network topology, and the corresponding molecular mechanism was analysed by the energy contribution during the stretching process. The results showed that the tensile stress of the end-linked network sample could be up to 20 times higher than that of the sample with dangling chains at an engineering strain of 1.4. Moreover, under the same fixed cross-linking degree, the tensile stress of the long-chain network sample was significantly higher than that of the short-chain network sample. This is because the molecular chains located in the main chain network will be highly oriented during the stretching process, while the proportion of highly oriented molecular chains is high in samples with end-linked networks or a large proportion of long chains. In addition, due to the limited relaxation of structural units, the end-linked network structure has good thermal stability. [ABSTRACT FROM AUTHOR]

With the extensive applications of the micro/nano-electro-mechanical systems, a great deal of attention has been paid to explore the influences of the arising size-dependent effect and surface effect on their performance. Along with these effects, the nonlocal elasticity, strain gradient theory, and surface elasticity theory were successively proposed. Moreover, it is inevitable for MEMS/NEMS to work in a variable temperature environment, correspondingly, the thermal-induced stress or deformation becomes another issue that needs serious concern. Thermoelastic damping (TED), as a main energy dissipation source, is a major challenge in designing higher-quality factor resonators. However, considering the thermoelastic coupling effect, the aforementioned theories are not capable enough to depict the thermoelastic performance of micro/nano-resonators. To amend this deficiency, based on nonlocal strain gradient theory, a new model for assessing the TED of nanobeam resonators by incorporating the thermal relaxation effect and the surface effect is developed. The corresponding governing equations for the Euler–Bernoulli microbeam resonator model are formulated, and then, solved by means of a complex frequency method. The influences of the nonlocal parameter, strain gradient coefficients, aspect ratio, surface stress and surface elasticity on the TED are examined and discussed in detail. [ABSTRACT FROM AUTHOR]

An interesting feature that appears in the thermoelastic interaction in an orthotropic material containing cylindrical cavities is addressed in this study. For this purpose, the Finite Element Method is applied to analyze a generalized thermoelasticity theory with a relaxation time. For the development of the model, a thermal conductivity that is dependent on the temperature of the orthotropic medium was considered. The boundary condition for the internal surface of a cylindrical hollow is defined by the thermal shocks and the traction on the free surface. The nonlinear formulations of thermoelastic based on thermal relaxation time in orthotropic mediums are abbreviated using the Finite Element Method. The nonlinear equations without Kirchhoff's transformations are presented. The results are graphically represented to demonstrate how changing thermal conductivity affects all physical values. [ABSTRACT FROM AUTHOR]

In this work, the finite element technique is employed to evaluate the effects of thermal relaxation durations on temperature, displacements, and stresses in a two-dimensional, polymeric, orthotropic, elastic medium. The problem is considered in a homogeneous, polymeric, orthotropic medium in the context of the Green and Lindsay model with two thermal relaxation times. The bounding surface of the half-space was subjected to a heat flux with an exponentially decaying pulse. Finite element techniques were used to solve the governing formulations, with eight-node isoparametric rectangular elements with three degrees of freedom (DOF) per node. The developed method was calculated using numerical results applied to the polymeric, orthotropic medium. The findings were implemented and visually shown. Finally, the results were displayed to demonstrate the differences between classical dynamic coupling (CT), the Lord–Shulman (LS) and the Green and Lindsay (GL) models. [ABSTRACT FROM AUTHOR]

Understanding the thermal relaxation dynamics of photoswitches is of crucial importance when considering application scenarios. Strategies for regulating the thermal relaxation rates of photoswitches have been mostly limited to modifying the chemical structures. Herein we demonstrate a complementary method of manipulating the thermal relaxation rate of indigo‐based photoswitches that does not require chemical modification. We used indigo‐based photoswitches in aprotic solvents as a model system to demonstrate this strategy. Our method creates a deactivated pathway that extends the thermal relaxation half‐life by selectively stabilizing the parent structure of the metastable Z‐isomer via non‐covalent interaction. In addition, by establishing a quantitative kinetic model, we showed that controlling the strength of such selective stabilization enables fine‐tuning of the thermal relaxation rates to precisely access to targeted values. [ABSTRACT FROM AUTHOR]

A model of thermal relaxation in the flow of a hot vapor–gas mixture and cold water drops is presented. The cooling of vapor and gas during heating and evaporation of droplets was numerically simulated. Approximation expressions are obtained for the cooling time of vapor and gas in a given temperature range depending on the initial droplet radius, the weight fraction of droplets, and the initial composition of the vapor–gas mixture. [ABSTRACT FROM AUTHOR]

We report anomalous heating in a colloidal system, an experimental observation of the inverse Mpemba effect, where for two initial temperatures lower than the temperature of the thermal bath, the colder of the two systems heats up faster when coupled to the same thermal bath. For an overdamped, Brownian colloidal particle moving in a tilted double-well potential, we find a nonmonotonic dependence of the heating times on the initial temperature of the system. Entropic effects make the inverse Mpemba effect generically weaker--harder to observe--than the usual Mpemba effect (anomalous cooling). We also observe a strong version of anomalous heating, where a cold system heats up exponentially faster than systems prepared under slightly different conditions. [ABSTRACT FROM AUTHOR]

Deep cold rolling (DCR) is a promising mechanical surface treatment which can be effectively used to improve the fatigue life of components by introducing deep and high beneficial compressive residual stresses on the surface and sub-surface layers. However, the application of conventional DCR on thin-walled geometries such as compressor blades can be very challenging as the applied load can damage the component. Double-sided deep rolling on thin-walled components has been proven to be a viable alternative solution as both sides of the component are treated simultaneously which thus decreases the risk of component distortion. In this study, a high-fidelity non-linear finite element model has been developed to simulate the double-sided DCR process on thin Ti-6Al-4V plate and to predict the residual stress profile introduced by the process and after thermal relaxation due to subsequent exposure to high temperature. The accuracy of the developed finite element model is validated by comparison with the experimental measurement available in the literature. Response surface method (RSM) has then been carried out on results obtained by the high-fidelity FE model to develop predictive analytical models to approximate residual stress profiles induced by the process. The developed analytical models can efficiently replace FE models to perform sensitivity analysis and design optimization of process parameters. Load distribution at high stress areas of a generic compressor blade is considered to formulate a design optimization problem of double-sided DCR process in order to achieve optimal residual stress distributions at room temperature and after thermal relaxation at elevated temperature of 450 °C. [ABSTRACT FROM AUTHOR]

Piezoelectric materials have become one of the most promising candidates for a new class of smart structures which are widely used as sensors and actuators in control systems due to their superior electromechanical performance and high‐efficiency in electro‐mechanical energy conversion. In recent years, although there are many papers of theoretical modeling of generalized piezoelectric thermoelasticity that considered the piezoelectric‐thermoelastic coupling of piezoelectric structures serving in the extreme fast heating environment (e.g. ultra‐fast laser), the strain relaxation effect has not been considered yet. This work aims to investigate the generalized piezoelectricity problem with strain rate with the aid of extended thermodynamic principles, and corresponding generalized variational theorem is also strictly formulated to provide a complete rationale for numerical method by using semi‐inverse method. For numerical evaluation, transient thermo‐electromechanical responses of a one‐dimensional semi‐infinite piezoelectric medium with one end subjecting to a sudden thermal loading are considered and solved by applying Laplace transformation methods. Then the transient responses of temperature, displacement, strain, stress and electric potential are obtained and illustrated graphically, and the influences of strain relaxation parameters on them are also analyzed and discussed. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Materials Engineering / Cailiao Gongcheng is the property of Journal of Materials Engineering Editorial Office 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 Scientia et Technica is the property of Scientia et Technica 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.)

In this paper, we study the thermal relaxation features of compressive residual stresses generated during laser-shock wave processing in high-alloyed heat-resistant Iron GH2036 alloy. A finite element modeling of thermal relaxation of the generated compressive residual stresses was performed. The features of the thermal effects on the redistribution of the compressive residual stresses in the temperature range from 200 to 650°C are studied. Based on comparative analysis, the results of the finite element modeling correlated well with the experimental data known in the literature. [ABSTRACT FROM AUTHOR]

The energy barrier for cis-to-trans isomerization is among the key parameters for photoswitchable molecules such as azobenzene. Recently, we introduced a well-defined model system based on thin films of crystalline, nanoporous metal-organic frameworks, MOFs. The system enables the precise investigation of the thermal cis-to-trans relaxation of virtually isolated azobenzene pendant groups by means of infrared spectroscopy in vacuum. Here, this approach is extended by using localized surface plasmon resonance spectroscopy. This simple and relatively inexpensive setup enables the investigation of the thermal cis-to-trans isomerization in different environments, here in argon gas or in liquid butanediol. The energy barrier for the cis-to-trans-relaxation in argon, 1.17±0.20eV, is identical to the barrier in vacuum, while the energy barrier in liquid butanediol is slightly larger, 1.26±0.15eV. [ABSTRACT FROM AUTHOR]

In the present study, a finite element model has been developed to simulate the deep-cold rolling process on Ti-6Al-4V specimens and the following short term exposure of the treated components to elevated temperature. The developed model can be effectively used to predict the residual stress profiles induced by the process at room temperature and the following residual stress relaxation at the elevated temperature. In the present study, the thermal relaxation stage is performed using a viscoplastic model which couples the creep and plasticity deformation mechanisms to predict the state of residual stresses at the elevated temperature. For this purpose, a new set of hyperbolic creep law coefficients are identified in order to describe the primary creep at 450 °C. The accuracy of the developed finite element model to predict residual stresses is validated by comparison with the experimental data available in the literature. It has been shown that the finite element predictions correlate well with experimental results with error generally less than 10%. The developed model can be effectively utilized for parametric studies to understand the effect of different process parameters on the induced residual stresses without performing expensive experimental tests. [ABSTRACT FROM AUTHOR]

A phenomenon of reection of plane waves from a thermally insulated surface of a solid half-space is studied in context of Lord-Shulman theory of generalized thermo-viscoelasti-city with voids. The governing equations of generalized thermo-viscoelastic medium with voids are specialized in x-z plane. The plane wave solution of these equations shows the existence of three coupled longitudinal waves and a shear vertical wave in a generalized thermo-viscoelastic medium with voids. For incident plane wave (longitudinal or shear), three coupled longitudinal waves and a shear vertical wave reect back in the medium. The mechanical boundary conditions at free surface of solid half-space are considered as impedance boundary conditions, in which the shear force tractions are assumed to vary linearly with the tangential displacement components multiplied by the frequency. The impedance corresponds to the constant of proportionality. The appropriate potentials of incident and reected waves in the half-space will satisfy the required impedance boundary conditions. A non-homogeneous system of four equations in the amplitude ratios of reected waves is obtained. These amplitude ratios are functions of material parameters, impedance parameter, angle of incidence, thermal relaxation and speeds of plane waves. Using relevant material parameters for medium, the amplitude ratios are computed numerically and plotted against certain ranges of impedance parameter and the angle of incidence. [ABSTRACT FROM AUTHOR]

We study thermal relaxation in a neutron star after internal heating events (outbursts) in the crust. We consider thin and thick spherically symmetric heaters, superfluid and non-superfluid crusts, stars with open and forbidden direct Urca processes in their cores. In particular, we analyze long-term thermal relaxation after deep crustal heating produced by nuclear transformations in fully or partly accreted crusts of transiently accreting neutron stars. This long-term relaxation has a typical relaxation time and an overall finite duration time for the crust to thermally equilibrate with the core. Neutron superfluidity in the inner crust greatly affects the relaxation if the heater is located in the inner crust. It shortens and unifies the time of emergence of thermal wave from the heater to the surface. This is important for the interpretation of observed outbursts of magnetars and transiently accreting neutron stars in quasi-persistent low-mass X-ray binaries. [ABSTRACT FROM AUTHOR]

Creation of a compressive residual stress in specimen that are exposed to fatigue induced failure, is considered to be a beneficial solution in order to neutralize all or some parts of the external force. Using components with this residual field stresses in high temperature applications can lead to reduction and termination of residual stress field and the effectiveness of this residual stress fields in high temperature is always questioned. So this paper aimed to simulate and study residual stress field made by multiple laser shot peening which is a novel method to create in depth residual stress. Thermal relaxation of this residual stress field due to working conditions was also investigated by FEM simulation in ABAQUS. Ti-6Al-4V was the employed material and since high strain rates were involved in dynamic loading process of simulation, Johnson-Cook material model was used to count for nonlinear material behavior. Results showed that created residual stress field from this method is much deeper than similar conventional shot peening process and by using multiple laser shot peening on the same spot, it is possible to achieve 640 MPa in one loading cycle, 834 MPa in two cycle loading and 889 MPa in three cycle loading. By applying 600 ℃ on specimen, it was observed that for each of single shot, double shot and triple shot specimens, a surface residual stress relaxation of 28.13%, 41.37% and 43.87% occurred, respectively. [ABSTRACT FROM AUTHOR]

The replica-exchange molecular dynamics (REMD) method has been used for conformational sampling of various biomolecular systems. To maximize sampling efficiency, some adjustable parameters must be optimized. Although it is agreed that shorter intervals between the replica-exchange attempts enhance traversals in the temperature space, details regarding the artifacts caused by these short intervals are controversial. In this study, we revisit this problem by performing REMD simulations on an alanine octapeptide in an implicit solvent. Fifty different sets of conditions, which are a combination of five replica-exchange periods, five different numbers of replicas, and two thermostat coupling time constants, were investigated. As a result, although short replica-exchange intervals enhanced the traversals in the temperature space, they led to artifacts in the ensemble average of the temperature, potential energy, and helix content. With extremely short replica-exchange intervals, i.e., attempted at every time step, the ensemble average of the temperature deviated from the thermostat temperature by ca. 7 K. Differences in the ensembles were observed even for larger replica-exchange intervals (between 100 and 1,000 steps). In addition, the shorter thermostat coupling time constant reduced the artifacts found when short replica-exchange intervals were used, implying that these artifacts are caused by insufficient thermal relaxation between the replica-exchange events. Our results will be useful to reduce the artifacts found in REMD simulations by adjusting some key parameters. [ABSTRACT FROM AUTHOR]

We have employed noise thermometry for investigations of thermal relaxation between the electrons and the substrate in nanowires patterned from 40-nm-thick titanium film on top of silicon wafers covered by a native oxide. By controlling the electronic temperature $$T_\mathrm{e}$$ by Joule heating at the base temperature of a dilution refrigerator, we probe the electron-phonon coupling and the thermal boundary resistance at temperatures $$T_\mathrm{e}= 0.5$$ -3 K. Using a regular $$T^5$$ -dependent electron-phonon coupling of clean metals and a $$T^4$$ -dependent interfacial heat flow, we deduce a small contribution for the direct energy transfer from the titanium electrons to the substrate phonons due to inelastic electron-boundary scattering. [ABSTRACT FROM AUTHOR]

Nickel-based alloys are widely employed in the manufacturing of aero-engines. These alloys are difficult to machine, and tensile residual stresses are generated during machining. These tensile residual stresses can negatively affect the performance of aero-engine components. Nevertheless, residual stresses can vary due to thermal or mechanical loading. These variations must be considered to evaluate the real influence of residual stresses on component behavior. This paper studies the effect of thermal loads on machining-induced residual stresses in the alloy Inconel 718. A ring-shaped Inconel 718 part was face-turned, and specimens were extracted from it. Specimens were exposed at 550 and 650 °C for 10 min, 1 and 10 h. Residual stresses were measured, and microstructure was observed before and after thermal exposure. Residual stress variations found after thermal exposure were the consequence of two factors: relaxation of strain bands during the early stage of exposure and diffusion-controlled creep. In addition, a modified Zener-Wert-Avrami model is proposed to predict residual stress relaxation caused by the diffusion-controlled creep. Once having fitted the modified Zener-Wert-Avrami model, the study was extended for a wider range of temperatures (400-650 °C). This analysis showed that surface residual stresses do not relax significantly at temperatures below 500 °C. [ABSTRACT FROM AUTHOR]

As is well known, the metallurgical microstructure of carbon steel is formed by ferrite and pearlite after the annealing heat treatment. When the cooling rate increases, the diffusive process is interrupted causing a change in the metallurgical microstructure which will affect steel properties. The aim of this work was to study thermal, structural, and microstructural properties of annealed carbon steel samples with four different carbon contents. Crystalline structure and crystalline quality were studied by the X-ray diffraction technique, where the full width at half maximum analysis showed that as the carbon content increased, the crystalline quality decreased. The metallurgical microstructure morphology was studied by scanning electron microscopy. The thermal diffusivity and the heat capacity were determined by the photoacoustic technique and by the thermal relaxation method, respectively. The thermal diffusivity and the thermal conductivity decreased as the carbon content increased. The amplitude signal of photothermal radiometry increased as the carbon content increased, while the phase signal of photothermal radiometry did not show significant differences among studied carbon steel types. The photoacoustic technique represents an important alternative in the steel characterization field. [ABSTRACT FROM AUTHOR]

The dynamic response of a piezoelectric-thermoelastic rod made of piezoelectric ceramics (PZT-4) subjected to a moving heat source is dealt with in the context of the fractional order theory of thermoelasticity. The piezoelectric-thermoelastic governing equations for the problem are formulated and then solved by means of Laplace transform together with its numerical inversion. The distributions of the considered nondimensional temperature, displacement, stress, and electric potential are obtained and illustrated graphically. The effects of fractional order parameter and the velocity of heat source on the variations of the considered variables are investigated, and the results show that they have significant influence on the variations of the considered variables. The present investigation could be helpful for better understanding the multi-field coupling effect of mechanical, electric, and thermal fields in real piezoelectric ceramics structures, and provide some guidelines in the optimal design of actuators or sensors made of piezoelectric ceramics serving in a thermoelastic environment. [ABSTRACT FROM PUBLISHER]

Comparative investigations are reported on poly(N-isopropylacrylamide) (PNIPA) gels of various carbon nanotube (CNT) and graphene oxide (GO) contents synthesized under identical conditions. The kind and concentration of the incorporated carbon nanoparticles (CNPs) influence the swelling and stress-strain behaviour of the composites. Practically independently of the filler content, incorporation of CNPs appreciably improves the fracture stress properties of the gels. The time constant and the swelling ratio of the shrinkage following an abrupt increase in temperature of the swelling medium from 20 to 50 °C can be adjusted by selecting both the type and the amount of nanoparticle loading. This offers a means of accurately controlling the deswelling kinetics of drug release with PNIPA systems, and could be employed in sensor applications where fast and excessive shrinkage are a significant drawback. Both CNTs and GO enhance the infrared sensitivity of the PNIPA gel, thus opening a route for the design of novel drug transport and actuator systems. It is proposed that the influence of the CNPs depends more on their surface reactivity during the gel synthesis rather than on their morphology. One of the important findings of this study is the existence of a thermally conducting network in the GO filled gels. [ABSTRACT FROM AUTHOR]

Femtosecond transient IR absorption spectroscopy was used to probe the decay mechanism of electronically excited thymine (a naturally occurring pyrimidine base in DNA) dissolved in an ionic liquid ([Bmim][ BF4 ]) or CD3CN after the absorption of UV light (267 nm). In both solvents, an absorption band grew on a picosecond timescale, along with decaying bleach and evolving red-shifted absorption signals. A population analysis of the observed kinetic data suggested that most of the photoexcited thymine underwent a sub-picosecond non-radiative relaxation to the vibrationally hot ground electronic state. About 4% (16%) of the excited thymine in the ionic liquid ( CD3CN) relaxed to an intermediate electronic state, which relaxed into a low-lying triplet state by intersystem crossing ( ISC) ( ISC did not relax to the ground electronic state within the experimental period (1 ns)). The low ISC yield for thymine in an ionic liquid was correlated with molecular properties of the solvent. This observation is significant because the ISC to triplet state transition for excited thymine has been considered as a precursor to cyclobutane-pyrimidine dimer formation, which led to functional damage of the base after UV absorption. This finding may shed light on the photostability of DNA in ionic liquids. [ABSTRACT FROM AUTHOR]

A mathematical theory has been developed for boundary-value problems of nonstationary heat conduction with a dual-phase lag. Features of analytical solutions of such heat problems are described. On the basis of the integral transformations proposed, an exact analytical solution of the practically important third boundary-value problem on the indicated heat conduction in the general formulation (plate, cylinder, sphere) has been obtained in the form of new functional constructions. [ABSTRACT FROM AUTHOR]

Experimental transient processes are compared with theoretical processes described by unsteady boundary value problems of the third kind with parabolic and hyperbolic heat conduction equations of a solid. Physical meaning of transfer rate is specified in the thermal relaxation formula. Thermal relaxation time of the solid is measured. [ABSTRACT FROM AUTHOR]

This paper presents studies on the role of Ge-doping concentration (6 to 18 mol. %) in the refractive index rollover fluence and thermal annealing characteristics of type IIa fiber Bragg gratings (FBGs). A 255 nm UV beam of low-pulse energy density (~2.2 mJ/cm²), nanosecond (~30 ns) duration, and high-repetition rate (~5.5 kHz) was used for FBG inscription. It is observed that the UV fluence needed for refractive index rollover was higher for fiber having low Ge-doping (~6 mol:%). The temperature sustainability of these gratings has been studied in a multistep thermal annealing process up to 800°C. It was observed that the higher the total UV fluence required for refractive index rollover, the higher the temperature sustainability of a type IIa grating. The temperature rise of the fiber for a single UV pulse and at the maximum cumulative UV fluence was estimated for different Ge-doping concentrations. The thermal stability of the grating is linked to the amount of Ge-doping concentration of the fiber. These observations may be due to the fact that a high cumulative fluence resulted in a larger stress relaxation, leading to enhanced FBG temperature stability. [ABSTRACT FROM AUTHOR]

An integrated experimental and modeling/simulation approach was developed to investigate and secure a quantified knowledge of the impact of high temperature exposures on the stability of residual stresses in a laser shock peened (LSP) high temperature aero-engine alloy, IN718 SPF (super-plastically formed). Single dimple LSP and overlap LSP treatments were carried out utilizing a Nd:Glass laser ( λ = 1.052 μm), and subsequent heat treatments on the LSP-treated coupons were conducted at different temperatures between 550 and 700 °C. A 3-D nonlinear finite element (FE) computational model and the rate-dependent Johnson-Cook material model were calibrated using the experimental results of residual stress from the single dimple LSP and thermal relaxation treatments, and were further extended to the overlap LSP treatment case. Both experimental and FE simulations show that: a) a high level of compressive residual stress (~700 MPa at surface) and residual stress depth (~0.4-0.6 mm) were achieved following LSP, and b) the overlap LSP treatment gave higher residual stress and greater depth. The magnitudes of the initial residual stress (and plastic strain), heating temperature and exposure time were identified as the key parameters controlling the thermal relaxation behavior. The stress relaxation mainly occurs initially before 20 min exposure and the extent of relaxation increases with an increase in temperature and a higher magnitude of the initial as-peened residual stress. In addition, in regions deeper than ~300 μm or after initial thermal exposure where the residual stress was lower than ~300 MPa, stress relaxation was found to be negligible. Kinetic analysis of the experimental thermal relaxation data based on Zener-Wert-Avrami model gave an activation enthalpy of 2.87 to 3.77 eV, which is near that reported in the literatures for volume and/or substitutional solute diffusion in Nickel. These results suggest that thermal relaxation of the LSP-induced residual stress occurs by a creep-like mechanism involving recovery, rearrangement and annihilation of dislocations by climb. [ABSTRACT FROM AUTHOR]

We study the relaxation properties of the quantized electromagnetic field in a cavity under repeated interactions with single two-level atoms, so-called one-atom maser. We improve the ergodic results obtained in Bruneau and Pillet (J Stat Phys 134(5-6):1071-1095, ) and prove that, whenever the atoms are initially distributed according to the canonical ensemble at temperature $$T>0$$ , all the invariant states are mixing. Under some non-resonance condition this invariant state is known to be thermal equilibirum at some renormalized temperature $$T^*$$ and we prove that the mixing is then arbitrarily slow, in other words that there is no lower bound on the relaxation speed. [ABSTRACT FROM AUTHOR]

A statistical analysis is presented to investigate the influence of temperature, rotation, viscosity and thermal relaxation time on the propagation characteristics of different waves in an elastic medium. The solution of complex secular equation governing the characteristics of the bulk waves in an infinite homogenous isotropic, Kelvin-Voigt type generalized viscothermoelastic rotating media is carried out by employing both direct and perturbation methods. The analytical developments are supported with numerical illustrations for copper material in respect of phase velocities, attenuation coefficients and specific loss factor of various possible waves. The computer simulated results have been presented graphically with respect to Kibel number. In order to explore and analyze the effects of viscosity and temperature on the elastic waves, the Karl-Pearson correlation coefficient has been used. The student t-test is used to judge and decide the suitability of Cardano’s method vis-à-vis perturbation one for computing different characteristics. The present study may be useful in geophysics and gyroscopic sensor applications and industry. [ABSTRACT FROM PUBLISHER]

The residual stress relaxation of the shot peened layer on the SiCw/Al composite during isothermal annealing was investigated. The results showed that the residual stresses relaxed in the whole deformation layer especially when the annealing temperature was higher than 200 °C. The relaxation process during isothermal annealing could be described precisely using Zener-Wert-Avrami function. Because of high intensity dislocation around reinforcements producing a large amount of stored energy, the residual stress relaxation activation enthalpy of shot peened SiCw/Al was smaller than self-diffusion activation enthalpy of pure aluminum. According to the analysis of full-width at half-maximum (FWHM) of the shot peened composite in different annealing temperatures, it can be concluded the recovery and recrystallization behavior became intensely when anneal temperature was larger than 200 °C. The small relaxation of residual stress in low annealing temperature was mainly due to partly recovery and recrystallization in a very low level. [ABSTRACT FROM AUTHOR]

We report a new computational model to incorporate carrier heating/cooling effects for the finite-difference time-domain (FDTD) simulation of electromagnetic interactions with semiconductor media. The model is formulated to be computationally efficient enough to be applied to FDTD simulations of photonic devices of complex structural geometry. The model developed here is built on top of a previous multi-level multi-electron (MLME) model we presented and the new model is called MLME-dynamical temperature (MLMEDT) model. The key developments here include the following. 1) Intraband transition terms with electron and hole temperature parameters that vary with time and space are introduced. 2) Rate equations for the explicit update of carrier temperature are formulated. A computationally efficient method is used to evaluate these carrier temperature rate equations which circumvent iterative procedures as well as the need to dynamically compute the chemical potential by presolving the relational functions required using dimensionless fitting functions. The temporal update of these fitting functions only needs the total carrier number densities, which are already obtained in the MLME model computation. 3) The changes in the total carrier kinetic energy density and carrier number density due to all interband processes such as stimulated emission/absorption and intraband processes such as free carrier absorption are tracked to drive the carrier temperature rate equations. 4) The thermal relaxation of the electron and hole temperatures to the lattice temperature and the thermal relaxation between electrons and holes are also included. In order to validate the approach, simulations of thermalization of nonequilibrium carrier distributions and nonlinear gain and refractive index dynamics in semiconductor optical amplifiers (SOA) are presented. Quantitative agreement with nonlinear gain dynamics experiments of SOA directly verifies the accuracy of the current approach. Additionally, a 2-D simulation of a microdisk laser is presented to depict how FDTD can be used to visualize the spatial profile of carrier temperatures. The computational time of the MLMEDT model is found to be only ~10% more than that of the MLME model, thus showing high computational efficiency. [ABSTRACT FROM PUBLISHER]

Coupled thermoelasticity with thermal relaxation admits plane waves with exponential decay in their wake. Wave speeds depend on the coefficient of exponential decay, and calculations indicate that speeds approach standard limit values in thermal relaxation for large coefficients. They approach Fourier model values when it is small. Two examples of reflection at a half-space surface with no stress but thermal convection are considered. Formulas and calculations for speeds and decay coefficients for reflected waves, reflection angles, and change in surface temperature are presented. [ABSTRACT FROM AUTHOR]

The governing equations of flexural vibrations in a transversely isotropic thermoelastic beam are derived in closed form based on Euler-Bernoulli theory. The out-of- plane vibrations have been studied under different beam dimensions and boundary conditions. The analytical expressions for thermoelastic damping and frequency shift of vibrations are obtained. The damping and frequency shift of beam vibrations significantly depend on thermal relaxation time and surface conditions at resonance. The expressions for displacement and temperature fields in the beam resonator are obtained. Some numerical results with help of MATLAB software have been computed and presented graphically for silicon material beams. [ABSTRACT FROM AUTHOR]

In this paper, we proposed a model of generalized magneto-thermoelastic for orthotropic hollow cylinder whose surfaces are subjected to a thermal relaxation under the effect of rotation with one relaxation time. The system of fundamental equations is solved by using an implicit finite-difference scheme. A numerical method is used to calculate the temperature, displacement and the components of stresses with time and through the radial of the cylinder. Numerical results are given and illustrated graphically for each case considered. The results indicate that the effect of rotation, inhomogeneity and magnetic field are very pronounced. Comparison made with the results predicted by the theory of generalized magneto-thermoelasticity with one relaxation time in the absence of rotation. [ABSTRACT FROM AUTHOR]

Light-sensitive materials as azo-polymers have interesting applications in microelectronics, biology, or energy storage, due to their capacity to change their supramolecular ordering. Light-induced modifications result in i) changes in the azobenzene-groups dipole moment due to the trans-cis isomerization, ii) thermal backward cistrans relaxation, and iii) re-ordering of the polymer chain conformation. Conjugation of these phenomena leads to mass transport in the solid state, which is still not well understood. Changes in the surface properties of non-substituted and p-CF3,-CN,-NO2-substituted azophenoxy-polysiloxane films, before and after photo-excitation, were examined. Molecular simulations were performed to evaluate the dipole-moments of the trans and cis p-substituted azobenzene groups and provide a general vision of the spatial arrangement of polymer chains. The role of trans-cis back relaxation and that of the polymer matrix relaxation on the surface and bulk of the materials was discussed. Surface free energy determination of the non-substituted azophenoxy-polysiloxane suggested that the relaxation process is dominated by the thermal slow back-isomerization of the cis fraction and not by the motion of a glassy polymer matrix involving both the surface and bulk. A less clear situation was presented by the semi-crystalline polysiloxanes with electron-withdrawing groups substituted in the para-position. This was attributed mainly to the similar values of the dipole-moment of trans and cis azo-group, the former being slightly more dipolar than the latter. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

A new innovative method was developed to measure the thermal-relaxation by maintaining isothermal condition in a Differential Scanning Calorimetry (DSC). The DSC thermal-relaxation characteristics of gelatin and date flesh were found to be related with the structural- and mechanical-glass transition measured by conventional DSC linear-heating and thermal-mechanical analysis (i.e, Differential Thermal Mechanical Analysis, DMTA). Initial slope of the thermal relaxation curve (i.e., heat flow versus relaxation time) was determined and it was plotted as a function of relaxation temperature (i.e., isothermal condition). The initial slope-temperature graph showed three thermal relaxation characteristics: limited mobile, freely mobile and restricted mobile regions. The region 1 showed limited molecular mobility with increasing temperature, while region 2 showed free mobility with increasing temperature sensitivity. The intersection of the regions 1 and 2 was related to the structural-glass transition measured by conventional linear-heating in a DSC. The region 3 showed restricted mobility due to enhanced interactions of the phases at higher temperature. This region 3 was related to the entangled flow region measured by thermal-mechanical analysis in a DMTA. [ABSTRACT FROM AUTHOR]