Temperature Relaxation Research Articles

가스터빈 엔진 터빈 블레이드의 냉각성능 상사시험 평가 연구

In this study, a similarity test was designed to evaluate the cooling performance of the high-pressure turbine blades of a gas turbine engine, and a study was conducted to verify the similarity through analysis and experiments. The main similarity variables representing the cooling performance of the turbine blades were defined, and the similarity test conditions were derived from the engine conditions so that the similarity variables could satisfy the similarity. It was confirmed that the similarity was satisfied by performing a conjugated heat transfer analysis on the same test conditions, and the cooling performance of the turbine blades was experimentally evaluated by conducting a heat transfer experiment using an infrared thermal imaging camera under the same conditions. In conclusion, it was confirmed that the cooling performance of high-temperature components such as high-pressure turbine nozzles and blades operating at high temperatures in a relaxed pressure and temperature environment without simulating a high-pressure and high-temperature environment such as an engine can be evaluated through a similar test.

Upcycling of PET from recycled food packaging trays via vitrimers chemistry

Poly (ethylene terephthalate) (PET) recycling process is well established nowadays for PET bottles. On the other hand, recycling of PET from food trays (tPET) is still challenging because of its lower molecular weight and the possible presence of other polymers as a consequence of the use of multi-layered trays. In this work, end-of-life PET trays have been chemically modified through the melt reactive processing into a covalent associative network, in order to enhance its performance. In particular, upcycling of tPET was obtained by the reaction of diglycidyl ether of bisphenol A (DGEBA) in the presence of zinc acetylacetonate as a transesterification catalyst, to obtain a reversibly cross-linked material, i.e. a vitrimeric material, which retains recyclability while significantly enhancing mechanical properties of tPET. Indeed, rheological test demonstrated clear crosslinking of tPET vitrimers, with a high temperature relaxation explained by the exchange of covalent bonds. Dynamic mechanical analysis showed high thermomechanical resistance, while tensile test at room temperature demonstrated strong enhancement in tensile strength and elongation at break compared to tPET. The results reported in this paper opens to the upcycling of other low grades of PET, including textiles and other goods produced with previously recycled polymer, thus contributing to the establishment of a circular economy for PET, beyond bottles.

Maltol-Incorporated Acetylated Cassava Starch Films for Shelf-Life-Extension Packaging of Bakery Products.

Maltol is widely used as a flavor enhancer in baked goods and has an antimicrobial function. Maltol can also be incorporated into biopolymer films to produce active biodegradable packaging for bakery products. This research investigated the incorporation of 1-10% maltol into acetylated cassava starch films as functional packaging for shelf-life extension of butter cake. Films were determined for morphology, chemical interaction and packaging properties. Infrared absorption indicated H-bonding between starch and maltol, while plasticization effects decreased mechanical relaxation temperature. Microstructures showed enhanced smoothness at up to 3% maltol, while maltol crystallization occurred at higher concentrations, giving non-homogeneous matrices. Tensile strength and elongation at break reduced by 37% and 34%, respectively, with the addition of maltol up to 10%. Maltol concentration modified the hydrophilicity and molecular mobility of the matrices, impacting water vapor and oxygen permeability. Films incorporated with maltol were used as packaging for preservative-free butter cake and delayed visible mold growth at room temperature. Starch films with maltol at 1-5% delayed fungal growth by up to 2.7-times, while films containing 10% maltol inhibited mold growth by 6-times (up to 19 days of storage). Incorporating maltol into starch films produced bioactive materials, extending shelf-life while maintaining the aroma of bakery products.

Polyesters Incorporating Gallic Acid as Oxygen Scavenger in Biodegradable Packaging.

Biodegradable polyesters polybutylene succinate (PBS) and polybutylene adipate-co-terephthalate (PBAT) were blended with gallic acid (GA) via cast extrusion to produce oxygen scavenging polymers. The effects of polyesters and GA contents (5 to 15%) on polymer/package properties were investigated. Increasing GA formed non-homogeneous microstructures and surface roughness due to immiscibility. GA had favorable interaction with PBAT than PBS, giving more homogeneous microstructures, reduced mechanical relaxation temperature, and modified X-ray diffraction and crystalline morphology of PBAT polymers. Non-homogenous dispersion of GA reduced mechanical properties and increased water vapor and oxygen permeability by two and seven folds, respectively. Increasing amounts of GA and higher humidity enhanced oxygen absorption capacity, which also depended on the dispersion characteristics of GA in the matrices. PBAT gave higher oxygen absorption than PBS due to better dispersion and higher reactive surface area. GA blended with PBAT and PBS increased oxygen scavenging activity as sustainable active food packaging using functional biodegradable polymers.

Multispecies structure-preserving particle discretization of the Landau collision operator

This paper proposes a novel numerical integrator for modeling multispecies Coulomb collisions in kinetic plasmas. The proposed scheme provides an energy-, momentum-, and positivity-preserving particle discretization of the nonlinear Landau collision operator, extending the works of Carrillo et al. [J. Comput. Phys. 7, 100066 (2020)] and Hirvijoki [Plasma Phys. Controlled Fusion 63, 044003 (2021)]. The discrete-time conservation properties are analyzed both algebraically and numerically, and an efficient, graphics processing unit-parallelized implementation is validated against inhomogeneous temperature relaxation, isotropization, and thermalization examples. The results agree with analytical estimates, confirming the method capable of reproducing physics.

Analysis of variable mass diffusivity in Maxwell's fluid with Cattaneo-Christov and nonlinear stratification

This investigation consists of Maxwell's fluid which describes rate type non-Newtonian fluid in best; it has great applications in engineering, technology and industry. Linear stretching sheet generates the flow in fluid. Flow momentum is measured with MHD effect. When Fourier's and Fick's laws are incorporated relaxation time factor then known as Cattaneo-Christov model which are implemented for heat and mass transport. The features of heat source or sink and non-linear type thermal stratification are employed with variable thermal conductivity. The features of chemical reaction and non-linear type solutal stratification are analyzed along with variable mass diffusivity. By the usage of boundary layer phenomenality in this problem, non-linear PDEs are achieved. These equations are transmuted into non-linear and non-homogeneous differential equations ramified with ordinary derivatives after applying similarity transformations. The most exclusive homotopic analysis method is used to get the analytic solutions of nonlinear and non-dimensional governing equations. The significant results of progressive parameters are dominant in this investigation. The arising parameters are examined in detail and results are shown graphically. It is found out that with the increment of time relaxation factor velocity, temperature and concentration profiles reduce. It increases the viscoelastic impacts related to stress relaxation time which makes viscoelastic materials more durable.

Aliovalent Calcium Substitution: An Effective Way to Enhance the Magnetoelectric Coupling Properties of Multiferroic BiFeO3

Kinetics of magnetoelectric coupling in bismuth ferrite (BiFeO3) with the substitution of aliovalent calcium ion is investigated. The resulting structural, dielectric, magnetic, and magnetoelectric (ME) coupling properties are explained in terms of chemical pressure originating from the substituent ion. Substitution of calcium finds to reduce the oxygen vacancies. Two important substitution concentrations find to be critical in ferroelectric (FE) and ME coupling properties. At 10 at% calcium, highest remanent polarization is obtained and maximum ME coupling coefficient is observed at 20 at%, which suggests calcium concentration between 10% and 20% can be optimized to obtain good electrical and ME coupling properties of BiFeO3. Maximum ME coupling coefficient at calcium concentration 20 at% is close to numerical calculations reported in the literature. Magnetic properties are also favorably modified by the substitution; a coupled antiferromagnetic and weak ferromagnetic ordering is obtained. Also, a variation in blocking temperature and spin relaxation is observed with respect to the substituent ion concentration.

A dynamic hysteresis model for customized glass transition in amorphous polymer towards multiple shape memory effects

Coexistence of multiple and discrete segments as well as their distinctive hysteresis relaxations enables amorphous shape memory polymers (SMPs) exhibiting complex disordered dynamics, which is critical for the glass transition behavior to determine the shape memory effect (SME), but remained largely unexplored. In this study, a dynamic hysteresis model is proposed to explore the working principle and collective dynamics in discrete segments of amorphous SMPs, towards a dynamic connection between complex relaxation hysteresis and glass transition behavior, which can be applied for design and realization of multiple SMEs in the amorphous SMPs. In combination of free volume theory and Adam-Gibbs domain size model, a phase transition model is formulated to identify the working principle of dynamic relaxation hysteresis in the glass transition of amorphous SMP. Furthermore, constitutive relationships among relaxation time, strain, storage modulus, loss angle and temperature have been established to describe the dynamic connection between complex relaxation hysteresis and customized glass transition, which is then utilized to achieve multiple SMEs based on the extended Maxwell model. Finally, effectiveness of the proposed models is verified using experimental results of SMPs with multiple SMEs reported in literature.

The effect of stress-annealing on the mechanical and magnetic properties of several Fe-based metal-amorphous nano-composite soft magnetic alloys

Fe-based metal-amorphous nanocomposites (MANCs) are the subject of many contemporary studies for their unique tunable soft-magnetic properties. The alloys can exhibit some of the smallest losses and highest power storage capabilities of available materials used in electromagnetic inductors. Here, the magnetic and mechanical properties of Fe72.5Nb2Mo2Cu1Si15.5B7 at.%, Fe68.5Co5Ta3Cu1Si16.5B6 at.%, Fe68.5Co5Ta3Cu1Si16B6.5 at.%, and Fe73.5Ta3Cu1Si16B6.5 at.% melt-spun alloys were investigated in relation to their ability to be stress-annealed to tune permeability while simultaneously minimizing losses in tape-wound inductor cores. Mechanical and physical properties of the as-cast and processed ribbons including relaxation and crystallization temperatures and failure strains were measured using thermomechanical analysis (TMA), uniaxial tension, and bend tests to help inform the stress-annealing parameters. Magnetic properties were measured for the as-cast and stress-annealed materials in both wound-cores and flat ribbon strips. The alloys exhibited severe embrittlement during heating, thus creating significant challenges when tuning magnetic properties with an in-line stress-annealing (SA) process. However, when conditions were optimized, core losses as low as 1.14 W·kg−1 were obtained when cores were excited at 10 kHz to a maximum induction field of 0.1 T, which are among the lowest reported in the literature. Based on this preliminary effort, understanding of the stress state in amorphous precursor ribbons prior to SA could reveal the key to developing more robust in-line SA processes for brittle Fe-based MANCs.

Single-Ion Magnets with Giant Magnetic Anisotropy and Zero-Field Splitting.

The design of mononuclear molecular nanomagnets exhibiting a huge energy barrier to the reversal of magnetization have seen a surge of interest during the last few decades due to their potential technological applications. More specifically, single-ion magnets are peculiarly attractive by virtue of their rich quantum behavior and distinct fine structure. These are viable candidates for implementation as single-molecule high-density information storage devices and other applications in future quantum technologies. The present review presents the comprehensive state of the art in the topic of single-ion magnets possessing an eminent magnetization-reversal barrier, very slow magnetic relaxation and high blocking temperature. We turn our attention to the achievements in the synthesis of 3d and 4f single-ion magnets during the last two decades and discuss the observed magnetostructural properties underlying the anisotropy behavior and the ensuing remanence. Furthermore, we highlight the fundamental theoretical aspects to shed light on the complex behavior of these nanosized magnetic entities. In particular, we focus on key notions, such as zero-field splitting, anisotropy energy and quantum tunneling of the magnetization and their interdependence.

Temperature Dependent Dielectric Relaxation Studies of 2-Nitrotoluene-DMSO mixture using Time Domain Relectometry from 10MHz to 50GHz

The dielectric relaxation properties of 2-Nitrotoluene (2-NT) with DMSO for 11 different concentrations has been studied in the frequency range from 10 MHz to 50 GHz using time domain reflectometry (TDR) method. In this frequency range Dielectric relaxation spectra of 2-NT-DMSO mixtures shows Debye type behavior. The temperature dependent static dielectric constant and relaxation time have been determined from 20oC to 5oC. Effective Kirkwood correlation factor is calculated to determine the effect of strong directional forces such as microwaves on heterogeneous molecules under different temperatures. The excess permittivity and excess inverse excess relaxation time is found to be negative for 2-NT-DMSO system with weak molecular interactions. The activation enthalpy have been calculated to find the energy required to rotate the molecules

Relaxation and Amorphous Structure of Polymers Containing Rigid Fumarate Segments.

The physical properties of polymers are significantly affected by relaxation processes. Recently, we reported that poly(diethyl fumarate) (PDEF) shows two thermal anomalies on DSC measurement, despite the fact that it is a homopolymer. We attribute these two relaxations α relaxation and β relaxation, respectively. In this study, we investigate the two relaxations of fumarate-containing polymers by DSC, solid-state NMR, and X-ray scattering. The two relaxations are present even in a copolymer of diethyl fumarate and ethyl acrylate with fumarate segments of 30%. We used poly(methyl methacrylate) (PMMA) as a model polymer for comparison, since there are detailed investigations of its dynamics and physical properties. Solid-state NMR indicates that the very local relaxation of poly(fumarate)s is not significantly different from that of PMMA. The tensile test showed that PDEF is still brittle at above β relaxation temperature and below α relaxation temperature. It was revealed that a structural anisotropy appeared when PDEF was extended at around α relaxation temperature. We discuss the effect of the glassy packing of the rigid polymer chain including the DEF segments on the strong β relaxation behavior. Our data provide insight into the microscopic mechanism of β relaxation of vinyl polymers.

Unconventional structure evolution stabilizes the ultrahigh specific strength in a nanostructured Al–Mg–Li alloy

A nanostructured (NS) Al–Mg–Li alloy with an average grain size of ∼ 26 nm was prepared via laser inert-gas condensation (laser-IGC) method. By integrating in-situ synchrotron-based high-energy X-ray diffraction, atom probe tomography and transmission electron microscopy, unconventional structure evolution (grain boundary segregation and ordered precipitates → Guinier–Preston (GP) zones) during annealing process was captured in this NS Al–Mg–Li alloy, which is contradictory to that of bulk counterparts (GP zones → ordered phases). The segregation and room temperature relaxation give rise to an ultrahigh specific strength by enhancing the stress level required for dislocation emission from interfaces in the alloy. Intriguingly, the highest specific strength can be maintained even thermally exposed at 200 °C, which benefits from GP zones, sub-structures and retained intragranular nanoprecipitation. Hitherto the unconventional structure evolution was unrecognized in any experimental observations in NS Al alloys, and is proved to be a reliable way to improve mechanical properties of NS Al alloys. This work provides insights into the relationship between modulated microstructure and superior mechanical properties, paving the road to the development of high-performance lightweight Al–Mg–Li alloys for diverse applications.

Study on micro crack propagation mechanism of ferrite–pearlite gas transmission pipeline steel with lamellar structure

The deformation and failure characteristics of pipeline steel depend on its atomic structure and microstructure. Based on the serial multi-scale analysis technology, the ferrite/cementite (α-Fe/Fe3C) lamellar atomic structure with Bagaryatskii orientation relationship is established. In order to obtain the experimental sample of the lowest energy state, The step-by-step relaxation method of conjugate gradient energy minimization and constant temperature and constant pressure relaxation under NPT conditions is carried out, and the energy state and atomic structure of the relaxed samples are analyzed. For the models of different cementite terminal plane structures, the tension displacement curves on the propagation path of mode I central through crack are extracted respectively, combined with the bilinear cohesion zone model, The cohesion parameters at the atomic scale are successfully transferred from bottom to top to the macro and micro scales. By simulating the reaction force and displacement response law at the loading point, the critical fracture toughness of each terminal interface of ferrite–pearlite pipeline steel at different scales is calculated, which provides a reliable path for exploring the micro mechanism of macro cracking behavior of pipeline steel.

A machine learning enabled hybrid optimization framework for efficient coarse-graining of a model polymer

This work presents a framework governing the development of an efficient, accurate, and transferable coarse-grained (CG) model of a polyether material. The framework combines bottom-up and top-down approaches of coarse-grained model parameters by integrating machine learning (ML) with optimization algorithms. In the bottom-up approach, bonded interactions of the CG model are optimized using deep neural networks (DNN), where atomistic bonded distributions are matched. In the top-down approach, optimization of nonbonded parameters is accomplished by reproducing the temperature-dependent experimental density. We demonstrate that developed framework addresses the thermodynamic consistency and transferability issues associated with the classical coarse-graining approaches. The efficiency and transferability of the CG model is demonstrated through accurate predictions of chain statistics, the limiting behavior of the glass transition temperature, diffusion, and stress relaxation, where none were included in the parametrization process. The accuracy of the predicted properties are evaluated in context of molecular theories and available experimental data.

Development of a new rejuvenator for aged SBS modified asphalt binder

The objective of this study is to evaluate the effectiveness of active reagents (i.e., methylene-bis(4-cyclohexylisocyanate) (HMDI) and 1,6-hexanediol diglycidyl ether (HDE)) and epoxidized soybean oil (ESO) in rejuvenating aged styrene-butadiene-styrene (SBS)-modified asphalt binder (SBSPAV) by promoting the interaction of aged binders with virgin asphalts. To achieve this objective, a multidisciplinary approach combining chemical and engineering methods was adopted. The chemical characterization of asphalt binders includes SARA fractionation (saturates, aromatics, resins and asphaltenes) and Fourier transform infrared spectroscopy (FTIR) tests. Rheological evaluation of the asphalt binders was utilized assessing fatigue, rutting, and thermal cracking resistance. The results indicated that the addition of ESO helped to adjust the low temperature performance of SBSPAV. Compared to SBS-modified asphalt (SBSMA), the low temperature relaxation modulus of ESO-rejuvenated asphalt has a 35.8% reduction. Whereas the addition of ESO alone could did not restore the performance of the SBSPAV. The addition of HMDI and ESO could improve the high-temperature performance of SBSPAV. Compared to SBSMA at 52 °C, the rutting factors of HMDI-rejuvenated asphalt with 0.5% and 1.0% were improved by 43.12% and 97.86%, respectively. According to the MSCR results, with a 1.0% content, the recovery rates of HDE-rejuvenated asphalt and HMDI-rejuvenated asphalt increased by 8.2% and −23.4%, respectively. The rejuvenated binders with HMDI showed better elastic recovery properties and permanent deformation resistance than the other studied binders. HMDI can increase the asphaltene content in rejuvenated asphalt, while HDE can increase the aromatic fraction content in rejuvenated asphalt, according to the SARA fraction results. The asphaltene content of 1.0% HMDI-rejuvenated asphalt increased by about 2.13%, and the aromatic content of 1.0% HDE-rejuvenated asphalt increased by about 3.46%. The FTIR results showed that HMDI chemically reacted with SBSPAV to form carbamate bonds with a stable chemical structure, and both HMDI and HDE could partially restore the broken chain structure of SBS. Overall, the results indicated that HMDI and HDE (combined with ESO) have the potential to be used to rejuvenate SBSPAV and that the recommended optimum contents for HMDI and HDE are 0.5%–1.0%.

Reconsidering spin-phonon relaxation in magnetic molecules

Because of the larger intra-molecular distortion, optical phonons usually have stronger spin-phonon coupling than acoustic phonons in molecular magnets. This property may pose problems to the theory of spin relaxation in ordinary paramagnetic materials, which have served as the basis for the understanding of spin dynamics in molecular magnets for decades. In this review, we explain why the Raman processes driven by optical phonons can play a dominant role at low temperature and provide unconventional dependence between relaxation time and temperature. Especially, we emphasize that the sub-barrier relaxation and anomalously low Raman exponents are two common signatures of the dominance. We also present the algorithm and implementation for calculating spin-phonon relaxation in molecular solids with density functional theory codes.

Electron temperature relaxation in the clusterized ultracold plasmas

Ultracold plasmas are a promising candidate for the creation of strongly coupled Coulomb systems. Unfortunately, the values of the coupling parameter Γe actually achieved after photoionization of the neutral atoms remain relatively small because of the considerable intrinsic heating of the electrons. A conceivable way to get around this obstacle might be to utilize a spontaneous ionization of the ultracold Rydberg gas, where the initial kinetic energies could be much less. However, the spontaneous avalanche ionization will result in a very inhomogeneous distribution (clusterization) of the ions, which can change the efficiency of the electron relaxation in the vicinity of such clusters substantially. In the present work, this hypothesis is tested by an extensive set of numerical simulations. As a result, it is found that despite a less initial kinetic energy, the subsequent relaxation of the electron velocities in the clusterized plasmas proceeds much more violently than in the case of the statistically uniform ionic distribution. The electron temperature, first, experiences a sharp initial jump (presumably, caused by the “virialization” of energies of the charged particles) and, second, exhibits a gradual subsequent increase (presumably, associated with a multi-particle recombination of the electrons at the ionic clusters). As a possible tool to reduce the anomalous temperature increase, we also considered a two-step plasma formation, involving the blockaded Rydberg states. This leads to a suppression of the clusterization due to a quasi-regular distribution of ions. In such a case, according to the numerical simulations, the subsequent evolution of the electron temperature proceeds more gently, approximately with the same rate as in the statistically uniform ionic distribution.

Dynamics and mechanisms of nonradiative photodissociation of glycine: A theoretical study

Photochemistry of small biomolecules is fundamental to understand the photochemical reactions of larger molecules, such as proteins. In this work, the dynamics and mechanisms of photodissociations of glycine conformers were studied using the DFT, TD-DFT and CASPT2 methods with the aug-cc-pVDZ basis set and microcanonical molecular dynamics simulations with surface hopping dynamics (NVE-MDSH). This study emphasized unimolecular dissociations and isomerization, nonradiative S1 → S0 relaxations that generate molecular products and the interplay between photoenergies and thermal energies. Four nonplanar conformers were suggested by the TD-DFT/B3LYP/aug-cc-pVDZ and CASPT2(8,14)/aug-cc-pVDZ methods to be stable in the S1 state. The potential energy curves obtained from the TD-DFT/B3LYP/aug-cc-pVDZ and CASPT2(8,14)/aug-cc-pVDZ methods and SA-CPMCSCF/6-31G(d) conical intersection optimizations suggested S0/S1 intersections for distorted glycine structures, Cα–N and NH dissociations and NH → OC isomerization. The NVE-MDSH results showed that although no dissociated molecular product was observed in the S1 state, isomerization-mediated dissociation and exothermic S1 → S0 relaxation temperature could lead to eight molecular product channels, in which the vertically excited Wigner-sampled structures generated eleven reactive and stable molecular products in different temperature ranges. These thermally selective reactions favored the lowest energy conformer (structure Ip) as the precursor, from which reactive and stable molecular products were formed above the threshold exothermic relaxation temperature. These theoretical results showed in detail for the first time how unimolecular photodissociations and nonradiative S1 → S0 relaxations create molecules in cold interstellar media without heat transfer from the surroundings. The results in this work could be used in future theoretical and experimental studies on the same or similar systems.

Semiconductorlike photocarrier dynamics in Dirac-semimetal Cd3As2 films probed with transient terahertz spectroscopy

The topological three-dimensional Dirac semimetal ${\mathrm{Cd}}_{3}{\mathrm{As}}_{2}$ has drawn great attention for the novel physics and promising applications in optoelectronic devices operating in the infrared and terahertz (THz) regimes. Among the extensive studies in the past decades, one intriguing debate is the underlined mechanism governing the nonequilibrium carrier dynamics following photoexcitation. In this study, the temperature-dependent photocarrier dynamics in ${\mathrm{Cd}}_{3}{\mathrm{As}}_{2}$ film has been investigated with time-resolved terahertz spectroscopy. The experimental results demonstrate that photoexcitation results in abrupt increase in THz photoconductivity, and the subsequent relaxation shows a single exponential relaxation for various temperatures and pump fluences. The relaxation time increases from 4.7 ps at 5 K to 7.5 ps at 220 K, while the lifetime remains almost constant at $\ensuremath{\sim}7.5$ ps with temperature above 220 K. A Rothwarf-Taylor model was employed to fit the temperature-dependent relaxation time, and a narrow energy gap of $\ensuremath{\sim}35\ifmmode\pm\else\textpm\fi{}6$ meV is obtained, which occurs around the Dirac node. Our THz spectroscopy results demonstrate that the photocarrier relaxation in ${\mathrm{Cd}}_{3}{\mathrm{As}}_{2}$ shows a semiconductorlike behavior, rather than hot-carrier scatterings in graphene and most of metals.