Constant Properties Research Articles

Effects of barium titanate on the dielectric constant, radiopacity, and biological properties of tricalcium silicate-based bioceramics.

This study evaluated the effect of barium titanate (BT) on the dielectricity, radiopacity, and biological properties of tricalcium silicate (C3S). C3S/BT samples were prepared with varying proportions of BT (0, 20, 40, and 60 wt%; referred to as BT00, BT20, BT40, and BT60, respectively). Dielectric constant and radiopacity were measured. Cytocompatibility was evaluated on human dental pulp cells. After surgical procedures on rat mandible, immunohistochemistry and Masson's trichrome staining were performed. The dielectric constant increased with higher proportions of BT (p<0.05). BT40 and BT60 satisfied the clinical guideline of radiopacity. There were no significant differences among groups in the cytocompatibility tests (p>0.05). New bone was observed well, along with the expressions of the dentin matrix protein 1 (DMP1), osteocalcin (OC), and osteonectin (ON) in BT40 and BT60. Conclusively, the contents of 40-60 wt% of BT in C3S provided proper radiopacity, favorable cytocompatibility, and beneficial effect on bone regeneration.

Interpretation of well logs and core data via Bayesian inversion

Estimating in situ petrophysical and compositional properties of rocks (e.g., porosity, mineralogy, and fluid saturation) from well logs and core measurements is critical for the evaluation of subsurface fluid resources. Traditional multimineral analysis of well logs is susceptible to abnormal borehole and geometric conditions, such as shoulder-bed effects and tool/borehole-related biases. Moreover, traditional multimineral analysis rarely includes uncertainty quantification, much less assessments of the impact of measurement noise, borehole conditions, and/or inaccurate rock-physics models (RPMs) on estimated properties. Probabilistic formation evaluation with credible-interval estimations can improve the outcome of mineral and fluid evaluations from well logs by explicitly incorporating the effects of measurement biases and a priori compositional and petrophysical constraints in the estimation. A probabilistic workflow is developed to estimate petrophysical/compositional properties from well logs and available core data. The workflow consists of two sequential steps: borehole measurements (e.g., density, resistivity, and gamma ray) are first converted into a layer-by-layer earth model, which consists of piecewise constant property values, with associated uncertainty estimations. The estimated earth model is tool/borehole independent, allowing for a common baseline to effectively compare properties among neighboring wells. Next, the estimated earth-model physical properties are used to derive petrophysical properties (e.g., volumetric concentration of fluid and solid rock constituents) via petrophysical joint inversion. In each step, Bayesian inversion is implemented with Markov chain Monte Carlo sampling in contrast to deterministic algorithms used by traditional multimineral methods. The developed method has the following advantages over traditional approaches: (1) it propagates uncertainty from well logs to petrophysical properties by assimilating measurement noise, tool/borehole-related biases, and RPM errors and (2) it enables the implementation of a priori knowledge per rock class to constrain the petrophysical estimation, effectively integrating field-specific core/regional geologic data. Examples of thinly laminated and organic shale formations successfully verify the reliability, efficiency, and accuracy of our estimation method.

Electrokinetic energy conversion in the nanochannel coupled with surface charge and slip effects

Inspired by the universal phenomena in nature and advances in nanotechnology, the ion transport in nanochannel receives increasing attention and shows great promising in energy conversion. The precedent studies generally predicted the ion transport by tuning the single physical parameter, the understanding of ion dynamics in the real multi-physical coupling systems is still scarce. Here, an ion transport model coupled with surface charge and slip effects is proposed to investigate the energy conversion behavior in nanochannel. The results show that the surface charge density increases with the increasing bulk concentration, nanochannel size and solution pH. The original boundary slip tends to decrease the surface charge density and the surface charge in turn reduces the boundary slip significantly, which manifests the strong coupling effect of diverse factors. The output power and energy conversion efficiency increases first and then decrease with the increasing bulk concentration and pH. The increase of channel size is beneficial for promoting output power, but unfavorable on energy conversion efficiency. More important, the boundary slip greatly enhances the output power and energy conversion efficiency, leading to a maximum output power and energy conversion efficiency is 2.7 pW and 30%, respectively. As a proof of concept, this work shows the distinct deviation in power generation in ion nanochannel with the constant and dependent physical property, providing the useful information to guide the design of real fluidic energy devices.

Highly sensitive short-range mode resonance sensor with multilayer structured hyperbolic metamaterials.

Hyperbolic metamaterial (HMM) based sensors can achieve superior sensing performance than conventional surface plasmon resonance sensors. In this work, the operator approach to effective medium approximation (OEMA) is used to characterize the HMM dielectric constant properties of metal-dielectric multilayer structures, which are classified into short-range (SR) mode and long-range (LR) mode according to the propagation length of the bulk high K waves in HMM. The dispersion relations of SR modes are derived, and a high-sensitivity refractive index sensor is designed for the near-infrared SR mode resonance. The effects of the number of periods, cell thickness, metal fill rate and incidence angle on the SR mode resonance were analyzed for the multilayer structured HMM. Our designed sensing structure achieves a maximum sensitivity of 330 µm/RIU in the near-infrared band with a quality factor of 492 RIU-1. In addition, the simulations show that the SR mode resonance wavelength is flexible and tunable. We believe that the study of HMM-based SR mode resonance sensors offers potential applications for high-sensitivity biochemical detection.

Aramid Nanofiber/XNBR Nanocomposite with High Mechanical, Thermal, and Electrical Performance

Aramid nanofibers (ANFs) were successfully produced by deprotonation of Kevlar fiber followed by grafting epichlorohydrin in dimethyl sulfoxide solution. The ANFs were then incorporated into carboxylated acrylonitrile butadiene rubber (XNBR) by means of latex blending, followed by vulcanization. The interaction between ANFs and XNBR, and the effects of ANFs on the mechanical strength, dielectric properties, and thermal stability of ANF/XNBR nanocomposites were investigated. The results revealed that hydrogen bonding and covalent bonding interactions existed between ANFs and the XNBR matrix and played a critical role in the reinforcement of ANFs to XNBR nanocomposites. After adding 5 phr (parts per hundred rubber) of ANFs, the XNBR nanocomposite exhibited a significant improvement in mechanical properties, namely a 182% increase in tensile strength and a 101% increase in tear strength. In addition, the dielectric constant and thermal properties of ANF/XNBR also increased dramatically. ANFs may thus make an ideal candidate for high-performance rubber materials.

Importance of Temperature-Dependent Non-Newtonian Fluid in Conventional Thermal Processing

Abstract Computational fluid dynamics (CFD) simulation provides full-field variables, enabling a better understanding of flow physics and associated heat transfer. However, assumptions involved in CFD simulation should not affect flow and temperature fields and their correspondence to practical situations. Therefore, the present study analyzed the importance of temperature-dependent fluid properties in a sealed container during thermal treatment. We compared the thermal behavior trends of temperature-dependent fluid properties with those obtained from constant properties for two carboxyl methyl cellulose (CMC) solution concentrations. The results show that natural convection occurs earlier in the temperature-dependent fluid properties, which leads to attaining a desired level of sterility within a shorter time than the constant properties of the fluid. The variations in the viscosity with the shear rate and temperature played essential roles in affecting thermal behavior. So, results indicate that temperature-dependent non-Newtonian fluid must be considered to avoid miscalculating heating time in conventional thermal treatment. Besides, the thermal trends of both cases approach pure conduction when CMC solutions’ apparent viscosity increases.

Enhanced dielectric and energy storage properties of P(VDF-HFP) through elevating β -phase formation under unipolar nanosecond electric pulses

Structural manipulation of electroactive β-phase of poly(vinylidene fluoride-co-hexafluoropropylene) [P(VDF-HFP)] is of great importance in high-energy-density polymer devices. In this Letter, an efficient way to improve dielectric and energy storage properties of P(VDF-HFP) films by inducing a high β-phase content and lowering the crystallite size through repetitive unipolar nanosecond electric pulses (nsEP) is proposed. It is found that the percentage of the β-phase in P(VDF-HFP) can be significantly enhanced to ∼84% under a low unipolar nsEP of 5 V/mm vs only 35% in pristine P(VDF-HFP). Meanwhile, the orientation of the amorphous chains is also achieved, which improves the dielectric constant, electric breakdown, and energy storage properties of P(VDF-HFP). Specifically, the P(VDF-HFP) film processed under nsEP of 5 V/mm exhibits a high breakdown field of 541 MV/m, and discharged energy density of 14 J/cm3, which is 28.8% and 127% higher than those of the pristine polymer, respectively. This work provides a facile approach to optimize the crystalline morphology of P(VDF-HFP) polymers for dielectric energy storage applications.

The impact of film deposition and annealing on the nanostructure and dielectric constant of organic semiconductor thin films.

The strategy of using a bulk-heterojunction light-absorbing layer has led to the most efficient organic solar cells. However, optimising the blend morphology to maximise light absorption, charge generation and extraction can be challenging. Homojunction devices containing a single component have the potential to overcome the challenges associated with bulk heterojunction films. A strategy towards this goal is to increase the dielectric constant of the organic semiconductor to ≈10, which in principle would lead to free charge carrier generation upon photoexcitation. However, the factors that affect the thin film dielectric constants are still not well understood. In this work we report an organic semiconductor material that can be solution processed or vacuum evaporated to form good quality thin films to explore the effect of chromophore structure and film morphology on the dielectric constant and other optoelectronic properties. 2,2'-[(4,4,4',4'-Tetrakis{2-[2-methoxyethoxy]ethyl}-4H,4'H-{2,2'-bi[cyclo-penta[2,1-b:3,4-b']dithiophene]}-6,6'-diyl)bis(methaneylylidene)]dimalononitrile [D(CPDT-DCV)] was designed to have high electron-affinity end groups and low ionisation-potential central moieties. It can be processed from solution or be thermally evaporated, with the film morphology changing from face-on to a herringbone arrangement upon solvent or thermal annealing. The glycol solubilising groups led to the static dielectric constant (taken from capacitance measurements) of the films to be between 6 and 7 (independent of processing conditions), while the optical frequency dielectric constant depended on the processing conditions. The less ordered solution processed film was found to have the lowest optical frequency dielectric constant of 3.6 at 2.0 × 1014 Hz, which did not change upon annealing. In contrast, the more ordered evaporated film had an optical frequency dielectric constant 20% higher at 4.2 and thermal annealing further increased it to 4.5, which is amongst the highest reported for an organic semiconductor at that frequency. Finally, the more ordered evaporated films had more balanced charge transport, which did not change upon annealing.

The boson peak in silicate glasses: insight from molecular dynamics.

In the low-frequency regime, ≈1 THz, glasses show an anomalous excess in their vibrational density of states called the boson peak (BP). The origin of BP has been a subject of debate since its first discovery a few decades ago. Although BP has been the focus of numerous studies, no conclusive answers have been found about its origins, which remained elusive to date. Here, we present results based on molecular dynamics of several binary and ternary silicate glasses with different network intermediates and modifier oxides. The vibrational density of states and the BP are reported for all the studied glasses. Their correlation with the elastic constant C44, structural, and dynamical properties are extensively discussed in terms of Voronoi atomic volume and the vibrational mean square displacement of Q4 species specifically. We also question the classical classification of alkali oxides as modifiers, and we suggest that Li2O plays the role of pseudo-intermediate oxide in lithium silicate glasses. This claim is supported by the effect of Li on various vibrational modes, and this effect differs from the other alkali metals. Furthermore, we demonstrate a correlation between the BP intensities and both the Voronoi volume of the Q4 and Q3 units and vibrational mean square displacements.

Exergy efficiency and exergy destruction assessment of heat transfer and fluid flow through spiral passages using source-sink model

Exergy efficiency and exergy destruction of forced turbulent convective fluid flow through spiral passages using sourcesink model are assessed. Constant and temperature dependent thermophysical properties of process fluid in sink regions have been considered, while in the source regions phase change material is kept at constant temperature. Moreover, the effect of a secondary flow phenomenon due to spiral motion of the fluid flow through narrowing spiral passages has been evaluated in the sink passage domain. It was found that this phenomenon plays an important role in decreasing the exergy destruction as a result of energy exchange between source and sink in this compact type of energy carrier or storage equipment. It was found that the De (Dean Number) whose magnitude is a measure of the secondary flow, has positive impact on exergy efficiency while decreasing along the spiral passage. The fluid properties that are temperature dependent have a significant influence on the enhancement of heat transfer process, exergy efficiency and exergy destruction. It is concluded that the source-sink model could be considered from engineering point of view as a good simple model for evaluating the thermodynamic performance of this type of thermal energy process device.

A radiating straight fin with constant thermal properties by modified perturbation method

A radiating straight fin with constant thermal properties by modified perturbation method

Room temperature exciton formation and robust optical properties of CVD-grown ultrathin Bi2O2Se crystals on arbitrary substrates.

The appealing success of non-van der Waals (non-VdW) two-dimensional (2D) bismuth oxyselenide (Bi2O2Se) crystals in optoelectronics provides an exciting avenue to investigate their fundamental physical properties. To date, the majority of efforts have focused on understanding the properties of 2D Bi2O2Se, usually grown on a mica substrate. However, a gap exists in realizing the origin of photoluminescence (PL) of new age non-VdW Bi2O2Se at visible and near-infrared (NIR) wavelengths and the effect of growth substrates on the structure and optical properties. Herein, we report that the formation of multiple excitons in momentum valleys is responsible for broadband absorption and visible PL from a few layer thick 2D Bi2O2Se. The effect of growth substrates on the structure and optical properties is investigated in detail. Our studies unfold that the growth substrates (mica, sapphire, quartz, SiO2, glass) introduce strain/doping in chemical vapor deposition (CVD)-grown Bi2O2Se crystals, and consequently, the morphology, lattice constant, absorption coefficient, optical bandgap, refractive index, and PL properties are modulated. In addition, the possible direct/indirect multiple exciton formation at the valence band to the conduction band at different symmetry points of Bi2O2Se is analyzed from experimental data on different growth substrates and corroborated with the density functional theory (DFT) calculation of the electronic band structure. Furthermore, temperature-dependent photo-carrier dynamics discloses an A/Γ-exciton activation energy of 209.6 meV in Bi2O2Se. These findings are significant for the futuristic optoelectronic applications of Bi2O2Se and the choice of growth substrates on directly fabricated nanodevices.

Copper doped strontium Indium-borate glasses: FTIR, Raman, EPR, optical and structural studies

Strontium borate glasses containing Indium oxide with chemical composition 69B2O3–(30-x) SrO- xIn2O3-1CuO varying ‘x’ from 0.5 to 2.5 mol% were synthesized by quenching method. The non-crystalline characteristics of these glasses were established by X-Ray diffraction patterns. Physical parameters like density (ρ), molar volume (Vm), dielectric constant (ε) and other properties were described with varying mole percent of indium oxide. Spectroscopic findings, viz. optical absorption, EPR were conducted to understand the influence of In2O3 and CuO on strontium-borate glass network. Optical energy band gap (Eopt) and Urbach energies were calculated. Spin-Hamiltonian values from EPR of Cu2+ spin probes obeyed g‖‖> g⊥>ge and A‖‖> A⊥ revealing dx2-y2 (2B1g state) as ground state of Cu2+ ions and site symmetry in the neighbourhood of Cu2+ is tetragonally distorted octahedral. FTIR studies established the existence of typical BO3, BO4 units in addition to In3+O6 groups. The various Raman peaks shown by the glass samples were appropriate assigned and corresponding structural variations were discussed.

Using a linear inverse heat conduction model to estimate the boundary heat flux with a material undergoing phase transformation

Modeling heat conduction during steel-cooling processes is challenging because solid–solid phase transformations can take place, introducing highly non-linear phenomena to the heat equation. Using a linear model for the inverse problem can be helpful for estimating the dissipated heat flux, especially because complex phase transformations models that use empirical parameters are not always available. However, the performance and applicability of such a simplified inverse model for a strongly non-linear process is still unclear. This study presents several numerical simulations to evaluate the accuracy and limitations of solving a linear inverse heat conduction problem (i.e. constant thermophysical properties and no internal heat source) to estimate the boundary heat flux during cooling of a material undergoing phase transformations. Preliminary simulations with stable materials but with temperature-dependent thermophysical properties showed that the linear model performs well to estimate the boundary heat flux, except when the material has a highly temperature-dependent specific heat, like pure iron near its Curie temperature. Then, we performed several simulations for 42CrMo4 steel, which undergoes phase transformations and, hence, has phase- and temperature-dependent thermophysical properties and latent heat of phase transformations as an internal heat source. The latent heat has a very small effect on the heat flux estimation for fast cooling conditions; however, it can lead to an interpretation bias in medium and slow cooling conditions due to temporary underestimates of the heat flux, reaching errors up to 100%. Even when the estimated heat fluxes seem accurate (average errors smaller than 10%), further estimates of the temperature evolution or phase transformations kinetics are inaccurate (range of uncertainties as large as 200 °C and 20%, respectively) because of the phase-dependent thermophysical properties. Hence, using a linear inverse heat conduction problem for a material undergoing phase transformations is acceptable only for fast cooling conditions ( h > 1500 Wm −2 K −1 ) and exclusively to estimate the boundary heat flux without further simulations. • Numerical simulations of a coupled heat conduction-phase transformation model. • Simulated temperature data were used in a linear inverse model to estimate the heat flux. • The inverse model performs well for AISI 304 and Ni201, which do not undergo phase transformations. • For the 42CrMo4 steel, which undergoes phase transformation, it performs well only for h > 1500 Wm − 2 K − 1 . • For lower h, the latent heat plays an important role, so the simplified model is no longer acceptable.

The local entropy rate of production in unsteady-state conditions at presence of a gradient of temperature

Problems of a linear mode of thermodynamics with the purpose of studying the change of local entropy rate of production in a non-stationary thermal mode at presence of a gradient of temperature in bodies of the simple form are considered. Article is development of earlier work of authors in which on the basis of experimental thermogram by the electrostatic levitation method received and fixing process of spontaneous cooling of the spherical sample of the molybdenum which is being a solid phase, change of local entropy rate of production from time has been calculated. It has been shown, that in absence of a gradient of temperature on radius of sphere change of local entropy rate of production from time corresponds to a principle of an extremum. In the given work change of local entropy rate of production from time for a case when the non-stationary thermal mode is combined with presence of a gradient of temperature is defined. The task is solved on the basis of known analytical decisions of one-dimensional problems of heating of bodies of the simple form (a unlimited plate, sphere and the unlimited cylinder), under boundary conditions of the second sort which have been received in approach of constant properties. The general meaning of local entropy rate of production is calculated as the sum of the task with gradient of temperature by a making constant in time and the non-stationary task counted in absence of a gradient of temperature. The estimation of the contribution of temperature drop on thickness of a plate in a general meaning of local entropy rate of production is executed, as product of force and a heat flux corresponding force and is widespread to a case of sphere and the cylinder by virtue of equality of temperature drop for all three bodies. The size of a nonstationary component in a general meaning of local entropy rate of production pays off as function of the logarithm, which argument is the relation of two instant temperatures, and the function of the logarithm is divided on a difference the values of time. It is shown, that the non-stationary component in a general meaning of local entropy rate of production also corresponds to a principle of an extremum at increase of Fourier number. For the first time have made comparison a part of non-stationary local entropy rate of production for a plate, sphere and the cylinder which shows, that the principle of an extremum is most brightly shown for sphere.

Exploring the antioxidant, antimicrobial, cytotoxic and biothermodynamic properties of novel morpholine derivative bioactive Mn(ii), Co(ii) and Ni(ii) complexes - combined experimental and theoretical measurements towards DNA/BSA/SARS-CoV-2 3CLPro.

A novel class of bioactive complexes (1-3) [MII(L)2(bpy)], where, L = 2-(4-morpholinobenzylideneamino)phenol, bpy = 2,2'-bipyridine, MII = Mn (1), Co (2) or Ni (3), were assigned to octahedral geometry based on analytical and spectral measurements. Gel electrophoresis showed that complex (2) demonstrated significant DNA cleavage activity compared to the other complexes under the action of oxidation agent (H2O2). The DNA binding constant properties measured by various techniques were in the following sequence: (2) > (3) > (1) > (HL), which suggests that the complexes might intercalate DNA, a possibility that is also supported by their biothermodynamic characteristics. The binding constant results for BSA from electronic absorption and fluorometric titrations demonstrate that complex (2) exhibits the highest binding effectiveness among them all, which means that all the compounds could interact with BSA through a static approach, additionally supported by FRET measurements. DFT and docking calculations were employed to realize the electronic structure, reactivity, and interaction capability of all substances with DNA, BSA, and the SARS-CoV-2 main protease. These binding energies fell within the ranges -7.7 to -8.5, -8.2 to -10.1 and -6.7 to -9.3 kcal mol-1, respectively. The higher reactivity of the complexes than the ligand is supported by FMO theory. The in vitro antibacterial, cytotoxicity, and radical scavenging characteristics revealed that complexes (2-3) have better biological efficacy than the others. The cytotoxicity and binding properties also show good correlation with the partition coefficient (log P), which is encouraging because all of the experimental findings are closely correlated with the theoretical measurements.

A Comprehensive Review on Barium Titanate Nanoparticles as a Persuasive Piezoelectric Material for Biomedical Applications: Prospects and Challenges.

Stimulation of cells with electrical cues is an imperative approach to interact with biological systems and has been exploited in clinical practices over a wide range of pathological ailments. This bioelectric interface has been extensively explored with the help of piezoelectric materials, leading to remarkable advancement in the past twodecades. Among other members of this fraternity, colloidal perovskite barium titanate (BaTiO3 ) has gained substantial interest due to its noteworthy properties which includes high dielectric constant and excellent ferroelectric properties along with acceptable biocompatibility. Significant progression is witnessed for BaTiO3 nanoparticles (BaTiO3 NPs) as potent candidates for biomedical applications and in wearable bioelectronics, making them a promising personal healthcare platform. The current review highlights the nanostructured piezoelectric bio interface of BaTiO3 NPs in applications comprising drug delivery, tissue engineering, bioimaging, bioelectronics, and wearable devices. Particular attention has been dedicated toward the fabrication routes of BaTiO3 NPs along with different approaches for its surface modifications. This review offers a comprehensive discussion on the utility of BaTiO3 NPs as active devices rather than passive structural unit behaving as carriers for biomolecules. The employment of BaTiO3 NPs presents new scenarios and opportunity in the vast field of nanomedicines for biomedical applications.

Stretching-insensitive stretchable and biocompatible triboelectric nanogenerators using plasticized PVC gel and graphene electrode for body-integrated touch sensor

Triboelectric nanogenerators (TENG) can generate strong electrical signals even with low frequencies and weak forces, thus research has been conducted to use them as wearable, body-attachable, and body-embeddable devices using biomechanical energies. For this reason, the TENG components, such as dielectric materials and electrodes, should be stretchable. A stretchable and biocompatible single electrode TENG based on plasticized polyvinyl chloride (PVC) gel with a graphene electrode is fabricated. PVC gel is a suitable stretchable TENG dielectric material owing to its high stretchability, dielectric constant, and tribo-negative properties, and graphene is a highly conductive electrode. Graphene and PVC gel-based stretchable and biocompatible TENGs display excellent electrical outputs (48 V, 2.5 μA, and 0.49 W/m2). The electrical resistance range of the electrode which does not affect the TENG output performance, and a stretching-insensitive TENG with approximately 50% stretching rate is successfully demonstrated through this study. In addition, both PVC gel and graphene are biocompatible. These stretching-insensitive and biocompatible TENGs may be used as a self-powered touch sensor that can be integrated into the human body.

Enhanced dielectric constant and mechanical investigation of epoxidized natural rubber with TM-doped CeO2 nanocomposites

The dielectric constant and mechanical properties of epoxidized natural rubber (ENR) were improved by forming composites with CeO2 and various types of transition metal (TM) doped CeO2 nanoparticles (TM-doped CeO2 such as Fe-CeO2, Co-CeO2, Ni-CeO2, Cu-CeO2, Mn-CeO2 and Zn-CeO2). The CeO2 samples and TM-doped CeO2 nanoparticles were prepared using a co-precipitation method at room temperature and were calcined at 600 °C. The composites were prepared with 2 phr of CeO2 and TM-doped CeO2 nanoparticles referred to as CeO2 @ENR, Fe-CeO2 @ENR, Co-CeO2 @ENR, Ni-CeO2 @ENR, Cu-CeO2 @ENR, Mn-CeO2 @ENR and Zn-CeO2 @ENR. A carbon black (CB) and ENR composite was also prepared for comparison and referred to as CB@ENR. The morphology, phase and valence states of prepared samples were characterized using transmission electron microscopy (TEM), X-ray diffraction (XRD), field emission scanning electron microscopy, X-ray photoelectron spectroscopy. The samples exhibited XRD peaks and TEM-selected area electron diffraction corresponding to a face centered cubic CeO2 structure, confirming a single phase. They showed average crystallite sizes in the range of 10.5 ± 0.3–15.0 ± 1.4 nm. All TM-doped CeO2 @ENR composites exhibited higher dielectric constants and lower dielectric losses at room temperature as a function of frequency than that of CB@ENR composites. A maximum value of ∼392.6 at 102 Hz for the Cu-CeO2 @ENR composite was shown. Additionally, this dielectric constant was about 3 and 4.7 times higher than those of CeO2 @ENR and CB@ENR, respectively. Also, the breakdown strength of the Cu-CeO2 @ENR nanocomposite was increased compared to CB@ENR. Furthermore, TM-doped CeO2 nanocomposites display increased torque, higher 100% & 300% moduli and greater tensile strength caused by nano-filler affects. As a result, this research may open up new avenues for the development of insulating elastomers.

Modeling frictional precursory phenomena using a wear-based rate- and state-dependent friction model in the laboratory

We examine numerical models that employ the rate-and-state frictional (RSF) framework to investigate earthquake sequences using laboratory driven descriptions of heterogeneous frictional properties. Using previously obtained experimental measurement of roughness, we observed that wear produced a bimodal Gaussian distribution of surface heights, which we hypothesized produced spatial heterogeneity of the critical slip distance Dc. In this numerical study, the fault surface was binarized into discrete smooth or rough sections, producing a barcode style version of frictional heterogeneity. The fault was predominantly rough except for two dominant asperities (A1 and A2) representative of larger polished sections. We simulated the resistive effect of increasing the fracture energy (toughness) of the rough barriers while maintaining constant properties of the embedded brittle/smooth asperities. Our numerical simulations generated burst-like seismic events and aseismic transients throughout the interseismic phase. At the late interseismic phase, bursts of seismicity (foreshocks) interacted with the accelerating preslip region at the transition to the preseismic (nucleation) phase. At lower levels of toughness heterogeneity, the slip rate increase was roughly inversely proportional to the time-to-failure tf for larger events. As fault toughness was increased, the dominant asperities initiated nucleation and thus force deviations of the fault from the smooth 1/tf acceleration observed for the homogeneous case, producing a rate-dependent cascade response. The calculations were validated by comparing two independently measured metrics from the experiments: (1) The expansion rate of slow ruptures during the interseismic and preslip phase and (2) the scalar seismic moment and source dimensions. While our study does not address the scaling problem, these results help to understand laboratory experiments that investigate transition to the preseismic (nucleation) phase during complex earthquake sequences.