Mean Relaxation Time Research Articles

Polaron-assisted dielectric relaxation processes in donor-doped BaTiO3-based ceramics

Ceramic samples based on the Ba1-xGdxTiO3 system, where x = 0.001, 0.002, 0.003, 0.004 and 0.005, were prepared via the Pechini’s chemical synthesis route. Structural properties, analyzed from X-ray diffraction and Rietveld refinement, revealed the formation of the pure ABO3 perovskite structure with tetragonal symmetry (P4mm) for all the studied compositions. Doping with Gd3+ promoted a reduction in the unit-cell volume, confirming the preferential substitution of the rare-earth cation at the A-site. The dielectric properties have been analyzed over a wide temperature and frequency range, revealing a significant contribution of the conduction mechanisms in the dielectric response of the studied ceramics. In fact, by using the Davidson-Cole formalism, the observed electrical behavior was found to be associated with relaxation processes related to intrinsic defects mobility promoted by a thermally-activated polaronic mechanism. The obtained values of the activation energy for the relaxation processes, estimated from the Arrhenius’ law for the mean relaxation time, revealed a decrease from 0.29 up to 0.21 eV as the Gd-doping concentration increases, which suggests the conduction process to be associated with the polaronic effects due to the coexistence of Ti4+ and Ti3+ ions in the structure. Analysis from the conductivity formalism, by using the Jonscher’s universal power-law, confirmed the polaron-type conduction mechanism for the dielectric dispersion, as suggested by the dielectric analysis, being the nature of the hopping mechanism governed by small polaron hopping (SPH) charge transport in the studied Ba1–xGdxTiO3 ceramics.

Stationary distribution and mean extinction time in a generalist prey–predator model driven by Lévy noises

In this study, a delayed generalist prey–predator model incorporating the logistic-like growth and Holling type-III functional response for predator subjected to two Lévy noises is established. Such environmental fluctuations can describe abrupt change in population density. First, we conduct stability analysis and determine the critical value of time delay when Hopf bifurcation takes place. Then, the existence of the global positive solution and stability in distribution of stochastic model are studied. Numerical results are given to illustrate the analytical findings, and mainly dedicated to the consequences of time delay and Lévy noises on the stationary distribution, mean extinction time and reproduction rate of prey–predator populations, via stationary probability distribution function (PDF), mean first passage time (MFPT) and relaxation time, respectively. Our findings indicate that the decreases in time delay, noise intensities (Di,i=1,2), and stability indexes within the range of αi∈[1,2] are more likely to maintain the population in a high density state. Phase transition occurs when the system is in the suitable parameter regime. Additionally, there exist optimal noise intensities that slow down switching of prey species from a stable state to an extinction state. Smaller time delay τ and stability indexes αi inhibit population extinction, whereas smaller skewness parameter β speed up prey extinction. More importantly, two noises can tune the enhanced stability characteristic of the system.

Fast cardiac T1ρ,adiab mapping using slice-selective adiabatic spin-lock preparation pulses.

Myocardial T1ρ mapping techniques commonly acquire multiple images in one breathhold to calculate a single-slice T1ρ map. Recently, non-selective adiabatic pulses have been used for robust spin-lock preparation (T1ρ,adiab). The objective of this study was to develop a fast multi-slice myocardial T1ρ,adiab mapping approach. The proposed-sequence reduces the number of breathholds required for whole-heart 2D T1ρ,adiab mapping by acquiring multiple interleaved slices in each breathhold using slice-selective T1ρ,adiab preparation pulses. The proposed-sequence was implemented with two interleaved slices per breathhold scan and was quantitatively evaluated in phantom experiments and 10 healthy-volunteers against a single-slice T1ρ,adiab mapping sequence. The sequence was demonstrated in two patients with myocardial scar. The phantom experiments showed the proposed-sequence had slice-to-slice variation of 1.62% ± 1.05% and precision of 4.51 ± 0.68 ms. The healthy volunteer cohort subject-wise mean relaxation time was lower for the proposed-sequence than the single-slice sequence (137.7 ± 5.3 ms vs. 148.4 ± 8.3 ms, p < 0.001), and spatial-standard-deviation was better (18.7 ± 1.8 ms vs. 21.8 ± 3.4 ms, p < 0.018). The mean within-subject, coefficient of variation was 5.93% ± 1.57% for the proposed-sequence and 6.31% ± 1.92% for the single-slice sequence (p = 0.35) and the effect of slice variation (0.81 ± 4.87 ms) was not significantly different to zero (p = 0.61). In both patient examples increased T1ρ,adiab (maximum American Heart Association-segment mean = 174 and 197 ms) was measured within the myocardial scar. The proposed sequence provides a twofold acceleration for myocardial T1ρ,adiab mapping using a multi-slice approach. It has no significant difference in within-subject variability, and significantly better precision, compared to a 2D T1ρ,adiab mapping sequence based on non-selective adiabatic spin-lock preparations.

Analysis of how Serum Ferritin and the Aspartate Aminotransferase-to-Platelet Ratio Index (APRI) are correlated to Hepatic MRI T2* Findings in Children with Beta-Thalassemia Major

Background: Iron overload is a major complication in patients with beta-thalassemia major. Excessive iron accumulation leads to organ dysfunction. The regular assessment of iron is crucial to effectively manage iron overload in these patients. This study evaluated the correlation between serum ferritin levels, the Aspartate Aminotransferase-to-Platelet Ratio Index (APRI), and hepatic MRI T2* findings in children with beta-thalassemia major. Materials and Methods: This retrospective analytical study was conducted at Shahid Sadoughi Hospital in Yazd in 2023. The research population comprised all the children under the age of 15 with beta-thalassemia major who had undergone multiple blood transfusions (at least ten units of blood). Results: The participants in this study were 70 children with beta-thalassemia major, including 35 males and 35 females. Their mean age was 3.52 ± 10.76 years. The mean relaxation time of liver MRI T2* was 4.42 ± 4.91 ms. The participants also had the APRI score of 0.55 ± 1.90, the aspartate aminotransferase (AST) level of 23.82 ± 36.29, and the serum ferritin level of 285.01 ± 3244.04 (ng/mL). Based on MRI T2* results, 30% of the patients had a severe liver iron overload, 27.1% had a moderate overload, 21.4% had a severe overload, 18.6% had a mild overload, and 2.9% had near-normal iron levels.The AST level demonstrated a significant association with the type of chelation treatment (P = 0.003). The duration of blood transfusion (in years) showed a strong positive correlation with the patients' age (Pearson's coefficient = 0.996). Conclusion: This study indicates the elevated serum ferritin levels and APRI scores in patients with beta-thalassemia major, most of whom have abnormal MRI T2* findings. However, no significant correlation was observed between the APRI score, serum ferritin level, and MRI T2* results.

Viscoelastic Hertzian Impact

The problem of normal impact of a rigid sphere on a Maxwell viscoelastic solid half-space is considered. The first-order asymptotic solution is constructed in the framework of Hunter’s model of viscoelastic impact. In particular, simple analytical approximations have been derived for the maximum contact force and the time to achieve it. A linear regression method is suggested for evaluating the instantaneous elastic modulus and the mean relaxation time from a set of experimental data collected for different spherical impactors and impact velocities.

A meta-analysis of left ventricular dysfunction in ankylosing spondylitis.

Ankylosing spondylitis (AS) is a chronic inflammatory arthritis affecting the spine, presenting a considerable morbidity risk. Although evidence consistently indicates an elevated risk of ischemic heart disease among AS patients, debates persist regarding the likelihood of these patients developing left ventricular dysfunction (LVD). Our investigation aimed to determine whether individuals with AS face a greater risk of LVD compared to the general population. To accomplish this, we identified studies exploring LVD in AS patients across five major databases and Google Scholar. Initially, 431 studies were identified, of which 30 met the inclusion criteria, collectively involving 2933 participants. Results show that AS patients had: (1) poorer Ejection Fraction (EF) [mean difference (MD): -0.92% (95% CI: -1.25 to -0.59)], (2) impaired Early (E) and Late (atrial-A) ventricular filling velocity (E/A) ratio [MD: -0.10m/s (95% CI: -0.13 to -0.08)], (3) prolonged deceleration time (DT) [MD: 12.30ms (95% CI: 9.23-15.36)] and, (4) a longer mean isovolumetric relaxation time (IVRT) [MD: 8.14ms (95% CI: 6.58-9.70)] compared to controls. Though AS patients show increased risks of both systolic and diastolic LVD, we found no significant differences were observed in systolic blood pressure [MD: 0.32mmHg (95% Confidence Interval (CI): -2.09 to 2.73)] or diastolic blood pressure [MD: 0.30mmHg (95% CI: -0.40 to 1.01)] compared to the general population. This study reinforces AS patients' susceptibility to LVD without a notable difference in HTN risk.

Engineering phonon transport through cation disorder in dimensionally constricted high entropy MXene

Designing materials with low thermal conductivity is a crucial objective for applications in thermal insulation and thermoelectrics. Traditional methods such as doping, mechanical strain and introducing defects in perfect crystals have been widely explored to impede the flow of heat. This work introduces dimensional constriction and cationic disorder as novel avenues to manipulate lattice thermal conductivity (LTC). High entropy materials characterized by random distribution of multiple elements, creates a suitable environment for thermal insulation due to its configurational disorder and local lattice distortions. On the other hand, MXenes, derived from MAX-phase, have garnered considerable attention due to their unique structural attributes, leading to potential applications in catalysis and energy storage. Ti2AlC MAX-phase is examined to understand the impact of dimensional constriction on phonon transport of Ti2C with cationic disorder, i.e., (Ti0.25Nb0.25Cr0.25Ta0.25)2C. The exponential reduction in LTC of HE-MXene is attributed to disorder scattering that significantly limits phonon mean free path (MFP) and relaxation time. The spread of mode-resolved LTC with MFP highlights the influence of disorder on phonon scattering. This work provides a systematic approach to engineer LTC through dimensional constriction and cationic disorder, laying the foundation for tailored materials with desired thermal properties.

Hydrogenation driven ultra-low lattice thermal conductivity in β 12 borophene

Borophene gathered large interest owing to its polymorphism and intriguing properties such as Dirac point, inherent metallicity, etc but oxidation limits its capabilities. Hydrogenated borophene was recently synthesised experimentally to harness its applications. Motivated by experimental work, in this paper, using first-principles calculations and Boltzmann transport theory, we study the freestanding β 12 borophene nanosheet doped and functionalised with hydrogen (H), lithium (Li), beryllium (Be), and carbon (C) atoms at different β 12 lattice sites. Among all possible configurations, we screen two stable candidates, pristine and hydrogenated β 12 borophene nanosheets. Both nanosheets possess dynamic and mechanical stability while the hydrogenated sheet has different anisotropic metallicity compared to pristine sheet leading to enhancement in brittle behaviour. Electronic structure calculations reveal that both nanosheets host Dirac cones (DCs), while hydrogenation leads to shift and enhancement in tilt of the DCs. Further hydrogenation leads to the appearance of additional Fermi pockets in the Fermi surface. Transport calculations reveals that the lattice thermal conductivity changes from 12.51 to 0.22 W m−1 K−1 (along armchair direction) and from 4.42 to 0.07 W m−1 K−1 (along zigzag direction) upon hydrogenation at room temperature (300 K), demonstrating a large reduction by two orders of magnitude. Such reduction is mainly attributed to decreased phonon mean free path and relaxation time along with the enhanced phonon scattering rates stemming from high frequency phonon flat modes in hydrogenated nanosheet. Comparatively larger weighted phase space leads to increased anharmonic scattering in hydrogenated nanosheet contributing to ultra-low lattice thermal conductivity. Consequently, hydrogenated β 12 nanosheet exhibits a comparatively higher thermoelectric figure of merit (∼0.75) at room temperature along armchair direction. Our study demonstrates the effects of functionalisation on transport properties of freestanding β 12 borophene nanosheets which can be utilised to enhance the thermoelectric performance in two-dimensional (2D) systems and expand the applications of boron-based 2D materials.

Enhanced dielectric, electrical and electro-optical properties: Towards understanding the interaction in mesophases of 8OCB liquid crystal dispersed with CdSe/ZnS quantum dots

The current advancements in developing new liquid crystalline materials for the next generation applications focus mainly on improving the physical characteristics of the liquid crystal (LC) systems. Recent progress has shown that the functionalized nanoparticles embedded in LC matrices can significantly alter the characteristics of the LC material based on the mutual interaction between the host molecules and guest particles. In this aspect, the present study reports the impact of dispersing core-shell type CdSe/ZnS quantum dots (QDs) on the dielectric, electrical and electro-optical properties of the 8OCB LC doped at various concentrations. The doped samples exhibit an ion releasing behavior and this effect becomes more evident as the doping concentration increases up to 0.2 wt% in the LC system. It is explained as a result of the growing tactoid-like ellipsoidal form acquired by QDs owing to the enhanced mutual interaction among QD ligands and rod-like LC molecules. The temperature variation of the diffusion constant, conductivity, ionic mobility and mean relaxation time of ions significantly follows each other in all the studied samples. Moreover, thermal profiles of the dielectric anisotropy, threshold voltage and splay elastic constant show a decreasing pattern with an increment in doping concentration. A dual-relaxation regime is experimentally investigated, corresponding to the contribution of nematic director and dimers, providing two kinds of rotational viscosity in the pristine and QDs dispersed LC samples. The transmittance-voltage curve reveals the presence of residual value in the dispersed samples and is related to the volatile memory effect. A slight enhancement is observed in the photoluminescence intensity for the lower doped sample and reduces further with increasing doping concentration in the pristine LC system. All these findings suggest the considerable contribution of functionalized QDs to the studied properties in terms of interaction between the LC and dopant material. This study will further elucidate the selection of optimal QDs concentration based on the required properties for their potential applications in futuristic devices based on LCs.

Aqueous Laponite® dispersions are attractive gels, not repulsive Wigner glasses: A critical commentary

An aqueous dispersion of Laponite® has been studied in the literature for over the past three decades. Typically, the aqueous dispersion of Laponite® undergoes incessant evolution of its microstructure, wherein its elastic modulus and the mean relaxation time show a continuous increase as a function of time. A considerable amount of discussion has revolved around the nature of this dispersion, specifically whether it can be classified as a repulsive Wigner glass state, characterized by disconnected Laponite® particles stabilized by electrostatic repulsions, or an attractive gel state, in which the particles form a percolated space-spanning network. The proponents of the Wigner glass state also conjecture that this system experiences a glass–glass transition after a period of 2 days has elapsed since its preparation. In this Commentary, we explore this topic from a rheological point of view, analyzing the published literature and performing new experiments. Aided by additional evidence from the literature, we propose that rheological behavior overwhelmingly suggests that an aqueous dispersion of Laponite® undergoes a sol–attractive gel transition and remains in the attractive gel state over at least up to 7 days without undergoing any additional transition. Importantly, rheology, despite being a macroscopic tool governed by principles of mechanics, offers profound insight into the microstructure of this particular system. The corresponding analysis conclusively determines the state of an aqueous dispersion of Laponite® to be an attractive gel.

The implication of PMMA molecular weight on compatibility of SAN/PMMA blends containing GO-g-PMMA hybrid compatibilizers

The molecular weight of a polymer is one of the most important factors defining material properties and performance. Within the current study, poly(styrene-co-acrylonitrile)/poly(methyl methacrylate) (SAN/PMMA) blends containing hybrid particles of graphene oxide-g-poly(methyl methacrylate) (GO-g-PMMA) were designed so that the molecular weight of the PMMA chains tethered on the GO particles was correlated with the molecular weight of the PMMA matrix. Hybrid particles were prepared using surface-initiated atom transfer radical polymerization (ATRP). The number average molecular weight of the matrix PMMA was Mn = 20,100 or 130,900 g/mol, while in the case of hybrids it was Mn = 5600, 27,300 or 191,600 g/mol. Two blend compositions were investigated: SAN/PMMA= 70/30 and 90/10 wt/wt, and the content of GO-g-PMMA was 1 wt%. Based on rheological studies it was demonstrated that higher molecular weights of the matrix PMMA promoted the compatibility of SAN/PMMA due to the similar viscosity of both blend components. Furthermore, the length of the PMMA chains grafted to the GO influenced the viscoelastic response of the material, resulting in different relaxation behavior as confirmed by mean relaxation times calculated from Cole-Cole plots. In addition, the effect of neat GO and GO-g-PMMA particles on the blend morphology and size distribution of PMMA droplets was discussed based on rheology and TEM analyses.

The Structural Layers of the Porcine Iris Exhibit Inherently Different Biomechanical Properties.

The purpose of this study was to isolate the structural components of the ex vivo porcine iris tissue and to determine their biomechanical properties. The porcine stroma and dilator tissues were separated, and their dimensions were assessed using optical coherence tomography (OCT). The stroma underwent flow test (n = 32) to evaluate for permeability using Darcy's Law (ΔP = 2000 Pa, A = 0.0391 mm2), and both tissues underwent stress relaxation experiments (ε = 0.5 with initial ramp of δε = 0.1) to evaluate for their viscoelastic behaviours (n = 28). Viscoelasticity was characterized by the parameters β (half width of the Gaussian distribution), τm (mean relaxation time constant), E0 (instantaneous modulus), and E∞ (equilibrium modulus). For the stroma, the hydraulic permeability was 9.49 ± 3.05 × 10-6 mm2/Pa · s, and the viscoelastic parameters were β = 2.50 ± 1.40, and τm = 7.43 ± 4.96 s, with the 2 moduli calculated to be E0 = 14.14 ± 6.44 kPa and E∞ = 6.08 ± 2.74 kPa. For the dilator tissue, the viscoelastic parameters were β = 2.06 ± 1.33 and τm = 1.28 ± 1.27 seconds, with the 2 moduli calculated to be E0 = 9.16 ± 3.03 kPa and E∞ = 5.54 ± 1.98 kPa. We have established a new protocol to evaluate the biomechanical properties of the structural layers of the iris. Overall, the stroma was permeable and exhibited smaller moduli than those of the dilator muscle. An improved characterization of iris biomechanics may form the basis to further our understanding of angle closure glaucoma.

Cardiac iron overload in pediatric oncology and bone marrow transplant survivors.

e22022 Background: Cardiovascular late effects are a leading cause of mortality and morbidity in childhood cancer and Bone Marrow Transplant (BMT) survivors. In patients receiving chronic red blood cell transfusions, excess iron may be deposited in the liver, heart, and pituitary gland. Iron overload cardiomyopathy is characterized as a restrictive physiology with early diastolic dysfunction ultimately progressing to end-stage dilated cardiomyopathy. Iron loading in the heart can also lead to arrhythmias and increase myocardial ischemia reperfusion injury due to increased formation of reactive oxygen species. It is not yet known whether high transfused packed red blood cell (PRBC) volumes in cancer and BMT patients leads to cardiac iron deposition, and whether iron-induced cardiac injury contributes to the known cardiovascular late effects in these patients. Methods: 83 childhood cancer and BMT survivors with elevated serum ferritin levels and subsequent liver Magnetic Resonance (MR) imaging were identified. 18 patients (21.7%) who had liver iron content of &gt; 12mg/g (mean 16.0 ± 7.36 mg/g) also underwent Cardiac MRI (CMR) to determine cardiac iron content. Results: Median transfused blood volume was 393 ml/kg [95% Confidence Interval (CI) 170-780 ml/kg]. All 18 patients had at least one echocardiogram showing normal ventricular ejection fractions [mean 65.1 ± Standard Deviation (SD) 3.53%] and normal shortening fractions (mean 35.4 ± 3.67%). All patients had myocardial iron content within normal ranges (T2* relaxation time mean 35.1 msec ± 7.1 [normal &gt;20 msec], mean ± SD iron content 0.63± 0.2 mg/g dry weight, range 0.5-1.1). There was no association of cardiac iron content with transfused blood volume, anthracycline dose (mg/m2) or liver iron content (Pearson Correlation Coefficients 0.27, 0.29 and 0.89 respectively). Conclusions: Childhood cancer and BMT patients receive multiple PRBC transfusions to treat symptomatic anemia. It is currently unknown whether excess iron deposition in the heart contributes to the cardiac effects of impaired diastolic function and ultimately systolic dysfunction. In this study, 11 of 18 patients (61.1%) with high levels of liver iron had at least 1 other risk factor for the development of future cardiac dysfunction (either anthracycline exposure, radiation to the chest or total body irradiation or both). Larger studies are needed to determine whether oncology patients with high levels of iron deposition in their liver are also at risk for clinically significant cardiac iron loading, and what risk factors may exist for elevated myocardial iron content.

Nonstationary thermophysical characterization of exfoliated graphite with carbon nanotubes composites

The sheet samples of thermally exfoliated graphite (TEG)–carbon nanotubes (CNT) composites (TEG-CNT-cs) were obtained by persulphate oxidation using chemical (CO) and electrochemical (anode) oxidation (ECAO). Electron microscopy reveals multi-layered structures of few-layer graphene nanosheets with folded and tubular-like fragments. The effective thermal diffusivity values were estimated by nonstationary photo-pyroelectric thermophysical characterization using the heat pulse and thermowave modulation methods. Comparison with other carbon (C-) based thermal management materials shows that TEG-CNT-cs exhibit thermal diffusivity, effusivity, and conductivity comparable with those of actual C–polymer- and C–C-composites. For TEG-CNT-cs, evaluated values of phonon mean free path (MFP) and relaxation time (RT) are in the ranges estimated for defective graphene. The values of diffusivity and effusivity, MFP, and RT are lower for denser TEG-CNT-cs obtained by ECAO and are higher for less dense TEG-CNT-cs obtained by CO. The obtained diffusivity and effusivity values designate TEG-CNT-cs as suitable thermal management materials.

Nuclear magnetic resonance at the laboratory and field scale as a tool for detecting redox fronts in aquifers

Surface nuclear magnetic resonance (NMR) provides information not only on the lithology and water transport characteristics of aquifer systems but also on the state of iron mineralization within the pore space. This feature makes surface NMR a potential tool for the observation of changing redox conditions in the aquifer, which control the type and oxidation state of iron minerals and, relatedly, the buffering or release of pollutants that may pose a threat to drinking water resources. Our study aims on testing this potential and focuses on pyrite contained in the matrix of a sandy aquifer that serves as a natural denitrification buffer in a drinking water catchment area with intensive agricultural use. We observe a significant change in the surface-NMR relaxation times related to the pyrite content in the subsurface, which is most obvious at the transition from the pyrite-free oxic zone and the pyrite-bearing reducing zone. Complementary laboratory experiments using core material from the study site, including laboratory NMR and geochemical analyses, verify that the influence of pyrite content predominates the NMR relaxation behavior rather than pore size, porosity, or carbon content. The mean relaxation times measured in the sediment without pyrite exceed those with pyrite by approximately 20%–100%. We conclude that surface NMR can serve as a capable tool to locate and monitor the pyrite-based denitrification buffer. However, for general applicability within the given framework, more research is needed to address the natural ambiguity among iron content, its redox state and speciation, and pore size.

A new perception to the spectroscopic, dielectric and impedance behavior of graphene oxide

The present study explores the synthesis of graphene oxide (GO) using Hummer’s method followed by a characterization that uses XRD, FTIR, Raman spectroscopy, UV, zeta potential, dielectric, and impedance study. The study of XRD, FTIR, UV, and Raman spectra revealed the presence of polar functional groups containing oxygen and structural deformity induced in GO. The nature of the surface charge, hydrodynamic diameter, and stability of graphite and GO in colloidal solution was ascertained from the zeta potentiometer. Raman spectra and zeta potential showed the presence of defects. The dielectric study of GO pellets with variation in frequency (1 Hz to 1 MHz) revealed the large dielectric constant of GO (∼105 at 26 °C and 1 Hz), which is comparable to conventional perovskite titanates dielectric materials. Both Lydanne–Sachs–Teller (LST) and Debye’s models of dielectric relaxation were taken into account while explaining the findings of giant dielectric constant in GO. Various mechanisms such as the presence of polar groups, Dirac fermions, and surface plasmon resonance have been discussed to explain the giant dielectric constant and its subsequent variation with frequency. The frequency dependence impedance and dielectric spectra were fitted using origin software to analyze poly dispersive nature and departure from Debye’s relaxation with an appraisal of static dielectric constant, static resistance, optical dielectric constant, optical resistance, mean relaxation time, and spreading factor. Nyquist plot was exploited to study the conductivity behavior of the GO by measuring grain capacitance, grain resistance, grain boundary capacitance, grain boundary resistance, and electrode resistance as well as capacitance. An equivalent electrical circuit was proposed for the measured data and it was correlated with the experimental findings. The findings suggest that synthesized GO pellets can be used for replacing perovskite materials and ferroelectric materials in high-performance electronic devices and energy storage devices such as supercapacitors.

Study on molecular dynamics and phase transitions in 1,2-cyclohexanediol and 1,3-cyclohexanediol isomers by calorimetry and dielectric spectroscopy

The results of broadband dielectric spectroscopy and differential scanning calorimetry of the trans and cis isomers of 1,2-cyclohexanediol and 1,3-cyclohexandiol are presented. Numerical analysis of the dielectric spectra points to complex dynamics of presented compounds in isotropic liquid, ordered crystalline, and orientationally disordered (plastic) crystal phases. Two relaxation processes were found in plastic crystal phases in cis-1,2-cyclohexanediol and trans-1,3-cyclohexanediol. These processes are responsible for the α-relaxation and forming/breaking hydrogen bonds between molecules forming clusters. One relaxation process was found in crystal phases and isotropic liquid phase. Temperature dependences of mean relaxation times are of the Arrhenius type, except for trans-1,3-cyclohexanediol compound for which the Vogel-Fulcher-Tammann dependence is fitted. The electric conductivity, fitted by Jonscher power law, is of similar order as for semiconducting materials. The electrode polarization effect is strong, especially in isotropic liquid and plastic crystal phases.

Electric field-induced phase transition from the glasslike to paraelectric phase and dielectric spectra hardening in PMN single crystal

One of the key points in the physics of the relaxors is their response to the applied DC field. Many studies of this topic were made, in particular on the influence of the field on the dielectric properties. However, practically, in all the cases, the measurements were performed at a fixed frequency and usually with the change in the temperature at the fixed field strength. In this paper, we report the evolution of the dielectric spectra at low frequencies (0.1 Hz [Formula: see text] 1 kHz) at fixed temperature 246 K on changing the DC electric field applied in (111) from 1 kV to 7 kV. Cole-Cole function was used to describe the spectra and the field dependences of the mean relaxation time [Formula: see text], the oscillation strength [Formula: see text] and the width parameter [Formula: see text] were determined. The obtained [Formula: see text]([Formula: see text]) and [Formula: see text] [Formula: see text]([Formula: see text]) provide evidence of the field-induced transition from the nonpolar glass-like phase to the nonpolar paraelectric phase at around 1.5 kV/cm. In the paraelectric phase, very fast hardening of the spectra was observed with [Formula: see text] changing from 10 s to about [Formula: see text]s. The performed analysis demonstrated that the earlier reported positive C-V effect is completely determined by the spectra hardening, while [Formula: see text][Formula: see text] does not show any change in the glass-like phase and monotonously decreases with a field increase in the paraelectric state. For complete understanding of the microscopic origin of the observed phenomena, a detailed study on the short-and long-range structures at the same condition is necessary.

Lattice Boltzmann method with effective correction of phonon properties for nano/microscale heat transfer

The significant self-heating effect severely restricts the performance and reliability of nano-electronic devices. Accordingly, it is very important to understand the process and mechanism of nano/microscale heat transfer for thermal management and thermal design of devices. In this work, we propose a new Lattice Boltzmann Method (LBM) scheme with effective correction of phonon mean free path (MFP) and relaxation time to study phonon heat transfer in silicon thin films and silicon medium with defects, where the correction factor is dependent on the lattice structure of LBM. The transformation analysis of phonon transfer mechanism at different scales shows that the size effect of cross-plane thermal conductivity is more remarkable than that of in-plane thermal conductivity. And the thermal conductivity of silicon medium with defects decreases exponentially as defect density increases. The proposed new LBM scheme can generate more accurate results than the traditional ones in the heat conduction simulations of different nano/microscale structures.

Raiders of the lost SAR: Radiofrequency cycles of magnetic nanoflowers inside a tumor

Radiofrequency magnetic cycles of ex vivo melanoma tumor tissue loaded with Fe3O4 nanoflowers (NF) were measured for several field conditions and compared with the cycles of a ferrogel (FG) obtained incorporating identical NF in agarose gel. Results were studied in order to understand a reported specific power dissipation (SAR) reduction of the NF in the actual application medium (tumor) in comparison with a typical characterization model as the FG. The linearity of the response, together with coercive field and SAR values were analyzed.Additionally, a novel method for the determination of the NF mean relaxation time is presented. Results show a systematic difference in magnetic response between the NF incorporated in the tumor and those in the FG for all field settings ({98, 170, 260} kHz and {17.4, 54.0} kA/m) with SAR reductions above 50%.