Amplitude Of Relaxation Research Articles

Ultrafast fluorescence dynamics of NADH in aprotic solvents: Quasi-static self-quenching unmasked

We have recently provided some experimental evidence that there are ultrafast quenched conformation(s) (“dark states”) of NADH. In this paper, the ultrafast fluorescence dynamics of NADH free in aprotic solvents (DMSO/DMF) has been investigated, using both a femtosecond up-conversion spectrophotofluorometer and a picosecond time-correlated single-photon counting (TCSPC) apparatus. The fluorescence kinetics in three solvents were recovered by constructing DAS (decay associated spectra) and TRES (time-resolved emission spectra). With the decrease of the ability of solvent to provide hydrogen bond interaction, apparent slow solvent relaxation (SSR) amplitudes were reduced, and the signal of “pure” quasi-static self-quenching (QSSQ) emerges. This fully positive DAS (positive at all emission wavelengths) appeared only in DMF, and this component accounts for about 20% of the total DAS. This confirms a model in which the ultrafast quenching portion of DAS is masked at times by the negative-going signal from slow solvent relaxation (SSR). Further, we have shown that the ratio of any slow solvent relaxation and QSSQ terms should be accounted for when quantifying NADH via fluorescence lifetime imaging microscopy (FLIM). Eventually, the other properties of the solvent (not only hydrogen bonding, but also polarity, viscosity, etc.) incorporated in QM-MM simulation must be fully considered to predict this ultrafast quenching vs SSR mixture more accurately. For now, we exploit the greatly reduced H-bonding to decrypt the QSSQ in a mixture.

Stimulation of the endogenous hydrogen sulfide synthesis restores constitutive nitric oxide synthesis and endothelium-dependent vasodilation in old rats

Abstract Funding Acknowledgements Type of funding sources: None. Introduction Hydrogen sulfide (H2S) is a gas transmitter of endogenous origin, which has an important regulatory function in the human body. Endogenous H2S is synthesized by three enzymes, cistationine-β-synthase (CBS), cistationine-γ-liase (CSE), and 3-mercaptopyruvate sulfurtransferase (3-MTS), which is coupled to the activity of cysteine aminotransferase (CAT). CAT, CBS, and CSE are pyridoxal-5- phosphate (PLP)-dependent enzymes. It is known that with age the exchange of hydrogen sulfide is disturbed against the background of increasing oxidative and nitrosative stress. At the same time there is a decrease of constitutive synthesis of nitric oxide (NO). Recent studies show that hydrogen sulfide closely interacts with the NO system. Activation of H2S biosynthesis and restoration of its pools in tissues of old animals may be a promising direction of cardiovascular disease prevention. The aim of the current work was to study the effect of H2S-synthesizing enzymes cofactor pyridoxal-5-phosphate (PLP) on the endothelium-dependent relaxation of smooth muscle vessels in old rats, as well as the H2S content and cNOS activity in aortic tissues. Methods Old rats (22-24 months old) were PLP administered per os in dose of 0,7 mg per kg daily for 2 weeks.The content of hydrogen sulfide, activity of cNOS and iNOS was measured in aortic tissues.Vascular reactions were determined in experiments on isolated aortic strips. To clarify the role of either NO or H2S in the endothelium-dependent vasorelaxation, N-nitro-L-arginine methyl ester hydrochloride (L-NAME) (Sigma, USA, 27 mg/kg) or O-carboxymethylhydroxylamine (O-CMH) (50 mg/kg) (Sigma, USA) was injected intraperitoneally 30 min before sacrificing. Results We showed that the H2S content was 1.6 times lower in old rat aorta compared to adult ones. PLP administration for 2 weeks induced a significant increase of H2S content in aortic tissue of old rats (P<0.05). It was found that with aging, the activity of cNOS decreases by 3 times, and the stimulation of endogenous Н2S leads to an increase in the activity of this enzyme in the aortic tissues by 2.1 times as compared with those in old animals. At the same time, the activity of the iNOS enzyme with aging increases by 3.8 times, and after the introduction of PLP, it decreases almost halved. Also shown, that PLP significantly improved endothelium-dependent aortic smooth muscle relaxation in old rats. The amplitude of acetylcholine-induced relaxation which was significantly reduced in old rats was increased more than 2.5-fold. This effect was reversed by inhibitors of NO-synthase and 3-mercaptopyruvate sulfurtransferase indicating the involvement of NO and H2S in the improved endothelium-dependent vascular relaxation. Conclusions Thus, H2S acts as a regulator of the NO system that increases cNOS activity and NO synthesis in aortic tissue, which improves endothelium-dependent relaxation of aortic smooth muscle in aged rats.

Establishing the role of shear viscosity on the rate constants of conformational fluctuations in unsaturated aldehydes

The goal of the present work was to evaluate the viscosity effect on the constants of rotational isomerism exhibited by acrolein and crotonaldehyde unsaturated aldehydes in various frequencies and temperatures by means of ultrasonic relaxation spectroscopy. Only one relaxation process has been detected in a wide frequency range for both liquids, which is assigned to a unimolecular reaction due to rotational isomerism of the corresponding molecules. The rate constants attributed to these conformational changes were determined by analyzing in detail the ultrasonic absorption coefficient as a function of temperature. Temperature rise induces increase of the relaxation frequency with a parallel reduction of the relaxation amplitude for both systems. Quantum mechanical calculations have been performed in an effort to confirm the assignment of the relaxation process to rotational isomerism and to evaluate theoretically the energetics of the optimized isomeric structures of the aldehyde molecules. From the temperature dependence of the acoustic parameters, the experimental activation energy and the energy difference between isomeric forms have been evaluated for both aldehydes in the liquid state. The behavior of the rate constants as a function of viscosity is interpreted and analyzed in the context of stochastic and phenomenological models of the field.

Elucidating Postprogramming Relaxation in Multilevel Cell‐Resistive Random Access Memory by Means of Experimental and Kinetic Monte Carlo Simulation Data

This work explores the phenomenon of HfO2 resistive random access memory (RRAM) postprogramming resistance relaxation using experimental data and kinetic Monte Carlo (KMC) physical simulation. This issue has become an important limitation for multilevel cell (MLC) applications. The physical KMC simulation replicates the RRAM cell‐to‐cell intrinsic resistance variability due to the conductive filament (CF) morphology fluctuations and the weak correlation between the number of oxygen vacancies and the resulting resistance. It furthermore accurately simulates the vacancies’ microscopic dynamics within the CF that are responsible for the RRAM resistance relaxation. A link between programming current, CF size/configuration, and relaxation amplitude is clarified and shows the ensuing benefits and limitations of smart programming techniques (read & verify) for MLC applications. Coupled with experimental data obtained on HfO2‐based RRAM arrays, this simulation paves the way to a better understanding of the physics at stake in the RRAM relaxation process and provides guidelines to potential technological solutions for MLC reliability prediction.

Interfacial viscosity and ionic reorientation probed using electrochemical surface plasmon resonance at the gold electrode interface of ionic liquids

• Interfacial dielectric relaxation of ionic liquids has been studied by ESPR. • Interfacial viscosity of ionic liquids is demonstrated to be extremely high. • Smaller ions tend to form the electric double layer with more solid-like structure. • Imidazolium ring has weak reorientation response to the potential steps. The interfacial dielectric relaxation of ionic liquids (ILs) at the gold electrode interface has been investigated using electrochemical surface plasmon resonance (SPR), by analyzing the SPR response to the potential step for four ILs with the two cations, trioctylmethylammonium and 1-butyl-3-methylimidazolium, and three amide anions, bis(fluorosulfonyl)amide, bis(trifluoromethanesulfonyl)amide, and bis(nonafluorobutanesulfonyl)amide. For all the four ILs, the SPR response to the potential step exhibits a fast relaxation process mainly ascribable to the ionic reorientation, followed by an ultraslow relaxation process ascribable to the ionic translation, with the opposite directions of SPR shift to each other. The ultraslow relaxations by the positive potential steps are always significantly slower than those by the negative steps. The average time constants of the ultraslow relaxation process and the amplitudes of the fast relaxation process are evaluated by the fitting with a multiple exponential function and are compared with the measured bulk viscosity and the dipole moments of each ion. The interfacial viscosity, estimated from the time constants of the ultraslow relaxation process, is several orders of magnitude higher than the bulk viscosity, and the viscosity increase is larger for the ILs composed of smaller ions. The amplitude of the fast relaxation, reflecting the ionic reorientation, is moderately correlated with the dipole moments of counter-ions on the electrode at the pre-step potential.

Thermal stability study of TC11 titanium alloy thin component after surface nanocrystallization induced by laser shock processing

Laser shock peening (LSP) can induce the compressive residual stress (CRS) on the surface of the material, and surface nanocrystallization can be realized with a nanocrystal layer, thereby significantly improving the high-cycle fatigue performance. However, due to weak material constrain and the high working temperature of thin aero-engine compressor blades, CRS and refined grain structure are more likely to result in stress relaxation and microstructural recovery under thermal stress load, resulting in reducing the anti-fatigue effect of LSP. In this paper, on the basis of the surface nanocrystallization induced by LSP, residual stress and microstructure of TC11 titanium alloy thin components were measured and observed. The residual stress relaxation was characterized and the microstructure evolution was discussed. Also, the thermal stability mechanism of CRS and the nanostructure on the surface were analyzed. The experimental results show that after thermal loads, the CRS was decreased, and the stress relaxation amplitude was increased with an increase in temperature. After annealing at 400 °C, the dislocation density was significantly reduced, but the grain sizes of surface nanostructure did not greatly increase. After annealing at 400 °C for 2 h, the fatigue strength of the LSPed specimen was reduced compared with that before annealing, but it was still increased compared with the original state without LSP, especially under high-power density for multiple LSP treatment. It can be concluded that the surface nanostructure has good stability and effectively retards the initiation of fatigue cracks on the surface, which ensures the effectiveness of LSP under thermal loads.

Stress relaxation amplitude of hydrogels determines migration, proliferation, and morphology of cells in 3-D culture.

The viscoelastic behavior of hydrogel matrices sensitively influences the cell behavior in 3-D culture and biofabricated tissue model systems. Previous reports have demonstrated that cells tend to adhere, spread, migrate and proliferate better in hydrogels with pronounced stress relaxation. However, it is currently unknown if cells respond more sensitively to the amplitude of stress relaxation, or to the relaxation time constant. To test this, we compare the behavior of fibroblasts cultured for up to 10 days in alginate and oxidized alginate hydrogels with similar Young's moduli but diverging stress relaxation behavior. We find that fibroblasts elongate, migrate and proliferate better in hydrogels that display a higher stress relaxation amplitude. By contrast, the cells' response to the relaxation time constant was less pronounced and less consistent. Together, these data suggest that it is foremost the stress relaxation amplitude of the matrix that determines the ability of cells to locally penetrate and structurally remodel the matrix on a molecular level, which subsequently leads to better spreading, faster migration, and higher cell proliferation. We conclude that the stress relaxation amplitude is a central design parameter for optimizing cell behavior in 3-D hydrogels.

Effect of Structurally Different Pectin on Dough Rheology, Structure, Pasting and Water Distribution Properties of Partially Meat-Based Sugar Snap Cookies.

Pectin has been widely used as a hydrocolloid in foods, but its effectiveness based on hydrodynamics radius (Rh), average side chain length (ACL) and degree of esterification (DE) has been less studied. This study investigated the effect of 4 types of pectin (with different molecular weight and structures) at a level of 1.5% w/w of wheat flour on functional, structural and water binding properties of sugar snap cookies partially substituted with fish meat. The results showed that pectin (CU-201 and CU-601) with higher ACL and Rh controlled excessive expansion, while the improved rheology of dough in terms of behavior as viscous matrix compared to control and other pectin. Texture was found to be highly dependent on Rh and ACL compared to DE of pectin. The pasting properties, especially peak viscosity and final viscosity, were significantly (p < 0.05) increased with increasing DE, as well as ACL, by entangling and increasing the interaction between starch and pectin. The scanning electron microscopy (SEM) analysis exhibited that control sample showed wide voids and more intercellular spaces, while samples prepared with CU-601, CU-201, and CUL displayed compact structure, which was also evidenced by controlled expansion and improved hardness of the cookies. Low field nuclear magnetic resonance (LF-NMR) analysis showed that T21 relaxation time and amplitude were found to be shorter for CU-601 and CU-201 treatments, signifying the high amount of tightly bound water compared to control. The findings endorse the feasibility of adding CU-601, and CU-201 as an efficient hydrocolloid for the improved structural and functional properties of cookies.

Kinetics and mechanisms of stress relaxation in sputtered silver thin films

The post-growth stress relaxation in thin polycrystalline Ag films, deposited by direct-current magnetron sputtering under different growth conditions, was explored through wafer curvature measurements. It exhibits exponential behaviour with three distinct characteristic time components τ. The slowest one, namely τth≃200 s, is ascribed to thermal stress inherent to the deposition method. In fact, the performed temperature measurements match perfectly with an exponential stress variation with heating or cooling, as predicted by a thermal exchange model detailed in this work. Based on a comparison between different deposition conditions (continuous/interrupted sputter deposition and evaporation), the case of Mo deposition and stress relaxation modelling, the remaining components are assigned to the out-diffusion of atoms from grain boundaries (τgb≃3 s) and to changes in the grain surface shape induced by grain boundary grooving (τsurf≃20 s). The relaxation amplitude of the first mechanism varies linearly with the steady-state stress at the end of growth in agreement with theoretical expectations. Yet, that of the second one does not. However, clues point to a kinetic limitation of atomic diffusion mechanism along grain boundaries. This study provides proofs of the simultaneous occurrence of several mechanisms of stress relaxation in thin metallic films.

Phospholipids in Motion: High-Resolution 31P NMR Field Cycling Studies.

Diverse phospholipid motions are key to membrane function but can be quite difficult to untangle and quantify. High-resolution field cycling 31P NMR spin-lattice relaxometry, where the sample is excited at high field, shuttled in the magnet bore for low-field relaxation, then shuttled back to high field for readout of the residual magnetization, provides data on phospholipid dynamics and structure. This information is encoded in the field dependence of the 31P spin-lattice relaxation rate (R1). In the field range from 11.74 down to 0.003 T, three dipolar nuclear magnetic relaxation dispersions (NMRDs) and one due to 31P chemical shift anisotropy contribute to R1 of phospholipids. Extraction of correlation times and maximum relaxation amplitudes for these NMRDs provides (1) lateral diffusion constants for different phospholipids in the same bilayer, (2) estimates of how additives alter the motion of the phospholipid about its long axis, and (3) an average 31P-1H angle with respect to the bilayer normal, which reveals that polar headgroup motion is not restricted on a microsecond timescale. Relative motions within a phospholipid are also provided by comparing 31P NMRD profiles for specifically deuterated molecules as well as 13C and 1H field dependence profiles to that of 31P. Although this work has dealt exclusively with phospholipids in small unilamellar vesicles, these same NMRDs can be measured for phospholipids in micelles and nanodisks, making this technique useful for monitoring lipid behavior in a variety of structures and assessing how additives alter specific lipid motions.

Molecular relaxation dynamics and self-association of dexamethasone sodium phosphate solutions.

Detailed concentration-dependent measurements of sound absorption and velocity have been performed in dexamethasone sodium phosphate (DSP) aqueous solutions in the MHz frequency range. A single well-resolved relaxation process dominates the experimental acoustic spectra following a Debye-type distribution function. The analysis of the temperature-dependent ultrasonic relaxation data also revealed analogous effect with concentration on the relaxation spectra. All acoustic parameters were estimated by means of a fitting procedure. The behavior of the relaxation frequency and amplitude with concentration allowed us to assign the observed process to self-association mechanism. Combining the ultrasonic and electric conductivity data, the self-association scheme has been established. The thermodynamic constants and the rate of the aggregation due to hydrophobic interactions have been estimated in view of the Eyring’s theory. The concentration dependence of relaxation amplitude and characteristic frequency revealed that the presence of additional relaxation processes in the spectra related to additional mechanisms, such as conformational changes and proton-transfer reaction is excluded and the self-association process considered here was found to dominate in this frequency range. The results have been discussed in view of the fair ability of DSP for hydrophobic interactions and aggregate formation in aqueous environment.Graphic abstract

Cooperative dynamics and speciation in deep eutectic solvent + DMSO mixtures

Dielectric relaxation (DR) spectra within the frequency range of 0.05 ≤ ν/GHz ≤ 89 were measured at T = 308.15 K to reveal structure and dynamics of mixtures of deep eutectic solvents (DESs) with dimethylsulfoxide (DMSO). Studied DESs were reline, glyceline and ethaline, ie. 1:2 molar ratio mixtures of choline chloride (ChCl) and the hydrogen bond donors (HBDs) urea, glycerol and ethylene glycol. The obtained DR spectra were best fit by a superposition of relaxations associated with the reorientation of dipolar DES components and individual DMSO molecules. In contrast to previously studied mixtures of glyceline and reline with water, the analysis of the obtained relaxation amplitudes revealed that the present DES/DMSO systems cannot be simply regarded as mixtures of individual Ch+, Cl−, HBD and DMSO units over the entire mixture range. Instead, a significant amount of ChCl contact ion pairs (CIPs) is formed at moderate DES concentrations. Due to their high dipole moment these CIPs cause pronounced maxima at ChCl:HBD:DMSO ratios of ~1 : 2 : 9 in the static permittivity of the mixtures. Pronounced solute-solvent interactions slow down the rotational motion of solvating DMSO molecules. At infinite dilution the derived total effective solvation numbers, Zt, extrapolate to ~8 − 9 DMSO per ethaline, ~16 per glyceline and ~7 − 8 per reline unit but numbers decrease rapidly with rising DES mole fraction. For the latter two DESs Zt could be split into ChCl and HBD contributions. Finally, careful analysis of the relaxation times provided evidence for pronounced micro-heterogeneity of the studied mixtures.

Spatiotemporal Temperature and Pressure in Thermoplasmonic Gold Nanosphere-Water Systems.

We offer a detailed investigation of the photophysical properties of plasmonic solid and hollow gold nanospheres suspended in water by combining ultrafast transient absorption (TA) spectroscopy with molecular dynamics (MD) simulations. TA reveals that hollow gold nanospheres (HGNs) exhibit faster excited state relaxation and larger amplitude acoustic phonon modes than solid gold nanoparticles of the same outer diameter. MD simulation carried out on full scale nanoparticle-water models (over 10 million atoms) to simulate the temporal evolution (0-100 ps) of the thermally excited particles (1000 or 1250 K) provides atomic-scale resolution of the spatiotemporal temperature and pressure maps, as well as visualization of the lattice vibrational modes. For the 1000 K HGN, temperatures upward of 500 K in the vicinity of the shell surface were observed, along with pressures up to several hundred MPa in the inner cavity, revealing potential use as a photoinduced nanoreactor. Our approach of combining TA and MD provides a path to better understanding how thermal-structural properties (such as expansion and contraction) and thermal-optical properties (such as modulated dielectrics) manifest themselves as TA signatures. The detailed picture of heat transfer at interfaces should help guide nanoparticle design for a wide range of applications that rely on photothermal conversion, including photothermal coupling agents for nanoparticle-mediated photothermal therapy and photocatalysts for light-driven chemical reactions.

Study of Some Physical Properties for Polyvinyl Alcohol-Polyethylene Glycol Blends

A polymer blends (PVA/PEG) have been prepared at various concentrations(6%, 8%, 10%, 12%, and 14%) g /ml by dissolving different weights from the powders{Pva and Peg}.The behavior of this mixture has been studied utilize some physical properties such as ultrasonic absorption coefficient, relaxation amplitude, specific acoustic Impedance, compression, bulk modulus, shear viscosity, and Reduced viscosity. The outcomes referenced that each of these characteristics increased with increasing concentration of polymeric solutions, "while compressibility decreased with increasing concentration solutions".

Sampling reflex: pathogenic role in functional defecation disorder.

The sampling reflex is necessary to begin defecation or flatulence. It consists of a simultaneous rectoanal inhibitory reflex (RAIR) mediated by relaxation of the internal anal sphincter and rectoanal excitatory reflex (RAER) mediated by contraction of the external anal sphincter. The aim of this study was to evaluate the sampling reflex in patients with functional defecation disorder (FDD). A prospective cohort study was conducted on 58 obstructed defecation syndrome (ODS) patients with FDD. All 58 patients and 20 controls were evaluated with anorectal manometry to study the sampling reflex. Quantitative RAIR (total duration of reflex; maximal amplitude of relaxation; residual pressure at the lowest point of the RAIR) and RAER data (maximal amplitude of contraction; duration) were obtained. The straining test on manometry was considered positive for FDD if there was a muscle contraction/lack of relaxation or an insufficient pressure gradient for the passage of feces. Defecography was performed on all the patients with assessment of the anorectal angle and persistence or increase of puborectalis indentation. Fifty (86.2%) FDD patients had an altered sampling reflex, showing incomplete/short duration of RAIR and excessive contraction/duration of RAER. More specifically, there was a correlation between a positive straining test and a short total duration of RAIR (ρ 0.92) as well as with excessive duration of RAER (ρ 0.89). There was also a correlation between lack of muscle relaxation on defecography and short total duration of RAIR ((ρ 0.79) and between lack of muscle relaxation on defecography and excessive duration of RAER (ρ 0.83). Altered maximal amplitude relaxation had the highest sensitivity in detecting impairment of RAIR (87.9) while maximal amplitude contraction had the highest sensitivity in detecting impairment of RAER (89.6). High residual pressure at the lowest point of RAIR had the highest specificity in detecting impairment of RAIR (80.0) while RAER duration had the highest specificity in detecting impairment of RAER (77.7). The sampling reflex is impaired in patients with FDD. This finding provides an important insight into the pathogenesis of obstructed functional defecation.

Ultrafast dynamics in the high-symmetry and in the charge density wave phase of 2H−NbSe2

We investigate carrier and collective mode dynamics in 2H-NbSe$_2$ using time-resolved optical pump-probe spectroscopy and compare the results with first-principle calculations. Broadband ultrafast reflectivity studies of 2H-NbSe$_2$ in a wide temperature interval covering the normal, charge density wave (CDW) and superconducting phase were performed. Spectral features observed in the transient reflectivity experiment were associated with specific optical transitions obtained from band structure calculations. Displacive excitation of coherent phonons showed CDW-associated coherent oscillations of the soft phonon mode across the whole spectral range. Temperature evolution of this coherent phonon mode in the low-excitation linear regime shows softening of the mode down to the CDW transition temperature T$_{CDW}$ with subsequent hardening below T$_{CDW}$. The global fit of the broadband probe data reveals four different relaxation times associated with characteristic electron-electron, electron-phonon and phonon-phonon relaxation processes. From first principle calculations of electron-phonon coupling we associate the few picosecond electron-phonon relaxation time $\tau_2$ with a specific group of phonons with frequencies around 20 meV. On the other hand, the anomalously long relaxation time of $\tau_3$~100 ps is associated with anharmonicity-driven phonon-phonon scattering. All relaxation processes result from anomalies near the second order CDW phase transition that are reflected in the temperature dependencies of the characteristic relaxation times and amplitudes of optical densities. At highest fluences we observe electronic melting of the CDW and disappearance of the mode hardening below T$_{CDW}$.

Broadband multi-magnon relaxometry using a quantum spin sensor for high frequency ferromagnetic dynamics sensing

Development of sensitive local probes of magnon dynamics is essential to further understand the physical processes that govern magnon generation, propagation, scattering, and relaxation. Quantum spin sensors like the NV center in diamond have long spin lifetimes and their relaxation can be used to sense magnetic field noise at gigahertz frequencies. Thus far, NV sensing of ferromagnetic dynamics has been constrained to the case where the NV spin is resonant with a magnon mode in the sample meaning that the NV frequency provides an upper bound to detection. In this work we demonstrate ensemble NV detection of spinwaves generated via a nonlinear instability process where spinwaves of nonzero wavevector are parametrically driven by a high amplitude microwave field. NV relaxation caused by these driven spinwaves can be divided into two regimes; one- and multi-magnon NV relaxometry. In the one-magnon NV relaxometry regime the driven spinwave frequency is below the NV frequencies. The driven spinwave undergoes four-magnon scattering resulting in an increase in the population of magnons which are frequency matched to the NVs. The dipole magnetic fields of the NV-resonant magnons couple to and relax nearby NV spins. The amplitude of the NV relaxation increases with the wavevector of the driven spinwave mode which we are able to vary up to 3 × 106 m−1, well into the part of the spinwave spectrum dominated by the exchange interaction. Increasing the strength of the applied magnetic field brings all spinwave modes to higher frequencies than the NV frequencies. We find that the NVs are relaxed by the driven spinwave instability despite the absence of any individual NV-resonant magnons, suggesting that multiple magnons participate in creating magnetic field noise below the ferromagnetic gap frequency which causes NV spin relaxation.

Tuning the dynamics in Fe3O4 nanoparticles for hyperthermia optimization

The AC magnetic susceptibility (ACS) of Fe3O4 nanoparticles was measured between 10 kHz and 4 MHz at different temperatures and in applied DC fields. In this frequency range, magnetostatic interactions impact magnetization dynamics even for dilute assemblies. The ACS spectrum of relaxation frequencies changes both with temperature and the addition of a small DC field. Because both the relaxation peak frequency and amplitude can be tuned with the DC field, these results could be applied to magnetic hyperthermia applications to optimize heat delivery.

Inotropic assessment in engineered 3D cardiac tissues using human induced pluripotent stem cell-derived cardiomyocytes in the BiowireTM II platform

To develop therapeutics for cardiovascular disease, especially heart failure, translational models for assessing cardiac contractility are necessary for preclinical target validation and lead optimization. The availability of stem cell-derived cardiomyocytes (SC-CM) has generated a great opportunity in developing new in-vitro models for assessing cardiac contractility. However, the immature phenotype of SC-CM is a well-recognized limitation in inotropic evaluation, especially regarding the lack of or diminished positive inotropic response to β-adrenergic agonists. Recent development of 3D engineered cardiac tissues (ECTs) using human induced pluripotent stem cell derived-cardiomyocytes (hiPSC-CM) in the BiowireTM II platform has shown improved maturation. To evaluate their suitability to detect drug-induced changes in cardiac contractility, positive inotropes with diverse mechanisms, including β-adrenergic agonists, PDE3 inhibitors, Ca2+-sensitizers, myosin and troponin activators, and an apelin receptor agonist, were tested blindly. A total of 8 compounds were evaluated, including dobutamine, milrinone, pimobendan, levosimendan, omecamtiv mecarbil, AMG1, AMG2, and pyr-apelin-13. Contractility was evaluated by analyzing the amplitude, velocity and duration of contraction and relaxation. All tested agents, except pyr-apelin-13, increased contractility by increasing the amplitude of contraction and velocity. In addition, myosin and troponin activators increase contraction duration. These results indicate that ECTs generated in the BiowireTM II platform can identify inotropes with different mechanisms and provides a human-based in-vitro model for evaluating potential therapeutics.

Reinforcement the Mechanical Properties of (NR50/SBRs50/OSP) Composites with Oyster Shell Powder and Carbon Black

In this study, the rubber batches composites were prepared using Natural rubber (NR) and synthetic rubber (SBR) as model materials. The composites were reinforced using oyster shell powder (OSP) with particle size less than (225μm). Two groups of samples were prepared with (0, 5, 10, 15, 20, 25, 30, 40 and 60 pphr) with loading ratio of OSP and (CB-10pphr) of CB, whereas other composites were without CB. Density, viscosity and multi ultrasound velocity wave devices were applied to characterize the density according to the specification (ASTM-D1817-66) (Densitron), rheological properties with specification (ASTM-D2084-89) standard and mechanical properties, respectively. The result showed significant influence of the reinforcements (OSP) material and (CB) on some of these properties that exhibited an increasing with the increasing of loading ratio of (OSP) and (CB), such as density, relaxation amplitude and compressibility, but the other properties were decreasing like viscosity, relaxation time, velocity waves, bulk modulus and specific acoustic impedance.