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Investigation of the Dynamic and Diffusional Properties of Supported Membranes on Bioinspired Materials using HRMAS NMR.
Abstract not provided.
Primate translational vestibuloocular reflexes. I. High-frequency dynamics and three-dimensional properties during lateral motion
The dynamics and three-dimensional (3-D) properties of the primate translational vestibuloocular reflex (trVOR) for high-frequency (4-12 Hz, +/-0.3-0.4 g) lateral motion were investigated during near-target viewing at center and eccentric targets. Horizontal response gains increased with frequency and depended on target eccentricity. The larger the horizontal and vertical target eccentricity, the steeper the dependence of horizontal response gain on frequency. In addition to horizontal eye movements, robust torsional response components also were present at all frequencies. During center-target fixation, torsional response phase was opposite (anticompensatory) to that expected for an "apparent" tilt response. Instead torsional response components depended systematically on vertical-target eccentricity, increasing in amplitude when looking down and reversing phase when looking up. As a result the trVOR eye velocity vector systematically tilted away from a purely horizontal direction, through an angle that increased with vertical eccentricity with a slope of approximately 0.7. This systematic dependence of torsional eye velocity tilt on vertical eye position suggests that the trVOR might follow the 3-D kinematic requirements that have been shown to govern visually guided eye movements and near-target fixation.
Viscoelastic properties of concentrated dispersions in a molten polymer
Dynamic, viscoelastic properties of molten polyethylene with fillers
Method and apparatus for determining the physical properties of materials using dynamic light scattering techniques
A system for determining the physical properties of materials through the use of dynamic light scattering is disclosed. The system includes a probe, a laser source for directing a laser beam into the probe, and a photodetector for converting scattered light detected by the probe into electrical signals. The probe includes at least one optical fiber connected to the laser source and a second optical fiber connected to the photodetector. Each of the fibers may adjoin a gradient index microlens which is capable of providing a collimated laser beam into a scattering medium. The position of the second optical fiber with respect to the optical axis of the probe determines whether homodyne or self-beating detection is provided. Self-beating detection may be provided without a gradient index microlens. This allows a very small probe to be constructed which is insertable through a hypodermic needle or the like into a droplet extending from such a needle. A method of detecting scattered light through the use of a collimated, Gaussian laser beam is also provided. A method for controlling the waist and divergence of the optical field emanating from the free end of an optical fiber is also provided.
Viscoelastic properties of addition-cured polyimides used in high temperature polymer matrix composites
Viscoelastic properties of the addition cured polyimide, PMR-15, were studied using dynamic mechanical and stress relaxation tests. For temperatures below the glass transition temperature, T sub g, the dynamic mechanical properties measured using a temperature scan rate of 10 C/min were strongly affected by the presence of absorbed moisture in the resin. Dynamic mechanical properties measured as a function of time during an isothermal hold provided an indication of chemical changes occurring in the resin. For temperatures above (T sub g + 20 C), the storage modulus increased continuously as a function of time indicating that additional crosslinking is occurring in the resin. Because of these changes in chemical structures, the stress relaxation modulus could not be measured over any useful time interval for temperatures above T sub g. For temperatures below T sub g, dynamic mechanical properties appeared to be unaffected by chemical changes for times exceeding 1 hr. Since the duration of the stress relaxation tests was less than 1 hr, the stress relaxation modulus could be measured. As long as the moisture content of the resin was less than 2 pct, stress relaxation curves measured at different temperatures could be superimposed using horizontal shifts along the log(time) axis with only small shifts along the vertical axis.
AGC-1 Irradiation Induced Property Changes Analysis Report: Dynamic Elastic Modulus
Recent analyses of some of the test property data from the AGC-1 creep capsule are reported. Specifically the analyses of data for the effects of compressive creep strain on the Dynamic elastic modulus (by the fundamental frequency and ultrasonic velocity/tof methods) are reported. Statistical “t” testing was used to establish the statistical significance of any differences observed between the Dynamic elastic modulus of the creep (irradiated with compressive stress) and the control (irradiated without stress) specimens. Compressive creep strain does have a small effect on Dynamic elastic modulus, reducing it at the higher doses as volume turnaround is approached.
Mechanical, Dynamic Mechanical and Thermal Properties of Banana Fiber/Recycled High Density Polyethylene Biocomposites Filled with Flyash Cenospheres
This study presents the preparation of Natural fiber-reinforced biocomposites based on Recycled High Density Polyethylene (RHDPE)/Banana Fiber (BF)/Fly ash Cenospheres (FACS) and aims to increase the economic value of these waste materials. Maleic anhydride grafted HDPE (MA-g-HDPE) was used as a compatibilizer to increase the dispersion of fibers into the polymer matrix as well as to increase the compatibility between the matrix and fillers. Variation in mechanical, thermal and dynamic mechanical properties with the addition of FACS in RHDPE/BF composites was investigated. It was observed that 7.5 wt% FACS, 30 wt% BF and 3 wt% MA-g-HDPE within RHDPE matrix resulted in an increase in tensile strength to 17%, tensile modulus to 188%, flexural strength to 38%, flexural modulus to 159% and hardness to 37% as compared with the RHDPE matrix. Significant enhancement in the thermal stability of the RHDPE/BF biocomposites was also observed in presence of FACS under thermogravimetric analysis. The morphology of the prepared biocomposites has been examined by using scanning electron microscopy. Dynamic mechanical analysis tests revealed an increase in storage and loss modulus of the biocomposite system. The use of such recycled material, agricultural and industrial wastes increased the properties of the final product suggesting their use to be a good alternative in the production of polymeric composites.
Molecular Dynamics Simulation of Thermodynamic Properties in Uranium Dioxide
In the present study, we investigated the thermodynamic properties of uranium dioxide (UO2) by molecular dynamics (MD) simulations. As for solid UO2, the lattice parameter, density, and enthalpy obtained by MD simulations were in good agreement with existing experimental data and previous theoretical predictions. The calculated thermal conductivities matched the experiment results at the midtemperature range but were underestimated at very low and very high temperatures. The calculation results of mean square displacement represented the stability of uranium at all temperatures and the high mobility of oxygen toward 3000 K. By fitting the diffusivity constant of oxygen with the Vogel-Fulcher-Tamman law, we noticed a secondary phase transition near 2006.4 K, which can be identified as a ‘‘strong’’ to ‘‘fragile’’ supercooled liquid or glass phase transition in UO2. By fitting the oxygen diffusion constant with the Arrhenius equation, activation energies of 2.0 and 2.7 eV that we obtained were fairly close to the recommended values of 2.3 to 2.6 eV. Xiangyu Wang, Bin Wu, Fei Gao, Xin Li, Xin Sun, Mohammed A. Khaleel, Ademola V. Akinlalu and Li Liu
Review of NMR studies of nanoscale molecular magnets composed of geometrically frustrated antiferromagnetic triangles
This paper presents a comprehensive review of nuclear magnetic resonance (NMR) studies performed on three nanoscale molecular magnets with different novel configurations of geometrically frustrated antiferromagnetic (AFM) triangles: (1) the isolated single AFM triangle K 6 [V 15 As 6 O 42 (H 2 O)]·8H 2 O (in short V15), (2) the spin ball [Mo 72 Fe 30 O 252 (Mo 2 O 7 (H 2 O)) 2 (Mo 2 O 8 H 2 (H 2 O)) (CH 3 COO) 12 (H 2 O) 91 ]·150H 2 O (in short Fe30 spin ball), and (3) the twisted triangular spin tube [(CuCl 2 tachH) 3 Cl]Cl 2 (in short Cu3 spin tube). In V15t, from 51 V NMR spectra, the local spin configurations were directly determined in both the nonfrustrated total spin S T = 3/2 state at higher magnetic fields (H ge; 2.7 T) and the two nearly degenerate S T = 1/2 ground states at lower magnetic fields (H ≤ 2.7 T). The dynamical magnetic properties of V15 were investigated by proton spin-lattice relaxation rate (1/T 1 ) measurements. In the S T = 3/2 state, 1/T 1 shows thermally activated behaviour as a function of temperature. On the other hand, the temperature independent behaviour of 1/T 1 at very low temperatures is observed in the frustrated S T = 1/2 ground state. Possible origins for the peculiar behaviour of 1/T 1 will be discussed in terms of magnetic fluctuations due to spin frustrations. In Fe30, static and dynamical properties of Fe 3+ (s = 5/2) have been investigated by proton NMR spectra and 1/T 1 measurements. From the temperature dependence of 1/T 1 , the fluctuation frequency of the Fe 3+ spins is found to decrease with decreasing temperature, indicating spin freezing at low temperatures. The spin freezing is also evidenced by the observation of a sudden broadening of 1 H NMR spectra below 0.6 K. Finally, 1 H NMR data in Cu3 will be described. An observation of magnetic broadening of 1 H NMR spectra at low temperatures below 1 K directly revealed a gapless ground state. The 1/T 1 measurements revealed a usual slow spin dynamics in the Cu3 spin tube.
Estimating Material Properties Under Extreme Conditions by Using Bayesian Model Calibration with Functional Outputs
Summary Dynamic material properties experiments provide access to the most extreme temperatures and pressures attainable in a laboratory setting; the data from these experiments are often used to improve our understanding of material models at these extreme conditions. We apply Bayesian model calibration to dynamic material property applications where the experimental output is a function: velocity over time. This framework can accommodate more uncertainties and facilitate analysis of new types of experiments relative to techniques traditionally used to analyse dynamic material experiments. However, implementation of Bayesian model calibration requires more sophisticated statistical techniques, because of the functional nature of the output as well as parameter and model discrepancy identifiability. We propose a novel Bayesian model calibration process to simplify and improve the estimation of the material property calibration parameters. Specifically, we propose scaling the likelihood function by an effective sample size rather than modelling the auto-correlation function to accommodate the functional output. Additionally, we propose sensitivity analyses by using the notion of 'modularization' to assess the effect of experiment-specific nuisance input parameters on estimates of the physical parameters. The Bayesian model calibration framework proposed is applied to dynamic compression of tantalum to extreme pressures, and we conclude that the procedure results in simple, fast and valid inferences on the material properties for tantalum.
Effect of niobium doping on excitonic dynamics in MoSe 2
Abstract Transition metal dichalcogenides (TMDs) have emerged as attractive two-dimensional semiconductors for future electronic and optoelectronic applications. Their charge transport properties, such as conductivity and the type of charge carriers, can be effectively controlled by substitutional doping of the transition metal atoms. However, the effects of doping on the excitonic properties, particularly their dynamical properties, have been less studied. Using Nb-doped MoSe 2 as a case study, we experimentally investigate the effect of doping on excitonic dynamics in TMDs. Transient absorption measurements are used to directly compare the dynamical properties of excitons in Nb-doped MoSe 2 across monolayer, bilayer, and bulk flakes with their undoped counterparts. The exciton lifetimes in Nb-doped flakes are significantly shorter than those in their undoped counterparts. This effect is attributed to the trapping of excitons in defect states introduced by Nb impurities. These results reveal an important consequence of Nb doping on excitonic dynamics in TMDs.
Assessment of structural, thermal, and mechanical properties of portlandite through molecular dynamics simulations
The structural, thermal, and mechanical properties of portlandite, the primary solid phase of ordinary hydrated cement paste, are investigated using the molecular dynamics method. To understand the effects of temperature on the structural properties of portlandite, the coefficients of thermal expansion of portlandite are determined in the current study and validated with what reported from the experimental tests. The atomic structure of portlandite equilibrated at various temperatures is then subjected to uniaxial tensile strains in the three orthogonal directions and the stress-strain curves are developed. Based on the obtained results, the effect of the direction of straining on the mechanical properties of portlandite is investigated in detail. Structural damage analysis is performed to reveal the failure mechanisms in different directions. The energies of the fractured surfaces are calculated in different directions and compared to those of the ideal surfaces available in the literature. The key mechanical properties, including tensile strength, Young's modulus, and fracture strain, are extracted from the stress-strain curves. The sensitivity of the obtained mechanical properties to temperature and strain rate is then explored in a systematic way. This leads to valuable information on how the structural and mechanical properties of portlandite are affected under various exposure conditions and loading rates. - Graphical abstract: Fracture mechanism of portlandite under uniaxial strain in the z-direction. - Highlights: • The structural, thermal, and mechanical properties of portlandite are investigated. • The coefficients of thermal expansion are determined. • The stress-strain relationships are studied in three orthogonal directions. • The effects of temperature and strain rate on mechanical properties are examined. • The plastic energy required for fracture in the crystalline structure is reported.
Thickness and Spin Dependence of Raman Modes in Magnetic Layered Fe 3 GeTe 2
2D layered Fe 3 GeTe 2 has attracted increasing attention due to its high magnetic ordering temperature and novel physical properties. Lattice dynamics is a fundamental property of Fe 3 GeTe 2 , and its relationships with the number of layers and interlayer spin ordering have not yet been explored in depth. Here, by first-principles density functional theory calculations, the phonon vibrations and Raman intensities of Fe 3 GeTe 2 are systematically studied from the bulk to monolayer structures. Furthermore, the spin-phonon coupling effect is investigated by considering different interlayer magnetic orderings: ferromagnetic and antiferromagnetic. It is found that the frequencies of Raman modes in Fe 3 GeTe 2 exhibit considerable dependence on the layer number and spin ordering. In this work, the results not only reveal the notable spin-phonon interactions in Fe 3 GeTe 2 , but also demonstrate that Raman modes can be utilized for characterizing the sample thickness and interlayer spin ordering in this 2D magnet.
Exciton-vibrational dynamics induces efficient self-trapping in a substituted nanoring
Cycloparaphenylenes, being the smallest segments of carbon nanotubes, have emerged as prototypes of the simplest carbon nanohoops. Their unique structure–dynamics–optical properties relationships have motivated a wide variety of synthesis of new related nanohoop species. Studies of how chemical changes, introduced in these new materials, lead to systems with new structural, dynamics and optical properties, expand their functionalities for optoelectronics applications. Herein, we study the effect that conjugation extension of a cycloparaphenylene through the introduction of a satellite tetraphenyl substitution has on its structural and dynamical properties. Our non-adiabatic excited state molecular dynamics simulations suggest that this substitution accelerates the electronic relaxation from the high-energy band to the lowest excited state. This is partially due to efficient conjugation achieved between specific phenyl units as introduced by the tetraphenyl substitution. We observe a particular exciton redistribution during relaxation, in which the tetraphenyl substitution plays a significant role. As a result, an efficient inter-band energy transfer takes place. Besides, the observed phonon-exciton interplay induces a significant exciton self-trapping. Finally, our results encourage and guide the future studies of new phenyl substitutions in carbon nanorings with desired optoelectronic properties.
Li Intercalation in MoS 2 : In Situ Observation of Its Dynamics and Tuning Optical and Electrical Properties
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Thermophysical properties of liquid Ni around the melting temperature from molecular dynamics simulation
Thermophysical properties of liquid nickel (Ni) around the melting temperature are investigated by means of classical molecular dynamics (MD) simulation, using three different embedded atom method potentials to model the interactions between the Ni atoms. Melting temperature, enthalpy, static structure factor, self-diffusion coefficient, shear viscosity, and thermal diffusivity are compared to recent experimental results. Using ab initio MD simulation, we also determine the static structure factor and the mean-squared displacement at the experimental melting point. For most of the properties, excellent agreement is found between experiment and simulation, provided the comparison relative to the corresponding melting temperature. We discuss the validity of the Hansen-Verlet criterion for the static structure factor as well as the Stokes-Einstein relation between self-diffusion coefficient and shear viscosity. The thermal diffusivity is extracted from the autocorrelation function of a wavenumber-dependent temperature fluctuation variable.
Molecular dynamics study of mechanical properties of carbon nanotube reinforced aluminum composites
Atomistic simulations were conducted to estimate the effect of the carbon nanotube (CNT) reinforcement on the mechanical behavior of CNT-reinforced aluminum (Al) nanocomposite. The periodic system of CNT-Al nanocomposite was built and simulated using molecular dynamics (MD) software LAMMPS (Large-scale Atomic/Molecular Massively Parallel Simulator). The mechanical properties of the nanocomposite were investigated by the application of uniaxial load on one end of the representative volume element (RVE) and fixing the other end. The interactions between the atoms of Al were modeled using embedded atom method (EAM) potentials, whereas Adaptive Intermolecular Reactive Empirical Bond Order (AIREBO) potential was used for the interactions among carbon atoms and these pair potentials are coupled with the Lennard-Jones (LJ) potential. The results show that the incorporation of CNT into the Al matrix can increase the Young’s modulus of the nanocomposite substantially. In the present case, i.e. for approximately 9 with % reinforcement of CNT can increase the axial Young’s modulus of the Al matrix up to 77 % as compared to pure Al.