Simple Approximate Solutions for Dynamic Response of Suspension System

An approximate simplified analytic solution is proposed for the one DOF (degree of freedom) static and dynamic displacements alongside the stiffness (dynamic and static) and damping coefficients (minimum and maximum/critical values) of a parallel spring-damper suspension system connected to a solid mass-body gaining its energy by falling from height h. The analytic solution for the prescribed system is based on energy conservation equilibrium, considering the impact by a special G parameter. The formulation is based on the works performed by Timoshenko (1928), Mindlin (1945), and the U. S. army-engineering handbook (1975, 1982). A comparison between the prescribed studies formulations and current development has led to qualitative agreement. Moreover, quantitative agreement was found between the current prescribed suspension properties approximate value - results and the traditionally time dependent (transient, frequency) parameter properties. Also, coupling models that concerns the linkage between different work and energy terms, e.g., the damping energy, friction work, spring potential energy and gravitational energy model was performed. Moreover, approximate analytic solution was proposed for both cases (friction and coupling case), whereas the uncoupling and the coupling cases were found to agree qualitatively with the literature studies. Both coupling and uncoupling solutions were found to complete each other, explaining different literature attitudes and assumptions. In addition, some design points were clarified about the wire mounting isolators stiffness properties dependent on their physical behavior (compression, shear tension), based on Cavoflex catalog. Finally, the current study aims to continue and contribute the suspension, package cushioning and containers studies by using an initial simple pre – design analytic evaluation of falling mass- body (like cushion, containers, etc.).

Characterization of ultra-intense laser in radiation damping regime using ponderomotive scattering

We present a novel approach to analyzing phase-space distributions of electrons ponderomotively scattered off an ultra-intense laser pulse and comment on implications for thus conceivable in-situ laser-characterization schemes. To this end, we present fully relativistic test particle simulations of electrons scattered from an ultra-intense, counter-propagating laser pulse. The simulations unveil non-trivial scalings of the scattered electron distribution with the laser intensity, pulse duration, beam waist, and energy of the electron bunch. We quantify the found scalings by means of an analytical expression for the scattering angle of an electron bunch ponderomotively scattered from a counter-propagating, ultra-intense laser pulse, also accounting for radiation reaction (RR) through the Landau-Lifshitz (LL) model. For various laser and bunch parameters, the derived formula is in excellent quantitative agreement with the simulations. We also demonstrate how in the radiation-dominated regime a simple re-scaling of our model's input parameter yields quantitative agreement with numerical simulations based on the LL model.

Understanding the Rheological Transitions in Semi-Solid Alloys by a Combined In Situ Imaging and Granular Micromechanics Modeling Approach

To gain better understanding of rheological transitions from suspension flow to granular deformation and shear cracking, this research conducted shear-deformation on globular semi-solid Al-Cu alloys to study the rheological behavior of semi-solid as a function of solid fraction (38% - 85%) and shear rate (10-4 – 10-1 s-1) under real-time synchrotron radiography observation. By analyzing 17 X-ray imaging datasets, we define three rheological transitions: (i) the critical solid fraction from a suspension to a loosely percolating assembly; (ii) from the net contraction of a loose assembly to the net dilation of a densely packed assembly, and (iii) to shear cracking at high solid fraction and shear rate. Inspired by in-situ observations of semi-solid deformation showing a disordered assembly of percolating crystals in partially-cohesive contact with liquid flow, we reproduced a two-phase sample using the coupled lattice Boltzmann method-discrete element method (LBM-DEM) simulation approach for granular micromechanical modeling. In DEM, each globular Al grain is represented by a discrete element, and the flow of interstitial liquid is solved by LBM. The LBM-DEM simulations show quantitative agreement of semi-solid strain localization with the experiments and are used to explore the components involved in the shear rate dependence of the transitions, and the role of liquid pressure on the initiation of shear cracking.

Light Scattering by a Subwavelength Plasmonic Array: Anisotropic Model

We calculate the light transmission by a subwavelength plasmonic array using the boundary element method for parallel cylinders with different cross-sections: circular or elliptic with axis ratio 4:1. We demonstrate that plasmonic resonance is sharper for the case of horizontal ellipses. This structure is susceptible to refractive index variations in the media since the high derivatives of reflection and transmission coefficients are near the angle of total internal reflection. To obtain an approximate analytical expression, we used the model of a metallic layer. We explore the “sandwich” structure with an anisotropic film between two dielectrics and demonstrate its quantitative agreement with numerical results.

Excited States Computation of Models of Phenylalanine Protein Chains: TD-DFT and Composite CC2/TD-DFT Protocols

The present benchmark calculations testify to the validity of time-dependent density functional theory (TD-DFT) when exploring the low-lying excited states potential energy surfaces of models of phenylalanine protein chains. Among three functionals suitable for systems exhibiting charge-transfer excited states, LC-ωPBE, CAM-B3LYP, and ωB97X-D, which were tested on a reference peptide system, we selected the ωB97X-D functional, which gave the best results compared to the approximate coupled-cluster singles and doubles (CC2) method. A quantitative agreement for both the geometrical parameters and the vibrational frequencies was obtained for the lowest singlet excited state (a ππ* state) of the series of capped peptides. In contrast, only a qualitative agreement was met for the corresponding adiabatic zero-point vibrational energy (ZPVE)-corrected excitation energies. Two composite protocols combining CC2 and DFT/TD-DFT methods were then developed to improve these calculations. Both protocols substantially reduced the error compared to CC2 and experiment, and the best of both even led to results of CC2 quality at a lower cost, thus providing a reliable alternative to this method for very large systems.

Binding free energies for the SAMPL8 CB8 “Drugs of Abuse” challenge from umbrella sampling combined with Hamiltonian replica exchange

Umbrella sampling along a one-dimensional order parameter in combination with Hamiltonian replica exchange was employed to calculate the binding free energy of five guest molecules with known affinity to cucurbit[8]uril. A simple empirical approach correcting for the overestimation of the affinity by the GAFF force field was proposed and subsequently applied to the seven guest molecules of the “Drugs of Abuse” SAMPL8 challenge. Compared to the uncorrected binding free energies, the systematic error decreased but quantitative agreement with experiment was only reached for a few compounds. From a retrospective analysis a weak point of the correction term was identified.

Low-Frequency Content of THz Emission from Two-Color Femtosecond Filament

We experimentally investigate the low-frequency (below 1 THz) spectral content of broadband terahertz (THz) emission from two-color femtosecond filament formed by the 2.7-mJ, 40-fs, 800+400-nm pulse focused into air. For incoherent detection, we screened the Golay cell by the bandpass filters and measured the THz angular distributions at the selected frequencies ν=0.5, 1, 2 and 3 THz. The measured distributions of THz fluence were integrated over the forward hemisphere taking into account the transmittance of the filters, thus providing the estimation of spectral power at the frequencies studied. The spectral power decreases monotonically with the frequency increasing from 0.5 to 3 THz, thus showing that the maximum of THz spectrum is attained at ν≤0.5 THz. The THz waveform measured by electro-optical sampling (EOS) based on ZnTe crystal and transformed into the spectral domain shows that there exists the local maximum of the THz spectral power at ν≈1 THz. This disagrees with monotonic decrease of THz spectral power obtained from the filter-based measurements. We have introduced the correction to the spectral power reconstructed from EOS measurements. This correction takes into account different focal spot size for different THz frequencies contained in the broadband electromagnetic pulse. The corrected EOS spectral power is in semi-quantitative agreement with the one measured by a set of filters.

Searching for a fingerprint of global warming in the Asian summer monsoon

This study investigates possible trends in several large scale indices that describe the Asian summer monsoon. Results from recent atmospheric general circulation experiments are used to provide clues as to how the monsoon might be changing due to the effects of global warming. Interestingly, this study has found that the large-scale wind shear monsoon indices have been decreasing at a rate of 0.1-0.3% per year (based on NCEP/CAR reanalysis 1958-98) in quantitative agreement with recent results from doubled CO2 simulations made using several state-of-the-art climate models. Nevertheless, despite the weakening of the monsoon circulation, all-India rainfall shows no clear trend in either the model results or in the observation reanalysis from 1958-98. Multiple regression is used to separate out the "dynamical" contribution from the observed all-India rainfall index, and a clear increasing trend then emerges in the "non-dynamical" residual. A simple dimensionless Multivariate Monsoon Index (MMI) is proposed that could be of use in monitoring global warming changes in the monsoon.

Adsorption Free Energy of Glycine on TiO2 in Water from First Principles Simulations and Electrochemical Impedance Spectroscopy

The adhesion of amino acids and small organic molecules on TiO2 nanoparticles is fundamental for bio-nano functionalization of peptides and proteins. The adsorption free energy is the main physical quantity that regulates the adsorption process. Its evaluation is particularly challenging both experimentally, due to the weak interfacial signal in aqueous environments, and by atomistic simulations, due to the complexity of the physical phenomena occurring at the solid-water interface (polarization and charge transfer effects). We report here an accurate experimental-computational study of hydrated TiO2 nanoparticles interacting with Glycine where we obtain quantitative agreement of the measured adsorption free energy. Ab-initio simulations are performed within the Tight Binding Density Functional Theory in combination with enhanced free energy sampling techniques. The experiments adopt a new and efficient set-up for electrochemical impedance spectroscopy measurements based on screen-printed gold electrodes. The measured adsorption free energy is about -30 kJ/mol (both from experiment and calculation), with preferential interaction of the charged NH3 group which strongly adsorbs on the TiO2 bridging oxygens. The perfect agreement between computation and experiment opens the doors to an extended exploration of the bio-nano interaction for different materials and molecules.

A diffuse interface method for solid-phase modeling of regression behavior in solid composite propellants

Solid composite propellants (SCPs) are ubiquitous in the field of propulsion. In order to design and control solid SCP rocket motors, it is critical to understand and accurately predict SCP regression. Regression of the burn surface is a complex process resulting from thermo-chemical-mechanical interactions, often exhibitingextreme morphological changes and topological transitions. Diffuse interface methods, such as phase field (PF), are well-suited for modeling processes of this type, and offer some distinct numerical advantages over their sharp-interface counterparts. In this work, we present a phase-field framework for modelingthe regression of SCPs with varying species and geometry. We construct the model from a thermodynamic perspective, leaving the base formulation general. A diffuse-species-interface field is employed as a mechanism for capturing complex burn chemistry in a reduced-order fashion, making it possible to model regressionfrom the solid phase only. The computational implementation, which uses block-structured adaptive mesh refinement and temporal substepping for increased performance, is briefly discussed. The model is then applied to four test cases: (i) pure AP monopropellant, (ii) AP/PBAN sandwich, (iii) AP/HTPB sandwich,and (iv) spherical AP particles packed in HTPB matrix. In all cases, reasonable quantitative agreement is observed, even when the model is applied predictively (i.e., no parameter adjustment), as in the case of (iv). The validation of the proposed PF model demonstrates its efficacy as a numerical design tool for future SCP investigation.