A simple shear deformation theory for nonlocal beams

In this paper, a simple beam theory accounting for shear deformation effects with one unknown is proposed for static bending and free vibration analysis of isotropic nanobeams. The size-dependent behaviour is captured by using the nonlocal differential constitutive relations of Eringen. The governing equation of the present beam theory is obtained by using equilibrium equations of elasticity theory. The present theory has strong similarities with nonlocal Euler–Bernoulli beam theory in terms of the governing equation and boundary conditions. Analytical solutions for static bending and free vibration are derived for nonlocal beams with various types of boundary conditions. Verification studies indicate that the present theory is not only more accurate than Euler–Bernoulli beam theory, but also comparable with Timoshenko beam theory

Mechanical behavior and properties of hydrogen bonded graphene/polymer nano-interfaces

There is increasing evidence in literature for significant improvements in both toughness and strength of graphene-based nanocomposites through engineering their nano-interfaces with hydrogen bonds (H-bonds). However, the underlying mechanical behaviors and properties of these H-bonded interfaces at the microscopic level were still not experimentally clarified and evaluated. Herein, this work reports a study on the interfacial stress transfer between a monolayer graphene and a commonly used poly(-methyl methacrylate) (PMMA) matrix under pristine vdW and modified H-bonding interactions. A nonlinear shear-lag model considering friction beyond linear bonding was proposed to understand evolution of interfacial stresses and further identify key interfacial parameters (such as interfacial stiffness, strength, frictional stress and adhesion energy) with the aid of in situ Raman spectroscopy and atomic force microscopy. The present study can provide fundamental insight into the reinforcing mechanism and unique mechanical behavior of chemically modified graphene nano-interfaces and develop further a basis for interfacial optimal design of graphene-based high-performance nanocomposites. (C) 2016 Published by Elsevier Ltd

Computational Prediction and Experimental Validation of ADMET Properties for Potential Therapeutics

The drug development process in the United States is an expensive and lengthy process, usually taking a decade or more to gain approval for a drug candidate. The majority of proposed, early stage therapeutics fail, even though the typical process narrows from hundreds or thousands of small molecules down to one late stage candidate. One reason for failure is due to the drugs poor or unexpected absorption, distribution, metabolism, excretion, and toxicity (ADMET) properties. Researchers attempt to predict ADMET properties as a way to help prioritize compounds for lead development to minimize expense and time. It was the overall goal of this project to further the prediction of two ADMET properties (absorption and distribution) through the development and application of quantitative structure-activity (QSAR) relationship computational models predicting human intestinal absorption (HIA), Caco-2 permeability (in vivo & in vitro measurements of absorption), and protein binding (measurement of distribution). These combined models would then be paired with additional experimental methods to help prioritize compounds for future ligand discovery efforts in our lab group and for our collaborators. Five computational QSAR models for each of these three properties were created using different molecular descriptor types and solvation models in an effort to examine which approach resulted in optimal performance. The model development process and validation stages of these QSAR models is outlined herein, along with analysis and discussion of commonly mispredicted compounds. Performance was similar across all models (independent of the molecular descriptor used and the solvation models applied. Future efforts at model development will depend on the size of the dataset to be analyzed. If the dataset is small, the i3D-Born solvation models will be used because these models better represent physiological conditions and performed slightly better than the other models. However, if the dataset is large, the 2D descriptor models will be used as these models do not require that a time and resource-intensive conformational search be performed and because it performed nearly as well as the i3D-Born solvation models. There were no common structural features consistently found associated with mispredicted structures. As such we are unable, at this time to pinpoint classes of compounds to avoid in future effortsThe experimental methods outlined in this work focused on developing methods to determine protein binding, specifically determining a fast, inexpensive workflow to classify the difference between high and low protein binding small molecules. Two techniques were used to determine protein binding of small molecules to bovine serum albumin (BSA): fluorescence polarization (FP) competition, and Nano Differential Scanning Fluorimetry (NanoDSF). FP assays quantifies the change in polarization of a target fluorophore between its protein bound and free states, an equilibrium that can be impacted by the presence of small molecule competitors. This method can be performed in a quantitative manner, but it also requires more time and more expensive and specialized instrumentation. In contrast, NanoDSF determines the melting temperature of BSA in the presence (higher) or in the absence (lower) small molecules by determining the intrinsic fluorescence of tryptophan and tyrosine residues while applying a temperature gradient. This method is qualitative, at least in our approach, but is very fast and requires much less expensive instrumentation. In our hands both techniques were successful in distinguishing differences between small molecules exhibiting low and high BSA binding. In summary, this project was successful in that we 1) developed computational tools capable of correctly predicting ADMET properties including HIA, Caco-2 permeability, and protein binding and 2) developed experimental workflows to quantitatively and qualitatively separate small molecules into low and high affinity BSA binders. With these in silico models and in vitro methods established, future research in our group and with our collaborators can make use of these tools to help prioritize compounds in ligand/ inhibitor discovery efforts

Advanced Mechanical Modeling of Nanomaterials and Nanostructures

This reprint presents a collection of contributions on the application of high-performing computational strategies and enhanced theoretical formulations to solve a wide variety of linear or nonlinear problems in a multiphysical sense, together with different experimental studies

Nonlocal analysis of the flexural–torsional stability for FG tapered thin-walled beam-columns

none5siThis paper addresses the flexural–torsional stability of functionally graded (FG) nonlocal thin-walled beam-columns with a tapered I-section. The material composition is assumed to vary continuously in the longitudinal direction based on a power-law distribution. Possible small-scale effects are included within the formulation according to the Eringen nonlocal elasticity assump-tions. The stability equations of the problem and the associated boundary conditions are derived based on the Vlasov thin-walled beam theory and energy method, accounting for the coupled interaction between axial and bending forces. The coupled equilibrium equations are solved numer-ically by means of the differential quadrature method (DQM) to determine the flexural–torsional buckling loads associated to the selected structural system. A parametric study is performed to check for the influence of some meaningful input parameters, such as the power-law index, the nonlocal parameter, the axial load eccentricity, the mode number and the tapering ratio, on the flexural–torsional buckling load of tapered thin-walled FG nanobeam-columns, whose results could be used as valid benchmarks for further computational validations of similar nanosystems.openSoltani M.; Atoufi F.; Mohri F.; Dimitri R.; Tornabene F.Soltani, M.; Atoufi, F.; Mohri, F.; Dimitri, R.; Tornabene, F

Dyakonov Surface Waves: Anisotropy-Enabling Confinement on the Edge

The title “Dyakonov surface waves: anisotropy enabling confinement on the edge” plainly sets the scope for this chapter. The focus here is on the formation of bounded waves at the interface of two distinct media, at least one of them exhibiting optical anisotropy, which are coined as Dyakonov surface waves (DSWs) in recognition to the physicist who reported their existence for the first time. First, the general aspects of the topic are discussed. It also treats the characterization of bounded waves in isotropic-uniaxial multilayered structures, allowing not only the derivation of the dispersion equation of DSWs but also that of surface plasmons polaritons (SPPs), for instance. Furthermore, the interaction of such surfaces waves, with the possibility of including guided waves in a given planar layer and external sources mimicking experimental setups, can be accounted for by using the transfer matrix formalism introduced here. Finally, special attention is devoted to hyperbolic media with indefinite anisotropy-enabling hybridized scenarios integrating the prototypical DSWs and SPPs

Application of Plasmon Resonances to Surface Enhanced Raman Scattering (SERS), Heat-Assisted Magnetic Recording (HAMR), and All-Optical Magnetic Recording

In this work, we perform the analytical and numerical analyses of the plasmon modes in different metallic nanostructures for the applications to surface-enhanced Raman scattering (SERS), heat-assisted magnetic recording (HAMR) and all-optical magnetic recording. We start with the introduction of physical origin of plasmon resonances in nanoparticles and the eigenmode analysis technique adopted throughout this work in Chap. 1. The excitation of the plasmon modes in nanoparticles subject to optical radiation is also presented. In Chap. 2, we study the dispersion in the SERS enhancement factors with silver nanocube dimers. We perform the mode analysis and calculated the resonance wavelengths of the dipolar plasmon modes in silver nanocube dimers with different configurations. The results show that the SERS enhancement factors are related to the resonance frequencies of the dimers, which are determined by their gap distances and orientations. In Chap. 3, we analytically derive the formula for the computation of resonance permittivities of plasmon modes in spheroidal nanoshells. The dipolar plasmon modes in spheroidal nanoshells possess rotational symmetry which preserves the helicity of circularly polarized light, and consequently, they are useful in all-optical magnetic recording. We have also derived the formulas which indicate how the dipolar plasmon modes in ellipsoidal nanoshells can be excited by uniformly incident field. Light intensities of the optical spots generated by the circularly polarized plasmon modes in spherical nanoshells are computed and compared with those generated by circularly polarized plasmon modes in spheroidal nanoshells. In Chap. 4, we study the plasmon resonances in T-shaped aperture metallic nanofilms and lollipop metallic nanodisks placed nearby different dielectric substrates used in heat-assisted magnetic recording. We developed a constrained eigenvalue problem for specific coupled boundary integral equations to take into account the effect of the surrounding finite dielectric objects. By solving this problem, the resonance frequencies of such metallic nanostructures as well as the corresponding plasmon modes can be computed. The effect of heat sink layers on the plasmon resonances is also discussed. Finally, in Chap. 5, we study the radiation corrections of plasmon resonances in nanoparticles. The red-shifts in resonance frequencies of dipolar plasmon modes with nanocube size are computed and compared with experimental measurement. The results suggest that different dipolar modes have different sensitivities to the rounding of the cube corners and edges

Localised States of Fabry-Perot Type in Graphene Nano-Ribbons

This book collects some new progresses on research of graphene from theoretical and experimental aspects in a variety of topics, such as graphene nanoribbons, graphene quantum dots, and graphene-based resistive switching memory. The authors of each chapter give a unique insight about the specific intense research area of graphene. This book is suitable for graduate students and researchers with background in physics, chemistry, and materials as reference

Coupling, lifetimes and "strong coupling" maps for single molecules at plasmonic interfaces

The interaction between excited states of a molecule and excited states of metal nanostructure (e.g. plasmons) leads to hybrid states with modified optical properties. When plasmon resonance is swept through molecular transition frequency an avoided crossing may be observed, which is often regarded as a signature of strong coupling between plasmons and molecules. Such strong coupling is expected to be realized when $2|U|/{\hbar\Gamma}>1$, where $U$ and ${\Gamma}$ are the molecule-plasmon coupling and the spectral width of the optical transition respectively. Because both $U$ and ${\Gamma}$ strongly increase with decreasing distance between a molecule and a plasmonic structure it is not obvious that this condition can be satisfied for any molecule-metal surface distance. In this work we investigate the behavior of $U$ and ${\Gamma}$ for several geometries. Surprisingly, we find that if the only contributions to ${\Gamma}$ are lifetime broadenings associated with the radiative and nonradiative relaxation of a single molecular vibronic transition, including effects on molecular radiative and nonradiative lifetimes induced by the metal, the criterion $2|U|/{\hbar\Gamma}>1$ is easily satisfied by many configurations irrespective of the metal-molecule distance. This implies that the Rabi splitting can be observed in such structures if other sources of broadening are suppressed. Additionally, when the molecule-metal surface distance is varied keeping all other molecular and metal parameters constant, this behavior is mitigated due to the spectral shift associated with the same molecule-plasmon interaction, making the observation of Rabi splitting more challenging