Terahertz Photon Mixing Effect in Gapped Graphene

We theoretically calculate the terahertz waves mixing effect in doped graphene with a finite bandgap. The temperature dependence of the nonlinear intraband optical response at bandgap opening of few tens of meV are investigated. When the external electric field is weak, a moderate level of bandgap opening is found to slightly enhance the nonlinear optical response. The optical response is however significantly altered under strong-field condition. The strong-field nonlinear optical conductivity exhibits two distinct response ‘hot spot’: (i) low temperature with large bandgap and (ii) high temperature with small bandgap. The electric field required for the nonlinear response to dominate over the linear response is typically in the order of 10⁴ V/cm. This value increases rapidly by a factor of 10 in large bandgap and high temperature regimes. Our results suggest that photon mixing effect in gapped graphene is strongly gapped dependent and hence the bandgap opening has to be carefully engineered in order to optimize the photon mixing effect in gapped graphene.     

Proportional damping approximation using the energy gain and simultaneous perturbation stochastic approximation

The design of vector second-order linear systems for accurate proportional damping approximation is addressed. For this purpose an error system is defined using the difference between the generalized coordinates of the non-proportionally damped system and its proportionally damped approximation in modal space. The accuracy of the approximation is characterized using the energy gain of the error system and the design problem is formulated as selecting parameters of the non-proportionally damped system to ensure that this gain is sufficiently small. An efficient algorithm that combines linear matrix inequalities and simultaneous perturbation stochastic approximation is developed to solve the problem and examples of its application to tensegrity structures design are presented.     

Microbial-Catalyzed Biotransformation of Multifunctional Triterpenoids Derived from Phytonutrients

Microbial-catalyzed biotransformations have considerable potential for the generation of an enormous variety of structurally diversified organic compounds, especially natural products with complex structures like triterpenoids. They offer efficient and economical ways to produce semi-synthetic analogues and novel lead molecules. Microorganisms such as bacteria and fungi could catalyze chemo-, regio- and stereospecific hydroxylations of diverse triterpenoid substrates that are extremely difficult to produce by chemical routes. During recent years, considerable research has been performed on the microbial transformation of bioactive triterpenoids, in order to obtain biologically active molecules with diverse structures features. This article reviews the microbial modifications of tetranortriterpenoids, tetracyclic triterpenoids and pentacyclic triterpenoids.     

Impact of salts on polyacrylamide hydrolysis and gelation: New insights

Polyacrylamide (PAM) and its derivatives are the most commonly used polymers in the preparation of polymeric gels for water control in petroleum reservoirs. This study involved the use of polyethylenimine (PEI) as a crosslinker for PAM. In this study, we investigated PAM alkaline hydrolysis at high temperatures. The effects of salts [sodium chloride (NaCl) and ammonium chloride (NH₄Cl)] on the degree of hydrolysis (DH) of PAM were investigated. These salts were used as retarders to elongate the gelation time of the PAM/PEI system. The data obtained from ¹³C‐NMR was used to understand the retardation mechanisms by salts. We found that NH₄Cl accelerated the extent of hydrolysis more in comparison with NaCl. Moreover, the apparent viscosity of the hydrolyzed samples was measured. PAM hydrolysis in the presence of NH₄Cl resulted in a lower solution viscosity than that in the presence of NaCl. Therefore, NH₄Cl was more effective in shielding negative charges on the carboxylate groups of the partially hydrolyzed polyacrylamide (PHPA) chain. NaCl and NH₄Cl were compatible with the PHPA/PEI system, but sodium carbonate showed a white precipitate. In addition, high‐temperature/high‐pressure elastic modulus data were reported for the first time for this system. Differential scanning calorimetry was coupled with rheology to explain the PAM/PEI crosslinking in the presence of salts. Models were developed to assess the impact of the salts on the PAM DH and the induction period before gelation. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41185.     

Chemical polymerization of aniline using periodic acid in acetonitrile

The chemical polymerization of aniline in anhydrous medium was investigated using periodic acid, H₅IO₆ as an oxidant. This is the first time that H₅IO₆ has been used as an oxidant in the chemical synthesis of conductive polymers. The product was characterized by FTIR, UV–vis spectroscopies, scanning electron microscope (SEM), energy dispersive X-ray (EDX) spectroscopy, thermogravimetric (TG) analysis, and electrical conductivity measurements. EDX and thermogravimetric analysis showed that Pani includes ClO₄⁻ and iodine or iodide ion as dopants. Electrical conductivity of polyaniline with H₅IO₆ was measured as 100 S cm⁻¹. H₅IO₆ oxidant produces first IO₃⁻ and then I₂. Therefore, it could ensure both oxidation of aniline by IO₃⁻ and then doping polyaniline with I₂, without any residual oxidant contamination. I₂, which is a well known extrinsic dopant, was produced intrinsically in this study. Thus, H₅IO₆ was found to be an effective oxidant material for the chemical polymerization of aniline.     

Use of multisensor and multitemporal geospatial datasets to extract the foundation characteristics of a large building: a case study

Bulletin of Engineering Geology and the Environment - The assessment of the ground conditions for large buildings is important because the results are sensitive to the ground conditions, especially...     

Laser Ablation and Laser-Hybrid Ablation Processes: A Review

Laser beam machining (LBM) has proven its applications and advantages over almost all the range of engineering materials. It offers its competences from macro-machining to micro- and nano-machining of simple-to-complex shapes. The hybrid approaches in laser ablation have demonstrated much improved results in terms of material removal rate, surface integrity, geometrical tolerances, thermal damage, metallurgical alterations, and many more. The flipside of LBM is the existence of universal problems associated with its thermal ablation mechanism. In order to alleviate or reduce the inherent problems of LBM, a massive research has been done during the past decade in order to build a relatively new route of laser-hybrid processes. This paper reviews the research work carried out so far in the area of LBM and its hybrid processes for different materials and shapes. The article also highlights the research gaps and future research directions in the context of laser and laser-hybrid ablation.     

Marker-Based and Marker-Less Motion Capturing Video Data: Person and Activity Identification Comparison Based on Machine Learning Approaches

Biomechanics is the study of physiological properties of data and the measurement of human behavior. In normal conditions, behavioural properties in stable form are created using various inputs of subconscious/conscious human activities such as speech style, body movements in walking patterns, writing style and voice tunes. One cannot perform any change in these inputs that make results reliable and increase the accuracy. The aim of our study is to perform a comparative analysis between the marker-based motion capturing system (MBMCS) and the marker-less motion capturing system (MLMCS) using the lower body joint angles of human gait patterns. In both the MLMCS and MBMCS, we collected trajectories of all the participants and performed joint angle computation to identify a person and recognize an activity (walk and running). Using five state of the art machine learning algorithms, we obtained 44.6% and 64.3% accuracy in person identification using MBMCS and MLMCS respectively with an ensemble algorithm (two angles as features). In the second set of experiments, we used six machine learning algorithms to obtain 65.9% accuracy with the k-nearest neighbor (KNN) algorithm (two angles as features) and 74.6% accuracy with an ensemble algorithm. Also, by increasing features (6 angles), we obtained higher accuracy of 99.3% in MBMCS for person recognition and 98.1% accuracy in MBMCS for activity recognition using the KNN algorithm. MBMCS is computationally expensive and if we re-design the model of OpenPose with more body joint points and employ more features, MLMCS (low-cost system) can be an effective approach for video data analysis in a person identification and activity recognition process.     

Diffusion-limited evaporation of thin polar liquid films

The stability of evaporating very thin films of a polar liquid is investigated. The microscopic interaction with the substrate and capillarity are taken into account in a lubrication equation. The stability of a flat interface is studied when evaporation is limited by the diffusion of the vapour in the gas phase. The evaporation rate is computed and evaporation is shown to be stabilizing. A stability phase diagram is obtained. A weakly nonlinear analysis leads to a film-thickness amplitude equation that is non local in space. Physical consequences of the results are eventually discussed.