On the response of MEMS resonators under generic electrostatic loadings: experiments and applications

Nonlinear Dynamics - We present an investigation of the dynamic behavior of an electrostatically actuated clamped–clamped microbeam, under the simultaneous excitation of primary and...     

Synthesis of Spirocyclic Ethers by Enantioselective Copper‐Catalyzed Carboetherification of Alkenols

Spirocyclic ethers can be found in bioactive compounds. This copper‐catalyzed enantioselective alkene carboetherification provides 5,5‐, 5,6‐ and 6,6‐spirocyclic products containing fully substituted chiral carbon centers with up to 99 % enantiomeric excess. This reaction features the formation of two rings from acyclic substrates, 1,1‐disubstituted alkenols functionalized with either arenes, alkenes, or alkynes, and clearly constitutes a powerful way to synthesize chiral spirocyclic ethers.     

Poly (ether amide) and silica nanocomposites derived from sol–gel process

The sol–gel derived chemically combined organic–inorganic nanocomposites were synthesized from poly(etheramide) and tetraethoxysilane. Reaction of a mixture of 4-aminophenyl ether and 1,3-phenyldiamine with terephthaloyl chloride (TPC) in dimethylacetamide (DMAc) produced the amide chains. These chains were modified with carbonyl chloride end groups using a slight excess of diacid chloride and were then reacted with aminophenyl trimethoxysilane (APTMOS), where the amine group reacted with carbonyl chloride end groups. Hydrolysis/condensation of tetraethoxysilane (TEOS) and alkoxy groups present in APTMOS developed bonding between the polyamide chains and inorganic silica network generated in situ. By changing the relative proportions of the polymer solution and the amount of TEOS, the composition of hybrid films was varied. Thin hybrid films with various concentrations of silica network obtained after evaporation of the solvent were subjected to mechanical, dynamic mechanical thermal and morphological measurements. The results indicate a gradual increase in the modulus (3.84 GPa) and tensile strength (121 MPa) up to 15-wt.% silica relative to the pure polyamide. The elongation at break point and toughness gradually decrease with addition of silica content. These hybrids were found to be thermally stable up to a temperature of 500 °C. The weight retained above 800 °C was roughly proportional to amount of silica in the matrix. The glass transition temperature and the storage moduli increased with increasing silica concentration. The maximum increase in the T _g value (358 °C) was observed with 15-wt.% silica. Scanning electron micrographs indicated the uniform distribution of silica in the composites with an average particle size ranging from 9 to 47 nm.     

Intravital Imaging Study on Photodamage Produced by Femtosecond Near‐infrared Laser Pulses In Vivo

Ultrashort femtosecond pulsed lasers may provide indispensable benefits for medical bioimaging and diagnosis, particularly for noninvasive biopsy. However, the ability of femtosecond laser irradiation to produce biodamage in the living body is still a concern. To solve this biosafety issue, results of theoretical estimations as well as the in vitro and in situ experiments on femtosecond biodamage should be verified by experimental studies conducted in vivo. Here, we analyzed photodamage produced by femtosecond (19, 42 and 100 fs) near‐infrared (NIR; ~800 nm) laser pulses with an average power of 5 and 15 mW in living undissected Drosophila larvae (in vivo). These experimental data on photodamage in vivo agree with the results of theoretical modeling of other groups. Femtosecond NIR laser pulses may affect the concentration of fluorescent biomolecules localized in mitochondria of the cells of living undissected Drosophila larva. Our findings confirm that the results of the mathematical models of femtosecond laser ionization process in living tissues may have a practical value for development of noninvasive biopsy based on the use of femtosecond pulses.     

Superoxidation of retinoic acid

Atmospheric pressure chemical ionization mass spectroscopy (APCI-MS) was used to examine the light-induced oxidation products of retinoic acid under conditions that favor and preclude its aggregation. We observed that in conditions that favor aggregation, i.e. in aqueous solutions, retinoic acid undergoes superoxidation to yield highly oxidized species. Oxidation is limited, however, in the absence of such communication, i.e. when the polyene is fully solvated. From a comparison of the measured MS with that obtained from chemical oxidation of retinoic acid under conditions that promote radical oxidation and singlet oxygen-mediated oxidation, we conclude that superoxidation is mediated by reactive oxygen species other than singlet oxygen.     

FTIR analysis of natural and synthetic collagen

Collagen is the most abundant protein in humans and animals, comprising of one third of the total proteins that accounts for three quarters of the dry weight skin in humans. Collagen containing a range of proteins has been reported for tissue engineering applications, but, only a small number of studies related to chemical structure evaluation of collagen are found in the literature. Collagen can be obtained from both the natural and synthetic sources and offers a wide range of biomedical applications due to its excellent biocompatibility and low immunogenicity. Hence, it is important to identify chemical structural properties of collagen and Fourier transform infrared (FTIR) appears to be a technique of choice to study their chemical structure. This review aims to highlight the use of FTIR to study collagen-based biomaterials, using it for characterization of collagen extracted from various sources. Characterization of collagen-based materials used in wound healing, skin substitutes, derma fillers, and aging of skin, collagen containing drug delivery agents, collagen-based materials used in tissue engineering, bone regeneration, and osteogenic differentiation is discussed in detail. FTIR analysis of collagen-containing materials used for dental applications, cleft-palate, and in alveolar-ridge preservation has also been highlighted.     

Energy conditions in modified <Emphasis Type="Italic">f</Emphasis>(<Emphasis Type="Italic">G</Emphasis>) gravity

In this paper, we have considered flat Friedmann–Lemaître–Robertson–Walker metric in the framework of perfect fluid models and modified f(G) gravity (where G is the Gauss Bonnet invariant). Particularly, we have considered particular realistic f(G) configurations that could be used to cure finite-time future singularities arising in the late-time cosmic accelerating epochs. We have then developed the viability bounds of these models induced by weak and null energy conditions, by using the recent estimated numerical figures of the deceleration, Hubble, snap and jerk parameters.     

Enhancing the melting properties of small molecule-DNA hybrids through designed hydrophobic interactions: an experimental-computational study

Detailed experimental and computational studies revealed the important role that hydrophobic interactions play in the aqueous assembly of rigid small molecule-DNA hybrid (rSMDH) building blocks into nanoscale cage and face-to-face (ff) dimeric structures. In aqueous environments, the hydrophobic surfaces of the organic cores in these nanostructures are minimized by interactions with the core in another rSMDHs, with the bases in the attached DNA strands, and/or with the base pairs in the final assembled structures. In the case that the hydrophobic surfaces of the cores could not be properly isolated in the assembly process, an ill-defined network results instead of dimers, even at low concentration of DNA. In contrast, if ff dimers can be formed with good minimization of the exposed hydrophobic surfaces of the cores, they are highly stable structures with enhanced melting temperatures and cooperative melting behavior.     

Design and development of an optical beam splitter assembly and high precision colinearity measurements of laser beams

Laser beams with extremely high colinearity are often required where precision position monitoring is important. In order to achieve the said objective, a special type of Laser Beam Splitter Assembly (BSA) has been designed and fabricated in a very small volume due to space constraints. The main features and details of such a system are described here. This type of beam splitter assembly coupled with a diode laser through fibers can be remotely used for alignment or position monitoring of different medium to large size structures with a reconstruction accuracy of 10 μm. In this way, BSA generates two counter propagating laser beams from a single diode laser coupled to an optical fiber. In the present work, the colinearity between two beams within 1 mrad with the variation of 50 μrad has been achieved. The laser's power in the two arms may be controlled precisely, which is an important feature of this BSA. The BSA has been tested to work over a temperature range between ?20 °C to +40 °C. It has also been exposed to 1.0 MeV neutrons at a flux of ～5.0×10¹⁰ n/cm²/s and found compatible.