Construction of an optical tweezer for nanometer scale rheology

The optical tweezer is a versatile set-up that can be employed in a wide variety of studies investigating the microscopic properties of materials. In particular, this set-up has in recent times been gainfully employed in probing rheological properties of materials that exhibit viscoelasticity. These measurements can provide data at the micro and nanometer scales, not normally accessible by rheometers that are used for measurements on bulk samples. In this work we describe a single laser beam optical tweezer set-up, which is built around an inverted open microscope. The trapped polystyrene particle bead’s deviation from the trap potential minimum is monitored by laser backscattering technique and the bead position measured by a quadrant photodiode detector. Additionally, a provision is made for video microscopic studies on dispersed beads using a CCD camera. A single particle microrheological experiment that can be performed using the set-up is described with relevant calculations.     

ZnO: An Ecofriendly,Green Nano‐catalyst for the Synthesis of Pyrazole Derivatives under Aqueous Media

An efficient nano ZnO catalyzed green protocol for the synthesis of pyrazol derivatives by condensation of different substituted phenyl hydrazines/semicarbazide/thiosemicarbazide with 1,3‐diketone/ketoester at ambient temperature has been achieved. ZnO nanocatalyst was prepared by low temperature solution combustion method. From the Scherrer method the crystallite size of ZnO was estimated and found to be in the range of 30–50 nm. The main advantage of this protocol is an excellent yield, short reaction time and easy work up procedure. The catalyst was found to be reusable up to five catalytic cycles without any appreciable loss in activity of the catalyst.     

A Catalyst‐free Green Protocol for the Synthesis of Pyranopyrazoles Using Room Temperature Ionic Liquid Choline Chloride‐urea

An efficient and rapid four component reaction of aldehydes, malanonitrile, β‐ketoesters and hydrazine hydrate (or phenyl hydrazine) in environmentally benign room temperature ionic liquid choline chloride‐urea has been developed for the synthesis of substituted 4H‐pyrano[2,3‐c]pyrazoles.     

Dynamic programming—neural network real-time traffic adaptive signal control algorithm

In this paper, an “intelligent” isolated intersection control system was developed. The developed “intelligent” system makes “real time” decisions as to whether to extend (and how much) current green time. The model developed is based on the combination of the dynamic programming and neural networks. Many tests show that the outcome (the extension of the green time) of the proposed neural network is nearly equal to the best solution. Practically negligible CPU times were achieved, and were thus absolutely acceptable for the “real time” application of the developed algorithm.     

Regioselective Synthesis of Highly Aryl‐Substituted Pyrrole Carboxylates as Useful Medicinal Chemistry Leads

The regioselective syntheses of two pharmaceutically relevant pyrrole scaffolds are described. A synthetic route for the preparation of differentially substituted pyrrole‐3,4‐dicarboxylates is presented and exemplified. This route circumvents some of the problems and limitations associated with previous butynedioic diester condensations and 1,3‐dipolar cycloaddition reactions. A route to the related 4,5‐diarylpyrrole‐2‐carboxylic acid scaffold is also presented. Both routes allow for the regiocontrolled preparation of highly substituted pyrrole pharmacophore cores.     

Oxidative Bromination of Aromatic Compounds Using O-Iodoxybenzoic Acid with Tetraethylammonium Bromide

A mild and selective procedure for the bromination of activated arenes using o-iodoxybenzoic acid and tetraethylammonium bromide is presented. The reactions were carried out at room temperature and gave moderate to excellent yields.     

Influence of electric field on SERS: frequency effects, intensity changes, and susceptible bonds

The fundamental mechanism proposed to explain surface-enhanced Raman scattering (SERS) relies on electromagnetic field enhancement at optical frequencies. In this work, we demonstrate the use of microfabricated, silver nanotextured electrode pairs to study, in situ, the influence of low frequency (5 mHz to 1 kHz) oscillating electric fields on the SERS spectra of thiophenol. This applied electric field is shown to affect SERS peak intensities and influence specific vibrational modes of the analyte. The applied electric field perturbs the polar analyte, thereby altering the scattering cross section. Peaks related to the sulfurous bond which binds the molecule to the silver nanotexture exhibit strong and distinguishable responses to the applied field, due to varying bending and stretching mechanics. Density functional theory simulations are used to qualitatively verify the experimental observations. Our experimental and simulation results demonstrate that the SERS spectral changes relate to electric field induced molecular reorientation, with dependence on applied field strength and frequency. This demonstration creates new opportunities for external dynamic tuning and multivariate control of SERS measurements.     

Transient ζ‐potential measurements in hydrophobic,TOPAS microfluidic substrates

We utilize time‐resolved electrokinetic measurements in order to study the electrokinetic properties of silica and TOPAS microfluidic channels as a function of the time history of the fluid–solid interface. In pressure‐driven flow through TOPAS microchannels, the ζ‐potential as inferred from streaming potential measurements decays exponentially by a factor of 1.5 with a characteristic decay time of 3 h after the initial formation of the fluid–solid interface. A similar exponential decay is observed immediately after water is exchanged for ethanol as the solvent in the system. In electroosmotically driven flow through TOPAS microchannels, the ζ‐potential as inferred through current monitoring experiments was constant in time. No electrokinetic transients were observed in silica microchannels under these flow conditions.