6-Hydroxyhexyl 4-(E)-4-alkoxy/halostyryl)benzoates: synthesis,characterisation and study of mesomorphic and fluorescent properties

Hydroxyhexyl esters of alkoxy and halostilbene carboxylic acids were prepared and studied for thermal, liquid crystalline and fluorescent properties. The decomposition temperatures were determined thermogravimetrically and the compounds were found stable at least up to 200°C. Differential scanning calorimetry (DSC) indicated two mesophases in alkoxystilbene caboxylates. The smectic nature of the liquid crystal (LC) compounds was identified from the optical textures and confirmed through X-ray diffraction (XRD) measurements, where SmA, SmB and CrE mesophases were observed. The compounds 3a-g and 3h-k show single absorption maxima in UV-visible spectra at around 338 and 322 nm, respectively. All the alkoxy compounds emit blue light in solution and in solid state in the wavelength range of 422–425 nm.     

Improving the Retrieval of Arabic Web Search Results Using Enhanced k-Means Clustering Algorithm

Traditional information retrieval systems return a ranked list of results to a user’s query. This list is often long, and the user cannot explore all the results retrieved. It is also ineffective for a highly ambiguous language such as Arabic. The modern writing style of Arabic excludes the diacritical marking, without which Arabic words become ambiguous. For a search query, the user has to skim over the document to infer if the word has the same meaning they are after, which is a time-consuming task. It is hoped that clustering the retrieved documents will collate documents into clear and meaningful groups. In this paper, we use an enhanced k-means clustering algorithm, which yields a faster clustering time than the regular k-means. The algorithm uses the distance calculated from previous iterations to minimize the number of distance calculations. We propose a system to cluster Arabic search results using the enhanced k-means algorithm, labeling each cluster with the most frequent word in the cluster. This system will help Arabic web users identify each cluster’s topic and go directly to the required cluster. Experimentally, the enhanced k-means algorithm reduced the execution time by 60% for the stemmed dataset and 47% for the non-stemmed dataset when compared to the regular k-means, while slightly improving the purity.     

Normal mode splitting in hybrid BEC-optomechanical system

We consider an opto-mechanical cavity system consisting of Bose-Einstein condensate (BEC), trapped inside the optical cavity and driven by single mode laser field. The intracavity field acts as nonlinear spring which couples the condensate mode with moving end mirror of the cavity. We study the occurrence of normal mode splitting in the position spectra of the mechanical oscillator and condensate mode as a consequence of hybridization of the fluctuations of intracavity field, mechanical mode and condensate mode. We also discuss the modification in the dynamics of the mechanical oscillator due to frequency of the collective oscillations of cold atoms and the back action of the atoms on the mechanical mirror. Moreover, we investigate the normal mode splitting in the transmission spectrum of cavity field.     

A novel route to synthesize libraries of quinoxalines via Petasis methodology in two synthetic operations

This Letter reveals an innovative and facile procedure to prepare quinoxalines in two synthetic steps. The microwave assisted Petasis reaction is followed by the acid mediated unmasking of an internal amino nucleophile, cyclodehydration and oxidation to give collections of quinoxalines in good to excellent yields.     

Structural changes in tin oxide thin film with laser exposure

The effects of laser irradiation on the surface, structure and optical properties of SnO thin films deposited on glass substrates using electron beam evaporation, are investigated. The thin film samples are irradiated using fundamental beam at 1064 nm from Q-switched Nd:YAG pulsed laser with different power densities. Structural morphology of the film is investigated using XRD patterns and AFM image. Both XRD pattern and AFM image show increase in grain size of the film with increasing laser power density. Other optical phenomena, photoluminescence emission, transmission, refractive index determination and optical band gaps calculations are also carried out at various laser power densities. Results from all these investigations reveal expansion in grain size of the crystalline SnO thin film with increasing laser power density.     

Radiation properties of a uniaxial chiral quadratic inhomogeneous slab under oblique incidence

In this paper, the focussing of the transmitted electromagnetic field through a quadric inhomogeneous slab of lossless uniaxial chiral medium is derived using transmission coefficient under oblique incidence. The inhomogeneity in the uniaxial chiral slab has been incorporated through permittivity parameter. Asymptotic ray theory provides valid field everywhere except at focal point where it gives infinite value. Singularity of the field at focal point is addressed using Maslov's method. The derived analytical field expressions at caustic or focal point of uniaxial quadratic inhomogeneous slab have been solved numerically using MATHEMATICA. The effects of chirality parameter, axial permittivity, transvers permittivity, angle of incidence on the refracted field are discussed and the effects of Brewster angle on the focussed field are also discussed. The results obtained using Maslov's method are compared with Huygens–Kirchhoff's integral which are in good agreement.