Effect of transmitter positions on received power and bandwidth in diffuse indoor optical wireless systems

Diffuse Indoor Optical wireless systems (DIOWS) have potential applications in indoor WLAN. The major problems faced by these systems are their reduced bandwidth and restricted mobility caused by multi-path reflections from the indoor surfaces. These systems also suffer from non-uniform power distribution. Over the last decade several techniques have been suggested to circumvent these problems, most of them requiring complex trans-receiver design. One simple technique that can solve the non-uniformity problem is the use of multiple sources in place of a single source. In this paper we compare the received power levels on the floor computed using the extended ceiling bounce and the modified recursive models. The effect of multiple sources and their positions on the channel bandwidth is also analyzed. We show that the channel bandwidth for a given trans-receiver configuration depends on both the horizontal separation (between the transmitter and the receiver) and their actual positions.     

Dielectrophoretic trapping of single bacteria at carbon nanofiber nanoelectrode arrays

We present an ac dielectrophoretic (DEP) technique for single-cell trapping using embedded carbon nanofiber (CNF) nanoelectrode arrays (NEAs). NEAs fabricated by inlaying vertically aligned carbon nanofibers in SiO2 matrix are applied as "points-and-lid" DEP devices in aqueous solution. The miniaturization of the electrode size provides a highly focused electrical field with the gradient enhanced by orders of magnitude. This generates extremely large positive DEP forces near the electrode surface and traps small bioparticles against strong hydrodynamic forces. This technology promises new capabilities to perform novel cell biology experiments at the nanoscale. We anticipate that the bottom-up approach of such nano-DEP devices allows the integration of millions of nanolectrodes deterministically in lab-on-a-chip devices and will be generally useful for manipulating submicron particles.     

Amino substituted bisketenes: generation, structure, and reactivity

Hitherto unknown diamino-substituted bisketenes with both free (14) and tethered (16) amino substituents have been generated by using laser flash photolysis for ring opening of the corresponding cyclobutenediones. The time-resolved kinetics of ring closure of the amino bisketenes back to the cyclobutenediones were measured by IR or UV spectroscopy, and give first-order rate constants which vary by a factor of 7.5x10(4), and the bis(Me2N) bisketene 14 is the most reactive in ring closure that has been reported. Rate constants for ring closure of these and previously observed bisketenes vary by a factor of 10(13). The dialkylamino bisketenes 16 (R=Me, n-Bu) with tethered substituents and restricted geometries are less reactive than the bis(Me2N) bisketene 14 by factors of 1700 and 540, respectively. Computational results obtained with DFT methods suggest angle strain in the tethered cyclobutenediones 15 inhibits facile cyclization of bisketenes 16.     

Heterogeneous acylation of phenol with acetic anhydride over hydrotalcite-like compounds

Liquid phase acylation of phenol with acetic anhydride was studied over the mixed oxides obtained from Mg-Al, Ni-Al, and Cu-Al hydrotalcites (HTs). The mixed oxides were characterized by XRD and SEM. The main acylation products of phenol over these oxide catalysts are phenylacetate and o-hydroxyacetophenone.     

A concise enantioselective synthesis of (+)-lentiginosine

A high yielding enantioselective synthesis of the indolizidine alkaloid, (+)-lentiginosine, has been described based on asymmetric aza-Cope rearrangement and the l-proline catalyzed α-aminooxylation of aldehydes. The strategy also makes use of ring-closing metathesis for the construction of piperidine core.     

Structural and spectroscopic investigations on Eu3+-doped alkali fluoroborate glasses

Eu³⁺-doped alkali fluoroborate glasses B₂O₃–XCO₃–NaF–Eu₂O₃ (where X = Li₂, Na₂, K₂, and Ca, Mg) have been prepared using the conventional melting technique and their structural and optical properties have been evaluated. The XRD pattern of the glasses confirmed the amorphous nature and the FTIR spectra reveal the presence of BO₃ and BO₄ units as their local structures along with the strong OH^? groups. From the absorption spectra the bonding parameters have been calculated and confirmed that the Eu–O bonds in the studied glasses are of covalent nature. Judd–Ofelt (JO) analysis has been carried out from the emission spectra. The JO parameters have been used to calculate transition probabilities (A), lifetime (τ_R) and branching ratios (β_R) and peak stimulated emission cross-section (σ_P^E) for the ⁵D₀ → ⁷F_J (J = 1, 2, 3 and 4) transitions of the Eu³⁺ ions. The decay from the ⁵D₀ level of Eu³⁺ ions in the title glasses has been measured and analysed. The lifetime of the ⁵D₀ level is found to be shorter than the reported glasses which may be due to the presence of OH^? groups.     

Stereoselective synthesis of bis-β-lactam grafted macrocycles

The synthesis of a series of macrocyclic bis-β-lactam derivatives via a highly stereoselective (2+2) cycloaddition is described.     

Giant dipole resonance and shape transitions in warm and rapidly rotating nuclei

We discuss the shape transitions in few medium heavy-mass nuclei with emphasis on low-temperature behaviour of the giant dipole resonance (GDR) observables. We employ a macroscopic approach towards GDR in which the GDR observables are related to the nuclear shapes. Shape calculations were done using the cranked Nilsson-Strutinsky method (CNSM) extended to finite temperature. Thermal shape fluctuations are computed with free energies calculated employing Landau parameterization as well as those calculated exactly (without using parameterizations) at given spin and temperature. The results obtained are confronted with the experimental data wherever available. Our study reveals that if the fluctuations are treated properly, then, in spite of thermal fluctuations, GDR observables could very well reflect the shape transitions at low temperature.     

Graphoidal bipartite graphs

A graphoidal cover of a graph G is a collection ψ of (not necessarily open) paths inG such that every path in ψ has at least two vertices, every vertex ofG is an internal vertex of at most one path in ψ and every edge of G is in exactly one path in ψ. Let Ω (ψ) denote the intersection graph of ψ. A graph G is said to be graphoidal if there exists a graphH and a graphoidal cover ψof H such that G is isomorphic to Ω(ψ). In this paper we study the properties of graphoidal graphs and obtain a forbidden subgraph characterisation of bipartite graphoidal graphs.