WDM-OTDM based spectral efficient hybrid multiplexing technique inherent with properties of bandwidth elasticity and scalability

In this paper a hybrid multiplexing technique has been presented that merges WDM and OTDM multiplexing technologies. The WDM-OTDM hybrid realizes wavelength parallel bus architecture and is inherent with features of high spectral efficiency, high scalability and bandwidth elasticity. Simulations and experiments were carried out to investigate the selection of most suitable modulation format, dispersion compensation technique and erbium doped fiber amplifier (EDFA) noise figure for WDM-OTDM hybrid, where link lengths exceeding 500 km at high Q-values was achieved.     

Low‐temperature sol–gel transformation of methyl silicon precursors to silica‐based hybrid materials

Six new methyl silicon (IV) precursors of the type [MeSi{ON?C(R)Ar}₃] [when R = Me, Ar = 2‐C₅H₄N ( 1 ), 2‐C₄H₃O ( 2 ) or 2‐C₄H₃S ( 3 ); and when R = H, Ar = 2‐C₅H₄N ( 4 ), 2‐C₄H₃O ( 5 ) or 2‐C₄H₃S ( 6 )] were prepared and structurally characterized by various spectroscopic techniques. Molecular weight measurements and FAB (Fast Atomic Bombardment) mass spectral studies indicated their monomeric nature. ¹H and ¹³C{¹H} NMR spectral studies suggested the oximate ligands to be monodentate in solution, which was confirmed by ²⁹Si{¹H} NMR signals in the region expected for tetra‐coordinated methylsilicon (IV) derivatives. Thermogravimetric analysis of 1 revealed the complex to be thermally labile, decomposing to a hybrid material of definite composition. Two representative compounds ( 2 and 4 ) were studied as single source molecular precursor for low‐temperature transformation to silica‐based hybrid materials using sol–gel technique. Formation of homogenous methyl‐bonded silica materials (MeSiO_3/2) at low sintering temperature was observed. The thermogravimetric analysis of the methylsilica material indicated that silicon‐methyl bond is thermally stable up to a temperature of 400 °C. Reaction of 2 and Al(OPrⁱ)₃ in equimolar ratio in anhydrous toluene yielded a brown‐colored viscous liquid of the composition [MeSi{ON?C(CH₃)C₄H₃O}₃.Al(OPrⁱ)₃]. Spectroscopic techniques ¹H, ¹³C{¹H}, ²⁷Al{¹H} and ²⁹Si{¹H} NMR spectra of the viscous product indicated the presence of tetracoordination around both silicon and aluminum atoms. On hydrolysis it yielded methylated aluminosilicate material with high specific surface area (464 m²/g). Scanning electron micrography confirmed a regular porous structure with porosity in the nanometric range. Copyright © 2008 John Wiley & Sons, Ltd.     

Periodic orbits around the collinear libration points in the restricted three body problem when the smaller primary is a triaxial rigid body and bigger primary is a source of radiation pressure

Periodic orbits belonging to the stromgren families A, B and C around the collinear libration points in the restricted three body problem have been studied when the smaller primary is a triaxial rigid body and more massive body is a source of radiation pressure. These families are determined in three different cases: (i) classical case, (ii) when bigger primary is a source of radiation pressure, (iii) when smaller primary is a triaxial rigid body and bigger primary is a source of radiation pressure. The Liapunov stability of each periodic solution has also been examined.      

Approximate range searching

The range searching problem is a fundamental problem in computational geometry, with numerous important applications. Most research has focused on solving this problem exactly, but lower bounds show that if linear space is assumed, the problem cannot be solved in polylogarithmic time, except for the case of orthogonal ranges. In this paper we show that if one is willing to allow approximate ranges, then it is possible to do much better. In particular, given a bounded range Q of diameter w and >0, an approximate range query treats the range as a fuzzy object, meaning that points lying within distance w of the boundary of Q either may or may not be counted. We show that in any fixed dimension d, a set of n points in can be preprocessed in O(n+logn) time and O(n) space, such that approximate queries can be answered in O(logn(1/)^d) time. The only assumption we make about ranges is that the intersection of a range and a d-dimensional cube can be answered in constant time (depending on dimension). For convex ranges, we tighten this to O(logn+(1/)^d−1) time. We also present a lower bound for approximate range searching based on partition trees of Ω(logn+(1/)^d−1), which implies optimality for convex ranges (assuming fixed dimensions). Finally, we give empirical evidence showing that allowing small relative errors can significantly improve query execution times.     

A new mixed birefringent filter

Birefringent filters can be used for tuning lasers, with some advantages over prisms, gratings and tilted etalons. In this paper the transmission characteristics of a new mixed birefringent filter are investigated. The term ‘mixed’ is used because both circular birefringence and linear birefringence have been utilized in the fabrication of this filter.It has a loss-less core, formed by a cascaded system of alternate rotators and retarders, and a linear polarizer at each end. The performance of this filter is better because of the more effective suppression of side peaks. Unlike previous birefringent filters, this one may be used inside a linear resonator.     

Reversibility of thought: An instance in multiplicative tasks

In line with current efforts to understand the piece-by-piece structure and articulation of children’s mathematical concepts, this case study compares the reversibility schemes of two eighth-grade students. The aim of the study was to identify the mechanism through which students reverse their thought processes in a multiplicative situation. Data collected through clinical interviews depict the precise strategies that the participants used to work back to find the missing values in an inverse proportional task. This study also illustrates how a conceptual template generated by one of the participants afforded him considerable flexibility in the multiplicative task. Another outcome of the study is that it shows how the numerical characteristics of the parameters in the problem affected the students’ ability to reverse their thought processes. We infer that there is a need for further research on how students might represent their reversibility schemes in the form of algebraic equations.     

Anti-inflammatory chromone alkaloids and glycoside from Dysoxylum binectariferum

Herein we report isolation of a new chromone alkaloid chrotacumine K (12) from fruits and a chromone glycoside schumaniofioside A (13) from leaves of Dysoxylum binectariferum Hook f. Schumaniofioside A is reported for the first time from Meliaceae family. Other known alkaloids isolated include rohitukine (1) and chrotacumine E (6). The structure of new alkaloid 12 was elucidated on the basis of extensive 1D and 2D NMR analysis, synthesis and chemical hydrolysis. Chemically, chrotacumine K (12) is a 3′-O-acetyl rohitukine which on chemical or enzymatic hydrolysis produces rohitukine. The new alkaloid 12 is also present in seeds and stem-barks of this plant. The glycoside schumaniofioside A (13) is present only in leaves, and in abundance (～1% w/w of dried leaves). The isolated compounds and extracts were evaluated for in vitro effect on the proinflammatory cytokines (TNF-α and IL-6) in human monocytic THP-1 cells. The alkaloid 12 displayed potent inhibition (57%) of TNF-α at 0.3 µM, and was non-toxic to THP-1 cells up to 40 µM, indicating its excellent therapeutic window. Furthermore, a nitrobenzoyl ester analog 15e showed better inhibition of IL-6 than parent natural product chrotacumine K.     

Palladium(II)-catalyzed intramolecular aminoacetoxylation of sugar derived alkenyl tosylsulfonamide: Total synthesis of l-deoxyallonojirimycin

Palladium catalyzed intramolecular aminoacetoxylation of d-ribose derived alkenyl tosylsulfonamide to deliver l-deoxyallonojirimycin in an overall yield of 19%. The preliminary screening of l-deoxyallonojirimycin against carbohydrate processing enzymes showed moderate inhibitory activity against α-glucosidase (yeast) and α-mannosidases.     

Higher hydrogen uptake capacity of C2H4Ti+ than C2H4Ti: a quantum chemical study

Using density functionals theory, we show that gravimetric hydrogen uptake of C₂H₄Ti complex and its cation, C₂H₄Ti⁺, differ by about 2 wt%. Six and five hydrogen molecules are found to be adsorbed on C₂H₄Ti⁺ and C₂H₄Ti complexes thereby showing a hydrogen-uptake capacity of 13.74 and 11.72 wt%, respectively. All hydrogen molecules are adsorbed in molecular form on C₂H₄Ti⁺ ion with an increase in metal bond strength, whereas in some cases, the hydrogen molecules are found to be dissociated on C₂H₄Ti neutral complex. The uptake capacity of neutral C₂H₄Ti complex shown in this work is in excellent agreement with that reported experimentally, Phillips and Shivaram (Phys Rev Lett 100:105505, 2008). The H₂ adsorption energy and its dependence on exchange and correlation functions in density functionals method were illustrated. Even after the adsorption of maximum number of hydrogen molecules on C₂H₄Ti and C₂H₄Ti⁺ complexes, Ti and Ti⁺ remain strongly bound to C₂H₄ substrate.     

Simulative investigation the impact of optical amplification techniques on single- and dual-electrode MZM and direct modulator's in single-tone RoF system

Since the introduction of erbium-doped fiber amplifier (EDFA) in optical fiber communication systems at 1550 nm, the fiber loss is no longer considered as the limiting factor but the fiber dispersion and chirp parameters play an important role in degrading the performance of optical communication systems. Further, the invention of external modulators of Mach-Zehnder (MS) type minimizes the transmission power penalty due to fiber chromatic dispersion as these modulators are consider almost chirp-free modulators. Also, better suppression of nonlinear distortions consists of harmonic distortions (HDs) and intermodulation distortions (IMDs) were achieved by using Mach-Zehnder external modulator [8]. In this work, a simulation comparison of external- and direct-modulation schemes using different optical amplifiers; SOA and EDFA in single-tone RoF system is reported. A single-tone channel of 20 GHz is transmitted over single-mode fiber (SMF) either externally modulated by using single-electrode (SEMZM) - and dual-electrode (DEMZM) - Mach-Zehnder modulator or by direct-modulation scheme. Better improvements in the measurement of received RF power of a 20 km linked single-tone RoF system are achieved by using SEMZM with EDFA, which means maximum optical link is achieved between Central Office (CO) and Base Station (BS). Further, this scheme provides better BER as compare to other schemes discussed in this paper.