Microwave and millimeter-wave losses in conventional optoelectronic devices

In this paper, microwave characteristics of conventional optoelectronic devices, with emphasis on devices with microstrip (MS) and coplanar waveguide (CPW) electrode structures, are obtained. This analysis is essential for any improvement in the structure of the conventional optoelectronic devices so as to obtain a high performance. Microwave loss is one of the important bandwidth limitation factors in microwave and millimeter-wave (mmW) optical devices. Different sources of loss including ohmic, dielectric and radiating loss in MS and CPW of conventional optical devices are analyzed and compared. The results show that the total microwave loss increases with frequency in conventional MS and CPW waveguides. Also, in traveling-wave optoelectronic devices, the bandwidth is limited in the optical part by effects such as the carrier transit time effect and in the microwave part by factors such as length of the devices in active and non-active sections. In addition, validation of the results in the paper is performed with published theoretical and/or measurement results.     

Numerical investigation of the submonolayer growth and relaxation of stepped Ag (110) and Au (110) surfaces

The terrace width distribution (TWD) as well as the adatom and island densities for some stepped fcc?(110) surfaces with parallel and equidistant steps of equal stiffness are studied by means of kinetic Monte Carlo simulations. Reliable energy barriers for surface diffusion are used. They have been calculated by means of many-body potentials derived within the second moment approximation to the tight-binding model. The effects of the temperature, atom deposition flux and surface diffusion on quantities of interest in the early stage of the surface evolution process have been singled out. In most cases, linear, logarithmic and power-law behaviors are recovered for the evolution of the step width and terrace defects. The TWD is well described by the Gaussian distribution (GD) in the domain of temperature investigated but deviates from the Generalized Wigner Distribution (GWD).     

Few‐cycle,broadband, mid‐infrared optical parametric oscillator pumped by a 20‐fs Ti:sapphire laser

A few‐cycle, broadband, singly‐resonant optical parametric oscillator (OPO) for the mid‐infrared based on MgO‐doped periodically‐poled LiNbO₃ (MgO:PPLN), synchronously pumped by a 20‐fs Ti:sapphire laser is reported. By using crystal interaction lengths as short as 250 µm, and careful dispersion management of input pump pulses and the OPO resonator, near‐transform‐limited, few‐cycle idler pulses tunable across the mid‐infrared have been generated, with as few as 3.7 optical cycles at 2682 nm. The OPO can be continuously tuned over 2179‐3732 nm (4589‐2680 cm^‐1) by cavity delay tuning, providing up to 33 mW of output power at 3723 nm. The idler spectra exhibit stable broadband profiles with bandwidths spanning over 422 nm (FWHM) recorded at 3732 nm. The effect of crystal length on spectral bandwidth and pulse duration is investigated at a fixed wavelength, confirming near‐transform‐limited idler pulses for all grating interaction lengths. By locking the repetition frequency of the pump laser to a radio‐frequency reference, and without active stabilization of the OPO cavity length, an idler power stability better than 1.6% rms over >2.75 hours is obtained when operating at maximum output power, in excellent spatial beam quality with TEM₀₀ mode profile. Photograph shows a multigrating MgO:PPLN crystal used as a nonlinear gain medium in the few‐cycle femtosecond mid‐IR OPO. The visible light is the result of non‐phase‐matched sum‐frequency mixing between the interacting beams.     

Hyperreflexivity of bounded N-cocycle spaces of banach algebras

Let \(X\) and \(Y\) be Banach spaces, \(n\in \mathbb {N}\) , and \(B^n(X,Y)\) the space of bounded \(n\) -linear maps from \(X\times \ldots \times X\) ( \(n\) -times) into \(Y\) . The concept of hyperreflexivity has already been defined for subspaces of \(B(X,Y)\) , where \(X\) and \(Y\) are Banach spaces. We extend this concept to the subspaces of \(B^n(X,Y)\) , taking into account its \(n\) -linear structure. We then investigate when \(\mathcal {Z}^n(A,X)\) , the space of all bounded \(n\) -cocycles from a Banach algebra \(A\) into a Banach \(A\) -bimodule \(X\) , is hyperreflexive. Our approach is based on defining two notions related to a Banach algebra, namely the strong property \((\mathbb {B})\) and bounded local units, and then applying them to find uniform criterions under which \(\mathcal {Z}^n(A,X)\) is hyperreflexive. We also demonstrate that these criterions are satisfied in variety of examples including large classes of C \(^*\) -algebras and group algebras and thereby providing various examples of hyperreflexive \(n\) -cocyle spaces. One advantage of our approach is that not only we obtain the hyperreflexivity for bounded \(n\) -cocycle spaces in different cases but also our results generalize the earlier ones on the hyperreflexivity of bounded derivation spaces, i.e. when \(n=1\) , in the literature. Finally, we investigate the hereditary properties of the strong property \((\mathbb {B})\) and b.l.u. This allows us to come with more examples of bounded \(n\) -cocycle spaces which are hyperreflexive.     

Bromamine-T as a new oxidimetric titrant

A new oxidimetric titrant, bromamine-T (sodium salt of N-bromo-p-toluene sulphonamide), is introduced for use in aqueous medium. Direct potentiometric and visual indicator titration methods as well as back-titration procedures have been developed for the determination of a variety of substances.     

An efficient diastereoselective synthesis of spiro pyrido[2,1-b][1,3]oxazines via a novel pyridine-based three-component reaction

The zwitterions generated from pyridine and dialkyl acetylenedicarboxylate (DAAD) reacted with benzofuran-2,3-diones to form highly substituted spiro pyrido[2,1-b][1,3]oxazines in good to high yields without using a catalyst.     

Presence of galactosylated core fucose on N-glycans in the planaria Dugesia japonica

Planarial species are of especial interest to biologists due to the phenomenon of pluripotency and, in comparison to other developmental processes, it can be hypothesised that glycan-lectin interactions may play a role. In order to examine the N-glycans of one of these organisms, Dugesia japonica, peptide:N-glycosidase A was employed and the released glycans were subject to pyridylamination, HPLC and mass spectrometric analysis. A range of oligomannosidic glycans was observed with a trimethylated Man(5) GlcNAc(2) structure being the dominant species. Three glycans were also observed to contain deoxyhexose; in particular, a glycan with the composition Hex(4) HexNAc(2) Fuc(1) Me(2) was revealed by exoglycosidase digestion, in combination with MS/MS, to contain a galactosylated core α1,6-fucose residue, whereas this core modification was found to be capped with a methylhexose residue in the case of a Hex(5) HexNAc(2) Fuc(1) Me(3) structure. This is the first report of these types of structures in a platyhelminth and indicates that the 'GalFuc' modification of N-glycans is not just restricted to molluscs and nematodes.     

CONVERSION OF IN SITU GENERATED STABILIZED PHOSPHORUS YLIDES TO CHROMENE DERIVATIVES IN SOLVENT-FREE CONDITIONS

Protonation of the highly reactive 1:1 intermediates, produced in the reaction between triphenylphosphine and dialkyl acetylenedicarboxylates, by phenols (1-hydroxynaphthalene, 2-hydroxynaphthalene, 4-bromophenol, 2-hydroxybenzaldehyde, and 5-bromo-2-hydroxyben- zaldehyde) leads to vinyltriphenylphosphonium salts, which undergo electrophilic substitution reaction with conjugate base to produce corresponding stabilized phosphorus ylides. Microwave was found to catalyze conversion of the stabilized phosphorus ylides to chromene derivatives in the presence of solid catalysts in solvent-free conditions at microwave power 0.4 KW in 3 min.