Synthesis of highly enantioenriched hydroxy- and dihydroxy-fatty esters: substrate precursors for cytochrome P450BioI

A series of highly enantioenriched hydroxy- and dihydroxy-fatty esters were required as part of our ongoing investigation into cytochrome P450_BioI. This mediates the biosynthesis of pimelic acid via C–C bond cleavage of long chain fatty acids within Bacillus subtilis. Herein we report the synthesis of various stereoisomers of methyl 7-hydroxytetradecanoate, methyl 8-hydroxytetradecanoate, and methyl 7,8-dihydroxytetradecanoate in highly enantioenriched form, using a combination of asymmetric synthesis and a preparative enantioselective HPLC is reported.     

Gain-flattened S-band depressed cladding erbium doped fiber amplifier with a flat bandwidth of 12 nm using a Tunable Mach-Zehnder Filter

S-band amplification is an important area of optical communications research, focusing on meeting the ever-increasing demands for traffic bandwidth as the C- and L-bands approaches to their limits. In this paper a novel method of providing an S-band optical amplifier with a flat gain-bandwidth is proposed. The proposed method utilizes a Depressed Cladding Erbium Doped Fibre together with a Tunable Mach-Zehnder Filter as to generate a flat amplification bandwidth of 12 nm stretching from 1492 to 1504 nm. The average gain value is approximately 24.21 dB, with a peak to peak fluctuation of 0.83 dB and a noise figure ranges from 7.13 to 10.94 dB for input signals of 1484 to 1510 nm.     

S-band multiwavelength Brillouin Raman Fiber Laser

In this paper we propose and demonstrate an S-band Brillouin-Raman Fiber Laser (BRFL). The S-band BRFL utilizes a Dispersion Compensating Fiber (DCF) as the non-linear gain medium in a linear cavity configuration and amplified by two 1425 nm, 380 mW pumped Raman Fiber Amplifiers (RFAs). A Brillouin Pump (BP) signal of 1515 nm at 12 dBm in power is injected into the setup to generate Stokes lines via the Stimulated Brillouin Scattering (SBS) process. The S-band BRFL is able of generating a Brillouin comb with 32 Stokes lines with a flat peak output power of − 18 dBm. The best BP to Stokes power ratio of the system is determined to be 50:50, while a ratio of 70:30 is observed to generate Stokes with a higher peak power, but at the expense of the number of wavelengths. The S-band BRFL has many potential applications as multiwavelength sources for communications and sensors.     

Fractal-like Aggregates: Relation between Morphology and Physical Properties

A number of modern technological applications require a detailed calculation of the physical properties of aggregated aerosol particles. For example, in probing soot aerosols by the method called laser-induced incandescence (LII), the soot clusters are suddenly heated by a short, powerful laser pulse and then cool down to the temperature of the carrier gas. LII sizing is based on rigorous calculation of the soot aggregate heat-up and cooling and involves prediction of laser light absorption and energy and mass transfer between aggregated particles and the ambient gas. This paper describes results of numerical simulations of the mass or energy transfer between the gas and fractal-like aggregates of N spherical particles in either the free-molecular or continuum regime, as well as the light scattering properties of random fractal-like aggregates, based on Rayleigh-Debye-Gans (RDG) theory. The aggregate geometries are generated numerically using specially developed algorithms allowing "tuning" of the fractal dimension and prefactor values. Our results are presented in the form of easily applicable scaling laws, with special attention paid to relations between the aggregate gyration radius and the effective radius describing various transport processes between the aggregates and the carrier gas. Copyright 2000 Academic Press.     

Highly Luminescent Heterostructured Copper‐Doped Zinc Sulfide Nanocrystals for Application in Cancer Cell Labeling

The structural characteristics of the seed‐mediated synthesis of heterostructured CuS–ZnS nanocrystals (NCs) and Cu‐doped ZnS (ZnS:Cu) NCs synthesized by two different protocols are compared and analyzed. At high Cu dopant concentrations, segregated subclusters of ZnS and CuS are observed. The photoluminescence quantum yield of ZnS:Cu NCs is about 50–80 %; a value much higher than that of ZnS NCs (6 %). Finally, these NCs are coated with a thin silica shell by using (3‐mercaptopropyl)triethoxysilane in a reverse microemulsion to make them water soluble. Cytotoxicity experiments show that these silica‐coated NCs have greatly reduced toxicity on both cancerous HeLa and noncancerous Chinese hamster ovary cells. The labeling of cancerous HeLa cells is also demonstrated.     

Dynamic phase profile of phase objects based in the use of a quasi-common path interferometer

In this paper, we propose a quasi common-path interferometer based on a two beams configuration (TBC) using simultaneous phase shifting interferometry modulated by polarization that shows insensitivity against external vibration. Due to the fact that the configuration is capable of obtaining two beams whose separation can be varied, according to the characteristics of the grid used, to obtain the interference patterns. It can be used to implement a quasi-common path interferometer that allows the measurement of dynamic events with high accuracy. For demodulate the fringe patterns generated by the optical system we using the conventional four step phase shifting method. Experimental results are also given.     

Triclosan release from coated polyglycolide threads

Copolymerization of lactide, epsilon-caprolactone, and trimethylene carbonate is performed. The synthesis is focused on obtaining materials with adequate properties for application as a suture coating that could contain an antimicrobial agent like triclosan. An amorphous character, a low glass transition temperature, a moderate susceptibility to degradation, and a hydrophobic nature are the conditions required for the optimal behavior of this coating. These properties can be attained with a copolymer of composition 10:60:30. Triclosan is added to the surface of polyglycolide threads and its release is studied in different media with high-performance liquid chromatography. The influence of the temperature, the diameter of the thread, the initial concentration of the antibacterial agent, and the applied procedure on the incorporation of triclosan is also evaluated. A total release of triclosan is attained after a few days of exposure to a Dulbecco's based medium, whereas equilibrium concentrations are reached when a S?rensen hydrophilic medium is used. Partition and diffusion coefficients are also estimated.     

Wide-band fanned-out supercontinuum source covering O-, E-, S-, C-, L- and U-bands

A wide-band supercontinuum source generated by mode-locked pulses injected into a Highly Non-Linear Fiber (HNLF) is proposed and demonstrated. A 49 cm long Bismuth–Erbium Doped Fiber (Bi–EDF) pumped by two 1480 nm laser diodes acts as the active gain medium for a ring fiber laser, from which mode-locked pulses are obtained using the Non-Polarization Rotation (NPR) technique. The mode-locked pulses are then injected into a 100 m long HLNF with a dispersion of 0.15 ps/nm km at 1550 nm to generate a supercontinuum spectrum spanning from 1340 nm to more than 1680 nm with a pulse width of 0.08 ps and an average power of ?17 dBm. The supercontinuum spectrum is sliced using a 24 channel Arrayed Waveguide Grating (AWG) with a channel spacing of 100 GHz to obtain a fanned-out laser output covering the O-, E-, S-, C-, L- and U-bands. The lasing wavelengths obtained have an average pulse width of 9 ps with only minor fluctuations and a mode-locked repetition rate of 40 MHz, and is sufficiently stable to be used in a variety of sensing and communication applications, most notably as cost-effective sources for Fiber-to-the-Home (FTTH) networks.