Chirped fibre Bragg grating based multiplexer and demultiplexer for DWDM applications

A multiplexer/demultiplexer for 100 GHz channel spacing based on chirped fibre Bragg gratings with different bandwidths and optical circulators is presented. The spectral characteristics, specifications and operation of these passive devices are described, showing its potential use in dense wavelength division multiplexing (DWDM) applications.     

A 12-bit intrinsic accuracy high-speed CMOS DAC

A 12-bit intrinsic accuracy digital-to-analog (D/A) converter integrated in a standard digital 0.5 μm CMOS technology is presented. It is based on a current steering doubly segmented 6+2+4 architecture and requires no calibration, no trimming, or dynamic averaging. The differential nonlinearity (DNL) and integral nonlinearity (INL) are 0.3 and 0.6 least significant bits (LSB's), respectively. The measured glitch energy is 1.9 pV.s. For a 12-bit resolution, the converter reaches an update rate of 300 MS/s. By reducing the voltage supply of the latches to 2.0 V, the glitch energy is reduced to sub-pV.s, and the update rate reaches 500 MS/s, for a resolution of 8 bits. The worst case power consumption is 320 mW, and it operates from a single 3.3 V voltage supply. The die area is 3.2 mm²     

Structure Determination of Hydroxytrypargine: A New Tetrahydro‐β‐Carboline Toxin from the Venom of the Spider Parawixia bistriata

A new, highly active tetrahydro‐β‐carboline toxin from the spider Parawixia bistriata, the most‐common species of social spider occurring in Brazil, was isolated. The new toxin was identified as 1,2,3,4‐tetrahydro‐6‐hydroxy‐β‐carboline (=N‐[3‐(2,3,4,9‐tetrahydro‐6‐hydroxy‐1H‐pyrido[3,4‐b]indol‐1‐yl)propyl]guanidine; 3 ). This type of alkaloid, not common among spider toxins, was found to be the most‐potent constituent of the spider's chemical weaponry to kill prey. When P. bistriata catch arthropods in their web, they apparently attack their prey in groups of many individuals injecting their venoms. In vivo toxicity assays with 3 demonstrated a potent lethal effect to honeybees, giving rise to clear neurotoxic effects (paralysis) before death. The compound's toxicity (LD₅₀ value) was determined to be ca. 8 ng/g of honeybee. The investigation of the pharmacological properties and neurotoxic actions of 3 may be used in the future for the development of new drugs to be applied for pest control in agriculture.     

A new LC series element for compact bandpass filter design

A new LC series element based on a modified version of the split rings resonator introduced in is proposed. Owing to its small electrical size, the new open split ring resonator (OSRR) is a very attractive element for compact bandpass filter design. As an example, we have designed and fabricated a filter to produce a bandpass around the resonance frequency of the employed OSRRs. The filter bandwidth is controlled by the length of the transmission lines connecting the OSRRs. Sharp and deep out-of-band rejection is achieved by cascading several OSRRs. Circuit theory and electromagnetic based simulations reasonably agree with experiments.     

EVIDENCE FOR AN ULTRAVIOLET SUNSCREEN ROLE OF THE EXTRACELLULAR PIGMENT SCYTONEMIN IN THE TERRESTRIAL CYANOBACTERIUM Chiorogloeopsis sp.

The proposed photoprotective role of the UV-A absorbing, extracellular pigment scytonemin was studied in the terrestrial cyanobacterium Chlorogloeopsis sp. strain O-89-Cgs(1). UV-A (315-400 nm) caused growth delay, cell growth restarting only when scytonemin had accumulated in the extracellular envelopes. Cultures with scytonemin were more resistant to photoinhibition of photosynthesis than cultures without scytonemin, the differential resistance being much greater to UV-A-caused photoinhibition than to photoinhibition caused by visible light. The presence of scytonemin in the extracellular envelopes was correlated with the inability of UV-A radiation to induce strong photopigment fluorescence (685 nm emission), regardless of the specific content os photosynthetic pigments. The physical removal of the scytonemin containing extracellular envelopes brought about the loss of UV-A resistance as measured by photobleaching rates of chlorophyll a under conditions of physiological inactivity (desiccation). These observations provide strong evidence for the proposed protective role of scytonemin, as a passive UV-A sunscreen, in cyanobacteria.     

An efficient numerical spectral domain method to analyze a largeclass of nonreciprocal planar transmission lines

Presents an efficient numerical application of the Galerkin method in the spectral domain (SD) to the analysis of striplike/slotlike coplanar transmission lines embedded in a bianisotropic multilayered medium. The method is based on obtaining the spectral dyadic Green's function by the equivalent boundary method (EBM), a suitable third order extraction technique of the asymptotic behavior of the Green's dyad, an enhanced numerical integration scheme, and the use of an adequate contour integral method for searching zeros in the complex plane. This method, namely the SD-EBM, has been found to be very suitable for analyzing transmission lines with semiconductors and/or ferrites magnetized at an arbitrary direction, including the study of magnetostatic wave propagation phenomena     

Enantioselective heterogeneous catalytic production of alpha-amino acids

Summary In the present paper the heterogeneous catalytic preparation of alpha-amino acids by hydrogenation of the dehydroamino acids catalyzed by palladium is described. Enantiomeric excess of up to 26% was achieved when the hydrogenation was carried out in ethanol at 0.5 MPa, 298 K with substrate concentration kept at 80 mmol L^-1, 50 mol% cinchonidine as modified and triethylamine as addictive.</o:p>     

Modulated Taylor-Couette Flow: Onset of Spiral Modes

The linear stability of the flow between concentric cylinders, with the inner cylinder rotating at a constant angular velocity and the outer cylinder with an angular velocity varying harmonically about a zero mean, is addressed. The bifurcations of the base state are analyzed using Floquet theory, paying particular attention to non-axisymmetric bifurcations which are dominant in significant regions of parameter space. In these regions the spiral modes of the unforced system become parametrically excited and dominant. This is typical behavior of parametrically forced extended systems, where some modes are stabilized, but others are simultaneously excited. The flow structure of the bifurcated states are examined in detail, paying particular attention to the dynamic implications of their symmetries, and in particular how and when subsequent period doublings are inhibited. Received 5 November 2001 and accepted 29 March 2002 Published online: 2 October 2002 RID="*" ID="*" This work was supported by NSF Grants INT-9732637 and CTS-9908599 (U.S.A.) and MCYT Grants PB97-0685 and BFM2001-2350 (Spain). Communicated by H.J.S. Fernando     

Optimal design of experiments applied to headspace solid phase microextraction for the quantification of vicinal diketones in beer through gas chromatography-mass spectrometric detection

Vicinal diketones, namely diacetyl (DC) and pentanedione (PN), are compounds naturally found in beer that play a key role in the definition of its aroma. In lager beer, they are responsible for off-flavors (buttery flavor) and therefore their presence and quantification is of paramount importance to beer producers. Aiming at developing an accurate quantitative monitoring scheme to follow these off-flavor compounds during beer production and in the final product, the head space solid-phase microextraction (HS-SPME) analytical procedure was tuned through experiments planned in an optimal way and the final settings were fully validated. Optimal design of experiments (O-DOE) is a computational, statistically-oriented approach for designing experiences that are most informative according to a well-defined criterion. This methodology was applied for HS-SPME optimization, leading to the following optimal extraction conditions for the quantification of VDK: use a CAR/PDMS fiber, 5 ml of samples in 20 ml vial, 5 min of pre-incubation time followed by 25 min of extraction at 30 °C, with agitation. The validation of the final analytical methodology was performed using a matrix-matched calibration, in order to minimize matrix effects. The following key features were obtained: linearity (R² > 0.999, both for diacetyl and 2,3-pentanedione), high sensitivity (LOD of 0.92 μg L⁻¹ and 2.80 μg L⁻¹, and LOQ of 3.30 μg L⁻¹ and 10.01 μg L⁻¹, for diacetyl and 2,3-pentanedione, respectively), recoveries of approximately 100% and suitable precision (repeatability and reproducibility lower than 3% and 7.5%, respectively). The applicability of the methodology was fully confirmed through an independent analysis of several beer samples, with analyte concentrations ranging from 4 to 200 g L⁻¹.