Robert S. Rogowski

Loss and dispersion analysis of microstructured fibers by finite-difference method

The dispersion and loss in microstructured fibers are studied using a full-vectorial compact-2D finite-difference method in frequency-domain. This method solves a standard eigen-value problem from the Maxwells equations directly and obtains complex propagation constants of the modes using anisotropic perfectly matched layers. A dielectric constant averaging technique using Amperes law across the curved media interface is presented. Both the real and the imaginary parts of the complex propagation constant can be obtained with a high accuracy and fast convergence. Material loss, dispersion and spurious modes are also discussed.

Comparative analysis of Bragg fibers.

In this paper, we compare three analysis methods for Bragg fibers, viz. the transfer matrix method, the asymptotic method and the Galerkin method. We also show that with minor modifications, the transfer matrix method is able to calculate exactly the leakage loss of Bragg fibers due to a finite number of H/L layers. This approach is more straightforward than the commonly used Chews method. It is shown that the asymptotic approximation condition should be satisfied in order to get accurate results. The TE and TM modes, and the band gap structures are analyzed using Galerkin method.

Photonic band gap analysis using finite-difference frequency-domain method

A finite-difference frequency-domain (FDFD) method is applied for photonic band gap calculations. The Maxwells equations under generalized coordinates are solved for both orthogonal and non-orthogonal lattice geometries. Complete and accurate band gap information is obtained by using this FDFD approach. Numerical results for 2D TE/TM modes in square and triangular lattices are in excellent agreements with results from plane wave method (PWM). The accuracy, convergence and computation time of this method are also discussed.

The enhanced oxidation of SO2 by NO2 on carbon particulates

Abstract The oxidation of SO 2 on carbon particles in dry air and in air at 65% relative humidity (RH) was found to be greatly enhanced by the presence of gaseous NO 2 . Exposures of 20–80 ppm SO 2 + 10 ppm NO 2 on 1 mg samples of commercial carbon black were found to produce both sorption and desorption coverages (weight retained after desorption into N 2 ) of over one order of magnitude greater than for corresponding SO 2 exposures. Significant agglomeration and wetting were observed to occur progressively during exposures at 65% RH and samples, even after 150 h exposure, rarely reached steady-state weight gain. The wetting may have regenerated fresh reactive carbon surface. Sorptions conducted in nitrogen atmospheres, rather than in air, appeared to produce slightly higher sorptions and weight retentions for equivalent exposure concentrations and times, indicating that NO 2 served as the oxidizer and that molecular oxygen, or some trace constituents in air, may have weakly inhibited the oxidation by NO 2 . Wet chemical analysis of the desorbed phase indicated that sulfate, presumably H 2 SO 4 , accounted for over half of the retained weight. Measurements of pH from water-quenched samples indicated a highly acidic surface phase and suggested the oxidation process could process in an acidic environment.

The oxidation of SO2 on carbon particles in the presence of O3, NO2 and N2O

Abstract The oxidation of SO 2 on carbon particles at 65 % relative humidity (RH) by O 3 , NO 2 and N 2 O was investigated gravimetrically and compared with oxidation by air. Approximately 1 mg samples of carbon black were exposed to continuously flowing mixtures of SO 2 , SO 2 + O 3 , SO 2 + NO 2 , and SO 2 + N 2 O in air (or in N 2 ). Both O 3 and NO 2 in the 0.07–10ppmv range with 20–40ppmv SO 2 were found to produce sorption and desorption coverages significantly higher than those for corresponding SO 2 in air exposures. N 2 O was determined to be much less effective as an oxidant than O 3 or NO 2 . Identical concentrations of O 3 or NO 2 were found to produce equivalent conversions of SO 2 to sulfate on carbon for equal exposure times. Wet chemical analysis of the residue following desorption indicated that sulfate generally accounted for well over half of the retained weight. Exposure at low concentrations (0.10 ppmv SO 2 + 0.02 ppmv O 3 or NO 2 ), however, appeared to produce little, if any, enhancement in SO 2 transformation when compared with equivalent SO 2 in air. Weight retentions for these runs were very small, however, and measurement errors of up to 25% would be anticipated.

Fiber optic sensors for health monitoring of morphing airframes: I. Bragg grating strain and temperature sensor

Fiber optic sensors are being developed for health monitoring of future aircraft. Aircraft health monitoring involves the use of strain, temperature, vibration and chemical sensors to infer integrity of the aircraft structure. Part 1 of this two part series describes sensors that will measure load and temperature signatures of these structures. In some cases a single fiber may be used for measuring these parameters. Part 2 will describe techniques for using optical fibers to monitor composite cure in real time during manufacture and to monitor in-service integrity of composite structures using a single fiber optic sensor capable of measuring multiple chemical and physical parameters. The facilities for fabricating optical fiber and associated sensors and the methods of demodulating Bragg gratings for strain measurement will be described.

Infrared vibration–rotation spectra of the CIO radical using tunable diode laser spectroscopy

Tunable diode laser spectroscopy is used to measure the infrared vibration-rotation spectra of the ClO radical. The radical is generated in a flow system where a Cl2-He mixture passes through a microwave discharge to dissociate the Cl2. An O3-O2 mixture from an ozone generator is injected into the system downstream of the microwave discharge where O3 combines with Cl to form ClO. By adjusting the gas flow rates to yield an excess of Cl atoms, all the ozone is combined. ClO concentration is measured with UV absorption at 2577 and 2772 A and a deuterium lamp as a continuous source. Total cell pressure is 5.5 torr. The diode laser spectrometer is calibrated with ammonia lines as a reference where possible. The frequency of vibration-rotation lines is expressed as a function of rotational quantum number, fundamental vibrational frequency, and the rotational constants of the upper and lower vibrational states.

Fabrication of self-apodized short-length fiber Bragg gratings

A new technique for writing extremely short-length Bragg gratings in optical fibers is demonstrated. A physical model describes the diffraction effects on the spatial and wavelength spectra of the Bragg gratings. Selection of appropriate diffraction patterns and related parameters permits self-apodized Bragg gratings with a typical spatial length of several hundred micrometers and a bandwidth of several nanometers to be obtained. These gratings with well-defined spectra are suitable for use as miniature distributed strain sensors and other applications requiring small physical dimensions and broadband spectra.

Analysis of the ATP-induced conformational changes in sarcoplasmic reticulum

Abstract A series of group-specific spin-labeled compounds was used to investigate the mechanism of the ATP-induced conformational changes in rabbit skeletal sarcoplasmic reticulum. The spin labels used can be divided into three classes according to their specificities: (I) N (1-oxyl-2,2,6,6-tetramethyl-4-piperidinyl)maleimide for SH groups; (II) N (1-oxyl-2,2,6,6-tetramethyl-4-piperidinyl)isothiocyanate for amine or hydroxyl groups; and (III) N -oxyl-4′,4′-dimethyl-oxazolidine derivatives of stearic acid for fatty acids. Of the three classes of compounds tested, only the mobility of probe (I) changed upon addition of ATP to the spin-labeled sarcoplasmic reticulum. This ATP-induced conformational change could be depressed by 5 m m propranolol, a concentration which by itself had no effect on the mobility of the spin label. Since similar concentrations of propranolol inhibited the breakdown but did not influence the formation of a phosphorylated intermediate during the hydrolysis of ATP, these observations suggest that the conformational change takes place at a step in ATP hydrolysis beyond the formation of the phosphorylated intermediate. The same basic series of experiments was also performed with the purified sarcoplasmic reticulum enzyme. Even though similar results were obtained, the sensitivity of the enzyme toward propranolol and also the mobility of probe (I) in the enzyme were different from that of the sarcoplasmic reticulum. Large doses (10–20 m m ) of propranolol, however, were found to directly alter the mobilities of all the classes of probes used. The effect of 20 m m propranolol on probe (III) in the sarcoplasmic reticulum was equivalent to a 10 °C rise in temperature of the membrane.

Fiber Optic Sensors for Health Monitoring of Morphing Aircraft

Fiber optic sensors are being developed for health monitoring of future aircraft. Aircraft health monitoring involves the use of strain, temperature, vibration and chemical sensors. These sensors will measure load and vibration signatures that will be used to infer structural integrity. Since the aircraft morphing program assumes that future aircraft will be aerodynamically reconfigurable there is also a requirement for pressure, flow and shape sensors. In some cases a single fiber may be used for measuring several different parameters.