Characterization of metal-clad TE/TM mode splitters using thefinite element method

A metal-clad directional coupler-based polarizer with two-dimensional (2-D) modal confinement has been designed and its performance has been rigorously computed by using the accurate vector H-field finite element method after taking into consideration the polarization-dependent coupling lengths, phase mismatchings and losses due to metal-cladding of the system involved     

Optimization of the optical properties of a deeply etched semiconductor electrooptic modulator

A rigorous numerical study of a deeply etched semiconductor electrooptic modulator is presented. A Laplace equation solver followed by a full-vectorial modal solution technique for general anisotropic optical waveguides, all based on the versatile finite-element method, is used to find the potential distribution, the modulating electric fields, the changes in the permittivity tensor associated with the electrooptic effect, and the different modes of propagation. In particular, the optimization of the optical properties of the modulator structure such as the half-wave voltage length product V/sub /spl pi//L and the optical losses due to the imperfectly conducting electrodes has been carefully carried out and results reported. In addition, the effect of the waveguide parameters on the microwave properties such as the microwave index n/sub m/ and characteristic impedance Z/sub c/ is explained.     

Computation of 3-D Magnetic Field Distribution in Long-Lifetime Electromagnetic Actuators

This paper involves the computation of 3-D magnetic fields in high-performance, long-lifetime solenoid actuators by finite-element (FE) modeling. Operating at frequencies between 150 and 300 Hz, these actuators are unique in terms of the large force they produce (8-15 N) and their very long lifetime (over five billion continuous duty cycles). Their magnetic circuit typically operates at saturation and, because of the compact dimensions, the 3-D nature of the field distribution needs to be taken into account for their design. Results are presented in terms of the effects of design parameters on saturation and force calculation     

Use of the Neuropsychiatric Inventory in traumatic brain injury: A pilot investigation.

Objective: The goal of this investigation was to pilot the Neuropsychiatric Inventory (NPI) among individuals with traumatic brain injury (TBI) and their caregivers, assessing its screen-metric approach. Design and Participants: Using the NPI, caregivers rated neurobehavioral disturbances in 51 individuals with moderate-to-severe TBI. The NPI was completed 1 or 2 years after the individuals were injured. Results: Caregivers reported the highest symptom levels for participants on Irritability/Lability, Apathy, and Agitation/Aggression, and rated greater levels of distress tied to those domains and to Dysphoria. Caregivers endorsing domain screening items endorsed significantly more metric items (vs. screen non-endorsers) within that domain, as would be expected if the screen accurately measured the psychopathology under consideration. In addition, the screen-metric yielded extremely low false-positive rates, although 5 of the 12 domains had elevated false-negative rates. Conclusions: Findings provide preliminary support for the accuracy of the NPI's screen-metric in this population and are consistent with prior work detailing common problematic neurobehavioral consequences of TBI. These results lay groundwork for research and clinical use of this measure in populations with TBI. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Use of Eutectic Fixed Points to Characterize a Spectrometer for Earth Observations

A small palm-sized, reference spectrometer, mounted on a remote-controlled model helicopter is being developed and tested by the National Physical Laboratory (NPL) in conjunction with City University, London. The developed system will be used as a key element for field vicarious calibration of optical earth observation systems in the visible-near infrared (VNIR) region. The spectrometer is hand held, low weight, and uses a photodiode array. It has good stray light rejection and wide spectral coverage, allowing simultaneous measurements from 400 to 900 nm. The spectrometer is traceable to NPL’s primary standard cryogenic radiometer via a high-temperature metal-carbon eutectic fixed-point blackbody. Once the fixed-point temperature has been determined (using filter radiometry), the eutectic provides a high emissivity and high stability source of known spectral radiance over the emitted spectral range. All wavelength channels of the spectrometer can be calibrated simultaneously using the eutectic transition without the need for additional instrumentation. The spectrometer itself has been characterized for stray light performance and wavelength accuracy. Its long-term and transportation stability has been proven in an experiment that determined the “World’s Bluest Sky”—a process that involved 56 flights, covering 100,000 km in 72 days. This vicarious calibration methodology using a eutectic standard is presented alongside the preliminary results of an evaluation study of the spectrometer characteristics.     

Birefringence compensation of silica waveguides

A novel method of compensating stress-induced birefringence in silica waveguides by incorporating a layered structure is introduced and analyzed by using a numerically efficient, vectorial H-field finite element-based modal solution approach.     

Numerical modeling of second harmonic generation in opticalwaveguides using the finite element method

A numerical study of second harmonic generation (SHG) in optical waveguides is presented using the finite element method (FEM) and the Crank-Nicholson split-step procedure. Results are given for a Cherenkov radiation scheme in both planar and channel waveguides. Also presented are results obtained on frequency doubling for guided modes in both planar and channel waveguides, using the quasi-phase-matching scheme     

Sol-Gel Properties for Fiber Optic Sensor Applications

This work reports a discussion of several sol-gels formed using a variety of preparation procedures with a view to the production of a suitable substrate for chemically sensitive dyes for various fiber optic fluorescence-based sensor applications. The compositions, qualitative appearance, and coating abilities of a series of gels are discussed, as is their suitability as substrates for indicator materials for the sensor purpose in view.     

The Effect of Selected Water-Soluble Excipients on the Dissolution of Paracetamol and Ibuprofen

The purpose of this investigation was to study the dissolution behavior of paracetamol and ibuprofen in the presence of a range of selected potential excipients. First, a pH-solubility profile was generated for both drugs, and the effect of changing hydrodynamic conditions on the intrinsic dissolution rate was investigated. It was established that both drugs dissolved according to the diffusion-layer model. Paracetamol solubility (approximately 20.3 mg mL^{? 1}) did not vary from pH 1.2–8.0, corresponding to the in vivo range in the gastrointestinal tract. Ibuprofen had an intrinsic solubility of approximately 0.06 mg mL^{? 1}, and pK_a was calculated as 4.4. Second, the effects of selected potential excipients (lactose, potassium bicarbonate, sodium bicarbonate, sodium chloride, and tartaric acid) were evaluated by measuring the effect of the inclusion of each additive in the dissolution medium on drug solubility, drug intrinsic dissolution rate, and solution viscosity. The results were evaluated using the diffusion-layer model, and it was determined that for paracetamol, the collected data fitted the model for all the excipients studied. For ibuprofen, it was found that there were differences between the excipients that raised the solution pH above the pK_a to those that did not. For the excipients raising the pH above the pK_a, the effect on intrinsic dissolution rate was not as high as that expected from the change in drug solubility. It was postulated that this might be due to lack of penetration of the excipient into the drug boundary layer microenvironment. Formulators may calculate the effect of adding an excipient based on solubility increases but may not find the dissolution rate improvement expected.     

Improved design of a polarization converter based on semiconductor optical waveguide bends

By using an efficient vector finite-element-based beam-propagation method, we present an improved design of a polarization converter. This design relies on the use of a single-section deeply etched bent semiconductor waveguide with slanted sidewalls. By careful adjustment of the bend radius, the waveguide width, and the sidewall angle we obtained a nearly 100% polarization conversion ratio with no appreciable radiation loss and a bending angle of less than 180 degrees .