Natural convection for slip flow in a vertical polygonal duct

Free convection with velocity slip and temperature jump in a vertical polygonal duct with a heated circular core is semianalytically solved by the methods of eigenfunction expansion and point match. The conditions of the core wall being at uniform wall temperature or uniform heat flux are considered. It is shown that the temperature and flowfields can be very different from those without the velocity slip and temperature jump. The optimum core radius and the corresponding maximum flow rate are numerically determined for some values of the slip length, temperature jump coefficient, and the number of sides of the polygon. Read More: http://arc.aiaa.org/doi/abs/10.2514/1.T4406postprin

A novel self-routing address scheme for all-optical packet-switched networks with arbitrary topologies

Pure all-optical packet-switched networks in which both header processing and packet routing are carried out in the optical domain overcome the bandwidth bottlenecks of optoelectronic conversions and therefore are expected to meet the needs of next generation high speed networks. Due to the limited capabilities of available optical logic devices, realizations of pure all-optical packet-switched networks in the near future will likely employ routing schemes that minimize the complexity of routing control. In this paper, we propose a novel self-routing scheme that identifies the output ports of the nodes in a network instead of the nodes themselves. The proposed address scheme requires single bit processing only and is applicable to small to medium size pure all-optical packet-switched networks with arbitrary topologies. Unlike traditional self-routing schemes, multiple paths between two nodes can be defined. Hierarchical address structure can be used in the proposed routing scheme to shorten the address.published_or_final_versio

Multicasting in deflection-routed all-optical packet-switched networks

Two multicast protocols are proposed for deflection-routed all-optical packet-switched networks. One scheme sends a deflected multicast packet back to the root node while the other sends it back to the deflection point Both schemes can be implemented using demonstrated optical signal processing technology. The performance of the two proposed multicast schemes are compared using Manhattan Street Networks. We found that the back-to-the-root-node scheme performed better than the back-to-the-deflection-node scheme. A hybrid approach can further improve the system performance.published_or_final_versio

A novel self-routing scheme for all-optical packet switched networks with arbitrary topology

Due to limited available photonic devices, optical networks in the near future will likely employ routing schemes that do not require sophisticated processing of optical packets. In this paper, we propose a novel self-routing scheme for all-optical packet networks that can be applied to networks with arbitrary topology. The proposed routing scheme requires only single bit processing and can be implemented with existing technologies.published_or_final_versio

Quantum well intermixing for the fabrication of InGaAsN/GaAs lasers with pulsed anodic oxidation

Quantum well (QW) intermixing was carried out by post-growth rapid thermal annealing in InGaAsN/GaAs QW laser structures grown by solid-source molecular-beam epitaxy. The intensity and width of the photoluminescence peak showed a dependence on annealing temperature and time, and the maximum intensity and minimum linewidth were obtained after the wafer was annealed at 670 °C for 60 s. The peak luminescence energy blueshifted with increasing annealing time, although it plateaued at an annealing time that corresponded to that yielding the maximum luminescence intensity. The diffusion coefficient for indium was determined from a comparison between experimental data and modeling, but showed that QW intermixing alone was not sufficient to account for the relatively large blueshift after annealing. Defects related to the incorporation of nitrogen in the QW layer were responsible for the low photoluminescence efficiency in the as-grown samples and were annealed out during rapid thermal annealing. During annealing, nitrogen interstitials moved to vacancy sites within the QW and thus suppressed QW intermixing. After annealing wafers under conditions giving the maximum luminescence intensity, lasers were fabricated with pulsed anodic oxidation. © 2004 American Institute of Physics.published_or_final_versio

Deflection routing in slotted self-routing networks with arbitrary topology

A deflection routing algorithm that can be applied to a novel self-routing address scheme for networks with arbitrary topology is proposed. The proposed deflection routing algorithm can be implemented all-optically using bitwise optical logic gates. Besides the primary output link selection, alternate output link choices by a packet at each node in case of deflection are also encoded in the address header. Priority classes can also be defined in the proposed address scheme. The performance of the deflection routing algorithm is studied using the AT&T North America OC-48 optical fiber network topology.published_or_final_versio

Reduction of motion artifact in pulse oximetry by smoothed pseudo Wigner-Ville distribution

BACKGROUND: The pulse oximeter, a medical device capable of measuring blood oxygen saturation (SpO2), has been shown to be a valuable device for monitoring patients in critical conditions. In order to incorporate the technique into a wearable device which can be used in ambulatory settings, the influence of motion artifacts on the estimated SpO2 must be reduced. This study investigates the use of the smoothed psuedo Wigner-Ville distribution (SPWVD) for the reduction of motion artifacts affecting pulse oximetry. METHODS: The SPWVD approach is compared with two techniques currently used in this field, i.e. the weighted moving average (WMA) and the fast Fourier transform (FFT) approaches. SpO2 and pulse rate were estimated from a photoplethysmographic (PPG) signal recorded when subject is in a resting position as well as in the act of performing four types of motions: horizontal and vertical movements of the hand, and bending and pressing motions of the finger. For each condition, 24 sets of PPG signals collected from 6 subjects, each of 30 seconds, were studied with reference to the PPG signal recorded simultaneously from the subject's other hand, which was stationary at all times. RESULTS AND DISCUSSION: The SPWVD approach shows significant improvement (p < 0.05), as compared to traditional approaches, when subjects bend their finger or press their finger against the sensor. In addition, the SPWVD approach also reduces the mean absolute pulse rate error significantly (p < 0.05) from 16.4 bpm and 11.2 bpm for the WMA and FFT approaches, respectively, to 5.62 bpm. CONCLUSION: The results suggested that the SPWVD approach could potentially be used to reduce motion artifact on wearable pulse oximeters

Using 2x2 switching modules to build large 2-D MEMS optical switches

MEMS optical switch technology is one of the key technologies in wavelength division multiplexing (WDM) optical networks. Although the 2-D MEMS optical switch technology is mature, the commonly used crossbar architecture is not amenable to building large switches. In this paper, we propose a design of 2x2 switching modules, and use it to build large 2-D MEMS optical switches with architectures such as Spanke-Benes and Benes networks.published_or_final_versio

Temperature-dependent photoluminescence of GaInP/AlGaInP multiple quantum well laser structure grown by metalorganic chemical vapor deposition with tertiarybutylarsine and tertiarybutylphosphine

A GaInP/AlGaInP multiple quantum well laser structure was grown by low-pressure metalorganic chemical vapor deposition with tertiarybutylarsine and tertiarybutylphosphine. Laser diodes fabricated from this structure lased at room temperature. Photoluminescence ~PL! measurements were performed from 10 to 230 K. The PL energy increased with temperature from 10 to 70 K and decreased above 70 K. The former was attributed to thermal activation of trapped carriers due to localization in the quantum wells, while the latter was attributed to temperature-induced band-gap shrinkage. The PL intensity as a function of temperature was fitted by employing two nonradiative recombination mechanisms with good agreement, resulting in two activation energies that correspond to losses of photogenerated carriers to nonradiative centers. © 2003 American Institute of Physics.published_or_final_versio

Determinants of the creatinine clearance to glomerular filtration rate ratio in patients with chronic kidney disease: a cross-sectional study

BACKGROUND: Creatinine secretion, as quantified by the ratio of creatinine clearance (CrCl) to glomerular filtration rate (GFR), may introduce another source of error when using serum creatinine concentration to estimate GFR. Few studies have examined determinants of the CrCl/GFR ratio. We sought to study whether higher levels of albuminuria would be associated with higher, and being non-Hispanic black with lower, CrCl/GFR ratio. METHODS: We did a cross-sectional analysis of 1342 patients with chronic kidney disease from the Chronic Renal Insufficiency Cohort (CRIC) who had baseline measure of iothalamate GFR (iGFR) and 24-hour urine collections. Our predictors included urine albumin as determined from 24-hour urine collections (categorized as: <30, 30-299, 300-2999 and ≥3000 mg), and race/ethnicity (non-Hispanic white, non-Hispanic black, Hispanic). Our outcome was CrCl/iGFR ratio, a measure of creatinine secretion. RESULTS: Mean iGFR was 48.0 ± 19.9 mL/min/1.73 m(2), median albuminuria was 84 mg per day, and 36.8% of the study participants were non-Hispanic black. Mean CrCl/iGFR ratio was 1.19 ± 0.48. There was no association between the CrCl/iGFR ratio and urine albumin (coefficient 0.11 [95% CI−0.01-0.22] for higest verus lowest levels of albuminuria, p = 0.07). Also, there was no association between race/ethnicity and CrCl/iGFR ratio (coefficient for non-Hispanic blacks was−0.03 [95% CI−0.09-0.03] compared with whites, p = 0.38). CONCLUSIONS: Contrary to what had been suggested by prior smaller studies, CrCl/GFR ratio does not vary with degree of proteinuria or race/ethnicity. The ratio is also closer to 1.0 than reported by several frequently cited reports in the literature