Channel Positioning Research Articles

Efficient power scaling of laser radiation by spectral beam combining

The possibility of achieving multikilowatt laser radiation by spectrally combining beams using volume Bragg gratings (VBGs) is shown. The VBGs recorded in a photothermorefractive glass exhibit long-term stability of all its parameters in high-power laser beams with power density >1 MW/cm2 in the cw beam of total power on a kilowatt level. We consider an architecture-specific beam-combining scheme and address the cross-talk minimization problem based on optimal channel positioning. Five-channel high efficiency spectral beam combining resulted in a >750 W near-diffraction-limited cw beam has been demonstrated experimentally.

Effect of channel positioning on the 1∕f noise in silicon-on-insulator metal-oxide-semiconductor field-effect transistors

p -channel metal-oxide-semiconductor field-effect transistors (MOSFETs) fabricated on silicon-on-insulator (SOI) substrates with an ultrathin (∼20nm) lightly p-doped Si body were found to show about an order of magnitude lower 1∕f noise than that in conventional bulk Si pMOSFETs when biased in strong inversion. In order to investigate the origin of the 1∕f noise and find an explanation for the 1∕f noise reduction, the 1∕f noise in the SOI devices was studied as a function of the back gate voltage. The 1∕f noise was found to increase with increasing back gate voltage, which acts to push the carriers closer towards the front gate oxide interface. The average distance of the inversion carriers from the gate oxide interface was obtained from simulations and used to interpret the 1∕f noise behavior. The Hooge parameter, extracted for several different 1∕f noise experiments where one or two terminal voltages were varied, exhibited a general behavior similar for both the SOI and bulk Si pMOSFETs. The Hooge parameter was shown to increase markedly when the average carrier-oxide separation is around 2nm. Possible explanations of the results were discussed in terms of the mobility fluctuation noise model.

A Dual-Channel System for Providing Location Estimation in Mobile Computing

A dual channel system, which is based on the GPS and the GSM Network, is being developed to compensate the problem of the lost of GPS signals in providing location services to mobile users in urban areas. In this design, when GPS signals are being blocked in blind spot areas, GSM positioning algorithms would be used as an alternative method to provide location estimations. This research is an investigation in search of a set of location estimation algorithms based on signal attenuation to work with GPS, so as to develop a dual channel positioning system. With the technical support from a local mobile operator, we have constructed and conducted several real world experiments for our investigation and results are promising.

Factors that influence lymphocyte yields in lymphocytapheresis.

The recent use of lymphocytapheresis to treat immune-mediated diseases such as rheumatoid arthritis prompted a study of factors that influence the cell composition of lymphocytapheresis concentrates. Following single cytapheresis procedures, using protocols recommended by manufacturers, lymphocyte yields were significantly higher with the model 2997 (IBM) and CS-3000 (Fenwal) cell separators as compared to the model 30 (Haemonetics) separator (9.8 +/- 1.1 and 7.1 +/- 1.2 X 10(9) lymphocytes, respectively, versus 4.6 +/- 1.1 X 10(9); p less than 0.01). The lymphocyte concentrate obtained with the CS-3000 separator contained the smallest number of monocytes (0.6 +/- 0.4 X 10(9) versus 1.4 +/- 1.6 and 1 +/- 0.3 X 10(9) for the model 2997 and 30 cell separators, respectively). Platelet contamination of the lymphocyte concentrate was highest with the CS-3000 (6.5 +/- 2.4 X 10(11], and erythrocyte contamination was highest when the model 30 was used (21 +/- 3.0%). Studies using the model 2997 indicated that lymphocyte yields were significantly influenced by donor pre-apheresis absolute lymphocyte counts, and for this cell separator by specific operating variables, such as channel centrifugation speed and positioning of the red cell interface during lymphocyte collection. Maximal yields were obtained when the channel centrifugation speed was 800 to 1000 rpm (equivalent to 100-150 X g) and the red cell interface was adjusted to yield a cell concentrate with a hematocrit less than 4 percent. These results suggest that it will be necessary to standardize lymphocytapheresis collection protocols in future studies to assess the role of lymphocytapheresis in the management of immune-mediated diseases such as rheumatoid arthritis.