Zero chirp asymmetric Fabry-Perot electroabsorption modulator using coupled quantum wells

A zero-chirp asymmetric Fabry-Perot reflection InGaAs QW modulator is created by placing coupled quantum wells in the intrinsic region of a reverse-biased p-i-n diode asymmetric Fabry-Perot cavity. Unlike single quantum wells which necessarily produce chirping during the switching cycle, these coupled quantum wells provide large absorption changes with zero refractive index changes over the entire voltage swing; the resultant cavity structure shows reflectivity changes with zero experimental phase change over the same voltage range. The tradeoff in reflectivity change required in order to obtain zero chirp is described. This tradeoff is a result of the different switching mechanisms used in coupled quantum wells versus single quantum wells.     

Adaptive modulation and MIMO coding for broadband wireless datanetworks

Link adaptation techniques, where the modulation, coding rate, and/or other signal transmission parameters are dynamically adapted to the changing channel conditions, have emerged as powerful tools for increasing the data rate and spectral efficiency of wireless data-centric networks. While there has been significant progress on understanding the theoretical aspects of time adaptation in LA protocols, new challenges surface when dynamic transmission techniques are employed in broadband wireless networks with multiple signaling dimensions. Those additional dimensions are mainly frequency, especially in multicarrier systems, and space in multiple-antenna systems, particularly multiarray multiple-input multiple-output communication systems. We give an overview of the challenges and promises of link adaptation in future broadband wireless networks. We suggest guidelines to help in the design of robust, complexity/cost-effective algorithms for these future wireless networks     

Fabrication and performance of selectively oxidized vertical-cavitylasers

We report the high yield fabrication and reproducible performance of selectively oxidized vertical-cavity surface emitting lasers. We show that linear oxidation rates of AlGaAs without an induction period allows reproducible fabrication of buried oxide current apertures within monolithic distributed Bragg reflectors. The oxide layers do not induce obvious crystalline defects, and continuous wave operation in excess of 650 h has been obtained. The high yield fabrication enables relatively high laser performance over a wide wavelength span. We observe submilliamp threshold currents over a wavelength range of up to 75 nm, and power conversion efficiencies at 1 mW output power of greater than 20% over a 50-nm wavelength range     

The propagation of ultrasonic waves through a bubbly liquid intotissue: a linear analysis

The steady-state response induced by a harmonically driven, ultrasonic wave in a structure comprised of two layers, the first a bubbly liquid, and the second a viscoelastic solid with a rigid boundary, is studied in the linear approximation. This structure is intended to model a cavitating liquid in contact with tissue. The upper surface of the liquid is driven harmonically and models the source. The lower surface of the solid is rigid and models the bone. While cavitation is inherently nonlinear, the propagation process is approximated as linear. The transient response is not calculated. The model of the bubbly liquid is a simple continuum one, supplemented by allowing for a distribution of different equilibrium bubble radii and for the relaxation of the oscillations of each bubble. The model contains three functions, the probability distribution describing the distribution of bubble radii, and two functions modeling the mechanical response of the individual bubble and the tissue, respectively. Numerical examples are worked out by adapting data taken from various published sources to deduce the parameters of these functions. These examples permit an assessment of the overall attenuation of the structure, and of the magnitudes of the pressure and particle velocity in the bubbly liquid and of the traction and the particle displacement in the tissue     

The origins of entropy and irreversibility

The origins of entropy and irreversibility in thermodynamics are re-examined once more, in the light of 45 years of influence from information-theoretic concepts. Familiar, but elusive notions of the approach to equilibrium, and time-dependent entropy, are subjected to renewed scrutiny.     

Si-implantation activation annealing of GaN up to 1400°C

Implant activation annealing of Si-implanted GaN is reported for temperatures from 1100 to 1400°C. Free electron concentrations up to 3.5×10²⁰ cm⁻³ are estimated at the peak of the implanted profile with Hall mobilities of ∼60 cm²/Vs for annealing at 1300°C for 30 s with an AIN encapsulant layer. This mobility is comparable to epitaxial GaN doped at a similarly high level. For annealing at ≥1300°C, the sample must be encapsulated with AIN to prevent decomposition of the GaN layer. Channeling Rutherford backscattering demonstrates the partial removal of the implant damage after a 1400°C anneal with a minimum channeling yield of 12.6% compared to 38.6% for the as-implanted spectrum. Scanning electron microscope images show evidence of decomposition of unencapsulated GaN after a 1300°C anneal and complete sublimation after 1400°C. The use of AIN encapsulation and annealing at temperatures of ∼1300°C will allow the formation of selective areas of highly doped GaN to reduce the contact and access resistance in GaN-based transistors and thyristors.     

"Nature of priming effects in semantic matching": Correction to Whitlow.

Reports an error in "Nature of priming effects in semantic matching" by J. W. Whitlow (Journal of Experimental Psychology: Learning, Memory, and Cognition, 1986[Jul], Vol 12[3], 353-360). The Appendix table was constructed incorrectly. The correct table appears in the erratum. (The following abstract of the original article appeared in record 1986-29114-001.) Studied priming effects in a semantic matching task that distinguished visually based matching processes from nominally and semantically based matching processes, using 24 undergraduates. Ss judged semantic matches for 3 types of word pairs: identical (e.g., robin-robin), same category (e.g., robin-sparrow), and different category (e.g., robin-truck). Visual matching was isolated by comparing performance between physical identity (e.g., robin-robin) and nominal identity (e.g., robin-ROBIN) pairs. Physical identity pairs, which allowed visually based matching, exhibited an interaction between priming and the typicality of category exemplars that was absent in nominal identity and same-category pairs. Priming had no effect on nominal identity pairs. For same-category pairs, which required semantically based matching, priming produced facilitation at all levels of typicality. The results bring the semantic matching paradigm into agreement with other procedures that show that priming facilitates processing for all related targets. Categories and exemplars used as stimulus materials are appended. (18 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Early observations on an emerging Great Lakes invader Hemimysis anomala in Lake Ontario

Hemimysis anomala, a Ponto-Caspian littoral mysid, is an emerging Great Lakes invader that was discovered in Lakes Michigan and Ontario in 2006. Similar to the native mysid Mysis diluviana, Hemimysis exhibits a diel vertical migration pattern but generally inhabits shallower and warmer waters than M. diluviana. Because basic information on the distribution, habitat use, and biology of Hemimysis in the Great Lakes is scarce, the potential for food web disruption by Hemimysis cannot easily be predicted. Preliminary observations indicate widespread invasion of Hemimysis in Lake Ontario. In this study, we confirm the presence of Hemimysis at sites spanning the northern and southern shores of Lake Ontario and the presence of the individuals during winter months. In one horizontal tow in November 2007, over 26,000 individuals were collected with a length range of 4.4 to 9.0 mm and an average caloric density of 611 cal/g wet weight. The most effective methods for sampling Hemimysis were horizontal tows with either a zooplankton net in the water column or a benthic sled near the lake bottom. Although more quantitative data on the life history and distribution of this species is necessary, our preliminary observations support the prediction that the potential for Hemimysis to impact the nearshore food web in Lake Ontario appears high.