Publications

Air traffic in the United States is highly congested in its "Northeast Corridor", an area that roughly encompasses the airspace from Washington, DC to Boston. This region is frequently affected by low cloud ceiling and visibility conditions during the cool season, often in association with synoptic-scale low pressure systems. Operating under IFR (Instrument Flight Rules) for extended periods of time substantially reduces airport capacity and can cause significant delay at major airports. Anticipating transitions into and out of IFR ceiling and visibility conditions can mitigate air traffic disruption by allowing for appropriate upstream planning. For instance, an accurate forecast of the lifting of cloud ceiling out of IFR range would allow for the release of more planes upstream to take advantage of the anticipated increase in capacity. The Federal Aviation Administration (FAA), through its Aviation Weather Research Program (AWRP), is currently sponsoring the Northeast Winter Ceiling and Visibility Project (NECV). Its purpose is to provide situational awareness of current ceiling and visibility conditions in the Northeast United States in a way tailored to the needs of air traffic control (ATC), as well as to bring a number of various but complimentary technologies to bear on providing automated 0-12 hour forecasts of upcoming conditions. Methodologies currently under development include numerical weather prediction (NWP) applications, 1-dimensional column modeling, tracking of aviation-impacting cloud, and statistical forecast models (Clark 2006). This presentation describes the development of statistical forecast models for major New York City airports. The statistical forecast models use routine regional meteorological observations as predictors for future values of ceiling and visibility for selected locations. These predictors consist primarily of hourly surface observations, but upper air soundings and buoy data are available for use as well. The methodology for building the models is based on non-linear regression, with the nonlinearity entering in the spirit of Generalized Additive Models (Hastie and Tibshiriani 1990). Several innovations are introduced to aid in predictor selection and to enhance the skill and stability of the final models. Statistical models such as these have been successfully developed and used recently in an operational setting for ATC. The recently completed San Francisco (SFO) Marine Stratus Initiative (also sponsored by AWRP) features a real-time display and forecast system, which contains as one of its components a regional statistical forecast model (Wilson 2004, Clark et al. 2005). The model uses hourly surface observations from the San Francisco Bay area along with the Oakland sounding to produce regular forecasts of stratus dissipation during the warm season. The performance of this model during two years (May – October) of real-time operations is given in Table 1. The context for the marine stratus model differs from that for NECV in several important ways. In SFO, warm season stratus dissipation is a diurnal phenomenon, governed primarily by mesoscale and radiative processes in conjunction with local topography. The NECV problem is more affected by synoptic dynamics, and less by the diurnal component. This paper next provides a high-level summary of the methodology that has been developed to build these statistical forecast models followed by details of the initial NECV problem, including some discussion of the quality of the predictor data. Model accuracy can be improved by development over phenomenological partitions of the available cases; a method of partitioning the cases is described. The paper concludes with a discussion of near-term tasks.

Remote, oceanic regions have few, if any, high resolution weather products that indicate the current or future locations of aviation hazards such as volcanic ash, convection, turbulence, icing or adverse headwinds. Moreover, oceanic regions present unique challenges due to severely limited data availability, the long duration of transoceanic flights and the difficulty of transmitting critical information into the cockpit. In 2001, the Oceanic Weather Program Development Team (OWPDT; Herzegh et al. 2002) was organized within the Federal Aviation Administration (FAA) Aviation Weather Research Program (AWRP) to focus on resourceful methods for overcoming these limitations through the use of a diverse range of satellite observations, global model results and satellite-based communications. Resulting products focus on the needs of pilots, dispatchers, air traffic managers and forecasters within the oceanic aviation community. The team is a leader in the inflight display of weather products and will continue to develop new displays as products become available.

We report the demonstration of a 1.5 um InGaAsP mode-locked slab-coupled optical waveguide laser (SCOWL) producing 10 ps pulses with energies of 58 pJ and average output powers of 250 mW at a repetition rate of 4.29 GHz. To the best of our knowledge, this is the first passively mode-locked slab-coupled optical waveguide laser. The large mode and low confinement factor of the SCOWL architecture allows the realization of monolithic mode-locked lasers with high output power and pulse energy. The laser output is nearly diffraction limited with M2 values less than 1.2 in both directions.

Advanced separation assurance concepts involving higher degrees of automation must meet the challenge of maintaining safety in the presence of inevitable subsystem faults, including the complete failure of the supporting automation infrastructure. This paper examines the types of design features and safeguards that might be used to preserve safety in a highly automated environment. The Advanced Airspace Concept (AAC) being developed by NASA is used as the basis for a fault-tree analysis. Multiple layers of protection, with carefully specified fault management strategies, appear to be important to achieving the desired level of safety.

This study presents methods for engineering the electrocapillary behavior of fluoropolymer surfaces through the use of surfactants and an external insulating liquid. By the scaling of the appropriate surface energies, electrocapillary behavior is obtained at a record low voltage, with contact angle changes in excess of 100[degrees] at 4 V. A consistent description of electrocapillary saturation is presented, identifying three separate regimes: breakdown, thermodynamic instability, and relaxation. Methods for identifying and mitigating some of the saturation behaviors are discussed. Finally, the parameters influencing the observed voltage of zero charge are summarized.

Three algorithms based on geostationary visible and infrared (IR) observations, are used to identify convective cells that do (or may) present a hazard to aviation over the oceans. The algorithms were developed at the Naval Research Laboratory (NRL), National Center for Atmospheric Research (NCAR), and Aviation Weather Center (AWC). The performance of the algorithms in detecting potentially hazardous cells is determined through verification based upon data from National Aeronautical and Space Administration (NASA) Tropical Rainfall Measuring Mission (TRMM) satellite observations of lightning and radar reflectivity, which provide internal information about the convective cells. The probability of detection of hazardous cells using the satellite algorithms can exceed 90% when lightning is used as a criterion for hazard, but the false alarm ratio with all three algorithms is consistently large (~40%), thereby exaggerating the presence of hazardous conditions. This shortcoming results in part from limitations resulting from the algorithms' dependence upon visible and IR observations, and can be traced to the widespread prevalence of deep cumulonimbi with weak updrafts but without lightning, whose origin is attributed to pronounced departures from non-dilute ascent.

Algorithm implementation efficiency is key to delivering high-performance computing capabilities to demanding, high throughput DoD signal and image processing applications and simulations. Significant progress has been made in compiler optimization of serial programs, but many applications require parallel processing, which brings with it the difficult task of determining efficient mappings of algorithms to multiprocessor computers. The pMapper infrastructure addresses the problem of performance optimization of multistage MATLAB applications on parallel architectures. pMapper is an automatic performance tuning library written as a layer on top of pMatlab. pMatlab is a parallel Matlab toolbox that provides MATLAB users with global array semantics. While pMatlab abstracts the message-passing interface, the responsibility of generating maps for numerical arrays still falls on the user. A processor map for a numerical array is defined as an assignment of blocks of data to processing elements. Choosing the best mapping for a set of numerical arrays in a program is a nontrivial task that requires significant knowledge of programming languages, parallel computing, and processor architecture. pMapper automates the task of map generation, increasing the ease of programming and productivity. In addition to automating the mapping of parallel Matlab programs, pMapper could be used as a mapping tool for embedded systems. This paper addresses the design details of the pMapper infrastructure and presents preliminary results.

We demonstrate Mach-Zehnder-type interferometry in a superconducting flux qubit. The qubit is a tunable artificial atom, the ground and excited states of which exhibit an avoided crossing. Strongly driving the qubit with harmonic excitation sweeps it through the avoided crossing two times per period. Because the induced Landau-Zener transitions act as coherent beamsplitters, the accumulated phase between transitions, which varies with microwave amplitude, results in quantum interference fringes for n = 1 to 20 photon transitions. The generalization of optical Mach-Zehnder interferometry, performed in qubit phase space, provides an alternative means to manipulate and characterize the qubit in the strongly driven regime.

III-N materials currently enjoy a predominant role in the formation of solid-state light emitters for [lamda]

An entry level overview of state-of-the-art CMOS detector technology is presented. Operating principles and system architecture are explained in comparison to the well-established CCD technology, followed by a discussion of important benefits of modern CMOS-based detector arrays. A number of unique CMOS features including different shutter modes and scanning concepts are described. In addition, sub-field stitching is presented as a technique for producing very large imagers. After a brief introduction to the concept of monolithic CMOS sensors, hybrid detectors technology is introduced. A comparison of noise reduction methods for CMOS hybrids is presented. The final sections review CMOS fabrication processes for monolithic and vertically integrated image sensors.