Self-stabilizing Numerical Iterative Computation

Many challenging tasks in sensor networks, including sensor calibration, ranking of nodes, monitoring, event region detection, collaborative filtering, collaborative signal processing, {\em etc.}, can be formulated as a problem of solving a linear system of equations. Several recent works propose different distributed algorithms for solving these problems, usually by using linear iterative numerical methods. In this work, we extend the settings of the above approaches, by adding another dimension to the problem. Specifically, we are interested in {\em self-stabilizing} algorithms, that continuously run and converge to a solution from any initial state. This aspect of the problem is highly important due to the dynamic nature of the network and the frequent changes in the measured environment. In this paper, we link together algorithms from two different domains. On the one hand, we use the rich linear algebra literature of linear iterative methods for solving systems of linear equations, which are naturally distributed with rapid convergence properties. On the other hand, we are interested in self-stabilizing algorithms, where the input to the computation is constantly changing, and we would like the algorithms to converge from any initial state. We propose a simple novel method called \syncAlg as a self-stabilizing variant of the linear iterative methods. We prove that under mild conditions the self-stabilizing algorithm converges to a desired result. We further extend these results to handle the asynchronous case. As a case study, we discuss the sensor calibration problem and provide simulation results to support the applicability of our approach

Stability of Magneto-optical Traps with Large Field Gradients: Limits on the Tight Confinement of Single Atoms

We report measurements of the stability of magneto-optical traps (MOTs) for neutral atoms in the limit of tight confinement of a single atom. For quadrupole magnetic field gradients at the trap center greater than ∼1 kG/cm, we find that stochastic diffusion of atoms out of the trapping volume becomes the dominant particle loss mechanism, ultimately limiting the MOT size to greater than ∼5 μm. We measured and modeled the diffusive loss rate as a function of laser power, detuning, and field gradient for trapped cesium atoms. In addition, for as few as two atoms, the collisional loss rates become very high for tightly confined traps, allowing the direct observation of isolated two-body atomic collisions in a MOT

Spontaneous radiative decay of translational levels of an atom near a dielectric surface

We study spontaneous radiative decay of translational levels of an atom in the vicinity of a semi-infinite dielectric. We systematically derive the microscopic dynamical equations for the spontaneous decay process. We calculate analytically and numerically the radiative linewidths and the spontaneous transition rates for the translational levels. The roles of the interference between the emitted and reflected fields and of the transmission into the evanescent modes are clearly identified. Our numerical calculations for the silica--cesium interaction show that the radiative linewidths of the bound excited levels with large enough but not too large vibrational quantum numbers are moderately enhanced by the emission into the evanescent modes and those for the deep bound levels are substantially reduced by the surface-induced red shift of the transition frequency

Archeological Excavation and Reburial of Unmarked Historic Graves in the Pioneer Cemetery (41BO202), Brazoria County, Texas

This report signals the completion of a cultural resource consultation process that began several years ago. In 1998, a planning meeting was held between archeologists with the Texas Department of Transportation and the Texas Historical Commission to discuss the planned improvements to State Highway 332 in Brazoria County, Texas, This work required a cultural resources surveys of many segments of the highway, one of which is adjacent to the historic Pioneer Cemetery, a predominantly African American burial ground in the town of Brazoria. Archeological investigations were conducted adjacent to the cemetery but within the highway right of way in 1998 and 1999, and the results of this work were reported in 2002. The investigations identified several unmarked graves that appeared to be within the highway right of way on the east side of SH 332. A subsequent property survey showed that three well-defined graves, and a possible fourth grave, were within the right of way and two others were very close to the right of way line. Following the state and federal cultural resources laws and the state laws pertaining to cemeteries in the Health and Safety Code of Texas, the Texas Department of Transportation undertook a project to remove and relocate the graves within the highway right of way. Prewitt and Associates, Inc., of Austin, Texas, was contracted to do the work (Contract No. 573XXSA001, Work Authorization No. 57304SA001). The exhumation of the burials took place from March 31 to April 3, 2003, and the remains were reburied during a ceremony held on April 4, 2003. This report documents the excavation, removal, and reburial of three unmarked graves dating to the late nineteenth or early twentieth centuries. This archeological study brings closure to this project. From a historical perspective, the remains of three unidentified people—a young woman, an older woman, and an infant—provide a glimpse at African American life in turn-of-the century Brazoria. From a human perspective, the remains from each grave—all human bones, remnants of the wooden caskets, and personal items buried with the person—were treated with the respect and dignity they deserve, and all three have been reburied in a new location safely inside the Pioneer Cemeter

Measurement and analysis of a small nozzle plume in vacuum

Pitot pressures and flow angles are measured in the plume of a nozzle flowing nitrogen and exhausting to a vacuum. Total pressures are measured with Pitot tubes sized for specific regions of the plume and flow angles measured with a conical probe. The measurement area for total pressure extends 480 mm (16 exit diameters) downstream of the nozzle exit plane and radially to 60 mm (1.9 exit diameters) off the plume axis. The measurement area for flow angle extends to 160 mm (5 exit diameters) downstream and radially to 60 mm. The measurements are compared to results from a numerical simulation of the flow that is based on kinetic theory and uses the direct-simulation Monte Carlo (DSMC) method. Comparisons of computed results from the DSMC method with measurements of flow angle display good agreement in the far-field of the plume and improve with increasing distance from the exit plane. Pitot pressures computed from the DSMC method are in reasonably good agreement with experimental results over the entire measurement area

Archeological Excavation and Reburial of Unmarked Historic Graves in the Pioneer Cemetary (41BO202), Brazoria County, Texas

Three unmarked graves within the predominantly African American Pioneer Cemetery in the City of Brazoria (Brazoria County), Texas, were exhumed and reburied within the cemetery. The graves were located within the right of way of State Highway 332, and were found during an earlier search phase done in conjunction with a planned expansion of the highway. The burial excavations and reburial were done in March and April 2003, by Prewitt and Associates, Inc., for the Texas Department of Transportation (TxDOT). The graves contained the remains of three unknown individuals—a young woman (17–23 years old), an older woman (45–60 years old), and an infant (2–4 years old)—who died in the late nineteenth or early twentieth centuries

Enhanced Two-Photon Absorption in a Hollow-Core Photonic Bandgap Fiber

We show that two-photon absorption (TPA) in Rubidium atoms can be greatly enhanced by the use of a hollow-core photonic bandgap fiber. We investigate off-resonant, degenerate Doppler-free TPA on the 5S1/2 - 5D5/2 transition and observe 1% absorption of a pump beam with a total power of only 1 mW in the fiber. These results are verified by measuring the amount of emitted blue fluorescence and are consistent with the theoretical predictions which indicate that transit time effects play an important role in determining the two-photon absorption cross-section in a confined geometry.Comment: 5 pages, 6 figure

Self-aligned 0.12mm T-gate In.53Ga.47As/In.52Al.48As HEMT Technology Utilising a Non Annealed Ohmic Contact Strategy

An InGaAs/InAlAs based HEMT structure, lattice matched to an InP substrate, is presented in which drive current and transconductance has been optimized through a double-delta doping strategy. Together with an increase in channel carrier density, this allows the use of a non-annealed ohmic contact process. HEMT devices with 120 nm standard and self-aligned T-gates were fabricated using the non-annealed ohmic process. At DC, self-aligned and standard devices exhibited transconductances of up to 1480 and 1100 mS/mm respectively, while both demonstrated current densities in the range 800 mA/mm. At RF, a cutoff frequency f/sub T/ of 190 GHz was extracted for the self-aligned device. The DC characteristics of the standard devices were then calibrated and modelled using a compound semiconductor Monte Carlo device simulator. MC simulations provide insight into transport within the channel and illustrate benefits over a single delta doped structure