345 research outputs found
Load Balancing via Random Local Search in Closed and Open systems
In this paper, we analyze the performance of random load resampling and
migration strategies in parallel server systems. Clients initially attach to an
arbitrary server, but may switch server independently at random instants of
time in an attempt to improve their service rate. This approach to load
balancing contrasts with traditional approaches where clients make smart server
selections upon arrival (e.g., Join-the-Shortest-Queue policy and variants
thereof). Load resampling is particularly relevant in scenarios where clients
cannot predict the load of a server before being actually attached to it. An
important example is in wireless spectrum sharing where clients try to share a
set of frequency bands in a distributed manner.Comment: Accepted to Sigmetrics 201
Small-Scale Interstellar Na I Structure Toward M92
We have used integral field echelle spectroscopy with the DensePak
fiber-optic array on the KPNO WIYN telescope to observe the central 27" x 43"
of the globular cluster M92 in the Na I D wavelength region at a spatial
resolution of 4". Two interstellar Na I absorption components are evident in
the spectra at LSR velocities of 0 km/s (Cloud 1) and -19 km/s (Cloud 2).
Substantial strength variations in both components are apparent down to scales
limited by the fiber-to-fiber separations. The derived Na I column densities
differ by a factor of 4 across the Cloud 1 absorption map and by a factor of 7
across the Cloud 2 map. Using distance upper limits of 400 and 800 pc for Cloud
1 and Cloud 2, respectively, the absorption maps indicate structure in the ISM
down to scales of 1600 and 3200 AU. The fiber-to-fiber Na I column density
differences toward M92 are comparable to those found in a similar study of the
ISM toward the globular cluster M15. Overall, the structures in the
interstellar components toward M92 have significantly lower column densities
than those toward M15. We interpret these low column density structures as
small-scale turbulent variations in the gas and compare them to the
larger-scale, higher column density variations toward M15, which may be the
hallmarks of actual H I structures.Comment: 9 pages, 2 figures, accepted for publication in ApJ Letter
Distances to the high galactic latitude molecular clouds G192-67 and MBM 23-24
We report on distance determinations for two high Galactic latitude cloud
complexes, G192-67 and MBM 23-24. No distance determination exists in the
literature for either cloud. Thirty-four early type stars were observed towards
the two clouds, more than half of which have parallaxes measured by the
Hipparcos satellite. For the remaining stars we have made spectroscopic
distance estimates. The data consist of high resolution echelle spectra
centered on the Na I D lines, and were obtained over six nights at the Coude
Feed telescope at Kitt Peak National Observatory. Interstellar absorption lines
were detected towards some of the stars, enabling estimates of the distances to
the clouds of 109 +/- 14 pc for G192-67, and of 139 +/- 33 pc for MBM 23-24. We
discuss the relationship of these clouds to other ISM features such as the
Local Hot Bubble and the local cavity in neutral hydrogen.Comment: 15 pages, 6 embedded figures, to be published in the ApJ Vol. 516,
No.
Experimental analysis of gas-sensitive Braitenberg vehicles
This article addresses the problem of localizing a static gas source in an indoor environment by a mobile robot. In contrast to previous works, the environment is not artificially ventilated to produce a strong unidirectional airflow. Here, the dominant transport mechanisms of gas molecules are turbulence and convection flow rather than diffusion, which results in a patchy, chaotically fluctuating gas distribution. Two Braitenberg-type strategies (positive and negative tropotaxis) based on the instantaneously measured spatial concentration gradient were investigated. Both strategies were shown to be of potential use for gas source localization. As a possible solution to the problem of gas source declaration (the task of determining with certainty that the gas source has been found), an indirect localization strategy based on exploration and concentration peak avoidance is suggested. Here, a gas source is located by exploiting the fact that local concentration maxima occur more frequently near the gas source compared to distant regions
Radar observations of geomagnetic disturbance effects on midlatitude mesosphere/lower thermosphere dynamics
Zeitreihen von Monatsmittelwerten des Windes in der Mesosphäre/unteren Thermosphäre über Collm werden auf mögliche Korrelationen mit der Nordatlantischen Oszillation (NAO) und der Südlichen Oszillation (SO) hin untersucht. Während eine positive Korrelation bis in die 1990er Jahre existiert, schwächt sich diese in der Folge ab und kehrt sich teilweise um. Da NAO und SO gekoppelt sind, erfolgen diese Änderungen etwa zur selben Zeit. Die Änderung der Kopplung steht wahrscheinlich in Verbindung mit einer generellen Änderung der Dynamik der mittleren Atmosphäre
Bostonia: The Boston University Alumni Magazine. Volume 25
Founded in 1900, Bostonia magazine is Boston University's main alumni publication, which covers alumni and student life, as well as university activities, events, and programs
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Integrating Renewable Energy into the Transmission and Distribution System of the U. S. Virgin Islands
This report focuses on the economic and technical feasibility of integrating renewable energy technologies into the U.S. Virgin Islands transmission and distribution systems. The report includes three main areas of analysis: 1) the economics of deploying utility-scale renewable energy technologies on St. Thomas/St. John and St. Croix; 2) potential sites for installing roof- and ground-mount PV systems and wind turbines and the impact renewable generation will have on the electrical subtransmission and distribution infrastructure, and 3) the feasibility of a 100- to 200-megawatt power interconnection of the Puerto Rico Electric Power Authority (PREPA), Virgin Islands Water and Power Authority (WAPA), and British Virgin Islands (BVI) grids via a submarine cable system
Force Characterization and Manufacturing of a Dynamic Unilateral Clubfoot Brace
Clubfoot is a musculoskeletal birth defect that is characterized by an inward twisting of an infant’s feet. The current method for correction involves several casts and a bilateral boots-and-bar maintenance brace. This method of maintenance requires 5 years of bracing and has issues with compliance, comfort, and social stigma. CURE International in Kijabe, Kenya is currently using the boots-and-bar brace but is interested in implementing a design that reduces these concerns. Mr. Jerald Cunningham, CPO, designed and is utilizing a unilateral clubfoot maintenance brace, the Cunningham Brace, which he expects will reduce treatment time to 2-3 years, lessen the social stigma, and increase the child’s mobility. However, there is not enough published research on its biomechanics and patient success rates to confirm his findings.
The Collaboratory Cunningham Clubfoot Brace project seeks to validate the effectiveness of this design and increase accessibility through force testing and standardized manufacturing. We are working on measuring the biomechanical forces created and applied by the brace with a series of force sensors that are attached to the child’s brace. In addition, a new wrapping process for manufacturing the Cunningham Brace is being developed to increase the productivity and reproducibility of brace manufacturing in Kenya. Along with a clinical study that was started in Kenya, this testing and manufacturing will allow for further understanding of the effectiveness of the Cunningham Brace and provide more research for the medical community for it to potentially be accepted as an alternative clubfoot maintenance brace.https://mosaic.messiah.edu/engr2020/1014/thumbnail.jp
A Physics-based Investigation of Pt-salt Doped Carbon Nanotubes for Local Interconnects
We investigate, by combining physical and electrical measurements together with an atomistic-to-circuit modeling approach, the conductance of doped carbon nanotubes (CNTs) and their eligibility as possible candidate for next generation back-end-of-line (BEOL) interconnects. Ab-initio simulations predict a doping-related shift of the Fermi level, which reduces shell chirality variability and improves electrical conductance up to 90% by converting semiconducting shells to metallic. Circuit-level simulations predict up to 88% signal delay improvement with doped vs. pristine CNT. Electrical measurements of Pt-salt doped CNTs provide up to 50% of resistance reduction which is a milestone result for future CNT interconnect technology
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