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1. Convergecast and Broadcast by Power-Aware Mobile Agents

Author

Anaya, Julian, Chalopin, Jérémie, Czyzowicz, Jurek, Labourel, Arnaud, Pelc, Andrzej, and Vaxès, Yann

Subjects
Computer Science - Distributed, Parallel, and Cluster Computing
Abstract

A set of identical, mobile agents is deployed in a weighted network. Each agent has a battery -- a power source allowing it to move along network edges. An agent uses its battery proportionally to the distance traveled. We consider two tasks : convergecast, in which at the beginning, each agent has some initial piece of information, and information of all agents has to be collected by some agent; and broadcast in which information of one specified agent has to be made available to all other agents. In both tasks, the agents exchange the currently possessed information when they meet. The objective of this paper is to investigate what is the minimal value of power, initially available to all agents, so that convergecast or broadcast can be achieved. We study this question in the centralized and the distributed settings. In the centralized setting, there is a central monitor that schedules the moves of all agents. In the distributed setting every agent has to perform an algorithm being unaware of the network. In the centralized setting, we give a linear-time algorithm to compute the optimal battery power and the strategy using it, both for convergecast and for broadcast, when agents are on the line. We also show that finding the optimal battery power for convergecast or for broadcast is NP-hard for the class of trees. On the other hand, we give a polynomial algorithm that finds a 2-approximation for convergecast and a 4-approximation for broadcast, for arbitrary graphs. In the distributed setting, we give a 2-competitive algorithm for convergecast in trees and a 4-competitive algorithm for broadcast in trees. The competitive ratio of 2 is proved to be the best for the problem of convergecast, even if we only consider line networks. Indeed, we show that there is no (2 -- $\epsilon$)-competitive algorithm for convergecast or for broadcast in the class of lines, for any $\epsilon$ \textgreater{} 0.

Published
2016
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3. Collecting Information by Power-Aware Mobile Agents

Author

Anaya, Julian, Chalopin, Jérémie, Czyzowicz, Jurek, Labourel, Arnaud, Pelc, Andrzej, Vaxès, Yann, Hutchison, David, editor, Kanade, Takeo, editor, Kittler, Josef, editor, Kleinberg, Jon M., editor, Mattern, Friedemann, editor, Mitchell, John C., editor, Naor, Moni, editor, Nierstrasz, Oscar, editor, Pandu Rangan, C., editor, Steffen, Bernhard, editor, Sudan, Madhu, editor, Terzopoulos, Demetri, editor, Tygar, Doug, editor, Vardi, Moshe Y., editor, Weikum, Gerhard, editor, and Aguilera, Marcos K., editor

Published
2012
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6. The effects of grain size and grain boundary characteristics on the thermal conductivity of nanocrystalline diamond.

Author

Spiteri, David, Anaya, Julian, and Kuball, Martin

Subjects
*THERMAL conductivity, *NANOCRYSTALS, *NANODIAMONDS, *MICROSTRUCTURE, *THERMAL properties
Abstract

Molecular dynamics simulation was used to study the effects of each grain dimension and of grain boundary characteristics on the inter-grain thermal boundary resistance (TBR) and intragrain thermal conductivity of nanocrystalline diamond. The effect of the grain boundaries perpendicular to the heat flow was studied using a multiple slab configuration, which greatly reduced the artifacts associated with the heat source/sink. The TBR between the slabs was found to be more sensitive to the atomic arrangement at the boundary than to the tilt angle between the slabs. When the atomic arrangement at the interface was altered from the minimum energy configuration, the TBR increased by a factor of three, suggesting that a sub-optimal interface quality between the grains could play a large role in reducing the thermal conductivity of nanocrystalline diamond. The thermal conductivity between the boundaries was found to be similar to the bulk value, even when the boundaries were only 25 nm apart. The effect of grain boundaries parallel to the heat flow was found to have a large dependence on the microstructural details. Parallel boundaries which were 2 nm apart reduced the thermal conductivity of defect-free diamond by between one third and a factor of ten. [ABSTRACT FROM AUTHOR]

Published
2016
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7. Desafíos de confiabilidad para los FET basados ??en GaN

Author

Kuball, Martin, Uren, Michael J., Pomeroy, James W., Karboyan, Serge, Chatterjee, Indranil, Liu, Dong, Anaya, Julian, and Brazzini, Tommaso

Subjects
GaN-based, Hardware_INTEGRATEDCIRCUITS, Power electronic applications
Abstract

GaN-based field effect transistors (FETs) are being developed for microwave and power electronic applications. Presently there are two main aspects that are being considered in the device reliability field: (i) for ultra-high power microwave electronic applications GaN integration with diamond for optimal heat sinking which poses reliability challenges in the integration of dissimilar materials such as related the coefficient in thermal expansion (CTE), and (ii) for power electronic applications the most optimal use of carbon doping of GaN as insulating buffer, as this can result in large dynamic Ron effects, which requires a detailed understanding of the underlying device physics to mitigate potential negative effects of trap states introduced. The latest results in this field will be discussed.

Published
2016

14. Thermal characterization of polycrystalline diamond thin film heat spreaders grown on GaN HEMTs.

Author

Yan Zhou, Ramaneti, Rajesh, Anaya, Julian, Korneychuk, Svetlana, Derluyn, Joff, Huarui Sun, Pomeroy, James, Verbeeck, Johan, Haenen, Ken, and Kuball, Martin

Subjects
DIAMOND thin films, MODULATION-doped field-effect transistors, ALUMINUM gallium nitride, INTERFACIAL resistance, GALLIUM nitride, POLYCRYSTALS, THERMAL properties
Abstract

Polycrystalline diamond (PCD) was grown onto high-k dielectric passivated AlGaN/GaN-on-Si high electron mobility transistor (HEMT) structures, with film thicknesses ranging from 155 to 1000 nm. Transient thermoreflectance results were combined with device thermal simulations to investigate the heat spreading benefit of the diamond layer. The observed thermal conductivity (κDia) of PCD films is one-to-two orders of magnitude lower than that of bulk PCD and exhibits a strong layer thickness dependence, which is attributed to the grain size evolution. The films exhibit a weak temperature dependence of κDia in the measured 25–225 °C range. Device simulation using the experimental κDia and thermal boundary resistance values predicts at best a 15% reduction in peak temperature when the source-drain opening of a passivated AlGaN/GaN-on-Si HEMT is overgrown with PCD. [ABSTRACT FROM AUTHOR]

Published
2017
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18. Enhanced thermal management solutions for RF power amplifiers.

Author

OBELOER, THOMAS, TWITCHEN, DANIEL, ELLIS, JULIAN, BOLLIGER, BRUCE, KUBALL, MARTIN, and ANAYA, JULIAN

Subjects
*POWER amplifiers, *CHEMICAL vapor deposition, *THERMAL resistance, *ELECTRIC conductivity, *METALLIZING
Abstract

The article discusses issues that must be addressed by advanced thermal solutions, particularly for radio frequency (RF) power amplifiers. It focuses on the chemical vapor deposition (CVD) diamond as a heat spreader to reduce overall package thermal resistance. It mentions the functional considerations includes electrical conductivity of the heat spreader, thermal simulation to optimize the heat spreader configuration and metallizations.

Published
2015

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