3,780 research outputs found
Sprinklers: A Randomized Variable-Size Striping Approach to Reordering-Free Load-Balanced Switching
Internet traffic continues to grow exponentially, calling for switches that
can scale well in both size and speed. While load-balanced switches can achieve
such scalability, they suffer from a fundamental packet reordering problem.
Existing proposals either suffer from poor worst-case packet delays or require
sophisticated matching mechanisms. In this paper, we propose a new family of
stable load-balanced switches called "Sprinklers" that has comparable
implementation cost and performance as the baseline load-balanced switch, but
yet can guarantee packet ordering. The main idea is to force all packets within
the same virtual output queue (VOQ) to traverse the same "fat path" through the
switch, so that packet reordering cannot occur. At the core of Sprinklers are
two key innovations: a randomized way to determine the "fat path" for each VOQ,
and a way to determine its "fatness" roughly in proportion to the rate of the
VOQ. These innovations enable Sprinklers to achieve near-perfect load-balancing
under arbitrary admissible traffic. Proving this property rigorously using
novel worst-case large deviation techniques is another key contribution of this
work
Intensity-Dependent Enhancement of Saturable Absorption in PbS-Au4 Nanohybrid Composites: Evidence for Resonant Energy Transfer by Auger Recombination
Intensity-dependent enhancement of saturable absorption in a film of PbS-Au4
nanohybrid composites has been observed by femtosecond time-resolved transient
absorption measurement at 780 nm. The nonlinear absorption coefficient of
saturable absorption in PbS-Au4 nanohybrid composites is found to be dependent
on excitation irradiance and it is determined to be -2.9 cm/GW at 78 GW/cm2, an
enhancement of nearly fourfold in comparison with that of pure PbS quantum dots
(QDs). The enhancement is attributed to excitation of surface plasmon by
resonant energy transfer between PbS QDs and Au nanoparticles through Auger
recombination.Comment: 14 pages, 3 figures. Accepted in Appl. Phys. Lett. (2008
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Ionic Hydrogenation of Pyridinium and Azetidinium Cations
Research described herein seeks to study the reactivity of CpRu(P-P)H with pyridinium and azetidinium cations. For the former, we wish to determine if a previously established methodology for the regioselective reduction of a particular pyridinium cation may be extended to other pyridinium cations and if the methodology may be improved with the introduction of a pendant amine in the diphosphine. Our studies have shown that this methodology could not be extended to pyridinium cations having substituents on the pyridinium ring. For the latter, we seek to establish the reactivity of CpRu(P-P)H with azetidinium cations and compare these results to what the Norton Group has previously established in studies concerning aziridinium cations. Our studies have shown that opening of azetidinium is about six orders of magnitude slower compared to the opening of aziridinium
Ascertaining the proper law of an arbitration agreement: The artificiality of inferring intention when there is none
Measurements of the methane relaxation times for application to the infrared emission models of the upper atmospheres of outer planets and Titan
The 7.8 micrometer emission from the nu(sub 4) band of methane (CH4) is a regularly observed feature in the stratosphere of all the giant planets and Titan. On Jupiter, enhancements in this emission are associated with the infrared hot spots in the auroral zone. Attempts to model this phenomenon in particular, and to understand the role of methane in general, have been hampered in part by a lack of adequate laboratory measurements of the collisional relaxation times for the nu(sub 3) and nu(sub 4) levels over the appropriate temperature range. To provide this needed data, a series of laboratory experiments were initiated. In the experimental arrangement the nu(sub3) band of methane is pumped at 3.3 micrometers using a pulsed infrared source (Nd:YAG/dye laser system equipped with a wave-length extender). The radiative lifetime of the nu(sub 3) level (approximately 37 ms) is much shorter than the nu(sub 4) lifetime (approximately 390 ms); however, a rapid V-V energy transfer rate ensures that the nu(sub 4) level is substantially populated. The photoacoustic technique is used to acquire relaxation rate information. The experiments are performed using a low-temperature, low-pressure cell. Experimental apparatus and technique are described. In addition some of the experimental difficulties associated with making these measurements are discussed and some preliminary results are presented
Single Stranded DNA Induced Assembly of Gold Nanoparticles
The binding affinity of single stranded DNA (ssDNA) for gold nanoparticle surface is studied in this work. The data indicate that the strength of interaction between ssDNA and Au particle surface is closely related to the particle size, with smaller particles (5 nm) producing the most pronounced effects. From these experimental findings, a single stranded DNA (ssDNA) based method to assimilate 13 and 5 nm gold nanoparticles was developed, and verified by transmission electron microscopy (TEM).Singapore-MIT Alliance (SMA
Constraining Model Uncertainty in Plasma Equation-of-State Models with a Physics-Constrained Gaussian Process
Equation-of-state (EOS) models underpin numerical simulations at the core of
research in high energy density physics, inertial confinement fusion,
laboratory astrophysics, and elsewhere. In these applications EOS models are
needed that span ranges of thermodynamic variables that far exceed the ranges
where data are available, making uncertainty quantification (UQ) of EOS models
a significant concern. Model uncertainty, arising from the choice of functional
form assumed for the EOS, is a major challenge to UQ studies for EOS that is
usually neglected in favor of parameteric and data uncertainties which are
easier to capture without violating the physical constraints on EOSs. In this
work we introduce a new statistical EOS construction that naturally captures
model uncertainty while automatically obeying the thermodynamic consistency
constraint. We apply the model to existing data for \ to place an upper
bound on the uncertainty in the EOS and Hugoniot, and show that the neglect of
thermodynamic constraints overestimates the uncertainty by factors of several
when data are available and underestimates when extrapolating to regions where
they are not. We discuss extensions to this approach, and the role of GP-based
models in accelerating simulation and experimental studies, defining portable
uncertainty-aware EOS tables, and enabling uncertainty-aware downstream tasks.Comment: 11 pages, 5 figure
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