4,317 research outputs found
Mechanism of Poisoning the Catalytic Activity of Pd(100) by a Sulfur Adlayer
The modification of the potential-energy surface (PES) of H_2 dissociation
over Pd(100) as induced by the presence of a (2x2) S adlayer is investigated by
density-functional theory and the linear augmented plane wave method. It is
shown that the poisoning effect of S originates from the formation of energy
barriers hindering the dissociation of H_2. The barriers are in the entrance
channel of the PES and their magnitude strongly depends on the lateral distance
of the H_2 molecule from the S adatoms.Comment: RevTeX, 14 pages, 3 figure
Localized Support for Injection Point Election in Hybrid Networks
Ad-hoc networks, a promising trend in wireless technology, fail to work
properly in a global setting. In most cases, self-organization and cost-free
local communication cannot compensate the need for being connected, gathering
urgent information just-in-time. Equipping mobile devices additionally with GSM
or UMTS adapters in order to communicate with arbitrary remote devices or even
a fixed network infrastructure provides an opportunity. Devices that operate as
intermediate nodes between the ad-hoc network and a reliable backbone network
are potential injection points. They allow disseminating received information
within the local neighborhood. The effectiveness of different devices to serve
as injection point differs substantially. For practical reasons the
determination of injection points should be done locally, within the ad-hoc
network partitions. We analyze different localized algorithms using at most
2-hop neighboring information. Results show that devices selected this way
spread information more efficiently through the ad-hoc network. Our results can
also be applied in order to support the election process for clusterheads in
the field of clustering mechanisms.Comment: The Sixth International Conference on Networking (ICN 2007
Small Worlds: Strong Clustering in Wireless Networks
Small-worlds represent efficient communication networks that obey two
distinguishing characteristics: a high clustering coefficient together with a
small characteristic path length. This paper focuses on an interesting paradox,
that removing links in a network can increase the overall clustering
coefficient. Reckful Roaming, as introduced in this paper, is a 2-localized
algorithm that takes advantage of this paradox in order to selectively remove
superfluous links, this way optimizing the clustering coefficient while still
retaining a sufficiently small characteristic path length.Comment: To appear in: 1st International Workshop on Localized Algorithms and
Protocols for Wireless Sensor Networks (LOCALGOS 2007), 2007, IEEE Compuster
Society Pres
Does Foreign Aid Improve Governance?
This paper analyses the impact of aid flows on governance. Using an instrumental variable approach and a large country sample, we find that aid has a negative rather than a positive influence on governance. This outcome is robust to various model specifications. --Official Development Assistance,Governance
Modeling the diffuse X-ray emission of Planetary Nebulae with different chemical composition
Based on time-dependent radiation-hydrodynamics simulations of the evolution
of Planetary Nebulae (PNe), we have carried out a systematic parameter study to
address the non-trivial question of how the diffuse X-ray emission of PNe with
closed central cavities is expected to depend on the evolutionary state of the
nebula, the mass of the central star, and the metallicity of stellar wind and
circumstellar matter. We have also investigated how the model predictions
depend on the treatment of thermal conduction at the interface between the
central `hot bubble' and the `cool' inner nebula, and compare the results with
recent X-ray observations. Our study includes models whose properties resemble
the extreme case of PNe with Wolf-Rayet type central stars. Indeed, such models
are found to produce the highest X-ray luminosities.Comment: 5 pages, 2 figures, to appear in proceedings of the IAU Symposium
283: "Planetary Nebulae: An Eye to the Future", Eds.: A. Manchado, L.
Stanghellini and D. Schoenberne
Gerbil: A Fast and Memory-Efficient -mer Counter with GPU-Support
A basic task in bioinformatics is the counting of -mers in genome strings.
The -mer counting problem is to build a histogram of all substrings of
length in a given genome sequence. We present the open source -mer
counting software Gerbil that has been designed for the efficient counting of
-mers for . Given the technology trend towards long reads of
next-generation sequencers, support for large becomes increasingly
important. While existing -mer counting tools suffer from excessive memory
resource consumption or degrading performance for large , Gerbil is able to
efficiently support large without much loss of performance. Our software
implements a two-disk approach. In the first step, DNA reads are loaded from
disk and distributed to temporary files that are stored at a working disk. In a
second step, the temporary files are read again, split into -mers and
counted via a hash table approach. In addition, Gerbil can optionally use GPUs
to accelerate the counting step. For large , we outperform state-of-the-art
open source -mer counting tools for large genome data sets.Comment: A short version of this paper will appear in the proceedings of WABI
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