6,106 research outputs found
Quality-Aware Broadcasting Strategies for Position Estimation in VANETs
The dissemination of vehicle position data all over the network is a
fundamental task in Vehicular Ad Hoc Network (VANET) operations, as
applications often need to know the position of other vehicles over a large
area. In such cases, inter-vehicular communications should be exploited to
satisfy application requirements, although congestion control mechanisms are
required to minimize the packet collision probability. In this work, we face
the issue of achieving accurate vehicle position estimation and prediction in a
VANET scenario. State of the art solutions to the problem try to broadcast the
positioning information periodically, so that vehicles can ensure that the
information their neighbors have about them is never older than the
inter-transmission period. However, the rate of decay of the information is not
deterministic in complex urban scenarios: the movements and maneuvers of
vehicles can often be erratic and unpredictable, making old positioning
information inaccurate or downright misleading. To address this problem, we
propose to use the Quality of Information (QoI) as the decision factor for
broadcasting. We implement a threshold-based strategy to distribute position
information whenever the positioning error passes a reference value, thereby
shifting the objective of the network to limiting the actual positioning error
and guaranteeing quality across the VANET. The threshold-based strategy can
reduce the network load by avoiding the transmission of redundant messages, as
well as improving the overall positioning accuracy by more than 20% in
realistic urban scenarios.Comment: 8 pages, 7 figures, 2 tables, accepted for presentation at European
Wireless 201
A Method Based on Total Variation for Network Modularity Optimization using the MBO Scheme
The study of network structure is pervasive in sociology, biology, computer
science, and many other disciplines. One of the most important areas of network
science is the algorithmic detection of cohesive groups of nodes called
"communities". One popular approach to find communities is to maximize a
quality function known as {\em modularity} to achieve some sort of optimal
clustering of nodes. In this paper, we interpret the modularity function from a
novel perspective: we reformulate modularity optimization as a minimization
problem of an energy functional that consists of a total variation term and an
balance term. By employing numerical techniques from image processing
and compressive sensing -- such as convex splitting and the
Merriman-Bence-Osher (MBO) scheme -- we develop a variational algorithm for the
minimization problem. We present our computational results using both synthetic
benchmark networks and real data.Comment: 23 page
Provenance of Tin in the Late Bronze Age Balkans: Preparation of Cassiterite for Sn Isotope Analysis and the Probabilistic and Spatial Analysis of Sn Isotopes
The sources of tin for the European Bronze Age (2200-1050 B.C.E.) have remained undetermined. Isotopic analysis has shown promise as a means of providing “fingerprints” of bronze artifacts that can be matched to their parental ore sources. This project has accomplished the following: (1) further tested and defined a method for the preparation of cassiterite for isotopic analysis, and (2), determined the provenance of tin used for metallurgy in the central Balkans during the later Bronze Age based on Sn isotopic compositions of bronze artifacts and local tin ores.
Two distinct methods have been applied in recent isotopic studies of cassiterite: (1) reduction to tin metal with potassium cyanide (KCN) at high temperature (800 °C), with subsequent dissolution in HCl, and (2) reduction to a Sn solution with hydroiodic acid (HI) at low temperature (100 °C). The most robust method for preparing cassiterite is via the Haustein et al. (2010) method with a flux to sample ratio of between 4:1 and 6:1 for a duration of 40 minutes or more. The HI method proposed by Yamazaki et al. (2013) can produce unreliable results because Sn may fractionate as a volatile during the HI reduction process and this method is not recommended for the preparation of cassiterite for isotopic analysis. The laboratory induced fractionation observed here (up to 0.35‰ per mass unit) suggests that Sn isotope fractionation can span a range greater than previously recorded in the literature.
We report the largest published dataset to date of Sn-isotopic compositions of Bronze Age artifacts (338) along with 150 cassiterite samples (75 new) from six potential tin ore sources from which the tin in these artifacts were thought to have originated. Artifacts enriched in heavy isotopes (δ124Sn \u3e 0.7‰) that cluster in west-central Serbia are likely associated with the ores from Mt. Cer in west Serbia. Mixed artifact assemblages (high and low δ124Sn) in this region are attributed to the use of cassiterite from the two Serbian sites (Mt. Cer and Mt. Bukulja). Moderate composition artifacts that occur north of the Middle Danube in Vojvodina, Transylvania, and Central Europe are likely associated primarily with ores from the West Pluton of the Erzgebirge. Compositionally light bronzes (δ124S
Multivariate Spatiotemporal Hawkes Processes and Network Reconstruction
There is often latent network structure in spatial and temporal data and the
tools of network analysis can yield fascinating insights into such data. In
this paper, we develop a nonparametric method for network reconstruction from
spatiotemporal data sets using multivariate Hawkes processes. In contrast to
prior work on network reconstruction with point-process models, which has often
focused on exclusively temporal information, our approach uses both temporal
and spatial information and does not assume a specific parametric form of
network dynamics. This leads to an effective way of recovering an underlying
network. We illustrate our approach using both synthetic networks and networks
constructed from real-world data sets (a location-based social media network, a
narrative of crime events, and violent gang crimes). Our results demonstrate
that, in comparison to using only temporal data, our spatiotemporal approach
yields improved network reconstruction, providing a basis for meaningful
subsequent analysis --- such as community structure and motif analysis --- of
the reconstructed networks
Identification of Rhizobia Species that can Establish Nitrogen-Fixing Nodules in Crotalaria Longirostrata
Due to the growing US Hispanic population, there is an agricultural incentive to grow the El Salvadoran leguminous herb Chipilin (Crotalaria longirostrata) on New England farms. Legumes require a symbiotic relationship with rhizobia in order to utilize atmospheric nitrogen. However, it is not known which strains of rhizobia are appropriate for establishing nitrogen-fixing nodules in Chipilin. Six strains of rhizobia were evaluated for increased plant yield and decreased nitrogen application. Upon harvest, Western Blotting was used to successfully probe for leghemoglobin, a protein indicator of nitrogen fixation
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