34,062 research outputs found
Study on QoS support in 802.11e-based multi-hop vehicular wireless ad hoc networks
Multimedia communications over vehicular ad hoc networks (VANET) will play an important role in the future intelligent transport system (ITS). QoS support for VANET therefore becomes an essential problem. In this paper, we first study the QoS performance in multi-hop VANET by using the standard IEEE 802.11e EDCA MAC and our proposed triple-constraint QoS routing protocol, Delay-Reliability-Hop (DeReHQ). In particular, we evaluate the DeReHQ protocol together with EDCA in highway and urban areas. Simulation results show that end-to-end delay performance can sometimes be achieved when both 802.11e EDCA and DeReHQ extended AODV are used. However, further studies on cross-layer optimization for QoS support in multi-hop environment are required
Drought events and their effects on vegetation productivity in China
Many parts of the world have experienced frequent and severe droughts during the last few decades. Most previous studies examined the effects of specific drought events on vegetation productivity. In this study, we characterized the drought events in China from 1982 to 2012 and assessed their effects on vegetation productivity inferred from satellite data. We first assessed the occurrence, spatial extent, frequency, and severity of drought using the Palmer Drought Severity Index (PDSI). We then examined the impacts of droughts on China\u27s terrestrial ecosystems using the Normalized Difference Vegetation Index (NDVI). During the period 1982â2012, China\u27s land area (%) experiencing drought showed an insignificant trend. However, the drought conditions had been more severe over most regions in northern parts of China since the end of the 1990s, indicating that droughts hit these regions more frequently due to the drier climate. The severe droughts substantially reduced annual and seasonal NDVI. The magnitude and direction of the detrended NDVI under drought stress varied with season and vegetation type. The inconsistency between the regional means of PDSI and detrended NDVI could be attributed to different responses of vegetation to drought and the timing, duration, severity, and lag effects of droughts. The negative effects of droughts on vegetation productivity were partly offset by the enhancement of plant growth resulting from factors such as lower cloudiness, warming climate, and human activities (e.g., afforestation, improved agricultural management practices)
The small mixing angle and the lepton asymmetry
We present the correlation of low energy CP phases, both Dirac and Majorana,
and the lepton asymmetry for the baryon asymmetry in the universe, with a
certain class of Yukawa matrices that consist of two right-handed neutrinos and
include one texture zero in themselves. For cases in which the amount of the
lepton asymmetry turns out to be proportional to , we
consider the relation between two types of CP phases and the relation of
versus the Jarlskog invariant or the amplitude of neutrinoless double beta
decay as varies.Comment: 17 pages, 14 figures, information for figures added, version
published in PR
Structural evolution drives diversification of the large LRR-RLK gene family
Cells are continuously exposed to chemical signals that they must discriminate between and respond to appropriately. In embryophytes, the leucineârich repeat receptorâlike kinases (LRRâRLKs) are signal receptors critical in development and defense. LRRâRLKs have diversified to hundreds of genes in many plant genomes. Although intensively studied, a wellâresolved LRRâRLK gene tree has remained elusive. To resolve the LRRâRLK gene tree, we developed an improved gene discovery method based on iterative hidden Markov model searching and phylogenetic inference. We used this method to infer complete gene trees for each of the LRRâRLK subclades and reconstructed the deepest nodes of the full gene family. We discovered that the LRRâRLK gene family is even larger than previously thought, and that protein domain gains and losses are prevalent. These structural modifications, some of which likely predate embryophyte diversification, led to misclassification of some LRRâRLK variants as members of other gene families. Our work corrects this misclassification. Our results reveal ongoing structural evolution generating novel LRRâRLK genes. These new genes are raw material for the diversification of signaling in development and defense. Our methods also enable phylogenetic reconstruction in any large gene family
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