832 research outputs found
An age-of-allele test of neutrality for transposable element insertions
How natural selection acts to limit the proliferation of transposable
elements (TEs) in genomes has been of interest to evolutionary biologists for
many years. To describe TE dynamics in populations, many previous studies have
used models of transposition-selection equilibrium that rely on the assumption
of a constant rate of transposition. However, since TE invasions are known to
happen in bursts through time, this assumption may not be reasonable in natural
populations. Here we propose a test of neutrality for TE insertions that does
not rely on the assumption of a constant transposition rate. We consider the
case of TE insertions that have been ascertained from a single haploid
reference genome sequence and have subsequently had their allele frequency
estimated in a population sample. By conditioning on the age of an individual
TE insertion (using information contained in the number of substitutions that
have occurred within the TE sequence since insertion), we determine the
probability distribution for the insertion allele frequency in a population
sample under neutrality. Taking models of varying population size into account,
we then evaluate predictions of our model against allele frequency data from
190 retrotransposon insertions sampled from North American and African
populations of Drosophila melanogaster. Using this non-equilibrium model, we
are able to explain about 80% of the variance in TE insertion allele
frequencies based on age alone. Controlling both for nonequilibrium dynamics of
transposition and host demography, we provide evidence for negative selection
acting against most TEs as well as for positive selection acting on a small
subset of TEs. Our work establishes a new framework for the analysis of the
evolutionary forces governing large insertion mutations like TEs, gene
duplications or other copy number variants.Comment: 40 pages, 6 figures, Supplemental Data available: [email protected]
Impact of Food Safety Incident on Consumers\u27 Willingness to Pay: the Case of China
Oral Presentatio
PS-TRUST: Provably Secure Solution for Truthful Double Spectrum Auctions
Truthful spectrum auctions have been extensively studied in recent years.
Truthfulness makes bidders bid their true valuations, simplifying greatly the
analysis of auctions. However, revealing one's true valuation causes severe
privacy disclosure to the auctioneer and other bidders. To make things worse,
previous work on secure spectrum auctions does not provide adequate security.
In this paper, based on TRUST, we propose PS-TRUST, a provably secure solution
for truthful double spectrum auctions. Besides maintaining the properties of
truthfulness and special spectrum reuse of TRUST, PS-TRUST achieves provable
security against semi-honest adversaries in the sense of cryptography.
Specifically, PS-TRUST reveals nothing about the bids to anyone in the auction,
except the auction result. To the best of our knowledge, PS-TRUST is the first
provably secure solution for spectrum auctions. Furthermore, experimental
results show that the computation and communication overhead of PS-TRUST is
modest, and its practical applications are feasible.Comment: 9 pages, 4 figures, submitted to Infocom 201
Continuous Arsine Detection Using a Peltier-Effect Cryogenic Trap To Selectively Trap Methylated Arsines
Hydride generation (HG) is an effective technique that eliminates interfering matrix species and enables hydride separation. Arsenic speciation analysis can be fulfilled by cryogenic trapping (CT) based on boiling points of resulting arsines using liquid nitrogen (LN2) as a coolant. In this work, LN2 was replaced by the thermoelectric effect using a cryogenic trap that consisted of a polytetrafluoroethylene (PTFE) body sandwiched by two Peltier modules. After the trap was precooled, the arsines flew along a zigzag channel in the body and reached a sorbent bed of 0.2 g of 15% OV-3 on Chromosorb W-AW-DMCS imbedded near the exit of the trap. CH3AsH2 and (CH3)2AsH were trapped, while AsH3, that passed the trap unaffected, was detected by atomic fluorescence spectrometry. Continuous operation led to enhanced throughput. For inorganic As, the limit of detection (LOD) was 1.1 ng/g and recovery was 101.0 ± 1.1%. Monomethylarsonic acid and dimethylarsinic acid did not interfere with 0.2 ± 1.2% and −0.3 ± 0.5% recoveries, respectively
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