182 research outputs found
Non-thermal particle acceleration and power-law tails via relaxation to universal Lynden-Bell equilibria
Collisionless and weakly collisional plasmas often exhibit non-thermal
quasi-equilibria. Among these quasi-equilibria, distributions with power-law
tails are ubiquitous. It is shown that the statistical-mechanical approach
originally suggested by Lynden-Bell (1967) can easily recover such power-law
tails. Moreover, we show that, despite the apparent diversity of Lynden-Bell
equilibria, a generic form of the equilibrium distribution at high energies is
a `hard' power-law tail , where is the
particle energy. The shape of the `core' of the distribution, located at low
energies, retains some dependence on the initial condition but it is the tail
(or `halo') that contains most of the energy. Thus, a degree of universality
exists in collisionless plasmas.Comment: 33 pages, 5 figure
Retinometra albeolae n.sp. (Cestoda: Hymenolepididae) from the bufflehead duck, Bucephala albeola L.
Retinometra albeolae n.sp. is described from bufflehead ducks (Bucephala albeola L.) from Manitoba, Canada. It is armed with eight skrjabinoid rostellar hooks 69–75 μm long, and has a cirrus sac 240–480 μm long that extends to approximately the midline of mature proglottids, a trilobed ovary, and a lobed vitelline gland. Staphylepis indica and Staphylepis meggitti, currently included in the genus Retinometra, are returned to Staphylepis on the basis of proglottid morphology and the apparent lack of a cirrus stylet in both species
Phase-space entropy cascade and irreversibility of stochastic heating in nearly collisionless plasma turbulence
We consider a nearly collisionless plasma consisting of a species of `test
particles' in 1D-1V, stirred by an externally imposed stochastic electric
field. The mean effect on the particle distribution function is stochastic
heating. Accompanying this heating is the generation of fine-scale structure in
the distribution function, which we characterize with the collisionless
(Casimir) invariant . We find
that is transferred from large scales to small scales in both position
and velocity space via a phase-space cascade enabled by both particle streaming
and nonlinear interactions between particles and the stochastic electric field.
We compute the steady-state fluxes and spectrum of in Fourier space, with
and denoting spatial and velocity wavenumbers, respectively. Whereas
even the linear phase mixing alone would lead to a constant flux of to
high (towards the collisional dissipation range) at every , the
nonlinearity accelerates this cascade by intertwining velocity and position
space so that the flux of is to both high and high
simultaneously. Integrating over velocity (spatial) wavenumbers, the -space
(-space) flux of is constant down to a dissipation length (velocity)
scale that tends to zero as the collision frequency does, even though the rate
of collisional dissipation remains finite. The resulting spectrum in the
inertial range is a self-similar function in the plane, with power-law
asymptotics at large and . We argue that stochastic heating is made
irreversible by this entropy cascade and that, while collisional dissipation
accessed via phase mixing occurs only at small spatial scales rather than at
every scale as it would in a linear system, the cascade makes phase mixing even
more effective overall in the nonlinear regime than in the linear one.Comment: 26 pages, 6 figure
Empirical Evaluation of Oligonucleotide Probe Selection for DNA Microarrays
DNA-based microarrays are increasingly central to biomedical research. Selecting oligonucleotide sequences that will behave consistently across experiments is essential to the design, production and performance of DNA microarrays. Here our aim was to improve on probe design parameters by empirically and systematically evaluating probe performance in a multivariate context. We used experimental data from 19 array CGH hybridizations to assess the probe performance of 385,474 probes tiled in the Duchenne muscular dystrophy (DMD) region of the X chromosome. Our results demonstrate that probe melting temperature, single nucleotide polymorphisms (SNPs), and homocytosine motifs all have a strong effect on probe behavior. These findings, when incorporated into future microarray probe selection algorithms, may improve microarray performance for a wide variety of applications
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Pesticides of interest to Northwestern U.S. deciduous tree fruit producers
Evaluation of polygenic risk scores for breast and ovarian cancer risk prediction in BRCA1 and BRCA2 mutation carriers
Background: Genome-wide association studies (GWAS) have identified 94 common single-nucleotide polymorphisms (SNPs) associated with breast cancer (BC) risk and 18 associated with ovarian cancer (OC) risk. Several of these are also associated with risk of BC or OC for women who carry a pathogenic mutation in the high-risk BC and OC genes BRCA1 or BRCA2. The combined effects of these variants on BC or OC risk for BRCA1 and BRCA2 mutation carriers have not yet been assessed while their clinical management could benefit from improved personalized risk estimates.
Methods: We constructed polygenic risk scores (PRS) using BC and OC susceptibility SNPs identified through population-based GWAS: for BC (overall, estrogen receptor [ER]-positive, and ER-negative) and for OC. Using data from 15 252 female BRCA1 and 8211 BRCA2 carriers, the association of each PRS with BC or OC risk was evaluated using a weighted cohort approach, with time to diagnosis as the outcome and estimation of the hazard ratios (HRs) per standard deviation increase in the PRS.
Results: The PRS for ER-negative BC displayed the strongest association with BC risk in BRCA1 carriers (HR = 1.27, 95% confidence interval [CI] = 1.23 to 1.31, P = 8.2 x 10(53)). In BRCA2 carriers, the strongest association with BC risk was seen for the overall BC PRS (HR = 1.22, 95% CI = 1.17 to 1.28, P = 7.2 x 10(-20)). The OC PRS was strongly associated with OC risk for both BRCA1 and BRCA2 carriers. These translate to differences in absolute risks (more than 10% in each case) between the top and bottom deciles of the PRS distribution; for example, the OC risk was 6% by age 80 years for BRCA2 carriers at the 10th percentile of the OC PRS compared with 19% risk for those at the 90th percentile of PRS.
Conclusions: BC and OC PRS are predictive of cancer risk in BRCA1 and BRCA2 carriers. Incorporation of the PRS into risk prediction models has promise to better inform decisions on cancer risk management
Submarine back-arc lava with arc signature : Fonualei Spreading Center, northeast Lau Basin, Tonga
Author Posting. © American Geophysical Union, 2008. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 113 (2008): B08S07, doi:10.1029/2007JB005451.We present major, volatile, and trace elements for quenched glasses from the Fonualei Spreading Center, a nascent spreading system situated very close to the Tofua Volcanic Arc (20 km at the closest), in the northeast Lau Basin. The glasses are basalts and basaltic andesites and are inferred to have originated from a relatively hot and depleted mantle wedge. The Fonualei Spreading Center shows island arc basalt (IAB) affinities, indistinguishable from the Tofua Arc. Within the Fonualei Spreading Center no geochemical trends can be seen with depth to the slab and/or distance to the arc, despite a difference in depth to the slab of >50 km. Therefore we infer that all the subduction-related magmatism is captured by the back arc as the adjacent arc is shut off. There is a sharp contrast between the main spreading area of the Fonualei Spreading Center (FSC) and its northernmost termination, the Mangatolu Triple Junction (MTJ). The MTJ samples are characteristic back-arc basin basalts (BABB). We propose that the MTJ and FSC have different mantle sources, reflecting different mantle origins and/or different melting processes. We also document a decrease in mantle depletion from the south of the FSC to the MTJ, which is the opposite to what has been documented for the rest of the Lau Basin where depletion generally increases from south to north. We attribute this reverse trend to the influx of less depleted mantle through the tear between the Australian and the Pacific plates, at the northern boundary of the Lau Basin.NSK acknowledges the
support of an A.E. Ringwood Scholarship from the RSES
A Genotype-First Approach for the Molecular and Clinical Characterization of Uncommon De Novo Microdeletion of 20q13.33
Background: Subtelomeric deletions of the long arm of chromosome 20 are rare, with only 11 described in the literature. Clinical features of individuals with these microdeletions include severe limb malformations, skeletal abnormalities, growth retardation, developmental and speech delay, mental retardation, seizures and mild, non-specific dysmorphic features. Methodology/Principal Findings: We characterized microdeletions at 20q13.33 in six individuals referred for genetic evaluation of developmental delay, mental retardation, and/or congenital anomalies. A comparison to previously reported cases of 20q13.33 microdeletion shows phenotypic overlap, with clinical features that include mental retardation, developmental delay, speech and language deficits, seizures, and behavior problems such as autistic spectrum disorder. There does not appear to be a clinically recognizable constellation of dysmorphic features among individuals with subtelomeric 20q microdeletions. Conclusions/Significance: Based on genotype-phenotype correlation among individuals in this and previous studies, we discuss several possible candidate genes for specific clinical features, including ARFGAP1, CHRNA4 and KCNQ2 and neurodevelopmental deficits. Deletion of this region may play an important role in cognitive development
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