Gamma-induced background in the KATRIN main spectrometer

International audienceThe KArlsruhe TRItium Neutrino (KATRIN) experiment aims to make a model-independent determination of the effective electron antineutrino mass with a sensitivity of 0.2 eV/c 2 . It investigates the kinematics of β -particles from tritium β -decay close to the endpoint of the energy spectrum. Because the KATRIN main spectrometer (MS) is located above ground, muon-induced backgrounds are of particular concern. Coincidence measurements with the MS and a scintillator-based muon detector system confirmed the model of secondary electron production by cosmic-ray muons inside the MS. Correlation measurements with the same setup showed that about 12% of secondary electrons emitted from the inner surface are induced by cosmic-ray muons, with approximately one secondary electron produced for every 17 muon crossings. However, the magnetic and electrostatic shielding of the MS is able to efficiently suppress these electrons, and we find that muons are responsible for less than 17% (90% confidence level) of the overall MS background

The design, construction, and commissioning of the KATRIN experiment

The KArlsruhe TRItium Neutrino (KATRIN) experiment, which aims to make a direct and model-independent determination of the absolute neutrino mass scale, is a complex experiment with many components. More than 15 years ago, we published a technical design report (TDR) [1] to describe the hardware design and requirements to achieve our sensitivity goal of 0.2 eV at 90% C.L. on the neutrino mass. Since then there has been considerable progress, culminating in the publication of first neutrino mass results with the entire beamline operating [2]. In this paper, we document the current state of all completed beamline components (as of the first neutrino mass measurement campaign), demonstrate our ability to reliably and stably control them over long times, and present details on their respective commissioning campaigns

Evolutionary Significance of Epigenetic Variation

Several chapters in this volume demonstrate how epigenetic work at the molecular level over the last few decades has revolutionized our understanding of genome function and developmental biology. However, epigenetic processes not only further our understanding of variation and regulation at the genomic and cellular levels, they also challenge our understanding of heritable phenotypic variation at the level of whole organisms and even the process of evolution by natural selection (Jablonka and Lamb 1989, 1995; Danchin et al. 2011). Although many of the epigenetic mechanisms involved in differential gene expression are reset each generation, some epigenetic marks are faithfully transmitted across generations (Jablonka and Raz 2009; Verhoeven et al. 2010a). In addition, we now know that natural variation exists not only at the DNA sequence level but also the epigenetic level (e.g., Vaughn et al. 2007; Herrera and Bazaga 2010). This may be particularly common in plants, and several studies suggest that epigenetic variation alone can cause significant heritable variation in phenotypic traits (e.g., Cubas et al. 1999; Johannes et al. 2009; Scoville et al. 2011). Because of these observations, there is currently increasing interest in understanding the role of epigenetic processes in ecology and evolution (e.g., Richards 2006, 2011; Bossdorf et al. 2008; Johannes et al. 2008; Richards et al. 2010a)

Advanced backcross quantitative trait locus analysis of fiber elongation in a cross between Gossypium hirsutum and G. mustelinum

In an effort to explore the secondary gene pool for the enhancement of upland cotton (Gossypium hirsutum L.) germplasm, we developed advanced-generation backcross populations by crossing G. hirsutum (PD94042) and Gossypium mustelinum Miers ex Watt (AD4-8), then backcrossing to the G. hirsutum parent for three cycles. Genome-wide mapping revealed introgressed alleles at an average of 13.8% of loci in each BC3F1 plant, collectively representing G. mustelinum introgression in 80.9% of the genome. Twenty-one BC3F1 plants were selfed to generate BC3F2 families of 127 to 160 plants per family (totaling 3203 plants), which were field-tested for fiber elongation and genetically mapped. One-way ANOVA detected 15 nonoverlapping quantitative trail loci (QTLs) distributed over 12 chromosomes. Individual loci explained from 10.0 to 25.24% of phenotypic variance. Nine stringent QTLs were detected in one-way ANOVAs and composite interval mapping; two of the nine QTLs explained more than 20% of variance and one was detected in four different families simultaneously with similar additive effects. Although the G. mustelinum parent does not produce spinnable fiber, G. mustelinum alleles contributed to increased fiber elongation for three of the nine stringent QTLs and five of the 15 total QTLs. Two-way ANOVA detected significant (P < 0.001) among-family genotype effects and genotype × family interactions, suggesting that the phenotypic effects of some introgressed chromosomal segments are dependent on the existence of other chromosomal segments. Gossypium mustelinum alleles that contribute to increased fiber elongation are of great interest to be further exploited in cotton breeding. © Crop Science Society of America | 5585 Guilford Rd., Madison, WI 53711 USA All rights reserved