115 research outputs found
Multi-site Event Discrimination in Large Liquid Scintillation Detectors
Simulation studies have been carried out to explore the ability to
discriminate between single-site and multi-site energy depositions in large
scale liquid scintillation detectors. A robust approach has been found that is
predicted to lead to a significant statistical separation for a large variety
of event classes, providing a powerful tool to discriminate against backgrounds
and break important degeneracies in signal extraction. This has particularly
relevant implications for liquid scintillator searches for neutrinoless double
beta decay () from Te and Xe, where it is
possible for a true signal to be distinguished from most
radioactive backgrounds (including those from cosmogenic production) as well as
unknown gamma lines from the target isotope.Comment: 20 pages, 10 figure
Another Look at Confidence Intervals: Proposal for a More Relevant and Transparent Approach
The behaviors of various confidence/credible interval constructions are
explored, particularly in the region of low statistics where methods diverge
most. We highlight a number of challenges, such as the treatment of nuisance
parameters, and common misconceptions associated with such constructions. An
informal survey of the literature suggests that confidence intervals are not
always defined in relevant ways and are too often misinterpreted and/or
misapplied. This can lead to seemingly paradoxical behaviours and flawed
comparisons regarding the relevance of experimental results. We therefore
conclude that there is a need for a more pragmatic strategy which recognizes
that, while it is critical to objectively convey the information content of the
data, there is also a strong desire to derive bounds on models and a natural
instinct to interpret things this way. Accordingly, we attempt to put aside
philosophical biases in favor of a practical view to propose a more transparent
and self-consistent approach that better addresses these issues.Comment: 23 pages, 11 figure
Combined Constraints on Majorana Masses from Neutrinoless Double Beta Decay Experiments
Combined bounds on the Majorana neutrino mass for light and heavy neutrino
exchange mechanisms are derived from current neutrinoless double beta decay
(0{\nu}\b{eta}\b{eta}) search results for a variety of nuclear matrix element
(NME) models. The approach requires self-consistency of a given model to
predict NMEs across different isotopes. The derived bounds are notably stronger
than those from any single experiment and show less model-to-model variation,
highlighting the advantages of using multiple isotopes in such searches.
Projections indicate that the combination of near-term experiments should be
able to probe well into the inverted mass hierarchy region. A method to
visually represent 0{\nu}\b{eta}\b{eta} experimental results is also suggested
to more transparently compare across different isotopes and explicitly track
model dependencies.Comment: 5 pages, 5 figure
Heterotroph Interactions Alter Prochlorococcus Transcriptome Dynamics during Extended Periods of Darkness
Microbes evolve within complex ecological communities where biotic interactions impact both individual cells and the environment as a whole. Here we examine how cellular regulation in the marine cyanobacterium Prochlorococcus is influenced by a heterotrophic bacterium, Alteromonas macleodii, under different light conditions. We monitored the transcriptome of Prochlorococcus, grown either alone or in coculture, across a diel light:dark cycle and under the stress of extended darkness-a condition that cells would experience when mixed below the ocean's euphotic zone. More Prochlorococcus transcripts exhibited 24-h periodic oscillations in coculture than in pure culture, both over the normal diel cycle and after the shift to extended darkness. This demonstrates that biotic interactions, and not just light, can affect timing mechanisms in Prochlorococcus, which lacks a self-sustaining circadian oscillator. The transcriptomes of replicate pure cultures of Prochlorococcus lost their synchrony within 5Â h of extended darkness and reflected changes in stress responses and metabolic functions consistent with growth cessation. In contrast, when grown with Alteromonas, replicate Prochlorococcus transcriptomes tracked each other for at least 13Â h in the dark and showed signs of continued biosynthetic and metabolic activity. The transcriptome patterns suggest that the heterotroph may be providing energy or essential biosynthetic substrates to Prochlorococcus in the form of organic compounds, sustaining this autotroph when it is deprived of solar energy. Our findings reveal conditions where mixotrophic metabolism may benefit marine cyanobacteria and highlight new impacts of community interactions on basic Prochlorococcus cellular processes. IMPORTANCE: Prochlorococcus is the most abundant photosynthetic organism on the planet. These cells play a central role in the physiology of surrounding heterotrophs by supplying them with fixed organic carbon. It is becoming increasingly clear, however, that interactions with heterotrophs can affect autotrophs as well. Here we show that such interactions have a marked impact on the response of Prochlorococcus to the stress of extended periods of darkness, as reflected in transcriptional dynamics. These data suggest that diel transcriptional rhythms within Prochlorococcus, which are generally considered to be strictly under the control of light quantity, quality, and timing, can also be influenced by biotic interactions. Together, these findings provide new insights into the importance of microbial interactions on Prochlorococcus physiology and reveal conditions where heterotroph-derived compounds may support autotrophs-contrary to the canonical autotroph-to-heterotroph trophic paradigm.National Science Foundation (U.S.) (OCE-1356460)National Science Foundation (U.S.) (DBI-0424599)Center for Microbial Oceanography: Research and EducationGordon and Betty Moore Foundation (Grant GBMF495)Simons Foundation (SCOPE Award 329108)Simons Foundation (LIFE 337262
Draft Genome Sequence of Alteromonas Macleodii Strain MIT1002, Isolated from an Enrichment Culture of the Marine Cyanobacterium Prochlorococcus
Alteromonas spp. are heterotrophic gammaproteobacteria commonly found in marine environments. We present here the draft genome sequence of Alteromonas macleodii MIT1002, which was isolated from an enrichment culture of the marine cyanobacterium Prochlorococcus NATL2A. This genome contains a mixture of features previously seen only within either the âsurfaceâ or âdeepâ Alteromonas ecotype.Gordon and Betty Moore Foundation (Grant GBMF495)National Science Foundation (U.S.) (Grant OCE-1356460)National Science Foundation (U.S.). Center for Microbial Oceanography Research and Education (Grant DBO-0424599)Simons Foundation (Grant 337262
Recognition and management of stroke in young adults and adolescents.
Approximately 15% of all ischemic strokes (IS) occur in young adults and adolescents. To date, only limited prior public health and research efforts have specifically addressed stroke in the young. Early diagnosis remains challenging because of the lack of awareness and the relative infrequency of stroke compared with stroke mimics. Moreover, the causes of IS in the young are heterogeneous and can be relatively uncommon, resulting in uncertainties about diagnostic evaluation and cause-specific management. Emerging data have raised public health concerns about the increasing prevalence of traditional vascular risk factors in young individuals, and their potential role in increasing the risk of IS, stroke recurrence, and poststroke mortality. These issues make it important to formulate and enact strategies to increase both awareness and access to resources for young stroke patients, their caregivers and families, and health care professionals. The American Academy of Neurology recently convened an expert panel to develop a consensus document concerning the recognition, evaluation, and management of IS in young adults and adolescents. The report of the consensus panel is presented herein
Characterization of membrane vesicles in Alteromonas macleodii indicates potential roles in their copiotrophic lifestyle
Bacterial membrane vesicles (MVs) are abundant in the oceans, but their potential functional roles remain unclear. In this study we characterized MV production and protein content of six strains of Alteromonas macleodii, a cosmopolitan marine bacterium. Alteromonas macleodii strains varied in their MV production rates, with some releasing up to 30 MVs per cell per generation. Microscopy imaging revealed heterogenous MV morphologies, including some MVs aggregated within larger membrane structures. Proteomic characterization revealed that A. macleodii MVs are rich in membrane proteins related to iron and phosphate uptake, as well as proteins with potential functions in biofilm formation. Furthermore, MVs harbored ectoenzymes, such as aminopeptidases and alkaline phosphatases, which comprised up to 20% of the total extracellular enzymatic activity. Our results suggest that A. macleodii MVs may support its growth through generation of extracellular âhotspotsâ that facilitate access to essential substrates. This study provides an important basis to decipher the ecological relevance of MVs in heterotrophic marine bacteria
Nitrogen cost minimization is promoted by structural changes in the transcriptome of N-deprived Prochlorococcus cells
Prochlorococcus is a globally abundant marine cyanobacterium with many adaptations that reduce cellular nutrient requirements, facilitating growth in its nutrient-poor environment. One such genomic adaptation is the preferential utilization of amino acids containing fewer N-atoms, which minimizes cellular nitrogen requirements. We predicted that transcriptional regulation might further reduce cellular N budgets during transient N limitation. To explore this, we compared transcription start sites (TSSs) in Prochlorococcus MED4 under N-deprived and N-replete conditions. Of 64 genes with primary and internal TSSs in both conditions, N-deprived cells initiated transcription downstream of primary TSSs more frequently than N-replete cells. Additionally, 117 genes with only an internal TSS demonstrated increased internal transcription under N-deprivation. These shortened transcripts encode predicted proteins with an average of 21% less N content compared to full-length transcripts. We hypothesized that low translation rates, which afford greater control over protein abundances, would be beneficial to relatively slow-growing organisms like Prochlorococcus. Consistent with this idea, we found that Prochlorococcus exhibits greater usage of glycine-glycine motifs, which causes translational pausing, when compared to faster growing microbes. Our findings indicate that structural changes occur within the Prochlorococcus MED4 transcriptome during N-deprivation, potentially altering the size and structure of proteins expressed under nutrient limitation.Gordon and Betty Moore Foundation (Grant GBMF495)Simons Foundation (Award 329108)National Science Foundation (U.S.) (Grant DBI-0424599
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