Tests on \(B-L\) symmetry breaking models are important probes to search for new physics. One proposed model with \(\Delta(B-L)=2\) involves the oscillations of a neutron to an antineutron. In this ...paper a new limit on this process is derived for the data acquired from all three operational phases of the Sudbury Neutrino Observatory experiment. The search was concentrated in oscillations occurring within the deuteron, and 23 events are observed against a background expectation of 30.5 events. These translate to a lower limit on the nuclear lifetime of \(1.48\times 10^{31}\) years at 90% confidence level (CL) when no restriction is placed on the signal likelihood space (unbounded). Alternatively, a lower limit on the nuclear lifetime was found to be \(1.18\times 10^{31}\) years at 90% CL when the signal was forced into a positive likelihood space (bounded). Values for the free oscillation time derived from various models are also provided in this article. This is the first search for neutron-antineutron oscillation with the deuteron as a target.
We have peformed three searches for high-frequency signals in the solar neutrino flux measured by the Sudbury Neutrino Observatory (SNO), motivated by the possibility that solar g-mode oscillations ...could affect the production or propagation of solar {sup 8}B neutrinos. The first search looked for any significant peak in the frequency range l/day to 144/day, with a sensitivity to sinusoidal signals with amplitudes of 12% or greater. The second search focused on regions in which g-mode signals have been claimed by experiments aboard the SoHO satellite, and was sensitive to signals with amplitudes of 10% or greater. The third search looked for extra power across the entire frequency band. No statistically significant signal was detected in any of the three searches.
The African naked mole-rat’s (Heterocephalus glaber) social and subterranean lifestyle generates a hypoxic niche. Under experimental conditions, naked mole-rats tolerate hours of extreme hypoxia and ...survive 18 minutes of total oxygen deprivation (anoxia) without apparent injury. During anoxia, the naked mole-rat switches to anaerobic metabolism fueled by fructose, which is actively accumulated and metabolized to lactate in the brain. Global expression of the GLUT5 fructose transporter and high levels of ketohexokinase were identified as molecular signatures of fructose metabolism. Fructose-driven glycolytic respiration in naked mole-rat tissues avoids feedback inhibition of glycolysis via phosphofructokinase, supporting viability. The metabolic rewiring of glycolysis can circumvent the normally lethal effects of oxygen deprivation, a mechanism that could be harnessed to minimize hypoxic damage in human disease.
A new, fully dated total-evidence phylogeny of baleen whales (Mysticeti) shows that evolutionary phases correlate strongly with Caenozoic modernization of the oceans and climates, implying a major ...role for bottom-up physical drivers. The phylogeny of 90 modern and dated fossil species suggests three major phases in baleen whale history: an early adaptive radiation (36–30 Ma), a shift towards bulk filter-feeding (30–23 Ma) and a climate-driven diversity loss around 3 Ma. Evolutionary rates and disparity were high following the origin of mysticetes around 38 Ma, coincident with global cooling, abrupt Southern Ocean eutrophication and the development of the Antarctic Circumpolar Current (ACC). Subsequently, evolutionary rates and disparity fell, becoming nearly constant after approximately 23 Ma as the ACC reached its full strength. By contrast, species diversity rose until 15 Ma and then remained stable, before dropping sharply with the onset of Northern Hemisphere glaciation. This decline coincided with the final establishment of modern mysticete gigantism and may be linked to glacially driven variability in the distribution of shallow habitats or an increased need for long-distance migration related to iron-mediated changes in glacial marine productivity.
Baleen whales (Mysticeti) are the largest animals on Earth, thanks to their ability to filter huge volumes of small prey from seawater. Mysticetes appeared during the Late Eocene, but evidence of ...their early evolution remains both sparse and controversial 1, 2, with several models competing to explain the origin of baleen-based bulk feeding 3–6. Here, we describe a virtually complete skull of Llanocetus denticrenatus, the second-oldest (ca. 34 Ma) mysticete known. The new material represents the same individual as the type and only specimen, a fragmentary mandible. Phylogenetic analysis groups Llanocetus with the oldest mysticete, Mystacodon selenensis 2, into the basal family Llanocetidae. Llanocetus is gigantic (body length ∼8 m) compared to other early mysticetes 7–9. The broad rostrum has sharp, widely spaced teeth with marked dental abrasion and attrition, suggesting biting and occlusal shearing. As in extant mysticetes, the palate bears many sulci, commonly interpreted as osteological correlates of baleen 3. Unexpectedly, these sulci converge on the upper alveoli, suggesting a peri-dental blood supply to well-developed gums, rather than to inter-alveolar racks of baleen. We interpret Llanocetus as a raptorial or suction feeder, revealing that whales evolved gigantism well before the emergence of filter feeding. Rather than driving the origin of mysticetes, baleen and filtering most likely only arose after an initial phase of suction-assisted raptorial feeding 2, 4, 5. This scenario differs strikingly from that proposed for odontocetes, whose defining adaptation—echolocation—was present even in their earliest representatives 10.
•Llanocetus denticrenatus, from Antarctica, is the second-oldest baleen whale known•Llanocetus had well-developed gums, but no baleen•Early whales did not filter, but most likely used raptorial feeding and suction•At least some whales became giants long before the emergence of filter feeding
Fordyce and Marx describe Llanocetus denticrenatus, the second-oldest baleen whale. Llanocetus has notably worn teeth and well-developed palatal blood vessels, consistent with large gums, but not baleen. Unlike their modern descendants, early whales most likely did not filter, but at least some of them still grew into giants.
The Sudbury Neutrino Observatory (SNO) has confirmed the standard solar model and neutrino oscillations through the observation of neutrinos from the solar core. In this paper we present a search for ...neutrinos associated with sources other than the solar core, such as gamma-ray bursters and solar flares. We present a new method for looking for temporal coincidences between neutrino events and astrophysical bursts of widely varying intensity. No correlations were found between neutrinos detected in SNO and such astrophysical sources.
PDF
