Breakdown of sound in superfluid helium

Like elementary particles carry energy and momentum in the Universe, quasiparticles are the elementary carriers of energy and momentum quanta in condensed matter. And, like elementary particles, under certain conditions quasiparticles can be unstable and decay, emitting pairs of less energetic ones. Pitaevskii proposed that such processes exist in superfluid helium, a quantum fluid where the very concept of quasiparticles was borne, and which provided the first spectacular triumph of that concept. Pitaevskii's decays have important consequences, including possible breakdown of a quasiparticle. Here, we present neutron scattering experiments, which provide evidence that such decays explain the collapsing lifetime (strong damping) of higher-energy phonon-roton sound-wave quasiparticles in superfluid helium. This damping develops when helium is pressurized towards crystallization or warmed towards approaching the superfluid transition. Our results resolve a number of puzzles posed by previous experiments and reveal the ubiquity of quasiparticle decays and their importance for understanding quantum matter.Comment: 5 pages, 4 figures main text; 11 supplementary pages with 8 supplementary figure

Infrared Behaviour of Propagators and Vertices

We elucidate constraints imposed by confinement and dynamical chiral symmetry breaking on the infrared behaviour of the dressed-quark and -gluon propagators, and dressed-quark-gluon vertex. In covariant gauges the dressing of the gluon propagator is completely specified by P(k^2):= 1/[1+Pi(k^2)], where Pi(k^2) is the vacuum polarisation. In the absence of particle-like singularities in the dressed-quark-gluon vertex, extant proposals for the dressed-gluon propagator that manifest P(k^2=0)=0 and Max[P(k^2)]~10 neither confine quarks nor break chiral symmetry dynamically. This class includes all existing estimates of P(k^2) via numerical simulations.Comment: 10 pages, 2 figure

Complete Genomic Sequences of Three Salmonella enterica subsp. enterica Serovar Muenchen Strains from an Orchard in San Joaquin County, California.

We present here the complete genome sequences of three Salmonella enterica subsp. enterica serovar Muenchen strains, LG24, LG25, and LG26. All three strains were isolated from almond drupes grown in an orchard in San Joaquin County, California, in 2016. These genomic sequences are nonidentical and will contribute to our understanding of S. enterica genomics

Effects of cochlear implantation on binaural hearing in adults with unilateral hearing loss

A FDA clinical trial was carried out to evaluate the potential benefit of cochlear implant (CI) use for adults with unilateral moderate-to-profound sensorineural hearing loss. Subjects were 20 adults with moderate-to-profound unilateral sensorineural hearing loss and normal or near-normal hearing on the other side. A MED-EL standard electrode was implanted in the impaired ear. Outcome measures included: (a) sound localization on the horizontal plane (11 positions, −90° to 90°), (b) word recognition in quiet with the CI alone, and (c) masked sentence recognition with the target at 0° and the masker at −90°, 0°, or 90°. This battery was completed preoperatively and at 1, 3, 6, 9, and 12 months after CI activation. Normative data were also collected for 20 age-matched control subjects with normal or near-normal hearing bilaterally. The CI improved localization accuracy and reduced side bias. Word recognition with the CI alone was similar to performance of traditional CI recipients. The CI improved masked sentence recognition when the masker was presented from the front or from the side of normal or near-normal hearing. The binaural benefits observed with the CI increased between the 1- and 3-month intervals but appeared stable thereafter. In contrast to previous reports on localization and speech perception in patients with unilateral sensorineural hearing loss, CI benefits were consistently observed across individual subjects, and performance was at asymptote by the 3-month test interval. Cochlear implant settings, consistent CI use, and short duration of deafness could play a role in this result

Sampling Assemblages of Turtles in Central Illinois: A Case Study of Capture Efficiency and Species Coverage

Low and variable rates of capture are chronic problems in chelonian studies. We conducted a pilot study to evaluate protocols for future inventories of turtles in Illinois by comparing capture efficiency and species coverage for 2 devices (hoop net and cage trap), baits (fresh and day-old fish), habitats (lentic and lotic) and time periods . We accrued 402 captures of 378 individuals representing 7 species. At Sanganois State Fish and Wildlife Area (Sanganois), hoop nets produced more captures of more species (n = 231; 6 species) than cage traps (n = 119; 4 species). Statistical tests were equivocal for a reach of the Sangamon River, where both devices had 26 captures but hoop nets detected more species (n = 6) than cage traps (n = 3). At Sanganois, catch per unit effort varied with sampling session (time) and freshness of baits; one measure of species coverage varied with session. Results helped us make informed decisions about protocols for future inventories

High-resolution and high-accuracy topographic and transcriptional maps of the nucleosome barrier.

Nucleosomes represent mechanical and energetic barriers that RNA Polymerase II (Pol II) must overcome during transcription. A high-resolution description of the barrier topography, its modulation by epigenetic modifications, and their effects on Pol II nucleosome crossing dynamics, is still missing. Here, we obtain topographic and transcriptional (Pol II residence time) maps of canonical, H2A.Z, and monoubiquitinated H2B (uH2B) nucleosomes at near base-pair resolution and accuracy. Pol II crossing dynamics are complex, displaying pauses at specific loci, backtracking, and nucleosome hopping between wrapped states. While H2A.Z widens the barrier, uH2B heightens it, and both modifications greatly lengthen Pol II crossing time. Using the dwell times of Pol II at each nucleosomal position we extract the energetics of the barrier. The orthogonal barrier modifications of H2A.Z and uH2B, and their effects on Pol II dynamics rationalize their observed enrichment in +1 nucleosomes and suggest a mechanism for selective control of gene expression

Deconfinement and Hadron Properties at Extremes of Temperature and Density

After introducing essential, qualitative concepts and results, we discuss the application of Dyson-Schwinger equations to QCD at finite T and mu. We summarise the calculation of the critical exponents of two-light-flavour QCD using the chiral and thermal susceptibilities; and an algebraic model that elucidates the origin of an anticorrelation between the mu- and T-dependence of a range of meson properties. That model also provides an algebraic understanding of why the finite-T behaviour of bulk thermodynamic properties is mirrored in their mu-dependence, and why meson masses decrease with mu even though f_pi and - increase. The possibility of diquark condensation is canvassed. Its realisation is uncertain because it is contingent upon an assumption about the quark-quark scattering kernel that is demonstrably false in some applications; e.g., it predicts the existence of coloured diquarks in the strong interaction spectrum, which are not observed.Comment: Summary of presentations at the Workshop on QCD at Finite Baryon Density, Bielefeld, Germany, 27-30/April/1998, 13 pages, 9 figures, espcrc1.sty, epsfig.sty. Correcting typsetting problem