2,600 research outputs found
Empirical line lists and absorption cross sections for methane at high temperature
Hot methane is found in many "cool" sub-stellar astronomical sources
including brown dwarfs and exoplanets, as well as in combustion environments on
Earth. We report on the first high-resolution laboratory absorption spectra of
hot methane at temperatures up to 1200 K. Our observations are compared to the
latest theoretical spectral predictions and recent brown dwarf spectra. The
expectation that millions of weak absorption lines combine to form a continuum,
not seen at room temperature, is confirmed. Our high-resolution transmittance
spectra account for both the emission and absorption of methane at elevated
temperatures. From these spectra, we obtain an empirical line list and
continuum that is able to account for the absorption of methane in high
temperature environments at both high and low resolution. Great advances have
recently been made in the theoretical prediction of hot methane, and our
experimental measurements highlight the progress made and the problems that
still remain.Comment: 9 pages, 5 figures and 3 tables. For associated online data see
http://dx.doi.org/10.1088/0004-637X/813/1/1
Mapping atomic and diffuse interstellar band absorption across the Magellanic Clouds and the Milky Way
Diffuse interstellar bands (DIBs) trace warm neutral and weakly-ionized
diffuse interstellar medium (ISM). Here we present a dedicated, high
signal-to-noise spectroscopic study of two of the strongest DIBs, at 5780 and
5797 \AA, in optical spectra of 666 early-type stars in the Small and Large
Magellanic Clouds, along with measurements of the atomic Na\,{\sc i}\,D and
Ca\,{\sc ii}\,K lines. The resulting maps show for the first time the
distribution of DIB carriers across large swathes of galaxies, as well as the
foreground Milky Way ISM. We confirm the association of the 5797 \AA\ DIB with
neutral gas, and the 5780 \AA\ DIB with more translucent gas, generally tracing
the star-forming regions within the Magellanic Clouds. Likewise, the Na\,{\sc
i}\,D line traces the denser ISM whereas the Ca\,{\sc ii}\,K line traces the
more diffuse, warmer gas. The Ca\,{\sc ii}\,K line has an additional component
at --220 km s seen towards both Magellanic Clouds; this may be
associated with a pan-Magellanic halo. Both the atomic lines and DIBs show
sub-pc-scale structure in the Galactic foreground absorption; the 5780 and 5797
\AA\ DIBs show very little correlation on these small scales, as do the
Ca\,{\sc ii}\,K and Na\,{\sc i}\,D lines. This suggests that good correlations
between the 5780 and 5797 \AA\ DIBs, or between Ca\,{\sc ii}\,K and Na\,{\sc
i}\,D, arise from the superposition of multiple interstellar structures.
Similarity in behaviour between DIBs and Na\,{\sc i} in the SMC, LMC and Milky
Way suggests the abundance of DIB carriers scales in proportion to metallicity.Comment: Accepted for publication in MNRA
The diagonal graph
According to the O'Nan--Scott Theorem, a finite primitive permutation group either preserves a structure of one of three types (affine space, Cartesian lattice, or diagonal semilattice), or is almost simple. However, diagonal groups are a much larger class than those occurring in this theorem. For any positive integer m and group G (finite or infinite), there is a diagonal semilattice, a sub-semilattice of the lattice of partitions of a set Ω, whose automorphism group is the corresponding diagonal group. Moreover, there is a graph (the diagonal graph), bearing much the same relation to the diagonal semilattice and group as the Hamming graph does to the Cartesian lattice and the wreath product of symmetric groups. Our purpose here, after a brief introduction to this semilattice and graph, is to establish some properties of this graph. The diagonal graph ΓD(G,m) is a Cayley graph for the group Gm, and so is vertex-transitive. We establish its clique number in general and its chromatic number in most cases, with a conjecture about the chromatic number in the remaining cases. We compute the spectrum of the adjacency matrix of the graph, using a calculation of the Möbius function of the diagonal semilattice. We also compute some other graph parameters and symmetry properties of the graph. We believe that this family of graphs will play a significant role in algebraic graph theory.PostprintPeer reviewe
Formant-frequency variation and informational masking of speech by extraneous formants:evidence against dynamic and speech-specific acoustical constraints
How speech is separated perceptually from other speech remains poorly understood. Recent research indicates that the ability of an extraneous formant to impair intelligibility depends on the variation of its frequency contour. This study explored the effects of manipulating the depth and pattern of that variation. Three formants (F1+F2+F3) constituting synthetic analogues of natural sentences were distributed across the 2 ears, together with a competitor for F2 (F2C) that listeners must reject to optimize recognition (left = F1+F2C; right = F2+F3). The frequency contours of F1 - F3 were each scaled to 50% of their natural depth, with little effect on intelligibility. Competitors were created either by inverting the frequency contour of F2 about its geometric mean (a plausibly speech-like pattern) or using a regular and arbitrary frequency contour (triangle wave, not plausibly speech-like) matched to the average rate and depth of variation for the inverted F2C. Adding a competitor typically reduced intelligibility; this reduction depended on the depth of F2C variation, being greatest for 100%-depth, intermediate for 50%-depth, and least for 0%-depth (constant) F2Cs. This suggests that competitor impact depends on overall depth of frequency variation, not depth relative to that for the target formants. The absence of tuning (i.e., no minimum in intelligibility for the 50% case) suggests that the ability to reject an extraneous formant does not depend on similarity in the depth of formant-frequency variation. Furthermore, triangle-wave competitors were as effective as their more speech-like counterparts, suggesting that the selection of formants from the ensemble also does not depend on speech-specific constraints
Acoustic source characteristics, across-formant integration, and speech intelligibility under competitive conditions
An important aspect of speech perception is the ability to group or select formants using cues in the acoustic source characteristics-for example, fundamental frequency (F0) differences between formants promote their segregation. This study explored the role of more radical differences in source characteristics. Three-formant (F1+F2+F3) synthetic speech analogues were derived from natural sentences. In Experiment 1, F1+F3 were generated by passing a harmonic glottal source (F0 = 140 Hz) through second-order resonators (H1+H3); in Experiment 2, F1+F3 were tonal (sine-wave) analogues (T1+T3). F2 could take either form (H2 or T2). In some conditions, the target formants were presented alone, either monaurally or dichotically (left ear = F1+F3; right ear = F2). In others, they were accompanied by a competitor for F2 (F1+F2C+F3; F2), which listeners must reject to optimize recognition. Competitors (H2C or T2C) were created using the time-reversed frequency and amplitude contours of F2. Dichotic presentation of F2 and F2C ensured that the impact of the competitor arose primarily through informational masking. In the absence of F2C, the effect of a source mismatch between F1+F3 and F2 was relatively modest. When F2C was present, intelligibility was lowest when F2 was tonal and F2C was harmonic, irrespective of which type matched F1+F3. This finding suggests that source type and context, rather than similarity, govern the phonetic contribution of a formant. It is proposed that wideband harmonic analogues are more effective informational maskers than narrowband tonal analogues, and so become dominant in across-frequency integration of phonetic information when placed in competition
Influence of genome-scale RNA structure disruption on the replication of murine norovirus--similar replication kinetics in cell culture but attenuation of viral fitness in vivo
Mechanisms by which certain RNA viruses, such as hepatitis C virus, establish persistent infections and cause chronic disease are of fundamental importance in viral pathogenesis. Mammalian positive-stranded RNA viruses establishing persistence typically possess genome-scale ordered RNA secondary structure (GORS) in their genomes. Murine norovirus (MNV) persists in immunocompetent mice and provides an experimental model to functionally characterize GORS. Substitution mutants were constructed with coding sequences in NS3/4- and NS6/7-coding regions replaced with sequences with identical coding and (di-)nucleotide composition but disrupted RNA secondary structure (F1, F2, F1/F2 mutants). Mutants replicated with similar kinetics to wild-type (WT) MNV3 in RAW264.7 cells and primary macrophages, exhibited similar (highly restricted) induction and susceptibility to interferon-coupled cellular responses and equal replication fitness by serial passaging of co-cultures. In vivo, both WT and F1/F2 mutant viruses persistently infected mice, although F1, F2 and F1/F2 mutant viruses were rapidly eliminated 1–7 days post-inoculation in competition experiments with WT. F1/F2 mutants recovered from tissues at 9 months showed higher synonymous substitution rates than WT and nucleotide substitutions that potentially restored of RNA secondary structure. GORS plays no role in basic replication of MNV but potentially contributes to viral fitness and persistence in vivo
An update on peptide-based therapies for type 2 diabetes and obesity
Long-acting analogues of the naturally occurring incretin, glucagon-like peptide-1 (GLP-1) and those modified to interact also with receptors for glucose-dependent insulinotropic polypeptide (GIP) have shown high glucose-lowering and weight-lowering efficacy when administered by once-weekly subcutaneous injection. These analogues herald an exciting new era in peptide-based therapy for type 2 diabetes (T2D) and obesity. Of note is the GLP-1R agonist semaglutide, available in oral and injectable formulations and in clinical trials combined with the long-acting amylin analogue, cagrilintide. Particularly high efficacy in both glucose- and weight lowering capacities has also been observed with the GLP-1R/GIP-R unimolecular dual agonist, tirzepatide. In addition, a number of long-acting unimolecular GLP-1R/GCGR dual agonist peptides and GLP-1R/GCGR/GIPR triagonist peptides have entered clinical trials. Other pharmacological approaches to chronic weight management include the human monoclonal antibody, bimagrumab which blocks activin type II receptors and is associated with growth of skeletal muscle, an antibody blocking activation of GIPR to which are conjugated GLP-1R peptide agonists (AMG-133), and the melanocortin-4 receptor agonist, setmelanotide for use in certain inherited obesity conditions. The high global demand for the GLP-1R agonists liraglutide and semaglutide as anti-obesity agents has led to shortage so that their use in T2D therapy is currently being prioritized. [Abstract copyright: Copyright © 2023 The Authors. Published by Elsevier Inc. All rights reserved.
African trypanosomiasis in travelers returning to the United Kingdom.
Two returning safari tourists with African trypanosomiasis were admitted to the Hospital for Tropical Diseases, London, in a 3-day period, compared with six cases in the previous 14 years. We describe the clinical features, diagnosis, and problems encountered in accessing appropriate therapy, and discuss the potential for emergence of this disease in increasingly adventurous international travelers
A lower bound on HMOLS with equal sized holes
It is known that , the maximum number of mutually orthogonal latin
squares of order , satisfies the lower bound for large
. For , relatively little is known about the quantity ,
which denotes the maximum number of `HMOLS' or mutually orthogonal latin
squares having a common equipartition into holes of a fixed size . We
generalize a difference matrix method that had been used previously for
explicit constructions of HMOLS. An estimate of R.M. Wilson on higher
cyclotomic numbers guarantees our construction succeeds in suitably large
finite fields. Feeding this into a generalized product construction, we are
able to establish the lower bound for any
and all
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