1,984 research outputs found
1-(Butan-2-ylidene)-2-(2-nitrophenyl)hydrazine
Crystals of the title compound, C10H13N3O2, were obtained from a condensation reaction of butan-2-one and 1-(2-nitrophenyl)hydrazine. The molecule exhibits a nearly coplanar structure, except for the methyl and methylene H atoms, the largest deviations from the mean plane defined by all non-H atoms, except for the nitro group, being 0.120 (2) Å for one of the nitro O atoms. Intramolecular N—H⋯O hydrogen bonding helps to establish the molecular configuration
Phylogenomic reconstruction of lactic acid bacteria: an update
<p>Abstract</p> <p>Background</p> <p>Lactic acid bacteria (LAB) are important in the food industry for the production of fermented food products and in human health as commensals in the gut. However, the phylogenetic relationships among LAB species remain under intensive debate owing to disagreements among different data sets.</p> <p>Results</p> <p>We performed a phylogenetic analysis of LAB species based on 232 genes from 28 LAB genome sequences. Regardless of the tree-building methods used, combined analyses yielded an identical, well-resolved tree topology with strong supports for all nodes. The LAB species examined were divided into two groups. Group 1 included families Enterococcaceae and Streptococcaceae. Group 2 included families Lactobacillaceae and Leuconostocaceae. Within Group 2, the LAB species were divided into two clades. One clade comprised of the acidophilus complex of genus <it>Lactobacillus </it>and two other species, <it>Lb. sakei </it>and <it>Lb. casei</it>. In the acidophilus complex, <it>Lb. delbrueckii </it>separated first, while <it>Lb. acidophilus</it>/<it>Lb. helveticus </it>and <it>Lb. gasseri</it>/<it>Lb. johnsonii </it>were clustered into a sister group. The other clade within Group 2 consisted of the salivarius subgroup, including five species, <it>Lb. salivarius</it>, <it>Lb. plantarum</it>, <it>Lb. brevis</it>, <it>Lb. reuteri</it>, <it>Lb. fermentum</it>, and the genera <it>Pediococcus, Oenococcus</it>, and <it>Leuconostoc</it>. In this clade, <it>Lb. salivarius </it>was positioned most basally, followed by two clusters, one corresponding to <it>Lb. plantarum</it>/<it>Lb. brevis </it>pair and <it>Pediococcus</it>, and the other including <it>Oenococcus</it>/<it>Leuconostoc </it>pair and <it>Lb. reuteri</it>/<it>Lb. fermentum </it>pair. In addition, phylogenetic utility of the 232 genes was analyzed to identify those that may be more useful than others. The genes identified as useful were related to translation and ribosomal structure and biogenesis (TRSB), and a three-gene set comprising genes encoding ultra-violet resistance protein B (<it>uvrB</it>), DNA polymerase III (<it>polC</it>) and penicillin binding protein 2B (<it>pbpB</it>).</p> <p>Conclusions</p> <p>Our phylogenomic analyses provide important insights into the evolution and diversification of LAB species, and also revealed the phylogenetic utility of several genes. We infer that the occurrence of multiple, independent adaptation events in LAB species, have resulted in their occupation of various habitats. Further analyses of more genes from additional, representative LAB species are needed to reveal the molecular mechanisms underlying adaptation of LAB species to various environmental niches.</p
Magnetism of Free and Embedded Rhodium Clusters
The electronic structures of rhodium clusters with sizes of 6, 9, 13, 19, and 43 are studied by the first-principles spin-polarized calculations within the local density functional formalism. The bondlengths of all clusters are optimized by minimizing the binding energies. The magnetic moments of the clusters are presented and compared with the experiments. The electronic structure of Rh_ cluster has almost the similar features of rhodium bulk. Results for the Rh clusters embedded in the nickel matrix are also presented
Tentative evidence of spatially extended GeV emission from SS433/W50
We analyze 10 years of Fermi-LAT data towards the SS433/W50 region. With the
latest source catalog and diffuse background models, the gamma-ray excess from
SS433/W50 is detected with a significance of 6{\sigma} in the photon energy
range of 500 MeV - 10 GeV. Our analysis indicates that an extended flat disk
morphology is preferred over a point-source description, suggesting that the
GeV emission region is much larger than that of the TeV emission detected by
HAWC. The size of the GeV emission is instead consistent with the extent of the
radio nebula W50, a supernova remnant being distorted by the jets, so we
suggest that the GeV emission may originate from this supernova remnant. The
spectral result of the GeV emission is also consistent with an supernova
remnant origin. We also derive the GeV flux upper limits on the TeV emission
region, which put moderate constrains on the leptonic models to explain the
multiwavelength data.Comment: 7 pages, 4 figures, accepted for publication in A&
Balanced Binary Tree Schemes for Computing Zernike Radial Polynomials
Zernike radial polynomials play a significant role in application areas such
as optics design, imaging systems, and image processing systems. Currently,
there are two kinds of numerical schemes for computing the Zernike radial
polynomials automatically with computer programs: one is based on the
definition in which the factorial operations may lead to the overflow problem
and the high order derivatives are troublesome, and the other is based on
recursion which is either unstable or with high computational complexity. In
this paper, our emphasis is focused on exploring the balanced binary tree (BBT)
schemes for computing Zernike radial polynomials: firstly we established an
elegant formulae for computation; secondly we proposed the recursive and
iterative algorithms based-on BBT; thirdly we analyzed the computational
complexity of the algorithms rigorously; finally we verified and validated the
performance of BBT schemes by testing the running time. Theoretic analysis
shows that the computational complexity of BBT recursive algorithm and
iterative algorithm are exponential and quadratic respectively, which coincides
with the running time test very well. Experiments show that the time
consumption is about microseconds with different computation
platforms for the BBT iterative algorithm (BBTIA), which is stable and
efficient for realtime applications
Detection of gamma-ray emission from the Coma cluster with Fermi Large Area Telescope and tentative evidence for an extended spatial structure
Many galaxy clusters have giant halos of non-thermal radio emission,
indicating the presence of relativistic electrons in the clusters. Relativistic
protons may also be accelerated by merger and/or accretion shocks in galaxy
clusters. These cosmic-ray (CR) electrons and/or protons are expected to
produce gamma-rays through inverse-Compton scatterings or inelastic
collisions respectively. Despite of intense efforts in searching for
high-energy gamma-ray emission from galaxy clusters, conclusive evidence is
still missing so far. Here we report the discovery of MeV gamma-ray
emission from the Coma cluster direction with an unbinned likelihood analysis
of the 9 years of {\it Fermi}-LAT Pass 8 data. The gamma-ray emission shows a
spatial morphology roughly coincident with the giant radio halo, with an
apparent excess at the southwest of the cluster. Using the test statistic
analysis, we further find tentative evidence that the gamma-ray emission at the
Coma center is spatially extended. The extended component has an integral
energy flux of in the
energy range of 0.2 - 300 GeV and the spectrum is soft with a photon index of
. Interpreting the gamma-ray emission as arising from CR proton
interaction, we find that the volume-averaged value of the CR to thermal
pressure ratio in the Coma cluster is about . Our results show that
galaxy clusters are likely a new type of GeV gamma-ray sources, and they are
probably also giant reservoirs of CR protons.Comment: 10 pages, 10 figures, Accepted by Physical Review D, more spatial
models for the gamma-ray emission are used, systematic checks on the results
are adde
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