86 research outputs found
Simonsenia aveniformis sp nov (Bacillariophyceae), molecular phylogeny and systematics of the genus, and a new type of canal raphe system
The genus Simonsenia is reviewed and S. aveniformis described as new for science by light and electron microscopy. The new species originated from estuarine environments in southern Iberia (Atlantic coast) and was isolated into culture. In LM, Simonsenia resembles Nitzschia, with bridges (fibulae) beneath the raphe, which is marginal. It is only electron microscope (EM) examination that reveals the true structure of the raphe system, which consists of a raphe canal raised on a keel (wing), supported by rib like braces (fenestral bars) and tube-like portulae; between the portulae the keel is perforated by open windows (fenestrae). Based on the presence of portulae and a fenestrated keel, Simonsenia has been proposed to be intermediate between Bacillariaceae and Surirellaceae. However, an rbcL phylogeny revealed that Simonsenia belongs firmly in the Bacillariaceae, with which it shares a similar chloroplast arrangement, rather than in the Surirellaceae. Lack of homology between the surirelloid and simonsenioid keels is reflected in subtle differences in the morphology and ontogeny of the portulae and fenestrae. The diversity of Simonsenia has probably been underestimated, particularly in the marine environment.Polish National Science Centre in Cracow within the Maestro program [N 2012/04/A/ST10/00544]; Sciences and Technologies Foundation-FCT (Portugal) [SFRH/BD/62405/2009]info:eu-repo/semantics/publishedVersio
On Propagation of Excitation Waves in Moving Media: The FitzHugh-Nagumo Model
BACKGROUND: Existence of flows and convection is an essential and integral feature of many excitable media with wave propagation modes, such as blood coagulation or bioreactors. METHODS/RESULTS: Here, propagation of two-dimensional waves is studied in parabolic channel flow of excitable medium of the FitzHugh-Nagumo type. Even if the stream velocity is hundreds of times higher that the wave velocity in motionless medium (), steady propagation of an excitation wave is eventually established. At high stream velocities, the wave does not span the channel from wall to wall, forming isolated excited regions, which we called "restrictons". They are especially easy to observe when the model parameters are close to critical ones, at which waves disappear in still medium. In the subcritical region of parameters, a sufficiently fast stream can result in the survival of excitation moving, as a rule, in the form of "restrictons". For downstream excitation waves, the axial portion of the channel is the most important one in determining their behavior. For upstream waves, the most important region of the channel is the near-wall boundary layers. The roles of transversal diffusion, and of approximate similarity with respect to stream velocity are discussed. CONCLUSIONS: These findings clarify mechanisms of wave propagation and survival in flow
Observation of a J^PC = 1-+ exotic resonance in diffractive dissociation of 190 GeV/c pi- into pi- pi- pi+
The COMPASS experiment at the CERN SPS has studied the diffractive
dissociation of negative pions into the pi- pi- pi+ final state using a 190
GeV/c pion beam hitting a lead target. A partial wave analysis has been
performed on a sample of 420000 events taken at values of the squared
4-momentum transfer t' between 0.1 and 1 GeV^2/c^2. The well-known resonances
a1(1260), a2(1320), and pi2(1670) are clearly observed. In addition, the data
show a significant natural parity exchange production of a resonance with
spin-exotic quantum numbers J^PC = 1-+ at 1.66 GeV/c^2 decaying to rho pi. The
resonant nature of this wave is evident from the mass-dependent phase
differences to the J^PC = 2-+ and 1++ waves. From a mass-dependent fit a
resonance mass of 1660 +- 10+0-64 MeV/c^2 and a width of 269+-21+42-64 MeV/c^2
is deduced.Comment: 7 page, 3 figures; version 2 gives some more details, data unchanged;
version 3 updated authors, text shortened, data unchange
Hunting down the X17 boson at the CERN SPS
Recently, the ATOMKI experiment has reported new evidence for the excess of
events with a mass 17 MeV in the nuclear transitions of He,
that they previously observed in measurements with Be. These observations
could be explained by the existence of a new vector boson. So far, the
search for the decay with the NA64 experiment at the
CERN SPS gave negative results. Here, we present a new technique that could be
implemented in NA64 aiming to improve the sensitivity and to cover the
remaining parameter space. If a signal-like event is detected, an
unambiguous observation is achieved by reconstructing the invariant mass of the
decay with the proposed method. To reach this goal an optimization of the
production target, as well as an efficient and accurate reconstruction of
two close decay tracks, is required. A dedicated analysis of the available
experimental data making use of the trackers information is presented. This
method provides independent confirmation of the NA64 published results [Phys.
Rev. D101, 071101 (2020)], validating the tracking procedure. The detailed
Monte Carlo study of the proposed setup and the background estimate shows that
the goal of the proposed search is feasible
Idiomarina gen. nov., comprising novel indigenous deep-sea bacteria from the Pacific Ocean, including descriptions of two species, Idiomarina abyssalis sp nov and Idiomarina zobellii sp nov.
Two bacterial strains, KMM 227(T) and 231(T), were isolated from seawater samples collected from the north-western Pacific Ocean at a depth of 4000-5000 m and were characterized using polyphasic taxonomy, Both were Gram-negative, psychrotolerant, heterotrophic, aerobic and required NaCl for growth (0.6-15.0%). The temperature for growth was 4-30 degrees C. Both strains were rod-shaped, with a single flagellum, However, strain KMM 231(T) revealed a single long fimbrium, Cellular fatty acids detected in the isolates were predominantly odd-numbered and iso-branched, with 15 and 17 carbons (ca. 70%), Also present were saturated and monounsaturated straight-chain fatty acids. Results of phylogenetic analyses, employing three tree-making methods, strongly indicated that the two strains formed a distinct lineage within a clade containing the genera Alteromonas, Colwellia and Pseudoalteromonas. in the gamma-Proteobacteria, The two strains shared 16S rDNA sequence similarity of 96.9% and genomic DNA relatedness of 27%; the latter was determined by dot-blot hybridization, The strains were differentiated by the presence of fimbria, production of chitinase, ability to grow on 15% NaCl and BIOLOG profiles. Given the polyphasic evidence accumulated in this study, it is proposed that the two deep-sea isolates be classified in the genus Idiomarina gen, nov., as Idiomarina abyssalis sp, nov. (type strain is KMM 227(T)) and Idiomarina zobellii sp, nov. (type strain is KMM 231(T)).
- âŠ