432 research outputs found
A dynamic fluid landscape mediates the spread of bacteria
Microbial interactions regulate their spread and survival in competitive
environments. It is not clear if the physical parameters of the environment
regulate the outcome of these interactions. In this work, we show that the
opportunistic pathogen Pseudomonas aeruginosa occupies a larger area on the
substratum in the presence of yeast such as Cryptococcus neoformans , than
without it. At the microscopic level, bacterial cells show an enhanced activity
in the vicinity of yeast cells. We observe this behaviour even when the live
yeast cells are replaced with heat-killed cells or with spherical glass beads
of similar morphology, which suggests that the observed behaviour is not
specific to the biology of microbes. Upon careful investigation, we find that a
fluid pool is formed around yeast cells which facilitates the swimming of the
flagellated P. aeruginosa , causing their enhanced motility. Using mathematical
modeling we demonstrate how this local enhancement of bacterial motility leads
to the enhanced spread observed at the level of the plate. We find that the
dynamics of the fluid landscape around the bacteria, mediated by the growing
yeast lawn, affects the spreading. For instance, when the yeast lawn grows
faster, a bacterial colony prefers a lower initial loading of yeast cells for
optimum enhancement in the spread. We confirm our predictions using Candida
albicans and C. neoformans, at different initial compositions. In summary, our
work shows the importance of considering the dynamically changing physical
environment while studying bacterial motility in complex environments.Comment: 14 pages of main text, 5 figures, 4 pages of SI adde
A small angle neutron scattering study of the vortex matter in La{2-x}Sr{x}CuO{4} (x=0.17)
The magnetic phase diagram of slightly overdoped La{2-x}Sr{x}CuO{4} (x=0.17)
is characterised by a field-induced hexagonal to square transition of the
vortex lattice at low fields (~0.4 Tesla) [R. Gilardi et al., Phys. Rev. Lett.
88, 217003 (2002)]. Here we report on a small angle neutron scattering study of
the vortex lattice at higher fields, that reveals no further change of the
coordination of the square vortex lattice up to 10.5 Tesla applied
perpendicular to the CuO2 planes. Moreover, it is found that the diffraction
signal disappears at temperatures well below Tc, due to the melting of the
vortex lattice.Comment: 3 pages, 2 figures. Presented at the New3SC-4 meeting, San Diego,
Jan. 16-21 2003; to be published in Int. J. Mod. Phys.
Non-developing ascospores in apothecia of asexually reproducing lichen-forming fungi
The presence of apothecia in mixed species (vegetatively reproducing lichens, occasionally producing ascomata) has been interpreted as a mechanism to increase genetic variability in mostly clonal populations. However, spore viability from these apothecia has not been studied. We asked whether ascospores of the mixed species Physconia grisea are viable and thereby contribute to increasing the genetic diversity within populations of this species. An ontogenetic study of spores in cultures of P. grisea and a related sexual species (P. distorta), showed that although mature apothecia from both species produced and discharged meiospores capable of germination, spores from P. grisea were only rarely (0.43 %) able to continue development whereas those from P. distorta germinated and developed successfully. The strongly reduced viability of P. grisea spores suggested that they do not have a strong reproductive function, at least in the two local populations analyzed. Additionally, we show that the segregation of Physconia grisea ssp. lilacina does not have molecular support. [Int Microbiol 2013; 16(3):XXX-XXX]Keywords: Physconia spp. · apothecia · sexual reproduction · germination · ontogenetic development · mixed specie
Molecular contrast in optical coherence tomography using a pump-probe technique and a optical switch suppression technique
We describe two novel techniques for contrast enhancement in optical coherence tomography (OCT) which enables molecular specific imaging. The first, a pump-probe technique, is employed in which a pulsed pump laser is tuned to ground-state absorption in a molecule of interest. The location of the target molecule population is derived from the resulting transient absorption of OCT sample arm light acting as probe light. Preliminary results exhibiting contrast enhancement in cross-sectional OCT images using methylene blue dye are presented. The second method is an optical switch suppression technique based on the use of a transmembrane protein called bacteriorhodopsin. Initial experiments indicate that biochemical optical switches, such as bacteriorhodopsin, are excellent contrast agent candidates for molecular contrast OCT
Molecular contrast in optical coherence tomography using a pump-probe technique and a optical switch suppression technique
We describe two novel techniques for contrast enhancement in optical coherence tomography (OCT) which enables molecular specific imaging. The first, a pump-probe technique, is employed in which a pulsed pump laser is tuned to ground-state absorption in a molecule of interest. The location of the target molecule population is derived from the resulting transient absorption of OCT sample arm light acting as probe light. Preliminary results exhibiting contrast enhancement in cross-sectional OCT images using methylene blue dye are presented. The second method is an optical switch suppression technique based on the use of a transmembrane protein called bacteriorhodopsin. Initial experiments indicate that biochemical optical switches, such as bacteriorhodopsin, are excellent contrast agent candidates for molecular contrast OCT
Muons as Local Probes of Three-body Correlations in the Mixed State of Type-II Superconductors
The vortex glass state formed by magnetic flux lines in a type-II
superconductor is shown to possess non-trivial three-body correlations. While
such correlations are usually difficult to measure in glassy systems, the
magnetic fields associated with the flux vortices allow us to probe these via
muon-spin rotation measurements of the local field distribution. We show via
numerical simulations and analytic calculations that these observations provide
detailed microscopic insight into the local order of the vortex glass and more
generally validate a theoretical framework for correlations in glassy systems.Comment: 4+ pages, high-quality figures available on reques
Direct observation of the flux-line vortex glass phase in a type II superconductor
The order of the vortex state in La_{1.9} Sr_{0.1} CuO_{4} is probed using
muon spin rotation and small-angle neutron scattering. A transition from a
Bragg glass to a vortex glass is observed, where the latter is composed of
disordered vortex lines. In the vicinity of the transition the microscopic
behavior reflects a delicate interplay of thermally-induced and pinning-induced
disorder.Comment: 14 pages, 4 colour figures include
Atmospheric dispersion corrector for a multi-object spectroscopic mode of HROS-TMT
Highly multiplexed spectroscopic surveys have changed the astronomy landscape
in recent years. However, these surveys are limited to low and medium spectral
resolution. High spectral resolution spectroscopy is often photon starved and
will benefit from a large telescope aperture. Multiplexed high-resolution
surveys require a wide field of view and a large aperture for a suitable large
number of bright targets. This requirement introduces several practical
difficulties, especially for large telescopes, such as the future ELTs. Some of
the challenges are the need for a wide field atmospheric dispersion corrector
and to deal with the curved non-telecentric focal plane. Here, we present a
concept of Multi-Object Spectroscopy (MOS) mode for TMT High-Resolution Optical
Spectrograph (HROS), we have designed an atmospheric dispersion corrector for
individual objects that fit inside a fiber positioner. We present the ZEMAX
design and the performance of the atmospheric dispersion corrector for all
elevations accessible by TMT
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