2,059 research outputs found
Serratia marcescens, the “Flame” Strain: The Genesis of a New Variant A Newly Described Strain with Prolific Pigment Produced at High Temperature
Serratia marcescens, a Gram-negative, rod-shaped, facultative anaerobe (Fig. 1), is ubiquitous in water, soil, and natural settings. It is easily grown in the lab and may serve as an ideal model for adaptation studies because of the natural color variation of S. marcescens (Gillen 2008). In this paper, we describe a new variant with prolific pigment (prodigiosin) production at high temperatures. In the wild and in buildings, S. marcescens is noted for the production of a bright red pigment called prodigiosin (Williams 1973). We have found a new strain that appears to have adapted to a relatively new pond system called Liberty Library Lake. It produces pigment up to 40°C without any enrichment to media. Most wild-type strains, like NIMA, produce pigment normally up to 30°C, but with extensive enrichment, wild-type strains can produce pigment up to 40°C. This new strain, called the “Flame” strain, not only produces prodigiosin to 39–40°C but also in higher abundance at 35°C and at a brighter hue. NIMA strains can produce pigment at 39–40°C with Serratia Synergy Agar (glycerol, peptone, agar) but not on TSA nor any common agar. It takes significant enhancement for any other Serratia marcescens strains to produce pigment even at 35°C.
The Flame strain’s brief appearance in a local, small lake appears to be a phenotypic diversification and adaptation to an environmental perturbation this past school year. The environmental stress prior to its appearance was an autumn drought. Eventually, heavy rainfall occurred and the new strain was discovered. Its appearance coincided with an unusually high abundance of coliforms, avian Giardia, and Cryptosporidium, along with chemical treatment of the lake. The unusual conditions seem to favor a rapid phenotypic diversification and adaptation. The new strain still retains the pigment production at nearly 10°C higher for “normal” prodigiosin production by wild-type Serratia marcescens. This genesis of this new strain seems to have occurred as special conditions favored this new variant. It may be closer to a “proto-type” (ancestral) strain than to more common wild-type strains, like NIMA and BS303. It appears that most wild-type strains, like NIMA and BS303, may have lost this information over time since added enrichment is necessary to produce pigment at 39–40°C. The unusual conditions may have selected for this newly adapted strain to be common for a short time. Also as conditions returned to “normal,” a common wild-type strain reappeared at the local lake, and the Flame strain was no longer found.
The objective of this article is to explain the mysterious origin of a new strain of Serratia marcescens that produces prodigiosin up to 40°C without any enrichment to media. This strain can naturally produce prolific pigment that is a bright, flame-red. Since Serratia marcescens offers protection from other microbes, UV light, and drought, it is a wonderful example of intelligent design commonly seen in the microbial world
The order-disorder transition of the (3x3)Sn/Ge(111) phase
Growing attention has been drawn in the past years to the \alpha-phase (1/3
monolayer) of Sn on Ge(111), which undergoes a transition from the low
temperature (3x3) phase to the room temperature (\sqrt3 x \sqrt3)R30 one. On
the basis of scanning tunnelling microscopy experiments, this transition was
claimed to be the manifestation of a surface charge density wave (SCDW), i.e. a
periodic redistribution of charge, possibly accompanied by a periodic lattice
distortion, which determines a change of the surface symmetry. As further
experiments with different techniques were being performed, increasing doubts
were cast about the SCDW model. We have measured by He scattering the long
range order of the 1/3 monolayer phase of Sn on the Ge(111) surface throughout
the phase transition. The transition has been found of the order-disorder type
with a critical temperature Tc=220 K. The expected 3-State Potts critical
exponents are shown to be consistent with the observed power law dependence of
the (3x3) order parameter and its correlation length close to Tc, thus
excluding a charge density wave driven phase transition.Comment: 6 pages with 4 figures; updated reference
Acting without being in control: Exploring volition in Parkinson's disease with impulsive compulsive behaviours.
BACKGROUND: Several aspects of volitional control of action may be relevant in the pathophysiology of impulsive-compulsive behaviours (ICB) in Parkinson's disease (PD). We aimed to explore multiple aspects of action control, assessing reward-related behaviour, inhibition (externally and internally triggered) and sense of agency in PD patients, with and without ICB compared to healthy subjects. METHODS: Nineteen PD patients with ICB (PD-ICB), 19 PD without ICB (PD-no-ICB) and 19 healthy controls (HC) underwent a battery of tests including: Intentional Binding task which measures sense of agency; Stop Signal Reaction Time (SSRT) measuring capacity for reactive inhibition; the Marble task, assessing intentional inhibition; Balloon Analog Risk Task for reward sensitivity. RESULTS: One-way ANOVA showed significant main effect of group for action binding (p = 0.004, F = 6.27). Post hoc analysis revealed that PD-ICB had significantly stronger action binding than HC (p = 0.004), and PD-no-ICB (p = 0.04). There was no difference between PD-no-ICB and HC. SSRT did not differ between PD groups, whereas a significant difference between PD-no-ICB and HC was detected (p = 0.01). No other differences were found among groups in the other tasks. CONCLUSIONS: PD patients with ICB have abnormal performance on a psychophysical task assessing sense of agency, which might be related to a deficit in action representation at cognitive/experiential level. Yet, they have no deficit on tasks evaluating externally and internally triggered inhibitory control, or in reward-based decision-making. We conclude that impaired sense of agency may be a factor contributing to ICB in PD patients
Quantum size effects in the low temperature layer-by-layer growth of Pb on Ge(001)
The electronic properties of thin metallic films deviate from the
corresponding bulk ones when the film thickness is comparable with the
wavelength of the electrons at the Fermi level due to quantum size effects
(QSE). QSE are expected to affect the film morphology and structure leading to
the low temperature (LT) ``electronic growth'' of metals on semiconductors. In
particular, layer-by-layer growth of Pb(111) films has been reported for
deposition on Ge(001) below 130 K. An extremely flat morphology is preserved
throughout deposition from four up to a dozen of monolayers. These flat films
are shown to be metastable and to reorganize into large clusters uncovering the
first Pb layer, pseudomorphic to the substrate, already at room temperature.
Indications of QSE induced structural variations of the growing films have been
reported for Pb growth on Ge(001), where the apparent height of the Pb(111)
monatomic step was shown to change in an oscillatory fashion by He atom
scattering (HAS) during layer-by-layer growth. The extent of the structural QSE
has been obtained by a comparison of the HAS data with X-ray diffraction (XRD)
and reflectivity experiments. Whereas step height variations as large as 20 %
have been measured by HAS reflectivity, the displacement of the atomic planes
from their bulk position, as measured by XRD, has been found to mainly affect
the topmost Pb layer, but with a lower extent, i.e. the QSE observed by HAS are
mainly due to a perpendicular displacement of the topmost layer charge density.
The effect of the variable surface relaxation on the surface vibration has been
studied by inelastic HAS to measure the acoustic dispersion of the low energy
phonons.Comment: 28 pages (laTex,elsart) and 13 figures (eps); updated reference
Study of the isotropic contribution to the analysis of photoelectron diffraction experiments at the ALOISA beamline
The angular distribution of the intensity in photoemission experiments is
affected by electron diffraction patterns and by a smoothly varying ISO
contribution originated by both intrumental details and physical properties of
the samples. The origin of the various contributions to the ISO component has
been identified since many years. Nonetheless in this work we present original
developement of the ED analysis, which arises from the evolution of
instrumental performance, in terms of analyzers positioning and angular
resolution, as well as collimation and size of X-ray beams in third generation
synchrotron sources. The analytical treatement of the instrumental factors is
presented in detail for the end station of the ALOISA beamline (Trieste
Synchrotron), where a wide variety of scattering geometries is available for ED
experiments. We present here the basic formulae and their application to
experimental data taken on the Fe/Cu3Au(001) system in order to highlight the
role of the various parameters included in the distribution function. A
specific model for the surface illumination has been developed as well as the
overlayer thickness and surface roughness have been considered.Comment: RevTex, nine pages with five eps figures; to be published in J.
Electron Spectrosc. Relat. Pheno
The pseudomorphic to bulk fcc phase transition of thin Ni films on Pd(100)
We have measured the transformation of pseudomorphic Ni films on Pd(100) into
their bulk fcc phase as a function of the film thickness. We made use of x-ray
diffraction and x-ray induced photoemission to study the evolution of the Ni
film and its interface with the substrate. The growth of a pseudomorphic film
with tetragonally strained face centered symmetry (fct) has been observed by
out-of-plane x-ray diffraction up to a maximum thickness of 10 Ni layers (two
of them intermixed with the substrate), where a new fcc bulk-like phase is
formed. After the formation of the bulk-like Ni domains, we observed the
pseudomorphic fct domains to disappear preserving the number of layers and
their spacing. The phase transition thus proceeds via lateral growth of the
bulk-like phase within the pseudomorphic one, i.e. the bulk-like fcc domains
penetrate down to the substrate when formed. This large depth of the walls
separating the domains of different phases is also indicated by the strong
increase of the intermixing at the substrate-film interface, which starts at
the onset of the transition and continues at even larger thickness. The
bulk-like fcc phase is also slightly strained; its relaxation towards the
orthomorphic lattice structure proceeds slowly with the film thickness, being
not yet completed at the maximum thickness presently studied of 30 Angstrom
(i.e. about 17 layers).Comment: 8 pages, 7 figure
Planck Low Frequency Instrument: Beam Patterns
The Low Frequency Instrument on board the ESA Planck satellite is coupled to
the Planck 1.5 meter off-axis dual reflector telescope by an array of 27
corrugated feed horns operating at 30, 44, 70, and 100 GHz. We briefly present
here a detailed study of the optical interface devoted to optimize the angular
resolution (10 arcmin at 100 GHz as a goal) and at the same time to minimize
all the systematics coming from the sidelobes of the radiation pattern. Through
optical simulations, we provide shapes, locations on the sky, angular
resolutions, and polarization properties of each beam.Comment: On behalf of the Planck collaboration. 3 pages, 1 figure. Article
published in the Proceedings of the 2K1BC Experimental Cosmology at
millimetre wavelength
The Planck Low Frequency Instrument
The Low Frequency Instrument (LFI) of the "Planck Surveyor" ESA mission will
perform high-resolution imaging of the Cosmic Microwave Background anisotropies
at four frequencies in the 30-100 GHz range. We review the LFI main scientific
objectives, the current status of the instrument design and the on-going effort
to develop software simulations of the LFI observations. In particular we
discuss the design status of the PLANCK telescope, which is critical for
reaching adequate effective angular resolution.Comment: 10 pages, Latex (use epsfig.sty); 4 Postscript figures; Astrophys.
Lett & Comm, in press. Proc. of the Conference: "The Cosmic Microwave
Background and the Planck Mission", Santander, Spain, 22-25 June 199
Dynamic validation of the Planck/LFI thermal model
The Low Frequency Instrument (LFI) is an array of cryogenically cooled
radiometers on board the Planck satellite, designed to measure the temperature
and polarization anisotropies of the cosmic microwave backgrond (CMB) at 30, 44
and 70 GHz. The thermal requirements of the LFI, and in particular the
stringent limits to acceptable thermal fluctuations in the 20 K focal plane,
are a critical element to achieve the instrument scientific performance.
Thermal tests were carried out as part of the on-ground calibration campaign at
various stages of instrument integration. In this paper we describe the results
and analysis of the tests on the LFI flight model (FM) performed at Thales
Laboratories in Milan (Italy) during 2006, with the purpose of experimentally
sampling the thermal transfer functions and consequently validating the
numerical thermal model describing the dynamic response of the LFI focal plane.
This model has been used extensively to assess the ability of LFI to achieve
its scientific goals: its validation is therefore extremely important in the
context of the Planck mission. Our analysis shows that the measured thermal
properties of the instrument show a thermal damping level better than
predicted, therefore further reducing the expected systematic effect induced in
the LFI maps. We then propose an explanation of the increased damping in terms
of non-ideal thermal contacts.Comment: Planck LFI technical papers published by JINST:
http://www.iop.org/EJ/journal/-page=extra.proc5/1748-022
Thermal susceptibility of the Planck-LFI receivers
This paper is part of the Prelaunch status LFI papers published on JINST:
http://www.iop.org/EJ/journal/-page=extra.proc5/jinst .
This paper describes the impact of the Planck Low Frequency Instrument front
end physical temperature fluctuations on the output signal. The origin of
thermal instabilities in the instrument are discussed, and an analytical model
of their propagation and impact on the receivers signal is described. The
experimental test setup dedicated to evaluate these effects during the
instrument ground calibration is reported together with data analysis methods.
Finally, main results obtained are discussed and compared to the requirements.Comment: This is an author-created, un-copyedited version of an article
accepted for publication in Journal of Instrumentation. IOP Publishing Ltd is
not responsible for any errors or omissions in this version of the manuscript
or any version derived from it. The definitive publisher authenticated
version is available online at 10.1088/1748-0221/4/12/T1201
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