1,059 research outputs found
On the Calibration of a Size-Structured Population Model from Experimental Data
The aim of this work is twofold. First, we survey the techniques developed in
(Perthame, Zubelli, 2007) and (Doumic, Perthame, Zubelli, 2008) to reconstruct
the division (birth) rate from the cell volume distribution data in certain
structured population models. Secondly, we implement such techniques on
experimental cell volume distributions available in the literature so as to
validate the theoretical and numerical results. As a proof of concept, we use
the data reported in the classical work of Kubitschek [3] concerning
Escherichia coli in vitro experiments measured by means of a Coulter
transducer-multichannel analyzer system (Coulter Electronics, Inc., Hialeah,
Fla, USA.) Despite the rather old measurement technology, the reconstructed
division rates still display potentially useful biological features
Archival wild-type poliovirus 1 infected central nervous system tissues of the pre-vaccination era in Switzerland reveal a distinct virus genotype.
Visibilities and bolometric corrections for stellar oscillation modes observed by Kepler
Kepler produces a large amount of data used for asteroseismological analyses,
particularly of solar-like stars and red giants. The mode amplitudes observed
in the Kepler spectral band have to be converted into bolometric amplitudes to
be compared to models. We give a simple bolometric correction for the
amplitudes of radial modes observed with Kepler, as well as the relative
visibilities of non-radial modes. We numerically compute the bolometric
correction c_{K-bol} and mode visibilities for different effective temperatures
Teff within the range 4000-7500 K, using a similar approach to a recent one
from the literature (Michel et al. 2009, A&A 495, 979). We derive a law for the
correction to bolometric values: c_{K-bol} = 1 + a_1 (Teff-To) + a_2
(Teff-To)^2, with To = 5934 K, a_1 = 1.349e-4 K^{-1}, and a_2 = -3.120e-9
K^{-2} or, alternatively, as the power law c_{K-bol} = (Teff/To)^alpha with
alpha = 0.80. We give tabulated values for the mode visibilities based on
limb-darkening (LD), computed from ATLAS9 model atmospheres for Teff in
[4000,7500] K, log g in [2.5,4.5], and [M/H] in [-1.0,+1.0]. We show that using
LD profiles already integrated over the spectral band provides quick and good
approximations for visibilities. We point out the limits of these classical
visibility estimations.Comment: 5 pages, 4 figures, 1 table, minor language edition. Published in A&
Archive Mining Brings to Light a 25-Year Old Astrovirus Encephalitis Case in a Sheep
In mammals, the small, positive-sense single-stranded RNA astroviruses are known as being mostly enterotropic and host-specific. Over the past years, however, they were identified several times in central nervous system tissues of humans, minks, cattle, sheep, and pigs with nonsuppurative inflammatory disease of that organ system. We recently reported such neurotropic astroviruses, amongst which bovine astrovirus CH15 (BoAstV-CH15) in two cows, and ovine astrovirus CH16 (OvAstV-CH16) in a sheep, which were genetically almost identical to one another. In order to investigate the occurrence of this virus species in Switzerland over time, we selected formalin-fixed, paraffin-embedded (FFPE) brain tissues of small ruminants diagnosed with severe encephalitis between 1969 and 2012 and screened those by immunohistochemistry for the capsid protein of BoAstV-CH15/OvAstV-CH16. We found one sheep, which died in 1992, that displayed positive immunostaining in various brain regions, and observed that immunostained cells were generally co-localized with the strongest histopathological lesions. We confirmed the virus presence with a second immunohistochemical protocol and demonstrated its close genetic relationship to other BoAstV-CH15/ OvAstV-CH16 strains by next-generation sequencing of an RNA extract from FFPE brain material. Our findings demonstrate that astrovirus BoAstV-CH15/OvAstV-CH16 existed in Switzerland already more than 2 decades ago and underline again the close relationship of the bovine and ovine strains of this virus
Calpain-mediated cleavage of collapsin response mediator protein-2 drives acute axonal degeneration
Axonal degeneration is a key initiating event in many neurological diseases. Focal lesions to axons result in a rapid disintegration of the perilesional axon by acute axonal degeneration (AAD) within several hours. However, the underlying molecular mechanisms of AAD are only incompletely understood. Here, we studied AAD in vivo through live-imaging of the rat optic nerve and in vitro in primary rat cortical neurons in microfluidic chambers. We found that calpain is activated early during AAD of the optic nerve and that calpain inhibition completely inhibits axonal fragmentation on the proximal side of the crush while it attenuates AAD on the distal side. A screening of calpain targets revealed that collapsin response mediator protein-2 (CRMP2) is a main downstream target of calpain activation in AAD. CRMP2-overexpression delayed bulb formation and rescued impairment of axonal mitochondrial transport after axotomy in vitro. In vivo, CRMP2-overexpression effectively protected the proximal axon from fragmentation within 6 hours after crush. Finally, a proteomic analysis of the optic nerve was performed at 6 hours after crush, which identified further proteins regulated during AAD, including several interactors of CRMP2. These findings reveal CRMP2 as an important mediator of AAD and define it as a putative therapeutic target
Detectability of Strange Matter in Heavy Ion Experiments
We discuss the properties of two distinct forms of hypothetical strange
matter, small lumps of strange quark matter (strangelets) and of hyperon matter
(metastable exotic multihypernuclear objects: MEMOs), with special emphasis on
their relevance for present and future heavy ion experiments. The masses of
small strangelets up to A = 40 are calculated using the MIT bag model with
shell mode filling for various bag parameters. The strangelets are checked for
possible strong and weak hadronic decays, also taking into account multiple
hadron decays. It is found that strangelets which are stable against strong
decay are most likely highly negative charged, contrary to previous findings.
Strangelets can be stable against weak hadronic decay but their masses and
charges are still rather high. This has serious impact on the present high
sensitivity searches in heavy ion experiments at the AGS and CERN facilities.
On the other hand, highly charged MEMOs are predicted on the basis of an
extended relativistic mean-field model. Those objects could be detected in
future experiments searching for short-lived, rare composites. It is
demonstrated that future experiments can be sensitive to a much wider variety
of strangelets.Comment: 26 pages, 5 figures, uses RevTeX and epsf.st
Accurate and precise real-time RT-PCR assays for the identification of astrovirus associated encephalitis in cattle
A novel bovine astrovirus genotype species (BoAstV-CH13/NeuroS1) was recently identified in brain tissues of cattle as a plausible cause of encephalitis. The purpose of the present study was to develop and validate real time RT-PCR assays for the detection of BoAstV-CH13/NeuroS1 in brain tissues of cattle. Three different primer-probe combinations were designed based on BoAstV-CH13/NeuroS1 full-genome sequences of 11 different strains identified in cattle, and established in three distinct one-step real time RT-PCR protocols. These protocols were compared regarding their diagnostic performance using brain tissues of cattle with and without astrovirus associated encephalitis. The limit of detection (LOD) of all three assays was between 1.34 × 101 and 1.34 × 102 RNA copies, leading to an analytical sensitivity two orders of magnitude superior compared to a conventional pan-astrovirus RT-PCR protocol (LOD 1.31 × 104 RNA copies). Amplification efficiency was in the range of 97.3% to 107.5% with linearity (R2) > 0.99. The diagnostic sensitivity and specificity of the assays was determined as 100%, and all three revealed good intra- and inter-test repeatability. In conclusion, the newly developed RT-qPCRs are sensitive, specific, and reliable test formats that will facilitate BoAstV-CH13/NeuroS1 detection in routine diagnostics as well as in research settings
Probing the core structure and evolution of red giants using gravity-dominated mixed modes observed with Kepler
We report for the first time a parametric fit to the pattern of the \ell = 1
mixed modes in red giants, which is a powerful tool to identify
gravity-dominated mixed modes. With these modes, which share the
characteristics of pressure and gravity modes, we are able to probe directly
the helium core and the surrounding shell where hydrogen is burning. We propose
two ways for describing the so-called mode bumping that affects the frequencies
of the mixed modes. Firstly, a phenomenological approach is used to describe
the main features of the mode bumping. Alternatively, a quasi-asymptotic
mixed-mode relation provides a powerful link between seismic observations and
the stellar interior structure. We used period \'echelle diagrams to emphasize
the detection of the gravity-dominated mixed modes. The asymptotic relation for
mixed modes is confirmed. It allows us to measure the gravity-mode period
spacings in more than two hundred red giant stars. The identification of the
gravity-dominated mixed modes allows us to complete the identification of all
major peaks in a red giant oscillation spectrum, with significant consequences
for the true identification of \ell = 3 modes, of \ell = 2 mixed modes, for the
mode widths and amplitudes, and for the \ell = 1 rotational splittings. The
accurate measurement of the gravity-mode period spacing provides an effective
probe of the inner, g-mode cavity. The derived value of the coupling
coefficient between the cavities is different for red giant branch and clump
stars. This provides a probe of the hydrogen-shell burning region that
surrounds the helium core. Core contraction as red giants ascend the red giant
branch can be explored using the variation of the gravity-mode spacing as a
function of the mean large separation.Comment: Accepted in A&
Kepler-20: A Sun-like Star with Three Sub-Neptune Exoplanets and Two Earth-size Candidates
We present the discovery of the Kepler-20 planetary system, which we
initially identified through the detection of five distinct periodic transit
signals in the Kepler light curve of the host star 2MASSJ19104752+4220194. We
find a stellar effective temperature Teff=5455+-100K, a metallicity of
[Fe/H]=0.01+-0.04, and a surface gravity of log(g)=4.4+-0.1. Combined with an
estimate of the stellar density from the transit light curves we deduce a
stellar mass of Mstar=0.912+-0.034 Msun and a stellar radius of
Rstar=0.944^{+0.060}_{-0.095} Rsun. For three of the transit signals, our
results strongly disfavor the possibility that these result from astrophysical
false positives. We conclude that the planetary scenario is more likely than
that of an astrophysical false positive by a factor of 2e5 (Kepler-20b), 1e5
(Kepler-20c), and 1.1e3 (Kepler-20d), sufficient to validate these objects as
planetary companions. For Kepler-20c and Kepler-20d, the blend scenario is
independently disfavored by the achromaticity of the transit: From Spitzer data
gathered at 4.5um, we infer a ratio of the planetary to stellar radii of
0.075+-0.015 (Kepler-20c) and 0.065+-0.011 (Kepler-20d), consistent with each
of the depths measured in the Kepler optical bandpass. We determine the orbital
periods and physical radii of the three confirmed planets to be 3.70d and
1.91^{+0.12}_{-0.21} Rearth for Kepler-20b, 10.85 d and 3.07^{+0.20}_{-0.31}
Rearth for Kepelr-20c, and 77.61 d and 2.75^{+0.17}_{-0.30} Rearth for
Kepler-20d. From multi-epoch radial velocities, we determine the masses of
Kepler-20b and Kepler-20c to be 8.7\+-2.2 Mearth and 16.1+-3.5 Mearth,
respectively, and we place an upper limit on the mass of Kepler-20d of 20.1
Mearth (2 sigma).Comment: accepted by ApJ, 58 pages, 12 figures revised Jan 2012 to correct
table 2 and clarify planet parameter extractio
Transit Timing Observations from Kepler: III. Confirmation of 4 Multiple Planet Systems by a Fourier-Domain Study of Anti-correlated Transit Timing Variations
We present a method to confirm the planetary nature of objects in systems
with multiple transiting exoplanet candidates. This method involves a
Fourier-Domain analysis of the deviations in the transit times from a constant
period that result from dynamical interactions within the system. The
combination of observed anti-correlations in the transit times and mass
constraints from dynamical stability allow us to claim the discovery of four
planetary systems Kepler-25, Kepler-26, Kepler-27, and Kepler-28, containing
eight planets and one additional planet candidate.Comment: Accepted to MNRA
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