1,641 research outputs found
Analysis of concentration-dependent effects of copper and PCB on different Chattonella spp. microalgae (Raphidophyceae) cultivated in artificial seawater medium
In the present study, the effect on the chlorophyll a and the total protein content as well as the Chattonella spp. cell viability were examined after concentration-dependent exposure to CuCl2 and Aroclor 1242. The comparison between various raphidophyte strains provides an insight into the different susceptibilities to contaminants of Chattonella subsalsa
(CSNAV-1), C. marina var . marina (CMCV-1) and C. marina var. ovata (COPV-2). The microalgae were cultivated in artificial seawater medium. Exponentially growing microalgae (8-10 days in culture) were used for exposure experiments. We observed in all three raphidophyte species cytotoxicity-mediated modifications beginning at concentrations of 150 and 200μM of the
heavy metal copper after 24 hours exposure. But interestingly, the three strains exhibited only slight differences in their susceptibility to CuCl2. C. subsalsa and C. marina var. marina cells were first affected at the chlorophyll a level and in cell viability. The total protein amount was reduced significantly only after exposure to 300μM of CuCl2. However, C. marina var.
ovata microalgae showed similar reduction curves for all three analysed cytotoxicity endpoints after heavy metal exposure. On the other hand, after Aroclor 1242 incubation the cytotoxic modification pattern indicated clearly the different susceptibilities of
the three raphidophyte strains. C. subsalsa
cells noticeably exhibited a decrease in the analysed pigment amount (30-20% compared to that of the control) already after 0.007mg/L PCB exposure. In contrast, cell viability and total protein content were slightly reduced and fell below the 50% threshold after 0.7 and 3.3mg/L of Aroclor 1242, respectively. Interestingly, C. marina
var. ovata showed almost no cytotoxic modification caused by the PCB mixture. Only the concentration of 0.7mg/L Aroclor 1242 clearly affected the cell viability. As opposed to that we observed a concentration-dependent decrease of cell viability and chlorophyll a amount in CMCV-1 microalgae. These observations confirmed that the susceptibility of the raphidophytes strains
CSNAV-1, CMCV-1 and COPV-2 is contaminant-
dependent. We showed differences even between two variants of Chattonella (Chattonella marina var. marina and C. marina
var. ovata). Furthermore, we were able to show the different mode of action of two common pollutants by simple cytotoxic parameters like total protein and chlorophyll a content as well as by cell counting analysis
Initial data sets for the Schwarzschild spacetime
A characterisation of initial data sets for the Schwarzschild spacetime is
provided. This characterisation is obtained by performing a 3+1 decomposition
of a certain invariant characterisation of the Schwarzschild spacetime given in
terms of concomitants of the Weyl tensor. This procedure renders a set of
necessary conditions --which can be written in terms of the electric and
magnetic parts of the Weyl tensor and their concomitants-- for an initial data
set to be a Schwarzschild initial data set. Our approach also provides a
formula for a static Killing initial data set candidate --a KID candidate.
Sufficient conditions for an initial data set to be a Schwarzschild initial
data set are obtained by supplementing the necessary conditions with the
requirement that the initial data set possesses a stationary Killing initial
data set of the form given by our KID candidate. Thus, we obtain an algorithmic
procedure of checking whether a given initial data set is Schwarzschildean or
not.Comment: 16 page
The Non-thermal Radio Jet Toward the NGC 2264 Star Formation Region
We report sensitive VLA 3.6 cm radio observations toward the head of the Cone
nebula in NGC 2264, made in 2006. The purpose of these observations was to
study a non-thermal radio jet recently discovered, that appears to emanate from
the head of the Cone nebula. The jet is highly polarized, with well-defined
knots, and one-sided. The comparison of our images with 1995 archive data
indicates no evidence of proper motions nor polarization changes. We find
reliable flux density variations in only one knot, which we tentatively
identify as the core of a quasar or radio galaxy. An extragalactic location
seems to be the best explanation for this jet.Comment: 12 pages, 5 figure
Discovery of water vapour in the carbon star V Cygni from observations with Herschel/HIFI
We report the discovery of water vapour toward the carbon star V Cygni. We
have used Herschel's HIFI instrument, in dual beam switch mode, to observe the
1(11) - 0(00) para-water transition at 1113.3430 GHz in the upper sideband of
the Band 4b receiver. The observed spectral line profile is nearly parabolic,
but with a slight asymmetry associated with blueshifted absorption, and the
integrated antenna temperature is 1.69 \pm 0.17 K km/s. This detection of
thermal water vapour emission, carried out as part of a small survey of water
in carbon-rich stars, is only the second such detection toward a carbon-rich
AGB star, the first having been obtained by the Submillimeter Wave Astronomy
Satellite toward IRC+10216. For an assumed ortho-to-para ratio of 3 for water,
the observed line intensity implies a water outflow rate ~ (3 - 6) E-5 Earth
masses per year and a water abundance relative to H2 of ~ (2-5) E-6. This value
is a factor of at least 1E+4 larger than the expected photospheric abundance in
a carbon-rich environment, and - as in IRC+10216 - raises the intriguing
possibility that the observed water is produced by the vapourisation of
orbiting comets or dwarf planets. However, observations of the single line
observed to date do not permit us to place strong constraints upon the spatial
distribution or origin of the observed water, but future observations of
additional transitions will allow us to determine the inner radius of the
H2O-emitting zone, and the H2O ortho-to-para ratio, and thereby to place
important constraints upon the origin of the observed water emission.Comment: Accepted for publication in A&A (HIFI special issue
Causal Relationship: a new tool for the causal characterization of Lorentzian manifolds
We define and study a new kind of relation between two diffeomorphic
Lorentzian manifolds called {\em causal relation}, which is any diffeomorphism
characterized by mapping every causal vector of the first manifold onto a
causal vector of the second. We perform a thorough study of the mathematical
properties of causal relations and prove in particular that two given
Lorentzian manifolds (say and ) may be causally related only in one
direction (say from to , but not from to ). This leads us to the
concept of causally equivalent (or {\em isocausal} in short) Lorentzian
manifolds as those mutually causally related. This concept is more general and
of a more basic nature than the conformal relationship, because we prove the
remarkable result that a conformal relation \f is characterized by the fact
of being a causal relation of the {\em particular} kind in which both \f and
\f^{-1} are causal relations. For isocausal Lorentzian manifolds there are
one-to-one correspondences, which sometimes are non-trivial, between several
classes of their respective future (and past) objects. A more important feature
of isocausal Lorentzian manifolds is that they satisfy the same causality
constraints. This indicates that the causal equivalence provides a possible
characterization of the {\it basic causal structure}, in the sense of mutual
causal compatibility, for Lorentzian manifolds. Thus, we introduce a partial
order for the equivalence classes of isocausal Lorentzian manifolds providing a
classification of spacetimes in terms of their causal properties, and a
classification of all the causal structures that a given fixed manifold can
have. A full abstract inside the paper.Comment: 47 pages, 10 figures. Version to appear in Classical and Quantum
Gravit
The widespread occurence of water vapor in the circumstellar envelopes of carbon-rich AGB stars: first results from a survey with Herschel/HIFI
We report the preliminary results of a survey for water vapor in a sample of
eight C stars with large mid-IR continuum fluxes: V384 Per, CIT 6, V Hya, Y
CVn, IRAS 15194-5115, V Cyg, S Cep, and IRC+40540. This survey, performed using
the HIFI instrument on board the Herschel Space Observatory, entailed
observations of the lowest transitions of both ortho- and para-water: the
556.936 GHz 1(10)-1(01) and 1113.343 GHz 1(11)-0(00) transitions, respectively.
Water vapor was unequivocally detected in all eight of the target stars. Prior
to this survey, IRC+10216 was the only carbon-rich AGB star from which thermal
water emissions had been discovered, in that case with the use of the
Submillimeter Wave Astronomy Satellite (SWAS). Our results indicate that
IRC+10216 is not unusual, except insofar as its proximity to Earth leads to a
large line flux that was detectable with SWAS. The water spectral line widths
are typically similar to those of CO rotational lines, arguing against the
vaporization of a Kuiper belt analog (Ford & Neufeld 2001) being the general
explanation for water vapor in carbon-rich AGB stars. There is no apparent
correlation between the ratio of the integrated water line fluxes to the 6.3
micron continuum flux - a ratio which measures the water outflow rate - and the
total mass-loss rate for the stars in our sample.Comment: Accepted for publication in the Astrophysical Journal Letter
Observation of an Excited Bc+ State
Using pp collision data corresponding to an integrated luminosity of 8.5 fb-1 recorded by the LHCb experiment at center-of-mass energies of s=7, 8, and 13 TeV, the observation of an excited Bc+ state in the Bc+π+π- invariant-mass spectrum is reported. The observed peak has a mass of 6841.2±0.6(stat)±0.1(syst)±0.8(Bc+) MeV/c2, where the last uncertainty is due to the limited knowledge of the Bc+ mass. It is consistent with expectations of the Bc∗(2S31)+ state reconstructed without the low-energy photon from the Bc∗(1S31)+→Bc+γ decay following Bc∗(2S31)+→Bc∗(1S31)+π+π-. A second state is seen with a global (local) statistical significance of 2.2σ (3.2σ) and a mass of 6872.1±1.3(stat)±0.1(syst)±0.8(Bc+) MeV/c2, and is consistent with the Bc(2S10)+ state. These mass measurements are the most precise to date
Bose-Einstein correlations of same-sign charged pions in the forward region in pp collisions at √s=7 TeV
Bose-Einstein correlations of same-sign charged pions, produced in protonproton collisions at a 7 TeV centre-of-mass energy, are studied using a data sample collected
by the LHCb experiment. The signature for Bose-Einstein correlations is observed in the
form of an enhancement of pairs of like-sign charged pions with small four-momentum
difference squared. The charged-particle multiplicity dependence of the Bose-Einstein correlation parameters describing the correlation strength and the size of the emitting source
is investigated, determining both the correlation radius and the chaoticity parameter. The
measured correlation radius is found to increase as a function of increasing charged-particle
multiplicity, while the chaoticity parameter is seen to decreas
Measurement of the inelastic pp cross-section at a centre-of-mass energy of 13TeV
The cross-section for inelastic proton-proton collisions at a centre-of-mass energy of 13TeV is measured with the LHCb detector. The fiducial cross-section for inelastic interactions producing at least one prompt long-lived charged particle with momentum p > 2 GeV/c in the pseudorapidity range 2 < η < 5 is determined to be ϭ acc = 62:2 ± 0:2 ± 2:5mb. The first uncertainty is the intrinsic systematic uncertainty of the measurement, the second is due to the uncertainty on the integrated luminosity. The statistical uncertainty is negligible. Extrapolation to full phase space yields the total inelastic proton-proton cross-section ϭ inel = 75:4 ± 3:0 ± 4:5mb, where the first uncertainty is experimental and the second due to the extrapolation. An updated value of the inelastic cross-section at a centre-of-mass energy of 7TeV is also reported
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