6,855 research outputs found
The Chemical Composition of an Extrasolar Minor Planet
We report the relative abundances of 17 elements in the atmosphere of the
white dwarf star GD 362, material that, very probably, was contained previously
in a large asteroid or asteroids with composition similar to the Earth/Moon
system. The asteroid may have once been part of a larger parent body not unlike
one of the terrestrial planets of our solar system.Comment: ApJ, in pres
Critical curves in conformally invariant statistical systems
We consider critical curves -- conformally invariant curves that appear at
critical points of two-dimensional statistical mechanical systems. We show how
to describe these curves in terms of the Coulomb gas formalism of conformal
field theory (CFT). We also provide links between this description and the
stochastic (Schramm-) Loewner evolution (SLE). The connection appears in the
long-time limit of stochastic evolution of various SLE observables related to
CFT primary fields. We show how the multifractal spectrum of harmonic measure
and other fractal characteristics of critical curves can be obtained.Comment: Published versio
Rigidity and intermediate phases in glasses driven by speciation
The rigid to floppy transitions and the associated intermediate phase in
glasses are studied in the case where the local structure is not fully
determined from the macroscopic concentration. The approach uses size
increasing cluster approximations and constraint counting algorithms. It is
shown that the location and the width of the intermediate phase and the
corresponding structural, mechanical and energetical properties of the network
depend crucially on the way local structures are selected at a given
concentration. The broadening of the intermediate phase is obtained for
networks combining a large amount of flexible local structural units and a high
rate of medium range order.Comment: 4 pages, 4 figure
A nitrite microsensor for profiling environmental biofilms
A highly selective liquid membrane nitrite microsensor based on the hydrophobic ion-carrier aquocyano-cobalt(III) -hepta(2-phenylethyl)-cobrynate is described, The sensor has a tip diameter of 10 to 15 mu m. The response is log-linear in freshwater down to 1 mu M NO2- and in seawater to 10 mu M NO2-. A method is described for preparation of relatively large polyvinyl chloride (PVC)-gelled liquid membrane microsensors with a tip diameter of 5 to 15 mu m, having a hydrophilic coating on the tip, The coating and increased tip diameter resulted in more sturdy sensors, with a lower detection limit and a more stable signal than uncoated nitrite sensors with a tip diameter of 1 to 3 mu m. The coating protects the sensor membrane from detrimental direct contact with biomass and can be used for all PVC-gelled liquid membrane sensors meant for profiling microbial mats, biofilms, and sediments. Thanks to these improvements, liquid membrane sensors can now be used in complex environmental samples and in situ, e.g., in operating bioreactors. Examples of measurements in denitrifying, nitrifying, and nitrifying/denitrifying biofilms from wastewater treatment plants are shown. In all of these biofilms high nitrite concentrations were found in narrow zones of less than 1 mm
Glueball Production in Peripheral Heavy-Ion Collisions
The method of equivalent quanta is applied both to photon-photon and, by
analogy, to double pomeron exchange in heavy-ion collisions. This
Weizs\"acker-Williams approach is used to calculate production cross sections
for the glueball candidate meson via photon-photon and
pomeron-pomeron fusion in peripheral heavy-ion collisions at both RHIC and LHC
energies. The impact-parameter dependence for total and elastic cross sections
are presented, and are compared to results for proton-proton collisions.Comment: 15 pages, 6 figure
The acute effects of daily nicotine intake on heart rate--a toxicokinetic and toxicodynamic modelling study.
Abstract Joint physiologically-based toxicokinetic and toxicodynamic (PBTK/TD) modelling was applied to simulate concentration–time profiles of nicotine, a well-known stimulant, in the human body following single and repeated dosing. Both kinetic and dynamic models were first calibrated by using in vivo literature data for the Caucasian population. The models were then used to estimate the blood and liver concentrations of nicotine in terms of the Area Under Curve (AUC) and the peak concentration (Cmax) for selected exposure scenarios based on inhalation (cigarette smoking), oral intake (nicotine lozenges) and dermal absorption (nicotine patches). The model simulations indicated that whereas frequent cigarette smoking gives rise to high AUC and Cmax in blood, the use of nicotine-rich dermal patches leads to high AUC and Cmax in the liver. Venous blood concentrations were used to estimate one of the most common acute effects, mean heart rate, both at rest and during exercise. These estimations showed that cigarette smoking causes a high peak heart rate, whereas dermal absorption causes a high mean heart rate over 48 h. This study illustrates the potential of using PBTK/TD modelling in the safety assessment of nicotine-containing products
Production of eta Mesons in Double Pomeron Exchange
We estimate the production cross sections for and mesons
via pomeron-pomeron fusion in peripheral heavy-ion collisions. Total and
elastic PP cross sections are calculated in an equivalent pomeron
approximation.Comment: 9 pages, 3 Postscript figure
Proposal for a CFT interpretation of Watts' differential equation for percolation
G. M. T. Watts derived that in two dimensional critical percolation the
crossing probability Pi_hv satisfies a fifth order differential equation which
includes another one of third order whose independent solutions describe the
physically relevant quantities 1, Pi_h, Pi_hv.
We will show that this differential equation can be derived from a level
three null vector condition of a rational c=-24 CFT and motivate how this
solution may be fitted into known properties of percolation.Comment: LaTeX, 20p, added references, corrected typos and additional content
Blowin' in the wind: both `negative' and `positive' feedback in an obscured high-z Quasar
Quasar feedback in the form of powerful outflows is invoked as a key
mechanism to quench star formation in galaxies, preventing massive galaxies to
over-grow and producing the red colors of ellipticals. On the other hand, some
models are also requiring `positive' AGN feedback, inducing star formation in
the host galaxy through enhanced gas pressure in the interstellar medium.
However, finding observational evidence of the effects of both types of
feedback is still one of the main challenges of extragalactic astronomy, as few
observations of energetic and extended radiatively-driven winds are available.
Here we present SINFONI near infrared integral field spectroscopy of XID2028,
an obscured, radio-quiet z=1.59 QSO detected in the XMM-COSMOS survey, in which
we clearly resolve a fast (1500 km/s) and extended (up to 13 kpc from the black
hole) outflow in the [OIII] lines emitting gas, whose large velocity and
outflow rate are not sustainable by star formation only. The narrow component
of Ha emission and the rest frame U band flux from HST-ACS imaging enable to
map the current star formation in the host galaxy: both tracers independently
show that the outflow position lies in the center of an empty cavity surrounded
by star forming regions on its edge. The outflow is therefore removing the gas
from the host galaxy (`negative feedback'), but also triggering star formation
by outflow induced pressure at the edges (`positive feedback'). XID2028
represents the first example of a host galaxy showing both types of feedback
simultaneously at work.Comment: 9 pages, 5 figures, accepted for publication in Ap
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