915 research outputs found
Adsorption of Hydrocarbons Using Natural Adsorbents of Plant Origin
The paper investigates adsorption activity of natural sorbents to be used to clean up water surface from hydrocarbons under various temperatures. The natural adsorbents were compared by their oil capacity, buoyancy, and water absorption. It was revealed that Nature sorb (Canada) and Sphagnum Dill (Russia) natural sorbents demonstrate good buoyancy (up to 700 hours) and great oil capacity, and better sorption properties in comparison with the sawdust. The natural sorbents introduced can increase the efficiency of water surface cleaning-up until the water is almost clean and the residual oil content in water is less than 0.03 g/l
Abundance stratification in Type Ia supernovae - I. The case of SN 2002bo
The abundance stratification in the ejecta of the normal Type Ia supernova
2002bo is derived by fitting a series of spectra obtained at close time
intervals. A Monte Carlo code, modified to include abundance stratification, is
used to compute synthetic spectra at 13 epochs in the photospheric phase,
starting 13d before B maximum. A description of the abundance distribution
above 7600 km/s is thus obtained. Abundances in deeper layers, down to zero
velocity, are derived from models of two nebular-phase spectra. Elements
synthesized in different stages of burning are significantly, but not
completely, mixed in the ejecta. A total 56Ni mass of 0.52M_sun is derived.
Evidence for intermediate-mass elements at high velocities (> 18 000 km/s) is
found, most clearly in Si II 6355A, in Ca II H&K, and in the Ca II infrared
triplet. Carbon lines are not seen at any velocity, with possible implications
for the progenitor/explosion scenario. A synthetic bolometric light curve
computed using the inferred abundance distribution is in very good agreement
with the observed one, providing an independent check. In particular, the fast
rise of the light curve is reproduced very well. This is due to outward mixing
of 56Ni, which is clearly well determined by the spectroscopic modelling.Comment: 13 pages; changed content; accepted versio
Young stellar object jet models: From theory to synthetic observations
Astronomical observations, analytical solutions and numerical simulations
have provided the building blocks to formulate the current theory of young
stellar object jets. Although each approach has made great progress
independently, it is only during the last decade that significant efforts are
being made to bring the separate pieces together. Building on previous work
that combined analytical solutions and numerical simulations, we apply a
sophisticated cooling function to incorporate optically thin energy losses in
the dynamics. On the one hand, this allows a self-consistent treatment of the
jet evolution and on the other, it provides the necessary data to generate
synthetic emission maps. Firstly, analytical disk and stellar outflow solutions
are properly combined to initialize numerical two-component jet models inside
the computational box. Secondly, magneto-hydrodynamical simulations are
performed in 2.5D, following properly the ionization and recombination of a
maximum of ions. Finally, the outputs are post-processed to produce
artificial observational data. The first two-component jet simulations, based
on analytical models, that include ionization and optically thin radiation
losses demonstrate promising results for modeling specific young stellar object
outflows. The generation of synthetic emission maps provides the link to
observations, as well as the necessary feedback for the further improvement of
the available models.Comment: accepted for publication A&A, 20 pages, 11 figure
Kinetic Mechanism of the Ca2+-Dependent Switch-On and Switch-Off of Cardiac Troponin in Myofibrils
The kinetics of Ca2+-dependent conformational changes of human cardiac troponin (cTn) were studied on isolated cTn and within the sarcomeric environment of myofibrils. Human cTnC was selectively labeled on cysteine 84 with N-((2-(iodoacetoxy)ethyl)-N-methyl)amino-7-nitrobenz-2-oxa-1,3-diazole and reconstituted with cTnI and cTnT to the cTn complex, which was incorporated into guinea pig cardiac myofibrils. These exchanged myofibrils, or the isolated cTn, were rapidly mixed in a stopped-flow apparatus with different [Ca2+] or the Ca2+-buffer 1,2-Bis(2-aminophenoxy)ethane-N,N,N′,N′-tetraacetic acid to determine the kinetics of the switch-on or switch-off, respectively, of cTn. Activation of myofibrils with high [Ca2+] (pCa 4.6) induced a biphasic fluorescence increase with rate constants of >2000 s−1 and ∼330 s−1, respectively. At low [Ca2+] (pCa 6.6), the slower rate was reduced to ∼25 s−1, but was still ∼50-fold higher than the rate constant of Ca2+-induced myofibrillar force development measured in a mechanical setup. Decreasing [Ca2+] from pCa 5.0–7.9 induced a fluorescence decay with a rate constant of 39 s−1, which was approximately fivefold faster than force relaxation. Modeling the data indicates two sequentially coupled conformational changes of cTnC in myofibrils: 1), rapid Ca2+-binding (kB ≈ 120 μM−1 s−1) and dissociation (kD ≈ 550 s−1); and 2), slower switch-on (kon = 390s−1) and switch-off (koff = 36s−1) kinetics. At high [Ca2+], ∼90% of cTnC is switched on. Both switch-on and switch-off kinetics of incorporated cTn were around fourfold faster than those of isolated cTn. In conclusion, the switch kinetics of cTn are sensitively changed by its structural integration in the sarcomere and directly rate-limit neither cardiac myofibrillar contraction nor relaxation
Myeloid-derived suppressor cells are implicated in regulating permissiveness for tumor metastasis during mouse gestation.
Metastasis depends on the ability of tumor cells to establish a relationship with the newly seeded tissue that is conducive to their survival and proliferation. However, the factors that render tissues permissive for metastatic tumor growth have yet to be fully elucidated. Breast tumors arising during pregnancy display early metastatic proclivity, raising the possibility that pregnancy may constitute a physiological condition of permissiveness for tumor dissemination. Here we have shown that during murine gestation, metastasis is enhanced regardless of tumor type, and that decreased NK cell activity is responsible for the observed increase in experimental metastasis. Gene expression changes in pregnant mouse lung and liver were shown to be similar to those detected in premetastatic sites and indicative of myeloid cell infiltration. Indeed, myeloid-derived suppressor cells (MDSCs) accumulated in pregnant mice and exerted an inhibitory effect on NK cell activity, providing a candidate mechanism for the enhanced metastatic tumor growth observed in gestant mice. Although the functions of MDSCs are not yet understood in the context of pregnancy, our observations suggest that they may represent a shared mechanism of immune suppression occurring during gestation and tumor growth
Formation of Episodic Magnetically Driven Radiatively Cooled Plasma Jets in the Laboratory
We report on experiments in which magnetically driven radiatively cooled
plasma jets were produced by a 1 MA, 250 ns current pulse on the MAGPIE pulsed
power facility. The jets were driven by the pressure of a toroidal magnetic
field in a ''magnetic tower'' jet configuration. This scenario is characterized
by the formation of a magnetically collimated plasma jet on the axis of a
magnetic ''bubble'', confined by the ambient medium. The use of a radial
metallic foil instead of the radial wire arrays employed in our previous work
allows for the generation of episodic magnetic tower outflows which emerge
periodically on timescales of ~30 ns. The subsequent magnetic bubbles propagate
with velocities reaching ~300 km/s and interact with previous eruptions leading
to the formation of shocks.Comment: 6 pages, 5 figures. Accepted for publication in Astrophysics & Space
Scienc
Properties of the ultraviolet flux of type Ia supernovae: an analysis with synthetic spectra of SN 2001ep and SN 2001eh
The spectral properties of type Ia supernovae in the ultraviolet (UV) are
investigated using the early-time spectra of SN 2001ep and SN 2001eh obtained
using the Hubble Space Telescope (HST). A series of spectral models is computed
with a Monte Carlo spectral synthesis code, and the dependence of the UV flux
on the elemental abundances and the density gradient in the outer layers of the
ejecta is tested. A large fraction of the UV flux is formed by reverse
fluorescence scattering of photons from red to blue wavelengths. This process,
combined with ionization shifts due to enhanced line blocking, can lead to a
stronger UV flux as the iron-group abundance in the outer layers is increased,
contrary to previous claims.Comment: 14 pages, 13 figures. Replaced with revised version accepted for
publication in MNRA
Change of biological soil quality in organic and conventional farming systems of the DOK trial
The DOK trial has started in the 1970ies, when first reports warned us on the consequences of our actions and the limits to growth. Even though farmers and a huge research community know better, we are still not managing our soils in a sustainable way. It seems inevitable that the mainstream agriculture wants to go beyond natural frontiers. Soils have an enormous buffering capacity, but this ends, when ecosystems are collapsing not only at the local, but also at the global level
High-Velocity Features: a ubiquitous property of Type Ia SNe
Evidence of high-velocity features such as those seen in the near-maximum
spectra of some Type Ia Supernovae (eg SN 2000cx) has been searched for in the
available SNIa spectra observed earlier than one week before B maximum. Recent
observational efforts have doubled the number of SNeIa with very early spectra.
Remarkably, all SNeIa with early data (7 in our RTN sample and 10 from other
programmes) show signs of such features, to a greater or lesser degree, in CaII
IR, and some also in SiII 6255A line. High-velocity features may be interpreted
as abundance or density enhancements. Abundance enhancements would imply an
outer region dominated by Si and Ca. Density enhancements may result from the
sweeping up of circumstellar material by the highest velocity SN ejecta. In
this scenario, the high incidence of HVFs suggests that a thick disc and/or a
high-density companion wind surrounds the exploding white dwarf, as may be the
case in Single Degenerate systems. Large-scale angular fluctuations in the
radial density and abundance distribution may also be responsible: this could
originate in the explosion, and would suggest a deflagration as the more likely
explosion mechanism. CSM-interaction and surface fluctuations may coexist,
possibly leaving different signatures on the spectrum. In some SNe the HVFs are
narrowly confined in velocity, suggesting the ejection of blobs of burned
material.Comment: 12 pages, 2 figures, ApJ Letters in pres
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