717 research outputs found
Persistenz bodenphysikalischer Wirkungen perennierender Futterpflanzen mit Pfahlwurzelsystemen
Taprooted crops create large sized biopores in the subsoil which in turn facilitate root growth of following crops. To date it was unclear, over which periods of time biopores
created by taproots remain stable. This study based on a long-term field experiment provides evidence that soil physical effects of taprooted chicory are persistent even 6 years after cultivation. Moreover, repeated cultivation of taprooted crops probably has cumulative beneficial effects on soil structure
Theoretical search for Chevrel phase based thermoelectric materials
We investigate the thermoelectric properties of some semiconducting Chevrel
phases. Band structure calculations are used to compute thermopowers and to
estimate of the effects of alloying and disorder on carrier mobility. Alloying
on the Mo site with transition metals like Re, Ru or Tc to reach a
semiconducting composition causes large changes in the electronic structure at
the Fermi level. Such alloys are expected to have low carrier mobilities.
Filling with transition metals was also found to be incompatible with high
thermoelectric performance based on the calculated electronic structures.
Filling with Zn, Cu, and especially with Li was found to be favorable. The
calculated electronic structures of these filled Chevrel phases are consistent
with low scattering of carriers by defects associated with the filling. We
expect good mobility and high thermopower in materials with the composition
close to (Li,Cu)MoSe, particularly when Li-rich, and recommend this
system for experimental investigation.Comment: 4 two-column pages, 4 embedded ps figure
Trigonometric parallaxes of ten ultracool subdwarfs
We measured absolute trigonometric parallaxes and proper motions with respect
to many background galaxies for a sample of ten ultracool subdwarfs.
The observations were taken in the H-band with the OMEGA2000 camera at the
3.5m-telescope on Calar Alto, Spain during a time period of 3.5 years. For the
first time, the reduction of the astrometric measurements was carried out
directly with respect to background galaxies. We obtained absolute parallaxes
with mean errors ranging between 1 and 3 mas.
With six completely new parallaxes we more than doubled the number of
benchmark ultracool (>sdM7) subdwarfs. Six stars in the M_{K_s} vs. J-K_s
diagram fit perfectly to model subdwarf sequences from M7 to L4 with [M/H]
between -1.0 and -1.5, whereas 4 are consistent with a moderately low
metallicity ([M/H]=-0.5) from M7 to T6. All but one of our objects have large
tangential velocities between 200 and 320 km/s typical of the Galactic halo
population.
Our results are in good agreement with recent independent measurements for
three of our targets and confirm the previously measured parallax and absolute
magnitude M_{K_s} of the nearest and coolest (T-type) subdwarf 2MASS 0937+29
with higher accuracy.
For all targets, we also obtained infrared J,H,K_s photometry at a level of a
few milli-magnitudes relative to 2MASS standards.Comment: Letter 4 pages 1 figure. accepted by Astronomy and Astrophysic
Predictors of clinically significant postprocedural hypotension after carotid endarterectomy and carotid angioplasty with stenting
ObjectivesSignificant hypotension after carotid endarterectomy (CEA) and carotid angioplasty with stenting (CAS) has been correlated with adverse outcomes. The objective of this study was to determine risk factors that predict hypotension after patients undergo CEA and CAS.MethodsThe review included 1474 CEA patients and 157 CAS patients who underwent procedures from 2002 to 2008. Specific patient characteristics, such as comorbid diseases, degree of carotid stenosis, presence of neurologic symptoms, and preprocedure medications, were assessed. Also reviewed were specific postprocedural clinical outcomes, including hypotension requiring pressors, myocardial infarction, stroke, death, and hospital length of stay.ResultsThe incidence of clinically significant hypotension was 12.6% in CEA patients and 35% in CAS patients (P < .001). Clinically significant hypotension was correlated with increased postprocedural myocardial infarction (2.1% vs 0.5%, P = .022), increased mortality (2.1% vs 0.1%, P < .001), and length of stay >2 days (46.3% vs 27.4%, P = .01). Hypotension was not associated with increased postprocedural strokes (0.8% vs 0.6%, P = .75) or recurrent neurologic symptoms (0.4% vs 0.3%, P = .55). Preoperative nitrate use predicted a greater incidence of postprocedural hypotension (P = .043). A history of tobacco use was correlated with postprocedure hypotension (P = .033). Preprocedural strokes, the use of calcium channel blockers, β-blockers, angiotensin-converting enzyme inhibitors, prior myocardial infarction, degree of preprocedural carotid stenosis, type of stent, previous ipsilateral and contralateral interventions, and female gender did not correlate with postprocedural hypotension (P >.05).ConclusionsPostprocedural hypotension occurs more commonly with CAS than CEA and is associated with increased postprocedural myocardial infarction and length of stay, and death. Nitrates and tobacco use predict a higher incidence of postprocedural hypotension. High-risk patients should be aggressively managed to prevent the increased morbidity and mortality due to postprocedural hypotension
Four nearby L dwarfs
We present spectroscopic, photometric and astrometric observations of four
bright L dwarfs identified in the course of the 2MASS near-infrared survey. Our
spectroscopic data extend to wavelengths shortward of 5000\AA in the L0 dwarf
2MASSJ0746+2000 and the L4 dwarf 2MASSJ0036+1840, allowing the identification
of absorption bands due to MgH and CaOH. The atomic resonance lines Ca I
4227\AA and Na I 5890/5896\AA are extremely strong, with the latter having an
equivalent width of 240\AA in the L4 dwarf. By spectral type L5, the D lines
extend over \AA and absorb a substantial fraction of the flux emitted
in the V band, with a corresponding effect on the (V-I) broadband colour. The
KI resonance doublet at 7665/7699\AA increases in equivalent width from
spectral type M3 to M7, but decreases in strength from M7 to L0 before
broadening substantially at later types. These variations are likely driven by
dust formation in these cool atmospheres.Comment: to appear in AJ, January 2000; 27 pages, including 3 tables and 7
figures embedded in the tex
Epsilon Indi B: a new benchmark T dwarf
We have identified a new early T dwarf only 3.6pc from the Sun, as a common
proper motion companion (separation 1459AU) to the K5V star Epsilon Indi
(HD209100). As such, Epsilon Indi B is one of the highest proper motion sources
outside the solar system (~4.7 arcsec/yr), part of one of the twenty nearest
stellar systems, and the nearest brown dwarf to the Sun. Optical photometry
obtained from the SuperCOSMOS Sky Survey was combined with approximate infrared
photometry from the 2MASS Quicklook survey data release, yielding colours for
the source typical of early T dwarfs. Follow up infrared spectroscopy using the
ESO NTT and SOFI confirmed its spectral type to be T2.5+/-0.5. With Ks=11.2,
Epsilon Indi B is 1.7 magnitudes brighter than any previously known T dwarf and
4 magnitudes brighter than the typical object in its class, making it highly
amenable to detailed study. Also, as a companion to a bright nearby star, it
has a precisely known distance (3.626pc) and relatively well-known age
(0.8-2Gyr), allowing us to estimate its luminosity as logL/Lsun=-4.67, its
effective temperature as 1260K, and its mass as ~40-60Mjup. Epsilon Indi B
represents an important addition to the census of the Solar neighbourhood and,
equally importantly, a new benchmark object in our understanding of substellar
objects.Comment: Accepted by A&A (Letters); 5 pages, 3 figure
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