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)$_4$Mo$_6$Se$_8$, particularly when Li-rich, and recommend this system for experimental investigation.Comment: 4 two-column pages, 4 embedded ps figure

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 $\sim1000$\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

A new strongly X-ray flaring M9 dwarf in the solar neighborhood

We report on the discovery of a very low mass (VLM) star in the solar neighborhood, originally identified as an optical counterpart of a flaring X-ray source detected in the ROSAT All-Sky survey. Optical spectroscopy and infrared photometry consistently reveal a spectral type of M9 \pm 0.5 and a distance of ~11 pm 2pc. The optical counterpart of 1RXS J115928.5-524717 shows a large proper motion of 1.08\pm0.06 "/year. 1RXS~J115928.5-524717 is the fourth object among the VLM stars displaying a huge X-ray flare, reaching the unprecedent value of L_X/L_{bol}~0.1.Comment: 8 pages, 5 figures. A&A, accepte

Epsilon Indi Ba/Bb: the nearest binary brown dwarf

We have carried out high angular resolution near-infrared imaging and low-resolution (R~1000) spectroscopy of the nearest known brown dwarf, Eps Indi B, using the ESO VLT NAOS/CONICA adaptive optics system. We find it to be a close binary (as also noted by Volk et al. 2003) with an angular separation of 0.732 arcsec, corresponding to 2.65AU at the 3.626pc distance of the Eps Indi system. In our discovery paper (Scholz et al. 2003), we concluded that Eps Indi B was a ~50Mjup T2.5 dwarf: our revised finding is that the two system components (Eps Indi Ba and Eps Indi Bb) have spectral types of T1 and T6, respectively, and estimated masses of 47 and 28Mjup, respectively, assuming an age of 1.3Gyr. Errors in the masses are +/-10 and +/-7Mjup, respectively, dominated by the uncertainty in the age determination (0.8-2Gyr range). This uniquely well-characterised T dwarf binary system should prove important in the study of low-mass, cool brown dwarfs. The two components are bright and relatively well-resolved: Eps Indi B is the only T dwarf binary in which spectra have been obtained for both components. They have a well-established distance and age. Finally, their orbital motion can be measured on a fairly short timescale (nominal orbital period 15 yrs), permitting an accurate determination of the true total system mass, helping to calibrate brown dwarf evolutionary models.Comment: Accepted for publication by Astronomy & Astrophysics main journal. This replacement version includes minor changes made following comments by the referee, along with a reworking of the photometric data and derived quantities using 2MASS catalogue photometry as the basis, with only a minor impact on the final result

L Dwarfs and the Substellar Mass Function

Analysis of initial observations from near-infrared sky surveys has shown that the resulting photometric catalogues, combined with far-red optical data, provide an extremely effective method of finding isolated, very low-temperature objects in the general field. Follow-up observations have already identified more than 25 sources with temperatures cooler than the latest M dwarfs. A comparison with detailed model predictions (Burrows & Sharp) indicates that these L dwarfs have effective temperatures between ~2000\pm100 K and 1500\pm100 K, while the available trigonometric parallax data place their luminosities at between 10^{-3.5} and 10^{-4.3} L_solar. Those properties, together with the detection of lithium in one-third of the objects, are consistent with the majority having substellar masses. The mass function cannot be derived directly, since only near-infrared photometry and spectral types are available for most sources, but we can incorporate VLM/brown dwarf models in simulations of the Solar Neighbourhood population and constrain Psi(M) by comparing the predicted L-dwarf surface densities and temperature distributions against observations from the DENIS and 2MASS surveys. The data, although sparse, can be represented by a power-law mass function, Psi(M) ~ M^{-alpha}, with 1 < alpha < 2. Current results favour a value nearer the lower limit. If alpha = 1.3, then the local space density of 0.075 > M/M_solar > 0.01 brown dwarfs is 0.10 systems pc^{-3}. In that case brown dwarfs are twice as common as main-sequence stars, but contribute no more than ~15% of the total mass of the disk.Comment: To appear in Astrophysical Journal (20 August 1999). 44 Pages. For related preprints, see http://www.ipac.caltech.edu/2mass/overview/ldwarfs.htm