1,787 research outputs found
Low redshift AGN in the Hamburg/ESO Survey: II. The active black hole mass function and the distribution function of Eddington ratios
We estimated black hole masses and Eddington ratios for a well defined sample
of local (z<0.3) broad line AGN from the Hamburg/ESO Survey (HES), based on the
Hbeta line and standard recipes assuming virial equilibrium for the broad line
region. The sample represents the low-redshift AGN population over a wide range
of luminosities, from Seyfert 1 galaxies to luminous quasars. From the
distribution of black hole masses we derived the active black hole mass
function (BHMF) and the Eddington ratio distribution function (ERDF) in the
local universe, exploiting the fact that the HES has a well-defined selection
function. While the directly determined ERDF turns over around L/L_Edd ~ 0.1,
similar to what has been seen in previous analyses, we argue that this is an
artefact of the sample selection. We employed a maximum likelihood approach to
estimate the intrinsic distribution functions of black hole masses and
Eddington ratios simultaneously in an unbiased way, taking the sample selection
function fully into account. The resulting ERDF is well described by a
Schechter function, with evidence for a steady increase towards lower Eddington
ratios, qualitatively similar to what has been found for type~2 AGN from the
SDSS. Comparing our best-fit active BHMF with the mass function of inactive
black holes we obtained an estimate of the fraction of active black holes, i.e.
an estimate of the AGN duty cycle. The active fraction decreases strongly with
increasing black hole mass. A comparison with the BHMF at higher redshifts also
indicates that, at the high mass end, black holes are now in a less active
stage than at earlier cosmic epochs. Our results support the notion of
anti-hierarchical growth of black holes, and are consistent with a picture
where the most massive black holes grew at early cosmic times, whereas at
present mainly smaller mass black holes accrete at a significant rate.Comment: 19 pages, 15 figures, accepted for publication in A&
Accounting for selection effects in the BH-bulge relations: No evidence for cosmological evolution
The redshift evolution of the black hole - bulge relations is an essential
observational constraint for models of black hole - galaxy coevolution. In
addition to the observational challenges for these studies, conclusions are
complicated by the influence of selection effects. We demonstrate that there is
presently no statistical significant evidence for cosmological evolution in the
black hole-bulge relations, once these selection effects are taken into account
and corrected for. We present a fitting method, based on the bivariate
distribution of black hole mass and galaxy property, that accounts for the
selection function in the fitting and is therefore able to recover the
intrinsic black hole - bulge relation unbiased. While prior knowledge is
restricted to a minimum, we at least require knowledge of either the sample
selection function and the mass dependence of the active fraction, or the
spheroid distribution function and the intrinsic scatter in the black hole -
bulge relation. We employed our fitting routine to existing studies of the
black hole-bulge relation at z~1.5 and z~6, using our current best knowledge of
the distribution functions. There is no statistical significant evidence for
positive evolution in the MBH-M* ratio out to z~2. At z~6 the current
constraints are less strong, but we demonstrate that the large observed
apparent offset from the local black hole-bulge relation at z~6 is fully
consistent with no intrinsic offset. The method outlined here provides a tool
to obtain more reliable constraints on black hole - galaxy co-evolution in the
future.Comment: 13 pages, 8 figures, published in MNRA
Randomized crossover comparison of proportional assist ventilation and patient-triggered ventilation in extremely low birth weight infants with evolving chronic lung disease
Background: Refinement of ventilatory techniques remains a challenge given the persistence of chronic lung disease of preterm infants. Objective: To test the hypothesis that proportional assist ventilation ( PAV) will allow to lower the ventilator pressure at equivalent fractions of inspiratory oxygen (FiO(2)) and arterial hemoglobin oxygen saturation in ventilator-dependent extremely low birth weight infants in comparison with standard patient-triggered ventilation ( PTV). Methods: Design: Randomized crossover design. Setting: Two level-3 university perinatal centers. Patients: 22 infants ( mean (SD): birth weight, 705 g ( 215); gestational age, 25.6 weeks ( 2.0); age at study, 22.9 days ( 15.6)). Interventions: One 4- hour period of PAV was applied on each of 2 consecutive days and compared with epochs of standard PTV. Results: Mean airway pressure was 5.64 ( SD, 0.81) cm H2O during PAV and 6.59 ( SD, 1.26) cm H2O during PTV ( p < 0.0001), the mean peak inspiratory pressure was 10.3 ( SD, 2.48) cm H2O and 15.1 ( SD, 3.64) cm H2O ( p < 0.001), respectively. The FiO(2) ( 0.34 (0.13) vs. 0.34 ( 0.14)) and pulse oximetry readings were not significantly different. The incidence of arterial oxygen desaturations was not different ( 3.48 ( 3.2) vs. 3.34 ( 3.0) episodes/ h) but desaturations lasted longer during PAV ( 2.60 ( 2.8) vs. 1.85 ( 2.2) min of desaturation/ h, p = 0.049). PaCO2 measured transcutaneously in a subgroup of 12 infants was similar. One infant met prespecified PAV failure criteria. No adverse events occurred during the 164 cumulative hours of PAV application. Conclusions: PAV safely maintains gas exchange at lower mean airway pressures compared with PTV without adverse effects in this population. Backup conventional ventilation breaths must be provided to prevent apnea-related desaturations. Copyright (c) 2007 S. Karger AG, Base
Cortical Mirror-System Activation During Real-Life Game Playing: An Intracranial Electroencephalography (EEG) Study
Analogous to the mirror neuron system repeatedly described in monkeys as a
possible substrate for imitation learning and/or action understanding, a
neuronal execution/observation matching system (OEMS) is assumed in humans, but
little is known to what extent this system is activated in non-experimental,
real-life conditions. In the present case study, we investigated brain activity
of this system during natural, non-experimental motor behavior as it occurred
during playing of the board game "Malefiz". We compared spectral modulations of
the high-gamma band related to ipsilateral reaching movement execution and
observation of the same kind of movement using electrocorticography (ECoG) in
one participant. Spatially coincident activity during both conditions execution
and observation was recorded at electrode contacts over the premotor/primary
motor cortex. The topography and amplitude of the high-gamma modulations
related to both, movement observation and execution were clearly spatially
correlated over several fronto-parietal brain areas. Thus, our findings
indicate that a network of cortical areas contributes to the human OEMS, beyond
primary/premotor cortex including Brocas area and the temporo-parieto-occipital
junction area, in real-life conditions.Comment: 4 pages, 2 figure, CCN 2018 conference pape
Primary stability of cementless threaded acetabular cups at first implantation and in the case of revision regarding micromotions as indicators
The primary stability of cementless total hip endoprosthesis is of vital importance for proximate, long-term osteointegration. The extent of micromotions between implant and acetabulum is an indicator of primary stability. Based on this hypothesis, different cementless hip joint endoprosthesis were studied with regard to their micromotions. The primary stability of nine different cementless threaded acetabular cups was studied in an experimental setup with blocks of rigid foam. The micromotions between implant and implant bearing were therefore evaluated under cyclic, sinusoidal exposure. The blocks of polymer foam were prepared according to the Paprosky defect classifications. The micromotions increased with the increasing degree of the defect with all acetabuli tested. Occasionally coefficients of over 200 mu m were measured. From a defect degree of 3b according to Paprosky, the implants could no longer be appropriately placed. The exterior form of the spherical implants tended to exhibit better coefficients than the conical/parabolic implants
Gear skiving with minimum twist errors – Modeling and optimization of flank twist in gear skiving [Verschränkungsarmes Wälzschälen – Modellierung und Optimierung der Verschränkung beim Wälzschälen]
Over the last 15 years, gear skiving has established itself as a highly productive gear cutting process for the production of internal gears and gears with near interference contours. As with all processes with crossed axes, gear skiving generally results in a pronounced natural twist when gears with lead crowning or other flank modifications are produced. In practical applications, the unintended profile angle changes over the tooth width resulting from the twist leading to unwanted contact patterns and unfavorable NVH behavior. In this work, a contact line-based method for tool profile calculation for gear skiving is developed based on conical-screw gear theory. The relationship between contact line and natural twist errors is worked out. The process and tool design strategies for minimizing the twist are elaborated and finally, an adaptive process kinematics for low-twist error gear skiving is presented
Regulierung der Strom- und Gasmärkte aus wettbewerbstheoretischer Sicht
Der deutsche Sonderweg, die Liberalisierung der leitungsgebundenen Energieversorgung ohne staatliche Regulierung des Netzzugangs zu beschreiten, ist in Wissenschaft und Praxis umstritten. In jüngster Zeit mehren sich die Rufe nach Regulierer und einer Netzzugangsverordnung, die mehr Wettbewerb auf den seit 1998 geöffneten Strom- und Gasmärkten durchsetzen sollen. Wäre dies wirklich die überlegene Lösung für Netzzugangsprobleme ? --
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