3,121 research outputs found
Search for Supergalactic Anisotropies in the 3B Catalog
The angular distribution of GRBs is isotropic, while the brightness
distribution of bursts shows a reduced number of faint events. These
observations favor a cosmological burst origin. If GRBs are indeed at
cosmological distances and if they trace luminous matter, we must eventually
find an anisotropic distribution of bright bursts. If a significant number of
bursts originate at redshifts less than z~1, the concentration of nearby
galaxies towards the supergalactic plane is pronounced enough that we could
discover the corresponding clustering of burst locations. We used the 3B
catalog to search for a pattern visible in supergalactic coordinates. No
compelling evidence for anisotropies was found. The absence of anisotropies in
SG coordinates implies a minimum sampling distance of 200h^-1 Mpc.Comment: 5 pages, uuencoded postscript, to appear in the Proceedings of the
Huntsville Conference on Gamma Ray Burst
Development of innovative solutions for displacement variation in hydrostatic machines
Along with the general requirement of continuously increasing efficiency of hydrostatic drivetrains, variable displacement machines are of major concern in research and development. To this effect, the whole machine performance is mainly dependent of the displacement variation system (DVS) performance. A lot of work to this topic focusses on the controller and actuator level. The aim of this paper is to offer a more fundamental view on DVS by giving a focus to the basic hydro-mechanical principles
Lexical Culture
The paper focuses on the mutual relations between linguistics and lexicographAgainst the background of etymology and comparative-historical linguistic studies and using the words 'lexical' and 'culture' as examples, an attempt is made to demonstrate the relevance of morphology, grammar and semantics to the description of vocabulary and its lexicographic codification. Issues of intra lingual variety and interlingual diversity can now also be addressed Within the theoretical framework of contrastive textology, supported by computer-aided parallel text corpus analysis. However, lexicography is not entirely dependent on the results of linguistic research; it needs to move on and develop its own theoretical base. Recent progress in four fields of dictionary research has indeed contributed to an international upsurge of 'lexical culture'
General lexicography in Europe
On the basis of several surveys of experts, centres and projects in lexicography, and against the author's own experience of metalexicography, the paper traces the recent progress of academic lexicography, especially in Europe. Particular attention is paid to 'dictionary research' in four of its divisions. One special concern is the professionalisation of the discipline in terms of conferences, publications and training initiatives.Keywords:Â dictionary research, europe, lexicography, surve
On the nature of the Herbig B[e] star binary system V921 Scorpii: Geometry and kinematics of the circumprimary disk on sub-AU scales
V921 Scorpii is a close binary system (separation 0.025") showing the
B[e]-phenomenon. The system is surrounded by an enigmatic bipolar nebula, which
might have been shaped by episodic mass-loss events, possibly triggered by
dynamical interactions between the companion and the circumprimary disk (Kraus
et al. 2012a). In this paper, we investigate the spatial structure and
kinematics of the circumprimary disk, with the aim to obtain new insights into
the still strongly debated evolutionary stage. For this purpose, we combine,
for the first time, infrared spectro-interferometry (VLTI/AMBER, R=12,000) and
spectro-astrometry (VLT/CRIRES, R=100,000), which allows us to study the
AU-scale distribution of circumstellar gas and dust with an unprecedented
velocity resolution of 3 km*s^-1. Using a model-independent photocenter
analysis technique, we find that the Br-gamma-line emission rotates in the same
plane as the dust disk. We can reproduce the wavelength-differential
visibilities and phases and the double-peaked line profile using a
Keplerian-rotating disk model. The derived mass of the central star is
5.4+/-0.4 M_sun*(d/1150 pc), which is considerably lower than expected from the
spectral classification, suggesting that V921 Sco might be more distant (d
approx 2kpc) than commonly assumed. Using the geometric information provided by
our Br-gamma spectro-interferometric data and Paschen, Brackett, and Pfund line
decrement measurements in 61 hydrogen recombination line transitions, we derive
the density of the line-emitting gas (N_e=2...6*10^19 m^-3). Given that our
measurements can be reproduced with a Keplerian velocity field without
outflowing velocity component and the non-detection of age-indicating
spectroscopic diagnostics, our study provides new evidence for the
pre-main-sequence nature of V921 Sco.Comment: 17 pages, 11 figures, 3 tables, accepted by Ap
A modeling-based evaluation of isothermal rebreathing for breath gas analyses of highly soluble volatile organic compounds
Isothermal rebreathing has been proposed as an experimental technique for
estimating the alveolar levels of hydrophilic volatile organic compounds (VOCs)
in exhaled breath. Using the prototypic test compound acetone we demonstrate
that the end-tidal breath profiles of such substances during isothermal
rebreathing show characteristics that contradict the conventional pulmonary
inert gas elimination theory due to Farhi. On the other hand, these profiles
can reliably be captured by virtue of a previously developed mathematical model
for the general exhalation kinetics of highly soluble, blood-borne VOCs, which
explicitly takes into account airway gas exchange as major determinant of the
observable breath output.
This model allows for a mechanistic analysis of various rebreathing protocols
suggested in the literature. In particular, it clarifies the discrepancies
between in vitro and in vivo blood-breath ratios of hydrophilic VOCs and yields
further quantitative insights into the physiological components of isothermal
rebreathing.Comment: 21 page
Physiological modeling of isoprene dynamics in exhaled breath
Human breath contains a myriad of endogenous volatile organic compounds
(VOCs) which are reflective of ongoing metabolic or physiological processes.
While research into the diagnostic potential and general medical relevance of
these trace gases is conducted on a considerable scale, little focus has been
given so far to a sound analysis of the quantitative relationships between
breath levels and the underlying systemic concentrations. This paper is devoted
to a thorough modeling study of the end-tidal breath dynamics associated with
isoprene, which serves as a paradigmatic example for the class of low-soluble,
blood-borne VOCs.
Real-time measurements of exhaled breath under an ergometer challenge reveal
characteristic changes of isoprene output in response to variations in
ventilation and perfusion. Here, a valid compartmental description of these
profiles is developed. By comparison with experimental data it is inferred that
the major part of breath isoprene variability during exercise conditions can be
attributed to an increased fractional perfusion of potential storage and
production sites, leading to higher levels of mixed venous blood concentrations
at the onset of physical activity. In this context, various lines of supportive
evidence for an extrahepatic tissue source of isoprene are presented.
Our model is a first step towards new guidelines for the breath gas analysis
of isoprene and is expected to aid further investigations regarding the
exhalation, storage, transport and biotransformation processes associated with
this important compound.Comment: 14 page
Efficient and high performing hydraulic systems in mobile machines
Hydraulic systems represent a crucial part of the drivetrain of mobile machines. The most important drivers of current developments, increasing energy efficiency and productivity, are leading to certain trends in technology. On a subsystem level, working hydraulics are utilizing effects by improving control functions and by maximum usage of energy recovery potential. Independent metering and displacement control, partly in combination with hybrid concepts, are the dominating approaches. Traction drives gain advantage from optimized power split transmissions, which consequently are being used in a growing number of applications. On the level of components, increase of efficiency and dynamics as well as power density are important trends. Altogether, design of systems and components is more and more based on modular concepts. In this sense, among others, sensors and control elements are being integrated to actuators; electric and hydraulic technology is being merged. In order to achieve maximum efficiency and performance of the entire machine, control of hydraulics has to include the whole drivetrain and the entire mobile machine in its application. In modern words, mobile hydraulic systems are a part of cyber physical systems
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