Automated Reconstruction of Particle Cascades in High Energy Physics Experiments

We present a procedure for reconstructing particle cascades from event data measured in a high energy physics experiment. For evaluating the hypothesis of a specific physics process causing the observed data, all possible reconstruction versions of the scattering process are constructed from the final state objects. We describe the procedure as well as examples of physics processes of different complexity studied at hadron-hadron colliders. We estimate the performance by 20 microseconds per reconstructed decay vertex, and 0.6 kByte per reconstructed particle in the decay trees.Comment: 8 pages, 2 figures. Submitted to Computational Science & Discover

Recurrent shell infall events in a B0.5e star: HD 58978 1979-1988

Infall from the circumstellar envelope onto the bright B0.5 IVe star, HD 58978 was studied. The IUE data indicate that the star was surrounded by a low and moderately ionized circumstellar shell at least 12 times between 1979 and 1988. During 6 of these episodes, the signatures of cool circumstellar material were redshifted with respect to the photosphere by 20 to 80 km/sec. The data indicate that the transition from infall to minimal shell absorption can occur in under 10 days, and are consistent either with infall phases lasting up to 6 months, or with infall episodes shorter than 10 to 15 days. The long term behavior of the shell episodes is compared with variability in the stellar wind

Marine ecosystem services: Linking indicators to their classification

© 2014 Elsevier Ltd. All rights reserved. There is a multitude of ecosystem service classifications available within the literature, each with its own advantages and drawbacks. Elements of them have been used to tailor a generic ecosystem service classification for the marine environment and then for a case study site within the North Sea: the Dogger Bank. Indicators for each of the ecosystem services, deemed relevant to the case study site, were identified. Each indicator was then assessed against a set of agreed criteria to ensure its relevance and applicability to environmental management. This paper identifies the need to distinguish between indicators of ecosystem services that are entirely ecological in nature (and largely reveal the potential of an ecosystem to provide ecosystem services), indicators for the ecological processes contributing to the delivery of these services, and indicators of benefits that reveal the realized human use or enjoyment of an ecosystem service. It highlights some of the difficulties faced in selecting meaningful indicators, such as problems of specificity, spatial disconnect and the considerable uncertainty about marine species, habitats and the processes, functions and services they contribute to

Choice of tip, signal stability, and practical aspects of piezoresponse-force-microscopy

Piezoresponse force-microscopy (PFM) has become the standard tool to investigate ferroelectrics on the micro- and nanoscale. However, reliability of PFM signals is often problematic and their quantification is challenging and thus not widely applied. Here, we present a study of the reproducibility of PFM signals and of the so-called PFM background signal which has been reported in the literature. We find that PFM signals are generally reproducible to certain extents. The PFM signal difference between 180°domains on periodically poled lithium niobate (PPLN) is taken as the reference signal in a large number of measurements, carried out in a low frequency regime (30-70 kHz). We show that in comparison to Pt coated tips, diamond coated tips exhibit improved signal stability, lower background signal, and less imaging artifacts related to PFM which is reflected in the spread of measurements. This is attributed to the improved mechanical stability of the conductive layer. The average deviation of the mean PFM signal is 38.3%, for a diamond coated tip. Although this deviation is relatively high, it is far better than values from the literature which showed a deviation of approx. 73.1%. Additionally, we find that the average deviation of the background signal from 0 is 11.6% of the PPLN domain contrast. Thus, the background signal needs to be taken into account when quantifying PFM signals and should be subtracted from PFM signals. Those results are important for quantification of PFM signals, since PPLN might be used for this purpose when PFM signals measured on PPLN are related to its macroscopic d33 coefficient. Finally, the crucial influence of sample polishing on PFM signals is shown and we recommend to use a multistep polishing route with a final step involving 200 nm sized colloidal silica particles

Calculation of the average Green's function of electrons in a stochastic medium via higher-dimensional bosonization

The disorder averaged single-particle Green's function of electrons subject to a time-dependent random potential with long-range spatial correlations is calculated by means of bosonization in arbitrary dimensions. For static disorder our method is equivalent with conventional perturbation theory based on the lowest order Born approximation. For dynamic disorder, however, we obtain a new non-perturbative expression for the average Green's function. Bosonization also provides a solid microscopic basis for the description of the quantum dynamics of an interacting many-body system via an effective stochastic model with Gaussian probability distribution.Comment: RevTex, no figure

Search for the magnetic field of the O7.5 III star xi Persei

Cyclical wind variability is an ubiquitous but as yet unexplained feature among OB stars. The O7.5 III(n)((f)) star xi Persei is the brightest representative of this class on the Northern hemisphere. As its prominent cyclical wind properties vary on a rotational time scale (2 or 4 days) the star has been already for a long time a serious magnetic candidate. As the cause of this enigmatic behavior non-radial pulsations and/or a surface magnetic field are suggested. We present a preliminary report on our attempts to detect a magnetic field in this star with high-resolution measurements obtained with the spectropolarimeter Narval at TBL, France during 2 observing runs of 5 nights in 2006 and 5 nights in 2007. Only upper limits could be obtained, even with the longest possible exposure times. If the star hosts a magnetic field, its surface strength should be less than about 300 G. This would still be enough to disturb the stellar wind significantly. From our new data it seems that the amplitude of the known non-radial pulsations has changed within less than a year, which needs further investigation.Comment: 2 pages, 6 figures, contributed poster at IAU Symposium 259 "Cosmic Magnetic Fields: from Planets, to Stars and Galaxies", Tenerife, Spain, November 3-7, 200

Investigating the origin of cyclical wind variability in hot, massive stars - I. On the dipolar magnetic field hypothesis

OB stars exhibit various types of spectral variability associated with wind structures, including the apparently ubiquitous discrete absorption components (DACs). These are proposed to be caused by either magnetic fields or non-radial pulsations (NRPs). In this paper, we evaluate the possible relation between large-scale, dipolar magnetic fields and the DAC phenomenon by investigating the magnetic properties of a sample of 13 OB stars exhibiting well-documented DAC behaviour. Using high-precision spectropolarimetric data acquired in part in the context of the Magnetism in Massive Stars (MiMeS) project, we find no evidence for surface dipolar magnetic fields in any of these stars. Using Bayesian inference, we compute upper limits on the strengths of the fields and use these limits to assess two potential mechanisms by which the field may influence wind outflow: magnetic wind confinement and local photospheric brightness enhancements. Within the limits we derive, both mechanisms fail to provide a systematic process capable of producing DACs in all of the stars of our sample. Therefore, this implies that dipolar fields are highly unlikely to be responsible for these structures in all massive stars, meaning that some other mechanism must come into play.Comment: 17 pages, 6 figures, accepted for publication in MNRA