Supersymmetry on Graphs and Networks

We show that graphs, networks and other related discrete model systems carry a natural supersymmetric structure, which, apart from its conceptual importance as to possible physical applications, allows to derive a series of spectral properties for a class of graph operators which typically encode relevant graph characteristics.Comment: 11 pages, Latex, no figures, remark 4.1 added, slight alterations in lemma 5.3, a more detailed discussion at beginning of sect.6 (zero eigenspace

Central stars of planetary nebulae : II. New OB-type and emission-line stars

Context. There are more than 3000 confirmed and probably known Galactic planetary nebulae (PNe), but central star spectroscopic information is available for only 13% of them. Aims. We have undertaken a spectroscopic survey of the central stars in PNe to identify their spectral types. Methods. We performed spectroscopic observations at low resolution with the 2-m telescope at CASLEO, Argentina. Results. We present the spectra of 46 central stars of PNe, most of them are OB-type and emission-line stars.Facultad de Ciencias Astronómicas y GeofísicasInstituto de Astrofísica de La Plat

Central stars of planetary nebulae : II. New OB-type and emission-line stars

Context. There are more than 3000 confirmed and probably known Galactic planetary nebulae (PNe), but central star spectroscopic information is available for only 13% of them. Aims. We have undertaken a spectroscopic survey of the central stars in PNe to identify their spectral types. Methods. We performed spectroscopic observations at low resolution with the 2-m telescope at CASLEO, Argentina. Results. We present the spectra of 46 central stars of PNe, most of them are OB-type and emission-line stars.Facultad de Ciencias Astronómicas y GeofísicasInstituto de Astrofísica de La Plat

Central stars of planetary nebulae: New spectral classifications and catalogue

Context. There are more than 3000 confirmed and probable known Galactic planetary nebulae (PNe), but central star spectroscopic information is available for only 13% of them. Aims. We undertook a spectroscopic survey of central stars of PNe at low resolution and compiled a large list of central stars for which information was dispersed in the literature. Methods. We observed 45 PNs using the 2.15 m telescope at Casleo, Argentina. Results. We present a catalogue of 492 confirmed and probable CSPN and provide a preliminary spectral classification for 45 central star of PNe. This revises previous values of the proportion of CSPN with atmospheres poor in hydrogen in at least 30% of cases and provide statistical information that allows us to infer the origin of H-poor stars.Instituto de Astrofísica de La PlataFacultad de Ciencias Astronómicas y Geofísica

Photometric and spectroscopic variations of the Be star HD 112999

Be objects are stars of B spectral type showing lines of the Balmer series in emission. The presence of these lines is attributed to the existence of an extended envelope, disk type, around them. Some stars are observed in both the Be and normal B-type spectroscopic states and they are known as transient Be stars. In this paper we show the analysis carried out on a new possible transient Be star, labelled HD 112999, using spectroscopic optical observations and photometric data.Comment: 10 pages, 5 figures, accepted for publication in IBV

Stormwater methods and trends for “first flush” treatment in Georgia

With the NPDES Phase II Final Rule taking effect, more municipalities are confronted with the requirement to develop, implement, and enforce a management plan to control post-construction stormwater runoff. The ultimate objective is to reduce pollutant loads and improve water quality. To accomplish this goal, many municipalities have adopted regulations that require all new and redeveloped areas to treat the “first flush” (first 1.2”) of rainfall prior to discharge. The engineer/developer must design a system that accomplishes this goal. Plans must then be approved by the local governing authority. The most common “first flush” treatment method to control post-construction stormwater (within the Metropolitan North Georgia Water Planning District) is Extended Dry Detention Ponds (EDDP). This paper will discuss the use of the EDDP as post-construction stormwater treatment and how it is being applied to new and re-development projects. In addition, the paper will address how the common practice of installing the EDDP online has negative, long term consequences that are only now becoming apparent.Sponsored by: Georgia Environmental Protection Division U.S. Geological Survey, Georgia Water Science Center U.S. Department of Agriculture, Natural Resources Conservation Service Georgia Institute of Technology, Georgia Water Resources Institute The University of Georgia, Water Resources Facult

Slow crack propagation in glass

Slow crack propagation in glass is examined in a variety of environments using the double-torsion technique. The results are interpreted in terms of a limited plasticity fracture criterion and the time dependence of the yield stress

nlGis: A use case in linked historic geodata

While existing Linked Datasets provide detailed representations of Cultural Heritage objects, the locations where the objects originate from is often not accurately represented. Countries, municipalities, and excavation sites are commonly represented by geospatial points, and the fact that countries and municipalities change their geometry over time is not reflected in the data. We present nlGis, a collection of existing geo-historic datasets that are now published as Linked Open Data. The datasets in nlGis contain detailed geographic information about historic regions, with an emphasis on the Netherlands. We describe the creation of this Linked Geodataset and how it can be used to enrich Cultural Heritage data. We also distill several 'lessons learned' that can guide future attempts at publishing detailed Linked Geodata in the Cultural Heritage domain

Improved spectral descriptions of planetary nebulae central stars

Context. At least 492 central stars of Galactic planetary nebulae (CSPNs) have been assigned spectral types. Since many CSPNs are faint, these classification efforts are frequently made at low spectral resolution. However, the stellar Balmer absorption lines are contaminated with nebular emission; therefore in many cases a low-resolution spectrum does not enable the determination of the H abundance in the CSPN photosphere. Whether or not the photosphere is H deficient is arguably the most important fact we should expect to extract from the CSPN spectrum, and should be the basis for an adequate spectral classification system. Aims. Our purpose is to provide accurate spectral classifications and contribute to the knowledge of central stars of planetary nebulae and stellar evolution. Methods. We have obtained and studied higher quality spectra of CSPNs described in the literature as weak emission-line star (WELS). We provide descriptions of 19 CSPN spectra. These stars had been previously classified at low spectral resolution. We used medium-resolution spectra taken with the Gemini Multi-Object Spectrograph (GMOS). We provide spectral types in the Morgan-Keenan (MK) system whenever possible. Results. Twelve stars in our sample appear to have normal H rich photospheric abundances, and five stars remain unclassified. The rest (two) are most probably H deficient. Of all central stars described by other authors as WELS, we find that at least 26% of them are, in fact, H rich O stars, and at least 3% are H deficient. This supports the suggestion that the denomination WELS should not be taken as a spectral type, because, as a WELS is based on low-resolution spectra, it cannot provide enough information about the photospheric H abundance.Facultad de Ciencias Astronómicas y GeofísicasInstituto de Astrofísica de La Plat