921 research outputs found
Plant functional types and elevated CO2: A method of scanning for causes of community alteration
In this paper, a general method for an a posteriori plant functional type (PFT) analysis of global change effects on community composition is developed. We apply the method to a case study, specifically the Giessen-FACE experiment. This experiment involves a Central European meadow that has been exposed to moderate CO2-enrichment since May 1998.The method for an a posteriori PFT-analysis: The method consists of four working steps and uses a combination of standard gradient analysis and Random Forests (RF). (1) The trait composition of the species is studied using Principal Components Analysis. Species trait information is gathered from databases. Natural PFT, i.e. groups of species with similar trait-sets, are identified specifically for the community under study. (2) A ranking of the species according to standardized/absolute CO2 abundance response is obtained from Redundancy Analysis. Initially, species with a response above or below the median are grouped into three response groups (RG) each having similar behaviour, i.e. positive/negative or no-response. (3) The outlyingness measure of RF is used to shift RG boundaries until satisfactory RG homogeneity is achieved. RF is utilized to find the best traits for the RG classification. The behaviour of species representative of the RG is derived from RF class centers. (4) From knowledge gained in steps 1-3, hypotheses about the causes underlying the community alteration are built. Strengths/weaknesses of the method are discussed.Application of the method to the case study: The community consists of three natural PFT. Five species are summer-green forbs of varying competitiveness. Four species are evergreen ruderal forbs characterized as (semi-) basal rosette plants. The third natural PFT contains evergreen, more or less competitive species, mostly grasses, but also a few forbs.Negative standardized CO2-response was practically restricted to two natural PFT, i.e. the summer-greens, irrespective of their competitiveness, and the evergreen ruderals. Standard positive response covered part of the evergreen competitive natural PFT. Among them was Glechoma hederacea, one of the forbs with the greatest similarity to grasses. Two hypotheses were formulated to explain the response pattern: (1) Summer-greens lost in competition with evergreens, because the annual time-integral they can use for enhanced growth was more limited with year-round CO2-enrichment. (2) As rosette plants, ruderal evergreens lagged behind evergreen competitors because periods with full sunlight, which enabled them to gain additional carbon, were shorter for them.Absolute responses were additionally dependent on dominance patterns. The most striking difference to standard responses was the restriction of positive response to (sub-)dominant grasses
Institute of Ion Beam Physics and Materials Research: Annual Report 2001
Summary of the scientific activities of the institute in 2001 including selected highlight reports, short research contributions and an extended statistics overview
Infrared Spectra of Meteoritic SiC Grains
We present here the first infrared spectra of meteoritic SiC grains. The mid-infrared transmission spectra of meteoritic SiC grains isolated from the Murchison meteorite were measured in the wavelength range 2.5--16.5 micron, in order to make available the optical properties of presolar SiC grains. These grains are most likely stellar condensates with an origin predominately in carbon stars. Measurements were performed on two different extractions of presolar SiC from the Murchison meteorite. The two samples show very different spectral appearance due to different grain size distributions. The spectral feature of the smaller meteoritic SiC grains is a relatively broad absorption band found between the longitudinal and transverse lattice vibration modes around 11.3 micron, supporting the current interpretation about the presence of SiC grains in carbon stars. In contrast to this, the spectral feature of the large (> 5 micron) grains has an extinction minimum around 10 micron. The obtained spectra are compared with commercially available SiC grains and the differences are discussed. This comparison shows that the crystal structure (e.g., beta-SiC versus alpha-SiC) of SiC grains plays a minor role on the optical signature of SiC grains compared to e.g. grain size
Precision Calculations for Future Colliders
I discuss the motivations for, and the status of, precision calculations for
the Large Hadron Collider (LHC) and the planned International Linear Collider
(ILC).Comment: latex, uses ws-ijmpe.cls, 19 pages, 9 figures, 1 table, based on a
talk given at the symposium "50 Years of High Energy Physics at UB", to
appear in International Journal of Modern Physics
Internal kinematics of spiral galaxies in distant clusters. Part II. Observations and data analysis
We have conducted an observing campaign with FORS at the ESO-VLT to explore
the kinematical properties of spiral galaxies in distant galaxy clusters. Our
main goal is to analyse transformation- and interaction processes of disk
galaxies within the special environment of clusters as compared to the
hierarchical evolution of galaxies in the field. Spatially resolved MOS-spectra
have been obtained for seven galaxy clusters at 0.3<z<0.6 to measure rotation
velocities of cluster members. For three of the clusters, Cl0303+17, Cl0413-65,
and MS1008-12, for which we presented results including a TF-diagram in Ziegler
et al. 2003, we describe here in detail the observations and data analysis.
Each of them was observed with two setups of the standard FORS MOS-unit.With
typical exposure times of >2 hours we reach an S/N>5 in the emission lines
appropriate for the deduction of the galaxies' internal rotation velocities
from [OII], Hbeta, or [OIII] profiles. Preselection of targets was done on the
basis of available redshifts as well as from photometric and morphological
information gathered from own observations, archive data, and from the
literature. Emphasis was laid on the definition of suitable setups to avoid the
typical restrictions of the standard MOS unit for this kind of observations. In
total we assembled spectra of 116 objects of which 50 turned out to be cluster
members. Position velocity diagrams, finding charts as well as tables with
photometric, spectral, and structural parameters of individual galaxies are
presented.Comment: 18 pages, 6 figures, accepted for publication in Astronomy and
Astrophysics. A version with full resolution figures can be downloaded from
http://www.uni-sw.gwdg.de/~vwgroup/publications.htm
Institute of Ion Beam Physics and Materials Research; Annual Report 2000
Summary of the Scientific Activities of the Institute in 200
The FORS Deep Field: Field selection, photometric observations and photometric catalog
The FORS Deep Field project is a multi-colour, multi-object spectroscopic
investigation of an approx. 7 times 7 region near the south galactic pole based
mostly on observations carried out with the FORS instruments attached to the
VLT telescopes. It includes the QSO Q 0103-260 (z = 3.36). The goal of this
study is to improve our understanding of the formation and evolution of
galaxies in the young Universe. In this paper the field selection, the
photometric observations, and the data reduction are described. The source
detection and photometry of objects in the FORS Deep Field is discussed in
detail. A combined B and I selected UBgRIJKs photometric catalog of 8753
objects in the FDF is presented and its properties are briefly discussed. The
formal 50% completeness limits for point sources, derived from the co-added
images, are 25.64, 27.69, 26.86, 26.68, 26.37, 23.60 and 21.57 in U, B, g, R,
I, J and Ks (Vega-system), respectively. A comparison of the number counts in
the FORS Deep Field to those derived in other deep field surveys shows very
good agreement.Comment: 15 pages, 11 figures (included), accepted for publication in A&
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