438 research outputs found
FACT -- the First Cherenkov Telescope using a G-APD Camera for TeV Gamma-ray Astronomy (HEAD 2010)
Geiger-mode Avalanche Photodiodes (G-APD) bear the potential to significantly
improve the sensitivity of Imaging Air Cherenkov Telescopes (IACT). We are
currently building the First G-APD Cherenkov Telescope (FACT) by refurbishing
an old IACT with a mirror area of 9.5 square meters and construct a new, fine
pixelized camera using novel G-APDs. The main goal is to evaluate the
performance of a complete system by observing very high energy gamma-rays from
the Crab Nebula. This is an important field test to check the feasibility of
G-APD-based cameras to replace at some time the PMT-based cameras of planned
future IACTs like AGIS and CTA. In this article, we present the basic design of
such a camera as well as some important details to be taken into account.Comment: Poster shown at HEAD 2010, Big Island, Hawaii, March 1-4, 201
On defining the Hamiltonian beyond quantum theory
Energy is a crucial concept within classical and quantum physics. An
essential tool to quantify energy is the Hamiltonian. Here, we consider how to
define a Hamiltonian in general probabilistic theories, a framework in which
quantum theory is a special case. We list desiderata which the definition
should meet. For 3-dimensional systems, we provide a fully-defined recipe which
satisfies these desiderata. We discuss the higher dimensional case where some
freedom of choice is left remaining. We apply the definition to example toy
theories, and discuss how the quantum notion of time evolution as a phase
between energy eigenstates generalises to other theories.Comment: Authors' accepted manuscript for inclusion in the Foundations of
Physics topical collection on Foundational Aspects of Quantum Informatio
The Outer Disks of Early-Type Galaxies. I. Surface-Brightness Profiles of Barred Galaxies
We present a study of 66 barred, early-type (S0-Sb) disk galaxies, focused on
the disk surface brightness profile outside the bar region and the nature of
Freeman Type I and II profiles, their origins, and their possible relation to
disk truncations. This paper discusses the data and their reduction, outlines
our classification system, and presents -band profiles and classifications
for all galaxies in the sample.
The profiles are derived from a variety of different sources, including the
Sloan Digital Sky Survey (Data Release 5). For about half of the galaxies, we
have profiles derived from more than one telescope; this allows us to check the
stability and repeatability of our profile extraction and classification. The
vast majority of the profiles are reliable down to levels of mu_R ~ 27 mag
arcsec^-2; in exceptional cases, we can trace profiles down to mu_R > 28. We
can typically follow disk profiles out to at least 1.5 times the traditional
optical radius R_25; for some galaxies, we find light extending to ~ 3 R_25.
We classify the profiles into three main groups: Type I (single-exponential),
Type II (down-bending), and Type III (up-bending). The frequencies of these
types are approximately 27%, 42%, and 24%, respectively, plus another 6% which
are combinations of Types II and III. We further classify Type II profiles by
where the break falls in relation to the bar length, and in terms of the
postulated mechanisms for breaks at large radii ("classical trunction" of star
formation versus the influence of the Outer Lindblad Resonance of the bar). We
also classify the Type III profiles by the probable morphology of the outer
light (disk or spheroid). Illustrations are given for all cases. (Abridged)Comment: 41 pages, 26 PDF figures. To appear in the Astronomical Journal.
Version with full-resolution figures available at
http://www.mpe.mpg.de/~erwin/research
FACT -- The G-APD revolution in Cherenkov astronomy
Since two years, the FACT telescope is operating on the Canary Island of La
Palma. Apart from its purpose to serve as a monitoring facility for the
brightest TeV blazars, it was built as a major step to establish solid state
photon counters as detectors in Cherenkov astronomy. The camera of the First
G-APD Cherenkov Telesope comprises 1440 Geiger-mode avalanche photo diodes
(G-APD), equipped with solid light guides to increase the effective light
collection area of each sensor. Since no sense-line is available, a special
challenge is to keep the applied voltage stable although the current drawn by
the G-APD depends on the flux of night-sky background photons significantly
varying with ambient light conditions. Methods have been developed to keep the
temperature and voltage dependent response of the G-APDs stable during
operation. As a cross-check, dark count spectra with high statistics have been
taken under different environmental conditions. In this presentation, the
project, the developed methods and the experience from two years of operation
of the first G-APD based camera in Cherenkov astronomy under changing
environmental conditions will be presented.Comment: Proceedings of the Nuclear Science Symposium and Medical Imaging
Conference (IEEE-NSS/MIC), 201
FACT - The First G-APD Cherenkov Telescope: Status and Results
The First G-APD Cherenkov telescope (FACT) is the first telescope using
silicon photon detectors (G-APD aka. SiPM). It is built on the mount of the
HEGRA CT3 telescope, still located at the Observatorio del Roque de los
Muchachos, and it is successfully in operation since Oct. 2011. The use of
Silicon devices promises a higher photon detection efficiency, more robustness
and higher precision than photo-multiplier tubes. The FACT collaboration is
investigating with which precision these devices can be operated on the
long-term. Currently, the telescope is successfully operated from remote and
robotic operation is under development. During the past months of operation,
the foreseen monitoring program of the brightest known TeV blazars has been
carried out, and first physics results have been obtained including a strong
flare of Mrk501. An instantaneous flare alert system is already in a testing
phase. This presentation will give an overview of the project and summarize its
goals, status and first results
Gewalt in der Schule
Vortrag auf der Tagung Bindung, Trauma und soziale Gewalt , 3.-5.12.2004 in Frankfurt am Main
Comment on opinion paper: Forest management and biodiversity : The role of protected areas is greater than the sum of its number of species
No abstract available
The impact of bars on the mid-infrared dust emission of spiral galaxies: global and circumnuclear properties
We study the mid-infrared properties of a sample of 69 nearby spiral
galaxies, selected to avoid Seyfert activity contributing a significant
fraction of the central energetics, or strong tidal interaction, and to have
normal infrared luminosities. These observations were obtained with ISOCAM,
which provides an angular resolution of the order of 10 arcsec (half-power
diameter of the point spread function) and low-resolution spectro-imaging
information. Between 5 and 18 microns, we mainly observe two dust phases,
aromatic infrared bands and very small grains, both out of thermal equilibrium.
On this sample, we show that the global F15/F7 colors of galaxies are very
uniform, the only increase being found in early-type strongly barred galaxies,
consistent with previous IRAS studies. The F15/F7 excesses are unambiguously
due to galactic central regions where bar-induced starbursts occur. However,
the existence of strongly barred early-type galaxies with normal circumnuclear
colors indicates that the relationship between a distortion of the
gravitational potential and a central starburst is not straightforward. As the
physical processes at work in central regions are in principle identical in
barred and unbarred galaxies, and since this is where the mid-infrared activity
is mainly located, we investigate the mid-infrared circumnuclear properties of
all the galaxies in our sample. We show how surface brightnesses and colors are
related to both the available molecular gas content and the mean age of stellar
populations contributing to dust heating. Therefore, the star formation history
in galactic central regions can be constrained by their position in a
color-surface brightness mid-infrared diagram.Comment: 22 pages, 25 figures, accepted for publication in A&A ; small errors
corrected and references update
Global effects of non-native tree species on multiple ecosystem services
Non-native tree (NNT) species have been transported worldwide to create or enhance services that are fundamental
for human well-being, such as timber provision, erosion control or ornamental value; yet NNTs can also produce
undesired effects, such as fire proneness or pollen allergenicity. Despite the variety of effects that NNTs have on multiple
ecosystem services, a global quantitative assessment of their costs and benefits is still lacking. Such information is critical
for decision-making, management and sustainable exploitation of NNTs. We present here a global assessment of NNT
effects on the three main categories of ecosystem services, including regulating (RES), provisioning (PES) and cultural
services (CES), and on an ecosystem disservice (EDS), i.e. pollen allergenicity. By searching the scientific literature,
country forestry reports, and social media, we compiled a global data set of 1683 case studies from over 125 NNT
species, covering 44 countries, all continents but Antarctica, and seven biomes. Using differentmeta-analysis techniques,
we found that, while NNTs increase most RES (e.g. climate regulation, soil erosion control, fertility and formation),
they decrease PES (e.g. NNTs contribute less than native trees to global timber provision). Also, they have different
effects on CES (e.g. increase aesthetic values but decrease scientific interest), and no effect on the EDS considered.
NNT effects on each ecosystem (dis)service showed a strong context dependency, varying across NNT types, biomes
and socio-economic conditions. For instance, some RES are increased more by NNTs able to fix atmospheric nitrogen,
and when the ecosystem is located in low-latitude biomes; some CES are increased more by NNTs in less-wealthy
countries or in countries with higher gross domestic products. The effects of NNTs on several ecosystem (dis)services
exhibited some synergies (e.g. among soil fertility, soil formation and climate regulation or between aesthetic values
and pollen allergenicity), but also trade-offs (e.g. between fire regulation and soil erosion control). Our analyses provide
a quantitative understanding of the complex synergies, trade-offs and context dependencies involved for the effects of
NNTs that is essential for attaining a sustained provision of ecosystem servicesinfo:eu-repo/semantics/publishedVersio
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