657 research outputs found
Dynamical friction and the evolution of satellites in virialized halos: the theory of linear response
The evolution of a small satellite inside a more massive truncated isothermal
spherical halo is studied using both the Theory of Linear Response for
dynamical friction and N-Body simulations. The analytical approach includes the
effects of the gravitational wake, of the tidal deformation and the shift of
the barycenter of the primary, so unifying the local versus global
interpretation of dynamical friction. Sizes, masses, orbital energies and
eccentricities are chosen as expected in hierarchical clustering models. We
find that in general the drag force in self-gravitating backgrounds is weaker
than in uniform media and that the orbital decay is not accompanied by a
significant circularization. We also show that the dynamical friction time
scale is weakly dependent on the initial circularity. We provide a fitting
formula for the decay time that includes the effect of mass and angular
momentum loss. Live satellites with dense cores can survive disruption up to an
Hubble time within the primary, notwithstanding the initial choice of orbital
parameters. Dwarf spheroidal satellites of the Milky Way, like Sagittarius A
and Fornax, have already suffered mass stripping and, with their present
masses, the sinking times exceed 10 Gyr even if they are on very eccentric
orbits.Comment: 27 pages including 9 figures. Accepted for publication in the
Astrophysical Journal. Part 2, issue November 10 1999, Volume 52
HARDROC, Readout chip of the Digital Hadronic Calorimeter of ILC
HARDROC (HAdronic Rpc Detector ReadOut Chip) [1] is the very front end chip designed for the readout of the RPC or Micromegas foreseen for the Digital HAdronic CALorimeter (DHCAL) of the future International Linear Collider. The very fine granularity of the ILC hadronic calorimeters (1cm2 pads) implies a huge number of electronics channels (4 105 /m3) which is a new feature of “imaging” calorimetry. Moreover, for compactness, the chips must be embedded inside the detector making crucial the reduction of the power consumption to 10 μW per channel. This is achieved using power pulsing, made possible by the ILC bunch pattern (1 ms of data acquisition for 199 ms of dead time). HARDROC readout is a semi-digital readout with three thresholds which allows both good tracking and coarse energy measurement, and also integrates on chip data storage. The overall performance of HARDROC will be described with detailed measurements of all the characteristics. Hundreds of chips have indeed been produced and tested before being mounted on printed boards developed for the readout of large scale (1m2) RPC and Micromegas prototypes. These prototypes have been tested with cosmics and also in testbeam at CERN in 2008 and 2009 to evaluate the performance of different kinds of GRPCs and to validate the semi-digital electronics readout system in beam conditions
OMEGAPIX: 3D integrated circuit prototype dedicated to the ATLAS upgrade Super LHC pixel project
In late 2008, an international consortium for development of vertically integrated (3D) readout electronics was created to explore features available from this technology. In this paper, the OMEGAPIX circuit is presented. It is the first front-end ASIC prototype designed at LAL in 3D technology. It has been submitted on May 2009. At first, a short reminder of 3D technology is presented. Then the IC design is explained: analogue tier, digital tier and testability
MAROC: Multi-Anode ReadOut Chip for MaPMTs
International audienceFor the ATLAS luminometer, made of Roman pots, a complete readout ASIC has been designed in 0.35 SiGe technology. It is used to readout 64 channels multi anode photomultipliers and supplies 64 trigger outputs and a multiplexed charge. Since its delivery in November 2005, the MAROC chip has been tested at LAL. Despite a substrate coupling effect which affects the performance when all channels are used in high gain, the chip has shown nice global behavior and it has been used during beam tests at CERN in October 2006
Performance of Glass Resistive Plate Chambers for a high granularity semi-digital calorimeter
A new design of highly granular hadronic calorimeter using Glass Resistive
Plate Chambers (GRPCs) with embedded electronics has been proposed for the
future International Linear Collider (ILC) experiments. It features a 2-bit
threshold semi-digital read-out. Several GRPC prototypes with their electronics
have been successfully built and tested in pion beams. The design of these
detectors is presented along with the test results on efficiency, pad
multiplicity, stability and reproducibility.Comment: 16 pages, 15 figure
Construction and commissioning of a technological prototype of a high-granularity semi-digital hadronic calorimeter
A large prototype of 1.3m3 was designed and built as a demonstrator of the
semi-digital hadronic calorimeter (SDHCAL) concept proposed for the future ILC
experiments. The prototype is a sampling hadronic calorimeter of 48 units. Each
unit is built of an active layer made of 1m2 Glass Resistive Plate
Chamber(GRPC) detector placed inside a cassette whose walls are made of
stainless steel. The cassette contains also the electronics used to read out
the GRPC detector. The lateral granularity of the active layer is provided by
the electronics pick-up pads of 1cm2 each. The cassettes are inserted into a
self-supporting mechanical structure built also of stainless steel plates
which, with the cassettes walls, play the role of the absorber. The prototype
was designed to be very compact and important efforts were made to minimize the
number of services cables to optimize the efficiency of the Particle Flow
Algorithm techniques to be used in the future ILC experiments. The different
components of the SDHCAL prototype were studied individually and strict
criteria were applied for the final selection of these components. Basic
calibration procedures were performed after the prototype assembling. The
prototype is the first of a series of new-generation detectors equipped with a
power-pulsing mode intended to reduce the power consumption of this highly
granular detector. A dedicated acquisition system was developed to deal with
the output of more than 440000 electronics channels in both trigger and
triggerless modes. After its completion in 2011, the prototype was commissioned
using cosmic rays and particles beams at CERN.Comment: 49 pages, 41 figure
Hadron beam test of a scintillating fibre tracker system for elastic scattering and luminosity measurement in ATLAS
A scintillating fibre tracker is proposed to measure elastic proton
scattering at very small angles in the ATLAS experiment at CERN. The tracker
will be located in so-called Roman Pot units at a distance of 240 m on each
side of the ATLAS interaction point. An initial validation of the design
choices was achieved in a beam test at DESY in a relatively low energy electron
beam and using slow off-the-shelf electronics. Here we report on the results
from a second beam test experiment carried out at CERN, where new detector
prototypes were tested in a high energy hadron beam, using the first version of
the custom designed front-end electronics. The results show an adequate
tracking performance under conditions which are similar to the situation at the
LHC. In addition, the alignment method using so-called overlap detectors was
studied and shown to have the expected precision.Comment: 12 pages, 8 figures. Submitted to Journal of Instrumentation (JINST
Mapping and assessment of ecosystems and their services. Urban ecosystems
Action 5 of the EU Biodiversity Strategy to 2020 requires member states to Map and Assess the state of Ecosystems and their Services (MAES). This report provides guidance for mapping and assessment
of urban ecosystems. The MAES urban pilot is a collaboration between the European Commission, the European Environment Agency, volunteering Member States and cities, and stakeholders. Its ultimate
goal is to deliver a knowledge base for policy and management of urban ecosystems by analysing urban green infrastructure, condition of urban ecosystems and ecosystem services. This report presents guidance for mapping urban ecosystems and includes an indicator framework to assess the condition of urban ecosystems and urban ecosystem services. The scientific framework of mapping and assessment is designed to support in particular urban planning policy and policy on green infrastructure at urban, metropolitan and regional scales. The results are based on the following different sources of information: a literature survey of 54 scientific articles, an online-survey (on urban ecosystems, related policies and planning instruments and with participation of 42 cities), ten case studies (Portugal: Cascais, Oeiras, Lisbon; Italy: Padua, Trento, Rome; The Netherlands: Utrecht; Poland: Poznań; Spain: Barcelona; Norway: Oslo), and a two-day expert workshop. The case studies constituted the core of the MAES urban pilot. They provided real examples and applications of how mapping and assessment can be organized to support policy; on top, they provided the necessary expertise to select a set of final indicators for condition and ecosystem services. Urban ecosystems or cities are defined here as socio-ecological systems which are composed of green infrastructure and built infrastructure. Urban green infrastructure (GI) is understood in this report as the multi-functional network of urban green spaces situated within the boundary of the urban ecosystem. Urban green spaces are the structural components of urban GI.
This study has shown that there is a large scope for urban ecosystem assessments. Firstly, urban policies increasingly use urban green infrastructure and nature-based solutions in their planning process. Secondly, an increasing amount of data at multiple spatial scales is becoming available to support these policies, to provide a baseline, and to compare or benchmark cities with respect to the extent and management of the urban ecosystem. Concrete examples are given on how to delineate urban ecosystems, how to choose an appropriate spatial scale, and how to map urban ecosystems based on a combination of national or European datasets (including Urban Atlas) and locally collected information (e.g., location of trees). Also examples of typologies for urban green spaces are presented.
This report presents an indicator framework which is composed of indicators to assess for urban ecosystem condition and for urban ecosystem services. These are the result of a rigorous selection
process and ensure consistent mapping and assessment across Europe. The MAES urban pilot will continue with work on the interface between research and policy. The framework presented in this report needs to be tested and validated across Europe, e.g. on its applicability at city scale, on how far the methodology for measuring ecosystem condition and ecosystem service delivery in urban areas can be used to assess urban green infrastructure and nature-based solutions
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