466 research outputs found
Influence of the Leakage Current on the Performance of Large Area Silicon Drift Detectors
In this paper we investigate the influence of the leakage current on the performance of Silicon Drift Detectors. First, analytical considerations are given in order to highlight the problems, specific for this type of detector, that emerge with leakage current. Then the obtained results are compared with the data of laboratory measurements. Aiming at a mass production of SDDs for the Inner Tracking System of the ALICE experiment at LHC we propose a simple and fast measurement for a preliminary selection before passing to a detailed acceptance test
Beam test results of the irradiated Silicon Drift Detector for ALICE
The Silicon Drift Detectors will equip two of the six cylindrical layers of
high precision position sensitive detectors in the ITS of the ALICE experiment
at LHC. In this paper we report the beam test results of a SDD irradiated with
1 GeV electrons. The aim of this test was to verify the radiation tolerance of
the device under an electron fluence equivalent to twice particle fluence
expected during 10 years of ALICE operation.Comment: 6 pages,6 figures, to appear in the proceedings of International
Workshop In high Multiplicity Environments (TIME'05), 3-7 October 2005,
Zurich,Switzerlan
Mass Transportation on Sub-Riemannian Manifolds
We study the optimal transport problem in sub-Riemannian manifolds where the
cost function is given by the square of the sub-Riemannian distance. Under
appropriate assumptions, we generalize Brenier-McCann's Theorem proving
existence and uniqueness of the optimal transport map. We show the absolute
continuity property of Wassertein geodesics, and we address the regularity
issue of the optimal map. In particular, we are able to show its approximate
differentiability a.e. in the Heisenberg group (and under some weak assumptions
on the measures the differentiability a.e.), which allows to write a weak form
of the Monge-Amp\`ere equation
Characteristics of the ALICE Silicon Drift Detector
A Silicon Drift Detector (SDD) with an active area of 7.0 x 7.5 cm2 has been designed, produced and tested for the ALICE Inner Tracking System. The development of the SDD has been focussed on the capability of the detector to work without an external support to the integrated high voltage divider. Severalfeatures have been implemented in the design in order to increase the robustness and the long-term electrical stability of the detector. One of the prototypes has been tested in a pion beam at the CERN SPS. Preliminary results on the position resolution are given
On the Hausdorff volume in sub-Riemannian geometry
For a regular sub-Riemannian manifold we study the Radon-Nikodym derivative
of the spherical Hausdorff measure with respect to a smooth volume. We prove
that this is the volume of the unit ball in the nilpotent approximation and it
is always a continuous function. We then prove that up to dimension 4 it is
smooth, while starting from dimension 5, in corank 1 case, it is C^3 (and C^4
on every smooth curve) but in general not C^5. These results answer to a
question addressed by Montgomery about the relation between two intrinsic
volumes that can be defined in a sub-Riemannian manifold, namely the Popp and
the Hausdorff volume. If the nilpotent approximation depends on the point (that
may happen starting from dimension 5), then they are not proportional, in
general.Comment: Accepted on Calculus and Variations and PD
Recent results from beam tests of large area silicon drift detectors
Silicon drift detectors with an active area of 7.0 Ă— 7.5 cm2 will equip the two middle layers of the Inner Tracking System of the ALICE experiment. The performance of several prototypes was studied during beam tests carried out at the CERN SPS facility. The results of the beam test data analysis are discussed in this paper
LOFT - a Large Observatory For x-ray Timing
The high time resolution observations of the X-ray sky hold the key to a
number of diagnostics of fundamental physics, some of which are unaccessible to
other types of investigations, such as those based on imaging and spectroscopy.
Revealing strong gravitational field effects, measuring the mass and spin of
black holes and the equation of state of ultradense matter are among the goals
of such observations. At present prospects for future, non-focused X-ray timing
experiments following the exciting age of RXTE/PCA are uncertain. Technological
limitations are unavoidably faced in the conception and development of
experiments with effective area of several square meters, as needed in order to
meet the scientific requirements. We are developing large-area monolithic
Silicon Drift Detectors offering high time and energy resolution at room
temperature, which require modest resources and operation complexity (e.g.,
read-out) per unit area. Based on the properties of the detector and read-out
electronics that we measured in the lab, we developed a realistic concept for a
very large effective area mission devoted to X-ray timing in the 2-30 keV
energy range. We show that effective areas in the range of 10-15 square meters
are within reach, by using a conventional spacecraft platform and launcher of
the small-medium class.Comment: 13 pages, 8 figures, 1 table, Proceedings of SPIE Vol. 7732, Paper
No. 7732-66, 201
Local behavior of p-harmonic Green's functions in metric spaces
We describe the behavior of p-harmonic Green's functions near a singularity
in metric measure spaces equipped with a doubling measure and supporting a
Poincar\'e inequality
Information inequalities and Generalized Graph Entropies
In this article, we discuss the problem of establishing relations between
information measures assessed for network structures. Two types of entropy
based measures namely, the Shannon entropy and its generalization, the
R\'{e}nyi entropy have been considered for this study. Our main results involve
establishing formal relationship, in the form of implicit inequalities, between
these two kinds of measures when defined for graphs. Further, we also state and
prove inequalities connecting the classical partition-based graph entropies and
the functional-based entropy measures. In addition, several explicit
inequalities are derived for special classes of graphs.Comment: A preliminary version. To be submitted to a journa
Recent Developments on the Silicon Drift Detector readout scheme for the ALICE Inner Tracking System
Proposal of abstract for LEB99, Snowmass, Colorado, 20-24 September 1999Recent developments of the Silicon Drift Detector (SDD) readout system for the ALICE Experiment are presented. The foreseen readout system is based on 2 main units. The first unit consists of a low noise preamplifier, an analog memory which continuously samples the amplifier output, an A/D converter and a digital memory. When the trigger signal validates the analog data, the ADCs convert the samples into a digital form and store them into the digital memory. The second unit performs the zero suppression/data compression operations. In this paper the status of the design is presented, together with the test results of the A/D converter, the multi-event buffer and the compression unit prototype.Summary:In the Inner Tracker System (ITS) of the ALICE experiment the third and the fourth layer of the detectors are SDDs. These detectors provide the measurement of both the energy deposition and the bi-dimensional position of the track. In terms of readout an SDD can be viewed as a matrix, where the rows are the detector anodes and the columns are the samples to be read during the drift time; therefore, a very large amount of data has to be amplified, converted in digital form and preprocessed in order to avoid the storage of non-significatn data.Since the electron mobility is a strong temperature function, detector temperature has to be kept constant; on the other hand, it is not possible to use very efficient cooling systems because the amount of material in this area is very limited, so the power budget for the electronic readout is very low (less than 6 mW/anode).The simplest solution would be to send the analog signals outside the sensitive area immediately after a preamplification; unfortunately, the ratio between the number of channels (around 200 000) and the space available is so high that the simple solution of sending all the SDD anodes output outside teh detector zone after a low-noise amplification is not practically manageable.Abstract:The adopted solution is based on three main units:(i) A front-end chip that performs low noise amplification, fast analog storage and A/D conversion(ii) A multi-event digital buffer for data derandomization(iii) A data compression/zero suppression and system control boardThe first two units are distributed on the ladders near the detectors and have stringent power and space requirements, while the third unit is placed at both ends of the ladders and in boxes placed on both ends of the TPC detector.The first unit is the most critical part of the system. It works as follows: the detector signals are continuously amplified, sampled and stored in the analog memory with a frequency of 40 MSamples/s The L0d trigger signal stops the write operation, while the L1 trigger signal starts the conversion phase. This phase will continue until the event data are stored in the event buffer if the L2y confirm trigger signal is received, or rejected if the L2n abort signal will be issued by the trigger system.Prototypes of the three parts have been designed and tested while the full chip is currently under design. Tests of the A/D converter will be presented.The multi-event buffer purpose is to de-randomize the even data in order to reduce the transmission speed. Preliminary tests of the first prototype will be presented.The board placed at the end of the ladders performs various functions. It reduces the amount of data through various cascaded algorithms with variable parameters and transmits the data to the SIU board. It also controls the test and slow control system for the ladder circuitry. Tests of the FPGA-based prototypes will be presented.Special care has been taken for the test problem. The ASICs designed are provided of a test control port based on teh IEEE 1149.1 JTAG standard. The same protocol is used for downloading configuration information
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