367 research outputs found
Front-end multi-channel PMT-associated readout chip for hodoscope application
International audienceThe system development requires a dedicated multi-channel readout ASIC (Application Specific Integrated Circuit) to be associated with the MaPMTs. Each channel should have very low input impedance to avoid electrical crosstalk between adjacent channels and to minimize effects of detector and wiring capacitances (Cd + Cw). Crosstalk between channels may degrade position resolution, while these capacitances may degrade both frequency and noise performances. Each channel should also provide two separated outputs corresponding respectively to high-speed signal-event detection and low-noise signal-charge quantification at low counting rate. This paper presents a readout chip for this purpose. It has been designed in a 0.35”m SiGe BiCMOS process (AMS). This process allows the use of RF and large-transconductance bipolar components, which is useful for the design of wide-band, low-impedance and low-noise circuits with improved performances
A Low Noise and High Dynamic Charge Sensitive Amplifier-Shaper associated with Silicon Strip Detector for Compton Camera in hadrontherapy
submitted to conference record of IEEE NSS-MIC, Anaheim USA, 29 october-3 november 2012International audienceA 8 channel Front End Electronics (FEE) circuit has been designed and fabricated in 0.35 ÎŒm CMOS process from Austria Micro System to be coupled with the Silicon Strip Detector (SSD) of the Compton Camera for quality control of hadrontherapy. Each channel includes a Charge Sensitive Amplifier (CSA) followed by two parallel CR-RC shapers. Slow and fast shapers, with 1 ÎŒs and 15 ns shaping time, are used to measure the energy and to time stamp all events respectively. The two sides of the SSD are read thanks to a configurable system for holes and electrons. The CSA presents an open loop gain of 67 dB and 90 degrees phase margin assuring a high stability. The circuit has been successfully tested. The test results are in good agreement with analytic and simulation calculations. Here, we describe the principles and present measured performances of the prototype. A high linearity over the range of 3E3 to 3E6 electrons is reached with a conversion gain of 3.6 mV/fC. The circuit achieves an ENC (Equivalent Noise Charge) of 412 electrons rms. 75% of the total noise is generated by the small value of the feedback resistor chosen to avoid pile up phenomenon due to the 1E5 hits/s occupancy rate. A cross-talk of 2 % was measured, 99% of which is due to the power supply disturbances. The power supply dissipation is 21 mW/channel for 3.3 V supply voltage. The area of this design is 2871Ă1881 ÎŒm2 including pads
Accretion Disk Instabilities, CDM models and their role in Quasar Evolution
We have developed a consistent analytical model to describe the observed
evolution of the quasar luminosity function. Our model combines black hole mass
distributions based on the Press - Schechter theory of the structure formation
in the Universe with quasar luminosity functions resulting from a physics-based
emission model that takes into account the time-dependent phenomena occurring
in the accretion disks. Quasar evolution and CDM models are mutually
constraining, therefore our model gives an estimation of the exponent, n, of
the power spectrum, P(k), which is found to be -1.8 < n < -1.6. We were able to
reject a generally assumed hypothesis of a constant ratio between Dark Matter
Halo and the Black Hole mass, since the observed data could not be fitted under
this assumption. We found that the relation between the Dark Matter Halos and
Black Hole masses is better described by M_{BH}=M_{DMH}^{0.668}. This model
provides a reasonable fit to the observed quasar luminosity function at
redshifts higher than ~2.0. We suggest that the disagreement at lower redshift
is due to mergers. Based on the agreement at high redshift, we estimated the
merger rate at lower redshift, and argue that this rate should depend on the
redshift, like (1+z)^3.Comment: 15 pages, 18 figures, Accepted for Publication in Ap
The VIRMOS-VLT Deep Survey
The aim of the VIRMOS VLT Deep Survey (VVDS) is to study of the evolution of
galaxies, large scale structures and AGNs from a sample of more than 150,000
galaxies with measured redshifts in the range 0<z<5+. The VVDS will rely on the
VIMOS and NIRMOS wide field multi-object spectrographs, which the VIRMOS
consortium is delivering to ESO. Together, they offer unprecedented multiplex
capability in the wavelength range 0.37-1.8microns, allowing for large surveys
to be carried out. The VVDS has several main aspects: (1) a deep multi-color
imaging survey over 18deg^2 of more than one million galaxies, (2) a "wide"
spectroscopic survey with more than 130,000 redshifts measured for objects
brighter than IAB=22.5 over 18deg^2, (3) a "deep" survey with 50,000 redshifts
measured to IAB=24, (4) ultra-deep" surveys with several thousand redshifts
measured to IAB=25, (5) multi-wavelength observations with the VLA and XMM.Comment: 5 pages including figures; to appear in Proc. of the ESO/ECF/STSCI
"Deep Fields" workshop, Garching Oct 2000, (Publ: Springer
The VIMOS Integral Field Unit: data reduction methods and quality assessment
With new generation spectrographs integral field spectroscopy is becoming a
widely used observational technique. The Integral Field Unit of the VIsible
Multi-Object Spectrograph on the ESO-VLT allows to sample a field as large as
54" x 54" covered by 6400 fibers coupled with micro-lenses. We are presenting
here the methods of the data processing software developed to extract the
astrophysical signal of faint sources from the VIMOS IFU observations. We focus
on the treatment of the fiber-to-fiber relative transmission and the sky
subtraction, and the dedicated tasks we have built to address the peculiarities
and unprecedented complexity of the dataset. We review the automated process we
have developed under the VIPGI data organization and reduction environment
(Scodeggio et al. 2005), along with the quality control performed to validate
the process. The VIPGI-IFU data processing environment is available to the
scientific community to process VIMOS-IFU data since November 2003.Comment: 19 pages, 10 figures and 1 table. Accepted for publication in PAS
The VVDS data reduction pipeline: introducing VIPGI, the VIMOS Interactive Pipeline and Graphical Interface
The VIMOS VLT Deep Survey (VVDS), designed to measure 150,000 galaxy
redshifts, requires a dedicated data reduction and analysis pipeline to process
in a timely fashion the large amount of spectroscopic data being produced. This
requirement has lead to the development of the VIMOS Interactive Pipeline and
Graphical Interface (VIPGI), a new software package designed to simplify to a
very high degree the task of reducing astronomical data obtained with VIMOS,
the imaging spectrograph built by the VIRMOS Consortium for the European
Southern Observatory, and mounted on Unit 3 (Melipal) of the Very Large
Telescope (VLT) at Paranal Observatory (Chile). VIPGI provides the astronomer
with specially designed VIMOS data reduction functions, a VIMOS-centric data
organizer, and dedicated data browsing and plotting tools, that can be used to
verify the quality and accuracy of the various stages of the data reduction
process. The quality and accuracy of the data reduction pipeline are comparable
to those obtained using well known IRAF tasks, but the speed of the data
reduction process is significantly increased, thanks to the large set of
dedicated features. In this paper we discuss the details of the MOS data
reduction pipeline implemented in VIPGI, as applied to the reduction of some
20,000 VVDS spectra, assessing quantitatively the accuracy of the various
reduction steps. We also provide a more general overview of VIPGI capabilities,
a tool that can be used for the reduction of any kind of VIMOS data.Comment: 10 pages, submitted to Astronomy and Astrophysic
The VIMOS-VLT Deep Survey - The evolution of galaxy clustering per spectral type to z~1.5
We measure the evolution of clustering for galaxies with different spectral
types from 6495 galaxies with 17.5<=I_AB<=24 and measured spectroscopic
redshift in the first epoch VIMOS-VLT Deep Survey. We classify our sample into
4 classes, based on the fit of well-defined galaxy spectral energy
distributions on observed multi-color data. We measure the projected function
wp(rp) and estimate the best-fit parameters for a power-law real-space
correlation function. We find the clustering of early-spectral-type galaxies to
be markedly stronger than that of late-type galaxies at all redshifts up to
z<=1.2. At z~0.8, early-type galaxies display a correlation length
r_0=4.8+/-0.9h^{-1}Mpc, while late types have r_0=2.5+/-0.4h^{-1}Mpc. The
clustering of these objects increases up to r_0=3.42+/-0.7h^{-1}Mpc for z~1.4.
The relative bias between early- and late-type galaxies within our
magnitude-limited survey remains approximately constant with b~1.7-1.8 from
z~=0.2 up to z~=1, with indications for a decrease at z>1.2, due to the growth
in clustering of the star-forming population. We find similar results when
splitting the sample into `red' and `blue' galaxies using the observed color
bi-modality. When compared to the expected linear growth of mass fluctuations,
a natural interpretation of these observations is that: (a) the assembly of
massive early type galaxies is already mostly complete in the densest dark
matter halos at z~=1; (b) luminous late-type galaxies are located in
higher-density, more clustered regions of the Universe at z~=1.5 than at
present, indicating that star formation activity is progressively increasing,
going back in time, in the higher-density peaks that today are mostly dominated
by old galaxies.Comment: 12 pages, Accepted on 11-Feb-06 for publication in Astronomy and
Astrophysic
The VIMOS VLT Deep Survey - First epoch VVDS-Deep survey: 11564 spectra with 17.5<=IAB<=24, and the redshift distribution over 0< z <=5
This paper presents the ``First Epoch'' sample from the VIMOS VLT Deep Survey
(VVDS). The VVDS goals, observations, data reduction with VIPGI, and redshift
measurement with KBRED are discussed. Data have been obtained with the VIsible
Multi Object Spectrograph (VIMOS) on the ESO-VLT UT3, allowing to observe ~600
slits simultaneously at R~230. A total of 11564 objects have been observed in
the VVDS-02h and VVDS-CDFS Deep fields over a total area of 0.61deg^2, selected
solely on the basis of apparent magnitude 17.5 <=I_{AB} <=24. The VVDS covers
the redshift range 0 < z <= 5. It is successfully going through the ``redshift
desert'' 1.5<z<2.2, while the range 2.2<z<2.7 remains of difficult access
because of the VVDS wavelength coverage.A total of 9677 galaxies have a
redshift measurement, 836 are stars, 90 are AGNs, and a redshift could not be
measured for 961 objects. There are 1065 galaxies with a measured redshift
z>1.4. The survey reaches a redshift measurement completeness of 78% overall
(93% including less reliable objects), with a spatial sampling of the
population of galaxies of 25% and ~30% in the VVDS-02h and VVDS-CDFS. The
redshift accuracy measured from repeated observations with VIMOS and comparison
to other surveys is ~276km/s. From this sample we present for the first time
the redshift distribution of a magnitude limited spectroscopic sample down to
IAB=24. The redshift distribution has a median of z=0.62, z=0.65, z=0.70, and
z=0.76, for magnitude limited samples with IAB<=22.5, 23, 23.5, and 24. A high
redshift tail above redshift 2 and up to redshift 5 becomes readily apparent
for IAB>23.5, probing the bright star forming population of galaxies. This
sample provides an unprecedented dataset to study galaxy evolution over 90% of
the life of the universeComment: 30 pages, accepted 22-Feb-05 in A&
The Vimos VLT Deep Survey: Compact structures in the CDFS
We have used the Vimos VLT Deep Survey in combination with other
spectroscopic, photometric and X-ray surveys from literature to detect several
galaxy structures in the Chandra Deep Field South (CDFS). Both a
friend-of-friend based algorithm applied to the spectroscopic redshift catalog
and an adaptative kernel galaxy density and colour maps correlated with
photometric redshift estimates have been used. We mainly detect a chain-like
structure at z=0.66 and two massive groups at z=0.735 and 1.098 showing signs
of ongoing collapse. We also detect two galaxy walls at z=0.66 and at z=0.735
(extremely compact in redshift space). The first one contains the chain-like
structure and the last one contains in its center one of the two massive
groups. Finally, other galaxy structures that are probably loose low mass
groups are detected. We compare the group galaxy population with simulations in
order to assess the richness of these structures and we study their galaxy
morphological contents. The higher redshift structures appear to probably have
lower velocity dispersion than the nearby ones. The number of moderatly massive
structures we detect is consistent with what is expected for an LCDM model, but
a larger sample is required to put significant cosmological constraints.Comment: 15 pages, 17 figures, accepted in A&
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
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