1,721,247 research outputs found
Development of the DEPFET sensor with signal compression: a large format X-ray imager with mega-frame readout capability for the European XFEL
No full textWe present the development of the DSSC instrument: an ultra-high speed detector system for the new European XFEL in Hamburg. The DSSC will be able to record X-ray images with a maximum frame rate of 4.5 MHz. The system is based on a silicon pixel sensor with a DEPFET as a central amplifier structure and has detection efficiency close to 100% for X-rays from 0.5 keV up to 10 keV. The sensor will have a size of approximately 210x210 mm(2) composed of 1024x1024 pixels with hexagonal shape. 256 mixed signal readout ASICs are bump-bonded to the detector. They are designed in 130 nm CMOS technology and provide full parallel readout. The signals coming from the sensor are processed by an analog filter, immediately digitized by 8-bit ADCs and locally stored in an SRAM, which is able to record at least 640 frames. In order to fit the dynamic range of about 10(4) photons of 1 keV per pixel into a reasonable output signal range, achieving at the same time single 1 keV photon resolution, a non-linear characteristic is required. The proposed DEPFET provides the needed dynamic range compression at the sensor level. The most exciting and challenging property is that the single 1 keV photon resolution and the high dynamic range are accomplished within the 220 ns frame rate of the system. The keV properties and the main design issues of the different building blocks of the system will be discussed. Measurements with the analog front-end of the readout ASIC and a standard DEPFET have already shown a very low noise which makes it possible to achieve the targeted single photon resolution for 1 keV photons at 4.5 MHz and also for 0.5 ke V photons at half of the speed. In the paper the new experimental results obtained coupling a single pixel to an 8x8 ASIC prototype are shown. This 8x8 ASIC comprises the complete readout chain from the analog front-end to the ADC and the memory. The characterization of a newly fabricated nonlinear DEPFET is presented for the first time
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
A 8-channels low-noise CMOS readout circuit for silicon detectors with on-chip front-end JFET
No full textWe propose a CMOS circuit designed to be used with silicon drift detectors (SDDs) coupled to scintillators for /spl gamma/-ray imaging applications. The circuit is composed by 8 analog channels, each including a low-noise preamplifier, a 6th order semiGaussian shaping amplifier with four selectable peaking times from 1.8 /spl mu/s up to 6 /spl mu/s, a peak stretcher and a baseline holder. The integrated time constant used for the shaping are implemented by means of a recently proposed 'RC' cell. This cell is based on the de-magnification of the current flowing in a resistor R by means of the use of current mirrors. The 8 analog channels of the chip are multiplexed to a single analog output. A suitable digital section provides self-resetting of the channels, trigger output and the programming of independent threshold on the analog channels by means of a programmable serial register and 3-bit DACs. In this work, the main features of the circuit are first presented. The experimental results obtained in the characterization of the prototype are then reported and discussed. The energy resolution measured using a single channel of the chip with a silicon drift detector droplet (SDD/sup 3/) is of 128 eV at 6 keV with the detector cooled at -20/spl deg/C
An 8-channel DRAGO readout circuit for silicon detectors with integrated front-end JFET
No full textWe have developed a CMOS circuit to be used with Silicon Drift Detectors (SDDs) for X-ray spectroscopy and γ-ray imaging applications. The circuit operates with the input transistor integrated directly on the detector wafer. The circuit is composed of 8 analog channels, each including a low-noise voltage preamplifier, a 6th order semi-Gaussian shaping amplifier, with four selectable peaking times from 1.8 μs up to 6 μs, and a peak stretcher. The integrated time constant used for the shaping are implemented by means of a recently proposed 'RC' cell. This cell is based on the de-magnification of the current flowing in a resistor R thanks to the use of current mirrors. The 8 analog channels of the chip are multiplexed to a single analog output. A digital section provides self-resetting of the channels, trigger output and the external programming of independent threshold on the analog channels by means of a 3 bit DAC and a programmable serial register. In this work, the main features of the circuit are described. The measurement results obtained in the characterization of the prototype are then reported and discussed. The energy resolution measured using a single channel of the chip with a Silicon Drift Detector Droplet (SDD 3) is of 128 eV at 6 keV with the detector cooled at -20°C. Spectroscopy measurements using a multi-element SDD are also shown. © 2006 IEEE
Multi Correlated Double Sampling with exponential reset
No full textMultiple Correlated Double Sampling is often used to readout detectors with known periodic signal arrival time. New high rate applications such as X-ray Evolving Universe Spectroscopy mission demand high energy resolution which requires the filter properties to be optimized under the experimental constraints. Here we present an analysis and interpretation of the filter performance of a Multi Correlated Double Sampling system in terms of the signal-to-noise ratio as a function of the number of samples and the bandwidth of the sampling device including an exponential reset. In a real device, a signal arriving before the measurement cycle has an effect, on the measurement itself, which depends on the time difference between the signal arrival time and beginning of the actual measurement cycle. The effect of the reset on the sampling window will be approximated by an exponentially decaying time function. The introduction of such a reset is necessary to describe correctly a Multi Correlated Double Sampling system with the weighting function concept. Once the signal and the noise at the input of the filter are known, the present work provides the designer with a guideline to derive the filter parameters that optimize the signal-to-noise-ratio according to specific application constraints
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Axial flow compressor stability enhancement: Circumferential T-shape grooves performance investigation
Full text linkThis work focuses its attention on possibilities to enhance the stability of an axial compressor using a casing treatment technique. Circumferential grooves machined into the case are considered and their performances evaluated using three-dimensional steady state computational simulations. The effects of rectangular and new T-shape grooves on NASA Rotor 37 performances are investigated, resolving in detail the flow field near the blade tip in order to understand the stall inception delay mechanism produced by the casing treatment. First, a validation of the computational model was carried out analysing a smooth wall case without grooves. The comparisons of the total pressure ratio, total temperature ratio and adiabatic efficiency profiles with experimental data highlighted the accuracy and validity of the model. Then, the results for a rectangular groove chosen as the baseline case demonstrated that the groove interacts with the tip leakage flow, weakening the vortex breakdown and reducing the separation at the blade suction side. These effects delay stall inception, improving compressor stability. New T-shape grooves were designed keeping the volume as a constant parameter and their performances were evaluated in terms of stall margin improvement and efficiency variation. All the configurations showed a common efficiency loss near the peak condition and some of them revealed a stall margin improvement with respect to the baseline. Due to their reduced depth, these new configurations are interesting because they enable the use of a thinner light-weight compressor case as is desirable in aerospace applications
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Theoretical comparison between two different filtering techniques suitable for the VLSI spectroscopic amplifier ROTOR
No full textThe development of new detection systems based on arrays of Silicon Drift Detectors (SDD) used for new X-ray spectroscopy applications, like X-ray Holography and EXAFS experiments, requires the realization of suitable integrated low-noise electronics for the readout of the detector signals. Recently, a new VLSI time-variant signal processor called ROTOR has been developed. Despite its time-variant nature ROTOR is capable of correctly processing events randomly distributed along the time axis, thanks to the employment of the Concurrent Wheel Technique (CWT). Two different possible solutions for the ROTOR chip have been developed, both suitable for the CWT working mechanism. A theoretical comparison between the noise performances of the two filtering methods has been carried out and is presented in this work. © 2003 Elsevier B.V. All rights reserved
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