Minimum Dead Time Research Articles

A FPGA based time analyser for stochastic methods in experimental physics

A two-channel time analyser data acquisition system is developed for analysis of stochastic processes of random time interval pulses. The system is implemented on a typical low cost FPGA device. Two stochastic processes of nuclear interactions can be recorded by the system independently without any inter-channel dead time behaviour. The experimental results without any hardware based data reduction are transferred to the computer to perform arbitrary post analysis of the data using powerful software engineering tools to estimate the statistical properties of the processes. The performance of the system is verified experimentally. The maximum time digitization period and the minimum channel dead time are measured equal to 3.3 and 10 ns, respectively, using a typical prototype hardware platform. A brief description about theory of Rossi-α diagnostic method (a type of zero power reactor noise analysis) is initiated in the text as an application of the system. The method is applied to multiplying and non-multiplying media using the proposed measuring system.

A Digital Video System for Observing and Recording Occultations

AbstractStellar occultations by asteroids and outer solar system bodies can offer ground based observers with modest telescopes and camera equipment the opportunity to probe the shape, size, atmosphere, and attendant moons or rings of these distant objects. The essential requirements of the camera and recording equipment are: good quantum efficiency and low noise; minimal dead time between images; good horological faithfulness of the image timestamps; robustness of the recording to unexpected failure; and low cost. We describe an occultation observing and recording system which attempts to fulfil these requirements and compare the system with other reported camera and recorder systems. Five systems have been built, deployed, and tested over the past three years, and we report on three representative occultation observations: one being a 9 ± 1.5 s occultation of the trans-Neptunian object 28978 Ixion (mv =15.2) at 3 seconds per frame; one being a 1.51 ± 0.017 s occultation of Deimos, the 12 km diameter satellite of Mars, at 30 frames per second; and one being a 11.04 ± 0.4 s occultation, recorded at 7.5 frames per second, of the main belt asteroid 361 Havnia, representing a low magnitude drop (Δmv = ~0.4) occultation.

GM counter deadtime dependence on applied voltage, operating temperature and fatigue

This paper utilized standard two-source method and the simple non-paralyzing model assumption to examine a GM counter's deadtime dependence on applied voltage, operating temperature, and fatigue. Both 60Co and 137Cs sources were used for deadtime measurements. The results gathered suggest the presence of three distinct regions of deadtime behavior. At low voltages, the deadtime decreases as the voltage increases (Region I) followed by a region of stable deadtime plateau (Region II) and finally a region of increasing deadtime with increasing voltage. Region II is the best region for operating with a minimum deadtime which is not sensitive to the applied voltage. Typical deadtime values for GM counters were between 100 and 300 μs; the deadtime values in Region II were within this range. The results examined in this study also indicate a strong temperature dependence of deadtime, with a correlation coefficient of 0.93. The GM counter deadtime for various fatigues (aging) were investigated for three fatigue levels with a correlation coefficient of 0.48. The experimental results confirm that deadtime increases as both temperature and fatigue increase. The fundamental nature of deadtime seems to be different for voltages lower than the stable deadtime plateau (Region II) and for voltages higher than the plateau.

Robust PID controller design using particle swarm optimization-enabled automated quantitative feedback theory approach for a first-order lag system with minimal dead time

This paper presents the design of a robust proportional integral and derivative (PID) controller for a first-order lag with pure delay (FOLPD) model using particle swarm optimization (PSO)-enabled automated quantitative feedback theory (QFT). The plant model considered here can be approximated as a first-order system with a non-minimum phase (NMP) zero. Synthesis of controller for the FOLPD model via manual graphical technique involved in the QFT method is always a challenging and cumbersome task, because an NMP system stabilizes by a small gain. In this paper, a proposal is being presented to automate the loop-shaping phase in the QFT design method to synthesize a robust controller that can undertake the exact amount of plant uncertainty even in the presence of larger uncertainties than those assumed initially and can ensure a proper trade-off between robust stability and tracking performance specifications over the entire range of design frequencies. In this paper,s the PSO technique has been employed to tune the controller automatically,which can significantly reduce the computational effort compared with manual graphical techniques. It has also been demonstrated that this methodology not only automates loop shaping but also improves design quality and, most usefully, improves performance with optimally tuned PID controller in quantitative manner.

Narrow Line X-Ray Calibration Source for High Resolution Microcalorimeters

We are developing a narrow line calibration source for use with X-ray microcalorimeters. At energies below 300 eV fluorescent lines are intrinsically broad, making calibration of high resolution detectors difficult. This source consists of a 405 nm (3 eV) laser diode coupled to an optical fiber. The diode is pulsed to create approximately one hundred photons in a few microseconds. If the pulses are short compared to the rise time of the detector, they will be detected as single events with a total energy in the soft X-ray range. Poisson fluctuations in photon number per pulse create a comb of X-ray lines with 3 eV spacing, so detectors with energy resolution better than 2 eV are required to resolve the individual lines. Our currently unstabilized diode has a multimode width less than 1 nm, giving a 300 eV event a FWHM less than 0.1 eV. By varying the driving voltage, or pulse width, the source can produce a comb centered on a wide range of energies. The calibration events are produced at precisely known times. This allows continuous calibration of a flight mission without contaminating the observed spectrum and with minimal deadtime.

A system for accurate and automated injection of hyperpolarized substrate with minimal dead time and scalable volumes over a large range

Over recent years hyperpolarization by dissolution dynamic nuclear polarization has become an established technique for studying metabolism in vivo in animal models. Temporal signal plots obtained from the injected metabolite and daughter products, e.g. pyruvate and lactate, can be fitted to compartmental models to estimate kinetic rate constants. Modeling and physiological parameter estimation can be made more robust by consistent and reproducible injections through automation. An injection system previously developed by us was limited in the injectable volume to between 0.6 and 2.4ml and injection was delayed due to a required syringe filling step. An improved MR-compatible injector system has been developed that measures the pH of injected substrate, uses flow control to reduce dead volume within the injection cannula and can be operated over a larger volume range. The delay time to injection has been minimized by removing the syringe filling step by use of a peristaltic pump. For 100μl to 10.000ml, the volume range typically used for mice to rabbits, the average delivered volume was 97.8% of the demand volume. The standard deviation of delivered volumes was 7μl for 100μl and 20μl for 10.000ml demand volumes (mean S.D. was 9 ul in this range). In three repeat injections through a fixed 0.96mm O.D. tube the coefficient of variation for the area under the curve was 2%. For in vivo injections of hyperpolarized pyruvate in tumor-bearing rats, signal was first detected in the input femoral vein cannula at 3–4s post-injection trigger signal and at 9–12s in tumor tissue. The pH of the injected pyruvate was 7.1±0.3 (mean±S.D., n=10). For small injection volumes, e.g. less than 100μl, the internal diameter of the tubing contained within the peristaltic pump could be reduced to improve accuracy. Larger injection volumes are limited only by the size of the receiving vessel connected to the pump.

A Reconfigurable Single-Photon-Counting Integrating Receiver for Optical Communications

A reconfigurable Single-Photon Avalanche Diode integrating receiver in standard 130 nm CMOS is presented for optical links with an array readout bandwidth of 100 MHz. A maximum count rate of 58 G photon/s is observed, with a dynamic range of ≈ 79 dB, a sensitivity of ≈ - 31.7 dBm at 100 MHz and a BER of ≈ 1 ×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-9</sup> . The sensor core draws 89 mW at the maximum count rate and obtains a peak SNR of ≈157 dB. We investigate the properties of the receiver for optical communications in the visible spectrum, using its added functionality and reconfigurability to experimentally explore non-ideal influences. The all-digital 32 × 32 SPAD array, achieves a minimum dead time of 5.9 ns, and a median dark count rate of 2.5 kHz/SPAD. The internal gain of SPADs and spatio-temporal summation removes the need for analogue amplification. High noise devices can be weighted or removed to optimize the SNR. The power requirements, transient response and received data are explored and limiting factors similar to those of photodiode receivers are observed.

Stacked planar micro coils for single-sided NMR applications

This paper describes planar micro structured coils fabricated in a novel multilayer assembly for single-sided NMR experiments. By arranging the coil’s turns in both lateral and vertical directions, all relevant coil parameters can be tailored to a specific application. To this end, we implemented an optimization algorithm based on simulations applying finite element methods (FEMs), which maximizes the coil’s sensitivity and thus signal-to-noise ratio (SNR) while incorporating boundary conditions such as the coil’s electrical properties and a localized sensitivity needed for single-sided applications. Utilizing thin-film technology and microstructuring techniques, the planar character is kept by a sub-millimeter overall thickness. The coils are adapted to the Profile NMR-MOUSE® magnet with a homogeneous slice of about 200μm in height and a uniform depth gradient of about 20T/m. The final design of a coil with 20 turns, separated in four layers with five turns each, and an outer dimension of 4×4mm2 is able to measure a sample volume almost five times smaller than that of a state-of-the-art 14×16mm2 Profile NMR-MOUSE® coil with the same SNR. This allows for volume-limited measurements with high SNR and enables different future developments. The minimal dead time of 4μs facilitates further improvements of the SNR by echo adding techniques and the characterization of samples with short T2 relaxation times. Measurements on solid polymers like polyethylene (PE) and polypropylene (PP) with T2 components as short as 200μs approve the overall beneficial coil properties. Furthermore the ability to perform depth profiling with microscopic resolution is demonstrated.

Parallel recording of neurotransmitters release from chromaffin cells using a 10×10 CMOS IC potentiostat array with on-chip working electrodes

Neurotransmitter release is modulated by many drugs and molecular manipulations. We present an active CMOS-based electrochemical biosensor array with high throughput capability (100 electrodes) for on-chip amperometric measurement of neurotransmitter release. The high-throughput of the biosensor array will accelerate the data collection needed to determine statistical significance of changes produced under varying conditions, from several weeks to a few hours. The biosensor is designed and fabricated using a combination of CMOS integrated circuit (IC) technology and a photolithography process to incorporate platinum working electrodes on-chip. We demonstrate the operation of an electrode array with integrated high-gain potentiostats and output time-division multiplexing with minimum dead time for readout. The on-chip working electrodes are patterned by conformal deposition of Pt and lift-off photolithography. The conformal deposition method protects the underlying electronic circuits from contact with the electrolyte that covers the electrode array during measurement. The biosensor was validated by simultaneous measurement of amperometric currents from 100 electrodes in response to dopamine injection, which revealed the time course of dopamine diffusion along the surface of the biosensor array. The biosensor simultaneously recorded neurotransmitter release successfully from multiple individual living chromaffin cells. The biosensor was capable of resolving small and fast amperometric spikes reporting release from individual vesicle secretions. We anticipate that this device will accelerate the characterization of the modulation of neurotransmitter secretion from neuronal and endocrine cells by pharmacological and molecular manipulations of the cells.

Continuous Control for Buffering Conveyors in Beverage Bottling Plants

In beverage bottling plants, buffering conveying systems are used to decouple the various machines. They avoid propagation of machine breakdowns along the plant by assimilating or releasing bottles or containers. Today, they are controlled in steps by mechanical jam switches. In many cases, they enable an enduring filling process, which is necessary to gain good product quality and high plant efficiency. But with longer faults, the filling process still has to stop or slow down. Additionally, today's conveyors run very noisy. This affects the operator's health and conflicts with legal regulations. This paper presents an alternative control approach for buffering conveyors. It was created to improve the buffering effect and to reduce the noise emissions of today's systems. Instead of using jam switches, it uses counting sensor systems to obtain stepless information on the bottles entering and leaving the buffering conveyor. On this basis, the first continuous control algorithm for buffering conveyors was developed. It was described mathematically for all possible buffer situations. It was programmed and implemented in an industrial scale pilot plant. Finally, experiments in comparison with the commonly used jam switch control were carried out for all relevant settings. The practical experiments showed a stable behaviour of the new control algorithm. It reacted appropriately to state changes. Readjustment times and an almost minimal dead time (shortest transportation time of bottles) proved a high buffering effect. Above all, the new control algorithm resulted in a clearly audible and measureable reduction of the noise level. Copyright © 2012 John Wiley & Sons, Ltd.

Active quench and reset integrated circuit with novel hold-off time control logic for Geiger-mode avalanche photodiodes

This Letter presents an active quench-and-reset circuit for Geiger-mode avalanche photodiodes (GM-APDs). The integrated circuit was fabricated using a conventional 0.35 μm complementary metal oxide semiconductor process. Experimental results show that the circuit is capable of linearly setting the hold-off time from several nanoseconds to microseconds with a resolution of 6.5 ns. This allows the selection of the optimal afterpulse-free hold-off time for the GM-APD via external digital inputs or additional signal processing circuitry. Moreover, this circuit resets the APD automatically following the end of the hold-off period, thus simplifying the control for the end user. Results also show that a minimum dead time of 28.4 ns is achieved, demonstrating a saturated photon-counting rate of 35.2 Mcounts/s.

All nMOS 10-T AQRC for Monolithic Chlorophyll Fluorescence SPAD Sensor

Development of monolithic all nMOS Automatic Quenching and Reset Circuit (AQRC) for chlorophyll fluorescence SPAD sensor is reported using Microwind 3.1 and LTSpice version IV for 120 nm technology. An efficient bio-signal acquisition with single-photon counting facility, fast quenching, and reset is described using only ten nMOS transistors. The uniqueness of the design ensures a minimum dead time of 1 nS between adjacent incident photons. This corresponds to a maximum attainable count rate of 1000 MCounts/sec, not previously reported. The power dissipation is low (20-mW standby), making the circuit an ideal candidate for portable instruments. This is the first of its kind complete monolithic nMOS AQRC reported ever with better features than its CMOS counterparts.

Flow compensation for the fast spin echo triple-echo Dixon sequence

The fast spin echo (FSE) triple-echo Dixon (FTED) sequence uses bipolar triple-echo readout during each echo-spacing period of FSE to collect all the images necessary for Dixon water and fat separation in a single scan. In comparison to other FSE implementations of the Dixon technique, the triple echo readout used in FTED incurs minimal deadtime in the pulse sequence design and thus greatly enhances the overall scan efficiency. A potential drawback of FTED is that the time dependence of the gradient moment along the frequency encode direction becomes more complicated than in FSE and flow compensation based on the gradient moment (GM) nulling is difficult to achieve. In this work, the first order GM along the frequency encode direction of FTED was examined and two different methods to minimize the GM were proposed. The first method nulls the GM at all the locations of the refocusing radiofrequency pulses so that the Carr-Purcell Meiboom-Gill condition is always maintained. The second method minimizes the GM of the spin echo component of the FSE signal at the echo locations. The efficacy of both methods in reducing the first order GM and flow-related artefacts was demonstrated both in phantom and in images in vivo.

Single Photon Counting Module Based on Large Area APD and Novel Logic Circuit for Quench and Reset Pulse Generation

We present the design, implementation, and characterization of a single-photon counting module (SPCM) based on large-area avalanche photodiode (APD) and new logic circuit based on TTL integrated circuits (ICs) for generating precise quench and reset delays. Low dark count rate, high linearity of 2 MHz, maximum dynamic range of 12 MHz, and minimum dead time of 35 ns have been achieved with 0.2 mm peltier-cooled single photon avalanche diode (SPAD) [model C30902S-DTC, Perkin Elmer Optoelectronics (PKI)]. The developed module was fiberized and tested for the detection of fluorescently labeled DNA sequences. Detection sensitivity at the level of single fluorescent molecule has been demonstrated.

POETS: Portable Occultation, Eclipse, and Transit System

ABSTRACTOccultations of stars by small bodies in the outer solar system are opportunities to make high‐resolution measurements of their geometries and orbital elements and to detect or probe their atmospheres. Such events are limited in space and time, so it is desirable to deploy highly capable camera systems on multiple fixed and/or portable telescopes anywhere in the world, potentially on short notice. Similar considerations apply to planetary transits and solar eclipses. We have designed a camera system called POETS (Portable Occultation, Eclipse, and Transit System), which is optimized for occultation and related observations, and have assembled five such systems. The core of this system is the Andor Technology DV‐887 (now DU‐897) frame‐transfer camera, featuring a high frame rate, minimal dead time, high quantum efficiency, and low read noise. An electron‐multiplying mode lowers effective read noise to below 1 e− pixel−1 and is capable of photon counting. Each POETS includes a compact GPS timing system with microsecond accuracy, and a high‐performance computer system capable of sustained fast frame rates. Each POETS is designed to be transportable as carry‐on luggage and is adaptable to a wide variety of sites. POETS were deployed for the first time for the 2005 July 11 Charon occultation event, and they performed extremely well on telescopes with apertures from 0.6 to 6.5 m. Three POETS were subsequently deployed for the 2006 March 29 total solar eclipse, and five for the 2006 June 12 Pluto occultation.

Realisation of the zero-voltage switching condition for asymmetrical half-bridge DC∕DC forward converters

An analytical analysis for the zero-voltage switching (ZVS) asymmetrical half-bridge (AHB) PWM DC/DC forward converter is presented to gain insight sufficient to understand as well as design the system. It is concluded that the ZVS condition of the converter can definitely not be calculated by simply regarding the stored energy in leakage inductance. The derived closed-form relationships can also be used to guarantee required minimum dead time and boundary conditions. As a result, the converter design can be optimised for ZVS in all desired operation ranges. An off-line 250 W prototype is constructed for verifying the effectiveness of the proposed analytical derivations.

The front-end electronics for the COMPASS MWPCs

In the COMPASS experiment 34 planes of MWPCs for about 26,000 readout channels of MWPCs are used. The very high rate of the muon and hadron beams, and the consequently high trigger rate, requires the use of a front-end electronics with new conceptual design, to have a fast DAQ with a minimum dead-time. Its scheme will be described, together with some results of the performances achieved.

A portable, high-speed, vacuum-outlet GC vapor analyzer employing air as carrier gas and surface acoustic wave detection.

Vacuum-outlet GC with atmospheric-pressure air as the carrier gas is implemented at outlet pressures up to 0.8 atm using a low-dead-volume polymer-coated surface acoustic wave (SAW) detector. Increases in the system outlet pressure from 0.1 to 0.8 atm lead to proportional increases in detector sensitivity and significant increases in column efficiency. The latter effect arises from the fact that optimal carrier gas velocities are lower in air than in more conventional carrier gases such as helium or hydrogen due to the smaller binary diffusion coefficients of vapors in air. A 12-m-long, 0.25-mm-i.d. tandem column ensemble consisting of 4.5-m dimethyl polysiloxane and 7.5-m trifluoropropylmethyl polysiloxane operated at an outlet pressure of 0.5 atm provides up to 4 x 10(4) theoretical plates and a peak capacity of 65 (resolution, 1.5) for a 3-min isothermal analysis. At 30 degrees C, mixtures of vapors ranging in vapor pressure from 8.6 to 76 Torr are separated in this time frame. The SAW detector cell has an internal volume of < 2 microL, which allows the use of higher column outlet pressures with minimal dead time. The sensor response is linear with solute mass over at least 2-3 decades and provides detection limits of 20-50 ng for the vapors tested. The combination of atmospheric-pressure air as carrier gas, modest operating pressures, and SAW sensor detection is well-suited for field instrumentation since it eliminates the need for support gases, permits smaller, low-power pumps to be used, and provides sensitivity to a wide range of vapor analytes.

An integrated active-quenching circuit for single-photon avalanche diodes

We introduce the first integrated active quenching circuit (I-AQC) that drives an avalanche photodiode (APD) above its breakdown voltage, in order to detect single photons. Based on the I-AQC, we developed a compact and versatile photon-counting module suitable for applications in which very weak optical signals have to be detected, as for instance, photon correlation spectroscopy, luminescence measurements, and laser ranging. The prototype photon-counting module features quenching pulses up to 60 V amplitude, minimum dead time of less than 36 ns, corresponding to a saturated counting rate exceeding 25 Mcounts/s, user-controllable hold-off time, for reducing the afterpulsing effect, and nanosecond gating capability. The power dissipation is 60 mW in stand-by conditions, and the module size is less than 1 cm/spl times/2 cm.

Status of the digital pixel array detector for protein crystallography

A two-dimensional photon counting digital pixel array detector is being designed for static and time resolved protein crystallography. The room temperature detector will significantly enhance monochromatic and polychromatic protein crystallographic through-put data rates by more than three orders of magnitude. The detector has an almost infinite photon counting dynamic range and exhibits superior spatial resolution when compared to present crystallographic phosphor imaging plates or phosphor coupled CCD detectors. The detector is a high resistivity N-type Si with a pixel pitch of 150×150 μm, and a thickness of 300 μm, and is bump bonded to an application specific integrated circuit. The event driven readout of the detector is based on the column architecture and allows an independent pixel hit rate above 1 million photons/s/pixel. The device provides energy discrimination and sparse data readout which yields minimal dead-time. This type of architecture allows a continuous (frameless) data acquisition, a feature not found in any current detector being used for protein crystallographic applications. For the targeted detector size of 1000×1000 pixels, average hit rates greater than 8 billion photons/s for the complete detector appears achievable. This paper will present a review of the 8×8 detector array pixel performance which includes the analog amplifier response and the photon counting capabilities. In addition, operational results of a 16×16 detector array prototype, that includes both the analog amplifier and digital readout circuitry functioning together on one integrated circuit.