Pulse Amplitude Distribution Research Articles

Stochastic modeling of blob-like plasma filaments in the scrape-off layer: Theoretical foundation

A stochastic model for a superposition of uncorrelated pulses with a random distribution of amplitudes, sizes, and velocities is presented. The pulses are assumed to move radially with fixed shape and amplitudes decaying exponentially in time due to linear damping. The pulse velocities are taken to be time-independent but randomly distributed. The implications of a distribution of pulse amplitudes, sizes, and velocities are investigated. Closed-form expressions for the cumulants and probability density functions for the process are derived in the case of exponential pulses and a discrete uniform distribution of pulse velocities. The results describe many features of the boundary region of magnetically confined plasmas, such as high average particle densities, broad and flat radial profiles, and intermittent large-amplitude fluctuations. The stochastic model elucidates how these phenomena are related to the statistical properties of blob-like structures. In particular, the presence of fast pulses generally leads to flattened far scrape-off layer profiles and enhanced intermittency, which amplifies plasma–wall interactions.

In-Plane, In-Series Nanopores with Circular Cross Sections for Resistive-Pulse Sensing.

Resistive-pulse sensing with solid-state nanopores is a sensitive, label-free technique for analyzing single molecules in solution. To add functionality to resistive-pulse measurements, direct coupling of the nanopores to other pores and nanoscale fluidic elements, e.g., reactors, separators, and filters, in the same device is an important next step. One approach is monolithic fabrication of the fluidic elements in the plane of the substrate, but methods to generate pores with circular cross sections are needed to improve sensing performance with in-plane devices. Here, we report a fabrication method that directly patterns nanopores with circular cross sections in series and in plane with the substrate. A focused ion beam instrument is used to mill a lamella in a nanochannel and, subsequently, bore a nanopore through the lamella. The diameter and geometry of the nanopore are controlled by the current and dose of the ion beam and by the tilt angle and thickness of the lamella. We fabricated devices with vertical and tilted lamellae and nanopores with diameters from 40 to 90 nm in cylindrical and conical geometries. To test device performance, we conducted resistive-pulse measurements of hepatitis B virus capsids. Current pulses from T = 3 capsids (∼31 nm diameter) and T = 4 capsids (∼35 nm diameter) were well resolved and exhibited relative pulse amplitudes (Δi/i) up to 5 times higher than data obtained on nanopores with rectangular cross sections. For smaller pore diameters (<45 nm), which approach the diameters of the capsids, a dramatic increase in the pulse amplitude was observed for both T = 3 and T = 4 capsids. Two and three pores fabricated in series further improved the resolution between the relative pulse amplitude distributions for the T = 3 and T = 4 capsids by up to 2-fold.

Probabilistic Energy-to-Amplitude Mapping in a Tapered Superconducting Nanowire Single-Photon Detector.

A spectrum-resolved photon detector is crucial for cutting-edge quantum optics, astronomical observation, and spectroscopic sensing. However, such an ability is rarely obtained because a direct linear conversion from weak single-photon energy to a readable electrical signal above the noise level without causing an avalanche is challenging. Here, we overcame these difficulties by building a probabilistic energy-to-amplitude mapping in a tapered superconducting nanowire single-photon detector and combining a computational reconstruction to obtain equivalent spectral resolving capacity. Distinguished dependence of pulse amplitude distributions on varied input spectra has been observed experimentally. As the energy-to-amplitude mapping is probabilistic, statistical measurements are required. By collecting around a few hundred photons, we have demonstrated wavelength perception over a wide spectral range from 600 to 1700 nm with a resolution of 100 nm. These findings represent a new approach to designing spectrum-sensitive SNSPDs for low-light spectroscopic applications.

Measurement of Pulsatile Insulin Secretion: Rationale and Methodology.

Pancreatic β-cells are responsible for the synthesis and exocytosis of insulin in response to an increase in circulating glucose. Insulin secretion occurs in a pulsatile manner, with oscillatory pulses superimposed on a basal secretion rate. Insulin pulses are a marker of β-cell health, and secretory parameters, such as pulse amplitude, time interval and frequency distribution, are impaired in obesity, aging and type 2 diabetes. In this review, we detail the mechanisms of insulin production and β-cell synchronization that regulate pulsatile insulin secretion, and we discuss the challenges to consider when measuring fast oscillatory secretion in vivo. These include the anatomical difficulties of measuring portal vein insulin noninvasively in humans before the hormone is extracted by the liver and quickly removed from the circulation. Peripheral concentrations of insulin or C-peptide, a peptide cosecreted with insulin, can be used to estimate their secretion profile, but mathematical deconvolution is required. Parametric and nonparametric approaches to the deconvolution problem are evaluated, alongside the assumptions and trade-offs required for their application in the quantification of unknown insulin secretory rates from known peripheral concentrations. Finally, we discuss the therapeutical implication of targeting impaired pulsatile secretion and its diagnostic value as an early indicator of β-cell stress.

Influence of He mixture on the pulse amplitude and spatial distribution of an Ne-like Ar 46.9 nm laser under gain saturation

In the experiment of an Ne-like Ar 46.9 nm laser produced by capillary discharge, the effects of the addition of He into Ar on an Ne-like Ar 46.9 nm laser pulse and laser spot were studied. It was found that the laser pulse amplitude increased first and then decreased with pressure increase of He. In comparison with the laser pulse amplitude with pure Ar, the maximum amplitude with Ar–He mixture increased by approximately 34%. Under the condition of gain saturation of a 46.9 nm laser, the laser spatial distribution changed gradually with the addition of He into pure Ar. To analyze the influence of the addition of He into Ar on the laser spot, a theoretical simulation was performed.

Influence of optical radiation parameters on the amplitude characteristics of silicon photoelectron multipliers

At present, silicon photoelectronic multipliers with a low voltage, high sensitivity in the visible and near infrared spectral regions, and large amplification factors are often used to record optical radiation in a wide range of intensities of the visible and near infrared spectral regions. The purpose of this article is to determine the dependence of the type of amplitude distribution of pulses, created by silicon photoelectronic multipliers, on the intensity of the recorded optical radiation. As research objects, commercially available Ketek PM 3325 and ON Semi FC 30035 silicon photomultiplier tubes have been used, as well as multipliers from a pilot batch manufactured by OJSC “INTEGRAL” (Republic of Belarus). The paper studies the amplitude distribution of voltage pulses, formed on the load resistor of silicon photoelectronic multipliers by the photocurrent for various values of the energy exposure of optical pulses. The range of values of the energy exposure of optical pulses was determined at which the amplitude distributions of these pulses have pronounced peaks. It was found out that with increasing energy exposure of the optical pulse, part of the peaks disappears. It was established that all the dependencies of the average amplitude of such pulses on the magnitude of the energy exposure of the optical pulse for silicon photomultiplier tubes have a linear section. The performed experimental studies showed that an increase in the energy exposure of optical pulses results in an increase in the dispersion of the amplitude distribution of pulses. It was found that for a linear dependence of the energy exposure of the optical pulse on the optical pulse duration in the range from 50 ns to 1 μs, the studied silicon photoelectronic multipliers formed voltage pulses of 1 μs duration with the same rising and falling edges. In this case, the average amplitude of these pulses had a linear dependence on the duration of the optical pulse. The results can be used in design of photodetector devices for monitoring the level of ionization radiation for nuclear power plants, for quantum information systems and in optical communications for transmitting information with monitoring the presence of information leakage channels.

Skewed Lorentzian pulses and exponential frequency power spectra

Frequency power spectra due to a super-position of uncorrelated Lorentzian pulses with a random distribution of amplitudes are considered. For pulses with a constant duration, there is an exponential frequency spectrum which is independent of the degree of pulse overlap and the pulse amplitude distribution. The spectrum is furthermore shown to be unaffected by skewness of the Lorentzian pulses and even a random distribution of the pulse asymmetry parameter and its correlation with the pulse amplitude. This stochastic model provides new insight into the ubiquitous exponential spectra in fluids and magnetized plasmas exhibiting deterministic chaos, where non-linear advection processes lead to amplitude dependent steepening of smooth pulses.

Nanofluidic Devices with 8 Pores in Series for Real-Time, Resistive-Pulse Analysis of Hepatitis B Virus Capsid Assembly.

To improve the precision of resistive-pulse measurements, we have used a focused ion beam instrument to mill nanofluidic devices with 2, 4, and 8 pores in series and compared their performance. The in-plane design facilitates the fabrication of multiple pores in series which, in turn, permits averaging of the series of pulses generated from each translocation event. The standard deviations (σ) of the pulse amplitude distributions decrease by 2.7-fold when the average amplitudes of eight pulses are compared to the amplitudes of single pulses. Similarly, standard deviations of the pore-to-pore time distributions decrease by 3.2-fold when the averages of the seven measurements from 8-pore devices are contrasted to single measurements from 2-pore devices. With signal averaging, the inherent uncertainty in the measurements decreases; consequently, the resolution (mean/σ) improves by a factor equal to the square root of the number of measurements. We took advantage of the improved size resolution of the 8-pore devices to analyze in real time the assembly of Hepatitis B Virus (HBV) capsids below the pseudocritical concentration. We observe that abundances of assembly intermediates change over time. During the first hour of the reaction, the abundance of smaller intermediates decreased, whereas the abundance of larger intermediates with sizes closer to a T = 4 capsid remained constant.

The evolution of statistical characteristics of acoustic emission upon fiberglass destruction

It is established that statistical characteristics of acoustic emission during plastic deformation and destruction obey the scaling relations. Increasing the degree of deformation leads to a change of the dominant destruction mechanism, and it is manifested in appearance of new “branches” in the distribution of acoustic pulse amplitudes with other indicators of scaling. The proposed approach made it possible to reveal the influence of destruction mechanisms on the evolution and nature of acoustic emission.

Single-particle electrophoresis in nanochannels.

Electrophoretic mobilities and particle sizes of individual Hepatitis B Virus (HBV) capsids were measured in nanofluidic channels with two nanopores in series. The channels and pores had three-dimensional topography and were milled directly in glass substrates with a focused ion beam instrument assisted by an electron flood gun. The nanochannel between the two pores was 300 nm wide, 100 nm deep, and 2.5 μm long, and the nanopores at each end had dimensions 45 nm wide, 45 nm deep, and 400 nm long. With resistive-pulse sensing, the nanopores fully resolved pulse amplitude distributions of T = 3 HBV capsids (32 nm outer diameter) and T = 4 HBV capsids (35 nm outer diameter) and had sufficient peak capacity to discriminate intermediate species from the T = 3 and T = 4 capsid distributions in an assembly reaction. Because the T = 3 and T = 4 capsids have a wiffle-ball geometry with a hollow core, the observed change in current due to the capsid transiting the nanopore is proportional to the volume of electrolyte displaced by the volume of capsid protein, not the volume of the entire capsid. Both the signal-to-noise ratio of the pulse amplitude and resolution between the T = 3 and T = 4 distributions of the pulse amplitudes increase as the electric field strength is increased. At low field strengths, transport of the larger T = 4 capsid through the nanopores is hindered relative to the smaller T = 3 capsid due to interaction with the pores, but at sufficiently high field strengths, the T = 3 and T = 4 capsids had the same electrophoretic mobilities (7.4 × 10–5 cm2 V–1 s–1) in the nanopores and in the nanochannel with the larger cross-sectional area.

Statistical modelling of discharge behavior of atmospheric pressure dielectric barrier discharge

In this work, stochastic behavior of atmospheric pressure dielectric barrier discharge (DBD) has been investigated. The experiment is performed in a DBD reactor consisting of a pair of stainless steel parallel plate electrodes powered by a 50 Hz ac high voltage source. Current pulse amplitude distributions for different space gaps and the time separation between consecutive current pulses are studied. A probability distribution function is proposed to predict the experimental distribution function for the current pulse amplitudes and the occurrence of the transition regime of the pulse distribution. Breakdown voltage at different positions on the dielectric surface is suggested to be stochastic in nature. The simulated results based on the proposed distribution function agreed well with the experimental results and able to predict the regime of transition voltage. This model would be useful for the understanding of stochastic behaviors of DBD and the design of DBD device for effective operation and applications.

Comments on the stochastic characteristics of fission chamber signals

This paper reports on theoretical investigations of the stochastic properties of the signal series of ionisation chambers, in particular fission chambers. First, a simple and transparent derivation is given of the higher order moments of the random detector signal for incoming pulses with a non-homogeneous Poisson distribution and random pulse heights and arbitrary shape. Exact relationships are derived for the higher order moments of the detector signal, which constitute a generalisation of the so-called higher order Campbelling techniques. The probability distribution of the number of time points when the signal exceeds a certain level is also derived. Then, a few simple pulse shapes and amplitude distributions are selected as idealised models of the detector signals. Assuming that the incoming particles form a homogeneous Poisson process, explicit expressions are given for the higher order moments of the signal and the number of level crossings in a given time interval for the selected pulse shapes.

Parallel superconducting strip-line detectors: reset behaviour in the single-strip switch regime

Superconducting strip-line detectors (SSLDs) are an important emerging technology for the detection of single molecules in time-of-flight mass spectrometry (TOF-MS). We present an experimental investigation of a SSLD laid out in a parallel configuration, designed to address selected single strip-lines operating in the single-strip switch regime. Fast laser pulses were tightly focused onto the device, allowing controllable nucleation of a resistive region at a specific location and study of the subsequent device response dynamics. We observed that in this regime, although the strip-line returns to the superconducting state after triggering, no effective recovery of the bias current occurs, in qualitative agreement with a phenomenological circuit simulation that we performed. Moreover, from theoretical considerations and by looking at the experimental pulse amplitude distribution histogram, we have the first confirmation of the fact that the phenomenological London model governs the current redistribution in these large area devices also after detection events.

A Galactic origin for the fast radio burst FRB010621

Abstract The recent detection of fast radio bursts has generated strong interest in identifying the origin of these bright, non-repeating, highly dispersed pulses. The principal limitation in understanding the origin of these bursts is the lack of reliable distance estimates; their high dispersion measures imply that they may be at cosmological distances (0.1 &amp;lt; z &amp;lt; 1.0). Here, we discuss new distance constraints to the FRB010621 (a.k.a J1852−08) first reported by Keane. We use velocity resolved Hα and Hβ observations of diffuse ionized gas towards the burst to calculate an extinction-corrected emission measure along the line of sight. We combine this emission measure with models of Galactic rotation and of electron distribution to derive a 90 per cent probability of the pulse residing in the Galaxy. However, we cannot differentiate between the two Galactic interpretations of Keane: a neutron star with unusual pulse amplitude distribution or Galactic black hole annihilation.

Correlation between the piezo-Barkhausen effect and the fatigue limit of steel

Many types of ferrous metals can sustain an indefinite number of repeated loading cycles (N ⩾ 107 cycles) provided that the maximum imposed stresses do not exceed certain critical values usually referred to as fatigue or endurance limits. In current practice, these limits are primarily inferred from statistical analyses of numerous fatigue experiments that relate the number of cycles to failure, Nf, to the loading programs. Numerous attempts have been made to bypass these time consuming tests by the direct observation of changes in material microstructures utilizing a variety of physical effects ranging from neutron diffraction, x-ray radiography, acoustic emission and even positron radiation patterns; but none of these approaches has yielded any unambiguous indices of damage. Recently, it has been found that the evolution of piezomagnetic hysteresis, due to magnetization changes induced in ferromagnetic steels by tension and compression, is a reliable indicator of the development of fatigue damage and can lead to practical predictions of service life. Further detailed information concerning processes at the microstructural level can be obtained from measurements of flux jumps associated with the piezomagnetic fields. Sequences of flux variations of the order of 10−3 Mx or 10−11 Wb, comparable to those observed in conventional Barkhausen experiments, appear when ferromagnetic steels are subjected to tension or compression. The amplitude distribution of these piezo-Barkhausen pulses increases markedly in the vicinity of the endurance limit and appears to provide a rapid means for distinguishing between stable, i.e. safe, loading regimes and those terminating in fatigue failure.

Radio emission structure of cloud-to-ground lightning discharge

Cloud-to-ground lightning discharge radio frequency emission is analysed on the base of measurements with high temporal resolution allowed to fully resolve its structure. Discharge radio emission mainly consists of independent random bi-polar pulses. Pulse length, amplitude and interpulse period distributions are studied at different stages of lightning discharge. The significant change of radio frequency emission structure during discharge development is demonstrated.

Calculation of the light pulse distributions induced by fast neutrons in organic scintillation detectors

We develop a fully analytic and self-contained description of the amplitude distribution of light pulses in an organic scintillation detector due to a monoenergetic source of fast neutrons. To this end, two classes of problems have to be handled. One is a formula for the light pulse amplitude distribution for the complete life history of neutrons slowing down in a mixture of hydrogen and carbon as a statistical average over all collision sequences that can occur, accounting also for neutron leakage. A complete solution is given in terms of a non-recursive convolution integral expansion with respect to the various possible collision histories. These latter are dependent on the collision probabilities of neutrons of a given energy. The second is the calculation of this collision probability from analytical expressions for the geometry of the detector, in the present case a right cylinder. This quantity was taken from Monte Carlo simulations in previous work. Recursive formulae are derived for the probabilities of arbitrary collision sequences, and quantitative results are given for up to five consecutive collisions of all combinations. These probabilities can be used to determine how to truncate the non-recursive expansion of the full light amplitude distribution in quantitative work. The calculational method serves to lend insight and understanding into the structure of the pulse height spectra, as well as it provides a computationally cheap method of generating a large number of such spectra for various detector compositions, sizes and neutron energies, for the development and test of new spectrum unfolding techniques.

HEMT-Based Readout Technique for Dark- and Photon-Count Studies in NbN Superconducting Single-Photon Detectors

Dark counts in superconducting single-photon detectors (SSPDs) manifest themselves as spontaneous, transient voltage pulses, typically indistinguishable from photon counts. We present here a new readout technique based on integrating the SSPD with a low-noise, cryogenic high-electron-mobility transistor (HEMT) with high-input impedance. This arrangement allowed us to achieve amplitude resolution of the recorded output transients. In two-dimensional superconducting nanostripes, the physics of photon counting is based on the hotspot formation mechanism, while the dark counts correspond to voltage transients triggered by the vortex-antivortex motion and/or phase-slip centers. Thus, their respective transients can be distinguished by comparing the output pulse amplitude distributions. Our scheme also allowed us to perform photon-energy-resolution studies by comparing the SSPD output pulse amplitude distributions (the mean pulse amplitude and the distribution width) collected for incident single photons with different energies.

Analysis of amplitude characteristics of quantum photodetectors with a large photosensitive area

Pulse amplitude distributions of avalanche photodetectors with a metal-resistive layer-semiconductor structure and a 7-mm2 photosensitive area are investigated in the photon-counting mode. It is shown that p-n junction heterogeneities in a space charge region affect the shape of amplitude distributions of photocurrent pulses, as the overvoltage increases and light spot changes its position on the photosensitive area. The comparative analysis of the amplitude characteristics of the above avalanche photodetectors and commercial ΦД-115д avalanche photodiodes is conducted.

Critical behavior of a passively mode-locked laser: rational harmonic mode locking

The critical behavior of passive mode locking has been demonstrated in a figure-eight fiber laser that performs rational harmonic mode locking (RHML). On both the repetition rate and the pulse amplitude distribution, the observed pulse trains near the threshold exhibit the same regulations as the rational harmonic mode-locked ones. The theory also shows that there should be a middle status of RHML before achieving normal mode locking. It is important to note that the results provide what we believe to be the first confirmed attempt to address a fundamental question: how does a laser become mode locking with an increase of pump power?