Sampling Gate Research Articles

Design of Logic Circuit for All Optical Sampling Gate Based on FIBER-FWM Nonlinear Fiber

Design of Logic Circuit for All Optical Sampling Gate Based on FIBER-FWM Nonlinear Fiber

Benchmarking the performance of portfolio optimization with QAOA

We present a detailed study of portfolio optimization using different versions of the quantum approximate optimization algorithm (QAOA). For a given list of assets, the portfolio optimization problem is formulated as quadratic binary optimization constrained on the number of assets contained in the portfolio. QAOA has been suggested as a possible candidate for solving this problem (and similar combinatorial optimization problems) more efficiently than classical computers in the case of a sufficiently large number of assets. However, the practical implementation of this algorithm requires a careful consideration of several technical issues, not all of which are discussed in the present literature. The present article intends to fill this gap and thereby provides the reader with a useful guide for applying QAOA to the portfolio optimization problem (and similar problems). In particular, we will discuss several possible choices of the variational form and of different classical algorithms for finding the corresponding optimized parameters. Viewing at the application of QAOA on error-prone NISQ hardware, we also analyse the influence of statistical sampling errors (due to a finite number of shots) and gate and readout errors (due to imperfect quantum hardware). Finally, we define a criterion for distinguishing between ‘easy’ and ‘hard’ instances of the portfolio optimization problem.

Frequency-Modulated Signal Measurement Using Closed-Loop Methodology.

Frequency-modulated (FM) signals are widely used in sensing, measurement, and signal detection due to their strong anti-interference and easy transmission characteristics. Although the high-precision measurement methods for static signals are quite complete, the high-precision measurement methods for dynamic FM signals still need to be studied, and the measurement accuracy in the high-sampling system still has room for improvement. Traditionally, the equal-precision measurement method is widely applied in most scenarios. However, its accuracy is limited by the quantization error of ±1 word and the sampling gate time, making it difficult to improve the frequency measurement accuracy while ensuring a high sampling rate at the same time. In this paper, a high-precision feedback frequency measurement system with the capability to eliminate the quantization error of ±1 word is proposed. The proposed system consists of two stages, the rough measurement stage based on the equal-precision measurement method and the precise measurement stage based on the negative feedback tracking architecture using the phase–frequency detector (PFD) and direct digital synthesizer (DDS). The effectiveness and feasibility of the system are verified by both simulation and experiment. At the sampling rate of 2 kHz, the frequency measurement accuracy is improved by more than 30 dB.

Novel Method for Fetal and Maternal Heart Rate Measurements Using 2-D Ultrasound Color Doppler Flow Images.

Fetal heart rate (FHR) and maternal heart rate (MHR) are important indicators of fetal well-being during pregnancy. A common method in clinical examination is to estimate the FHR using the Doppler shift of echoes from umbilical artery blood flow based on an ultrasound pulsed-wave (PW) Doppler technique. Similarly, a sampling gate can be located at the maternal blood flow to measure MHR using PW Doppler. Ultrasound color Doppler flow imaging (CDFI) is one of the most commonly used imaging modes for clinical fetal examinations. Color coding is employed to display the blood flow velocity and direction in color grades according to the Doppler shift. Continuous CDF images contain dynamic changes characteristics of the blood flow. The periodic characteristics can be used to obtain heart rate information. Therefore, here we propose a novel method to measure FHR and MHR simultaneously using CDF images. The proposed method calculates the histogram of color similarity of CDF images to initially extract the periodic characteristics of the CDF image sequence. The histogram of color similarity function is then processed by a bandpass filter and autocorrelation operation to reduce noise and enhance periodicity. Finally, peak detection is performed on the processed signal to obtain the period and estimate the heart rate. The proposed method can measure the FHR and MHR in parallel after selecting two regions containing the umbilical artery and maternal blood flow, respectively. Thus, the method has high computational efficiency. The proposed method was evaluated on a Doppler flow phantom and clinical CDF images and then compared with the PW Doppler method. The correlation analysis and Bland-Altman plots reveal that the proposed method agrees well with the PW Doppler. It is a sanity check method for real-time clinical FHR and MHR measurements.

High‐Resolution Time‐Correlated Single‐Photon Counting Using Electro‐Optic Sampling

AbstractA simple, practical method based on electro‐optic gating is experimentally shown to improve the temporal resolution of single‐photon detection by more than 16 times. Delay times between ultrafast single photons and a reference clock are stretched by a desired programmable sampling gate factor, allowing reconstruction of delay histograms with ≈0.001 photons per pulse to within 60 ps. By transferring the bandwidth of RF electronics to single‐photon counting, complex single‐photon signals with large time‐bandwidth products > 2000 are temporally stretched up so that they can be resolved by slow detectors, irrespective of the quality of the detector instrument response function. This method is also applied to biphotons, in order to reconstruct the 2D histogram of joint detection delays with 15 times better resolution. The phenomenon of nonlocal dispersion, which is not resolvable directly with the slow detectors, is then observable to within the 98 ps level. The proof‐of‐concept demonstration uses off‐the‐shelf commercial fiber‐integrated LiNbO3 modulators and RF electronics, and the method is readily integrable on‐chip and to speeds >100 GHz, offering a practical solution to ultrafast time‐correlated single‐photon counting beyond the research laboratory.

Variation in the uterine arteries Doppler parameters when obtained transvaginally or transabdominally at different sampling locations

Introduction To evaluate differences in Doppler velocimetry parameters when the uterine arteries (UtA) are evaluated transabdominally (TA) at different sampling locations and transvaginally (TV). Materials and methods Five hundred and fifty-seven pregnant women were evaluated between 11 and 39 weeks of gestation. The mean UtA pulsatility index (PI) and prevalence of bilateral notching were obtained at four different locations: (1) TA just above the crossing with the iliac artery; (2) TA just below the crossing with the iliac artery; (3) TA well above approximately 3 cm away from the crossing with the iliac artery; and (4) TV at the point closest to the internal cervical os. Measurements obtained just above the external iliac artery were considered the standard for comparison. Differences among different locations per gestational week were calculated. Results The mean UtA-PI and prevalence of bilateral notching were similar when the uterine arteries were sampled TA just above or just below the crossing with the external iliac artery. The mean UtA-PI values and prevalence of bilateral notching were significantly higher (p < .0001) when obtained TV and significantly lower when obtained 3 cm above the crossing with the external iliac artery (p = .004), as compared to the standard plane just above the crossing. Conclusion The mean UtA-PI and prevalence of bilateral notching vary significantly when the uterine arteries are sampled far above the crossing with the external iliac artery or when obtained transvaginally. Key Message The predictive performance of the uterine arteries during pregnancy can significantly vary in relation to the approach selected for evaluation and to the location of the Doppler sampling gate.

FRET-based ‘ratiometric’ molecular switch for multiple ions with efficacy towards real-time sampling and logic gate applications

Fluorescent nanoaggregates comprised of rhodamine based amphiphilic probe has been designed, which can simultaneously detect Al 3+ , Cr 3+ and F¯ ions in the aqueous medium (pH 7.4). Mechanistic investigation indicates that both the carbonyl oxygen of the spirolactam ring and the nitrogen center of indole participate in the coordination of metal ions. Consequently, metal ion-binding induces the opening of the spirolactam ring and allows the Förster energy transfer from indole to xanthene moiety. As a result, the colorless probe solution turns pink in presence of metal ions, with ratiometric fluorescence change from blue to yellow. Further, the addition of fluoride leads to dissociation of preformed Al 3+ -complex, resulting in the fading of pink color and reverting the fluorescence signal to the original. This not only serves as a tool to discriminate between Al 3+ and Cr 3+ ion but also acts as a strategy for detecting fluoride in the aqueous medium. Thus, using a single FRET probe, ‘ratiometric’, naked-eye sensing of multiple ions was achieved. Also, considering the differential response of probe molecule towards Cr(III) and Cr(VI), a colorimetric assay for biogenic thiols was developed. Simultaneously, a combinatorial molecular logic gate was designed based on the multiple ion sensing ability of the probe molecule. Further, the system showed real-time detection of Al 3+ and Cr 3+ in natural water samples, estimation of Al 3+ in antacid tablets and fluoride in mouthwash, etc. Lastly, low-cost, reusable paper strips were developed, which offers an alternative strategy for on-site detection of metal ions without engaging any sophisticated instruments or trained personnel. • Ratiometric sensing of Al 3+ , Cr 3+ and F − ions at nanomolar levels in water. • Assay for biogenic thiols based on differential response for Cr(III) and Cr(VI). • Design combinatorial logic gate based on multiple ion sensing. • Analysis of real-life samples: fluoride in mouthwash, Aluminium in antacid tablets. • Low-cost, reusable paper strips for onsite detection of ions.

Using models to improve optimizers for variational quantum algorithms

Variational quantum algorithms are a leading candidate for early applications on noisy intermediate-scale quantum computers. These algorithms depend on a classical optimization outer-loop that minimizes some function of a parameterized quantum circuit. In practice, finite sampling error and gate errors make this a stochastic optimization with unique challenges that must be addressed at the level of the optimizer. The sharp trade-off between precision and sampling time in conjunction with experimental constraints necessitates the development of new optimization strategies to minimize overall wall clock time in this setting. In this work, we introduce two optimization methods and numerically compare their performance with common methods in use today. The methods are surrogate model-based algorithms designed to improve reuse of collected data. They do so by utilizing a least-squares quadratic fit of sampled function values within a moving trusted region to estimate the gradient or a policy gradient. To make fair comparisons between optimization methods, we develop experimentally relevant cost models designed to balance efficiency in testing and accuracy with respect to cloud quantum computing systems. The results here underscore the need to both use relevant cost models and optimize hyperparameters of existing optimization methods for competitive performance. The methods introduced here have several practical advantages in realistic experimental settings, and we have used one of them successfully in a separately published experiment on Google’s Sycamore device.

FPGA-Based Real-Time &lt;inline-formula&gt; &lt;tex-math notation="LaTeX"&gt;$n/\gamma$ &lt;/tex-math&gt; &lt;/inline-formula&gt; Discrimination With Liquid Scintillator

A real-time $n/\gamma $ discrimination prototype system based on high-speed waveform sampling and high-performance field-programmable gate array (FPGA) is presented in this paper. In order to accurately record detector signals, a high-speed sampling board with a 14-bit analog-to-digital converter (AD9680) is designed. The BC501A liquid scintillator is employed as the neutron detector, and a discrimination algorithm is implemented in the FPGA of the sampling board. The system is calibrated by 22Na, 137Cs, and 60Co $\gamma $ -sources. A PuC neutron source is used to evaluate the discrimination ability. The figure-of-merit of PuC neutron source is determined to be about 1.005 over an energy range of 0–4000 keVee, which is consistent with the test results of the commercial digitizer, and the false alarm rate of 60Co is 0.19%. This system has been successfully applied for the environmental neutron monitoring experiment during the first commissioning of white neutron source tunnel of China spallation neutron source.

The intensity detection of single-photon detectors based on photon counting probability density statistics**Projiect supported by the Fundamental Research Funds for the Central Universities, China (Grant No. AUGA5710056414), the Program for Innovation Research of Science in Harbin Institute of Technology (Grant Nos. PIRS OF HIT A201412 and PIRS OF HIT Q201505), the National Natural Science Foundation of China (Grant No. 11675046),

Single-photon detectors possess the ultra-high sensitivity, but they cannot directly respond to signal intensity. Conventional methods adopt sampling gates with fixed width and count the triggered number of sampling gates, which is capable of obtaining photon counting probability to estimate the echo signal intensity. In this paper, we not only count the number of triggered sampling gates, but also record the triggered time position of photon counting pulses. The photon counting probability density distribution is obtained through the statistics of a series of the triggered time positions. Then Minimum Variance Unbiased Estimation (MVUE) method is used to estimate the echo signal intensity. Compared with conventional methods, this method can improve the estimation accuracy of echo signal intensity due to the acquisition of more detected information. Finally, a proof-of-principle laboratory system is established. The estimation accuracy of echo signal intensity is discussed and a high accuracy intensity image is acquired under low-light level environments.

ISUOG Practice Guidelines: role of ultrasound in twin pregnancy.

ISUOG Practice Guidelines: role of ultrasound in twin pregnancy.

Low-Complexity TOAD-Based All-Optical Sampling Gate With Ultralow Switching Energy and High Linearity

We present experimentally a low-complexity ultralow switching energy and high-linearity all-optical sampling gate based on a terahertz optical asymmetric demultiplexer, constructed by placing a polarization-insensitive multiple-quantum-well semiconductor optical amplifier (PI-MQW-SOA) asymmetrically within a fiber loop mirror. Using a picosecond pulse train as the trigger clock, we analyze, in detail, the influence of the sampling pulse power and the offset of the PI-MQW-SOA from the loop midpoint on the shape, width, and amplitude of the sampling window, respectively. Furthermore, the switching energy and linearity of this sampling gate under different widths of sampling windows are specifically investigated. Results demonstrate that our sampling gate possesses a switching energy as low as 25 fJ and a high linearity above 0.99.

High-resolution, low-injection-signal-power optical sampling

We have demonstrated a high-resolution, low-injection-signal-power optical sampling system using a 20-m-length dispersion-flattened photonics crystal fiber as optical sampling gate, and employing bridge-form low noise optical fiber amplifier. Optical pulse trains with −35 dBm input power and 1.25 ps interval were clearly displayed by using our all optical sampling system. To measure the temporal resolution of system accurately, optical pulse trains from a commercial 40 GHz actively mode-locked fiber laser, were injected into the optical sampling system and an autocorrelator with 5-fs resolution, respectively. 1.02 and 0.83 ps pulse-width were obtained by using our optical sampling system and the autocorrelator, respectively. These measured results show that the resolution of the system is as high as 0.6 ps.

Standards of the Polish Ultrasound Society - Update. Ultrasound examination of renal arteries.

This paper has been prepared on the basis of the Standards of the Polish Ultrasound Society and updated based on the latest reports from the relevant literature. The author presents a renal artery examination technique, patient preparation for the testing, limitations of the method, currently recommended proper blood flow standards and criteria for the diagnosis of significant stenoses. Renal artery ultrasound is performed using a 2–5 MHz probe, usually a convex 3.5 MHz one. The ultrasound machine must be equipped with the Doppler options for the evaluation of color coded blood flow and recording of the blood flow spectrum, including the triplex Doppler mode. Patients have to fast for at least eight hours before testing. Ultrasound always begins with the assessment of renal structure using the grayscale. Next, color coded blood flow imaging is used, followed by placing a sampling gate in the lumen of the target vessel to record the spectral image. The aim of renal artery ultrasound is to assess the course and position of arteries, evaluate blood flow parameters, as well as visualize possible changes: stenoses, occlusions, aneurysms, or arteriovenous fistulas. Blood flow velocity is always measured in a longitudinal projection/ longitudinal section of the vessel, after placing the sampling gate in the central part of the flowing bloodstream, which normally corresponds to the central part of the vascular cross-section. When diagnosing renal artery stenosis, it is necessary to know the nature of the blood flow and norms for flow parameters in healthy vessels. The spectrum of the blood flow velocity in renal arteries and their branches is a low resistance one. The following parameters are used to evaluate normal renal arteries and to identify the narrowed ones: Vmax, Vmin, RAR, AT, AI, RI and PI.

FBG‐assisted ICI reduction for AO‐OFDM demultiplexed signal

ABSTRACTIn an all‐optical orthogonal frequency division multiplexing (AO‐OFDM) system, the demultiplexed subcarriers from an optical discrete fourier transform circuit are needed to be sampled by optical gates in the intercarrier interference (ICI)‐free narrow interval. In this article, we present a theoretical investigation of fiber Bragg grating (FBG) assisted ICI reduction in an AO‐OFDM system in place of an optical sampling gate (SG). The optimum durations of SG and FBG are analyzed for different symbol rise times (trise) and the analysis is extended to chromatic dispersion (CD) effects. The proposed FBG device provides tolerance to dispersion, which causes shifting of narrowed ICI‐free region. The FBG achieves BER &lt; 10−3 for transmission of 45 km without cyclic prefix, and synchronization with shifted ICI‐free region is not needed. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:2320–2324, 2014

Pulsed Driver Control System for High-Power LED

Pulsed current source is used to drive high-power LED in thermal analysis and testing. A new scheme to design the high-power LED pulsed current source, which integrates FPGA device, with highly quality single-chip microcomputer C8051F as the control center, is introduced. In order to obtain the LED automatic current control, the negative feedback is used in the LED pulsed driver. The pulsed current source consists of constant-current source and couple output interface controlled by square pulse signal, which ensures the stability of pulsed current, rise time and fall time. It is convenient to adjust the pulse current amplitude, pulse width, pulse cycle and sampling gate independently. Results show that the current stability of the driver control system can obtain 0.01%.

Measurement of Range-Weighting Function for Range Imaging of VHF Atmospheric Radars Using Range Oversampling

Abstract Multifrequency range imaging (RIM) used with the atmospheric radars at ultra- and very high-frequency (VHF) bands is capable of retrieving the power distribution of the backscattered radar echoes in the range direction, with some inversion algorithms such as the Capon method. The retrieved power distribution, however, is weighted by the range-weighting function (RWF). Modification of the retrieved power distribution with a theoretical RWF may cause overcorrection around the edge of the sampling gate. In view of this, an effective RWF that is in a Gaussian form and varies with the signal-to-noise ratio (SNR) of radar echoes has been proposed to mitigate the range-weighting effect and thereby enhance the continuity of the power distribution at gate boundaries. Based on the previously proposed concept, an improved approach utilizing the range-oversampled signals is addressed in this article to inspect the range-weighting effects at different range locations. The shape of the Gaussian RWF for describing the range-weighting effect was found to vary with the off-center range location in addition to the SNR of radar echoes—that is, the effective RWF for the RIM was SNR and range dependent. The use of SNR- and range-dependent RWF can be of help to improve the range imaging to some degree at the range location outside the range extent of a sampling gate defined by the pulse length. To verify the proposed approach, several radar experiments were carried out with the Chung-Li (24.9°N, 121.1°E) and middle and upper atmosphere (MU; 34.85°N, 136.11°E) VHF radars.

Photon-counting chirped amplitude modulation lidar using a smart premixing method

We proposed a new premixing method for photon-counting chirped amplitude modulation lidar (PCCAML). Earlier studies used the counting results of the returned signal detected by a Geiger mode avalanche photodiode detector (Gm-APD) to mix with the reference signal, called the postmixing method. We use an alternative method known as the premixing method, in which the reference signal is used to directly modulate the sampling gate width of the Gm-APD, and the mixing of the returned signal and the reference signal is completed before the Gm-APD. This premixing method is more flexible and may perform better than the postmixing method in terms of signal-to-noise ratio by cutting down a separated mixer commonly used in the postmixing lidar system. Furthermore, this premixing method lowers the demand for the sampling frequency of the Gm-APD. It allows the use of a much wider modulation bandwidth to improve the range accuracy and resolution. To the best of our knowledge, this is the first report to use the premixing method in the PCCAML system, which will benefit future lidar applications.

Nonlinear cross-talk mitigation in polychromatic parametric sampling gate

New technique for cancellation of nonlinear cross-talk in polychromatic parametric sampling gate is described and quantified. The method relies on a newly derived look-up table method that achieves equalization and suppresses nonlinear response associated with parametric sampling operation. The new cancellation scheme is implemented in a framework of a specific parametric photonics assisted analog-to-digital conversion (ADC) copy-and-sample-all (CaSA) architecture. A 20 dB improvement in total harmonic distortion is demonstrated experimentally.

Extraction of correlated count rates using various gate generation techniques: Part I theory

This paper presents an overview of different gate generation techniques that can be used to extract correlated counting rates from neutron pulse trains in the context of Passive Neutron Multiplicity Counting (PNMC). PNMC based on shift register pulse train time autocorrelation analyzers is an important Non-Destructive Assay (NDA) method used in the quantification of plutonium and other spontaneously fissile materials across the nuclear fuel cycle. Traditionally PNMC employs signal-triggered gate generation followed by a random gate, separated from the trigger pulse by a long delay, to extract the totals rate (gross or singles), the pairs (coincidences or doubles) rate, and the triplets (or triples) rate of correlated neutron pulse trains. In this paper we provide expressions for singles, doubles and triples rates using the information available in both, the random and signal-triggered gates (traditional shift register analysis), in the randomly triggered gates only, and introduce a third approach to extract the correlated rates using signal-triggered gates only. In addition, we expand the formalism for randomly triggered gate generation to include Fast Accidental Sampling (FAS) and consecutive gate generation.