Required Acquisition Time Research Articles

Inspection techniques in photovoltaic power plants: A review of electroluminescence and photoluminescence imaging

The growth of photovoltaic power plants in both size and number has spurred the development of new approaches in inspection techniques. The most commonly employed methods include visual inspections, current-voltage measurements, infrared thermography, and luminescence imaging. Luminescence, rooted in the electromagnetic radiation capture of semiconductor structures that make up solar cells, proves effective in detecting various failures that may occur throughout the lifespan of a photovoltaic module. This phenomenon can be induced either by injecting current into the photovoltaic module (Electroluminescence) or through optical excitation using an appropriate light source (Photoluminescence). This paper offers an overview of the conventional outdoor luminescence imaging technique, delving into its applications and limitations. Additionally, it provides a comprehensive review of innovative outdoor luminescence technique approaches. These novel techniques aim to address several limitations of conventional methods, such as the considerably lower luminescence emission intensity compared to solar radiation, the need for external energy sources for current injection, the required acquisition time, and the necessity of disconnecting the solar module.

Accessing self-diffusion on nanosecond time and nanometre length scales with minute kinetic resolution.

Neutron spectroscopy uniquely and non-destructively accesses diffusive dynamics in soft and biological matter, including for instance proteins in hydrated powders or in solution, and more generally dynamic properties of condensed matter on the molecular level. Given the limited neutron flux resulting in long counting times, it is important to optimize data acquisition for the specific question, in particular for time-resolved (kinetic) studies. The required acquisition time was recently significantly reduced by measurements of discrete energy transfers rather than quasi-continuous neutron scattering spectra on neutron backscattering spectrometers. Besides this reduction in acquisition times, smaller amounts of samples can be measured with better statistics, and most importantly, kinetically changing samples, such as aggregating or crystallizing samples, can be followed. However, given the small number of discrete energy transfers probed in this mode, established analysis frameworks for full spectra can break down. Presented here are new approaches to analyze measurements of diffusive dynamics recorded within fixed windows in energy transfer, and these are compared with the analysis of full spectra. The new approaches are tested by both modeled scattering functions and a comparative analysis of fixed energy window data and full spectra on well understood reference samples. This new approach can be employed successfully for kinetic studies of the dynamics focusing on the short-time apparent center-of-mass diffusion.

Feasibility of an accelerated PVAL method for the collection of GSR and biological traces.

The polyvinyl alcohol method (PVAL) is known as an effective technique to thoroughly collect traces of gunshot residue (GSR) from different surfaces, e.g., from hands or gunshot wounds. Despite obvious advantages over other methods using adhesive tapes, PVAL is still not widely accepted and applied in routine case work due to a required acquisition time of at least 15 to 20 min for a single shooting hand. In this study, the feasibility of a modified procedure taking 6 to 8 min per sample is tested within the frame of an experimental setting including (1) the collection of GSR from experimental gunshots with a semi-automatic pistol and lead-containing primer ammunition and (2) a simple experimental setting involving dry and moist artificial blood traces. In a third step, samples of four gun-associated suicide cases and one attempted suicide case were taken and analyzed. Furthermore, an exemplary implementation into a work flow of modern instrumental techniques of GSR analysis is presented.

Development of a scanning electron microscopy with polarization analysis system for magnetic imaging with ns time resolution and phase-sensitive detection.

Scanning electron microscopy with polarization analysis is a powerful lab-based magnetic imaging technique offering simultaneous imaging of multiple magnetization components and a very high spatial resolution. However, one drawback of the technique is the long required acquisition time resulting from the low inherent efficiency of spin detection, which has limited the applicability of the technique to certain quasi-static measurement schemes and materials with high magnetic contrast. Here we demonstrate the ability to improve the signal-to-noise ratio for particular classes of measurements involving periodic excitation of the magnetic structure via the implementation of a digital phase-sensitive detection scheme facilitated by the integration of a time-to-digital converter to the system. The modified setup provides dynamic imaging capabilities using selected time windows and finally full time-resolved imaging with a demonstrated time resolution of better than 2 ns.

High resolution terahertz spectroscopy of a whispering gallery mode bubble resonator using Hilbert analysis.

We report on data processing for continuous wave (CW) terahertz (THz) spectroscopy measurements based on a Hilbert spectral analysis to achieve MHz resolution. As an example we investigate the spectral properties of a whispering gallery mode (WGM) THz bubble resonator at critical coupling. The experimental verification clearly demonstrates the significant advantages in relative frequency resolution and required acquisition time of the proposed method over the traditional data analysis. An effective frequency resolution, only limited by the precision and stability of the laser beat signal, can be achieved without complex extensions to a standard commercially available CW THz spectrometer.

Parallel Spectral Acquisition with Orthogonal ICR Cells.

FT-based high performance mass analyzers yield increased resolving power and mass measurement accuracy, yet require increased duration of signal acquisition that can limit many applications. The implementation of stronger magnetic fields, multiple detection electrodes for harmonic signal detection, and an array of multiple mass analyzers arranged along the magnetic field axis have been used to decrease required acquisition time. The results presented here show that multiple ion cyclotron resonance (ICR) mass analyzers can also be implemented orthogonal to the central magnetic field axis. The orthogonal ICR cell system presented here consisting of two cells (master and slave cells) was constructed with printed circuit boards and installed within a single superconducting magnet and vacuum system. A master cell was positioned, as is normally done with ICR cells, on the central magnetic field axis and a slave cell was located off this central axis, but directly adjacent and alongside the master cell. To achieve ion transfer between cells, ions that were initially trapped in the master cell were drifted across the magnetic field into the slave cell with application of a small DC field applied perpendicularly to the magnetic field axis. A subsequent population of ions was injected and accumulated in the master cell. Simultaneous excitation of cyclotron motion of ions in both cells was carried out; ICR signals from each cell were independently amplified and recorded in parallel. Presented here are the initial results of successful parallel spectral acquisition with this orthogonal dual ICR cell array. Graphical Abstract ᅟ.

Comparison of breath-hold, respiratory navigated and free-breathing MR elastography of the liver

PurposeHepatic magnetic resonance elastography (MRE) is currently a breath-hold imaging technique. Patients with chronic liver disease can have comorbidities that limit their ability to breath-hold (BH) for the required acquisition time. Our aim was to evaluate whether stiffness measurements obtained from a navigator-triggered MRE acquisition are comparable to standard expiratory breath-hold, inspiratory breath-hold or free-breathing in healthy participants. Materials and methodsTwelve healthy participants were imaged using the four methods on a clinical 1.5T MR system equipped with a product MRE system. Mean liver stiffness, and measurable area of stiffness (with a confidence threshold >95%) were compared between sequences using the concordance correlation coefficient. Repeatability of each sequence between two acquisitions was also assessed. ResultsThe standard BH expiratory technique had high concordance with the navigated technique (r=0.716), and low concordance with the BH inspiration (r=0.165) and free-breathing (r=0.105) techniques. The navigator-triggered technique showed no statistical difference in measurable area of liver or in repeatability compared with the standard expiratory acquisition (p=0.997 and p=0.407 respectively). The free-breathing technique produced less measurable liver area and was less repeatable than the alternative techniques. The increase in acquisition time for navigator techniques was 3min 6s compared to standard expiratory breath-hold. ConclusionNavigator-based hepatic MRE measurements are comparable to the reference standard expiratory breath-hold acquisition in healthy participants.

Ultrafast compound doppler imaging: providing full blood flow characterization

Doppler-based flow analysis methods require acquisition of ultrasound data at high spatio-temporal sampling rates. These rates represent a major technical challenge for ultrasound systems because a compromise between spatial and temporal resolution must be made in conventional approaches. Consequently, ultrasound scanners can either provide full quantitative Doppler information on a limited sample volume (spectral Doppler), or averaged Doppler velocity and/or power estimation on a large region of interest (Doppler flow imaging). In this work, we investigate a different strategy for acquiring Doppler information that can overcome the limitations of the existing Doppler modes by significantly reducing the required acquisition time. This technique is called ultrafast compound Doppler imaging and is based on the following concept: instead of successively insonifying the medium with focused beams, several tilted plane waves are sent into the medium and the backscattered signals are coherently summed to produce high-resolution ultrasound images. We demonstrate that this strategy allows reduction of the acquisition time by a factor of up to of 16 while keeping the same Doppler performance. Depending on the application, different directions to increase performance of Doppler analysis are proposed and the improvement is quantified: the ultrafast compound Doppler method allows faster acquisition frame rates for high-velocity flow imaging, or very high sensitivity for low-flow applications. Full quantitative Doppler flow analysis can be performed on a large region of interest, leading to much more information and improved functionality for the physician. By leveraging the recent emergence of ultrafast parallel beamforming systems, this paper demonstrates that breakthrough performances in flow analysis can be reached using this concept of ultrafast compound Doppler.

Multirate adaptive filtering for low complexity DS/CDMA code acquisition

Code acquisition in CDMA systems is conventionally conducted with a matched-filter based structure. However, the performance of this method degrades greatly while multiple access interference presents. Recently, an adaptive filtering scheme was proposed to solve this problem. It has been shown that the computational complexity of this approach is proportional to the delay uncertainty and inversely proportional to the required acquisition time. When propagation delay is large and the required acquisition time is short, the computational complexity of the adaptive filtering approach will become high. In this paper, we propose a multirate adaptive code acquisition approach to alleviate this problem. The proposed scheme is comprised of several acquisition units operating in different processing rates. Thanks to the decimation property in multirate processing, the overall computational complexity can be greatly reduced. Theoretical analysis of adaptive filters and mean acquisition time is also provided. Experimental results show that while the proposed scheme can have comparable performance with respect to the original adaptive acquisition scheme, its computational complexity is much lower.

Error analysis of marker‐based object localization using a single‐plane XRII

The role of imaging and image guidance is increasing in surgery and therapy, including treatment planning and follow-up. Fluoroscopy is used for two-dimensional (2D) guidance or localization; however, many procedures would benefit from three-dimensional (3D) guidance or localization. Three-dimensional computed tomography (CT) using a C-arm mounted x-ray image intensifier (XRII) can provide high-quality 3D images; however, patient dose and the required acquisition time restrict the number of 3D images that can be obtained. C-arm based 3D CT is therefore limited in applications for x-ray based image guidance or dynamic evaluations. 2D-3D model-based registration, using a single-plane 2D digital radiographic system, does allow for rapid 3D localization. It is our goal to investigate-over a clinically practical range-the impact of x-ray exposure on the resulting range of 3D localization precision. In this paper it is assumed that the tracked instrument incorporates a rigidly attached 3D object with a known configuration of markers. A 2D image is obtained by a digital fluoroscopic x-ray system and corrected for XRII distortions (+/- 0.035 mm) and mechanical C-arm shift (+/- 0.080 mm). A least-square projection-Procrustes analysis is then used to calculate the 3D position using the measured 2D marker locations. The effect of x-ray exposure on the precision of 2D marker localization and on 3D object localization was investigated using numerical simulations and x-ray experiments. The results show a nearly linear relationship between 2D marker localization precision and the 3D localization precision. However, a significant amplification of error, nonuniformly distributed among the three major axes, occurs, and that is demonstrated. To obtain a 3D localization error of less than +/- 1.0 mm for an object with 20 mm marker spacing, the 2D localization precision must be better than +/- 0.07 mm. This requirement was met for all investigated nominal x-ray exposures at 28 cm FOV, and for all but the lowest two at 40 cm FOV. However, even for those two nominal exposures, the expected 3D localization error is less than +/- 1.2 mm. The tracking precision was +/- 0.65 mm for the out-of-plane translations, +/- 0.05 mm for in-plane translations, and +/- 0.05 degrees for the rotations. The root mean square (RMS) difference between the true and projection-Procrustes calculated location was 1.07 mm. It is believed these results show the potential of this technique for dynamic evaluations or real-time image guidance using a single x-ray source and XRII detector.

Molecular Imaging Using a Targeted Magnetic Resonance Hyperpolarized Biosensor

A magnetic resonance approach is presented that enables high-sensitivity, high-contrast molecular imaging by exploiting xenon biosensors. These sensors link xenon atoms to specific biomolecular targets, coupling the high sensitivity of hyperpolarized nuclei with the specificity of biochemical interactions. We demonstrated spatial resolution of a specific target protein in vitro at micromolar concentration, with a readout scheme that reduces the required acquisition time by >3300-fold relative to direct detection. This technique uses the signal of free hyperpolarized xenon to dramatically amplify the sensor signal via chemical exchange saturation transfer (CEST). Because it is approximately 10,000 times more sensitive than previous CEST methods and other molecular magnetic resonance imaging techniques, it marks a critical step toward the application of xenon biosensors as selective contrast agents in biomedical applications.

Sensitivity Enhancement of Multidimensional NMR Experiments by Paramagnetic Relaxation Effects

One of the main goals of NMR method development is to increase the sensitivity of multidimensional NMR experiments or reduce the required acquisition time. In these experiments, more than 80% of the NMR instrument time is spent on the recycle delay, where the instrument idles to wait for the recovery of proton magnetization. In this study, we report a method of using paramagnetic relaxation effects to shorten the recycle delays required in multidimensional NMR experiments of biological macromolecules. This approach significantly reduces the NMR instrument time required. Ni(2+) ion, complexed with the chelating molecule DO2A, is used to decrease the proton T(1) relaxation time of biological macromolecules without the significant line-broadening effects that are associated with most paramagnetic ions. The Ni(DO2A) also significantly decreases the T(1) relaxation time of water, thus providing additional sensitivity gain by eliminating the saturation of labile amide resonances.

A sliding Goertzel algorithm

This paper presents a sliding Goertzel algorithm to accurately estimate the Fourier coefficients of multifrequency (MF) sinusoidal signals buried in noise. The algorithm is based on second-order digital resonators that are tuned at the desired frequencies. The proposed method provides the following advantages when compared with the conventional Goertzel algorithm. Firstly, it computes Fourier coefficients in less than one signal period. Therefore, faster detection time is achieved, particularly when the greatest common divisor (GCD) of the input frequencies is small. Secondly, it is less prone to numerical overflow problems in fixed-point arithmetic implementation. Thirdly, the algorithm is quite suitable for time varying sinusoidal signal estimation. An analysis is undertaken to provide additional insight into the issue of required acquisition time versus the desired accuracy for the proposed algorithm. Extensive simulation tests are also included to demonstrate its performance.

A new passive synthetic aperture technique for towed arrays

An algorithm that synthesizes apertures in the beam domain using FFT transformations and performs coherent processing of subaperture signals at successive time intervals is presented. Experimental tests of the algorithm show that for ocean environments with spatial coherence longer than the synthetic aperture length and for signals with temporal coherence longer than the required acquisition time, a synthetic array gain is achieved which roughly corresponds to the length of an equivalent fully populated array. In the experiments, transducer generated CW with phase stability and pseudorandom signals were used. Limitations on the spatial and temporal coherence were introduced only by the medium, the temporal coherence of the pseudorandom signal, and the shape and stability of the line array used. >

The limits of NMR imaging

The limits of isotropic spatial resolution in NMR imaging are estimated starting from an explicit formula for S N ratios. It is shown that the limit is essentially imposed by the sensitivity of the NMR experiment. The required acquisition time is of course also a factor, but since it increases with the 7th power of resolution, changing acquisition time from quite short to excessively long will cause only a relatively modest increase of the latter. For 1H NMR microscopy (samples of the order of 1 cm in diameter), there is an “impassable” barrier of about 40 microns even at high-fields (e.g., 300 MHz) for samples very rich in hydrogen. On the other hand, there is no particularly sharp degradation of resolution when going to lower fields (e.g., 10 MHz), or hydrogen-poor samples, or some of the heteronuclei (e.g., 23Na). Consequently, NMR microscopy applications requiring isotropic voxel sizes of 100–500 microns have good chances of success even at surprisingly low fields/concentrations.