Time-resolved Data Acquisition Research Articles

Laboratory Study of Magnetic Reconnection in Lunar-relevant Mini-magnetospheres

Mini-magnetospheres are small ion-scale structures that are well suited to studying kinetic-scale physics of collisionless space plasmas. Such ion-scale magnetospheres can be found on local regions of the Moon, associated with the lunar crustal magnetic field. In this paper, we report on the laboratory experimental study of magnetic reconnection in laser-driven, lunar-like ion-scale magnetospheres on the Large Plasma Device at the University of California, Los Angeles. In the experiment, a high-repetition rate (1 Hz), nanosecond laser is used to drive a fast-moving, collisionless plasma that expands into the field generated by a pulsed magnetic dipole embedded into a background plasma and magnetic field. The high-repetition rate enables the acquisition of time-resolved volumetric data of the magnetic and electric fields to characterize magnetic reconnection and calculate the reconnection rate. We notably observe the formation of Hall fields associated with reconnection. Particle-in-cell simulations reproducing the experimental results were performed to study the microphysics of the interaction. By analyzing the generalized Ohm’s law terms, we find that the electron-only reconnection is driven by kinetic effects through the electron pressure anisotropy. These results are compared to recent satellite measurements that found evidence of magnetic reconnection near the lunar surface.

Time-resolved pressure-sensitive paint measurements for cryogenic wind tunnel tests

A first time-resolved pressure-sensitive paint (PSP) test campaign at the European Transonic Wind Tunnel (ETW) was conducted within the research initiative “Unsteady flow and interaction phenomena at High Speed Stall conditions”. One of the objectives of this wind tunnel campaign was to resolve time-series of surface pressure distributions caused by complex 3-D buffet phenomena on a full-span airplane model XRF-1 transport aircraft configuration. At higher angle-of-attack and high Mach number, pressure fluctuations with a frequency of several hundred Hertz are expected to occur on the main wing and the horizontal tail plane (HTP) caused by the buffet effect. To capture the expected buffet phenomena by PSP, the German Aerospace Center developed a time-resolved PSP measurement and data acquisition system as well as a post-processing method for measurements in ETW. The measurements were conducted on the main wing and HTP simultaneously, with a camera frame rate of up to 2 kHz. The transonic buffet phenomena were observed at the flight relevant Reynolds number Re = 12.9 × 106 and Re = 25.0 × 106. The time-varying surface pressure distribution on the model was successfully captured by PSP. The time-series and spectra of both PSP and pressure transducer data match very well.

Measuring the Time-evolution of Nanoscale Materials with Stopped-flow and Small-angle Neutron Scattering.

This paper presents the use of a stopped-flow small-angle neutron-scattering (SANS) sample environment to quickly mix liquid samples and study nanoscale kinetic processes on time scales of seconds to minutes. The stopped-flow sample environment uses commercially available syringe pumps to mix the desired volumes of liquid samples that are then injected through a dynamic mixer into a quartz glass cell in approximately 1 s. Time-resolved SANS data acquisition is synced with the sample mixing to follow the evolution of the nanostructure in solution after mixing. To make the most efficient use of neutron beam time, we use a series of flow selector valves to automatically load, rinse, and dry the cell between measurements, allowing for repeated data collection throughout multiple sample injections. Sample injections are repeated until sufficient neutron scattering statistics are collected. The mixing setup can be programmed to systematically vary conditions to measure the kinetics at different mixing ratios, sample concentrations, additive concentrations, and temperatures. The minimum sample volume required per injection is approximately 150 µL depending on the path length of the quartz cell. Representative results using this stopped-flow sample environment are presented for rapid lipid exchange kinetics in the presence of an additive, cyclodextrin. The vesicles exchange outer-leaflet (exterior) lipids on the order of seconds and fully exchange both interior and exterior lipids within hours. Measuring lipid exchange kinetics requires in situ mixing to capture the faster (seconds) and slower (minutes) processes and extract the kinetic rate constants. The same sample environment can also be used to probe molecular exchange in other types of liquid samples such as lipid nanoparticles, proteins, surfactants, polymers, emulsions, or inorganic nanoparticles. Measuring the nanoscale structural transformations and kinetics of exchanging or reacting systems will provide new insights into processes that evolve at the nanoscale.

Synchronizing gas injections and time-resolved data acquisition for perturbation-enhanced APXPS experiments.

An experimental approach is described in which well-defined perturbations of the gas feed into an Ambient Pressure X-ray Photoelectron Spectroscopy (APXPS) cell are fully synchronized with the time-resolved x-ray photoelectron spectroscopy data acquisition. These experiments unlock new possibilities for investigating the properties of materials and chemical reactions mediated by their surfaces, such as those in heterogeneous catalysis, surface science, and coating/deposition applications. Implementation of this approach, which is termed perturbation-enhanced APXPS, at the SPECIES beamline of MAX IV Laboratory is discussed along with several experimental examples including individual pulses of N2 gas over a Au foil, a multi-pulse titration of oxygen vacancies in a pre-reduced TiO2 single crystal with O2 gas, and a sequence of alternating precursor pulses for atomic layer deposition of TiO2 on a silicon wafer substrate.

Total Emission Time Resolved Decay: a Method for Measurement and Resolution of Broad-Band Emission.

This article reports a time-resolved fluorescence data acquisition technique termed as "Total Emission Time Resolved Decay" (TETRD). TETRD is recorded by using zero-order diffraction of emission grating in TCSPC instrument. TETRD decay curve has entire wavelength dependent decay information buried in it. Cut-off filters are used to avoid scattering contamination. Two existing approaches are used for analysing the interconnected TETRD data. (i) First, global analysis: for discretely decaying multiple components, TETRD dataset is analyzed using global analysis. The normalized pre-exponentials (αi) and relative amplitudes (fi) recovered from global analysis reflect the individual component emission more faithfully and resembles with steady-state spectral data as well. (ii) Second, stretched exponential fitting (StrEF): for continuous lifetime distribution systems, StrEF (I(t) = I0 exp[-(t/τ)1/h]) has been used to analyse TETRD data. The average lifetime (τ) of StrEF matches well with the average lifetime of multi-exponential fitting, the heterogeneity factor (h) of StrEF is an additional parameter, which informs about local heterogeneity in the system. It is shown that the lifetimes obtained with TETRD matches well with the lifetimes obtained using conventional time resolved emission spectra (TRES). TETRD holds advantage in rapid data acquisition and facilitates inclusion of another variable (like concentration, solvent composition, pH, excitation wavelength etc.) into experimental design. Further, with the use of an appropriate data analysis tool, the multi-component decay profiles can be resolved conveniently.

Automated multi-atlas segmentation of cardiac 4D flow MRI

Four-dimensional (4D) flow magnetic resonance imaging (4D Flow MRI) enables acquisition of time-resolved three-directional velocity data in the entire heart and all major thoracic vessels. The segmentation of these tissues is typically performed using semi-automatic methods. Some of which primarily rely on the velocity data and result in a segmentation of the vessels only during the systolic phases. Other methods, mostly applied on the heart, rely on separately acquired balanced Steady State Free Precession (b-SSFP) MR images, after which the segmentations are superimposed on the 4D Flow MRI. While b-SSFP images typically cover the whole cardiac cycle and have good contrast, they suffer from a number of problems, such as large slice thickness, limited coverage of the cardiac anatomy, and being prone to displacement errors caused by respiratory motion. To address these limitations we propose a multi-atlas segmentation method, which relies only on 4D Flow MRI data, to automatically generate four-dimensional segmentations that include the entire thoracic cardiovascular system present in these datasets. The approach was evaluated on 4D Flow MR datasets from a cohort of 27 healthy volunteers and 83 patients with mildly impaired systolic left-ventricular function. Comparison of manual and automatic segmentations of the cardiac chambers at end-systolic and end-diastolic timeframes showed agreements comparable to those previously reported for automatic segmentation methods of b-SSFP MR images. Furthermore, automatic segmentation of the entire thoracic cardiovascular system improves visualization of 4D Flow MRI and facilitates computation of hemodynamic parameters.

Super-resolution reconstruction of 4D-CT lung data via patch-based low-rank matrix reconstruction

Lung 4D computed tomography (4D-CT), which is a time-resolved CT data acquisition, performs an important role in explicitly including respiratory motion in treatment planning and delivery. However, the radiation dose is usually reduced at the expense of inter-slice spatial resolution to minimize radiation-related health risk. Therefore, resolution enhancement along the superior–inferior direction is necessary.In this paper, a super-resolution (SR) reconstruction method based on a patch low-rank matrix reconstruction is proposed to improve the resolution of lung 4D-CT images. Specifically, a low-rank matrix related to every patch is constructed by using a patch searching strategy. Thereafter, the singular value shrinkage is employed to recover the high-resolution patch under the constraints of the image degradation model. The output high-resolution patches are finally assembled to output the entire image.This method is extensively evaluated using two public data sets. Quantitative analysis shows that the proposed algorithm decreases the root mean square error by 9.7%–33.4% and the edge width by 11.4%–24.3%, relative to linear interpolation, back projection (BP) and Zhang et al’s algorithm.A new algorithm has been developed to improve the resolution of 4D-CT. In all experiments, the proposed method outperforms various interpolation methods, as well as BP and Zhang et al’s method, thus indicating the effectivity and competitiveness of the proposed algorithm.

Mechanisms of the structural modification of Ti films by pulsed direct current and inductively coupled plasma-assisted pulsed direct current sputtering

Titanium (Ti) thin films have been deposited by direct current (dc), pulsed dc, and inductively coupled plasma (ICP)-assisted pulsed dc sputtering to investigate the effects of current pulsing and ICP assistance on film structure and properties. Ti thin films were deposited from a Ti target using Ar as a discharge gas. Ion energy was measured by energy-resolved mass spectrometry. The discharge plasma parameters were measured using a single probe with a time-resolved data acquisition system. The crystal structure was investigated by X-ray diffraction. Surface and cross-sectional morphologies were investigated by atomic force microscopy and scanning electron microscopy, respectively. The cross-sectional images demonstrated that the film structure changed from a coarse columnar structure with voids to a fine columnar structure. Changes in the roughness and crystallite sizes of the deposited Ti thin films indicated that the thin films were amorphized by the ICP-assisted sputtering, resulting in the smoothing of the film surface. Energy and mass analyses indicated that the energy fluxes to the substrate via Ar+ and Ti+ ions increased by more than four and two orders of magnitude, respectively, when ICP assistance was employed. This large difference in degree of enhancement generated by ICP assistance for Ar+ and Ti+ ions suggests different ionization efficiencies between gas-phase Ar and sputter-emitted energetic Ti, particularly in the ICP-assisted pulsed dc discharge. As a result of the increase in energy flux to the substrate, the mean energy transferred by both Ar+ and Ti+ ions per Ti metal particle (atom or ion) arriving at the substrate increased from approximately 40eV for dc sputtering to >104eV for ICP-assisted pulsed dc sputtering, and the mean energy transferred by Ti+ ions per Ti metal particle (atom or ion) arriving at the substrate increased from a few eV for dc sputtering to approximately 29–30eV for ICP-assisted pulsed dc sputtering. These increases in transferred energy reflect the formation of intense and broad high-energy peaks, as shown in the ion-energy spectra. It is shown that the formation of an additional high-energy peak to the single peak of the dc discharge results from the current pulsing, and that the further high-energy shift and splitting of the bimodal peaks result from the combination of the increase in plasma sheath potential to the grounded substrate and the increases in the electron density and electron temperature due to the subsequent ICP assistance to the pulsed dc discharge.

Design and validation of magnetic particle spectrometer for characterization of magnetic nanoparticle relaxation dynamics.

The design and validation of a magnetic particle spectrometer (MPS) system used to study the linear and nonlinear behavior of magnetic nanoparticle suspensions is presented. The MPS characterizes the suspension dynamic response, both due to relaxation and saturation effects, which depends on the magnetic particles and their environment. The system applies sinusoidal excitation magnetic fields varying in amplitude and frequency and can be configured for linear measurements (1 mT at up to 120 kHz) and nonlinear measurements (50 mT at up to 24 kHz). Time-resolved data acquisition at up to 4 MS/s combined with hardware and software-based signal processing allows for wide-band measurements up to 50 harmonics in nonlinear mode. By cross-calibrating the instrument with a known sample, the instantaneous sample magnetization can be quantitatively reconstructed. Validation of the two MPS modes are performed for iron oxide and cobalt ferrite suspensions, exhibiting Néel and Brownian relaxation, respectively.

The Use of Fluorescently Labeled Lipids to Determine Dynamics of Protein Mediated In Vitro Lipid Transfer

In recent years, phosphatidylinositol (PtdIns) transfer proteins (PITPs) have been established as essential regulators of phosphoinositide signaling outcomes in eukaryotic cells. The key function of these proteins is to mediate a PtdIns/phosphatidylcholine (PtdCho) exchange reaction. This function is central to their abilities to regulate lipid signaling. Despite its importance the mechanistic details of this lipid exchange remain largely undetermined. In order to decipher some aspects of the exchange reaction, we have modified an in vitro lipid transfer method first described by Somerharju et al. (Biochemistry, 1984). By utilizing pyrene-labeled PtdCho and PtdIns lipid species the membrane extraction and lipid transfer mediated by the mammalian StART-like PITP, PITPα (and other lipid transfer proteins) has been fluorescently monitored. We have also further modified the method to include the measuring of protein mediated transfer of the intrinsically fluorescent sterol, dehydroergosterol (DHE). Using the method, we have studied how point mutations in the binding pocket of PITPα and the yeast Sec14-like PtdIns transfer protein, Sfh3, affect PC/PI and DHE binding and transfer respectively. The advantages of using fluorescently labeled lipids to measure protein mediated transfer includes time-resolved data acquisition and greater sensitivity compared to other established methods. The possible artefacts introduced by the pyrene label can, however, not be dismissed. To address this, we have used a well-established in vitro radiolabeled transfer assay to verify and validate the results obtained using the fluorescence assay. These results will help to increase the understanding of how cells utilize PITPs in regulating lipid signaling cascades.

Focus on software and semiconductor equipment

Focus on software and semiconductor equipment

A new peak recognition algorithm for detection of ultra-small nano-particles by single particle ICP-MS using rapid time resolved data acquisition on a sector-field mass spectrometer

The size detection limit of single particle ICP-MS is improved by rapid data acquisition combined with a new peak recognition algorithm.

Correction for dynamic bias error in transmission measurements of void fraction

Dynamic bias errors occur in transmission measurements, such as X-ray, gamma, or neutron radiography or tomography. This is observed when the properties of the object are not stationary in time and its average properties are assessed. The nonlinear measurement response to changes in transmission within the time scale of the measurement implies a bias, which can be difficult to correct for. A typical example is the tomographic or radiographic mapping of void content in dynamic two-phase flow systems. In this work, the dynamic bias error is described and a method to make a first-order correction is derived. A prerequisite for this method is variance estimates of the system dynamics, which can be obtained using high-speed, time-resolved data acquisition. However, in the absence of such acquisition, a priori knowledge might be used to substitute the time resolved data. Using synthetic data, a void fraction measurement case study has been simulated to demonstrate the performance of the suggested method. The transmission length of the radiation in the object under study and the type of fluctuation of the void fraction have been varied. Significant decreases in the dynamic bias error were achieved to the expense of marginal decreases in precision.

Fast time-correlated single-photon counting fluorescence lifetime acquisition using a 100 MHz semiconductor excitation source

The fast and efficient collection of time-resolved fluorescence decay data is shown using a high repetition rate semiconductor laser excitation source optimally matched to low dead-time counting electronics. The 100 MHz repetition rate allows a measurement range of 10 ns without re-excitation of the sample. Rapid acquisition of time-resolved fluorescence data is essential for microscopy applications, such as fluorescence lifetime imaging. With this in mind we measured a representative dye (lifetime 376 ps) to determine the fastest collection time for a single exponential decay. Other dyes were also used with lifetimes ranging from ∼90 ps to 4 ns.

EPICS oscilloscope for time-resolved data acquisition

Abstract The Sector 7 undulator beamline (7 ID) of the Advanced Photon Source (APS) is dedicated to time-resolved X-ray research [1] . Silicon avalanche photodiodes (APDs) are used as the primary point detector for time-resolved Bragg diffraction experiments for their fast recovery time ( [2] . Common practice has been to attenuate the monochromatic beam entering the experimental hutch to an appropriately low flux [3] . For these high-flux experiments, an APD operated in proportional mode is a better detector choice due to a large dynamic range and linearity. With the ZT4212 ZTEC, EPICS based oscilloscope, the operating procedure to use an APD in proportional mode has been improved. This article shows the setup and operating procedure for this oscilloscope and demonstrates its application to measuring time-resolved rocking curves of laser excited semiconductors.

Assessment of inflow and washout of indocyanine green in the adult human brain by monitoring of diffuse reflectance at large source-detector separation

Recently, it was shown in measurements carried out on humans that time-resolved near-infrared reflectometry and fluorescence spectroscopy may allow for discrimination of information originating directly from the brain avoiding influence of contaminating signals related to the perfusion of extracerebral tissues. We report on continuation of these studies, showing that the near-infrared light can be detected noninvasively on the surface of the tissue at large interoptode distance. A multichannel time-resolved optical monitoring system was constructed for measurements of diffuse reflectance in optically turbid medium at very large source-detector separation up to 9 cm. The instrument was applied during intravenous injection of indocyanine green and the distributions of times of flight of photons were successfully acquired showing inflow and washout of the dye in the tissue. Time courses of the statistical moments of distributions of times of flight of photons are presented and compared to the results obtained simultaneously at shorter source-detector separations (3, 4, and 5 cm). We show in a series of experiments carried out on physical phantom and healthy volunteers that the time-resolved data acquisition in combination with very large source-detector separation may allow one to improve depth selectivity of perfusion assessment in the brain.

In situ neutron diffraction studies of a commercial, soft lead zirconate titanate ceramic: response to electric fields and mechanical stress

Structural changes in commercial lead zirconate titanate (PZT) ceramics (EC-65) under the application of electric fields and mechanical stress were measured using neutron diffraction instruments at the Australian Nuclear Science and Technology Organisation (ANSTO) and the Oak Ridge National Laboratory (ORNL). The structural changes during electric-field application were measured on the WOMBAT beamline at ANSTO and include non-180° domain switching, lattice strains and field-induced phase transformations. Using time-resolved data acquisition capabilities, lattice strains were measured under cyclic electric fields at times as short as 30 μs. Structural changes including the (002) and (200) lattice strains and non-180° domain switching were measured during uniaxial mechanical compression on the NRSF2 instrument at ORNL. Contraction of the crystallographic polarization axis, (002), and reorientation of non-180° domains occur at lowest stresses, followed by (200) elastic strains at higher stresses.

Optimized time‐gated generalized polarization imaging of Laurdan and di‐4‐ANEPPDHQ for membrane order image contrast enhancement

The membrane dyes Laurdan and di-4-ANEPPDHQ can be used to image membrane order due to a spectral blue-shift in the fluorescence emission between the liquid-ordered and liquid-disordered phases. These images typically take the form of a normalized intensity ratio image known as a generalized polarization (GP) plot. Here, we exploit the known excited state photophysics and time-resolved data acquisition via time-correlated single-photon counting (TCSPC) to demonstrate GP contrast enhancement for these two probes of 7 and 31%, respectively. This improvement in image contrast enhancement will be invaluable when studying the role of lipid rafts in fixed and live cell systems.

Attenuation correction of four dimensional (4D) PET using phase-correlated 4D-computed tomography

The image quality in a conventional positron emission tomography (PET)/computed tomography (CT) scanner is degraded by respiratory motion because of erroneous attenuation correction when three-dimensional image acquisition is used. To overcome this problem, time-resolved data acquisition (4D) is required. For this, a Siemens Biograph 16 PET/CT scanner has been modified and its normal capability has been extended to a true 4D-PET/4D-CT imaging device including phase-correlated attenuation correction. To verify the correct functionality of this device, experiments on a respiratory motion phantom that allowed movement in two dimensions have been performed. The measurements showed good spatial correlation as well as good time synchronization between the PET and CT data. Furthermore, the motion pattern of the phantom and the shape of the activity distribution have been examined, and the volume of the reconstructed PET images has been analyzed. The results demonstrate the feasibility of such a procedure, and we therefore recommend that 4D-PET data should be reconstructed using 4D-CT data, which can be acquired on the same machine.

Particle sample introduction system for inductively coupled plasma–atomic emission spectrometry

Development and characterization of a new, relatively inexpensive, computer-controlled, particle sample introduction (PSI) system for programmable delivery of small amounts of diluted powdered samples into an inductively coupled plasma (ICP) and measurement by atomic emission spectrometry (AES) is described. The PSI was developed for use with non-hygroscopic particles, in particular those with a particle weight in the ng range (i.e., with a diameter in low μm-range) and for solids that can be converted to a powder (i.e., a collection of particles). In this first report on PSI–ICP–AES, linearity of calibration curves and plasma loading concerns were addressed using three modes of operation. In the first mode, the PSI operated similar to a nebulizer and it delivered to the plasma for a period of 5–10 s a relatively constant amount of particles diluted with graphite. In the second mode, the PSI delivered to the plasma a small “puff” of a diluted sample, thus generating a transient, time-domain signal with duration of about a second. In the third mode, an even smaller “puff” was delivered to the plasma and, using high-speed data acquisition (in the kHz range), time-resolved emission signals from individual, μm-diameter and ng-weight particles were observed. Thus, the PSI can also be thought of as a nano-particle (i.e., ng rather than nm) sample introduction system. Similarly, the high-speed, wide-bandwidth single-channel time-resolved data acquisition mode enabled the determination of particle-size distribution. In addition, a dual-channel (or dual-element) mode enabled homogeneity studies on a per-individual-particle basis. In all modes, linear calibration curves were obtained (provided that plasma loading was avoided). Per-cent relative standard deviation ranged between 3.1% and 4.2% for Ni in certified reference materials but was as high as 50% for heterogeneous soil samples. Tungsten emission signals from refractory tungsten carbide powders were enhanced using mixed gases and by modifying the chemical environment of the ICP using SF 6. Furthermore, when coupled with high-speed data acquisition, PSI brought unique capabilities to ICP–AES for homogeneity studies from individual ng-weight particles and for the determination of particle size distributions. Overall, it was concluded that PSI is an attractive alternative to powder sample introduction systems described in the literature.