Siemens (Canada)

PURPOSE: To validate a new saturation recovery single-shot acquisition (SASHA) pulse sequence for T1 mapping and to compare SASHA T1 values in heart failure patients and healthy controls. THEORY: The SASHA sequence consists of 10 electrocardiogram-triggered single-shot balanced steady-state free precession images in a breath-hold. The first image is acquired without magnetization preparation and the remaining nine images follow saturation pulses with variable saturation recovery times. METHODS: SASHA was validated through Bloch equation simulations, Monte Carlo simulations, and phantom experiments. Pre- and postcontrast myocardial and blood T1 values were measured in 29 healthy volunteers and 7 patients with heart failure. RESULTS: SASHA T1 values had excellent agreement (bias, 5 ± 5 ms) with spin echo experiments in phantoms with a wide range of physiologic T1 and T2 values and its accuracy was independent of flip angle, absolute T1 , T2 , and heart rate. The average baseline myocardial T1 in heart failure patients was higher than in healthy controls (1200 ± 32 vs. 1170 ± 9 ms, P < 0.05) at 1.5T, as was the calculated blood-tissue partition coefficient, λ, (0.42 ± 0.04 vs. 0.38 ± 0.02, P < 0.05), consistent with diffuse myocardial fibrosis. CONCLUSIONS: The SASHA sequence is a simple and fast approach to in vivo T1 mapping with good accuracy in simulations and phantom experiments.

PURPOSE: Frequency and phase drifts are a common problem in the acquisition of in vivo magnetic resonance spectroscopy (MRS) data. If not accounted for, frequency and phase drifts will result in artifactual broadening of spectral peaks, distortion of spectral lineshapes, and a reduction in signal-to-noise ratio (SNR). We present herein a new method for estimating and correcting frequency and phase drifts in in vivo MRS data. METHODS: We used a simple method of fitting each spectral average to a reference scan (often the first average in the series) in the time domain through adjustment of frequency and phase terms. Due to the similarity with image registration, this method is referred to as "spectral registration." Using simulated data with known frequency and phase drifts, the performance of spectral registration was compared with two existing methods at various SNR levels. RESULTS: Spectral registration performed well in comparison with the other methods tested in terms of both frequency and phase drift estimation. CONCLUSIONS: Spectral registration provides an effective method for frequency and phase drift correction. It does not involve the collection of navigator echoes, and does not rely on any specific resonances, such as residual water or creatine, making it highly versatile.

As the penetration of variable renewable generation increases in power systems, issues, such as grid stiffness, larger frequency deviations, and grid stability, are becoming more relevant, particularly in view of 100% renewable energy networks, which is the future of smart grids. In this context, energy storage systems (ESSs) are proving to be indispensable for facilitating the integration of renewable energy sources (RESs), are being widely deployed in both microgrids and bulk power systems, and thus will be the hallmark of the clean electrical grids of the future. Hence, this article reviews several energy storage technologies that are rapidly evolving to address the RES integration challenge, particularly compressed air energy storage (CAES), flywheels, batteries, and thermal ESSs, and their modeling and applications in power grids. An overview of these ESSs is provided, focusing on new models and applications in microgrids and distribution and transmission grids for grid operation, markets, stability, and control.

Metal additive manufacturing is gaining immense research attention. Some of these research efforts are associated with physics, statistical, or artificial intelligence-driven process modelling and optimisation, structure–property characterisation, structural design optimisation, or equipment enhancements for cost reduction and faster throughputs. In this review, the focus is drawn on the utilisation of topology optimisation for structural design in metal additive manufacturing. First, the symbiotic relationship between topology optimisation and metal additive manufacturing in aerospace, medical, automotive, and other industries is investigated. Second, support structure design by topology optimisation for thermal-based powder-bed processes is discussed. Third, the introduction of capabilities to limit manufacturing constraints and generate porous features in topology optimisation is examined. Fourth, emerging efforts to adopt artificial intelligence models are examined. Finally, some open-source and commercial software with capabilities for topology optimisation and metal additive manufacturing are explored. This study considers the challenges faced while providing perceptions on future research directions.

For time-resolved acquisitions with k-space undersampling, a simulation method was developed for selecting imaging parameters based on minimization of errors in signal intensity versus time and physiologic parameters derived from tracer kinetic analysis. Optimization was performed for time-resolved angiography with stochastic trajectories (TWIST) algorithm applied to contrast-enhanced MR renography. A realistic 4D phantom comprised of aorta and two kidneys, one healthy and one diseased, was created with ideal tissue time-enhancement pattern generated using a three-compartment model with fixed parameters, including glomerular filtration rate (GFR) and renal plasma flow (RPF). TWIST acquisitions with different combinations of sampled central and peripheral k-space portions were applied to this phantom. Acquisition performance was assessed by the difference between simulated signal intensity (SI) and calculated GFR and RPF and their ideal values. Sampling of the 20% of the center and 1/5 of the periphery of k-space in phase-encoding plane and data-sharing of the remaining 4/5 minimized the errors in SI (<5%), RPF, and GFR (both <10% for both healthy and diseased kidneys). High-quality dynamic human images were acquired with optimal TWIST parameters and 2.4 sec temporal resolution. The proposed method can be generalized to other dynamic contrast-enhanced MRI applications, e.g., MR angiography or cancer imaging.

The increasing availability of low-cost and low pressure, renewable H2 from wind and solar means has triggered tremendous interest in developing low pressure ammonia synthesis with N2 as the energy carrier as well as fertilizer. As such, Cs-promoted Ru/MgO catalysts used in the Kellogg process show superiority to Fe-based catalysts at milder conditions; however, as known, the surface poisoning of Ru sites by competitive strong H2 dissociative adsorption limits the overall rate. In this study, it is demonstrated that the use of simple electrostatically polar MgO(111) to replace nonpolar MgO as the support can significantly alleviate the hydrogen poisoning and facilitate an unprecedented ammonia production rate by its high intrinsic proton capture ability.

Several algorithms have been developed for tracking formant frequency trajectories of speech signals, however most of these algorithms are either not robust in real-life noise environments or are not suitable for real-time implementation. The algorithm presented in this paper obtains formant frequency estimates from voiced segments of continuous speech by using a time-varying adaptive filterbank to track individual formant frequencies. The formant tracker incorporates an adaptive voicing detector and a gender detector for formant extraction from continuous speech, for both male and female speakers. The algorithm has a low signal delay and provides smooth and accurate estimates for the first four formant frequencies at moderate and high signal-to-noise ratios. Thorough testing of the algorithm has shown that it is robust over a wide range of signal-to-noise ratios for various types of background noises.

Ignition delay time measurements for multi-component natural gas mixtures were carried out using a rapid compression machine at conditions relevant to gas turbine operation, at equivalence ratios of 0.5–2.0 in ‘air’ in the temperature range 650–1050 K, at pressures of 10–30 bar. Natural gas mixtures comprising C1–C7 n-alkanes with methane as the major component (volume fraction: 0.35–0.98) were considered. A design of experiments was employed to minimize the number of experiments needed to cover the wide range of pressures, temperatures and equivalence ratios. The new experimental data, together with available literature data, were used to develop and assess a comprehensive chemical kinetic model. Replacing 1.875% methane with 1.25% n-hexane and 0.625% n-heptane in a mixture containing C1–C5 components leads to a significant increase in a mixture's reactivity. The mixtures containing heavier hydrocarbons also tend to show a strong negative temperature coefficient and two-stage ignition behavior. Sensitivity analyses of the C1–C7 blends have been performed to highlight the key reactions controlling their ignition behavior.

Periodic structures with extremely low porosities capable of forming large band gaps—frequency ranges with strong wave attenuation—are designed by patterning an elastic sheet with an array of alternating crack-like pores separated by small ligaments. The results indicate that the presence and size of the band gaps are controlled by the smallest geometric ­feature in the system (which can be easily controlled by tuning the aspect ratio of the pores), providing an important guideline for the design of systems with the ­desired response. As a service to our authors and readers, this journal provides supporting information supplied by the authors. Such materials are peer reviewed and may be re-organized for online delivery, but are not copy-edited or typeset. Technical support issues arising from supporting information (other than missing files) should be addressed to the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

OBJECTIVE: The purpose of this study is to compare ultrashort TR, segmented trueFISP (fast imaging with steady-state precession) cine MR imaging with segmented FLASH (fast low-angle shot) cine MR imaging for the detection and characterization of congenital and acquired adult cardiac abnormalities. SUBJECTS AND METHODS: Twenty-five patients with known or clinically suspected cardiac abnormalities were imaged on a 1.5-T scanner. Valve plane movies were obtained in patients with suspected valve morphology or function abnormalities or whose horizontal long-axis images showed jets. For each patient, three radiologists independently compared corresponding matched cine FLASH and trueFISP movies for image quality in evaluating anatomy and function of the great vessels and heart. Image quality was rated on a five-point scale, and data were analyzed using both a Wilcoxon's signed rank test and a repeated-measures analysis of variance. RESULTS: Image quality ratings of trueFISP and FLASH showed a statistically significant difference (F = 58.67; df = 1, 72; p < 0.0001), with the average rating for the trueFISP images being significantly higher (mean rating, 4.1 +/- 0.92) than that for the FLASH images (mean, 3.0 +/- 1.0). However, valve architecture in the aortic valves appeared to be better visualized and was more easily measured in valve plane images with FLASH. No statistically significant differences among the ratings of the interpreters (F = 0.018; df = 2, 72; p = 0.9821) were evident, and, therefore, no suggestion of bias was indicated (F = 0.775; df = 1, 2; p = 0.4645). TrueFISP yielded the correct diagnosis prospectively in 13 (100%) of 13 patients, whereas FLASH yielded the correct diagnosis in 12 (92%) of 13 patients. CONCLUSION: TrueFISP images depict morphologic and functional abnormalities with greater clarity and provide greater diagnostic confidence than FLASH images-and in a fraction of the time. A specific exception is in the assessment of valve leaflet architecture and cross-sectional area calculation (i.e., bicuspid aortic valves); in these evaluations, FLASH maintains a complementary diagnostic imaging role.

In this study, we report a novel periodic material with negative Poisson's ratio (also called auxetic materials) fabricated by denting spherical dimples in an elastic flat sheet. While previously reported auxetic materials are either porous or comprise at least two phases, the material proposed here is non-porous and made of a homogeneous elastic sheet. Importantly, the auxetic behavior is induced by a novel mechanism which exploits the out-of-plane deformation of the spherical dimples. Through a combination of experiments and numerical analyses, we demonstrate the robustness of the proposed concept, paving the way for developing a new class of auxetic materials that significantly expand their design space and possible applications.

The oxidation of propane (C3H8), with the addition of different oxides of nitrogen (NO, NO2, and N2O) in concentrations of 0 – 2000 ppm, has been investigated for stoichiometric mixtures, at compressed temperatures of (TC) = 690 – 1420 K, and at compressed pressures of (pC) = 2.0 – 3.0 MPa using both a rapid compression machine and a high-pressure shock tube. These new ignition delay time (IDT) measurements, together with C3/NOx data available in the literature, provide a direct validation of NUIGMech1.3 which includes an updated C3/NOx sub-mechanism. The experimental results show that the mixtures with NO2 and NO/NO2 added have longer IDTs, inhibiting reactivity at TC〈 800 K, and shorter IDTs, promoting reactivity at TC〉 800 K, compared to the base C3H8/‘air’ mixtures indicating the complex chemical interactions involved. Both the inhibiting and prompting effects depend on the concentrations of NO and NO2 added and on the temperature regime. The addition of 1000 ppm NO2 significantly reduces the negative temperature coefficient (NTC) behavior of C3H8 in the temperature range 715–800 K compared to the addition of 200 ppm. Model predictions with 1000 ppm NO added, assuming no conversion of NO to NO2, are significantly slower than for both the 0 and 1000 ppm NO2 addition cases at TC < 800 K. Although NO and NO2 addition have different impacts on C3H8 oxidation at low-, intermediate, and high-temperatures, the addition of 1000 ppm N2O did not show any chemical effect at the conditions studied. NUIGMech1.3, with the updated C3/NOx sub-mechanism, reproduces the sensitisation effect of NOx on C3H8 with generally good agreement. Sensitivity and flux analyses have been performed to highlight the key reactions controlling ignition. The analyses show that competition between the reactions Ṙ+NO2↔RȮ+NO and Ṙ +NO2 (+M) ↔ RNO2 (+M) governs NOx sensitization on propane ignition. The inhibiting effect of NO and NO2 addition to propane stems from the nĊ3H7+ NO2↔ nC3H7Ȯ + NO and nC3H7Ȯ2 + NO ↔ nC3H7Ȯ + NO2 reactions, which compete for nC3H7Ȯ2 radicals, reducing the rate of isomerization of nC3H7Ȯ2 into Ċ3H6OOH1–3 (RȮ2 ⇌ Q˙OOH).

Bayesian neural networks (BNNs) have been demonstrated to be effective in accurate retrieval of sea ice concentration (SIC) from multi-source data, while providing estimates of uncertainty, which are essential for downstream services. However, uncertainty obtained by BNNs are intrinsically uncalibrated, which indicates that it may not correlate well with model error. To address this issue, we investigate a new approach that combines an auxiliary prediction interval (PI) estimator with the BNN-based SIC mean estimator to develop a well-calibrated SIC retrieval model that is both accurate and reliable. We adopt a training strategy called “uncertainty matching" to train the model, which ensures that the estimated uncertainties match the estimated PIs. We use a subset of AMSR2 brightness temperature data and ERA5 atmospheric data collected from 2014 to 2015 in the Baffin Bay area as input features of the model. Comparison between model inference and SIC labels obtained from the enhanced NASA Team (NT2) algorithm shows that the proposed approach is able to produce well-calibrated uncertainty with more accurate predictions in marginal ice zones.

An experimental and kinetic modeling study of the influence of NOx (i.e. NO2, NO and N2O) addition on the ignition behavior of methane/‘air’ mixtures is performed. Ignition delay time measurements are taken in a rapid compression machine (RCM) and in a shock tube (ST) at temperatures and pressures ranging from 900–1500 K and 1.5–3.0 MPa, respectively for equivalence ratios of 0.5–2.0 in ‘air’. The conditions chosen are relevant to spark ignition and homogeneous charge compression ignition engine operating conditions where exhaust gas recirculation can potentially add NOx to the premixed charge. The RCM measurements show that the addition of 200 ppm NO2 to the stoichiometric CH4/oxidizer mixture results in a factor of three increase in reactivity compared to the baseline case without NOx for temperatures in the range 600–1000 K. However, adding up to 1000 ppm N2O does not show any appreciable effect on the measurements. The promoting effect of NO2 was found to increase with temperature in the range 950–1150 K, while the sensitization effect decreases at higher pressures. The experimental results measured are simulated using NUIGMech1.2 comprising an updated NOx sub-chemistry in this work. A kinetic analysis indicates that the competition between the reactions ĊH3 + NO2 ↔ CH3Ȯ + NO and ĊH3 + NO2 (+M) ↔ CH3NO2 (+M), the former being a propagation reaction and the latter being a termination reaction governs NOx sensitization on CH4 ignition. Recent calculations by Matsugi and Shiina (A. Matsugi, H. Shiina, J. Phys. Chem. A. 121 (2017) 4218–4224) for the nitromethane formation reaction CH3 + NO2 (+M) ↔ CH3NO2 (+M), together with the recently calculated rate constants for HONO/HNO2 reactions significantly improve ignition delay time predictions in the temperature range 600–1000 K. Furthermore, the experiments with NO addition reveal a non-monotonous sensitization impact on CH4 ignition at lower temperatures with NO initially acting as an inhibitor at low NO concentrations and then as a promoter as NO concentrations increase in the mixture. This non-monotonous trend is attributed to the role of the chain-termination reaction ĊH3 + NO2 (+M) ↔ CH3NO2 (+M) and the impact of NO on the transition to the chain-branching steps CH2O + HȮ2 ↔ HĊO + H2O2, H2O2 (+M) ↔ ȮH + ȮH (+M), HĊO ↔ CO + Ḣ followed by CO + O2 ↔ CO2 + Ö and Ḣ + O2 ↔ Ö + ȮH. NUIGMech1.2 is systematically validated against the new ignition delay measurements taken here together with species measurements and high temperature ignition delay time data available in the literature for CH4/oxidizer mixtures diluted with NO2/N2O/NO and is observed to accurately capture the sensitization trends.

The effect of contour laser welding parameters (laser speed, laser power, and weld pressure) on T-joint weld strength and meltdown of 30% glass reinforced nylon 6 is presented. For the range of parameters studied, meltdown was a strong function of the energy input, expressed as line energy, and pressure. Maximum weld strength, approximating that of the base material, could be obtained by optimizing the energy input. Weld strength diminished with increasing weld pressure.

In humans, cerebrovascular responses to alterations in arterial Pco(2) and Po(2) are well documented. However, few studies have investigated human coronary vascular responses to alterations in blood gases. This study investigated the extent to which the cerebral and coronary vasculatures differ in their responses to euoxic hypercapnia and isocapnic hypoxia in healthy volunteers. Participants (n = 15) were tested at rest on two occasions. On the first visit, middle cerebral artery blood velocity (V(P)) was assessed using transcranial Doppler ultrasound. On the second visit, coronary sinus blood flow (CSBF) was measured using cardiac MRI. For comparison with V(P), CSBF was normalized to the rate pressure product [an index of myocardial oxygen consumption; normalized (n)CSBF]. Both testing sessions began with 5 min of euoxic [end-tidal Po(2) (Pet(O(2))) = 88 Torr] isocapnia [end-tidal Pco(2) (Pet(CO(2))) = +1 Torr above resting values]. Pet(O(2)) was next held at 88 Torr, and Pet(CO(2)) was increased to 40 and 45 Torr in 5-min increments. Participants were then returned to euoxic isocapnia for 5 min, after which Pet(O(2)) was decreased from 88 to 60, 52 and 45 Torr in 5-min decrements. Changes in V(P) and nCSBF were normalized to isocapnic euoxic conditions and indexed against Pet(CO(2)) and arterial oxyhemoglobin saturation. The V(P) gain for euoxic hypercapnia (%/Torr) was significantly higher than nCSBF (P = 0.030). Conversely, the V(P) gain for isocapnic hypoxia (%/%desaturation) was not different from nCSBF (P = 0.518). These findings demonstrate, compared with coronary circulation, that the cerebral circulation is more sensitive to hypercapnia but similarly sensitive to hypoxia.

A new method of measuring cytoplasmic free Ca2+ ([Ca2+]i) of individual intact cardiovascular endothelial cells by using imaging fluorescence microscopy was designed. Application of agonist to the aortic or pulmonary valve of the rabbit triggered an increase in [Ca2+]i, which depended on the existence of endothelium on the surface of the valve. Under resting conditions, sudden reversal of the Na+ gradient by substituting external Na+ with N-methyl D-glucamine (NMDG) resulted in a [Ca2+]i spike, which then returned toward the resting level. Increasing intracellular Na+ concentration ([Na+]i) by application of ouabain or monensin induced a sustained [Ca2+]i increase. Na+ substitution by NMDG during the agonist- or monensin-induced [Ca2+]i increase gave rise to a further [Ca2+]i spike, which subsequently declined to a level higher than that before removal of external Na+. A selective inhibitor of Na(+)-Ca2+ exchange, 3',4'-dichlorobenzamyl (DCB), abolished the transient [Ca2+]i increase induced by Na+ substitution, and Mg2+, an inorganic inhibitor of Na(+)-Ca2+ exchanger, markedly reduced this transient [Ca2+]i increase. On the other hand, the selective Na(+)-H+ exchanger blocker 5-(N,N-hexamethylene)amiloride (HMA) did not abolish the transient [Ca2+]i increase caused by Na+ substitution. In summary, decreasing the Na+ gradient of the endothelial cells through either receptor stimulation (agonist), Na(+)-K+ pump inhibition (ouabain), pretreatment with Na+ ionophore (monensin), or reversing the Na+ gradient through Na+ substitution (NMDG) all increased [Ca2+]i. This raised [Ca2+]i was antagonized by agents such as DCB or Mg2+, which are thought to inhibit Na(+)-Ca2+ exchange, but not by HMA, an inhibitor of Na(+)-H+ exchange.(ABSTRACT TRUNCATED AT 250 WORDS)

The paper presents a unified approach for the design of PID controllers, based on the contours of the Nichols chart. Using a maximum peak resonance specification, the controller parameters are adjusted such that the open-loop frequency response curve follows the corresponding contour. This approach gives the possibility of handling (at the same time) the maximum peak overshoot, the minimum phase and amplitude margins and the bandwidth of the closed-loop system. The method can be applied to a wide range of processes and it provides useful a priori information concerning the behaviour of the closed-loop system. Different ways are proposed for the calculations of the controller parameters. An optimisation procedure is first proposed to illustrate the basic idea of the method, but the aim of the paper is to provide simple tuning expressions for low-order models. These expressions are given for stable, integrating and unstable processes.

This paper presents a nonlinear control scheme for deflection control of a flexible beam using shape memory alloy (SMAs) actuators. These actuators possess interesting properties in terms of force generation capacity, possibility of miniaturization, and power consumption. However, their use in precision applications is hampered by undesirable characteristics, such as nonlinearities, hysteresis, extreme temperature dependencies, and slow response. By taking into account the nonlinear and thermal characteristics, a control scheme based on partial feedback linearization is developed to regulate the forces exerted by a differential SMA actuator pair attached to a flexible beam. The regulated force corresponds to a specific position of the flexible beam; hence, regulating the force results in position regulation. Using a Lyapunov stability analysis, qualitative guidelines are provided for selecting controller gain parameters. Furthermore, performance of the developed control scheme is tested experimentally on a laboratory testbed.

A microprocessor implementation of the field-oriented control scheme for the permanent magnet (PM) hysteresis synchronous motor is reported. The basic principle is to decouple the torque-current component from the flux-current component so that these two components can be independently controlled. A d-q axis model of the PM hysteresis synchronous motor is presented, and the field-oriented control obtained from the basic machine model. A control scheme that decouples the stator current components and orients it to the rotor frame is described. A scheme for detecting the rotor position is proposed. A software package based on the Intel 8086 microprocessor has been developed. A sine PWM voltage source inverter is used in the experimental work. The test results validate the theoretical steady state and dynamic performances of the laboratory prototype motor.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>