Magnetic resonance imaging (MRI) is being increasingly utilized to assess, diagnose, and plan treatment for a variety of diseases. The ability to visualize tissue in varied contrasts in the form of ...MR pulse sequences in a single scan provides valuable insights to physicians, as well as enabling automated systems performing downstream analysis. However, many issues like prohibitive scan time, image corruption, different acquisition protocols, or allergies to certain contrast materials may hinder the process of acquiring multiple sequences for a patient. This poses challenges to both physicians and automated systems since complementary information provided by the missing sequences is lost. In this paper, we propose a variant of generative adversarial network (GAN) capable of leveraging redundant information contained within multiple available sequences in order to generate one or more missing sequences for a patient scan. The proposed network is designed as a multi-input, multi-output network which combines information from all the available pulse sequences and synthesizes the missing ones in a single forward pass. We demonstrate and validate our method on two brain MRI datasets each with four sequences, and show the applicability of the proposed method in simultaneously synthesizing all missing sequences in any possible scenario where either one, two, or three of the four sequences may be missing. We compare our approach with competing unimodal and multi-modal methods, and show that we outperform both quantitatively and qualitatively.
Ribonucleic acid (RNA) structures and dynamics play a crucial role in elucidating RNA functions and facilitating the design of drugs targeting RNA and RNA-protein complexes. However, obtaining RNA ...structures using conventional biophysical techniques, such as X-ray crystallography and solution nuclear magnetic resonance (NMR), presents challenges due to the inherent flexibility and susceptibility to degradation of RNA. In recent years, solid-state NMR (SSNMR) has rapidly emerged as a promising alternative technique for characterizing RNA structure and dynamics. SSNMR has several distinct advantages, including flexibility in sample states, the ability to capture dynamic features of RNA in solid form, and suitability to character RNAs in various sizes. Recent decade witnessed the growth of 1H-detected SSNMR methods on RNA, which targeted elucidating RNA topology and base pair dynamics in solid state. They have been applied to determine the topology of RNA segment in human immunodeficiency virus (HIV) genome and the base pair dynamics of riboswitch RNA. These advancements have expanded the utility of SSNMR techniques within the RNA research field. This review provides a comprehensive discussion of recent progress in 1H-detected SSNMR investigations into RNA structure and dynamics. We focus on the established 1H-detected SSNMR methods, sample preparation protocols, and the implementation of rapid data acquisition approaches.
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•New 11-interval pulse sequence developed for measuring gas velocity in porous media.•New pulse sequence more accurate than previous pulse sequences in packed beds.•Greater accuracy ...due to shorter echo time, minimizing background gradient effects.
Magnetic resonance (MR) was used to measure SF6 gas velocities in beds filled with particles of 1.1mm and 0.5mm in diameter. Four pulse sequences were tested: a traditional spin echo pulse sequence, the 9-interval and 13-interval pulse sequence of Cotts et al. (1989) and a newly developed 11-interval pulse sequence. All pulse sequences measured gas velocity accurately in the region above the particles at the highest velocities that could be achieved (up to 0.1ms−1). The spin echo pulse sequence was unable to measure gas velocity accurately in the bed of particles, due to effects of background gradients, diffusivity and acceleration in flow around particles. The 9- and 13-interval pulse sequence measured gas velocity accurately at low flow rates through the particles (expected velocity <0.06ms−1), but could not measure velocity accurately at higher flow rates. The newly developed 11-interval pulse sequence was more accurate than the 9- and 13-interval pulse sequences at higher flow rates, but for velocities in excess of 0.1ms−1 the measured velocity was lower than the expected velocity. The increased accuracy arose from the smaller echo time that the new pulse sequence enabled, reducing selective attenuation of signal from faster moving nuclei.
Neutral point clamped inverter (NPC) features low harmonics, high efficiency, and low voltage stress, et al. NPC is widely applied in renewable energy power generation systems, such as wind turbine ...power and photovoltaic. However, due to unbalanced power losses, NPC suffers inherent thermal unbalance among inner and outer power switches. A split-inductor active neutral point clamped inverter (SI-ANPC) was initially proposed to improve the operating reliability, providing the structural basis for balanced loss distributions. With this purpose, a novel modulation strategy with balanced loss distribution for SI-ANPC is proposed in this article. The modulation strategy is analyzed under the unity and nonunity power factors. In specially, two redundant zero-state paths are fully used. Under the unity power factor, the power switches operate at the switching frequency or maintain the conduction state complementarily. Considering the phase angle in the nonunity power factor situation, the working patterns of power switches are rearranged to reduce the loss difference. The thermal stress is decreased on both occasions. Finally, loss calculation results, experimental waveforms, and thermal images of the inner and outer switches are presented to confirm the effectiveness of the proposed modulation strategy.
Magnetic particle imaging (MPI) is a promising new tracer-based imaging modality. The steady-state, nonlinear magnetization physics most fundamental to MPI typically predicts improving resolution ...with increasing tracer magnetic core size. For larger tracers, and given typical excitation slew rates, this steady-state prediction is compromised by dynamic processes that induce a significant secondary blur and prevent us from achieving high resolution using larger tracers. Here, we propose a new method of excitation and signal encoding in MPI we call pulsed MPI to overcome this phenomenon. Pulsed MPI allows us to directly encode the steady-state magnetic physics into the time-domain signal. This in turn gives rise to a simple reconstruction algorithm to obtain images free of secondary relaxation-induced blur. Here, we provide a detailed description of our approach in 1D, discuss how it compares with alternative approaches, and show experimental data demonstrating better than 500-μm resolution (at 7 T/m) with large tracers. Finally, we show experimental images from a 2D implementation.
A new method for high-speed photonic arbitrary waveform generation using optical sinc-pulse sequences and Mach-Zehnder modulators is presented, enabling a three- to four-fold increase in sampling ...rate compared to the bandwidth of the used modulator for generating the pulses and an <inline-formula> <tex-math notation="LaTeX">N </tex-math></inline-formula>-fold increase compared to the bandwidth of the incorporated electronics, with <inline-formula> <tex-math notation="LaTeX">N </tex-math></inline-formula> as the number of parallel branches. Proof of concept experimental results, using conventional off-the-shelf fiber components have been presented in this study. Due to its simplicity and the possibility to achieve high sampling rates with low bandwidth photonic and electronic equipment, this method is beneficial for integration on a silicon photonics platform.
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•Experimental performance of homonuclear dipolar decoupling sequences are compared.•Guidelines for the optimization of CRAMPS experiments are provided.•BR-24 gives excellent ...performance at low spinning speeds on modern consoles.•eDUMBO-122 yields highest resolution at higher spinning rates.•LG4 has the most homogeneous scaling factor across the sequences we tested.
The development of homonuclear dipolar decoupling sequences to obtain high-resolution 1H NMR spectra from solids has recently celebrated its 50th birthday. Over the years, a series of different decoupling schemes have been developed, starting with the pioneering Lee-Goldburg and WAHUHA sequences up to the most recent generation of experimentally optimized phase-modulated schemes such as eDUMBO-122 and LG4. These schemes can all yield over an order of magnitude reduction in 1H NMR linewidths in solids. Here we provide an overview and a broad experimental comparison of the performance of the main sequences, which has so far been absent in the literature, especially between the newest and the oldest decoupling schemes. We compare experimental results obtained using eight different decoupling schemes (LG, WHH-4, MREV-8, BR-24, FSLG/PMLG, DUMBO-1, eDUMBO-122 and LG4) on three different microcrystalline powdered samples (alanine, glycine and β-AspAla) and at three different MAS rates (3.0, 12.5 and 22.0 kHz). Finally, since these sequences can be technically demanding, we describe the experimental protocol we have used to optimize these schemes with the aim to provide simple guidelines for the optimization of CRAMPS experiments for all NMR users.
•The dynamic counter-imbibition processes along the core samples were monitored in-time using low-field NMR technique.•The imbibition front and oil recoveries within individual layers along the core ...sample were determined.•Nanofluid advanced farther than DI water along the core sample during the counter-imbibition process.•The nanofluid on interfacial properties and rock pore structure are the dominant mechanism for nanofluid in EOR.
Counter-current imbibition behavior is an important mechanism for exploiting oil recovery during shut-in periods after hydraulic fracturing in tight oil reservoirs. However, most researches mainly focused on imbibition recovery and its influencing factors in tight oil reservoirs, while experimental investigations to quantitatively characterize the imbibition distance is still inadequate. In this work, counter-current imbibition experiments under one end open (OEO) boundary condition were conducted, and the dynamic imbibition process in porous media were monitored in real-time by nuclear magnetic resonance (NMR) pulse sequences and NMR imaging to quantify the range of counter-current imbibition and the reduction of oil saturation in-situ. In addition, a one-dimensional (1D) imbibition numerical model with OEO boundary condition at core scale was developed, and the influencing factors on oil production was further discussed in detail. The experimental results illustrated that the overall oil recoveries of nanofluid and deionized (DI) water were 25.37 % and 5.19 %, respectively. Moreover, the advancing distance of nanofluid was 4.44 cm, while DI water advanced only 2.38 cm along the core sample. Nanofluid considerably reduced residual oil saturation and increased movable fluid saturation, making the crude oil to be highly mobilized in micro- and mesopores. The simulated results well verified the counter-current imbibition experimental data, and indicated that the influences of core permeability and fluid viscosity on imbibition performances were more significant than that of core length. The purpose of this work is to provide a new method to determine the extent of counter-current imbibition.
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