High Field Devices Research Articles

Numerical modelling and measurement of the E-I characteristics of MgB2 wire in sub-cooled water ice

This work presents a comprehensive 3D numerical model of MgB2 multi-filamentary superconducting wires using the Finite Element Method (FEM) software, COMSOL Multiphysics® 6.0. The study aims to investigate the electro-thermal behavior of MgB2 composite wires during standard transport measurements at various initial temperatures under subcooled water ice conditions. By solving a series of partial differential equations governing heat transfer and dynamic current transport, the model provides detailed insights into the wire’s performance. The simulation results are rigorously compared with experimental E-I characteristics measured for 6-filament MgB2 wires with internal copper stabilization. This comparison validates the model and highlights its capability to predict the behavior of superconducting wires under cryogenic conditions. The findings offer valuable data on the current distribution, ohmic losses, and overall thermal stability of the composite wires, contributing to the advancement of cryogen-free superconducting technologies. This study bridges the gap in the literature regarding the electrothermal dynamics of MgB2 wires cooled by subcooled water ice, providing a foundation for further research and practical applications in high-field generation devices.

Property Variations in Modern REBCO Coated Conductors from Multiple Manufacturers

The complex, multilayer structure of REBCO Coated Conductor (CC) poses significant challenges in the fabrication of high magnetic field devices where large stresses may initiate various forms of damage. Our goal is to peer below the cartoon representations of CC so that, amongst other things, we might better understand whether a CC from one manufacturer is interchangeable with that from another. This involves knowledge of a broad range of electromagnetic, geometric, microstructural, and Jc (θ,B,T) properties, and their variations that collectively pose challenges for the fault tolerance of REBCO CC devices. Accordingly, comparative measurements of Jc , visualization of flux penetration with Magneto-Optical Imaging (MOI), tape geometry from Scanning Electron Microscopy (SEM) of polished cross-sections, and extensive optical microscopy was performed on recently purchased samples from multiple manufacturers. Our analyses reveal many deviations from or characteristics absent from manufacturers’ specifications, while a comparison of different manufacturers’ mechanically and laser slit tapes shows a diverse array of slitting characteristics amongst the manufacturers and variation in properties those made to the same specification. Laser slit tapes from several manufacturers reveal ablated edges with damaged regions extending up to 50 μm, comparable to the damaged region found in the mechanically slit CC of this study. Overall, the aim of this study is to flesh out appropriate ways to understand the real conductor below the manufacturers’ cartoons to avoid surprises in our REBCO CC coil development program. The goal of this work was to perform a broad array of characterizations of the type needed for validation of purpose for making high field magnets: to our surprise we found a wide range of properties which greatly impact the mechanical strength and electromagnetic performance of solenoids composed of these conductors and reinforced the need for a broad characterization program for each conductor prior to its implementation.

Intraoperative magnetic resonance imaging in glioma surgery: a single-center experience.

To investigate the effect of intraoperative magnetic resonance imaging (Io MRI) on overall and progression-free survival (OS and PFS), on the extent of resection (EOR) in patients with glioma, and impact of the radiological diagnosis on the decision to continue the surgery when a residual mass was detected on Io MRI. The study comprised 153 glioma patients who received surgical treatment between 2013 and 2023. One-hundred twenty-five of them had Io MRI guidance during surgery. The remainder 28 patients constituted the control group who did not undergo Io MRI. All patients' age at surgery, gender, initial radiological diagnosis, primary tumor localization, EOR, last histopathological diagnosis, and the follow-up periods were recorded. The rate of tumor recurrence in Io MRI cases was significantly lower compared to the cases in the control group (p < .0001). It was decided to continue the operation in 45 Io MRI applied cases. This raised the gross total resection (GTR) rate from 33.6% to 49.6% in the Io MRI group. The frequency of GTR was significantly higher in patients with an initial radiological diagnosis of low grade glioma than those with high grade glioma. The shortest OS was seen in occipital gliomas. In this study, the convenience provided by the high-field MRI device was explored and proven both in reducing the tumor burden, increasing the PFS, and providing the surgeon with a maximal resection in the first operation.

Simulating vacuum arc initiation by coupling emission, heating and plasma processes

Vacuum arcing poses significant challenges for high-field vacuum devices, underscoring the importance of understanding it for their efficient design. A detailed description of the physical mechanisms involved in vacuum arcing is yet to be achieved, despite extensive research. In this work, we further develop the modeling of the physical processes involved in the initiation of vacuum arcing, starting from field emission and leading to plasma onset. Our model concurrently combines particle-in-cell with Monte Carlo collisions (PIC-MCC) simulations of plasma processes with finite element-based calculations of electron emission and the associated thermal effects. Including the processes of evaporation, impact ionization and direct field ionization allowed us to observe the dynamics of plasma buildup from an initially cold cathode surface. We simulated a static nanotip at various local fields to study the thresholds for thermal runaway and plasma initiation, identifying the significance of various interactions. We found that direct field ionization of neutrals has a significant effect at high fields on the order of 10 GV/m. Furthermore, we find that cathode surface interactions such as evaporation, sputtering and bombardment heating play a major role in the initiation of vacuum arcs. Consequently, the inclusion of these interactions in vacuum arc simulations is imperative.

CVD Encapsulation of Laser-Graphitized Electrodes in Diamond Electro-Optical Devices

Conductive graphitized grooves on the dielectric surface of diamond have been created by KrF excimer laser radiation. The advantages of such a circuit board in high-field applications is rather limited because the crystal surface has a relatively low electrical breakdown threshold. To increase the electrical strength, a method of encapsulating surface conductive graphitized structures by chemical vapor deposition of an epitaxial diamond layer has been proposed and realized. The quality of the growth diamond is proved by Raman spectroscopy. A comparative study of the electrical resistivity of graphitized wires and the breakdown fields between them before and after diamond growth was carried out. The proposed technique is crucial for diamond-based high-field electro-optical devices, such as THz photoconductive emitters.

Superior temperature stability of electromechanical properties and resonant frequency in PYN-PZT piezoelectric ceramics

In this study, the Pb(Yb1/2Nb1/2)O3 (PYN) relaxor with high Curie temperature (TC ∼300 °C) was incorporated into PbZrO3-PbTiO3 (PZ-PT) ceramics to form 0.1PYN-(1-x)PZ-xPT ternary ceramics, and their phase compositions were systematically investigated, providing the more detailed phase diagrams, dielectric, piezoelectric, and ferroelectric properties. Excellent piezoelectric performance (d33 ∼ 450 pC/N, d33* ∼714 pm/V), with high coercive field (EC ∼17.5 kV/cm) and TC (∼398 °C) were simultaneously achieved in the 0.1PYN-0.41PZ-0.49PT composition near the morphotropic phase boundary (MPB). The value of d33 × EC, which exhibits higher than commercial PZT ceramics, indicates its suitability for high-field excitation devices. Additionally, the temperature stability of the resonant frequency (fr) is qualitatively studied by analyzing the main factors influencing fr from a theoretical perspective. Superior stability is achieved in the 0.1PYN-0.38PZ-0.52PT composition (TC ∼ 405 °C) with tetragonal phase, and the temperature coefficient of resonant frequency (Δfr /fr25 °C) remains within 0.5% up to 300 °C, far outperformance than previous reports.

Very low excess noise Al0.75Ga0.25As0.56Sb0.44 avalanche photodiode.

AlxGa1-xAsySb1-y grown lattice-matched to InP has attracted significant research interest as a material for low noise, high sensitivity avalanche photodiodes (APDs) due to its very dissimilar electron and hole ionization coefficients, especially at low electric fields. All work reported to date has been on Al concentrations of x = 0.85 or higher. This work demonstrates that much lower excess noise (F = 2.4) at a very high multiplication of 90 can be obtained in thick Al0.75Ga0.25As0.56Sb0.44 grown on InP substrates. This is the lowest excess noise that has been reported in any III-V APD operating at room temperature. The impact ionization coefficients for both electrons and holes are determined over a wide electric field range (up to 650 kV/cm) from avalanche multiplication measurements undertaken on complementary p-i-n and n-i-p diode structures. While these ionization coefficients can fit the experimental multiplication over three orders of magnitude, the measured excess noise is significantly lower than that expected from the β/α ratio and the conventional local McIntyre noise theory. These results are of importance not just for the design of APDs but other high field devices, such as transistors using this material.

The Critical Current of REBCO Coated Conductors Subjected to a Mechanical Loading at Varying Angles

High-temperature superconducting REBCO coated conductors and cables made from them are required in the building of fusion reactors, high-field magnets, and other high-current and high magnetic field devices. In the construction phase, the coated conductors undergo mechanical loading throughout the coated conductor production, cable manufacturing and when the resulting device is put in operation. Therefore, a simple method for investigating the loss of critical current after bending at different diameters and angles would be helpful. Here, we present a setup designed with simplicity in mind, allowing easy replication of testing conditions. As an example, the behaviour of two conductors has been characterized. We found differences in critical bending diameter when CC tapes were bent at 30 degrees angle and 45 degrees angle. The measurements were complemented by numerical and analytical calculations. The analytical calculations are an idealized 2D model serving as a first approach method for a fast prediction of loading severity. 3D numerical modelling of the measurement setup was performed in finite element software ANSYS, allowing us in-depth investigation of the strain/stress distribution in the multilayer structure of REBCO coated conductors. Scanning electron microscope study of the surface of the superconducting layer on one of the samples helped explain the measurement results.

Time-extended inductive tokamak discharges with differentially-tilted toroidal field coils

The strong toroidal magnetic field required for plasma confinement in tokamaks is generated by a set of D-shaped coils lying equidistant on meridian planes toroidally located around the central axis of the device. A major technological challenge tied to this configuration is represented by the large Lorentz force acting on the coils and arising from the interaction of the coils’ currents with the magnetic field generated by the coil system itself. As this force is given by the cross product of the coil current and the magnetic field, various kinds of coil geometry modification have been proposed to alleviate this problem, from an inclination of the entire coil in order to maintain its planarity, to azimuthal tilting of all, or parts of, the coil profile. When the inner legs of the coils are tilted, apart from a reduction of the electromagnetic forces, a solenoid-like structure is formed which introduces additional magnetic flux linked to the plasma. Considering compact, high field devices, it is shown that when this additional flux is exploited, totally or in part, to ramp up the plasma current, the discharge time can be extended by a significant amount without resorting to noninductive current drive systems. Operational scenarios with inner-leg-tilted toroidal field coils are presented.

High-Power Test of Two Prototype X-Band Accelerating Structures Based on SwissFEL Fabrication Technology

This article presents the design, construction, and high-power test of two <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$X$ </tex-math></inline-formula> -band radio frequency (RF) accelerating structures built as part of a collaboration between CERN and the Paul Scherrer Institute (PSI) for the compact linear collider (CLIC) study. The structures are a modified “tuning-free” variant of an existing CERN design and were assembled using Swiss free electron laser (SwissFEL) production methods. The purpose of the study is two-fold. The first objective is to validate the RF properties and high-power performance of the tuning-free, vacuum brazed PSI technology. The second objective is to study the structures’ high-gradient behavior to provide insight into the breakdown and conditioning phenomena as they apply to high-field devices in general. Low-power RF measurements showed that the structure field profiles were close to the design values, and both structures were conditioned to accelerating gradients in excess of 100 MV/m in CERN’s high-gradient test facility. Measurements performed during the second structure test suggest that the breakdown rate (BDR) scales strongly with the accelerating gradient, with the best fit being a power law relation with an exponent of 31.14. In both cases, the test results indicate that stable, high-gradient operation is possible with tuning-free, vacuum brazed structures of this kind.

Influence of High Magnetic Field-Thermal Coupling Processing on Diffusion Bonding Properties and Element Diffusion of 1420 Al-Li Alloy

The high uniform magnetic field combined with pre-deformation and vacuum heat treatment processing is designed for improving the diffusion bonding properties of the 1420 Al-Li alloy. Serial magneto-thermal coupling treatment experiments of 1420 Al-Li alloy and the pure aluminium diffusion couple, together with the gallium interlayer, is carried out in a superconducting high magnetic field device. Various parameter combinations are used to produce different samples on which interface organization and connection performance are studied. Electron microscopic analysis reveals various interface topographies and fracture morphologies after shear strength tests. Influence of diffusion bonding temperature on element diffusion under a high uniform magnetic field is investigated. The diffusion activation energy of Mg element in pure aluminum under a 12 T magnetic field is calculated in this paper. It is found that the bonding quality and bonding performance of the interface are improved greatly after heat treatment with a strong magnetic field, and the bonding temperature is an important factor affecting the interface bonding and bonding strength. The diffusion coefficient of the Mg element in the 1420 Al-Li alloy to L2 pure aluminum increases with the increase of diffusion bonding temperature. Reducing the activation energy of elemental diffusion is beneficial to atomic diffusion.

Low-field MRI: Clinical promise and challenges.

Modern MRI scanners have trended toward higher field strengths to maximize signal and resolution while minimizing scan time. However, high-field devices remain expensive to install and operate, making them scarce outside of high-income countries and major population centers. Low-field strength scanners have drawn renewed academic, industry, and philanthropic interest due to advantages that could dramatically increase imaging access, including lower cost and portability. Nevertheless, low-field MRI still faces inherent limitations in image quality that come with decreased signal. In this article, we review advantages and disadvantages of low-field MRI scanners, describe hardware and software innovations that accentuate advantages and mitigate disadvantages, and consider clinical applications for a new generation of low-field devices. In our review, we explore how these devices are being or could be used for high acuity brain imaging, outpatient neuroimaging, MRI-guided procedures, pediatric imaging, and musculoskeletal imaging. Challenges for their successful clinical translation include selecting and validating appropriate use cases, integrating with standards of care in high resource settings, expanding options with actionable information in low resource settings, and facilitating health care providers and clinical practice in new ways. By embracing both the promise and challenges of low-field MRI, clinicians and researchers have an opportunity to transform medical care for patients around the world. LEVEL OF EVIDENCE: 5 TECHNICAL EFFICACY: Stage 6.

Laryngeal Radioanatomy

The larynx, a specialized segment of the airways, is the essential organ of phonation, breathing and protection of the lower airways when swallowing by a complex anatomic structures organized around a cartilaginous skeleton. We realized a prospective study on three months, ranging from March 01 to May 31 2020, of patients referred to our service for cervical CT scan or MRI exploration in different contextes. We retained the normal exams. For scanographic exploration we used a multi-slice CT scan consisting of 64 rows of detectors. Helical acquisition in native axial slices 0.627 mm thick from the base of the skull to the arch of the aorta was performed in indifferent breathing after asking the patient not to swallow. Iodinated contrast product was injected according to the administration protocol in a single bolus of 90 ml at an average flow rate of 1.5 ml / s and to perform the acquisition with 50 second delay. A dynamic phonation maneuver (saying “eee” continuously and evenly) was used to analyse the true and false vocal cords. On MRI exploration of the larynx, we used a high-field device (1.5Tesla) with a semi-circular specific surface antenna, the phase oriented in an anteroposterior direction, the 3DT1 spin echo sequence without fat signal saturation was performed. In ultrasound, we used literature data. Knowledge of laryngeal radioanatomy contributes to the diagnosis of laryngeal cancers which occupy an important place in all cancers of the upper aerodigestive tract. They can be diagnosed early and the refinement of their endoscopic exploration and imaging allows them to make a precise extension assessment.

Benchtop versus high field NMR: Comparable performance found for the molecular weight determination of lignin

Lignin is a promising renewable biopolymer being investigated worldwide as an environmentally benign substitute of fossil-based aromatic compounds, e.g. for the use as an excipient with antioxidant and antimicrobial properties in drug delivery or even as active compound. For its successful implementation into process streams, a quick, easy, and reliable method is needed for its molecular weight determination. Here we present a method using 1H spectra of benchtop as well as conventional NMR systems in combination with multivariate data analysis, to determine lignin’s molecular weight (Mw and Mn) and polydispersity index (PDI). A set of 36 organosolv lignin samples (from Miscanthus x giganteus, Paulownia tomentosa and Silphium perfoliatum) was used for the calibration and cross validation, and 17 samples were used as external validation set. Validation errors between 5.6% and 12.9% were achieved for all parameters on all NMR devices (43, 60, 500 and 600 MHz). Surprisingly, no significant difference in the performance of the benchtop and high-field devices was found. This facilitates the application of this method for determining lignin’s molecular weight in an industrial environment because of the low maintenance expenditure, small footprint, ruggedness, and low cost of permanent magnet benchtop NMR systems.

Conceptual design of Thomson scattering diagnostics for the COMPASS-U tokamak.

The Thomson scattering (TS) diagnostic, one of the key diagnostics used on the tokamaks around the world, is planned for the COMPASS-U tokamak, which is recently under design and construction in the Institute of Plasma Physics in Prague, Czech Republic. This tokamak is supposed to be a world-unique, high magnetic field device with hot walls, allowing for the study of the plasma exhaust in advanced operational scenarios and testing cutting-edge technologies relevant to future fusion reactors, e.g., use of liquid metals. The core and edge TS systems are planned to be designed and operational, with a limited performance, already in the early stage of the tokamak operation. In this contribution, requirements and the most important constraints defining the TS system design are presented. The impact of both the possible collection lens location and spatial resolution on the plasma pedestal observation is simulated. Design considerations also take into account the high-resolution TS core and edge systems available from the COMPASS tokamak, which will be reused. The collection lenses will be newly built. Extension of the detection system will complete the plasma radius coverage in the future. The divertor TS is considered for later periods.

MO154ASSESSMENT OF MILD COGNITIVE IMPAIRMENT IN PRE-DIALYSIS CHRONIC KIDNEY DISEASE AND ITS ASSOCIATION WITH INFLAMMATION AND CHANGES IN MRI: WHAT THE EYES DON´T SEE

Abstract Background and Aims Mild cognitive impairment (MCI) consists of a decline of one or more cognitive domains, independent of functional impairment. There are common pathophysiological factors between chronic kidney disease (CKD) and MCI. The aim of this study was to evaluate the association of MCI in pre-dialysis CKD with inflammation markers and alterations of image exams (Nuclear Magnetic Resonance-MRI). Method Cross-sectional study, were evaluated non-dialysis CKD patients in categories 1 to 5 in a secondary care clinic, from 2013 to 2015. Inclusion Criteria: age ≥ 21 and ≤ 65 years and having signed the informed consent form. Non-inclusion criteria: previous history of stroke, degenerative and infectious diseases of the CNS, presence of delirium and / or psychotic disorders, previous history of mental retardation and cranioencephalic trauma, visual and auditory disorders that prevented the tests, HIV and / or AIDS, contraindication or intolerance to MRI. The project was approved by the Research Ethics Committee. MCI was assessed using the Montreal Cognitive Assessment (MoCA) and the estimated glomerular filtration rate (eGFR), using the CKDEPI formula. Socio-demographic and clinical data were collected from medical records. Laboratory data were collected a maximum of 3 months after the MoCA evaluation, as well as the measurement of IL4, IL6, IL17, TNF alpha and hs-CRP. The brain MRI scans were performed in a Siemens Avanto high-field device (1.5 Tesla), without the use of paramagnetic contrast. Fazekas scales were used to quantify white matter lesions, MTA scale to quantify hippocampal involvement, ACG scale for global cortical atrophy. Statistical analysis a descriptive analysis was performed, followed by a comparison of abnormal vs normal MoCA among all variables with the relevant tests; MoCA and eGFR were also correlated with all variables. Finally, we performed a linear regression using MoCA as a dependent variable, adjusting for relevant confounding variables. Results 111 patients were invited, 80 were included in the neuropsychological assessment and 56 patients performed all stages of the study. The mean age was 56.3 ± 8.3 years, 51.8% had an altered MoCA. Comparing those with altered vs normal MoCA, we observed that there were fewer years of schooling (p = 0.04), greater use of diuretics (p = 0.04) and AAS (p = 0.002); in addition to higher levels of IL6 (p = 0.02) and IL17 (p = 0.05) among those with altered MoCA. There was no correlation between MoCA and eGFR. MoCA correlated with IL6 (R-0.201, p = 0.04). There was a correlation between eGFR (IL4 (R- -0.467, p = 0.005; IL6 (R- -0.652, p &amp;lt;0.001); IL17 (R- -0.554, p = 0.001), TNF alpha (R- -0.684, p &amp;lt;0,001). There was no correlation between the findings in MRI and eGFR or MoCA. In a linear regression model, the variables IL17 and IL6 were independent predictors of lower values of MoCA (CI -0.031 to -0.002, p = 0.002; CI-0.012 to -0.001, p = 0.002). Conclusion The prevalence of changes in MoCA in this population was 51.8%, the eGFR was correlated with inflammation, MoCA was negatively correlated with IL6. There was no association between MRI findings and eGFR or inflammatory variables, and eGFR was not a predictor of MoCA values, while IL17 and IL6 were.

Defect states and their electric field-enhanced electron thermal emission in heavily Zr-doped β -Ga2O3 crystals

Performing deep level transient spectroscopy (DLTS) on Schottky diodes, we investigated defect levels below the conduction band minima (Ec) in Czochralski-grown unintentionally doped (UID) and vertical gradient freeze-grown Zr-doped β-Ga2O3 crystals. In UID crystals with an electron concentration of 1017 cm−3, we observe levels at 0.18 eV and 0.46 eV in addition to the previously reported 0.86 (E2) and 1.03 eV (E3) levels. For 1018 cm−3 Zr-doped Ga2O3, signatures at 0.30 eV (E15) and 0.71 eV (E16) are present. For the highest Zr doping of 5 × 1018 cm−3, we observe only one signature at 0.59 eV. Electric field-enhanced emission rates are demonstrated via increasing the reverse bias during measurement. The 0.86 eV signature in the UID sample displays phonon-assisted tunneling enhanced thermal emission and is consistent with the widely reported E2 (FeGa) defect. The 0.71 eV (E16) signature in the lower-Zr-doped crystal also exhibits phonon-assisted tunneling emission enhancement. Taking into account that the high doping in the Zr-doped diodes also increases the electric field, we propose that the 0.59 eV signature in the highest Zr-doped sample likely corresponds to the 0.71 eV signature in lower-doped samples. Our analysis highlights the importance of testing for and reporting on field-enhanced emission, especially the electric field present during DLTS and other characterization experiments on β-Ga2O3 along with the standard emission energy, cross section, and lambda-corrected trap density. This is important because of the intended use of β-Ga2O3 in high-field devices and the many orders of magnitude of possible doping.

Interface-induced ferromagnetism in μ-Fe2O3/β-Ga2O3 superlattices

Superlattices of antiferromagnetic μ-Fe2O3 and diamagnetic β-Ga2O3 are grown by plasma-assisted molecular beam epitaxy on (010) oriented β-Ga2O3 substrates in which ferromagnetism emerges above room temperature. To investigate the suspected interface origin of the ferromagnetic phase, identical superlattice structures are grown at various substrate temperatures and beam fluxes. Atomic-resolution scanning transmission electron microscopy images confirm the registry of μ-Fe2O3 to the β-Ga2O3 layers in these superlattices. Atomic force microscopy and high-resolution x-ray diffraction are used to examine the growth morphology and characterize the superlattice interface roughness. The saturation magnetization of the ferromagnetic phase is observed to increase strongly with the interface roughness. Conversely, smoother superlattices exhibit a weaker ferromagnetic response and a higher density of paramagnetic moments along with evidence of superparamagnetic clusters. These findings are consistent with the interface origin for the ferromagnetic response in these superlattices. The demonstration of an interface magnetic phase in nearly lattice-matched monoclinic Fe2O3/Ga2O3 opens the door to ultrawide bandgap heterostructure-engineered magnetoelectronic devices, where ferromagnetic switching of the interface phase can be incorporated into high-field devices.

Abstract 57: Deployment of Portable, Bedside, Low-Field Magnetic Resonance Imaging for Evaluation of Stroke Patients

Background: Magnetic resonance imaging (MRI) is a powerful modality for diagnosing stroke. Conventionally, patients must travel to the location of a high-field MRI device. Advances in low-field MRI have enabled acquisition of clinically useful images using a portable device at the bedside. The feasibility of using point of care (POC) MRI in a clinical stroke setting is unknown. Objective: To determine the safety and feasibility of portable, bedside, low-field MRI in a clinical setting. Design/Methods: POC MRI exams were performed in Yale’s Neuroscience Intensive Care Unit (NICU) from July 2018 to August 2019. Images were acquired at the bedside using a standard 110V, 15A power outlet. The environment included the bedside vitals monitor, ventilators and intravenous infusion pumps. Exams were performed by research staff trained to operate the POC scanner in the absence of a trained MRI technician. No special precautions were necessary to remove ferrous metals from the room. Scan parameters were controlled using a tablet computer interface, and images were available immediately after acquisition. Results: POC MRI was obtained in 85 stroke cases (46% female, ages 18-96 years, 46% ischemic stroke, 34% intracerebral hemorrhage, 20% subarachnoid hemorrhage). Scans were obtained within 7 days of symptom onset. NIHSS scores ranged from 1 to 29 (median of 7). Of the 85 patients analyzed, 68 underwent T2-weighted imaging, 72 underwent FLAIR imaging, and 39 underwent diffusion weighted imaging (DWI). DWI was only tested in ischemic stroke cases. Patients’ BMI ranged from 20.0 to 46.5 with a median of 26.7. The majority 74 (87%) of patients completed the entire exam. Five patients (6%) were unable to fit in the scanner’s 30 cm opening, while 6 patients (7%) experienced claustrophobia resulting in early termination of the exam. Mean exam time was 28.9 ± 8.4 minutes. The 64 mT static magnetic field, gradient and RF pulses of the POC MRI scanner did not interfere with NICU equipment, and no significant adverse events occurred. Conclusions: We report the first use of a portable, low-field MRI system to image stroke patients at the bedside. This early work suggests our approach is safe and viable in a complex clinical care environment.

Interface crack growth rate and fatigue life of multilayer-coated conductor tapes

Rare-earth barium copper oxide (REBCO) coated conductor (CC) tapes in high-field magnet applications usually experience fatigue due to a variety of cyclic mechanical and thermal loads. Therefore, estimation of the fatigue life of a particular REBCO CC is vital for the successful development and applications of high-field magnets devices, which are crucial components for aerospace, automotive, and maglev train transportation. For these needs, the authors evaluated the interfaces fatigue crack growth rate, and fatigue life of multilayered yttrium barium copper oxide (YBCO) coated conductor (CC) tape at room temperature via a displacement-energy model (DEM) approach. The DEM approach can measure the damage initiation and propagation rate in specific interfaces of a multi-layer film structure simultaneously. It assumed transverse intrinsic tensile/compressive cyclic loading and adopted the linear-elastic damage law with the maximum normal stress failure criterion to characterize the degradation in the tape. With an initial Eigenfunction (W0) (a parameter equivalent to the stress loading amplitude range) set as 2.30 × 10-12 m, the computed results show a strain (ε) range from 0.35 to 0.46 % and fatigue ratio range from 0.002 to 0.07 in the interfaces of the tape. Under the given parameters, it was found out that the tape has a critical interface fatigue crack growth rate of 2.54 pm/cycle corresponding to fatigue life of 3.9372 × 105 cycles. According to our previous studies, the results on the DEM approach has good agreement with those on the Finite Element Method (FEM) counterpart model, closed-form solution (CFS) model, and X-ray diffraction method (XRD). This technique can help to avoid enormous resources usually spent experimentally on the calculation of fatigue life of REBCO CC tapes.