Gradient coil design with enhanced shielding constraint for a cryogen-free superconducting MRI system

The relatively fragile low-temperature stability of cryogen-free superconducting magnetic resonance imaging(MRI)magnets requires the careful management of exogenous heat sources.A strongly shielded gradient magnetic field is important for the optimal operation of cryogen-free MRI systems.In this study,we present an enhanced shielding method incorporating a regionalized stray field constraining strategy.By optimizing the constraint parameters,we could develop engineering-feasible gradient coil schemes without increasing system complexity but with the stray field intensity reduced by half.In real measurement in an integrated MRI system,the developed gradient assembly demonstrated good performance and supported to output images of excellent quality.Our findings suggested that the proposed method could potentially form a useful design paradigm for cryogen-free MRI magnets.

Application of SPAC method and electromagnetic wave CT in karst detection of Wuhan Metro Line 8

In recent years,karst construction projects in the built-up area of Wuhan(capital of Hubei Province,China)are increasing,and the karst geological disasters have aroused social concerns.The actual engineering projects usually use shallow geophysical exploration methods to explore karst.This paper uses Spatial Auto-Correlation Method(SPAC)and electromagnetic Computerized Tomography(CT)to detect karst in urban built-up areas.Depending on the different physical properties of rock and soil,the SPAC method can better reveal the interface between soil and rock strata and the interface between soil layers.The electromagnetic CT method can identify strata according to the apparent absorption coefficient,which can better reveal the interface between soil and rock,the interface between the more intact and weathered rock.The SPAC method is mainly qualitative to measure the low-speed area,namely,the wrong geological body i.e.,karst cave,but also can detect the fracture zone or filling mode of karst cave,and at the same time,cannot use exploration holes or logging observation.The electromagnetic CT method can accurately detect the location and scale of the karst caves and has a higher accuracy detecting karst bands.In addition,exploration holes or well logging observations are also expected to be conducted,and their detection effect is greatly affected by lithology.

Groundwater level prediction of landslide based on classification and regression tree

According to groundwater level monitoring data of Shuping landslide in the Three Gorges Reservoir area, based on the response relationship between influential factors such as rainfall and reservoir level and the change of groundwater level, the influential factors of groundwater level were selected. Then the classification and regression tree（CART） model was constructed by the subset and used to predict the groundwater level. Through the verification, the predictive results of the test sample were consistent with the actually measured values, and the mean absolute error and relative error is 0.28 m and 1.15%respectively. To compare the support vector machine（SVM） model constructed using the same set of factors, the mean absolute error and relative error of predicted results is 1.53 m and 6.11% respectively. It is indicated that CART model has not only better fitting and generalization ability, but also strong advantages in the analysis of landslide groundwater dynamic characteristics and the screening of important variables. It is an effective method for prediction of ground water level in landslides.

Source rupture process of the 2015 Gorkha, Nepal Mw7.9 earthquake and its tectonic implications

On 25 April, 2015, an Mw7.9 earthquake occurred in Nepal, which caused great economic loss and casualties. However, almost no surface ruptures were observed. Therefore, in order to interpret the phenomenon, we study the rupture process of the earthquake to seek answers. Inversion of teleseismic body-wave data is applied to estimate the rupture process of the 2015 Nepal earthquake. To obtain stable solutions, smoothing and non-negative constraints are introduced. 48 teleseismic stations with good coverage are chosen. Finite fault model is established with length and width of 195 km and 150 km, and we set the initial seismic source parameters referring to CMT solutions. Inversion results indicate that the focal mechanism of this earthquake is a thrust fault type, and the strike, dip and rake angle are in accordance with CMT results. The seismic moment is 0.9195 ×10^（21）Nm（Mw7.9）, and source duration is about 70s. The rupture nucleated near the hypocenter and then propagated along the dip direction to the southeast, and the maximum slip amounts to 5.2 m. Uncertainties on the amount of slip retrieved by different inversion methods still exist, the overall characteristics are inconsistent. The lack of shallow slip during the 2015 Gorkha earthquake implies future seismic hazard and this region should be paid more attention to.

Analysis of the relationship between water level fluctuation and seismicity in the Three Gorges Reservoir(China)

The Three Gorges Reservoir is a good site for the further researches on reservoir induced seismicity due to decades＇ seismic monitoring. After the first water impounding in 2003, seismic activity becomes more frequent than that before water impoundment. In order to quantitatively study, the relationship between the water level fluctuation and earthquakes in TGR, we introduced statistical methods to attain the goal. First of all, we relocated the earthquakes in TGR region with double difference method and divided the earthquakes into 5 clusters with clustering analysis method. Secondly, to examine the impacts of water level fluctuation in different water filling stages on the seismic activity in the 5 clusters, a series of statistical analyses are applied. Pearson correlation results show that only the 175 m water level fluc- tuation has significantly positive impacts on the seismic activity in clusters I, II, III and V with correlation coefficients of 0.44, 0.38, 0.66 and 0.63. Cross-correlation analysis demonstrates that 0, ], 0 and 0 month time delay separately for the clusters I, II, III and V exists. It illustrated the influences of the water loading and pore pressure diffusion on induced earthquakes. Cointegration tests and impulse response analysis denoted that the 175 m water level only had long term and significant effects just on the seismic events in the intersection region of the Fairy Mount Fault and Nine-brook Fault. One standard deviation shock to 175 m water level increased the seismic activity in cluster V for the first 3 months, and then the negative influence was shown. After 7 months, the negative impulse response becomes stable. The long-term effect of the 175 m water impoundment also proved the important role of pore pressure diffusion in RIS with time.

Review:Recent Progress on the Application of REBCO Superconductor Bulks

The high temperature superconducting REBa2 Cu3 O7-x(REBCO)bulk with a diameter of only a few centimeters can trap a tesla⁃level magnetic field at a moderate temperature.The high magnetic field in such a compact structure makes the REBCO bulk magnet widely applicable in many scenarios,such as in motor,generator,and bearing for flywheel.This review focuses on some research areas using the REBCO bulk magnet,which is quite interesting but has attracted little attention,including magnet lens,compact NMR,magnetron sputtering system,drug magnetic targeting system,magnetic separation,and magnetic mirror.In all of these areas,the REBCO bulk magnet shows its own advantages of having a high magnetic field but a small size to improve the final function.

Source parameters determination for earthquakes in Kushiro,Japan considering source time function

This paper applies a new formulation to do moment tensor inversion for earthquakes in the Kushiro area of Japan. Comparing with conventional moment tensor inversion method, the new one takes the effect of source time function into consideration. For the inversion, best solution is obtained by minimizing the difference between the observed seismograms and the synthetic ones. And the best-fitting focal depth is determined from the variance reduction. The results indicate that half duration of source time function is proportional to the magnitude of earthquakes. Large earthquakes have long half duration, whereas that of moderate-small earthquakes is comparatively shorter. The focal mechanisms of all three earthquakes are of thrust fault type, which is mainly ascribed to the collision of the North American plate with the Eurasia plate in the late Cretaceous or Paleogene.

Effect of Magnetic Field Configuration on Stray-Crystal Formation with Different Platform Sizes during Directional Solidification of Single-Crystal Superalloy

The magnetic field is an effective means to control the solidification structure and the defects of metal and semiconductor crystals.This work investigates the effects of Cusp magnetic field(CMF)and longitudinal magnetic field(LMF)on the stray-crystal formation in the platform regions during the directional solidification of single-crystal superalloy with the different cross section sizes.The application of CMF reduces the formation of platform stray-crystal,while LMF increases its generation.As the platform size increases,the stray-crystal ratio increases regardless of whether the magnetic fields are applied or not,the effectiveness of CMF increases,while that of LMF decreases.The reason that the effects of CMF and LMF on the platform stray-crystal formation could be attributed to the change of flow structure from the distribution characteristics of the thermoelectric magnetic force and the magnetic damping force near the liquid-solid interface.

Fully depleted vdW heterojunction based high performance photovoltaic photodetector

Van der Waals(vdW)heterojunctions,with their unique electronic and optoelectronic properties,have become promising candidates for photodetector applications.Amplifying the contribution of the depletion region in vdW heterojunction,which would enhance both of the collection efficiency and speed of the photogenerated carriers,presents an effective strategy for achieving high performance vdW heterojunction photodetectors.Herein,a fully depleted vdW heterojunction photodetector is built on two-dimensional(2D)semiconductor materials(GaTe and InSe)layered on a pattered bottom electrode in vertical structure,in which the generation and motion of carriers are exclusively achieved in the depletion region.Attributed to the intrinsic built-in electric field,the elimination of series resistance and the depletion region confinement of carriers,the as-fabricated photodetector exhibits prominent photovoltaic properties with a high open-circuit voltage of 0.465 V,as well as photoresponse characteristics with outstanding responsivity,detectivity and photoresponse speed of 63.7 A/W,3.88×10^(13)Jones,and 32.7 ms respectively.The overall performance of this fully depleted GaTe/InSe vdW heterojunctions photodetectors are ranking high among the top level of 2D materials based photodetectors.It indicates the device architecture can provide new opportunities for the fabrication of high-performance photodetectors.

Magnetic Actuation Systems and Magnetic Robots for Gastrointestinal Examination and Treatment

Magnetic actuation technology(MAT)provides novel diagnostic tools for the early screening and treatment of digestive cancers,which have high morbidity and mortality rates worldwide.The application of magnetic actuation systems and magnetic robots in gastrointestinal(GI)diagnosis and treatment to provide a comprehensive reference manual for scholars in the field of MAT research are reviewed.It describes the basic principles of magnetic actuation and magnetic field safety,introduces the design,manufacturing,control,and performance parameters of magnetic actuation systems,as well as the applicability and limitations of each system for different parts of the GI tract.It analyzes the characteristics and advantages of different types and functions of magnetic robots,summarizes the challenges faced by MAT in clinical applications,and provides an outlook on the future prospects of the field.

Pulsed High Magnetic Field Facility in China:Current status and future

The upgrade of the Pulsed High Magnetic Field Facility(PHMFF-U,stage II),which is one of the National Major Science and Technology Infrastructure Projects within the“National Fourteenth Five-Year Plan”funded by the Chinese National Development and Reformation Committee,was officially approved in October,2023.The PHMFF-U represents the upgrade of the PHMFF(stage I)and is planned to be built right next to stage I on the campus of Huazhong University of Science and Technology,Wuhan,China.

Recent advances in magnetic targeting based on high magnetic field and magnetic particles

In the past few decades,the multifunctional magnetic drug carrier based on the magnetic nanoparticles and high magnetic field has been intensively researched.The magnetic drug carrier can be targeted to the tumour area not only by the chemical protocol but also by the physical one(external field).In this review,the authors first briefly discuss the fabrication process of magnetic drug carriers,which includes the synthesis of magnetic nanoparticles,fabrication of magnetic drug carriers and conjugation of anti-tumour agents.Then different targeted protocols have been summarised,including passive targeting,biochemical active targeting and biophysical active targeting namely magnetic targeting(MT).Multiple MT results both in vitro and in vivo are introduced,in which two unconventional cases are emphasised and described.The first MT clinical research with 14 peoples was performed in the last century.A 0.5–0.8 T permanent magnet was attached to the tumour area when magnetic particles conjugated with epirubicin were injected.The side effect of epirubicin had been decreased,and the four patients showed the decreasing of a tumour which proved the feasibility of MT.Different from other targeting protocols,MT needs an extra external magnetic field.So various types of MT instruments have been shown in the final part of this review,including a single strong magnetic field,homemade electronic solenoid coil assay and commercial magnetic resonance imaging.

Engineering-based design and fabrication procedure for mid-temperature REBCO magnets accommodating the strong Ic anisotropy

An engineering-feasible design and fabrication procedure for REB2aCu3O7-x(REBCO)magnets based on the strong Ic angle dependence at moderate temperatures(40–77 K)was developed.In this procedure,the Ic value of every REBCO coil of the magnet is calculated from the Ic(B,θ)data of REBCO tape at operating temperature with different applied fields,which is called the“full field-angle dependent Ic method.”This approach has significantly higher accuracy than the conventional method,which only focuses on the Ic value at the coil with the highest perpendicular field component.Additionally,the fitted lift factor at 45 K with different applied fields was closely related to the minimum Ic value at 77 K and 0.5 T.The engineering-feasible design and fabrication procedure for the REBCO magnet was developed on the basis of the Ic values calculated via the“full field-angle dependent Ic method”and lifting-factor fitted method,and it had a design error of<5%.The proposed technique is a more accurate method for the design and fabrication of cooling REBCO coils and will improve the applicability of REBCO magnets in this temperature range.

High-Speed Visualization of Bubble Behaviors for Pool Boiling of R-141b

A visualization study on the behavior of bubbles has been carried out for pool boiling of R141b on a horizontal transparent heater at pressure 0.1 MPa. The behaviors of bubbles were recorded by a high-speed camera placed beneath the heater surface. The departure diameter, departure time of bubbles and nucleation site density at different heat flux were obtained. The visualization results show that bubble departure diameter and departure time decrease, while the nucleation site density increases as the heat flux increases. R is also observed that there is no liquid recruited into the microlayer in the experiment. Based on the experimental results, boiling curve for R141b was predicted by using the dynamic microlayer model. As a resuR, the agreement between the predictive result based on the dynamic microlayer model and the experiment data for boiling curve of R141b is good at high heat flux.

Foreword

Superconducting materials have attracted extensive attention of scientists around the world thanks to their unique physical properties.The worldwide research focuses on the fundamental frontier to explore novel superconducting materials and even room-temperature superconductors with higher superconducting transition temperature.In recent years,significant progresses have been achieved in such fundamental frontier study of superconductivity.The superconductivity of magic-angle graphene was discovered in 2017 and lanthanum hydride room temperature superconductor was discovered in 2019,which has aroused widespread attention and great sensation.

Jun Zheng,Minghui Wei,Siyi Quan,Yicheng Feng,Peng Wen State Key Laboratory of Traction Power,Southwest Jiaotong University,Chengdu 610031,People’s Republic of China

This review paper summarizes and analyses the current literature on the synthesis of dense MgB_(2) bulk with high density and by both the modified solid reaction method and the Mg infiltration method.MgB_(2) bulk shows Telsa‐level magnetic field‐trapping ability in small volumes(1–5 cm^(3))at 15–20 K,which is beneficial for multiple applications,particularly where light weighting is beneficial.The review also compares the properties of MgB_(2) to rare earth barium cuprate bulk magnets and NbTi solenoid magnets and discuess potential applications such as magnetic lenses,compact NMR,and magnetic shielding.