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Based on the platform of a proton accelerator facility, a 200 MHz high intensity continuous wave (CW) radio frequency quadrupole (RFQ) accelerator has been designed at the Sino-French Institute of Nuclear Engineering and Technology of Sun Yat-Sen University, China. Employing the conventional four-vane structure, the RFQ can accelerate 20 mA proton beam from 20 keV to 2.5 MeV. In the beam dynamics design, the simulated transmission efficiency reaches 99.5% and the vane length is less than 4 m. In the electromagnetic design, for the long-term stable operation, Pi-mode Stabilizer Loops (PISLs) are utilized to achieve more than 10 MHz mode frequency separation and to decrease the effects of dipole modes. The 48 tuners are optimized to provide a range of ± 2 MHz frequency tuning. Additionally, the undercuts are optimized to ensure a good field flatness along the longitudinal direction. Based on the coolant channel design, the multi-physics analysis is performed to investigate the deformation and stress resulting from the dissipation of RF power within the cavity, as well as determine the temperature tuning coefficients of the coolants within the vane and wall. The entire design and analysis of PAFA-RFQ has been completed, and the scheme of the design can also be applied to the design of other RFQ cavities.

Fluid–structure interaction (FSI) problems with large fluid deformations can be a great challenge for numerical simulations using conventional methods. In this paper, we propose a novel hybrid approach of an improved Smoothed Particle hydrodynamics and smoothed finite Element Method (SPEM) for modeling FSI problems. In SPEM, the edge-based smoothed finite element method (S-FEM) is developed in Lagrangian frame and is used for the first time to model both elastic structures and incompressible flows. For fluid regions with large deformations, the associated finite elements are adaptively converted into particles and the corresponding regions are subsequently modeled using the decoupled finite particle method (DFPM), which is an improved smoothed particle hydrodynamics (SPH) method suitable for modeling incompressible flows with free surfaces. A ghost particle-based interface algorithm to couple existing S-FEM elements and DFPM particles is developed in SPEM to implement the modeling of FSI problems. As the smoothed FEM and decoupled FPM are enhanced FEM and SPH respectively and DFPM is only used for local fluid regions with large deformations, it is expected that SPEM is more accurate and more efficient than the existing coupling approaches of conventional FEM and SPH. Five numerical examples are tested using the proposed SPEM and the comparative studies with results from other sources reveal that SPEM is an effective approach for modeling FSI problems with large fluid deformations.

In particulate flows, particle-particle collisions play a very important role in determining the flow behavior of the fluid-particle two-phase systems. Thus, it is very important in the numerical simulations of particulate flows to treat the particle-particle interactions with a felicitous method. In this paper, a recently developed direct numerical simulation (DNS) technique, the Finite Element Fictitious Boundary Method (FEM-FBM), for thermal convective particulate flows is used for the simulations of dense particulate suspensions of elliptic shaped particles. The momentum and temperature flow fields are coupled with the aid of Boussinesq approximation. The thermal and momentum interactions between solid and fluid phases are handled by using the Fictitious boundary method (FBM). The continuity, momentum, and energy equations are solved on a fixed Eulerian mesh which is independent of flow features by using a multi-grid finite element scheme. A modified collision model is proposed that can handle not only the interactions between the circular particles but also effectively treat the collisions between the elliptic shaped particles. Firstly, we validate the newly developed collision model for isothermal circular particles together with a comparative study of “drafting, kissing and tumbling” (DKT) motion of both elliptic and circular shaped isothermal particles. Then we investigated the DKT motions of the hot and cold elliptic particles with energy exchange and studied the lateral behavior of the particles in numerous settings. Further, we studied the DKT motion of catalyst particles and investigate the particles behavior at different Grashof numbers. Numerical tests are performed to show that the present method is robust and provides an efficient approach for the simulations of particulate flows with a large number of elliptic particles.

Explosive welding (EXW) involves processes like the detonation of explosive charge, impact of metal structures and strong fluid-structure interaction with complex features. The EXW has not been well modeled before since in most numerical simulations the EXW is simply treated as the impact of two plates at high velocities. Recently, the authors developed a density adaptive smoothed particle hydrodynamics (SPH) method to successfully model the whole EXW process considering the high explosive explosion and its driving effects on flyer plate [ 1 ]. Later, this model is applied to investigate the mechanisms in EXW such as the wave formation mechanism and weldability windows [ 2 ]. The explosive TNT used in the previous model can be regarded as an ideal explosive while the complex and non-ideal explosive ANFO is more frequently used in practical welding operations. In this paper, the JWL++ model is incorporated into the density adaptive SPH to simulate the detonation of ANFO. The slab detonation and the explosive welding with TNT or ANFO explosive are simulated using the developed models. Good agreement can be observed between computational results and analytical solutions or experimental observations. Some typical characteristics in TNT and ANFO EXW including the detonation of explosive, wavy interface, jet formation, weldability windows are comparatively studied.

Hypervelocity impact (HVI) is associated with large deformations of structures, phase transitions of materials and scattered debris cloud. It is a great challenge to accurately model the HVI process and predict the damage produced by HVI for conventional numerical methods. In this paper, a recently developed corrective smoothed particle hydrodynamics (SPH) method, decoupled finite particle method (DFPM), is extended to model HVI problems. Validation examples show that DFPM is as flexible as SPH while having much better performance in improving accuracy and removing tensile instability. DFPM is also very attractive for modeling problems with extremely disordered particle distribution (e.g., HVI) as no matrix inversion is required. DFPM is then applied to model the penetration of a sphere on a target plate at various impact velocities and impact angles. It is found that as the impact velocity increases, the hole size increases accordingly and maintains basically constant in a steady state after the impact velocity reaches a critical value. Based on extensive DFPM simulation results, novel formulae are given for predicting the hole size produced by normal and oblique HVIs, which can reproduce experimental data and shows better performance than existing empirical formulae in a wider range of impact velocity.

Particulate flows with thermal convection are very challenging to simulate numerically due to the existence of constantly moving boundaries and complex heat-fluid coupling effects. Meshfree and particle methods have special advantages in modeling complex fluid flows with moving boundaries. However, previous works based on meshfree modeling mainly focused on either particulate flows only with momentum exchange or natural thermal convection. In this paper, a finite particle method integrated with particle shifting technique (FPM-PST) is developed for modeling particulate flows with thermal convection. FPM is an improved smoothed particle hydrodynamics (SPH) method with better accuracy while extremely irregular particle distribution may lead to ill-conditioned corrective matrix and terminate the simulation. PST can achieve regular particle distribution through shifting highly disordered particles while current PST is based on conventional SPH of poor accuracy. A number of numerical examples demonstrated that FPM-PST is a novel approach for modeling thermal particulate flows with good performance in accuracy and stability. It has better accuracy than the conventional SPH and can obtain comparable results with those from other sources. The unphysical voids can also be avoided by FPM-PST. From the FPM-PST simulations, it is observed that at relatively low Reynolds numbers thermal convection between hotter or colder particles and the fluid causes significant increase or decrease in the drag force acting on particles, while the thermal convection has little influence on the particle motion at relatively high Reynolds numbers.

Purpose Donor lungs often contain clots. Retrograde flush removes a portion of these clots and improves graft quality. It's very likely that some clots remain after retrograde flush and case studies of thrombolytic treatment of donor lungs has shown a beneficial effect. We studied donor lung clots to determine their composition and age. Methods At procurement of donor lungs, in situ antegrade flush was followed by a back table retrograde flush. Retrograde flush fluid was collected and filtered using a 0,2mm filter. The material left in the filter was instantly fixed in 4% formalin for at least 24 hours and studied by a haematoxylin-Eosin(HE) stain and with Martius scarlet blue(MSB) stain. The presence and maturity of fibrin and the presence of lines of Zahn were analyzed. Zahn lines are altering bands of light and dark colors indicating the clot was formed in an area of high blood flow. Clots where then classified based on the composition of fibrin. Clot classification was based on the oldest (most dense fibrin) part of the clot. Results In the retrograde flush of all included lungs (n=15) clots were found. A total of 129 clots were found in 15 donor lungs. 12 clots were found at a 2nd retrograde flush at EVLP. Up to 20 clots were seen in a lung varying in size from 0.3 to 70 mm. Composition varied from young, red blood cell-containing clots to more mature dense fibrin meshes (fig 1).A vast majority of clots showed either an outer layer, lines of Zahn or absence of RBC's that we consider characteristics suggestive of formation before death. Conclusion All donor lungs contain clots, emphasizing the importance of retrograde flush at retrieval. Of the clots, 39/129 were more mature and had absence of red blood cells and a more mature dense fibrin mesh. These characteristics may render these clots less susceptible to thrombolysis. However, 90/129 clots were more recently formed and might therefore be more accessible to thrombolysis. Further studies are needed to evaluate the effect of thrombolysis on donor lung clots and primary graft function.

Purpose Ex vivo lung perfusion (EVLP) is an established technique for the reconditioning and evaluation of marginal lungs. However, the use of EVLP for logistical reasons is still under discussion. We present our experience with EVLP for medical and logistical reasons. Methods In this single center retrospective study, all EVLP's performed between July 2012 and October 2019 were analyzed. PaO2, PVR, dynamic lung compliance and plateau airway pressure were analyzed for the EVLP's. PGD, lung function, CLAD free and overall survival were included for the lung transplant recipients. Results In total 50 EVLP's were performed, 33 for medical reasons which resulted in 26 lung transplants (MT) while 7 were rejected (MR). In addition, 17 EVLP's for logistical reasons resulted in 15 lung transplants (LT), 2 were rejected (LR). Pulmonary oedema was the main reason for rejection.During EVLP, there was an increase in PaO2 in MT, PaO2 remained stable in LT. Pre-EVLP PaO2 was significantly lower in MT versus LT (p Conclusion Transplantation of lungs after logistic EVLP is safe and makes transplantation of lungs with otherwise very extended cold ischemia time more controllable.Furthermore, this study confirms that EVLP is an excellent tool for reconditioning of injured lungs and that lung compliance and plateau airway pressure are more important than PaO2 in the evaluation on EVLP.

Fast radio bursts (FRBs) are short pulses observed in radio band from cosmological distances, some of which emit repeating bursts. The physical origins of these mysterious events have been subject to wide speculations and heated debates. One class of models invoke soft gamma-ray repeaters (SGRs), or magnetars, as the sources of FRBs. Magnetars are rotating neutron stars with extremely strong magnetic field and can sporadically emit bursts from X-ray (keV) to soft gamma-ray (sub-MeV) with duration from 10􀀀2 s to 102 s. However, even though some bright radio bursts have been observed from some magnetars, no FRB-like events had been detected to be associated with any magnetar burst, including one giant flare, and no radio burst has been associated with any X-ray event from any magnetar. Therefore, there is still no observational evidence for magnetar-FRB association up to today. Recently, a pair of FRB-like bursts (FRB~200428 hereafter) separated by 30 milliseconds (ms) were detected from the general direction of the Galactic magnetar SGR~J1935+2154. Here we report the detection of a non-thermal X-ray burst in the 1--250\,keV energy band with the Insight-HXMT satellite, which we identify as emitted from SGR~J1935+2154. The burst showed two hard peaks with a separation of ms, consistent with the separation between the two bursts in FRB~200428. The delay time between the double radio and X-ray peaks is 8:57s, fully consistent with the dispersion delay of FRB~200428. We thus identify the non-thermal X-ray burst is associated with FRB~200428 whose high energy counterpart is the two hard peaks in X-ray. Our results suggest that the non-thermal X-ray burst and FRB~200428 share the same physical origin in an explosive event from SGR~J1935+2154.

We use the In data collected during the 2019 outburst from X-ray pulsar 4U 1901+03 to complement the orbital parameters reported by Fermi/GBM. Using the Insight-HXMT, we examine the correlation between the derivative of the intrinsic spin frequency and bolometric flux based on accretion torque models. It was found that the pulse profiles significantly evolve during the outburst. The existence of two types of the profile's pattern discovered in the Insight-HXMT data indicates that this source experienced transition between a super-critical and a sub-critical accretion regime during its 2019 outburst. Based on the evolution of the pulse profiles and the torque model, we derive the distance to 4U 1901+03 as 12.4+-0.2 kpc., 8 pages, 5 figures, accepted by JHEAP

Explosive welding (EXW) involves processes like the detonation of explosive charge, impact of metal structures and strong fluid-structure interaction with complex features such as interfacial waves and jet generation. The whole EXW process has not been well modeled before due to the large deformation and moving interfaces while the associated mechanisms inherent in EXW are also not well understood. In this paper, the whole EXW process is simulated using a density adaptive smoothed particle hydrodynamics (SPH) model, in which a density adaptive algorithm is used to treat variable large density ratio in EXW and the kernel gradient correction (KGC) is used to improve computational accuracy of SPH. The mechanisms in EXW are investigated, and typical phenomena including the wavy interface, jet formation, interfacial temperature and pressure distribution as well as melting voids are examined. The mechanisms of wave formation are studied while two existing mechanisms, namely, the Jet Indentation Mechanism and the Vortex Shedding Mechanism are revealed with the present SPH simulations. It is demonstrated that with proper amount of explosive charge and initial welding angle, the present SPH method can well reproduce the morphology evolution of the welding interface from straight to wavy and further to wavy with vortex shedding. Furthermore, based on comprehensive numerical data from SPH simulations, two types of numerical weldability windows for EXW are presented together with discussions about different welding limits and effective explosive charge.

Smoothed particle hydrodynamics (SPH) is a meshfree Lagrangian particle method, and it has been applied to different areas in engineering and sciences. One concern of the conventional SPH is its low accuracy due to particle inconsistency, which hinders the further methodology development. The finite particle method (FPM) restores the particle consistency in the conventional SPH and thus significantly improves the computational accuracy. However, as pointwise corrective matrix inversion is necessary, FPM may encounter instability problems for highly disordered particle distribution. In this paper, through Taylor series analyses with integration approximation and assuming diagonal dominance of the resultant corrective matrix, a new meshfree particle approximation method, decoupled FPM (DFPM), is developed. DFPM is a corrective SPH method, and is flexible, cost-effective and easy in coding with better computational accuracy. It is very attractive for modeling problems with extremely disordered particle distribution as no matrix inversion is required. One- and two-dimensional numerical tests with different kernel functions, smoothing lengths and particle distributions are conducted. It is demonstrated that DFPM has much better accuracy than conventional SPH, while particle distribution and the selection of smoothing function and smoothing length have little influence on DFPM simulation results. DFPM is further applied to model incompressible flows including Poiseuille flow, Couette flow, shear cavity and liquid sloshing. It is shown that DFPM is as accurate as FPM while as flexible as SPH, and it is very attractive in modeling incompressible flows with possible free surfaces.

Purpose To investigate the impact of cerebral reperfusion on cardiac contractile function after normothermic regional perfusion (NRP) after anoxic circulatory death in a porcine model. Methods The animals were anaesthetized and biventricular pressure-volume catheters and a pulmonary artery catheter were inserted percutaneously. Through a midline sternotomy, the heparinised animals were cannulated for extracorporeal circulation. Baseline data were obtained before cessation of mechanical ventilation. Death was determined 5 minutes after mechanical asystole and after additional 3 minutes of warm ischemia NRP was started using a heart-lung machine. The animals were randomized before reperfusion to either clamping (CL) (n=8) or non-clamping (NCL) (n=8) of the aortic arch vessels; the infrarenal aorta was clamped in both groups. The NRP-protocol includes early volume loading of the right ventricle, infusion of dobutamine and norepinephrine and gradual wean over 30 minutes. The animals were observed for 180 minutes after weaning from NRP. Results All animals were successfully weaned from NRP. Both groups demonstrated an acceptable cardiac function after weaning with a mean arterial blood pressure above 75 mmHg and low filling pressures. The NCL group received significantly more norepinephrine (p=0.0484) than the CL group. The left ventricle End-systolic pressure-volume relationship as an index of contractility showed improvement in both groups after wean from NRP compared to baseline (p=0.0009). In the CL group, LV contractility showed a tendency to a better improvement compared to the NCL group (p=0.226) (Fig. 1). The RV showed preserved contractility in both groups. Conclusion LV contractility but not RV contractility improves after circulatory death and weaning from NRP. The improvement of the left ventricular contractility tends to be better when the aortic arch vessels are clamped compared to upper-body perfusion.

Purpose Ex Vivo Lung Perfusion (EVLP) is an excellent method to preserve and recondition donor lungs, thus increasing the lung donor pool. This systematic review summarizes studies comparing both primary graft dysfunction (PGD) and survival between EVLP and conventional lung transplantation (c-LTx), or between different EVLP protocols. The objective is to evaluate outcomes of the three main EVLP protocols: ‘Lund’, ‘Toronto’ and ‘Organ Care System’ (OCS), through a network meta-analysis (NMA). Methods A systematic search was performed in Pubmed, Embase, the Cochrane library and Web of Science. Studies performing EVLP on initially discarded donor lungs were independently assessed for eligibility by two researchers. Data on study design, participants, and EVLP methods were extracted, together with outcomes such as survival and PGD. The generated database was assessed on meeting the assumptions for NMA. Results Nine studies were included: two non-randomised clinical trials (n = 240), and four prospective (n = 1360) and three retrospective observational cohort studies (n = 540). The study protocols could be divided into: Toronto (5/9), Lund (3/9) and OCS (1/9). Most frequently reported outcomes were PGD grade 3 at 72 hours post-LTx, and one-month and one-year survival. All included studies compared EVLP to c-LTx, providing solely indirect evidence for comparison between protocols and thus no loops within the NMA model. In the absence of loops, consistency within the model cannot be statistically assessed. Thus, thorough examination for differences that could modify the treatment effect is required. Substantial variations were found in study design, type of LTx, and participant characteristics. It was therefore not feasible to construct a subset of studies that met the similarity and consistency assumptions of NMA. Conclusion Currently, no substantiated statistical comparison can be made between different EVLP protocols. Further attempts at NMA are dependent on the introduction of studies comparing multiple EVLP protocols, or an increase in randomised controlled trials performing EVLP on standard donor lungs. Alternatively, collaborative data management between EVLP centres would be a promising way to explore the effect of different protocols, and their individual components, on patient outcomes.

Liquid sloshing flows interacting with deformable structures are difficult to be numerically simulated due to the co-existence of moving fluid-structure interfaces and breaking free surfaces. As a Lagrangian and particle-based method, the smoothed particle hydrodynamics (SPH) method has natural advantages in handling free-surface flows. The smoothed finite element method (SFEM) provides a reliable tool to capture the associated structural deformations, and it can solve the “overly-stiff” problem in the conventional FEM. In this work, the coupling strategy of an improved SPH version and SFEM is integrated with advanced fluid modeling techniques, and is extended and validated for modeling liquid sloshing with rigid or deformable structures. Both the rigid wall boundaries and deformable structures are reproduced by the elements, whereas the fluid particles with a different resolution can be adopted. The integrated δ-SPH model can significantly alleviate the spurious high-frequency noise of the computed impact pressure in a sloshing process. The particle shifting technique helps improve both accuracy and robustness of the fluid flow model. The virtual particle coupling strategy is effective to transfer information between SPH particles and SFEM elements. Various numerical tests show that the present coupling approach is very effective for modeling violent sloshing with deformable baffles or deformable container walls. This method is more accurate than the conventional coupling of SPH-FEM and can obtain results very close to the experimental observations compared with some numerical approaches from other sources.

High velocity impact (HVI) is associated with large deformations of structures, phase transition of materials, big craters and possible flying debris. It is thus challenging for conventional numerical methods to well capture the major physics of HVI problems. This paper presents the development of an improved smoothed particle hydrodynamics (SPH) method with kernel gradient correction (KGC) technique and the original application of the improved SPH method to modeling high velocity impact problems in two-dimensional and three-dimensional spaces. The SPH method with KGC is first validated by the 3D Taylor-Bar-Impact (TBI) test with Armco iron and OFHC copper. It is demonstrated that the obtained results agree well with experimental observations and with existing numerical results. The improved SPH method is then used to model a hypervelocity impact problem with an aluminum sphere impacting onto an aluminum plate in two- and three-dimensional spaces. It is shown that the presented SPH method can qualitatively and quantitatively model the HVI problem with main physics well captured. It is also demonstrated that the presented SPH method can reproduce experimental observations better than other numerical approaches, including the characteristic shape and evolution of the debris cloud as well the particle distribution.

Explosive welding involves processes like the detonation of explosive, impact of metal structures and strong fluid---structure interaction, while the whole process of explosive welding has not been well modeled before. In this paper, a novel smoothed particle hydrodynamics (SPH) model is developed to simulate explosive welding. In the SPH model, a kernel gradient correction algorithm is used to achieve better computational accuracy. A density adapting technique which can effectively treat large density ratio is also proposed. The developed SPH model is firstly validated by simulating a benchmark problem of one-dimensional TNT detonation and an impact welding problem. The SPH model is then successfully applied to simulate the whole process of explosive welding. It is demonstrated that the presented SPH method can capture typical physics in explosive welding including explosion wave, welding surface morphology, jet flow and acceleration of the flyer plate. The welding angle obtained from the SPH simulation agrees well with that from a kinematic analysis.