Risk factors for delayed postoperative hemorrhage in patients with brain arteriovenous malformations: an analysis of the nationwide multicenter prospective registry MATCH study.

OBJECTIVE: Reducing the incidence of delayed postoperative hemorrhage (DPH) is one of the challenges in the surgical treatment of patients with brain arteriovenous malformations (bAVMs). This study aimed to identify several risk factors for DPH after bAVM resection and evaluate the impact of these risk factors in patients with bAVMs. METHODS: The authors retrospectively reviewed consecutive patients with bAVMs who underwent microsurgical resection between August 2011 and September 2021. Patients were divided into either the DPH group or non-DPH group based on whether they experienced a postoperative intracerebral hemorrhage into the bAVM bed within 14 days after bAVM resection. Factors associated with DPH were assessed using multivariate logistic regression analyses. RESULTS: A total of 1284 consecutive patients with bAVMs were evaluated; DPH events occurred in 18 patients (1.4%). There were several differences in vascular architecture between the two cohorts. A giant nidus, a nidus involved in the eloquent area, a periventricular nidus, and a nidus accompanied by venous ectasia were more likely to be associated with DPH events. The multivariate analysis identified two independent factors associated with DPH: maximum diameter (OR 1.44 per 1-cm increase, 95% CI 1.13-1.83) and periventricular lesion (OR 4.10, 95% CI 1.33-12.59). The area under the receiver operating characteristic curve for the maximum lesion diameter and development of DPH was 0.71 (95% CI 0.58-0.84). The cutoff value for the maximum bAVM diameter was 4.15 cm. Furthermore, patients with a giant bAVM, of which the maximum diameter was ≥ 4.15 cm, had a higher DPH risk after surgery (HR 5.79, 95% CI 2.01-16.67; p < 0.01). The incidence rates of DPH for patients with periventricular lesions were higher than those for patients without periventricular lesions (HR 4.50, 95% CI 1.77-11.40; p < 0.01). CONCLUSIONS: Patients with giant bAVMs or periventricular lesions are at higher risk for DPH after surgery. Strategies such as blood pressure control, preoperative embolization, intraoperative monitoring, and careful patient selection should be considered to reduce the risk of DPH in high-risk patients.

Spatial Galloping Behavior of Iced Conductors under Multimodal Coupling.

In this study, the coupled ordinary differential equations for the galloping of the first two modes in iced bundled conductors, including in-plane, out-of-plane, and torsional directions, are derived. Furthermore, through numerical analysis, the critical conditions of this modal galloping are determined in the range of wind speed-sag parameters, and the galloping patterns and variation laws in different parameter spaces are analyzed. The parameter space is then divided into five regions according to the different galloping modes. Under the multimodal coupling mechanism of galloping, the impact of single and two kinds of coupled mode galloping on the spatial nonlinear behavior is explored. The results reveal that the system exhibits an elliptical orbit motion during single mode galloping, while an "8" motion pattern emerges during coupled mode galloping. Moreover, two patterns of "8" motion are displayed under different parameter spaces. This research provides a theoretical foundation for the design of transmission lines.

Suppressing Viscous Fingering in Porous Media with Wetting Gradient.

The viscous fingering phenomenon often occurs when a low-viscosity fluid displaces a high-viscosity fluid in a homogeneous porous media, which is an undesirable displacement process in many engineering applications. The influence of wetting gradient on this process has been studied over a wide range of capillary numbers (7.5 × 10-6 to 1.8 × 10-4), viscosity ratios (0.0025 to 0.04), and porosities (0.48 to 0.68), employing the lattice Boltzmann method. Our results demonstrate that the flow front stability can be improved by the gradual increase in wettability of the porous media. When the capillary number is less than 3.5 × 10-5, the viscous fingering can be successfully suppressed and the transition from unstable to stable displacement can be achieved by the wetting gradient. Moreover, under the conditions of high viscosity ratio (M > 0.01) and large porosity (Φ > 0.58), wetting gradient improves the stability of the flow front more significantly.

The Effect of Ti Particles Addition on the Microstructure and Mechanical Behavior of Mg AZ31/Al 6082 Composite Sheets.

In this study, Ti particles reinforced Mg AZ31/Al 6082 composite sheets were successfully prepared by hot rolling, with the aim of revealing the effect of Ti particles addition on the mechanical behavior and microstructure of Mg AZ31/Al 6082 composite sheets. The results showed that Ti particles were uniformly distributed at the interface of the Mg/Al-Ti composite sheets, which could greatly reduce the amount of Mg-Al intermetallic compounds during annealing treatment. Compared to the Mg/Al sheet, the tensile strength and elongation of the Mg/Al-Ti sheet could be improved simultaneously after the annealing treatment. Ti particles addition hardly affected the grain size, texture type, and tensile fracture morphology of the Mg layer and Al layer in the composite sheets before and after annealing. This present study provides a new perspective on the mechanical behavior and microstructure of Mg/Al composites through the addition of metal particles.

Effect of Nano-Ti Particles on Microstructure and Mechanical Properties of Mg-3Al-1Zn Matrix Composites.

In this paper, a new nanoscale metal Ti particle-reinforced Mg-3Al-1Zn matrix composite was successfully designed and prepared, which is mainly characterized by the fact that in addition to the "light" advantages of magnesium matrix composite, it also realizes bidirectional improvement of strength and ductility of the composite, and can be used as an alternative material for military light vehicle armor and individual armor. The SEM test shows that the nano-Ti particles are uniformly distributed at the grain boundary under the extruded state, which nails the grain boundary, inhibits the grain growth, and significantly refines the grain. XRD tests show that the addition of nano-Ti particles increases the crystallinity of the composite, which is consistent with the SEM test results. In addition, the EBSD test shows that the weakening of the texture of Ti/Mg-3Al-1Zn matrix composites and the increase in the starting probability of slip system are the main reasons for the improvement in ductility. Mechanical tests show that the yield strength, tensile strength, and elongation of the 0.5 wt% Ti/Mg-3Al-1Zn matrix composites exceed the peak values of ASTM B107/B107M-13 by 38.6%, 26.7%, and 20%, respectively.

Study on Microstructure and Mechanical Properties of TC4/AZ31 Magnesium Matrix Nanocomposites.

In the field of metal matrix composites, it is a great challenge to improve the strength and elongation of magnesium matrix composites simultaneously. In this work, xTC4/AZ31 (x = 0.5, 1, 1.5 wt.%) composites were fabricated by spark plasma sintering (SPS) followed by hot extrusion. Scanning electron microscopy (SEM) showed that nano-TC4 (Ti-6Al-4V) was well dispersed in the AZ31 matrix. We studied the microstructure evolution and tensile properties of the composites, and analyzed the strengthening mechanism of nano-TC4 on magnesium matrix composites. The results showed that magnesium matrix composites with 1 wt.%TC4 had good comprehensive properties; compared with the AZ31 matrix, the yield strength (YS) was increased by 20.4%, from 162 MPa to 195 MPa; the ultimate tensile strength (UTS) was increased by 11.7%, from 274 MPa to 306 MPa, and the failure strain (FS) was increased by 21.1%, from 7.6% to 9.2%. The improvement in strength was mainly due to grain refinement and good interfacial bonding between nano-TC4 and the Mg matrix. The increase in elongation was the result of grain refinement and a weakened texture.

Turbulent CFD Simulation of Two Rotor-Stator Agitators for High Homogeneity and Liquid Level Stability in Stirred Tank.

Good solid-liquid mixing homogeneity and liquid level stability are necessary conditions for the preparation of high-quality composite materials. In this study, two rotor-stator agitators were utilized, including the cross-structure rotor-stator (CSRS) agitator and the half-cross structure rotor-stator (HCSRS) agitator. The performances of the two types of rotor-stator agitators and the conventional A200 (an axial-flow agitator) and Rushton (a radial-flow agitator) in the solid-liquid mixing operations were compared through CFD modeling, including the homogeneity, power consumption and liquid level stability. The Eulerian-Eulerian multi-fluid model coupling with the RNG k-ε turbulence model were used to simulate the granular flow and the turbulence effects. When the optimum solid-liquid mixing homogeneity was achieved in both conventional agitators, further increasing stirring speed would worsen the homogeneity significantly, while the two rotor-stator agitators still achieving good mixing homogeneity at the stirring speed of 600 rpm. The CSRS agitator attained the minimum standard deviation of particle concentration σ of 0.15, which was 42% smaller than that achieved by the A200 agitators. Moreover, the average liquid level velocity corresponding to the minimum σ obtained by the CSRS agitator was 0.31 m/s, which was less than half of those of the other three mixers.

Effects of Intercooling Intensity on Temperature Field and Microstructure of Large-Scale 2219 Al Alloy Billet Prepared by Internal Electromagnetic Stirring Casting.

Internal electromagnetic stirring is an advanced melt treatment method, which can be used in direct chill casting to prepare large-scale Al alloy billets. Intercooling intensity is a primary parameter of internal electromagnetic stirring; its effects on temperature fields and microstructures have been investigated via numerical simulations and industrial experiments, respectively. The simulated results show an increase in the intercooling affected area and a decrease in sump depth with an increase in the intercooling heat transfer coefficient. The heat transfer coefficient should not exceed 500 W/(m2 °C) because the solid fraction of the intercooling end bottom may exceed 50%. The experiment's results demonstrate that the average grain sizes in the edge, 1/2 radius, and center are 151 ± 13 µm, 159 ± 14 µm, and 149 ± 16 µm, respectively, under a liquid nitrogen flow rate of 160 L/min, which is much finer than that of 80 L/min and more homogeneous than that of 240 L/min. Furthermore, an experimental liquid nitrogen flow rate of 80 L/min, 160 L/min, and 240 L/min approximately correspond to the simulated heat transfer coefficient of 200 W/(m2 °C), 300 W/(m2 °C), and 400 W/(m2 °C), respectively.

The growth restriction effect of TiCN nanoparticles on Al-Cu-Zr alloys via ultrasonic treatment.

Ex situ and in situ synchrotron X-radiography study on Al-Cu-Zr alloys with addition of Al-5Ti-1B and TiCN nanoparticles (TiCNnp) were carried out at different cooling rates. Al-Zr alloy can be effectively refined by TiCNnp via Ultrasonic treatment as compared with Al-5Ti-1B which has Zr poisoning effect. The influence of cooling rate on the nucleation and growth of grains have been studied quantitatively. The results show that the grain size was decreased and the growth rate was increased with the increasing of cooling rate. At the same cooling rate, the grain size with addition of 0.5% TiCNnp was smaller than that with the same addition of Al-5Ti-1B. The blocking factor f of TiCNnp decreases with increasing cooling rate. Based on the free growth model, a new numerical model considering the growth restriction effect of nanoparticles was established. The growth of grain was inhibited by the combining effect of solute and nanoparticles. The growth rate of grain is reduced due to part of the solid/liquid interface coated by nanoparticles. The blocking factor f is linearly decreased with the coverage ratio ω which is proportional to the critical grain radius. The grain size decreases with increasing cooling rate and decreasing f . This study is especially beneficial for Al alloys that have poisoning phenomenon inoculated by traditional refiner.

Well-aligned multi-walled carbon nanotubes and their photoresponse.

In this paper we report efficient growth of well-aligned multi-walled carbon nanotube (MWNT) forest by chemical vapor deposition (CVD). Under optimized parameters, the growth rate can be 15 microm/min and the average diameter is about 10 nm. Large photocurrent can be generated in a bundle of MWNT using camera flash. The photocurrent depends linearly on the light intensity. We propose that photon induced electron-hole pair generation in multi-walled carbon nanotubes and subsequent charge separation across the Schottky barrier is the main origin of the photocurrent.

Oxygen desorption from single-walled carbon nanotubes by camera flash.

In this paper, we report that the electrical conductance of single-walled carbon nanotubes networks decreases when the nanotubes are illuminated by camera flash in high vacuum up to 10(-6) Torr. The decreasing conductance shows step-like characteristics at each illumination. The magnitude of conductance change step reduces gradually after each illumination; finally, the conductance reaches saturation. Controlled experiments in air, oxygen and nitrogen gas indicate that mechanism for these observations is photodesorption of molecular oxygen from singled-walled carbon nanotubes.

Novel resistance behavior of single-walled carbon nanotubes under large currents.

The resistance of single-walled carbon nanotube (SWNT) bundles has been investigated by two-terminal measurements. We find that the time dependence of resistance (dR/dt) exhibits different behaviors at different currents. At low currents, a positive dR/dt is observed. However, dR/dt shows a negative sign when the applied current exceeds a critical current (Ic). Ic coincides with the current when the sample begins to emit light. The variation of dR/dt can be interpreted as the thermal effects owing to Joule heating in the SWNTs. Our lighting SWNTs sample has a small change in resistance and exhibits high stability.

Coulomb explosion: a novel approach to separate single-walled carbon nanotubes from their bundle.

A novel approach based on Coulomb explosion has been developed to separate single-walled carbon nanotubes (SWNTs) from their bundle. With this technique, we can readily separate a bundle of SWNTs into smaller bundles with uniform diameter as well as some individual SWNTs. The separated SWNTs have a typical length of several microns and form a nanotree at one end of the original bundle. More importantly, this separating procedure involves no surfactant and includes only one-step physical process. The separation method offers great conveniences for the subsequent individual SWNT or multiterminal SWNTs device fabrication and their physical properties studies.

Highly dense and perfectly aligned single-walled carbon nanotubes fabricated by diamond wire drawing dies.

We have developed a low-cost and effective method to align single-walled carbon nanotubes (SWNTs) using a series of diamond wire drawing dies. The obtained SWNTs are highly dense and perfectly aligned. X-ray diffraction (XRD) indicates that the highly dense and perfectly aligned SWNTs (HDPA-SWNTs) form a two-dimensional triangular lattice with a lattice constant of 19.62 A. We observe a sharp (002) reflection in the XRD pattern, which should be ascribed to an intertube spacing 3.39 A of adjacent SWNTs. Raman spectra reveal that the radical breath mode (RBM) of SWNTs with larger diameter in the HDPA-SWNTs is suppressed compared with that of as-grown SWNTs. The HDPA-SWNTs have a large density, approximately 1.09 g/cm 3, and a low resistivity, approximately 2 m Omega cm, at room temperature, as well as a large response to light illumination.