Search

Clinical follow-up data of pediatric patients with cerebral arteriovenous malformations (AVMs) are limited. This study investigated the characteristics of AVMs in children and analyzed the clinical outcomes of multimodality therapy in pediatric patients with AVMs at a single center.This retrospective study included consecutive patients diagnosed with AVMs at our institution between August 2008 and June 2018. Data on demographic characteristics, AVM features, and clinical outcomes were collected. Patients aged18 years at admission were defined as children.Overall, 1009 patients with AVMs were included, with 304 (30.1%) patients aged18 years. AVMs in pediatric patients were more likely to present with intracranial hemorrhage, mostly located in deep areas of the brain. A small nidus, exclusively deep drainage, and deep AVM location were associated with hemorrhage in children; Kaplan-Meier analysis revealed that patients with ruptured AVMs had a higher risk of developing a follow-up hemorrhage than those with unruptured AVMs. Among 290 children who were followed up, the multivariate regression analysis showed that a higher pretreatment modified Rankin Scale score, deep AVM location, and conservative treatment were significantly associated with unfavorable outcomes.In pediatric patients, AVMs were more likely to present with intracranial hemorrhage than that in adults. Hemorrhagic presentation in children was associated with a small nidus, exclusively deep drainage, and deep AVM location. Pediatric patients with ruptured AVMs had significantly higher risks of follow-up hemorrhage than those with unruptured AVMs. Our clinical results suggest that nonconservative treatment is better for pediatric patients with AVMs.

In this paper, we demonstrate a terahertz (THz) binary encoder based on graphene metasurface. The unit cell of the device consists of two parallel metal bars and two split-ring resonators (SRRs) embedded with two graphene ribbons. For two SRRs in the unit cell, one is connected to an electrode on the right side, and the other is connected to the electrode on the left side of the device, respectively. When no voltage is applied, the device has two passbands whose central frequencies locating at 0.85 THz and 1.14 THz, respectively. Unlike many THz tunable filters which modulate the amplitude of different bands at the same time, this encoder can achieve separately modulation of each passband. By electrically adjusting the Fermi energy of graphene on each SRR individually, the maximum modulation depth at the two central frequencies can be up to 80% and 87%, respectively. Furthermore, the function of THz frequency range binary coding is realized, i.e., four different binary coders of 11, 10, 01 and 00 are obtained in the transmission. Our work paves a new way for the development of multifunctional integrated THz devices, which will be of great significance in THz switching, communication and one-chip integrated THz system.

Transparent polyurethane has been widely applied in laminated windshield glasses as the interlayer material to enhance the reliability due to its outstanding impact resistance. Under impact loading such as bird strike, the interlayer undergoes large tensile deformation mainly at intermediate strain rates (at the order of magnitudes from 100 to 103, excluding 1000/s). In addition, the interlayer is on service over a wide range of temperatures for a plane traveling around the world. The mechanical behavior of transparent polyurethane under these conditions is not fully understood. In this study, systematical experiments were performed on transparent polyurethane. The viscoelasticity of the material was firstly verified by several quasi-static cyclic tests. Then a series of large tensile deformation and tensile failure experiments were conducted under intermediate strain rates and at temperatures of − 40 ° C to 40 ° C using a servo-hydraulic high-speed tensile machine. All strain data were acquired by the DIC technique. The experimental results show that tensile stress–strain curves and failure behaviors are significantly temperature and strain rate dependent. The rate-temperature equivalence was also observed. Finally, a phenomenological analysis of mechanical quantities of the material was carried out.

The pure shear responses of Ti6Al4V alloy and Ti3Al2.5V alloy, conceived for unique applications in jet engine components, are compared using Digital Image Correlation technique from quasi-static (10−3/s), medium strain rate (101/s) and high strain rates (103/s). A series of bespoke torsion tests have been performed on a screw driven mechanical system, a fast hydraulic Instron machine and a Campbell split Hopkinson torsion bar, equipped with high speed photographic equipment. Observations have provided the strain rate dependence and the relation of pure shear failure at quasi-static and high strain rates. The quasi-static shear constitutive relationships including shear modulus, yield stress and failure strain of both alloys are compared at the location of failure initiation, using a bespoke four camera system. The Ti3Al2.5V alloy presents lower shear flow stress and strain rate sensitivity with higher ductility, as opposed to the Ti6Al4V alloy with limited plastic deformation capacity. Associated with modest estimated overall temperature rise until final collapse of the specimen, both ductile Ti3Al2.5V alloy and brittle Ti6Al4V alloy fail by adiabatic shear banding at high strain rates. This is different from the void growth induced failure at medium strain rate with mild temperature rise and at quasi-isothermal condition. The present results show a general description of brittle and ductile alloys in engineering design. Likewise, this study will guide the characterization of pure shear flow and failure for current and future developed impact resistant alloys.

Ultrafast laser interaction with the layered semiconductors has attracted wide interest due to not only the fundamental physical understanding of the light-matter interaction in these advanced materials, but also the potential optoelectronic devices from visible region to THz region based on these emergent semiconductors. Herein, we investigated the THz radiation property from the layered WSe2 due to the d-d photo-transition by an ultrafast laser excitation. We observed strong broadband p-polarized THz radiation under different pump polarization and an evident THz radiation saturation with the pump fluence. The THz radiation demonstrated a cosine function with the polarization angle of the pump beam. Angular dependent THz radiation had a polarity reverse with the opposite incident angle and could be fitted well with a dipole approximation model. These results reveal that the dominant mechanism of THz emission is the photocarrier surging under the surface field. The azimuthal angle dependence of THz radiation suggests that the dominant contribution is due to the surface depletion field rather than surface field induced optical rectification. In addition, we inferred that the laser damage threshold for the WSe2 crystal is 3.11 mJ/cm2 confirmed by both THz emission spectroscopy and Raman Spectroscopy. Our results could provide the fundamental light-matter interaction data for the layered WSe2 and promise the potential applications of this semiconductor for THz devices.

This paper investigates the thermo-mechanical response and failure behaviour of near β Ti-5Al-5Mo-5V-1Cr-1Fe (Ti-55511) and near α Ti3Al2.5 V alloy under high strain rate loading. A series of dynamic compression and shear compression tests have been performed, using a high-speed infrared detector synchronized with a Kolsky bar (split Hopkinson pressure bar). The results show that Ti-55511 presents a higher flow stress with little strain hardening, as opposed to Ti3Al2.5 V. The measured temperature rise preceding the onset of load drop is modest and insufficient to trigger thermal instabilities. Near α Ti3Al2.5 V is characterized by a higher Taylor–Quinney coefficient– β int , which is close to ~0.6 compared to ~0.35 for near β Ti-55511. Microstructural examination reveals that both alloys fail by dynamic shear localization.

Syntactic foam is being increasingly conceived for aero engine applications to enhance overall structural reliability under impact loading. Systematic compressive tests without and with lateral confinement are carried out to investigate the deformation and failure of an epoxy syntactic foam (ESF) at quasi-static 0.01/s, medium rate 10–100/s and high strain rates 500–1100/s at gradually increasing temperatures from room temperature 25 °C to 150 °C. The stress–strain response and the corresponding deformation process, complemented by Digital Image Correlation (DIC) technique, were monitored to reveal the dynamic deformation and strain localization of the foam. The elastic-brittle behavior without confinement at high strain rates can be suppressed by the lateral confinement and by elevated temperatures above 100 °C. The lateral confinement slightly increases yield stress and significantly improves the energy absorption of ESF. Both confined yield stress and energy absorption evolve nonlinearly with strain rate and temperature. The strain hardening in the elastic–plastic behavior of ESF under confinement is strain rate independent, compared to its modest temperature dependency. A nonlinear phenomenological model is found to be able to describe the unconfined and confined responses of ESF and its temperature-strain rate equivalence, and reveal the competition between strain hardening and strain softening which is influenced by temperature.

The efficiency of the thermomechanical conversion, expressed as the Taylor–Quinney coefficient (TQC) is seldom reported in the literature and generally assumed to be equal to 0.9. Moreover, an eventual dependence of this coefficient on the dynamic loading mode has not been investigated so far. This work presents a systematic characterization of the TQC for seven different metals and alloys loaded in dynamic tension, compression and dominant shear. The results show that the TQC varies greatly with the investigated material, instead of its assumed constant value of 0.9. Likewise, until final collapse of the specimen, the overall temperature rise remains quite modest. Moreover, we clearly observe that for commercially pure Titanium, which exhibits an asymmetric mechanical response in tension and compression, the measured TQC values are mode dependent too. Microstructural characterization reveals profuse twinning in compression and shear, as opposed to tension. Twinning is related to heat generation in accord with previous studies. In addition to reporting a wide database of TQC values, this study reveals a new correlation between the thermomechanical characteristics of a material and its deformation micromechanisms, that should find its way into constitutive models.

A separately tunable terahertz (THz) two-peak absorber based on graphene is presented. From bottom to top, the absorber contains four layers, i.e., gold reflector, graphene patch array, polyimide and metal split-ring resonator (SRR) array layer. The controlling voltage is applied between the reflector and two separated surface electrodes to tune the Fermi level of graphene. As a result, these two absorption peaks can be separately tuned by the controlling voltages. The finite integral technique (FIT) is used to study the absorption theory and modulation mechanism. The simulation results show that the absorption of low-frequency and that of high-frequency are 95.5% and 90.0%, respectively. And the maximum modulation depths of them are about 49% and 71%, respectively. Moreover, the absorber is insensitive to polarization and still has good absorption at large angle. The separately tunable THz two-peak absorber offers a new way for the development of frequency selective detectors working in the range of microwave, THz and infrared.

The tensile response of a near α Ti3Al2.5V alloy, conceived for jet engine fan containment applications, is characterized by Digital Image Correlation (DIC) technique at quasi-static 0.001 s−1, medium rate 12 s−1 and high strain rates 700 s−1-3000 s−1 at room temperature and elevated temperatures 100°C and 200°C. The material is found to present noticeable strain rate sensitivity. Observations indicate that the dynamic true strain rate in the necking cross-section can reach values up to 10,000 s−1 due to strain localization. True stress-strain relationship beyond necking at high strain rates presents limited rate dependent response, however, there is clearly no locking of strain rate effect from medium rate to high rates. A series of tests undertaken at elevated temperatures indicate that the higher temperature results in a higher true strain rate for corresponding values of true strain. Experimental results from quasi-static test condition to high strain rates are used to determine an appropriate constitutive model for finite element simulations of the tensile experiments. The model accurately predicts the experimentally dynamic macroscopic force-time response and local true stress-strain relationship, and reveals the increasing trend of true strain rate evolution and decreasing trend of dynamic amplification evolution in good agreement with the experimental measurements with the average absolute relative error less than 8.4 % and the Pearson correlation coefficient larger than 0.957.

Metamorphosis is the most critical life stage for abalone. There are morphogenetic transformations and habitat selection with metamorphosis. A large amount of larvae often die during this stage. Insulin/insulin-like growth factor signaling pathway (IIS) plays a role in the development. However, there is little knowledge of IIS function in metamorphosis. IGFBP7, a component of IIS, was found to be involved in metamorphosis of small abalone Haliotis diversicolor . The expression of saIGFBP7 mRNA rapidly increased before metamorphosis, which were mainly localized in the velum and foot. There was a significant decrease of metamorphosis rate after competent larvae were exposed to 5 μg/mL dsRNA of saIGFBP7 (p = 2.50 × 10 − 10 , F = 389.05). The expressions of three downstream genes of IIS ( PI3K , ERKα and AKT ) as well as saIGFBP7 were decreased in the dsRNA exposure experiment. There was no significant difference of metamorphosis rate (p = 0.97, F = 0.071) after competent larvae were induced in different concentrations of insulin. The expression of saIGFBP7 , PI3K and ERKα also had no significant difference in insulin inducing assay. However, AKT expression level of 1 μmol/L insulin induced group was significantly higher than that of other concentrations (p = 3.41 × 10 − 7 , F = 26.68). These results suggested that IGFBP7 is involved in metamorphosis of abalone larvae. Our study provides insight on developing new methods for increasing the metamorphosis rate in abalone aquaculture. However, it does not work as a negative regulator of IIS activity, or plays its role in an IGF- and insulin-independent manner during metamorphosis of abalone larvae.

Fully resolved simulation (FRS) for gas–solid multiphase flow considers solid objects as finite sized regions in flow fields and their behaviours are predicted by solving equations in both fluid and solid regions directly. Fixed mesh numerical methods, such as fictitious domain method, are preferred in solving FRS problems and have been widely researched. However, for reacting gas–solid flows no suitable fictitious domain numerical method has been developed. This work presents a new fictitious domain finite element method for FRS of reacting particulate flows. Low Mach number reacting flow governing equations are solved sequentially on a regular background mesh. Particles are immersed in the mesh and driven by their surface forces and torques integrated on immersed interfaces. Additional treatments on energy and surface reactions are developed. Several numerical test cases validated the method and a burning carbon particles array falling simulation proved the capability for solving moving reacting particle cluster problems.

During airplane related accidents, the transparent polyurethane interlayer is finding new applications in the aircraft protection as an interlayer of windshield to enhance structural survivability under impact loading. Using dynamic mechanical analysis, Instron testing system and low impedance Split Hopkinson Tension Bar (SHTB), dynamic tensile response of a transparent polyurethane interlayer is studied experimentally under wide ranges of strain rates and temperatures. Based on the constitutive theory and the experimental data, thermal-viscoelastic Zhu–Wang–Tang (ZWT) constitutive model is employed to describe the tensile response of the polyurethane interlayer. The experimental results also reveal the time–temperature equivalence relation for the polyurethane interlayer. Strain rate and temperature are put together to a unified parameter by introducing a dimensionless parameter, and a unified curve reflecting the time–temperature equivalence relation is obtained.

The tensile behaviour of three ductile titanium alloys, Ti0.7Al4V, Ti1Al4V and Ti3Al2.5V, conceived for impact containment applications, is characterised at quasi-static, intermediate and high strain rates. Tests have been performed using a screw driven mechanical system and a bespoke in-house developed split Hopkinson tension bar equipped with ultra-high speed photographic equipment. The three alloys present noticeable strain rate sensitivity. Ti1Al4V is characterised by the lowest flow stress and highest ductility of the three alloys. Ti3Al2.5V higher flow stress but lowest strain to failure while Ti0.7Al4V has similar flow stress but larger engineering failure strain compared to Ti3Al2.5V. The dynamic true strain rate, determined by measuring the time history of the minimum cross-section diameter during necking, reaches values up to one order of magnitude higher than the nominal strain rate. This phenomenon, occurring during dynamic strain localisation, is of fundamental importance for understanding and modelling the dynamic behaviour of ductile alloys designed to withstand impact loading. The experimental results are used to determine the material parameters of the Johnson-Cook (JC) and Khan–Huang–Liang (KHL) models, which are incorporated in the ABAQUS/explicit code for finite element simulations of the dynamic tensile tests. It is found that the KHL model predicts the experimentally measured strain field, deformed geometry, effective strain rate and macroscopic force-displacement response during the high strain rate experiments with significantly better agreement than the JC model.

Sulfur-free hydrogen production is significant for sustainable energy such as fuel cell to avoid poisoning catalysts. The hollow fiber membrane is proposed as sulfur trapper for the hydrocarbon fuels. Hollow fiber membranes with polyimide (PI) matrix and adsorptive zeolites fillers are fabricated by dry–wet spinning with subsequent imidization process. By detailed investigation of FT-IR, thermal degradation cures, morphology and sulfur trapping performance, the molecular structure, thermostability and adsorption channels of membranes have been analyzed. The hollow fiber membranes have abundant pores, and the zeolites particles are incorporated in the three-dimension polymer matrix. The inlet fuel can be desulfurized to below 0.1 mg L −1 , which means that the outlet fuel can be used as sulfur-free hydrogen source for fuel cell applications. Excellent sustainability of the system with hollow fiber configuration show attractive on-board application potential.

Sulfur removal from gasoline by pervaporation (PV) membrane has attracted considerable attention. A novel strategy has been proposed to improve the desulphurization performance by building movable bridges in PV membrane matrix. Based on the designed polyrotaxane (PR) crosslinking agent, the EC membranes with PR bridges are fabricated. The selectivity and permeation flux of fabricated membranes are 8.1 and 3.5 kg/(m 2 h), respectively. The membrane performance is at higher level compared with the literature data, which is markedly related with the movable bridges in membrane matrix.

Sulfur removal is significant for fuels used as hydrogen source for modern fuel cell applications and to avoid sulfur poisoning of therein used catalysts. Novel membranes for the polymer–zeolite system with well-defined transport channels are proposed for the sulfur removal. Membranes are fabricated using polyimide (PI) as matrix material and Y zeolites as adsorptive functional materials. By detailed analysis of FT-IR, morphology and adsorption performance of membranes, the process-structure-function relationship is obtained. The results show that the functional zeolites particles are incorporated into three-dimensional channels. For all cases, the inlet fuel can be desulfurized to below 0.1 mg L −1 , which means that the outlet fuel can be used as sulfur-free hydrogen source for fuel cell applications. The proposed membranes adsorber may be applied as sulfur trap before the reformer for fuel cells on-board or on-site, and it may be applied in a periodically replaceable form. The desulfurization efforts by membrane are likely to play an influential role for the development of sulfur-free hydrogen source and fuel cell area.

Two kinds of chars were used in this research, the original rice straw char and the acid washed rice straw char. Their reactivity evolution during the char–NO reaction was studied in a fixed bed reactor at 900 °C and 1000 °C. The char samples obtained at different conversion were analyzed by BET and Inductively Coupled Plasma–Atomic Emission Spectrometry (ICP–AES). The reactivity of the acid washed char increased first and then decreased with the turning point at the char conversion of about 70% at both 900 °C and 1000 °C. This was consistent with the development of specific surface area. The reactivity evolution of the original char was similar as acid washed char at 900 °C, but the reactivity decreased continually to zero at 1000 °C, which contradicted the specific surface area development of original char. The measurements of mineral concentrations in char showed that K, Ca and Mg were the primary minerals in the original char. During the char–NO reaction, the transformation of K, Mg and Ca occurred, the concentrations of acid soluble K and Mg decreased 26.5% and 2.7% respectively, while the concentration of Ca increased 20.4% from char conversion X char = 0% to X char = 44.6% at 1000 °C. The transformation of acid soluble K was consistent with the reactivity evolution of char during the char–NO reaction, which indicates that acid soluble K played an important role on char reactivity evolution during the char–NO reaction. The specific reactivity of char had a nearly linear relationship with the concentration of acid soluble potassium in char.

Sulfur removal is significant for fuels used as hydrogen source for fuel cell applications and to avoid sulfur poisoning of therein used catalysts. Novel mixed matrix membranes (MMMs) with well-defined transport channels are proposed for sulfur removal. MMMs are fabricated using polyimide (PI) as matrix material and Y zeolites as adsorptive functional materials. The influence of architecture conditions on the morphology transition from finger-like to sponge-like structure and the “short circuit” effect are investigated. The adsorption and regeneration behavior of MMMs is discussed, combining the detailed analysis of FT-IR, morphology, XPS, XRD and thermal properties of MMMs, the process-structure-function relationship is obtained. The results show that the functional zeolites are incorporated into three-dimensional network and the adsorption capacity of MMMs comes to 8.6 and 9.5 mg S g −1 for thiophene and dibenzothiophene species, respectively. And the regeneration behavior suggests that the spent membranes can recover about 88% and 96% of the desulfurization capacity by solvent washing and thermal treating regeneration, respectively. The related discussions provide some general suggestions in promoting the novel application of MMMs on the separation of organic–organic mixtures, and a potential alternative for the production of sulfur-free hydrogen source for fuel cell applications.