包覆层厚度对Fe_3O_4@SiO_2核壳结构纳米粒子磁共振性能的影响

二氧化硅包覆四氧化三铁核壳结构纳米粒子在生物医学领域有着广泛的用途。本文采用单质硅粉水解法,以单分散水溶性Fe3O4纳米粒子为内核,通过改变反应体系中单质硅粉的加入质量,制备了不同包覆厚度的Fe3O4@SiO2纳米粒子,并对SiO2包覆层厚度对Fe3O4纳米粒子磁共振性能的影响进行了研究。结果表明:随着SiO2壳层厚度的增加,横向弛豫效率r2逐渐降低。弛豫效率降低是由水分子与磁性纳米粒子内核之间的距离逐渐增大引起的。

Effects of Fe_(2)O_(3) content on microstructure and mechanical properties of CaO-Al_(2)O_(3)-SiO_(2) system

The effects of Fe2O3 content on the microstructure and mechanical properties of the CaO-Al2O3-SiO2 system were investigated by differential thermal analysis（DTA）, X-ray diffraction（XRD）, scanning electron microscopy（SEM）, electron spin resonance（ESR）, and Mssbauer spectroscopy. The results show that the addition of Fe2O3 does not affect the main crystalline phase in the prepared glasses, but it reduces the crystallisation peak temperature, increases the crystallisation activation energy, and reduces the crystal granularity. The ESR results indicate that Fe2O3 can promote crystallization, as it leads to the phase separation of the CaO-Al2O3-SiO2 system due to axial distortion. Moreover, Fe2O3 alters the network structure of the CaO-Al2O3-SiO2 system, allowing Fe3＋ to enter octahedral sites that exhibit higher symmetry than tetrahedral sites. All of these factors are favourable to increasing the bending strength. The Mssbauer results reveal that there are two types of coordination for both Fe3＋ and Fe2＋ and the bending strength of the CaO-Al2O3-SiO2 system increases with the amount of six-coordinate Fe3＋. The increasing interaction between Fe3＋ and Fe2＋ can also enhance the bending strength of the CaO-Al2O3-SiO2 system. The microhardness of the CaO-Al2O3-SiO2 system was determined to be HV 896.9 and the bending strength to be 217 MPa under the heat treatment conditions of nucleation temperature of 700 °C and nucleation time of 2 h, crystallization temperature of 910 °C and crystallization time of 3 h.

Effects of microwave radiation on dynamic compressive properties of basalt

The dynamic mechanical properties of basalt affected by microwave were investigated by performing dynamic compressive tests using the SHPB system.Meanwhile,the thermal damage of the treated basalt was characterized by ultrasonic non-destructive testing and nuclear magnetic resonance technology.The results show that with the increase of microwave power and exposure time,the P-wave velocity,dynamic compressive strength and elastic modulus decrease continuously,and the dynamic failure mode tends to be a more complex fracturing.The increase in microwave power and exposure time can enhance the temperature difference and transfer coefficient among minerals,hence intensifying the rock damage induced by thermal shock.

Obstacles Facing the Implementation of Functional Magnetic Resonance Imaging （fMRI） of Brain in Jeddah City

fMRI （Functional Magnetic Resonance Imaging） is a relatively new technique that uses MRI （Magnetic Resonance Imaging） to measure the hemodynamic response （change in blood flow） related to neural activity in the brain. This paper aims to explore and identify the obstacles facing the implementation and applications of IMRI in radiology departments within Jeddah city by analyzing related data received by direct questionnaires and interviews with all the people working in MRI units in Jeddah city and finds that the major obstacle is lacking of awareness of fMRI among medical professionals and their training.

An Improved Fixed-point Algorithm for Independent Component Analysis of Functional MRI Data

The fixed-point algorithm and infomax algorithm are two of the most popular algorithms in independent component analysis(ICA).However,it is hard to take both stability and speed into consideration in processing functional magnetic resonance imaging(fMRI)data.In this paper,an optimization model for ICA is presented and an improved fixed-point algorithm based on the model is proposed.In the new algorithms a small step size is added to increase the stability.In order to accelerate the convergence,an improvement on Newton method is made,which makes cubic convergence for the new algorithm.Applying the algorithm and two other algorithms to invivo fMRI data,the results show that the new algorithm separates independent components stably,which has faster convergence speed and less computation than the other two algorithms.The algorithm has obvious advantage in processing fMRI signal with huge data.

Frequency-specific abnormalities in regional homogeneity among children with attention deficit hyperactivity disorder: a resting-state f MRI study

Although many functional magnetic resonance imaging(f MRI) studies have investigated the neurophysiology of attention deficit hyperactivity disorder(ADHD),the existing studies have not yielded consistent findings.This may be related to the different properties of different frequency bands. To investigate the frequency-specific regional homogeneity(Re Ho) of spontaneous neural activities in ADHD, the current study used resting-state f MRI to explore the Re Ho properties of five frequency bands, slow-5(0.01–0.027 Hz), slow-4(0.027–0.073 Hz),slow-3(0.073–0.198 Hz), slow-2(0.198–0.25 Hz) and the extra-low frequency(0–0.01 Hz), in 30 drug-naive boys with ADHD and 30 healthy controls. Compared with controls, the ADHD group showed decreased Re Ho in the default mode network(DMN) including the medial prefrontal cortex and precuneus, middle frontal gyrus and angular gyrus. ADHD patients also showed increased Re Ho in the posterior cerebellum. Significant interactions between frequency band and group were observed predominantly in the dorsolateral prefrontal and parietal cortices, orbital frontal cortex, supplementary motor area,inferior occipital gyrus, thalamus and anterior cerebellum.In particular, we found that the between-group difference in the extra-low frequency band(0–0.01 Hz) seemed to be greater than that in the other frequency bands for most brain regions. The findings suggest that ADHD children display widespread abnormalities in regional brain activity,particularly in the DMN and attention network, and these abnormalities show frequency specificity.

Effect of defects on photocatalytic activity of rutile TiO2 nanorods

To further understand the effect of structural defects on the electrochemical and photocatalytic properties of TiO2, two synthetic approaches based on hydrothermal synthesis and post-synthetic chemical reduction to achieve oxygen defect- implantation were developed herein. These approaches led to the formation of TiO2 nanorods with uniformly distributed defects in either the bulk or on the surface, or the combination of both, in the formed TiO2 nanorods （NRs）. Both approaches utilize unique TiN nanoparticles as the reaction precursor. Electron microscopy and Brunauer-Emmett-Teller （BET） analyses indicate that all the studied samples exhibit similar morphology and similar specific surface areas. X-ray photoelectron spectroscopy （XPS） and electron paramagnetic resonance （EPR） data confirm the existence of oxygen defects （Vo）. The photocatalytic properties of TiO2 with different types of implanted Vo were evaluated based on photocatalytic H2 production. By optimizing the concentration of Vo among the TiO2 NRs subjected to different treatments, significantly higher photocatalytic activities than that of the stoichiometric TiO2 NRs was achieved. The incident photon-to-current efficiency （IPCE） data indicate that the enhanced photocatalytic activity arises mainly from defect-assisted charge separation, which implies that photo-generated electrons or holes can be captured by Vo and suppress the charge recombination process. The results show that the defective TiO2 obtained by combining the two approaches exhibits the greatest photocatalytic activity enhancement amon~ all the samples.

Effects of Metal Ions and EDTA on Free Radical Reaction Intermediates of Laccase-catalyzed Oxidation of Wood Powder from Szemao Pine

Certain activator was expected to be developed to improve the free radical intermediates relative intensity, and thus to enhance the adhesion between wood fibers when fiberboard was made by laccase treated wood fibers. Reactive oxygen species (ROS) was detected in laccase-catalyzed oxidation of wood powder using ESR spin trapping technique. The effects of five metal ions (Cu2+, K+, Fe2+, Mg2+, Fe3+) and EDTA on ROS relative strengths were investigated under the condition of pH 5.6 by electron spin resonance spectrometry. The result shows that Cu2+ slightly activates the free radical reaction, and Fe2+ ion has a significant inhibitive effect on the ROS relative strength in the suspension liquid. There is a marked inhibition of the ROS relative intensity when 0.5 mmol/L EDTA is used. The metal ions that enhance laccase activity may be utilized to increase physical properties of fiberboard made by laccase oxidized wood fibers.