A structural study of biocompatible magnetic nanofluid with synchrotron radiation-based X-ray scattering techniques

In this paper, water colloidal solutions of nanoparticles of magnetite (magnetic nanofluids, (MNFs)) are investigated by synchrotron X-ray diffraction (XRD) and small-angle scattering (SAXS). To prevent aggregation, nanoparticles are coated with polyacrylic acid (PAA) in a single solution and citric (CA) in the other solutions. In both cases, the maxima of the particle size distribution from SAXS (9?C10 nm) correspond to the sizes of the magnetite crystallites that were estimated from the broadening of the diffraction lines. In addition, the SAXS data indicate the presence of a significant proportion of aggregates (up to 60 nm in diameter) in both colloidal solutions, although fundamental differences in the structures of aggregates between the MNFs stabilized by PAA and CA were not observed. In this study determination of the structural characteristics of MNFs were carried out in order to obtain stable dispersive non-aggregating nanoparticles of magnetite for use as contrast agents in magnetic resonance tomography, drug carriers, and other biomedical applications.     

Determination of nanostructure of liposomes containing two model drugs by X‐ray scattering from a synchrotron source

Small‐angle X‐ray scattering has been employed to study how the introduction of paracetamol and acetylsalicylic acid into a liposome bilayer system affects the system's nanostructure. An X‐ray scattering model, developed for multilamellar liposome systems [Pabst et al. (2000), Phys. Rev. E, 62 , 4000–4009], has been used to fit the experimental data and to extract information on how structural parameters, such as the number and thickness of the bilayers of the liposomes, thickness of the water layer in between the bilayers, size and volume of the head and tail groups, are affected by the drugs and their concentration. Even though the experimental data reveal a complicated picture of the drug–bilayer interaction, they clearly show a correlation between nanostructure, drug and concentration in some aspects. The localization of the drugs in the bilayers is discussed.     

Thermal equation-of-state of osmium: a synchrotron X-ray diffraction study

The pressure-volume-temperature behavior of osmium was studied at pressures and temperatures up to 15 GPa and 1273 K. In situ measurements were conducted using energy-dispersive synchrotron X-ray diffraction in a T-cup 6-8 high pressure apparatus. A fit of room-temperature data by the third-order Birch-Murnaghan equation-of-state yielded isothermal bulk modulus K₀=435(19) GPa and its pressure derivative K′₀=3.5(0.8) GPa. High-temperature data were analyzed using Birch-Murnaghan equation of state and thermal pressure approach. The temperature derivative of bulk modulus was found to be −0.061(9) GPa K⁻¹. Significant anisotropy of osmium compressibility was observed.     

Effect of a rhombohedral phase on lithium intercalation capacity in graphite

Five natural graphites with different rhombohedral phase (3R phase) content have been investigated as anode materials for rechargeable lithium-ion batteries. The reversible capacity varies from 250 mA h/g to 350 mA h/g for the same intercalation conditions depending on the content of the 3R-phase. With increasing rhombohedral phase in the graphite, the intercalation capacity will be high. A peak at about 10 mV in the cyclic voltammograms (CV) of a sample with a large 3R-phase content is caused by lithium ions occupying boundaries between the rhombohedral (3R) phase and the hexagonal (2H) phase and is responsible for a capacity exceeding the theoretical value.     

A simulation study of Tsinghua Thomson scattering X-ray source

Thomson scattering X-ray sources are compact and affordable facilities that produce short duration, high brightness X-ray pulses enabling new experimental capacities in ultra-fast science studies, and also medical and industrial applications. Such a facility has been built at the Accelerator Laboratory of Tsinghua University, and upgrade is in progress. In this paper, we present a proposed layout of the upgrade with design parameters by simulation, aiming at high X-ray pulses flux and brightness, and also enabling advanced dynamics studies and applications of the electron beam. Design and construction status of main subsystems are also presented.     

Diffusion of Li ion in graphite cluster model at 800 K: a direct molecular orbital dynamics study

Using the hydrogen terminated planar cluster model, C₅₄H₁₈, the stabilization site of Li⁺ ion was determined by the unrestricted Hartree-Fock (UHF) AM1 energy gradient method. Six kinds of stabilization sites are considered, suggesting that the Li⁺ ion is rather stable at the two distinct sites in the bulk where the potential energy difference between them is 2.0 kcal/mol. For the Li⁺ ions stabilized at these two sites, the diffusion processes were simulated at 800 K through the direct molecular orbital dynamics procedure which was newly developed by one of the present authors. No jumping diffusion occurs with Li⁺ ions among the stabilization sites, but they diffuse along the outline of the cluster model with the fluctuations. It takes 2.0 ps for a Li⁺ ion to diffuse from the lower potential site to another equivalent site. On the other hand, it takes 0.7 ps to move from the higher potential site to the unstable circumference site composed of corner (armchair edge) carbon atoms. As the result, the diffusivity is approximated as 10⁻⁸-10⁻⁷ m²/s.     

热损伤奥克托金(HMX) 缺陷的X射线小角散射研究

奥克托金(HMX) 在温度作用下, 会发生热膨胀、 相转变、 热分解等物理、 化学变化, 导致在材料内部产生大量缺陷, 进而会对其宏观性能造成明显影响. 为了深入了解热损伤HMX内部的缺陷演化, 本文采用X射线小角散射和原子力显微技术研究了热损伤HMX的内部缺陷. 结果发现HMX在180 °C相变过程中散射曲线有明显的变化, 颗粒内部生成了大量10nm左右的孔洞, 随着加载时间延长, 其尺寸增大到25nm, 数量明显降低. 当HMX在190 °C、 200 °C保温5h时, 由于HMX热分解内部有新缺陷生成, 小角散射发现其尺寸约为5至8nm, 随着加载温度升高, 其数量增加.     

Dynamics of water in real space and time

Owing to marked advances in instrumentation in X-ray and neutron scattering the time-dependent pair correlation function, the Van Hove function, can now be determined by inelastic X-ray and neutron scattering measurements. The local dynamics of water in real space and time is visualised by this approach. We discuss how the dynamic properties, such as viscosity and diffusion, can be elucidated through the Van Hove function of water.     

NMR microimaging studies of water diffusivity in saturated, microporous systems

A novel microimaging method is described for measuring the effective diffusion coefficient (D_∞) of water in saturated, microporous materials. A simple multicompartment computer simulation was used to show how the value of D_∞, when combined with measurements of water proton relaxation times and pulsed field gradient spin-echo amplitudes, allows the pore size distribution and pore connectivity to be characterized.     

Ultrasonic wave propagation in cementitious materials: A multiphase approach of a self-consistent multiple scattering model

This paper examines ultrasonic wave propagation through strongly heterogeneous materials such as cementitious materials, and deals meanly with the formulation of a multiphase approach of a self-consistent multiple scattering model, the so-called dynamic generalized self-consistent model (DGSCM) proposed by Yang [J. Appl. Mech. 70(2003) 575-582]. This extended model can describe the influence of the size and volume fraction of aggregates on cementitious materials, as well as the interaction, contribution, and influence of entrapped air voids together with the aggregates on frequency-dependent parameters such as the phase velocity and the attenuation coefficient. To show the performance of this approach, theoretical predictions were compared with experimental ultrasonic measurements over a wide frequency range from several mortar specimens with different features in their microstructure properties and concentrations of aggregates up to 60%. The multiphase approaches of both the DGSCM and the Waterman-Truell model (WT) were also compared. The obtained results of the multiphase DGSCM were found to be significantly better than those obtained from the N-phase WT model for ultrasonic measurements from cementitious materials at high aggregate concentrations. The feasibility of material characterization using the multiphase approach of DGSCM was also discussed.     

小角X射线散射应用研究若干进展

文章从小角X射线散射（small-angle X-ray scattering, SAXS）的理论分析出发,结合国内外SAXS理论和应用研究的最新动态,总结了文章作者所在的研究小组近年来在SAXS技术用于材料微结构表征方面的研究成果。主要包括以下三个方面的内容：（1）有机/无机杂化材料中电子密度波动的研究;（2）弦长度分布函数材料的周期结构的研究;（3）纳米粉末晶化过程的研究。     

小角X射线散射应用研究若干进展

文章从小角X射线散射（small-ande X-ray scattering，SAXS）的理论分析出发，结合国内外SAXS理论和应用研究的最新动态，总结了文章作者所在的研究小组近年来在SAXS技术用于材料微结构表征方面的研究成果。主要包括以下三个方面的内容：（1）有机／无机杂化材料中电子密度波动的研究；（2）弦长度分布函数材料的周期结构的研究；（3）纳米粉末晶化过程的研究。     

Li-ion migration in Li2FeSiO4-related cathode materials: A DFT study

The orthosilicate family of materials Li₂MSiO₄ for M = Fe, Mn and Co are coming to be seen as potentially cheap cathode materials for large-scale Li-ion batteries, not least through the possibility for significant capacity gains if more than one Li-ion can be removed per formula unit. To gain insights into possible Li-ion migration pathways and diffusion barriers for Li-ions, model systems for Li_xFeSiO₄ (x ≈ 1, 2) are here studied using the Density Functional Theory (DFT) approach. Li-ion and ion-vacancy migration barriers are calculated for a number of model systems. The results help explain why the Li/Fe site-mixing observed during electrochemical cycling of Li₂FeSiO₄ does not lead to any noticeable loss in cell performance, despite the increased tortuosity introduced into the Li-migration pathways by this ion-mixing process.     

Depletion-induced sphere-cylinder transition in C12E5 microemulsion: a small-angle X-ray scattering study

Small-angle X-ray scattering was used to study the mixture of C₁₂E₅ (pentaethylene glycol monododecyl ether)/H₂O/n-decane microemulsion and polyethylene glycol (PEG). The size, shape and the structure factor of the microemulsion were investigated by adding the polymer (PEG) to the mixture. Attractive depletion potential was induced between the microemulsion droplets by the non-adsorb polymer. The range and strength of the attractive potential were changed by varying the molecular weight and concentration of PEG. The forward scattering, S(0), of the spherical microemulsion, declined gradually as the polymer concentration decreased. For PEG with the molecular weight of M_n = 285?315, the microemulsion morphology remained spherical, but the main peak of the structure factor moved towards a bigger q. When PEG with molecular weights of M_n = 2200 and M_n = 6000 were used, a shape transition from spherical to cylindrical was induced in line with increasing polymer concentration.     

MR-visible water content in human brain: A proton MRS study

In vivo measurement of metabolite concentrations in the human brain by means of proton-MRS contributes significantly to the clinical evaluation of patients with diseases of the brain. The fully relaxed water signal has been proposed as an internal standard for calibration of the MRS measurements. The major drawbacks are the necesity to make the assumptions that the water concentration in the brain and that all tissue water is MR-visible. A number of in vivo measurements were carried out to estimate the concentration of MR-visible water in the brain of healthy volunteers divided into four age groups: newborn (0–23 days), adolescents (10–15 yr), adults (22–28 yr), and elderly people (60–74 yr). The examinations were carried out using a Siemens Helicon SP 63/84 MR-scanner operating at 1.5 T. Except for the newborn, four regions were studied in each subject using stimulated echo (STEAM) sequences without water suppression. In vitro measurements on a standard phantom were used for calibration. The calculated water concentrations ranged between 35.8 and 39.6 (mean 36.9) mol·[kg wet weight]⁻¹ in the three groups, whereas it was 51.5 mol·[kg wet weight]⁻¹ in the newborn, p<.01. The observed water concentration of neither the four regions nor of the three oldest age groups were significantly different. Comparisons between the water concentrations measured and those expected based on estimation of the content of grey and white matter in the region of interest from T₁-weighted images and biochemical data published, suggest that only a small fraction (<5%) of the tissue water may be MR-invisible. The study of healthy volunteers thus shows that errors introduced by using the unsaturated water signal for calibration are less than 10%, which is comparable to expected errors when other calibration procedures are used under similar measurement conditions.     

Transfer characteristics of arterial pulsatile force in regional intracranial tissue using dynamic diffusion MRI: A phantom study

Introduction

To clarify the mechanism underlying apparent diffusion coefficient (ADC) changes in regional intracranial tissue during the cardiac cycle, we investigated relationships among ADC changes, volume loading, and intracranial pressure using a hemodialyzer phantom in magnetic resonance imaging (MRI).

Materials and Methods

The hemodialyzer phantom consisted of hollow fibers (HF), the external space of HFs (ES), and a gateway of dialysis solution, filled with syrup solution and air. The high-volume and low-volume loadings were periodically applied to HFs by a to-and-fro flow pump, and syrup solution was permitted to enter or leave HFs during the volume loading cycles. ADC maps at each volume loading phase were obtained using ECG-triggered single-shot diffusion echo-planar imaging. Dynamic phase contrast MRI was also used to measure volume loading to the phantom. We compared the ADC changes, volume loading, and intracranial pressure in the phantom during the cardiac cycle.

Results

ADC changes synchronized significantly with absolute volumetric flow rate change. The maximum ADC change was higher in high-volume loading cycles than in low-volume loading cycles. Results showed that the water molecules in ES fluctuated according to the force transferred from HF to ES. ADC changes were dependent upon the volumetric flow rate during the cardiac cycle.

Conclusions

Our original phantom allowed us to clarify the mechanism underlying water fluctuations in intracranial tissues. Measurement of maximum changes in ADC is an effective method to define the transfer characteristics of the arterial pulsatile force in regional intracranial tissue.     

Morphology and structure of gold-lithium niobate thin film: A laboratory source X-ray scattering study

Laboratory source X-ray scattering set-up has been used to determine the complete morphology and structure of an optically important composite thin film. Analysis of grazing incidence small angle X-ray scattering, X-ray reflectivity and powder diffraction data of Au/LiNbO₃ thin film prepared by sequential deposition of gold and lithium niobate on float glass substrate suggest that the Au-nanocrystallites are dispersed in amorphous medium, which although have average separation but do not have any long range periodicity other than growth or z-direction. The morphology of the nanocomposite thin film determined through X-ray scattering measurements agrees well with the measured optical absorption.     

Ageing of calcium silicate cements for endodontic use in simulated body fluids: a micro‐Raman study

To evaluate bioactivity properties, a calcium silicate experimental cement (wTC) and a phosphate‐doped wTC cement (wTC‐TCP) were aged for different times (1–180 days) at 37 °C in two simulated body fluids, i.e. Dulbecco's phosphate buffered saline (DPBS) and Hank's balanced salt solution (HBSS). The cements were analyzed by micro‐Raman spectroscopy to investigate the presence of calcium phosphate deposits and the composition changes as a function of the storage time (hydration of anhydrite/gypsum and formation of ettringite; hydration of belite/alite and formation of hydrated silicates). After 1 day of ageing in DPBS, the two cements already showed a different behavior: only the surface of wTC‐TCP cement showed the band at 965 cm⁻¹, suggesting the formation of a detectably thick calcium phosphate deposit. The trend of the I₉₆₅/I₉₉₀ Raman intensity ratio indicated the formation of a meanly thicker apatite deposit on the wTC‐TCP cement until 90 days. After 60 days of ageing in DPBS, the thickness of the apatite deposit on wTC and wTC‐TCP was about 200 and 500 µm, respectively, whereas at 180 days, the two cements did not appear significantly different (thickness of about 900 µm). The bioactivity of both cements in HBSS was less pronounced than in DPBS, according to the lower phosphate concentration of HBSS; at the same time, higher amounts of calcite were found on the surface of both cements. The wTC‐TCP cement showed a higher bioactivity in this medium also; after 180 days, the thickness of the apatite deposit on wTC and wTC‐TCP was < 50 µm and about 100 µm, respectively. Copyright © 2009 John Wiley & Sons, Ltd.     

Intermediate-temperature polymorphic phase transition in KH2PO4: A synchrotron X-ray diffraction study

We have used synchrotron X-ray diffraction to investigate the structural and chemical changes undergone by polycrystalline KH₂PO₄ (KDP) upon heating within the 30-250 °C temperature interval. Our data show evidence of a polymorphic transition at T∼190 °C from the room-temperature tetragonal KDP phase to a new intermediate-temperature monoclinic KDP modification (spacegroup P2₁/m and lattice parameters a=7.590, b=6.209, c=4.530 Å, and β=107.36°). The monoclinic RDP polymorph remains stable upon further heating to 235 °C, and is isomorphic to its RbH₂PO₄ and CsH₂PO₄ counterparts.