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1.
Liquid perfluorocarbon nanodroplets (NDs) are an attractive alternative to microbubbles (MBs) for ultrasound-mediated therapeutic and diagnostic applications. ND size and size distribution have a strong influence on their behaviour in vivo, including extravasation efficiency, circulation time, and response to ultrasound stimulation. Thus, it is desirable to identify ways to tailor the ND size and size distribution during manufacturing. In this study phospholipid-coated NDs, comprising a perfluoro-n-pentane (PFP) core stabilised by a DSPC/PEG40s (1,2-distearoyl-sn-glycero-3-phosphocholine and polyoxyethylene(40)stearate, 9:1 molar ratio) shell, were produced in phosphate-buffered saline (PBS) by sonication. The effect of the following production-related parameters on ND size was investigated: PFP concentration, power and duration of sonication, and incorporation of a lipophilic fluorescent dye. ND stability was also assessed at both 4 °C and 37 °C. When a sonication pulse of 6 s and 15% duty cycle was employed, increasing the volumetric concentration of PFP from 5% to 15% v/v in PBS resulted in an increase in ND diameter from 215.8 ± 16.8 nm to 408.9 ± 171.2 nm. An increase in the intensity of sonication from 48 to 72 W (with 10% PFP v/v in PBS) led to a decrease in ND size from 354.6 ± 127.2 nm to 315.0 ± 100.5 nm. Increasing the sonication time from 20 s to 40 s (using a pulsed sonication with 30% duty cycle) did not result in a significant change in ND size (in the range 278–314 nm); however, when it was increased to 60 s, the average ND diameter reduced to 249.7 ± 9.7 nm, which also presented a significantly lower standard deviation compared to the other experimental conditions investigated (i.e., 9.7 nm vs. > 49.4 nm). The addition of the fluorescent dye DiI at different molar ratios did not affect the ND size distribution. NDs were stable at 4 °C for up to 6 days and at 37 °C for up to 110 min; however, some evidence of ND-to-MB phase transition was observed after 40 min at 37 °C. Finally, phase transition of NDs into MBs was demonstrated using a tissue-mimicking flow phantom under therapeutic ultrasound exposure conditions (ultrasound frequency: 0.5 MHz, acoustic pressure: 2–4 MPa, and pulse repetition frequency: 100 Hz).  相似文献   

2.
Abstract

The quartz resonator method measures the complex shear modulus or compliance of viscoelastic materials in the frequency range from 50 kHz to 140 MHz at temperatures between ?150°C and 300°C and pressures up to 1 GPa. This method can be applied to viscous fluids or polymer melts -even in their glassy or seminystalline regime.

The phase diagram of poly(diethylsiloxane) PDES (a mesophase polymer) was determined for two samples with different molecular weight at pressures up to 400 MPa and temperatures between 20°C and 100°C. Phase transitions are indicated by a sharp bend in the shear compliance although the volume effect of the mesophase-isotropic transition vanishes around 80 MPa.

The pressure dependence of the glass relaxation process (in PVAc), was studied by measuring the change of the complex shear modulus with pressure at constant temperatures between 95°C and 145°C and pressures up to 600 MPa. Additionally to the relaxation process, also the pressure dependence of the real part of the shear modulus in the glassy region can be determined for testing the dislocation concept in the meandermodell by W. Pechhold.  相似文献   

3.
This work addresses the production of stand-alone ceramic nanotubes by the template-based ALD method at low temperature. Nitrogen-doped multiwalled carbon nanotubes (CNTs) were coated with ZnO. Afterward, the template removal was evaluated by two different approaches: using oxidation in dry air or in an ozone-rich atmosphere. The samples treated by the two different methods were analyzed by XRD, TEM, SAED, and Raman spectroscopy. The dry air atmosphere requires high temperatures (~?700 °C) for a complete CNT removal; at that temperature, the ZnO tubular shape is completely collapsed due to recrystallization. Under ozone atmosphere, the template can be removed at temperatures as low as 85 °C; this temperature is lower than the ALD preparation temperature (120 °C). The ozone treatment maintains the tubular shape of the ZnO nanostructures. Photocatalytic activity of the ZnO samples was evaluated using the photo-oxidation of Amaranth as probe reaction, showing a higher activity the ZnO nanotubes obtained from the low-temperature ozone treatment than the high-temperature processed materials. The use of ozone for the template removal reinforces the template-based ALD method to produce inorganic nanotubes.  相似文献   

4.
The co-precipitation method can make the materials react uniformly at molecular level and has the advantages of lower polycrystalline synthesized temperature and shorter sintering time. Therefore, it is expected that the mass production of Li1.5Al0.5Ti1.5(PO4)3 (LATP) solid electrolyte would be possible by application of the co-precipitation method for LATP preparation. In this study, an application of the co-precipitation method for a preparation of LATP solid electrolyte is attempted. Crystallized LATP powder is obtained by heating precipitant containing Li, Al, Ti, and PO4 at 800 °C for 30 min. The LATP bulk sintered pellet is successfully prepared using the crystallized LATP powder by calcinating at 1,050 °C. The cross-sectional SEM images show that many crystal grains exist, and the grains are in good contact with each other, i.e., there is no void space. All diffraction peaks of the pellet are attributed to LATP in XRD pattern. The sintered pellet is obtained by calcinating at 1,050 °C, which is more than 150 °C lower than that of conventional method. The LATP solid electrolyte shows a good conductivity which is 1.4?×?10?3 S cm?1 for bulk and 1.5?×?10?4 S cm?1 for total conductivities, respectively.  相似文献   

5.
Yanyu Liu  Feng Zhang  Zheng Liu  Zhi Wang 《哲学杂志》2018,98(12):1068-1086
In order to investigate the effect of temperature on the anisotropic behaviour of AZ31 magnesium alloy rolling sheet under high strain rate deformation, the Split Hopkinson Pressure Bar was used to analyse the dynamic mechanical properties of AZ31 magnesium alloy rolling sheet in three directions, rolling direction(RD), transverse direction (TD) and normal direction (ND). The texture of the rolling sheet was characterised by X-ray analysis and the microstructure prior and after high strain rate deformation was observed by optical microscope (OM). The results demonstrated that AZ31magnesium alloy rolling sheet has strong initial {0?0?0?2} texture, which resulted at the obvious anisotropy in high strain rate deformation at 20 °C. The anisotropy reflected in stress–strain curve, yield stress, peak stress and microstructure. The anisotropy became much weaker when the deformation temperature increased up to 250 °C. Continuing to increase the deformation temperature to 350 °C the anisotropy of AZ31 rolling sheet essentially disappeared. The decreasing tendency of anisotropy with increasing temperature was due to the fact that when the deformation temperature increased, the critical resolved shear stress (CRSS) for pyramidal 〈c + a〉 slip, which was the predominant slip mechanism for ND, decreased close to that of twinning, which was the predominant deformation mechanism for RD and TD. The deformation mechanism at different directions and temperatures and the Schmid factor (SF) at different directions were discussed in the present paper.  相似文献   

6.
ABSTRACT

We investigated the gas-sensing performance of tin oxide nanowires for ammonia gas at low temperature (~ 50°C). Tin oxide nanostructures were deposited at 1000°C and 1100°C on gold-coated silicon substrates using the physical vapor deposition method. Gas-sensing measurements were made for ammonia gas at various strengths (i.e. 50, 100 and 200?ppm) and the sensing performance was compared at low temperature for both the samples e.g. nanostructures deposited at 1000°C and 1100°C. Due to the highly oriented structure, the sample deposited at 1000°C shows high sensing capability at low temperature as compared to the regular tetragonal phase observed at 1100°C. The morphological and structural properties of nanowires were systematically examined using the scanning electron microscopy and X-ray diffraction.  相似文献   

7.
Zinc oxide thin films were grown on a glass substrate by a sol-gel process using a spin-coating technique. The obtained thin films were annealed between 350?°C and 550?°C in 50?°C steps and were then characterized using X-ray diffraction, scanning electron microscopy, and X-ray fluorescence techniques. The samples were stimulated by 59.5?keV gamma rays emitted from an Americium-241 annular radioisotope source. K X-rays emitted by samples were counted using an ultra-low energy germanium detector with a resolution of 150?eV at 5.96?keV. It was found that there was generally a decrease in both the / X-ray intensity ratios and the K X-ray fluorescence cross sections for zinc oxide between 350?°C and 500?°C, but not at 550?°C. In addition, the X-ray diffraction patterns of the films showed that the transition phase from an amorphous to a polycrystalline hexagonal wurtzite structure was complete at an annealing temperature of 500?°C. The results show that variations in these parameters can be explained by the reorganization of atoms and the charge transfer process due to the effect of the annealing temperature on the elements forming the compounds.  相似文献   

8.
Recent studies in our laboratory have proved that electrochemical etching (ECE) of polycarbonate track detectors (PCTD) under 50 Hz – high voltage (HV) field conditions has potentials for time-integrated heavy charged particle detection and dosimetry applications. The rationale in the study is the ECE process of alpha particle tracks in 1 mm thick PCTDs by a 50 Hz – HV generator at optimized ECE conditions. Tracks of 3.2 MeV alpha particles from a collimated beam of an 241Am source degraded in air and background tracks were registered. The effects of HV and ECE duration on alpha track registration efficiency and track diameters were studied for 3 sets of 50 Hz – 4, 5 and 6 kV field conditions in a PEW solution (potassium hydroxide, ethanol and water) at 26 °C. The optimized ECE conditions obtained at this stage of development for 1 mm thick PCTDs are 50 Hz – 4 kV in PEW solution at 26 °C for 10 h. Alpha track registration efficiency at 3.2 MeV is about 30% with 37 ± 6 μm mean track diameter. The mean background track density at the above stated optimized conditions is about 571 ± 16 tracks.cm−2 with a mean diameter of 65 ± 5 μm. All tracks are observable by the unaided eyes. The mean background track diameter is near two times larger than that of alpha particle tracks at the optimum conditions applied; they are easily distinguished against each other. This high background track density while at this stage of development seems a drawback for low dose and low fluence particle applications, it has minimal effects on high fluence ion detection applications. The simple 50 Hz – HV generator used proved to be convenient for efficient alpha track amplifications. Studies are underway for improvement of the method in particular for reducing background track density.  相似文献   

9.
Composition of corrosion layers on steel 20 in aerated solutions with hydrazine concentrations less than 11 ppm was studied at 50, 60, and 80°C in dynamic conditions by transmission Mössbauer spectroscopy and X-ray diffraction as supplementary technique. Corrosion rates were determined by gravimetric method. A comparison with corrosion in water at 80°C was made. The observed layers have not any protective character. For 0.1 m/s linear velocity, they are composed by nonstoichiometric magnetite, (Fe3?x O4,x=0.02–0.04) with lepidocrocite (γ-FeOOH) as secondary phase at 50°C. Haematite (α-Fe2O3) is observed at 60 and 80°C with a 19 nm particle size. It becomes smaller for higher velocity (0.7 m/s).  相似文献   

10.
《Solid State Ionics》2006,177(17-18):1437-1442
Pure and dense La2Mo2O9 ceramic electrolytes with grain sizes of 1–3 μm were fabricated from nanocrystalline powders by a novel three-stage, one-cycle, pressureless thermal processing method at temperatures as low as 600 °C. Phase formation, microstructure and grain size of the samples were examined using X-ray diffraction and scanning electron microscopy. Density of the sintered samples was determined as in the range of 94–96% of the theoretical density by weight/geometric measurements. Impedance spectroscopy was used to characterize the electrical properties of the sintered samples. The conductivity of the three-stage sintered samples reaches a value of 0.018 S/cm at 600 °C and 0.05 S/cm at 700 °C, much higher than that of the samples fabricated by conventional solid-state reaction method, but similar to that of the samples sintered at 950 °C for 12 h from the same nanocrystalline powders. The high conductivity of these samples was attributed to the co-operation of the excellent performance of nanocrystalline powders and the advantages of the novel three-stage low-temperature thermal processing.  相似文献   

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