A low-cost,high-performance pulse generator for ultrasound imaging

The design of a low-cost pulse generator for ultrasound imaging is presented. The pulser can provide 10 kW pulses with less than 0.7 Vpp ringing. Pulses ranging from 10 to 500 ns have been successfully generated     

Effect of CNTs on morphology and electromagnetic properties of non-firing CNTs/silica composite ceramics

Carbon composite ceramics have much attention for industry because of their excellent properties such as strong toughness, high electrical conductivity as well as low percolation threshold. Therefore, carbon nanotubes (CNTs) were used to incorporate with silica ceramics in order to improve their electromagnetic properties. The amount of CNTs in CNTs/silica composite ceramics was varied in order to investigate its effect on morphologies and electromagnetic properties of those. The composites were successfully fabricated by non-firing process. The results revealed that the obtained CNTs/silica composite ceramic have an electrical resistivity of 66.6?Ω·cm with a bending strength of 13.8?MPa. At the same time, the electromagnetic wave absorption ability achieved 70% over a wild frequency. This indicates that the CNTs in CNTs/silica composite ceramics may be potentially applied for an electromagnetic wave reflective material.     

An emulsion method for producing fine,low density,high surface area silica powder from alkoxides

Fine silica powders were prepared by the hydrolysis and condensation of an emulsion of tetraethyl orthosilicate (TEOS) droplets in a continuous water phase. No additions of alcohol, as a mutual solvent for the TEOS and water, or of strong acid or base catalysts, as required in the more conventional sol-gel methods, were used. The emulsion was produced by mechanical mixing and was stabilized against separating out of the phases by increasing the viscosity of the water with a commercial thickening agent, Texipol.The TEOS/water emulsion reacted to form into a loose particulate gel, which could be crushed to a powder after drying at 40 °C. The amorphous silica powders produced had low tapping densities (approximately 0.2 g cm^–3), small particle sizes (<30 nm) and high specific surface areas (50–400 m²g^–1).     

A new method for producing bimetallic rods

In this research, a new method for producing bimetallic rods is introduced. The method is a new application of equal channel angular extrusion (ECAE) process. Advantages of using this method can be expressed as; good dimensional control on both the core and clad layer, possibility of performing the process in more than one pass which can result in larger bonding strength, and the possibility of performing the process in different temperatures which is critical for producing most of the bimetallic joints as well as aluminum–copper joint. The shear strength obtained using this method is compared with the same final product produced by general extrusion process. While the shear strength after the first pass of ECAE is almost equal to the sample produced by general extrusion process, using two passes of ECAE result in a 12.5% increase in the shear strength of the joint.     

Growth of CNTs on Fe-Si catalyst prepared on Si and Al coated Si substrates

In this paper we report the effect of Al interlayers on the growth characteristics of carbon nanotubes (CNTs) using as-deposited and plasma etched Fe-Si catalyst films as the catalysts. Al interlayers having various thicknesses ranging from 2 to 42?nm were deposited on Si substrates prior to the deposition of Fe-Si catalysts. It was found that the Al interlayer diffuses into the Fe-Si catalyst during the plasma etching prior to the CNT growth, leading to the swelling and amorphization of the catalyst. This allows enhanced carbon diffusion in the catalyst and therefore a faster growth rate of the resulting CNTs. It was also found that use of an Al interlayer having a thickness of ～3 ± 1?nm is most effective. Due to the effectiveness of this, the normally required catalyst etching is no longer needed for the growth of CNTs.     

溶剂法纤维素膜的制备改性与气体渗透性能

以N-甲基吗啉-N-氧化物（NMMO）为溶剂物理溶解纤维素，是纺织行业中新兴的Lyocell纤维制备过程中采用的溶解方法．本实验室创造性地借鉴此工艺。以NMMO为溶剂制备出新型纤维素膜．本文介绍了纤维素作为膜材料的优点以及溶剂法新型纤维素膜的制备、干燥、改性以及气体渗透性能等．     

A facile method for production of high-purity silica xerogels from bagasse ash

In this paper, we systematically report the synthesis of mesoporous silica xerogels in high purity from bagasse ash. The bagasse ash was chosen as the raw material due to its availability and low-price, and environmental considerations also were important. Silica was extracted as sodium silicate from bagasse ash using NaOH solution. The sodium silicate was then reacted with HCl to produce silica gel. To produce high-purity silica xerogels, three different purification methods were investigated, i.e., acid treatment, ion exchange treatment, and washing with de-mineralized water. We were able to produce high-purity silica (>99 wt.%) by washing the produced gels with either de-mineralized water or with ion exchange resin. The specific surface area of the prepared silica xerogels ranged from 69 to 152 m² g^?1 and the pore volume ranged from 0.059 to 0.137 cm³ g^?1. The pore radii were 3.2–3.4 nm, which indicated that the silica xerogels was mesoporous. From the adsorption characterization, it was obvious that adsorptive capacity was better for high-purity silica xerogels compared with low-purity. The maximum adsorption capacity by high-purity silica xerogel was 0.18 g-H₂O/g-SiO₂. Finally, we demonstrate the potential of bagasse ash for mesoporous silica production with its excellent adsorptive capacity that makes it beneficial as an environmental solution.     

A low-cost laser range finder based on an FMCW-like method

The purpose of this paper is to present the prototype of a low-cost laser range finder. It belongs to the flight time measurement category. In this case, the time of flight is converted into a beat frequency proportional to the distance to be measured. This physical conversion is realized with an optical power modulation of the laser beam by a chirped wave. The experimental set-up is detailed with the main functional blocks. Experimental results are provided and the main possible improvements are discussed     

Single-layered porous silica films on polyethylene terephthalate substrates for antireflection coatings

Single-layered porous silica films were prepared on polyethylene terephthalate (PET) substrates as antireflection coatings for efficient, large-scale flexible optoelectronic devices. Cetyltrimethylammonium bromide (CTAB)-templated synthesis was employed to form porous silica films. Without using high temperature treatment, CTAB was removed by washing in water to create a porous structure in the films. To spin-coat on PET substrates, contact angle between silica sol and PET surface was measured to optimize the molar ratio of the solution. Pore size and surface sharpness were estimated using atomic force microscope data. The average reflectance of as-prepared AR coatings on PET substrates was ≤ 2%.     

A low-cost method for preliminary separation of reduced graphene oxide nanosheets

Reduced graphene oxide (RGO) nanosheets were produced by chemical reduction of exfoliated graphite oxide. Atomic force microscopy (AFM) images show that the obtained RGO nanosheets vary greatly in lateral-dimensional sizes, ranging from less than 100  100 nm to more than 2000  2000 nm. In order to separate these nanosheets, one simple and low-cost method mainly based on magnetic-stirring and centrifugation treatments was proposed. Preliminary statistical analysis of RGO nanosheets, based on AFM images, shows that the dot-like RGO nanosheets (with lateral dimensions less than 100  100 nm) and leaf-like RGO nanosheets (with lateral dimensions more than 500  500 nm) were effectively separated by this simple method.     

A new and clean method on synthesis of gold nanoparticles from bulk gold substrates

In this work, we report a new pathway to prepare clean gold nanoparticles in neutral solutions with aid of natural chitosan. First, an Au substrate was cycled in a deoxygenated aqueous solution containing 0.1N NaCl and 1 g L^?1 chitosan from ?0.28 to +1.22 V vs. Ag/AgCl at 500 mV s^?1 for 200 scans. The durations at the cathodic and anodic vertices are 10 and 5 s, respectively. After this process, positively charged Au- and chitosan-containing complexes were produced in the solution. Then the solution was heated from room temperature to boiling at a heating rate of 6 °C min^?1 to prepare Au nanoparticles. The particle sizes of prepared Au (1 1 1) nanoparticles are ca. 10 nm. Moreover, the prepared Au nanoparticles in solutions are capable for anti-oxidation and stable in an ambient atmosphere for at least three months.     

Thermal and mechanical properties of mullitic substrates for low-cost solar cells obtained by dry-pressing

A study has been made of the possibility of producing ceramic substrates for low-cost solar cells by means of the simple technology of moulding by dry-pressing. Special attention was taken to avoid adding costly materials (organic and inorganic) to the basic commercial kaolin. It emerged that the only treatment necessary was the precalcination of approximately half the powder at temperatures of 1200 to 1350° C. The various characterization techniques showed that, in spite of the simplicity of the technologies utilized, after a final firing at 1600° C, one can obtain finished products with the same thermal expansion coefficient as silicon (from ambient temperature to 800° C) and with mechanical characteristics that make the products perfectly suitable for resistance to the thermal shock, resulting from contact with molten silicon (the lower resistance to bending compared to products made with sophisticated production techniques being perfectly well compensated for by the greater elasticity, which is due to a considerably lower Young's modulus value). Even if this methodology has been applied on a laboratory scale, it is quite easy to automate it for industrial scale production.     

A general method for producing bioaffinity MALDI probes.

A bioaffinity probe based on the idea of immobilizing avidin on the probe surface to extract biotinylated oligosaccharide is described. The probe is produced by taking advantage of the natural affinity of proteins for hydrophobic polymer films. The avidin is immobilized by simply drying the solution on a polymer film surface. This produces a bioaffinity probe that shows enhanced activity for biotin-labeled oligosaccharides. The probe is produced in a matter of minutes but is highly effective for concentrating biotinylated oligosaccharide on the surface. The best matrix for the analysis is DHB, and the best film for the probe is a polyester material commonly used for transparency film. The efficacy of the probe is illustrated with neutral and anionic oligosaccharides. Oligosaccharides derivatized with biotin are retained while those that are unlabeled are washed away. No trace of the unlabeled oligosaccharide is observed in the mass spectrum.     

A novel method for the fabrication of homogeneous hydroxyapatite/collagen nanocomposite and nanocomposite scaffold with hierarchical porosity

Homogeneous nanocomposites composed of hydroxyapatite (HAp) and collagen were synthesized using a novel in situ precipitation method through dual template-driven. The morphological and componential properties of nanocomposites were investigated. The HAp particulates, in sizes of about 50–100 nm, were distributed homogeneously in the organic collagen hydrogel. Highly magnified TEM observation showed that HAp inorganic particles were composed of fine sub-particles (2–5 nm) without regular crystallographic orientation. Based on these homogeneous nanocomposites, a novel HAp/collagen nanocomposite scaffold with hierarchical porosity was prepared by multilevel freeze-drying technique. Compared to other conventional scaffolds for tissue engineering, this novel in situ method endows synthesized composite scaffolds with unique morphology—ultrafine HAp particles dispersed homogenously in collagen at nano level and the foam scaffold with hierarchical pore structures. The mechanical performance increased obviously compared with neat collagen. These results provided an efficient approach toward new biomimetic tissue scaffold for the biomedical applications with enhanced intensity/bioactivity and controlled resorption rates. This novel method, we expect, will lead to a wide application in many other hydrogel systems and may be useful for fabrication of various homogeneous inorganic/organic nanocomposites.     

A facile method for the production of high-surface-area mesoporous silica gels from geothermal sludge

Mesoporous silica gels were successfully produced from geothermal sludge by alkali extraction followed by acidification. The silica in the geothermal sludge was dissolved by NaOH solution to produce a sodium silicate solution, which was then reacted with HCl or tartaric acid to produce silica gels. The effects of silica concentration and pH on the silica gel properties were investigated. In addition, an improved method was proposed by incorporating two-step aging. The first aging step, which was conducted at pH 10, was used to induce Ostwald ripening to increase the size of the primary particles, and the second step was used to strengthen the gel network. Decreasing the silica concentration by diluting the as-prepared sodium silicate solution tended to increase the surface area and pore volume of the prepared silica gels. The silica gels produced by tartaric acid possessed higher surface area and pore volume than those by HCl. The surface area and pore volume reached approximately 450 m² g⁻¹ and 0.8 cm³ g⁻¹, respectively. When the gelation pH was decreased to 6, the surface area exceeded 600 m² g⁻¹. The first aging process increased the size and uniformity of the primary particles, which in turn increased the surface area of the particles. The pore diameter for all cases was greater than 5 nm, indicating that the silica gels were mesoporous.     

A cross-sectional TEM sample preparation method for films deposited on metallic substrates

This paper concerns the method on how to prepare TEM samples for the films deposited on metallic substrates. This method is described in a step-by-step way and applied to the VN/SiO₂ superlattice to testify to its feasibility in the second part.     

A simple method for the quantification of molecular decorations on silica particles

A simple, rapid quantitative approach to determining attachment density on silica nanoparticles has been demonstrated using attenuated total reflectance Fourier transform infrared spectroscopy and verified by thermogravimetric analysis. A very high attachment of approximately 5 attachments per nm² has been achieved through photoinduced thiol–ene click reaction of 11-bromo-1-undecene with a thiol functionalized silica nanoparticle formed from mercaptopropyltrimethoxysilane as the sole precursor. Attachment density with concentration of alkene and reaction time is shown to be highly nonlinear and appears to be limited by accessability of thiols on the surface of the particle. This method opens the opportunity to form nanoparticles with controlled functionality including multifunctional particles, which have been produced in this work.