The First Template‐Free Growth of Crystalline Silicon Microtubes

A simple template‐free high‐temperature evaporation method was developed for the growth of crystalline Si microtubes for the first time. As‐grown Si microtubes were characterized using X‐ray diffraction, scanning electron microscopy, transmission electron microscopy, and room‐temperature photoluminescence. The lengths of the Si tubes can reach several hundreds of micrometers; some of them have lengths on the order of millimeters. Each tube has a uniform outer diameter along its entire length, and the typical outer diameter is ≈ 2–3 μm. Most of the tubes have a wall thickness of ≈ 400–500 nm, though a considerable number of them exhibit a very thin wall thickness of ≈ 50 nm. Room‐temperature photoluminescence measurement shows the as‐synthesized Si microtubes have two strong emission peaks centered at ≈ 589 nm and ≈ 617 nm and a weak emission peak centered at ≈ 455 nm. A possible mechanism for the formation of these Si tubes is proposed. We believe that the present discovery of the crystalline Si microtubes will promote further experimental studies on their physical properties and smart applications.     

Numerical Analysis of the Catalytic Combustion of Premixed Methane/Air Mixtures in Microtubes

The combustion characteristics and extinction limits for the catalytic combustion of a methane/air mixture in a microtube are investigated computationally using the commercial CFD code FLUENT coupled to an external subroutine DETCHEM. The effects of the microtube dimensions, conductivities of wall materials, external heat losses and flow velocity on the combustion stability, are also studied. The numerical model is set as either adiabatic or non‐adiabatic with a fixed exterior heat transfer coefficient. Numerical results indicate that thermal conductivity and wall thickness are vital to preheat the methane/air mixture through the conducting wall. Two types of extinction occur, i.e., thermal quenching and blow out. These extinction limits are characterized by wall surface temperature in the microtube and the ratio of Pt(s)/O(s).     

Single-phase laminar and turbulent heat transfer in smooth and rough microtubes

An experimental campaign was carried out studying laminar and turbulent heat transfer in uniformly heated smooth glass and rough stainless steel microtubes from 0.5 mm down to 0.12 mm. Heat transfer in turbulent regime proved to be coherent—within experimental accuracy—with the classic Gnielinski correlation for the Nusselt number. For the laminar case, an anomalous drop in Nusselt number for decreasing Reynolds number was observed in the smooth glass tubes. As the stainless steel tubes manifested relatively normal diabatic behaviour in this regime (apart from the evident influence of the thermal development region that increases heat transfer above the thermally fully developed value), the explanation of this unexpected diminution of the Nusselt number must be sought in the dispersion of heat, put in externally through the thin film deposited on the glass tube outer surface, to peripheral attachments to the test section. This distorts the measured energy balance of the experiment, especially as the convective force of the fluid diminishes, resulting in lower Nusselt numbers at lower Reynolds numbers.     

微柱凝胶卡式法检测红细胞不规则抗体的效果

目的评价微柱凝胶卡式法(microtubes gel test,MGT)检测红细胞不规则抗体的效果。方法分别采用MGT和传统试管抗人球蛋白法(test tube Coombs test,TT-Coombs’T)对2011年9月～2012年12月在河北省大名县人民医院输血治疗的1 147例患者的血清样本进行不规则抗体筛查,并以TT-Coombs’T作为"金标准",对MGT进行敏感性、特异性评价;采用MGT对不规则抗体检测为阳性的样本进行进一步的抗体鉴定。结果 MGT及TT-Coombs’T测定1 147份样本不规则抗体的结果均为阳性的为10份,阴性为1 137份,阳性率为0.87%,MGT的敏感性和特异性均为100%;经MGT进一步鉴定,10份不规则抗体中Rh系统抗体9份(抗-E 5份,抗-c 2份,抗-D 1份,抗-C 1份),MNS系统抗体1份(抗-M)。结论微柱凝胶卡式法检测红细胞不规则抗体敏感性和特异性好,其操作较传统试管法简便、快捷,且操作和结果的判读易于标准化,影响因素少,更适用于临床输血前不规则抗体筛查试验。     

High-strength superelastic Ti–Ni microtubes fabricated by sputter deposition

Ti–Ni microtubes are attractive materials for biomedical devices, such as micro-catheters and micro-stents, but it is difficult to fabricate them with dimensions of less than 100 μm by conventional tube-drawing. In this study, Ti–Ni microtubes with 50 μm inner diameter and a tube wall thickness of 6 μm was successfully fabricated using a novel method in which Ti–Ni was sputter-deposited on a Cu wire with a diameter of 50 μm. All the microtubes exhibited shape memory behavior after crystallization at 873 K for 3.6 ks. Microtubes fabricated without rotating the Cu wire during deposition have low fracture strength due to the columnar grains and non-uniform tube wall thickness. Microtubes fabricated by depositing Ti–Ni on a rotating wire have a uniform wall thickness and the fracture strength increased with increasing rotation speed. Microtubes made by the rotating-wire method exhibited superelasticity of 3% strain at room temperature with high fracture stress of 950 MPa, suggesting that they are suitable for practical applications.     

Single-crystalline Te microtubes: Synthesis and NO2 gas sensor application

Tellurium tubular crystals were grown by direct thermal evaporation of tellurium metal in an inert atmosphere on quartz substrates at ambient pressure without employing any catalyst. Tellurium powder was evaporated by heating at 600 °C and was condensed at a substrate temperature of 300–350 °C in the downstream of argon gas at a flow rate of 100 mL/min. The structure and chemical composition of the as-synthesized samples were examined by X-ray diffraction analysis, scanning electron microscopy, energy-dispersive X-rays microanalysis and micro-Raman spectroscopy. Scanning electron microscopy images and X-ray diffraction patterns showed that the as-synthesized Te had a tubular single-crystalline morphology with a hexagonal cross-section. The Te microtubes were typically 0.5–6 mm long, 30–70 μm in external diameter, and 5–20 μm thick. NO₂ gas-sensing properties of the Te microtubes at room temperature were also investigated. They showed a promising sensitivity and response towards tested gas.     

Morphology characterization of polyaniline nano- and microstructures

Small-angle neutron scattering (SANS), nuclear magnetic resonance (NMR), wide-angle and small-angle X-ray scattering (WAXS and SAXS) measurements were carried out to investigate the three morphological forms of polyaniline emeraldine base (PANI-EB): unstructured, microtubes, and nanofibers. Although the chemical backbone between these two materials is quite similar, their solid structures are quite different, showing differences in the molecular conformation and supramolecular packing. Detailed solid-state ¹³C and ¹⁵N NMR characterization of PANI nanofibers (compared to the unstructured, granular form) revealed a slight variation in the structural features of the polymer that led to some differences in the chemical environments of the respective nuclei. The presence of two extra-sharp peaks at 96.5 and 179.8 ppm is a distinct feature found exclusively in the nanofiber spectra. Moreover, the crosspolarization (CP) dynamics study disclosed the presence of a complete set of sharp NMR peaks that are responsible for the presence of a more ordered morphology in the nanofiber. Small-angle neutron scattering indicated very sharp interfaces in the PANI fibers, which are well organized and have extremely sharp domains within the length scales probed (∼10–1 nm). Overall, the X-ray scattering and spectroscopy data suggest that the nanofiber form is structurally different from the unstructured, PANI-EB powder. These differences are manifested, in part, by the additional chemistry occurring during the synthesis of the nanofibers.     

Synthesis of Nanowalled Polymer Microtubes Using Glass Fiber Templates

Covalently crosslinked flexible polymer microtubes with wall thicknesses of 1–3 nm, diameters of 2–10 μm, and lengths of 0.1–0.5 mm have been fabricated using glass wool and silica wool as templates. Fluorescent‐dye‐tagged polyamines were adsorbed onto the glass and silica templates and crosslinked by reductive amination with glutaraldehyde and sodium cyanoborohydride, then the templates were dissolved with hydrofluoric acid. Microtubes were prepared from polyallylamine (PAA), polyethyleneimine (PEI), and poly(iminohexamethylene) (PIH) labeled with sulforhodamine B. These flexible hollow structures were characterized by bright‐field and fluorescent optical microscopy and confocal laser scanning microscopy; they adopt open tubular conformations when suspended in water, and dry to give flat ribbons.     

Formation of transition-metal sulfide microspheres or microtubes

Cu_xS (x = 1, 2) microtubes, and a series of transition-metal sulfide (CdS, ZnS, NiS, CoS, CuS and Cu₂S) compounds microspheres were successfully synthesized through a facile hydrothermal reaction. These compounds have been characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The optical properties of ZnS and CdS have also been investigated by UV–vis absorption and fluorescence spectroscopy. The possible formation mechanism of these microspheres or microtubes was discussed based on the experimental results.