Many parents move from rural China to urban areas in search of job opportunities, and leave their children behind to be raised by relatives. We aimed to assess the immunisation coverage, including the 1:3:3:3:1 vaccine series (one dose of Bacilli Chalmette–Guérin vaccine; three doses of live attenuated oral poliomyelitis vaccine; three doses of diphtheria, tetanus and pertussis combined; three doses of hepatitis B vaccine; and one dose of measles-containing vaccine), in children aged 12–72 months and identify the determinants of immunisation uptake among left-behind children in Hubei Province, Central China, in 2014. In this cross-sectional study using the World Health Organization's cluster sampling technique, we surveyed 1368 children from 44 villages in 11 districts of Hubei Province. The socio-demographic and vaccination status data were collected by interviewing primary caregivers using a semi-structured questionnaire and reviewing the immunisation cards of the children. Univariate and multivariate analyses were used to identify the determinants of complete vaccination and age-appropriate vaccination. For each dose of the five vaccines, the vaccination coverage in the left-behind and non-left-behind children was >90%; however, the age-appropriate vaccination coverage for each vaccine was lower in left-behind than in non-left-behind children. For the five vaccines, the fully vaccinated rate of left-behind children were lower than those of non-left-behind children (89·1%, 92·7%; P = 0·013) and age-appropriate immunisation rate of left-behind children were lower than those of non-left-behind children (65·7%, 79·9%; P < 0·001). After controlling for potential confounders, we found that the parenting pattern, annual household income and attitude of the primary caregiver towards vaccination significantly influenced the vaccination status of children. Moreover, we noted a relatively high prevalence of delayed vaccination among left-behind children. Hence, we believe that the age-appropriate immunisation coverage rate among left-behind children in rural areas should be further improved by delivering and sustaining primary care services.

Organic photovoltaic (OPV) cells with improved efficiency using thermal annealing-induced nanostructured copper phthalocyanine as a donor layer were fabricated. A power conversion efficiency of 1.47% in the OPV cell with interdigitated CuPc/C60 bulk heterojunction has been obtained under AM 1.5 solar illumination at an intensity of 100 mW/cm2, which is higher than 0.63% of CuPc/C60 planar cell. Through varying the annealing temperature of CuPc films, the influence of interface morphology and crystallinity of CuPc films on the performance of OPV cells was systematically studied. Field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD) and spectrophotometry were used to characterize the CuPc films. The results showed that at an optimal annealing temperature, the crystalline nature and vertical orientation of nanostructured CuPc have been modified, which can facilitate the separation of interfacial electron-hole pairs and charge carrier transport to electrodes.

We use a two-dimensional particle-in-cell simulation to investigate the dynamic polarization and stopping power for an ion beam propagating through a two-component plasma, which is simultaneously irradiated by a strong laser pulse. Compared to the laser-free case, we observe a reduction in the instantaneous stopping power that initially follows the shape of the laser pulse and becomes particularly large as the laser frequency approaches the plasma electron frequency. We attribute this large reduction in the ion stopping power to an increase in plasma temperature due to the energy absorbed in the plasma from the laser pulse through the process of wave heating. In addition, dynamic polarization of the plasma by the ion is found to be strongly modulated by the laser field.

Objective: To investigate the effects of various activation methods on freeze–thawed rabbit oocytes developmental potential. Methods: Rabbit oocytes were vitrified by cryoleafs and cryoprotected with ethylene glycol and propanediol. After thawing, the oocytes were fertilized by intracytoplasmic sperm injection (ICSI). Surviving oocytes after ICSI were divided into five groups at random. Group 1: Oocytes (n = 30) activated 1 h after ICSI by calcium ionomycin (I0634); Group 2: Oocytes (n = 26) activated by strontium chloride an hour after ICSI; Group 3: Oocytes (n = 33) activated by I0634 twice; Group 4: Oocytes (n = 28) were activated by strontium chloride twice; Control Group: Inactivated oocytes (n = 39). Blastocysts derived from each group were transplanted to recipient rabbits. Results: Rates of fertilization, cleavage and blastocyst formation of Group 3 were higher than those of Group 1 and Group 2 (81.8% vs 33.3% vs 53.8%, 54.5% vs 16.7% vs 26.9%, p < 0.05; 15.2% vs 3.3% vs 7.7%, p > 0.05). The rabbit transplanted with embryos derived from Group 3 became pregnant. Embryos derived from double activation could implant into endometrium. Conclusion: Double activation may increase freeze–thawed oocytes developmental potential. After activation, oocytes cleavage velocity may be faster than that of oocytes without activation.

We demonstrated a facile route based on the use of acetone and polyvinylpyrrolidone (PVP) to prepare polystyrene (PS)/Ag/TiO2 multilayered colloids with controllable shell thickness. In this route, PVP absorbed directly onto PS colloid surface, and the Ag seed shell composed of Ag nanoparticles was synthesized directly under the PVP shell by swelling the surface layer of the PS core. Because the PVP shell increased the affinity of the Ag shell to TiO2, the hydrolyzed titania particles could deposit directly onto the core to form the outer TiO2 shell. A seed growth technique and the controllable hydrolysis reaction of tetra-n-butyl titanate were developed to grow the shell thickness of Ag and TiO2, respectively. Studies of the absorption properties indicate that the optical properties of these multilayered composite colloids can be modified by changing the coating species and shell thickness.

Explosive shock compaction was used to consolidate powders obtained from melt-spun Pr2Fe14B/α–Fe nanocomposite ribbons, to produce fully dense cylindrical compacts of 17–41-mm diameter and 120-mm length. Characterization of the compacts revealed refinement of the nanocomposite structure, with approximately 15 nm uniformly sized grains. The compact produced at a shock pressure of approximately 1 GPa maintained a high coercivity, and its remanent magnetization and maximum energy product were measured to be 0.98 T and 142 kJ/m3, respectively. The compact produced at 4–7 GPa showed a decrease in magnetic properties while that made at 12 GPa showed a magnetic softening behavior. However, in both of these cases, a smooth hysteresis loop implying exchange coupling and a coercivity of 533 kA/m were fully recovered after heat treatment. The results illustrate that the explosive compaction followed by post-shock heat treatment can be used to fabricate exchange-coupled nanocomposite bulk magnets with optimized magnetic properties.

Extended abstract of a paper presented at Microscopy and Microanalysis 2004 in Savannah, Georgia, USA, August 1–5, 2004.

Extended abstract of a paper presented at Microscopy and Microanalysis 2004 in Savannah, Georgia, USA, August 1–5, 2004.

Atomic wafer fusion of GaSb to GaAs, and the transfer of epitaxial GaSb/GaInAsSb/GaSb heterostructures to GaAs by fusion and substrate removal are demonstrated for the first time. Wafers and epilayers were fused with or without application of mechanical pressure at temperatures as low as 350 °C. A periodic pattern of grooves etched into the GaAs wafer and an overpressure of As and Sb vapor were used to improve covalent bonding. Varying degrees of mass transport and covalent bond formation between wafers were observed in cleaved crosssections under high-resolution scanning electron microscopy. Epilayers fused without pressure application exhibited significantly better structural and optical properties compared to those fused with pressure.

We have recently reported the synthesis of one-dimensional nanobelt structures of ZnO, SnO2, In2O3, CdO, Ga2O3, and PbO2 by evaporating the desired commercial metal oxide powders at high temperatures (Science (2001), 291, 1947). The as-synthesized oxide nanobelts are pure, structurally uniform, single crystalline, and most of them free from dislocations. The beltlike morphology appears to be a unique and common structural characteristic for the family of semiconducting oxides. In the present article, we focus on the twin and stacking fault planar defects found in oxide nanobelts and nanowires although they are rarely observed. Some interesting and unique growth morphologies are presented to illustrate the roles played by surface energy and kinetics in growth. It is shown that the surfaces of the oxide nanobelts are enclosed by the low-index, low-energy crystallographic facets. The growth morphology is largely dominated by the growth kinetics.

Characterizing the physical properties of individual nanostructures is rather challenging because of the difficulty in manipulating the objects of sizes from nanometer to micrometer. Most of the nanomeasurements have been carried using STM and AFM. In this presentation, we demonstrate that transmission electron microscopy can be a powerful tool for quantitative measurements the mechanical, electrical and thermodynamic properties of a single nanostructure, such as a carbon nanotube or a nanoparticle.

Using a customer-built specimen holder, in-situ measurements on the mechanical properties of carbon nanotubes has been carried out using the resonance phenomenon induced by an externally applied alternating voltage [1]. If an oscillating voltage is applied on the nanotube with tunable frequency, resonance can be induced (Fig. 1). The bending modulus is calculated from the resonance frequency. The bending modulus is as high as 1.2 TPa (as strong as diamond) for nanotubes with diameters smaller than 8 nm, and it drops to as low as 0.2 TPa for those with diameters larger than 30 nm.

Nanomaterials have attracted a great deal of research interest recently. The small size of nanostructures constrains the applications of well-established testing and measurement techniques, thus new methods and approaches must be developed for quantitative measurement of the properties of individual nanostructures. This article reports our progress in using in situ transmission electron microscopy to measure the electrical, mechanical, and field-emission properties of individual carbon nanotubes whose microstructure is well-characterized. The bending modulus of a single carbon nanotube has been measured by an electric field-induced resonance effect. A nanobalance technique is demonstrated that can be applied to measure the mass of a tiny particle as light as 22 fg (1 fg = 10−15 g), the smallest balance in the world. Quantum conductance was observed in defect-free nanotubes, which led to the transport of a superhigh current density at room temperature without heat dissipation. Finally, the field-emission properties of a single carbon nanotube are observed, and the field-induced structural damage is reported.

Ordered self-assembly of nanocrystals is scientifically interesting due to not only the unique properties of the nanocrystals, but also the collective properties of the assembly. Compared to lithography method, self-assembly is limited by a lack of control over the sizes of the ordered arrays, resulting in difficulties in characterizing their physical and chemical properties. New techniques are needed to manipulate the self-assembling process and the nanostructures formed.

In this work, polystyrene (PS) spheres were used as the template to form large bulk ordered anatase nanostructure with cobalt doping. The ordered PS template was infiltrated with absolute alcohol solution of titanium butoxide. After the precursor was dried, it was treated at 160°C for 5 hours and then at 450°C for another 5 hours. To dope cobalt into the structure, the porous titania host was immersed in a heptane solution with cobalt carbonyl. After drying in vacuum at room temperature, it was treated at 160°C.

Ordered assembly of hollow structures of silica and carbon have drawn much attention recently because of their applications in low-loss dielectrics, catalysis, filtering and photonics. The structure is ordered on the length-scale of the template spheres and the pore sizes are in submicron to micron range. Alternatively, ordered porous silica with much smaller pore sizes in nanosize range (< 30 nm), produced deliberately by introducing surfactant, has also been processed, in which the porosity is created by co-polymers. In this research, a new silica nanostructure with double length-scale ordered porosities was processed, one being at the submicron scale of hollow spheres created by a template of polystyrene (PS), and the other at nano-scale created by self-assembled co-polymers.

Typical processing route includes three steps. Firstly, the ordered template of PS was created. The as-received PS with mean particle size of 203 nm was used as the raw material.

The catalytic activity and selectivity of nanosize colloidal platinum (Pt) nanocrystals may depend strongly on their sizes and shapes. To determine the shape dependent catalytic behavior of Pt nanocrystals, two key steps are involved. First, shape controlled Pt nanocrystals must be synthesized at a high yield. Secondly, the passivation layer on the nanocrystal must be removed in order to measure the catalytic selectivity and activity while the particle shape is preserved. The former had been successfully demonstrated by us that platinum nanoparticles with a high percentage of cubic-, tetrahedral- and octahedral-like shapes, respectively, can be synthesized by a colloidal chemistry method [1,2]. The growth of the shape controlled Pt nanocrystal has been found to be the result of kinetic process [3]. To measure the shape dependent catalytic activity and selectivity of the Pt nanocrystals, the capping polymer must be removed. One method could be annealing the nanocrystals supported on a substrate for evaporating the capping polymer. Several questions, however, must be considered: (1) how high does the annealing temperature need to be to remove the capping polymer while the particle shape is still preserved? (2) to what temperature is the particle shape still stable? (3) is there a temperature induced shape transformation due to surface diffusion? (4) how high is the melting point of the Pt particles? and (5) what is the effect of substrate on nanoparticle melting? These questions have not only fundamental importance, but also practical impact on the catalysis applications of the particles because the chemical reaction may take place at a higher temperature.

Some properties of transition metal oxides are related to the presence of elements with mixed valences. In electron energy-loss spectroscopy (EELS), the L or M ionization edges of transition-metal, rare-earth and actinide elements usually display sharp threshold peaks known as white-lines. EELS experiments have shown that a change in cation valence state introduces a significant change in the White-line intensity ratio [1]. With the use of valence state information provided by the white lines, an experimental approach is demonstrated here to map the valence state distributions of Mn and Co using an energy-filtered transmission electron microscope (TEM). A spatial resolution of ˜ 2 nm has been achieved. This technique should be particularly useful in studying valence states of cations in magnetic oxides.

To map the distribution of ionization states, an energy window of ˜ 10 eV in width is required to isolate the L3 from L2 white lines (Figure 1).

Carbon tubes or spheres synthesized by arc-discharge are usually mixed with other byproducts, prohibiting direct measurements of their physical properties by the well established optical techniques because a large quantity of pure specimen is required. Electron energy-loss spectroscopy (EELS) is a unique technique that can be applied to probe the electronic structure of a single carbon tube or sphere. In this paper, the classical dielectric response theory is applied to calculate the EELS spectra acquired from a graphitic carbon sphere at various impact parameters. Graphite is an anisotropic dielectric medium whose dielectric function is described by a tensor. A graphitic carbon sphere is composed of concentric graphitic shells whose dielectric tensor in the spherical geometry, under the local response approximation, is given by (Figure 1)

where are the dielectric function of graphite for an electric field perpendicular and parallel, respectively, to the c axis. In the non-relativistic approximation, the surface excitation is calculated by [1]

Silicon carbide is a versatile material possessing properties such as a wide energy bandgap, high thermal conductivity, high elastic modulus and high-temperature creep resistance, which enable it to be used in a variety of electronic, optical and structural applications. Chemical vapor infiltration/deposition (CVI/CVD) coupled with the application of a temperature gradient and forced flow of reagents is particularly suited to the production of SiC structural composites due to the benefits of reduced infiltration time and uniform composite density. In this work, the growth and orientation of polycrystalline SiC on graphite during CVI is investigated using TEM and HRTEM.

The composites studied possess a laminated matrix of alternating layers of carbon and SiC which were deposited by alternating the reagent streams from one layer to the next. Specimens for TEM examination were obtained by cutting ∽1 mm thickness slices from the bulk sample with a low speed diamond saw.