Hollow and yolk-shell metal oxide powders used as energy storage materials exhibit good electrochemical properties at high current density because of their shortened diffusion length and increased amount of contact area between the electrolyte and the electrode for Li + insertion/extraction. Although various types of hollow-structured oxide materials have been studied as anode and cathode electrode materials for lithium secondary batteries, [13][14][15][16][17][18][19][20][21][22][23][24][25] the hollow-structured powders cannot be readily applied as battery materials because of their low energy densities due to low tab density. The disadvantages of the hollow materials can be overcome using core@void@shellconfi gured yolk-shell-structured powder particles. The core of such yolk-shell-structured powder particles will improve the rate capability as well as the energy density of the powders by increasing the weight fraction of the electrochemically active component. [ 12 , 15 ] The structures of the metal oxides that undergo large changes in volume during Li + insertion/extraction strongly affect the electrochemical properties of the anodes produced using such materials. The voids between the yolk and the shell can also serve as a buffering space for the electroactive core material during lithium insertion and extraction; therefore, various types of yolk-shell-structured metal oxides prepared using hydrothermal, coprecipitation, and shell-by-shell deposition methods have previously been studied as anode electrode materials. [ 1-7 , 9-14 ] According to previous reports, the yolk-shell-structured powders were mainly prepared using a multistep solution method; [ 1-10 , 12-14 , 27-37 ] therefore, a scalable one-pot method should be developed for the large-scale production of yolk-shellstructured powders. We report a novel, simple one-pot method of systematically synthesizing double-shelled yolk-shell-structured powders by scalable spray pyrolysis, which is one of the gas phase reaction methods. The electrochemical properties of yolk-shell-structured SnO 2 powders prepared using the hydrothermal method have previously been well studied. [3][4][5] Therefore, in this study, SnO 2 was selected as the fi rst target material to develop the yolk-shell-structured powders with spray pyrolysis. The mechanism of the formation of the double-shelled SnO 2 yolk-shell-structured powders in spray pyrolysis was investigated.The morphologies and dot-mapping images of the SnO 2 powder particles directly prepared using spray pyrolysis are shown in Figure 1 . The SEM and TEM images show that the powder particles of all sizes exhibit uniform yolk-shell structures. Mobile spherical core powder is located inside the uniformly thick spherical shell, as shown in the SEM image in the insert of Figure 1 a. The HR-TEM images of the powder particles, as shown in Figure 1 c, reveal the double-shelled yolkshell structure of the particles. The dot mappings for the Sn and O components, as shown in Figure 1 e, are consistent with the double-shelle...

BackgroundTransposable elements are major evolutionary forces which can cause new genome structure and species diversification. The role of transposable elements in the expansion of nucleotide-binding and leucine-rich-repeat proteins (NLRs), the major disease-resistance gene families, has been unexplored in plants.ResultsWe report two high-quality de novo genomes (Capsicum baccatum and C. chinense) and an improved reference genome (C. annuum) for peppers. Dynamic genome rearrangements involving translocations among chromosomes 3, 5, and 9 were detected in comparison between C. baccatum and the two other peppers. The amplification of athila LTR-retrotransposons, members of the gypsy superfamily, led to genome expansion in C. baccatum. In-depth genome-wide comparison of genes and repeats unveiled that the copy numbers of NLRs were greatly increased by LTR-retrotransposon-mediated retroduplication. Moreover, retroduplicated NLRs are abundant across the angiosperms and, in most cases, are lineage-specific.ConclusionsOur study reveals that retroduplication has played key roles for the massive emergence of NLR genes including functional disease-resistance genes in pepper plants.Electronic supplementary materialThe online version of this article (doi:10.1186/s13059-017-1341-9) contains supplementary material, which is available to authorized users.

A structure denoted as a "bubble-nanorod composite" is synthesized by introducing the Kirkendall effect into the electrospinning method. Bubble-nanorod-structured Fe2O3-C composite nanofibers, which are composed of nanosized hollow Fe2O3 spheres uniformly dispersed in an amorphous carbon matrix, are synthesized as the target material. Post-treatment of the electrospun precursor nanofibers at 500 °C under 10% H2/Ar mixture gas atmosphere produces amorphous FeOx-carbon composite nanofibers. Post-treatment of the FeOx-carbon composite nanofibers at 300 °C under air atmosphere produces the bubble-nanorod-structured Fe2O3-C composite nanofibers. The solid Fe nanocrystals formed by the reduction of FeOx are converted into hollow Fe2O3 nanospheres during the further heating process by the well-known Kirkendall diffusion process. The discharge capacities of the bubble-nanorod-structured Fe2O3-C composite nanofibers and hollow bare Fe2O3 nanofibers for the 300th cycles at a current density of 1.0 A g(-1) are 812 and 285 mA h g(-1), respectively, and their capacity retentions measured from the second cycle are 84 and 24%, respectively. The hollow nanospheres accommodate the volume change that occurs during cycling. The unique structure of the bubble-nanorod-structured Fe2O3-C composite nanofibers results in their superior electrochemical properties by improving the structural stability during long-term cycling.

The humidity dependence of the gas sensing characteristics of metal oxide semiconductors has been one of the greatest obstacles for gas sensor applications during the last five decades because ambient humidity dynamically changes with the environmental conditions. Herein, a new and novel strategy is reported to eliminate the humidity dependence of the gas sensing characteristics of oxide chemiresistors via dynamic self-refreshing of the sensing surface affected by water vapor chemisorption. The sensor resistance and gas response of pure In2 O3 hollow spheres significantly change and deteriorate in humid atmospheres. In contrast, the humidity dependence becomes negligible when an optimal concentration of CeO2 nanoclusters is uniformly loaded onto In2 O3 hollow spheres via layer-by-layer (LBL) assembly. Moreover, In2 O3 sensors LBL-coated with CeO2 nanoclusters show fast response/recovery, low detection limit (500 ppb), and high selectivity to acetone even in highly humid conditions (relative humidity 80%). The mechanism underlying the dynamic refreshing of the In2 O3 sensing surfaces regardless of humidity variation is investigated in relation to the role of CeO2 and the chemical interaction among CeO2 , In2 O3 , and water vapor. This strategy can be widely used to design high performance gas sensors including disease diagnosis via breath analysis and pollutant monitoring.

A continuous, single-step, and large-scale preparation of Pd-catalyst-loaded SnO2 yolk-shell spheres is demonstrated. These nanostructures show an unusually high response and selectivity to methyl benzenes, such as xylene and toluene, with very low cross-responses to various interfering gases, making them suitable for precise monitoring of indoor air quality.