Probing the local coordination environment for transition metal dopants in zinc oxide nanowires

It is hypothesized that a highly ordered, relatively defect-free dilute magnetic semiconductor system should act as a weak ferromagnet. Transition-metal-doped ZnO nanowires, being single crystalline, single domain, and single phase, are used here as a model system for probing the local dopant coordination environments using X-ray absorption spectroscopy and diffraction. Our X-ray spectroscopic data clearly show that the dopant resides in a uniform environment, and that the doping does not induce a large degree of disorder in the nanowires. This homogeneous nature of the doping inside the oxide matrix correlates well with observed weakly ferromagnetic behavior of the nanowires.     

Automated liquid-liquid extraction by pneumatic recirculation on a centrifugal microfluidic platform

In this technical note, a liquid-liquid extraction technique was performed using pneumatic liquid recirculation on a centrifugal microfluidic device. Non-contact pneumatic pumping enabled a multi-cycle liquid-liquid extraction process using aqueous iodine in a potassium iodide solution and hexadecane while requiring a minimal amount of space on the device. The extraction process was completely automated on the device following sample introduction and required only 50 s for each extraction cycle. The pumping rate achieved during liquid recirculation was 120 ± 10 μL/min. A recycling process such as the one demonstrated would be difficult to implement in a conventional centrifugal microfluidic system.     

Differential mass spectrometry: a label-free LC-MS method for finding significant differences in complex peptide and protein mixtures

Efficiently identifying and quantifying disease- or treatment-related changes in the abundance of proteins is an important area of research for the pharmaceutical industry. Here we describe an automated, label-free method for finding differences in complex mixtures using complete LC-MS data sets, rather than subsets of extracted peaks or features. The method selectively finds statistically significant differences in the intensity of both high-abundance and low-abundance ions, accounting for the variability of measured intensities and the fact that true differences will persist in time. The method was used to compare two complex peptide mixtures with known peptide differences. This controlled experiment allowed us to assess the validity of each difference found and so to analyze the method's sensitivity and specificity. The method detects both presence versus absence and a 2-fold change in peptide concentration near the limit of detection of the instrument used, where chromatographic peaks may not be sufficiently well defined to be detected in individual samples. The method is more sensitive and gives fewer false positives than subtractive methods that ignore signal variability. Differential mass spectrometry combined with targeted MS/MS analysis of only identified differences may save both computation time and human effort compared to shotgun proteomics approaches.     

Nanostructure fabrication by ultra-high-resolution environmental scanning electron microscopy

Electron beam induced deposition (EBID) is a maskless nanofabrication technique capable of surpassing the resolution limits of resist-based lithography. However, EBID fabrication of functional nanostructures is limited by beam spread in bulk substrates, substrate charging, and delocalized film growth around deposits. Here, we overcome these problems by using environmental scanning electron microscopy (ESEM) to perform EBID and etching while eliminating charging artifacts at the nanoscale. Nanostructure morphology is tailored by slimming of deposits by ESEM imaging in the presence of a gaseous etch precursor and by pre-etching small features into a deposit (using a stationary or a scanned electron beam) prior to a final imaging process. The utility of this process is demonstrated by slimming of nanowires deposited by EBID, by the fabrication of gaps (between 4 and 7 nm wide) in the wires, and by the removal of thin films surrounding such nanowires. ESEM imaging provides a direct view of the slimming process, yielding process resolution that is limited by ESEM image resolution ( approximately 1 nm) and surface roughening occurring during etching.     

Regional development in South Korea: accounting for research area in centrality and networks

This paper provides a first-ever look at differences of centrality scores (i.e., networks) over time and across research specializations in Korea. This is a much needed development, given the variance which is effectively ignored when Science Citation Index (SCI) publications are aggregated. Three quantitative tests are provided—OLS, two sample t-tests, and unit-root tests—to establish the patterns of centrality scores across Korea over time. The unit-root test is particularly important, as it helps identify patterns of convergence in each region’s centrality scores. For all other geographic regions besides Seoul, Gyeonggi, and Daejeon, there appears to be little promise—at least in the immediate future—of being network hubs. For these top three regions, though, there is a pattern of convergence in three-quarters of all research specializations, which we attribute in part to policies in the mid- and late-1990s.     

Integrated Circuits Based on Bilayer MoS(2) Transistors

Two-dimensional (2D) materials, such as molybdenum disulfide (MoS(2)), have been shown to exhibit excellent electrical and optical properties. The semiconducting nature of MoS(2) allows it to overcome the shortcomings of zero-bandgap graphene, while still sharing many of graphene's advantages for electronic and optoelectronic applications. Discrete electronic and optoelectronic components, such as field-effect transistors, sensors, and photodetectors made from few-layer MoS(2) show promising performance as potential substitute of Si in conventional electronics and of organic and amorphous Si semiconductors in ubiquitous systems and display applications. An important next step is the fabrication of fully integrated multistage circuits and logic building blocks on MoS(2) to demonstrate its capability for complex digital logic and high-frequency ac applications. This paper demonstrates an inverter, a NAND gate, a static random access memory, and a five-stage ring oscillator based on a direct-coupled transistor logic technology. The circuits comprise between 2 to 12 transistors seamlessly integrated side-by-side on a single sheet of bilayer MoS(2). Both enhancement-mode and depletion-mode transistors were fabricated thanks to the use of gate metals with different work functions.     

Vibration-induced arching in a deep granular bed

Forced vertical vibration of a granular layer can drive flow phenomena such as heaping, convection, fluidization, densification, surface waves and arching. Food, mineral processing, and pharmaceuticals industries all utilize vibratory processes for the handling and transport of granular materials. Understanding how a granular material responds when subjected to vibration is essential for equipment design. Three-dimensional discrete element simulations have been used in this study to investigate the convective motion leading to arching in a vertically vibrated, deep granular bed. The undulating granular layer contains alternating regions that first compact and then relax. The dynamics of these regions may depend on material properties such as restitution and friction coefficients; as well as particle shape. The effects of these factors on the kinematics and dynamics of the arching pattern are investigated here. The arching pattern is found to arise from synchronised momentum transfer between the rise and fall of the deforming granular layer and horizontally travelling waves. The arching pattern was found to be stable across a broad range of restitution and friction levels and particle shapes. Particles with high restitution tend to disrupt the timing between the vertical and horizontal periodic flows and affect the stability of the pattern selection. Large friction results in shear resistance, higher bed pressures, lower bulk densities, and delays in the timing of the vertical and horizontal momentum transfer. Non-sphericity leads to increased dilation of the bed, slower sideways velocities, and increased loading on the floor and dissipation rate in the bed.     

Direct spectrophotometric analysis of Cr(VI) using a liquid waveguide capillary cell

Hexavalent chromium Cr(VI) is a notorious ground water contaminant toxic to humans and animals. Assessment of an exposure risk for aquatic receptors necessitates frequent Cr(VI) concentration data from a range of surface and groundwater locations at Cr(VI) contamination sites. In this work, we demonstrate that enhanced ultraviolet-visible (UV-vis) spectroscopy using a liquid waveguide capillary cell (LWCC) offers an easy-to-use and economical methodology for the determination of chromate anion CrO(4)(2-) in Hanford natural waters without chemical pretreatment and generation of hazardous waste. Direct determination of CrO(4)(2-) in actual surface and ground water samples with the complexities of competing ions, dissolved organics, and other potential interfering agents was achieved by measuring the chromate optical absorbance at 372 nm. For a 100 cm path length LWCC, the detection limit for chromate was found to be as low as 0.073 ppb. A quantitative relationship between the intensity of the absorbance signal and water pH allowed for the straightforward calculation of total Cr(VI) content in natural water. The described method is applicable for in-field monitoring of Cr(VI) in environmental water samples at trace levels.     

Reflection symmetry of a sphere's internal field and its consequences on scattering: a microphysical approach

We examine the reflection symmetries of the electromagnetic wave inside of a uniform spherical particle and identify the consequences of the symmetries for the Stokes parameters describing the polarization state of the far-field scattered wave. The connection between the two waves is described from a microphysical perspective that illustrates the wavelet-superposition origin of the scattered wave. In contrast to more conventional approaches, this microphysical perspective yields new insight into the physical character of the scattering of a plane wave by a sphere. The results of simulations are presented, which graphically demonstrate the relation between the symmetries present in the internal wave and the polarization state of the scattered wave.     

Characterization of the phosphatic mineral of the barnacle Ibla cumingi at atomic level by solid-state nuclear magnetic resonance: comparison with other phosphatic biominerals

Ibliform barnacles are among the few invertebrate animals harnessing calcium phosphate to construct hard tissue. The ³¹P solid-state NMR (SSNMR) signal from the shell plates of Ibla cumingi (Iblidae) is broader than that of bone, and shifted by ca 1 ppm to low frequency. ¹H–³¹P heteronuclear correlation (HETCOR) experiments show a continuum of different phosphorus/phosphate atomic environments, close to hydrogen populations with resonance frequencies between ca 10 and 20 ppm. Associated ¹H and ³¹P chemical shifts argue the coexistence of weakly (high ³¹P frequency, low ¹H frequency) to more strongly (lower ³¹P frequency, higher ¹H frequency) hydrogen-bonded hydrogen phosphate-like molecular/ionic species. There is no resolved signal from discrete OH⁻ ions. ¹³C SSNMR shows chitin, protein and other organic biomolecules but, unlike bone, there are no significant atomic scale organic matrix–mineral contacts. The poorly ordered hydrogen phosphate-like iblid mineral is strikingly different, structurally and compositionally, from both vertebrate bone mineral and the more crystalline fluoroapatite of the linguliform brachiopods. It probably represents a previously poorly characterized calcium phosphate biomineral, the evolution of which may have reflected either the chemical conditions of ancestral seas or the mechanical advantages of phosphatic biomineralization over a calcium carbonate equivalent.