AuxAg1-x alloy seeds: A way to control growth, morphology and defect formation in Ge nanowires

Germanium (Ge) nanowires are of current research interest for high speed nanoelectronic devices due to the lower band gap and high carrier mobility compatible with high K-dielectrics and larger excitonic Bohr radius ensuing a more pronounced quantum confinement effect [1-6]. A general way for the growth of Ge nanowires is to use liquid or a solid growth promoters in a bottom-up approach which allow control of the aspect ratio, diameter, and structure of 1D crystals via external parameters, such as precursor feedstock, temperature, operating pressure, precursor flow rate etc [3, 7-11]. The Solid-phase seeding is preferred for more control processing of the nanomaterials and potential suppression of the unintentional incorporation of high dopant concentrations in semiconductor nanowires and unrequired compositional tailing of the seed-nanowire interface [2, 5, 9, 12]. There are therefore distinct features of the solid phase seeding mechanism that potentially offer opportunities for the controlled processing of nanomaterials with new physical properties. A superior control over the growth kinetics of nanowires could be achieved by controlling the inherent growth constraints instead of external parameters which always account for instrumental inaccuracy. The high dopant concentrations in semiconductor nanowires can result from unintentional incorporation of atoms from the metal seed material, as described for the Al catalyzed VLS growth of Si nanowires [13] which can in turn be depressed by solid-phase seeding. In addition, the creation of very sharp interfaces between group IV semiconductor segments has been achieved by solid seeds [14], whereas the traditionally used liquid Au particles often leads to compositional tailing of the interface [15] . Korgel et al. also described the superior size retention of metal seeds in a SFSS nanowire growth process, when compared to a SFLS process using Au colloids [12]. Here in this work we have used silver and alloy seed particle with different compositions to manipulate the growth of nanowires in sub-eutectic regime. The solid seeding approach also gives an opportunity to influence the crystallinity of the nanowires independent of the substrate. Taking advantage of the readily formation of stacking faults in metal nanoparticles, lamellar twins in nanowires could be formed.

Charge compensation and Ce3+ formation in trivalent doping of the CeO2(110) surface: The key role of dopant ionic radius

In this paper, we use density functional theory corrected for on-site Coulomb interactions (DFT + U) and hybrid DFT (HSE06 functional) to study the defects formed when the ceria (110) surface is doped with a series of trivalent dopants, namely, Al3+, Sc3+, Y3+, and In 3+. Using the hybrid DFT HSE06 exchange-correlation functional as a benchmark, we show that doping the (110) surface with a single trivalent ion leads to formation of a localized MCe / + O O • (M = the 3+ dopant), O- hole state, confirming the description found with DFT + U. We use DFT + U to investigate the energetics of dopant compensation through formation of the 2MCe ′ +VO ̈ defect, that is, compensation of two dopants with an oxygen vacancy. In conjunction with earlier work on La-doped CeO2, we find that the stability of the compensating anion vacancy depends on the dopant ionic radius. For Al3+, which has the smallest ionic radius, and Sc3+ and In3+, with intermediate ionic radii, formation of a compensating oxygen vacancy is stable. On the other hand, the Y3+ dopant, with an ionic radius close to that of Ce4+, shows a positive anion vacancy formation energy, as does La3+, which is larger than Ce4+ (J. Phys.: Condens. Matter 2010, 20, 135004). When considering the resulting electronic structure, in Al3+ doping, oxygen hole compensation is found. However, Sc 3+, In3+, and Y3+ show the formation of a reduced Ce3+ cation and an uncompensated oxygen hole, similar to La3+. These results suggest that the ionic radius of trivalent dopants strongly influences the final defect formed when doping ceria with 3+ cations. In light of these findings, experimental investigations of these systems will be welcome.

NOX-driven ROS formation in cell transformation of FLT3-ITD positive AML

In different types of myeloid leukemia, increased formation of reactive oxygen species (ROS) has been noted and associated with aspects of cell transformation including the promotion of leukemic cell proliferation and migration, as well as DNA-damage and accumulation of mutations. Work reviewed in this article has shown the involvement of NADPH oxidase (NOX)-derived ROS downstream of oncogenic protein-tyrosine kinases in both processes, and the related pathways have been partially identified. FLT3-ITD, an important oncoprotein in a subset of AML, causes activation of AKT and subsequently stabilization of p22phox, a regulatory subunit for NOX1-4. This process is linked to ROS formation and DNA damage. Moreover, FLT3-ITD signaling through STAT5 enhances expression of NOX4, ROS formation and inactivation of the protein-tyrosine phosphatase DEP-1/PTPRJ, a negative regulator of FLT3 signaling, by reversible oxidation of its catalytic cysteine residue. Genetic inactivation of NOX4 restored DEP-1 activity and attenuated cell transformation by FLT3-ITD in vitro and in vivo. Future work is required to further explore these mechanisms and their causal involvement in leukemic cell transformation, which may result in the identification of novel candidate targets for therapy.

Floral and faunal characteristics and content of photosynthetic pigment in soils of northern Victoria Land, Antarctica

Although soil algae are among the main primary producers in most terrestrial ecosystems of continental Antarctica, there are very few quantitative studies on their relative proportion in the main algal groups and on how their distribution is affected by biotic and abiotic factors. Such knowledge is essential for understanding the functioning of Antarctic terrestrial ecosystems. We therefore analyzed biological soil crusts from northern Victoria Land to determine their pH, electrical conductivity (EC), water content (W), total and organic C (TC and TOC) and total N (TN) contents, and the presence and abundance of photosynthetic pigments. In particular, the latter were tested as proxies for biomass and coarse-resolution community structure. Soil samples were collected from five sites with known soil algal communities and the distribution of pigments was shown to reflect differences in the relative proportions of Chlorophyta, Cyanophyta and Bacillariophyta in these sites. Multivariate and univariate models strongly indicated that almost all soil variables (EC, W, TOC and TN) were important environmental correlates of pigment distribution. However, a significant amount of variation is independent of these soil variables and may be ascribed to local variability such as changes in microclimate at varying spatial and temporal scales. There are at least five possible sources of local variation: pigment preservation, temporal variations in water availability, temporal and spatial interactions among environmental and biological components, the local-scale patchiness of organism distribution, and biotic interactions.

(Tables 1-3) Geochemical composition of seepage water in soils obtained in Schleswig-Holstein, Germany

Under defined laboratory and field conditions, the investigation of percolating water through soil columns (podsol, lessive and peat) down to groundwater table shows that the main factors which control the chemical characteristics of the percolates are: precipitation, evaporation, infiltration rate, soil type, depth and dissolved organic substances. Evaporation and percolation velocity influences the Na+, SO4**2- and Cl- concentrations. Low percolation velocity leads also to longer percolation times and water logging in less permeable strata, which results in lower Eh-values and higher CO2-concentrations due to low gas exchange with the atmosphere. Ca2+ and Mg2+ carbonate concentration depends on soil type and depth. Metamorphism and decomposition of organic substances involve NO3 reduction and K+, Mg2+, SO4**2-, CO2, Fe2+,3+ transport. The analytical data were evaluated with multi variate statistical methods.

Heavy Minerals in Soils from the Athabasca Basin and the Implications for Exploration Geochemistry of Uranium Deposits at Depth

The Centennial deposit is a high grade (~8% U3O8), deeply buried (~950m), unconformity-related U deposit located in the south-central region of the Athabasca Basin in northern Saskatchewan, Canada. The mineral chemistry of fine fractions (<63 μm) of soils from grids above the Centennial deposit were examined to understand possible controls on the geochemistry and radiogenic 207Pb/206Pb ratios measured in the clay-size (<2 μm) fractions used for exploration. Soil samples distal and proximal to the deposit projection to the surface and geophysically defined structures were selected. Mineral abundances were determined using the scanning electron microscope and Mineral Liberation Analysis. Zircon was the only U-rich mineral identified with modal abundances >0.02% by weight. Monazite, which can be U-rich, was identified, but not in significant abundances. The source of the zircon and other heavy minerals is interpreted to be from sub-cropping sources that are >100 km up-ice from Centennial. Trace element analysis using laser ablation inductively coupled plasma mass spectrometry of hydroseparated zircon grains indicate that zircon abundances and zircon Pb concentrations in surficial samples have minimal effect on the radiogenic 207Pb/206Pb ratios in the clay-fraction of the samples, with the dominant source of radiogenic Pb being clay mineral surfaces that trapped Pb during secondary dispersion from the Centennial uranium deposit through faults and fractures to the surface. The REE patterns indicate HREE enrichment in the clay-fractions of samples that have higher abundances of zircon in the <20 μm fraction. Immobile elements such as HREE that are concentrated in zircon can be used as indicators of radiogenic Pb being sourced from minerals at the surface rather than being sourced from secondary dispersion from deeply buried U deposits.

Crack propagation in non-homogenous materials: Evaluation of mixed-mode SIFs, T-stress and kinking angle using a variant EFG method

A new variant of the Element-Free Galerkin (EFG) method, that combines the diffraction method, to characterize the crack tip solution, and the Heaviside enrichment function for representing discontinuity due to a crack, has been used to model crack propagation through non-homogenous materials. In the case of interface crack propagation, the kink angle is predicted by applying the maximum tangential principal stress (MTPS) criterion in conjunction with consideration of the energy release rate (ERR). The MTPS criterion is applied to the crack tip stress field described by both the stress intensity factor (SIF) and the T-stress, which are extracted using the interaction integral method. The proposed EFG method has been developed and applied for 2D case studies involving a crack in an orthotropic material, crack along an interface and a crack terminating at a bi-material interface, under mechanical or thermal loading; this is done to demonstrate the advantages and efficiency of the proposed methodology. The computed SIFs, T-stress and the predicted interface crack kink angles are compared with existing results in the literature and are found to be in good agreement. An example of crack growth through a particle-reinforced composite materials, which may involve crack meandering around the particle, is reported.

A sub-kiloparsec scale view of star formation in M31

Thesis (Ph.D.)--University of Washington, 2016-08

Finite volume modelling of shrinkage porosity formation in metal casting

Abstract not available

Time-resolved fluorescence observation of di-tyrosine formation in horseradish peroxidase upon ultrasound treatment leading to enzyme inactivation

The application of ultrasound to a solution can induce cavitional phenomena and generate high localised temperatures and pressures. These are dependent of the frequency used and have enabled ultrasound application in areas such as synthetic, green and food chemistry. High frequency (100 kHz to 1 MHz) in particular is promising in food chemistry as a means to inactivate enzymes, replacing the need to use periods of high temperature. A plant enzyme, horseradish peroxidase, was studied using time-resolved fluorescence techniques as a means to assess the effect of high frequency (378 kHz and 583 kHz) ultrasound treatment at equivalent acoustic powers. This uncovered the fluorescence emission from a newly formed species, attributed to the formation of di-tyrosine within the horseradish peroxidase structure caused by auto-oxidation, and linked to enzyme inactivation.

Silicon Promotes Exodermal Casparian Band Formation in Si-Accumulating and Si-Excluding Species by Forming Phenol Complexes

We studied the effect of Silicon (Si) on Casparian band (CB) development, chemical composition of the exodermal CB and Si deposition across the root in the Si accumulators rice and maize and the Si non-accumulator onion. Plants were cultivated in nutrient solution with and without Si supply. The CB development was determined in stained root cross-sections. The outer part of the roots containing the exodermis was isolated after enzymatic treatment. The exodermal suberin was transesterified with MeOH/BF3 and the chemical composition was measured using gas chromatography-mass spectroscopy (GC-MS) and flame ionization detector (GC-FID). Laser ablation-inductively coupled plasma-mass spectroscopy (LA-ICP-MS) was used to determine the Si deposition across root cross sections. Si promoted CB formation in the roots of Si-accumulator and Si non-accumulator species. The exodermal suberin was decreased in rice and maize due to decreased amounts of aromatic suberin fractions. Si did not affect the concentration of lignin and lignin-like polymers in the outer part of rice, maize and onion roots. The highest Si depositions were found in the tissues containing CB. These data along with literature were used to suggest a mechanism how Si promotes the CB development by forming complexes with phenols.

Devaluation, competitiveness and new business formation in emerging countries

In September 2010, Brazil’s Finance Minister, Guido Mantega, used the term “currency war” with reference to monetary policies implemented by different countries to generate an artificial devaluation of their currency and achieve a cheaper, more competitive domestic economy that may be attractive to foreign investors. Similar cases have been documented since the 1930s Great Depression, when several countries abandoned the gold standard as backing for their currencies. More recently, a large-scale asset purchase by Japan’s Central Bank in 2013 was singled out as a strategy aimed at generating devaluation of the yen. This research uses statistics of new business formation density reported by Doing Business for 30 emerging countries in the period 2004-2011 to evaluate the impact of devaluation measured by the behavior of the real effective exchange rate (REER) on the rate of new business formation (NBF). It is determined how variables associated with competitiveness affect the relationship between devaluation and business formation. Results show that devaluation has a positive effect on NBF in the short term, which gets diluted in the long term. Countries with greater competitiveness have less dependence on devaluation to increase the number of businesses.