Hybrid LTA vehicle controllability as affected by buoyancy ratio

The zero and low speed controllability of heavy lift airships under various wind conditions as affected by the buoyancy ratio are investigated. A series of three hybrid LTA vehicls were examined, each having a dynamic thrust system comprised of four H-34 helicopters, but with buoyant envelopes of different volumes (and hence buoyancies), and with varying percentage of helium inflation and varying useful loads (hence gross weights). Buoyancy ratio, B, was thus examined varying from approximately 0.44 to 1.39. For values of B greater than 1.0, the dynamic thrusters must supply negative thrust (i.e. downward)

CCD Times of Minima of Eclipsing Binaries

We present 7 times of minima of 3 eclipsing binaries

Evaporation kinetics of Mg2SiO4 crystals and melts from molecular dynamics simulations

Computer simulations based on the molecular dynamics (MD) technique were used to study the mechanisms and kinetics of free evaporation from crystalline and molten forsterite (i.e., Mg2SiO4) on an atomic level. The interatomic potential employed for these simulations reproduces the energetics of bonding in forsterite and in gas-phase MgO and SiO2 reasonably accurately. Results of the simulation include predicted evaporation rates, diffusion rates, and reaction mechanisms for Mg2SiO4(s or l) yields 2Mg(g) + 20(g) + SiO2(g)

The infuence of glycosidic linkage neighbors on disaccharide conformation in vacuum

Correct description of the free energy of conformation change of disaccharides is important in understanding a variety of biochemical processes and, ultimately, in the manufacture of better food and paper products. In this study, we determine the relative free energy of a series of 12 disaccharides in vacuum using replica exchange molecular dynamics (repMD) simulations. The chosen sugars and the novel application of this method allow the exploration of the role of glycosidic linkage neighbors in conformer stabilization. In line with expectations, we find that hydrogen bonding (and therefore energetically preferred conformations) are determined both by the nature of the glycosidic linkage (i.e., 1 f 2, 1 f 3, or 1 f 4), the C1 epimer of the of the nonreducing monosaccharide, and by the configuration of carbon atoms once removed from the glycosidic linkage. Contrary to suggestions by prior authors for repMD more generally, we also demonstrate that repMD provides enhanced sampling, relative to conventional MD simulations of equivalent length, for disaccharides in vacuum at 300 K.Fundação para a Ciência e a Tecnologia (FCT)SFRH/BPD/20555/2004/0GVLNational Science Foundation under Grant CHE-043132

Quantum mechanical calculation of aqueuous uranium complexes: carbonate, phosphate, organic and biomolecular species

<p>Abstract</p> <p>Background</p> <p>Quantum mechanical calculations were performed on a variety of uranium species representing U(VI), U(V), U(IV), U-carbonates, U-phosphates, U-oxalates, U-catecholates, U-phosphodiesters, U-phosphorylated N-acetyl-glucosamine (NAG), and U-2-Keto-3-doxyoctanoate (KDO) with explicit solvation by H₂O molecules. These models represent major U species in natural waters and complexes on bacterial surfaces. The model results are compared to observed EXAFS, IR, Raman and NMR spectra.</p> <p>Results</p> <p>Agreement between experiment and theory is acceptable in most cases, and the reasons for discrepancies are discussed. Calculated Gibbs free energies are used to constrain which configurations are most likely to be stable under circumneutral pH conditions. Reduction of U(VI) to U(IV) is examined for the U-carbonate and U-catechol complexes.</p> <p>Conclusion</p> <p>Results on the potential energy differences between U(V)- and U(IV)-carbonate complexes suggest that the cause of slower disproportionation in this system is electrostatic repulsion between UO₂[CO₃]₃^5-ions that must approach one another to form U(VI) and U(IV) rather than a change in thermodynamic stability. Calculations on U-catechol species are consistent with the observation that UO₂²⁺can oxidize catechol and form quinone-like species. In addition, outer-sphere complexation is predicted to be the most stable for U-catechol interactions based on calculated energies and comparison to ¹³C NMR spectra. Outer-sphere complexes (i.e., ion pairs bridged by water molecules) are predicted to be comparable in Gibbs free energy to inner-sphere complexes for a model carboxylic acid. Complexation of uranyl to phosphorus-containing groups in extracellular polymeric substances is predicted to favor phosphonate groups, such as that found in phosphorylated NAG, rather than phosphodiesters, such as those in nucleic acids.</p

A report on erosion and range condition in the West Kimberley area of Western Australia

Nearly 30 per cent (26 700 sq. kilometres) of the West Kimberley survey area is in bad range condition. Nearly 51 per cent (45 400 sq. kilometres) of the area is in fair range condition. Nearly 20 per cent (17 500 sq. kilometres) of the area is in good range condition. The worst areas of degradation and erosion are on the most valuable pasture lands. These areas are readily accessible, close to permanent water supplies, and support attractive pastures. Carrying capacity estimations of the pasture lands of ded areas, co-operative programmes for rehabilitation should be planned by the station lesses and the Department of Lands and Surveys

Local Structure and Dynamics in Methylammonium, Formamidinium, and Cesium Tin(II) Mixed-Halide Perovskites from 119Sn Solid-State NMR.

Organic-inorganic tin(II) halide perovskites have emerged as promising alternatives to lead halide perovskites in optoelectronic applications. While they suffer from considerably poorer performance and stability in comparison to their lead analogues, their performance improvements have so far largely been driven by trial and error efforts due to a critical lack of methods to probe their atomic-level microstructure. Here, we identify the challenges and devise a 119Sn solid-state NMR protocol for the determination of the local structure of mixed-cation and mixed-halide tin(II) halide perovskites as well as their degradation products and related phases. We establish that the longitudinal relaxation of 119Sn can span 6 orders of magnitude in this class of compounds, which makes judicious choice of experimental NMR parameters essential for the reliable detection of various phases. We show that Cl/Br and I/Br mixed-halide perovskites form solid alloys in any ratio, while only limited mixing is possible for I/Cl compositions. We elucidate the degradation pathways of Cs-, MA-, and FA-based tin(II) halides and show that degradation leads to highly disordered, qualitatively similar products, regardless of the A-site cation and halide. We detect the presence of metallic tin among the degradation products, which we suggest could contribute to the previously reported high conductivities in tin(II) halide perovskites. 119Sn NMR chemical shifts are a sensitive probe of the halide coordination environment as well as of the A-site cation composition. Finally, we use variable-temperature multifield relaxation measurements to quantify ion dynamics in MASnBr3 and establish activation energies for motion and show that this motion leads to spontaneous halide homogenization at room temperature whenever two different pure-halide perovskites are put in physical contact