28,301 research outputs found
Proton modified Pt zeolite fuel cell electrocatalysts
NaY Zeolite is selected as a suitable material to host 1.5 wt% Platinum (Pt) loading on zeolite using ion exchange method (a) Pt(NH3)4(NO3)2 without excess NH4NO3 nitrate and (b) Pt(NH3)4(NO3)2 with excess NH4NO3 nitrate. The structure/reactivity relationship of Pt nanoparticle has been experimentally studied via Nafion@ bound electrodes to investigate the interaction nature of Pt with zeolite and electron transfer using the extended X-ray adsorption fine structure (EXAFS) and Pt particle was predicted at 0.7 – 1.5 (nm). Pt oxides can be electrochemically reduced via a hydrogen ‘spillover’ phenomenon. A highly dispersed small Pt particle distribution can be achieved with excessive H+ ions on zeolite acidic sites
Physico-chemical factors and bacteria in fish ponds
Analyses of pond water and mud samples show that nitrifying bacteria (including ammonifying bacteria, nitrite bacteria, nitrobacteria and denitrifying bacteria) are in general closely correlated with various physico-chemical factors, ammonifying bacteria are mainly correlated with dissolved oxygen; denitrifying bacteria are inversely correlated with phosphorus; nitrite bacteria are closely correlated with nitrites, nitrobacteria are inversely correlated with ammoniac nitrogen. The nitrifying bacteria are more closely correlated with heterotrophic bacteria. Nitrobacteria are inversely correlated with anaerobic heterotrophic bacteria. The correlation is quite weak between all the nitrite bacteria which indicates that the nitrite bacteria have a controlling and regulating function in water quality and there is no interdependence as each plays a role of its own. The paper also discusses how the superficial soil (pond mud down to 3.5 cm deep) and different layers of the mud affect the biomass of bacteria. The study shows that the top superficial layer (down to 1.5 cm deep) is the major area for decomposing and converting organic matter
Non-Hermitian dynamics of slowly-varying Hamiltonians
We develop a theoretical description of non-Hermitian time evolution that
accounts for the break- down of the adiabatic theorem. We obtain closed-form
expressions for the time-dependent state amplitudes, involving the complex
eigen-energies as well as inter-band Berry connections calculated using basis
sets from appropriately-chosen Schur decompositions. Using a two-level system
as an example, we show that our theory accurately captures the phenomenon of
"sudden transitions", where the system state abruptly jumps from one eigenstate
to another.Comment: 12 pages, 4 figure
Elimination of cracks in self-assembled photonic band gap crystals
Thin colloidal crystals (or synthetic opals) composed of Stober silica
spheres typically develop cracks when they are utilized to obtain photonic band
gap crystals (or inverted opals). We find that by sintering the silica spheres
prior to assembly of the opal these cracks can be avoided. We report the
effects of temperature and duration of the heat treatment on 850 nm silica
spheres using electron microscopy, thermogravimetry, and light scattering. We
also find a large dependence of the refractive index of the silica on the
temperature of the heat treatment. This may allow tuning of the refractive
index of silica spheres.Comment: REvTex: 4 pages, 3 figure
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