We synthesized star-shaped pentagonal microcrystals of boron carbide with an extremely low carbon content (~5%), from m-carborane under high pressure (7 GPa) and high temperature (1370–1670 K). These ...crystals have five-fold symmetry and grow in the shape of stars. A 5-fold symmetry in large micron-sized crystals is extremely rare making this a striking observation.
Fluorescence spectra of graphitic (g-C3N4) and spherical (s-C3N4) modifications of carbon nitride were measured as a function of green pulsed (6 ns-pulse) laser intensity. It was found that the ...intensity of the laser increases the maximum of the fluorescence shifts towards the anti-Stokes side of the fluorescence for s-C3N4 spherical nanoparticles. This phenomenon was not observed for g-C3N4 particles. The maximum of the anti-Stokes fluorescence in s-C3N4 nanoparticles was observed at 480 nm. The ratio of the intensity of the anti-Stokes peak (centered at 480 nm) to that of the Stokes peak (centered at 582 nm) was measured to be I484/582 = 6.4 × 10−3 at a low level of intensity (5 mW) of a green pulsed laser, whereas it rose to I484/582 = 2.27 with a high level of laser intensity (1500 mW).
In this report, we demonstrate that combining the laser heating system in a diamond anvil cell (LH-DAC) with a tandem acoustic-optical tunable filter (LH-DAC–TAOTF) allows for the simultaneous ...measurement of (a) the relative infrared (IR, 1070nm) power distribution on a specimen surface in the DAC; (b) the temperature distribution under laser heating of a specimen under high-pressure in a DAC; it also (c) provides an opportunity to control the shape of the IR laser spot on the surface of the heated specimen. The effect of the π-shaper on the shape and the position of the focus of the IR laser beam on a specimen using a TAOTF is also presented. For a 10× long-working distance objective, the smallest diameter of the IR laser was found to be around 10μm, when the focal plane coincides with that of the imaging optical system of LH-DAC. The highest diameter of the IR laser was shown to be 20μm when the rim of the π-shaper was set at 3μm. It is demonstrated also that the TAOFT not only permits to measure the two-dimensional (2-D) distribution of the IR laser power, but also allows for the alignment of the laser before each heating event at different pressures.
A new media, iron coated pottery granules (ICPG) has been developed for As removal from drinking water. ICPG is a solid phase media that produces a stable Fe–Si surface complex for arsenic ...adsorption. Scanning electron microscopy (SEM) was used to document the physical attributes (grain size, pore size and distribution, surface roughness) of the ICPG media. Several advantages of the ICPG media such as (a) its granular structure, (b) its ability to absorb As via the
F(0) coating on the granules’ surface; (c) the inexpensive preparation process for the media from clay material make ICPG media a highly effective media for removing arsenic at normal pH. A column filtration test demonstrated that within the stability region (flow rate lower than 15
L/h, EBCT >3
min), the concentration of As in the influent was always lower than 50
μg/L. The 2-week system ability test showed that the media consistently removed arsenic from test water to below the 5
μg/L level. The average removal efficiencies for total arsenic, As(III), and As(V) for a 2-week test period were 98%, 97%, and 99%, respectively, at an average flow rate of 4.1
L/h and normal pH. Measurements of the Freundlich and Langmuir isotherms at normal pH show that the Freundlich constants of the ICPG are very close to those of ferric hydroxide, nanoscale zero-valent iron and much higher than those of nanocrystalline titanium dioxide. The parameter 1/
n is smaller than 0.55 indicating a favorable adsorption process K. Hristovski, A. Baumgardner, P. Westerhoff, Selecting metal oxide nanomaterials for arsenic removal in fixed bed columns: from nanopowders to aggregated nanoparticle media, J. Hazard. Mater. 147 (2007) 265–274. The maximum adsorption capacity (
q
e) of the ICPG from the Langmuir isotherm is very close to that of nanoscale zero-valent indicating that zero-valent iron is involved in the process of the As removal from the water. The results of the toxicity characteristic leaching procedure (TCLP) analysis revealed that the media was non-hazardous, as shown by the ND (non-detectable) result for arsenic. The mechanism of As adsorption by ICPG has not been determined. Formation of Fe–Si complexes on the surface of the ICPG system may be responsible for the tight bonding of the As to the IGPC media.
We studythe effect of shear deformation on graphitic
-C
N
under pressures of up to 80 GPa at room temperature.
-C
N
samples are transformed from initial amorphous flakes into onion-like structures, ...in which the nitrogen content in the quenched samples decreases with increasing pressure (from 42% in the initial conditions to 1% at 80 GPa). The concentration of the
bonds also decreases from 1 (the initial sample) to 0.62 with increasing pressure to 80 GPa. This transformation of the sample is due to the fact that in the pressure range of 55-115 GPa, the equilibrium phase is not a diamond, but instead, carbon onions cross-linked by
bonds, which are denser than diamonds. The results of our study show that the presence of nitrogen in
-bonded structures at pressures of higher than 55 GPa reduces the density and, accordingly, carbon structures without nitrogen become thermodynamically favorable.
In this paper, we describe a new, high-frequency, time-resolved scanning acoustic microscope developed for studying dynamical processes in biological cells. The new acoustic microscope operates in a ...time-resolved mode. The center frequency is 0.86 GHz, and the pulse duration is 5 ns. With such a short pulse, layers thicker than 3 mum can be resolved. For a cell thicker than 3 mum, the front echo and the echo from the substrate can be distinguished in the signal. Positions of the first and second pulses are used to determine the local impedance of the cell modeled as a thin liquid layer that has spatial variations in its elastic properties. The low signal-to-noise ratio in the acoustical images is increased for image generation by averaging the detected radio frequency signal over 10 measurements at each scanning point. In conducting quantitative measurements of the acoustic parameters of cells, the signal can be averaged over 2000 measurements. This approach enables us to measure acoustical properties of a single HeLa cell in vivo and to derive elastic parameters of subcellular structures. The value of the sound velocity inside the cell (1534.5 plusmn 33.6 m/s) appears to be only slightly higher than that of the cell medium (1501 m/s).
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