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Summary: Heterochromatin is a physical state of the chromatin fiber that maintains gene repression during cell development. Although evidence exists on molecular mechanisms involved in heterochromatin formation, a detailed structural mechanism of heterochromatin formation needs a better understanding. We made use of a simple Monte Carlo simulation model with explicit representation of key molecular events to observe molecular self-organization leading to heterochromatin formation. Our simulations provide a structural interpretation of several important traits of the heterochromatinization process. In particular, this study provides a depiction of how small amounts of HP1 are able to induce a highly condensed chromatin state through HP1 dimerization and bridging of sequence-remote nucleosomes. It also elucidates structural roots of a yet poorly understood phenomenon of a nondeterministic nature of heterochromatin formation and subsequent gene repression. Experimental chromatin in vivo assay provides an unbiased estimate of time scale of repressive response to a heterochromatin-triggering event.

Gas dispersion characteristics are of significant importance in froth flotation. Studies show that cyclonic static microbubble flotation column (FCSMC) is an efficient device to recover fine minerals. In the present study, the gas holdup distribution and the mean gas holdup in a laboratory gas-liquid FCSMC are first quantitatively measured by electrical resistance tomography (ERT). Different flowrates of gas and liquid are considered. Performed experiments show that when the air flowrate increases from 1.1 L/min to 2.3 L/min, the mean gas holdups on measured planes increase to about 4 ~ 5 times the original value. The gas dispersion along the radial direction is poor, which is dense in the center and rare in the periphery. This uneven bubble distribution aggravates as the amount of the supplying air increases. As the circulating liquid flux increases, the corresponding measured gas holdup gradually decreases and the bubble shrinks to the center along the radial direction. When the liquid flux increases from 1.5 m3/h to 1.8 m3/h, the averaged decline of the mean gas holdup on measured planes reduces to 54 ~ 65% of the original value. Finally, it is validated that the sieve plate packing effectively reduces non-uniform radial and axial distributions of the gas holdup. The obtained results might lead to more effective operating of FCSMC, provide a reference for further numerical study and ERT application in other complicated devices. [ABSTRACT FROM AUTHOR]

Organic and inorganic matters are two main compositions of coal, and their occurrence forms in flotation products are closely associated with the ultimate flotation performance. Considering that pulp-mixing stage can strongly affect particle surface properties, this study tentatively investigated the effect of slurry preconditioning on the element distribution of major minerals in flotation products of coal using a jet-flow mixer under various energy inputs. Measurements were obtained using X-ray diffraction, X-ray fluorescence, laser particle size analyzer, X-ray photoelectron spectroscopy, and a scanning electron microscope. The flotation results indicated that the optimal performance was obtained at 98.57 W/kg with a maximum combustible matter recovery (93.51%) and yield (85.56%). Throughout the flotation time, three variational stages of particle diameters were identified from relatively medium size to finer size and then to coarser size, corresponding to a progressive increase in the ash content of concentrates. Furthermore, the combined analyses of mineral phase and morphological characteristics revealed that kaolinite exhibited a higher removal rate than quartz in concentrates, for an appropriate conditioning intensity could detach fine slimes coating on coal surface but weakly influence the interlocked coal-mineral bodies. On the whole, an optimized preconditioning process could intensify the selective mineral migration to some extent. [ABSTRACT FROM AUTHOR]

Numerous oxygen elements are present on the oxidized coal surfaces, resulting in the difficulties for flotation. In this study, the enhancement of oxidized coal flotation using the impact flow conditioning pulp was investigated, and the impact flow velocity was optimized. The enhancement mechanism of the impact flow conditioning pulp was investigated via a series of experiments. The results showed that the use of impact flow conditioning pulp could improve the cumulative combustible recovery and flotation kinetics of oxidized coal, and these increased with the increasing impact flow velocity. In the experimental range, an optimum flotation result was obtained at an impact flow velocity of 5 m/s. The SEM analysis showed that the impact flow conditioning pulp could remove the aggregations on the oxidized coal surface, exposing a fresh surface. The XPS analysis confirmed that the impact flow conditioning pulp could increase the carbon contents and decrease the oxygen contents on the oxidized coal surface. Further, the impact flow conditioning pulp could significantly enhance the hydrophobicity and floatability of oxidized coal. [ABSTRACT FROM AUTHOR]