Nano⁃Silica Production by Rice Husk Combustion in a 0.7 MW Double⁃Circulating Fluidized Bed after Acid Pretreatment

Rice husk is an organic silicon source for amorphous nano⁃silica particles.This paper reports the experimental study on the industrial production of nano⁃silica by rice husk combustion in a specially⁃designed 0.7 MW double⁃circulating fluidized bed(DCFB)based on acid pretreatment process.The physicochemical properties of RHA were characterized by various testing instruments.Results showed that acid pretreatment removed a large amount of metal impurities in the rice husk and thus inhibited the formation of crystalline silica or the agglomeration during the fluidized bed combustion process.The combustion efficiencies were as high as 99.5%.The obtained RHA comprised white fine particles and exhibited an amorphous structure,but factors such as collection point and acid type had certain influences on the quality of RHA.The highest SiO2 purity was greater than 98.6 wt.%,the lowest content of unburned carbon was 0.2 wt.%,the specific surface area reached 178 m2/g,and the pore size reached 5 nm.The circulating fluidized bed combustion of rice husk based on acid pretreatment can prepare nano⁃silica while providing heat for industrial processes,which is a highly energy⁃rich process.

On Isodual Double Toeplitz Codes

Double Toeplitz(shortly DT)codes are introduced here as a generalization of double circulant codes.The authors show that such a code is isodual,hence formally self-dual(FSD).FSD codes form a far-reaching generalization of self-dual codes,the most important class of codes of rate one-half.Self-dual DT codes are characterized as double circulant or double negacirculant.Likewise,even binary DT codes are characterized as double circulant.Numerical examples obtained by exhaustive search show that the codes constructed have best-known minimum distance,up to one unit,amongst formally self-dual codes,and sometimes improve on the known values.For q=2,the authors find four improvements on the best-known values of the minimum distance of FSD codes.Over F4 an explicit construction of DT codes,based on quadratic residues in a prime field,performs equally well.The authors show that DT codes are asymptotically good over Fq.Specifically,the authors construct DT codes arbitrarily close to the asymptotic Varshamov-Gilbert bound for codes of rate one half.

On the Computing of the Minimum Distance of Linear Block Codes by Heuristic Methods

The evaluation of the minimum distance of linear block codes remains an open problem in coding theory, and it is not easy to determine its true value by classical methods, for this reason the problem has been solved in the literature with heuristic techniques such as genetic algorithms and local search algorithms. In this paper we propose two approaches to attack the hardness of this problem. The first approach is based on genetic algorithms and it yield to good results comparing to another work based also on genetic algorithms. The second approach is based on a new randomized algorithm which we call 'Multiple Impulse Method (MIM)', where the principle is to search codewords locally around the all-zero codeword perturbed by a minimum level of noise, anticipating that the resultant nearest nonzero codewords will most likely contain the minimum Hamming-weight codeword whose Hamming weight is equal to the minimum distance of the linear code.

Longitudinal residual circulation in the South Passage of Yangtze Estuary:Combined influences from runoff,tide and bathymetry

Classical estuary circulation theory states that in the longitudinal direction of an estuary there exists a single circulation with landward,near-bottom,and seaward,near-surface flows;however,the situation becomes complicated with the presence of a river mouth bar.Here we conducted tidal-cycle observations in the South Passage of the Yangtze Estuary during both the wet and dry seasons of 2018(July and December,respectively).The simultaneous current velocity,temperature,and salinity profile data were obtained from anchored boats and base tripods at three stations along the channel in the mouth bar area.The results reveal two distinct longitudinal residual circulation patterns:a classic circulation which is formed on the seaward slope of the mouth bar during the wet season,and a double circulation system which is composed of two circulation cells over the landward and seaward slopes of the mouth bar during the dry season.The Simpson number(Si),mixing parameter(M),and salinity data were used to quantify the mixing intensity,which shows that horizontal baroclinic pressure gradient is the dominant factor in the formation of the longitudinal residual circulation.Furthermore,the double circulation pattern during the dry season is related to the mouth bar bathymetry,which affects saltwater intrusion.The double circulations can significantly influence the spatial and temporal evolution of the stagnation point in the estuarine channel,which in turn modifies the distribution patterns of suspended sediment concentration in the maximum turbidity zone.Evidently,the changes in the mouth bar sandbar bathymetry in response to human activities and river basin hydrographic conditions indirectly affect the occurrence and scale of the double circulations.