Domino instability effect of surrounding rock-coal pillars in a room-and-pillar gob

To discuss the domino instability effect and large area roof falling and roof accidents of surrounding rockcoal pillars in a room-and-pillar gob,the equilibrium equation for a roof-coal pillar-floor system with the influence of mining floor was developed based on the engineering conditions of the surrounding rock in a room-and-pillar gob in the 3^(-2)coal seam of Tanggonggou mine.The conditions of system instability and the relationship between system stability and system stiffness were analyzed from an energetic point of view.Numerical simulation using the discrete element software UDEC was also carried out to simulate conditions causing the domino effect on surrounding rock-coal pillars in a 3^(-2)room-and-pillar gob.The results show that:if we want the system to destabilize,the collective energy in roof-and-floor must be larger than that in the coal pillar.When the stiffness of the coal pillars and the roof-and-floor are both greater than zero,the system is stable.When the stiffness of the coal pillars is negative but the summed stiffness of the coal pillars and roof-and-floor is larger than or equal to zero,the system is statically destroyed.When the sum of the coal pillars and the roof-floor stiffness is negative,the system suffers from severe damages.For equal advance distances of the coal mining face,the wider coal pillars can reduce the probability of domino type instability.Conversely,the smaller width pillars can increase the instability probability.Domino type instability of surrounding rock-coal pillars is predicted to be unlikely when the width of coal pillars is not less than 8 m.

3-D modeling of rock burst in pillar No. 19 of Fetr6 chromite mine

Fetr6 is an underground mine in which chromite is extracted using stope and pillar mining method. Despite of all improving works such as roof supporting and replacing of ore pillars with concrete pillars, pillar No. 19 failed and other pillars failed progressively as a domino effect and 4000 m2 of mine collapsed within a few minutes, consequently. For detail investigation, two 3-D numerical models were developed by 3Dec. The first, a base model, was used for estimation of stress on pillars just before failure and the other for investigation of rock burst in pillar No. 19. The results show that discontinuity parameters such as friction angle and shear stiffness is critical parameters in this pillar failure. In addition, it indicates that W/H ratio equal 0.3, the lack of ore extraction strategy and inadequate roof support are the major reasons for this failure. In this paper, the procedure of study was described.

Temperature-gradient method for gaining insights into the luminescence origin and formation mechanism of carbon dots

Carbon dots(CDs)are a fascinating new class of fluorescent nanomaterials,yet the understanding of the fluorescent origin of CDs still lags well behind their applications.The key challenges for unveiling the fluorescent mechanism of CDs relate to the insufficient basis for structural evaluation.This work presents a temperature-gradient route to control the bottom-up approach of CDs,enabling the precise structural characterization of intermediates and the establishment of definite structure-property relationships,akin to the domino reaction synthesis of complex natural products from small organic molecules.Taking the binary components citric acid and meta-dimethylaminophenol generated CDs as a case study,their emissive mechanism,particularly the unique excitation-dependent fluorescence behavior,is reasonably explained and supported by structural evaluation through retrosynthetic analysis.The formation process of CDs is investigated using a combination of spectroscopic,thermal,and theoretical calculation techniques,demonstrating the significant potential of the temperature-gradient route in the exploration structure-property relationships and guiding the rational design of advanced CD applications.

Induction and modulation of supramolecular chirality in side-chain azobenzene polymers through the covalent chiral domino effect

Induction,transfer,and modulation of intriguing supramolecular chirality were achieved in a chiral domino-type polymer system using a chiralα-end azobenzene(Azo)moiety as one chiral terminus and achiral Azo repeating units as building blocks.The Azo polymers prepared by atom transfer radical polymerization were imparted with well-controlled chain lengths and a chiral moiety at a well-defined position.One chiral terminus can effectively dictate the helical orientation of the achiral Azo stacks in the aggregation state.The spacer length between the chiral residue and the achiral repeating units dominates the preferred handedness of the side-chain Azo stacks.For instance,the R-configuration moiety with a short alkyl chain(with 0,2,and 3 carbons)induces right-handed supramolecular chirality,whereas those with long alkyl chains(with 4,5,and 6 carbons)induce the opposite helical orientation of the Azo units.Moreover,the chiral regulation of polymer aggregates is successfully achieved using the unique photoisomerization transition of the Azo chromophore and the heat-assisted reassembly approach.Chiral induction and chiral-to-achiral communication are further verified via theoretical simulations.

Generalized congestion of power systems:insights from the massive blackouts in India

The Indian power system underwent two separate massive blackouts on 30th and 31st of July 2012.These blackouts exposed a series of inherent problems underlying the power system of India,such as its generation planning,transmission planning,grid infrastructure,management systems,primary energy resources,environmental constraints,electricity market,and information technology,which together aggravate the massive blackouts.These factors which affect the adequacy and security of the power supply in a similar manner as the transmission congestion of physical grids does,can be called by a generic term as generalized congestion.Competitive manipulations and“game-playing”between various interested parties further intensifies these congestions.Here,from the perspective of generalized congestions,the paper reflects the inevitability of India’s massive blackouts,discusses occasional effects of trigger events,inherent evolution law of blackouts and the enlightenment on power industry in China,and explores risk control measures to defend blackouts in China.The positive role of strong smart grid in insuring energy and environment security is highlighted.