Two-Parameter Block Triangular Splitting Preconditioner for Block Two-by-Two Linear Systems

This paper proposes a two-parameter block triangular splitting(TPTS)preconditioner for the general block two-by-two linear systems.The eigenvalues of the corresponding preconditioned matrix are proved to cluster around 0 or 1 under mild conditions.The limited numerical results show that the TPTS preconditioner is more efficient than the classic block-diagonal and block-triangular preconditioners when applied to the flexible generalized minimal residual(FGMRES)method.

Utilization of MSWI fly ash as partial cement or sand substitute with focus on cementing efficiency and health risk assessment

The strength of cement substituted mortar decreases with the increase in fly ash amount,whereas the strength increases when the fly ash is blended as sand substitute.A mortar with highest strength(compressive strength=30.2 Mpa;flexural strength=7.0 Mpa)was obtained when the sand replacement ratio was 0.75%.The k value(cementing efficiency)of fly ash varied between 0.36 and 0.15 for the fly ash fraction in binder between 5%and 25%.The k values of fly ash used for sand replacement were all significantly above that used for cement substitution.The macropores assigned to the gaps between particles decreased when the fly ash was used as sand replacement,providing an explanation for the strength enhancement.The waste-extraction procedure(toxicity-sulphuric acid and nitric acid method(HJ/T 299-2007))was used to evaluate metal leaching,indicating the reuse possibility of fly ash blended mortar.For the mortar with the mass ratio of fly ash to binder of 0.5%,the carcinogenic risks(CR)and non-carcinogenic hazard quotient(HQ)in sensitive scenario for blended mortar utilization were 9.66 x 10 and 0.06,respectively;these results were both lower than the threshold values,showing an acceptable health risk.The CR(9.89 x 105)and HQ(3.89)of the nonsensitive scenario for fly ash treatment exceeded the acceptable threshold values,indicating health risks to onsite workers.The main contributor to the carcinogenic and non-carcinogenic risk is Cr and Cd,respectively.The CR and HQ from inhalation was the main route of heavy metal exposure.

Release of elements from municipal solid waste incineration fly ash

The element-release behavior of municipal solid waste incineration fly ash was explored through leaching test with continuous set-point pH(pH_(stat) test)and serial single reaction cell(SSRC)tests.First,the relationship between element release and acid neutralizing capacity(ANC)consumption was examined with a pHstat test.Four types of release behaviors were identified which are characteristic for different elements:(1)release curves that were almost linear with ANC consumption(Ca,Zn,and Cd);(2)release that was significantly faster than ANC(Na,K,and Cl);(3)curves that featured a strong increase with ANC consumption,after a transient release,followed by an almost equal decrease(Si and S);and(4)release that is strongly retarded compared with ANC consumption(Cr,Cu,and Pb).In the SSRC system,it the existence of a pH front and a wash-out phenomenon is demonstrated.Combining the results from the SSRC test with the kinetic analysis of the ANC system in the pH_(stat) test,it was inferred that less than one-third of the ANC measured from a batch pH titration plays a neutralization role in a field situation.The methodologies described may provide a powerful set of tools for systematic evaluation of element release from solid wastes.