Gedanken experiments to destroy a BTZ black hole

We consider Gedanken experiments to destroy an extremal or near-extremal Banados-Teitelboim-Zanelli (BTZ) black hole by throwing matter into the horizon. These black holes are vacuum solutions to (2+1)-dimensional gravity theories, and are asymptotically AdS_3. Provided the null energy condition for the falling matter, we prove the following—(i) in a Mielke-Baekler model without ghost fields, when torsion is present, an extremal BTZ black hole can be overspun and becomes a naked conical singularity; (ii) in three-dimensional Einstein gravity and chiral gravity, which both live in the torsionless limits of the Mielke-Baekler model, an extremal BTZ black hole cannot be overspun; and (iii) in both Einstein gravity and chiral gravity, a near-extremal BTZ black hole cannot be overspun, leaving the weak cosmic censorship preserved. To obtain these results, we follow the analysis of Sorce and Wald on their Gedanken experiments to destroy a Kerr-Newman black hole, and calculate the second order variation of the black hole mechanics. Furthermore, Wald’s type of Gedanken experiments provide an operational procedure of proving the third law of black hole dynamics. Through the AdS/CFTcorrespondence, our results on BTZ black holes also indicate that a third law of thermodynamics holds for the holographic conformal field theories dual to three-dimensional Einstein gravity and chiral gravity

Correlation of PK/PD Indices with Resistance Selection for Cefquinome against Staphylococcus aureus in an In Vitro Model

Cefquinome is a fourth-generation Cephalosporin approved for use in animals exclusively. The objective of this study was to explore the relationship of cefquinome pharmacokinetic/pharmacodynamic (PK/PD) indices with resistance selection of Staphylococcus aureus ATCC25923 in an in vitro model. Six dosing regiments of cefquinome at an interval of 24 h for three consecutive times were simulated, resulting in maximum concentrations (Cmax) from 1/2 MIC to 16 MIC and half-lives (t1/2β) of 3 and 6 h, respectively. The in vitro sensitivity of S. aureus was monitored by bacterial susceptibility and dynamic time-kill curve experiments over the six cefquinome concentrations. The correlation between changes in bacterial susceptibility (MIC72/MIC0) and the percentage of time within mutant selection window (MSW) versus dosing interval (TMSW %) was subjected to Gaussian function and regression analysis. The results favored the consensus that time above MIC (T>MIC) was recognized as an important PK/PD parameter of cephalosporins for antibacterial efficiency. Cefquinome reached the maximum killing effect when T>MIC% attained approximately 40%~60%. The subsequent correlation analysis demonstrated that resistant S. aureus ATCC25923 was easy to occur when TMSW% attained an index of about 20% with t1/2β of 3 h after multiple dosing, and 40% with t1/2β of 6 h after multiple dosing

Cellular automaton modeling of semisolid microstructure formation

Computer modeling of semi-solid structure formation is of significance in both understanding the mechanisms of globular structure formation and determining the effect of solidification conditions on final microstructure. A modified cellular automaton (mCA) model has been developed, which is coupled with macroscopic models for heat transfer calculation and microscopic models for nucleation and grain growth. The mCA model is applied to A356 Al alloy – one of the most widely used semi-solid alloys, to predict grain morphology and grain size during semi-solid solidification, and determines the effects of pouring temperature on the final microstructure. The modeling results show that the lower the initial temperature, the finer grain size will be obtained. In addition, the model can be used to predict the solutal micro-segregation

GRACE satellite-based drought index indicating increased impact of drought over major basins in China during 2002–2017

International audienceThe frequency of recurrence of drought has major societal, economical, and environmental impacts. However, our ability to capture drought conditions accurately are limited due to the uncertainties in current drought indices. In the present study, we proposed a Gravity Recovery and Climate Experiment (GRACE) total water storage (TWS) based drought severity index (DSI) using the detrended GRACE-TWS time series, to eliminate the effect of non-climatic factors on drought estimation and reflect true drought conditions. Based on the improved GRACE-DSI, we characterized the drought conditions over major basins in China during 2002–2017. Our results indicate that the improved GRACE-DSI can reasonably capture the drought process compared to existing non-detrended GRACE-based drought indices. The observed behavior of GRACE-DSI time series agrees reasonably well with the Palmer drought severity index, standardized precipitation index, and standardized runoff index, although differences exist due to intrinsic differences in the indicators of drought. Spatially, the Yellow River Basin, Huai River Basin, Hai River Basin, Southwest River Basin, and Continental River Basin share a similar pattern with droughts prevailing after 2013, and with both increases in duration and severity of the drought episodes. Moreover, pixel-based drought assessment also suggests an increasing trend in drought frequency in most basins in China during the GRACE era, with a prominent drought event in the Southwest River Basin beginning in April 2015 and ending in May 2016, with a severity of -25.38 and affecting 39.47 % of the total basin area. Our analyses demonstrate that the proposed GRACE-DSI can serve as a useful tool for integrated drought monitoring and provide a better understanding of drought conditions in major basins in China during 2002–2017

Mitochondrial Dysfunction and Therapeutic Targets in Auditory Neuropathy

Sensorineural hearing loss (SNHL) becomes an inevitable worldwide public health issue, and deafness treatment is urgently imperative; yet their current curative therapy is limited. Auditory neuropathies (AN) were proved to play a substantial role in SNHL recently, and spiral ganglion neuron (SGN) dysfunction is a dominant pathogenesis of AN. Auditory pathway is a high energy consumption system, and SGNs required sufficient mitochondria. Mitochondria are known treatment target of SNHL, but mitochondrion mechanism and pathology in SGNs are not valued. Mitochondrial dysfunction and pharmacological therapy were studied in neurodegeneration, providing new insights in mitochondrion-targeted treatment of AN. In this review, we summarized mitochondrial biological functions related to SGNs and discussed interaction between mitochondrial dysfunction and AN, as well as existing mitochondrion treatment for SNHL. Pharmaceutical exploration to protect mitochondrion dysfunction is a feasible and effective therapeutics for AN

Long-term stability and salt-responsive behavior of polyzwitterionic brushes with cross-linked structure

Long-term stability and salt-responsive behavior of polyzwitterionic brushes with cross-linked structur

Encaging Palladium Nanoparticles in Chitosan Modified Montmorillonite for Efficient, Recyclable Catalysts

Metal nanoparticles, once supported by a suitable scaffolding material, can be used as highly efficient heterogeneous catalysts for numerous organic reactions. The challenge, though, is to mitigate the continuous loss of metals from the supporting materials as reactions proceed, so that the catalysts can be recycled multiple times. Herein, we combine the excellent chelating property of chitosan (CS) and remarkable stability of montmorillonite (MMT) into a composite material to support metal catalysts such as palladium (Pd). The in situ reduction of Pd²⁺ into Pd⁰ in the interstices of MMT/CS composites effectively encages the Pd⁰ nanoparticles in the porous matrices, while still allowing for reactant and product molecules of relatively small sizes to diffuse in and out the matrices. The prepared Pd⁰@MMT/CS catalysts are highly active for the Heck reactions of aromatic halides and alkenes, and can be recycled 30 times without significant loss of activities. Positron annihilation lifetime analysis and other structural characterization methods are implemented to elucidate the unique compartmentalization of metal catalysts in the composite matrices. As both CS and MMT are economical and abundant materials in nature, this approach may facilitate a versatile platform for developing highly recyclable, heterogeneous catalysts containing metal nanoparticles