Does Two-Step Infusion Improve the Pharmacokinetics/Pharmacodynamics Target Attainment of Meropenem in Critically Ill Patients?

The optimal method for administering meropenem remains controversial. This study was conducted to explore the optimal two-step infusion strategy (TIT), and to investigate whether TIT is superior to intermittent infusion therapy (IIT) and prolonged infusion therapy (PIT). A physiologically based pharmacokinetics model for critically ill patients was established and evaluated. The validated model was utilized to evaluate the pharmacokinetics/pharmacodynamics (PK/PD) target attainment of meropenem. The PK/PD target attainment of different TITs varied greatly, and the total infusion duration and the first-step dose greatly affected these values. The optimal TIT was 0.25 g (30 min) + 0.75 g (150 min) at MICs of ≤2 mg/L, and 0.25 g (45 min) + 0.75 g (255 min) at MICs of 4-8 mg/L. The PK/PD target attainment of optimal TIT, PIT, and IIT were 100 % at MICs of ≤1 mg/L. When MIC increased to 2-8 mg/L, the PK/PD target attainment of optimal TIT was similar to that of PIT and higher than IIT. In conclusion, TIT did not significantly improve the PK/PD target attainment of meropenem compared with PIT. IIT is adequate at MICs of ≤1 mg/L, and PIT may be the optimal meropenem infusion method in critically ill patients with MICs of 2-8 mg/L.

Research and engineering practice on space characteristics of gangue slurry filling.

The macroscopic characteristics of the fractured space and the microscopic pore features are critical factors determining the effectiveness of gangue slurry backfilling. To identify the key areas for slurry backfilling, a combination of theoretical analysis, simulation experiments, and on-site industrial trials was used to reveal the movement laws of backfilling space overlying the fractured zone. The distribution characteristics of voids available for slurry backfilling within the fractured space were explored, and the interaction between gangue slurry and goaf voids was clarified. A formula for calculating the void ratio in the caved zone was derived, and a model for the distribution of voids in the slurry backfilling space was established. This model identified the main areas where slurry backfilling should be focused, namely the overlapping space between the free accumulation zone and the load-influenced zone. Experimental results demonstrated that the porosity of the collapsed rock mass within the goaf follows a negative logarithmic function along both the dip and strike directions, which was consistent with the theoretical calculations. Through in-situ grouting backfilling experiments on the ground, the feasibility of gangue slurry backfilling in the goaf was verified, and the process of interaction between gangue slurry and goaf voids was elaborated. This process generally involves three stages: initial flow, vertical upwelling, and horizontal diffusion, all of which are closely interconnected. Practical engineering applications of gangue slurry backfilling were carried out in the free accumulation zone and the load-influenced zone at the Huangling No. 2 coal mine. The successful validation of underground gangue slurry backfilling technology demonstrated its feasibility and the correctness of the theoretical approach. This research provides new evidence for environmentally friendly disposal of gangue materials.

Time-Dependent Rheological Properties of Cemented Aeolian Sand-Fly Ash Backfill Vary with Particles Size and Plasticizer.

The use of cemented Aeolian sand-fly ash backfill (CAFB) material to fill the mining area to improve the surface subsidence damage caused by underground coal mining is in the development stage. Their performance with large overflow water and strength loss is not well understood. Few research has been conducted to understand the effects of aeolian sand and coal gangue on the rheological properties of CAFB with plasticizers. Therefore, this study aims to investigate the effects of a plasticizer on the rheological properties, specifically yield stress and viscosity, of CAFB prepared with aeolian sand and coal gangue. CAFB mixes containing 0%, 0.05%, and 0.1% plasticizers were prepared, and yield stress and viscosity were determined at different intervals. Additional tests, such as thermal analysis and zeta potential analysis, were also conducted. It was found that the rheological properties of CAFB are the comprehensive manifestation of the composite characteristics of various models. Reasonable particle size distribution and less plasticizer can ensure the stability of the slurry structure and reduce the slurry settlement and the risk of pipe blocking. The findings of this study will be beneficial in the design and production of CAFB material.

The Failure Mechanical Properties of Cemented Paste Backfill with Recycled Rubber.

Understanding the mechanical properties and failure process of cemented paste backfill with recycled rubber (RCPB) is the foundation of backfill design in underground mining. In this study, physical and mechanical tests were conducted on RCPB to obtain its mechanical property parameters, such as its uniaxial compressive strength (UCS), toughness, and peak strain. The influence of the rubber dosage on the mechanical properties of RCPB was also analyzed. In addition, the deformation behavior, fracture development, and failure process of RCPB with different rubber contents were observed using the digital image correlation (DIC) technique. The experimental results suggested that, although the UCS of RCPB is reduced as more rubber is added, its toughness and ability to absorb energy is increased. Moreover, the impact resistance of RCPB is improved by this increased toughness. With the increase in the rubber content, the deformation corresponding to the plastic yield stage of RCPB increased, which resulted in better ductility and improved impact resistance. The failure of the RCPB specimens mainly showed an "X" shape. The results of this study help us to better understand the mechanical behavior of RCPB after backfilling underground.

Mechanical properties of cemented tailings backfill with chloride-free antifreeze.

In cold regions with sub-zero surface temperatures, the addition of chloride-free antifreeze (Ca(NO2)2, Ca(NO3)2, and CO(NH2)2) is an inexpensive method to prevent pipeline freezing during cemented tailings backfill (CTB) transport. However, the curing temperature of CTB after reaching the mine cavity tends to be above-zero. The mechanical properties of CTB with a chloride-free antifreeze in above-zero environments have not been investigated. Therefore, this study aimed at thoroughly exploring the effect of chloride-free antifreeze on the mechanical properties of CTB in above-zero environments. CTB samples with chloride-free antifreeze (Ca(NO2)2, Ca(NO3)2, and CO(NH2)2) and different concentrations (0, 5, 15, and 35 g/L) were prepared and cured in different above-zero environments (2, 20, and 35 °C). The unconfined compressive strength tests were performed after 1, 3, 7, and 28 days. In addition, a series of microstructural analyses and monitoring experiments were conducted. The results indicated that the addition of a 15-g/L chloride-free antifreeze decreased the strength of CTB curing at 20 °C after 1, 3, and 7 days and increased the strength after 28 days. Moreover, the CTB strength evolution with the curing time depends on the chloride-free antifreeze concentration and above-zero curing temperature. According to the TG/DTG analyses results, calcium ions had a promoting effect on the carbonation of calcium hydroxide. The findings of this study can provide a guideline for the application of chloride-free antifreeze on the mine backfill in cold regions.

Preparation and performance of composite activated slag-based binder for cemented paste backfill.

The utilization of blast furnace slag (BFS) and fly ash (FA) to replace ordinary portland cement (OPC) has become a hot topic in the preparation of low-cost cemented paste backfill (CPB). This study has prepared a composite activated slag-based binder (CASB) using BFS and FA as the basic raw materials and desulfurization gypsum (DG) and cement clinker (CC) as the activator. The optimum ratio of CASB was determined based on the orthogonal test and the efficacy coefficient method. The hydration products and hydration mechanism of CASB materials were further investigated using XRD, TG, and SEM tests; on this basis, the compressive strength of hardened CASB-CPB under different working conditions and the rheological properties of fresh slurry were investigated, and the cost analysis and environmental effects of CASB were carried out. The results show that the optimum ratio of CASB was 15:12:13:60 for FA: CC: DG: BFS; the hydration mechanism of CASB was the coupled alkali-sulfate activation of CC and DG, and the main hydration products were hydrated calcium silicate gels (C-S-H gels) and ettringite (AFt); increasing the mass concentration (Cw) at a constant cement-aggregate ratio (C/A), which caused a significant improvement in the compressive strength at 7 and 28 d while reduced the flowability of the slurry; CASB considerably reduced the filling cost compared to OPC, and effectively immobilization the heavy metals in the tailings. This paper has developed a cement alternative binder of CASB, which has considerable significance for the comprehensive utilization of solid waste, reduction of filling costs, and improvement of economic and ecological benefits of the mine.

[Effect of clinical experience on the shade matching accuracy].

PURPOSE: To evaluate the effect of clinical experience on the shade matching accuracy. METHODS: Thirty-seven dental students (group A) who had 1 to 2 years of clinical experience and 57 dental students (group B) who didn't have clinical experience took part in this experiment. Participants were divided into two groups (TTB group and TT group) and used the Toothguide Training (TT) and Toothguide Training Box (TTB) respectively. All participants received training session once a week for 3 weeks. Before training and each time after finished training all participants were asked to identify ten unlabeled tabs which had been randomly chosen from Vita 3D-master shadeguide. SPSS 16.0 software package was used for Wilcoxon signed rank test. RESULTS: Before training, the accuracy rate of group A and group B was (65.67±20.4)% and (70.17±17.57)% respectively. After training, the accuracy rate of group A and group B was (78.91±22.82)% and (80.17±17.77)% respectively. No significant difference was found between group A and B, but significant difference was found between before and after training. CONCLUSIONS: This study shows clinical experience is not found to be a significant factor to the teeth shade matching. The training can improve the accuracy of shade matching.