Power and sample sizes estimation in clinical trials with treatment switching in intention-to-treat analysis: a simulation study.

BACKGROUND: Treatment switching, also called crossover, is common in clinical trials because of ethical concerns or other reasons. When it occurs and the primary objective is to identify treatment effects, the most widely used intention-to-treat analysis may lead to underpowered trials. Here, we presented an approach to preview power reductions and to estimate sample sizes required to achieve the desired power when treatment switching occurs in the intention-to-treat analysis. METHODS: We proposed a simulation-based approach and developed an R package to perform power and sample sizes estimation in clinical trials with treatment switching. RESULTS: We simulated a number of randomized trials incorporating treatment switching and investigated the impact of the relative effectiveness of the experimental treatment to the control, the switching probability, the switching time, and the deviation between the assumed and the real distributions for the survival time on power reductions and sample sizes estimation. The switching probability and the switching time are key determinants for significant power decreasing and thus sample sizes surging to maintain the desired power. The sample sizes required in randomized trials absence of treatment switching vary from around four-fifths to one-seventh of the sample sizes required in randomized trials allowing treatment switching as the switching probability increases. The power reductions and sample sizes increase with the decrease of switching time. CONCLUSIONS: The simulation-based approach not only provides a preview for power declining but also calculates the required sample size to achieve an expected power in the intention-to-treat analysis when treatment switching occurs. It will provide researchers and clinicians with useful information before randomized controlled trials are conducted.

Improvement of the reduction of condensable particulate matter in flue gas scrubbing process.

Condensable particulate matter (CPM) is characterized by complex composition, non-negligible emission concentration, and fine or ultrafine in size after conversion to particles, which is difficult to remove. Current methods to control CPM are not fully developed and mainly focus on synergistic removal of CPM in existing air pollution control devices, such as CPM reduction through scrubbing processes in wet flue gas desulfurization (WFGD) systems. In this work, an experimental system including a simulated WFGD scrubber, also referred to as the primary scrubber (PS), and a secondary scrubber (SS) was built to explore measures to improve the CPM reduction performance during scrubbing. The operating parameters of the liquid-to-gas (L/G) ratio and the spray temperature in the two scrubbers were tuned in the experiments. The results indicated that CPM could be reduced in the PS by conversion to filterable particulate matter (FPM), and captured by the spray droplets through the effects of dissolution and condensation, but the reduction was not very efficient. In the SS, the reduction performance of CPM could be further improved due to increased dissolution of CPM caused by increased opportunities for gas-liquid contact, and increased condensation of CPM due to lower spray temperature. The FPM transformed from the CPM in the PS could also be reduced in the SS by the effects of diffusiophoresis and thermophoresis contributed by water vapor condensation. An increase in the L/G ratio could improve the CPM reduction.

Method of smoldering combustion for the treatment of oil sludge-contaminated soil.

There is an urgent need to globally remediate oil sludge-contaminated soil (OSS). Smoldering combustion is a new low-energy approach for the treatment of organic waste. Therefore, the feasibility of smoldering combustion for the treatment of OSS was investigated in this study using a series of laboratory-scale experiments. The effective remediation of OSS was found to be achievable when the mass ratio of oil sludge in the sample reached 1/12 and above. Experimental results showed that smoldering at peak temperatures above 500 °C was found to completely remove petroleum hydrocarbons from the samples. The mass ratio of oil sludge in the sample had little effect on the distribution of the major elements (Si, Al, and Ca) in the smoldering products, and most of the minerals in the oil sludge adhered to the surface of the soil particles after smoldering. The smoldering heating environment is detrimental to the reusability of the soil, increases soil pH and available phosphorus content, and decreases organic carbon and total nitrogen content. Moreover, the influence of the airflow rate and material height on smoldering characteristics was investigated. Matching the appropriate airflow rate can help maintain optimal smoldering conditions, and smoldering remains stable with increasing material height. The addition of recovered oil to a sample with a low mass ratio of oil sludge can help with smoldering ignition and improve the removal efficiency of petroleum hydrocarbons. This study has confirmed that smoldering can be used to treat OSS within a broad range of oil sludge concentrations without pretreatment.

Distribution of the existence forms of condensable particulate matter during condensation: The surface collection and the space suspension forms.

Condensable particulate matter (CPM), as an air pollutant that has received wide attention in recent years, has a high emission concentration compared to filterable particulate matter (FPM), yet there is not a well-developed removal method. Air pollution control devices (APCDs) with a condensation process have a certain effect on CPM removal, which inspired us to study the condensation behavior of CPM. During the condensation process, the condensed CPM may exist in two final forms: one was collected by the cold surface that caused the condensation; the other was converted to fine particles and suspended in the space of the flue. In a sense, the surface collection form can reflect the removal of CPM, while the CPM in the space suspension form should be further separated with the aim of removal. In this work, we adopted a CPM sampling system based on EPA Method 202 to reveal the distribution of the condensation behavior of CPM. In this sampling system, the CPM collected by all the cooling surfaces, including the cooling coil and impingers, can be counted as the surface collection form, while those collected by the terminal CPM filter can be regarded as the space suspension form. It was found that about 75 % of CPM was collected by the cooling surfaces, which suggested that CPM preferred to be in the surface collection form than the space suspension form. This preference characteristic also could be observed in the inorganic (CPMi) and organic components of the CPM (CPMo). Among the CPMi, almost all NH4+ and SO42- condensed in the form of surface collection. The preference characteristics in CPM's (and its components') condensation behavior are similar under every temperature reduction condition. In this work, the interference of CPM measurement error was resolved by the statistical method of ANOVA.