Reactive Crystallization Kinetics of K2SO4 from Picromerite-Based MgSO4 and KCl

In this work, the kinetic parameters, the degrees of initial supersaturation (S0) and the profiles of supersaturation (S) were determined for the reactive crystallization of K2SO4 from picromerite (K2SO4.MgSO4.6H2O) and KCl. Different reaction temperatures between 5 and 45 °C were considered, and several process analytical techniques were applied. Along with the solution temperature, the crystal chord length distribution (CLD) was continuously followed by an FBRM probe, images of nucleation and growth events as well as the crystal morphology were captured, and the absorbance of the solution was measured via ATR-FTIR spectroscopy. In addition, the ion concentrations were analyzed. It was found that S0 is inversely proportional to the reactive crystallization temperature in the K+, Mg2+/Cl−, SO42−//H2O system at 25 °C, where S0 promotes nucleation and crystal growth of K2SO4 leading to a bimodal CLD. The CLD was converted to square-weighted chord lengths for each S0 to determine the secondary nucleation rate (B), crystal growth rate (G), and suspension density (MT). By correlation, from primary nucleation rate (Bb) and G with S0, the empirical parameters b = 3.61 and g = 4.61 were obtained as the order of primary nucleation and growth, respectively. B versus G and MT were correlated to the reaction temperature providing the rate constants of B and respective activation energy, E = 69.83 kJ∙mol−1. Finally, a general Equation was derived that describes B with parameters KR = 13,810.8, i = 0.75 and j = 0.71. The K2SO4 crystals produced were of high purity, containing maximal 0.51 wt% Mg impurity, and were received with ~73% yield at 5 °C

QSPR Models for Octane Number Prediction

Quantitative structure-property relationship (QSPR) is performed as a means to predict octane number of hydrocarbons via correlating properties to parameters calculated from molecular structure; such parameters are molecular mass M, hydration energy EH, boiling point BP, octanol/water distribution coefficient logP, molar refractivity MR, critical pressure CP, critical volume CV, and critical temperature CT. Principal component analysis (PCA) and multiple linear regression technique (MLR) were performed to examine the relationship between multiple variables of the above parameters and the octane number of hydrocarbons. The results of PCA explain the interrelationships between octane number and different variables. Correlation coefficients were calculated using M.S. Excel to examine the relationship between multiple variables of the above parameters and the octane number of hydrocarbons. The data set was split into training of 40 hydrocarbons and validation set of 25 hydrocarbons. The linear relationship between the selected descriptors and the octane number has coefficient of determination (R2=0.932), statistical significance (F=53.21), and standard errors (s =7.7). The obtained QSPR model was applied on the validation set of octane number for hydrocarbons giving RCV2=0.942 and s=6.328.</jats:p

Posttraumatic Stress Disorder Symptoms and Incarceration: The Impact on Sexual Risk-Taking, Sexually Transmitted Infections, and Depression Among Black Sexual Minority Men in HIV Prevention Trials Network (HPTN) 061

Black men and people belonging to sexual minority groups are disproportionately impacted by criminal legal involvement and sexually transmitted infections (STIs). Traumatic experiences are often associated with later criminal legal involvement, depression symptoms, sexual risk behavior, and STIs. Research on the joint influence of trauma and incarceration on STI risk among racial and/or sexual minority people is limited. This study tested the association between post-traumatic stress disorder (PTSD) symptoms and incarceration on sexual risk behavior and STI among Black sexual minority men, a population that may be at higher risk for contracting STIs. Using data from the HIV Prevention Trials Network 061 Study, a longitudinal study of adult Black sexual minority men in six U.S. cities (N = 855), we tested associations between past six-month incarceration and subsequent sexual risk behavior, STI, and depression symptoms, for those with and without pre-incarceration PTSD symptoms. PTSD symptoms were elevated among participants who reported Hispanic ethnicity, having sex with both men and women, and previous incarceration. Although there were not significant differences between recent incarceration and sexual risk for those with and without PTSD, incarceration was linked to some sexual risk behaviors regardless of PTSD symptoms. Among people with PTSD symptoms, there was a higher prevalence of sexual risk and depression symptoms, regardless of incarceration. These findings suggest a potentially compounding influence of PTSD symptoms and incarceration on sexual risk and infection among Black sexual minority men

Triple Co-Administration of Ivermectin, Albendazole and Praziquantel in Zanzibar: A Safety Study

This paper describes how the use of three drugs which are used separately in mass drug distribution programmes when given together appear safe for use in large populations which have been previously treated with the same drugs separately (Mectizan [ivermectin], albendazole and praziquantel). The target diseases—lymphatic filariasis, soil-transmitted worms and schistosomiasis—were prevalent in Zanzibar up to 2000 but have been largely controlled by mass drug administration. The Ministry of Health and Social Welfare, with the support of WHO, initiated a small scale trial in a population of triple therapy in over 5,000 people initially in two sites, and having found there were no severe adverse events associated with the combined treatment then upscaled to treat the whole of the eligible population of over 700,000. Similarly, there were no severe adverse events. This is the first time the three drugs have been used together at the same time at scale in Africa and provide a basis for expansion of integrated preventive chemotherapy of helminths (worms). The next steps need to be initiated in populations which have heavier worm loads and such interventions need to be subject to close monitoring and ethical review

Defining organizational contributions to sustaining an ageing workforce:a bibliometric review

The ageing of populations worldwide has implications for workforces in developed countries, and labour shortages have increasingly become a political concern. Governments in developed countries have responded by increasing the retirement age as a strategy for overcoming the fall in labour supply. Using bibliometric techniques, we reviewed 122 articles published between 1990 and 2018 to examine the effectiveness of the strategy in addressing the labour shortages and, in particular, to identify the factors that contribute positively to maintaining worker participation within an ageing workforce at an organizational level. The results identified five organizational factors that support continued participation: health, institutions, human resource management, human capital and technology tools. Employers will increasingly need to develop “age-friendly” workplaces and practices if they are to recruit and retain older workers.</p

DESCRIPCIÓN DEL CURSO DE CÁLCULO DIFERENCIAL DE AIMÉ BERGERON EN EL COLEGIO MILITAR

En este trabajo hacemos la descripción de un manuscrito, que reposa en la Biblioteca Nacional de Colombia, el cual contiene las notas de Sixto T. Barriga tomadas en el curso de cálculo diferencial, dictado en el Colegio Militar por Aimé Bergeron, en 1851. La importancia de este manuscrito estriba en que documenta de manera incontestable la enseñanza del cálculo en Colombia a nivel universitario, en el siglo XIX, aunque no podernos afirmar que se trate de la primera vez que esta materia se hubiese enseñado en el país. Recalcamos, así mismo, la hipótesis de que la edición de textos por parte de los profesores del Colegio Militar era parte de una política institucional, inspirada posiblemente en las influencias francesas en su estructura y funcionamiento