Computational Modeling of Magnesium Hydroxide Precipitation and Kinetics Parameters Identification

Magnesium is a critical raw material and its recovery as Mg(OH)₂ from saltwork brines can be realized via precipitation. The effective design, optimization, and scale-up of such a process require the development of a computational model accounting for the effect of fluid dynamics, homogeneous and heterogeneous nucleation, molecular growth, and aggregation. The unknown kinetics parameters are inferred and validated in this work by using experimental data produced with a T_2mm-mixer and a T_3mm-mixer, guaranteeing fast and efficient mixing. The flow field in the T-mixers is fully characterized by using the k-ε turbulence model implemented in the computational fluid dynamics (CFD) code OpenFOAM. The model is based on a simplified plug flow reactor model, instructed by detailed CFD simulations. It incorporates Bromley's activity coefficient correction and a micro-mixing model for the calculation of the supersaturation ratio. The population balance equation is solved by exploiting the quadrature method of moments, and mass balances are used for updating the reactive ions concentrations, accounting for the precipitated solid. To avoid unphysical results, global constrained optimization is used for kinetics parameters identification, exploiting experimentally measured particle size distribution (PSD). The inferred kinetics set is validated by comparing PSDs at different operative conditions both in the T_2mm-mixer and the T_3mm-mixer. The developed computational model, including the kinetics parameters estimated for the first time in this work, will be used for the design of a prototype for the industrial precipitation of Mg(OH)₂ from saltwork brines in an industrial environment.

Use of Microfluidic Capillary Electrophoresis for the Determination of Multi-Component Protein Adsorption Isotherms: Application to High-Throughput Analysis for Hydrophobic Interaction Chromatography

Chromatography is a widely used separation process for purification of biopharmaceuticals that is able to obtain high purities and concentrations. The phenomena that occur during separation, mass transfer and adsorption are quite complex. To better understand these phenomena and their mechanisms, multi-component adsorption isotherms must be investigated. High-throughput methodologies are a very powerful tool to determine adsorption isotherms and they waste very small amounts of sample and chemicals, but the quantification of component concentrations is a real bottleneck in multi-component isotherm determination. The behavior of bovine serum albumin, Corynebacterium diphtheriae CRM₁₉₇ protein and lysozyme, selected as model proteins in binary mixtures with hydrophobic resin, is investigated here. In this work we propose a new method for determining multi-component adsorption isotherms using high-throughput experiments with filter plates, by exploiting microfluidic capillary electrophoresis. The precision and accuracy of the microfluidic capillary electrophoresis platform were evaluated in order to assess the procedure; they were both found to be high and the procedure is thus reliable in determining adsorption isotherms for binary mixtures. Multi-component adsorption isotherms were determined with a totally high-throughput procedure that turned out to be a very fast and powerful tool. The same procedure can be applied to every kind of high-throughput screening.

Advanced/metastatic bladder cancer: current status and future directions

In 2015 bladder cancer was the fourth most frequent malignancy and the eighth cause of death for cancer. At diagnosis, about 30% of bladder cancer (BC) patients present a muscle-invasive bladder cancer (MIBC) and 5% a metastatic bladder carcinoma (MBC). For fit MBC patients, combination chemotherapy (CC) is the standard of care for first-line treatment. CC includes both the treatment with methotrexate, vinblastine, doxorubicin, and cisplatin (MVAC) either the classical or the dose-dense MVAC regimen, and the doublet therapy with cisplatin and gemcitabine (CG). Median progression free survival (PFS) was 7 months and median overall survival (OS) was 15 months. The present review provides an update on the management of MBC, with focus on target therapies, immune checkpoint inhibition, looking for prognostic and predictive factors.

Penile cancer: prognostic and predictive factors in clinical decision-making

Penile cancer (PC) is a typical tumor of non-industrialized countries. The incidence is 20-30 times higher in Africa and South America, considering the elevated prevalence of sexually transmitted diseases. Histologically, PC includes squamous cell carcinoma (SCPC), the most frequent, and nonsquamous carcinoma (NSCPC). Early diagnosis is the goal, whereas later diagnosis relates to poor functional outcomes and worse prognosis. The 5-year survival rate is 85% for patients with histologically regional negative lymph nodes, compared to 29%-40% for those with histologically regional positive lymph nodes. To date no new drugs are approved, and there are few new data about molecular mechanisms underlying tumorigenesis. The SCPC remains a rare tumor and the current therapeutic algorithm is based principally on retrospective analysis and less on prospective trials. In this review article, biomarkers of prognosis and efficacy of current treatments are summarized with a focus on those that have the potential to affect treatment decision-making in SCPC.

Shear-Induced Heteroaggregation of Oppositely Charged Colloidal Particles

This paper investigates numerically the shear-induced aggregation of mixed populations of colloidal particles leading to the formation of clusters. Suspensions with different amounts of positively and negatively charged colloidal particles are simulated. To resolve the aggregation kinetics and structural properties of the formed clusters, we resort to a mixed deterministic-stochastic simulation method. The method is built on a combination of a Monte Carlo algorithm to sample a statistically expected sequence of encounter events between the suspended particles and a discrete element method built in the framework of Stokesian dynamics to simulate the encounters in a fully predictive manner. Results reveal a strong influence of the composition of the population on both the aggregation kinetics and the aggregate structure. In particular, we observe a size-stabilization phenomenon taking place in the suspension when the relative concentration of the majority particles lies in the range 80-85%; i.e., starting from primary particles, after a short growth period, we observed a cessation of aggregation. Inspection of the aggregate morphology shows that the formed clusters are composed of few minority particles placed in the inner region, while the aggregate surface is covered by majority particles, acting to provide a shielding effect against further growth.

Numerical Methods for the Solution of Population Balance Equations Coupled with Computational Fluid Dynamics

This review article discusses the solution of population balance equations, for the simulation of disperse multiphase systems, tightly coupled with computational fluid dynamics. Although several methods are discussed, the focus is on quadrature-based moment methods (QBMMs) with particular attention to the quadrature method of moments, the conditional quadrature method of moments, and the direct quadrature method of moments. The relationship between the population balance equation, in its generalized form, and the Euler-Euler multiphase flow models, notably the two-fluid model, is thoroughly discussed. Then the closure problem and the use of Gaussian quadratures to overcome it are analyzed. The review concludes with the presentation of numerical issues and guidelines for users of these modeling approaches.

Fluoroquinolone resistance and molecular characterization of gyrA and parC quinolone resistance-determining regions in Escherichia coli isolated from poultry

Escherichia coli are a common inhabitant of the gastrointestinal tract of mammals and birds; nevertheless, they may be associated with a variety of severe and invasive infections. Whereas fluoroquinolones (FQ) have been banned in the United States for use in poultry production, the use of these antimicrobials in poultry husbandry is still possible in the European Union, although with some restrictions. The aim of this study was to investigate the FQ resistance of 235 E. coli isolates recovered from chickens and turkeys. Minimum inhibitory concentrations were determined by a microdilution method, whereas mutations in the quinolone resistance-determining regions of the target genes, gyrA and parC, were detected by a PCR-based method. High resistance rates (>60%) were observed for nalidixic acid, flumequine, and difloxacin, whereas resistance to ciprofloxacin, danofloxacin, enrofloxacin, marbofloxacin, and sarafloxacin was less frequently reported (<40%). Sixty-four isolates (27.2%) showed full susceptibility toward the tested FQ, but 57 isolates (24.2%) were resistant to all tested FQ. The remaining 114 E. coli isolates (48.5%) were grouped in 5 different resistance patterns. Isolates resistant only to flumequine or nalidixic acid or both possessed 1 gyrA mutation, whereas isolates with further resistance to enrofloxacin, difloxacin, danofloxacin, and sarafloxacin had in addition 1 or 2 parC substitutions. Two gyrA mutations coupled with 1 substitution in parC were detected in isolates resistant to all tested FQ. The number of mutations and their correlation with the in vitro activity of FQ reflected the currently accepted model, according to which a single gyrA substitution is associated with resistance or decreased susceptibility to older quinolones, whereas further gyrA or parC substitutions are needed for a higher level of resistance.

Hydrodynamic forces and critical stresses in low-density aggregates under shear flow

The distribution of stresses in rigid colloidal aggregates under a shear flow was investigated numerically for particle-cluster and cluster-cluster aggregates with fractal dimensions ranging from 1.7 to 2.3. stokesian dynamics was used to calculate the hydrodynamic force on each monomer, while the internal intermonomer interactions were calculated by applying force and torque balances on each primary particle. Although the hydrodynamic forces act mainly on the periphery of the clusters, their filamentous structure propagates and accumulates internal stresses toward the inner region of the aggregates, where consequently the most loaded intermonomer bonds are located. The spatial stress distribution, when scaled by the proper power of the radius of gyration, is independent of aggregate size and fractal dimension. This feature has made it possible to identify the most probable locations of bond failure in the structure and to estimate the relationship between shear rate and particle size for the occurrence of restructuring and of breakage.

Antimicrobial susceptibility of Staphylococcus intermedius and Staphylococcus schleiferi isolated from dogs

The susceptibility to 23 antimicrobial agents was determined in 114 isolates of Staphylococcus intermedius and eight isolates of Staphylococcus schleiferi of canine origin. Overall, 73% of S. intermedius isolates and 37.5% of S. schleiferi isolates were susceptible to all the 23 antimicrobials tested. The large majority of S. intermedius strains retained susceptibility to antimicrobials currently employed in treatment of pyoderma (cephalosporins, cotrimoxazole and association amoxicillin-clavulanic acid) as well as to those effective against staphylococci (fusidic acid, rifampicin and fluoroquinolones). Resistance in S. intermedius was observed mainly against macrolides, chloramphenicol and lincosamides, while S. schleiferi isolates retained susceptibility to all antimicrobials except three of six fluoroquinolones. Although, our results confirm susceptibility to antimicrobials currently employed in pyoderma treatment, the several different resistance patterns observed for S. intermedius emphasize the importance of antimicrobial susceptibility testing of canine staphylococci to choose the most appropriate treatment of infections and to allow the prudent use of antimicrobial drugs in companion animals.

Antimicrobial susceptibility and mechanism of resistance to fluoroquinolones in Staphylococcus intermedius and Staphylococcus schleiferi

The objective of the present study was to determine the antimicrobial susceptibility of 136 canine isolates of Staphylococcus intermedius and 10 canine isolates of S. schleiferi subspecies coagulans to 16 fluoroquinolones (FQs), and to investigate the mechanisms of resistance in the nonsusceptible isolates. Of the 136 of S. intermedius tested 98.5% were susceptible to all 16 FQs whereas only 40% of the 10 isolates of S. schleiferi subspecies coagulans were susceptible. Two isolates of S. intermedius and six isolates of S. schleiferi, were found to be resistant to 13 out of 16 FQs, while they retained their susceptibility to fourth generation FQs such as gatifloxacin, moxifloxacin and trovafloxacin. Sequencing of the quinolone-resistance determining regions of gyrA and grlA genes showed that in S. intermedius, dichotomous resistance to FQs was associated with the occurrence of one alteration in GyrA-84 and one in GrlA-80, while in S. schleiferi the same pattern of resistance was observed in isolates showing these changes only in gyrA. This study is the first to screen FQs of the second, third and fourth generation for antimicrobial resistance in clinical isolates of S. intermedius and S. schleiferi of canine origin, and to describe mutations in gyrA and grlA associated with FQ resistance in these bacterial species.

Short-term ursodeoxycholic acid treatment improves gallbladder bile turnover in gallstone patients: a randomized trial

Ursodeoxycholic acid (UDCA) prevents in vitro gallbladder (GB) muscle damage caused by acute cholecystitis and reduces risk of biliary pain and complications in gallstone (GS) patients. These effects could be partially explained by the improved GB bile turnover.

OBJECTIVES

To assess the effect of short-term UDCA treatment on GB motility and bile turnover.

METHODS

Ultrasonographic (US) assessment of GB volumes was performed in 16 GS patients, in the postprandial phase, for 90 min with a time sampling of 1 min, before and after 30 days of UDCA (10 mg kg(-1) die(-1)) or placebo, randomly assigned. US data were analysed with statistical tools and with computer fluido-dynamic (CFD) software Fluent(TM) to simulate GB bile flow.

RESULTS

After therapy, fasting volume (FV) increased from 21.6 +/- 9 to 28.2 +/- 12 mL (p < 0.001) while the ejection fraction (EF) remained unchanged (44.5 +/- 17% vs 45.1 +/- 20%; p: ns). Volumes before and after treatment were poorly correlated (0.02 < r < 0.35), unlike those in placebo patients (r > 0.6). The average GB volume was increased in 7 out of 10 patients following UDCA (range 7-67%). CFD analysis supports the finding of improved bile flow after treatment.

CONCLUSIONS

Unlike results of conventional US parameters of GB motility, CFD analysis shows that UDCA improves GB bile turnover in GS patients.

Fluid Dynamics Modeling of Particulate Deposition in the Lungs

Detailed knowledge of the transport of air and particles in the human lungs is needed for two reasons: the selection of the right dosage of aerosol drugs used in respiratory therapy and the analysis of the maximum allowable concentration for particulate in air. This work is the first step of a more complex study, purpose of which is to provide some predictive relationships in order to evaluate the depth reached by the particles in the lungs as a function of their size using numerical modeling. In this phase we validated our numerical method, comparing the obtained results with those found in the literature. The Computational Fluid Dynamics code FLUENT 6 with the Eulerian-Lagrangian approach was used to simulate particle trajectories. A model of double bifurcation, based on the morphometric studies by Weibel and Hammersley and Olson, was adopted in order to represent the whole central part of the respiratory system with the same geometry, appropriately scaled down. A method to create a realistic velocity profile at the inlet of the domain was developed, in order to obtain data about particle deposition also reliable about the first bifurcation, unlike previous works.

Extension of the method of moments for population balances involving fractional moments and application to a typical agglomeration problem

The method of moment (MOM) is a powerful tool for solving population balance. Nevertheless it cannot be used in every circumstance. Sometimes, in fact, it is not possible to write the governing equations in closed form. Higher moments, for instance, could appear in the evolution of the lower ones. This obstacle has often been resolved by prescribing some functional form for the particle size distribution. Another example is the occurrence of fractional moment, usually connected with the presence of fractal aggregates. For this case we propose a procedure that does not need any assumption on the form of the distribution but it is based on the "moments generating function" (that is the Laplace transform of the distribution). An important result of probability theory is that the kth derivative of the moments generating function represents the kth moment of the original distribution. This result concerns integer moments but, taking in account the Weyl fractional derivative, could be extended to fractional orders. Approximating fractional derivative makes it possible to express the fractional moments in terms of the integer ones and so to use regularly the method of moments.

Familial Axenfeld-Rieger anomaly, cardiac malformations, and sensorineural hearing loss: a provisionally unique genetic syndrome?

Axenfeld-Rieger anomaly (ARA) is an autosomal dominant disorder of the anterior chamber of the eye that includes a prominent and anteriorly displaced Schwalbe line and an iridocorneal synechiae, and is associated with iris hypoplasia, corectopia, and hole formation. Extraocular developmental abnormalities, especially of the teeth, facial bones, and periumbilical skin, have also been reported with ARA, in the context of the so-called Axenfeld-Rieger syndrome (ARS). Genetic heterogeneity exists, as ARA maps to chromosome 6p25, whereas ARS can be linked to both chromosome 4q25 and chromosome 13q14. Here we describe a new family in which ARA is associated with cardiac malformations and sensorineural hearing loss. No abnormalities of the teeth, facial bone, or periumbilical skin, which are considered of paramount importance in the diagnosis of ARS, were observed in our patients. Genetic studies will clarify if these patients represent a unique phenotypic expression of ARS or constitute the clinical presentation of a new genetic syndrome.

Coagulation efficiency of colloidal particles in shear flow

The mechanism of shear-induced coagulation of colloidal particles is reviewed, in order to define a method to evaluate the collision efficiency according to the present knowledge of the phenomenon. Therefore, a detailed description of the procedure for trajectory analysis and identification of collision is presented, as well as of the role and estimation of colloidal forces. Recent analytical expressions have been adopted for the Van der Waals interaction, that are based on the Lifshitz theory of dispersion forces and that are capable of considering ionic screening. The obtained results have been compared with those of older expressions for the dispersion force. The two formulations agree fairly well for the case of strongly destabilised systems; on the contrary, they may lead to significantly different results for slow coagulation. The proposed method results in a fully predictive procedure for estimating collision efficiency. The results have been compared favourably with experimental data concerning the system polystyrene-water for the regime of fast coagulation. Finally, the transition between primary and secondary coagulation has been analysed in detail and it has been shown that, in the fast coagulation regime, the type of coagulation depends only on surface potential and ionic strength, but not on particle size and shear rate.

Approximate Population Balance Equations for Aggregation-Breakage Processes

A number of approximate methods for modeling aggregation of particulate suspensions have been extended to simulate breakup as well and have been tested by comparison with rigorous solutions for conditions representative of most aggregation-fragmentation processes. The simplest methods, based on a geometric discretization with size ratio equal to two, can calculate satisfactorily the average values of the population for particularly well-conditioned situations only and, even in those cases, are not capable of predicting the shape of the particle size distribution. Therefore more complex methods are usually required, capable of using denser size discretization. The characteristics of these models and the guidelines for their choice are discussed in the paper, by considering their accuracy, ability to produce error estimates, ease of implementation and speed. Copyright 2000 Academic Press.