Independent Repetitions Research Articles

Effect of peeling, cutting, or shredding of lettuce, carrot, or potato on the efficacy of chlorine disinfection.

Minimally processed vegetables are washed and subsequently disinfected by immersion in water solutions with antimicrobials which reduce the initial pathogenic or spoilage microbial load. Chlorine remains one of the most widely used disinfectants for vegetables and hence the importance of studying its properties. The aim of this study was to evaluate the effect of peeling, cutting, and shredding on the effectiveness of chlorine (200 ppm) as a disinfectant in lettuce, carrot, and potato. Three independent repetitions of each experiment were completed, and data was statistically analyzed. Results showed that the maintenance of the chlorine concentration in the disinfectant solution, over time, depended on the vegetables' preliminary processing technique (whole, peeled, cut, or shredded) (p < 0.05). In general, the disinfection treatments studied reduced Escherichia coli by 1-8 logs. The addition of chlorine in the disinfectant solution allowed greater reduction in E. coli than using water immersions (p < 0.05) and disinfection times longer than 5 min did not improve these microbiological reductions (p>0.05). The vegetables' subdivision (whole, peeled, cut, or shredded) can affect both E coli's reduction and the vegetables' residual chlorine concentration. No trend was observed in terms of sensory differences and their relationship to the vegetables' processing and disinfection. These results suggest that each facility must validate its disinfection processes, according to the conditions established on site and reduction goals related to initial microbial counts, vegetables' quality, processing operations, and other important aspects.

Staphylococcus epidermidis biofilm assembly and self-dispersion: bacteria and matrix dynamics.

Staphylococcus epidermidis, despite being a commensal of human skin and mucosa, is a major nosocomial pathogen implicated in device-associated infections. The dissemination of infection to other body sites is related to biofilm dispersal. This study focused on the dispersion stage of S. epidermidis CIP 444 biofilm, with the assessment of biofilm matrix composition in a time-dependent experiment (7days extended) with 3 independent repetitions, using confocal laser scanning microcopy (CLSM) in association with ZEN 3.4 blue edition, COMSTAT, and ImageJ software. SYTO-9, propidium iodide (PI), DID'OIL, FITC, and calcofluor white M2R (CFW) were used to stain biofilm components. The results indicated that the biomass of dead cells increased from 15.18 ± 1.81 µm3/µm2 (day 3) to 23.15 ± 6.075 µm3/µm2 (day 4), along with a decrease in alive cells' biomass from 22.75 ± 2.968 µm3/µm2 (day 3) to 18.95 ± 5.713 µm3/µm2 (day 4). When the intensities were measured after marking the biofilm components, in a 24-h-old biofilm, polysaccharide made up the majority of the investigated components (52%), followed by protein (18.9%). Lipids make up just 11.6% of the mature biofilm. Protein makes up the largest portion (48%) of a 4-day-old biofilm, followed by polysaccharides (37.8%) and lipids (7.27%). According to our findings, S. epidermidis CIP 444 dispersion occurred on day 4 of incubation, and new establishment of the biofilm occurred on day 7. Remarkable changes in biofilm composition will pave the way for a new approach to understanding bacterial strategies inside biofilms and finding solutions to their impacts in the medical field.

Microbiota of vaccinated and non-vaccinated clinically inconspicuous and conspicuous piglets under natural Lawsonia intracellularis infection.

Lawsonia (L.) intracellularis is a widespread, economically important bacterium causing the porcine proliferative enteropathy (PPE). In this study, we evaluated intestinal microbiota of naturally exposed L. intracellularis-positive pigs under standardized conditions. To obtain three independent repetitions, 27 L. intracellularis-infected pigs (19.0 ± 1.50 kg body weight) from one farm were divided into three groups at an age of 7 to 8 weeks (nine pigs/group). Pigs were either vaccinated against L. intracellularis via oral drenching on their 21st day of life (attenuated live vaccine) or non-vaccinated and selected according to clinical findings (pigs without deviating fecal consistency or with moderate to soft fecal consistency). Comparison of the clinically inconspicuous piglets that differed regarding their vaccination status showed fewer significant differences in fecal microbiota composition. The vaccination led to an overall enrichment of bacterial species belonging to the order Clostridiales, while species of the genus Collinsella and Prevotella were decreased. Several bacterial species belonging to the order Bacteroidales, mainly of the family Prevotellacecae, often closely matching Prevotella copri differed significantly between non-vaccinated clinically inconspicuous and conspicuous piglets. Whether those bacterial species play a role in mitigating the severity of an L. intracellularis infection remains to be defined.

Repetitions of fundamental research models for homeopathically prepared dilutions beyond 10-23: a bibliometric study

Introduction: Repeatability of experiments is an important criterion of modern research and a major challenge for homeopathic basic research. There is a lack of a recent overview about basic research studies in high homeopathic potencies that have been subjected to laboratory-internal, multicenter or independent repetition trials. Methods: We considered biochemical, immunological, botanical, cell biological and zoological studies on high potencies, i.e. beyond a dilution of 10-23. Main sources of information were reviews, personal contact with members of the homeopathic basic research community, and the MEDLINE and HOMBREX databases. Studies were extracted from the publications and grouped into models. Studies were further sorted according to repetition type (laboratory-internal, multicenter, or independent) and results achieved. Results: A total of 107 studies have been found. From these, 30 were initial studies. In the attempt to reproduce one of these initial studies, 53 follow up studies yielded comparable effects (35 laboratory-internal, 8 multicenter, 10 independent repetitions), eight studies showed a consistent, yet different result from the initial study (2 laboratory-internal, 2 multicenter, 4 independent repetitions), and 16 studies yielded zero effects (5 laboratory-internal, 2 multicenter, 9 independent repetitions). When all repetitive studies are considered, 69% reported effects comparable to that of the initial study, 10% different effects, and 21% zero effects. Independently performed repetition studies reported 44% comparable effects, 17% different effects, and 39% zero effects. Conclusions: We identified 24 experimental models in basic research on high homeopathic potencies, which were repeatedly investigated. 22 models were reproduced with comparable results, 6 models with different results, and repetition showed no results for 15 models. Independent reproductions with either comparable or different results were found for seven models. We encourage further repetition trials of published studies, in order to learn more about the model systems used and in order to test their repeatability

Assessment of the Effect of Thermotherapy on 'Candidatus Liberibacter asiaticus' Viability in Woody Tissue of Citrus via Graft-Based Assays and RNA Assays.

In 2019, citrus production in Florida declined by more than 70%, mostly because of Huanglongbing (HLB), which is caused by the bacterium 'Candidatus Liberibacter asiaticus' (CLas). Thermotherapy for HLB-affected trees was proposed as a short-term management solution to maintain field productivity. It was hypothesized that thermotherapy could eliminate HLB from affected branches; therefore, the study objectives were to show which time-temperature combinations eliminated CLas from woody tissues. Hardening, rounded Valencia twigs collected from HLB-affected field trees were treated in a steam chamber at different time-temperature combinations (50°C for 60 s; 55°C for 0, 30, 60, 90, and 120 s; 60°C for 30 s; and an untreated control). Three independent repetitions of 13 branches per treatment were grafted onto healthy rootstocks and tested to detect CLas after 6, 9, and 12 months. For the RNA-based CLas viability assay, three branches per treatment were treated and bark samples were peeled for RNA extraction and subsequent gene expression analyses. During the grafting study, at 12 months after grafting, a very low frequency of trees grafted with twigs treated at 55°C for 90 s and 55°C for 120 s had detectable CLas DNA. In the few individuals with CLas, titers were significantly lower (P ≤ 0.0001) and could have been remnants of degrading DNA. Additionally, there was a significant decrease (P ≤ 0.0001) in CLas 16S rRNA expression at 55°C for 90 s, 55°C for 120 s, and 60°C for 30 s (3.4-fold change, 3.4-fold change, and 2.3-fold change, respectively) in samples 5 days after treatment. Heat injury, not total CLas kill, could explain the limited changes in transcriptional activity; however, failed recovery and eventual death of CLas resulted in no CLas detection in most of the grafted trees treated with the highest temperatures or longest durations.

On the use of repeated measurement errors in linear regression models

In a linear mean regression setting with repeated measurement errors, we develop asymptotic properties of a naive estimator to better clarify the effects of these errors. We then construct a group of unbiased estimating equations with independent repetitions and make use of these equations in two ways to obtain two estimators: a weighted averaging estimator and an estimator based on the generalized method of moments. The proposed estimators do not require any additional information about the measurement errors. We also prove the consistency and asymptotic normality of the two estimators. Our theoretical results are verified by simulation studies and a real data analysis.

Delineation of Soil Texture Suitability Zones for Soybean Cultivation: A Case Study in Continental Croatia

Soil texture is a vital criterion in most cropland suitability analyses, so an accurate method for the delineation of soil texture suitability zones is necessary. In this study, an automated method was developed and evaluated for the delineation of these zones for soybean cultivation. A total of 255 soil samples were collected in the Continental biogeoregion of Croatia. Three methods for interpolation of clay, silt and sand soil content were evaluated using the split-sample method in five independent random repetitions. An automated algorithm for soil texture classification based on the United States Department of Agriculture (USDA) in 12 classes was performed using Python script. Suitability classes for soybean cultivation per soil texture class were determined according to previous agronomic and soybean land suitability studies. Ordinary kriging produced the highest accuracy of tested interpolation methods for clay, silt and sand. Highly suitable soil texture classes for soybean cultivation, loam and clay loam, were detected in the northern part of the study area, covering 5.73% of the study area. The analysis of classification results per interpolation method indicated a necessity of the evaluation of interpolation methods as their performance depended on the normality and stationarity of input samples.

Kinetic Cytokine Secretion Profile of LPS-Induced Inflammation in the Human Skin Organ Culture.

Several in vitro models that mimic different aspects of local skin inflammation exist. The use of ex vivo human skin organ culture (HSOC) has been reported previously. However, comprehensive evaluation of the cytokine secretory capacity of the system and its kinetics has not been performed. Objective: the aim of the current study was to investigate the levels and secretion pattern of key cytokine from human skin tissue upon lipopolysaccharide (LPS) stimulation. HSOC maintained in an air–liquid interface was used. Epidermal and tissue viability was monitored by MTT and Lactate Dehydrogenase (LDH) activity assay, respectively. Cytokine levels were examined by ELISA and multiplex array. HSOCs were treated without or with three different LPS subtypes and the impact on IL-6 and IL-8 secretion was evaluated. The compounds enhanced the secreted levels of both cytokines. However, differences were observed in their efficacy and potency. Next, a kinetic multiplex analysis was performed on LPS-stimulated explants taken from three different donors to evaluate the cytokine secretion pattern during 0–72 h post-induction. The results revealed that the pro-inflammatory cytokines IL-6, IL-8, TNFα and IL-1β were up-regulated by LPS stimuli. IL-10, an anti-inflammatory cytokine, was also induced by LPS, but exhibited a different secretion pattern, peak time and maximal stimulation values. IL-1α and IL-15 showed donor-specific changes. Lastly, dexamethasone attenuated cytokine secretion in five independent repetitions, supporting the ability of the system to be used for drug screening. The collective results demonstrate that several cytokines can be used as valid inflammatory markers, regardless of changes in the secretion levels due to donor’s specific alterations.

Optimization of a Quantitative Real-Time RT-PCR Technique for Evaluation of Concentration of Genomic +RNA of Tick-Borne Encephalitis Virus

Background. The specific detection of genomic/template +RNA and replicative –RNA of tick-born encephalitis virus (TBEV) is necessary to study the mechanisms of viral replication in the cells of reservoir and accidental hosts. However, the current approaches of quantitative reverse transcription – polymerase chain reaction (qRT-PCR) are rather focused on the detection of total viral RNA load in the sample. Thus, the significant optimization is necessary both for RT-PCR and for RNA copy number standard preparation.Aims. To develop the set of standard samples of synthetic +RNA of TBEV and to optimize qRT-PCR for quantification of genomic +RNA of the virus.Materials and methods. Fragment of the genomic +RNA of TBEV was synthesized using pTZ57R-T\A plasmid vector with embedded T7 promoter and T7 RNA polymerase. The DNA contamination was removed using RNase-free DNase I treatment followed by additional RNA purification step. Reverse transcription was performed using specific antisense primer 11154R 5`- AGCGGGTGTTTTTCCG-3` and qPCR detection was used according to the modified procedure of M. Schwaiger and P. Cassinotti (2003).Results. As a result of the amplification of standard samples, the concentration of positive polarity ТBEV RNA, carried out in five independent repetitions on different days, the correlation coefficient R2 between the quantification cycle and the concentration of the standard sample was 0.99, and the efficiency of PCR was 100 %. The coefficient of variation in assessing the inter-test accuracy of determination averaged 2.8 %.Conclusions. Optimized qRT-PCR procedure and set of +RNA standards allow to determine the concentration of genomic +RNA of TBEV in routine laboratory practice.

Effect of Selected Nonsteroidal Anti-inflammatory Drugs on the Viability of Canine Osteosarcoma Cells of the D-17 Line: In Vitro Studies.

IntroductionNon-steroidal anti-inflammatory drugs (NSAIDs) are widely used in veterinary medicine. They are used in pain control and in anti-inflammatory and antipyretic therapies. Some NSAIDs, e.g piroxicam, also have a documented anticancer effect. The objective of this study was to evaluate which of the commonly used NSAIDs (etodolac, flunixin, tolfenamic acid, carprofen, and ketoprofen) are cytotoxic to the D-17 cell line of canine osteosarcoma.Material and MethodsThe viability of the cells was evaluated using the MTT assay. Four independent repetitions were performed and the results are given as the average of these values; EC50 values (half maximal effective concentration) were also calculated.ResultsThe analysis of results showed that carprofen and tolfenamic acid displayed the highest cytotoxicity. Other drugs either did not provide such effects or they were very poor. For carprofen, it was possible to determine an EC50 which fell within the limits of concentrations obtainable in canine serum after the administration of routinely used doses.ConclusionThe results are promising but further studies should be conducted to confirm them, since this study is only preliminary. The possibility of introducing carprofen and tolfenamic acid into the routine treatment of osteosarcoma in dogs should be considered.

412 Ex-vivo cytokine secretion pattern of LPS-induced inflammation in human skin explants

The skin serves an important role in the defense mechanism against pathogens and possesses immunomodulatory functions. Several in vitro models that mimic different aspects of local skin inflammation exists. The use of ex vivo human skin organ culture had been reported previously. However, comprehensive data of the cytokine secretory profile of the system and kinetics have not been reported. The aim of the current study was to investigate the levels of key cytokines secretion upon lipopolysaccharide (LPS) stimuli. First, the skin explants were treated without or with three different LPS subtype and the impact on IL-6 and IL-8 secretion was evaluated. All LPS compounds enhance the two cytokine secreted levels in a dose-dependent manner. However, efficacy and potency differed. Next, a kinetic multiplex analysis was performed on LPS (E.coli O111:B4)-stimulated explants, taken from three different skin donors. Cytokine secretion pattern during 72 hr period was recorded. The levels of the pro-inflammatory cytokines IL-6, IL-8, TNFα, IL-1β were affected by LPS stimuli, but with differential secretion pattern. In addition, the anti-inflammatory cytokine IL-10 was also enhanced in the system, suggesting an auto-regulatory prosses. IL-1α and IL-15 showed donor-specific changes. Lastly, dexamethasone attenuated cytokine secretion in five independent repetitions, re-enforcing the ability of the system to be used as a drug screening platform.

Interactions of Carvacrol, Caprylic Acid, Habituation, and Mild Heat for Pressure-Based Inactivation of O157 and Non-O157 Serogroups of Shiga Toxin-Producing Escherichia coli in Acidic Environment.

The current study investigated synergism of elevated hydrostatic pressure, habituation, mild heat, and antimicrobials for inactivation of O157 and non-O157 serogroups of Shiga toxin-producing Escherichia coli. Various times at a pressure intensity level of 450 MPa were investigated at 4 and 45 °C with and without carvacrol, and caprylic acid before and after three-day aerobic habituation in blueberry juice. Experiments were conducted in three biologically independent repetitions each consist of two replications and were statistically analyzed as a randomized complete block design study using ANOVA followed by Tukey- and Dunnett’s-adjusted mean separations. Under the condition of this experiment, habituation of the microbial pathogen played an influential (p < 0.05) role on inactivation rate of the pathogen. As an example, O157 and non-O157 serogroups were reduced (p < 0.05) by 1.4 and 1.6 Log CFU/mL after a 450 MPa treatment at 4 °C for seven min, respectively, before habituation. The corresponding log reductions (p < 0.05) after three-day aerobic habituation were: 2.6, and 3.3, respectively at 4 °C. Carvacrol and caprylic acid addition both augmented the pressure-based decontamination efficacy. As an example, Escherichia coli O157 were reduced (p < 0.05) by 2.6 and 4.2 log CFU/mL after a seven-min treatment at 450 MPa without, and with presence of 0.5% carvacrol, respectively, at 4 °C.

The Effect of the Presence of Very Cohesive Geldart C Ultra-Fine Particles on the Fluidization of Geldart A Fine Particle Beds

The effect of the presence of ultra-fines (d &lt; 10 μm) on the fluidization of a bed containing fine particles (d &lt; 100 μm), is the subject of this paper. Practically, it can happen due to breakage or surface abrasion of the fine particles in some processes which totally changes the size distribution and also fluidization behaviour. The materials used in this study are both ground calcium carbonate (GCC); fine is CALCIT MVT 100 (Geldart’s group A) and ultra-fine is CALCIT MX 10 (group C). The experimental results for different binary mixtures of these materials (ultra-fines have 30%, 50%, or 68% of the total mixture weight) show that the physical properties of the mixtures are close to those of pure ultra-fine powders. Using mean values of the bed pressure drop calculated from several independent repetitions, the fluidization behaviour of different mixtures are compared and discussed. The fluidization behaviour of the mixtures is non-reproducible and includes cracking, channelling and agglomeration (like for pure ultra-fine powders). Increasing the portion of ultra-fine materials in the mixture causes a delay in starting partial fluidization, an increase in the bed pressure drop as well as a delay in reaching the peak point.

Enhancement of Ant Colony Optimization for QoS-Aware Web Service Selection

In service-oriented computing, web services composition is the process of translating user requirements into a workflow. This workflow comprises many tasks, each of which includes an abstract definition for some of the user requirements. Web services can be aggregated to handle the workflow. Many of these services are available from various providers for each task; they are referred to, in aggregate, as the candidate list. The web service selection (WSS) problem centers on selecting the best service from these candidates based on the quality of service (QoS) features. In this paper, we propose an enhancement to the ant colony optimization (ACO) algorithm based on a swap concept for the QoS-aware WSS problem. The aim of the enhancement to the ACO is to avoid the trap of local optima and reduce the search duration. We believe that the integration of many potent solutions will help the ACO algorithm yield a better solution and avoid stagnation. Several experiments were conducted to compare the proposed algorithm with the ACO and flying ACO (FACO) algorithms. Two different types of experiments using 22 datasets were done with 30 independent repetitions. The first type of experiment's results shows that the proposed algorithm is better than ACO by 12% and FACO by 11% in terms of quality of solutions. The results in the second type of experiment show that the proposed algorithm continuously outperforms both algorithms in terms of quality of solutions.

Binary orbits from combined astrometric and spectroscopic data

An efficient Bayesian technique for estimation problems in fundamental stellar astronomy is tested on simulated data for a binary observed both astrometrically and spectroscopically. Posterior distributions are computed for the components’ masses and for the binary’s parallax. One thousand independent repetitions of the simulation demonstrate that the 1- and 2-σ credibility intervals for these fundamental quantities have close to the correct coverage fractions. In addition, the simulations allow the investigation of the statistical properties of a Bayesian goodness-of-fit criterion and of the corresponding p-value. The criterion has closely similar properties to the traditional χ2 test for minimum-χ2 solutions.

Identification of early jasmonate-responsive genes in Taxus × media cells by analyzing time series digital gene expression data.

Jasmonate, an effective elicitor, can induce the biosynthesis of paclitaxel, a well-known anticancer drug, in Taxus cell culture. The jasmonate signaling pathway has been well studied in Arabidopsis, and many early jasmonate-responsive genes have beenfound to be involved in signaling pathway. In Taxus, only a few late jasmonate-responsive genes related to paclitaxel biosynthesis were identified. So, identification of early responsive genes and knowledge of the jasmonate signaling pathway are essential for understanding the effects of jasmonate on paclitaxel biosynthesis and for improving paclitaxel production in Taxus cells. In this study, total RNA of Taxus × media cells cultured in liquid medium was extracted after 0, 0.5, 3, and 24h of methyl jasmonate treatment. Three biological independent repetitions were performed. The 12 extracted RNA samples were integrated and sequenced on an Illumina HiSeq2500 platform using the paired-end method. A total of 45,583 transcript clusters were obtained by de novo assembly of the sequenced reads. Based on the transcriptome data, the digital gene expressions of each RNA sample were investigated. We found that after 0.5, 3, and 24h of methyl jasmonate treatment; 134, 1008, and 987 unigenes were differentially expressed. For the secondary metabolism pathways, phenylalanine pathway unigenes were responsive to jasmonate after 3h of treatment, while genes related to paclitaxel biosynthesis were induced after 0.5h of treatment. The digital gene expression levels of candidate genes related to paclitaxel biosynthesis were confirmed by qRT-PCR. Transcriptome sequencing and digital gene expression profiling identified early jasmonate-responsive genes in cultured Taxus × media cells. The comprehensive time series jasmonate-responsive gene expression data have provided transcriptome-wide information about the mechanism of paclitaxel biosynthesis regulation by jasmonate signaling.

Varicella-Zoster Virus Expresses Multiple Small Noncoding RNAs.

Many herpesviruses express small noncoding RNAs (sncRNAs), including microRNAs (miRNAs), that may play roles in regulating lytic and latent infections. None have yet been reported in varicella-zoster virus (VZV; also known as human herpesvirus 3 [HHV-3]). Here we analyzed next-generation sequencing (NGS) data for small RNAs in VZV-infected fibroblasts and human embryonic stem cell-derived (hESC) neurons. Two independent bioinformatics analyses identified more than 20 VZV-encoded 20- to 24-nucleotide RNAs, some of which are predicted to have stem-loop precursors potentially representing miRNAs. These sequences are perfectly conserved between viruses from three clades of VZV. One NGS-identified sequence common to both bioinformatics analyses mapped to the repeat regions of the VZV genome, upstream of the predicted promoter of the immediate early gene open reading frame 63 (ORF63). This miRNA candidate was detected in each of 3 independent biological repetitions of NGS of RNA from fibroblasts and neurons productively infected with VZV using TaqMan quantitative PCR (qPCR). Importantly, transfected synthetic RNA oligonucleotides antagonistic to the miRNA candidate significantly enhanced VZV plaque growth rates. The presence of 6 additional small noncoding RNAs was also verified by TaqMan qPCR in productively infected fibroblasts and ARPE19 cells. Our results show VZV, like other human herpesviruses, encodes several sncRNAs and miRNAs, and some may regulate infection of host cells.IMPORTANCE Varicella-zoster virus is an important human pathogen, with herpes zoster being a major health issue in the aging and immunocompromised populations. Small noncoding RNAs (sncRNAs) are recognized as important actors in modulating gene expression, and this study demonstrates the first reported VZV-encoded sncRNAs. Many are clustered to a small genomic region, as seen in other human herpesviruses. At least one VZV sncRNA was expressed in productive infection of neurons and fibroblasts that is likely to reduce viral replication. Since sncRNAs have been suggested to be potential targets for antiviral therapies, identification of these molecules in VZV may provide a new direction for development of treatments for painful herpes zoster.

Tongue movement during articulation in magnetic resonance imaging: Findings in 20 healthy volunteers and a patient with anterior floor of the mouth squamous cell carcinoma

PurposeCombined ablative and reconstructive oral maxillofacial surgery involves a multitude of anatomical and functional structures for speech and swallowing. Although there are a few methods to objectively examine swallowing function, this is not true for speech. We describe the development of an objective visualization and measurement tool for magnetic resonance imaging (MRI) to evaluate speech and its first application in a patient. Material and methodsA total of 20 healthy patients and one patient with squamous cell carcinoma localized in the anterior floor of the mouth were included in the study. Examination included an MRI examination of a paced, defined set of fictive words representing all sounds of the German language. The patient underwent MRI preoperatively and 1, 3, 6 and 12 months postoperatively. MRI findings were correlated with speech intelligibility. ResultsIn sagittal planes, the correct identification of vowels and consonants was feasible and showed a high accordance between two independent observers and repetitions. Measurements for the patient showed significant deviations 1 month postoperatively but gradually decreased over time. Aberrant values were persistent for sound /s/. Findings correlated with clinical findings of speech intelligibility. ConclusionThe presented tool seems to be promising for evaluating articulation in (tumor) patients.

Transitional flow in a Rushton turbine stirred tank

The way in which the single phase flow of Newtonian liquids in the vicinity of the impeller in a Rushton turbine stirred tank goes through a laminar‐turbulent transition has been studied in detail experimentally (with Particle Image Velocimetry) as well as computationally. For Reynolds numbers equal to or higher than 6000, the average velocities and velocity fluctuation levels scale well with the impeller tip speed, that is, show Reynolds independent behavior. Surprising flow structures were measured—and confirmed through independent experimental repetitions—at Reynolds numbers around 1300. Upon reducing the Reynolds number from values in the fully turbulent regime, the trailing vortex system behind the impeller blades weakens with the upper vortex weakening much stronger than the lower vortex. Simulations with a variety of methods (direct numerical simulations, transitional turbulence modeling) and software implementations (ANSYS‐Fluent commercial software, lattice‐Boltzmann in‐house software) have only partial success in representing the experimentally observed laminar‐turbulent transition. © 2017 American Institute of Chemical Engineers AIChE J, 63: 3610–3623, 2017

The Generalized Birthday Problem

SummaryHow many independent repetitions of an experiment are required so that the probability of a repeated outcome is at least one-half? We find a simple formula that determines the number of repetitions in terms of the number of outcomes to within one of the exact answer.