Hydrodynamic Simulation of Cyclone Separators

Cyclone separators are commonly used for separating dispersed solid particles from gas phase. These devices have simple construction; are relatively inexpensive to fabricate and operate with moderate pressure losses. Therefore, they are widely used in many engineering processes such as dryers, reactors, advanced coal utilization such as pressurized and circulating fluidized bed combustion and particularly for removal of catalyst from gases in petroleum refinery such as in fluid catalytic cracker (FCC). Despite its simple operation, the fluid dynamics and flow structures in a cyclone separator are very complex. The driving force for particle separation in a cyclone separator is the strong swirling turbulent flow. The gas and the solid particles enter through a tangential inlet at the upper part of the cyclone. The tangential inlet produces a swirling motion of gas, which pushes the particles to the cyclone wall and then both phases swirl down over the cyclone wall. The solid particles leave the cyclone through a duct at the base of the apex of the inverted cone while the gas swirls upward in the middle of the cone and leaves the cyclone from the vortex finder. The swirling motion provides a centrifugal force to the particles while turbulence disperses the particles in the gas phase which increases the possibility of the particle entrainment. Therefore, the performance of a cyclone separator is determined by the turbulence characteristics and particle-particle interaction.Full Tex

Comparative antioxidant activity, total phenol and total flavonoid contents of two Nigerian ocimum species

Antioxidants are compounds which act as a major defense against oxidative stress caused by free radicals. In this study, a comparative evaluation of the antioxidant properties, phenolic and flavonoid contents of the methanolic extracts of Ocimum gratissimum Linn and Ocimum canum Sims was carried out. Crude extracts of both plants were obtained by maceration of powdered plant materials in methanol (80%) for 24hrs. The phenolic and flavonoid contents were determined using standard methods while the antioxidant capacities were evaluated using six different in vitro radical scavenging assays: total antioxidant potential, reductive potential, I, 1-diphenyl-2-picryl-hydrazyl (DPPH) free radical scavenging, lipid peroxidation inhibition, hydroxyl radical and nitric oxide scavenging activity. The total phenolic content in O. gratissimum and O. canum were found to be 32.66 ± 6.21 and 17.19 ± 2.54 mg GAE/g dw while total flavonoid content gave 1.94 ± 0.23 and 0.67 ± 0.01 mg QUE/g dw, respectively. Both extracts had effective reductive potential as well as exhibited strong total antioxidant capacity with increasing concentration of extract. Comparatively, O. gratissimum exhibited a significantly (p < 0.05) higher capacity to quench the DPPH free radical with IC50 value of 26.01 ± 3.2 µg/ml than O. canum, which has an IC50 value of 60.45 ± 5.22 µg/m. O. gratissimum also significantly inhibited membrane lipid peroxidation and hydroxyl radical formation with IC50 of 99.37 ± 8.56 µg/ml and 465.33 ± 21.62 µg/ml, respectively while O. canum correspondingly gave IC50 values of 447.5 ± 35.61 µg/ml and 868.16 ± 43.05 µg/ml. In the nitric oxide scavenging activity, however, O. canum showed a stronger inhibitory effect than O. gratissimum as indicated by their IC50 values of 277.22 ± 15.09 µg/ml and 731 ± 56.99 µg/ml, respectively. These activities are however several folds lower than those of butylated hydroxyl toluene (BHT), ascorbic acid and quercetin used as antioxidant standards. The results demonstrate that O. gratissimum has greater antioxidant capacity than O. canum because of its relatively higher radical scavenging activity in all antiradical tests carried out except the nitric acid scavenging test and higher contents of flavonoid and phenolic compounds. O. gratissimum is therefore more beneficial therapeutically than O. canum since it provides better defense against free radical induced oxidative stress, and this attribute probably explains its relative preference in ethnomedicine for both culinary and medicinal purposes amongst the Ocimum species widely cultivated in South Western Nigeria

Effect of a cluster on gas–solid drag from lattice Boltzmann simulations

Fast fluidization of fine particles leads to formation of particle clusters, which significantly affects the drag force between the phases. Existing gas–solid drag models, both empirical and theoretical, do not account for the effect of the clusters on the drag force, and as a result, the computational studies using them are unable to capture the inherent heterogeneity of fast fluidization beds. The limitation of the current drag models is generally attributed to poor understanding of the effect of the clusters. In this study, the effect of a single cluster on the drag force has been investigated by conducting lattice Boltzmann simulations of gas–particle flow under a wide range of the overall voidage and particle Reynolds numbers. It was observed that simulations with the particles in a cluster configuration gave considerably lower drag than those with particles in a random arrangement. Furthermore, for the cluster voidage between maximum to 0.7, a significant drag reduction was observed when the inter-particle distances within a cluster was decreased. The simulations with a constant cluster voidage of 0.7 showed that the drag force decreased on decreasing the overall voidage from the maximum voidage to approximately 0.96; however any further decrease in the overall voidage caused a steep increase in the drag force. The results of this study are important in quantifying the drag reduction due to the formation of clusters

A universal optical modulator for synthetic topologically tuneable structured matter

Topologically structured matter, such as metasurfaces and metamaterials, have given rise to impressive photonic functionality, fuelling diverse applications from microscopy and holography to encryption and communication. Presently these solutions are limited by their largely static nature and preset functionality, hindering applications that demand dynamic photonic systems with reconfigurable topologies. Here we demonstrate a universal optical modulator that implements topologically tuneable structured matter as virtual pixels derived from cascading low functionality tuneable devices, altering the paradigm of phase and amplitude control to encompass arbitrary spatially varying retarders in a synthetic structured matter device. Our approach opens unprecedented functionality that is user-defined with high flexibility, allowing our synthetic structured matter to act as an information carrier, beam generator, analyser, and corrector, opening an exciting path to tuneable topologies of light and matter

The Alvarado score for predicting acute appendicitis: a systematic review

Background: The Alvarado score can be used to stratify patients with symptoms of suspected appendicitis; the validity of the score in certain patient groups and at different cut points is still unclear. The aim of this study was to assess the discrimination (diagnostic accuracy) and calibration performance of the Alvarado score. Methods: A systematic search of validation studies in Medline, Embase, DARE and The Cochrane library was performed up to April 2011. We assessed the diagnostic accuracy of the score at the two cut-off points: score of 5 (1 to 4 vs. 5 to 10) and score of 7 (1 to 6 vs. 7 to 10). Calibration was analysed across low (1 to 4), intermediate (5 to 6) and high (7 to 10) risk strata. The analysis focused on three sub-groups: men, women and children. Results: Forty-two studies were included in the review. In terms of diagnostic accuracy, the cut-point of 5 was good at 'ruling out' admission for appendicitis (sensitivity 99% overall, 96% men, 99% woman, 99% children). At the cut-point of 7, recommended for 'ruling in' appendicitis and progression to surgery, the score performed poorly in each subgroup (specificity overall 81%, men 57%, woman 73%, children 76%). The Alvarado score is well calibrated in men across all risk strata (low RR 1.06, 95% CI 0.87 to 1.28; intermediate 1.09, 0.86 to 1.37 and high 1.02, 0.97 to 1.08). The score over-predicts the probability of appendicitis in children in the intermediate and high risk groups and in women across all risk strata. Conclusions: The Alvarado score is a useful diagnostic 'rule out' score at a cut point of 5 for all patient groups. The score is well calibrated in men, inconsistent in children and over-predicts the probability of appendicitis in women across all strata of risk

Global economic burden of unmet surgical need for appendicitis

Background: There is a substantial gap in provision of adequate surgical care in many low-and middle-income countries. This study aimed to identify the economic burden of unmet surgical need for the common condition of appendicitis. Methods: Data on the incidence of appendicitis from 170 countries and two different approaches were used to estimate numbers of patients who do not receive surgery: as a fixed proportion of the total unmet surgical need per country (approach 1); and based on country income status (approach 2). Indirect costs with current levels of access and local quality, and those if quality were at the standards of high-income countries, were estimated. A human capital approach was applied, focusing on the economic burden resulting from premature death and absenteeism. Results: Excess mortality was 4185 per 100 000 cases of appendicitis using approach 1 and 3448 per 100 000 using approach 2. The economic burden of continuing current levels of access and local quality was US $92 492 million using approach 1 and$73 141 million using approach 2. The economic burden of not providing surgical care to the standards of high-income countries was $95 004 million using approach 1 and$75 666 million using approach 2. The largest share of these costs resulted from premature death (97.7 per cent) and lack of access (97.0 per cent) in contrast to lack of quality. Conclusion: For a comparatively non-complex emergency condition such as appendicitis, increasing access to care should be prioritized. Although improving quality of care should not be neglected, increasing provision of care at current standards could reduce societal costs substantially

Laparoscopy in management of appendicitis in high-, middle-, and low-income countries: a multicenter, prospective, cohort study.

BACKGROUND: Appendicitis is the most common abdominal surgical emergency worldwide. Differences between high- and low-income settings in the availability of laparoscopic appendectomy, alternative management choices, and outcomes are poorly described. The aim was to identify variation in surgical management and outcomes of appendicitis within low-, middle-, and high-Human Development Index (HDI) countries worldwide. METHODS: This is a multicenter, international prospective cohort study. Consecutive sampling of patients undergoing emergency appendectomy over 6 months was conducted. Follow-up lasted 30 days. RESULTS: 4546 patients from 52 countries underwent appendectomy (2499 high-, 1540 middle-, and 507 low-HDI groups). Surgical site infection (SSI) rates were higher in low-HDI (OR 2.57, 95% CI 1.33-4.99, p = 0.005) but not middle-HDI countries (OR 1.38, 95% CI 0.76-2.52, p = 0.291), compared with high-HDI countries after adjustment. A laparoscopic approach was common in high-HDI countries (1693/2499, 67.7%), but infrequent in low-HDI (41/507, 8.1%) and middle-HDI (132/1540, 8.6%) groups. After accounting for case-mix, laparoscopy was still associated with fewer overall complications (OR 0.55, 95% CI 0.42-0.71, p < 0.001) and SSIs (OR 0.22, 95% CI 0.14-0.33, p < 0.001). In propensity-score matched groups within low-/middle-HDI countries, laparoscopy was still associated with fewer overall complications (OR 0.23 95% CI 0.11-0.44) and SSI (OR 0.21 95% CI 0.09-0.45). CONCLUSION: A laparoscopic approach is associated with better outcomes and availability appears to differ by country HDI. Despite the profound clinical, operational, and financial barriers to its widespread introduction, laparoscopy could significantly improve outcomes for patients in low-resource environments. TRIAL REGISTRATION: NCT02179112

Pseudorapidity dependence of long-range two-particle correlations in pPb collisions at root sNN=5.02 TeV

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