Expansion of non-spherical media during fluidization

Liquid-solid fluidization has a number of applications in engineering. The expansion of granular filter media during backwashing is of particular interest. Another area of application that is of growing importance is fluidized-bed reactors used in wastewater treatment. It is important to have an understanding of fluidization principles and an ability to predict bed expansion as a function of liquid velocity to design such systems properly. More often than not, the media involved are not spherical and it is necessary to have an expansion model that can be applied to beds of non-spherical particles. Numerous equations have been proposed to predict the expansion of liquid fluidized beds of spherical particles. Very few general equations exist, however, for non-spherical media. Furthermore, the accuracies of the expansion models for non-spherical media have not been evaluated or compared in a conclusive manner to this date. This study considers the expansion of beds of possibly non-spherical particles during particulate fluidization. New experimental data with both spherical and non-spherical media are presented. Fluidization experiments have been carried out with glass balls of eight different sizes (1.11, 1.19, 2.03, 2.99, 3.18,  4.03, 4.98 and 6.01 mm), plastic balls of three different sizes (1.97, 2.48 and 2.87 mm), ten sieved fractions of silica sand, eleven sieved fractions of crushed glass, and seven sieved fractions of perlite. Perlite and crushed glass were included in this study because their properties (densities and sphericities) are different than those of silica sand, and as such they can provide additional fluidization data. It may also be noted that both materials have been considered as substitutes for silica sand in rapid filters. To obtain additional fractions of crushed glass material, particles retained in the topmost sieve tray were crushed again and sieved. In this manner sufficient quantities of additional fractions of crushed glass were obtained. Glass fractions obtained by repeated crushing and sieving were observed to have higher sphericity values. Using this procedure, crushed glass fractions with approximately the same size and density but different sphericities were produced. This allowed the collection of additional fluidization data to investigate the effect of shape on expansion behavior.The sand, perlite, and crushed glass fractions were obtained by a manual sieving procedure followed by an additional 1 minute of manual sieving such that the change in weight during the latter was less than 1% for each fraction. Densities were measured by a water-displacement technique. Equivalent diameters have been measured by counting and weighing 200 grains of each fraction. Porosities were calculated from bed weight, bed height, and density values. Sphericity of each material was determined using fixed-bed head loss data in conjunction with the Ergun equation. For all the materials studied in this work, sphericity values calculated using fixed-bed head loss measurements and the Ergun equation allowed successful prediction of the effect of particle shape on bed expansion during fluidization. Sphericity values of the materials studied was found to be 0.74, 0.66, 0.42 and 0.55 for sand, perlite, crushed glass and crushed glass produced by repeated crushing, respectively. For the eight different sizes of glass and plastic balls, the calculated sphericities by using the Ergun equation were always close to 1.0. A new equation is developed by analyzing fluidization data from the literature and the data collected in this work. The proposed equation represents the mentioned data very accurately and can be used to predict the expansion of both spherical and non-spherical media.The non-spherical particle data fall below the curve for spheres on the friction factor versus the modified Reynolds number diagram. For the materials studied, it has been observed that this shape effect depends on the Reynolds number and is considerably stronger than documented previously in the literature.  The proposed equation can be used to predict the expansion of both spherical and non-spherical media. When applied to the non-spherical particle data obtained in this work (bed expansions from 20% to about 100%, sphericities between 0.410 and 0.757), the mean error in the predicted porosity values is 2.45%. The corresponding mean error that results from Dharmarajah-Cleasby (1986) equation is 4.4%.     Keywords: Filter backwash hydraulics, fluidization, filter material, sphericity.Akışkan yatakların genişlemesi sırasındaki hız-gözeneklilik ilişkileri üzerine önerilen pek çok denklem mevcuttur. Bununla birlikte bu denklemlerin tamamına yakını sadece küresel malzemelere uygulanabilir nitelikte olup küresel olmayan tanecikler için önerilen az sayıda modelin büyük çoğunluğu da ampiriktir ve şekil faktörü etkisini açık bir şekilde ortaya koymamaktadırlar. Ayrıca küresel olmayan tanecikler için geçerli genişleme modellerinin doğrulukları sistematik bir şekilde değerlendirilmemiş ve karşılaştırılmamıştır. Bu çalışmada küresel olmayan malzemeler ile ilgili akışkanlaşma deneyleri yürütülmüştür. Bu amaçla 10 farklı kum, 7 farklı perlit ve 11 farklı kırılarak oluşturulmuş cam fraksiyonu hazırlanmış, malzemelerin şeklinin akışkanlaşma sırasındaki davranışları üzerine etkisini belirlemek amacıyla sabit yatak yük kayıpları ve Ergun denklemi kullanılarak elde edilen küresellik katsayıları tespit edilmiştir. Bu şekilde her malzeme için ayrı ayrı hesaplanan küresellik parametresi akışkanlaşma çalışmalarının modellenmesinde oldukça iyi neticeler vermiştir. Çalışılan malzemelerin küresellik katsayıları kum, perlit, tek seferde kırılarak oluşturulmuş kırık cam ve tekrarlı kırma suretiyle oluşturulmuş kırık cam fraksiyonları için sırasıyla yaklaşık 0.74, 0.66, 0.42 ve 0.55 olarak bulunmuştur. Literatürde sıklıkla atıf alan küresel olmayan malzemelerin akışkanlaşma sırasındaki hız-gözeneklilik ilişkisini veren Dharmarajah-Cleasby (1986) denklemi bu çalışmada elde edilen deneysel veriler kullanılarak irdelenmiş ve küresel ve küresel olmayan malzemelerin genişlemiş yatak yükseklikleri ve gözenekliliklerinin tahmininde kullanılacak alternatif yeni bir denklem ile karşılaştırılmıştır. Geliştirilen yeni modelin Dharmarajah-Cleasby (1986) denklemine göre çok daha tutarlı sonuçlar verdiği görülmüştür. Anahtar Kelimeler: Filtre geri yıkama hidroliği, akışkanlaşma, fitre malzemesi, küresellik. &nbsp

Actinic keratosis-related signs predictive of squamous cell carcinoma in renal transplant recipients: a nested case-control study

Background Squamous cell carcinoma (SCC) and intraepidermal carcinoma (IEC) commonly arise in actinically damaged skin

An integrated computational-experimental approach reveals Yersinia pestis genes essential across a narrow or a broad range of environmental conditions

This is the final version. Available from BMC via the DOI in this recordAvailability of data and materials: The datasets supporting the conclusions of this article are available at the NCBI GEO website https://www.ncbi.nlm.nih.gov/geo/query/acc.cgi?acc=GSE100226.BACKGROUND: The World Health Organization has categorized plague as a re-emerging disease and the potential for Yersinia pestis to also be used as a bioweapon makes the identification of new drug targets against this pathogen a priority. Environmental temperature is a key signal which regulates virulence of the bacterium. The bacterium normally grows outside the human host at 28 °C. Therefore, understanding the mechanisms that the bacterium used to adapt to a mammalian host at 37 °C is central to the development of vaccines or drugs for the prevention or treatment of human disease. RESULTS: Using a library of over 1 million Y. pestis CO92 random mutants and transposon-directed insertion site sequencing, we identified 530 essential genes when the bacteria were cultured at 28 °C. When the library of mutants was subsequently cultured at 37 °C we identified 19 genes that were essential at 37 °C but not at 28 °C, including genes which encode proteins that play a role in enabling functioning of the type III secretion and in DNA replication and maintenance. Using genome-scale metabolic network reconstruction we showed that growth conditions profoundly influence the physiology of the bacterium, and by combining computational and experimental approaches we were able to identify 54 genes that are essential under a broad range of conditions. CONCLUSIONS: Using an integrated computational-experimental approach we identify genes which are required for growth at 37 °C and under a broad range of environments may be the best targets for the development of new interventions to prevent or treat plague in humans.This work was funded by the Defence Science and Technology Laboratory, award DSTLX-1000060221 (WP1)

Evolution under Fluctuating Environments Explains Observed Robustness in Metabolic Networks

A high level of robustness against gene deletion is observed in many organisms. However, it is still not clear which biochemical features underline this robustness and how these are acquired during evolution. One hypothesis, specific to metabolic networks, is that robustness emerges as a byproduct of selection for biomass production in different environments. To test this hypothesis we performed evolutionary simulations of metabolic networks under stable and fluctuating environments. We find that networks evolved under the latter scenario can better tolerate single gene deletion in specific environments. Such robustness is underlined by an increased number of independent fluxes and multifunctional enzymes in the evolved networks. Observed robustness in networks evolved under fluctuating environments was “apparent,” in the sense that it decreased significantly as we tested effects of gene deletions under all environments experienced during evolution. Furthermore, when we continued evolution of these networks under a stable environment, we found that any robustness they had acquired was completely lost. These findings provide evidence that evolution under fluctuating environments can account for the observed robustness in metabolic networks. Further, they suggest that organisms living under stable environments should display lower robustness in their metabolic networks, and that robustness should decrease upon switching to more stable environments

An integrated computational-experimental approach reveals Yersinia pestis genes essential across a narrow or a broad range of environmental conditions

Background The World Health Organization has categorized plague as a re-emerging disease and the potential for Yersinia pestis to also be used as a bioweapon makes the identification of new drug targets against this pathogen a priority. Environmental temperature is a key signal which regulates virulence of the bacterium. The bacterium normally grows outside the human host at 28 °C. Therefore, understanding the mechanisms that the bacterium used to adapt to a mammalian host at 37 °C is central to the development of vaccines or drugs for the prevention or treatment of human disease. Results Using a library of over 1 million Y. pestis CO92 random mutants and transposon-directed insertion site sequencing, we identified 530 essential genes when the bacteria were cultured at 28 °C. When the library of mutants was subsequently cultured at 37 °C we identified 19 genes that were essential at 37 °C but not at 28 °C, including genes which encode proteins that play a role in enabling functioning of the type III secretion and in DNA replication and maintenance. Using genome-scale metabolic network reconstruction we showed that growth conditions profoundly influence the physiology of the bacterium, and by combining computational and experimental approaches we were able to identify 54 genes that are essential under a broad range of conditions. Conclusions Using an integrated computational-experimental approach we identify genes which are required for growth at 37 °C and under a broad range of environments may be the best targets for the development of new interventions to prevent or treat plague in humans

Comparison of exhaled breath condensate pH using two commercially available devices in healthy controls, asthma and COPD patients

<p>Abstract</p> <p>Background</p> <p>Analysis of exhaled breath condensate (EBC) is a non-invasive method for studying the acidity (pH) of airway secretions in patients with inflammatory lung diseases.</p> <p>Aim</p> <p>To assess the reproducibility of EBC pH for two commercially available devices (portable RTube and non-portable ECoScreen) in healthy controls, patients with asthma or COPD, and subjects suffering from an acute cold with lower-airway symptoms. In addition, we assessed the repeatability in healthy controls.</p> <p>Methods</p> <p>EBC was collected from 40 subjects (n = 10 in each of the above groups) using RTube and ECoScreen. EBC was collected from controls on two separate occasions within 5 days. pH in EBC was assessed after degasification with argon for 20 min.</p> <p>Results</p> <p>In controls, pH-measurements in EBC collected by RTube or ECoScreen showed no significant difference between devices (p = 0.754) or between days (repeatability coefficient RTube: 0.47; ECoScreen: 0.42) of collection. A comparison between EBC pH collected by the two devices in asthma, COPD and cold patients also showed good reproducibility. No differences in pH values were observed between controls (mean pH 8.27; RTube) and patients with COPD (pH 7.97) or asthma (pH 8.20), but lower values were found using both devices in patients with a cold (pH 7.56; RTube, p < 0.01; ECoScreen, p < 0.05).</p> <p>Conclusion</p> <p>We conclude that pH measurements in EBC collected by RTube and ECoScreen are repeatable and reproducible in healthy controls, and are reproducible and comparable in healthy controls, COPD and asthma patients, and subjects with a common cold.</p

The Bicarbonate Transporter Is Essential for Bacillus anthracis Lethality

In the pathogenic bacterium Bacillus anthracis, virulence requires induced expression of the anthrax toxin and capsule genes. Elevated CO2/bicarbonate levels, an indicator of the host environment, provide a signal ex vivo to increase expression of virulence factors, but the mechanism underlying induction and its relevance in vivo are unknown. We identified a previously uncharacterized ABC transporter (BAS2714-12) similar to bicarbonate transporters in photosynthetic cyanobacteria, which is essential to the bicarbonate induction of virulence gene expression. Deletion of the genes for the transporter abolished induction of toxin gene expression and strongly decreased the rate of bicarbonate uptake ex vivo, demonstrating that the BAS2714-12 locus encodes a bicarbonate ABC transporter. The bicarbonate transporter deletion strain was avirulent in the A/J mouse model of infection. Carbonic anhydrase inhibitors, which prevent the interconversion of CO2 and bicarbonate, significantly affected toxin expression only in the absence of bicarbonate or the bicarbonate transporter, suggesting that carbonic anhydrase activity is not essential to virulence factor induction and that bicarbonate, and not CO2, is the signal essential for virulence induction. The identification of this novel bicarbonate transporter essential to virulence of B. anthracis may be of relevance to other pathogens, such as Streptococcus pyogenes, Escherichia coli, Borrelia burgdorferi, and Vibrio cholera that regulate virulence factor expression in response to CO2/bicarbonate, and suggests it may be a target for antibacterial intervention

Emergent Orthotopic Liver Transplantation for Hemorrhage from a Giant Cavernous Hepatic Hemangioma: Case Report and Review

IntroductionCavernous hemangiomas represent the most common benign primary hepatic neoplasm, often being incidentally detected. Although the majority of hepatic hemangiomas remain asymptomatic, symptomatic hepatic hemangiomas can present with abdominal pain, hemorrhage, biliary compression, or a consumptive coagulopathy. The optimal surgical management of symptomatic hepatic hemangiomas remains controversial, with resection, enucleation, and both deceased donor and living donor liver transplantation having been reported.Case reportWe report the case of a patient found to have a unique syndrome of multiorgan cavernous hemangiomatosis involving the liver, lung, omentum, and spleen without cutaneous involvement. Sixteen years following her initial diagnosis, the patient suffered from intra-abdominal hemorrhage due to her giant cavernous hepatic hemangioma. Evidence of continued bleeding, in the setting of Kasabach-Merritt Syndrome and worsening abdominal compartment syndrome, prompted MELD exemption listing. The patient subsequently underwent emergent liver transplantation without complication.ConclusionAlthough cavernous hemangiomas represent the most common benign primary hepatic neoplasm, hepatic hemangioma rupture remains a rare presentation in these patients. Management at a center with expertise in liver transplantation is warranted for those patients presenting with worsening DIC or hemorrhage, given the potential for rapid clinical decompensation

Regulation of proteinaceous effector expression in phytopathogenic fungi

Effectors are molecules used by microbial pathogens to facilitate infection via effector-triggered susceptibility or tissue necrosis in their host. Much research has been focussed on the identification and elucidating the function of fungal effectors during plant pathogenesis. By comparison, knowledge of how phytopathogenic fungi regulate the expression of effector genes has been lagging. Several recent studies have illustrated the role of various transcription factors, chromosome-based control, effector epistasis, and mobilisation of endosomes within the fungal hyphae in regulating effector expression and virulence on the host plant. Improved knowledge of effector regulation is likely to assist in improving novel crop protection strategies

The putative Tumor Suppressor VILIP-1 Counteracts Epidermal Growth Factor-Induced Epidermal-Mesenchymal Transition in Squamous Carcinoma Cells

Epithelial-mesenchymal transition (EMT) is a crucial step for the acquisition of invasive properties of carcinoma cells during tumor progression. Epidermal growth factor (EGF)-treatment of squamous cell carcinoma (SCC) cells provokes changes in the expression of lineage markers, morphological changes, and a higher invasive and metastatic potential. Here we show that chronic stimulation with EGF induces EMT in skin-derived SCC cell lines along with the down-regulation of the epithelial marker E-cadherin, and of the putative tumor suppressor VILIP-1 (visinin-like protein 1). In esophageal squamous cell carcinoma and non-small cell lung carcinoma the loss of VILIP-1 correlates with clinicopathological features related to enhanced invasiveness. VILIP-1 has previously been shown to suppress tumor cell invasion via enhancing cAMP-signaling in a murine SCC model. In mouse skin SCC cell lines the VILIP-1-negative tumor cells have low cAMP levels, whereas VILIP-1-positive SCCs possess high cAMP levels, but low invasive properties. We show that in VILIP-1-negative SCCs, Snail1, a transcriptional repressor involved in EMT, is up-regulated. Snail1 expression is reduced by ectopic VILIP-1-expression in VILIP-1-negative SCC cells, and application of the general adenylyl cyclase inhibitor 2′,3′-dideoxyadenosine attenuated this effect. Conversely, EGF-stimulation of VILIP-1-positive SCC cells leads to the down-regulation of VILIP-1 and the induction of Snail1 expression. The induction of Snail is inhibited by elevated cAMP levels. The role of cAMP in EMT was further highlighted by its suppressive effect on the EGF-induced enhancement of migration in VILIP-1-positive SCC cells. These findings indicate that VILIP-1 is involved in EMT of SCC by regulating the transcription factor Snail1 in a cAMP-dependent manner