Static and Dynamic Behaviour of Gas Bubbles in T-Shaped Non-Clogging Micro-Channels

Abstract Preventing micro-channels from clogging is a major issue in most micro and nanofluidic systems (Gravesen et al., J Micromech Microeng 3(4):168-182, 1993; Jensen et al., In: Proc. of MicroTAS 2002, Nara, Japan, pp 733-735, 2002 Wong et al., J Fluid Mech 292:71-94, 1995). The T-shaped channel first reported by Kohnle et al. (In: IEEE MEMS, the 15th international IEEE micro electro mechanical conference (ed), Las Vegas, pp 77-80, 2002) prevents micro-channels from clogging by the aid of the equilibrium bubble position in such a geometry. This work is concerned with the static and dynamic behaviour of bubbles in such T-shaped microchannels. The aspect ratio of a rectangle enclosing the Tshaped channel and the contact angle of the walls are the main parameters influencing the static and dynamic bubble behaviour. It is investigated in this article how these parameters relate to the equilibrium bubble shape and how optimum bubble velocities can be achieved inside the channel. An analytical model depending on the contact angle and the channel geometry is presented that allows to determine the bubble configuration inside the channel by minimizing the bubble's surface energy. A second model is derived to predict the velocity of gas bubbles driven by buoyancy in vertical T-shaped channels. The model is applied to design T-shaped channels with a maximum mobility of gas bubbles. Experiments with MEMS fabricated devices and CFD simulations are used to verify the models. Furthermore design rules for an optimum nonclogging channel geometry which provides the highest gas bubble mobility are given

Capillary-Driven Pumping for Passive Degassing and Fuel Supply in Direct Methanol Fuel Cells

Abstract In this paper we present a new concept of creating and using capillary pressure gradients for passive degassing and passive methanol supply in direct methanol fuel cells (DMFCs). An anode flow field consisting of parallel tapered channels structures is applied to achieve the passive supply mechanism. The flow is propelled by the surface forces of deformed CO 2 bubbles, generated as a reaction product during DMFC operation. This work focuses on studying the influence of channel geometry and surface properties on the capillary-induced liquid flow rates at various bubbly gas flow rates. Besides the aspect ratios and opening angles of the tapered channels, the static contact angle as well as the effect of contact angle hysteresis has been identified to significantly influence the liquid flow rates induced by capillary forces at the bubble menisci. Applying the novel concept, we show that the liquid flow rates are up to thirteen times higher than the methanol oxidation reaction on the anode requires. Experimental results are presented that demonstrate the continuous passive operation of a DMFC for more than 15 h

How can chiropractic become a respected mainstream profession? The example of podiatry

<p>Abstract</p> <p>Background</p> <p>The chiropractic profession has succeeded to remain in existence for over 110 years despite the fact that many other professions which had their start at around the same time as chiropractic have disappeared. Despite chiropractic's longevity, the profession has not succeeded in establishing cultural authority and respect within mainstream society, and its market share is dwindling. In the meantime, the podiatric medical profession, during approximately the same time period, has been far more successful in developing itself into a respected profession that is well integrated into mainstream health care and society.</p> <p>Objective</p> <p>To present a perspective on the current state of the chiropractic profession and to make recommendations as to how the profession can look to the podiatric medical profession as a model for how a non-allopathic healthcare profession can establish mainstream integration and cultural authority.</p> <p>Discussion</p> <p>There are several key areas in which the podiatric medical profession has succeeded and in which the chiropractic profession has not. The authors contend that it is in these key areas that changes must be made in order for our profession to overcome its shrinking market share and its present low status amongst healthcare professions. These areas include public health, education, identity and professionalism.</p> <p>Conclusion</p> <p>The chiropractic profession has great promise in terms of its potential contribution to society and the potential for its members to realize the benefits that come from being involved in a mainstream, respected and highly utilized professional group. However, there are several changes that must be made within the profession if it is going to fulfill this promise. Several lessons can be learned from the podiatric medical profession in this effort.</p

Daphnia revisited: Local stability and bifurcation theory for physiologically structured population models explained by way of an example

We consider the interaction between a general size-structured consumer population and an unstructured resource. We show that stability properties and bifurcation phenomena can be understood in terms of solutions of a system of two delay equations (a renewal equation for the consumer population birth rate coupled to a delay differetial equation for the resource concentration). As many results for such systems are available, we can draw rigorous conclusions concerning dynamical behaviour from an analysis of a characteristic equation. We derive the characteristic equation for a fairly general class of population models, including those based on the Kooijman-Metz Daphnia model and a model introduced by Gurney-Nisbet and Jones et al., and next obtain various ecological insights by analytical or numerical studies of special cases

The opposing homeobox genes Goosecoid and Vent1/2 self-regulate Xenopus patterning

We present a loss-of-function study using antisense morpholino (MO) reagents for the organizer-specific gene Goosecoid (Gsc) and the ventral genes Vent1 and Vent2. Unlike in the mouse Gsc is required in Xenopus for mesodermal patterning during gastrulation, causing phenotypes ranging from reduction of head structures—including cyclopia and holoprosencephaly—to expansion of ventral tissues in MO-injected embryos. The overexpression effects of Gsc mRNA require the expression of the BMP antagonist Chordin, a downstream target of Gsc. Combined Vent1 and Vent2 MOs strongly dorsalized the embryo. Unexpectedly, simultaneous depletion of all three genes led to a rescue of almost normal development in a variety of embryological assays. Thus, the phenotypic effects of depleting Gsc or Vent1/2 are caused by the transcriptional upregulation of their opposing counterparts. A principal function of Gsc and Vent1/2 homeobox genes might be to mediate a self-adjusting mechanism that restores the basic body plan when deviations from the norm occur, rather than generating individual cell types. The results may shed light on the molecular mechanisms of genetic redundancy

Profound Effect of Profiling Platform and Normalization Strategy on Detection of Differentially Expressed MicroRNAs – A Comparative Study

Adequate normalization minimizes the effects of systematic technical variations and is a prerequisite for getting meaningful biological changes. However, there is inconsistency about miRNA normalization performances and recommendations. Thus, we investigated the impact of seven different normalization methods (reference gene index, global geometric mean, quantile, invariant selection, loess, loessM, and generalized procrustes analysis) on intra- and inter-platform performance of two distinct and commonly used miRNA profiling platforms.We included data from miRNA profiling analyses derived from a hybridization-based platform (Agilent Technologies) and an RT-qPCR platform (Applied Biosystems). Furthermore, we validated a subset of miRNAs by individual RT-qPCR assays. Our analyses incorporated data from the effect of differentiation and tumor necrosis factor alpha treatment on primary human skeletal muscle cells and a murine skeletal muscle cell line. Distinct normalization methods differed in their impact on (i) standard deviations, (ii) the area under the receiver operating characteristic (ROC) curve, (iii) the similarity of differential expression. Loess, loessM, and quantile analysis were most effective in minimizing standard deviations on the Agilent and TLDA platform. Moreover, loess, loessM, invariant selection and generalized procrustes analysis increased the area under the ROC curve, a measure for the statistical performance of a test. The Jaccard index revealed that inter-platform concordance of differential expression tended to be increased by loess, loessM, quantile, and GPA normalization of AGL and TLDA data as well as RGI normalization of TLDA data.We recommend the application of loess, or loessM, and GPA normalization for miRNA Agilent arrays and qPCR cards as these normalization approaches showed to (i) effectively reduce standard deviations, (ii) increase sensitivity and accuracy of differential miRNA expression detection as well as (iii) increase inter-platform concordance. Results showed the successful adoption of loessM and generalized procrustes analysis to one-color miRNA profiling experiments

The Accuracy of the Electrocardiogram during Exercise Stress Test Based on Heart Size

BACKGROUND: Multiple studies have shown that the exercise electrocardiogram (ECG) is less accurate for predicting ischemia, especially in women, and there is additional evidence to suggest that heart size may affect its diagnostic accuracy. HYPOTHESIS: The purpose of this investigation was to assess the diagnostic accuracy of the exercise ECG based on heart size. METHODS: We evaluated 1,011 consecutive patients who were referred for an exercise nuclear stress test. Patients were divided into two groups: small heart size defined as left ventricular end diastolic volume (LVEDV) <65 mL (Group A) and normal heart size defined as LVEDV ≥65 mL (Group B) and associations between ECG outcome (false positive vs. no false positive) and heart size (small vs. normal) were analyzed using the Chi square test for independence, with a Yates continuity correction. LVEDV calculations were performed via a computer-processing algorithm. SPECT myocardial perfusion imaging was used as the gold standard for the presence of coronary artery disease (CAD). RESULTS: Small heart size was found in 142 patients, 123 female and 19 male patients. There was a significant association between ECG outcome and heart size (χ(2) = 4.7, p = 0.03), where smaller hearts were associated with a significantly greater number of false positives. CONCLUSIONS: This study suggests a possible explanation for the poor diagnostic accuracy of exercise stress testing, especially in women, as the overwhelming majority of patients with small heart size were women

Transcriptome Analysis of the Chinese White Wax Scale Ericerus pela with Focus on Genes Involved in Wax Biosynthesis

BACKGROUND: The Chinese white wax scale, Ericerus pela Chavannes is economically significant for its role in wax production. This insect has been bred in China for over a thousand years. The wax secreted by the male scale insect during the second-instar larval stage has been widespread used in wax candle production, wax printing, engraving, Chinese medicine, and more recently in the chemical, pharmaceutical, food, and cosmetics industries. However, little is known about the mechanisms responsible for white wax biosynthesis. The characterization of its larval transcriptome may promote better understanding of wax biosynthesis. METHODOLOGY/PRINCIPAL FINDINGS: In this study, characterization of the transcriptome of E. pela during peak wax secretion was performed using Illumina sequencing technology. Illumina sequencing produced 41,839 unigenes. These unigenes were annotated by blastx alignment against the NCBI Non-Redundant (NR), Swiss-Prot, KEGG, and COG databases. A total of 104 unigenes related to white wax biosynthesis were identified, and 15 of them were selected for quantitative real-time PCR analysis. We evaluated the variations in gene expression across different development stages, including egg, first/second instar larvae, male pupae, and male and female adults. Then we identified five genes involved in white wax biosynthesis. These genes were expressed most strongly during the second-instar larval stage of male E. pela. CONCLUSION/SIGNIFICANCE: The transcriptome analysis of E. pela during peak wax secretion provided an overview of gene expression information at the transcriptional level and a resource for gene mining. Five genes related to white wax biosynthesis were identified

The effect of tightly-bound water molecules on scaffold diversity in computer-aided de novo ligand design of CDK2 inhibitors

We have determined the effects that tightly bound water molecules have on the de novo design of cyclin-dependent kinase-2 (CDK2) ligands. In particular, we have analyzed the impact of a specific structural water molecule on the chemical diversity and binding mode of ligands generated through a de novo structure-based ligand generation method in the binding site of CDK2. The tightly bound water molecule modifies the size and shape of the binding site and we have found that it also imposed constraints on the observed binding modes of the generated ligands. This in turn had the indirect effect of reducing the chemical diversity of the underlying molecular scaffolds that were able to bind to the enzyme satisfactorily