Using Nyquist or Nyquist-Like Plot to Predict Three Typical Instabilities in DC-DC Converters

By transforming an exact stability condition, a new Nyquist-like plot is proposed to predict occurrences of three typical instabilities in DC-DC converters. The three instabilities are saddle-node bifurcation (coexistence of multiple solutions), period-doubling bifurcation (subharmonic oscillation), and Neimark bifurcation (quasi-periodic oscillation). In a single plot, it accurately predicts whether an instability occurs and what type the instability is. The plot is equivalent to the Nyquist plot, and it is a useful design tool to avoid these instabilities. Nine examples are used to illustrate the accuracy of this new plot to predict instabilities in the buck or boost converter with fixed or variable switching frequency.Comment: Submitted to an IEEE journal in 201

Peramorphosis, an evolutionary developmental mechanism in neotropical bat skull diversity

Background The neotropical leaf‐nosed bats (Chiroptera, Phyllostomidae) are an ecologically diverse group of mammals with distinctive morphological adaptations associated with specialized modes of feeding. The dramatic skull shape changes between related species result from changes in the craniofacial development process, which brings into focus the nature of the underlying evolutionary developmental processes. Results In this study, we use three‐dimensional geometric morphometrics to describe, quantify, and compare morphological modifications unfolding during evolution and development of phyllostomid bats. We examine how changes in development of the cranium may contribute to the evolution of the bat craniofacial skeleton. Comparisons of ontogenetic trajectories to evolutionary trajectories reveal two separate evolutionary developmental growth processes contributing to modifications in skull morphogenesis: acceleration and hypermorphosis. Conclusion These findings are consistent with a role for peramorphosis, a form of heterochrony, in the evolution of bat dietary specialists

Obesity, Physical Activity and Sedentary Behavior Amongst British and Saudi Youth: A Cross-Cultural Study

This study explores differences in weight status, obesity and patterns of physical activity (PA) in relation to gender and age of youth from two culturally, environmentally and geographically diverse countries, the United Kingdom (UK) and Saudi Arabia (SA). A total of 2,290 males and females (15–17 years) volunteered to participate in this study. Participants completed a validated self-report questionnaire that contained 47 items relating to patterns of PA, sedentary activity and eating habits. The questionnaire allows the calculation of total energy expenditure in metabolic equivalent (MET-min) values per week. Significant differences in percentage of overweight/obese and levels of PA were evident between the youth from the two countries, with males being generally more physically active than females. Additionally, there were significant associations between Body Mass Index (BMI), PA and sedentary behaviors; the youth with higher BMI reported lower levels of PA and higher amounts of sedentary time. These findings highlight the diverse nature of lifestyle of youth living in different geographical areas of the world and the need for further research to explore the socio-cultural factors that impact on the prevalence of obesity and patterns of PA of youth in different populations

Cdc42 promotes transendothelial migration of cancer cells through β1 integrin.

Cancer cells interact with endothelial cells during the process of metastatic spreading. Here, we use a small interfering RNA screen targeting Rho GTPases in cancer cells to identify Cdc42 as a critical regulator of cancer cell-endothelial cell interactions and transendothelial migration. We find that Cdc42 regulates β1 integrin expression at the transcriptional level via the transcription factor serum response factor (SRF). β1 integrin is the main target for Cdc42-mediating interaction of cancer cells with endothelial cells and the underlying extracellular matrix, as exogenous β1 integrin expression was sufficient to rescue the Cdc42-silencing phenotype. We show that Cdc42 was required in vivo for cancer cell spreading and protrusion extension along blood vessels and retention in the lungs. Interestingly, transient Cdc42 depletion was sufficient to decrease experimental lung metastases, which suggests that its role in endothelial attachment is important for metastasis. By identifying β1 integrin as a transcriptional target of Cdc42, our results provide new insight into Cdc42 function

Molecular flexibility of citrus pectins by combined sedimentation and viscosity analysis

The flexibility/rigidity of pectins plays an important part in their structure-function relationship and therefore on their commercial applications in the food and biomedical industries. Earlier studies based on sedimentation analysis in the ultracentrifuge have focused on molecular weight distributions and qualitative and semi-quantitative descriptions based on power law and Wales-van Holde treatments of conformation in terms of "extended" conformations [Harding, S. E., Berth, G., Ball, A., Mitchell, J.R., & Garcìa de la Torre, J. (1991). The molecular weight distribution and conformation of citrus pectins in solution studied by hydrodynamics. Carbohydrate Polymers, 168, 1-15; Morris, G. A., Foster, T. J., & Harding, S.E. (2000). The effect of degree of esterification on the hydrodynamic properties of citrus pectin. Food Hydrocolloids, 14, 227-235]. In the present study, four pectins of low degree of esterification 17-27% and one of high degree of esterification (70%) were characterised in aqueous solution (0.1 M NaCl) in terms of intrinsic viscosity [η], sedimentation coefficient (s°20,w) and weight average molar mass (Mw). Solution conformation/flexibility was estimated qualitatively using the conformation zoning method [Pavlov, G.M., Rowe, A.J., & Harding, S.E. (1997). Conformation zoning of large molecules using the analytical ultracentrifuge. Trends in Analytical Chemistry, 16, 401-405] and quantitatively (persistence length Lp) using the traditional Bohdanecky and Yamakawa-Fujii relations combined together by minimisation of a target function. Sedimentation conformation zoning showed an extended coil (Type C) conformation and persistence lengths all within the range Lp=10-13 nm (for a fixed mass per unit length)

Using SNSs for early detection of disease outbreak in developing countries:evidence from COVID-19 pandemic in Nigeria

Developing countries, particularly Nigeria, continually find it challenging to proactively and actively carry out early-stage surveillance for disease outbreaks due to the lack of quality workforce, a dearth of public health data, and the absence of automated surveillance systems in the country. This study presents the potential and ability of Twitter in tracking early detection of COVID-19, monitoring the dissemination of information, and exploration of public awareness and attitudes among Nigerians. Tweets mentioning COVID-19 and related keywords were collected in 11 batches via the NCapture™ plugin available on Google Chrome from February 20 - May 6, 2020. The analysis includes a time series analysis to track the distribution of data and content analysis to analyze the knowledge and attitudes of Nigerians. A total of 67,989 tweets (1,484 unique and 66,505 retweets) citing COVID-19 and related keywords were returned. The Tweets started to emerge earlier to the first confirmed case in Nigeria while maintaining a dangling-upward movement up to the 11th week under study. Matters arising from the tweets include a dearth of information on COVID-19 and optimism among others. The results provide insight into the intersection of SNSs and public health surveillance. Results show how helpful Twitter is to educate education in public health. Health organizations and the government may benefit from paying attention to both amusing and emotional contents from the Twitter community to formulate a viable policy for treatment and control

Elevated type-17 cytokines are present in Axial Spondyloarthritis stool

Axial Spondyloarthritis (axSpA) is characterized by type-17 immune-driven joint inflammation, and intestinal inflammation is present in around 70% of patients. In this study, we asked whether axSpA stool contained Th17-associated cytokines and whether this related to systemic Th17 activation. We measured stool cytokine and calprotectin levels by ELISA and found that patients with axSpA have increased stool IL-17A, IL-23, GM-CSF, and calprotectin. We further identified increased levels of circulating IL-17A+ and IL-17F+ T helper cell lymphocytes in patients with axSpA compared to healthy donors. We finally assessed stool metabolites by unbiased nuclear magnetic resonance (NMR) spectroscopy and found that multiple stool amino acids were negatively correlated with stool IL-23 concentrations. These data provide evidence of type-17 immunity in the intestinal lumen, and suggest its association with microbial metabolism in the intestine