Improved van der Pol Oscillators

This paper brings together and discusses some useful oscillator models. A unified approach is used to present different models in an evolutionary succession of ascending complexity. The presentation applies a rather informal physical viewpoint without stressing mathematical rigorosity. Applications of the models are also mentioned.     

微带贴片天线的简化全波分析

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US principals’ attitudes about and experiences with single-sex schooling

Despite a lack of scientific evidence supporting the use of single-sex education, the number of US public schools offering single-sex education has increased. However, our understanding as to why decision-makers have implemented single-sex education is lacking. To address this gap, we surveyed US public school principals and assessed their attitudes about and experiences with single-sex schooling. Sixty-seven principals from single-sex schools and 193 principals from co-educational schools participated. The results indicated that principals who had experience with single-sex schooling tended to have more positive attitudes about single-sex schooling, viewed it as more effective, and more often evoked gender-essentialist rationales for the use of single-sex schooling than did co-educational principals. However, both single-sex and co-educational principals noted issues with single-sex schooling. It was concluded that single-sex schooling is not a silver bullet to educational reform and that when single-sex schooling is implemented, one set of issues and problems is substituted for another.     

Political Participation and Ideological News Online: “Differential Gains” and “Differential Losses” in a Presidential Election Cycle

Observations of the contemporary news media environment often revolve around the topics of ideological polarization and blurred boundaries between mass and interpersonal communication. This study explores these topics through a focus on the association between ideologically oriented online news use, commenting on online news, and political participation. We hypothesize that both ideological online news use generally and proattitudinal online news use are positively related to political participation and that online news commenting creates “differential gains” by augmenting these relationships. Yet we also hypothesize that counterattitudinal online news use is negatively related to political participation and that online news commenting creates “differential losses” by exacerbating this relationship. Analyses of two independently collected and nationally representative surveys found that frequent ideological online news use, proattitudinal online news use, and commenting are all positively related to political participation. We found no evidence for differential gains as a result of online commenting but only for differential losses—counterattitudinal online news use interacts with commenting to create a negative relationship with political participation.     

Advances in three-dimensional rapid prototyping of microfluidic devices for biological applications

The capability of 3D printing technologies for direct production of complex 3D structures in a single step has recently attracted an ever increasing interest within the field of microfluidics. Recently, ultrafast lasers have also allowed developing new methods for production of internal microfluidic channels within the bulk of glass and polymer materials by direct internal 3D laser writing. This review critically summarizes the latest advances in the production of microfluidic 3D structures by using 3D printing technologies and direct internal 3D laser writing fabrication methods. Current applications of these rapid prototyped microfluidic platforms in biology will be also discussed. These include imaging of cells and living organisms, electrochemical detection of viruses and neurotransmitters, and studies in drug transport and induced-release of adenosine triphosphate from erythrocytes.     

Continuous removal of glycerol from frozen-thawed red blood cells in a microfluidic membrane device

Cryopreservation of human red blood cells (RBCs) in the presence of 40% glycerol allows a shelf-life of 10 years, as opposed to only 6 weeks for refrigerated RBCs. Nonetheless, cryopreserved blood is rarely used in clinical therapy, in part because of the requirement for a time-consuming (∼1 h) post-thaw wash process to remove glycerol before the product can be used for transfusion. The current deglycerolization process involves a series of saline washes in an automated centrifuge, which gradually removes glycerol from the cells in order to prevent osmotic damage. We recently demonstrated that glycerol can be extracted in as little as 3 min without excessive osmotic damage if the composition of the extracellular solution is precisely controlled. Here, we explore the potential for carrying out rapid glycerol extraction using a membrane-based microfluidic device, with the ultimate goal of enabling inline washing of cryopreserved blood. To assist in experimental design and device optimization, we developed a mass transfer model that allows prediction of glycerol removal, as well as the resulting cell volume changes. Experimental measurements of solution composition and hemolysis at the device outlet are in reasonable agreement with model predictions, and our results demonstrate that it is possible to reduce the glycerol concentration by more than 50% in a single device without excessive hemolysis. Based on these promising results, we present a design for a multistage process that is predicted to safely remove glycerol from cryopreserved blood in less than 3 min.