Microfluidic electrical sorting of particles based on shape in a spiral microchannel

Shape is an intrinsic marker of cell cycle, an important factor for identifying a bioparticle, and also a useful indicator of cell state for disease diagnostics. Therefore, shape can be a specific marker in label-free particle and cell separation for various chemical and biological applications. We demonstrate in this work a continuous-flow electrical sorting of spherical and peanut-shaped particles of similar volumes in an asymmetric double-spiral microchannel. It exploits curvature-induced dielectrophoresis to focus particles to a tight stream in the first spiral without any sheath flow and subsequently displace them to shape-dependent flow paths in the second spiral without any external force. We also develop a numerical model to simulate and understand this shape-based particle sorting in spiral microchannels. The predicted particle trajectories agree qualitatively with the experimental observation.     

A cell electrofusion microfluidic device integrated with 3D thin-film microelectrode arrays

A microfluidic device integrated with 3D thin film microelectrode arrays wrapped around serpentine-shaped microchannel walls has been designed, fabricated and tested for cell electrofusion. Each microelectrode array has 1015 discrete microelectrodes patterned on each side wall, and the adjacent microelectrodes are separated by coplanar dielectric channel wall. The device was tested to electrofuse K562 cells under a relatively low voltage. Under an AC electric field applied between the pair of the microelectrode arrays, cells are paired at the edge of each discrete microelectrode due to the induced positive dielectrophoresis. Subsequently, electric pulse signals are sequentially applied between the microelectrode arrays to induce electroporation and electrofusion. Compared to the design with thin film microelectrode arrays deposited at the bottom of the side walls, the 3D thin film microelectrode array could induce electroporation and electrofusion under a lower voltage. The staggered electrode arrays on opposing side walls induce inhomogeneous electric field distribution, which could avoid multi-cell fusion. The alignment and pairing efficiencies of K562 cells in this device were 99% and 70.7%, respectively. The electric pulse of low voltage (～9 V) could induce electrofusion of these cells, and the fusion efficiency was about 43.1% of total cells loaded into the device, which is much higher than that of the convectional and most existing microfluidics-based electrofusion devices.     

The power of institutional isomorphism: an analysis of the institutionalization of performance-based pay systems in Korean National Universities

The purpose of this study was to analyze the introduction of the performance-based pay system (PPS) in Korean national universities through the perspective of institutional isomorphism. Using three isomorphism concepts of coercive, mimetic, and normative, and further framing the PPS within the overarching theoretical frameworks of governmentality, neoliberalism, myth, and policy convergence, this study explored the historical and social background of the PPS, the reason the Korean government pursued the PPS form used in the US higher education, and the main factors that affected its introduction in Korean national universities. The result of this analysis shows that while the institutionalization of the PPS in Korean national universities seemed closely associated with the radical political, economic change in Korean society, it was in fact an exemplar of isomorphism from the US model of public and private higher education. This isomorphic activity functioned simultaneously as a norm, social order, and myth within Korean higher education while faculty displayed an anti-isomorphic tendency against the power of the institutional isomorphism of PPS in national universities.     

The effects of parent–child communication patterns on children's interactive communication in online communities: focusing on social self-efficacy and unwillingness to communicate as mediating factors

The purpose of this study is to determine which of the following factors influence children's online communication: parent–child communication (PCC), social self-efficacy (SSE), and unwillingness to communicate (UTC). To examine children's online communication, the researchers obtained survey data from 425 elementary school students in South Korea and tested a hypothesized structural model using EQS/Windows. The findings suggest that open communication between parents and children is associated with higher levels of SSE and lower levels of UTC among children. According to the two variables, open PCC has an indirect influence on interactive communication in online communities. Overall, this study offers meaningful results indicating that children's interactive online communication is influenced by their characteristics of interpersonal communication resulting from open PCC.     

Pressure-driven transport of particles through a converging-diverging microchannel

Pressure-driven transport of particles through a symmetric converging-diverging microchannel is studied by solving a coupled nonlinear system, which is composed of the Navier–Stokes and continuity equations using the arbitrary Lagrangian–Eulerian finite-element technique. The predicted particle translation is in good agreement with existing experimental observations. The effects of pressure gradient, particle size, channel geometry, and a particle’s initial location on the particle transport are investigated. The pressure gradient has no effect on the ratio of the translational velocity of particles through a converging-diverging channel to that in the upstream straight channel. Particles are generally accelerated in the converging region and then decelerated in the diverging region, with the maximum translational velocity at the throat. For particles with diameters close to the width of the channel throat, the usual acceleration process is divided into three stages: Acceleration, deceleration, and reacceleration instead of a monotonic acceleration. Moreover, the maximum translational velocity occurs at the end of the first acceleration stage rather than at the throat. Along the centerline of the microchannel, particles do not rotate, and the closer a particle is located near the channel wall, the higher is its rotational velocity. Analysis of the transport of two particles demonstrates the feasibility of using a converging-diverging microchannel for passive (biological and synthetic) particle separation and ordering.     

Event triggered reliable synchronization of semi-Markovian jumping complex dynamical networks via generalized integral inequalities

This paper focuses on the synchronization problem of semi-Markovian jumping complex dynamical networks with time-varying coupling delays against actuator failures. In an aim to shrink the treatment of network resources event triggered control strategy is proposed to achieve the synchronization criteria. By constructing Lyapunov–Krasovski functional, some delay dependent criteria that assures the synchronization of CDN are derived with the help of the general integral inequalities. It should be noted that the general integral inequality used here is general than that of Jensen inequality, the Wirtinger-based inequality, the Bessel-Legendre inequality, the Wirtinger-based double integral inequality, and the auxiliary function-based integral inequalities. The resulting LMIs can be easily verified with the help of the available softwares. Finally, simulation results are proposed to verify the effectiveness of the general integral inequality and designed control law.     

Is social networking a waste of time? The impact of social network and knowledge characteristics on job performance

People use social media to help them solve problems and enhance performance. Users may engage in diverse social interactions online, increasing their knowledge base through both weak and strong ties. In this study we investigate the impact of social networks on job performance, focusing on knowledge quality and diversity based on social network theory and the knowledge-based view. The empirical analysis reveals that the strength of social network ties is strongly associated with knowledge quality in offline interactions, while social network diversity is associated with knowledge quality in online interactions. Knowledge quality acquired from social network has a significant impact on both creativity and productivity of job performance in the workplace. However, knowledge diversity acquired from diverse social network interactions is strongly associated with creativity, but not with productivity. The results of this study increase our understanding of the knowledge sourcing behaviors of workers.     

Dielectrophoretic choking phenomenon in a converging-diverging microchannel

Experiments show that particles smaller than the throat size of converging-diverging microchannels can sometimes be trapped near the throat. This critical phenomenon is associated with the negative dc dielectrophoresis arising from nonuniform electric fields in the microchannels. A finite-element model, accounting for the particle-fluid-electric field interactions, is employed to investigate the conditions for this dielectrophoretic (DEP) choking in a converging-diverging microchannel for the first time. It is shown quantitatively that the DEP choking occurs for high nonuniformity of electric fields, high ratio of particle size to throat size, and high ratio of particle’s zeta potential to that of microchannel.     

Measurement Invariance Testing Across Between-Level Latent Classes Using Multilevel Factor Mixture Modeling

This simulation study examines the efficacy of multilevel factor mixture modeling (ML FMM) for measurement invariance testing across unobserved groups when the groups are at the between level of multilevel data. To this end, latent classes are generated with class-specific item parameters (i.e., factor loading and intercept) across the between-level classes. The efficacy of ML FMM is evaluated in terms of class enumeration, class assignment, and the detection of noninvariance. Various classification criteria such as Akaike’s information criterion, Bayesian information criterion, and bootstrap likelihood ratio tests are examined for the correct enumeration of between-level latent classes. For the detection of measurement noninvariance, free and constrained baseline approaches are compared with respect to true positive and false positive rates. This study evidences the adequacy of ML FMM. However, its performance heavily depends on the simulation factors such as the classification criteria, sample size, and the magnitude of noninvariance. Practical guidelines for applied researchers are provided.