When none of us perform better than all of us together: the role of analogical decision rules in groups

During social interactions, groups develop collective competencies that (ideally) should assist groups to outperform average standalone individual members (weak cognitive synergy) or the best performing member in the group (strong cognitive synergy). In two experimental studies we manipulate the type of decision rule used in group decision-making (identify the best vs. collaborative), and the way in which the decision rules are induced (direct vs. analogical) and we test the effect of these two manipulations on the emergence of strong and weak cognitive synergy. Our most important results indicate that an analogically induced decision rule (imitate-the-successful heuristic) in which groups have to identify the best member and build on his/her performance (take-the-best heuristic) is the most conducive for strong cognitive synergy. Our studies bring evidence for the role of analogy-making in groups as well as the role of fast-and-frugal heuristics for group decision-making

P2: Developing Methodologies for Wet-Sample Electron Microscopy Imaging

Scanning Electron Microscopy (SEM) is widely used to analyze the size, shape, and composition of material systems. However, using this tool for analyzing systems such as particles suspended in solution requires drastic sample alterations, such as precipitation and fixation. Besides altering their environment, this exposes the particles to the harsh conditions within an electron microscope, such as high vacuum and electron beam exposure. To this end, the first goal of this study was to develop methodologies for imaging wet samples using electron microscopy. This is realized by creating a sandwich structure containing the solution of interest between a partially electron transparent window and the aluminum stub. The ability of the developed imaging cells to provide good imaging conditions is demonstrated with a variety of samples including polystyrene spheres, polymeric microgels, and spindleshaped nanoparticles. As some of the systems investigated are temperature sensitive, the second goal of the project was to develop a temperature controlled stage that can be integrated with the SEM. In the future, this heating stage will be used alongside the wet samples to image microgels above and below their critical solution temperature.https://engagedscholarship.csuohio.edu/u_poster_2017/1029/thumbnail.jp

Analogy Between Thermodynamic Phase Transitions and Creeping Flows in Rectangular Cavities

© 2020, MDPI AG. All rights reserved. An analogy is found between the streamline function corresponding to Stokes flows in rectangular cavities and the thermodynamics of phase transitions and critical points. In a rectangular cavity flow, with no-slip boundary conditions at the walls, the corners are fixed points. The corners defined by a stationary and a moving wall, are found to be analogous to a thermodynamic first-order transition point. In contrast, the corners defined by two stationary walls correspond to thermodynamic critical points. Here, flow structures, also known as Moffatt eddies, form and act as stagnation regions where mixing is impeded. A third stationary point occurs in the middle region of the channel and it is analogous to a high temperature thermodynamic fixed point. The numerical results of the fluid flow modeling are correlated with analytical work in the proximity of the fixed points

Erosion in Extruder Flows: Analytical and Numerical Study

© 2017 Author(s). We consider the erosion of particles (e.g. carbonblack agglomerates) advected by the polymeric flow in a single screw extruder. We assume a particle to be made of primary fragments bound together. In the erosion process a primary fragment breaks out of a given particle. Particles disperse because of the shear stresses imparted by the fluid. The time evolution of the numbers of particles of different sizes is described by the Bateman coupled differential equations developed a century ago to model radioactivity. Using the particle size distribution we compute an entropic fragmentation index which varies from 0 for a monodisperse system to 1 for an extreme poly-disperse system. The time dependence of the index exhibits a maximum at some intermediate time as the system starts monodisperse (large size particle) and evolves through a poly-disperse regime at intermediate times to a monodisperse (small size particle) at late times

Paramagnetic Meissner Effect in Nb Disks

Further details of the zero-field-cooled-magnetization and field-cooled-magnetization results on Nb disks exhibiting the paramagnetic Meissner effect (PME) are described. These studies indicate that two well-defined temperatures can be associated with features in the magnetization results. The higher characteristic temperature Tu is correlated with appearance of the paramagnetic moment and is strongly dependent upon the process used in forming the disk-shaped geometry of these Nb samples. The lower temperature Tp is associated with the “intrinsic coupling” of the interior Nb platelets. These latest results are shown to be consistent with the flux compression model for the appearance of the PME

Gigahertz Optical Spin Transceiver

We present a time-resolved optical technique to measure electron spin dynamics with GHz dynamical bandwidth, transform-limited spectral selectivity, and phase-sensitive (lock-in) detection. Use of a continuous-wave (CW) laser and fast optical bridge enables greatly improved signal-to-noise characteristics compared to traditional optical sampling (pump-probe) techniques. We demonstrate the technique with a measurement of GHz-spin precession in n-GaAs. This approach may be applicable to other physical systems where stroboscopic techniques cannot be used because of either noise or spectral limitations

Gigahertz Optical Spin Transceiver

We present a time-resolved optical technique to measure electron spin dynamics with GHz dynamical bandwidth, transform-limited spectral selectivity, and phase-sensitive (lock-in) detection. Use of a continuous-wave (CW) laser and fast optical bridge enables greatly improved signal-to-noise characteristics compared to traditional optical sampling (pump-probe) techniques. We demonstrate the technique with a measurement of GHz-spin precession in n-GaAs. This approach may be applicable to other physical systems where stroboscopic techniques cannot be used because of either noise or spectral limitations

Assessment of Mixing in Passive Microchannels with Fractal Surface Patterning

We explore numerically the feasibility of enhancing the mixing capability of microchannels by employing the Weierstrass fractal function to generate a pattern of V-shaped ridges on the channel floor. Motivated by experimental limitations such as the finite resolution (similar to 10 mu m) associated with rapid prototyping through soft lithography techniques, we study the influence on the quality of mixing of having finite width ridges. The mixing capability of the designs studied is evaluated using an entropic measure and the designs are optimized with respect to: the distances between the ridges and the position range of their tip along the width of the channels. The results are evaluated with respect to the benchmarks established by the very successful staggered herring bone (SHB) design. We find that the use of a non periodic protocol to generate the geometry of the bottom surface of the microchannels can lead to consistently larger entropic mixing indices than in cyclic structures. Furthermore, since the optimization curves (mixing index vs. geometric parameters) are broader at the maximum for fractal microchannels than for their SHB counterparts, the microchannel designs using the Weierstrass fractal function are less sensitive to experimental uncertainties

Mixing Enhancement in Serpentine Micromixers with a Non-Rectangular Cross-Section

In this numerical study, a new type of serpentine micromixer involving mixing units with a non-rectangular cross-section is investigated. Similar to other serpentine/spiral shaped micromixers, the design exploits the formation of transversal vortices (Dean flows) in pressure-driven systems, associated with the centrifugal forces experienced by the fluid as it is confined to move along curved geometries. In contrast with other previous designs, though, the use of non-rectangular cross-sections that change orientation between mixing units is exploited to control the center of rotation of the transversal flows formed. The associated extensional flows that thus develop between the mixing segments complement the existent rotational flows, leading to a more complex fluid motion. The fluid flow characteristics and associated mixing are determined numerically from computational solutions to Navier–Stokes equations and the concentration-diffusion equation. It is found that the performance of the investigated mixers exceeds that of simple serpentine channels with a more consistent behavior at low and high Reynolds numbers. An analysis of the mixing quality using an entropic mixing index indicates that maximum mixing can be achieved at Reynolds numbers as small as 20 in less than four serpentine mixing units

Mixing Optimization in Grooved Serpentine Microchannels

© 2020 by the authors. Licensee MDPI, Basel, Switzerland. Computational fluid dynamics modeling at Reynolds numbers ranging from 10 to 100 was used to characterize the performance of a new type of micromixer employing a serpentine channel with a grooved surface. The new topology exploits the overlap between the typical Dean flows present in curved channels due to the centrifugal forces experienced by the fluids, and the helical flows induced by slanted groove-ridge patterns with respect to the direction of the flow. The resulting flows are complex, with multiple vortices and saddle points, leading to enhanced mixing across the section of the channel. The optimization of the mixers with respect to the inner radius of curvature (Rin) of the serpentine channel identifies the designs in which the mixing index quality is both high (M \u3e 0.95) and independent of the Reynolds number across all the values investigated