Recent advances in potentiometric biosensing

Potentiometric biosensors are incredibly versatile tools with budding uses in industry, security, environmental safety, and human health. This mini-review on recent (2018–2020) advances in the field of potentiometric biosensors is intended to give a general overview of the main types of potentiometric biosensors for novices while still providing a brief but thorough summary of the novel advances and trends for experienced practitioners. These trends include the incorporation of nanomaterials, graphene, and novel immobilization materials, as well as a strong push toward miniaturized, flexible, and self-powered devices for in-field or at-home use.     

Simulation of the Flow in a Ribbed Rotating Duct with a Hybrid k-ω RANS/LES Model

The objective of this work is to verify the capabilities of a hybrid k-ω RANS/LES model for simulation of the unsteady three-dimensional flow in a ribbed duct subjected to system rotation. The Reynolds number is 15,000 and the rotation number is 0.3, both based on hydraulic diameter and bulk velocity. A correction term for system rotation is introduced into the originating k-ω RANS model. Simulation results in the mid-span section are compared with experimental data by Coletti et al. (Exp. Fluids 52:1043–1061, 2012). The comparison is complemented by analysis of the flow features in cross-sections. It is demonstrated that the hybrid k-ω RANS/LES model produces an accurate simulation of the rotating ribbed duct flow. Results are compared with those by the originating time-accurate k-ω RANS model. The k-ω RANS model is not accurate concerning secondary features in the longitudinal mean flow recirculation patterns and the secondary flow in cross-sections, but it reproduces quite well the time-averaged longitudinal flow.     

A Monte Carlo Algorithm for Immiscible Two-Phase Flow in Porous Media

We present a Markov Chain Monte Carlo algorithm based on the Metropolis algorithm for simulation of the flow of two immiscible fluids in a porous medium under macroscopic steady-state conditions using a dynamical pore network model that tracks the motion of the fluid interfaces. The Monte Carlo algorithm is based on the configuration probability, where a configuration is defined by the positions of all fluid interfaces. We show that the configuration probability is proportional to the inverse of the flow rate. Using a two-dimensional network, advancing the interfaces using time integration, the computational time scales as the linear system size to the fourth power, whereas the Monte Carlo computational time scales as the linear size to the second power. We discuss the strengths and the weaknesses of the algorithm.     

Collaborative Workshops and Student Academic Performance in Introductory College Mathematics Courses: A Study of a Treisman Model Math Excel Program

High failure rates in introductory college mathematics courses, particularly among underrepresented groups of students, have been of concern for many years. One approach to the problem experiencing some success has been Treisman's Emerging Scholars workshop model. The model involves supplemental workshops in which students solve problems in collaborative learning groups. This study reports on the effectiveness of Math Excel, an implementation of the Treisman model for introductory mathematics courses (college algebra, precalculus, differential calculus, and integral calculus) at Oregon State University over five academic terms. Regression analyses revealed a significant effect on achievement (.671 grade points on a 4‐point scale) favoring Math Excel students. Even after adjusting for prior mathematics achievement using linear regression with SAT‐M as predictor, Math Excel groups' grade averages were over half a grade point better than predicted (significant at the .001 level). This study provides supporting evidence that programs like Math Excel can help students in making a successful transition to college mathematics study.     

Implications of a Dilaton in Gauge Theory and Cosmology

After a review of theoretical motivations to consider theories with direct couplings of scalar fields to Ricci and gauge curvature terms, we consider the dynamics and non-perturbative stabilization of a dilaton in three and in four dimensions. In particular, we derive generalized Coulomb potentials in the presence of a dilaton and discuss a low energy effective dilaton potential induced by instanton effects and the S-dual coupling to axions. We conclude with a discussion of cosmological implications of a light dilaton.     

Synthesis and Evaluation of Enantiomeric Purity of Protected α-Amino and Peptide Aldehydes

The synthesis of enantiomerically pure Ac-Tyr-Val-Ala-Asp(O^tBu)-H dimethyl acetal ((S)- 1 ) is reported, a protected tetrapeptide C-terminal aldehyde belonging to a class of potent, reversible inhibitors of cysteine proteases (e.g., interleukin-1β-converting enzyme (ICE), also called caspase-1). The coupling of the precursors Ac-Tyr-Val-Ala-OH ((S)- 8 ) and H-Asp(O^tBu)-H dimethyl acetal ((S)- 6 ) gave (S)- 1 in a yield of 85%, with epimerization of <2% at the alanine and aspartic-acid residue. (S)- 6 itself was synthesized in four steps in an overall yield of 83% with an ee >98%.     

Light‐Induced Demixing of Hole or Electron Transporting Moieties

Summary: This paper describes the synthesis of two triphenylamine monomers (hole conducting) and one triazine monomer (electron conducting) which differ in their copolymerization parameters because of their styrene and vinyl ester nature. A blend of triphenylamine monomer and poly(ethylene glycol) and mixtures of both types of monomers (triphenylamine and triazine) were illuminated through a line mask, creating laterally modulated radicals, thus leading to lateral demixing. The experiments with mixtures of triphenylamine and triazine monomers show that the concentration of p‐ or n‐type polymers can be modulated laterally in a controlled way.

AFM measurement of line pattern formed by illuminating a mixture of monomer 2 and 3 showing the height difference between illuminated and non‐illuminated areas.     

Utilizing nonlinear phenomena to locate grazing in the constrained motion of a cantilever beam

Grazing behavior in soft impact dynamics of a harmonically based excited flexible cantilever beam is investigated. Numerical and experimental methods are employed to study the dynamic behavior of macro- and micro-scale cantilever beam–impactor systems. For off-resonance excitation at two and a half times the fundamental frequency, the response of the oscillating cantilever experiences period doubling as the separation distance or clearance between the beam axis and the contact surface is decreased. The nonlinear phenomenon is studied by using phase portraits, Poincaré sections, and spectral analysis. Motivated by atomic force microscopy, this general dynamic behavior is studied as a means to locating the separation distance corresponding to grazing where the contact force is minimized.     

Further Development of a Dynamic Intermittency Model For Wake-Induced Transition

The transition model studied in this paper uses an equation for free-stream intermittency and one for near-wall intermittency, combined with the SST turbulence model. The model was already assessed in earlier work for wake-induced transition in boundary layers in separated state and in attached state. For separated state transition, the model predicts the start and growth of transition very well, except for the impossibility to describe the breakdown of the roll-up vortices in a 2D RANS simulation. In attached state transition, the model has the tendency to generate a delayed start of transition and a too slow growth rate in the initial phase of transition. We demonstrate that a delayed start of transition is inherent for a RANS simulation. We propose a repair for the too slow growth rate in the initial stage of the transition. Additionally, both for wake-induced transition in separated state and in attached state, the original model has the tendency to predict a state too near to laminar in between wakes at the trailing edge. We demonstrate that this is caused by the too rapid destruction of the near-wall intermittency during relaminarization and in the lack of activation of near-wall intermittency for low turbulence level in the free stream. We propose a repair for both deficiencies. The fourth improvement is that we take into account the influence of the free stream turbulence length scale in the criteria for onset of transition. We demonstrate the high quality of the improved model for wake-induced transition on a steam turbine stator blade for outlet Reynolds number 600,000 and two levels of turbulence in the background flow: 3% and 0.4%.     

A Quasi-Realizable Cubic Low-Reynolds Eddy-Viscosity Turbulence Model with a New Dissipation Rate Equation

A non-linear relationship of the Reynolds stresses in function of the strain rate and vorticity tensors, with terms up to third order, is developed. Anisotropies in the normal stresses, influence from streamline curvature or rotation of the reference frame, and swirl effects are accounted for. The relationship is linked to ak–ε model with a modified transport equation for the dissipation rate. A new low-Reynolds source term is introduced and a model parameter is written in terms of dimensionless rate-of-strain and vorticity. The model is checked on different realizability constraints. It is shown that practically all constraints are fulfilled. The model is numerically tested on a fully developed channel and pipe flow, both stationary and rotating. The plane jet–round jet anomaly is addressed. Finally, the model is applied to the flow over a backward-facing step. Results are compared with a linear low-Reynolds k–ε model and the shear stress transport model. This revised version was published online in July 2006 with corrections to the Cover Date.