In situ electrokinetic enhancement for self-assembled-monolayer-based electrochemical biosensing

This study reports a multifunctional electrode approach which directly implements electrokinetic enhancement on a self-assembled-monolayer-based electrochemical sensor for point-of-care diagnostics. Using urinary tract infections as a model system, we demonstrate that electrokinetic enhancement, which involves in situ stirring and heating, can enhance the sensitivity of the strain specific 16S rRNA hybridization assay for 1 order of magnitude and accelerate the time-limiting incubation step with a 6-fold reduction in the incubation time. Since the same electrode platform is used for both electrochemical signal enhancement and electrochemical sensing, the multifunctional electrode approach provides a highly effective strategy toward fully integrated lab-on-a-chip systems for various biomedical applications.     

Cargo-towing fuel-free magnetic nanoswimmers for targeted drug delivery

Fuel-free nanomotors are essential for future in-vivo biomedical transport and drug-delivery applications. Herein, the first example of directed delivery of drug-loaded magnetic polymeric particles using magnetically driven flexible nanoswimmers is described. It is demonstrated that flexible magnetic nickel-silver nanoswimmers (5-6 μm in length and 200 nm in diameter) are able to transport micrometer particles at high speeds of more than 10 μm s(-1) (more than 0.2 body lengths per revolution in dimensionless speed). The fundamental mechanism of the cargo-towing ability of these magnetic (fuel-free) nanowire motors is modelled, and the hydrodynamic features of these cargo-loaded motors discussed. The effect of the cargo size on swimming performance is evaluated experimentally and compared to a theoretical model, emphasizing the interplay between hydrodynamic drag forces and boundary actuation. The latter leads to an unusual increase of the propulsion speed at an intermediate particle size. Potential applications of these cargo-towing nanoswimmers are demonstrated by using the directed delivery of drug-loaded microparticles to HeLa cancer cells in biological media. Transport of the drug carriers through a microchannel from the pick-up zone to the release microwell is further illustrated. It is expected that magnetically driven nanoswimmers will provide a new approach for the rapid delivery of target-specific drug carriers to predetermined destinations.     

Hydrodynamics of the double-wave structure of insect spermatozoa flagella

In addition to conventional planar and helical flagellar waves, insect sperm flagella have also been observed to display a double-wave structure characterized by the presence of two superimposed helical waves. In this paper, we present a hydrodynamic investigation of the locomotion of insect spermatozoa exhibiting the double-wave structure, idealized here as superhelical waves. Resolving the hydrodynamic interactions with a non-local slender body theory, we predict the swimming kinematics of these superhelical swimmers based on experimentally collected geometric and kinematic data. Our consideration provides insight into the relative contributions of the major and minor helical waves to swimming; namely, propulsion is owing primarily to the minor wave, with negligible contribution from the major wave. We also explore the dependence of the propulsion speed on geometric and kinematic parameters, revealing counterintuitive results, particularly for the case when the minor and major helical structures are of opposite chirality.     

Parameter Optimization of the Radioisotope Gamma Albedo Method for Controlling Quality of Variable Composition Coals

The variant of the gamma albedo method is proposed for the radioisotope express control of coal ash content, which ensures the satisfactory accuracy under conditions of variable elemental composition of coal. It is shown that the integral intensity of the secondary (scattered and fluorescent) radiation weakened by filter of certain thickness is a univocal index of coal ash content. The analytical model for the optimization of the secondary radiation filtration parameters is developed. The utility value of the weakening filter is determined as function of ash content and composition of coal.

     

Waveguides based on alternating graphene-boron-nitride layers

The propagation of an ultimately short optical pulse in a layered structure composed of graphene-boron-nitride bilayers representing waveguide analogs has been theoretically studied. The motion of conduction electrons in this system at low temperatures is described in terms of a long-wavelength effective Hamiltonian, and the electromagnetic field is taken into account on the basis of the classical Maxwell equations. It is established that the amplitude of the propagating ultimately short optical pulse is virtually independent of the system characteristics.     

On the Use of Path-Independent Integrals in Calculating Mixed-Mode Stress Intensity Factors for Elastic and Thermoelastic Cases

It is well known that the energy release rates associated with translation, rotation and self-similar expansion of cavities or cracks in solids are expressed by path-independent integrals J, L and M, respectively. It is shown that for a crack under a uniform tension and for an insulated crack disturbing a uniform heat flow, the energy release rates can be calculated by first considering an elliptical cavity and then performing a limiting process. This limiting process, with certain special properties of the M-integral and the additional relationship provided by the L-integral makes it possible to find the mixed-mode stress intensity factors.     

Evaluation of weld metal hot cracking susceptibility in superaustenitic stainless steel

Solidification cracking susceptibilities of two types of superaustenitic stainless steel, 254SMO and SR50A, were evaluated by transverse Varestraint tests. The susceptibilities were compared with those of conventional austenitic stainless steel 316L, and factors influencing the difference of susceptibility were discussed. The comparison showed that 254SMO and SR50A are more sensitive to solidification cracking than 316L. In the transverse Varestraint tests, both total and maximum crack lengths are longer in the superaustenitic stainless steel. Because of the longer maximum crack length, the superaustenitic stainless steel also has a wider brittleness temperature range of cracking than 316L: about 178 °C for the superaustenitic stainless steel and 43 °C for 316L. It is believed that straight subgrain boundaries owing to the cellular dendritic solidification and segregations of sulfur and phosphorus in the subgrain boundaries of superaustenitic stainless steel make it more sensitive to solidification cracking. In addition to the solidification cracking, reheat cracking is also observed within the previous weld bead in the superaustenitic stainless steel because of fully austenitic solidification with significant segregations. This suggests that caution should be given to the occurrence of reheat cracking when superaustenitic stainless steel is multi pass welded.