Statistical Uncertainty and the Estimation of Log Law Parameters

It is experimentally demonstrated that fitting the log law to the mean velocity profile in turbulent open-channel flow to determine the friction velocity, roughness length, and zero-plane displacement, can lead to relatively high standard errors in these parameters. It is also demonstrated that this approach, where the log law alone is used to estimate these parameters, may yield values of these parameters that are significantly different from those obtained when the friction velocity is determined independently of the log law. Although the statistical estimation of the three log law parameters from mean velocity data alone is frequently necessary, this procedure can lead to inaccurate and imprecise estimates of these quantities.     

Probability of Individual Grain Movement and Threshold Condition

A new criterion for the experimental characterization of the threshold of motion of sediment as bed load is introduced and this criterion is implemented in an experimental investigation of the role of sediment packing density on bed behavior near the threshold of motion. The new criterion, which may be interpreted as the probability of individual grain movement, accounts for the statistical nature of sediment movement in turbulent flow and the time scale of the flow. The threshold of motion is specified by a fixed value of the probability. The criterion represents an objective, quantitative and consistent approach to the threshold condition for sediment of uniform size, shape, and density. The experimental investigation demonstrates that this criterion leads to results that are comparable to those of other approaches, for nearly isolated grains; however, it is found that a threshold criterion based upon the probability of grain movement can yield relatively active sediment beds where the level of activity is strongly dependent upon sediment packing density.     

Healing of carbon fiber reinforced plastics by Diels–Alder based polymers: Effects of healing agent concentration and curing cycle

Self-healing resin (Bismaleimide prepolymer, BMI pp) based on Diels–Alder reaction mechanism was integrated into high performance carbon fiber reinforced plastics (CFRPs). Reference and BMI pp modified CFRPs were manufactured by incorporating grains of the self-healing agent (SHA) in the mid-thickness interlaminar region through sieving. First, the effect of the SHA concentration on the toughening and healing performance of CFRPs was studied under mode I fracture loading. The SHA was able to enhance the interlaminar fracture toughness of the composite to a certain extent and also to offer a moderate thermally activated healing functionality. Also, the effect of the curing temperature on the same results was studied; it was found the decrease of the curing temperature slightly decreases the fracture toughness while increases the healing efficiency of the composite. Finally, optical microscopy examinations were conducted and three-point bending tests were utilized to study the in-plane mechanical properties of the composites. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47478.     

A triangular element based on Reissner-Mindlin plate theory

A new triangular plate bending element based on the Reissner-Mindlin theory is developed through a mixed formulation emanating from the Hu-Washizu variational principle. A main feature of the formulation is the use of a linear transverse shear interpolation scheme with discrete constraint conditions on the edges. The element is shown to avoid shear locking, converge to the Kirchhoff plate theory as the plate thickness approaches zero, and generally exhibit excellent behaviour on a series of standard problems and tests.     

Identifying attractive research fields for new scientists

Prior to the beginning of a scientific career, every new scientist is obliged to confront the critical issue of defining the subject area where his/her future research will be conducted. Regardless of the capabilities of a new scholar, an erroneous selection may condemn a dignified effort and result in wasted energy, time and resources. In this article we attempt to identify the research fields which are attractive to these individuals. To the best of our knowledge, this is a new topic that has never been discussed or addressed in the literature. Here we formally set the problem and we propose a solution combining the characteristics of the attractive research areas and the new scholars. Our approach is compared against a statistical model which reveals popular research areas. The comparison of this method to our proposed model leads to the conclusion that not all trendy research areas are suitable for new scientists. A secondary outcome reveals the existence of scientific fields which although they are not so emerging, they are promising for scientists who are starting their career.     

Novel PEGylated pH-sensitive polymeric hollow microspheres

Novel PEGylated pH-sensitive poly[methacrylic acid-co-poly(ethylene glycol) methyl ether methacrylate] [P(MAA-co-PEGMA)] hollow microspheres were synthesized by a two-stage distillation precipitation polymerization. PMAA@P(MAA-co-PEGMA) core shell microspheres were synthesized by the second-stage polymerization of MAA and PEGMA, using the N,N′-methylenebisacrylamide (MBAAm) as crosslinker in the presence of non-crosslinked PMAA microspheres. The cavity was formed by selective removal of PMAA core in ethanol. The resulted PEGylated hollow microspheres were characterized with Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM) and Fourier Transform Infrared Spectroscopy (FT-IR). The shrink and swelling behavior under different pH was studied by Dynamic Light Scattering (DLS).     

Computer Vision Technique for Tracking Bed Load Movement

An advanced image analysis system, called Khoros, was used to investigate the bed load movement of sediment particles in a laboratory flume. Incipient flow conditions prevailed throughout the experiments. Painted glass balls of identical diameter and density were used to simulate the sediment particles. They were uniformly placed on top of a tightly packed flat porous bed. Experiments were performed with two distinct surface packing configurations. A video camera was used to monitor their motion within a specified area of view. The resulting video record was converted to digital images using a frame grabber. These digital images were downloaded to a workstation for analysis. The outcome of this analysis provided quantitative information about the frequency of the entrainment of the glass beads, their displacement distance, and the mode of their motion. Such information, when used in conjunction with laser Doppler velocimeter measurements of the fluid velocity, can elucidate the physical mechanisms that are responsible for the entrainment of sediment. During the analysis of the tests, it was observed that the displacement of the beads was sporadic and occurred typically by rolling. The glass beads moved predominately along the flow direction, while on some occasions they were displaced in the transverse direction. For the two packing density tests that were examined, the minimum traveling distance in the longitudinal direction was found to be equal to one bead diameter and the maximum was equal to 10 bead diameters. In the transverse direction, the maximum particle traveling distance was equal to four bead diameters. Finally, it is shown that the existing imaging workspace can be used to accurately identify the displacements of small particles, which are typically encountered near incipient flow conditions and are not easily detectable with the bare eye. The imaging method described here is dynamic in nature and may prove to be a valuable tool for studying two-phase flows, as well as for visualizing flow structures taking place near the boundary in turbulent flows.