��Note on ��Flows induced by a plate moving normal to stagnation-point flow�� by P. D. Weidman and M. A. Sprague (Acta Mech. 219, 219�C229, 2011)��

In a recent paper of Weidman and Sprague (Acta Mech., 2011), the unsteady flows generated by an impermeable infinite flat plate advancing with constant velocity V toward, or receding from an orthogonal (plane or axisymmetric) stagnation-point flow, have been investigated by an exact similarity reduction of the Navier?CStokes equations. It has been shown that in the co-moving reference frame of the plate, the induced flow appears as a steady flow, with an additional term R f??? in the governing equation of the similar stream function f (??). The Reynolds number R involved in this additional term is proportional to the plate velocity V. The present paper shows, however, that with the aid of a simple transformation, the additional term R f??? can be removed from the governing equation, its effect being transferred in the boundary condition for f (??). As a consequence, the unsteady flow problems of Weidman and Sprague reduce to the classical steady stagnation-point flow problems for permeable surfaces with a uniform lateral suction or injection of the fluid, so that the transpiration parameter f (0) coincides with R for the plane and with R/2 for the axisymmetric flow, respectively. The main benefit of this approach is that all the results of the latter well-investigated problems can simply be transcribed for the problems formulated by Weidman and Sprague (Acta Mech, 2011).     

Shorter strings containing all k-element permutations

We consider the problem of finding short strings that contain all permutations of order k over an alphabet of size n, with k?n. We show constructively that k(n−2)+3 is an upper bound on the length of shortest such strings, for n?k?10. Consequently, for n?10, the shortest strings that contain all permutations of order n have length at most n²−2n+3. These two new upper bounds improve with one unit the previous known upper bounds.     

Intelligent framework for radio access network design

Wireless Networks - The evolution of 5G networks over the last few years has introduced a variety of technologies for more efficient radio access networks (RANs), which end up in ultra-dense...     

Comment on the paper “Microsystem Technologies: (2018) 24:2919–2928”

The present comment concerns some doubtful results included in the above paper.

     

Core–shell nanowires: From the ensemble to single-wire characterization

Recent investigations of core–shell nanowires using synchrotron radiation techniques deduced the average structural parameters of heterostructure core–shell nanowires. Here, we report on first results and discuss the problems arising when measuring such complex nanostructures by using nanofocusing X-ray techniques. InAs/InAsP core–shell nanowires exhibit a certain bending, the origin of which is described using finite element simulations assuming a displacement of the core, and a gradient in the chemical composition of the wire’s shell.     

Functional Composite Zinc Electrodeposition

The paper presents research into composite deposition with a electrolytic zinc matrix and inert particles.

This type of plating was studied in order to obtain superior functional performances over traditional zinc electrodepositions, such as higher hardness, wear and friction resistance and better corrosion resistance.

The study comprised: establishment of electrolyte composition; disperse phase behaviour on grain structure; effect of current density and electrolyte dynamic regime on co-deposition; plating characteristics.     

Periodic autoregressive model identification using genetic algorithms

Periodic autoregressive (PAR) models extend the classical autoregressive models by allowing the parameters to vary with seasons. Selecting PAR time‐series models can be computationally expensive, and the results are not always satisfactory. In this article, we propose a new automatic procedure to the model selection problem by using the genetic algorithm. The Bayesian information criterion is used as a tool to identify the order of the PAR model. The success of the proposed procedure is illustrated in a small simulation study, and an application with monthly data is presented.     

Manufacturing of dies from hardened tool steels by 3-axis micromilling

In this paper the results of an experimental investigation to analyze the machinability of a hardened, carbide-rich cold-work tool steel 1.2379 (approx. 62 HRC) with coated micro end-milling cutters are discussed. Fundamental experiments were performed to determine a cutting-parameter set, which enables an economic manufacturing of dies by 3-axis micromilling with commercially available cemented-carbide tools. The evaluation of the applicability of different tool types is conducted by analyzing the process forces, the tool wear, the surface quality, the material removal rate, and the entire chip volume. Design of experiments was used to significantly reduce the number of experiments and to model the active and passive forces. Concerning the design of tools for the micromilling of such difficult-to-machine materials, it is shown that cemented-carbide tools with robust cutting edges are applicable for this kind of machining. Furthermore, test microstructures were manufactured with the intention of validating the determined cutting-parameter set in combination with the selected tool types. In addition, the dimension and shape accuracy of the microstructures are analyzed.