On the application of Harris hawks optimization (HHO) algorithm to the design of microchannel heat sinks

Engineering with Computers - A novel Harris hawks optimization algorithm is applied to microchannel heat sinks for the minimization of entropy generation. In the formulation of the heat transfer...     

Nitric oxide as mediator of bradykinin-induced pancreatic circulatory and metabolic responses

Bradykinin (BK) is an endogenous nonapeptide with potent vasodilator properties of the visceral circulation. BK alters vascular tone via two BK receptor subtypes, B1 and B2. Current experimental evidence suggests that the dilator action of BK in some vessels is mediated primarily by B2 receptor activation. In addition, there are reports that BK increases endothelial generation of vasodilator factors, such as nitric oxide (NO). The present study had two aims. First, to explore the role of BK-receptors in the pancreatic vasodilatatory and metabolic responses to BK. Second aim was to examine whether endogenous NO play a role in the mediation of BK-receptors induced pancreatic circulatory and metabolic activity. In anesthetized dogs, the superior pancreatico-duodenal artery blood flow (SPBF) was measured by ultrasonic blood flowmeter (Transonic System T-206), pancreatic microcirculatory blood flow (PBF) was determined by laser Doppler flowmetry (Periflux 4001 Master). Pancreatic oxygen consumption (PVO2) was calculated as the product of the arteriovenous oxygen difference (AVO2) across the pancreatic circulation and SPBF. Drugs were infused into the superior pancreatico-duodenal artery. BK (0.01-1.0 mg/kg/min) increased maximally SPBF by 180 +/- 15%, PBF by 208 +/- 22% and PVO2 by 145 +/- 11%, respectively. Pretreatment with B2-subtype receptor antagonist, D-Arg, [Hyp3, Thi5,8, D-Phe7] BK inhibited significantly BK-induced increase in SPBF, PBF and PVO2 by 86 +/- 8%, 73 +/- 7% and 85 +/- 6%, respectively. A nitric oxide synthesis inhibitor (L-NNA) administered i.v. at dose of 25 mg/kg 20 min before BK, inhibited significantly the pancreatic hyperemic and metabolic responses. The results presented emphasize an important role of B2 receptors in the mediation of pancreatic circulatory and metabolic responses to bradykinin. Endogenous NO plays a mediatory role in the pancreatic vascular and metabolic responses due to stimulation of B2-receptors.     

Bivariate shrinkage functions for wavelet-based denoising exploiting interscale dependency

Most simple nonlinear thresholding rules for wavelet-based denoising assume that the wavelet coefficients are independent. However, wavelet coefficients of natural images have significant dependencies. We only consider the dependencies between the coefficients and their parents in detail. For this purpose, new non-Gaussian bivariate distributions are proposed, and corresponding nonlinear threshold functions (shrinkage functions) are derived from the models using Bayesian estimation theory. The new shrinkage functions do not assume the independence of wavelet coefficients. We show three image denoising examples in order to show the performance of these new bivariate shrinkage rules. In the second example, a simple subband-dependent data-driven image denoising system is described and compared with effective data-driven techniques in the literature, namely VisuShrink, SureShrink, BayesShrink, and hidden Markov models. In the third example, the same idea is applied to the dual-tree complex wavelet coefficients.     

A stabilizing augmented grid for rectangular discretizations of the convection–diffusion–reaction problems

We propose a numerical method for approximate solution of the convection–diffusion–reaction problems in the case of small diffusion. The method is based on the standard Galerkin finite element method on an extended space defined on the original grid plus a subgrid, where the original grid consists of rectangular elements. On each rectangular elements, we construct a subgrid with few points whose locations are critical for the stabilization of the problem, therefore they are chosen specially depending on some specific conditions that depend on the problem data. The resulting subgrid is combined with the initial coarse mesh, eventually, to solve the problem in the framework of Galerkin method on the augmented grid. The results of the numerical experiments confirm that the proposed method shows similar stability features with the well-known stabilized methods for the critical range of problem parameters.     

Fatigue characteristics of continuous welded rails and the effect of residual stress on fatigue-ratchetting interaction

ABSTRACT

The importance of ratchetting-fatigue interaction is garnering interest due to complex failure mechanism of rail welds under cyclic loading. The objective of this paper is to investigate the fatigue characteristics of continuous welded rails (CWRs) and the effect of residual stress on fatigue-ratchetting interaction. For this purpose, UIC60 rails have been modeled using a three-dimensional finite element model, including a combination of nonlinear kinematic and isotropic hardening. In addition, the interaction between cyclic loading and the effect of residual stress on fatigue is taken into consideration. Finite element model is validated against representative experimental findings. Smith–Watson–Topper (SWT) method is utilized in order to estimate the fatigue life of rail welds under static and cyclic loading. Lower fatigue life is predicted with increasing load due to the contact between rails and wheels. Simulation results also show that failure in the form of ratchetting occurs during the 10,236th cycle, while failure corresponds to the 15,290th cycle and the 145,161st cycle based on the SWT and Coffin-Manson fatigue models, respectively. These findings suggest that investigations on ratchetting and fatigue should be carried out simultaneously to estimate the failure of the CWRs.     

Applications of the pseudo residual-free bubbles to the stabilization of convection-diffusion-reaction problems

It is known that the enrichment of the polynomial finite element space of degree 1 by bubble functions results in a stabilized scheme of the SUPG-type for the convection-diffusion-reaction problems. In particular, the residual-free bubbles (RFB) can assure stabilized methods, but they are usually difficult to compute, unless the configuration is simple. Therefore it is important to devise numerical algorithms that provide cheap approximations to the RFB functions, contributing a good stabilizing effect to the numerical method overall. Here we propose a stabilization technique based on the RFB method and particularly designed to treat the most interesting case of small diffusion. We replace the RFB functions by their cheap, yet efficient approximations which retain the same qualitative behavior. The approximate bubbles are computed on a suitable sub-grid, the choice of whose nodes are critical and determined by minimizing the residual of a local problem with respect to L ₁ norm. The resulting numerical method has similar stability features with the RFB method for the whole range of problem parameters. This fact is also confirmed by numerical experiments. We also note that the location of the sub-grid nodes suggested by the strategy herein coincides with the one in Brezzi et al. (Math. Models Methods Appl. Sci. 13:445–461, 2003).     

Role of nitric oxide in the pancreatic vascular and metabolic responses associated with activation of capsaicin-sensitive neurons

A significant decrease in mean number of CD5+, CD8(+)-lymphocytes in persons, who worked in 30-km zone of Chernobyl nuclear power station was revealed. A significant increase in percent of CD5+, CD4(+)-cell percents was observed in workers, who worked for 1,2-2,5 years in zone, but absolute number, were decreased comparing a control and data received in people, who have just arrived to work in 30-km zone. The positive correlation exists between the percent of lymphocytes and years of service in 30-km zone. The lower level of alpha 1-thymosine was revealed in serum of the persons, who worked in zone for 4.5-5 years than data received in people, who worked for 0.5 year. Increase level of serum autoantibodies reacting with thymic epithelial cell was detected in men, who worked in zone for 3-3.5 years. In persons, who worked more 5 years and have just arrived in zone identical data were received.     

Nitric oxide mediates intestinal hyperaemic responses to intraluminal bile-oleate

It has long been recognized that intestinal blood flow increases at mealtimes. Mesenteric hyperaemia is also evoked by activation of sensory peptidergic nerves. Our studies explored the possible role of endogenous nitric oxide (NO) in the rat intestinal vasodilator response to luminal instillation of an oleic acid plus bile mixture before and after acute intrajejunal instillation of capsaicin and after chronic pretreatment with capsaicin. In anaesthetized rats we measured jejunal blood flow (BF) with an ultrasonic Doppler flowmeter and systemic arterial pressure (AP) with a pressure transducer. Intestinal perfusion with 80 mM oleic acid in bile increased BF by 98 +/- 12%. Instillation of 4 mg of capsaicin into the jejunal lumen initially increased BF by 42 +/- 9% but was followed by vasoconstriction. Inhibition of NO synthase with 25 mg/kg i.v. N-nitro-L-arginine (L-NNA) decreased BF by 27 +/- 5% and increased AP by 37 +/- 11%. After treatment with L-NNA and after acute and chronic administration of capsaicin, the bile-oleate-induced maximal increases in BF above control levels were 42 +/- 7%, 65 +/- 12%, and 58 +/- 8%, respectively. The observed inhibitory effect of L-NNA on the intestinal hyperaemic response to the bile-oleate mixture was reversed by pretreatment with L-arginine (100 mg/kg i.v.). In capsaicin pretreated rats the subsequent bile-oleate-induced hyperaemia was reduced in magnitude but the inhibitory effects of L-NNA were proportionately the same as in animals not receiving capsaicin. These findings support the hypothesis that NO is involved with bile-oleate-induced mesenteric hyperaemia.     

Experimental and Numerical Modal Characterization for Additively Manufactured Triply Periodic Minimal Surface Lattice Structures: Comparison between Free-Size and Homogenization-Based Optimization Methods

Homogenization-based topology optimization (HMTO) is one of the most extensively used grading methods to generate functionally graded lattice structures (FGLs). However, it requires a precharacterization of the lattices, which is time-consuming. As a remedy, free-size optimization-based graded lattice generation (FOGLG) is explored as an alternative method to generate the FGLs. This article builds on the authors’ previous work in which the HMTO and FOGLG approaches are studied to improve the dynamic characteristic of a design by using a single lattice type, namely, double gyroid (DG) structure. To show applicability of the proposed methods, different lattice types including diamond (D), gyroid (G), and I-WP are employed to create FGLs herein. The frequency response analysis is performed, and the results from HMTO and FOGLG are compared in terms of their accuracy and efficiency. The optimized designs are then reconstructed by relative density mapping (RDM) and enhanced relative density mapping (ERDM) methods. The fabricated test samples made of cobalt–chromium using the direct metal laser melting (DMLM) technique are then experimentally validated using a laser vibrometer. The results reveal that HMTO and FOGLG can be used on the lattice types with a variety of configurations and relative densities.