bluuebunny/crossref_metadata_2025 huggingface dataset:
The impact of negative mood state on sleep‐related attentional bias in insomnia
Authors: Zheng Senning , Feng Juan , Lin Rongmao , Yan Youwei , Zhang Renchuan , Huang Huiyuan , Wang Junjing , Huang Ruiwang
Published: August 2018

Sleep‐related attentional bias is thought to play a role in the maintenance of insomnia. However, this concept has been questioned by several studies that did not show the presence of sleep‐related attentional bias in clinical insomnia or poor sleepers. Our goal in the present study was to test whether the mood state of individuals with insomnia affects the presence of sleep‐related attentional bias. To this end, 31 individuals with insomnia and 34 good sleepers were randomly assigned to a negative mood‐inducing condition or a control condition. They then completed a visual probe task with three types of pictorial stimuli (general threat, sleep‐related negative pictures and sleep‐related positive pictures). Vigilance, maintenance and the overall bias indexes were calculated based on the reaction time. We found individuals with insomnia only showed a greater overall bias compared with good sleepers following a negative mood induction, regardless of the pictures presented. In addition, we found that a negative mood state was significantly correlated with the overall attentional bias in good sleepers but not in individuals with insomnia. These findings suggest that sleep‐related attentional bias in insomnia can be modulated by mood state. This effect may reflect the dysregulation of top‐down attentional control in individuals with insomnia.
Sleep spindle dynamics during NREM and REM sleep following distinct general anaesthesia in control rats and in a rat model of Parkinson’s disease cholinopathy
Authors: Lazic Katarina , Ciric Jelena , Saponjic Jasna
Published: August 2018

On the basis of our previous studies and the important role of the thalamo‐cortical network in states of unconsciousness, such as anaesthesia and sleep, and in sleep spindles generation, we investigated sleep spindles (SS) and high‐voltage sleep spindle (HVS) dynamics during non‐rapid eye movement (NREM) and rapid eye movement (REM) sleep following different types of general anaesthesia in both physiological controls and in a rat model of Parkinson's disease (PD) cholinopathy, to follow the impact of anaesthesia on post‐anaesthesia sleep at the thalamo‐cortical level through an altered sleep spindle dynamics. We recorded 6 hr of spontaneous sleep in all rats, both before and 48 hr after ketamine/diazepam or pentobarbital anaesthesia, and we used 1 hr of NREM or REM sleep from each to validate visually the automatically detected SS or HVS for their extraction and analysis. In the controls, SS occurred mainly during NREM, whereas HVS occurred only during REM sleep. Ketamine/diazepam anaesthesia promoted HVS, prolonged SS during NREM, induced HVS of increased frequency during REM, and increased SS/HVS densities during REM versus NREM sleep. Pentobarbital anaesthesia decreased the frequency of SS during NREM and the HVS density during REM sleep. Although the pedunculopontine tegmental nucleus lesion prolonged SS only during NREM sleep, in these rats, ketamine/diazepam anaesthesia suppressed HVS during both sleep states, whereas pentobarbital anaesthesia promoted HVS during REM sleep. The different impacts of two anaesthetic regimens on the thalamo‐cortical regulatory network are expressed through their distinct sleep spindle generation and dynamics that are dependent on the NREM and REM state regulatory neuronal substrate.
Developing a core outcome set for childhood obesity prevention: A systematic review
Authors: Matvienko‐Sikar Karen , Griffin Ciara , McGrath Niamh , Toomey Elaine , Byrne Molly , Kelly Colette , Heary Caroline , Devane Declan , Kearney Patricia M.
Published: August 2018

Synthesis of effects of infant feeding interventions to prevent childhood obesity is limited by outcome measurement and reporting heterogeneity. Core outcome sets (COSs) represent standardised approaches to outcome selection and reporting. The aim of this review is to identify feeding outcomes used in infant feeding studies to inform an infant feeding COS for obesity prevention interventions. The databases EMBASE, Medline, CINAHL, CENTRAL, and PsycINFO searched from inception to February 2017. Studies eligible for inclusion must examine any infant feeding outcome in children ≤1 year. Feeding outcomes include those measured using self‐report and/or observational methods and include dietary intake, parent–child interaction, and parental beliefs, among others. Data were extracted using a standardised data extraction form. Outcomes were assigned to outcome domains using an inductive, iterative process with a multidisciplinary team. We identified 82 unique outcomes, representing nine outcome domains. Outcome domains were “breast and formula feeding,” “introduction of solids,” “parent feeding practices and styles,” “parent knowledge and beliefs,” “practical feeding,” “food environment,” “dietary intake,” “perceptions of infant behaviour and preferences,” and “child weight outcomes.” Heterogeneity in definition and frequency of outcomes was noted in reviewed studies. “Introduction of solids” (59.5%) and “breastfeeding duration” (55.5%) were the most frequently reported outcomes. Infant feeding studies focus predominantly on consumption of milks and solids and infant weight. Less focus is given to modifiable parental and environmental factors. An infant feeding COS can minimise heterogeneity in selection and reporting of infant feeding outcomes for childhood obesity prevention interventions.
A diet rich in C3 plants reveals the sensitivity of an alpine mammal to climate change
Authors: Bhattacharyya Sabuj , Dawson Deborah A. , Hipperson Helen , Ishtiaq Farah
Published: August 2018

Plant–herbivore interactions provide critical insights into the mechanisms that govern the spatiotemporal distributions of organisms. These interactions are crucial to understanding the impacts of climate change, which are likely to have an effect on the population dynamics of alpine herbivores. The Royle's pika (Ochotona roylei, hereafter pika) is a lagomorph found in the western Himalaya and is dependent on alpine plants that are at risk from climate change. As the main prey of many carnivores in the region, the pika plays a crucial role in trophic interactions. We examined topographical features, plant genera presence and seasonal dynamics as drivers of the plant richness in the pika's diet across an elevational gradient (2,600–4,450 m). We identified 79 plant genera in the faecal pellets of pikas, of which 89% were forbs, >60% were endemic to the Himalaya, and 97.5% of the diet plant genera identified followed the C3 photosynthetic pathway. We found that, during the premonsoon season, the number of genera in the pika's diet decreased with increasing elevation. We demonstrate that a large area of talus supports greater plant diversity and, not surprisingly, results in higher species richness in the pika's diet. However, in talus habitat with deep crevices, pikas consumed fewer plant genera suggesting they may be foraging suboptimally due to predation risk. The continued increase in global temperature is expected to have an effect on the distribution dynamics of C3 plants and consequently influence pika diet and distribution, resulting in a significant negative cascading effect on the Himalayan ecosystem.
Are we underestimating the occurrence of sympatric populations?
Authors: Jorde Per Erik , Andersson Anastasia , Ryman Nils , Laikre Linda
Published: August 2018

Sympatric populations are conspecific populations that coexist spatially. They are of interest in evolutionary biology by representing the potential first steps of sympatric speciation and are important to identify and monitor in conservation management. Reviewing the literature pertaining to sympatric populations, we find that most cases of sympatry appear coupled to phenotypic divergence, implying ease of detection. In comparison, phenotypically cryptic, sympatric populations seem rarely documented. We explore the statistical power for detecting population mixtures from genetic marker data, using commonly applied tests for heterozygote deficiency (i.e., Wahlund effect) and the structure software, through computer simulations. We find that both tests are efficient at detecting population mixture only when genetic differentiation is high, sample size and number of genetic markers are reasonable and the sympatric populations happen to occur in similar proportions in the sample. We present an approximate expression based on these experimental factors for the lower limit of FST, beyond which power for structure collapses and only the heterozygote‐deficiency tests retain some, although low, power. The findings suggest that cases of cryptic sympatry may have passed unnoticed in population genetic screenings using number of loci typical of the pre‐genomics era. Hence, cryptic sympatric populations may be more common than hitherto thought, and we urge more attention being diverted to their detection and characterization.
The effect of a multispecies probiotic on microbiota composition in a clinical trial of patients with diarrhea‐predominant irritable bowel syndrome
Authors: Hod Keren , Dekel Roy , Aviv Cohen Nathaniel , Sperber Ami , Ron Yishai , Boaz Mona , Berliner Shlomo , Maharshak Nitsan
Published: August 2018

Background

Although probiotics are increasingly used in irritable bowel syndrome (IBS), their mechanism of action has not been elucidated sufficiently. We aimed to evaluate the impact of a multispecies probiotic on enteric microbiota composition in women with diarrhea‐predominant‐IBS (IBS‐D) and to determine whether these effects are associated with changes in IBS symptoms or inflammatory markers.

Methods

In a double‐blind, placebo‐controlled study, Rome III IBS‐D women completed a two‐week run‐in period and eligible women were assigned at random to a probiotic capsule (BIO‐25) or an indistinguishable placebo, twice daily for 8 weeks. IBS symptoms and stool consistency were rated daily by visual analogue scales and the Bristol stool scale. High sensitivity C‐reactive protein, fecal calprotectin and microbial composition were tested at baseline and at 4 and 8 weeks. Microbial sequencing of the 16S rRNA was performed and data were analyzed to compare patients who responded to treatment with those who did not.

Key Results

172 IBS‐D patients were recruited and 107 eligible patients were allocated to the intervention (n = 54) or placebo (n = 53) group. Compared to placebo, BIO‐25 did not result in changes in microbial diversity or taxa proportions, except for higher relative proportions of Lactobacillus in the BIO‐25 group (P = 0.002). Symptomatic responders to BIO‐25 showed a reduction in the proportion of Bilophila(P = 0.003) posttreatment. Patients with beneficial inflammatory‐marker changes had higher baseline proportions of Faecalibacterium(P = 0.03), Leuconostoc (P = 0.03), and Odoribacter (P = 0.05) compared to corresponding non‐responders.

Conclusions & Inferences

Identifying patients with a more amenable microbiome at treatment initiation may result in better treatment response.
Intermittent Price Changes in Production Plants: Empirical Evidence Using Monthly Data
Authors: Nilsen Øivind A. , Vange Magne
Published: August 2018

The price‐setting behaviour of manufacturing plants is examined using a large panel of monthly surveyed plant‐ and product‐specific prices. The sample shows a high frequency of zero changes, relatively small price changes and a strong seasonal price‐change pattern. The intermittent feature of price changes is modelled with thresholds which are smaller in January, and a quadratic loss function associated with the distance from the target price. The findings show statistically significant pricing thresholds, which are only two‐thirds in January, and partial adjustment parameters implying that 60% of the deviation between the target price and the current price is closed each month.
A regulatory role of autophagy for resetting the memory of heat stress in plants
Authors: Sedaghatmehr Mastoureh , Thirumalaikumar Venkatesh P. , Kamranfar Iman , Marmagne Anne , Masclaux‐Daubresse Celine , Balazadeh Salma
Published: August 2018

As sessile life forms, plants are repeatedly confronted with adverse environmental conditions, which can impair development, growth, and reproduction. During evolution, plants have established mechanisms to orchestrate the delicate balance between growth and stress tolerance, to reset cellular biochemistry once stress vanishes, or to keep a molecular memory, which enables survival of a harsher stress that may arise later. Although there are several examples of memory in diverse plants species, the molecular machinery underlying the formation, duration, and resetting of stress memories is largely unknown so far. We report here that autophagy, a central self‐degradative process, assists in resetting cellular memory of heat stress (HS) in Arabidopsis thaliana. Autophagy is induced by thermopriming (moderate HS) and, intriguingly, remains high long after stress termination. We demonstrate that autophagy mediates the specific degradation of heat shock proteins at later stages of the thermorecovery phase leading to the accumulation of protein aggregates after the second HS and a compromised heat tolerance. Autophagy mutants retain heat shock proteins longer than wild type and concomitantly display improved thermomemory. Our findings reveal a novel regulatory mechanism for HS memory in plants.
Intervening into mechanisms: Prospects and challenges
Authors: Kästner Lena , Andersen Lise Marie
Published: August 2018

In contemporary philosophy of science, the consensus view seems to be that scientific explanations describe mechanisms responsible for the phenomena to be explained. Two kinds of explanatory relevance figure in mechanistic accounts of explanation: causal (etiological) and constitutive. Following prominent accounts, it seems natural to analyze both these relations in terms of systematic interventions into some factor X with respect to another factor Y. However, such interventions are tailored to uncover causal relations only. Construing the constitutive relationship between parts and wholes in terms of interventions thus raises metaphysical, conceptual, and epistemological questions. We here review the barriers that intervention‐based inquiry into mechanisms encounters and consider some solutions.
Qualitative zoning of groundwater to assessment suitable drinking water using fuzzy logic spatial modelling via GIS
Authors: Mohebbi Tafreshi Amin , Mohebbi Tafreshi Ghazaleh , Bijeh Keshavarzi Mohammad Hosein
Published: August 2018

Due to shortage of surface water, resources of ground water in Iran (like many other countries with dry and semi‐dry weather) have turned into the most important and reliable source for water supply. Thus, it is necessary to consider the quality of this resource for drinking purposes. The aim of this study was to assessment suitable drinking water based on a fuzzy approach in Asalem region, Iran. For reduce the uncertainty, fuzzy logic spatial modelling via GIS was applied. To receive these aims, four stages were performed. In stage 1, we calculate the values of eighteen conventional and effective factors used for drinking water quality classification upon analysing the statistical quality data regarding various ions existing in 15 sample wells dug in 2015. In stage 2, interpolate these factors by kriging method via ArcGIS software. In stage 3, parameter standardization with fuzzy membership function were done. And in stage 4, for Aggregation factors, several fuzzy overlay operations were used. Finally, to identify the best operation, the ‘Optimum Index Factor’ was used. Results showed that the ‘GAMMA 0.9’ with highest OIF in most of the factors, is the best overly operation in our study area. According to classified the best operation map, 1.42% of understudied regions are classified in very poor class, 12.48% is grouped in poor class, 78.55% is grouped in fair class, 7.53% is classified in good group and 0.01% is classified as excellent group. In this regard only central parts of the study area have ‘fair’ to ‘good’ and ‘excellent’ groundwater quality for drinking water and in other parts, the quality is within ‘very poor’ and ‘poor’ to ‘fair’.
Elimination of donor CD47 protects against vascularized allograft rejection in mice
Authors: Chen Mo , Wang Yuantao , Wang Hui , Sun Liguang , Fu Yaowen , Yang Yong‐Guang
Published: August 2018

CD47 is a ubiquitously expressed transmembrane glycoprotein that plays a complex role in regulation of cell survival and function. We have previously shown that the interspecies incompatibility of CD47 plays an important role in triggering rejection of cellular xenografts by macrophages. However, the role of CD47 in solid organ transplantation remains undetermined. Here, we explored this question in mouse models of heart allotransplantation. We observed that the lack of CD47 in donor hearts had no deleterious effect on graft survival in syngeneic or single MHC class I‐mismatched recipients, in which both wild‐type (WT) and CD47 knockout (CD47 KO) mouse hearts survived long term with no sign of rejection. Paradoxically, elimination of donor CD47 was beneficial for graft survival in signal MHC class II‐ and class I‐ plus class II‐mismatched combinations, in which CD47 KO donor hearts showed significantly improved survival compared to WT donor hearts. Similarly, CD47 KO donor hearts were more resistant than WT hearts to humoral rejection in α1,3‐galactosyltransferase‐deficient mice. Moreover, a significant prolongation of WT allografts was observed in recipient mice treated with antibodies against a CD47 ligand thrombospondin‐1 (TSP1) or with TSP1 deficiency, indicating that TSP1‐CD47 signaling may stimulate vascularized allograft rejection. Thus, unlike cellular transplantation, donor CD47 expression may accelerate the rejection of vascularized allografts.
Analysis of Mathematical Thinking Skills of Sportsmen According to Certain Demographic Characteristics
Authors: Önal Halil , Inan Mehmet , Bozkurt Sinan
Published: August 2018

The aim of this research was examining the mathematical thinking of athletes who are actively engaged in sports in a sports club in terms of various variables. The research was designed as a screening model. The sample of the study consisted of 229 licensed athletes in various clubs. The "Mathematical Thinking Scale" developed by Ersoy (2012) was used in the research. Percentage frequency analysis was used for descriptive analyzes in the analyzes of the data. Mann Whitney-U and Kruskal-Wallis tests were performed among the non-parametric tests to measure the differences between the groups. According to the results of the research, the scores of the athletes depending on the gender variables on the mathematical thinking scale do not differ statistically. According to the educational variables, the total scores of the athletes attending primary education on the mathematical thinking scale are significantly higher than the other groups, and athletes with the lowest scores were the ones that still continue their undergraduate studies. According to the gender variables, there was a difference only in the scores of the problem-solving sub-dimension in mathematical thinking scale dimensions. When the educational status is analyzed by variables, statistical differences are observed among subscales of the mathematical thinking scale except for reasoning. There was no statistically significant difference between the total scores of individual athletes (billiards, tennis, shooting, archery) on the mathematical thinking scale and the scores they got from all subscales of the scale. In the case of team athletes (football, volleyball, basketball), there was a statistically significant difference in favour of those who played soccer and volleyball sports between the total scores they received on the mathematical thinking scale and the scores they received from all the subscales of the scale.
Investigation of the Experiment Design Skills of Biology and Science Teachers and Preservice Teachers
Authors: Şimşekli Yeter
Published: August 2018

In this study, it was aimed to examine the experiment design skills of Biology and Science teachers and preservice teachers. For this purpose, 85 Biology and 80 Science teachers and preservices given information about laboratory approaches, experiment types and science process skills were asked to design an experiment about germination. In the reports of the experiments designed by the teachers and the presevice teachers, they were expected to give information about the factors affecting germination, write the problem, determine the hypotheses and the variables, plan their experiments and reach a conclusion. In the analysis of the reports, the sets of data digitized by forming a graded scoring scale were analyzed by benefiting from SPSS package program and their experiment design levels were analyzed based on their fields, being a teacher or a preservice teacher and gender. From the obtained data, it was determined that the number of those who designed an experiment was very low and although there were significant differences between the Biology and the Science teachers and preservice teachers in terms of designing an experiment according to many criteria, there was a difference only in one criterium according to gender.
Effects of Density and Blowing Ratios on the Turbulent Structure and Effectiveness of Film Cooling
Authors: Stratton Zachary T. , Shih Tom I-P.
Published: August 2018

Large eddy simulations (LES) were performed to investigate film cooling of a flat plate, where the cooling jets issued from a plenum through one row of circular holes of diameter D and length 4.7D that are inclined at 35 deg relative to the plate. The focus is on understanding the turbulent structure of the film-cooling jet and the film-cooling effectiveness. Parameters studied include blowing ratio (BR = 0.5 and 1.0) and density ratio (DR = 1.1 and 1.6). Also, two different boundary layers (BL) upstream of the film-cooling hole were investigated—one in which a laminar BL was tripped to become turbulent from near the leading edge of the flat plate, and another in which a mean turbulent BL is prescribed directly. The wall-resolved LES solutions generated were validated by comparing its time-averaged values with data from PIV and thermal measurements. Results obtained show that having an upstream BL that does not have turbulent fluctuations enhances the cooling effectiveness significantly at low velocity ratios (VR) when compared to an upstream BL that resolved the turbulent fluctuations. However, these differences diminish at higher VRs. Instantaneous flow reveals a bifurcation in the jet vorticity as it exits the hole at low VRs, one branch forming the shear-layer vortex, while the other forms the counter-rotating vortex pair (CRVP). At higher VRs, the shear layer vorticity is found to reverse direction, changing the nature of the turbulence and the heat transfer. Results obtained also show the strength and structure of the turbulence in the film-cooling jet to be strongly correlated to VR.
Optimization of Structures Made From Composites With Elliptical Inclusions
Authors: Kozuch Christopher D. , Jasiuk Iwona M.
Published: August 2018

This paper seeks to determine the relationship between the parameters that define microstructures composed of a matrix with periodic elliptical inclusions and the effectiveness of structural optimization through the application of existing methods. Stiffness properties for a range of microstructures were obtained computationally through homogenization, and these properties were used to conduct separate homogeneous topology optimization and heterogeneous microstructural optimization on two canonical structural problems. Effectiveness was evaluated on the basis of final total strain energy when compared to a reference configuration. Local minima were found for the two structural problems and various microstructure configurations, indicating that the microstructure of composites with elliptical inclusions can be fine-tuned for optimization. For example, when applying topology optimization to a cantilever beam made from a material with soft, horizontal inclusions, ensuring that the aspect ratio of the inclusions is 2.25 will yield the stiffest structure. In the case of heterogeneous microstructural optimization, one of the results obtained from this analysis was that optimizing the aspect ratio of the inclusion is much more impactful in terms of increasing the stiffness than optimizing the inclusion orientation. The existence of these optimal designs have important implications in composite component design.
Convexity and Optimality Conditions for Constrained Least-Squares Fitting of Planes and Parallel Planes to Establish Datums
Authors: Shakarji Craig M. , Srinivasan Vijay
Published: August 2018

This paper addresses some important theoretical issues for constrained least-squares fitting of planes and parallel planes to a set of points. In particular, it addresses the convexity of the objective function and the combinatorial characterizations of the optimality conditions. These problems arise in establishing planar datums and systems of planar datums in digital manufacturing. It is shown that even when the set of points (i.e., the input points) are in general position, (1) a primary planar datum can contact 1, 2, or 3 input points, (2) a secondary planar datum can contact 1 or 2 input points, and (3) two parallel planes can each contact 1, 2, or 3 input points, but there are some constraints to these combinatorial counts. In addition, it is shown that the objective functions are convex over the domains of interest. The optimality conditions and convexity of objective functions proved in this paper will enable one to verify whether a given solution is a feasible solution, and to design efficient algorithms to find the global optimum solution.
A Novel, Needle-Array Dry-Electrode With Stainless Steel Micro-Tips, for Electroencephalography Monitoring
Authors: Radhakrishnan J. K. , Nithila S. , Kartik S. N. , Bhuvana T. , Kulkarni G. U. , Singh U. K.
Published: August 2018

A novel, needle array dry electrode consisting of 10 × 10 array of stainless steel (SS) Microtips was developed for electroencephalography (EEG) monitoring. The developed dry electrode uses commercially available, inexpensive, SS acupuncture needles certified for invasive use, to collect the EEG signal. The microtips of the acupuncture needles project out of a flat Teflon base by approximately 150 μm. Mechanical failure analysis was carried out, with theoretical calculations for individual needles and experimental measurements with a universal testing machine (UTM). The theoretically calculated critical load for failure for individual needle was 0.88 N, while the UTM measurements show the failure occurring at 0.95 N; this difference is probably due to the simplified assumptions used in calculations. The UTM measurements of the individual needle applied against a Silicone elastomer reveal that the force required for the penetration of the needle of the electrode into skin maybe as low as 0.01 N. Needle array insertion into silicone elastomer sheet and its optical inspection was carried out to assess the ability of the microneedles to penetrate the skin. The impedance of the electrode, measured in three electrode configuration in 0.9% NaCl solution, was approximately 6.8KΩ at 20 Hz, which is sufficiently low to fulfill the requirements of biopotential measurement. The construction and characteristics of the developed needle array dry electrode show that they are suitable for penetrating the stratum corneum of the skin and acquire the EEG signal directly from the interstitial fluidic layer underneath. The construction of the electrode and its mechanical and electrical characteristics show that it is a promising dry electrode for long duration EEG Monitoring.
Investigation of the Motion of Bubbles in a Centrifugal Pump Impeller
Authors: Stel Henrique , Ofuchi Edgar M. , Sabino Renzo H. G. , Ancajima Felipe C. , Bertoldi Dalton , Marcelino Neto Moisés A. , Morales Rigoberto E. M.
Published: August 2018

Centrifugal pumps operate below their nominal capacity when handling gas–liquid flows. This problem is sensitive to many variables, such as the impeller speed and the liquid flow rate. Several works evaluate the effect of operating conditions in the pump performance, but few bring information about the associated gas–liquid flow dynamics. Studying the gas phase behavior, however, can help understanding why the pump performance is degraded depending on the operating condition. In this context, this paper presents a numerical and experimental study of the motion of bubbles in a centrifugal pump impeller. The casing and the impeller of a commercial pump were replaced by transparent components to allow evaluating the bubbles' trajectories through high-speed photography. The bubble motion was also evaluated with a numerical particle-tracking method. A good agreement between both approaches was found. The numerical model is explored to evaluate how the bubble trajectories are affected by variables such as the bubble diameter and the liquid flow rate. Results show that the displacement of bubbles in the impeller is hindered by an increase of their diameter and impeller speed but facilitated by an increase of the liquid flow rate. A force analysis to support understanding the pattern of the bubble trajectories was provided. This analysis should enlighten the readers about the dynamics leading to bubble coalescence inside an impeller channel, which is the main reason behind the performance degradation that pumps experience when operating with gas–liquid flows.
Unsteady Effects on the Experimental Determination of Overall Effectiveness
Authors: Rutledge James L. , Baker William P.
Published: August 2018

An increasingly common experimental method allows determination of the overall effectiveness of a film cooled turbine component. This method requires the Biot number of the experimental model to match that of the engine component such that the nondimensional surface temperature, ϕ, is matched to that of the engine component. The matched Biot number requirement effectively places a requirement on the thermal conductivity of the model and the traditional implementation places no requirement on the model's density or specific heat. However, such is not the case if such a model is exposed to unsteadiness in the flow such as with film cooling unsteadiness. In this paper, we develop an additional nondimensional parameter that must also be theoretically matched to conduct overall effectiveness experiments with unsteady film cooling. Since finding suitable materials with an acceptable combination of thermodynamic properties for a typical low temperature experiment can be difficult, simulations were conducted to determine the impact of imperfectly matched parameters achievable with common materials. Because the disparity between the diffusion and the unsteadiness time scales can hinder numerical simulation, a novel analytical solution to the heat equation with relevant unsteady Robin type boundary conditions is developed. Particular solutions are examined to determine the sensitivity of the temperature response of a turbine blade (or a model of one) to its material properties and the form of the unsteady variation in the convection parameters. It is shown that it is possible to obtain useful experimental results even with imperfectly matched parameters.
Application of the Proper Orthogonal Decomposition Method for Cracked Rotors
Authors: Al-Shudeifat Mohammad A. , Al Mehairi Ayesha , Saeed Adnan S. , Balawi Shadi
Published: August 2018

The application of the proper orthogonal decomposition (POD) method to the vibration response of a cracked rotor system is investigated. The covariance matrices of the horizontal and vertical whirl amplitudes are formulated based on the numerical and experimental whirl response data for the considered cracked rotor system. Accordingly, the POD is directly applied to the obtained covariance matrices where the proper orthogonal values (POVs), and the proper orthogonal modes (POMs) are obtained for various crack depths, unbalance force vector angles, and rotational speeds. It is observed that both POVs and their corresponding POMs are highly sensitive to the appearance of the crack and the unbalance force angle direction in the neighborhoods of the critical rotational speeds. The sensitivity zones of the POVs and POMs to the crack propagation are found to be coinciding with the unstable zones found by the Floquet's theory of the considered cracked system.
Investigation of the Effect of Inlet Turbulence and Reynolds Number on Developing Duct Flow
Authors: Tuna Burak A. , Yarusevych Serhiy , Li Xianguo , Ren Yi , Shi Fanghui
Published: August 2018

This study investigates experimentally the effects of upstream flow conditions and Reynolds number on a developing duct flow. Particle image velocimetry (PIV) and hot-wire (HW) anemometry are employed to explore the flow dynamics in a rectangular duct with an aspect ratio of 2 and a length of 40 hydraulic diameters (Dh). Experiments are employed for two Reynolds numbers, ReDh = 17,750 and 35,500 where the inlet turbulence intensity is controlled using different turbulence grids. The results show that the inlet turbulence intensity and Reynolds number have a substantial effect on the flow evolution, the onset of shear layer interaction zone, and the subsequent relaxation to the fully developed flow. The main effect is linked to the development of the boundary layer, as the turbulence intensity decays rapidly in the core flow. The detailed analysis indicates that transition to turbulence advances upstream as the inlet turbulence intensity is increased, leading to an earlier onset of shear layer interaction and the decrease in entrance length. A similar upstream advancement of laminar-to-turbulent transition is induced as the Reynolds number is increased. However, a delay in the onset of shear layer interaction regime is observed at higher Reynolds number due to lower overall boundary layer growth rate. Thus, the focus of the analysis characterization of the boundary layer development and quantification of the associated changes in the duct flow development.
A New Asperity-Scale Mechanistic Model of Tribocorrosive Wear: Synergistic Effects of Mechanical Wear and Corrosion
Authors: Ghanbarzadeh Ali , Salehi Farnaz Motamen , Bryant Michael , Neville Anne
Published: August 2018

A corrosive wear model is considered at the asperity-scale of a tribocorrosive wear system as well as the traditional Archard-type mechanical wear model. The geometry of the surface asperities is modified in a contact mechanics model with respect to both corrosive and mechanical wear calculations. This model was presented and validated for prediction of the electrochemistry in the first part of this work. The material used in the experimental part of this work was CoCrMo plate working electrode (WE) and Si3N4 ball as the counter body in a reciprocating configuration. Experiments were conducted at loads of 5, 7.5, and 10 N and the contributions of total mechanical wear and corrosion were measured. The model is then tuned to predict the chemical and mechanical components of the total wear of the system. The synergistic effect of corrosion on mechanical wear and mechanical wear on corrosion are modeled numerically in this work. The values are then used to explain different components of mechanistic tribocorrosive wear models present in the literature. This deterministic model, for the first time, calculates the corrosion-enhanced wear in a tribocorrosive wear environment and proposes that changes in the topography are responsible for this synergistic effect. The results show a linear dependence of the corrosion enhanced wear, wear-enhanced corrosion, and the pure mechanical wear on the applied load. Results also suggest that the wear enhanced corrosion has a significant contribution in the overall degradation of the material.
A New Index to Evaluate the Potential Damage of a Surge Event: The Surge Severity Coefficient
Authors: Munari Enrico , Morini Mirko , Pinelli Michele , Brun Klaus , Simons Sarah , Kurz Rainer
Published: August 2018

Industrial compressors suffer from strong aerodynamic instability that arises when low ranges of flow rate are achieved; this instability is called surge. This phenomenon creates strong vibrations and forces acting on the compressor and system components due to the fact that it produces variable time-averaged mass flow and pressure. Therefore, surge is dangerous not only for aerodynamic structures but also for mechanical parts. Surge is usually prevented in industrial plants by means of anti-surge systems, which act as soon as surge occurs; however, some rapid transients or system upsets can lead the compressor to surge anyway. Despite the fact that surge can be classified as mild, classic, or deep, depending on the amplitudes and frequency of the fluctuations, operators are used to simply referring to surge, without making a distinction between the three main classes. This is one of the reasons why, when surge occurs in industrial plants, it is a common practice to stop the machine to perform inspections and check if any damage occurred. Obviously, this implies maintenance costs and time, during which the machine does not operate. On the other hand, not all surge events are dangerous in terms of damage, and they can be tolerated by the mechanical structures of the compressor; thus, in these cases, inspections would not be required. Unfortunately, a method for establishing the potential damage of a surge event is not available in literature. In order to fill this gap, this paper proposes a final formulation of a surge severity index, which was only preliminarily formulated by the authors in a previous work. The preliminary form of this coefficient demonstrated some limitations, which are overcome in this paper. The surge severity index derives from an energy-force based analysis. The coefficient demonstration is carried out in this paper by means of (i) the application of the Buckingham's Pi-theorem, and (ii) a careful analysis of the causative and restorative factors of surge. Finally, some simple practical evaluations are shown by means of a sensitivity analysis, using simulation results of an existing model, to effectively further highlight the consistency of this coefficient for industry.
Kinematics and Force Analysis of Flexible Screw Mechanism for a Worm Robot
Authors: Zhang Yanheng , Xu Jian , Wang Wei
Published: August 2018

This paper presents a new type of flexible screw mechanism (FSM), which is composed of a nut, flexible axle, and roller. It can be used in a worm robot to achieve flexible peristaltic motion, as well as curvilinear motion and deformation. This type of FSM uses a roller to decrease the friction. We investigated the transmission principle and the kinematic characteristics of this FSM, established the model of the velocity, acceleration of the roller, characterized the feed motion characteristics of the flexible shaft, and achieved an analytical solution of the flexible shaft's velocity. Furthermore, by considering the position of the pure rolling section of the roller, the spin slide model is proposed based on Hertz theory. To investigate the friction loss between the roller and the flexible axle, we established a friction work model of the entire FSM system. Finally, the motion characteristics of the FSM are evaluated through experiments.
Development of an Insect-Inspired Hexapod Robot Actuated by Soft Actuators
Authors: Nguyen Canh Toan , Phung Hoa , Hoang Phi Tien , Nguyen Tien Dat , Jung Hosang , Choi Hyouk Ryeol
Published: August 2018

Insects are one of the most diverse group of animals on the planet and are almost ubiquitous. Their walking locomotion has inspired engineers and provided effective solutions for designing transport methods for legged robots. In this paper, we introduce a hexapod walking robot that mimics the design and walking motions of insects. The robot is characterized by small size, light weight, simple structure, and considerably fast walking speed. Three pairs of its legs are driven by three five-degrees-of-freedom (5DOF) soft actuators based on dielectric elastomer (DE) actuators which can provide up to five movements (including three translations and two rotations) within a compact structure. The robot imitates the crawling motion of an insect using the alternating tripod gait. The experiments show that the robot can achieve an average walking speed of 5.2 cm/s (approximately 21 body-lengths per minute) at 7 Hz of actuation frequency on flat rigid surfaces. Furthermore, the robot also demonstrates the omnidirectional capabilities of walking sideways and rotating its body direction, which enhance the potential of applying the proposed robot in practical uses.
Transient Local Resolution of Flow Boiling in a Microchannel With a Streamlined Pin Fin
Authors: Parahovnik Anatoly , Wang Yingying , Peles Yoav
Published: August 2018

Flow boiling around a single streamlined pin fin in a microchannel with engineering fluid, HFE-7000, was experimentally studied. A micro heater and an array of resistance temperature detectors (RTDs) were integrated into the microchannel device to enable heating and local temperature measurements on the microchannel internal wall. Thermal behavior as a function of position, heat flux, mass flux, and pressure was investigated for single phase flow and flow boiling. High-speed visualization of the two-phase flow was used to identify pertinent flow patterns and to complement the surface temperature measurements. It was found that the nucleate boiling regime and the periodic behavior of the boiling process was strongly dependent on the system’s pressure.
Frost Formation on Aluminum and Hydrophobic Surfaces
Authors: Haque Mohammad Rejaul , Betz Amy Rachel
Published: August 2018

Ice and frost formation on the surfaces of car windshield, airplanes, air-conditioning duct, transportation, refrigeration and other structures is of great interest due to its negative impact in the efficiency and reliability of the system. Frost formation is a complex and fascinating phenomenon. Frequent defrosting are required to remove the ice that causes economic losses. In order to delay the freezing phenomenon, hydrophobic surfaces (Al-H) were prepared using a very simple and low cost method by dip coating of Aluminum in Teflon© and FC - 40 solution at a ratio of 2:10. Later, the samples were placed on a freezing stage in a computer controlled environmental chamber. The freezing stage was held at a constant temperature of 265 ± 0.5 K. The environmental temperature was set to 295 ± 0.5 K and the relative humidity (RH) was set to 40% and 60% respectively. The samples were observed via optical microscopy from the top and videos of the freezing dynamics were captured. The time required for the whole surface to freeze was named as ‘Freezing time’ and is determined by investigating the consecutive images. The inter-droplet freezing wave propagation was accelerated via a frozen droplet/area and then propagates through the surface very quickly. Ice bridging was also seen for the frost propagation. However, the maximum freezing front propagation velocity was found for Al surfaces at 60% RH. At 40% RH, the Al surface required approximately 10 ± 1 minutes to freeze while the Al-H surface delay freezing until 15 ± 1 minutes. This is due to a slow rate of nucleation and also increased rate of coalescence. At 60% RH, both surface froze faster than 40% RH. The Al surface required 6.5 ± 1 minutes and the Al-H surface froze after 10 ± 1 minutes. The change in freezing kinetics, freezing time, the size of droplets at freezing, and the surface area covered at freezing are all related to the rate of coalescence of droplets. Again, the added thermal resistance of the coating and less water-surface contact area of the droplet to the cooled hydrophobic surface inhibited the growth rate resulting the freezing delay.
Atmospheric Condensation Performance of Plain Copper and Graphene Oxide Coated Copper Surfaces
Authors: Haque Mohammad Rejaul , Betz Amy Rachel
Published: August 2018

Atmospheric condensation is important for multiple practical applications such as distillation/desalination of water, aerospace, dehumidification, and water harvesting etc. Graphene, an allotrope of carbon with two dimensional structure, has excellent thermal and electrical properties. Here we present condensation studies of water on plain copper and graphene oxide (GO) coated copper surface with different environmental conditions to explore the size distribution of the generated droplets and area coverage in order to characterize the surfaces for larger condensate harvesting. Later, droplet growth and size distributions were recorded for 41 minutes 20 seconds on the surfaces at 40% and 60% relative humidities with a surface temperature of 278 ± 0.5 K. The chamber was maintained at atmospheric pressure and 295 ± 0.5 K. The samples were observed via optical microscopy and videos of the condensation dynamics were captured. The droplet grew mainly by direct condensation and coalescence event. At later stages of condensation, surface coverage increased significantly compared to early stages for all the considered cases. Approximate 95% surface coverage was observed for GO coated copper surface which provides a great insight of this substrates for implementing it in the desired water harvesting applications. The pinning of droplets into the micro/nanostructures of the coated surfaces leads enough time for the first generation droplets to grow in larger size and made more preferential for subsequent coalescence events. Within the initial period of condensation, the number of droplets reduced according to power law decay. The contribution of coalescence mechanism in droplet growth was found larger for 60% RH than 40% RH. As droplet grew larger, direct growth became less significant compared to coalescence phenomenon.
System and Component Transport Considerations of Micro-Pin Based Solar Receivers With High Temperature Gaseous Working Fluids
Authors: Fronk Brian M. , Jajja Saad A.
Published: August 2018

This paper explores the interactions between micro-pin concentrated receiver designs with overall solar thermal energy system performance, with different operating conditions, working fluid, and required materials of construction. A 320 MW thermal plant coupled to a 160 MW electric sCO2 Brayton cycle is considered as the baseline. The circulating fluid enters the receiver at 550°C, and leaves at 720°C. The thermal storage/power block are located 150 m from the receiver at the base of the receiver tower. A resistance network based thermal and hydraulic model is used to predict heat transfer and pressure drop performance of the micro-pin receiver. This output of this model is coupled to a system level model of the pressure loss and compressor power required in the remainder of the high temperature gas loop. Overall performance is investigated for supercritical carbon dioxide and helium as working fluids, at pressures from 7.5 to 25 MPa, and at delivery temperatures of 720°C. The results show that by modifying pin depth and flow lengths, there are design spaces for micro-pin devices that can provide high thermal performance without significantly reducing the overall solar thermal system output at lower operating pressures. Use of lower pressure fluids enables lower cost materials of construction in the piping and distribution system, reducing the cost of electricity.