bluuebunny/crossref_metadata_2025 huggingface dataset:
Trends in inequalities in child stunting in South Asia
Authors: Krishna Aditi , Mejía‐Guevara Iván , McGovern Mark , Aguayo Víctor M. , Subramanian S. V.
Published: October 2017

We analysed socio‐economic inequalities in stunting in South Asia and investigated disparities associated with factors at the individual, caregiver, and household levels (poor dietary diversity, low maternal education, and household poverty). We used time‐series analysis of data from 55,459 children ages 6–23 months from Demographic and Health Surveys in Bangladesh, India, Nepal, and Pakistan (1991–2014). Logistic regression models, adjusted for age, sex, birth order, and place of residency, examined associations between stunting and multiple types of socio‐economic disadvantage. All countries had high stunting rates. Bangladesh and Nepal recorded the largest reductions—2.9 and 4.1 percentage points per year, respectively—compared to 1.3 and 0.6 percentage points in India and Pakistan, respectively. Socio‐economic adversity was associated with increased risk of stunting, regardless of disadvantage type. Poor children with inadequate diets and with poorly educated mothers experienced greater risk of stunting. Although stunting rates declined in the most deprived groups, socio‐economic differences were largely preserved over time and in some cases worsened, namely, between wealth quintiles. The disproportionate burden of stunting experienced by the most disadvantaged children and the worsening inequalities between socio‐economic groups are of concern in countries with substantial stunting burdens. Closing the gap between best and worst performing countries, and between most and least disadvantaged groups within countries, would yield substantial improvements in stunting rates in South Asia. To do so, greater attention needs to be paid to addressing the social, economic, and political drivers of stunting with targeted efforts towards the populations experiencing the greatest disadvantage and child growth faltering.
Babies in boxes and the missing links on safe sleep: Human evolution and cultural revolution
Authors: Bartick Melissa , Tomori Cecília , Ball Helen L.
Published: October 2017

Concerns about bedsharing as a risk for sudden infant death syndrome and other forms of sleep‐associated infant death have gained prominence as a public health issue. Cardboard “baby boxes” are increasingly promoted to prevent infant death through separate sleep, despite no proof of efficacy. However, baby boxes disrupt “breastsleeping” (breastfeeding with co‐sleeping) and may undermine breastfeeding. Recommendations enforcing separate sleep are based on 20th century Euro‐American social norms for solitary infant sleep and scheduled feedings via bottles of cow's milk‐based formula, in contrast to breastsleeping, an evolutionary adaptation facilitating the survival of mammalian infants for millennia. Interventions that aim to prevent bedsharing, such as the cardboard baby box, fail to consider the implications of evolutionary biology or of ethnocentrism in sleep guidance. Moreover, the focus on bedsharing neglects more potent risks such as smoking, drugs, alcohol, formula feeding, and poverty. Distribution of baby boxes may divert resources and attention away from addressing these other risk factors and lead to a false sense of security wherein we overlook that sudden unexplained infant deaths also occur in solitary sleep environments. Recognizing breastsleeping as the evolutionary and cross‐cultural norm entails re‐evaluating our research and policy priorities, such as providing greater structural support for families, supporting breastfeeding and safe co‐sleeping, investigating ways to safely minimize separation for formula‐fed infants, and mitigating the potential harms of mother–infant separation when breastsleeping is disrupted. Resources would be better spent addressing such questions rather than on a feel‐good solution such as the baby box.
The effect of montelukast on early‐life wheezing: A randomized, double‐blinded placebo‐controlled study
Authors: Keskin Ozlem , Arik Yilmaz Ebru , Motzkus Christine , Sackesen Cansin , Lilly Craig M. , Kalayci Omer
Published: October 2017

Background

Cysteinyl‐leukotrienes are increased in the airways of infants with virus‐associated wheezing. We aimed to determine the effects of a cysteinyl‐leukotriene‐1 receptor antagonist on symptoms during an early‐life wheezing illness and to investigate the factors that affect the response to this drug.

Method

This placebo‐controlled double‐blinded randomized controlled trial recruited children aged 3‐36 months with wheezing illness and randomized to active drug or placebo for 56 days. A symptom score diary (SSD) was kept by the children's caregivers.

Results

One‐hundred patients completed the study, and 62 (30 montelukast and 32 placebo) were analyzed. There were no significant differences in the percent of symptom‐free days, symptom scores, and the need for rescue salbutamol between the two groups. However, the percent of symptom‐free days within the first week was significantly higher for the montelukast than for the placebo group (13.8 ± 4.1% vs. 5.4 ± 3.4%; P = 0.028); wheezing score at 7th day was significantly lower for the montelukast than for the placebo group (0.5 ± 0.1 vs. 1.4 ± 0.2; P = 0.002). In addition, the number of inhaled ß2‐agonist rescue episodes per day during the first week was significantly lower for the montelukast compared with the placebo group (12.7 ± 1.8 vs. 19.2 ± 1.6; P = 0.013).

Conclusions

Our results indicate that montelukast may be effective for reducing caregiver‐observed wheezing and the need for salbutamol during the first week of treatment for early‐life wheezing. The impact for caregivers and the optimal duration of treatment will need to be explored in studies of larger size.
Follow‐up of patients with uncertain symptoms during an oral food challenge is useful for diagnosis
Authors: Miura Taro , Yanagida Noriyuki , Sato Sakura , Ogura Kiyotake , Ebisawa Motohiro
Published: October 2017

Background

Uncertain symptoms often emerge during an oral food challenge (OFC), and Open‐OFCs with those uncertain mild symptoms are ordinarily regarded as positive. Double‐blind placebo‐controlled food challenges should be conducted to determine these associations. Nevertheless, studies regarding the diagnosis of uncertain food allergy symptoms are lacking. We examined the diagnostic decision for a food allergy based on uncertain symptoms during an Open‐OFC.

Methods

We conducted an Open‐OFC between August 2005 and April 2012 with 2271 cases who suspected as allergic to hen's eggs, cow's milk, or wheat. For the primary diagnosis, Open‐OFCs with obvious symptoms were classified as “positive,” no symptoms as “negative,” and uncertain, indeterminate symptoms as “uncertain.” We encouraged the children in the uncertain group to consume the causative foods at home more than twice; if any definitive symptoms were induced, children were classified as “intolerant,” and children without any symptoms were classified as “tolerant,” for the final diagnosis.

Results

We analyzed 454 uncertain cases excluding 781 positive cases and 1036 negative cases. The symptoms that occurred for the uncertain cases included slight abdominal pain, localized skin rash, and an isolated cough. Of these cases, 362 (79.7%) were considered tolerant at the final diagnosis. Of the intolerant children at the final diagnosis, the induced symptoms at home were not serious.

Conclusions

Monitoring of recurring symptoms following consumption of causative foods at home by patients with uncertain symptoms improves the diagnostic accuracy of an Open‐OFC.
Increase in atopic sensitization rate among Dutch children with symptoms of allergic disease between 1994 and 2014
Authors: Koet Lukas B. M. , Brand Paul L. P.
Published: October 2017

Background

The prevalence of symptoms of allergic diseases has increased significantly during the last decades. However, studies into time trends of atopic sensitization among children are limited and have focused on aeroallergen sensitization. We aimed to investigate time trends in the prevalence and degree of atopic sensitization to inhalant and food allergens among children (0‐17 years) with symptoms of allergic disease.

Methods

Sensitization data of all children tested in our clinical laboratory during 1994‐2014 were analyzed. Sensitization was detected using the ImmunoCAP system and defined as a specific IgE level of ≥0.35 kU/L. Trends in sensitization rates to 5 food and 5 aeroallergens for different age categories were investigated with logistic regression, adjusted for age and sex.

Results

Sensitization data of 18 199 children were analyzed. Between 1994 and 2014, a steady and statistically significant increase in overall sensitization rate was found (from 40.5% in 1994 to 48.9% in 2014, adjusted odds ratio [aOR] 1.01 per year, 95% confidence interval [CI] 1.00 to 1.01, P = .003). This increase in sensitization rate was mainly explained by increasing aeroallergen sensitization among 4‐ to 11‐year‐old children (aOR 1.02, 95% CI 1.01 to 1.02, P < .001). We found no increase in sensitization rates to food and aeroallergens in other age categories. The degree of sensitization did not change significantly during the study period (all tests P > .15).

Conclusion

We observed a statistically significant increase in sensitization rate between 1994 and 2014 among children with symptoms of allergic disease. This was mainly explained by increasing aeroallergen sensitization among 4‐ to 11‐year‐olds.
Semiparametric Dynamic Max-Copula Model for Multivariate Time Series
Authors: Zhao Zifeng , Zhang Zhengjun
Published: October 2017

The paper presents a novel non-linear framework for the construction of flexible multivariate dependence structure (i.e. copulas) from existing copulas based on a straightforward ‘pairwise max-’rule. The newly constructed max-copula has a closed form and has strong interpretability. Compared with the classical ‘linear symmetric’ mixture copula, the max-copula can be viewed as a ‘non-linear asymmetric’ framework. It is capable of modelling asymmetric dependence and joint tail behaviour while also offering good performance in non-extremal behaviour modelling. Max-copulas that are based on single-factor and block factor models are developed to offer parsimonious modelling for structured dependence, especially in high dimensional applications. Combined with semiparametric time series models, the max-copula can be used to develop flexible and accurate models for multivariate time series. A new semiparametric composite maximum likelihood method is proposed for parameter estimation, where the consistency and asymptotic normality of estimators are established. The flexibility of the max-copula and the accuracy of the proposed estimation procedure are illustrated through extensive numerical experiments. Real data applications in value-at-risk estimation and portfolio optimization for financial risk management demonstrate the max-copula's promising ability to capture accurately joint movements of high dimensional multivariate stock returns under both normal and crisis regimes of the financial market.
Sickness absence following breast cancer surgery: a two‐year follow‐up cohort study
Authors: Petersson Lena‐Marie , Vaez Marjan , Nilsson Marie I. , Saboonchi Fredrik , Alexanderson Kristina , Olsson Mariann , Wennman‐Larsen Agneta
Published: October 2017

Rationale and aim

Most women of working ages with limited breast cancer (BC) have returned to work within the first year after diagnosis. However, little is known about what is happening during this year regarding sickness absence and return to work. Also, the knowledge is very limited about the occurrence of part‐time sickness absence after BC diagnosis. Therefore, the aim of this study was to describe occurrence, extent and length of SA during a two‐year follow‐up after BC surgery and to analyse the association between being SA and type of cancer treatment.

Methods

In this prospective cohort study, 497 women responded to questionnaires about different aspects of sickness absence at six occasions during two years after primary BC surgery (at baseline and after 4, 8, 12, 18 and 24 months). Treatment information was obtained from the National breast cancer register. Multinomial logistic regression was used to calculate odds ratios (OR) for likelihood of being sickness absent more than once.

Results

Two‐thirds of the women were sickness absent at baseline; this proportion decreased, especially during the first eight months. At 24 months, 13% were sickness absent. Of all women, 27% never reported sickness absence and 14% were sickness absent at most of the six survey times. At eight months, many had shifted from full‐ to part‐time sickness absence. Women with chemotherapy and/or advanced BC surgery had higher ORs for being sickness absent at most of the follow‐ups.

Conclusions

Most women returned to work within the first eight months after BC surgery and of those sickness absent after that, most had been part‐time sickness absent. Thus, it is important to differentiate between part‐ and full‐time sickness absence in future studies. Special attention should be paid to the impact of chemotherapy and type of surgery on the likelihood of being sickness absent.
Public Sector Employment and the Skill Premium: Sweden versus the United States 1970–2012
Authors: Domeij David , Ljungqvist Lars
Published: October 2017

Swedish census data and tax records reveal an astonishing decline in the aggregate skill premium of 30 percent between 1970 and 1990, with only a modest recovery in the next couple of decades. In contrast, the US skill premium rose by around 24 percent over those four decades. A theory that equalizes wages with marginal products can rationalize these disparate outcomes when we replace commonly used measures of total labor supplies by private sector employment. The dramatic decline in the skill premium in Sweden is the result of an expanding public sector that has disproportionately hired unskilled labor.
Macroeconomic Conditions at Entry and Injury Risk in the Workplace
Authors: Leombruni Roberto , Razzolini Tiziano , Serti Francesco
Published: October 2017

Using a unique dataset from Italy, we show that the local unemployment rate at entry has a persistent positive effect on severe and non‐severe workplace injuries of young workers. Entrants during recessions, despite receiving marginally higher entry wages, also experience slower wage growth. The observed pattern in the differences between severe and non‐severe injuries indicates that entrants during recessions might under‐report non‐severe workplace injuries. Our findings suggest that workers entering during recessions are persistently locked into low‐quality jobs and that the mix of hazardous tasks endogenously adjusts to the business cycle.
Around -independence
Authors: Chiarellotto Bruno , Lazda Christopher
Published: October 2017

In this article we study various forms of $\ell$-independence (including the case $\ell =p$) for the cohomology and fundamental groups of varieties over finite fields and equicharacteristic local fields. Our first result is a strong form of $\ell$-independence for the unipotent fundamental group of smooth and projective varieties over finite fields. By then proving a certain ‘spreading out’ result we are able to deduce a much weaker form of $\ell$-independence for unipotent fundamental groups over equicharacteristic local fields, at least in the semistable case. In a similar vein, we can also use this to deduce $\ell$-independence results for the cohomology of smooth and proper varieties over equicharacteristic local fields from the well-known results on $\ell$-independence for smooth and proper varieties over finite fields. As another consequence of this ‘spreading out’ result we are able to deduce the existence of a Clemens–Schmid exact sequence for formal semistable families. Finally, by deforming to characteristic $p$, we show a similar weak version of $\ell$-independence for the unipotent fundamental group of a semistable curve in mixed characteristic.
A Helmholtz Potential Approach to the Analysis of Guided Wave Generation During Acoustic Emission Events
Authors: Haider Mohammad Faisal , Giurgiutiu Victor
Published: October 2017

This paper addresses the predictive simulation of acoustic emission (AE) guided waves that appear due to sudden energy release during incremental crack propagation. The Helmholtz decomposition approach is applied to the inhomogeneous elastodynamic Navier–Lame equations for both the displacement field and body forces. For the displacement field, we use the usual decomposition in terms of unknown scalar and vector potentials, Φ and H. For the body forces, we hypothesize that they can also be expressed in terms of excitation scalar and vector potentials, A* and B*. It is shown that these excitation potentials can be traced to the energy released during an incremental crack propagation. Thus, the inhomogeneous Navier–Lame equation has been transformed into a system of inhomogeneous wave equations in terms of known excitation potentials A* and B* and unknown potentials Φ and H. The solution is readily obtained through direct and inverse Fourier transforms and application of the residue theorem. A numerical study of the one-dimensional (1D) AE guided wave propagation in a 6 mm thick 304-stainless steel plate is conducted. A Gaussian pulse is used to model the growth of the excitation potentials during the AE event; as a result, the actual excitation potential follows the error function variation in the time domain. The numerical studies show that the peak amplitude of A0 signal is higher than the peak amplitude of S0 signal, and the peak amplitude of bulk wave is not significant compared to S0 and A0 peak amplitudes. In addition, the effects of the source depth, higher propagating modes, and propagating distance on guided waves are also investigated.
An Engineering Model to Test for Sensory Reweighting: Nonhuman Primates Serve as a Model for Human Postural Control and Vestibular Dysfunction
Authors: Thompson Lara A. , Haburcakova Csilla , Goodworth Adam D. , Lewis Richard F.
Published: October 2017

Quantitative animal models are critically needed to provide proof of concept for the investigation of rehabilitative balance therapies (e.g., invasive vestibular prostheses) and treatment response prior to, or in conjunction with, human clinical trials. This paper describes a novel approach to modeling the nonhuman primate postural control system. Our observation that rhesus macaques and humans have even remotely similar postural control motivates the further application of the rhesus macaque as a model for studying the effects of vestibular dysfunction, as well as vestibular prosthesis-assisted states, on human postural control. Previously, system identification methodologies and models were only used to describe human posture. However, here we utilized pseudorandom, roll-tilt balance platform stimuli to perturb the posture of a rhesus monkey in normal and mild vestibular (equilibrium) loss states. The relationship between rhesus monkey trunk sway and platform roll-tilt was determined via stimulus–response curves and transfer function results. A feedback controller model was then used to explore sensory reweighting (i.e., changes in sensory reliance), which prevented the animal from falling off of the tilting platform. Conclusions involving sensory reweighting in the nonhuman primate for a normal sensory state and a state of mild vestibular loss led to meaningful insights. This first-phase effort to model the balance control system in nonhuman primates is essential for future investigations toward the effects of invasive rehabilitative (balance) technologies on postural control in primates, and ultimately, humans.
Hybrid State Space Modeling of a Spark Ignition Engine for Online Fault Diagnosis
Authors: Nadeer E. P. , Patra Amit , Mukhopadhyay Siddhartha
Published: October 2017

In this work, a nonlinear hybrid state space model of a complete spark ignition (SI) gasoline engine system from throttle to muffler is developed using the mass and energy balance equations. It provides within-cycle dynamics of all the engine variables such as temperature, pressure, and mass of individual gas species in the intake manifold (IM), cylinder, and exhaust manifold (EM). The inputs to the model are the same as that commonly exercised by the engine control unit (ECU), and its outputs correspond to available engine sensors. It uses generally known engine parameters, does not require extensive engine maps found in mean value models (MVMs), and requires minimal experimentation for tuning. It is demonstrated that the model is able to capture a variety of engine faults by suitable parameterization. The state space modeling is parsimonious in having the minimum number of integrators in the model by appropriate choice of state. It leads to great computational efficiency due to the possibility of deriving the Jacobian expressions analytically in applications such as on-board state estimation. The model was validated both with data from an industry standard engine simulation and those from an actual engine after relevant modifications. For the test engine, the engine speed and crank angle were extracted from the crank position sensor signal. The model was seen to match the true values of engine variables both in simulation and experiments.
An Efficient Method of Generating and Characterizing Filter Substrates for Lattice Boltzmann Analysis
Authors: Murdock John Ryan , Ibrahim Aamir , Yang Song-Lin
Published: October 2017

To provide porous media substrates that are quick to generate and characterize for lattice Boltzmann analysis, we propose a straightforward algorithm. The method leverages the benefits of the lattice Boltzmann method (LBM), and is extensible to multiphysics flows. Several parameters allow for simple customization. The generation algorithm and LBM are reviewed, and suggested implementation covered. Additionally, results are discussed and interpreted to evaluate the approach. Several verification tools are employed such as Darcy's law, the Ergun equation, the Koponen correlation, a newly proposed correlation, and experimental data. Agreement and repeatability are found to be excellent, suggesting this relatively simple method is a good option for engineering studies.
Calibration and Compensation of Dynamic Abbe Errors of a Coordinate Measuring Machine
Authors: Yuan Daocheng , Tao Xin , Xie Caijun , Zhao Huiying , Ren Dongxu , Zhu Xueliang
Published: October 2017

Error compensation technology is used for improving accuracy and reducing costs. Dynamic error compensation techniques of coordinate measuring machine (CMM) are still under study; the major problem is a lack of suitable models, which would be able to correctly and simply relate the dynamic errors with the structural and operational parameters. To avoid the complexity of local dynamic deformation measurement and modeling, a comprehensive calibration method is employed. Experimental research reveals specific qualities of dynamic Abbe errors; the results exceed the scope of ISO 10360-2 calibration method, showing the ISO 10360-2 dynamic error evaluation deficiencies. For calibrating the dynamic Abbe errors, the differential measurement method is presented based on the measurements of the internal and external dimensions. Referring probe tip radius correction, the dynamic Abbe errors compensation method is proposed for CMM end-users and is easy to use.
Structural Dynamic Analysis of a Tidal Current Turbine Using Geometrically Exact Beam Theory
Authors: Wang Qi , Zhang Pengkun , Li Ye
Published: October 2017

This paper presents a numerical study of the dynamic performance of a vertical axis tidal current turbine. First, we introduce the geometrically exact beam theory along with its numerical implementation the geometric exact beam theory (GEBT), which are used for structural modeling. We also briefly review the variational-asymptotic beam sectional analysis (VABS) theory and discrete vortex method with free-wake structure (DVM-UBC), which provide the one-dimensional (1D) constitutive model for the beam structures and the hydrodynamic forces, respectively. Then, we validate the current model with results obtained by ANSYS using three-dimensional (3D) solid elements and good agreements are observed. We investigate the dynamic performance of the tidal current turbine including modal behavior and transient dynamic performance under hydrodynamic loads. Finally, based on the results in the global dynamic analysis, we study the local stress distributions at the joint between blade and arm by VABS. It is concluded that the proposed analysis method is accurate and efficient for tidal current turbine and has a potential for future applications to those made of composite materials.
Highly Resolved Large Eddy Simulation Study of Gap Size Effect on Low-Pressure Turbine Stage
Authors: Pichler R. , Michelassi V. , Sandberg R. , Ong J.
Published: October 2017

Blade-to-blade interactions in a low-pressure turbine (LPT) were investigated using highly resolved compressible large eddy simulations (LESs). For a realistic setup, a stator and rotor configuration with profiles typical of LPTs was used. Simulations were conducted with an in-house solver varying the gap size between stator and rotor from 21.5% to 43% rotor chord. To investigate the effect of the gap size on the prevailing loss mechanisms, a loss breakdown was conducted. It was found that in the large gap (LG) size case, the turbulence kinetic energy (TKE) levels of the stator wake close to the rotor leading edge were only one third of those in the small gap (SG) case, due to the longer distance of constant area mixing. The small time-averaged suction side separation on the blade, found in the LG case, disappeared in the SG calculations, confirming how stronger wakes can keep the boundary layer attached. The higher intensity wake impinging on the blade, however, did not affect the time-averaged losses calculated using the control volume approach of Denton. On the other hand, losses computed by taking cross sections upstream and downstream of the blade revealed a greater distortion loss generated by the stator wakes in the SG case. Despite the suction side separation suppression, the SG case gave higher losses overall due to the incoming wake turbulent kinetic energy amplification along the blade passage.
Effects of Geometry, Spacing, and Number of Pin Fins in Additively Manufactured Microchannel Pin Fin Arrays
Authors: Ferster Katharine K. , Kirsch Kathryn L. , Thole Karen A.
Published: October 2017

The demand for higher efficiency is ever present in the gas turbine field and can be achieved through many different approaches. While additively manufactured parts have only recently been introduced into the hot section of a gas turbine engine, the manufacturing technology shows promise for more widespread implementation since the process allows a designer to push the limits on capabilities of traditional machining and potentially impact turbine efficiencies. Pin fins are conventionally used in turbine airfoils to remove heat from locations in which high thermal and mechanical stresses are present. This study employs the benefits of additive manufacturing to make uniquely shaped pin fins, with the goal of increased performance over conventional cylindrical pin fin arrays. Triangular, star, and spherical shaped pin fins placed in microchannel test coupons were manufactured using direct metal laser sintering (DMLS). These coupons were experimentally investigated for pressure loss and heat transfer at a range of Reynolds numbers. Spacing, number of pin fins in the array, and pin fin geometry were variables that changed pressure loss and heat transfer in this study. Results indicate that the additively manufactured triangles and cylinders outperform conventional pin fin arrays, while stars and dimpled spheres did not.
Probabilistic-Based Robotic Radiation Mapping Using Sparse Data
Authors: McDougall Robin , Nokleby Scott B. , Waller Ed
Published: October 2017

This paper presents a novel methodology for generating radiation intensity maps using a mobile robotic platform and an integrated radiation model. The radiation intensity mapping approach consists of two stages. First, radiation intensity samples are collected using a radiation sensor mounted on a mobile robotic platform, reducing the risk of exposure to humans from an unknown radiation field. Next, these samples, which need only to be taken from a subsection of the entire area being mapped, are then used to calibrate a radiation model of the area. This model is then used to predict the radiation intensity field throughout the rest of the area that could not be directly measured. The performance of the approach is evaluated through experiments. The results show that the developed system is effective at achieving the goal of generating radiation maps using sparse data.
A Review of Elastic–Plastic Contact Mechanics
Authors: Ghaednia Hamid , Wang Xianzhang , Saha Swarna , Xu Yang , Sharma Aman , Jackson Robert L.
Published: October 2017

In typical metallic contacts, stresses are very high and result in yielding of the material. Therefore, the study of contacts which include simultaneous elastic and plastic deformation is of critical importance. This work reviews the current state-of-the-art in the modeling of single asperity elastic–plastic contact and, in some instances, makes comparisons to original findings of the authors. Several different geometries are considered, including cylindrical, spherical, sinusoidal or wavy, and axisymmetric sinusoidal. As evidenced by the reviewed literature, it is clear that the average pressure during heavily loaded elastic–plastic contact is not governed by the conventional hardness to yield strength ratio of approximately three, but rather varies according to the boundary conditions and deformed geometry. For spherical contact, the differences between flattening and indentation contacts are also reviewed. In addition, this paper summarizes work on tangentially loaded contacts up to the initiation of sliding. As discussed briefly, the single asperity contact models can be incorporated into existing rough surface contact model frameworks. Depending on the size of a contact, the material properties can also effectively change, and this topic is introduced as well. In the concluding discussion, an argument is made for the value of studying hardening and other failure mechanisms, such as fracture as well as the influence of adhesion on elastic–plastic contact.
Flow Patterns During Flow Boiling Instability in Silicon-Based Pin-Fin Microchannels
Authors: Xu Fayao , Wu Huiying , Liu Zhenyu
Published: October 2017

In this paper, the flow patterns during water flow boiling instability in pin-fin microchannels were experimentally studied. Three types of pin-fin arrays (in-line/circular pin-fins, staggered/circular pin-fins, and staggered/square pin-fins) were used in the study. The flow instability started to occur as the outlet water reached the saturation temperature. Before the unstable boiling, a wider range of stable boiling existed in the pin-fin microchannels compared to that in the plain microchannels. Two flow instability modes for the temperature and pressure oscillations, which were long-period/large-amplitude mode and short-period/small-amplitude mode, were identified. The temperature variation during the oscillation period of the long-period/large-amplitude mode can be divided into two stages: increasing stage and decreasing stage. In the increasing stage, bubbly flow, vapor-slug flow, stratified flow, and wispy flow occurred sequentially with time for the in-line pin-fin microchannels; liquid single-phase flow, aforementioned four kinds of two-phase flow patterns, and vapor single-phase flow occurred sequentially with time for the staggered pin-fin microchannel. The flow pattern transitions in the decreasing stage were the inverse of those in the increasing stage for both in-line and staggered pin-fin microchannels. For the short-period/small-amplitude oscillation mode, only the wispy flow occurred. With the increase of heat flux, the wispy flow and the vapor single-phase flow occupied more and more time ratio during an oscillation period in the in-line and staggered pin-fin microchannels.
A Study on a Copolymer Gelant With High Temperature Resistance for Conformance Control
Authors: Zhang Lei , Jing Cheng , Liu Jing , Nasir Khan
Published: October 2017

Due to the limited temperature resistance, the deep conformance control technology of using the conventional hydrolyzed polyacrylamide (HPAM) gel failed to enhance oil recovery in high-temperature heterogeneous oil reservoirs. Therefore, it is necessary to develop a gelant with high temperature resistance to meet the demands of increasing oil production and decreasing water cut in high-temperature heterogeneous oil reservoirs. In this paper, a copolymer is first synthesized by the method of inverse emulsion polymerization using 2-acrylamide-2-tetradecyl ethyl sulfonic acid (AMC16S), acrylamide (AM), and acrylic acid (AA). The developed copolymer has a highly branching skeleton and can resist temperature up to 100 °C. And then, a gelant with high temperature resistance and good shear resistance can be formed by mixing a certain proportion of the developed copolymer and polyethyleneimine (PEI). After the controllable gelation, a copolymer gel is formed and the formed gel can maintain the stable performance for a long time in the high-temperature environment. Experimental results show that the developed gelant can be applied in the conformance control of high-temperature heterogeneous oil reservoir.
Transient Heat Conduction in a Thin Layer Between Semi-Infinite Media in Polymer Shaping
Authors: van der Tempel Leendert , Potze Willem , Lammers Jeroen H.
Published: October 2017

A series expansion and an approximation have been derived for the temperature in the general case of transient heat conduction in a thin layer with a surface heat flux between two semi-infinite media at different uniform initial temperatures. Their temperature accuracy has been evaluated for two test cases in the field of thermoplastic shaping of polymers. The series enables quick yet fairly accurate thermal analysis of compression molding (CM) and injection molding (IM) and its vitrification rate and of fused deposition modeling™ (FDM) and its bead welding and vitrification rate.
Can Measured Synergy Excitations Accurately Construct Unmeasured Muscle Excitations?
Authors: Bianco Nicholas A. , Patten Carolynn , Fregly Benjamin J.
Published: October 2017

Accurate prediction of muscle and joint contact forces during human movement could improve treatment planning for disorders such as osteoarthritis, stroke, Parkinson's disease, and cerebral palsy. Recent studies suggest that muscle synergies, a low-dimensional representation of a large set of muscle electromyographic (EMG) signals (henceforth called “muscle excitations”), may reduce the redundancy of muscle excitation solutions predicted by optimization methods. This study explores the feasibility of using muscle synergy information extracted from eight muscle EMG signals (henceforth called “included” muscle excitations) to accurately construct muscle excitations from up to 16 additional EMG signals (henceforth called “excluded” muscle excitations). Using treadmill walking data collected at multiple speeds from two subjects (one healthy, one poststroke), we performed muscle synergy analysis on all possible subsets of eight included muscle excitations and evaluated how well the calculated time-varying synergy excitations could construct the remaining excluded muscle excitations (henceforth called “synergy extrapolation”). We found that some, but not all, eight-muscle subsets yielded synergy excitations that achieved >90% extrapolation variance accounted for (VAF). Using the top 10% of subsets, we developed muscle selection heuristics to identify included muscle combinations whose synergy excitations achieved high extrapolation accuracy. For 3, 4, and 5 synergies, these heuristics yielded extrapolation VAF values approximately 5% lower than corresponding reconstruction VAF values for each associated eight-muscle subset. These results suggest that synergy excitations obtained from experimentally measured muscle excitations can accurately construct unmeasured muscle excitations, which could help limit muscle excitations predicted by muscle force optimizations.
Simulating Reversibility of Dense Core Vesicles Capture in En Passant Boutons: Using Mathematical Modeling to Understand the Fate of Dense Core Vesicles in En Passant Boutons
Authors: Kuznetsov I. A. , Kuznetsov A. V.
Published: October 2017

The goal of this paper is to use mathematical modeling to investigate the fate of dense core vesicles (DCVs) captured in en passant boutons located in nerve terminals. One possibility is that all DCVs captured in boutons are destroyed, another possibility is that captured DCVs can escape and reenter the pool of transiting DCVs that move through the boutons, and a third possibility is that some DCVs are destroyed in boutons, while some reenter the transiting pool. We developed a model by applying the conservation of DCVs in various compartments composing the terminal, to predict different scenarios that emerge from the above assumptions about the fate of DCVs captured in boutons. We simulated DCV transport in type Ib and type III terminals. The simulations demonstrate that, if no DCV destruction in boutons is assumed and all captured DCVs reenter the transiting pool, the DCV fluxes evolve to a uniform circulation in a type Ib terminal at steady-state and the DCV flux remains constant from bouton to bouton. Because at steady-state the amount of captured DCVs is equal to the amount of DCVs that reenter the transiting pool, no decay of DCV fluxes occurs. In a type III terminal at steady-state, the anterograde DCV fluxes decay from bouton to bouton, while retrograde fluxes increase. This is explained by a larger capture efficiency of anterogradely moving DCVs than of retrogradely moving DCVs in type III boutons, while the captured DCVs that reenter the transiting pool are assumed to be equally split between anterogradely and retrogradely moving components. At steady-state, the physiologically reasonable assumption of no DCV destruction in boutons results in the same number of DCVs entering and leaving a nerve terminal. Because published experimental results indicate no DCV circulation in type III terminals, modeling results suggest that DCV transport in these type III terminals may not be at steady-state. To better understand the kinetics of DCV capture and release, future experiments in type III terminals at different times after DCV release (molting) may be proposed.
Compositional Submanifolds of Prismatic–Universal–Prismatic and Skewed Prismatic–Revolute– Prismatic Kinematic Chains and Their Derived Parallel Mechanisms
Authors: Zhang Xinsheng , López-Custodio Pablo , Dai Jian S.
Published: October 2017

The kinematic chains that generate the planar motion group in which the prismatic-joint direction is always perpendicular to the revolute-joint axis have shown their effectiveness in type synthesis and mechanism analysis in parallel mechanisms. This paper extends the standard prismatic–revolute–prismatic (PRP) kinematic chain generating the planar motion group to a relatively generic case, in which one of the prismatic joint-directions is not necessarily perpendicular to the revolute-joint axis, leading to the discovery of a pseudo-helical motion with a variable pitch in a kinematic chain. The displacement of such a PRP chain generates a submanifold of the Schoenflies motion subgroup. This paper investigates for the first time this type of motion that is the variable-pitched pseudo-planar motion described by the above submanifold. Following the extraction of a helical motion from this skewed PRP kinematic chain, this paper investigates the bifurcated motion in a 3-prismatic–universal–prismatic (PUP) parallel mechanism by changing the active geometrical constraint in its configuration space. The method used in this contribution simplifies the analysis of such a parallel mechanism without resorting to an in-depth geometrical analysis and screw theory. Further, a parallel platform which can generate this skewed PRP type of motion is presented. An experimental test setup is based on a three-dimensional (3D) printed prototype of the 3-PUP parallel mechanism to detect the variable-pitched translation of the helical motion.
A Novel Robotic Tree Climbing Mechanism With Anti-Falling Functionality for Tree Pruning
Authors: Gui Pengfei , Tang Liqiong , Mukhopadhyay Subhas
Published: October 2017

This paper presents a novel mechanism of tree climbing robotic system for tree pruning. The unique features of this system include the passive and active anti-falling mechanisms, which prevent the robot from falling to the ground under either static or dynamic situations, the capability to vertically or spirally climb up a tree trunk, and the flexibility to suit different trunk sizes. The computer-aided design (CAD) models of the robotic mechanism, static and kinematic analysis, climbing simulation, and testing of the physical model are stated in detail. This research work reveals that this novel tree climbing mechanism can be served as a platform for tree pruning robot.
A Closed-Form Kinematic Model for Fiber-Reinforced Elastomeric Enclosures
Authors: Felt Wyatt , David Remy C.
Published: October 2017

In this work, we present a closed-form model, which describes the kinematics of fiber-reinforced elastomeric enclosures (FREEs). A FREE actuator consists of a thin elastomeric tube surrounded by reinforcing helical fibers. Previous models for the motion of FREEs have relied on the successive compositions of “instantaneous” kinematics or complex elastomer models. The model presented in this work classifies each FREE by the ratio of the length of its fibers. This ratio defines the behavior of the FREE regardless of the other parameters. With this ratio defined, the kinematic state of the FREE can then be completely described by one of the fiber angles. The simple, analytic nature of the model presented in this work facilitates the understanding and design of FREE actuators. We demonstrate the application of this model in an actuator design case study.
Numerical Post-Buckling Analysis of Mechanically Lined Corrosion Resistant Alloy Pipes
Authors: Dong Jiansha , Ozturk Fahrettin , Jarrar Firas , Sheikh-Ahmad Jamal Y.
Published: October 2017

As an economical alternative to solid corrosion resistant alloy (CRA) and clad pipes, mechanically lined or sleeved CRA pipes are proven to be effective in the transport of corrosive fluids in oil and gas industry. A major issue with these pipes is that pressure drop or fluctuations may cause buckling of the liner, resulting in irreparable and costly damage. This issue should be resolved in order to fully implement this type of pipes in oil and gas industry. In this study, post-buckling analysis of liner pipe encased in carbon steel outer pipe is carried out following the hydraulic expansion manufacturing process. Commercially available abaqus finite element software is employed. The proposed model is partly verified with an analytical solution and other numerical results under the condition of no residual contact pressure. Results of the parametric study reveal that increasing the residual contact pressure and decreasing the magnitude of geometric imperfection can both contribute to enhancing the buckling resistance.
Improved J Estimation by GE/EPRI Method for the Thin-Walled Pipes With Small Constant-Depth Circumferential Surface Cracks
Authors: Liu X. , Lu Z. X. , Chen Y. , Sui Y. L. , Dai L. H.
Published: October 2017

Application of thin-walled high strength steel has become a trend in the oil and gas transportation system over long distance. Failure assessment is an important issue in the construction and maintenance of the pipelines. This work provides an engineering estimation procedure to determine the J-integral for the thin-walled pipes with small constant-depth circumferential surface cracks subject to the tensile loading based upon the General Electric/Electric Power Research (GE/EPRI) method. The values of elastic influence functions for stress intensity factor and plastic influence functions for fully plastic J-integral are derived in tabulated forms through a series of three-dimensional (3D) finite element (FE) calculations for a wide range of crack geometries and material properties. Furthermore, the fit equations for elastic and plastic influence functions are developed, where the effects of crack geometries are explicitly revealed. The new influence functions lead to an efficient J estimation and can be well applied for structural integrity assessment of thin-walled pipes with small constant-depth circumferential surface cracks under tension.
Molecular Dynamics Simulation of Pool Boiling Heat Transfer of Nanofluids on Rough Walls
Authors: Yin Xunyan , Bai Minli , Hu Chengzhi , Lv Jizu
Published: October 2017

Molecular dynamics simulation was performed to investigate pool boiling heat transfer of nanofluids on rough walls. Nanoparticle movement was calculated to investigate the physical mechanisms of boiling heat transfer. The simulated system consisted of four regions: vapor argon, liquid argon, solid copper, and copper nanoparticles, and three cases were considered: base fluids (case A), nanoparticles far from the wall (case B), and nanoparticles near the wall (case C). Boiling heat transfer was enhanced by the addition of nanoparticles, and the enhancement increased with increasing heating temperature. Case C showed that nanoparticles were adsorbed on the nonevaporated film and did not move with the fluids. Thus, nanoparticles enhanced heat and energy transfer between the wall and fluids. Case B showed that nanoparticles moved randomly in the fluid area, which enhanced heat transfer within the fluid.
Performance of Mixing Ventilation System Coupled With Dynamic Personalized Ventilator for Thermal Comfort
Authors: Al-Assaad Douaa , Ghaddar Nesreen , Ghali Kamel
Published: October 2017

This study optimizes the performance of a mixing ventilation system coupled with a personalized ventilator that emits a cool sinusoidal horizontal airflow jet towards the occupant upper body in order to achieve good overall thermal comfort and good air quality in the occupant breathing zone. A transient 3-D computational fluid dynamics (CFD) model coupled with a transient bio-heat model was deployed to predict airflow and temperature fields in the space and around the occupant as well as segmental skin temperature profiles for local and overall thermal sensation and comfort analysis.

Simulations were performed using the CFD model to determine the airflow optimal supply frequency, mean flow rate and amplitude at room temperature of 25 °C and PV jet temperature of 22 °C. The system also showed, that when increasing frequency at fixed mean flow rate, thermal comfort increased from by 15.2 %. However when increasing mean flow rate at a fixed frequency, thermal comfort dropped at the low frequency of 0.3 Hz but remained acceptable at the higher frequency of 0.5 Hz.