bluuebunny/crossref_metadata_2025_split huggingface dataset:
Numerical Investigation of Rough Surfaces: Coupling Approach
Authors: Rovenskaya Olga , Croce Giulio 
Published: July 2013

A numerical analysis of the flow field in rough microchannel is carried out decomposing the computational physical domain into kinetic and continuum sub-domains. Each domain size is determined by the value of a proper threshold parameter, based on the local Knudsen number and local gradients of macro-parameters. This switching parameter is computed from a preliminary Navier–Stokes solution throughout the whole physical domain. The solution is then advanced in time simultaneously in both kinetic and continuum domains: the coupling is achieved by matching half fluxes at the interface of the kinetic and Navier–Stokes domains, taking care of the conservation of momentum, energy and mass through the interface.
The roughness geometry is modeled as a series of triangular obstructions with a relative roughness up to a maximum of 5% of the channel height. A wide range of Mach numbers is considered, from nearly incompressible to chocked flow conditions and a Reynolds number up to 100. Accuracy and discrepancies between full Navier Stokes, kinetic and coupled solutions are discussed, assessing the range of applicability of first order slip condition in rough geometries. The effect of the roughness is discussed via Poiseuille number as a function of local Knudsen and Mach numbers.
Analysis of Gaseous Flows in Minichannels by Molecular Tagging Velocimetry
Authors: Samouda Feriel , Barrot Christine , Colin Stéphane , Baldas Lucien , Laurien Nicolas 
Published: July 2013

The Molecular Tagging Velocimetry (MTV) technique has been widely used for analyzing velocity fields in liquid mini- and microflows. Concerning gaseous flows, only few works describe the implementation of MTV at millimetric scale, and these studies are limited to the analysis of external flows, such as jet flows. The goal of the present work is to develop this technique for the analysis of internal gas flows in minichannels. It is a first step toward the visualization of velocity profiles in rarefied conditions, and direct measurement of velocity slip at the walls.
A specific experimental setup has been designed. Its features are detailed. Velocity profiles are obtained in a pressure driven steady flow of argon through a long rectangular minichannel of 1.2 × 5 mm2 cross-section and 15 cm length using acetone molecules as tracer. Experiments are carried out at atmospheric pressure, in a laminar continuum flow regime. The accuracy of the method is discussed by comparison between experimental and theoretical velocity profiles.
The potential of the MTV technique for analyzing mini or micro gaseous internal flows is commented on. Perspectives of the work for discussing the validity of boundary conditions in the slip flow regime are presented.
The Effect of the Laser Beam Wavelength and Pulse Width on Micro Grooving: Comparison of Nanosecond and Femtosecond Laser
Authors: Nonaka Shinri , Mori Tastuhiro , Takata Yasuyuki , Kohno Masamichi 
Published: July 2013

Processing technique of micro grooves and channels is very important to study the phenomenon of fluids in micro scale. Micro grooves and microchannels play an important role in various devices, such as μ-TAS (Micro-Total Analysis Systems) and micro reactors.
Laser processing is currently widely used for drilling and grooving of various materials including metals, polymers, glasses and composite materials, since laser machining can avoid the problems that conventional machining methods have. For example wear of a working tool, lowering of processing accuracy, and wear debris becoming contaminants are some of the problems of the conventional method. Additionally, compared to other non-contact machining processes such as electron beam machining (EBM) and focused ion beam (FIB), machining a vacuum is not required. Therefore, applicability is wider and setup costs can be more economical.
In-Line Characterization of Micro-Droplets Based on Partial Light Reflection at the Solid-Liquid Interface
Authors: Weber Emanuel , Puchberger-Enengl Dietmar , Vellekoop Michael J. 
Published: July 2013

In this paper a novel optofluidic setup, fabricated on a single layer device for in-line droplet characterization yielding droplet-size, droplet-frequency, and optical properties with compatibility for full on-chip integration is presented. Chips were fabricated using a simple, fast, and cost effective technology. A T-junction arrangement on the device is used for droplet generation. The optical part of the setup consists of an external light source, external silicon photodetectors, integrated air micro-lenses, and an integrated waveguide. The design makes use of partial light reflection/transmission at the solid-liquid interface to count, size, and discriminate droplets based on their optical properties. When passing the interrogation point, droplets having a lower refractive index as the continuous phase result in light deflections. Both, reflected and transmitted light, are detected simultaneously. A relation of those two signals is then used for the analysis resulting in a continuously stable signal. The generated pattern is unique for different droplets and can be exploited for droplet characterization.
Using this arrangement, droplets of de-ionized water (DI) were counted at frequencies of up to 320 droplets per second. In addition, information about the droplet sizes and their variations could be obtained. Finally, 5 mol/L CaCl2 and DI droplets, having different indices of refraction were examined and could clearly be discriminated based on their unique reflected and transmitted light signals. This principle can be applied for the detection of dissolved molecules in droplets as long as they influence the index of refraction. Examples could be the determination of DNA or protein content in the droplet.
Fabrication of a Microstructure-Enhanced Surface Area Solar Thermal Collector
Authors: Ogbonnaya E. , Chukwu S. , Wood D. , Weiss L. 
Published: July 2013

Solar energy is a renewable and sustainable energy source that has a promising potential for the rapidly growing energy demands across the world. Large scale power generation from the energy of the sun is well established utilizing both direct thermal energy conversion and conversion to electricity via photovoltaic processes. Solar thermal systems have been limited to macro systems, even though they operate at higher efficiency compared to photovoltaic systems. Solar energy harvesting requires the use of collector plates to capture incident radiation. The surface area exposed to incident radiation is critical in solar thermal energy harvesting. In this work, we have integrated micro technology processes and solar thermal energy to design and fabricate a micro solar thermal system for power generation. This work specifically examined surface area enhancement using MEMS-based techniques to maximize solar thermal absorption. Selective absorber coating and enhanced surface areas due to the incorporation of micro structures on the collector substrates were utilized. In this manner, an important component to an autonomous micro power supply is investigated.
Advanced microfabrication and electrochemical deposition techniques were employed to generate a selective absorber surface with enhanced surface area on a silicon substrate. Microchannels were used to enhance the surface area on the substrate. The selective absorber coating consists of a bimetallic structure consisting of tin and nickel.
A Preliminary Study for 3D Numerical Simulation of a Through-Plane Temperature Profile in a PEMFC Incorporating Coolant Channels
Authors: Koz Mustafa , Kandlikar Satish G. 
Published: July 2013

In a proton exchange membrane fuel cell (PEMFC), the water removal from the cathode to reactant flow channels is a critical aspect of cell operation. This is an active area of research to understand the transport mechanisms of water. In the available literature, it has been shown that a significant portion of the product water is removed in vapor form by the heat pipe effect through the gas diffusion layer (GDL). The intensity of the heat pipe effect is dependent on the local mean temperature and the through-plane temperature gradient across the GDL. This gradient is spatially affected by the reactant channel-land patterns of the bipolar plate (BPP) and the coolant plate operation. Therefore, the heat pipe effect can have spatial variances depending on the BPP design and cooling method.
In order to show the local temperature and through-plane temperature gradient distribution in a GDL, a numerical approach was taken in this work using a commercially available software package, COMSOL Multiphysics® 4.2a. A repetitive cathode section of the PEMFC was modeled in 3D with domains of a GDL and BPP. In-plane thermal conductivity of the GDL was incorporated by using experimentally obtained values from the available literature. By changing the design and operating conditions of the coolant system, the thermal profile and so, the vapor flux across the GDL were investigated. It was found that the increasing temperature non-uniformity on coolant plates leads to less uniform distribution of vapor flux. This is expected to lead to more condensation of water vapor under the lands.
A Novel Thermo-Hydraulic Test Platform for Micropillared Array Thermal Wick Optimization
Authors: Miers Collier , Wehmeyer Geoff , Hidrovo Carlos H. 
Published: July 2013

Heat pipes have immense potential in the future of thermal management in electronic devices. As a passive device, they rely solely upon capillary forces to recirculate the coolant from the condenser to the evaporator via a wicking structure. In intermediate temperature heat pipes the limiting factor for heat removal is the capillary limit, which indicates the maximum recirculation rate that the capillary forces can induce. This capillary limit must be increased to allow heat pipes to remain a viable option for heat management within electronic devices. The aim of this work is to characterize and optimize the capillary limit of micropillared thermal wicks for heat pipe application in micro-electronics cooling.
Towards this goal, an analytical model, and a novel thermo-hydraulic experimental setup was developed. The analytical model of the micropillared array wicking structure provides a theoretical basis from which the pillar geometry and arrangement can be optimized. A capillary limit model was used to determine the geometric relationship between the pillar arrays and the maximum capillary flow rate through the wick. This model considers the effects of gravity and mass transfer due to evaporation.
Finally, the thermo-hydraulic characterization setup, designed to minimize environmental losses, was used to experimentally determine the capillary limits of different silicon based micropillared wick samples. The heater and wicking structure were enclosed in a temperature and humidity controlled vacuum chamber. The results obtained from this setup were used to validate the analytical model shown in this paper.
CFD Modeling of Droplet Flows in Microchannels in Slip Flow Regime
Authors: García Janneth M. , Pineda Saira F. , Blanco Armando J. 
Published: July 2013

Flow in microchannels is an important area of research in engineering because its importance in areas such as micro-machinery. In addition, hydrophobic materials have become increasingly attractive for use in fabrication of microfluidic devices. However, even when in macroscopic flows the non-slip boundary condition on solid wall has been well accepted, a number of recent studies have found evidences of slip velocities for liquid flow on hydrophobic surface.
In this study, numerical simulations of two-phase flow of micro-droplet in a continuous base fluid in a 2D microchannel were performed using a commercial software package. Both slip and non-slip flows were considered. Continuous phase slip over wall channels was considered modeling all range of possible Knudsen numbers. Three drops of different sizes were modeled. Results were expressed in term of pressure drop and Reynolds numbers.
Droplet interface deformation and velocity fields inside both droplets and continuous phase were determined. Results show that for Knudsen numbers between 0.01 and 0.1, Reynolds number increases in a proportion in the order of 20%. In addition pressure drop notably increase when large drops are considered.
Axisymmetric Low-Reynolds Motion of Drops Through Circular Microchannels
Authors: Pineda Saira F. , Kamp Arjan M. , Legendre D. , Blanco Armando J. 
Published: July 2013

Flow constituted by drops appears in a wide range of natural, biological and engineering situations. For example, liquid-liquid two phase flow inside capillaries constitutes a model commonly used to represent fluid flow in a petroleum reservoir. The typical modeling approach considers inertial forces negligible in comparison to viscous forces, allowing the use of Stokes equation to study flow dynamics. Very few numerical simulations have been made considering inertial effects. In this project, the flow of a periodic train of drops in a viscous suspending fluid, due to the influence of a fixed pressure gradient, was studied by numerical simulation considering the full Navier-Stokes equations.
A numerical approach based on a Volume of Fluid (VOF) formulation was employed using JADIM software, developed by the Institut de Mécanique des Fluides de Toulouse, France. JADIM solves Navier-Stokes equations using a VOF finite volume method, second order in space and time using structured mesh. This two-fluid approach without reconstruction of the interface allows simulating two-phase flows with complex interface shapes.
Densities of the drops equal to those of the suspending fluid and a constant interface tension were assumed. The effect of drop size, viscosity ratio, interfacial forces and system pressure gradient on the flow dynamics was studied. Parameters values were chosen to be representative for some particular viscous oil.
The result validation shows an excellent agreement between both numerical results. However, there are relative differences between them due to the increase in flow velocity when drop relative size increase and validity of Stokes approach is questionable.
Results show non-symmetric eddies in the continuum phase, in a referential frame fixed to the drop. The shape of eddies is strongly influenced by viscosity radio. Drop mobility decreases with increasing size. Additionally, drop mobility also decreases when the viscosity ratio increases. Extra pressure gradient of the system due to the presence of the drop shows a strong dependency on the size ratio between the drop and the pore. For size ratio lower than 0.5, the extra pressure gradient required to move the continuum phase is small. However, when drop to micro-channel ratio exceeds 0.5, the extra pressure gradient significantly increases when the drop size increases. Also, viscosity ratio affects on the system pressure loss, especially in cases where the viscosity ratio is high. The analysis of the capillary number effect on the dynamics of the two-phase system shows that it does not influence drop mobility for the drop sizes considered.
Central giant cell granuloma: a case report
Authors: Mohan Ravi Prakash Sasankoti , Verma Sankalp , Agarwal Neha , Singh Udita 
Published: July 2013

Central giant cell granuloma (CGCG) is a relatively uncommon benign bony lesion of a variably aggressive nature. Thought to represent a reparative response to intrabony haemorrhage and inflammation, CGCG was once regarded as a reactive lesion. It is actually an asymptomatic lesion which becomes evident during routine radiographic examination or as a result of painless but visible expansion of the affected jaw. This paper presents the case of a 4-year-old boy with CGCG in the right mandibular region.
Prospective Study of Breakfast Eating and Incident Coronary Heart Disease in a Cohort of Male US Health Professionals
Authors: Cahill Leah E. , Chiuve Stephanie E. , Mekary Rania A. , Jensen Majken K. , Flint Alan J. , Hu Frank B. , Rimm Eric B. 
Published: July 2013

Background—
Among adults, skipping meals is associated with excess body weight, hypertension, insulin resistance, and elevated fasting lipid concentrations. However, it remains unknown whether specific eating habits regardless of dietary composition influence coronary heart disease (CHD) risk. The objective of this study was to prospectively examine eating habits and risk of CHD.

Methods and Results—
Eating habits, including breakfast eating, were assessed in 1992 in 26 902 American men 45 to 82 years of age from the Health Professionals Follow-up Study who were free of cardiovascular disease and cancer. During 16 years of follow-up, 1527 incident CHD cases were diagnosed. Cox proportional hazards models were used to estimate relative risks and 95% confidence intervals for CHD, adjusted for demographic, diet, lifestyle, and other CHD risk factors. Men who skipped breakfast had a 27% higher risk of CHD compared with men who did not (relative risk, 1.27; 95% confidence interval, 1.06–1.53). Compared with men who did not eat late at night, those who ate late at night had a 55% higher CHD risk (relative risk, 1.55; 95% confidence interval, 1.05–2.29). These associations were mediated by body mass index, hypertension, hypercholesterolemia, and diabetes mellitus. No association was observed between eating frequency (times per day) and risk of CHD.

Conclusions—
Eating breakfast was associated with significantly lower CHD risk in this cohort of male health professionals.
Aerosol Effects of the Condensation Process on a Convective Cloud Simulation
Authors: Seiki Tatsuya , Nakajima Teruyuki 
Published: July 2013

Abstract
Using a nonhydrostatic model with a double-moment bulk cloud microphysics scheme, the authors introduce an aerosol effect on a convective cloud system by accelerating the condensation and evaporation processes (the aerosol condensational effect). To evaluate this effect, the authors use an explicit condensation scheme rather than the saturation adjustment method and propose a method to isolate the aerosol condensational effect. This study shows that the aerosol condensational effect not only accelerates growth rates but also increases cloud water, even though the degree of the acceleration of evaporation exceeds that of condensation. In the early developing stage of the convective system, increased cloud water is, in turn, linked to ice-phase processes and modifies the ice water path of anvil clouds and the ice cloud fraction. In the mature stage, although the aerosol condensational effect has a secondary role in dynamical feedbacks when combined with other aerosol effects, the degree of modulation of the cloud microphysical parameters by the aerosol condensational effect continues to be nonnegligible. These findings indicate that feedback mechanisms, such as latent heat release and the interaction of various aerosol effects, are important in convective cloud systems that involve ice-phase processes.
Analysis of Resolved and Parameterized Vertical Transports in Convective Boundary Layers at Gray-Zone Resolutions
Authors: Shin Hyeyum Hailey , Hong Song-You 
Published: July 2013

Abstract
The gray zone of a physical process in numerical models is defined as the range of model resolution in which the process is partly resolved by model dynamics and partly parameterized. In this study, the authors examine the grid-size dependencies of resolved and parameterized vertical transports in convective boundary layers (CBLs) for horizontal grid scales including the gray zone. To assess how stability alters the dependencies on grid size, four CBLs with different surface heating and geostrophic winds are considered. For this purpose, reference data for grid-scale (GS) and subgrid-scale (SGS) fields are constructed for 50–4000-m mesh sizes by filtering 25-m large-eddy simulation (LES) data.
As relative importance of shear increases, the ratio of resolved turbulent kinetic energy increases for a given grid spacing. Vertical transports of potential temperature, momentum, and a bottom-up diffusion passive scalar behave in a similar fashion. The effects of stability are related to the horizontal scale of coherent large-eddy structures that change in the different stability. The subgrid-scale vertical transport of heat and the bottom-up scalar are divided into a nonlocal mixing owing to the coherent structures and remaining local mixing. The separate treatment of the nonlocal and local transports shows that the grid-size dependency of the SGS nonlocal flux and its sensitivity to stability predominantly determine the dependency of total (nonlocal plus local) SGS transport.
On the Sensitivity of Field Reconstruction and Prediction Using Empirical Orthogonal Functions Derived from Gappy Data
Authors: Taylor Marc H. , Losch Martin , Wenzel Manfred , Schröter Jens 
Published: July 2013

AbstractEmpirical orthogonal function (EOF) analysis is commonly used in the climate sciences and elsewhere to describe, reconstruct, and predict highly dimensional data fields. When data contain a high percentage of missing values (i.e., gappy), alternate approaches must be used in order to correctly derive EOFs. The aims of this paper are to assess the accuracy of several EOF approaches in the reconstruction and prediction of gappy data fields, using the Galapagos Archipelago as a case study example. EOF approaches included least squares estimation via a covariance matrix decomposition [least squares EOF (LSEOF)], data interpolating empirical orthogonal functions (DINEOF), and a novel approach called recursively subtracted empirical orthogonal functions (RSEOF). Model-derived data of historical surface chlorophyll-a concentrations and sea surface temperature, combined with a mask of gaps from historical remote sensing estimates, allowed for the creation of true and observed fields by which to gauge the performance of EOF approaches. Only DINEOF and RSEOF were found to be appropriate for gappy data reconstruction and prediction. DINEOF proved to be the superior approach in terms of accuracy, especially for noisy data with a high estimation error, although RSEOF may be preferred for larger data fields because of its relatively faster computation time.