bluuebunny/crossref_metadata_2025 huggingface dataset:
Infected bronchogenic cyst causing dysphagia and retrosternal pain
Authors: Søndergaard Eva Bjerre , Pedersen Jesper Holst , Kleive Dyre
Published: May 2012

Bronchogenic cysts are congenital. They are typically discovered in infancy or early childhood. Secondary infection of the cyst is uncommon. We present the case of a 17‐year‐old female who presented to the emergency department with intermediate onset of upper abdominal, and retrosternal chest pain and fever. Subsequent X‐ray and computerised tomography scan showed a bronchogenic cyst. The patient underwent subacute thoracotomy where a bronchogenic cyst filled with pus was located and excised. Bronchogenic cysts can be a rare cause of retrosternal pain.

Please cite this paper as: Søndergaard EB, Pedersen JH and Kleive D. Infected bronchogenic cyst causing dysphagia and retrosternal pain. Clin Respir J 2013; 7: e1–e2.
New Danish reference values for spirometry
Authors: Løkke Anders , Marott Jacob Louis , Mortensen Jann , Nordestgaard Børge Grønne , Dahl Morten , Lange Peter
Published: May 2012

Introduction:  International recommendations state that reference values for lung function should derive from cross‐sectional studies of healthy nonsmokers and be renewed from time to time because of cohort effect and newer, more accurate, technical equipment. In 1986, the Danish Lung Society published reference values for spirometry based on 570 individuals aged 30–70 years.

Objectives:  To produce new reference values for lung function and to extend the existing values by including individuals between 20 and 30 years of age and older than 70 years of age.

Methods:  Two similar but independent studies was used: The 2001–2003 examination of the Copenhagen City Heart Study and the 2003–2010 examination of the Copenhagen General Population Study. Of a total of 69 822 individuals, we included 11 288 healthy never‐smoking white individuals to produce the reference values: 6307 women and 4981 men, 20 years of age or older with adequate lung function.

Results:  We used sex‐stratified multiple linear regression analysis to find prediction formulas for forced expiratory volume in 1 s (FEV1), forced vital capacity (FVC) and FEV1/FVC adjusted for age and height. The cutoff value of normal lung function was defined as the fifth percentile (also named the 5% quantile) according to gender, age and height. The robustness of the data was tested and validated in several ways.

Conclusion:  Compared with the 1986 data, our 2001–2010 material contributes with a substantial number of individuals in the more extreme groups of age and height, and in general, our dataset shows that in most subgroups, the lung function level has improved during the last two decades.

Please cite this paper as: Løkke A, Marott JL, Mortensen J, Nordestgaard BG, Dahl M and Lange P. New Danish reference values for spirometry. Clin Respir J 2013; 7: 153–167.
Stromanthe idroboi sp. nov. (Marantaceae) from the montane forests of Colombia and Venezuela
Authors: Yoshida‐Arns Karla Norye , Mayo Simon Joseph , Braga João Marcelo Alvarenga
Published: May 2012

Stromanthe idroboi Yoshida‐Arns, Mayo & J. M. A. Braga, a new species from the montane forests of Colombia and Venezuela, is described and illustrated. Its morphological relationship with S. jacquinii (Roemer & Schultes) Kennedy & Nicolson is discussed. The description, distribution and a detailed illustration of the new species are provided.
Are only Emotional Strengths Emotional? Character Strengths and Disposition to Positive Emotions
Authors: Güsewell Angelika , Ruch Willibald
Published: May 2012

This study aimed to examine the relations between character strengths and dispositional positive emotions (i.e. joy, contentment, pride, love, compassion, amusement, and awe). A sample of 574 German‐speaking adults filled in the Dispositional Positive Emotion Scales (DPES;Shiota, Keltner, & John, 2006), and the Values in Action Inventory of Strengths (VIA‐IS;Peterson, Park, & Seligman, 2005). The factorial structure of the DPES was examined on item level. Joy and contentment could not be clearly separated; the items of the other five emotions loaded on separate factors. A confirmatory factor analysis assuming two latent factors (self‐orientedandobject/situation specific) was computed on scale level. Results confirmed the existence of these factors, but also indicated that the seven emotions did not split up into two clearly separable families. Correlations between dispositional positive emotions and character strengths were positive and generally low to moderate; a few theoretically meaningful strengths–emotions pairs yielded coefficients > .40. Finally, the link between five character strengths factors (i.e. emotional strengths, interpersonal strengths, strengths of restraint, intellectual strengths, and theological strengths) and the emotional dispositions was examined. Each of the factors displayed a distinctive “emotional pattern”;emotional strengthsevidenced the most numerous and strongest links to emotional dispositions.
Emphasis on Autonomy and Propensity for Suicidal Behavior in Younger and Older Adults
Authors: O’Riley Alisa A. , Fiske Amy
Published: May 2012

A cognitive style marked by emphasis on autonomy has been linked to negative outcomes throughout the life span. Two preliminary studies are presented that examined factors on a measure of autonomy (Personal Style Inventory‐Revised) in relation to propensity for suicidal behavior (Suicidal Behaviors Questionnaire‐14; SBQ‐14). Perfectionism, B = .15, SE = 0.03, p < .01, and Defensive Separation, B = .04, SE = 0.01, p ≤ .01, predicted SBQ‐14 in younger adults. Need for Control, B = .234, SE = 0.10, p < .05, predicted SBQ‐14 in older adults. Findings suggest that aspects of autonomy may be relevant to understanding suicidal behavior; however, more research is needed examining the association between autonomy and suicidal behavior in the context of depression. Nonetheless, these studies suggest a promising avenue for future research.
A general theory of multimetric indices and their properties
Authors: Schoolmaster Donald R. , Grace James B. , William Schweiger E.
Published: May 2012

1. Stewardship of biological and ecological resources requires the ability to make integrative assessments of ecological integrity. One of the emerging methods for making such integrative assessments is multimetric indices (MMIs). These indices synthesize data, often from multiple levels of biological organization, with the goal of deriving a single index that reflects the overall effects of human disturbance. Despite the widespread use of MMIs, there is uncertainty about why this approach can be effective. An understanding of MMIs requires a quantitative theory that illustrates how the properties of candidate metrics relates to MMIs generated from those metrics.

2. We present the initial basis for such a theory by deriving the general mathematical characteristics of MMIs assembled from metrics. We then use the theory to derive quantitative answers to the following questions: Is there an optimal number of metrics to comprise an index? How does covariance among metrics affect the performance of the index derived from those metrics? And what are the criteria to decide whether a given metric will improve the performance of an index?

3. We find that the optimal number of metrics to be included in an index depends on the theoretical distribution of signal of the disturbance gradient contained in each metric. For example, if the rank‐ordered parameters of a metric‐disturbance regression can be described by a monotonically decreasing function, then an optimum number of metrics exists and can often be derived analytically. We derive the conditions by which adding a given metric can be expected to improve an index.

4. We find that the criterion defining such conditions depends nonlinearly of the signal of the disturbance gradient, the noise (error) of the metric and the correlation of the metric errors. Importantly, we find that correlation among metric errors increases the signal required for the metric to improve the index.

5. The theoretical framework presented in this study provides the basis for understanding the properties of MMIs. It can also be useful throughout the index construction process. Specifically, it can be used to aid understanding of the benefits and limitations of combining metrics into indices; it can inform selection/collection of candidate metrics; and it can be used directly as a decision aid in effective index construction.
Fano 3-folds in codimension 4, Tom and Jerry. Part I
Authors: Brown Gavin , Kerber Michael , Reid Miles
Published: May 2012

We introduce a strategy based on Kustin–Miller unprojection that allows us to construct many hundreds of Gorenstein codimension 4 ideals with 9×16 resolutions (that is, nine equations and sixteen first syzygies). Our two basic games are called Tom and Jerry; the main application is the biregular construction of most of the anticanonically polarised Mori Fano 3-folds of Altınok’s thesis. There are 115 cases whose numerical data (in effect, the Hilbert series) allow a Type I projection. In every case, at least one Tom and one Jerry construction works, providing at least two deformation families of quasismooth Fano 3-folds having the same numerics but different topology.
Slopes of the U7 operator acting on a space of overconvergent modular forms
Authors: Kilford L. J. P. , McMurdy Ken
Published: May 2012

Let χ be the primitive Dirichlet character of conductor 49 defined by χ(3)=ζ for ζ a primitive 42nd root of unity. We explicitly compute the slopes of the U7 operator acting on the space of overconvergent modular forms on X1(49) with weight k and character χ7k−6 or χ8−7k, depending on the embedding of ℚ(ζ) into ℂ7. By applying results of Coleman and of Cohen and Oesterlé, we are then able to deduce the slopes of U7 acting on all classical Hecke newforms of the same weight and character.
Uniform Expansion of a Polymeric Helical Stent
Authors: Paryab Nasim , Cronin Duane , Lee-Sullivan Pearl , Ying Xiong , Boey Freddy Y. C. , Venkatraman Subbu
Published: May 2012

Helical coil polymeric stents provide an alternative method of stenting compared to traditional metallic stents, but require additional investigation to understand deployment, expansion, and fixation. A bilayer helical coil stent consisting of PLLA and PLGA was investigated using the finite element model to evaluate performance by uniform expansion and subsequent recoiling. In vitro material characterization studies showed that a preinsertion water-soaking step to mimic body implantation conditions provided the required ductility level expansion. In this case, the mechanical contribution of the outer PLGA layer was negligible since it softened significantly under environmental conditions. The viscoelastic response was not considered in this study since the strain rate during expansion was relatively slow and the material response was primarily plastic. The numerical model was validated with available experimental expansion and recoiling data. A parametric study was then undertaken to investigate the effect of stent geometry and coefficient of friction at the stent-cylinder interface on the expansion and recoiling characteristics. The model showed that helical stents exhibit a uniform stress distribution after expansion, which is important for controlled degradation when using biodegradable materials. The results indicated that increasing stent width, pitch value, and coil thickness resulted in a larger diameter after recoiling, which would improve fixation in the artery. It was also noted that a helical stent should have more than five coils to be stable after recoiling. This work is part of a larger research study focused on the performance of a balloon-inflated polymeric helical stent for artery applications.
Augmented Technical Drawings: A Novel Technique for Natural Interactive Visualization of Computer-Aided Design Models
Authors: Fiorentino Michele , Uva Antonio E. , Monno Giuseppe , Radkowski Rafael
Published: May 2012

Engineering 3D models become complex that paper drawings representation and monitor/mouse navigation on a computer-aided design (CAD) system is difficult and also frustrating. We present a novel interface paradigm for natural interactive visualization. It incorporates augmented reality enhanced engineering drawings and natural and tangible interfaces. We embedded ID markers on technical drawings to provide CAD data retrieval and tangible navigation. A user gets access to the CAD navigation functions using the drawing itself as a tangible device. In addition, CAD functions are triggered with gestures recognized by a video camera. We performed a pilot test assessment with industrial engineers. The results demonstrate the feasibility and the effectiveness of these techniques.
Experimental Investigation of a Scaled-Up Passive Curved Channel Micromixer With Slanted Grooves
Authors: Cook Kristina J. , Hassan Ibrahim G.
Published: May 2012

The flow patterns and concentration distribution in a passive scaled-up micromixer is investigated experimentally over 5 ≤ Re ≤ 100. Four meandering elements serve to enlarge species interface area through the formation of Dean vortices, while 36 slanted grooved structures enhance secondary flow by promoting helical flow. The alternating direction of the curved channel segments and slanted grooves alternated the direction of secondary flow, increasing mixing. Flow visualization provides flow pattern information as seen from the top view, while induced fluorescence provides concentration distribution information at the outlet along the center plane. At low Re (Re = 5), species appear nearly horizontally stacked at the outlet, with a curved interface. As the Reynolds number increases, the angle the species interface makes with the horizontal direction increases due to the increased strength in rotational flow. At higher Re, the formation of Dean vortices is apparent.
Focusing and Defocusing Effects in a Single Liquid-Core/Liquid-Clad Optical Waveguide: An Optical Coupler
Authors: Mahmoudi Seyed Reza
Published: May 2012

A single-liquid-core/liquid-clad L2 optical waveguide/coupler is studied numerically. The device consists of a large aspect ratio-microchannel isothermally heated on its both parallel flat walls. Steady state laminar Poiseuille flow of cold water which is introduced to the heated-microchannel forms a stable thermal boundary layer adjacent to the isothermal heated walls. Thermal boundary layer development causes the lateral refractive index gradient across the channel which is required for waveguiding. At a particular mass flow rate for a given wall temperature, the waveguiding occurs. Since the thermal boundary layer, cladding region, is actively tunable through varying both surface temperature and mass flow rate, The waveguiding effect along the channel is highly configurable. We demonstrated that the excitation in the flow direction leads to defocusing of the beam at fundamental TE mode. By reversing the flow direction, the Counter-flow excitation of the waveguide also results in focusing effects. The current waveguide can be exploited as an integrated optical coupler at specific channel wall temperature and mass flow rate.
Microflow Heat Transfer Effectiveness: Questioning the “Area/Volume-Argument”
Authors: Herwig Heinz
Published: May 2012

The often used argument that heat transfer in micro-sized devices is superior due to the fact that the transfer area scales like L2 but the volume like L3 with L as a characteristic length is critically analyzed for various heat transfer situations. It turns out that for steady state heat transfer cases the thermal boundary layer behavior is more important. In general, dimensional analysis should be applied to understand how the heat transfer performance changes when scales are reduced from macro- to micro-size.
Decision of the Best Blend Proportional Factor Value of Two Staggered Grids Used in LBM for PEFC Simulation
Authors: Gong Jia-ming , Oshima Nobuyuki , Kurihara Eru , Tabe Yutaka
Published: May 2012

The appropriate blend proportional factor value which combines two kinds of staggered grids used in Lattice Boltzmann Method (LBM) for simulating the multiphase flow phenomena with large density ratio in the Polymer electrolyte fuel cell (PEFC) is fixed on. The shape deformation of the water droplet is found when using the two kinds of staggered grids to prevent the pressure oscillation when solving the Poisson equation of this LBM model and the shape of the water droplet varies with the changes of the blend proportional factor values. Two methods are adopted to find out the two staggered grids’ appropriate blend proportional factor value that can diminish or minimize the deformation of the droplet. The first one is to compare the simulation results of different blend proportional factors with the theoretical value and find the one mostly approaches the theoretical value; the second one is to compare the current velocity divergences of the two staggered grids using the results calculated by different blend proportional factor values. A water droplet resting in a tunnel is simulated with different blend proportional factor values and the appropriate value is decided.
The Study of Microfilter Performance in Different Environments Using DSMC
Authors: Darbandi Masoud , Karchani Abolfazl , Khaledi-Alidusti Rasoul , Schneider Gerry E.
Published: May 2012

Microfilters are commonly used to block undesirable particles in the fluid flows and to control the flow patterns in MEMS. The main purpose of this study is to understand the effect of gas type on density, pressure, Mach number, and velocity distributions of fluid flows through a microfilter. The Knudsen number is the slip flow regime passing through the microfilter. We use direct simulation Monte Carlo (DSMC) method to simulate the flow of nitrogen, helium, oxygen, air and methane passing through a specific microfilter. The geometry of microfilter is unique in all cases. Our results confirm that every gas performs a different performance passing through a specific microfilter, and that the efficiency of a microfilter varies in different gas type environments. For example, among different gases, nitrogen and air have the lowest the pressure drops and that helium has the maximum pressure loss passing through a microfilter.
A New Scheme for Improving the Mixing Efficiency in Micro Scale
Authors: Anbari Ali Mohammad , Haroutunian Artin , Saidi Mohammed Said , Shafii Mohammad Behshad
Published: May 2012

Generally speaking, most micro-fluidic mixing systems are limited to the low Reynolds number regime in which diffusion dominates convection, and consequently the mixing process tends to be slow and it takes a relatively long time to have two fluids completely mixed. Therefore, rapid mixing is essential in micro-fluidic systems. In order to hasten the mixing process in micro scale, in this study we come up with a novel scheme for a two dimensional micro-fluidic mixer which encompasses three pairs of electrodes, one pair embedded in the mixing chamber and two pairs located in the micro-channels before and after the mixing chamber. The width of the middle pair is assumed to be twice of the other pairs. In addition, the fluids enter the device via two different entrances within a T-junction. The width of all micro-channels is equal to 50 micrometer and the whole mixer is less than 1 millimeter in length. While Electrical potentials are applied to three electrodes in the outlet and inlet ports in order to conduct the fluids within the mixer, the chaotic electrical fields applied to the mixing chamber are derived by the Duffing-Holmes nonlinear system. We numerically simulate the performance of our micro-mixer by solving Navier-Stokes and continuity equations for fluid velocity field, Poisson-Boltzmann equation for describing the electrical double layer potential distribution, Laplace equation for the externally induced electrical field distribution and concentration transport equation in order to obtain the concentration distribution of two fluids within the geometry. Then, the mixing efficiency is calculated in the outlet cross section of the mixer and the results indicate that a mixing performance efficiency of up to 98% is obtainable by utilizing this proposed scheme.
Developing Cross Drag Expressions for Nanotube Bundles Using Molecular Dynamics
Authors: Darbandi Masoud , Khaledi-Alidusti Rasoul , Abbaspour Majid , Abbasi Hossein Reza , Sabouri Moslem , Schneider Gerry E.
Published: May 2012

The nonequilibrium molecular dynamics (NEMD) simulations are performed to calculation the cross drag over a nanotube located in a uniform liquid argon flow. As is known, the behavior of fluid flows in nano-scale sizes is very different from that in microscopic and macroscopic sizes. In this work, our concern is on the flow of argon molecules over a nanotube which occurs in nanoscale sizes. We calculate the cross drag enforced the nanotube at Re≤1.0. In this regard, we use the molecular dynamics and simulate the flow of argon molecules over (6,0), (8,0) and (10,0) nanotubes. The simulations are performed at different velocities and the cross drag coefficient is computed at different Reynolds numbers. To improve the efficiency of simulations, we use USHER algorithm and examin the insertion of molecules at the end of the simulation box, the argon molecules are located out of box. Using the power trend line, we derived a formula, which approximates the cross drag of chosen nanotube. In all simulations, only the first two and the last two rings of the nanotube are frozen. All non-bonded interactions are calculated based on the Lennard-Jones potential. The results if molecular dynamics are compared with two empirical expressions provided by experiments performed on the flow over a macro-scale cylinder. The results show that the cross drag force on a single-walled nanotube calculated from MD simulations is larger than that provided by the empirical expressions in slow flows (Re≪ 1.0). As is expected the results of continuum flow calculations cannot be trusted to predict the drag of a nanotubes if Re≪1.0. The difference increases as the flow velocity decreases.
Voltage Phase Control for Enhanced Addressability in Highly-Parallel Digital Microfluidic Architectures
Authors: Collier Christopher M. , Born Brandon , Holzman Jonathan F.
Published: May 2012

Digital microfluidic architectures have been a source of great enthusiasm for on-chip fluid applications requiring precise control and reconfigurability. Droplet-based systems operating with exceedingly small volumes (pL) can make use of digital microfluidic control systems to direct fluid motion using voltages on cascaded electrode structures. The voltage on these electrodes can be adapted via software, thus the generalized templates offered by digital microfluidic systems can be tailored for numerous end-user applications. The work presented here addresses the two major challenges for implementing these digital microfluidics systems for end-user applications: parallel addressability and reduced input voltages. The challenges are overcome through dual-phase AC voltage routing in a 16×16 digital microfluidic multiplexer using low (10 Vrms) input voltages. The first challenge, related to parallel addressability, comes about because of the generalized template for digital microfluidics, with underlying square-grid electrodes forming a two-dimensional, M×N, plane. Such a structure cannot be readily scaled up for use in single-layered highly-parallel architectures as external address lines cannot be effectively contacted to internal square electrodes lying within a 2-dimensional. With this in mind, the work here introduces multiplexing with a cross-referenced architecture having only M+N input lines. Microdroplets lie between orthogonal overlying row electrodes and underlying column electrodes, and nonlinear threshold-voltage localization is used to initiate motion of the desired microdroplet in the two-dimensional plane. Microdroplet interference (motion of undesired microdroplets) along the activated row and column is avoided, as the applied voltage initiates motion only at the overlapped electrode region (where the voltage is doubled and above-threshold). A dual-phase AC voltage control system is used to address the above bi-layered cross-referenced electrode structure and simultaneously provides a natural solution to the second, reduced voltage, challenge of practical digital microfluidic architectures. Reduced input voltages can be achieved in the digital microfluidic system through an integrated centre-tap AC transformer (a dielectric layer in the digital microfluidic multiplexer limits the current and power consumption, allowing for step-up voltage transformation). The dual-phase outputs from this voltage transformer are 180° out-of-phase, and the AC signals from these outputs are routed to the appropriate row and column electrodes to bring about above-threshold motion. Controlled switching is demonstrated in this work for input voltages below 10 Vrms. Structural and electrical design issues for this dual-phase AC digital microfluidic integrated chip are addressed in this work, and results are presented for an integrated digital microfluidic multiplexer prototype.
Flow Patterns and Electrokinetic Mixing Performance in Heterogeneous Microchannels
Authors: Jamaati Jafar , Niazmand Hamid , Renksizbulut Metin
Published: May 2012

Due to the recent advances in microfabrication techniques, it is possible to produce microchannels with positive, negative, or even neutral surface charges. According to several numerical and experimental investigations, such a combination of charge patterns on the microchannel walls results in complex flow fields with circulation zones that are highly desirable for fluid mixing requirements as in lab-on-a-chip devices. In this paper, the mixing efficiency associated with electro-osmotic flows in heterogeneous microchannels is investigated. The Navier-Stokes equations are solved for the flow field along with species transport equations to obtain the concentration field. The effects of the Electric Double Layer (EDL) on the flow field are considered using the Helmholtz-Smoluchowski model in which the EDL effects on the fluid adjacent to the walls are replaced by velocity slip at walls. Different configurations and profiles for the wall charges can be applied to the microchannel walls. In the present study, heterogeneous patterns consisting of different patches with constant zeta-potentials are considered. The flow pattern of a single patch consists of a single vortex attached to the channel wall, which significantly increases the mixing performance. It is expected that a combination of several patches would increase the mixing performance considerably. Therefore, the effects of the size, number, and locations of multiple patches on the mixing performance are investigated in detail. The results for a single patch indicate that the mixing efficiency increases with the size of the patch and its proximity to the microchannel inlet. It is expected that with a suitable combination of patches, an optimized configuration can be found in which the mixing efficiency is maximized and the length of the mixing section is minimized. The results can be applied to the design of micro-mixers to minimize their size while achieving the desired mixing requirements.
Heat Transfer Enhancement by Slurry of Phase Change Material Through Rectangular Porous Channel
Authors: Shukla Manali , Hassanipour Fatemeh
Published: May 2012

This study attempts to take advantage of porous media with high conductivity and the latent heat capacity of phase change material together to enhance the overall heat transfer rate. A 3-D laminar model of a rectangular porous channel with high thermal conductivity and constant wall heat flux is chosen to see the enhancement of heat transfer when used in conjunction with the phase change material slurry. Numerical simulations for various wall heat fluxes and inlet velocities are carried out. The heat transfer coefficient along the heated surface of the channel is compared when adding micro-encapsulated phase change material to the flow passing through porous channel. There is a significant heat transfer enhancement when using phase change material slurry through porous channel, only under specific conditions of heat fluxes, inlet velocities and the particle concentrations. This study also investigates the effect of various porous media properties e.g. porosity and permeability on the heat transfer coefficient when applied with slurry of phase change material.
Modeling of Interfacial Component for Two-Phase Frictional Pressure Gradient in Microchannels and Minichannels
Authors: Awad M. M. , Muzychka Y. S.
Published: May 2012

A simple approach for calculating the interfacial component of frictional pressure gradient in two-phase flow in microchannels and minichannels is presented. This approach is developed using superposition of three pressure gradients: single-phase liquid, single-phase gas, and interfacial pressure gradient. The proposed model can be transformed in two different ways. First, two-phase interfacial multiplier for liquid flowing alone (φl,i2) as a function of two-phase frictional multiplier for liquid flowing alone (φl2) and the Lockhart-Martinelli parameter, X. Second, two-phase interfacial multiplier for gas flowing alone (φg,i2) as a function of two-phase frictional multiplier for gas flowing alone (φg2) and the Lockhart-Martinelli parameter, X. This proposed model allows for the interfacial pressure gradient to be easily modeled. Comparisons of the proposed model with experimental data for microchannels and minichannels and existing correlations for both φl and φg versus X are presented.
Effect of Microgroove Dimensions on Deformation of the Liquid Film Under Vibration Conditions
Authors: Guo Chaohong , Hu Xuegong , Cao Wei , Wang Tao , Tang Dawei
Published: May 2012

Deformation of the triple-phase contact line in various sizes of rectangular microgrooves under vertical vibration conditions was studied in this paper. Width of the rectangular microgroove ranges from 0.2 mm to 0.4mm and depth of the microgrooves is 0.2∼0.6mm. The frequency of vibration is 10Hz, and the amplitude of vibration is approximately 3.5mm. The research results show that oscillation of the liquid film in microgrooves becomes more obvious, and the triple-phase contact line is deformed more greatly when the groove width or the groove depth increases. The main reason is that the flow resistance of the liquid film in microgrooves decreases when the groove width or the groove depth increases.
Experimental Investigations of Laminar, Transitional to Turbulent Gas Flow in Rib-Patterned Micro-Channels
Authors: Hong Chungpyo , Yamada Toru , Asako Yutaka , Faghri Mohammad , Ueno Ichiro
Published: May 2012

The effects of rib-patterned surfaces on laminar, transitional to turbulent gas flow in micro-channels were experimentally investigated in the present study. The experiments were performed for two micro-channels having either smooth or rib-patterned surfaces. The micro-channels were etched into silicon wafers and capped with glass substrates. The micro-ribs were patterned on the microchannel surfaces and oriented perpendicular to the flow direction. The pressure was measured at seven locations along the channel length to determine local values of Mach number and friction factor for a wide range of flow regime from laminar to turbulent flow. The friction factors with the hydraulic diameter based on the rib-to-upper-wall height were compared with that for incompressible theory on Moody chart. The values of the product of friction factor and Reynolds number (f·Re) as a function of Mach number were also compared with those of smooth micro-channels and incompressible theory.
Detailed Investigation of Thermal and Hydrodynamic Flow Behaviour in Micro/Nano Cavity Using DSMC and NSF Equations
Authors: Mohammadzadeh Alireza , Roohi Ehsan , Niazmand Hamid , Stefanov Stefan Kanchev
Published: May 2012

We utilized direct simulation Monte Carlo (DSMC) method to investigate the effectiveness of the NSF equations in the slip and transition regimes. Monatomic argon confined in a micro/nano lid-driven cavity is considered in this study. Full NSF equations accompanied by the first and second order velocity slip and temperature jump boundary conditions are used to investigate non-equilibrium phenomena. It is seen that although velocity profiles are predicted quite accurately by means of proper slip boundary conditions, the NSF equations fail to predict correct shear stress distribution and heat flux direction even in the middle slip regime. It is also seen that applying the second order velocity slip boundary condition in the transition regime reduces the accuracy of the continuum approach. Fourier law, which assumes the heat always fluxes from hotter to colder region, loses its validity in the slip regime and beyond.
Exergy Analysis of Nanofluids in Microchannel
Authors: Singh Pawan K. , Ahmed Nouman Zahoor , Das Sarit K. , Shatilla Youssef
Published: May 2012

Present study carries out an exergy analysis for nanofluids in microchannels. For this, two microchannels with diameter of 218 μm and 303 μm are chosen due to availability of experimental data.. The alumina nanoparticles with 45 nm average size are dispersed in DI water. The stability of these nanofluids is controlled by their pH. Three concentrations of 0.25 vol%, 0.5 vol% and 1vol% are chosen to observe the volume fraction effect. For the entropy generation analysis Bejan equations for internal flow are used. The order of magnitude method was used to simplify the equations. Initially, the analysis is carried out with the standard correlations (Dittus-Boelter and Blasius equations) for tube flow for laminar region. Frictional and thermal entropy generation rate ratios were found comparable and neither of them can be neglected. The entropy generation rate ratio was above unity for 218 μm channel while, it was below unity for 303 μm channel. The prediction of entropy generation rate ratio was higher for experimental correlations compared to that of theoretical correlations. The entropy generation number was higher for 303 μm channel and more prone to change with concentration. The thermal part of entropy generation was the major part of total entropy generation for 303 μm channel. Also, the absolute entropy generation was higher for 303 μm channel compared to 218 μm channel.
On the Heat Transfer Enhancement of Turbulent Gas Floes in Short Round Tubes Engaging a Light Gas Mixed With Selected Heavier Gases
Authors: Mobinipouya Neda , Mobinipouya Omid
Published: May 2012

A unique way for maximizing turbulent free convection from heated vertical plates to cold gases is studied in this paper. The central idea is to examine the attributes that binary gas mixtures having helium as the principal gas and xenon, nitrogen, oxygen, carbon dioxide, methane, tetrafluoromethane and sulfur hexafluoride as secondary gases may bring forward. From fluid physics, it is known that the thermo-physical properties affecting free convection with binary gas mixtures are viscosity ηmix, thermal conductivity λmix, density ρmix, and heat capacity at constant pressure. The quartet ηmix, λmix, ρmix, and Cp,mix is represented by triple-valued functions of the film temperature the pressure P, and the molar gas composition w. The viscosity is obtained from the Kinetic Theory of Gases conjoined with the Chapman-Enskog solution of the Boltzmann Transport Equation. The thermal conductivity is computed from the Kinetic Theory of Gases. The density is determined with a truncated virial equation of state. The heat capacity at constant pressure is calculated from Statistical Thermodynamics merged with the standard mixing rule. Using the similarity variable method, the descriptive Navier-Stokes and energy equations for turbulent Grashof numbers Grx > 109 are transformed into a system of two nonlinear ordinary differential equations, which is solved by the shooting method and the efficient fourth-order Runge-Kutta-Fehlberg algorithm. The numerical temperature fields T(x, y) for the five binary gas mixtures He-Xe, He-N2, He-O2, He-CO2, He-CH4, He-CF4 and He-SF6 are channeled through the allied mean convection coefficient hmix/B varying with the molar gas composition w in proper w-domain [0, 1]. For the seven binary gas mixtures utilized, the allied mean convection coefficient hmix/B versus the molar gas composition w is graphed in congruous diagrams. At a low film temperature Tf = 300 K, the global maximum allied mean convection coefficient hmix,max/B = 85 is furnished by the He-SF6 gas mixture at an optimal molar gas composition wopt = 0.93. The global maximum allied mean convection coefficient hmix,max/B = 57 is supplied by pure methane gas SF6 (w = 1) at a high film temperature Tf = 1000 K instead of the He-SF6 gas mixture.
Nano-Engineered Surfaces With Heterogeneous Wettability for Boiling Heat Transfer Enhancement
Authors: Betz Amy Rachel , Jenkins James , Kim Chang-Jin C. J. , Attinger Daniel
Published: May 2012

In this work we describe the manufacturing and characterization of multi-scale patterned heterogeneous wettability surfaces. We find drastic enhancements of the pool boiling performance in water. Compared to a hydrophilic SiO2 surface with a wetting angle of 7°, we find that surfaces combining superhydrophilic and superhydrophobic patterns can increase the heat transfer coefficient (HTC) by 300% and can increase the critical heat flux (CHF) by more than 100%.
A Novel Scanning Molecular Tagging Velocimetry Technique for Two Dimensional Microfluidic Applications
Authors: Ahmad Farhan , Nobes David S.
Published: May 2012

Micro particle image velocimetry forms the basis of modern microscale flow measurement techniques. However, the motion of tracking particles that have been introduced into the fluid to measure flow velocity in micro fluidic flows can be affected by a number of different body forces that may not affect the carrier fluid. Under these conditions, molecular tagging velocity (MTV) has a distinct advantage in resolving fluid motion. A MTV approach, based on the photobleaching mechanism, is presented that allows any desired pattern of flow markers to be written into the region-of-interest to track the flow. This allows standard particle master shadowgraphy algorithms to be used to track groups of tagged molecules in the flow resolving two components of the bulk fluid motion. The MTV techniques developed so far for microfluidic application provide only a one dimensional flow measurement, typically along the axial direction perpendicular to the tagged region. Other tagging methods include the use of a grid and a structured mask for macro-scale and micro-scale flows respectively. One of the limitations of these approaches is that velocity information for only a predefined pattern is available. The MTV technique presented here is capable of resolving two dimensional flow velocity information with the limitations associated with the application of a mask. The salient feature of the presented approach is the use of a laser scanner which allows unrestricted, repeatable and accurate movement of the write laser within the field-of-view. The temporal displacement of the tagged region is captured onto an imaging device. The proof of concept of the technique is presented in the current work. A known flow velocity through a curved section of a 750 μm wide serpentine channel is measured using the designed system. The tagged regions are in the form of dark dots which advect with the flow. The temporal and spatial evolution of these tagged regions is tracked to reveal the flow information. The aim of this technique is to perform velocity measurements in a dielectrophoretic flow of a mixture of nanoparticles and the caged fluorescent dye, which may show different flow behavior, possibly in two opposite directions due to the charge on them.
Numerical Simulation of Mass Transfer Characteristics in a Taylor Flow Microreactor
Authors: Ganapathy Harish , Al-Hajri Ebrahim , Ohadi Michael M.
Published: May 2012

The aim of this work is to investigate numerically the mass transfer characteristics in a Taylor flow microchannel reactor. Previous attempts to model gas-liquid mass transfer in microchannels have mainly been done by the unit cell based models. Limitations of this approach are its incapability to account for the mass transfer in the inlet mixing region and the dependence on empirical data to define the unit cell geometry. The present work attempts to overcome both these shortcomings by adopting a purely numerical approach to model the mass transfer in a Taylor flow microreactor. A finite-element implementation of the phase field method was used to predict the hydrodynamics of the two-phase flow The flow pattern obtained was used to define the computational domain to model the mass transfer. The reaction system of CO2 absorption into aqueous NaOH solution was considered for gas superficial velocities ranging from 0.09 to 0.25 m/s with the liquid phase superficial velocities ranging from 0.02 to 0.21 m/s. Channels with hydraulic diameters ranging from 100 μm to 500 μm were considered with flow focusing and cross flow types of inlet configuration. The effect of channel length was also studied by varying the residence time in the transient simulation. Results suggest that the conventional unit cell based approaches which do not model the inlet mixing region could over predict the mass transfer by up to 16%. Smaller diameter channels were found to have improved mass transfer characteristics. This was found to be further enhanced by higher concentration levels of the liquid reactant and higher temperatures. The channel wall wettability was found to negligibly affect the mass transfer characteristics. The predictions from the present model were compared with experimental data as well as with predictions of the unit cell based model and a good agreement was obtained with both models.
A Robust Superhydrophobic Surface for Digital Microfluidics
Authors: Barona David , Amirfazli A.
Published: May 2012

Digital microfluidics depends on efficient movement of individual drops for a variety of tasks, e.g. reagent delivery, mixing, sampling, etc. Superhydrophobic (SH) coatings generally show high repellency and low adhesion for a variety of liquids. Therefore, SH coatings can provide for an efficient drop delivery and hence low energy requirements for a fluidic chip. However, wide application of such coatings is hampered by fragile nature of such coatings to date. A new SH coating is developed that addresses the fragility challenge of such coatings. It is based on application of nanoparticles to fluoropolymers. The mechanical stability, wear resistance and durability under prolonged liquid exposure of this new coating is discussed. It is shown that the new SH coating can maintain high contact angles, low contact angle hysteresis needed for drop mobility under adverse conditions/application of digital microfluidic devices. The developed SH coating can also be sprayed onto various surfaces, including glass used in traditional lab-on-chip (LOC) devices, or even paper for enabling novel Lap-on-paper (LOP) devices.
Experimental Investigation of Inertial Mixing in Droplets
Authors: Carroll Brian , Hidrovo Carlos
Published: May 2012

Achieving the fast mixing requirements posed by the chemical, biological, and life science community for confined microchannel flows remains an engineering challenge. The viscous and surface tension forces that dominate conventional micro-flows undermine fast, efficient mixing. By increasing the collisional velocity of reagent droplets, inertia can be exploited to increase mixing rates. This paper experimentally investigates inertial droplet mixing in micro flows. A high speed, gaseous flow is used to detach, transport, and collide droplets of nanoliter-size volumes in standard T and Y-junction microchannel geometries. Mixing rates are quantified using differential fluorescent optical diagnostics. Measured droplet mixing times are compared to the characteristic time scales for mass and viscous diffusion and bulk convection. Results show that mixing times are decreased as the droplet inertia is increased, indicating the potential benefit of inertia-driven mixing.
Numerical Investigation of the Combined Effects of Biomolecular Adsorption and Microdroplet Evaporation on the Performance of the Electrocapillary-Based Digital Microfluidic Systems
Authors: Ahmadi Ali , Hoorfar Mina
Published: May 2012

In this article, microdroplet motion in the electrocapillary-based digital microfluidic systems is modeled accurately, and the combined effects of the biomolecular adsorption and micro-droplet evaporation on the performance of the device are investigated. An electrohydrodynamic approach is used to model the driving and resisting forces, and Fick’s law and Gibbs equation are used to calculate the microdroplet evaporation and adsorption rate. Effects of the adsorption and evaporation rates are then implemented into the microdroplet dynamics by adding new terms into the force balance equation. It is shown that mass loss due to the evaporation tends to increase the protein concentration, and on the other hand, the increased concentration due to the mass loss increases the biomolecular adsorption rate which has a reverse effect on the concentration. The modeling results indicate that evaporation and adsorption play crucial roles in the microdroplet dynamics.
Mass Flow Rate Measurement Through Rectangular Microchannels for Large Knudsen Number Range
Authors: Nacer M. Hadj , Perrier Pierre , Graur Irina
Published: May 2012

The mass flow rate through microchannels with rectangular cross section is measured for the wide Knudsen number range (0.0025–26.2) in isothermal steady conditions. The experimental technique called ‘Constant Volume Method’ is used for the measurements. This method consists of measuring the small pressure variations in the tanks upstream and downstream of the microchannel. The measurements of the mass flow rate are carried out for three gases (Helium, Nitrogen and Argon). The microchannel internal surfaces are covered with a thin layer of gold with mean roughness Ra = 0.87nm (RMS). The continuum approach (Navier-Stokes equations) with first order velocity slip boundary condition was used in the slip regime (Knudsen number varies from 0.0025 to 0.1) to obtain the experimental velocity slip and accommodation coefficients associated to the Maxwell kinetic boundary condition. In the transitional and near free molecular regimes the linearized kinetic BGK model was used to calculate numerically the mass flow rate. From the comparison of the numerical and measured values of the mass flow rate the accommodation coefficient was also deduced.
Mass Transport Measurements in Porous Transport Layers of a PEM Fuel Cell
Authors: Pant Lalit M. , Mitra Sushanta K. , Secanell Marc
Published: May 2012

Porous transport layers are an integral part of polymer electrolyte fuel cells (PEMFC). In order to optimize the catalyst layer performance and reduce catalyst consumption, a thorough understanding of mass transport through porous media is necessary. Currently, there is a lack of experimental measurements of effective mass transport properties of porous transport layers. Further, mass transport theories in the literature, such as the binary friction model by Kerkhof [1], have not been extensively validated for porous media. In the present study, mass transport measurements have been performed on the porous media of a PEMFC, namely a GDL and an MPL. The experimental setup described by Pant et al. [2] has been used. The setup uses the diffusion bridge/counter-diffusion technique for the mass transport measurements. The experimental setup has the advantage that it can be used to perform studies for pure diffusion and convection-diffusion mass transport. The setup also facilitates measurement of permeability of porous media, which can then be used in convection-diffusion studies. Preliminary permeability measurements of GDL and MPL from the setup show good agreement with values available in literature. In preliminary experimentation, the conventional diffusivity correlations like Bruggeman equation have been found to overpredict the diffusivities.