bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Cultivation Time on Production of Antifungal Metabolite(s) by Streptomyces hygroscopicus in Laboratory‐Scale Bioreactor
Authors: Tadijan Ivana , Grahovac Jovana , Dodić Jelena , Grahovac Mila , Dodić Siniša
Published: November 2015

Biological control agents offer one of the best alternatives to reduce the use of pesticides. Fungi from the genera Alternaria, Colletotrichum and Fusarium are listed among the most important storage pathogens of apple fruits. During storage, transport and marketing, pathogenic fungi can cause significant losses of apple fruits. This investigation studied the potential of Streptomyces hygroscopicus as a biocontrol agent against pathogenic fungi obtained from apple fruit samples expressing rot symptoms. Production of antifungal metabolites by S. hygroscopicus was carried out in 3‐l bench‐scale bioreactor (Biostat® Aplus, Sartorius AG, Germany) during 7 days. Fermentation was carried out at 27°C with aeration rate of 0.5 vvm and agitation rate of 200 rpm. The aim was to analyse bioprocess parameters of batch biofungicide production in medium containing glucose as a carbon source and to examine at which stage of bioprocess production of antifungal metabolite(s) against six phytopathogenic fungi occurs. In vitro antifungal activity of the produced metabolites against six fungi of the genera Colletotrichum, Fusarium and Alternaria grown on potato dextrose agar were determined every 24 h using wells technique. Antifungal activity of cell‐free culture filtrate and filtrate treated with high temperature were tested. The filtrate treated with high temperature did not show any antifungal activity suggesting that active components are thermo unstable. Stationary phase of growth occurred between the third and fourth day of cultivation when production of secondary metabolites begins. Obtained results showed that maximal antifungal activity is achieved on fifth and sixth day of S. hygroscopicus cultivation under defined conditions (inhibition zone diameter higher than 30 mm for all test fungi).
A retrospective evaluation of polyurethane, long‐stay, peripheral venous cannulae in dogs undergoing radiotherapy
Authors: Macfarlane M. J. , Morris J. , Burnside S. , Bell A.
Published: November 2015

OBJECTIVES

The aim of this retrospective study was to review placement duration and associated complications of long‐stay, peripheral venous cannulae in dogs undergoing a radiotherapy protocol. Factors affecting duration of stay of the cannulae were evaluated.

METHODS

The records of patients which had a single‐lumen, 16‐gauge, 16‐cm polyurethane cannulae inserted into a peripheral vein between 2010 and 2014 were reviewed.

RESULTS

Forty‐one cannulae were placed in 41 patients. Median duration of cannula stay was 14 days (range 2 to 26). In 14 cases (~34%) the cannula was removed at the end of the radiotherapy course. In 13 (~32%) cases, cannula‐related complications resulted in premature removal. Use of steroids and antibiotics appeared to be associated with a longer median duration of stay.

CLINICAL SIGNIFICANCE

No life‐threatening complications were encountered. Indwelling, polyurethane, saphenous cannulae were an effective and safe way to maintain venous access in this group of patients. Prednisolone and antibiotics were typically commenced for acute radiation side effects ‐midway through the protocol; therefore their association with length of stay may not be a direct result of their administration.
Hospital‐acquired Anemia in Critically Ill Dogs and Cats: A Multi‐Institutional Study
Authors: Lynch A.M. , Respess M. , Boll A.E. , Bozych M. , McMichael M. , Fletcher D.J. , De Laforcade A.M. , Rozanski E.A.
Published: November 2015

Background

Hospital‐acquired anemia is commonly described in people but limited information currently is available regarding its prevalence in animals.

Hypothesis/objectives

Assess the prevalence of hospital‐acquired anemia in hospitalized critically ill dogs and cats, and examine its relationship with phlebotomy practices, transfusion administration, and survival to discharge.

Animals

Eight hundred and fifty‐one client‐owned animals (688 dogs and 163 cats).

Methods

A multicenter, observational study was conducted in which packed cell volume (PCV) was recorded at the time of admission and on subsequent hospitalization days. Signalment, number of blood samples obtained, underlying disease, whether or not blood products were administered, duration of hospitalization, and survival to discharge were recorded.

Results

Admission anemia prevalence was 32%, with overall prevalence during the hospitalization period of 56%. The last recordedPCVwas significantly lower than the admissionPCVfor both dogs (admissionPCV, 42% [range, 6–67%]; last recordedPCV, 34% [range, 4–64%],P < .0001) and cats (admissionPCV, 31% [range, 6–55%]; last recordedPCV, 26% [range, 10–46%],P < .0001). Patients that developed anemia had significantly more blood samples obtained (nonanemic, 5 blood samples [range, 2–54]; anemic, 7 blood samples [range, 2–49],P < .0001). Hospitalized cats were significantly more likely to develop anemia compared to dogs (P < .0001), but anemic dogs were significantly less likely to survive to discharge (P = .0001). Surgical patients were at higher risk of developing hospital‐acquired anemia compared to medical patients (OR, 0.63; 95% CI, 0.4–0.9;P = .01).

Conclusions and Clinical Relevance

Hospital‐acquired anemia occurred frequently, especially in surgical patients. Additional studies focused on the direct effect of phlebotomy practices on the likelihood of anemia development in hospitalized animals are warranted.
Can Truth Reconcile a Nation? Truth and Reconciliation Commissions in Argentina and Chile: Lessons for Mexico
Authors: Chavez‐Segura Alejandro
Published: November 2015

The emergence of a moral power of the state—legitimacy through accountability and prosecution of perpetrators of human rights abuses—provides a new dimension of power in Latin American countries. Following a normative international approach, this article presents the relevance of truth commissions for the consolidation of a decisive democratic turn in Latin American countries, highlighting the relevance of having a trustworthy morality of the state through just policies toward its citizens. Truth commissions are important tools to restore citizens' trust in their authorities and set the basis for reconciliation. By engaging in active restorative and transitional justice, states can be reconciled, and the conditions for an effective peacebuilding within borders can be established as pillars of an improved, stronger democratic state, as the cases of truth commissions in Argentina and Chile represent. By examining the outcomes of these commissions, I argue that a truth commission in Mexico could promote a much‐needed reconciliation.
A Discursive Institutionalist Approach to Understanding Comparative Policy Change:Ireland andMexico in the 1980s
Authors: Hogan John , O'Rourke Brendan K.
Published: November 2015

Employing the critical juncture theory, a discursive institutionalist approach, this article examines the nature of changes toIrish industrial policy and toMexican macroeconomic policy in the early 1980s. Were these significant changes, or were they continuations of previously established policy pathways? The critical juncture theory consists of three elements—economic crisis, ideational change, and the nature of the policy change—that we must identify to be able to declare with some certainty if the policy changes constituted critical junctures. Our findings will help explain whyIrish industrial policy did not undergo a radical transformation during the 1980s, whereasMexican macroeconomic policy underwent major change.
The Washington Consensus and Social Policy: World Bank Projects and Health Sector Reform in Costa Rica
Authors: Noy Shiri
Published: November 2015

International financial institutions—namely the International Monetary Fund and the World Bank—have been central in diffusing neoliberal ideas. However, little is known about the World Bank's involvement in health policy reform in Latin American countries, and even less about governments' responses to these recommendations and directives. I use World Bank project and loan documents together with national policy documents to examine health sector reform in Costa Rica between 1980 and 2005. I trace World Bank involvement in and discourse surrounding Costa Rican health sector reform, including the ideal role of government in health, the shifting relationship between the Costa Rican social security system and the Ministry of Health, and the focus on primary care. Using the policy paradigm approach, I identify two paradigmatic goals apparent in World Bank and national documents: efficiency and equity. I find that, although the government and the World Bank are consistent in their approach to these goals, they do not emphasize them in the same way, and they describe them in the context of differing logics. I conclude by assessing the implications of this study for our understanding of the relationship between neoliberalism, international financial institutions, and health sector reform in Latin America.
Effectiveness and Legitimacy in Democratic Reform: The Case of Transparency Reform inMexico
Authors: Hernandez Mara I.
Published: November 2015

This article identifies political practices that simultaneously increase negotiation effectiveness and democratic legitimacy as key enabling factors for democratic legal reform. This finding goes against theHabermasian idea that success‐oriented negotiations run counter to the logic of reason‐based deliberations that are necessary to produce democratic legitimacy. Based on the sequence of practices that led to the 2007 transparency reform inMexico,Ioffer several examples of how negotiation effectiveness and democratic legitimacy may reinforce each other.Iconclude that champions of democratic reform need to engage in action that is both strategic and communicative to move beyond weak democracies or hybrid regimes toward more democratic institutions. Practices such as deliberation in small, but plural working groups, or the detailed discussion of specific policy options in plural public forums are examples of practices that may add democratic legitimacy and negotiation effectiveness to a reform process. Effective and legitimate reform processes might also entail some degree of compromise with powerfulde factoveto players, so long as the negotiation process is steered toward the effective institutionalization of insight acquired communicatively.
Rapid genetic restoration of a keystone species exhibiting delayed demographic response
Authors: Cosentino Bradley J. , Schooley Robert L. , Bestelmeyer Brandon T. , McCarthy Alison J. , Sierzega Kevin
Published: November 2015

Genetic founder effects are often expected when animals colonize restored habitat in fragmented landscapes, but empirical data on genetic responses to restoration are limited. We examined the genetic response of banner‐tailed kangaroo rats (Dipodomys spectabilis) to landscape‐scale grassland restoration in the Chihuahuan Desert of New Mexico, USA. Dipodomys spectabilis is a grassland specialist and keystone species. At sites treated with herbicide to remove shrubs, colonization by D. spectabilis is slow and populations persist at low density for ≥10 years (≥6 generations). Persistence at low density and low gene flow may cause strong founder effects. We compared genetic structure of D. spectabilis populations between treated sites and remnant grasslands, and we examined how the genetic response to restoration depended on treatment age, area, and connectivity to source populations. Allelic richness and heterozygosity were similar between treated sites and remnant grasslands. Allelic richness at treated sites was greatest early in the restoration trajectory, and genetic divergence did not differ between recently colonized and established populations. These results indicated that founder effects during colonization of treated sites were weak or absent. Moreover, our results suggested founder effects were not mitigated by treatment area or connectivity. Dispersal is negatively density‐dependent in D. spectabilis, and we hypothesize that high gene flow may occur early in the restoration trajectory when density is low. Our study shows genetic diversity can be recovered more rapidly than demographic components of populations after habitat restoration and that founder effects are not inevitable for animals colonizing restored habitat in fragmented landscapes.
New evidence for hybrid zones of forest and savanna elephants in Central and West Africa
Authors: Mondol Samrat , Moltke Ida , Hart John , Keigwin Michael , Brown Lisa , Stephens Matthew , Wasser Samuel K.
Published: November 2015

The African elephant consists of forest and savanna subspecies. Both subspecies are highly endangered due to severe poaching and habitat loss, and knowledge of their population structure is vital to their conservation. Previous studies have demonstrated marked genetic and morphological differences between forest and savanna elephants, and despite extensive sampling, genetic evidence of hybridization between them has been restricted largely to a few hybrids in the Garamba region of northeastern Democratic Republic of Congo (DRC). Here, we present new genetic data on hybridization from previously unsampled areas of Africa. Novel statistical methods applied to these data identify 46 hybrid samples – many more than have been previously identified – only two of which are from the Garamba region. The remaining 44 are from three other geographically distinct locations: a major hybrid zone along the border of the DRC and Uganda, a second potential hybrid zone in Central African Republic and a smaller fraction of hybrids in the Pendjari–Arli complex of West Africa. Most of the hybrids show evidence of interbreeding over more than one generation, demonstrating that hybrids are fertile. Mitochondrial and Y chromosome data demonstrate that the hybridization is bidirectional, involving males and females from both subspecies. We hypothesize that the hybrid zones may have been facilitated by poaching and habitat modification. The localized geography and rarity of hybrid zones, their possible facilitation from human pressures, and the high divergence and genetic distinctness of forest and savanna elephants throughout their ranges, are consistent with calls for separate species classification.
Graduates, Dropouts and Slow Finishers: The Effects of Credit Constraints on University Outcomes
Authors: Cardak Buly A. , Vecci Joe
Published: November 2015

The effect of credit constraints on university outcomes is studied. Credit constraints have a negative relationship with dropout, especially on lower achieving high school graduates. Credit constrained students with strong high school achievement are 13–15% more (less) likely to graduate (be slow finishers) relative to otherwise similar students who are potentially or unlikely constrained. Using competing risk analysis, we find dropout is most likely in the first year of study and falls over time for all students. After 3 years of study, the risk of dropout increases for students who are constrained suggesting constraints may eventually bind on these students.
Enhancing blast disease resistance by overexpression of the calcium‐dependent protein kinase OsCPK4 in rice
Authors: Bundó Mireia , Coca María
Published: November 2015

Rice is the most important staple food for more than half of the human population, and blast disease is the most serious disease affecting global rice production. In this work, the isoform OsCPK4 of the rice calcium‐dependent protein kinase family is reported as a regulator of rice immunity to blast fungal infection. It shows that overexpression of OsCPK4 gene in rice plants enhances resistance to blast disease by preventing fungal penetration. The constitutive accumulation of OsCPK4 protein prepares rice plants for a rapid and potentiated defence response, including the production of reactive oxygen species, callose deposition and defence gene expression. OsCPK4 overexpression leads also to constitutive increased content of the glycosylated salicylic acid hormone in leaves without compromising rice yield. Given that OsCPK4 overexpression was known to confer also salt and drought tolerance in rice, the results reported in this article demonstrate that OsCPK4 acts as a convergence component that positively modulates both biotic and abiotic signalling pathways. Altogether, our findings indicate that OsCPK4 is a potential molecular target to improve not only abiotic stress tolerance, but also blast disease resistance of rice crops.
Cellulitis‐Like Rash Associated with Kawasaki Disease
Authors: Itamura Shinji , Ishiguchi Yukiko , Kuwabara Kentaro , Yasui Kozo , Kamada Masahiro
Published: November 2015

We present the case of a 5‐year‐old‐boy who developed a fever and cellulitis‐like groin rash 5 days before developing conjunctivitis and 6 to 7 days before other typical signs of Kawasaki disease (KD) appeared. The cellulitis failed to respond to antibiotics and no pathogens were isolated. His fever and clinical signs resolved with intravenous immunoglobulin and high‐dose aspirin after discontinuation of antibiotics. Nonbacterial cellulitis is a rare presenting sign of KD, but in the appropriate clinical setting and population, a diagnosis of KD should be considered when cellulitis and fever fail to respond to an appropriate antibiotic regimen and no pathogen can be isolated.
Migration and Regional Trade Agreements: A (New) Gravity Estimation
Authors: Figueiredo Erik , Lima Luiz Renato , Orefice Gianluca
Published: November 2015

This paper investigates the role of regional trade agreements (RTAs) on bilateral international migration. Building on a gravity model for migration, our econometric strategy controls for the multilateral resistance to migration and solves the zero migration flows problem by using a censored quantile regression approach. Further, the endogeneity problem of RTAs in migration settlement is addressed by using instrumental variable censored quantile regression. Our results suggest that the presence of a RTA stimulates the migration stocks among member countries. The pro‐migration effect of RTAs is magnified if the agreement includes also provisions easing bureaucratic procedures for visa and asylum among member countries. Finally, we find an asymmetric effect of RTAs across the quantiles of the distribution of migration settlements.
Hydroxyproline O‐arabinosyltransferase mutants oppositely alter tip growth in Arabidopsis thaliana and Physcomitrella patens
Authors: MacAlister Cora A. , Ortiz‐Ramírez Carlos , Becker Jörg D. , Feijó José A. , Lippman Zachary B.
Published: November 2015

Hydroxyproline O‐arabinosyltransferases (HPATs) are members of a small, deeply conserved family of plant‐specific glycosyltransferases that add arabinose sugars to diverse proteins including cell wall‐associated extensins and small signaling peptides. Recent genetic studies in flowering plants suggest that different HPAT homologs have been co‐opted to function in diverse species‐specific developmental contexts. However, nothing is known about the roles of HPATs in basal plants. We show that complete loss of HPAT function in Arabidopsis thaliana and the moss Physcomitrella patens results in a shared defect in gametophytic tip cell growth. Arabidopsis hpat1/2/3 triple knockout mutants suffer from a strong male sterility defect as a consequence of pollen tubes that fail to fully elongate following pollination. Knocking out the two HPAT genes of Physcomitrella results in larger multicellular filamentous networks due to increased elongation of protonemal tip cells. Physcomitrella hpat mutants lack cell‐wall associated hydroxyproline arabinosides and can be rescued with exogenous cellulose, while global expression profiling shows that cell wall‐associated genes are severely misexpressed, implicating a defect in cell wall formation during tip growth. Our findings point to a major role for HPATs in influencing cell elongation during tip growth in plants.
Quantification of Vibration Localization in Periodic Structures
Authors: Chandrashaker A. , Adhikari S. , Friswell M. I.
Published: November 2015

The phenomenon of vibration mode localization in periodic and near periodic structures has been well documented over the past four decades. In spite of its long history, and presence in a wide range of engineering structures, the approach to detect mode localization remains rather rudimentary in nature. The primary way is via a visual inspection of the mode shapes. For systems with complex geometry, the judgment of mode localization can become subjective as it would depend on visual ability and interpretation of the analyst. This paper suggests a numerical approach using the modal data to quantify mode localization by utilizing the modal assurance criterion (MAC) across all the modes due to changes in some system parameters. The proposed MAC localization factor (MACLF) gives a value between 0 and 1 and therefore gives an explicit value for the degree of mode localization. First-order sensitivity based approaches are proposed to reduce the computational effort. A two-degree-of-freedom system is first used to demonstrate the applicability of the proposed approach. The finite element method (FEM) was used to study two progressively complex systems, namely, a coupled two-cantilever beam system and an idealized turbine blade. Modal data is corrupted by random noise to simulate robustness when applying the MACLF to experimental data to quantify the degree of localization. Extensive numerical results have been given to illustrate the applicability of the proposed approach.
Experimental Investigation of Enhanced Two-Phase Evaporator Using Aluminum Foams
Authors: Agostini Francesco , Puckett Waylon , Nelson Ryan , Torresin Daniele , Agostini Bruno , Habert Mathieu
Published: November 2015

A novel two-phase thermosyphon with a metal foam based evaporator is presented as a solution for the cooling of power-electronic semiconductor modules. A horizontal evaporator configuration is investigated: the evaporator consists of an aluminum chamber, with aluminum foam brazed to the base plate in three different configurations. One of the configurations has an open vapor chamber above the foam, another has foam filling the entire evaporator chamber, and the third has bores drilled in the foam parallel to the base plate from inlet to outlet along the direction of the vapor flow. The aluminum foam has a porosity of 95%, and a pore density of 20 PPI (pores per inch). A liquid distribution and a vapor collector chamber are respectively present at the entrance and at the exit of the evaporator. The power modules are attached on the evaporator body that collects the heat generated during the operation of the semiconductor devices. A vapor riser guides the vapor to a finned-tube air-cooled heat exchanger. A liquid downcomer from the condenser constantly feeds the evaporator channels. The system works with gravity-driven circulation only. The described system was designed and tested with an extensive experimental campaign. The evaporators were tested for power losses ranging between 500 and 3000 W, corresponding to applied heat fluxes between 3 and 20 W/cm2. The experimental results will be presented for inlet air at ambient temperature of 20°C with volumetric flow rates between 100 and 680 m3/h. The working fluid was refrigerant R245fa. The fluid filling effect was investigated. For each evaporator the results will be presented in terms of maximum thermal resistance and cooler base temperature. The base temperature distribution between different evaporators will also be presented and discussed being an important design parameter in power electronics cooling. Thermal resistances were measured between 15 and 30 K/kW. The experimental results indicated a promising conclusion favoring the implementation of aluminum foam evaporators for enhancement of heat transfer during pool boiling.
Turbulent Flow in the Micro Structures of Porous Media
Authors: Herwig Heinz , Jin Yan , Uth Marc-Florian , Kuznetsov Andrey V.
Published: November 2015

Some fundamental issues with respect to turbulent flows through a porous matrix are addressed by analyzing DNS results (DNS: direct numerical simulation, i.e. no turbulence modeling). In a porous matrix with pore sizes of micro or even nano dimensions turbulent flow may occur when the (local) Reynolds number is sufficiently large. An open question, however, is whether turbulence structures are restricted in size by the pore size dimensions or not. This is an important aspect that immediately affects the way turbulence has to be modelled. In order to find out which influence the solid matrix has on the turbulence a generic matrix built from a large number of bars with square cross sections is investigated. Two different DNS approaches are used, a finite volume one and a Lattice-Boltzmann approach. From both DNS calculations detailed flow field information about the influence of the solid matrix on the turbulence structure are obtained. Finally the extension of Darcy’s friction law by the Forchheimer term is investigated with respect to the question whether this extended law may be used in the fully turbulent flow regime.
Stability Analysis of Oscillating Electrolytes
Authors: Gupta Prateek , Bahga Supreet Singh
Published: November 2015

We present an investigation of instabilities that occur in a class of electrolytes, called oscillating-electrolytes, which become unstable under the effect of electric field. We analyze the onset of instability by modeling growth of small perturbations in concentration field of a binary electrolyte. Our analysis is based on linearizing the nonlinear species transport equations, which include the effects of electromigration, diffusion, and acid - base equilibria on electrophoretic transport of ions. Our linear stability analysis shows that, the growth rate of low wavenumber concentration disturbances increases with increase in wavenumber. Whereas, the growth rate of high wavenumber disturbances decreases with increasing wavenumber due to stabilizing effect of molecular diffusion. Our analysis also yields scaling for growth rates and the wavenumber of most unstable mode with electric field. The growth rates and scaling predicted by our linearized model compare well with those predicted by fully nonlinear simulations. In addition, we show that the oscillatory behavior is exhibited only over a range of species concentrations. We also discuss the physical mechanism that causes concentration disturbances to grow in oscillating electrolytes. We show that oscillations result when the binary electrolyte consists of a multivalent species with unusually high electrophoretic mobility in higher ionization states. Presence of such species causes abnormal variations in electrical conductivity due to concentration disturbances, which in turn alter the electric field in a way that destabilizes the electrophoretic system.
Effect of Surface Conduction on Propagation of Ion-Concentration Shock Waves in Isotachophoresis
Authors: Khichar Mayank , Moza Romir , Bahga Supreet Singh
Published: November 2015

Isotachophoresis (ITP) is a widely used nonlinear electrophoretic technique for preconcentration and separation of ionic species. Typically, ITP is performed in microchannels where the effect of surface conduction due to electric double layer (EDL) at channel walls is negligible compared to bulk conduction. However, when electrophoretic techniques such as ITP are integrated in nanochannels or shallow microchannels, surface conduction can alter bulk electrophoretic transport. The existing mathematical models for multispecies electrophoretic transport do not account for the competing effects of surface and bulk conduction. We present a mathematical model for multispecies electrophoretic transport incorporating the effects of surface conduction on bulk ion-transport. Our one-dimensional model is capable of describing electrophoretic systems consisting of arbitrarily large number of co-ions, having same charge polarity as the wall charge, and a single counter-ion. Based on numerical solutions of the governing equations, we show that unlike in conventional ITP where surface conduction is negligible, the zone concentrations do not obey the Kohlrausch regulating function when surface conduction is prominent. Moreover, our simulations show that surface conduction alters the propagation speeds of ion-concentration shock waves in ITP. In addition, surface conduction results in additional shock and expansion waves in ITP which are otherwise not present in conventional ITP.
CFD Analysis of Flow Boiling in a Silicon Microchannel With Non-Uniform Heat Flux
Authors: Lorenzini Daniel , Joshi Yogendra K.
Published: November 2015

Boiling systems are capable of dissipating high heat fluxes, and as such have potential applications in thermal management of high power microelectronics. Although there are a number of experimental investigations of flow boiling in small flow passages and several empirical correlations have been proposed, the computational fluid dynamics (CFD) modeling of such systems is much less explored. In the present investigation, a phase-change model representing the heat and mass transfer is coupled with the volume of fluid (VOF) model for the transient analysis of flow boiling. The analyzed domain consists of a silicon microchannel with a finite substrate thickness, subjected to non-uniform heat fluxes at localized regions, providing with a more realistic scenario for the case of microelectronics power maps. The results show the strong effect on the two-phase flow characteristics for these configurations and visualization of the induced flow regimes is presented. Furthermore, discussion about the heat transfer mechanisms, challenges and possible solutions are given in order to provide guidelines for effective cooling of these devices.
2D Lattice Boltzmann Simulation of Droplet Jumping in a Viscous Fluid
Authors: Lei Shenghui , Wang Ningning , Liu Haihu , Nolan Kevin , Enright Ryan
Published: November 2015

In order to investigate the coalescence and out-of-plane jumping of two incompressible droplets on a non-wetting surface surrounded by an incompressible fluid with matched viscosity in the low Ohnesorge number regime, a two-dimensional lattice Boltzmann phase-field model is implemented. An interfacial force of potential form is used to model the internal surface tension force and capture the fluid-surface interaction, viz. the contact-line dynamics. We evaluate the simulated velocity fields and interface shape evolution during coalescence and the subsequent jumping event. We confirm that the coalescence dynamics of the binary droplet system is similar to the case where the outer fluid viscosity is small compared to that of the droplet fluid, as is the case of condensed water droplet jumping on superhydrophobic surfaces in a gaseous ambient. An argument is also developed to demonstrate that the dynamics in 2D, when appropriately scaled, should be approximately equivalent to the corresponding 3D case. A simple drag model is used to capture the rapid velocity decay of the jumping droplet as it moves away from the surface into the viscous fluid. The results suggest the possibility of experimentally observing coalescence-induced droplet jumping in liquid-liquid systems that may be potentially exploited for microfluidic applications.
Numerical Investigation of Heat Transfer in Rough Microchannels Using a Kinetic Continuum Solver
Authors: Rovenskaya Olga , Croce Giulio
Published: November 2015

A numerical analysis of flow and heat transfer fields in a rough microchannel is carried out using a hybrid solver dynamically coupling kinetic and Navier–Stokes solutions computed in local rarefied and continuum areas of the flow, respectively. The roughness geometry is modeled as a series of triangular obstructions and a relative roughness up to 5% of the channel height is considered. Keeping Mach number low (incompressible flow) while varying Knudsen number allow us to investigate different rarefaction levels of the flow.

The competition between roughness, rarefaction and heat transfer effects is discussed in terms of averaged Nusselt and Poiseuille numbers and mass flow rate. Discrepancy between the full Navier–Stokes and hybrid solutions is investigated, assessing the range of applicability of the first order slip boundary condition for rough geometries with and without heat transfer presence.
An Improved Correlation for Void Fraction During In-Tube Condensation
Authors: Guo Cong , Wang Tao , Jiang Yuyan , Guo Chaohong , Zeng Miao , Yu Dong , Tang Dawei
Published: November 2015

A comprehensive literature research was undertaken for the available void fraction correlations and experimental void fraction data during condensation inside tubes. Comparisons between the correlations showed that slip ratio models were probably more suitable for the determination of void fraction at low mass velocity when the slip ratio was chosen appropriately. For high mass velocity, there was no apparent difference for the predictions of various models. In addition, the Froude rate parameter (dimensionless number) can be used for representing the flow characteristics during condensation inside tube and was defined in terms of mass flux and quality. Based on the observations made, a new correlation was developed through the weighted average method without resorting back to very complex expressions. This correlation was a simple model and obtained involving with the Froude rate parameter and slip ratio models. The improved correlation has been shown to be in good agreement with data ranging from low mass velocity up to very high mass velocity.
Flow Boiling Heat Transfer Coefficient of DI-Water/SiO2 Nanofluid Inside a 1.1 mm Round Microchannel
Authors: Moreira Tiago A. , do Nascimento Francisco J. , Ribatski Gherhardt
Published: November 2015

The scope of the present paper is the evaluation of the heat transfer coefficient during flow boiling of DI-water/silica nanofluid inside a 1.1 mm ID tube. The experiments were performed for nanoparticles and DI-water with both having thermal conductivities of the same order of magnitude (kDI-water = 0.6 W/mK, ksilica = 1.4 W/mK). So, it was possible investigating the effect of the nanoparticles on the heat transfer coefficient under condition of negligible thermal conductivity enhancement. Experiments were carried out for mass velocities of 200, 400 and 600 kg/m2s, heat fluxes from 60 kW/m2 to 350 kW/m2 and nanoparticles volumetric concentration of 0.001%, 0.01% and 0.1%. Moreover, flow boiling heat transfer data under similar experimental conditions were obtained for DI-water without nanoparticles before and after performing each nanofluid test. The experiments were performed at the same test section according to the following sequence: i) DI-water, ii) 0.001% vol. nanofluid, iii) DI-water, iv) 0.01% vol. nanofluid, v) DI-water, vi) 0.1% vol. nanofluid, and vii) DI-water. Such procedure was adopted in order to evaluate the influence of the deposition of nanoparticles at each concentration on the heat transfer coefficient. For single-phase flow the HTC decreases as the experiments were performed. The thermal resistance due to deposition of nanoparticles is relevant to the heat transfer coefficient for single-phase flow of nanofluids inside microchannels. The flow boiling HTC decreases with increasing the nanoparticle volumetric concentration from a concentration of 0.001%. Based on the flow boiling HTC behaviors for tests with pure DI-water before and after the nanofluid tests, the fact that the HTC decreases with increasing the nanoparticle volumetric concentration is not explained only by the deposition on the surface of a nanoparticle layer. Tests for pure DI-water before the tests of nanofluids (BBN condition) and after all the nanofluids tests (ABN 0.1% condition) presents similar heat transfer coefficients, despite the deposition of a nanoparticle layer on the surface.
Modeling Low Reynolds Number Flows Driven by Forward-Propagating and Reflected Boundary Waves in Concentric Micro-Cylinders
Authors: Coloma Mikhail , Buehler William M. , Schaffer J. David , Chiarot Paul R. , Huang Peter
Published: November 2015

We report on a computational model used to study the reversal of flow direction inside the annular region between concentric micro-cylinders filled with an incompressible Newtonian fluid. The flow is induced by boundary deformations on the inner and outer cylinder surfaces due to forward-propagating transverse waves and their reflections. This microfluidic transport mechanism is postulated as a vital pathway for removal of beta-amyloid from the brain along sub-millimeter cerebral arteries, and failure of this clearance is associated with Alzheimer’s disease. We show that the direction of this annular flow depends on superposition of the peristaltic waves and their reflection waves. A control volume analysis is developed to predict the transport characteristics and compared with numerical solutions of the Navier-Stokes equations. The identified set of microfluidic parameters that leads to a net reverse flow will aid biologists in understanding why an aging brain becomes prone to beta-amyloid accumulation.
Effect of Channel Width on Pool Boiling Enhancement of Open Microchannels With Selective Sintered Porous Coatings
Authors: Jaikumar Arvind , Kandlikar Satish G.
Published: November 2015

Thermal management in microelectronic devices involves development of high heat flux removal systems to meet the cooling requirements. Pool boiling addresses these demands by using latent heat transfer. In this study, heat transfer surfaces are fabricated by depositing porous coatings on an open microchannel surface. Screen printing and sintering are identified as techniques to deposit porous coatings and ensure substrate bonding respectively. Firstly, the effect of selective enhancement was studied by depositing porous coatings on (i) fin tops only (sintered-fin-tops), (ii) channels only (sintered-channels), and (iii) completely covering the boiling surface (sintered-throughout). The pool boiling performance with saturated distilled water at atmospheric pressure was obtained and a maximum critical heat flux (CHF) of 313 W/cm2 at a wall superheat of 7.5 °C was reported here for a sintered-throughout surface. Furthermore, the effect of channel width on sintered-throughout surfaces was studied. The results indicated that channel width plays an important in improving the performance. High speed videos are taken to understand the underlying mechanism. Additional nucleation sites and separate liquid-vapor pathways are identified as contributing mechanisms for the enhancement in CHF and heat transfer coefficient (HTC).
Critical Heat Flux of Graphene Coated Copper Surface at High Pressures
Authors: Li Nanxi , Betz Amy Rachel
Published: November 2015

Boiling is an efficient way to transfer heat due to the latent heat of vaporization. Many variables, such as surface properties, fluid properties, and system pressure, will affect the performance of pool boiling. Enhanced pool boiling has extensive applications in chemical, microelectronics, and power industries. Previous research has shown that micro- or nanostructured surfaces and coated surfaces will increase heat transfer coefficients up to one order of magnitude at atmospheric pressure. Graphene as a very good material with superb mechanical and electrical properties also has potential to enhance pool boiling performance. The purpose of this research is to investigate heat transfer enhancement on a graphene coated surface compared to a plane copper surface at atmospheric pressure and increased pressures with deionized water. The effect of the graphene coating on the critical heat flux is also investigated. To carry out the experiments, we designed and fabricated a special experimental facility that will withstand the high pressures (up to 20 bar) and high temperatures. Graphene is coated on a 1 cm2 copper surface using spray coating. The boiling vessel is pressurized with nitrogen and the system pressure is controlled by a back pressure regulator. The test fluid is preheated to saturation temperature by two 500 W cartridge heaters. Multiple 150 W cartridge heaters are inserted in a copper cylinder to provide wall superheat for bubbles to nucleate on the studied surface. When the system reaches steady state, a process controller controls these cartridge heaters to increase the heat flux gradually from 0 kW/m2 to the critical heat flux. The copper cylinder is insulated with PTFE to minimize heat loss from the side. The gap between the copper cylinder and the insulation surface is carefully sealed with high temperature epoxy to reduce undesired nucleation sites. The wall superheat corresponding to each heat flux is extrapolated using Fourier’s law from three thermocouple readings. The heat transfer coefficient can thus be calculated at each heat flux for the every test fluid at its corresponding pressure. A camera with 3.2 cm field of view at a working distance of 12 cm to 15 cm is used to visualize the bubble formation on the heated surface.
A New Algorithm for Contact Angle Estimation in Molecular Dynamics Simulations
Authors: Yd Sumith , Maroo Shalabh C.
Published: November 2015

It is important to study contact angle of a liquid on a solid surface to understand its wetting properties, capillarity and surface interaction energy. While performing transient molecular dynamics (MD) simulations it requires calculating the time evolution of contact angle. This is a tedious effort to do manually or with image processing algorithms. In this work we propose a new algorithm to estimate contact angle from MD simulations directly and in a computationally efficient way. This algorithm segregates the droplet molecules from the vapor molecules using Mahalanobis distance (MND) technique. Then the density is smeared onto a 2D grid using 4th order B-spline interpolation function. The vapor liquid interface data is estimated from the grid using density filtering. With the interface data a circle is fitted using Landau method. The equation of this circle is solved for obtaining the contact angle. This procedure is repeated by rotating the droplet about the vertical axis. We have applied this algorithm to a number of studies (different potentials and thermostat methods) which involves the MD simulation of water.
Experimental Verification of Analytical Prediction of Pool Boiling CHF Incorporating the Effects of EHD and Contact Angle
Authors: Kano Ichiro , Sato Takahiro , Okamoto Naoki
Published: November 2015

Boiling heat transfer enhancement via compound effect of Electro-Hydro-Dynamic (EHD) and contact angle has been experimentally and analytically investigated. A fluorinated dielectric liquid (Asahi Glass Co. Ltd, AE-3000) was selected as the working fluid. Pool boiling heat transfer in the saturated liquid was measured at atmospheric pressure. In order to change the contact angle between the boiling surface and the dielectric liquid, the different materials Cu, Cr, NiB, Sn, and mixture of 5 and 1.5 micro meter diamond particles were electrically deposited on a boiling surface. The critical heat flux (CHF) for different contact angles showed 20.5 ∼ 26.9 W/cm2 which was −7 ∼ 25 % of that for a non-coated Cu surface (21.5 W/cm2). Upon application of a −5 kV/mm electric field to the micro structured surface (the mixture of 5 and 1.5 micro meter particles), a CHF of 99 W/cm2 at a superheat of 33.5 K was obtained. The previous theoretical equation of pool boiling predicted the CHF with the electric field and without the electrode.
A Critical Review of Drag Reduction in Channel Flows and Numerical Study of Forced Convective Transport in a Channel With Conducting-Lubricating (CO-LUB) Surfaces
Authors: Reyes Jessica , Kota Krishna
Published: November 2015

Addressing the traditionally contradictory problem of obtaining considerable drag reduction without negatively impacting heat transfer as much is an arduous scientific challenge. In this paper, prior efforts on frictional drag reduction and the associated issues are discussed in relevant detail, and the effectiveness of Conducting-Lubricating (CO-LUB) surfaces as one of the potential options to address this challenge for single phase forced convection of liquids is numerically pursued. CO-LUB surfaces have exceptionally high wetting characteristics, and when saturated with a liquid microlayer, provide remarkable lubrication to bulk liquid flow and simultaneously facilitate heat transfer by conduction through the microlayer. In the simulations, the side walls of a high aspect ratio rectangular channel were assumed as CO-LUB surfaces and flow and heat transfer of bulk liquid flow were modeled using ANSYS FLUENT 14.5. Volume-of-Fluid (VOF) method was used to model the two phases with a free surface interface, with water as the microlayer liquid and oil as the bulk liquid, in a narrow channel of 5 mm width and 50 mm length under laminar flow, constant wall heat flux conditions. The results were compared with a regular channel of the same dimensions (without CO-LUB surfaces) and it was found that pressure drop decreased remarkably by ∼23 times for some cases but without any heat transfer attenuation (actually, improved heat transfer performance was observed) leading to highly energy-efficient convective transport.
Approaches Towards the Ultimate Luminous Output Power of Light-Emitting Diodes: Bottlenecks and Remedies
Authors: Zhang Xiaokun , Xiang Xiao-Dong , Xiang Yong
Published: November 2015

Although light-emitting diodes (LEDs) hold great promises for high-efficiency lighting applications, the cost per lumen still poses a challenge for LEDs to fast penetrate into the markets. Increasing the output power per LED chip reduces the number of chips required for a specific luminous flux, thus reducing the cost of LED luminaires. However, it is well known that the luminous output power of LEDs (Pout) cannot be enhanced simply by increasing the injection current density (Jinj) due to efficiency droop. Extensive efforts have been made towards avoiding efficiency droop at high injection current densities (e.g., Jinj > 50 A/cm2). Gardner et al. reported a double-heterostructure LED with an external quantum efficiency (EQE) of 40% at 200 A/cm2. Xie et al. introduced an electron-blocking layer into the LED devices and the EQE peak occurred at 900 A/cm2 approximately. Nevertheless, the EQE is always lower than 100%, excessive heat will accumulate in LEDs at high current densities and increase the junction temperatures, which will damage the device and limit its luminous output power and lifetime.

In this paper, the recombination mechanism in the LED active area is analyzed and an analytic relationship between Pout and Jinj is proposed. The calculated results show that the best Pout currently achieved is far lower than its potential value. The temperature dependence of the Pout-Jinj relationship is also calculated and the thermal state of LEDs at high injection current densities predicted. The results demonstrate that LED luminaires with thermal management based on conventional fin-shaped heat sinks suffer from thermal runaway due to excessive heat accumulation before reaching their ultimate output power. The gap between the existing and predicted Pout is mainly due to thermal runaway of LED devices at high injection current densities, instead of efficiency droop. Therefore, the short-term solution of LED luminous output power enhancement should be better cooling of LED modules, such as jet/spray cooling, heat pipe cooling, or 3D embedded two-phase cooling. Long-term solutions continue to focus on reducing the efficiency droop with improved LED device structures and advanced materials.