Branching Configurations Research Articles

3D transient numerical analysis of PCM dendritic cylindrical heat sinks designed by constructal theory

The phase change material (PCM) heat sink represents an important cooling tool for many applications. The presence of a heat sink in devices requires additional space to occupy it. This led to modeling this space to obtain the highest thermal performance with the smallest size. Among the modern modeling methods is constructal theory. This work presents a numerical modeling of the performance of cylindrical phase change material heat sinks with branched heat transfer fluid tubes in the manner of arterial and venous according to constructal theory. The aim of numerical simulations is to demonstrate the effect of growth in design by increasing the number of branches on thermal performance and melting time and the extent to which this is reflected in pressure drops. Several branching configurations are studied for comparison purpose. The governing continuity, momentum and energy equations were solved using the computational fluid dynamics method. Three-dimensional transient simulations of the melting process of phase change materials were performed using an enthalpy and porosity model. Four combinations of constructal dendritic tubes were considered. The results show that the proposed dendritic PCM heat sink significantly reduces the melting time of PCM compared to the traditional heat sink consisting of a shell and single tube up to 69.1 %. The drop in heat transfer fluid temperature at the outlet decreased by up to 51.7 %. The results proved also the heat transfer enhancement is governed with pressure drop increase because of changing branches configuration. Finally, this paper demonstrated the ability of constructal theory to provide promising solutions for cylindrical heat sinks of phase change materials in various applications.

Metal sequestration by Microcystis extracellular polymers: a promising path to greener water treatment.

The problem of heavy metal pollution in water bodies poses a significant threat to both the environment and human health, as these toxic substances can persist in aquatic ecosystems and accumulate in the food chain. This study investigates the promising potential of using Microcystis aeruginosa extracellular polymeric substances (EPS) as an environmentally friendly, highly efficient solution for capturing copper (Cu2+) and nickel (Ni2+) ions in water treatment, emphasizing their exceptional ability to promote green technology in heavy metal sequestration. We quantified saccharides, proteins, and amino acids in M. aeruginosa biomass and isolated EPS, highlighting their metal-chelating capabilities. Saccharide content was 36.5mgg-1 in biomass and 21.4mgg-1 in EPS, emphasizing their metal-binding ability. Proteins and amino acids were also prevalent, particularly in EPS. Scanning electron microscopy (SEM) revealed intricate 3D EPS structures, with pronounced porosity and branching configurations enhancing metal sorption. Elemental composition via energy dispersive X-ray analysis (EDAX) identified essential elements in both biomass and EPS. Fourier transform infrared (FTIR) spectroscopy unveiled molecular changes after metal treatment, indicating various binding mechanisms, including oxygen atom coordination, π-electron interactions, and electrostatic forces. Kinetic studies showed EPS expedited and enhanced Cu2+ and Ni2+ sorption compared to biomass. Thermodynamic analysis confirmed exothermic, spontaneous sorption. Equilibrium biosorption studies displayed strong binding and competitive interactions in binary metal systems. Importantly, EPS exhibited impressive maximum sorption capacities of 44.81mgg-1 for Ni2+ and 37.06mgg-1 for Cu2+. These findings underscore the potential of Microcystis EPS as a highly efficient sorbent for heavy metal removal in water treatment, with significant implications for environmental remediation and sustainable water purification.

On a barrier height problem for RNA branching

The branching of an RNA molecule is an important structural characteristic yet difficult to predict correctly, especially for longer sequences. Using plane trees as a combinatorial model for RNA folding, we consider the thermodynamic cost, known as the barrier height, of transitioning between branching configurations. Using branching skew as a coarse energy approximation, we characterize various types of paths in the discrete configuration landscape. In particular, we give sufficient conditions for a path to have both minimal length and minimal branching skew. The proofs offer some biological insights, notably the potential importance of both hairpin stability and domain architecture to higher resolution RNA barrier height analyses.

Topological quantification of the “anemone” (branching) solar flares

The so-called “anemone” solar flares are an interesting type of the space plasma phenomena, where multiple null points of the magnetic field are connected with each other and with the magnetic sources by the separators, thereby producing the complex branching configurations. Here, using the methods of dynamical systems and Morse–Smale theory, we derive a few universal topological relations between the numbers of the null points and sources of various kinds with arbitrary arrangement in the above-mentioned structures. Such relations can be a valuable tool both for a quantification of the already-observed anemone flares and for a prediction of the new ones in complex magnetic configurations.

Geometric and hydrodynamic influences on the droplet breakup dynamics in a branched microdevice

Droplet breakup phenomenon in a microchannel is a well-known potential approach for process intensification. Here we investigate a branched microdevice to explore the influence of Capillary number (Ca) and the ratio of branching arm width to the main channel (β) on droplet breakup dynamics by developing a 3-D computational model, which was firstly validated with the in-house as well as independent experimental results. A homogeneous pressure field inside a droplet is found to be the principal reason in droplet non-breakup for widely asymmetric configuration (i.e., β = 0.4 and 1.2). For other branching configurations (β = 0.6, 0.8 and 1.0), droplet breakup in three different regimes is identified, and a regime map is formulated as a function of Ca vs. β. It is observed that apart from Ca, a critical β also exists for the transition between breakup and non-breakup regimes, and the configuration with β = 0.8 is more susceptible for droplet breakup owing to the force balance in both arms with respect to confinement and flow direction. Additionally, the smaller critical Ca for β = 1.0 than for β = 0.6 indicates the significance of upstream flow distribution.

Topographic Evaluation of Superior Thyroid Artery-A Terrain to be Well Versed for Surgeon's Knife.

Observing the origin, varied branching configurations of superior thyroid artery (STA) and evaluating morphometric details with its surrounding relations was aimed at in this cadaveric neck dissection study to avoid surgical mishaps and its repercussions. This observational study was conducted on 40 fresh frozen embalmed and colored latex infused cadavers in the Department of Otorhinolaryngology and Head and Neck Surgery in collaboration with Department of Anatomy of our institute, which involved systematic evaluative dissection of both sides of neck especially focusing on superior thyroid artery, its branching variations and morphometric details with its surrounding relations. Details were measured using digital caliper. The collected data was statistically analyzed by applying chi-square test and significance was set at 5% level (p < 0.05). The analysis revealed the location of the origin of the superior thyroid artery of cadavers from carotid bifurcation and above it in 40% and from above the level of superior border of thyroid cartilage in 40% of cases. The distribution patterns of the superior thyroid artery were classified into three types depending on the branching pattern typical and variant glandular branching patterns were observed in 85% and 15% of the specimens respectively. A sound knowledge of the regional anatomy and its possible variations helps the surgeon in isolating and preserving the vital structures and avoid iatrogenic complications.

Selective Brain Hypothermia for Ischemic MCA-M1 Stroke: Influence of Cerebral Arterial Circulation in a 3D Brain Temperature Model.

Acute ischemic stroke is a major health problem with a high mortality rate and a high risk for permanent disabilities. Selective brain hypothermia has the neuroprotective potential to possibly lower cerebral harm. A recently developed catheter system enables to combine endovascular blood cooling and thrombectomy using the same endovascular access. By using the penumbral perfusion via leptomeningeal collaterals, the catheter aims at enabling a cold reperfusion, which mitigates the risk of a reperfusion injury. However, cerebral circulation is highly patient-specific and can vary greatly. Since direct measurement of remaining perfusion and temperature decrease induced by the catheter is not possible without additional harm to the patient, computational modeling provides an alternative to gain knowledge about resulting cerebral temperature decrease. In this work, we present a brain temperature model with a realistic division into gray and white matter and consideration of spatially resolved perfusion. Furthermore, it includes detailed anatomy of cerebral circulation with possibility of personalizing on base of real patient anatomy. For evaluation of catheter performance in terms of cold reperfusion and to analyze its general performance, we calculated the decrease in brain temperature in case of a large vessel occlusion in the middle cerebral artery (MCA) for different scenarios of cerebral arterial anatomy. Congenital arterial variations in the circle of Willis had a distinct influence on the cooling effect and the resulting spatial temperature distribution before vessel recanalization. Independent of the branching configurations, the model predicted a cold reperfusion due to a strong temperature decrease after recanalization (1.4-2.2 °C after 25min of cooling, recanalization after 20min of cooling). Our model illustrates the effectiveness of endovascular cooling in combination with mechanical thrombectomy and its results serve as an adequate substitute for temperature measurement in a clinical setting in the absence of direct intraparenchymal temperature probes.

A systematic study of blockage in three-dimensional branching networks with an application to model human bronchial tree

A major aim of the present study is to understand and thoroughly document the fluid dynamics in three-dimensional branching networks when an intermediate branch is partially or completely obstructed. Altogether, 26 different three-dimensional networks each comprising six generations of branches (involving 63 straight portions and 31 bifurcation modules) are constructed and appropriately meshed to conduct a systematic study of the effects of varying the locations of a blockage of a given relative extent and varying the extent of a blockage at a fixed location. The side-by-side consideration of two branching configurations (in-plane and $$90^{\circ }$$ out-of-plane) gives a quantitative assessment of the dependence of flow alteration due to blockage on the three-dimensional arrangement of the same individual branches. A blockage in any branch affects the flow in both downstream and upstream branches. The presence of a blockage can make three-dimensional asymmetric alteration to the flow field, even when the blockage itself is geometrically symmetric. The overall mass flow rate entering the network is found to remain nearly unaltered if a blockage is shifted within the same generation but is progressively reduced if the blockage is shifted to upstream generations. A blockage anywhere in the network increases the degree of mass flow asymmetry $$\delta _{\mathrm{G}n} $$ in any generation. The order of magnitude disparity in $$\delta _{\mathrm{G}n} $$ between the in-plane and out-of-plane configurations, characteristic of unobstructed networks, can be significantly reduced in the presence of a single blockage. The present three-dimensional computations show that the effects of blockage on the mass flow distribution in a large network are complex, often non-intuitive and sometimes dramatic, and cannot be captured by any simple one-dimensional model.

Experimental and Numerical Investigation of Mixing Phenomena in Double-Tee Junctions

This work investigates mixing phenomena in a pressurized pipe system with two sequential Tee junctions and experiments are conducted for a range of different inlet flow ratios, varying distances between Tee junctions and two pipe branching configurations. Additionally, obtained experimental results are compared with results from previous studies by different authors and are used to validate the numerical model using the open source computational fluid dynamics toolbox OpenFOAM. Two different numerical approaches are used—Passive scalar model and Multiphase model. It is found that both numerical models produce similar results and that they are both greatly dependent on the turbulent Schmidt number. After the calibration procedure, both models provided good results for all investigated flow ratios, double-Tee junction distances, and pipe branching configurations, therefore both numerical models can be applied for a wide range of pipe networks configurations, but passive scalar model is the viable choice due to its much higher computational efficiency. Obtained results also describe the relationship between the double-Tee distances and complete mixing occurrence.

Active Release of an Antimicrobial and Antiplatelet Agent from a Nonfouling Surface Modification

Two major challenges faced by medical devices are thrombus formation and infection. In this work, surface-tethered nitric oxide (NO)-releasing molecules are presented as a solution to combat infection and thrombosis. These materials possess a robust NO release capacity lasting ca. 1 month while simultaneously improving the nonfouling nature of the material by preventing platelet, protein, and bacteria adhesion. NO's potent bactericidal function has been implemented by a facile surface covalent attachment method to fabricate a triple-action coating-surface-immobilized S-nitroso- N-acetylpenicillamine (SIM-S). Comparison of NO loading amongst the various branching configurations is shown through the NO release kinetics over time and the cumulative NO release. Biological characterization is performed using in vitro fibrinogen and Staphylococcus aureus assays. The material with the highest NO release, SIM-S2, is also able to reduce protein adhesion by 65.8 ± 8.9% when compared to unmodified silicone. SIM-S2 demonstrates a 99.99% (i.e., ∼4 log) reduction for S. aureus over 24 h. The various functionalized surfaces significantly reduce platelet adhesion in vitro, for both NO-releasing and non-NO-releasing surfaces (up to 89.1 ± 0.9%), demonstrating the nonfouling nature of the surface-immobilized functionalities. The ability of the SIM-S surfaces to retain antifouling properties despite gradual depletion of the bactericidal source, NO, demonstrates its potential use in long-term medical implants.

First-Principles Study of Alkoxides Adsorbed on Au(111) and Au(110) Surfaces: Assessing the Roles of Noncovalent Interactions and Molecular Structures in Catalysis

Microscopic understanding of molecular adsorption on catalytic surfaces is crucial for controlling the activity and selectivity of chemical reactions. However, for complex molecules, the adsorption process is very system-specific and there is a clear need to elaborate systematic understanding of important factors that determine catalytic functionality. Here, we investigate the binding of eight molecules, including seven alkoxides and one carboxylate, on the Au(111) and Au(110) surfaces. Our density-functional theory calculations including long-range van der Waals interactions demonstrate the significant role of these “weak” noncovalent forces on the adsorption structures, energetics, and relative adsorbate stabilities. Interestingly, the binding energy trends are insensitive to the surface structure. Instead, the adsorption stability depends strongly on the structural and chemical characteristics of the molecules: linear vs branching configurations, number of unsaturated C–C bonds, bidentate adsorption, a...

Finding order in complexity: A study of the fluid dynamics in a three-dimensional branching network

The complex fluid dynamics associated with the flow in three-dimensional dichotomously branching networks is investigated. The flow physics described here is generic, though the particular flow geometry employed represents a model human bronchial tree. Up to six generations of branches (involving 63 straight portions and 31 bifurcation modules) are computed in one go; such computational challenges are rarely taken in the literature. In the present study, two branching configurations are considered side by side: the most widely studied in-plane configuration in which the centrelines of all generations lie on the same plane, and the 90∘ out-of-plane configuration in which the centreline of each generation is rotated with respect to its grandmother generation following a systematic methodology to form a space-filling three-dimensional structure. The paper develops a physical understanding of the fluid dynamics of branching networks and its dependence on the configuration (in-plane versus out-of-plane) and the extent (four, five, or six generations) of the network under consideration. The study of co-planar vis-à-vis non-planar configurations establishes a quantitative evaluation of the dependence of the fluid dynamics on the three-dimensional arrangement of the same individual branches. It is shown that apparent symmetry in the geometry of any two branches does not automatically imply symmetry in the flow field in those two branches. With the help of velocity contours, pressure contours, and distribution of mass flow in each branch, a qualitative and quantitative study is performed on the nature and evolution of flow asymmetry. The computations show that the degree of mass-flow asymmetry is smaller for the out-of-plane configuration (which is a more realistic model of a human bronchial tree) as compared to that for the in-plane configuration. The mass-flow asymmetry grows in each successive generation (starting from generation G2 for in-plane and G3 for out-of-plane configurations). In addition to mass-flow distribution, other types of asymmetries in the flow field are also analysed. It is established that, in spite of the complexity of the flow solutions, there also exists a systematic order such that it is possible to ascertain the flow field in all branches of a particular generation by determining the flow field in some systematically selected branches of that generation, indicating a possible route to the saving of computational resource and time.

Solitary waves in forked channel regions

Solitary water waves travelling through a forked channel region are studied via a new nonlinear wave model. This novel (reduced) one-dimensional (1D) model captures the effective features of the reflection and transmission of solitary waves passing through a two-dimensional (2D) branching channel region. Using an appropriate change of coordinates, the 2D wave system is defined in a simpler geometric configuration that allows a straightforward reduction to a 1D graph-like configuration. The Jacobian of the change of coordinates leads to a variable coefficient in the 1D model, which contains information about the angles of the diverting reaches, a feature that is not present in any previous water wave model on networks. Furthermore, this new formulation is more general, in allowing both symmetric and asymmetric branching configurations to be considered. A new compatibility condition is deduced, which is used at the corresponding branching node. The 2D and 1D dynamics are compared, with very good agreement.

Cooling a Solid Disc with Uniform Heat Generation Using Inserts of High Thermal Conductivity within the Constructal Design Platform

In the present study, the problem of cooling a solid disc by way of placing inserts with high thermal conductivity was examined analytically and numerically within the platform of Constructal Theory. The work was accomplished using a fixed amount of a highly conductive material distributed in the form of incomplete inserts from the center (sink). Using Constructal Theory, the magnitudes of the heat resistances in the radial and the branching configurations were calculated analytically. Additionally, to validate the analytical solution, a numerical solution with the Finite Element Method was employed. The one-to-one comparison between the two distinct results reveals a good agreement. In the present case, the length of the inserts was different from the disc radius viz. a new degree of freedom was considered and the solution was remarkably different from the case involving a complete insert. The heat resistance was minimized with respect to the aspect ratio in order to determine the optimal number of inserts as well as the disc radius. It was demonstrated that within in a certain range of parameters, the heat conduction performance of incomplete inserts in the solid disc surpasses the heat conduction performance of standard complete inserts.

Constructal design for cooling a disc-shaped body using incomplete inserts with temperature-dependent thermal conductivities

In this study, constructal theory is used to analyze the radial and branching configurations of highly conductive incomplete inserts embedded in a disc for cooling purposes. The thermal conductivities are considered temperature-dependent which are varied linearly and ascending. Applying the Kirchhoff transformation, the resulting nonlinear partial equations are transformed to linear ones which are more suitable to solve, analytically. Furthermore, the effect of temperature-dependency of the thermal conductivities is examined and compared with the case with constant thermal conductivities under different conditions where a decrease in heat resistance is observed. However, the effectiveness of this factor in decreasing the thermal resistance is dependent upon other parameters. The effect of considering variable cross-section for the highly conductive material is combined with the temperature-dependency of the conductivities where it is concluded that under certain circumstances where the effect of temperature-dependency of the conductivities is weak, the variable cross-section can be used to reduce the thermal resistance, efficiently. Finally, since the proposed analytical solution is accompanied with some approximations, the problem is also solved numerically to verify the solution where an acceptable agreement is observed.

Preparation and Analysis of Glycoconjugates

AbstractWhereas DNA, RNA, and proteins are linear polymers that can usually be directly sequenced, glycans show substantially more complexity, having branching and anomeric configurations (α and β linkages). The biosynthesis of glycans, termed glycosylation, is extremely complex, is not template‐driven, varies among different cell types, and cannot be easily predicted from simple rules. This overview discusses the stereochemistry of mono‐ and oligosaccharides and provides diagrammatic representations of monosaccharides (Fisher projections and Haworth representations) and formulas for representation of glycan chains. A glossary of terms used in glycobiology is also provided. Curr. Protoc. Mol. Biol. 88:17.0.1‐17.0.12. © 2009 by John Wiley &amp; Sons, Inc.

Overview of glycoconjugate analysis.

Whereas DNA, RNA, and proteins are linear polymers that can usually be directly sequenced, glycans show substantially more complexity, having branching and anomeric configurations (alpha and beta linkages). The biosynthesis of glycans, termed glycosylation, is extremely complex, is not template-driven, varies among different cell types, and cannot be easily predicted from simple rules. This overview discusses the stereochemistry of monosaccharides and glycans and provides diagrammatic representations of monosaccharides (Fisher projections and Haworth representations) and formulas for representation of glycan chains. A glossary of terms used in glycobiology is also provided.

Large Deviations for Random Trees and the Branching of RNA Secondary Structures

We give a Large Deviation Principle (LDP) with explicit rate function for the distribution of vertex degrees in plane trees, a combinatorial model of RNA secondary structures. We calculate the typical degree distributions based on nearest neighbor free energies, and compare our results with the branching configurations found in two sets of large RNA secondary structures. We find substantial agreement overall, with some interesting deviations which merit further study.

Patient-specific vascular NURBS modeling for isogeometric analysis of blood flow

We describe an approach to construct hexahedral solid NURBS (Non-Uniform Rational B-Splines) meshes for patient-specific vascular geometric models from imaging data for use in isogeometric analysis. First, image processing techniques, such as contrast enhancement, filtering, classification, and segmentation, are used to improve the quality of the input imaging data. Then, luminal surfaces are extracted by isocontouring the preprocessed data, followed by the extraction of vascular skeleton via Voronoi and Delaunay diagrams. Next, the skeleton-based sweeping method is used to construct hexahedral control meshes. Templates are designed for various branching configurations to decompose the geometry into mapped meshable patches. Each patch is then meshed using one-to-one sweeping techniques, and boundary vertices are projected to the luminal surface. Finally, hexahedral solid NURBS are constructed and used in isogeometric analysis of blood flow. Piecewise linear hexahedral meshes can also be obtained using this approach. Examples of patient-specific arterial models are presented.

Dynamics, stability, and bifurcations

Dynamics, stability, and bifurcations