Optimal concentrations in transport systems

Many biological and man-made systems rely on transport systems for the distribution of material, for example matter and energy. Material transfer in these systems is determined by the flow rate and the concentration of material. While the most concentrated solutions offer the greatest potential in terms of material transfer, impedance typically increases with concentration, thus making them the most difficult to transport. We develop a general framework for describing systems for which impedance increases with concentration, and consider material flow in four different natural systems: blood flow in vertebrates, sugar transport in vascular plants and two modes of nectar drinking in birds and insects. The model provides a simple method for determining the optimum concentration c[subscript opt] in these systems. The model further suggests that the impedance at the optimum concentration μ[subscript opt] may be expressed in terms of the impedance of the pure (c = 0) carrier medium μ[subscript 0] as μ[subscript opt]∼2[superscript α]μ[subscript 0], where the power α is prescribed by the specific flow constraints, for example constant pressure for blood flow (α = 1) or constant work rate for certain nectar-drinking insects (α = 6). Comparing the model predictions with experimental data from more than 100 animal and plant species, we find that the simple model rationalizes the observed concentrations and impedances. The model provides a universal framework for studying flows impeded by concentration, and yields insight into optimization in engineered systems, such as traffic flow.National Science Foundation (U.S.) (Grant 1021779)National Science Foundation (U.S.) (Grant DMS-0907955)National Science Foundation (U.S.). Materials Research Science and Engineering Centers (Program) (Grant DMR-0820484

Optimal transport strategies

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2013.Cataloged from PDF version of thesis.Includes bibliographical references (p. 103-112).It is generally presupposed that the shapes and mechanisms encountered in nature have evolved in such a way as to maximize the robustness of a species. However, most such optimization problems arising in biology are sufficiently complex that it is neither clear what is being optimized, nor what are the relevant constraints. We here consider a number of natural fluid transport systems that may be framed in terms of constrained optimization problems. We first examine natural drinking strategies. We classify the drinking strategies of a broad range of creatures according to the principal forces involved, and present physical pictures for each style. Simple scaling arguments are developed and tested against existing data. While suction is the most common drinking strategy, various alternative styles have evolved among creatures whose morphological, physiological and environmental constraints preclude it. Many small creatures rely on relatively subtle capillary effects for fluid uptake. Particular attention is given to nectar drinking strategies. Nectar drinkers must feed quickly and efficiently due to the threat of predation. While the sweetest nectar offers the greatest energetic rewards, the sharp increase of viscosity with sugar concentration makes it the most difficult to transport. An optimal sugar concentration is thus expected for which the energy intake rate is maximized. An extensive data set indicates that the sugar concentration that optimizes energy transport depends exclusively on the drinking technique employed. We identify three nectar drinking techniques: active suction, capillary suction, and viscous dipping and rationalize the reported optimal concentrations for each through consideration of the appropriate constrained optimization problem. Blood flow in vertebrates and phloem flow in plants are known to be optimized for efficient transport of oxygen and sugar, respectively. Efficient transport of material is similarly advantageous in engineered transport systems such as traffic and wireless networks. We thus develop a general framework for determining the concentration that maximizes the material flow in a number of transport systems.by Wonjung Kim.Ph.D

Electrocatalytic arsenite oxidation in bicarbonate solutions combined with CO₂ reduction to formate

Sunlight-driven water-energy nexus technologies are receiving increasing attention. This study presents a hybrid electrochemical system that catalyzes the oxidation of As(III) to As(V) with a nanoparticulate TiO₂ electrocatalyst (Ti/Ir_(1-x)Ta_xO_y/TiO₂; denoted as an n-TEC) while simultaneously converting CO₂ to formate on a Bi electrode in aqueous bicarbonate solutions at circum-neutral pH. Linear sweep voltammograms of n-TEC exhibit a specific As(III) oxidation peak (E_(p,As)), at which the Faradaic efficiency (FE) of As(V) production is ∼100%. However, the application of a potential higher than the peak (E > E_(p,As)) leads to a significant decrease in the FE due to water oxidation. Upon the addition of chloride, the oxidation of water and chloride occur competitively, producing reactive chlorine species responsible for mediating the oxidation of As(III). The Bi electrodes synthesized via the electrodeposition of Bi³⁺ typically show high FEs of >80% for formate production in bicarbonate solution purged with CO₂. The addition of chloride significantly enhances the current while maintaining the FE. The n-TEC catalyst and Bi electrodes are paired in a single device equipped with a membrane, and significant effort is made to achieve the same FEs in both the anodic and cathodic reactions as in their half-reactions. Finally, the optimized n-TEC/Bi pair is coupled with a low-cost, commercially available photovoltaic (PV). Various technical factors that drive the overall reactions with the PV are considered, and maximum FEs of ∼95% are achieved for the production of both As(V) and formate

PADA: Power-aware development assistant for mobile sensing applications

� 2016 ACM. We propose PADA, a new power evaluation tool to measure and optimize power use of mobile sensing applications. Our motivational study with 53 professional developers shows they face huge challenges in meeting power requirements. The key challenges are from the significant time and effort for repetitive power measurements since the power use of sensing applications needs to be evaluated under various real-world usage scenarios and sensing parameters. PADA enables developers to obtain enriched power information under diverse usage scenarios in development environments without deploying and testing applications on real phones in real-life situations. We conducted two user studies with 19 developers to evaluate the usability of PADA. We show that developers benefit from using PADA in the implementation and power tuning of mobile sensing applications.N

Empath-D: VR-based empathetic app design for accessibility

Singapore National Research Foundation under IDM Futures Funding Initiative; Ministry of Education, Singapore under its Academic Research Funding Tier

Optimal diameter reduction ratio of acinar airways in human lungs

In the airway network of a human lung, the airway diameter gradually decreases through multiple branching. The diameter reduction ratio of the conducting airways that transport gases without gas exchange is 0.79, but this reduction ratio changes to 0.94 in acinar airways beyond transitional bronchioles. While the reduction in the conducting airways was previously rationalized on the basis of Murray's law, our understanding of the design principle behind the acinar airways has been far from clear. Here we elucidate that the change in gas transfer mode is responsible for the transition in the diameter reduction ratio. The oxygen transfer rate per unit surface area is maximized at the observed geometry of acinar airways, which suggests the minimum cost for the construction and maintenance of the acinar airways. The results revitalize and extend the framework of Murray's law over an entire human lung

Effect of total intravenous versus inhalation anesthesia on long-term oncological outcomes in patients undergoing curative resection for early-stage non-small cell lung cancer: a retrospective cohort study

Background Propofol-based total intravenous anesthesia (TIVA) improves long-term outcomes after cancer surgery compared with inhalation anesthesia. However, its effect on patients undergoing non-small cell lung cancer (NSCLC) surgery remains unclear. We aimed to compare the oncological outcomes of TIVA and inhalation anesthesia after curative resection of early-stage NSCLC. Methods We analyzed the medical records of patients diagnosed with stage I or II NSCLC who underwent curative resection at a tertiary university hospital between January 2010 and December 2017. The primary outcomes were recurrence-free survival (RFS) and overall survival (OS) according to anesthesia type. Results We included 1,508 patients with stage I/II NSCLC. The patients were divided into the TIVA (n = 980) and Inhalation (n = 528) groups. The two groups were well-balanced in terms of baseline clinical characteristics. The TIVA group demonstrated significantly improved RFS (7.7 years, 95% CI [7.37, 8.02]) compared with the Inhalation group (6.8 years, 95% CI [6.30, 7.22], P = 0.003). Similarly, TIVA was superior to inhalation agents with respect to OS (median OS; 8.4 years, 95% CI [8.08, 8.69] vs. 7.3 years, 95% CI [6.81, 7.71]; P < 0.001). Multivariable Cox regression analysis revealed that TIVA was an independent prognostic factor related to recurrence (hazard ratio [HR]: 1.24, 95% CI [1.04, 1.47], P = 0.014) and OS (HR: 1.39, 95% CI [1.12, 1.72], P = 0.002). Conclusions Propofol-based TIVA was associated with better RFS and OS than inhalation anesthesia in patients with stage I/II NSCLC who underwent curative resection

Natural drinking strategies

We examine the fluid mechanics of drinking in nature. We classify the drinking strategies of a broad range of creatures according to the principal forces involved, and present physical pictures for each style. Simple scaling arguments are developed and tested against existing data. While suction is the most common drinking strategy, various alternative styles have evolved among creatures whose morphological, physiological and environmental constraints preclude it. Particular attention is given to creatures small relative to the capillary length, whose drinking styles rely on relatively subtle interfacial effects. We also discuss attempts to rationalize various drinking strategies through consideration of constrained optimization problems. Some biomimetic applications are discussed.National Science Foundation (U.S.)STX Scholarship Foundatio