Hummingbird wing efficacy depends on aspect ratio and compares with helicopter rotors

Hummingbirds are the only birds that can sustain hovering. This unique flight behaviour comes, however, at high energetic cost. Based on helicopter and aeroplane design theory, we expect that hummingbird wing aspect ratio (AR), which ranges from about 3.0 to 4.5, determines aerodynamic efficacy. Previous quasi-steady experiments with a wing spinner set-up provide no support for this prediction. To test this more carefully, we compare the quasi-steady hover performance of 26 wings, from 12 hummingbird taxa. We spun the wings at angular velocities and angles of attack that are representative for every species and measured lift and torque more precisely. The power (aerodynamic torque × angular velocity) required to lift weight depends on aerodynamic efficacy, which is measured by the power factor. Our comparative analysis shows that AR has a modest influence on lift and drag forces, as reported earlier, but interspecific differences in power factor are large. During the downstroke, the power required to hover decreases for larger AR wings at the angles of attack at which hummingbirds flap their wings (p < 0.05). Quantitative flow visualization demonstrates that variation in hover power among hummingbird wings is driven by similar stable leading edge vortices that delay stall during the down- and upstroke. A side-by-side aerodynamic performance comparison of hummingbird wings and an advanced micro helicopter rotor shows that they are remarkably similar.     

Phenolic composition in different genotypes of Guabiju fruits (Myrcianthes pungens) and their potential as antioxidant and antichemotactic agents

Fruits of Myrcianthes pungens Berg. Legr. (Myrtaceae), known as guabiju, are widely consumed fresh as well as dried, processed into jam, marmalade, and juices. In this study, chemical composition and antichemotactic and antioxidant activities of fruits from a wild type (GB) and 2 genotypes, PL2 and PL1, of guabiju were investigated. Total anthocyanins for the genotypes ranged from 334 to 531 mg/100 g dry weight (dwt). Total flavonoids and polyphenols ranged from 79.8 to 154 mg/100 g and 2438 to 4613 mg/100 g (dwt), respectively. A reversed phase liquid chromatography method with photodiode array detection was used to determine chemical profiles of the main anthocyanins found in the extracts. An HPLC method for the quantification of flavonoids is proposed, providing a simple procedure with rapid sample preparation. All samples contained 5 identical anthocyanidins, distributed differently, with cyanidin as the main compound. Identified flavonoids were quercitrin, hyperoside, and isoquercitrin; their relative amounts varied among the extracts. The antioxidant activity of guabiju methanolic extract was comparable to that of Trolox, and at a test concentration of 0.25 mg/mL, GB and PL2 activities were higher than those exhibited by Trolox. Total dry extracts of guabiju exhibited greater inhibition of chemotaxis at a concentration of 4 μg/mL, except for GBH (wild-type hydrolyzed extract) which already presented high values at a concentration of 2 μg/mL. These results suggest that the consumption of this fruit, rich in polyphenols, may be beneficial to human health. Practical Application: The paper is the first attempt on the improvement of this native fruit, since it is widely consumed regularly as part of the South American diet. The content of phenolic compounds demonstrates that consumption of guabiju would be beneficial to human health. Differences among samples, originating from open pollination of plants growing on the same site, lead to the conclusion that improvements can be made in the chemical composition and beneficial activity of guabiju fruits by simply selecting genotypes for these characteristics among open-pollinated seedlings.     

Selected Papers from the Joint 18th International Heat Pipe Conference and the 12th International Heat Pipe Symposium

The Joint 18th International Heat Pipe Conference (IHPC) and the 12th International Heat Pipe Symposium (IHPS) was held at Ramada Plaza Jeju Hotel in Jeju Korea during June 12–16, 2016. The joint conference organized by Heat Pipe Committee of the Korean Society of Mechanical Engineers (KSME) combines two historical triennial gatherings into one massive conference. More than 240 participants, sponsors, and exhibitors attended the conference from 24 countries around the world. Altogether 144 technical papers were presented in the technical sessions, which included the most up-to-date technologies associated with heat pipes.     

Increasing the efficiency of a portable PEM fuel cell by altering the cathode channel geometry: A numerical and experimental study

Portable fuel cells are receiving great attention today mainly because their energy density is higher than any portable battery solution. Among other types, portable polymer electrolyte membrane (PEM) fuel cells are an established technology where research on increasing their efficiency is leading product development and manufacturing. The objective of this work was to study and evaluate the redesign of a commercial portable fuel cell, improving its efficiency. A three-dimensional model of the original PEM fuel cell with parallel plus a transversal flow channel design was developed using Comsol Multiphysics, including the effects of liquid water formation and electric current production. Using this model, the effects of different channel geometries and respective cathode flow rates on the cell’s performance, including the local transport characteristics, were studied. Laboratory tests with various fuel cell stacks using the new channels structure were effectuated for an evaluation of the fuel cell’s performance, showing improvements in its efficiency of up to 26.4%.     

Theoretical variations of the thermal performance of different solar collectors and solar combi systems as function of the varying yearly weather conditions in Denmark

The thermal performances of solar collectors and solar combi systems with different solar fractions are studied under the influence of the Danish design reference year, DRY data file, and measured weather data from a solar radiation measurement station situated at the Technical University of Denmark in Kgs. Lyngby. The data from DRY data file are used for any location in Denmark. The thermal performances of the solar heating systems are calculated by means of validated computer models. The measured yearly solar radiation varies by approximately 23% in the period from 1990 until 2002, and the investigations show that it is not possible to predict the yearly solar radiation on a tilted surface based on the yearly global radiation.The annual thermal performance of solar combi systems cannot with reasonable approximation be fitted to a linear function of the annual total radiation on the solar collector or the annual global radiation. Solar combi systems with high efficient solar collectors are more influenced by weather variations from one year to another than systems with low efficient solar collectors.The annual thermal performance of solar collectors cannot be predicted from the global radiation, but both the annual thermal performance and the annual utilized solar energy can with a reasonable approximation be fitted to a linear function of the yearly solar radiation on the collector for both flat plate and evacuated tubular solar collectors. Also evacuated tubular solar collectors utilize less sunny years with large parts of diffuse radiation relatively better than flat plate collectors.     

Structural and Mechanical properties of Ti-Si-C-ON for biomedical applications

Ti-Si-C-ON films were deposited by DC reactive magnetron sputtering using different partial pressure of oxygen (p_O2) and nitrogen (p_N2) ratio. Compositional analysis revealed the existence of two different growth zones for the films; one zone deposited under low p_O2/p_N2 and another zone deposited under high p_O2/p_N2. The films produced under low p_O2/p_N2 were deposited at a lower rate and presented a fcc structure, as well as, dense and featureless morphologies. The films deposited with high p_O2/p_N2, consequently higher oxygen content, were deposited at a higher rate and developed an amorphous structure. The structural changes are consistent with the hardness and Young's modulus evolution, as seen by the significant reduction of the hardness and influence on the Young's modulus by increasing p_O2/p_N2.