John Young - Academia.edu (original) (raw)

Papers by John Young

Research paper thumbnail of Copolymers of Butadiene with Alkyl, Aryl, Alkoxyl, and Phenoxyl Styrenes

Industrial & Engineering Chemistry, 1948

Research paper thumbnail of Characterization of Granulations of Calcium and Apatite in Serum as Pleomorphic Mineralo-Protein Complexes and as Precursors of Putative Nanobacteria

PLOS One, 2009

Calcium and apatite granulations are demonstrated here to form in both human and fetal bovine ser... more Calcium and apatite granulations are demonstrated here to form in both human and fetal bovine serum in response to the simple addition of either calcium or phosphate, or a combination of both. These granulations are shown to represent precipitating complexes of protein and hydroxyapatite (HAP) that display marked pleomorphism, appearing as round, laminated particles, spindles, and films. These same complexes can be found in normal untreated serum, albeit at much lower amounts, and appear to result from the progressive binding of serum proteins with apatite until reaching saturation, upon which the mineralo-protein complexes precipitate. Chemically and morphologically, these complexes are virtually identical to the so-called nanobacteria (NB) implicated in numerous diseases and considered unusual for their small size, pleomorphism, and the presence of HAP. Like NB, serum granulations can seed particles upon transfer to serum-free medium, and their main protein constituents include albumin, complement components 3 and 4A, fetuin-A, and apolipoproteins A1 and B100, as well as other calcium and apatite binding proteins found in the serum. However, these serum mineralo-protein complexes are formed from the direct chemical binding of inorganic and organic phases, bypassing the need for any biological processes, including the long cultivation in cell culture conditions deemed necessary for the demonstration of NB. Thus, these serum granulations may result from physiologically inherent processes that become amplified with calcium phosphate loading or when subjected to culturing in medium. They may be viewed as simple mineralo-protein complexes formed from the deployment of calcification-inhibitory pathways used by the body to cope with excess calcium phosphate so as to prevent unwarranted calcification. Rather than representing novel pathophysiological mechanisms or exotic lifeforms, these results indicate that the entities described earlier as NB most likely originate from calcium and apatite binding factors in the serum, presumably calcification inhibitors, that upon saturation, form seeds for HAP deposition and growth. These calcium granulations are similar to those found in organisms throughout nature and may represent the products of more general calcium regulation pathways involved in the control of calcium storage, retrieval, tissue deposition, and disposal.

Research paper thumbnail of How to cope with severe acute respiratory syndrome (SARS)

Chang Gung medical journal, 2003

Research paper thumbnail of The rise and fall of nanobacteria

Scientific American, 2010

U n ive rsity of Te xa sa t A u stin (ca lcite crysta l) fossilized remains of bacteria. Like bac... more U n ive rsity of Te xa sa t A u stin (ca lcite crysta l) fossilized remains of bacteria. Like bacteria, these little blobs appeared to have cell walls and filamentous surface projections. Folk's spheres were quite small, however, significantly smaller than any known bacteria. ...

Research paper thumbnail of Meditation as a Voluntary Hypometabolic State of Biological Estivation

News in physiological sciences : an international journal of physiology produced jointly by the International Union of Physiological Sciences and the American Physiological Society, 1998

Meditation, a wakeful hypometabolic state of parasympathetic dominance, is compared with other hy... more Meditation, a wakeful hypometabolic state of parasympathetic dominance, is compared with other hypometabolic conditions, such as sleep, hypnosis, and the torpor of hibernation. We conclude that there are many analogies between the physiology of longterm meditators and hibernators across the phylogenetic scale. These analogies further reinforce the idea that plasticity of consciousness remains a key factor in successful biological adaptation.

Research paper thumbnail of The effects of a novel high intensity exercise intervention on established markers of cardiovascular disease and health in Scottish adolescent youth

Journal of public health research, Jan 15, 2012

This study examined the effects of high intensity exercise on physical fitness components and car... more This study examined the effects of high intensity exercise on physical fitness components and cardiovascular disease (CVD) risk factors in youth. Forty-one participants (15-17 years) were divided into a control and an intervention (high intensity exercise, HIT) group. The HIT group (15 boys, 2 girls) performed three weekly sessions over seven weeks consisting of either four to six repeats of maximal sprint running with 20-30 s recovery. The control group (20 boys, 4 girls) continued their normal activity patterns. All participants had indices of obesity and blood pressure (BP) recorded in addition to four physical performance measures pre-and post-intervention: cardiorespiratory fitness, muscular power, sprint speed and agility. In the HIT group, significant improvements in cardiorespiratory fitness (P<0.01) and agility (P<0.05) were noted. Participants in the control group, meanwhile, experienced a significant decrease in counter movement jump performance. These findings demonstrate that brief, intense exercise interventions are useful for improving indices of physical fitness in a short period of time.

Research paper thumbnail of cis-Resveratrol produces anti-inflammatory effects by inhibiting canonical and non-canonical inflammasomes in macrophages

Innate immunity, 2014

Resveratrol, a natural phenolic compound found in red grapes and wine, exists as cis and trans is... more Resveratrol, a natural phenolic compound found in red grapes and wine, exists as cis and trans isomers. Recent studies have shown that trans-resveratrol possesses anti-inflammatory, anti-oxidant, anti-carcinogenic, anti-tumor and immunomodulatory properties. However, it remains unclear whether cis-resveratrol may exhibit similar activities. The objective of the present study was to examine the effects of cis-and trans-resveratrol on the production of pro-inflammatory cytokines and mediators in human macrophages. We examined the possibility that cis-and trans-resveratrol may affect cytokine secretion by modulating inflammasomes, intracellular multi-protein complexes, the assembly of which leads to caspase-1 activation and secretion of active IL-1b by macrophages. Our results show that pre-treatment of macrophages with cis-resveratrol not only reduces pro-IL-1b production and IL-1b secretion, but also suppresses ATP-induced transcription and activation of caspase-1 and caspase-4. Notably, cis-resveratrol inhibits the expression of the purinergic receptor, P2X 7 R, and the endoplasmic reticulum stress marker, Glc-regulated protein 78, but also reduces reactive oxygen species production. Moreover, cis-resveratrol attenuates cyclooxygenase-2 expression and prostaglandin E 2 production. cis-Resveratrol also decreases the phosphorylation of p38 MAPK and expression of the c-Jun protein.

Research paper thumbnail of Identification of CD24 as a cancer stem cell marker in human nasopharyngeal carcinoma

PloS one, 2014

Cancer stem cells (CSCs) represent a unique sub-population of tumor cells with the ability to ini... more Cancer stem cells (CSCs) represent a unique sub-population of tumor cells with the ability to initiate tumor growth and sustain self-renewal. Although CSC biomarkers have been described for various tumors, only a few markers have been identified for nasopharyngeal carcinoma (NPC). In this study, we show that CD24 + cells isolated from human NPC cell lines express stem cell genes (Sox2, Oct4, Nanog, Bmi-1, and Rex-1), and show activation of the Wnt/b-catenin signaling pathway. CD24 + cells possess typical CSC characteristics that include enhanced cell proliferation, increased colony and sphere formation, maintenance of cell differentiation potential in prolonged culture, and enhanced resistance to chemotherapeutic drugs. Notably, CD24 + cells produce tumors following inoculation of as few as 500 cells in immunodeficient NOD/SCID mice. CD24 + cells further show increased invasion ability in vitro, which correlates with enhanced expression of matrix metalloproteinase 2 and 9. In summary, our results suggest that CD24 represents a novel CSC biomarker in NPC.

Research paper thumbnail of NK cells kill mycobacteria directly by releasing perforin and granulysin

Journal of leukocyte biology, 2014

Although the mechanisms underlying the cytotoxic effect of NK cells on tumor cells and intracellu... more Although the mechanisms underlying the cytotoxic effect of NK cells on tumor cells and intracellular bacteria have been studied extensively, it remains unclear how these cells kill extracellular bacterial pathogens. In this study, we examine how human NK cells kill Mycobacterium kansasii and M.tb. The underlying mechanism is contact dependent and requires two cytolytic proteins: perforin and granulysin. Mycobacteria induce enhanced expression of the cytolytic proteins via activation of the NKG2D/NCR cell-surface receptors and intracellular signaling pathways involving ERK, JNK, and p38 MAPKs. These results suggest that NK cells use similar cellular mechanisms to kill both bacterial pathogens and target host cells. This report reveals a novel role for NK cells, perforin, and granulysin in killing mycobacteria and highlights a potential alternative defense mechanism that the immune system can use against mycobacterial infection. J. Leukoc. Biol. 96: 000 -000; 2014.

Research paper thumbnail of Impact of the gut microbiota, prebiotics, and probiotics on human health and disease

Biomedical journal

Recent studies have revealed that the gut microbiota regulates many physiological functions, rang... more Recent studies have revealed that the gut microbiota regulates many physiological functions, ranging from energy regulation and cognitive processes to toxin neutralization and immunity against pathogens. Accordingly, alterations in the composition of the gut microbiota have been shown to contribute to the development of various chronic diseases. The main objectives of this review are to present recent breakthroughs in the study of the gut microbiota and show that intestinal bacteria play a critical role in the development of different disease conditions, including obesity, fatty liver disease, and lung infection. We also highlight the potential application of prebiotics and probiotics in maintaining optimal health and treating chronic inflammatory and immunity-related diseases.

Research paper thumbnail of Simulation and parameter variation of flapping-wing motion based on dragonfly hovering

AIAA Journal, 2008

The flapping motion of a wing based on the hind wing of the Aeschna juncea dragonfly is simulated... more The flapping motion of a wing based on the hind wing of the Aeschna juncea dragonfly is simulated using a three-dimensional incompressible Navier-Stokes solver. The performance of the wing is investigated by variation of a number of kinematic parameters. Flapping amplitudes of ...

Research paper thumbnail of Flapping-wing aerodynamics: Progress and challenges

AIAA Journal, 2008

It is the objective of this paper to review recent developments in the understanding and predicti... more It is the objective of this paper to review recent developments in the understanding and prediction of flapping-wing aerodynamics. To this end, several flapping-wing configurations are considered. First, the problem of single flapping wings is treated with special emphasis on the dependence of thrust, lift, and propulsive efficiency on flapping mode, amplitude, frequency, and wing shape. Second, the problem of hovering flight is studied for single flapping wings. Third, the aerodynamic phenomena and benefits produced by the flapping-wing interactions on tandem wings or biplane configurations are discussed. Such interactions occur on dragonflies or on a recently developed micro air vehicle. The currently available two-and three-dimensional inviscid and viscous flapping-wing flow solutions are presented. It is shown that the results are strongly dependent on flapping frequency, amplitude, and Reynolds number. These findings are substantiated by comparison with the available experimental data.

Research paper thumbnail of Reynolds number, thickness and camber effects on flapping airfoil propulsion

Journal of Fluids and Structures, 2011

The effect of varying airfoil thickness and camber on plunging and combined pitching and plunging... more The effect of varying airfoil thickness and camber on plunging and combined pitching and plunging airfoil propulsion at Reynolds number Re =200, 2000, 20 000 and 2 Â 10 6 was studied by numerical simulations for fully laminar and fully turbulent flow regimes. The thickness study was performed on 2-D NACA symmetric airfoils with 6-50% thick sections undergoing pure plunging motion at reduced frequency k= 2 and amplitudes h = 0.25 and 0.5, and for combined pitching and plunging motion at k=2, h =0.5, phase f=901, pitch angle y o =151 and 301 and the pitch axis was located at 1/3 of chord from leading edge. At Re = 200 for motions where positive thrust is generated, thin airfoils outperform thick airfoils. At higher Re significant gains could be achieved both in thrust generation and propulsive efficiency by using a thicker airfoil section for plunging and combined motion with low pitch amplitude. The camber study was performed on 2-D NACA airfoils with varying camber locations undergoing pure plunging motion at k=2, h = 0.5 and Re =20 000. Little variation in thrust performance was found with camber. The underlying physics behind the alteration in propulsive performance between low and high Reynolds numbers has been explored by comparing viscous Navier-Stokes and inviscid panel method results. The role of leading edge vortices was found to be key to the observed performance variation.

Research paper thumbnail of Numerical analysis of an oscillating-wing wind and hydropower generator

AIAA Journal, 2011

ABSTRACT The extraction of energy from wind or water streams is generally accomplished by means o... more ABSTRACT The extraction of energy from wind or water streams is generally accomplished by means of rotary systems. However, it is recognized and it has been demonstrated that oscillating wings can also be used for this purpose. A newly developed oscillating-wing wind and hydropower generator is described. Its potential for the generation of electric power from tidal flows and high-altitude jet streams is studied using two-dimensional Navier-Stokes simulations at Re = 20, 000. Results for a single NACA 0014 wing power generator undergoing nonsinusoidal pitch-plunge motion indicate around 17% increase in power generated and around 15% increase in efficiency over that for sinusoidal motion. Two airfoils operating in tandem, undergoing both sinusoidal and nonsinusoidal motions, are also studied. It is found that for sinusoidal motion both averaged power output and efficiency per foil are reduced by around 20% for tandem configurations compared with a single foil in sinusoidal motion, and similar performance reductions are experienced for nonsinusoidal motions.

Research paper thumbnail of Oscillation frequency and amplitude effects on plunging airfoil propulsion and flow periodicity

AIAA Journal, 2012

The flow over a NACA 0012 airfoil, oscillated sinusoidally in plunge, is simulated numerically us... more The flow over a NACA 0012 airfoil, oscillated sinusoidally in plunge, is simulated numerically using a compressible two-dimensional Navier-Stokes solver at a Reynolds number of 2× ×10 4 . The wake of the airfoil is visualized using a numerical particle tracing method. Close agreement is obtained between numerically simulated wake structures and experimental wake visualizations in the literature, when the flow is assumed to be fully laminar. The wake structures, and the lift and thrust of the airfoil, are shown to be strongly dependent on both the Strouhal number and the reduced frequency k of the plunge oscillation at this Reynolds number. Leading-edge separation appears to dominate the generation of aerodynamic forces for reduced frequencies below approximately k = 4 but becomes secondary for higher frequencies. Wake structures appear to be controlled primarily by trailing-edge effects at all frequencies tested up to k = 20. Aerodynamic force results obtained at this Reynolds number show marked differences from those predicted by potential flow analyses at low plunge frequency and high amplitude but are similar at high frequency and low amplitude, consistent with the effect of leading-edge separation.

Research paper thumbnail of Details of insect wing design and deformation enhance aerodynamic function and flight efficiency

Science (New York, N.Y.), Jan 18, 2009

Insect wings are complex structures that deform dramatically in flight. We analyzed the aerodynam... more Insect wings are complex structures that deform dramatically in flight. We analyzed the aerodynamic consequences of wing deformation in locusts using a three-dimensional computational fluid dynamics simulation based on detailed wing kinematics. We validated the simulation against smoke visualizations and digital particle image velocimetry on real locusts. We then used the validated model to explore the effects of wing topography and deformation, first by removing camber while keeping the same time-varying twist distribution, and second by removing camber and spanwise twist. The full-fidelity model achieved greater power economy than the uncambered model, which performed better than the untwisted model, showing that the details of insect wing topography and deformation are important aerodynamically. Such details are likely to be important in engineering applications of flapping flight.

Research paper thumbnail of Thyroid shields and neck exposures in cephalometric radiography

BMC Medical Imaging, 2006

The thyroid is among the more radiosensitive organs in the body. The goal of this study was twofo... more The thyroid is among the more radiosensitive organs in the body. The goal of this study was twofold: (1) to evaluate age-related changes in what is exposed to ionizing radiation in the neck area, and (2) to assess thyroid shield presence in cephalometric radiographs Methods: Cephalometric radiographs at one academic setting were sampled and neck exposure was related to calendar year and patient's gender and age.

Research paper thumbnail of Copolymers of Butadiene with Alkyl, Aryl, Alkoxyl, and Phenoxyl Styrenes

Industrial & Engineering Chemistry, 1948

Research paper thumbnail of Characterization of Granulations of Calcium and Apatite in Serum as Pleomorphic Mineralo-Protein Complexes and as Precursors of Putative Nanobacteria

PLOS One, 2009

Calcium and apatite granulations are demonstrated here to form in both human and fetal bovine ser... more Calcium and apatite granulations are demonstrated here to form in both human and fetal bovine serum in response to the simple addition of either calcium or phosphate, or a combination of both. These granulations are shown to represent precipitating complexes of protein and hydroxyapatite (HAP) that display marked pleomorphism, appearing as round, laminated particles, spindles, and films. These same complexes can be found in normal untreated serum, albeit at much lower amounts, and appear to result from the progressive binding of serum proteins with apatite until reaching saturation, upon which the mineralo-protein complexes precipitate. Chemically and morphologically, these complexes are virtually identical to the so-called nanobacteria (NB) implicated in numerous diseases and considered unusual for their small size, pleomorphism, and the presence of HAP. Like NB, serum granulations can seed particles upon transfer to serum-free medium, and their main protein constituents include albumin, complement components 3 and 4A, fetuin-A, and apolipoproteins A1 and B100, as well as other calcium and apatite binding proteins found in the serum. However, these serum mineralo-protein complexes are formed from the direct chemical binding of inorganic and organic phases, bypassing the need for any biological processes, including the long cultivation in cell culture conditions deemed necessary for the demonstration of NB. Thus, these serum granulations may result from physiologically inherent processes that become amplified with calcium phosphate loading or when subjected to culturing in medium. They may be viewed as simple mineralo-protein complexes formed from the deployment of calcification-inhibitory pathways used by the body to cope with excess calcium phosphate so as to prevent unwarranted calcification. Rather than representing novel pathophysiological mechanisms or exotic lifeforms, these results indicate that the entities described earlier as NB most likely originate from calcium and apatite binding factors in the serum, presumably calcification inhibitors, that upon saturation, form seeds for HAP deposition and growth. These calcium granulations are similar to those found in organisms throughout nature and may represent the products of more general calcium regulation pathways involved in the control of calcium storage, retrieval, tissue deposition, and disposal.

Research paper thumbnail of How to cope with severe acute respiratory syndrome (SARS)

Chang Gung medical journal, 2003

Research paper thumbnail of The rise and fall of nanobacteria

Scientific American, 2010

U n ive rsity of Te xa sa t A u stin (ca lcite crysta l) fossilized remains of bacteria. Like bac... more U n ive rsity of Te xa sa t A u stin (ca lcite crysta l) fossilized remains of bacteria. Like bacteria, these little blobs appeared to have cell walls and filamentous surface projections. Folk's spheres were quite small, however, significantly smaller than any known bacteria. ...

Research paper thumbnail of Meditation as a Voluntary Hypometabolic State of Biological Estivation

News in physiological sciences : an international journal of physiology produced jointly by the International Union of Physiological Sciences and the American Physiological Society, 1998

Meditation, a wakeful hypometabolic state of parasympathetic dominance, is compared with other hy... more Meditation, a wakeful hypometabolic state of parasympathetic dominance, is compared with other hypometabolic conditions, such as sleep, hypnosis, and the torpor of hibernation. We conclude that there are many analogies between the physiology of longterm meditators and hibernators across the phylogenetic scale. These analogies further reinforce the idea that plasticity of consciousness remains a key factor in successful biological adaptation.

Research paper thumbnail of The effects of a novel high intensity exercise intervention on established markers of cardiovascular disease and health in Scottish adolescent youth

Journal of public health research, Jan 15, 2012

This study examined the effects of high intensity exercise on physical fitness components and car... more This study examined the effects of high intensity exercise on physical fitness components and cardiovascular disease (CVD) risk factors in youth. Forty-one participants (15-17 years) were divided into a control and an intervention (high intensity exercise, HIT) group. The HIT group (15 boys, 2 girls) performed three weekly sessions over seven weeks consisting of either four to six repeats of maximal sprint running with 20-30 s recovery. The control group (20 boys, 4 girls) continued their normal activity patterns. All participants had indices of obesity and blood pressure (BP) recorded in addition to four physical performance measures pre-and post-intervention: cardiorespiratory fitness, muscular power, sprint speed and agility. In the HIT group, significant improvements in cardiorespiratory fitness (P<0.01) and agility (P<0.05) were noted. Participants in the control group, meanwhile, experienced a significant decrease in counter movement jump performance. These findings demonstrate that brief, intense exercise interventions are useful for improving indices of physical fitness in a short period of time.

Research paper thumbnail of cis-Resveratrol produces anti-inflammatory effects by inhibiting canonical and non-canonical inflammasomes in macrophages

Innate immunity, 2014

Resveratrol, a natural phenolic compound found in red grapes and wine, exists as cis and trans is... more Resveratrol, a natural phenolic compound found in red grapes and wine, exists as cis and trans isomers. Recent studies have shown that trans-resveratrol possesses anti-inflammatory, anti-oxidant, anti-carcinogenic, anti-tumor and immunomodulatory properties. However, it remains unclear whether cis-resveratrol may exhibit similar activities. The objective of the present study was to examine the effects of cis-and trans-resveratrol on the production of pro-inflammatory cytokines and mediators in human macrophages. We examined the possibility that cis-and trans-resveratrol may affect cytokine secretion by modulating inflammasomes, intracellular multi-protein complexes, the assembly of which leads to caspase-1 activation and secretion of active IL-1b by macrophages. Our results show that pre-treatment of macrophages with cis-resveratrol not only reduces pro-IL-1b production and IL-1b secretion, but also suppresses ATP-induced transcription and activation of caspase-1 and caspase-4. Notably, cis-resveratrol inhibits the expression of the purinergic receptor, P2X 7 R, and the endoplasmic reticulum stress marker, Glc-regulated protein 78, but also reduces reactive oxygen species production. Moreover, cis-resveratrol attenuates cyclooxygenase-2 expression and prostaglandin E 2 production. cis-Resveratrol also decreases the phosphorylation of p38 MAPK and expression of the c-Jun protein.

Research paper thumbnail of Identification of CD24 as a cancer stem cell marker in human nasopharyngeal carcinoma

PloS one, 2014

Cancer stem cells (CSCs) represent a unique sub-population of tumor cells with the ability to ini... more Cancer stem cells (CSCs) represent a unique sub-population of tumor cells with the ability to initiate tumor growth and sustain self-renewal. Although CSC biomarkers have been described for various tumors, only a few markers have been identified for nasopharyngeal carcinoma (NPC). In this study, we show that CD24 + cells isolated from human NPC cell lines express stem cell genes (Sox2, Oct4, Nanog, Bmi-1, and Rex-1), and show activation of the Wnt/b-catenin signaling pathway. CD24 + cells possess typical CSC characteristics that include enhanced cell proliferation, increased colony and sphere formation, maintenance of cell differentiation potential in prolonged culture, and enhanced resistance to chemotherapeutic drugs. Notably, CD24 + cells produce tumors following inoculation of as few as 500 cells in immunodeficient NOD/SCID mice. CD24 + cells further show increased invasion ability in vitro, which correlates with enhanced expression of matrix metalloproteinase 2 and 9. In summary, our results suggest that CD24 represents a novel CSC biomarker in NPC.

Research paper thumbnail of NK cells kill mycobacteria directly by releasing perforin and granulysin

Journal of leukocyte biology, 2014

Although the mechanisms underlying the cytotoxic effect of NK cells on tumor cells and intracellu... more Although the mechanisms underlying the cytotoxic effect of NK cells on tumor cells and intracellular bacteria have been studied extensively, it remains unclear how these cells kill extracellular bacterial pathogens. In this study, we examine how human NK cells kill Mycobacterium kansasii and M.tb. The underlying mechanism is contact dependent and requires two cytolytic proteins: perforin and granulysin. Mycobacteria induce enhanced expression of the cytolytic proteins via activation of the NKG2D/NCR cell-surface receptors and intracellular signaling pathways involving ERK, JNK, and p38 MAPKs. These results suggest that NK cells use similar cellular mechanisms to kill both bacterial pathogens and target host cells. This report reveals a novel role for NK cells, perforin, and granulysin in killing mycobacteria and highlights a potential alternative defense mechanism that the immune system can use against mycobacterial infection. J. Leukoc. Biol. 96: 000 -000; 2014.

Research paper thumbnail of Impact of the gut microbiota, prebiotics, and probiotics on human health and disease

Biomedical journal

Recent studies have revealed that the gut microbiota regulates many physiological functions, rang... more Recent studies have revealed that the gut microbiota regulates many physiological functions, ranging from energy regulation and cognitive processes to toxin neutralization and immunity against pathogens. Accordingly, alterations in the composition of the gut microbiota have been shown to contribute to the development of various chronic diseases. The main objectives of this review are to present recent breakthroughs in the study of the gut microbiota and show that intestinal bacteria play a critical role in the development of different disease conditions, including obesity, fatty liver disease, and lung infection. We also highlight the potential application of prebiotics and probiotics in maintaining optimal health and treating chronic inflammatory and immunity-related diseases.

Research paper thumbnail of Simulation and parameter variation of flapping-wing motion based on dragonfly hovering

AIAA Journal, 2008

The flapping motion of a wing based on the hind wing of the Aeschna juncea dragonfly is simulated... more The flapping motion of a wing based on the hind wing of the Aeschna juncea dragonfly is simulated using a three-dimensional incompressible Navier-Stokes solver. The performance of the wing is investigated by variation of a number of kinematic parameters. Flapping amplitudes of ...

Research paper thumbnail of Flapping-wing aerodynamics: Progress and challenges

AIAA Journal, 2008

It is the objective of this paper to review recent developments in the understanding and predicti... more It is the objective of this paper to review recent developments in the understanding and prediction of flapping-wing aerodynamics. To this end, several flapping-wing configurations are considered. First, the problem of single flapping wings is treated with special emphasis on the dependence of thrust, lift, and propulsive efficiency on flapping mode, amplitude, frequency, and wing shape. Second, the problem of hovering flight is studied for single flapping wings. Third, the aerodynamic phenomena and benefits produced by the flapping-wing interactions on tandem wings or biplane configurations are discussed. Such interactions occur on dragonflies or on a recently developed micro air vehicle. The currently available two-and three-dimensional inviscid and viscous flapping-wing flow solutions are presented. It is shown that the results are strongly dependent on flapping frequency, amplitude, and Reynolds number. These findings are substantiated by comparison with the available experimental data.

Research paper thumbnail of Reynolds number, thickness and camber effects on flapping airfoil propulsion

Journal of Fluids and Structures, 2011

The effect of varying airfoil thickness and camber on plunging and combined pitching and plunging... more The effect of varying airfoil thickness and camber on plunging and combined pitching and plunging airfoil propulsion at Reynolds number Re =200, 2000, 20 000 and 2 Â 10 6 was studied by numerical simulations for fully laminar and fully turbulent flow regimes. The thickness study was performed on 2-D NACA symmetric airfoils with 6-50% thick sections undergoing pure plunging motion at reduced frequency k= 2 and amplitudes h = 0.25 and 0.5, and for combined pitching and plunging motion at k=2, h =0.5, phase f=901, pitch angle y o =151 and 301 and the pitch axis was located at 1/3 of chord from leading edge. At Re = 200 for motions where positive thrust is generated, thin airfoils outperform thick airfoils. At higher Re significant gains could be achieved both in thrust generation and propulsive efficiency by using a thicker airfoil section for plunging and combined motion with low pitch amplitude. The camber study was performed on 2-D NACA airfoils with varying camber locations undergoing pure plunging motion at k=2, h = 0.5 and Re =20 000. Little variation in thrust performance was found with camber. The underlying physics behind the alteration in propulsive performance between low and high Reynolds numbers has been explored by comparing viscous Navier-Stokes and inviscid panel method results. The role of leading edge vortices was found to be key to the observed performance variation.

Research paper thumbnail of Numerical analysis of an oscillating-wing wind and hydropower generator

AIAA Journal, 2011

ABSTRACT The extraction of energy from wind or water streams is generally accomplished by means o... more ABSTRACT The extraction of energy from wind or water streams is generally accomplished by means of rotary systems. However, it is recognized and it has been demonstrated that oscillating wings can also be used for this purpose. A newly developed oscillating-wing wind and hydropower generator is described. Its potential for the generation of electric power from tidal flows and high-altitude jet streams is studied using two-dimensional Navier-Stokes simulations at Re = 20, 000. Results for a single NACA 0014 wing power generator undergoing nonsinusoidal pitch-plunge motion indicate around 17% increase in power generated and around 15% increase in efficiency over that for sinusoidal motion. Two airfoils operating in tandem, undergoing both sinusoidal and nonsinusoidal motions, are also studied. It is found that for sinusoidal motion both averaged power output and efficiency per foil are reduced by around 20% for tandem configurations compared with a single foil in sinusoidal motion, and similar performance reductions are experienced for nonsinusoidal motions.

Research paper thumbnail of Oscillation frequency and amplitude effects on plunging airfoil propulsion and flow periodicity

AIAA Journal, 2012

The flow over a NACA 0012 airfoil, oscillated sinusoidally in plunge, is simulated numerically us... more The flow over a NACA 0012 airfoil, oscillated sinusoidally in plunge, is simulated numerically using a compressible two-dimensional Navier-Stokes solver at a Reynolds number of 2× ×10 4 . The wake of the airfoil is visualized using a numerical particle tracing method. Close agreement is obtained between numerically simulated wake structures and experimental wake visualizations in the literature, when the flow is assumed to be fully laminar. The wake structures, and the lift and thrust of the airfoil, are shown to be strongly dependent on both the Strouhal number and the reduced frequency k of the plunge oscillation at this Reynolds number. Leading-edge separation appears to dominate the generation of aerodynamic forces for reduced frequencies below approximately k = 4 but becomes secondary for higher frequencies. Wake structures appear to be controlled primarily by trailing-edge effects at all frequencies tested up to k = 20. Aerodynamic force results obtained at this Reynolds number show marked differences from those predicted by potential flow analyses at low plunge frequency and high amplitude but are similar at high frequency and low amplitude, consistent with the effect of leading-edge separation.

Research paper thumbnail of Details of insect wing design and deformation enhance aerodynamic function and flight efficiency

Science (New York, N.Y.), Jan 18, 2009

Insect wings are complex structures that deform dramatically in flight. We analyzed the aerodynam... more Insect wings are complex structures that deform dramatically in flight. We analyzed the aerodynamic consequences of wing deformation in locusts using a three-dimensional computational fluid dynamics simulation based on detailed wing kinematics. We validated the simulation against smoke visualizations and digital particle image velocimetry on real locusts. We then used the validated model to explore the effects of wing topography and deformation, first by removing camber while keeping the same time-varying twist distribution, and second by removing camber and spanwise twist. The full-fidelity model achieved greater power economy than the uncambered model, which performed better than the untwisted model, showing that the details of insect wing topography and deformation are important aerodynamically. Such details are likely to be important in engineering applications of flapping flight.

Research paper thumbnail of Thyroid shields and neck exposures in cephalometric radiography

BMC Medical Imaging, 2006

The thyroid is among the more radiosensitive organs in the body. The goal of this study was twofo... more The thyroid is among the more radiosensitive organs in the body. The goal of this study was twofold: (1) to evaluate age-related changes in what is exposed to ionizing radiation in the neck area, and (2) to assess thyroid shield presence in cephalometric radiographs Methods: Cephalometric radiographs at one academic setting were sampled and neck exposure was related to calendar year and patient's gender and age.