SnO2@C@VO2 Composite Hollow Nanospheres as an Anode Material for Lithium-Ion Batteries.

PubMed

Guo, Wenbin; Wang, Yong; Li, Qingyuan; Wang, Dongxia; Zhang, Fanchao; Yang, Yiqing; Yu, Yang

2018-05-02

Porous SnO 2 @C@VO 2 composite hollow nanospheres were ingeniously constructed through the combination of layer-by-layer deposition and redox reaction. Moreover, to optimize the electrochemical properties, SnO 2 @C@VO 2 composite hollow nanospheres with different contents of the external VO 2 were also studied. On the one hand, the elastic and conductive carbon as interlayer in the SnO 2 @C@VO 2 composite can not only buffer the huge volume variation during repetitive cycling but also effectively improve electronic conductivity and enhance the utilizing rate of SnO 2 and VO 2 with high theoretical capacity. On the other hand, hollow nanostructures of the composite can be consolidated by the multilayered nanocomponents, resulting in outstanding cyclic stability. In virtue of the above synergetic contribution from individual components, SnO 2 @C@VO 2 composite hollow nanospheres exhibit a large initial discharge capacity (1305.6 mAhg -1 ) and outstanding cyclic stability (765.1 mAhg -1 after 100 cycles). This design of composite hollow nanospheres may be extended to the synthesis of other nanomaterials for electrochemical energy storage.

Increased plasma O2 solubility improves O2 uptake of in situ dog muscle working maximally.

PubMed

Hogan, M C; Willford, D C; Keipert, P E; Faithfull, N S; Wagner, P D

1992-12-01

A perfluorocarbon emulsion [formulation containing 90% wt/vol perflubron (perfluorooctylbromide); Alliance Pharmaceutical] was used to increase O2 solubility in the plasma compartment during hyperoxic low hemoglobin concentration ([Hb]) perfusion of a maximally working dog muscle in situ. Our hypothesis was that the increased plasma O2 solubility would increase the muscle O2 diffusing capacity (DO2) by augmenting the capillary surface area in contact with high [O2]. Oxygen uptake (VO2) was measured in isolated in situ canine gastrocnemius (n = 4) while working for 6 min at a maximal stimulation rate of 1 Hz (isometric tetanic contractions) on three to four separate occasions for each muscle. On each occasion, the last 4 min of the 6-min work period was split into 2 min of a control treatment (only emulsifying agent mixed into blood) and 2 min of perflubron treatment (6 g/kg body wt), reversing the order for each subsequent work bout. Before contractions, the [Hb] of the dog was decreased to 8-9 g/100 ml and arterial PO2 was increased to 500-600 Torr by having the dog breathe 100% O2 to maximize the effect of the perflubron. Muscle blood flow was held constant between the two experimental conditions. Plasma O2 solubility was almost doubled to 0.005 ml O2 x 100 ml blood-1 x Torr-1 by the addition of the perflubron. Muscle O2 delivery and maximal VO2 were significantly improved (at the same blood flow and [Hb]) by 11 and 12.6%, respectively (P < 0.05), during the perflubron treatment compared with the control. O2 extraction by the muscle remained the same between the two treatments, as did the estimate of DO2.(ABSTRACT TRUNCATED AT 250 WORDS)

Sputtering Deposition of Sandwich-Structured V2O5/Metal (V, W)/V2O5 Multilayers for the Preparation of High-Performance Thermally Sensitive VO2 Thin Films with Selectivity of VO2 (B) and VO2 (M) Polymorph.

PubMed

Liu, Hengwu; Wan, Dongyun; Ishaq, Ahmad; Chen, Lanli; Guo, Beibei; Shi, Siqi; Luo, Hongjie; Gao, Yanfeng

2016-03-01

For specific application to an uncooled infrared detector, VO2 thin films should have a series of characteristics including purposefully chosen polymorphs, accurate stoichiometry, phase stabilization, a high temperature-coefficient of resistance (TCR), and suitable square-resistance. This work reports controllable preparation of high-performance VO2 films via post annealing of a sandwich-structured V2O5/metal (V, W)/V2O5 multilayer precursor, which was deposited by RF magnetron sputtering. This sandwich structure can dynamically regulate oxygen contents and doping element levels in the films, enabling us to achieve accurate regulation of stoichiometry and polymorphs. The precursor films undergo a B to M phase transition depending on the quantity of the metal layers. At the thickness of the metal layer below a limitation, the resulting film after heat treatment was VO2 (B), and above the limitation, the product was VO2 (M). The optical modulation of the VO2 (M) in the near-infrared region can be tuned from 1.2 to 39.8% (ΔT2000 nm). TCR values can range from -1.89 to -4.29%/K and the square-resistances at room temperature (R0) from 69.68 to 12.63 kΩ. The simplicity in phase regulation of the present method and the superior optical and electrical properties of the films may allow its wide applications in thermo-opto-electro sensing devices.

C=C bond cleavage on neutral VO3(V2O5)n clusters.

PubMed

Dong, Feng; Heinbuch, Scott; Xie, Yan; Bernstein, Elliot R; Rocca, Jorge J; Wang, Zhe-Chen; Ding, Xun-Lei; He, Sheng-Gui

2009-01-28

The reactions of neutral vanadium oxide clusters with alkenes (ethylene, propylene, 1-butene, and 1,3-butadiene) are investigated by experiments and density function theory (DFT) calculations. Single photon ionization through extreme ultraviolet radiation (EUV, 46.9 nm, 26.5 eV) is used to detect neutral cluster distributions and reaction products. In the experiments, we observe products (V(2)O(5))(n)VO(2)CH(2), (V(2)O(5))(n)VO(2)C(2)H(4), (V(2)O(5))(n)VO(2)C(3)H(4), and (V(2)O(5))(n)VO(2)C(3)H(6), for neural V(m)O(n) clusters in reactions with C(2)H(4), C(3)H(6), C(4)H(6), and C(4)H(8), respectively. The observation of these products indicates that the C=C bonds of alkenes can be broken on neutral oxygen rich vanadium oxide clusters with the general structure VO(3)(V(2)O(5))(n=0,1,2...). DFT calculations demonstrate that the reaction VO(3) + C(3)H(6) --> VO(2)C(2)H(4) + H(2)CO is thermodynamically favorable and overall barrierless at room temperature. They also provide a mechanistic explanation for the general reaction in which the C=C double bond of alkenes is broken on VO(3)(V(2)O(5))(n=0,1,2...) clusters. A catalytic cycle for alkene oxidation on vanadium oxide is suggested based on our experimental and theoretical investigations. The reactions of V(m)O(n) with C(6)H(6) and C(2)F(4) are also investigated by experiments. The products VO(2)(V(2)O(5))(n)C(6)H(4) are observed for dehydration reactions between V(m)O(n) clusters and C(6)H(6). No product is detected for V(m)O(n) clusters reacting with C(2)F(4). The mechanisms of the reactions between VO(3) and C(2)F(4)/C(6)H(6) are also investigated by calculations at the B3LYP/TZVP level.

Structure and enhanced thermochromic performance of low-temperature fabricated VO2/V2O3 thin film

NASA Astrophysics Data System (ADS)

Sun, Guangyao; Cao, Xun; Gao, Xiang; Long, Shiwei; Liang, Mengshi; Jin, Ping

2016-10-01

For VO2-based smart window manufacture, it is a long-standing demand for high-quality thin films deposited at low temperature. Here, the thermochromic films of VO2 were deposited by a magnetron sputtering method at a fairly low temperature of 250 °C without subsequent annealing by embedding a V2O3 interlayer. V2O3 acts as a seed layer to lower the depositing temperature and buffer layer to epitaxial grow VO2 film. The VO2/V2O3 films display high solar modulating ability and narrow hysteresis loop. Our data can serve as a promising point for industrial production with high degree of crystallinity at a low temperature.

Williams with VO2max

NASA Image and Video Library

2012-08-08

ISS032-E-016876 (8 Aug. 2012) --- NASA astronaut Sunita Williams, Expedition 32 flight engineer, performs a VO2max experiment while using the Cycle Ergometer with Vibration Isolation System (CEVIS) in the Destiny laboratory of the International Space Station. VO2max uses the Portable Pulmonary Function System (PPFS), CEVIS, Pulmonary Function System (PFS) gas cylinders and mixing bag system, plus multiple other pieces of hardware to measure oxygen uptake and cardiac output.

Enhanced luminous transmittance of thermochromic VO2 thin film patterned by SiO2 nanospheres

NASA Astrophysics Data System (ADS)

Zhou, Liwei; Liang, Jiran; Hu, Ming; Li, Peng; Song, Xiaolong; Zhao, Yirui; Qiang, Xiaoyong

2017-05-01

In this study, an ordered SiO2 nanosphere array coated with vanadium dioxide (VO2) has been fabricated to enhance transmittance with the potential application as an energy-efficient coating in the field of smart windows. SiO2 arrays were formed using the methods of self-assembly, and VO2 thin films were prepared by rapid thermal annealing (RTA) of sputtered vanadium films. VO2@SiO2 arrays were characterized by scanning electron microscopy, X-ray diffraction, a four-point probe, and UV-vis-NIR spectrophotometry. Compared with the planar films, the films deposited on 300 nm diameter SiO2 nanospheres can offer approximately 18% enhancement of luminous transmission (Tlum) because the diameter is smaller than the given wavelength and the protuberance of the surface array behaves as a gradation of refractive index producing antireflection. The solar regulation efficiency was not much deteriorated.

A novel inorganic precipitation-peptization method for VO2 sol and VO2 nanoparticles preparation: Synthesis, characterization and mechanism.

PubMed

Li, Yao; Jiang, Peng; Xiang, Wei; Ran, Fanyong; Cao, Wenbin

2016-01-15

In this paper, a simple, safe and cost-saving precipitation-peptization method was proposed to prepare VO2 sol by using inorganic VOSO4-NH3⋅H2O-H2O2 reactants system in air under room temperature. In this process, VOSO4 was firstly precipitated to form VO(OH)2, then monometallic species of VO(O2)(OH)(-) were formed through the coordination between VO(OH)2 and H2O2. The rearrangement of VO(O2)(OH)(-) in a nonplanar pattern and intermolecular condensation reactions result in multinuclear species. Finally, VO2 sol is prepared through the condensation reactions between the multinuclear species. After drying the obtained sol at 40°C, VO2 xerogel exhibiting monoclinic crystal structure with the space group of C2/m was prepared. The crystal structure of VO2 nanoparticles was transferred to monoclinic crystal structure with the space group of P21/c (VO2(M)) by annealing the xerogel at 550°C. Both XRD and TEM analysis indicated that the nanoparticles possess good crystallinity with crystallite size of 34.5nm as estimated by Scherrer's method. These results suggest that the VO2 sol has been prepared successfully through the proposed simple method. Copyright © 2015 Elsevier Inc. All rights reserved.

Structure and enhanced thermochromic performance of low-temperature fabricated VO 2/V 2O 3 thin film

DOE PAGES

Sun, Guangyao; Cao, Xun; Gao, Xiang; ...

2016-10-06

For VO 2-based smart window manufacture, it is a long-standing demand for high-quality thin films deposited at low temperature. In this paper, the thermochromic films of VO 2 were deposited by a magnetron sputtering method at a fairly low temperature of 250 °C without subsequent annealing by embedding a V 2O 3 interlayer. V 2O 3 acts as a seed layer to lower the depositing temperature and buffer layer to epitaxial grow VO 2 film. The VO 2/V 2O 3 films display high solar modulating ability and narrow hysteresis loop. Finally, our data can serve as a promising point formore » industrial production with high degree of crystallinity at a low temperature.« less

Evaluation of Maximal Oxygen Uptake and Submaximal Estimates of VO2max Before, During, and After Long Duration International Space Station Missions

NASA Technical Reports Server (NTRS)

2008-01-01

Evaluation of Maximal Oxygen Uptake and Submaximal Estimates of VO2max Before, During, and After Long Duration International Space Station Missions (VO2max) will document changes in maximum oxygen uptake for crewmembers onboard the International Space Station (ISS) on long-duration missions, greater than 90 days. This investigation will establish the characteristics of VO2max during flight and assess the validity of the current methods of tracking aerobic capacity change during and following the ISS missions.

Ultrafast electron-lattice coupling dynamics in VO2 and V2O3 thin films

NASA Astrophysics Data System (ADS)

Abreu, Elsa; Gilbert Corder, Stephanie N.; Yun, Sun Jin; Wang, Siming; Ramírez, Juan Gabriel; West, Kevin; Zhang, Jingdi; Kittiwatanakul, Salinporn; Schuller, Ivan K.; Lu, Jiwei; Wolf, Stuart A.; Kim, Hyun-Tak; Liu, Mengkun; Averitt, Richard D.

2017-09-01

Ultrafast optical pump-optical probe and optical pump-terahertz probe spectroscopy were performed on vanadium dioxide (VO2) and vanadium sesquioxide (V2O3 ) thin films over a wide temperature range. A comparison of the experimental data from these two different techniques and two different vanadium oxides, in particular a comparison of the spectral weight oscillations generated by the photoinduced longitudinal acoustic modulation, reveals the strong electron-phonon coupling that exists in both materials. The low-energy Drude response of V2O3 appears more amenable than VO2 to ultrafast strain control. Additionally, our results provide a measurement of the temperature dependence of the sound velocity in both systems, revealing a four- to fivefold increase in VO2 and a three- to fivefold increase in V2O3 across the insulator-to-metal phase transition. Our data also confirm observations of strong damping and phonon anharmonicity in the metallic phase of VO2, and suggest that a similar phenomenon might be at play in the metallic phase of V2O3 . More generally, our simple table-top approach provides relevant and detailed information about dynamical lattice properties of vanadium oxides, paving the way to similar studies in other complex materials.

Time limit and VO2 slow component at intensities corresponding to VO2max in swimmers.

PubMed

Fernandes, R J; Cardoso, C S; Soares, S M; Ascensão, A; Colaço, P J; Vilas-Boas, J P

2003-11-01

The purpose of this study was to measure, in swimming pool conditions and with high level swimmers, the time to exhaustion at the minimum velocity that elicits maximal oxygen consumption (TLim at vVO(2)max), and the corresponding VO(2) slow component (O(2)SC). The vVO(2)max was determined through an intermittent incremental test (n = 15). Forty-eight hours later, TLim was assessed using an all-out swim at vVO(2)max until exhaustion. VO(2) was measured through direct oximetry and the swimming velocity was controlled using a visual light-pacer. Blood lactate concentrations and heart rate values were also measured. Mean VO(2)max for the incremental test was 5.09 +/- 0.53 l/min and the corresponding vVO(2)max was 1.46 +/- 0.06 m/s. Mean TLim value was 260.20 +/- 60.73 s and it was inversely correlated with the velocity of anaerobic threshold (r = -0.54, p < 0.05). This fact, associated with the inverse relationship between TLim and vVO(2)max (r = -0.47, but only for p < 0.10), suggested that swimmers' lower level aerobic metabolic rate might be associated with a larger capacity to sustain that exercise intensity. O(2)SC reached 274.11 +/- 152.83 l/min and was correlated with TLim (r = 0.54), increased ventilation in TLim test (r = 0.52) and energy cost of the respiratory muscles (r = 0.51), for p < 0.05. These data suggest that O(2)SC was also observed in the swimming pool, in high level swimmers performing at vVO(2)max, and that higher TLim seems to correspond to higher expected O(2)SC amplitude. These findings seem to bring new data with application in middle distance swimming.

Spectroscopic and optical properties of the VO2+ ion doped TeO2-TiO2-ZnO-Nb2O5 glass system

NASA Astrophysics Data System (ADS)

Swapna; Upender, G.; Sreenivasulu, V.; Prasad, M.

2016-04-01

Studies such as optical absorption, Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, Electron paramagnetic resonance (EPR) spectroscopy and Differential scanning calorimetry (DSC) were carried out on VO2+ ion doped TeO2-TiO2-ZnO-Nb2O5 glass system. Raman and FTIR spectra of the glasses revealed the presence of [TeO3], [TeO4] and [NbO6] structural units in the glass network. The Urbach energy (Δ E), cut-off wavelength (λ c ), optical band gap ( E opt ), optical basicity (Λ) and electron polarizability ( α) of the glasses were determined from optical absorption studies. The density ( ρ), molar volume ( V m ), oxygen molar volume ( V o ) and refractive index ( n) were also measured. Spin-Hamiltonian parameters were calculated from the EPR studies. When Nb2O5 was increased at the expense of ZnO, the density, optical band gap and Urbach energy of the glasses increased, and the electronic polarizability and optical basicity decreased. The EPR spectra clearly showed that vanadium was in the glass as VO2+ and occupied octahedral sites with tetrahedral compression. Spin-Hamiltonian parameters g‖ and g⊥ decreased as Nb2O5 content increased in the glass. The glass transition temperature ( T g ) also increased with increasing Nb2O5 content in the glass.

Min-By-Min Respiratory Exchange and Oxygen Uptake Kinetics During Steady-State Exercise in Subjects of High and Low Max VO2

ERIC Educational Resources Information Center

Weltman, Arthur; Katch, Victor

1976-01-01

No statistically meaningful differences in steady-state vo2 uptake for high and low max vo2 groups was indicated in this study, but a clear tendency was observed for the high max vo2 group to reach the steady-state at a faster rate. (MB)

Role of maximal heart rate and arterial O2 saturation on the decrement of VO2max in moderate acute hypoxia in trained and untrained men.

PubMed

Mollard, P; Woorons, X; Letournel, M; Cornolo, J; Lamberto, C; Beaudry, M; Richalet, J-P

2007-03-01

We aimed to evaluate 1) the altitude where maximal heart rate (HR (max)) decreases significantly in both trained and untrained subjects in moderate acute hypoxia, and 2) if the HR (max) decrease could partly explain the drop of V.O (2max). Seventeen healthy males, nine trained endurance athletes (TS) and eight untrained individuals (US) were studied. Subjects performed incremental exercise tests at sea level and at 5 simulated altitudes (1000, 1500, 2500, 3500, 4500 meters). Power output (PO), heart rate (HR), arterial oxygen saturation (SaO (2)), oxygen uptake (V.O (2)), arterialized blood pH and lactate were measured. Both groups showed a progressive reduction in V.O (2max). The decrement in HR (max) (DeltaHR (max)) was significant from 1000 m for TS and 2500 m for US and more important in TS than US (at 1500 m and 3500 m). At maximal exercise, TS had a greater reduction in SaO (2) (DeltaSaO (2)) at each altitude. DeltaHR (max) observed in TS was correlated with DeltaSaO (2). When the two groups were pooled, simple regressions showed that DeltaV.O (2max) was correlated with both DeltaSaO (2) and DeltaHR (max). However, a multiple regression analysis demonstrated that DeltaSaO (2) alone may account for DeltaV.O (2max). Furthermore, in spite of a greater reduction in SaO (2) and HR (max) in TS, no difference was evidenced in relative DeltaV.O (2max) between groups. Thus, in moderate acute hypoxia, the reduction in SaO (2) is the primary factor to explain the drop of V.O (2max) in trained and untrained subjects.

[{(Mo)Mo5O21(H2O)3(SO4)}12(VO)30(H2O)20]36-: a molecular quantum spin icosidodecahedron.

PubMed

Botar, Bogdan; Kögerler, Paul; Hill, Craig L

2005-07-07

Self-assembly of aqueous solutions of molybdate and vanadate under reducing, mildly acidic conditions results in a polyoxomolybdate-based {Mo72V30} cluster compound Na8K16(VO)(H2O)5[K10 subset{(Mo)Mo5O21(H2O)3(SO4)}12(VO)30(H2O)20].150H2O, 1, a quantum spin-based Keplerate structure.

Relation of oxygen uptake to work rate in prepubertal healthy children - reference for VO2/W-slope and effect on cardiorespiratory fitness assessment.

PubMed

Tompuri, Tuomo; Lintu, Niina; Laitinen, Tomi; Lakka, Timo A

2017-08-09

Exercise testing by cycle ergometer allows to observe the interaction between oxygen uptake (VO 2 ) and workload (W), and VO 2 /W-slope can be used as a diagnostic tool. Respectively, peak oxygen uptake (VO 2 PEAK ) can be estimated by maximal workload. We aim to determine reference for VO 2 /W-slope among prepubertal children and define agreement between estimated and measured VO 2 PEAK . A total of 38 prepubertal children (20 girls) performed a maximal cycle ergometer test with respiratory gas analysis. VO 2 /W-slopes were computed using linear regression. Agreement analysis by Bland and Altman for estimated and measured VO 2 PEAK was carried out including limits of agreement (LA). Determinants for VO 2 /W-slopes and estimation bias were defined. VO2/W-slope was in both girls and boys ≥9·4 and did not change with exercise level, but the oxygen cost of exercise was higher among physically more active children. Estimated VO 2 PEAK had 6·4% coefficient of variation, and LA varied from 13% underestimation to 13% overestimation. Bias had a trend towards underestimation along lean mass proportional VO 2 PEAK . The primary determinant for estimation bias was VO2/W-slope (β = -0·65; P<0·001). The reference values for VO 2 /W-slope among healthy prepubertal children were similar to those published for adults and among adolescents. Estimated and measured VO 2 PEAK should not be considered to be interchangeable because of the variation in the relationship between VO 2 and W. On other hand, variation in the relationship between VO 2 and W enables that VO 2 /W-slope can be used as a diagnostic tool. © 2017 Scandinavian Society of Clinical Physiology and Nuclear Medicine. Published by John Wiley & Sons Ltd.

Manganese Vanadate Chemistry in Hydrothermal BaF 2 Brines: Ba 3 Mn 2 (V 2 O 7 ) 2 F 2 and Ba 7 Mn 8 O 2 (VO 4 ) 2 F 23

DOE PAGES

Sanjeewa, Liurukara D.; McMillen, Colin D.; McGuire, Michael A.; ...

2016-12-05

We synthesized manganese vanadate fluorides using high-temperature hydrothermal techniques with BaF 2 as a mineralizer. Ba 3Mn 2(V 2O 7) 2F 2 crystallizes in space group C2/c and consists of dimers built from edge-sharing MnO 4F 2 trigonal prisms with linking V 2O 7 groups. Ba 7Mn 8O 2(VO 4) 2F 23 crystallizes in space group Cmmm, with a manganese oxyfluoride network built from edge- and corner-sharing Mn 2+/3+(O,F) 6 octahedra. The resulting octahedra form alternating Mn 2+ and Mn 2+/3+ layers separated by VO 4 tetrahedra. This latter compound exhibits a canted antiferromagnetic order below TN = 25 K.

Core-shell VO2@TiO2 nanorods that combine thermochromic and photocatalytic properties for application as energy-saving smart coatings.

PubMed

Li, Yamei; Ji, Shidong; Gao, Yanfeng; Luo, Hongjie; Kanehira, Minoru

2013-01-01

Vanadium dioxide (VO2) is a Mott phase transition compound that can be applied as a thermochromic smart material for energy saving and comfort, and titanium dioxide (TiO2) is a well-known photocatalyst for self-cleaning coatings. In this paper, we report a VO2@TiO2 core-shell structure, in which the VO2 nanorod core exhibits a remarkable modulation ability for solar infrared light, and the TiO2 anatase shell exhibits significant photocatalytic degradation of organic dye. In addition, the TiO2 overcoating not only increased the luminous transmittance of VO2 based on an antireflection effect, but also modified the intrinsic colour of VO2 films from yellow to light blue. The TiO2 also enhanced the chemical stability of VO2 against oxidation. This is the first report of such a single nanoparticle structure with both thermochromic and photocatalytic properties that offer significant potential for creating a multifunctional smart coating.

Core-shell VO2@TiO2 nanorods that combine thermochromic and photocatalytic properties for application as energy-saving smart coatings

PubMed Central

Li, Yamei; Ji, Shidong; Gao, Yanfeng; Luo, Hongjie; Kanehira, Minoru

2013-01-01

Vanadium dioxide (VO2) is a Mott phase transition compound that can be applied as a thermochromic smart material for energy saving and comfort, and titanium dioxide (TiO2) is a well-known photocatalyst for self-cleaning coatings. In this paper, we report a VO2@TiO2 core-shell structure, in which the VO2 nanorod core exhibits a remarkable modulation ability for solar infrared light, and the TiO2 anatase shell exhibits significant photocatalytic degradation of organic dye. In addition, the TiO2 overcoating not only increased the luminous transmittance of VO2 based on an antireflection effect, but also modified the intrinsic colour of VO2 films from yellow to light blue. The TiO2 also enhanced the chemical stability of VO2 against oxidation. This is the first report of such a single nanoparticle structure with both thermochromic and photocatalytic properties that offer significant potential for creating a multifunctional smart coating. PMID:23546301

Study on Thermochromic VO2 Films Grown on ZnO-Coated Glass Substrates for “Smart Windows”

NASA Astrophysics Data System (ADS)

Kato, Kazuhiro; Song, Pung Keun; Odaka, Hidehumi; Shigesato, Yuzo

2003-10-01

Vanadium dioxide (VO2) is one of the most attractive thermochromic materials, which show large changes in optical and electrical properties at the transition temperature (Tt) close to the atmospheric temperature (approximately 340 K). We already reported for VO2 deposition by rf magnetron sputtering using V2O3 or V2O5 targets that VO2 films thicker than 400 nm showed high thermochromic performance, whereas the VO2 films thinner than 200 nm did not show such performance because of their poor crystallinity and off-stoichiometry. In this study, very thin thermochromic VO2 films with thicknesses of about 50 nm were successfully deposited using highly < 001>-preferred oriented ZnO polycrystalline films as a buffer layer between the VO2 film and glass substrate (VO2/ZnO/glass) because of the heteroepitaxial growth of VO2 polycrystalline films. W-doped VO2 films were also deposited on the ZnO-coated glass substrates (ZnO/glass) by cosputtering. It was confirmed that W doping for thin VO2 films deposited on the ZnO/glass can decrease Tt systematically. Such very thin VO2 films should have high potential for application in “smart windows”.

Hydrothermal Syntheses and Structures of Three-Dimensional Oxo-fluorovanadium Phosphates: [H 2N(C 2H 4) 2NH 2] 0.5[(VO) 4V(HPO 4) 2(PO 4) 2F 2(H 2O) 4] · 2H 2O and K 2[(VO) 3(PO 4) 2F 2(H 2O)] · H 2O

NASA Astrophysics Data System (ADS)

Bonavia, Grant; Haushalter, R. C.; Zubieta, Jon

1996-11-01

The hydrothermal reactions of FPO3H2with vanadium oxides result in the incorporation of fluoride into V-P-O frameworks as a consequence of metal-mediated hydrolysis of the fluorophosphoric acid to produce F-and PO3-4. By exploiting this convenient source of F-, two 3-dimensional oxo-fluorovanadium phosphate phases were isolated, [H2N(C2H4)2NH2]0.5[(VO)4V(HOP4)2(PO4)2F2(H2O)4) · 2H2O (1 · 2H2O) and K2[(VO)3(PO4)2F2(H2O)] · H2O (2 · H2O). Both anionic frameworks contain (VIVO)-F--phosphate layers, with confacial bioctahedral {(VIVO)2FO6} units as the fundamental motif. In the case of 1, the layers are linked through {VIIIO6} octahedra, while for 2 the interlayer connectivity is provided by edge-sharing {(VIVO)2F2O6} units. Crystal data are 1 · 2H2O, CH10FN0.5O13P2V2.5, monoclinicC2/m,a= 18.425(4) Å,c= 8.954(2) Å, β = 93.69(2)0,V= 1221.1(4) Å3,Z= 4,Dcalc= 2.423 g cm-3; 2 · H2O, H4F2K2O13P2V3, triclinicPoverline1,a= 7.298(1) Å,b= 8.929(2) Å,c = 10.090(2) Å, α = 104.50(2)0, β = 100.39(2)0, δ = 92.13(2)0,V= 623.8(3) Å3,Z= 2,Dcalc= 2.891 g cm-3.

Enhanced Visible Transmittance of Thermochromic VO2 Thin Films by SiO2 Passivation Layer and Their Optical Characterization

PubMed Central

Yu, Jung-Hoon; Nam, Sang-Hun; Lee, Ji Won; Boo, Jin-Hyo

2016-01-01

This paper presents the preparation of high-quality vanadium dioxide (VO2) thermochromic thin films with enhanced visible transmittance (Tvis) via radio frequency (RF) sputtering and plasma enhanced chemical vapor deposition (PECVD). VO2 thin films with high Tvis and excellent optical switching efficiency (Eos) were successfully prepared by employing SiO2 as a passivation layer. After SiO2 deposition, the roughness of the films was decreased 2-fold and a denser structure was formed. These morphological changes corresponded to the results of optical characterization including the haze, reflectance and absorption spectra. In spite of SiO2 coating, the phase transition temperature (Tc) of the prepared films was not affected. Compared with pristine VO2, the total layer thickness after SiO2 coating was 160 nm, which is an increase of 80 nm. Despite the thickness change, the VO2 thin films showed a higher Tvis value (λ 650 nm, 58%) compared with the pristine samples (λ 650 nm, 43%). This enhancement of Tvis while maintaining high Eos is meaningful for VO2-based smart window applications. PMID:28773679

Rapid hydrothermal synthesis of VO2 (B) and its conversion to thermochromic VO2 (M1).

PubMed

Popuri, Srinivasa Rao; Miclau, Marinela; Artemenko, Alla; Labrugere, Christine; Villesuzanne, Antoine; Pollet, Michaël

2013-05-06

The present study provides a rapid way to obtain VO2 (B) under economical and environmentally friendly conditions. VO2 (B) is one of the well-known polymorphs of vanadium dioxide and is a promising cathode material for aqueous lithium ion batteries. VO2 (B) was successfully synthesized by rapid single-step hydrothermal process using V2O5 and citric acid as precursors. The present study shows that phase-pure VO2 (B) polytype can be easily obtained at 180 °C for 2 h and 220 °C for 1 h, that is, the lowest combination of temperature and duration reported so far. The obtained VO2 (B) is characterized by X-ray powder diffraction, high-resolution scanning electron microscopy, and Fourier transform infrared spectroscopy. In addition, we present an indirect way to obtain VO2 (M1) by annealing VO2 (B) under vacuum for 1 h.

Low-Cost and Facile Synthesis of the Vanadium Oxides V2O3, VO2, and V2O5 and Their Magnetic, Thermochromic and Electrochromic Properties.

PubMed

Mjejri, Issam; Rougier, Aline; Gaudon, Manuel

2017-02-06

In this study, vanadium sesquioxide (V 2 O 3 ), dioxide (VO 2 ), and pentoxide (V 2 O 5 ) were all synthesized from a single polyol route through the precipitation of an intermediate precursor: vanadium ethylene glycolate (VEG). Various annealing treatments of the VEG precursor, under controlled atmosphere and temperature, led to the successful synthesis of the three pure oxides, with sub-micrometer crystallite size. To the best of our knowledge, the synthesis of the three oxides V 2 O 5 , VO 2 , and V 2 O 3 from a single polyol batch has never been reported in the literature. In a second part of the study, the potentialities brought about by the successful preparation of sub-micrometer V 2 O 5 , VO 2 , and V 2 O 3 are illustrated by the characterization of the electrochromic properties of V 2 O 5 films, a discussion about the metal to insulator transition of VO 2 on the basis of in situ measurements versus temperature of its electrical and optical properties, and the characterization of the magnetic transition of V 2 O 3 powder from SQUID measurements. For the latter compound, the influence of the crystallite size on the magnetic properties is discussed.

Theoretical investigations of the local distortion and spectral properties for VO2+ in SiO2 Glass

NASA Astrophysics Data System (ADS)

Li, Mu-Neng; Zhang, Zhi-Hong; Wu, Shao-Yi

2017-11-01

The local distortions and the spin Hamiltonian parameters g factors g∥, g⊥ and the hyperfine structure constants A∥ and A⊥ for isolated vanadyl ions VO2+ doped in SiO2 glass at 700°C are theoretically investigated from the perturbation formulas of these parameters for a 3d1 ion in tetragonally compressed octahedra. In these formulas, the relationships between local structure of VO2+ ions center and the tetragonal crystal field parameters are established. As a result, the distortion of the ligand octahedron is attributed to the strong axial crystal-fields associated with the short V4+-O2- bond due to the strong V=O bonding in the silica matrix. The theoretical spin Hamiltonian parameters obtained in this work show reasonable agreement with the experimental data.

Low-level laser therapy improves the VO2 kinetics in competitive cyclists.

PubMed

Lanferdini, Fábio J; Krüger, Renata L; Baroni, Bruno M; Lazzari, Caetano; Figueiredo, Pedro; Reischak-Oliveira, Alvaro; Vaz, Marco A

2018-04-01

Some evidence supports that low-level laser therapy (LLLT) reduces neuromuscular fatigue, so incrementing sports performance. A previous randomized controlled trial of our group showed increased exercise tolerance in male competitive cyclists treated with three different LLLT doses (3, 6, and 9 J/diode; or 135, 270, and 405 J/thigh) before time-to-exhaustion cycling tests. Now, the present study was designed to evaluate the effects of these LLLT doses on the VO 2 kinetics of athletes during cycling tests. Twenty male competitive cyclists (29 years) participated in a crossover, randomized, double-blind, and placebo-controlled trial. On the first day, the participants performed an incremental cycling test to exhaustion to determine maximal oxygen uptake (VO 2MAX ) and maximal power output (PO MAX ), as well as a familiarization with the time-to-exhaustion test. In the following days (2 to 5), all participants performed time-to-exhaustion tests at PO MAX . Before the exhaustion test, different doses of LLLT (3, 6, and 9 J/diode; or 135, 270, and 405 J/thigh, respectively) or placebo were applied bilaterally to the quadriceps muscle. All exhaustion tests were monitored online by an open-circuit spirometry system in order to analyze the VO 2 amplitude, VO 2 delay time, time constant (tau), and O 2 deficit. Tau and O 2 deficit were decreased with LLLT applications compared to the placebo condition (p < 0.05). No differences (p > 0.05) were found between the experimental conditions for VO 2 amplitude and VO 2 delay time. In conclusion, LLLT decreases tau and O 2 deficit during time-to-exhaustion tests in competitive cyclists, and these changes in VO 2 kinetics response can be one of the possible mechanisms to explain the ergogenic effect induced by LLLT.

Characterization of pulsed laser deposition grown V2O3 converted VO2

NASA Astrophysics Data System (ADS)

Majid, Suhail; Shukla, D. K.; Rahman, F.; Gautam, Kamini; Sathe, V. G.; Choudhary, R. J.; Phase, D. M.

2016-10-01

Controllable tuning of Metal-insulator transition in VxOy thin film has been a field of extensive research. However controlled synthesis of desired Vanadium oxide phase is a challenging task. We have successfully achieved VO2 phase on Silicon substrate after post deposition annealing treatment to the PLD grown as deposited V2O3 thin films. The annealed thin film was characterized by x-ray diffraction (XRD), resistivity, Raman spectroscopy, X-ray absorption spectroscopy (XAS) and X-ray photoelectron spectroscopy (XPS) measurements. XRD confirms the crystalline nature and growth of VO2 phase in thin film. The characteristic MIT was observed from resistivity measurements and transition temperature appeared at lower value around 336 K, compared to bulk VO2. The structural transition accompanied with MIT from lower temperature monoclinic phase to higher temperature Rutile phase became evident from temperature dependent Raman measurements. Chemical state of vanadium was examined using XAS and XPS measurements which confirm the presence of +4 oxidation state of vanadium in thin film.

Anti-biofouling function of amorphous nano-Ta2O5 coating for VO2-based intelligent windows.

PubMed

Li, Jinhua; Guo, Geyong; Wang, Jiaxing; Zhou, Huaijuan; Shen, Hao; Yeung, Kelvin W K

2017-04-28

From environmental and health perspectives, the acquisition of a surface anti-biofouling property holds important significance for the usability of VO 2 intelligent windows. Herein, we firstly deposited amorphous Ta 2 O 5 nanoparticles on VO 2 film by the magnetron sputtering method. It was found that the amorphous nano-Ta 2 O 5 coating possessed a favorable anti-biofouling capability against Pseudomonas aeruginosa as an environmental microorganism model, behind which lay the mechanism that the amorphous nano-Ta 2 O 5 could interrupt the microbial membrane electron transport chain and significantly elevate the intracellular reactive oxygen species (ROS) level. A plausible relationship was established between the anti-biofouling activity and physicochemical nature of amorphous Ta 2 O 5 nanoparticles from the perspective of defect chemistry. ROS-induced oxidative damage gave rise to microbial viability loss. In addition, the amorphous nano-Ta 2 O 5 coating can endow VO 2 with favorable cytocompatibility with human skin fibroblasts. This study may provide new insights into understanding the anti-biofouling and antimicrobial actions of amorphous transition metal oxide nanoparticles, which is conducive to expanding their potential applications in environmental fields.

Anti-biofouling function of amorphous nano-Ta2O5 coating for VO2-based intelligent windows

NASA Astrophysics Data System (ADS)

Li, Jinhua; Guo, Geyong; Wang, Jiaxing; Zhou, Huaijuan; Shen, Hao; Yeung, Kelvin W. K.

2017-04-01

From environmental and health perspectives, the acquisition of a surface anti-biofouling property holds important significance for the usability of VO2 intelligent windows. Herein, we firstly deposited amorphous Ta2O5 nanoparticles on VO2 film by the magnetron sputtering method. It was found that the amorphous nano-Ta2O5 coating possessed a favorable anti-biofouling capability against Pseudomonas aeruginosa as an environmental microorganism model, behind which lay the mechanism that the amorphous nano-Ta2O5 could interrupt the microbial membrane electron transport chain and significantly elevate the intracellular reactive oxygen species (ROS) level. A plausible relationship was established between the anti-biofouling activity and physicochemical nature of amorphous Ta2O5 nanoparticles from the perspective of defect chemistry. ROS-induced oxidative damage gave rise to microbial viability loss. In addition, the amorphous nano-Ta2O5 coating can endow VO2 with favorable cytocompatibility with human skin fibroblasts. This study may provide new insights into understanding the anti-biofouling and antimicrobial actions of amorphous transition metal oxide nanoparticles, which is conducive to expanding their potential applications in environmental fields.

Role of interfacial transition layers in VO2/Al2O3 heterostructures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhou, Honghui; Chisholm, Matthew F; Yang, Tsung-Han

2011-01-01

Epitaxial VO2 films grown by pulsed laser deposition (PLD) on c-cut sapphire substrates ((0001) Al2O3) were studied by aberration-corrected scanning transmission electron microscopy (STEM). A number of film/substrate orientation relationships were found and are discussed in the context of the semiconductor-metal transition (SMT) characteristics. A structurally and electronically modified buffer layer was revealed on the interface and was attributed to the interface free-energy minimization process of accommodating the symmetry mismatch between the substrate and the film. This interfacial transition layer is expected to affect the SMT behavior when the interfacial region is a significant fraction of the VO2 film thickness.

Enhanced photoelectrochemical response of plasmonic Au embedded BiVO4/Fe2O3 heterojunction.

PubMed

Verma, Anuradha; Srivastav, Anupam; Khan, Saif A; Rani Satsangi, Vibha; Shrivastav, Rohit; Kumar Avasthi, Devesh; Dass, Sahab

2017-06-14

The effect of embedding Au nanoparticles (NPs) in a BiVO 4 /Fe 2 O 3 heterojunction for photoelectrochemical water splitting is studied here for the first time. The present nanostructured heterojunction offers three major advantages over pristine BiVO 4 and Fe 2 O 3 : (i) the formation of a heterojunction between BiVO 4 and Fe 2 O 3 enhances the charge carrier separation and transfer, (ii) the layer of Fe 2 O 3 provides protection to BiVO 4 from photocorrosion and, (iii) the Au NPs possessing surface plasmon resonance (SPR) enhance the photoelectrochemical response by transferring energy to metal oxides by hot electron transfer (HET) and plasmon resonant energy transfer (PRET). The present study reveals that the heterojunction ITO/BiVO 4 /Fe 2 O 3 (with 32% v/v Au solution in both layers) gives the best performance and mitigates the limitations of both pristine Fe 2 O 3 and BiVO 4 . A thirteen-fold increment in applied bias photon-to-current conversion efficiency (ABPE) was observed at 1.24 V vs. RHE under the condition of 1 Sun illumination. Monochromatic incident photon-to-current conversion efficiency (IPCE) measurements indicated that an Au embedded heterojunction is more effective in harvesting visible light in comparison to a heterojunction without Au NPs.

Facile Phase Control of Multivalent Vanadium Oxide Thin Films (V2O5 and VO2) by Atomic Layer Deposition and Postdeposition Annealing.

PubMed

Song, Gwang Yeom; Oh, Chadol; Sinha, Soumyadeep; Son, Junwoo; Heo, Jaeyeong

2017-07-19

Atomic layer deposition was adopted to deposit VO x thin films using vanadyl tri-isopropoxide {VO[O(C 3 H 7 )] 3 , VTIP} and water (H 2 O) at 135 °C. The self-limiting and purge-time-dependent growth behaviors were studied by ex situ ellipsometry to determine the saturated growth conditions for atomic-layer-deposited VO x . The as-deposited films were found to be amorphous. The structural, chemical, and optical properties of the crystalline thin films with controlled phase formation were investigated after postdeposition annealing at various atmospheres and temperatures. Reducing and oxidizing atmospheres enabled the formation of pure VO 2 and V 2 O 5 phases, respectively. The possible band structures of the crystalline VO 2 and V 2 O 5 thin films were established. Furthermore, an electrochemical response and a voltage-induced insulator-to-metal transition in the vertical metal-vanadium oxide-metal device structure were observed for V 2 O 5 and VO 2 films, respectively.

End-exercise ΔHHb/ΔVO2 and post-exercise local oxygen availability in relation to exercise intensity.

PubMed

Stöcker, F; Von Oldershausen, C; Paternoster, F K; Schulz, T; Oberhoffer, R

2017-07-01

Increased local blood supply is thought to be one of the mechanisms underlying oxidative adaptations to interval training regimes. The relationship of exercise intensity with local blood supply and oxygen availability has not been sufficiently evaluated yet. The aim of this study was to examine the effect of six different intensities (40-90% peak oxygen uptake, VO 2peak ) on relative changes in oxygenated, deoxygenated and total haemoglobin (ΔO 2 Hb, ΔHHb, ΔTHb) concentration after exercise as well as end-exercise ΔHHb/ΔVO 2 as a marker for microvascular O 2 distribution. Seventeen male subjects performed an experimental protocol consisting of 3 min cycling bouts at each exercise intensity in randomized order, separated by 5 min rests. ΔO 2 Hb and ΔHHb were monitored with near-infrared spectroscopy of the vastus lateralis muscle, and VO 2 was assessed. ΔHHb/ΔVO 2 increased significantly from 40% to 60% VO 2 peak and decreased from 60% to 90% VO 2 peak. Post-exercise ΔTHb and ΔO 2 Hb showed an overshoot in relation to pre-exercise values, which was equal after 40-60% VO 2peak and rose significantly thereafter. A plateau was reached following exercise at ≥80% VO 2peak . The results suggest that there is an increasing mismatch of local O 2 delivery and utilization during exercise up to 60% VO 2peak . This insufficient local O 2 distribution is progressively improved above that intensity. Further, exercise intensities of ≥80% VO 2peak induce highest local post-exercise O 2 availability. These effects are likely due to improved microvascular perfusion by enhanced vasodilation, which could be mediated by higher lactate production and the accompanying acidosis. © 2015 Scandinavian Society of Clinical Physiology and Nuclear Medicine. Published by John Wiley & Sons Ltd.

The 1201 superconductors Hg1-y(VO4)y(Ba, Sr)2CuO4-2y+δ: evidence for VO4 tetrahedra

NASA Astrophysics Data System (ADS)

Malo, S.; Hervieu, M.; Maignan, A.; Knížek, K.; Raveau, B.; Michel, C.

1997-02-01

A series of mercury based cuprates with nominal composition Hg1-yV(y)Ba2-xSrxCuO4+2y+δ has been prepared for x = 0, 0.25, 0.5, 0.75, 1 and 1.25. The actual solid solution limit from the EDS measurement is x = 1.1, y ranges from 0.2 to 0.35. The single crystal study coupled with high resolution electron microscopy shows for the first time the presence of VO4 tetrahedra replacing partly the mercury atoms according to the formulation Hg1-y(VO4)y(Ba,Sr)2 CuO4-2y+δ. The role of vanadium for the stabilisation of the structure and as a doping agent in the superconducting properties is discussed.

Understanding bactericidal performance on ambient light activated TiO2-InVO4 nanostructured films.

PubMed

He, Ziming; Xu, Qingchi; Tan, Timothy Thatt Yang

2011-12-01

TiO(2)-InVO(4) nanostructured films were coated onto glass substrates and systematically investigated for their bactericidal activities using Escherichia coli (E. coli) as the model bacterium under ambient light illumination. The uniform TiO(2)-InVO(4) nanostructured films were prepared using titanium isopropoxide (TTIP) as the precursor via a simple sol-gel approach. Polyethylenimine (PEI) was used as a surfactant to ensure uniform dispersion of InVO(4) and a sacrificial pore-inducing agent, generating nanostructured films. Compared to unmodified TiO(2) film, the current TiO(2)-InVO(4) films exhibited enhanced bactericidal activities under ambient light illumination. Bacterial cell "photo-fixation" was demonstrated to be crucial in enhancing the bactericidal activity. A bacterial-nanostructured surface interaction mechanism was proposed for the current ambient-light activated nanostructured film.

Synthesis of novel CeO2-BiVO4/FAC composites with enhanced visible-light photocatalytic properties.

PubMed

Zhang, Jin; Wang, Bing; Li, Chuang; Cui, Hao; Zhai, Jianping; Li, Qin

2014-09-01

To utilize visible light more effectively in photocatalytic reactions, a fly ash cenosphere (FAC)-supported CeO2-BiVO4 (CeO2-BiVO4/FAC) composite photocatalyst was prepared by modified metalorganic decomposition and impregnation methods. The physical and photophysical properties of the composite have been characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), and UV-Visible diffuse reflectance spectra. The XRD patterns exhibited characteristic diffraction peaks of both BiVO4 and CeO2 crystalline phases. The XPS results showed that Ce was present as both Ce(4+) and Ce(3+) oxidation states in CeO2 and dispersed on the surface of BiVO4 to constitute a p-n heterojunction composite. The absorption threshold of the CeO2-BiVO4/FAC composite shifted to a longer wavelength in the UV-Vis absorption spectrum compared to the pure CeO2 and pure BiVO4. The composites exhibited enhanced photocatalytic activity for Methylene Blue (MB) degradation under visible light irradiation. It was found that the 7.5wt.% CeO2-BiVO4/FAC composite showed the highest photocatalytic activity for MB dye wastewater treatment. Copyright © 2014. Published by Elsevier B.V.

Matching characteristics of different buffer layers with VO2 thin films

NASA Astrophysics Data System (ADS)

Yang, Kai; Zhang, Dongping; Liu, Yi; Guan, Tianrui; Qin, Xiaonan; Zhong, Aihua; Cai, Xingmin; Fan, Ping; Lv, Weizhong

2016-10-01

VO2 thin films were fabricated by reactive DC magnetron sputtering on different buffer layers of MgF2, Al2O3 and TiO2, respectively. The crystallinity and orientation relationship, thickness of VO2 thin films, atoms vibrational modes, optical and electrical property, surface morphology of films were characterized by X-ray diffraction, Raman scattering microscopy, step profiler, spectrophotometer, four-probe technique, and scanning electron microscopy, respectively. XRD results investigated that the films have preferential crystalline planes VO2 (011). The crystallinity of VO2 films grown on TiO2 buffer layers are superior to VO2 directly deposited on soda-lime glass. The Raman bands of the VO2 films correspond to an Ag symmetry mode of VO2 (M). The sample prepared on 100nm TiO2 buffer layer appears nanorods structure, and exhibits remarkable solar energy modulation ability as high as 5.82% in full spectrum and 23% in near infrared spectrum. Cross-sectional SEM image of the thin films samples indicate that MgF2 buffer layer has clear interface with VO2 layer. But there are serious interdiffusion phenomenons between Al2O3, TiO2 buffer layer with VO2 layer.

Synthesis and characterization of new fluoride-containing manganese vanadates A2Mn2V2O7F2 (A=Rb, Cs) and Mn2VO4F

NASA Astrophysics Data System (ADS)

Sanjeewa, Liurukara D.; McGuire, Michael A.; Smith Pellizzeri, Tiffany M.; McMillen, Colin D.; Ovidiu Garlea, V.; Willett, Daniel; Chumanov, George; Kolis, Joseph W.

2016-09-01

Large single crystals of A2Mn2V2O7F2 (A=Rb, Cs) and Mn2VO4F were grown using a high-temperature (~600 °C) hydrothermal technique. Single crystal X-ray diffraction and powder X-ray diffraction were utilized to characterize the structures, which both possess MnO4F2 building blocks. The A2Mn2V2O7F2 series crystallizes as a new structure type in space group Pbcn (No. 60), Z=4 (Rb2Mn2V2O7F2: a=7.4389(17) Å, b=11.574(3) Å, c=10.914(2) Å; Cs2Mn2V2O7F2: a=7.5615(15) Å, b=11.745(2) Å, c=11.127(2) Å). The structure is composed of zigzag chains of edge-sharing MnO4F2 units running along the a-axis, and interconnected through V2O7 pyrovanadate groups. Temperature dependent magnetic susceptibility measurements on this interesting one-dimensional structural feature based on Mn2+ indicated that Cs2Mn2V2O7F2 is antiferromagnetic with a Neél temperature, TN=~3 K and a Weiss constant, θ, of -11.7(1) K. Raman and infrared spectra were also analyzed to identify the fundamental V-O vibrational modes in Cs2Mn2V2O7F2. Mn2(VO4)F crystalizes in the monoclinic space group of C2/c (no. 15), Z=8 with unit cell parameters of a=13.559(2) Å, b=6.8036(7) Å, c=10.1408(13) Å and β=116.16(3)°. The structure is associated with those of triplite and wagnerite. Dynamic fluorine disorder gives rise to complex alternating chains of five-and six-coordinate Mn2+. These interpenetrating chains are additionally connected through isolated VO4 tetrahedra to form the condensed structure.

Bymixer system can measure O2 uptake and CO2 elimination in the anesthesia circle circuit.

PubMed

Rosenbaum, Abraham; Kirby, Christopher W; Breen, Peter H

2007-06-01

The ability to measure carbon dioxide elimination (Vco(2)), oxygen uptake (Vo(2)), and R (respiratory exchange ratio, Vco(2)/Vo(2)) during anesthesia may help the non-invasive detection of critical events (e.g., abrupt decrease in cardiac output) and metabolic upset (e.g., onset of anaerobic metabolism). We have developed a new clinical bymixer (inline mixing chamber) that can measure mixed inspired and expired gas fractions in the anesthesia circle circuit. The addition of a standard anesthesia gas analyzer and flowmeter, and a new airway temperature and humidity sensor, allow determinations of Vco(2) and Vo(2) at the airway opening of the circle circuit. Over a range of tidal volume and frequency, Vco(2) and Vo(2) were compared to reference values generated by the combustion of metered liquid ethanol in a new metabolic lung simulator. By linear regression, bymixer-flow measurements of Vco(2) (slope = 1.02, Y-intercept = -5.31, coefficient of determination, R(2) = 0.998) and Vo(2) (slope = 1.05, Y-intercept = -4.34, R(2) = 0.993) correlated closely to the reference values generated by the metabolic lung simulator. Limits of agreement analysis generated percent errors (mean +/- 1.96 SD) of -1.2 +/- 7.2% for Vco(2) and 2.5 +/- 9.8% for Vo(2). The new clinical bymixer is compact, lightweight, disposable, inexpensive, and has a fast and adjustable response time (time constant about 14 sec). Anesthesia circle circuit integrity is maintained. Bymixer-flow measurements of Vco(2) and Vo(2) are accurate and may add to clinical monitoring under anesthesia and surgery.

Effects of V2O3 buffer layers on sputtered VO2 smart windows: Improved thermochromic properties, tunable width of hysteresis loops and enhanced durability

NASA Astrophysics Data System (ADS)

Long, Shiwei; Cao, Xun; Sun, Guangyao; Li, Ning; Chang, Tianci; Shao, Zewei; Jin, Ping

2018-05-01

Vanadium dioxide (VO2) is one of the most well-known thermochromic materials, which exhibits a notable optical change from transparent to reflecting in the infrared region upon a metal-insulator phase transition. For practical applications, VO2 thin films should be in high crystalline quality to obtain a strong solar modulation ability (ΔTsol). Meanwhile, narrow hysteresis loops and robust ambient durability are also indispensable for sensitivity and long-lived utilization, respectively. In this work, a series of high-quality V2O3/VO2 bilayer structures were grown on quartz glass substrates by reactive magnetron sputtering. Basically, the bottom V2O3 acts as the buffer layer to improve the crystallinity of the top VO2, while the VO2 serves as the thermochromic layer to guarantee the solar modulation ability for energy-saving. We observed an obvious increase in ΔTsol of 76% (from 7.5% to 13.2%) for VO2 films after introducing V2O3 buffer layers. Simultaneously, a remarkable reduction by 79% (from 21.9 °C to 4.7 °C) in width of hysteresis loop was obtained when embedding 60 nm V2O3 buffer for 60 nm VO2. In addition, VO2 with non-stoichiometry of V2O3±x buffer demonstrates a broadening hysteresis loops width, which is derived from the lattice distortion caused by lattice imperfection. Finally, durability of VO2 has been significantly improved due to positive effects of V2O3 buffer layer. Our results lead to a comprehensive enhancement in crystallinity of VO2 and shed new light on the promotion of thermochromic property by homologous oxides for VO2.

Electric field induced metal-insulator transition in VO2 thin film based on FTO/VO2/FTO structure

NASA Astrophysics Data System (ADS)

Hao, Rulong; Li, Yi; Liu, Fei; Sun, Yao; Tang, Jiayin; Chen, Peizu; Jiang, Wei; Wu, Zhengyi; Xu, Tingting; Fang, Baoying

2016-03-01

A VO2 thin film has been prepared using a DC magnetron sputtering method and annealing on an F-doped SnO2 (FTO) conductive glass substrate. The FTO/VO2/FTO structure was fabricated using photolithography and a chemical etching process. The temperature dependence of the I-V hysteresis loop for the FTO/VO2/FTO structure has been analyzed. The threshold voltage decreases with increasing temperature, with a value of 9.2 V at 20 °C. The maximum transmission modulation value of the FTO/VO2/FTO structure is 31.4% under various temperatures and voltages. Optical modulation can be realized in the structure by applying an electric field.

Ab Initio Metadynamics Study of the VO2+/VO2+ Redox Reaction Mechanism at the Graphite Edge/Water Interface.

PubMed

Jiang, Zhen; Klyukin, Konstantin; Alexandrov, Vitaly

2018-06-20

Redox flow batteries (RFBs) are promising electrochemical energy storage systems, for which development is impeded by a poor understanding of redox reactions occurring at electrode/electrolyte interfaces. Even for the conventional all-vanadium RFB chemistry employing V 2+ /V 3+ and VO 2 + /VO 2+ couples, there is still no consensus about the reaction mechanism, electrode active sites, and rate-determining step. Herein, we perform Car-Parrinello molecular dynamics-based metadynamics simulations to unravel the mechanism of the VO 2 + /VO 2+ redox reaction in water at the oxygen-functionalized graphite (112̅0) edge surface serving as a representative carbon-based electrode. Our results suggest that during the battery discharge aqueous VO 2 + /VO 2+ species adsorb at the surface C-O groups as inner-sphere complexes, exhibiting faster adsorption/desorption kinetics than V 2+ /V 3+ , at least at low vanadium concentrations considered in our study. We find that this is because (i) VO 2 + /VO 2+ conversion does not involve the slow transfer of an oxygen atom, (ii) protonation of VO 2 + is spontaneous and coupled to interfacial electron transfer in acidic conditions to enable VO 2+ formation, and (iii) V 3+ found to be strongly bound to oxygen groups of the graphite surface features unfavorable desorption kinetics. In contrast, the reverse process taking place upon charging is expected to be more sluggish for the VO 2 + /VO 2+ redox couple because of both unfavorable deprotonation of the VO 2+ water ligands and adsorption/desorption kinetics.

Structural, thermal and optical properties of TeO2-ZnO-CdO-BaO glasses doped with VO(2+).

PubMed

Sreenivasulu, V; Upender, G; Chandra Mouli, V; Prasad, M

2015-09-05

The glasses with composition 64TeO2-15ZnO-(20-x)CdO-xBaO-1V2O5 (0⩽x⩽20 mol%) were prepared by conventional melt quenching technique. X-ray diffraction analysis was used to confirm the amorphous nature of the glasses. The optical absorption studies revealed that the cut-off wavelength (λα) decreases while optical band gap energy (Eopt) and Urbach energy (ΔE) values increase with an increase of BaO content. Refractive index (n) evaluated from Eopt was found to decrease with an increase of BaO content. The physical parameters such as density (ρ), molar volume (Vm), oxygen packing density (OPD), optical basicity (Λ), molar refraction (Rm), and metallization criterion (M) evaluated and discussed. FTIR and Raman spectroscopic studies showed that the glass network consists of TeO4, TeO3+1/TeO3 and ZnO4 units as basic structural units. The glass transition temperature (Tg) of glass sample, onset crystallization temperature (To) and thermal stability ΔT were determined from Differential Scanning Calorimetry (DSC). Using electron paramagnetic resonance (EPR) spectra of vanadium glasses the spin Hamiltonian parameters and dipolar hyperfine coupling parameters of VO(2+) ions were calculated. It was found that V(4+) ions in these glasses exist as VO(2+) in octahedral coordination with a tetragonal distortion and have C4V symmetry with ground state dxy. Tetragonality (Δg∥/Δg⊥) of vanadium ion sites exhibited non-linear variation with BaO content. Copyright © 2015 Elsevier B.V. All rights reserved.

Effect of Toe Clips During Bicycle Ergometry on VO2 max.

ERIC Educational Resources Information Center

Moffat, Roger S.; Sparling, Phillip B.

1985-01-01

Eight men participated in three randomized maximal oxygen uptake tests to investigate the hypothesis that the use of toe clips on bicycle ergometers produced a higher VO2 max. No significant difference in mean VO2 max or performance time was observed. (Author/MT)

Pulmonary O2 uptake and leg blood flow kinetics during moderate exercise are slowed by hyperventilation-induced hypocapnic alkalosis.

PubMed

Chin, Lisa M K; Heigenhauser, George J F; Paterson, Donald H; Kowalchuk, John M

2010-06-01

The effect of hyperventilation-induced hypocapnic alkalosis (Hypo) on the adjustment of pulmonary O2 uptake (VO2p) and leg femoral conduit artery ("bulk") blood flow (LBF) during moderate-intensity exercise (Mod) was examined in eight young male adults. Subjects completed four to six repetitions of alternate-leg knee-extension exercise during normal breathing [Con; end-tidal partial pressure of CO2 (PetCO2) approximately 40 mmHg] and sustained hyperventilation (Hypo; PetCO2 approximately 20 mmHg). Increases in work rate were made instantaneously from baseline (3 W) to Mod (80% estimated lactate threshold). VO2p was measured breath by breath by mass spectrometry and volume turbine, and LBF (calculated from mean femoral artery blood velocity and femoral artery diameter) was measured simultaneously by Doppler ultrasound. Concentration changes of deoxy (Delta[HHb])-, oxy (Delta[O2Hb])-, and total hemoglobin-myoglobin (Delta[HbTot]) of the vastus lateralis muscle were measured continuously by near-infrared spectroscopy (NIRS). The kinetics of VO2p, LBF, and Delta[HHb] were modeled using a monoexponential equation by nonlinear regression. The time constants for the phase 2 VO2p (Hypo, 49+/-26 s; Con, 28+/-8 s) and LBF (Hypo, 46+/-16 s; Con, 23+/-6 s) were greater (P<0.05) in Hypo compared with Con. However, the mean response time for the overall Delta[HHb] response was not different between conditions (Hypo, 23+/-5 s; Con, 24+/-3 s), whereas the Delta[HHb] amplitude was greater (P<0.05) in Hypo (8.05+/-7.47 a.u.) compared with Con (6.69+/-6.31 a.u.). Combined, these results suggest that hyperventilation-induced hypocapnic alkalosis is associated with slower convective (i.e., slowed femoral artery and microvascular blood flow) and diffusive (i.e., greater fractional O2 extraction for a given DeltaVO2p) O2 delivery, which may contribute to the hyperventilation-induced slowing of VO2p (and muscle O2 utilization) kinetics.

Fabrication of bristlegrass-like VO2 (B)-ZnO heteroarchitectures as anode materials for lithium-ion batteries

NASA Astrophysics Data System (ADS)

Ma, Yining; Li, Wenjing; Ji, Shidong; Zhou, Huaijuan; Li, Rong; Li, Ning; Yao, Heliang; Cao, Xun; Jin, Ping

2017-08-01

Three-dimensional bristlegrass-like hierarchical VO2 (B)-ZnO heteroarchitectures with ZnO nanorods grown radially on VO2 (B) nanorods were successfully fabricated via a simple two-step synthesized method. When applied as an anode material for lithium-ion batteries, the VO2 (B)-ZnO hybrid electrode exhibited high reversible capacity and excellent recyclability, which could be originated from the unique hierarchical structure of the bristlegrass. After 80 cycles, the nanocomposite still maintained a higher reversible capacity of 329.4 mA h g-1 at a current density of 50 mA g-1. Therefore, the particular architecture of VO2 (B)-ZnO nanocomposite can be a promising candidate as the anode material in lithium-ion batteries.

Investigation of the physical, optical, and photocatalytic properties of CeO2/Fe-doped InVO4 composite

NASA Astrophysics Data System (ADS)

Chaison, Jindaporn; Wetchakun, Khatcharin; Wetchakun, Natda

2017-12-01

The CeO2/Fe-doped InVO4 composites with various Fe concentrations (0.5, 1.0, 2.0, 5.0 and 6.0 mol%) was synthesized by homogeneous precipitation and hydrothermal methods. The as-synthesized samples were characterized by powder X-ray diffraction (XRD), Brunauer Emmett and Teller (BET)-specific surface area, field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), and UV-visible diffuse reflectance spectroscopy (DRS). Fe-doping into InVO4 crystal induces the distortion of the crystalline structure, the transformation of InVO4 morphology, and the new energy subband level generation of Fe between the CB and VB edge of InVO4. The electron excitation from the VB to Fe orbitals results in the decreased band gap and the extended absorption of visible-light, and thus enhances its photocatalytic performance. Visible-light-driven photocatalytic degradation of Rhodamine B (RhB) dye in water was used to evaluate the photocatalytic performance of CeO2/Fe-doped InVO4 composites. The results revealed that there is an optimum Fe (5.0 mol %) doping level. The composite with the optimum doping level obtains high photocatalytic activity of CeO2/Fe-doped InVO4 composite compared to pure CeO2 and pure InVO4 host. The increase of photocatalytic activity of CeO2/Fe-doped InVO4 composite was ascribed to the surface area, crystal defect, and band gap energy. Moreover, the photocatalytic enhancement is also because iron ions act as a trapping site, which results in the higher separation efficiency of photogenerated electrons and holes pairs in the CeO2/InVO4 composite. The evaluation of radical scavengers confirmed that hydroxyl radical was the main active species during the photodegradation of RhB. These synergistic effects are responsible for the enhanced photocatalytic activity of CeO2/Fe-doped InVO4 composite. Furthermore, the possible enhanced photocatalytic mechanism

The electro-optic mechanism and infrared switching dynamic of the hybrid multilayer VO2/Al:ZnO heterojunctions.

PubMed

Zhang, Peng; Zhang, Wu; Wang, Junyong; Jiang, Kai; Zhang, Jinzhong; Li, Wenwu; Wu, Jiada; Hu, Zhigao; Chu, Junhao

2017-06-30

Active and widely controllable phase transition optical materials have got rapid applications in energy-efficient electronic devices, field of meta-devices and so on. Here, we report the optical properties of the vanadium dioxide (VO 2 )/aluminum-doped zinc oxide (Al:ZnO) hybrid n-n type heterojunctions and the corresponding electro-optic performances of the devices. Various structures are fabricated to compare the discrepancy of the optical and electrical characteristics. It was found that the reflectance spectra presents the wheel phenomenon rather than increases monotonically with temperature at near-infrared region range. The strong interference effects was found in the hybrid multilayer heterojunction. In addition, the phase transition temperature decreases with increasing the number of the Al:ZnO layer, which can be ascribed to the electron injection to the VO 2 film from the Al:ZnO interface. Affected by the double layer Al:ZnO, the abnormal Raman vibration mode was presented in the insulator region. By adding the external voltage on the Al 2 O 3 /Al:ZnO/VO 2 /Al:ZnO, Al 2 O 3 /Al:ZnO/VO 2 and Al 2 O 3 /VO 2 /Al:ZnO thin-film devices, the infrared optical spectra of the devices can be real-time manipulated by an external voltage. The main effect of joule heating and assistant effect of electric field are illustrated in this work. It is believed that the results will add a more thorough understanding in the application of the VO 2 /transparent conductive film device.

Coherently coupled ZnO and VO2 interface studied by photoluminescence and electrical transport across a phase transition

NASA Astrophysics Data System (ADS)

Srivastava, Amar; Herng, T. S.; Saha, Surajit; Nina, Bao; Annadi, A.; Naomi, N.; Liu, Z. Q.; Dhar, S.; Ariando; Ding, J.; Venkatesan, T.

2012-06-01

We have investigated the photoluminescence and electrical properties of a coherently coupled interface consisting of a ZnO layer grown on top of an oriented VO2 layer on sapphire across the phase transition of VO2. The band edge and defect luminescence of the ZnO overlayer exhibit hysteresis in opposite directions induced by the phase transition of VO2. Concomitantly the phase transition of VO2 was seen to induce defects in the ZnO layer. Such coherently coupled interfaces could be of use in characterizing the stability of a variety of interfaces in situ and also for novel device application.

New intelligent multifunctional SiO2/VO2 composite films with enhanced infrared light regulation performance, solar modulation capability, and superhydrophobicity

NASA Astrophysics Data System (ADS)

Wang, Chao; Zhao, Li; Liang, Zihui; Dong, Binghai; Wan, Li; Wang, Shimin

2017-12-01

Highly transparent, energy-saving, and superhydrophobic nanostructured SiO2/VO2 composite films have been fabricated using a sol-gel method. These composite films are composed of an underlying infrared (IR)-regulating VO2 layer and a top protective layer that consists of SiO2 nanoparticles. Experimental results showed that the composite structure could enhance the IR light regulation performance, solar modulation capability, and hydrophobicity of the pristine VO2 layer. The transmittance of the composite films in visible region (Tlum) was higher than 60%, which was sufficient to meet the requirements of glass lighting. Compared with pristine VO2 films and tungsten-doped VO2 film, the near IR control capability of the composite films was enhanced by 13.9% and 22.1%, respectively, whereas their solar modulation capability was enhanced by 10.9% and 22.9%, respectively. The water contact angles of the SiO2/VO2 composite films were over 150°, indicating superhydrophobicity. The transparent superhydrophobic surface exhibited a high stability toward illumination as all the films retained their initial superhydrophobicity even after exposure to 365 nm light with an intensity of 160 mW.cm-2 for 10 h. In addition, the films possessed anti-oxidation and anti-acid properties. These characteristics are highly advantageous for intelligent windows or solar cell applications, given that they can provide surfaces with anti-fogging, rainproofing, and self-cleaning effects. Our technique offers a simple and low-cost solution to the development of stable and visible light transparent superhydrophobic surfaces for industrial applications.

New intelligent multifunctional SiO2/VO2 composite films with enhanced infrared light regulation performance, solar modulation capability, and superhydrophobicity.

PubMed

Wang, Chao; Zhao, Li; Liang, Zihui; Dong, Binghai; Wan, Li; Wang, Shimin

2017-01-01

Highly transparent, energy-saving, and superhydrophobic nanostructured SiO 2 /VO 2 composite films have been fabricated using a sol-gel method. These composite films are composed of an underlying infrared (IR)-regulating VO 2 layer and a top protective layer that consists of SiO 2 nanoparticles. Experimental results showed that the composite structure could enhance the IR light regulation performance, solar modulation capability, and hydrophobicity of the pristine VO 2 layer. The transmittance of the composite films in visible region ( T lum ) was higher than 60%, which was sufficient to meet the requirements of glass lighting. Compared with pristine VO 2 films and tungsten-doped VO 2 film, the near IR control capability of the composite films was enhanced by 13.9% and 22.1%, respectively, whereas their solar modulation capability was enhanced by 10.9% and 22.9%, respectively. The water contact angles of the SiO 2 /VO 2 composite films were over 150°, indicating superhydrophobicity. The transparent superhydrophobic surface exhibited a high stability toward illumination as all the films retained their initial superhydrophobicity even after exposure to 365 nm light with an intensity of 160 mW . cm -2 for 10 h. In addition, the films possessed anti-oxidation and anti-acid properties. These characteristics are highly advantageous for intelligent windows or solar cell applications, given that they can provide surfaces with anti-fogging, rainproofing, and self-cleaning effects. Our technique offers a simple and low-cost solution to the development of stable and visible light transparent superhydrophobic surfaces for industrial applications.

Multiple Pathways for Benzyl Alcohol Oxidation by Ru V=O 3+ and Ru IV=O 2+

DOE Office of Scientific and Technical Information (OSTI.GOV)

Paul, Amit; Hull, Jonathan F.; Norris, Michael R.

2011-01-20

Significant rate enhancements are found for benzyl alcohol oxidation by the Ru V=O 3+ form of the water oxidation catalyst [Ru(Mebimpy)(bpy)(OH 2)] 2+ [Mebimpy = 2,6-bis(1-methylbenzimidazol-2-yl)pyridine; bpy = 2,2'-bipyridine] compared to Ru IV=O 2+ and for the Ru IV=O 2+ form with added bases due to a new pathway, concerted hydride proton transfer (HPT).

Photocatalytic Water Splitting for O2 Production under Visible Light Irradiation Using NdVO4-V2O5 Hybrid Powders

PubMed Central

Chiang, Tzu Hsuan; Chen, Tso-Ming

2017-01-01

The study investigated photocatalytic water splitting for O2 production under visible light irradiation using neodymium vanadium oxide (NdVO4) and vanadium oxide (V2O5) hybrid powders. The results in a sacrificial agent of 0.01 M AgNO3 solution were obtained, and the highest photocatalytic O2 evolution was 2.63 μmol/h, when the hybrid powders were prepared by mixing Nd and V at a volume ratio of 1:3 at a calcination temperature of 350 °C for 1 h. The hybrid powders were synthesized by neodymium nitrate and ammonium metavanadate using the glycothermal method in ethylene glycol at 120 °C for 1 h. The hybrid powders consisted of two shapes, NdVO4 nanoparticles and the cylindrical V2O5 particles, and they possessed the ability for photocatalytic oxygen (O2) evolution during irradiation with visible light. The band gaps and structures of the hybrid powders were analyzed using UV-visible spectroscopy and transmission electron microscopy. PMID:28772692

Pulmonary and leg VO2 during submaximal exercise: implications for muscular efficiency

NASA Technical Reports Server (NTRS)

Poole, D. C.; Gaesser, G. A.; Hogan, M. C.; Knight, D. R.; Wagner, P. D.

1992-01-01

Insights into muscle energetics during exercise (e.g., muscular efficiency) are often inferred from measurements of pulmonary gas exchange. This procedure presupposes that changes of pulmonary O2 (VO2) associated with increases of external work reflect accurately the increased muscle VO2. The present investigation addressed this issue directly by making simultaneous determinations of pulmonary and leg VO2 over a range of work rates calculated to elicit 20-90% of maximum VO2 on the basis of prior incremental (25 or 30 W/min) cycle ergometry. VO2 for both legs was calculated as the product of twice one-leg blood flow (constant-infusion thermodilution) and arteriovenous O2 content difference across the leg. Measurements were made 3-5 min after each work rate imposition to avoid incorporation of the VO2 slow component above the lactate threshold. For all 17 subjects, the slope of pulmonary VO2 (9.9 +/- 0.2 ml O2.W-1.min-1) was not different (P greater than 0.05) from that for leg VO2 (9.2 +/- 0.6 ml O2.W-1.min-1). Estimation of "delta" efficiency (i.e., delta work accomplished divided by delta energy expended, calculated from slope of VO2 vs. work rate and a caloric equivalent for O2 of 4.985 cal/ml) using pulmonary VO2 measurements (29.1 +/- 0.6%) was likewise not significantly different (P greater than 0.05) from that made using leg VO2 measurements (33.7 +/- 2.4%). These data suggest that the net VO2 cost of metabolic "support" processes outside the exercising legs changes little over a relatively broad range of exercise intensities. Thus, under the conditions of this investigation, changes of VO2 measured from expired gas reflected closely those occurring within the exercising legs.

n-VO2/p-GaN based nitride-oxide heterostructure with various thickness of VO2 layer grown by MBE

NASA Astrophysics Data System (ADS)

Wang, Minhuan; Bian, Jiming; Sun, Hongjun; Liu, Weifeng; Zhang, Yuzhi; Luo, Yingmin

2016-12-01

High quality VO2 films with precisely controlled thickness were grown on p-GaN/sapphire substrates by oxide molecular beam epitaxy (O-MBE). Results indicated that a distinct reversible semiconductor-to-metal (SMT) phase transition was observed for all the samples in the temperature dependent electrical resistance measurement, and the influence of VO2 layer thickness on the SMT properties of the as-grown n-VO2/p-GaN based nitride-oxide heterostructure was investigated. Meanwhile, the clear rectifying transport characteristics originated from the n-VO2/p-GaN interface were demonstrated before and after SMT of the VO2 over layer, which were attributed to the p-n junction behavior and Schottky contact character, respectively. Moreover, the X-ray photoelectron spectroscopy (XPS) analyses confirmed the valence state of vanadium (V) in VO2 films was principally composed of V4+ with trace amount of V5+. The design and modulation of the n-VO2/p-GaN based heterostructure devices will benefit significantly from these achievements.

Metastable α-AgVO3 microrods as peroxidase mimetics for colorimetric determination of H2O2.

PubMed

Wang, Yi; Zhang, Dun; Wang, Jin

2017-12-01

Single phase metastable α-AgVO 3 microrods with high crystallinity, tetragonal rod-like microstructure, uniform particle size distribution, and good dispersion were synthesized by direct coprecipitation at room temperature. They are shown to be viable peroxidase mimics that catalyze the oxidation of 3,3',5,5'-tetramethylbenzidine in the presence of H 2 O 2 . Kinetic analysis indicated typical Michaelis-Menten catalytic behavior. The findings were used to design a colorimetric assay for H 2 O 2 , best measured at 652 nm. The method has a linear response in the 60 to 200 μM H 2 O 2 concentration range, with a 2 μM detection limit. Benefitting from the chemical stability of the microrods, the method is well reproducible. It also is easily performed and highly specific. Graphic abstract Single phase metastable α-AgVO 3 microrods with high crystallinity, tetragonal rod-like microstructure, uniform particle size distribution, and good dispersion can efficiently catalyze the oxidation reaction of peroxidase substrate 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of H 2 O 2 to produce a blue color change.

Two-Dimensional SiO2/VO2 Photonic Crystals with Statically Visible and Dynamically Infrared Modulated for Smart Window Deployment.

PubMed

Ke, Yujie; Balin, Igal; Wang, Ning; Lu, Qi; Tok, Alfred Iing Yoong; White, Timothy J; Magdassi, Shlomo; Abdulhalim, Ibrahim; Long, Yi

2016-12-07

Two-dimensional (2D) photonic structures, widely used for generating photonic band gaps (PBG) in a variety of materials, are for the first time integrated with the temperature-dependent phase change of vanadium dioxide (VO 2 ). VO 2 possesses thermochromic properties, whose potential remains unrealized due to an undesirable yellow-brown color. Here, a SiO 2 /VO 2 core/shell 2D photonic crystal is demonstrated to exhibit static visible light tunability and dynamic near-infrared (NIR) modulation. Three-dimensional (3D) finite difference time domain (FDTD) simulations predict that the transmittance can be tuned across the visible spectrum, while maintaining good solar regulation efficiency (ΔT sol = 11.0%) and high solar transmittance (T lum = 49.6%). Experiments show that the color changes of VO 2 films are accompanied by NIR modulation. This work presents a novel way to manipulate VO 2 photonic structures to modulate light transmission as a function of wavelength at different temperatures.

Multiple Pathways for Benzyl Alcohol Oxidation by Ru V=O 3+ and Ru IV=O 2+

DOE Office of Scientific and Technical Information (OSTI.GOV)

Paul, Amit; Hull, Jonathan F.; Norris, Michael R.

2011-01-20

Significant rate enhancements are found for benzyl alcohol oxidation by the Ru V=O 3+ form of the water oxidation catalyst [Ru(Mebimpy)(bpy)(OH 2)] 2+ [Mebimpy = 2,6-bis(1-methylbenzimidazol-2-yl)pyridine; bpy = 2,2'-bipyridine] compared to Ru IV=O 2+ and for the Ru IV=O 2+ form with added bases due to a new pathway involving concerted hydride proton transfer (HPT).

Influence of acute moderate hypoxia on time to exhaustion at vVO2max in unacclimatized runners.

PubMed

Billat, V L; Lepretre, P M; Heubert, R P; Koralsztein, J P; Gazeau, F P

2003-01-01

Eight unacclimatized long-distance runners performed, on a level treadmill, an incremental test to determine the maximal oxygen uptake (VO2max) and the minimal velocity eliciting VO2max (vVO2max) in normoxia (N) and acute moderate hypoxia (H) corresponding to an altitude of 2,400 m (PIO 2 of 109 mmHg). Afterwards, on separate days, they performed two all-out constant velocity runs at vO2 max in a random order (one in N and the other in H). The decrease in VO2max between N and H showed a great degree of variability amongst subjects as VO2max decreased by 8.9 +/- 4 ml x min(-1) x kg)(-1) in H vs. N conditions (-15.3 +/- 6.3 % with a range from -7.9 % to -23.8 %). This decrease in VO2max was proportional to the value of VO2max (VO2max vs. delta VO2max N-H, r = 0.75, p = 0.03). The time run at vVO2max was not affected by hypoxia (483 +/- 122 vs. 506 +/- 148 s, in N and H, respectively, p = 0.37). However, the greater the decrease in vVO2max during hypoxia, the greater the runners increased their time to exhaustion at vVO2max (vVO2max N-H vs. tlim @vVO2max N-H, r = -0.75, p = 0.03). In conclusion, this study showed that there was a positive association between the extent of decrease in vVO2max, and the increase in run time at vVO2max in hypoxia.

TiO2/BiVO4 Nanowire Heterostructure Photoanodes Based on Type II Band Alignment

PubMed Central

2016-01-01

Metal oxides that absorb visible light are attractive for use as photoanodes in photoelectrosynthetic cells. However, their performance is often limited by poor charge carrier transport. We show that this problem can be addressed by using separate materials for light absorption and carrier transport. Here, we report a Ta:TiO2|BiVO4 nanowire photoanode, in which BiVO4 acts as a visible light-absorber and Ta:TiO2 acts as a high surface area electron conductor. Electrochemical and spectroscopic measurements provide experimental evidence for the type II band alignment necessary for favorable electron transfer from BiVO4 to TiO2. The host–guest nanowire architecture presented here allows for simultaneously high light absorption and carrier collection efficiency, with an onset of anodic photocurrent near 0.2 V vs RHE, and a photocurrent density of 2.1 mA/cm2 at 1.23 V vs RHE. PMID:27163032

Facile synthesis, phase transition, optical switching and oxidation resistance properties of belt-like VO{sub 2}(A) and VO{sub 2}(M) with a rectangular cross section

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Yifu; Huang, Yanfen; Zhang, Juecheng

2012-08-15

Highlights: ► Belt-like VO{sub 2}(A) with a rectangular cross section was synthesized. ► The formation mechanism of belt-like VO{sub 2}(A) was proposed. ► Belt-like VO{sub 2}(M) was prepared by the irreversible transformation of VO{sub 2}(A). ► VO{sub 2}(A) and VO{sub 2}(M) can be used as the optical switching materials. ► VO{sub 2}(A) and VO{sub 2}(M) have good oxidation resistance below 400 °C in air. -- Abstract: Belt-like VO{sub 2}(A) with a rectangular cross section (VA-RCS) was successfully synthesized using V{sub 2}O{sub 5}, H{sub 2}C{sub 2}O{sub 4}·2H{sub 2}O and H{sub 2}O as the starting materials by a facile hydrothermal approach. Somemore » synthetic parameters, such as, the reaction time, reaction temperature and concentration of H{sub 2}C{sub 2}O{sub 4}·2H{sub 2}O, were systematically investigated to control the fabrication of belt-like VA-RCS. The formation mechanism of belt-like VA-RCS was proposed. Subsequently, belt-like VO{sub 2}(M) with a rectangular cross section (VM-RCS) was prepared by the irreversible transformation of VA-RCS at 700 °C for 2 h under the inert atmosphere. The phase transition temperature (T{sub c}) of VA-RCS and VM-RCS was evaluated by DSC test. The optical switching properties of VA-RCS and VM-RCS were studied by the variable-temperature infrared spectra, and it was found that the as-obtained VA-RCS and VM-RCS could be used as the optical switching materials. Furthermore, the oxidation resistance properties of VA-RCS and VM-RCS were investigated by TGA, indicating that they have good thermal stability and oxidation resistance below 400 °C in air.« less

New intelligent multifunctional SiO2/VO2 composite films with enhanced infrared light regulation performance, solar modulation capability, and superhydrophobicity

PubMed Central

Wang, Chao; Zhao, Li; Liang, Zihui; Dong, Binghai; Wan, Li; Wang, Shimin

2017-01-01

Abstract Highly transparent, energy-saving, and superhydrophobic nanostructured SiO2/VO2 composite films have been fabricated using a sol–gel method. These composite films are composed of an underlying infrared (IR)-regulating VO2 layer and a top protective layer that consists of SiO2 nanoparticles. Experimental results showed that the composite structure could enhance the IR light regulation performance, solar modulation capability, and hydrophobicity of the pristine VO2 layer. The transmittance of the composite films in visible region (T lum) was higher than 60%, which was sufficient to meet the requirements of glass lighting. Compared with pristine VO2 films and tungsten-doped VO2 film, the near IR control capability of the composite films was enhanced by 13.9% and 22.1%, respectively, whereas their solar modulation capability was enhanced by 10.9% and 22.9%, respectively. The water contact angles of the SiO2/VO2 composite films were over 150°, indicating superhydrophobicity. The transparent superhydrophobic surface exhibited a high stability toward illumination as all the films retained their initial superhydrophobicity even after exposure to 365 nm light with an intensity of 160 mW.cm−2 for 10 h. In addition, the films possessed anti-oxidation and anti-acid properties. These characteristics are highly advantageous for intelligent windows or solar cell applications, given that they can provide surfaces with anti-fogging, rainproofing, and self-cleaning effects. Our technique offers a simple and low-cost solution to the development of stable and visible light transparent superhydrophobic surfaces for industrial applications. PMID:28970866

Familial aggregation of VO(2max) response to exercise training: results from the HERITAGE Family Study.

PubMed

Bouchard, C; An, P; Rice, T; Skinner, J S; Wilmore, J H; Gagnon, J; Pérusse, L; Leon, A S; Rao, D C

1999-09-01

The aim of this study was to test the hypothesis that individual differences in the response of maximal O(2) uptake (VO(2max)) to a standardized training program are characterized by familial aggregation. A total of 481 sedentary adult Caucasians from 98 two-generation families was exercise trained for 20 wk and was tested for VO(2max) on a cycle ergometer twice before and twice after the training program. The mean increase in VO(2max) reached approximately 400 ml/min, but there was considerable heterogeneity in responsiveness, with some individuals experiencing little or no gain, whereas others gained >1.0 l/min. An ANOVA revealed that there was 2.5 times more variance between families than within families in the VO(2max) response variance. With the use of a model-fitting procedure, the most parsimonious models yielded a maximal heritability estimate of 47% for the VO(2max) response, which was adjusted for age and sex with a maternal transmission of 28% in one of the models. We conclude that the trainability of VO(2max) is highly familial and includes a significant genetic component.

Synthesis and characterization of new fluoride-containing manganese vanadates A 2Mn 2V 2O 7F 2 (A=Rb, Cs) and Mn 2VO 4F

DOE PAGES

Sanjeewa, Liurukara D.; McGuire, Michael A.; Smith Pellizzeri, Tiffany M.; ...

2016-05-10

In large single crystals of A 2Mn 2V 2O 7F 2 (A=Rb, Cs) and Mn 2VO 4F were grown using a high-temperature (~600 °C) hydrothermal technique. We utilized single crystal X-ray diffraction and powder X-ray diffraction in order to characterize the structures, which both possess MnO 4F 2 building blocks. The A 2Mn 2V 2O 7F 2 series crystallizes as a new structure type in space group Pbcn (No. 60), Z=4 (Rb 2Mn 2V 2O 7F 2: a=7.4389(17) Å, b=11.574(3) Å, c=10.914(2) Å; Cs 2Mn 2V 2O 7F 2: a=7.5615(15) Å, b=11.745(2) Å, c=11.127(2) Å). The structure is composed ofmore » zigzag chains of edge-sharing MnO 4F 2 units running along the a-axis, and interconnected through V 2O 7 pyrovanadate groups. Temperature dependent magnetic susceptibility measurements on this interesting one-dimensional structural feature based on Mn 2+ indicated that Cs 2Mn 2V 2O 7F 2 is antiferromagnetic with a Neél temperature, TN=~3 K and a Weiss constant, θ, of -11.7(1) K. Raman and infrared spectra were also analyzed to identify the fundamental V–O vibrational modes in Cs 2Mn 2V 2O 7F 2. Mn 2(VO 4)F crystalizes in the monoclinic space group of C2/c (no. 15), Z=8 with unit cell parameters of a=13.559(2) Å, b=6.8036(7) Å, c=10.1408(13) Å and β=116.16(3)°. The structure is associated with those of triplite and wagnerite. Dynamic fluorine disorder gives rise to complex alternating chains of five-and six-coordinate Mn 2+. Our interpenetrating chains are additionally connected through isolated VO 4 tetrahedra to form the condensed structure.« less

The self-paced VO2max test to assess maximal oxygen uptake in highly trained runners.

PubMed

Hogg, James S; Hopker, James G; Mauger, Alexis R

2015-03-01

The novel self-paced maximal-oxygen-uptake (VO2max) test (SPV) may be a more suitable alternative to traditional maximal tests for elite athletes due to the ability to self-regulate pace. This study aimed to examine whether the SPV can be administered on a motorized treadmill. Fourteen highly trained male distance runners performed a standard graded exercise test (GXT), an incline-based SPV (SPVincline), and a speed-based SPV (SPVspeed). The GXT included a plateau-verification stage. Both SPV protocols included 5×2-min stages (and a plateau-verification stage) and allowed for self-pacing based on fixed increments of rating of perceived exertion: 11, 13, 15, 17, and 20. The participants varied their speed and incline on the treadmill by moving between different marked zones in which the tester would then adjust the intensity. There was no significant difference (P=.319, ES=0.21) in the VO2max achieved in the SPVspeed (67.6±3.6 mL·kg(-1)·min(-1), 95%CI=65.6-69.7 mL·kg(-1)·min(-1)) compared with that achieved in the GXT (68.6±6.0 mL·kg(-1)·min(-1), 95%CI=65.1-72.1 mL·kg(-1)·min(-1)). Participants achieved a significantly higher VO2max in the SPVincline (70.6±4.3 mL·kg(-1)·min(-1), 95%CI=68.1-73.0 mL·kg(-1)·min(-1)) than in either the GXT (P=.027, ES=0.39) or SPVspeed (P=.001, ES=0.76). The SPVspeed protocol produces VO2max values similar to those obtained in the GXT and may represent a more appropriate and athlete-friendly test that is more oriented toward the variable speed found in competitive sport.

Facile and Low-Temperature Fabrication of Thermochromic Cr2O3/VO2 Smart Coatings: Enhanced Solar Modulation Ability, High Luminous Transmittance and UV-Shielding Function.

PubMed

Chang, Tianci; Cao, Xun; Li, Ning; Long, Shiwei; Gao, Xiang; Dedon, Liv R; Sun, Guangyao; Luo, Hongjie; Jin, Ping

2017-08-09

In the pursuit of energy efficient materials, vanadium dioxide (VO 2 ) based smart coatings have gained much attention in recent years. For smart window applications, VO 2 thin films should be fabricated at low temperature to reduce the cost in commercial fabrication and solve compatibility problems. Meanwhile, thermochromic performance with high luminous transmittance and solar modulation ability, as well as effective UV shielding function has become the most important developing strategy for ideal smart windows. In this work, facile Cr 2 O 3 /VO 2 bilayer coatings on quartz glasses were designed and fabricated by magnetron sputtering at low temperatures ranging from 250 to 350 °C as compared with typical high growth temperatures (>450 °C). The bottom Cr 2 O 3 layer not only provides a structural template for the growth of VO 2 (R), but also serves as an antireflection layer for improving the luminous transmittance. It was found that the deposition of Cr 2 O 3 layer resulted in a dramatic enhancement of the solar modulation ability (56.4%) and improvement of luminous transmittance (26.4%) when compared to single-layer VO 2 coating. According to optical measurements, the Cr 2 O 3 /VO 2 bilayer structure exhibits excellent optical performances with an enhanced solar modulation ability (ΔT sol = 12.2%) and a high luminous transmittance (T lum,lt = 46.0%), which makes a good balance between ΔT sol and T lum for smart windows applications. As for UV-shielding properties, more than 95.8% UV radiation (250-400 nm) can be blocked out by the Cr 2 O 3 /VO 2 structure. In addition, the visualized energy-efficient effect was modeled by heating a beaker of water using infrared imaging method with/without a Cr 2 O 3 /VO 2 coating glass.

Pulsed laser-deposited VO2 thin films on Pt layers

NASA Astrophysics Data System (ADS)

Sakai, Joe; Zaghrioui, Mustapha; Ta Phuoc, Vinh; Roger, Sylvain; Autret-Lambert, Cécile; Okimura, Kunio

2013-03-01

VO2 films were deposited on Pt (111)/TiO2/SiO2/Si (001) substrates by means of a pulsed laser deposition technique. An x-ray diffraction peak at 2θ = 39.9° was deconvoluted into two pseudo-Voigt profiles of Pt (111) and VOx-originated components. The VOx diffraction peak was more obvious in a VOx/Pt (111)/Al2O3 (0001) sample, having a narrower width compared with a VO2/Al2O3 (0001) sample. Temperature-controlled Raman spectroscopy for the VOx/Pt/TiO2/SiO2/Si sample has revealed the monoclinic VO2 phase at low temperature and the structural phase transition at about 72 °C in a heating process. The electronic conductive nature at the high temperature phase was confirmed by near normal incidence infrared reflectivity measurements. Out-of-plane current-voltage characteristics showed an electric field-induced resistance switching at a voltage as low as 0.2 V for a 50 nm-thick film. A survey of present and previous results suggests an experimental law that the transition voltage of VO2 is proportional to the square root of the electrodes distance.

Methanesulfonates of high-valent metals: syntheses and structural features of MoO2(CH3SO3)2, UO2(CH3SO3)2, ReO3(CH3SO3), VO(CH3SO3)2, and V2O3(CH3SO3)4 and their thermal decomposition under N2 and O2 atmosphere.

PubMed

Betke, Ulf; Neuschulz, Kai; Wickleder, Mathias S

2011-11-04

Oxide methanesulfonates of Mo, U, Re, and V have been prepared by reaction of MoO(3), UO(2)(CH(3)COO)(2)·2H(2)O, Re(2)O(7)(H(2)O)(2), and V(2)O(5) with CH(3)SO(3)H or mixtures thereof with its anhydride. These compounds are the first examples of solvent-free oxide methanesulfonates of these elements. MoO(2)(CH(3)SO(3))(2) (Pbca, a=1487.05(4), b=752.55(2), c=1549.61(5) pm, V=1.73414(9) nm(3), Z=8) contains [MoO(2)] moieties connected by [CH(3)SO(3)] ions to form layers parallel to (100). UO(2)(CH(3)SO(3))(2) (P2(1)/c, a=1320.4(1), b=1014.41(6), c=1533.7(1) pm, β=112.80(1)°, V=1.8937(3) nm(3), Z=8) consists of linear UO(2)(2+) ions coordinated by five [CH(3)SO(3)] ions, forming a layer structure. VO(CH(3)SO(3))(2) (P2(1)/c, a=1136.5(1), b=869.87(7), c=915.5(1) pm, β=113.66(1)°, V=0.8290(2) nm(3), Z=4) contains [VO] units connected by methanesulfonate anions to form corrugated layers parallel to (100). In ReO(3)(CH(3)SO(3)) (P1, a=574.0(1), b=1279.6(3), c=1641.9(3) pm, α=102.08(2), β=96.11(2), γ=99.04(2)°, V=1.1523(4) nm(3), Z=8) a chain structure exhibiting infinite O-[ReO(2)]-O-[ReO(2)]-O chains is formed. Each [ReO(2)]-O-[ReO(2)] unit is coordinated by two bidentate [CH(3)SO(3)] ions. V(2)O(3)(CH(3)SO(3))(4) (I2/a, a=1645.2(3), b=583.1(1), c=1670.2(3) pm, β=102.58(3), V=1.5637(5) pm(3), Z=4) adopts a chain structure, too, but contains discrete [VO]-O-[VO] moieties, each coordinated by two bidentate [CH(3)SO(3)] ligands. Additional methanesulfonate ions connect the [V(2)O(3)] groups along [001]. Thermal decomposition of the compounds was monitored under N(2) and O(2) atmosphere by thermogravimetric/differential thermal analysis and XRD measurements. Under N(2) the decomposition proceeds with reduction of the metal leading to the oxides MoO(2), U(3)O(7), V(4)O(7), and VO(2); for MoO(2)(CH(3)SO(3))(2), a small amount of MoS(2) is formed. If the thermal decomposition is carried out in a atmosphere of O(2) the oxides MoO(3) and V(2)O(5) are formed. Copyright �

Coherently Coupled ZnO and VO2 Interface studied by Photoluminescence and electrical transport across a phase transition

NASA Astrophysics Data System (ADS)

Srivastava, Amar; Saha, S.; Annadi, A.; Zhao, Y. L.; Gopinadhan, K.; Wang, X.; Naomi, N.; Liu, Z. Q.; Dhar, S.; Herng, T. S.; Nina, Bao; Ariando, -; Ding, Jun; Venkatesan, T.

2012-02-01

In this work we report a study of a coherently coupled interface consisting of a ZnO layer grown on top of an oriented VO2 layer on sapphire by photoluminescence and electrical transport measurements across the VO2 metal insulator phase transition (MIT). The photoluminescence of the ZnO layer showed a broad hysteresis induced by the phase transition of VO2 while the width of the electrical hysteresis was narrow and unaffected by the over layer. The enhanced width of the PL hysteresis was due to the formation of defects during the MIT as evidenced by a broad hysteresis in the opposite direction to that of the band edge PL in the defect luminescense. Unlike VO2 the defects in ZnO did not fully recover across the phase transition. From the defect luminescence data, oxygen interstitials were found to be the predominant defects in ZnO mediated by the strain from the VO2 phase transition. Such coherently coupled interfaces could be of use in characterizing the stability of a variety of interfaces and also for novel device application.

Genetic polymorphisms to predict gains in maximal O2 uptake and knee peak torque after a high intensity training program in humans.

PubMed

Yoo, Jinho; Kim, Bo-Hyung; Kim, Soo-Hwan; Kim, Yangseok; Yim, Sung-Vin

2016-05-01

The study aimed to identify single nucleotide polymorphisms (SNPs) that significantly influenced the level of improvement of two kinds of training responses, including maximal O2 uptake (V'O2max) and knee peak torque of healthy adults participating in the high intensity training (HIT) program. The study also aimed to use these SNPs to develop prediction models for individual training responses. 79 Healthy volunteers participated in the HIT program. A genome-wide association study, based on 2,391,739 SNPs, was performed to identify SNPs that were significantly associated with gains in V'O2max and knee peak torque, following 9 weeks of the HIT program. To predict two training responses, two independent SNPs sets were determined using linear regression and iterative binary logistic regression analysis. False discovery rate analysis and permutation tests were performed to avoid false-positive findings. To predict gains in V'O2max, 7 SNPs were identified. These SNPs accounted for 26.0 % of the variance in the increment of V'O2max, and discriminated the subjects into three subgroups, non-responders, medium responders, and high responders, with prediction accuracy of 86.1 %. For the knee peak torque, 6 SNPs were identified, and accounted for 27.5 % of the variance in the increment of knee peak torque. The prediction accuracy discriminating the subjects into the three subgroups was estimated as 77.2 %. Novel SNPs found in this study could explain, and predict inter-individual variability in gains of V'O2max, and knee peak torque. Furthermore, with these genetic markers, a methodology suggested in this study provides a sound approach for the personalized training program.

Synthesis of β-AgVO3 nanowires decorated with Ag2CrO4, with improved visible light photocatalytic performance

NASA Astrophysics Data System (ADS)

Ouyang, Qi; Li, Zhonghua; Liu, Jiawen

2018-05-01

Silver chromate‑silver vanadate (Ag2CrO4/β-AgVO3) heterojunction composites are synthesized through a facile precipitation process. The Ag2CrO4/β-AgVO3 hybrids obtained exhibit better photocatalytic activity in degradation of RhB than both pure Ag2CrO4 and β-AgVO3 under visible light irradiation. The 20 wt% Ag2CrO4/β-AgVO3 heterojunction possesses the best photocatalytic ability for degrading RhB: 24.4 times that of pristine β-AgVO3 nanowires and 3.2 times that of individual Ag2CrO4 particles. The phase of the nanocomposites was analyzed using x-ray diffraction as well as x-ray photoelectron spectroscopy. Their morphology was observed via scanning electron microscopy and transmission electron microscopy. The improvement in photocatalytic performance is chiefly ascribed to the synergies between Ag2CrO4/β-AgVO3 heterostructure, which can enhance the light absorbance ability and also accelerate the separation and transfer of photoinduced electrons and holes under visible light irradiation; this is also confirmed by UV–vis diffuse reflection spectrometry and fluorescence emission spectra.

The slow component of O(2) uptake is not accompanied by changes in muscle EMG during repeated bouts of heavy exercise in humans.

PubMed

Scheuermann, B W; Hoelting, B D; Noble, M L; Barstow, T J

2001-02-15

1. We hypothesized that either the recruitment of additional muscle motor units and/or the progressive recruitment of less efficient fast-twitch muscle fibres was the predominant contributor to the additional oxygen uptake (VO2) observed during heavy exercise. Using surface electromyographic (EMG) techniques, we compared the VO2 response with the integrated EMG (iEMG) and mean power frequency (MPF) response of the vastus lateralis with the VO2 response during repeated bouts of moderate (below the lactate threshold, < LT) and heavy (above the lactate threshold, > LT) intensity cycle ergometer exercise. 2. Seven male subjects (age 29 +/- 7 years, mean +/- S.D.) performed three transitions to a work rate (WR) corresponding to 90 % LT and two transitions to a work rate that would elicit a VO2 corresponding to 50 % of the difference between peak VO2 and the LT (i.e. Delta50 %, > LT1 and > LT2). 3. The VO2 slow component was significantly reduced by prior heavy intensity exercise (> LT1, 410 +/- 196 ml min(-1); > LT2, 230 +/- 191 ml min-1). The time constant (tau), amplitude (A) and gain (DeltaVO2/DeltaWR) of the primary VO2 response (phase II) were not affected by prior heavy exercise when a three-component, exponential model was used to describe the V2 response. 4. Integrated EMG and MPF remained relatively constant and at the same level throughout both > LT1 and > LT2 exercise and therefore were not associated with the VO2 slow component. 5. These data are consistent with the view that the increased O2 cost (i.e. VO2 slow component) associated with performing heavy exercise is coupled with a progressive increase in ATP requirements of the already recruited motor units rather than to changes in the recruitment pattern of slow versus fast-twitch motor units. Further, the lack of speeding of the kinetics of the primary VO2 component with prior heavy exercise, thought to represent the initial muscle VO2 response, are inconsistent with O2 delivery being the limiting factor

Effects of chronic nitric oxide synthase inhibition on V'O2max and exercise capacity in mice.

PubMed

Wojewoda, M; Przyborowski, K; Sitek, B; Zakrzewska, A; Mateuszuk, L; Zoladz, J A; Chlopicki, S

2017-03-01

Acute inhibition of NOS by L-NAME (N ω -nitro-L-arginine methyl ester) is known to decrease maximal oxygen consumption (V'O 2max ) and impair maximal exercise capacity, whereas the effects of chronic L-NAME treatment on V'O 2max and exercise performance have not been studied so far. In this study, we analysed the effect of L-NAME treatment, (LN2 and LN12, respectively) on V'O 2max and exercise capacity (in maximal incremental running and prolonged sub-maximal incremental running tests), systemic NO bioavailability (plasma nitrite (NO 2 - ) and nitrate (NO 3 - )) and prostacyclin (PGI 2 ) production in C57BL6/J mice. Mice treated with L-NAME for 2 weeks (LN2) displayed higher V'O 2max and better running capacity than age-matched control mice. In LN2 mice, NO bioavailability was preserved, as evidenced by maintained NO 2 - plasma concentration. PGI 2 production was activated (increased 6-keto-PGF 1α plasma concentration) and the number of circulating erythrocytes (RBC) and haemoglobin concentration were increased. In mice treated with L-NAME for 12 weeks (LN12), NO bioavailability was decreased (lower NO 2 - plasma concentration), and 6-keto-PGF 1α plasma concentration and RBC number were not elevated compared to age-matched control mice. However, LN12 mice still performed better during the maximal incremental running test despite having lower V'O 2max . Interestingly, the LN12 mice showed poorer running capacity during the prolonged sub-maximal incremental running test. To conclude, short-term (2 weeks) but not long-term (12 weeks) treatment with L-NAME activated robust compensatory mechanisms involving preservation of NO2- plasma concentration, overproduction of PGI 2 and increased number of RBCs, which might explain the fully preserved exercise capacity despite the inhibition of NOS.

Hydrothermal synthesis of mesoporous VO{sub 2}·½(H{sub 2}O) nanosheets and study of their electrical properties

DOE Office of Scientific and Technical Information (OSTI.GOV)

Soltane, L.; Sediri, F., E-mail: faouzi.sediri@ipeit.rnu.tn; Faculté des Sciences de Tunis, Université, Tunis-Elmanar, 2092 Elmanar, Tunis

Highlights: ► Sheet-like nanocrystalline VO{sub 2}·½(H{sub 2}O) was synthesized by a hydrothermal route. ► Reaction time is key factor for structure and morphology. ► Electrical properties were also studied. ► Conductivity value goes from 75 10{sup −6} Ω{sup −1} cm{sup −1} at 298 K to 68 10{sup −5} Ω{sup −1} cm{sup −1} at 386 K. -- Abstract: Layered sheet-like nanocrystalline VO{sub 2}·½(H{sub 2}O) has been synthesized by hydrothermal process using V{sub 2}O{sub 5} as vanadium source and 2-phenylethylamine as a reducing agent and a structure-directing template. Techniques X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transformmore » infrared spectroscopy (FTIR) and nitrogen adsorption/desorption isotherms have been used to characterize the structure, morphology and composition of the materials. Electrical conductivity measurements showed that the as synthesized VO{sub 2}·½(H{sub 2}O) nanosheets has a conductivity value which goes from 75 × 10{sup −6} Ω{sup −1} cm{sup −1} at 298 K, to 68 10{sup −5} Ω{sup −1} cm{sup −1} at 386 K with activation energy of 0.24 eV.« less

VO2 responses to intermittent swimming sets at velocity associated with VO2max.

PubMed

Libicz, Sebastien; Roels, Belle; Millet, Gregoire P

2005-10-01

While the physiological adaptations following endurance training are relatively well understood, in swimming there is a dearth of knowledge regarding the metabolic responses to interval training (IT). The hypothesis tested predicted that two different endurance swimming IT sets would induce differences in the total time the subjects swam at a high percentage of maximal oxygen consumption (VO(2)max). Ten trained triathletes underwent an incremental test to exhaustion in swimming so that the swimming velocity associated with VO(2)max (vVO(2)max) could be determined. This was followed by a maximal 400-m test and two intermittent sets at vVO(2)max: (a) 16 x 50 m with 15-s rest (IT(50)); (b) 8 x 100 m with 30-s rest (IT(100)). The times sustained above 95% VO(2)max (68.50 +/- 62.69 vs. 145.01 +/- 165.91 sec) and 95% HRmax (146.67 +/- 131.99 vs. 169.78 +/- 203.45 sec, p = 0.54) did not differ between IT(50) and IT(100)(values are mean +/- SD). In conclusion, swimming IT sets of equal time duration at vVO(2)max but of differing work-interval durations led to slightly different VO(2)and HR responses. The time spent above 95% of VO(2)max was twice as long in IT(100) as in IT (50), and a large variability between mean VO(2)and HR values was also observed.

Spanish genetic admixture is associated with larger V(O2) max decrement from sea level to 4338 m in Peruvian Quechua.

PubMed

Brutsaert, Tom D; Parra, Esteban J; Shriver, Mark D; Gamboa, Alfredo; Palacios, Jose-Antonio; Rivera, Maria; Rodriguez, Ivette; León-Velarde, Fabiola

2003-08-01

Quechua in the Andes may be genetically adapted to altitude and able to resist decrements in maximal O2 consumption in hypoxia (DeltaVo2 max). This hypothesis was tested via repeated measures of Vo2 max (sea level vs. 4338 m) in 30 men of mixed Spanish and Quechua origins. Individual genetic admixture level (%Spanish ancestry) was estimated by using ancestry-informative DNA markers. Genetic admixture explained a significant proportion of the variability in DeltaVo2 max after control for covariate effects, including sea level Vo2 max and the decrement in arterial O2 saturation measured at Vo2 max (DeltaSpO2 max) (R2 for admixture and covariate effects approximately 0.80). The genetic effect reflected a main effect of admixture on DeltaVo2 max (P = 0.041) and an interaction between admixture and DeltaSpO2 max (P = 0.018). Admixture predicted DeltaVo2 max only in subjects with a large DeltaSpO2 max (P = 0.031). In such subjects, DeltaVo2 max was 12-18% larger in a subgroup of subjects with high vs. low Spanish ancestry, with least squares mean values (+/-SE) of 739 +/- 71 vs. 606 +/- 68 ml/min, respectively. A trend for interaction (P = 0.095) was also noted between admixture and the decrease in ventilatory threshold at 4338 m. As previously, admixture predicted DeltaVo2 max only in subjects with a large decrease in ventilatory threshold. These findings suggest that the genetic effect on DeltaVo2 max depends on a subject's aerobic fitness. Genetic effects may be more important (or easier to detect) in athletic subjects who are more likely to show gas-exchange impairment during exercise. The results of this study are consistent with the evolutionary hypothesis and point to a better gas-exchange system in Quechua.

Semiconductor to Metal Transition Characteristics of VO2/NiO Epitaxial Heterostructures Integrated with Si(100)

NASA Astrophysics Data System (ADS)

Molaei, Roya

The novel functionalities of Vanadium dioxide (VO2), such as, several orders of magnitude transition in resistivity and IR transmittance, provide the exciting opportunity for the development of next generation memory, sensor, and field-effect based devices. A critical issue in the development of practical devices based on metal oxides is the integration of high quality epitaxial oxide thin films with the existing silicon technology which is based on silicon (100) substrates. However, silicon is not suitable for epitaxial growth of oxides owing to its tendency to readily form an amorphous oxide layer or silicide at the film-substrate interface. The oxide films deposited directly on silicon exhibit poor crystallinity and are not suitable for device applications. To overcome this challenge, appropriate substrate templates must be developed for the growth of oxide thin films on silicon substrates. The primary objective of this dissertation was to develop an integration methodology of VO2 with Si (100) substrates so they could be used in "smart" sensor type of devices along with other multifunctional devices on the same silicon chip. This was achieved by using a NiO/c- YSZ template layer deposited in situ. It will be shown that if the deposition conditions are controlled properly. This approach was used to integrate VO 2 thin films with Si (100) substrates using pulsed laser deposition (PLD) technique. The deposition methodology of integrating VO2 thin films on silicon using various other template layers will also be discussed. Detailed epitaxial relationship of NiO/c-YSZ/Si(100) heterostructures as a template to growth of VO2 as well as were studied. We also were able to create a p-n junction within a single NiO epilayer through subsequent nanosecond laser annealing, as well as established a structure-property correlation in NiO/c-YSZ/Si(100) thin film epitaxial heterostructures with especial emphasis on the stoichiometry and crystallographic characteristics. NiO

Transport properties of ultra-thin VO2 films on (001) TiO2 grown by reactive molecular-beam epitaxy

NASA Astrophysics Data System (ADS)

Paik, Hanjong; Moyer, Jarrett A.; Spila, Timothy; Tashman, Joshua W.; Mundy, Julia A.; Freeman, Eugene; Shukla, Nikhil; Lapano, Jason M.; Engel-Herbert, Roman; Zander, Willi; Schubert, Jürgen; Muller, David A.; Datta, Suman; Schiffer, Peter; Schlom, Darrell G.

2015-10-01

We report the growth of (001)-oriented VO2 films as thin as 1.5 nm with abrupt and reproducible metal-insulator transitions (MIT) without a capping layer. Limitations to the growth of thinner films with sharp MITs are discussed, including the Volmer-Weber type growth mode due to the high energy of the (001) VO2 surface. Another key limitation is interdiffusion with the (001) TiO2 substrate, which we quantify using low angle annular dark field scanning transmission electron microscopy in conjunction with electron energy loss spectroscopy. We find that controlling island coalescence on the (001) surface and minimization of cation interdiffusion by using a low growth temperature followed by a brief anneal at higher temperature are crucial for realizing ultrathin VO2 films with abrupt MIT behavior.

Verification testing to confirm VO2max attainment in persons with spinal cord injury.

PubMed

Astorino, Todd A; Bediamol, Noelle; Cotoia, Sarah; Ines, Kenneth; Koeu, Nicolas; Menard, Natasha; Nyugen, Brianna; Olivo, Cassandra; Phillips, Gabrielle; Tirados, Ardreen; Cruz, Gabriela Velasco

2018-01-22

Maximal oxygen uptake (VO 2 max) is a widely used measure of cardiorespiratory fitness, aerobic function, and overall health risk. Although VO 2 max has been measured for almost 100 yr, no standardized criteria exist to verify VO 2 max attainment. Studies document that incidence of 'true' VO 2 max obtained from incremental exercise (INC) can be confirmed using a subsequent verification test (VER). In this study, we examined efficacy of VER in persons with spinal cord injury (SCI). Repeated measures, within-subjects study. University laboratory in San Diego, CA. Ten individuals (age and injury duration = 33.3 ± 10.5 yr and 6.8 ± 6.2 yr) with SCI and 10 able-bodied (AB) individuals (age = 24.1 ± 7.4 yr). Peak oxygen uptake (VO 2 peak) was determined during INC on an arm ergometer followed by VER at 105 percent of peak power output (% PPO). Gas exchange data, heart rate (HR), and blood lactate concentration (BLa) were measured during exercise. Across all participants, VO 2 peak was highly related between protocols (ICC = 0.98) and the mean difference was equal to 0.08 ± 0.11 L/min. Compared to INC, VO 2 peak from VER was not different in SCI (1.30 ± 0.45 L/min vs. 1.31 ± 0.43 L/min) but higher in AB (1.63 ± 0.40 L/min vs. 1.76 ± 0.40 L/min). Data show similar VO 2 peak between incremental and verification tests in SCI, suggesting that VER confirms VO 2 max attainment. However, in AB participants completing arm ergometry, VER is essential to validate appearance of 'true' VO 2 peak.

Uptake properties of Ni2+ by nCaO.Al2O3.2SiO2 (n=1-4) prepared from solid-state reaction of kaolinite and calcite.

PubMed

Jha, Vinay Kumar; Kameshima, Yoshikazu; Nakajima, Akira; Okada, Kiyoshi; MacKenzie, Kenneth J D

2005-08-31

A series of nCaO.Al2O3.2SiO2 samples (n=1-4) were prepared by solid-state reaction of mechanochemically treated mixtures of kaolinite and calcite fired at 600-1000 degrees C for 24 h. All the samples were X-ray amorphous after firing at 600-800 degrees C but had crystallized by 900 degrees C. The main crystalline phases were anorthite (n=1), gehlenite (n=2 and 3) and larnite (n=4). The uptake of Ni2+ by nCaO.Al2O3.2SiO2 samples fired at 800 and 900 degrees C was investigated at room temperature using solutions with initial Ni2+ concentrations of 0.1-50 mmol/l. Amorphous samples (fired at 800 degrees C) showed a higher Ni2+ uptake capacity than crystalline samples (fired at 900 degrees C). Ni2+ uptake was found to increase with increasing of CaO content. Amorphous 4CaO.Al2O3.2SiO2 showed the highest Ni2+ uptake capacity (about 9 mmol/g). The Ni2+ uptake abilities of the present samples are higher than those of other materials reported in the literature. Since the sorbed Ni2+/released Ca2+ ratios of these samples are close to unity, ion replacement of Ni2+ for Ca2+ is thought to be the principal mechanism of Ni2+ uptake by the present samples.

Effects of electrical stimulation on VO2 kinetics and delta efficiency in healthy young men

PubMed Central

Perez, M; Lucia, A; Santalla, A; Chicharro, J

2003-01-01

Objective: To determine the effects of electrical stimulation (ES) on oxygen uptake (VO2) kinetics and delta efficiency (DE) during gradual exercise. The hypothesis was that ES would attenuate the VO2-workload relation and improve DE. Methods: Fifteen healthy, untrained men (mean (SD) age 22 (5) years) were selected. Ten were electrostimulated on both quadriceps muscles with a frequency of 45–60 Hz, with 12 seconds of stimulation followed by eight seconds recovery for a total of 30 minutes a day, three days a week for six weeks. The remaining five subjects were assigned to a control group. A standardised exercise test on a cycle ergometer (ramp protocol, workload increases of 20 W/min) was performed by each subject before and after the experimental period. The slope of the VO2-power output (W) relation (ΔVO2/ΔW) and DE were calculated in each subject at moderate to high intensities (above the ventilatory threshold—that is, from 50–60% to 100% VO2max). Results: The mean (SEM) values for ΔVO2/ΔW and DE had significantly decreased and increased respectively after the six week ES programme (p<0.05; 9.8 (0.2) v 8.6 (0.5) ml O2/W/min respectively and 27.7 (0.9) v 31.5 (1.4)% respectively). Conclusions: ES could be used as a supplementary tool to improve two of the main determinants of endurance capacity, namely VO2 kinetics and work efficiency. PMID:12663356

Hydrothermal synthesis of BiVO4/TiO2 composites and their application for degradation of gaseous benzene under visible light irradiation

NASA Astrophysics Data System (ADS)

Hu, Yin; Chen, Wei; Fu, Jianping; Ba, Mingwei; Sun, Fuqian; Zhang, Peng; Zou, Jiyong

2018-04-01

Benzene is currently recognized as one of the most toxic contaminants. Our previously published study revealed that BiVO4/TiO2 is an excellent photocatalyst toward the degradation of benzene. Herein, BiVO4/TiO2 has been synthesized via a sol-gel method and a facile hydrothermal route by adjusting the precursor hydrolysis rate with the use of different acids (CH3COOH, HNO3 and H2SO4). The influence of these acids on the physicochemical characteristics and photocatalytic performance is discussed in detail. X-ray diffraction and N2 sorption analyses confirm that acid has an important effect on the crystalline composition and BET specific surface area. BiVO4/TiO2 synthesized in CH3COOH has better photocatalytic activity for the degradation of gaseous benzene than that in HNO3 and H2SO4 under visible light irradiation. Results of XPS measurement demonstrate that the hydroxyl group in BiVO4/TiO2-CH3COOH is more abundant than that in BiVO4/TiO2-HNO3 and BiVO4/TiO2-H2SO4. The photocurrent signal is investigated by electrochemical measurement, which indicates that more effective separation of photogenerated carriers occurs in the BiVO4/TiO2/CH3COOH system. It is hoped that our work can offer valuable information on the design of TiO2 composites with enhanced properties.

Reduction of V2O5 thin films deposited by aqueous sol-gel method to VO2(B) and investigation of its photocatalytic activity

NASA Astrophysics Data System (ADS)

Monfort, Olivier; Roch, Tomas; Satrapinskyy, Leonid; Gregor, Maros; Plecenik, Tomas; Plecenik, Andrej; Plesch, Gustav

2014-12-01

A way of preparation of VO2(B) thin films by reduction of V2O5 films synthesized from an aqueous sol-gel system has been developed and photocatalytic properties of the obtained films were studied. The reduction was performed by annealing of the V2O5 film in vacuum as well as in H2/Ar atmosphere, which was followed by temperature dependent XRD. It has been shown that the reduction is influenced by the layered-structure of the vanadium oxides. It is a two-step process, where the mixed-valence vanadium oxide V4O9 is first formed before reaching the VO2(B) phase. The film microstructure was characterized by SEM and AFM and the valence states of vanadium in VO2(B) films were evaluated by XPS. The VO2(B) polymorph shows an energy band-gap around 2.8 eV and it exhibits photocatalytic properties. It was measured by following the degradation of rhodamine B under UVA as well as metalhalogenide lamp irradiation, which has similar spectral distribution as natural sunlight. The VO2(B) films show distinct photoactivities under both lamps, although they were found to be more active under the UVA irradiation. The film annealed under reducing hydrogen atmosphere, which exhibits higher granularity and surface roughness, shows higher photoactivity than the vacuum-annealed film.

Synthesis and characterization of new fluoride-containing manganese vanadates A{sub 2}Mn{sub 2}V{sub 2}O{sub 7}F{sub 2} (A=Rb, Cs) and Mn{sub 2}VO{sub 4}F

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sanjeewa, Liurukara D.; McGuire, Michael A.; Smith Pellizzeri, Tiffany M.

2016-09-15

Large single crystals of A{sub 2}Mn{sub 2}V{sub 2}O{sub 7}F{sub 2} (A=Rb, Cs) and Mn{sub 2}VO{sub 4}F were grown using a high-temperature (~600 °C) hydrothermal technique. Single crystal X-ray diffraction and powder X-ray diffraction were utilized to characterize the structures, which both possess MnO{sub 4}F{sub 2} building blocks. The A{sub 2}Mn{sub 2}V{sub 2}O{sub 7}F{sub 2} series crystallizes as a new structure type in space group Pbcn (No. 60), Z=4 (Rb{sub 2}Mn{sub 2}V{sub 2}O{sub 7}F{sub 2}: a=7.4389(17) Å, b=11.574(3) Å, c=10.914(2) Å; Cs{sub 2}Mn{sub 2}V{sub 2}O{sub 7}F{sub 2}: a=7.5615(15) Å, b=11.745(2) Å, c=11.127(2) Å). The structure is composed of zigzag chains ofmore » edge-sharing MnO{sub 4}F{sub 2} units running along the a-axis, and interconnected through V{sub 2}O{sub 7} pyrovanadate groups. Temperature dependent magnetic susceptibility measurements on this interesting one-dimensional structural feature based on Mn{sup 2+} indicated that Cs{sub 2}Mn{sub 2}V{sub 2}O{sub 7}F{sub 2} is antiferromagnetic with a Neél temperature, T{sub N}=~3 K and a Weiss constant, θ, of −11.7(1) K. Raman and infrared spectra were also analyzed to identify the fundamental V–O vibrational modes in Cs{sub 2}Mn{sub 2}V{sub 2}O{sub 7}F{sub 2}. Mn{sub 2}(VO{sub 4})F crystalizes in the monoclinic space group of C2/c (no. 15), Z=8 with unit cell parameters of a=13.559(2) Å, b=6.8036(7) Å, c=10.1408(13) Å and β=116.16(3)°. The structure is associated with those of triplite and wagnerite. Dynamic fluorine disorder gives rise to complex alternating chains of five-and six-coordinate Mn{sup 2+}. These interpenetrating chains are additionally connected through isolated VO{sub 4} tetrahedra to form the condensed structure. - Graphical abstract: New vanadate fluorides A{sub 2}Mn{sub 2}V{sub 2}O{sub 7}F{sub 2} (A=Rb, Cs) and Mn{sub 2}(VO{sub 4})F have been synthesized hydrothermally. Upon cooling, the one-dimensional Mn(II) substructure results in

Ag{sub 2}O/Ag{sub 3}VO{sub 4}/Ag{sub 4}V{sub 2}O{sub 7} heterogeneous photocatalyst prepared by a facile hydrothermal synthesis with enhanced photocatalytic performance under visible light irradiation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ran, Rong; McEvoy, Joanne Gamage; Centre for Catalysis Research and Innovation, University of Ottawa, Ottawa, Ontario, K1N 6N5

Highlights: • The photocatalyst was hydrothermally prepared by adjusting the ratio of Ag to V. • Multi-phase Ag{sub 2}O/Ag{sub 3}VO{sub 4}/Ag{sub 4}V{sub 2}O{sub 7} obtained exhibited multi-morphological features. • The photocatalyst exhibited strong visible light driven photoactivity towards RhB. - Abstract: A novel Ag{sub 2}O/Ag{sub 3}VO{sub 4}/Ag{sub 4}V{sub 2}O{sub 7} photocatalyst was synthesized by adjusting the molar ratio of silver–vanadium (Ag–V) in a facile hydrothermal method to obtain multi-phase Ag{sub 2}O/Ag{sub 3}VO{sub 4}/Ag{sub 4}V{sub 2}O{sub 7} photocatalyst. The photocatalytic activity of the prepared samples was quantified by the degradation of Rhodamine B (RhB) model organic pollutant under visible light irradiation.more » Compared to pure Ag{sub 3}VO{sub 4}, Ag{sub 4}V{sub 2}O{sub 7} and P25 TiO{sub 2}, respectively, the as-synthesized multi-phase Ag{sub 2}O/Ag{sub 3}VO{sub 4}/Ag{sub 4}V{sub 2}O{sub 7} powders gave rise to a significantly higher photocatalytic activity, achieving up to 99% degradation of RhB in 2 h under visible light. This enhanced photocatalytic performance was attributed to the effect of the multi-phase Ag{sub 2}O/Ag{sub 3}VO{sub 4}/Ag{sub 4}V{sub 2}O{sub 7} photocatalyst and the surface plasmon resonance (SPR) of the incorporated metallic silver (Ag{sup 0}) nanoparticles (NPs) generated during the photocatalysis, as evidenced by post-use characterization, resulting in improved visible light absorption and electron-hole (e{sup −}-h{sup +}) separation. A mechanism was proposed for the photocatalytic degradation of RhB on the surface of Ag{sub 2}O/Ag{sub 3}VO{sub 4}/Ag{sub 4}V{sub 2}O{sub 7}.« less

Aqueous citrato-oxovanadate(IV) precursor solutions for VO2: synthesis, spectroscopic investigation and thermal analysis.

PubMed

Peys, Nick; Adriaensens, Peter; Van Doorslaer, Sabine; Gielis, Sven; Peeters, Ellen; De Dobbelaere, Christopher; De Gendt, Stefan; Hardy, An; Van Bael, Marlies K

2014-09-07

An aqueous precursor solution, containing citrato-VO(2+) complexes, is synthesized for the formation of monoclinic VO2. With regard to the decomposition of the VO(2+) complexes towards vanadium oxide formation, it is important to gain insights into the chemical structure and transformations of the precursor during synthesis and thermal treatment. Hence, the conversion of the cyclic [V4O12](4-) ion to the VO(2+) ion in aqueous solution, using oxalic acid as an acidifier and a reducing agent, is studied by (51)Vanadium nuclear magnetic resonance spectroscopy. The citrate complexation of this VO(2+) ion and the differentiation between a solution containing citrato-oxalato-VO(2+) and citrato-VO(2+) complexes are studied by electron paramagnetic resonance and Fourier transform infra-red spectroscopy. In both solutions, the VO(2+) containing complex is mononuclear and has a distorted octahedral geometry with a fourfold R-CO2(-) ligation at the equatorial positions and likely a fifth R-CO2(-) ligation at the axial position. Small differences in the thermal decomposition pathway between the gel containing citrato-oxalato-VO(2+) complexes and the oxalate-free gel containing citrato-VO(2+) complexes are observed between 150 and 200 °C in air and are assigned to the presence of (NH4)2C2O4 in the citrato-oxalato-VO(2+) solution. Both precursor solutions are successfully used for the formation of crystalline vanadium oxide nanostructures on SiO2, after thermal annealing at 500 °C in a 0.1% O2 atmosphere. However, the citrato-oxalato-VO(2+) and the oxalate-free citrato-VO(2+) solution result in the formation of monoclinic V6O13 and monoclinic VO2, respectively.

Hyperventilation-induced hypocapnic alkalosis slows the adaptation of pulmonary O2 uptake during the transition to moderate-intensity exercise.

PubMed

Chin, Lisa M K; Leigh, Ryan J; Heigenhauser, George J F; Rossiter, Harry B; Paterson, Donald H; Kowalchuk, John M

2007-08-15

The effect of voluntary hyperventilation-induced hypocapnic alkalosis (RALK) on pulmonary O2 uptake (VO2) kinetics and muscle deoxygenation was examined in young male adults (n=8) during moderate-intensity exercise. Subjects performed five repetitions of a step-transition in work rate from 20 W cycling to a work rate corresponding to 90% of the estimated lactate threshold during control (CON; PET,CO2, approximately 40 mmHg) and during hyperventilation (RALK; PET,CO2, approximately 20 mmHg). was measured breath-by-breath and relative concentration changes in muscle deoxy- (DeltaHHb), oxy- (DeltaO2Hb) and total (DeltaHbtot) haemoglobin were measured continuously using near-infrared (NIR) spectroscopy (Hamamatsu, NIRO 300). The time constant for the fundamental, phase 2, VO2 response (tau VO2) was greater (P<0.05) in RALK (48+/-11 s) than CON (31+/-9 s), while tauHHb was similar between conditions (RALK, 12+/-4 s; CON, 11+/-4 s). The DeltaHb(tot) was lower (P<0.05) in RALK than CON, prior to (RALK, -3+/-5 micromol l(-1); CON, -1+/-4 micromol l(-1)) and at the end (RALK, 1+/-6 micromol l(-1); CON, 5+/-5 micromol l(-1)) of moderate-intensity exercise. Although slower adaptation of during RALK may be related to an attenuated activation of PDH (and other enzymes) and provision of oxidizable substrate to the mitochondria (i.e. metabolic inertia), the present findings also suggest a role for a reduction in local muscle perfusion and O2 delivery.

VO2 Kinetics and Metabolic Contributions Whilst Swimming at 95, 100, and 105% of the Velocity at VO2 max

PubMed Central

Sousa, Ana C.; Vilas-Boas, João P.; Fernandes, Ricardo J.

2014-01-01

A bioenergetical analysis of swimming at intensities near competitive distances is inexistent. It was aimed to compare the transient VO2 kinetics responses and metabolic contributions whilst swimming at different velocities around VO2max⁡. 12 trained male swimmers performed (i) an incremental protocol to determine the velocity at VO2max⁡ (vVO2max⁡) and (ii) three square wave exercises from rest to 95, 100, and 105% of vVO2max⁡. VO2 was directly measured using a telemetric portable gas analyser and its kinetics analysed through a double-exponential model. Metabolic contributions were assessed through the sum of three energy components. No differences were observed in the fast component response (τ 1—15, 18, and 16 s, A 1—36, 34, and 37 mL · kg−1 · min⁡−1, and Gain—32, 29, and 30 mL · min⁡−1 at 95, 100, and 105% of the vVO2max⁡, resp.) but A2 was higher in 95 and 100% compared to 105% intensity (480.76 ± 247.01, 452.18 ± 217.04, and 147.04 ± 60.40 mL · min⁡−1, resp.). The aerobic energy contribution increased with the time sustained (83 ± 5, 74 ± 6, and 59 ± 7% for 95, 100, and 105%, resp.). The adjustment of the cardiovascular and/or pulmonary systems that determine O2 delivery and diffusion to the exercising muscles did not change with changing intensity, with the exception of VO2 slow component kinetics metabolic profiles. PMID:25045690

Microwave-Assisted Solvothermal Synthesis of VO2 Hollow Spheres and Their Conversion into V2O5 Hollow Spheres with Improved Lithium Storage Capability.

PubMed

Pan, Jing; Zhong, Li; Li, Ming; Luo, Yuanyuan; Li, Guanghai

2016-01-22

Monodispersed hierarchically structured V2O5 hollow spheres were successfully obtained from orthorhombic VO2 hollow spheres, which are in turn synthesized by a simple template-free microwave-assisted solvothermal method. The structural evolution of VO2 hollow spheres has been studied and explained by a chemically induced self-transformation process. The reaction time and water content in the reaction solution have a great influence on the morphology and phase structure of the resulting products in the solvothermal reaction. The diameter of the VO2 hollow spheres can be regulated simply by changing vanadium ion content in the reaction solution. The VO2 hollow spheres can be transformed into V2O5 hollow spheres with nearly no morphological change by annealing in air. The nanorods composed of V2O5 hollow spheres have an average length of about 70 nm and width of about 19 nm. When used as a cathode material for lithium-ion batteries, the V2O5 hollow spheres display a diameter-dependent electrochemical performance, and the 440 nm hollow spheres show the highest specific discharge capacity of 377.5 mAhg(-1) at a current density of 50 mAg(-1) , and are better than the corresponding solid spheres and nanorod assemblies. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Interdependence of arterial PO2 and O2 consumption in the fetal sheep.

PubMed

Asakura, H; Ball, K T; Power, G G

1990-04-01

These experiments were undertaken to measure the effects of changing arterial oxygen tension (PaO2) on oxygen use by the fetal body (VO2). Six fetal sheep at 130-140 days gestation were prepared with an endotracheal tube, carotid artery catheter, body-core thermistor, cooling coil and loosely-applied umbilical cord snare. The next day the cord was occluded and the fetal lungs were ventilated with gas mixtures containing different concentrations of oxygen. While fetal core temperature was kept constant, fetal arterial PO2 was cycled between high and low values (span = 7 to 359 mmHg, n = 103) and O2 consumption was measured by the rate of O2 uptake from a closed-rebreathing circuit. VO2 changed directly with changes in PO2 from 10 to 40 mmHg but became insensitive to changes in PO2 above about 50 mmHg. The results were well described over the entire range by the equation: VO2 (ml/min per kg fetal wt) = -9.62 + 6.99 ln PO2(mmHg)-0.66 ln2 PO2. Thus the oxygen consumption of the near-term fetal sheep varies with changes in arterial PO2 in the physiologic range. This finding is distinctly different than the adult at rest but resembles adult tissues such as exercising muscle at VO2max. This finding is consistent with differences in fetal metabolic controls, limited cardiac reserve, and limited tissue diffusion rates in actively metabolizing tissues.

Evaluation of Maximal O[subscript 2] Uptake with Undergraduate Students at the University of La Reunion

ERIC Educational Resources Information Center

Tarnus, Evelyne; Catan, Aurelie; Verkindt, Chantal; Bourdon, Emmanuel

2011-01-01

The maximal rate of O[subscript 2] consumption (VO[subscript 2max]) constitutes one of the oldest fitness indexes established for the measure of cardiorespiratory fitness and aerobic performance. Procedures have been developed in which VO[subscript 2max]is estimated from physiological responses during submaximal exercise. Generally, VO[subscript…

VO2 Off Transient Kinetics in Extreme Intensity Swimming.

PubMed

Sousa, Ana; Figueiredo, Pedro; Keskinen, Kari L; Rodríguez, Ferran A; Machado, Leandro; Vilas-Boas, João P; Fernandes, Ricardo J

2011-01-01

Inconsistencies about dynamic asymmetry between the on- and off- transient responses in oxygen uptake are found in the literature. Therefore, the purpose of this study was to characterize the oxygen uptake off-transient kinetics during a maximal 200-m front crawl effort, as examining the degree to which the on/off regularity of the oxygen uptake kinetics response was preserved. Eight high level male swimmers performed a 200-m front crawl at maximal speed during which oxygen uptake was directly measured through breath-by-breath oxymetry (averaged every 5 s). This apparatus was connected to the swimmer by a low hydrodynamic resistance respiratory snorkel and valve system. The on- and off-transient phases were symmetrical in shape (mirror image) once they were adequately fitted by a single-exponential regression models, and no slow component for the oxygen uptake response was developed. Mean (± SD) peak oxygen uptake was 69.0 (± 6.3) mL·kg(-1)·min(-1), significantly correlated with time constant of the off- transient period (r = 0.76, p < 0.05) but not with any of the other oxygen off-transient kinetic parameters studied. A direct relationship between time constant of the off-transient period and mean swimming speed of the 200-m (r = 0.77, p < 0.05), and with the amplitude of the fast component of the effort period (r = 0.72, p < 0.05) were observed. The mean amplitude and time constant of the off-transient period values were significantly greater than the respective on- transient. In conclusion, although an asymmetry between the on- and off kinetic parameters was verified, both the 200-m effort and the respectively recovery period were better characterized by a single exponential regression model. Key pointsThe VO2 slow component was not observed in the recovery period of swimming extreme efforts;The on and off transient periods were better fitted by a single exponential function, and so, these effort and recovery periods of swimming extreme efforts are

Electron paramagnetic resonance spectra of CdO-Al2O3-Bi2O3-B2O3 quaternary glasses containing VO2+ ions

NASA Astrophysics Data System (ADS)

Lalithaphani, A. V.; Srinivas, B.; Hameed, Abdul; Chary, M. Narasimha; Shareefuddin, Md.

2018-04-01

Borate glasses containing different concentrations of heavy metal oxide (CdO) with 2mol% of V2O5 as the paramagnetic probe were prepared by the conventional melt quenching technique. The prepared glasses were characterized by XRD to confirm the amorphous nature. EPR and Optical absorption studies were carried out at room temperature. EPR spectra of these glass samples were recorded at X-band frequency with 100 kHz field modulation at room temperature. From the EPR spectra the spin-Hamiltonian parameters were evaluated. The spin-Hamiltonian parameter values indicated that g|| < g┴ < ge [=2.0023] and A∥︀ > A┴. This suggests that VO2+ ions are present in octahedral sites with tetragonal compression and belong to C4v symmetry with dxy being the ground state. The measure of tetragonal distortion (Δg∥︀/Δg┴)varies non-linearly with glass composition indicating change in tetragonal distortion. The covalency rates were estimated. The number of spins participating in the resonance [N] and susceptibility (χ) values were also evaluated.

Significance of the velocity at VO2max and time to exhaustion at this velocity.

PubMed

Billat, L V; Koralsztein, J P

1996-08-01

In 1923, Hill and Lupton pointed out that for Hill himself, 'the rate of oxygen intake due to exercise increases as speed increases, reaching a maximum for the speeds beyond about 256 m/min. At this particular speed, for which no further increases in O2 intake can occur, the heart, lungs, circulation, and the diffusion of oxygen to the active muscle-fibres have attained their maximum activity. At higher speeds the requirement of the body for oxygen is far higher but cannot be satisfied, and the oxygen debt continuously increases'. In 1975, this minimal velocity which elicits maximal oxygen uptake (VO2max) was called 'critical speed' and was used to measure the maximal aerobic capacity (max Eox), i.e. the total oxygen consumed at VO2max. This should not be confused with the term 'critical power' which is closes to the power output at the 'lactate threshold'. In 1984, the term 'velocity at VO2max' and the abbreviation 'vVO2max' was introduced. It was reported that vVO2max is a useful variable that combines VO2max and economy into a single factor which can identify aerobic differences between various runners or categories of runners. vVO2max explained individual differences in performance that VO2max or running economy alone did not. Following that, the concept of a maximal aerobic running velocity (Vamax in m/sec) was formulated. This was a running velocity at which VO2max occurred and was calculated as the ratio between VO2max (ml/kg/min) minus oxygen consumption at rest, and the energy cost of running (ml/kg/sec). There are many ways to determine the velocity associated with VO2max making it difficult to compare maintenance times. In fact, the time to exhaustion (tlim) at vVO2max is reproducible in an individual, however, there is a great variability among individuals with a low coefficient of variation for vVO2max. For an average value of about 6 minutes, the coefficient of variation is about 25%. It seems that the lactate threshold which is correlated with the

Isometric strength training lowers the O2 cost of cycling during moderate-intensity exercise.

PubMed

Zoladz, Jerzy A; Szkutnik, Zbigniew; Majerczak, Joanna; Grandys, Marcin; Duda, Krzysztof; Grassi, Bruno

2012-12-01

The effect of maximal voluntary isometric strength training of knee extensor muscles on pulmonary V'O(2) on-kinetics, the O(2) cost of cycling and peak oxygen uptake (V'O(2peak)) in humans was studied. Seven healthy males (mean ± SD, age 22.3 ± 2.0 years, body weight 75.0 ± 9.2 kg, V'O(2peak) 49.5 ± 3.8 ml kg(-1) min(-1)) performed maximal isometric strength training lasting 7 weeks (4 sessions per week). Force during maximal voluntary contraction (MVC) increased by 15 % (P < 0.001) after 1 week of training, and by 19 % (P < 0.001) after 7 weeks of training. This increase in MVC was accompanied by no significant changes in the time constant of the V'O(2) on-kinetics during 6 min of moderate and heavy cycling intensities. Strength training resulted in a significant decrease (by ~7 %; P < 0.02) in the amplitude of the fundamental component of the V'O(2) on-kinetics, and therefore in a lower O(2) cost of cycling during moderate cycling intensity. The amplitude of the slow component of V'O(2) on-kinetics during heavy cycling intensity did not change with training. Training had no effect on the V'O(2peak), whereas the maximal power output reached at V'O(2peak) was slightly but significantly increased (P < 0.05). Isometric strength training rapidly (i.e., after 1 week) decreases the O(2) cost of cycling during moderate-intensity exercise, whereas it does not affect the amplitude of the slow component of the V'O(2) on-kinetics during heavy-intensity exercise. Isometric strength training can have beneficial effects on performance during endurance events.

Seasonal variations in VO2max, O2-cost, O2-deficit, and performance in elite cross-country skiers.

PubMed

Losnegard, Thomas; Myklebust, Håvard; Spencer, Matt; Hallén, Jostein

2013-07-01

Long-term effects of training are important information for athletes, coaches, and scientists when associating changes in physiological indices with changes in performance. Therefore, this study monitored changes in aerobic and anaerobic capacities and performance in a group of elite cross-country skiers during a full sport season. Thirteen men (age, 23 ± 2 years; height, 182 ± 6 cm; body mass, 76 ± 8 kg; V2 roller ski skating VO2max, 79.3 ± 4.4 ml·kg·min or 6.0 ± 0.5 L·min) were tested during the early, middle, and late preparation phase: June (T1), August (T2), and October (T3); during the competition phase: January/February (T4); and after early precompetition phase: June (T5). O2-cost during submaximal efforts, V[Combining Dot Above]O2peak, accumulated oxygen deficit (ΣO2-deficit), and performance during a 1,000-m test were determined in the V2 ski skating technique on a roller ski treadmill. Subjects performed their training on an individual basis, and detailed training logs were categorized into different intensity zones and exercise modes. Total training volume was highest during the summer months (early preseason) and decreased toward and through the winter season, whereas the volume of high-intensity training increased (all p < 0.05). There was a significant main effect among testing sessions for 1,000 m time, O2-cost, and ΣO2-deficit (Cohen's d effect size; ES = 0.63-1.37, moderate to large, all p < 0.05). In general, the changes occurred between T1 and T3 with minor changes in the competitive season (T3 to T4). No significant changes were found in V[Combining Dot Above]O2peak across the year (ES = 0.17, trivial). In conclusion, the training performed by elite cross-country skiers induced no significant changes in V[Combining Dot Above]O2peak but improved performance, O2-cost, and ΣO2-deficit.

Microstructures and thermochromic characteristics of VO2/AZO composite films

NASA Astrophysics Data System (ADS)

Xiao, Han; Li, Yi; Yuan, Wenrui; Fang, Baoying; Wang, Xiaohua; Hao, Rulong; Wu, Zhengyi; Xu, Tingting; Jiang, Wei; Chen, Peizu

2016-05-01

A vanadium dioxide (VO2) thin film was fabricated on a ZnO doped with Al (AZO) conductive glass by magnetron sputtering at room temperature followed by annealing under air atmosphere. The microstructures and optical properties of the thin film were studied. The results showed that the VO2/AZO composite film was poly-crystalline and the AZO layer did not change the preferred growth orientation of VO2. Compared to the VO2 film fabricated on soda-lime glass substrate through the same process and condition, the phase transition temperature of the VO2/AZO composite film was decreased by about 25 °C, thermal hysteresis width narrowed to 6 °C, the visible light transmittance was over 50%, the infrared transmittances before and after phase transition were 21% and 55%, respectively at 1500 nm.

Improving the electrocatalytic performance of carbon nanotubes for VO2+/VO2+ redox reaction by KOH activation

NASA Astrophysics Data System (ADS)

Dai, Lei; Jiang, Yingqiao; Meng, Wei; Zhou, Huizhu; Wang, Ling; He, Zhangxing

2017-04-01

In this paper, carbon nanotubes (CNTs) was activated by KOH treatment at high temperature and investigated as catalyst for VO2+/VO2+ redox reaction for vanadium redox flow battery (VRFB). X-ray photoelectron spectroscopy results suggest that the oxygen-containing groups can be introduced on CNTs by KOH activation. The mass transfer of vanadium ions can be accelerated by chemical etching by KOH activation and improved wettability due to the introduction of hydrophilic groups. The electrochemical properties of VO2+/VO2+ redox reaction can be enhanced by introduced oxygen-containing groups as active sites. The sample treated at 900 °C with KOH/CNTs mass ratio of 3:1 (CNTs-3) exhibits the highest electrocatalytic activity for VO2+/VO2+ redox reaction. The cell using CNTs-3 as positive catalyst demonstrates the smallest electrochemical polarization, the highest capacity and efficiency among the samples. Using KOH-activated CNTs-3 can increase the average energy efficiency of the cell by 4.4%. This work suggests that KOH-activated CNTs is a low-cost, efficient and promising catalyst for VO2+/VO2+ redox reaction for VRFB system.

Localized surface plasmon resonance modulation of totally encapsulated VO2/Au/VO2 composite structure

NASA Astrophysics Data System (ADS)

Liang, Jiran; Guo, Jinbang; Zhao, Yirui; Zhang, Ying; Su, Tianyu

2018-07-01

We design and fabricate a totally encapsulated VO2/Au/VO2 composite structure which is aimed to improve the tunability of the localized surface plasmon resonance (LSPR) peak. In this work, the structure will ensure all the Au NPs’ resonant electric field area is filled with VO2. The modulation range of the totally encapsulated structure is larger than that of the semi-coated structure. To further improve the modulation range, we also explore the VO2 thickness dependence of the structure’s LSPR modulation. With the increase of the top layer VO2 thin film thickness, the modulation range becomes larger. When the thickness is about 80 nm, the absorption peak achieves a largest shift of 112 nm. FDTD solution and equivalent model of series capacitor are used to explain the phenomenon. These results will contribute to the area of metamaterial electromagnetic wave absorber and other fields.

Localized surface plasmon resonance modulation of totally encapsulated VO2/Au/VO2 composite structure.

PubMed

Liang, Jiran; Guo, Jinbang; Zhao, Yirui; Zhang, Ying; Su, Tianyu

2018-07-06

We design and fabricate a totally encapsulated VO 2 /Au/VO 2 composite structure which is aimed to improve the tunability of the localized surface plasmon resonance (LSPR) peak. In this work, the structure will ensure all the Au NPs' resonant electric field area is filled with VO 2 . The modulation range of the totally encapsulated structure is larger than that of the semi-coated structure. To further improve the modulation range, we also explore the VO 2 thickness dependence of the structure's LSPR modulation. With the increase of the top layer VO 2 thin film thickness, the modulation range becomes larger. When the thickness is about 80 nm, the absorption peak achieves a largest shift of 112 nm. FDTD solution and equivalent model of series capacitor are used to explain the phenomenon. These results will contribute to the area of metamaterial electromagnetic wave absorber and other fields.

A VO-seeded Approach for the Growth of Star-shaped VO2 and V2O5 Nanocrystals: Facile Synthesis Structural Characterization and Elucidation of Electronic Structure

DOE Office of Scientific and Technical Information (OSTI.GOV)

L Whittaker; J Velazquez; S Banerjee

2011-12-31

Obtaining shape and size control of strongly correlated materials is imperative to obtain a fundamental understanding of the influence of finite size and surface restructuring on electronic instabilities in the proximity of the Fermi level. We present here a novel synthetic approach that takes advantage of the intrinsic octahedral symmetry of rock-salt-structured VO to facilitate the growth of six-armed nanocrystallites of related, technologically important binary vanadium oxides VO2 and V2O5. The prepared nanostructures exhibit clear six-fold symmetry and most notably show remarkable retention of electronic structure. The latter has been evidenced through extensive X-ray absorption spectroscopy measurements.

Colloidal GdVO4:Eu3+@SiO2 nanocrystals for highly selective and sensitive detection of Cu2+ ions

NASA Astrophysics Data System (ADS)

Liang, Yanjie; Noh, Hyeon Mi; Park, Sung Heum; Choi, Byung Chun; Jeong, Jung Hyun

2018-03-01

Nowadays, in view of health and safety demands, the controlled design of selective and sensitive sensors for Cu2+ detection is of considerable importance. Therefore, we construct herein core-shell colloidal GdVO4:Eu3+@SiO2 nanocrystals (NCs) as optical sensor for the detection of Cu2+, which were synthesized by a facile hydrothermal reaction and encapsulated with a uniform layer of ultrathin silica through a sol-gel strategy. The NCs present strong red emission due to energy transfer from VO43- groups to Eu3+ when exciting with ultraviolet (UV) light. This intense red emission from Eu3+ could be selectively quenched in the presence of Cu2+ in comparison to other metal ions and the limit of detection is as low as 80 nM in aqueous solution. It is revealed that the spectral overlap between the emission band of NCs and the absorption of Cu2+ accounts for this intriguing luminescence behavior. The detection ability is highly reversible by the addition of ethylenediaminetetraacetic acid (EDTA) with the recovery of almost 100% of the original luminescence. The luminescence quenching and recovery processes can be performed repeatedly with good sensing ability. These remarkable performances allow the colloidal GdVO4:Eu3+@SiO2 NCs a promising fluorescence chemosensor for detecting Cu2+ ions in aqueous solution.

Epitaxial VO2 thin-film-based radio-frequency switches with electrical activation

NASA Astrophysics Data System (ADS)

Lee, Jaeseong; Lee, Daesu; Cho, Sang June; Seo, Jung-Hun; Liu, Dong; Eom, Chang-Beom; Ma, Zhenqiang

2017-09-01

Vanadium dioxide (VO2) is a correlated material exhibiting a sharp insulator-to-metal phase transition (IMT) caused by temperature change and/or bias voltage. We report on the demonstration of electrically triggered radio-frequency (RF) switches based on epitaxial VO2 thin films. The highly epitaxial VO2 and SnO2 template layer was grown on a (001) TiO2 substrate by pulsed laser deposition (PLD). A resistance change of the VO2 thin films of four orders of magnitude was achieved with a relatively low threshold voltage, as low as 13 V, for an IMT phase transition. VO2 RF switches also showed high-frequency responses of insertion losses of -3 dB at the on-state and return losses of -4.3 dB at the off-state over 27 GHz. Furthermore, an intrinsic cutoff frequency of 17.4 THz was estimated for the RF switches. The study on electrical IMT dynamics revealed a phase transition time of 840 ns.

Transport properties of ultra-thin VO{sub 2} films on (001) TiO{sub 2} grown by reactive molecular-beam epitaxy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Paik, Hanjong; Tashman, Joshua W.; Moyer, Jarrett A.

2015-10-19

We report the growth of (001)-oriented VO{sub 2} films as thin as 1.5 nm with abrupt and reproducible metal-insulator transitions (MIT) without a capping layer. Limitations to the growth of thinner films with sharp MITs are discussed, including the Volmer-Weber type growth mode due to the high energy of the (001) VO{sub 2} surface. Another key limitation is interdiffusion with the (001) TiO{sub 2} substrate, which we quantify using low angle annular dark field scanning transmission electron microscopy in conjunction with electron energy loss spectroscopy. We find that controlling island coalescence on the (001) surface and minimization of cation interdiffusion bymore » using a low growth temperature followed by a brief anneal at higher temperature are crucial for realizing ultrathin VO{sub 2} films with abrupt MIT behavior.« less

Evidence of cardiac functional reserve upon exhaustion during incremental exercise to determine VO2max.

PubMed

Elliott, Adrian D; Skowno, Justin; Prabhu, Mahesh; Noakes, Timothy David; Ansley, Les

2015-01-01

There remains considerable debate regarding the limiting factor(s) for maximal oxygen uptake (VO2max). Previous studies have shown that the central circulation may be the primary limiting factor for VO2max and that cardiac work increases beyond VO2max. We sought to evaluate whether the work of the heart limits VO2max during upright incremental cycle exercise to exhaustion. Eight trained men completed two incremental exercise trials, each terminating with exercise at two different rates of work eliciting VO2max (MAX and SUPRAMAX). During each exercise trial we continuously recorded cardiac output using pulse-contour analysis calibrated with a lithium dilution method. Intra-arterial pressure was recorded from the radial artery while pulmonary gas exchange was measured continuously for an assessment of oxygen uptake. The workload during SUPRAMAX (mean±SD: 346.5±43.2 W) was 10% greater than that achieved during MAX (315±39.3 W). There was no significant difference between MAX and SUPRAMAX for Q (28.7 vs 29.4 L/min) or VO2 (4.3 vs 4.3 L/min). Mean arterial pressure was significantly higher during SUPRAMAX, corresponding to a higher cardiac power output (8.1 vs 8.5 W; p<0.06). Despite similar VO2 and Q, the greater cardiac work during SUPRAMAX supports the view that the heart is working submaximally at exhaustion during an incremental exercise test (MAX). Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://group.bmj.com/group/rights-licensing/permissions.

An Accurate VO[subscript 2]max Nonexercise Regression Model for 18-65-Year-Old Adults

ERIC Educational Resources Information Center

Bradshaw, Danielle I.; George, James D.; Hyde, Annette; LaMonte, Michael J.; Vehrs, Pat R.; Hager, Ronald L.; Yanowitz, Frank G.

2005-01-01

The purpose of this study was to develop a regression equation to predict maximal oxygen uptake (VO[subscript 2]max) based on nonexercise (N-EX) data. All participants (N = 100), ages 18-65 years, successfully completed a maximal graded exercise test (GXT) to assess VO[subscript 2]max (M = 39.96 mL[middle dot]kg[superscript -1][middle…

BiVO4 -TiO2 Composite Photocatalysts for Dye Degradation Formed Using the SILAR Method.

PubMed

Odling, Gylen; Robertson, Neil

2016-09-19

Composite photocatalyst films have been fabricated by depositing BiVO4 upon TiO2 via a sequential ionic layer adsorption reaction (SILAR) method. The photocatalytic materials were investigated by XRD, TEM, UV/Vis diffuse reflectance, inductively coupled plasma optical emission spectrometry (ICP-OES), XPS, photoluminescence and Mott-Schottky analyses. SILAR processing was found to deposit monoclinic-scheelite BiVO4 nanoparticles onto the surface, giving successive improvements in the films' visible light harvesting. Electrochemical and valence band XPS studies revealed that the prepared heterojunctions have a type II band structure, with the BiVO4 conduction band and valence band lying cathodically shifted from those of TiO2 . The photocatalytic activity of the films was measured by the decolourisation of the dye rhodamine 6G using λ>400 nm visible light. It was found that five SILAR cycles was optimal, with a pseudo-first-order rate constant of 0.004 min(-1) . As a reference material, the same SILAR modification has been made to an inactive wide-band-gap ZrO2 film, where the mismatch of conduction and valence band energies disallows charge separation. The photocatalytic activity of the BiVO4 -ZrO2 system was found to be significantly reduced, highlighting the importance of charge separation across the interface. The mechanism of action of the photocatalysts has also been investigated, in particular the effect of self-sensitisation by the model organic dye and the ability of the dye to inject electrons into the photocatalyst's conduction band. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Ambiguous Role of Growth-Induced Defects on the Semiconductor-to-Metal Characteristics in Epitaxial VO2/TiO2 Thin Films.

PubMed

Mihailescu, Cristian N; Symeou, Elli; Svoukis, Efthymios; Negrea, Raluca F; Ghica, Corneliu; Teodorescu, Valentin; Tanase, Liviu C; Negrila, Catalin; Giapintzakis, John

2018-04-25

Controlling the semiconductor-to-metal transition temperature in epitaxial VO 2 thin films remains an unresolved question both at the fundamental as well as the application level. Within the scope of this work, the effects of growth temperature on the structure, chemical composition, interface coherency and electrical characteristics of rutile VO 2 epitaxial thin films grown on TiO 2 substrates are investigated. It is hereby deduced that the transition temperature is lower than the bulk value of 340 K. However, it is found to approach this value as a function of increased growth temperature even though it is accompanied by a contraction along the V 4+ -V 4+ bond direction, the crystallographic c-axis lattice parameter. Additionally, it is demonstrated that films grown at low substrate temperatures exhibit a relaxed state and a strongly reduced transition temperature. It is suggested that, besides thermal and epitaxial strain, growth-induced defects may strongly affect the electronic phase transition. The results of this work reveal the difficulty in extracting the intrinsic material response to strain, when the exact contribution of all strain sources cannot be effectively determined. The findings also bear implications on the limitations in obtaining the recently predicted novel semi-Dirac point phase in VO 2 /TiO 2 multilayer structures.

Resistance modulation in VO2 nanowires induced by an electric field via air-gap gates

NASA Astrophysics Data System (ADS)

Kanki, Teruo; Chikanari, Masashi; Wei, Tingting; Tanaka, Hidekazu; The Institute of Scientific; Industrial Research Team

Vanadium dioxide (VO2) shows huge resistance change with metal-insulator transition (MIT) at around room temperature. Controlling of the MIT by applying an electric field is a topical ongoing research toward the realization of Mott transistor. In this study, we have successfully switched channel resistance of VO2 nano-wire channels by a pure electrostatic field effect using a side-gate-type field-effect transistor (SG-FET) viaair gap and found that single crystalline VO2 nanowires and the channels with narrower width enhance transport modulation rate. The rate of change in resistance ((R0-R)/R, where R0 and R is the resistance of VO2 channel with off state and on state gate voltage (VG) , respectively) was 0.42 % at VG = 30 V in in-plane poly-crystalline VO2 channels on Al2O3(0001) substrates, while the rate in single crystalline channels on TiO2 (001) substrates was 3.84 %, which was 9 times higher than that using the poly-crystalline channels. With reducing wire width from 3000 nm to 400 nm of VO2 on TiO2 (001) substrate, furthermore, resistance modulation ratio enhanced from 0.67 % to 3.84 %. This change can not be explained by a simple free-electron model. In this presentation, we will compare the electronic properties between in-plane polycrystalline VO2 on Al2O3 (0001) and single crystalline VO2 on TiO2 (001) substrates, and show experimental data in detail..

Phase Transformation of VO2 Nanoparticles Assisted by Microwave Heating

PubMed Central

Sikong, Lek.

2014-01-01

The microwave assisted synthesis nowadays attracts a great deal of attention. Monoclinic phase VO2 (M) was prepared from NH4VO3 and H2C2O4 · 2H2O by a rapid microwave assisted technique. The synthesis parameters, microwave irradiation time, microwave power, and calcinations temperature were systematically varied and their influences on the structure and morphology were evaluated. The microwave power level has been carried out in range 180–600 W. TEM analysis demonstrated nanosized samples. The structural and morphological properties were measured using XRD, TEM, and thermal analyses. The variations of vanadium phase led to thermochromic properties. PMID:24688438

Solution-Processed VO2-SiO2 Composite Films with Simultaneously Enhanced Luminous Transmittance, Solar Modulation Ability and Anti-Oxidation property

PubMed Central

Zhao, Lili; Miao, Lei; Liu, Chengyan; Li, Chao; Asaka, Toru; Kang, Yipu; Iwamoto, Yuji; Tanemura, Sakae; Gu, Hui; Su, Huirong

2014-01-01

Recently, researchers spare no efforts to fabricate desirable vanadium dioxide (VO2) film which provides simultaneously high luminous transmittance and outstanding solar modulation ability, yet progress towards the optimization of one aspect always comes at the expense of the other. Our research devotes to finding a reproducible economic solution-processed strategy for fabricating VO2-SiO2 composite films, with the aim of boosting the performance of both aspects. Compare to VO2 film, an improvement of 18.9% (from 29.6% to 48.5%) in the luminous transmittance as well as an increase of 6.0% (from 9.7% to 15.7%) in solar modulation efficiency is achieved when the molar ratio of Si/V attains 0.8. Based on the effective medium theory, we simulate the optical spectra of the composite films and the best thermochromic property is obtained when the filling factor attains 0.5, which is consistent with the experimental results. Meanwhile, the improvement of chemical stability for the composite film against oxidation has been confirmed. Tungsten is introduced to reduce the phase transition temperature to the ambient temperature, while maintain the thermochromism required for application as smart window. Our research set forth a new avenue in promoting practical applications of VO2-based thermochromic fenestration. PMID:25384345

Solution-Processed VO2-SiO2 Composite Films with Simultaneously Enhanced Luminous Transmittance, Solar Modulation Ability and Anti-Oxidation property

NASA Astrophysics Data System (ADS)

Zhao, Lili; Miao, Lei; Liu, Chengyan; Li, Chao; Asaka, Toru; Kang, Yipu; Iwamoto, Yuji; Tanemura, Sakae; Gu, Hui; Su, Huirong

2014-11-01

Recently, researchers spare no efforts to fabricate desirable vanadium dioxide (VO2) film which provides simultaneously high luminous transmittance and outstanding solar modulation ability, yet progress towards the optimization of one aspect always comes at the expense of the other. Our research devotes to finding a reproducible economic solution-processed strategy for fabricating VO2-SiO2 composite films, with the aim of boosting the performance of both aspects. Compare to VO2 film, an improvement of 18.9% (from 29.6% to 48.5%) in the luminous transmittance as well as an increase of 6.0% (from 9.7% to 15.7%) in solar modulation efficiency is achieved when the molar ratio of Si/V attains 0.8. Based on the effective medium theory, we simulate the optical spectra of the composite films and the best thermochromic property is obtained when the filling factor attains 0.5, which is consistent with the experimental results. Meanwhile, the improvement of chemical stability for the composite film against oxidation has been confirmed. Tungsten is introduced to reduce the phase transition temperature to the ambient temperature, while maintain the thermochromism required for application as smart window. Our research set forth a new avenue in promoting practical applications of VO2-based thermochromic fenestration.

Voltage-induced switching dynamics based on an AZO/VO2/AZO sandwiched structure

NASA Astrophysics Data System (ADS)

Xiao, Han; Li, Yi; Fang, Baoying; Wang, Xiaohua; Liu, Zhimin; Zhang, Jiao; Li, Zhengpeng; Huang, Yaqin; Pei, Jiangheng

2017-11-01

A vanadium dioxide (VO2) thin film was prepared on an Al-doped ZnO (AZO) conductive glass substrate by DC magnetron sputtering and a post-annealing process. The AZO/VO2/AZO sandwiched structure was fabricated on the VO2/AZO composite film using photolithography and a chemical etching process. The composition, microstructure and optical properties of the VO2/AZO composite film were tested. The results showed that the VO2/AZO composite film was poly-crystalline and the AZO layer did not change the preferred growth orientation of VO2. When the voltage was applied on both of the transparent conductive layers of the AZO/VO2/AZO sandwiched structure, an abrupt change in the current was observed at different temperatures. The temperature dependence of I-V characteristic curves for the AZO/VO2/AZO sandwiched structure was analyzed. The phase transition voltage value is 7.5 V at 20 °C and decreases with increasing temperature.

Induction of cyto-protective autophagy by paramontroseite VO2 nanocrystals

NASA Astrophysics Data System (ADS)

Zhou, Wei; Miao, Yanyan; Zhang, Yunjiao; Liu, Liang; Lin, Jun; Yang, James Y.; Xie, Yi; Wen, Longping

2013-04-01

A variety of inorganic nanomaterials have been shown to induce autophagy, a cellular degradation process critical for the maintenance of cellular homeostasis. The overwhelming majority of autophagic responses elicited by nanomaterials were detrimental to cell fate and contributed to increased cell death. A widely held view is that the inorganic nanoparticles, when encapsulated and trapped by autophagosomes, may compromise the normal autophagic process due to the inability of the cells to degrade these materials and thus they manifest a detrimental effect on the well-being of a cell. Here we show that, contrary to this notion, nano-sized paramontroseite VO2 nanocrystals (P-VO2) induced cyto-protective, rather than death-promoting, autophagy in cultured HeLa cells. P-VO2 also caused up-regulation of heme oxygenase-1 (HO-1), a cellular protein with a demonstrated role in protecting cells against death under stress situations. The autophagy inhibitor 3-methyladenine significantly inhibited HO-1 up-regulation and increased the rate of cell death in cells treated with P-VO2, while the HO-1 inhibitor protoporphyrin IX zinc (II) (ZnPP) enhanced the occurrence of cell death in the P-VO2-treated cells while having no effect on the autophagic response induced by P-VO2. On the other hand, Y2O3 nanocrystals, a control nanomaterial, induced death-promoting autophagy without affecting the level of expression of HO-1, and the pro-death effect of the autophagy induced by Y2O3. Our results represent the first report on a novel nanomaterial-induced cyto-protective autophagy, probably through up-regulation of HO-1, and may point to new possibilities for exploiting nanomaterial-induced autophagy for therapeutic applications.

Epitaxial growth of VO2 by periodic annealing

NASA Astrophysics Data System (ADS)

Tashman, J. W.; Lee, J. H.; Paik, H.; Moyer, J. A.; Misra, R.; Mundy, J. A.; Spila, T.; Merz, T. A.; Schubert, J.; Muller, D. A.; Schiffer, P.; Schlom, D. G.

2014-02-01

We report the growth of ultrathin VO2 films on rutile TiO2 (001) substrates via reactive molecular-beam epitaxy. The films were formed by the cyclical deposition of amorphous vanadium and its subsequent oxidation and transformation to VO2 via solid-phase epitaxy. Significant metal-insulator transitions were observed in films as thin as 2.3 nm, where a resistance change ΔR/R of 25 was measured. Low angle annular dark field scanning transmission electron microscopy was used in conjunction with electron energy loss spectroscopy to study the film/substrate interface and revealed the vanadium to be tetravalent and the titanium interdiffusion to be limited to 1.6 nm.

Exertional oxygen uptake kinetics: a stamen of stamina?

PubMed

Whipp, Brian J; Rossiter, H B; Ward, S A

2002-04-01

The fundamental pulmonary O(2) uptake (.VO(2)) response to moderate, constant-load exercise can be characterized as (d.VO(2)/dt)(tau)+Delta.VO(2) (t)=Delta.VO(2SS) where Delta.VO(2SS) is the steady-state response, and tau is the time constant, with the .VO(2) kinetics reflecting intramuscular O(2) uptake (.QO(2)) kinetics, to within 10%. The role of phosphocreatine (PCr) turnover in .QO(2) control can be explored using (31)P-MR spectroscopy, simultaneously with .VO(2). Although tau.VO(2) and tauPCr vary widely among subjects (approx. 20-65 s), they are not significantly different from each other, either at the on- or off-transient. A caveat to interpreting the "well-fit" exponential is that numerous units of similar Delta.VO(2SS) but with a wide tau distribution can also yield a .VO(2) response with an apparent single tau. This tau is, significantly, inversely correlated with lactate threshold and .VO(2max)(but is poorly predictive; a frail stamen, therefore), consistent with tau not characterizing a compartment with uniform kinetics. At higher intensities, the fundamental kinetics become supplemented with a slowly-developing phase, setting .VO(2)on a trajectory towards maximum .VO(2). This slow component is also demonstrable in Delta[PCr]: the decreased efficiency thereby reflecting a predominantly high phosphate-cost of force production rather than a high O(2)-cost of phosphate production. We also propose that the O(2)-deficit for the slow-component is more likely to reflect shifting Delta.VO(2SS) rather than a single one with a single tau.

Self-Assembled Multilayer Structure and Enhanced Thermochromic Performance of Spinodally Decomposed TiO2-VO2 Thin Film.

PubMed

Sun, Guangyao; Zhou, Huaijuan; Cao, Xun; Li, Rong; Tazawa, Masato; Okada, Masahisa; Jin, Ping

2016-03-23

Composite films of VO2-TiO2 were deposited on sapphire (11-20) substrate by cosputtering method. Self-assembled well-ordered multilayer structure with alternating Ti- and V-rich epitaxial thin layer was obtained by thermal annealing via a spinodal decomposition mechanism. The structured thermochromic films demonstrate superior optical modulation upon phase transition, with significantly reduced transition temperature. The results provide a facile and novel approach to fabricate smart structures with excellent performance.

Contribution of central and peripheral adaptations to changes in VO₂max following four weeks of sprint interval training.

PubMed

Raleigh, James P; Giles, Matthew D; Islam, Hashim; Nelms, Matthew William; Bentley, Robert F; Jones, Joshua H; Neder, J Alberto; Boonstra, Kristen; Quadrilatero, Joe; Simpson, Craig A; Tschakovsky, Michael E; Gurd, Brendon J

2018-05-07

The current study examined the contribution of central and peripheral adaptations to changes in maximal oxygen uptake (VO₂max) following sprint interval training (SIT). Twenty-three males completed four weekly SIT sessions (8 x 20 second cycling bouts at ~170% of work rate at VO₂max, 10 second recovery) for four weeks. Following completion of training, the relationship between changes in VO₂max and changes in central (cardiac output) and peripheral (a-vO₂diff, muscle capillary density, oxidative capacity, fibre-type distribution) adaptations was determined in all participants using correlation analysis. Participants were then divided in to tertiles based on the magnitude of their individual VO₂max responses and differences in central/peripheral adaptations were examined in the top (HI; ~10 mL/kg/min increase in VO₂max, p<0.05) and bottom (LO; no change in VO₂max, p>0.05) tertiles (n=8 each). Training had no impact on Qmax and no differences were observed between the LO and HI groups (p>0.05). A-vO₂diff increased in the HI group only (p<0.05) and correlated significantly (r=0.71, p<0.01) with changes in VO₂max across all participants. Muscle capillary density (p<0.02) and ß-hydroxyacyl-CoA dehydrogenase maximal activity (p<0.05) increased in both groups, with no between-group differences (p>0.05). Citrate synthase maximal activity (p<0.01) and type IIA fibre composition (p<0.05) increased in the LO group only. Collectively, while the heterogeneity in the observed VO₂max response following four weeks of SIT appears to be attributable to individual differences in systemic vascular and/or muscular adaptations, the markers examined in the current study were unable to explain the divergent VO₂max responses in the LO and HI groups.

Effects of prior heavy exercise on VO(2) kinetics during heavy exercise are related to changes in muscle activity.

PubMed

Burnley, Mark; Doust, Jonathan H; Ball, Derek; Jones, Andrew M

2002-07-01

We hypothesized that the elevated primary O(2) uptake (VO(2)) amplitude during the second of two bouts of heavy cycle exercise would be accompanied by an increase in the integrated electromyogram (iEMG) measured from three leg muscles (gluteus maximus, vastus lateralis, and vastus medialis). Eight healthy men performed two 6-min bouts of heavy leg cycling (at 70% of the difference between the lactate threshold and peak VO(2)) separated by 12 min of recovery. The iEMG was measured throughout each exercise bout. The amplitude of the primary VO(2) response was increased after prior heavy leg exercise (from mean +/- SE 2.11 +/- 0.12 to 2.44 +/- 0.10 l/min, P < 0.05) with no change in the time constant of the primary response (from 21.7 +/- 2.3 to 25.2 +/- 3.3 s), and the amplitude of the VO(2) slow component was reduced (from 0.79 +/- 0.08 to 0.40 +/- 0.08 l/min, P < 0.05). The elevated primary VO(2) amplitude after leg cycling was accompanied by a 19% increase in the averaged iEMG of the three muscles in the first 2 min of exercise (491 +/- 108 vs. 604 +/- 151% increase above baseline values, P < 0.05), whereas mean power frequency was unchanged (80.1 +/- 0.9 vs. 80.6 +/- 1.0 Hz). The results of the present study indicate that the increased primary VO(2) amplitude observed during the second of two bouts of heavy exercise is related to a greater recruitment of motor units at the onset of exercise.

Prognostic impact of peakVO2-changes in stable CHF on chronic beta-blocker treatment.

PubMed

Frankenstein, L; Nelles, M; Hallerbach, M; Dukic, D; Fluegel, A; Schellberg, D; Katus, H A; Remppis, A; Zugck, C

2007-11-15

Peak oxygen uptake (pVO2) is used for risk stratification in chronic heart failure (CHF), but little is known about the prognostic impact of pVO2-changes in patients on chronic beta-blocker (BBL) therapy. We therefore prospectively evaluated individual pVO2-changes at a 6-month interval in patients all receiving BBL. 194 patients with stable CHF on stable medication were included (V1) and underwent clinical evaluation and exercise testing. Testing was repeated (V2) at 5.7+/-1.5 months after V1 and patients were followed >12 months after V2. Death or hospitalisation due to cardiac reasons was the predefined EP (EPP, end-point positive; n=62; EPN, end-point negative; n=113). Initial characteristics did not differ between EPP and EPN. Multivariate cox regression analysis revealed that change of pVO2 (EPP: -0.6+/-2.6 ml/kg min; EPN: +2.5+/-3.3 ml/kg min; p<0.001) was independent to pVO2, LVEF, NTproBNP and NYHA at V2 for prediction of the combined end-point during follow-up. An increase of pVO2 by 10% was identified as an adequate cut-off value for risk stratification and ROC-analysis showed the significant incremental prognostic value of the determination of pVO2 changes in combination with pVO2. Serial measurements of pVO2 yield additional information for risk stratification in clinically homogenous CHF patients receiving BBL. This is the first study demonstrating this fact within a narrow predefined interval with all patients on BBL.

Protecting hydrogenation-generated oxygen vacancies in BiVO4 photoanode for enhanced water oxidation with conformal ultrathin amorphous TiO2 layer

NASA Astrophysics Data System (ADS)

Zhang, Yang; Zhang, Xintong; Wang, Dan; Wan, Fangxu; Liu, Yichun

2017-05-01

Introducing appropriate amount of oxygen vacancies by hydrogenation treatment is a simple and efficient way to improve the photoelectrochemical performance of nanostructured oxide photoanodes. However, the hydrogenation effect is often not durable due to the gradual healing of oxygen vacancies at or close to surface of photoanodes. Herein, we tackled the problem by conformal coating the hydrogenated nanoporous BiVO4 (H-BiVO4) photoanode with an ultrathin layer of amorphous TiO2. Photoelectrochemical measurements showed that a 4 nm-thick TiO2 layer could significantly improve the stability of H-BiVO4 photoanode for repeated working test, with negligible influence on the initial photocurrent compared to the uncoated one. Mott-Schottky and linear sweep voltammetry measurements showed that donor density and photocurrent density of the H-BiVO4 electrode almost decayed to the values of pristine BiVO4 electrode after 3 h test, while the amorphous TiO2-coated electrode only degraded by 6% and 5% of the initial values respectively in the same period. The investigation thus suggested that the amorphous TiO2 layer did protect the oxygen vacancies in H-BiVO4 photoanode by isolating these oxygen vacancies from environmental oxygen, while at the same time not impeding the interfacial charge transfer to water molecules due to its leaky nature.

Multiple variables explain the variability in the decrement in VO2max during acute hypobaric hypoxia.

PubMed

Robergs, R A; Quintana, R; Parker, D L; Frankel, C C

1998-06-01

We used multiple regression analyses to determine the relationships between the decrement in sea level (SL, 760 Torr) VO2max during hypobaric hypoxia (HH) and variables that could alter or be related to the decrement in VO2max. HH conditions consisted of 682 Torr, 632 Torr, and 566 Torr, and the measured independent variables were SL-VO2max, SL lactate threshold (SL-LT), the change in hemoglobin saturation at VO2max between 760 and 566 Torr (delta SaO2max), lean body mass (LBM), and gender. Male (N = 14) and female (N = 14) subjects of varied fitness, training status, and residential altitude (1,640-2,460 m) completed cycle ergometry tests of VO2max at each HH condition under randomized and single-blinded conditions. VO2max decreased significantly from 760 Torr after 682 Torr (approximately 915 m) (3.5 +/- 0.9 to 3.4 +/- 0.8 L.min-1, P = 0.0003). Across all HH conditions, the slope of the relative decrement in VO2max (%VO2max) during HH was -9.2%/100 mm Hg (-8.1%/1000 m) with an initial decrease from 100% estimated to occur below 705 Torr (610 m). Step-wise multiple regression revealed that SL-VO2max, SL-LT, delta SaO2max, LBM, and gender each significantly combined to account for 89.03% of the variance in the decrement in VO2max (760-566 Torr) (P < 0.001). Individuals who have a combination of a large SL-VO2max, a small SL-LT (VO2, L.min-1), greater reductions in delta SaO2max, a large LBM, and are male have the greatest decrement in VO2max during HH. The unique variance explanation afforded by SL-LT, LBM, and gender suggests that issues pertaining to oxygen diffusion within skeletal muscle may add to the explanation of between subjects variability in the decrement in VO2max during HH.

Human mitochondrial haplogroup H: the highest VO2max consumer--is it a paradox?

PubMed

Martínez-Redondo, Diana; Marcuello, Ana; Casajús, José A; Ara, Ignacio; Dahmani, Yahya; Montoya, Julio; Ruiz-Pesini, Eduardo; López-Pérez, Manuel J; Díez-Sánchez, Carmen

2010-03-01

Mitochondrial background has been demonstrated to influence maximal oxygen uptake (VO(2max), in mLkg(-1)min(-1)), but this genetic influence can be compensated for by regular exercise. A positive correlation among electron transport chain (ETC) coupling, ATP and reactive oxygen species (ROS) production has been established, and mitochondrial variants have been reported to show differences in their ETC performance. In this study, we examined in detail the VO(2max) differences found among mitochondrial haplogroups. We recruited 81 healthy male Spanish Caucasian individuals and determined their mitochondrial haplogroup. Their VO(2max) was determined using incremental cycling exercise (ICE). VO(2max) was lower in J than in non-J haplogroup individuals (P=0.04). The H haplogroup was responsible for this difference (VO(2max); J vs. H; P=0.008) and this group also had significantly higher mitochondrial oxidative damage (mtOD) than the J haplogroup (P=0.04). In agreement with these results, VO(2max) and mtOD were positively correlated (P=0.01). Given that ROS production is the major contributor to mtOD and consumes four times more oxygen per electron than the ETC, our results strongly suggest that ROS production is responsible for the higher VO(2max) found in the H variant. These findings not only contribute to a better understanding of the mechanisms underneath VO(2max), but also help to explain some reported associations between mitochondrial haplogroups and mtOD with longevity, sperm motility, premature aging and susceptibility to different pathologies.

Optical, physical and structural studies of vanadium doped P2O5-BaO-Li2O glasses

NASA Astrophysics Data System (ADS)

Lakshmikantha, R.; Ayachit, N. H.; Anavekar, R. V.

2014-02-01

Glasses in the compositions (Li2O)25-(BaO)25-(P2O5)50-x-(V2O5)x (with x=0.5,1.0,1.5,2.0,2.5, and 3.0 mol%) have been prepared by the conventional melt quenching technique. X-ray powder diffractrogram show broad peaks which conforms glassy nature of the sample. Differential scanning calorimetry (DSC) thermograms show characteristic glass transition temperature (Tg) and it increases with increasing substitution of V2O5 for P2O5. The measured physical parameters like density, refractive index, ionic concentration and electronic polarizability are found to vary linearly with increasing x. Infrared spectra exhibits few bands, which are attributed to (P=O)AS, (P=O)S, (V=O), (P-O-P)AS,P-O-V, (P-O-P)AS and O-P-O vibrations. The optical absorption spectra of VO2+ ions in these glasses show three bands and are assigned to the 2B2→ 2E,2B2→ 2B1 and 2B2→ 2A1 transitions. Electron paramagnetic resonance spectra of all the glass samples exhibit resonance signals characteristic of VO2+ ions. The values of Spin-Hamiltonian parameters indicate that the VO2+ ions are present in octahedral sites with tetragonal compression and belong to C4V symmetry.

Spectroscopic analysis of phase constitution of high quality VO2 thin film prepared by facile sol-gel method

NASA Astrophysics Data System (ADS)

Wu, Y. F.; Fan, L. L.; Chen, S. M.; Chen, S.; Zou, C. W.; Wu, Z. Y.

2013-04-01

VO2 thin films with large-area were prepared on Al2O3 substrates by a simple sol-gel method. After an annealing treatment under low vacuum condition, all the VO2 films showed a preferred growth direction and exhibited excellent semiconductor-metal transition (SMT) characteristics. The structure and electrical properties of the obtained VO2 films were investigated systematically. Raman spectra, X-ray diffraction and X-ray absorption spectra measurements pointed out that the VO2 film on Al_2 O_3 ( {10overline 1 0}) substrate showed a M1 phase instead of M2 phase as reported in previous studies. Based on the experiment results, it was suggested that the strained structure of oriented VO2 films could be a mechanism for the formation of the intermediate M2 phase, whereas it is difficult to access the pure M2 phase of undoped VO2 films. VO2 film on Al_2 O_3 ( {10overline 1 0} ) substrate showed a lower SMT temperature compared to VO2 film on Al2O3 (0001), which can be mostly attributed to the differences of both lattice mismatch and thermal stress. The present results confirm and make clear the relevance of the substrate orientation in the growth of VO2 film and their different contributions to the SMT characteristics in vanadate systems.

Effect of W addition on the electrical switching of VO{sub 2} thin films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rajeswaran, Bharathi, E-mail: rajeswaran.bharathi@gmail.com, E-mail: rbharathi@mrc.iisc.ernet.in; Umarji, Arun M.

2016-03-15

Vanadium Oxide has been a frontrunner in the field of oxide electronics because of its metal-insulator transition (MIT). The interplay of different structures of VO{sub 2} has played a crucial role in deciding the magnitude of the first order MIT. Substitution doping has been found to introduce different polymorphs of VO{sub 2}. Hence the role of substitution doping in stabilizing the competing phases of VO{sub 2} in the thin film form remains underexplored. Consequently there have been reports both discounting and approving such a stabilization of competing phases in VO{sub 2}. It is reported in the literature that the bandwidthmore » of the hysteresis and transition temperature of VO{sub 2} can be tuned by substitutional doping of VO{sub 2} with W. In this work, we have adopted a novel technique called, Ultrasonic Nebulized Spray Pyrolysis of Aqueous Combustion Mixture (UNSPACM) to deposit VO{sub 2} and W- doped VO{sub 2} as thin films. XRD and Raman spectroscopy were used to investigate the role of tungsten on the structure of VO{sub 2} thin films. Morphology of the thin films was found to be consisting of globular and porous nanoparticles of size ∼ 20 nm. Transition temperature decreased with the addition of W. We found that for 2.0 at % W doping in VO{sub 2}, the transition temperature has reduced from 68 {sup o} C to 25 {sup o} C. It is noted that W-doping in the process of reducing the transition temperature, alters the local structure and also increases room temperature carrier concentration.« less

Thickness-dependent metal-to-insulator transition in epitaxial VO2 films

NASA Astrophysics Data System (ADS)

Zhi, Bowen; Gao, Guanyin; Tan, Xuelian; Chen, Pingfan; Wang, Lingfei; Jin, Shaowei; Wu, Wenbin

2014-12-01

The metal-to-insulator transition (MIT) of VO2 films with a thickness of 3-100 nm on TiO2(001) substrates has been investigated. When varying the film thickness from 10 to 100 nm, the MIT temperature was first kept at 290 K in the range of 10-14 nm, and then increased with thickness increasing due to the strain relaxation. The origin of the suppressed transition in VO2 films thinner than 6 nm was also investigated. When prolonging the in situ annealing time, the sharpness, amplitude and width of the transition for 4 nm thick films were all increased, suggesting improved crystallinity rather than Ti diffusion from the substrates. In addition, the MIT was suppressed when the VO2 films were covered by a TiO2 layer, indicating that the interface effect via the confinement of the dimerization of the V atoms should be the main reason.

Chemical composition of an aqueous oxalato-/citrato-VO(2+) solution as determinant for vanadium oxide phase formation.

PubMed

Peys, Nick; Maurelli, Sara; Reekmans, Gunter; Adriaensens, Peter; De Gendt, Stefan; Hardy, An; Van Doorslaer, Sabine; Van Bael, Marlies K

2015-01-05

Aqueous solutions of oxalato- and citrato-VO(2+) complexes are prepared, and their ligand exchange reaction is investigated as a function of the amount of citrate present in the aqueous solution via continuous-wave electron paramagnetic resonance (CW EPR) and hyperfine sublevel correlation (HYSCORE) spectroscopy. With a low amount of citrate, monomeric cis-oxalato-VO(2+) complexes occur with a distorted square-pyramidal geometry. As the amount of citrate increases, oxalate is gradually exchanged for citrate. This leads to (i) an intermediate situation of monomeric VO(2+) complexes with a mix of oxalate/citrate ligands and (ii) a final situation of both monomeric and dimeric complexes with exclusively citrato ligands. The monomeric citrato-VO(2+) complexes dominate (abundance > 80%) and are characterized by a 6-fold chelation of the vanadium(IV) ion by 4 RCO2(-) ligands at the equatorial positions and a H2O/R-OH ligand at the axial position. The different redox stabilities of these complexes, relative to that of dissolved O2 in the aqueous solution, is analyzed via (51)V NMR. It is shown that the oxidation rate is the highest for the oxalato-VO(2+) complexes. In addition, the stability of the VO(2+) complexes can be drastically improved by evacuation of the dissolved O2 from the solution and subsequent storage in a N2 ambient atmosphere. The vanadium oxide phase formation process, starting with the chemical solution deposition of the aqueous solutions and continuing with subsequent processing in an ambient 0.1% O2 atmosphere, differs for the two complexes. The oxalato-VO(2+) complexes turn into the oxygen-deficient crystalline VO2 B at 400 °C, which then turns into crystalline V6O13 at 500 °C. In contrast, the citrato-VO(2+) complexes form an amorphous film at 400 °C that crystallizes into VO2 M1 and V6O13 at 500 °C.

Electrochemical Synthesis of Amorphous VO2 Colloids and Their Rapid Thermal Transforming to VO2 (M) Nanoparticles with Good Thermochromic Performance.

PubMed

Wu, Hao; Li, Ming; Zhong, Li; Luo, Yuan Yuan; Li, Guang Hai

2016-12-05

Amorphous VO 2 (a-VO 2 ) colloids were synthesized by electrochemical anodic oxidation of metallic vanadium. It was found that the a-VO 2 colloids have a cotton-like morphology composed of very small clusters, and that the crystallization temperature of the a-VO 2 colloids can be adjusted either by the electrolyte of the anodic oxidation or/and the dispersion agent of the colloids. VO 2 (M) nanoparticles (NPs) (and a NP film) with an average size of about 50 nm can be obtained by a rapid thermal annealing of the a-VO 2 colloids at 310 °C under air, which is beneficial for practical applications. The VO 2 (M) NP film shows an obvious metal-semiconductor transition with a resistance less than 10 Ω in the metallic state. An integral visible transmittance of 40.7 %, a solar transmittance modulation of 9.4 %, and a resistance modulation in the order of 5×10 4 were realized in the VO 2 (M) NP film. © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

VO2+ ions in zinc lead borate glasses studied by EPR and optical absorption techniques.

PubMed

Prakash, P Giri; Rao, J Lakshmana

2005-09-01

Electron paramagnetic resonance (EPR) and optical absorption spectra of vanadyl ions in zinc lead borate (ZnO-PbO-B2O3) glass system have been studied. EPR spectra of all the glass samples exhibit resonance signals characteristic of VO2+ ions. The values of spin-Hamiltonian parameters indicate that the VO2+ ions in zinc lead borate glasses were present in octahedral sites with tetragonal compression and belong to C4V symmetry. The spin-Hamiltonian parameters g and A are found to be independent of V2O5 content and temperature but changing with ZnO content. The decrease in Deltag( parallel)/Deltag( perpendicular) value with increase in ZnO content indicates that the symmetry around VO2+ ions is more octahedral. The decrease in intensity of EPR signal above 10 mol% of V2O5 is attributed to a fall in the ratio of the number of V4+ ions (N4) to the number of V5+ ions (N5). The number of spins (N) participating in resonance was calculated as a function of temperature for VO2+ doped zinc lead borate glass sample and the activation energy was calculated. From the EPR data, the paramagnetic susceptibility was calculated at various temperatures and the Curie constant was evaluated from the 1/chi-T graph. The optical absorption spectra show single absorption band due to VO2+ ions in tetragonally distorted octahedral sites.

A comparison of practical assessment methods to determine treadmill, cycle and elliptical ergometer VO2peak

PubMed Central

Mays, Ryan J.; Boér, Nicholas F.; Mealey, Lisa M.; Kim, Kevin H.; Goss, Fredric L.

2015-01-01

This investigation compared estimated and predicted peak oxygen consumption (VO2peak) and maximal heart rate (HRmax) among the treadmill, cycle ergometer and elliptical ergometer. Seventeen women (mean ± SE: 21.9 ± .3 yrs) exercised to exhaustion on all modalities. ACSM metabolic equations were used to estimate VO2peak. Digital displays on the elliptical ergometer were used to estimate VO2peak. Two individual linear regression methods were used to predict VO2peak: 1) two steady state heart rate (HR) responses up to 85% of age-predicted HRmax, and 2) multiple steady state/non-steady state HR responses up to 85% of age-predicted HRmax. Estimated VO2peak for the treadmill (46.3 ± 1.3 ml · kg−1 · min−1) and the elliptical ergometer (44.4 ± 1.0 ml · kg−1 · min−1) did not differ. The cycle ergometer estimated VO2peak (36.5 ± 1.0 ml · kg−1 · min−1) was lower (p < .001) than the estimated VO2peak values for the treadmill and elliptical ergometer. Elliptical ergometer VO2peak predicted from steady state (51.4 ± .8 ml · kg−1 · min−1) and steady state/non-steady state (50.3 ± 2.0 ml · kg−1 · min−1) models were higher than estimated elliptical ergometer VO2peak, p < .01. HRmax and estimates of VO2peak were similar between the treadmill and elliptical ergometer, thus cross-modal exercise prescriptions may be generated. The use of digital display estimates of submaximal oxygen uptake for the elliptical ergometer may not be an accurate method for predicting VO2peak. Health-fitness professionals should use caution when utilizing submaximal elliptical ergometer digital display estimates to predict VO2peak. PMID:20393357

Nano crystalline Bi2(VO5) phases in lithium bismuth borate glasses containing mixed vanadium-nickel oxides

NASA Astrophysics Data System (ADS)

Yadav, Arti; Khasa, S.; Dahiya, M. S.; Agarwal, A.

2016-05-01

Glass composition 7V2O5.23Li2O.20Bi2O3.50B2O3 and x(2NiO.V2O5).(30-x)Li2O.20Bi2O3.50B2O3, x=0, 2, 5, 7 and 10, were produced by conventional melt quenching technique. The quenched amorphous glass samples were annealed at temperatures 400°C and 500°C for 6 hours. The Bi2(VO5) crystallite were grown in all prepared glass matrix. Tn vanadium lithium bismuth borate glass (annealed), the some phrase of V2O5-crystal were observed along with the nano crystalline Bi2(VO5) phase. The sharp peaks in FTTR spectra of all annealed compositions were also compatible with the XRD diffraction peaks of the system under investigation. Average crystalline size (D) of the Bi2(VO5) nano-crystallite was ~30nm for samples annealed at 400°C and ~42nm for samples annealed at 500°C. Lattice parameter and the lattice strain for all the samples was also calculated corresponding to the (113) plane of Bi2(VO5) crystallite.

Is Recreational Soccer Effective for Improving VO2max A Systematic Review and Meta-Analysis.

PubMed

Milanović, Zoran; Pantelić, Saša; Čović, Nedim; Sporiš, Goran; Krustrup, Peter

2015-09-01

Soccer is the most popular sport worldwide, with a long history and currently more than 500 million active participants, of whom 300 million are registered football club members. On the basis of scientific findings showing positive fitness and health effects of recreational soccer, FIFA (Fédération Internationale de Football Association) introduced the slogan "Playing football for 45 min twice a week-best prevention of non-communicable diseases" in 2010. The objective of this paper was to perform a systematic review and meta-analysis of the literature to determine the effects of recreational soccer on maximal oxygen uptake (VO2max). Six electronic databases (MEDLINE, PubMed, SPORTDiscus, Web of Science, CINAHL and Google Scholar) were searched for original research articles. A manual search was performed to cover the areas of recreational soccer, recreational physical activity, recreational small-sided games and VO2max using the following key terms, either singly or in combination: recreational small-sided games, recreational football, recreational soccer, street football, street soccer, effect, maximal oxygen uptake, peak oxygen uptake, cardiorespiratory fitness, VO2max. The inclusion criteria were divided into four sections: type of study, type of participants, type of interventions and type of outcome measures. Probabilistic magnitude-based inferences for meta-analysed effects were based on standardised thresholds for small, moderate and large changes (0.2, 0.6 and 1.2, respectively) derived from between-subject standard deviations for baseline fitness. Seventeen studies met the inclusion criteria and were included in the systematic review and meta-analysis. Mean differences showed that VO2max increased by 3.51 mL/kg/min (95 % CI 3.07-4.15) over a recreational soccer training programme in comparison with other training models. The meta-analysed effects of recreational soccer on VO2max compared with the controls of no exercise, continuous running and strength

Epitaxial stabilization and phase instability of VO2 polymorphs

NASA Astrophysics Data System (ADS)

Lee, Shinbuhm; Ivanov, Ilia N.; Keum, Jong K.; Lee, Ho Nyung

2016-01-01

The VO2 polymorphs, i.e., VO2(A), VO2(B), VO2(M1) and VO2(R), have a wide spectrum of functionalities useful for many potential applications in information and energy technologies. However, synthesis of phase pure materials, especially in thin film forms, has been a challenging task due to the fact that the VO2 polymorphs are closely related to each other in a thermodynamic framework. Here, we report epitaxial stabilization of the VO2 polymorphs to synthesize high quality single crystalline thin films and study the phase stability of these metastable materials. We selectively deposit all the phases on various perovskite substrates with different crystallographic orientations. By investigating the phase instability, phonon modes and transport behaviours, not only do we find distinctively contrasting physical properties of the VO2 polymorphs, but that the polymorphs can be on the verge of phase transitions when heated as low as ~400 °C. Our successful epitaxy of both VO2(A) and VO2(B) phases, which are rarely studied due to the lack of phase pure materials, will open the door to the fundamental studies of VO2 polymorphs for potential applications in advanced electronic and energy devices.

Epitaxial stabilization and phase instability of VO2 polymorphs.

PubMed

Lee, Shinbuhm; Ivanov, Ilia N; Keum, Jong K; Lee, Ho Nyung

2016-01-20

The VO2 polymorphs, i.e., VO2(A), VO2(B), VO2(M1) and VO2(R), have a wide spectrum of functionalities useful for many potential applications in information and energy technologies. However, synthesis of phase pure materials, especially in thin film forms, has been a challenging task due to the fact that the VO2 polymorphs are closely related to each other in a thermodynamic framework. Here, we report epitaxial stabilization of the VO2 polymorphs to synthesize high quality single crystalline thin films and study the phase stability of these metastable materials. We selectively deposit all the phases on various perovskite substrates with different crystallographic orientations. By investigating the phase instability, phonon modes and transport behaviours, not only do we find distinctively contrasting physical properties of the VO2 polymorphs, but that the polymorphs can be on the verge of phase transitions when heated as low as ~400 °C. Our successful epitaxy of both VO2(A) and VO2(B) phases, which are rarely studied due to the lack of phase pure materials, will open the door to the fundamental studies of VO2 polymorphs for potential applications in advanced electronic and energy devices.

Epitaxial stabilization and phase instability of VO2 polymorphs

PubMed Central

Lee, Shinbuhm; Ivanov, Ilia N.; Keum, Jong K.; Lee, Ho Nyung

2016-01-01

The VO2 polymorphs, i.e., VO2(A), VO2(B), VO2(M1) and VO2(R), have a wide spectrum of functionalities useful for many potential applications in information and energy technologies. However, synthesis of phase pure materials, especially in thin film forms, has been a challenging task due to the fact that the VO2 polymorphs are closely related to each other in a thermodynamic framework. Here, we report epitaxial stabilization of the VO2 polymorphs to synthesize high quality single crystalline thin films and study the phase stability of these metastable materials. We selectively deposit all the phases on various perovskite substrates with different crystallographic orientations. By investigating the phase instability, phonon modes and transport behaviours, not only do we find distinctively contrasting physical properties of the VO2 polymorphs, but that the polymorphs can be on the verge of phase transitions when heated as low as ~400 °C. Our successful epitaxy of both VO2(A) and VO2(B) phases, which are rarely studied due to the lack of phase pure materials, will open the door to the fundamental studies of VO2 polymorphs for potential applications in advanced electronic and energy devices. PMID:26787259

Epitaxial stabilization and phase instability of VO 2 polymorphs

DOE PAGES

Lee, Shinbuhm; Ivanov, Ilia N.; Keum, Jong K.; ...

2016-01-20

The VO 2 polymorphs, i.e., VO 2(A), VO 2(B), VO 2(M1) and VO 2(R), have a wide spectrum of functionalities useful for many potential applications in information and energy technologies. However, synthesis of phase pure materials, especially in thin film forms, has been a challenging task due to the fact that the VO 2 polymorphs are closely related to each other in a thermodynamic framework. Here, we report epitaxial stabilization of the VO 2 polymorphs to synthesize high quality single crystalline thin films and study the phase stability of these metastable materials. We selectively deposit all the phases on variousmore » perovskite substrates with different crystallographic orientations. By investigating the phase instability, phonon modes and transport behaviours, not only do we find distinctively contrasting physical properties of the VO 2 polymorphs, but that the polymorphs can be on the verge of phase transitions when heated as low as ~400 °C. In conclusion, our successful epitaxy of both VO 2(A) and VO 2(B) phases, which are rarely studied due to the lack of phase pure materials, will open the door to the fundamental studies of VO 2 polymorphs for potential applications in advanced electronic and energy devices.« less

Selective scanning tunneling microscope light emission from rutile phase of VO2.

PubMed

Sakai, Joe; Kuwahara, Masashi; Hotsuki, Masaki; Katano, Satoshi; Uehara, Yoichi

2016-09-28

We observed scanning tunneling microscope light emission (STM-LE) induced by a tunneling current at the gap between an Ag tip and a VO2 thin film, in parallel to scanning tunneling spectroscopy (STS) profiles. The 34 nm thick VO2 film grown on a rutile TiO2 (0 0 1) substrate consisted of both rutile (R)- and monoclinic (M)-structure phases of a few 10 nm-sized domains at room temperature. We found that STM-LE with a certain photon energy of 2.0 eV occurs selectively from R-phase domains of VO2, while no STM-LE was observed from M-phase. The mechanism of STM-LE from R-phase VO2 was determined to be an interband transition process rather than inverse photoemission or inelastic tunneling processes.

Electrocatalytic activity of cobalt phosphide-modified graphite felt toward VO2+/VO2+ redox reaction

NASA Astrophysics Data System (ADS)

Ge, Zhijun; Wang, Ling; He, Zhangxing; Li, Yuehua; Jiang, Yingqiao; Meng, Wei; Dai, Lei

2018-04-01

A novel strategy for improving the electro-catalytic properties of graphite felt (GF) electrode in vanadium redox flow battery (VRFB) is designed by depositing cobalt phosphide (CoP) onto GF surface. The CoP powder is synthesized by direct carbonization of Co-based zeolitic imidazolate framework (ZIF-67) followed by phosphidation. Cyclic voltammetry results confirm that the CoP-modified graphite felt (GF-CoP) electrode has excellent reversibility and electro-catalytic activity to the VO2+/VO2+ cathodic reaction compared with the pristine GF electrode. The cell using GF-CoP electrode shows apparently higher discharge capacity over that based on GF electrode. The cell using GF-CoP electrode has the capacity of 67.2 mA h at 100 mA cm-2, 32.7 mA h larger than that using GF electrode. Compared with cell using GF electrode, the voltage efficiency of the cell based on GF-CoP electrode increases by 5.9% and energy efficiency by 5.4% at a current density of 100 mA cm-2. The cell using GF-CoP electrode can reach 94.31% capacity retention after 50 cycles at a current density of 30 mA cm-2. The results show that the CoP can effectively promote the VO2+/VO2+ redox reaction, implying that metal phosphides are a new kind of potential catalytic materials for VRFB.

Probing the Release and Uptake of Water in α-MnO 2 · xH 2O

DOE PAGES

Yang, Zhenzhen; Ford, Denise C.; Park, Joong Sun; ...

2016-12-27

Alpha-MnO 2 is of interest as a cathode material for 3 V lithium batteries and as an electrode/electrocatalyst for higher energy, hybrid Li-ion/Li–O 2 systems. It has a structure with large tunnels that contain stabilizing cations such as Ba 2+, K + , NH 4 + , and H3O + (or water, H 2O). When stabilized by H 3O + /H 2O, the protons can be ion-exchanged with lithium to produce a Li 2O-stabilized α-MnO 2 structure. It has been speculated that the electrocatalytic process in Li–O 2 cells may be linked to the removal of lithium and oxygen frommore » the host α-MnO 2 structure during charge, and their reintroduction during discharge. In this investigation, hydrated α-MnO 2 was used, as a first step, to study the release and uptake of oxygen in α-MnO 2. Temperature-resolved in situ synchrotron X-ray diffraction (XRD) revealed a nonlinear, two-stage, volume change profile, which with the aide of X-ray absorption near-edge spectroscopy (XANES), redox titration, and density functional theory (DFT) calculations, is interpreted as the release of water from the α-MnO 2 tunnels. The two stages correspond to H 2O release from intercalated H 2O species at lower temperatures and H 3O + species at higher temperature. Thermogravimetric analysis confirmed the release of oxygen from α-MnO 2 in several stages during heating–including surface water, occluded water, and structural oxygen–and in situ UV resonance Raman spectroscopy corroborated the uptake and release of tunnel water by revealing small shifts in frequencies during the heating and cooling of α-MnO 2. Lastly, DFT calculations revealed the likelihood of disordered water species in binding sites in α-MnO 2 tunnels and a facile diffusion process.« less

[La(UO{sub 2})V{sub 2}O{sub 7}][(UO{sub 2})(VO{sub 4})] the first lanthanum uranyl-vanadate with structure built from two types of sheets based upon the uranophane anion-topology

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mer, A.; Obbade, S.; Rivenet, M.

2012-01-15

The new lanthanum uranyl vanadate divanadate, [La(UO{sub 2})V{sub 2}O{sub 7}][(UO{sub 2})(VO{sub 4})] was obtained by reaction at 800 Degree-Sign C between lanthanum chloride, uranium oxide (U{sub 3}O{sub 8}) and vanadium oxide (V{sub 2}O{sub 5}) and the structure was determined from single-crystal X-ray diffraction data. This compound crystallizes in the orthorhombic system with space group P2{sub 1}2{sub 1}2{sub 1} and unit-cell parameters a=6.9470(2) A, b=7.0934(2) A, c=25.7464(6) A, V=1268.73(5) A{sup 3}, Z=4. A full matrix least-squares refinement yielded R{sub 1}=0.0219 for 5493 independent reflections. The crystal structure is characterized by the stacking of uranophane-type sheets {sup 2}{sub {infinity}}[(UO{sub 2})(VO{sub 4})]{sup -}more » and double layers {sup 2}{sub {infinity}}[La(UO{sub 2})(V{sub 2}O{sub 7})]{sup +} connected through La-O bonds involving the uranyl oxygen of the uranyl-vanadate sheets. The double layers result from the connection of two {sup 2}{sub {infinity}}[La(UO{sub 2})(VO{sub 4}){sub 2}]{sup -} sheets derived from the uranophane anion-topology by replacing half of the uranyl ions by lanthanum atoms and connected through the formation of divanadate entities. - Graphical abstract: A view of the three-dimensional structure of [La(UO{sub 2})V{sub 2}O{sub 7}][(UO{sub 2})(VO{sub 4})]. Highlights: Black-Right-Pointing-Pointer New lanthanum uranyl vanadate divanadate has been synthesized. Black-Right-Pointing-Pointer Structure was determined from single-crystal X-ray diffraction data. Black-Right-Pointing-Pointer Structure is characterized by uranophane-type sheets and double layers {sup 2}{sub {infinity}}[La(UO{sub 2})(V{sub 2}O{sub 7})]{sup +}.« less

Patterns of Senescence in Human Cardiovascular Fitness: VO2max in Subsistence and Industrialized Populations

PubMed Central

Pisor, Anne C.; Gurven, Michael; Blackwell, Aaron D.; Kaplan, Hillard; Yetish, Gandhi

2014-01-01

Objectives This study explores whether cardiovascular fitness levels and senescent decline are similar in the Tsimane of Bolivia and Canadians, as well as other subsistence and industrialized populations. Among Tsimane, we examine whether morbidity predicts lower levels and faster decline of cardiovascular fitness, or whether their lifestyle (e.g., high physical activity) promotes high levels and slow decline. Alternatively, high activity levels and morbidity might counterbalance such that Tsimane fitness levels and decline are similar to those in industrialized populations. Methods Maximal oxygen uptake (VO2max) was estimated using a step test heart rate method for 701 participants. We compared these estimates to the Canadian Health Measures Survey and previous studies in industrialized and subsistence populations. We evaluated whether health indicators and proxies for market integration were associated with VO2max levels and rate of decline for the Tsimane. Results The Tsimane have significantly higher levels of VO2max and slower rates of decline than Canadians; initial evidence suggests differences in VO2max levels between other subsistence and industrialized populations. Low hemoglobin predicts low VO2max for Tsimane women while helminth infection predicts high VO2max for Tsimane men, though results might be specific to the VO2max scaling parameter used. No variables tested interact with age to moderate decline. Conclusions The Tsimane demonstrate higher levels of cardiovascular fitness than industrialized populations, but levels similar to other subsistence populations. The high VO2max of Tsimane is consistent with their high physical activity and few indicators of cardiovascular disease, measured in previous studies. PMID:24022886

Lvad pump speed increase is associated with increased peak exercise cardiac output and vo2, postponed anaerobic threshold and improved ventilatory efficiency.

PubMed

Vignati, Carlo; Apostolo, Anna; Cattadori, Gaia; Farina, Stefania; Del Torto, Alberico; Scuri, Silvia; Gerosa, Gino; Bottio, Tomaso; Tarzia, Vincenzo; Bejko, Jonida; Sisillo, Erminio; Nicoli, Flavia; Sciomer, Susanna; Alamanni, Francesco; Paolillo, Stefania; Agostoni, Piergiuseppe

2017-03-01

Peak exercise cardiac output (CO) increase is associated with an increase of peak oxygen uptake (VO 2 ), provided that arteriovenous O 2 difference [Δ(Ca-Cv)O 2 ] does not decrease. At anaerobic threshold, VO 2 , is related to CO. We tested the hypothesis that, in heart failure (HF) patients with left ventricular assistance device (LVAD), an acute increase of CO obtained through changes in LVAD pump speed is associated with peak exercise and anaerobic threshold VO 2 increase. Fifteen of 20 patients bearing LVAD (Jarvik 2000) enrolled in the study successfully performed peak exercise evaluation. All patients had severe HF as shown by clinical evaluation, laboratory tests, echocardiography, spirometry with alveolar-capillary diffusion, and maximal cardiopulmonary exercise testing (CPET). CPETs with non-invasive CO measurements at rest and peak exercise were done on 2days at LVAD pump speed set randomly at 2 and 4. Increasing LVAD pump speed from 2 to 4 increased CO from 3.4±0.9 to 3.8±1.0L/min (ΔCO 0.4±0.6L/min, p=0.04) and from 5.3±1.3 to 5.9±1.4L/min (ΔCO 0.6±0.7L/min, p<0.01) at rest and peak exercise, respectively. Similarly, VO 2 increased from 788±169 to 841±152mL/min (ΔVO 2 52±76mL/min, p=0.01) and from 568±116 to 619±124mL/min (ΔVO 2 69±96mL/min, p=0.02) at peak exercise and at anaerobic threshold, respectively. Δ(Ca-Cv)O 2 did not change significantly, while ventilatory efficiency improved (VE/VCO 2 slope from 39.9±5.4 to 34.9±8.3, ΔVE/VCO 2 -5.0±6.4, p<0.01). In HF, an increase in CO with a higher LVAD pump speed is associated with increased peak VO 2 , postponed anaerobic threshold, and improved ventilatory efficiency. Copyright © 2016 Elsevier Ireland Ltd. All rights reserved.

Tunable VO{sub 2}/Au hyperbolic metamaterial

DOE Office of Scientific and Technical Information (OSTI.GOV)

Prayakarao, S.; Noginov, M. A., E-mail: mnoginov@nsu.edu; Mendoza, B.

2016-08-08

Vanadium dioxide (VO{sub 2}) is known to have a semiconductor-to-metal phase transition at ∼68 °C. Therefore, it can be used as a tunable component of an active metamaterial. The lamellar metamaterial studied in this work is composed of subwavelength VO{sub 2} and Au layers and is designed to undergo a temperature controlled transition from the optical hyperbolic phase to the metallic phase. VO{sub 2} films and VO{sub 2}/Au lamellar metamaterial stacks have been fabricated and studied in electrical conductivity and optical (transmission and reflection) experiments. The observed temperature-dependent changes in the reflection and transmission spectra of the metamaterials and VO{sub 2}more » thin films are in a good qualitative agreement with theoretical predictions. The demonstrated optical hyperbolic-to-metallic phase transition is a unique physical phenomenon with the potential to enable advanced control of light-matter interactions.« less

VO2 attained during treadmill running: the influence of a specialist (400-m or 800-m) event.

PubMed

James, David V B; Sandals, Leigh E; Draper, Stephen B; Maldonado-Martin, Sara; Wood, Dan M

2007-06-01

Previously it has been observed that, in well-trained 800-m athletes, VO2max is not attained during middle-distance running events on a treadmill, even when a race-type pacing strategy is adopted. Therefore, the authors investigated whether specialization in a particular running distance (400-m or 800-m) influences the VO2 attained during running on a treadmill. Six 400-m and six 800-m running specialists participated in the study.A 400-m trial and a progressive test to determine VO2max were completed in a counterbalanced order. Oxygen uptakes attained during the 400-m trial were compared to examine the influence of specialist event. A VO2 plateau was observed in all participants for the progressive test, demonstrating the attainment of VO2max. The VO2max values were 56.2 +/- 4.7 and 69.3 +/- 4.5 mL x kg-1 x min-1 for the 400-m- and 800-m-event specialists, respectively (P = .0003). Durations for the 400-m trial were 55.1 +/- 4.2 s and 55.8 +/- 2.3 s for the 400-m- and 800-m-event specialists, respectively. The VO2 responses achieved were 93.1% +/- 2.0% and 85.7% +/- 3.0% VO2max for the 400-m- and 800-m-event specialists, respectively (P = .001). These results demonstrate that specialist running events do appear to influence the percentage of VO2max achieved in the 400-m trial, with the 800-m specialists attaining a lower percentage of VO2max than the 400-m specialists. The 400-m specialists appear to compensate for a lower VO2max by attaining a higher percentage VO2max during a 400-m trial.

Metamaterials based on the phase transition of VO2

NASA Astrophysics Data System (ADS)

Liu, Hongwei; Lu, Junpeng; Renshaw Wang, Xiao

2018-01-01

In this article, we present a comprehensive review on recent research progress in design and fabrication of active tunable metamaterials and devices based on phase transition of VO2. Firstly, we introduce mechanisms of the metal-to-insulator phase transition (MIPT) in VO2 investigated by ultrafast THz spectroscopies. By analyzing the THz spectra, the evolutions of MIPT in VO2 induced by different external excitations are described. The superiorities of using VO2 as building blocks to construct highly tunable metamaterials are discussed. Subsequently, the recently demonstrated metamaterial devices based on VO2 are reviewed. These metamaterials devices are summarized and described in the categories of working frequency. In each working frequency range, representative metamaterials based on VO2 with different architectures and functionalities are reviewed and the contributions of the MIPT of VO2 are emphasized. Finally, we conclude the recent reports and provide a prospect on the strategies of developing future tunable metamaterials based on VO2.

A reinvestigation of the crystal structure of α-Pb 2BiVO 6

NASA Astrophysics Data System (ADS)

Labidi, O.; Wignacourt, J. P.; Roussel, P.; Drache, M.; Conflant, P.; Steinfink, H.

2004-08-01

A previously reported β phase for Pb 2BiVO 6 has been characterized as a stable phase, and the phase transitions α→ β and β→ δ were identified in the mother phase as well as in Pb 2BiV 1- xM xO 6- y solid solutions (M=Cr, Mn); the high temperature form δ-Pb 2BiVO 6 eventually decomposes at 480 °C to a mixture of PbBiVO 5 and Pb 4BiVO 8 before showing recombination at 650 °C. The related substituted compositions behave the same way. The crystal structure of α-Pb 2BiVO 6 (I) is monoclinic, P2 1/ n, a=7.717(3) Å, b=5.845(3) Å, c=29.081(8) Å, β=94.27(1)°, Z=8. Oxygen atoms are in tetrahedral interstices formed by four Bi and Pb atoms. These tetrahedra articulate by BiPb edge sharing in two dimensions parallel to the b axis to form infinite chains. Mixed O(V Bi Pb) 4 tetrahedra bridge the O(Bi Pb) 4 ribbons by edge sharing to complete the three-dimensional articulation of the structure. α-Pb 2BiV 1- xMn xO 6- y ( x=0.06) (II) is monoclinic, P2 1/ m, a=7.684(3) Å, b=5.822(3) Å, c=14.708(6) Å, β=100.92(1)°, Z=4. Tetrahedral units of O(2Bi 2Pb) are also present in (II). They form dimers O 2Bi 4Pb 4 by BiBi edge sharing. The dimers form a chain along the b axis by sharing BiPb edges. Two independent MO 4 tetrahedra (M=V, Mn) are present in which one has V/Mn mixed occupancy. Both tetrahedra show statistical disorder by rotation around a VO apex. The disordered tetrahedral oxygen atoms are part of the coordination sphere of Bi and Pb. The matrix {-1 0 0, 0 -1 0, 1 0 2} relates the structures and unit cells of [I], and [II].

The role of the CeO 2 /BiVO 4 interface in optimized Fe–Ce oxide coatings for solar fuels photoanodes

DOE PAGES

Shinde, A.; Li, G.; Zhou, L.; ...

2016-09-09

Solar fuel generators entail a high degree of materials integration, and efficient photoelectrocatalysis of the constituent reactions hinges upon the establishment of highly functional interfaces. Our recent application of high throughput experimentation to interface discovery for solar fuels photoanodes has revealed several surprising and promising mixed-metal oxide coatings for BiVO 4. Furthermore, when using sputter deposition of composition and thickness gradients on a uniform BiVO 4 film, we systematically explore photoanodic performance as a function of the composition and loading of Fe–Ce oxide coatings. This combinatorial materials integration study not only enhances the performance of this new class of materialsmore » but also identifies CeO 2 as a critical ingredient that merits detailed study. A heteroepitaxial CeO 2(001)/BiVO4(010) interface is identified in which Bi and V remain fully coordinated to O such that no surface states are formed. Ab initio calculations of the integrated materials and inspection of the electronic structure reveals mechanisms by which CeO 2 facilitates charge transport while mitigating deleterious recombination. Our results support the observations that addition of Ce to BiVO 4 coatings greatly enhances photoelectrocatalytic activity, providing an important strategy for developing a scalable solar fuels technology.« less

Growth and study of first order metal insulator transition in VO2 films

NASA Astrophysics Data System (ADS)

Rathore, Ajay K.; Kumar, Satish; Kumar, Dhirendra; Sathe, V. G.

2015-06-01

VO2 films have been grown on Si substrate using pulse laser deposition technique. The as-deposited film prepared by V2O3 target is found to possess signatures of V2O5 phase. Up on annealing at 780°C the film transforms to VO2 phase. The annealed film is found to be highly oriented along (011) and single phase in nature. The high temperature Raman spectroscopic measurements on the annealed film showed first order transition from monoclinic insulating phase to conductive tetragonal rutile phase around 65°C.

Electronic and Thermal Effects in the Insulator-Metal Phase Transition in VO2 Nano-Gap Junctions

DTIC Science & Technology

2014-11-27

VO2 , air, or SiO2, the 2 -0.50 -0.25 0.00 0.25 0.50 0 2 4 6 V Gap V App V o lt ag e (V ) time (ms) t p V I→M V M→I 100 400 700 1000 0.0 2.5 5.0 7.5...Electronic and thermal effects in the insulator-metal phase transition in VO2 nano-gap junctions Arash Joushaghani,1 Junho Jeong,1 Suzanne Paradis,2...Canada (Dated: 27 November 2014) By controlling the thermal transport of VO2 nano-gap junctions using device geometry, contact material, and applied

Lung function parameters improve prediction of VO2peak in an elderly population: The Generation 100 study.

PubMed

Hassel, Erlend; Stensvold, Dorthe; Halvorsen, Thomas; Wisløff, Ulrik; Langhammer, Arnulf; Steinshamn, Sigurd

2017-01-01

Peak oxygen uptake (VO2peak) is an indicator of cardiovascular health and a useful tool for risk stratification. Direct measurement of VO2peak is resource-demanding and may be contraindicated. There exist several non-exercise models to estimate VO2peak that utilize easily obtainable health parameters, but none of them includes lung function measures or hemoglobin concentrations. We aimed to test whether addition of these parameters could improve prediction of VO2peak compared to an established model that includes age, waist circumference, self-reported physical activity and resting heart rate. We included 1431 subjects aged 69-77 years that completed a laboratory test of VO2peak, spirometry, and a gas diffusion test. Prediction models for VO2peak were developed with multiple linear regression, and goodness of fit was evaluated. Forced expiratory volume in one second (FEV1), diffusing capacity of the lung for carbon monoxide and blood hemoglobin concentration significantly improved the ability of the established model to predict VO2peak. The explained variance of the model increased from 31% to 48% for men and from 32% to 38% for women (p<0.001). FEV1, diffusing capacity of the lungs for carbon monoxide and hemoglobin concentration substantially improved the accuracy of VO2peak prediction when added to an established model in an elderly population.

Crystal Structure and Characterization of Ba 2V 3O 9: A Vanadyl(IV) Vanadate Containing Rutile-like Chains of VO 6Octahedra

NASA Astrophysics Data System (ADS)

Dhaussy, Anne-Claire; Abraham, Francis; Mentre, Olivier; Steinfink, Hugo

1996-11-01

The crystal structure of Ba2V3O9has been determined and refined to finalRandRwvalues of 0.025 and 0.028 from 1562 independent single crystal reflections. It crystallizes in the space groupP21/mwitha= 9.302(1) Å,b= 5.969(1) Å,c= 8.118(1) Å, and β = 113.96 (1)°. The structure consists of one-dimensional rutile-type chains of edge-sharing VO6octahedra parallel to thebaxis. The VO4tetrahedra share corners with VO6octahedra of a single rutile-type chain to form one-dimensional [V3O9]4-∞columns which are held together by Ba2+ions. In this mixed valence compound V4+and V5+ions are distributed in an ordered way in octahedra and tetrahedra, respectively. In the almost perfect O6octahedron the vanadium atom is off-center so that it forms a short vanadyl V_dbO bond of 1.686(3) Å, typical of a V4+ion. This compound is a barium vanadyl vanadate Ba2(VO)(VO4)2. It is the first example of isolated rutile-type chains found with V4+ions. Magnetic susceptibility measurements show that this phase is an antiferromagnet withTN≅ 58 K. At about 20 K magnetic anisotropy causes a canted spin arrangement.

Identifying the active site in nitrogen-doped graphene for the VO2+/VO2(+) redox reaction.

PubMed

Jin, Jutao; Fu, Xiaogang; Liu, Qiao; Liu, Yanru; Wei, Zhiyang; Niu, Kexing; Zhang, Junyan

2013-06-25

Nitrogen-doped graphene sheets (NGS), synthesized by annealing graphite oxide (GO) with urea at 700-1050 °C, were studied as positive electrodes in a vanadium redox flow battery. The NGS, in particular annealed at 900 °C, exhibited excellent catalytic performance in terms of electron transfer (ET) resistance (4.74 ± 0.51 and 7.27 ± 0.42 Ω for the anodic process and cathodic process, respectively) and reversibility (ΔE = 100 mV, Ipa/Ipc = 1.38 at a scan rate of 50 mV s(-1)). Detailed research confirms that not the nitrogen doping level but the nitrogen type in the graphene sheets determines the catalytic activity. Among four types of nitrogen species doped into the graphene lattice including pyridinic-N, pyrrolic-N, quaternary nitrogen, and oxidic-N, quaternary nitrogen is verified as a catalytic active center for the [VO](2+)/[VO2](+) couple reaction. A mechanism is proposed to explain the electrocatalytic performance of NGS for the [VO](2+)/[VO2](+) couple reaction. The possible formation of a N-V transitional bonding state, which facilitates the ET between the outer electrode and reactant ions, is a key step for its high catalytic activity.

High pressure spectroscopic studies of phase transition in VO2

NASA Astrophysics Data System (ADS)

Basu, Raktima; Mishra, K. K.; Ravindran, T. R.; Dhara, Sandip

2018-04-01

Vanadium dioxide (VO2) exhibits a reversible first-order metal to insulator transition (MIT) at a technologically important temperature of 340K. A structural phase transition (SPT) from monoclinic M1 to rutile tetragonal R is also reported via another two intermediate phases of monoclinic M2 and triclinic T. Metastable monoclinic M2 phase of VO2 was synthesized by Mg doping in the vapour transport process. Raman spectroscopic measurements were carried out at high pressure on V1-xMgxO2 microrods. Two reversible structural phase transitions from monoclinic M2 to triclinic T at 1.6 GPa and T to monoclinic M1 at 3.2 GPa are observed and are explained by structural relaxation of the strained phases.

A V(IV) Hydroxyhydrogenomonophosphate with an Intersecting Tunnel Structure: HK 4[V 10O 10(H 2O) 2(OH) 4(PO 4) 7]·9H 2O

NASA Astrophysics Data System (ADS)

Berrah, F.; Guesdon, A.; Leclaire, A.; Borel, M. M.; Provost, J.; Raveau, B.

1999-12-01

A V(IV) hydroxyhydrogenomonophosphate HK4[V10O10(H2O)2(OH)4(PO4)7]·9H2O has been obtained, using hydrothermal conditions. Its structure, closely related to that of (CH3)2NH2K4[V10O10(H2O)2(OH)4(PO4)7]·4H2O, differs from the latter by its I41/a space group (instead of P43). This difference corresponds to a "disordering" of the vanadium atoms, with respect to the dimethyl ammonium phase. It is shown that this disorder, which appears in the form of "V5O22" units distributed at random, does not affect the oxygen framework. The analysis of this complex structure shows that it can be described from the stacking along c of [V8P7O38(OH)4(H2O)2]∞ layers interconnected through layers of isolated VO6 octahedra. In this structure, built up of VO6, VO5OH, and VO4(OH)(H2O) octahedra, of VO4OH pyramids, and of PO4 tetrahedra, large "toffee" tunnels and smaller ones with a tulip-shape section are running along a (or b). The first ones are stuffed with H2O molecules forming aquo tubes, where protons are likely "delocalized," whereas the second ones are occupied by K+ cations.

Flexible thermochromic window based on hybridized VO2/graphene.

PubMed

Kim, Hyeongkeun; Kim, Yena; Kim, Keun Soo; Jeong, Hu Young; Jang, A-Rang; Han, Seung Ho; Yoon, Dae Ho; Suh, Kwang S; Shin, Hyeon Suk; Kim, TaeYoung; Yang, Woo Seok

2013-07-23

Large-scale integration of vanadium dioxide (VO2) on mechanically flexible substrates is critical to the realization of flexible smart window films that can respond to environmental temperatures to modulate light transmittance. Until now, the formation of highly crystalline and stoichiometric VO2 on flexible substrate has not been demonstrated due to the high-temperature condition for VO2 growth. Here, we demonstrate a VO2-based thermochromic film with unprecedented mechanical flexibility by employing graphene as a versatile platform for VO2. The graphene effectively functions as an atomically thin, flexible, yet robust support which enables the formation of stoichiometric VO2 crystals with temperature-driven phase transition characteristics. The graphene-supported VO2 was capable of being transferred to a plastic substrate, forming a new type of flexible thermochromic film. The flexible VO2 films were then integrated into the mock-up house, exhibiting its efficient operation to reduce the in-house temperature under infrared irradiation. These results provide important progress for the fabrication of flexible thermochromic films for energy-saving windows.

Origin of phase transition in VO2

NASA Astrophysics Data System (ADS)

Basu, Raktima; Sardar, Manas; Dhara, Sandip

2018-04-01

Vanadium dioxide (VO2) exhibits a reversible first-order metal to insulator transition (MIT) along with a structural phase transition (SPT) from monoclinic M1 to rutile tetragonal R via another two intermediate phases of monoclinic M2 and triclinic T at a technologically important temperature of 340K. In the present work, besides synthesizing M1 phase of VO2, we also stabilized M2 and T phases at room temperature by introducing native defects in the system and observed an increase in transition temperature with increase in native defects. Raman spectroscopic measurements were carried out to confirm the pure VO2 phases. Since the MIT is accompanied by SPT in these systems, the origin of the phase transition is still under debate. The controversy between MIT and SPT, whether electron-phonon coupling or strong electron-electron correlation triggers the phase transition in VO2 is also resolved by examining the presence of intermediate phase M2 during phase transition.

Characteristics of patients with a relatively greater minimum VE/VCO2 against peak VO2% and impaired exercise tolerance.

PubMed

Nakade, Taisuke; Adachi, Hitoshi; Murata, Makoto; Oshima, Shigeru

2018-05-14

Cardiopulmonary exercise testing (CPX) is used to evaluate functional capacity and assess prognosis in cardiac patients. Ventilatory efficiency (VE/VCO 2 ) reflects ventilation-perfusion mismatch; the minimum VE/VCO 2 value (minVE/VCO 2 ) is representative of pulmonary arterial blood flow in individuals without pulmonary disease. Usually, minVE/VCO 2 has a strong relationship with the peak oxygen uptake (VO 2 ), but dissociation can occur. Therefore, we investigated the relationship between minVE/VCO 2 and predicted peak VO 2 (peak VO 2 %) and evaluated the parameters associated with a discrepancy between these two parameters. A total of 289 Japanese patients underwent CPX using a cycle ergometer with ramp protocols between 2013 and 2014. Among these, 174 patients with a peak VO 2 % lower than 70% were enrolled. Patients were divided into groups based on their minVE/VCO 2 [Low group: minVE/VCO 2  < mean - SD (38.8-5.6); High group: minVE/VCO 2  > mean + SD (38.8 + 5.6)]. The characteristics and cardiac function at rest, evaluated using echocardiography, were compared between groups. The High group had a significantly lower ejection fraction, stroke volume, and cardiac output, and higher brain natriuretic peptide, tricuspid regurgitation pressure gradient, right ventricular systolic pressure, and peak early diastolic LV filling velocity/peak atrial filling velocity ratio compared with the Low group (p's < 0.01). In addition, the Low group had a significantly higher prevalence of pleural effusion than did the High group (26 vs 11%, p < 0.01). Patients with a relatively greater minVE/VCO 2 in comparison with peak VO 2 had impaired cardiac output as well as restricted pulmonary blood flow increase during exercise, partly due to accumulated pleural effusion.

Polysilicic acid gel method derived V2O5/SiO2 composite materials: Synthesis and characterization

NASA Astrophysics Data System (ADS)

Wang, Dawei; Zhou, Linzong; Feng, Xiaofei; Zhao, Ning; Yang, Bin

2017-01-01

The V2O5/SiO2 composite was prepared by a sol-gel method followed a sintering procedure. The low-cost Na2SiO3•9H2O was used as silicon source, while NH4VO3 was used as vanadium source. By adding NH4VO3 to Na2SiO3 solution and adjusting the mixture's pH with saturated (NH4)2SO4 solution the polysilicic acid gel was formed to give a homogeneous gel composite with VO3-well-distributed in it. The gel composite was dried at 100 °C to give the xerogel, then the xerogel was calcined in air to obtain the V2O5/SiO2 composite. The V2O5/SiO2 composites were characterized by SEM analysis, FT-IR spectroscopy and powder X-ray diffractions.

Role of O2 in regulating tissue respiration in dog muscle working in situ

NASA Technical Reports Server (NTRS)

Hogan, M. C.; Arthur, P. G.; Bebout, D. E.; Hochachka, P. W.; Wagner, P. D.

1992-01-01

This study was designed to investigate the role of tissue oxygenation in some of the factors that are thought to regulate muscle respiration and metabolism. Tissue oxygenation was altered by reductions in O2 delivery (muscle blood flow x arterial O2 content), induced by decreases in arterial PO2 (PaO2). O2 uptake (VO2) was measured in isolated in situ canine gastrocnemius at rest and while working at two stimulation intensities (isometric tetanic contractions at 0.5 and 1 contractions/s) on three separate occasions, with only the level of PaO2 (78, 30, and 21 Torr) being different for each occasion. Muscle blood flow was held constant (pump perfusion) at each work intensity for the three different levels of PaO2. Muscle biopsies were obtained at the end of each rest and work period. Muscle VO2 was significantly less (P less than 0.05) at both stimulation intensities for the hypoxemic conditions, whereas [ATP] was reduced only during the highest work intensity during both hypoxemic conditions (31% reduction at 21 Torr PaO2 and 17% at 30 Torr). For each level of PaO2, the relationships between the changes that occurred in VO2 and levels of phosphocreatine, ADP, and ATP/ADP.P(i) as the stimulation intensity was increased were significantly correlated; however, the slopes and intercepts of these lines were significantly different for each PaO2. Thus a greater change in any of the proposed regulators of tissue respiration (e.g., phosphocreatine, ADP) was required to achieve a given VO2 as PaO2 was decreased.(ABSTRACT TRUNCATED AT 250 WORDS).

Theoretical study of the local structures and the EPR parameters for RLNKB glasses with VO2+ and Cu2+ dopants

NASA Astrophysics Data System (ADS)

Ding, Chang-Chun; Wu, Shao-Yi; Wu, Li-Na; Zhang, Li-Juan; Peng, Li; Wu, Ming-He; Teng, Bao-Hua

2018-02-01

The electron paramagnetic resonance (EPR) parameters and local structures for impurities VO2+ and Cu2+ in RO-Li2O-Na2O-K2O-B2O3 (RLNKB; R = Zn, Mg, Sr and Ba) glasses are theoretically investigated by using the perturbation formulas of the EPR parameters for tetragonally compressed octahedral 3d1 and tetragonally elongated octahedral 3d9 clusters, respectively. The VO2+ and Cu2+ dopants are found to undergo the tetragonal compression (characterized by the negative relative distortion ratios ρ ≈ -3%, -0.98%, -1% and -0.8% for R = Zn, Mg, Sr and Ba) and elongation (characterized by the positive relative distortion ratios ρ ≈ 29%, 17%, 16% and 28%), respectively, due to the Jahn-Teller effect. Both dopants show similar overall decreasing trends of cubic field parameter Dq and covalency factor N with decreasing electronegativity of alkali earth cation R. The conventional optical basicities Λth and local optical basicities Λloc are calculated for both systems, and the local Λloc are higher for Cu2+ than for VO2+ in the same RLNKB glass, despite the opposite relationship for the conventional Λth. This point is supported by the weaker covalency or stronger ionicity for Cu2+ than VO2+ in the same RLNKB system, characterized by the larger N in the former. The above comparative analysis on the spectral and local structural properties would be helpful to understand structures and spectroscopic properties for the similar oxide glasses with transition-metal dopants of complementary electronic configurations.

Synthesis of LaVO4/TiO2 heterojunction nanotubes by sol-gel coupled with hydrothermal method for photocatalytic air purification.

PubMed

Zou, Xuejun; Li, Xinyong; Zhao, Qidong; Liu, Shaomin

2012-10-01

With the aim of improving the effective utilization of visible light, the LaVO(4)/TiO(2) heterojunction nanotubes were fabricated by sol-gel coupled with hydrothermal method. The photocatalytic ability was demonstrated through catalytic removal of gaseous toluene species. The nanotube samples were characterized by scanning electron microscope (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), surface photovoltage (SPV), Raman spectra and N(2) adsorption-desorption measurements. The characterization results showed that the samples with high specific surface areas were of typical nanotubular morphology, which would lead to the high separation and transfer efficiency of photo induced electron-hole pairs. The as-prepared nanotubes exhibited high photocatalytic activity in decomposing toluene species under visible light irradiation with fine photochemical stability. The enhanced photocatalytic performance of LaVO(4)/TiO(2) nanotubes might be attributed to the matching band potentials, the interconnected heterojunction of LaVO(4) versus TiO(2), and the large specific surface areas of nanotubes. Copyright © 2012 Elsevier Inc. All rights reserved.

Solvothermal synthesis of Bi2O3/BiVO4 heterojunction with enhanced visible-light photocatalytic performances

NASA Astrophysics Data System (ADS)

Ying, Wu; Jing, Wang; Yunfang, Huang; Yuelin, Wei; Zhixian, Sun; Xuanqing, Zheng; Chengkun, Zhang; Ningling, Zhou; Leqing, Fan; Jihuai, Wu

2016-08-01

Novel, three-dimensional, flower-like Bi2O3/BiVO4 heterojunction photocatalysts have been prepared by the combination of homogeneous precipitation and two-step solvothermal method followed by thermal solution of NaOH etching process. The as-obtained samples were fully characterized by X-ray diffraction, scanning electron microscopy, energy dispersive X-ray analysis, Brunauer-Emmett-Teller surface area, and UV—vis diffuse-reflectance spectroscopy in detail. The crystallinity, microstructure, specific surface area, optical property and photocatalytic activity of samples greatly changed depending on solvothermal reaction time. The photocatalytic activities of samples were evaluated on the degradation of methyl orange (MO) under visible-light irradiation. The Bi2O3/BiVO4 exhibited much higher photocatalytic activities than pure BiVO4 and conventional TiO2 (P25). The result revealed that the three-dimensional heterojunction played a critical role in the separation of the electron and hole pairs and enhancement of the interfacial charge transfer efficiency, which was responsible for the enhanced photocatalytic activity. Project supported by the National Natural Science Foundation of China (Nos. 61306077, 21301060), the Fundamental Research Funds for the Central Universities (Nos. JB-ZR1109, JB-ZR1212), the National Science Foundation of Quanzhou City (No. 2014Z108), the Promotion Program for Young and Middle-aged Teachers in Science and Technology Research of Huaqiao University (No. ZQN-PY207), Discipline Innovation Team Project of Huaqiao University (No. 201320), and the Instrumental Analysis Center Huaqiao University.

Effects of training status and exercise intensity on phase II VO2 kinetics.

PubMed

Koppo, Katrien; Bouckaert, Jacques; Jones, Andrew M

2004-02-01

To test the hypotheses that: 1) the time constant for the fast component of .VO2 kinetics (tau1) at exercise onset would be faster in trained than in untrained subjects for both moderate and heavy exercise, and that 2) tau1 would become progressively slower in untrained subjects at higher power outputs but be invariant in trained subjects. Eight untrained subjects (.VO2peak: 42.9 +/- 5.1 mL.kg-1.min-1) and seven trained cyclists (.VO2peak: 66.6 +/- 2.5 mL.kg-1.min-1) completed square-wave transitions to power outputs requiring 60% and 80% of gas exchange threshold (GET), and 50% of the difference between GET and .VO2 peak (50%Delta) from a baseline of "unloaded" cycling. .VO2 was measured breath-by-breath and individual responses were modeled using nonlinear regression techniques. A repeated measures ANOVA revealed that the tau1 was significantly smaller (i.e., the kinetics were faster) in the trained compared with the untrained subjects and that tau1 became significantly greater (i.e., the kinetics were slowed) at higher power outputs both in the untrained (60%GET: 17.8 +/- 3.8 s, 80%GET: 21.5 +/- 6.6 s, and 50%Delta: 23.5 +/- 2.8 s) and the trained (60%GET: 8.9 +/- 1.3 s, 80%GET: 11.7 +/- 2.5 s, and 50%Delta: 15.2 +/- 2.0 s) subjects (P < 0.05). Phase II .VO2 kinetics became progressively slower at higher power outputs in both trained and untrained subjects. That a greater tau1 was evident at a higher power output within the moderate exercise intensity domain (O2 availability is presumed not to be limiting, indicates that the slowing of the phase II .VO2 kinetics may be attributed to other factors besides O2 availability such as the recruitment of higher threshold motor units.

Hydrothermal growth of VO2 nanoplate thermochromic films on glass with high visible transmittance

PubMed Central

Zhang, Jiasong; Li, Jingbo; Chen, Pengwan; Rehman, Fida; Jiang, Yijie; Cao, Maosheng; Zhao, Yongjie; Jin, Haibo

2016-01-01

The preparation of thermochromic vanadium dioxide (VO2) films in an economical way is of interest to realizing the application of smart windows. Here, we reported a successful preparation of self-assembly VO2 nanoplate films on TiO2-buffered glass by a facile hydrothermal process. The VO2 films composed of triangle-shaped plates standing on substrates exhibit a self-generated porous structure, which favors the transmission of solar light. The porosity of films is easily controlled by changing the concentration of precursor solutions. Excellent thermochromic properties are observed with visible light transmittance as high as 70.3% and solar modulating efficiency up to 9.3% in a VO2 film with porosity of ~35.9%. This work demonstrates a promising technique to promote the commercial utilization of VO2 in smart windows. PMID:27296772

Order-disorder phase transition in the peroxidovanadium complex NH4[VO(O2)2(NH3)].

PubMed

Schwendt, Peter; Gyepes, Róbert; Chrappová, Jana; Němec, Ivan; Vaněk, Přemysl

2018-07-05

Complex NH 4 [VO(O 2 ) 2 (NH 3 )] (1) undergoes an order-disorder phase transition at T c ~258K. This transition is accompanied by change in the space group of the orthorhombic lattice and also by significant structural rearrangements of the constituent molecules, which are pertinent mostly to their NH 4 + ions and their ammonia ligands. The low-temperature solid state IR and Raman spectra of 1 were corroborated by solid-state computations that employed Gaussian functions as the basis set. Results of these computations yielded excellent agreement with experimental data. On the curves of temperature dependence of vibrational modes, the phase transition is expressed by an abrupt change of the slope above T c . Copyright © 2018 Elsevier B.V. All rights reserved.

Inverse relationship between VO2max and economy/efficiency in world-class cyclists.

PubMed

Lucía, Alejandro; Hoyos, Jesus; Pérez, Margarita; Santalla, Alfredo; Chicharro, José L

2002-12-01

To determine the relationship that exists between VO2max and cycling economy/efficiency during intense, submaximal exercise in world-class road professional cyclists. METHODS Each of 11 male cyclists (26+/-1 yr (mean +/- SEM); VO2max: 72.0 +/- 1.8 mL x kg(-1) x min(-1)) performed: 1) a ramp test for O2max determination and 2) a constant-load test of 20-min duration at the power output eliciting 80% of subjects' VO2max during the previous ramp test (mean power output of 385 +/- 7 W). Cycling economy (CE) and gross mechanical efficiency (GE) were calculated during the constant-load tests. CE and GE averaged 85.2 +/- 2.3 W x L(-1) x min(-1) and 24.5 +/- 0.7%, respectively. An inverse, significant correlation was found between 1) VO2max (mL x kg(-0.32) x min(-1)) and both CE (r = -0.71; P = 0.01) and GE (-0.72; P = 0.01), and 2) VO2max (mL x kg(-1) x min(-1)) and both CE (r = -0.65; P = 0.03) and GE (-0.64; P = 0.03). A high CE/GE seems to compensate for a relatively low VO2max in professional cyclists.

Higher Precision of Heart Rate Compared with VO2 to Predict Exercise Intensity in Endurance-Trained Runners.

PubMed

Reis, Victor M; den Tillaar, Roland Van; Marques, Mario C

2011-01-01

The aim of the present study was to assess the precision of oxygen uptake with heart rate regression during track running in highly-trained runners. Twelve national and international level male long-distance road runners (age 30.7 ± 5.5 yrs, height 1.71 ± 0.04 m and mass 61.2 ± 5.8 kg) with a personal best on the half marathon of 62 min 37 s ± 1 min 22 s participated in the study. Each participant performed, in an all-weather synthetic track five, six min bouts at constant velocity with each bout at an increased running velocity. The starting velocity was 3.33 m·s(-1) with a 0.56 m·s(-1) increase on each subsequent bout. VO2 and heart rate were measured during the runs and blood lactate was assessed immediately after each run. Mean peak VO2 and mean peak heart rate were, respectively, 76.2 ± 9.7 mL·kg(-1)·min(-1) and 181 ± 13 beats·min(-1). The linearity of the regressions between heart rate, running velocity and VO2 were all very high (r > 0.99) with small standard errors of regression (i.e. Sy.x < 5% at the velocity associated with the 2 and 4 mmol·L(-1) lactate thresholds). The strong relationships between heart rate, running velocity and VO2 found in this study show that, in highly trained runners, it is possible to have heart rate as an accurate indicator of energy demand and of the running speed. Therefore, in this subject cohort it may be unnecessary to use VO2 to track changes in the subjects' running economy during training periods. Key pointsHeart rate is used in the control of exercise intensity in endurance sports.However, few studies have quantified the precision of its relationship with oxygen uptake in highly trained runners.We evaluated twelve elite half-marathon runners during track running at various intensities and established three regressions: oxygen uptake / heart rate; heart rate / running velocity and oxygen uptake / running velocity.The three regressions presented, respectively, imprecision of 4,2%, 2,75% and 4,5% at the

A simple and low-cost combustion method to prepare monoclinic VO2 with superior thermochromic properties

PubMed Central

Cao, Ziyi; Xiao, Xiudi; Lu, Xuanming; Zhan, Yongjun; Cheng, Haoliang; Xu, Gang

2016-01-01

In this approach, the VO2 nanoparticles have been successfully fabricated via combusting the low-cost precursor solution consisted of NH4VO3, C2H6O2 and C2H5OH. By the XRD, TEM and XPS analysis, it can be found that the synthetic monoclinic VO2 is single crystal and no impurity is defined. After dispersing the VO2 nanoparticles into the polymer, the solar modulation of VO2-based composite film is up to 12.5% with luminous transmission and haze around 62.2% and 0.5%, respectively. In other words, the composite films show high performance of thermochromic properties. This could open an efficient way to fabricate low-cost and large-scale VO2 (M) nanoparticles and thermochromic films. PMID:27976748

Inelastic Neutron Scattering studies of pure and Mo doped VO2

NASA Astrophysics Data System (ADS)

Banerjee, Arnab; Granroth, Garrett E.; Yiu, Yuen; Aczel, Adam A.; Koleshnikov, Alexander I.; Luo, Huxia; Cava, Robert J.; Nagler, Stephen E.; Princeton University Collaboration; Sequoia Team

2014-03-01

For the last half-century VO2 has been viewed as an archetypal system for studying the metal-insulator transition (MIT). Moreover, there is currently intense interest in this material arising from its promising use in fast energy efficient electronic devices. There are key unresolved issues connected with the origin of the MIT, including the role of magnetism arising from the S =1/2 V4+ ions. It is known that below 340 K in undoped VO2 the V ions form structural dimers in the insulating M1 monoclinic phase. Here we report the results of new inelastic neutron scattering measurements of VO2 and V0.75Mo0.25O2. Using the SEQUOIA chopper spectrometer at the SNS possible lattice and magnetic excitations for energies up to 600 meV were investigated. We discuss the results in the context of current ideas concerning the MIT in VO2. The research at ORNL is supported by the DOE BES, Division of Scientific User Facilities. Work at Princeton University is supported by the DOE grant number DE-FG02-98ER45706.

VO2 and VCO2 variabilities through indirect calorimetry instrumentation.

PubMed

Cadena-Méndez, Miguel; Escalante-Ramírez, Boris; Azpiroz-Leehan, Joaquín; Infante-Vázquez, Oscar

2013-01-01

The aim of this paper is to understand how to measure the VO2 and VCO2 variabilities in indirect calorimetry (IC) since we believe they can explain the high variation in the resting energy expenditure (REE) estimation. We propose that variabilities should be separately measured from the VO2 and VCO2 averages to understand technological differences among metabolic monitors when they estimate the REE. To prove this hypothesis the mixing chamber (MC) and the breath-by-breath (BbB) techniques measured the VO2 and VCO2 averages and their variabilities. Variances and power spectrum energies in the 0-0.5 Hertz band were measured to establish technique differences in steady and non-steady state. A hybrid calorimeter with both IC techniques studied a population of 15 volunteers that underwent the clino-orthostatic maneuver in order to produce the two physiological stages. The results showed that inter-individual VO2 and VCO2 variabilities measured as variances were negligible using the MC while variabilities measured as spectral energies using the BbB underwent 71 and 56% (p < 0.05), increase respectively. Additionally, the energy analysis showed an unexpected cyclic rhythm at 0.025 Hertz only during the orthostatic stage, which is new physiological information, not reported previusly. The VO2 and VCO2 inter-individual averages increased to 63 and 39% by the MC (p < 0.05) and 32 and 40% using the BbB (p < 0.1), respectively, without noticeable statistical differences among techniques. The conclusions are: (a) metabolic monitors should simultaneously include the MC and the BbB techniques to correctly interpret the steady or non-steady state variabilities effect in the REE estimation, (b) the MC is the appropriate technique to compute averages since it behaves as a low-pass filter that minimizes variances, (c) the BbB is the ideal technique to measure the variabilities since it can work as a high-pass filter to generate discrete time series able to accomplish

Atomic layer deposition of VO2 films with Tetrakis-dimethyl-amino vanadium (IV) as vanadium precursor

NASA Astrophysics Data System (ADS)

Lv, Xinrui; Cao, Yunzhen; Yan, Lu; Li, Ying; Song, Lixin

2017-02-01

VO2 thin films have been grown on Si(100) (VO2/Si) and fused silica substrates (VO2/SiO2) by atomic layer deposition (ALD) using tetrakis-dimethyl-amino vanadium (IV) (TDMAV) as a novel vanadium precursor and water as reactant gas. The quartz crystal microbalance (QCM) measurement was performed to study the ALD process of VO2 thin film deposition, and a constant growth rate of about 0.95 Å/cycle was obtained at the temperature range of 150-200 °C. XRD measurement was performed to study the influence of deposition temperature and post-annealing condition on the crystallization of VO2 films, which indicated that the films deposited between 150 and 200 °C showed well crystallinity after annealing at 475 °C for 100 min in Ar atmosphere. XPS measurement verified that the vanadium oxidation state was 4+ for both as-deposited film and post-annealed VO2/Si film. AFM was applied to study the surface morphology of VO2/Si films, which showed a dense polycrystalline film with roughness of about 1 nm. The resistance of VO2/Si films deposited between 150 °C and 200 °C as a function of temperature showed similar semiconductor-to-metal transition (SMT) characters with the transition temperature for heating branch (Tc,h) of about 72 °C, a hysteresis width of about 10 °C and the resistance change of two orders of magnitude. The increase of Tc,h compared with the bulk VO2 (68 °C) may be attributed to the tensile stress along the c-axis in the film. Transmittance measurement of VO2/SiO2 films showed typical thermochromic property with a NIR switching efficiency of above 50% at 2 μm across the transition.

Diamagnetic to ferromagnetic switching in VO2 epitaxial thin films by nanosecond excimer laser treatment

NASA Astrophysics Data System (ADS)

Molaei, R.; Bayati, R.; Nori, S.; Kumar, D.; Prater, J. T.; Narayan, J.

2013-12-01

VO2(010)/NiO(111) epitaxial heterostructures were integrated with Si(100) substrates using a cubic yttria-stabilized zirconia (c-YSZ) buffer. The epitaxial alignment across the interfaces was determined to be VO2(010)‖NiO(111)‖c-YSZ(001)‖Si(001) and VO2[100]‖NiO⟨110⟩‖c-YSZ⟨100⟩‖Si⟨100⟩. The samples were subsequently treated by a single shot of a nanosecond KrF excimer laser. Pristine as-deposited film showed diamagnetic behavior, while laser annealed sample exhibited ferromagnetic behavior. The population of majority charge carriers (e-) and electrical conductivity increased by about two orders of magnitude following laser annealing. These observations are attributed to the introduction of oxygen vacancies into the VO2 thin films and the formation of V3+ defects.

Improved photoelectrochemical performance of BiVO4/MoO3 heterostructure thin films

NASA Astrophysics Data System (ADS)

Kodan, Nisha; Mehta, B. R.

2018-05-01

Bismuth vanadate (BiVO4) and Molybdenum trioxide (MoO3) thin films have been prepared by RF sputtering technique. BiVO4 thin films were deposited on indium doped tin oxide (In: SnO2; ITO) substrates at room temperature and 80W applied rf power. The prepared BiVO4 thin films were further annealed at 450°C for 2 hours in air to obtain crystalline monoclinic phase and successively coated with MoO3 thin films deposited at 150W rf power and 400°C for 30 minutes. The effect of coupling BiVO4 and MoO3 on the structural, optical and photoelectrochemical (PEC) properties have been studied. Optical studies reveal that coupling of BiVO4 and MoO3 results in improvement of optical absorption in visible region of solar spectrum. PEC study shows approximate 3-fold and 38-fold increment in photocurrent values of BiVO4/MoO3 (0.38 mA/cm2) heterostructure thin film as compared to MoO3 (0.15 mA/cm2) and BiVO4 (10 µA/cm2) thin films at applied bias of 1 V vs Ag/AgCl in 0.5 M Na2SO4 (pH=7) electrolyte.

Submaximal exercise VO2 and Qc during 30-day 6 degrees head-down bed rest with isotonic and isokinetic exercise training

NASA Technical Reports Server (NTRS)

Greenleaf, J. E.; Ertl, A. C.; Bernauer, E. M.

1996-01-01

BACKGROUND: Maintaining intermediary metabolism is necessary for the health and well-being of astronauts on long-duration spaceflights. While peak oxygen uptake (VO2) is consistently decreased during prolonged bed rest, submaximal VO2 is either unchanged or decreased. METHODS: Submaximal exercise metabolism (61 +/- 3% peak VO2) was measured during ambulation (AMB day-2) and on bed rest days 4, 11, and 25 in 19 healthy men (32-42 yr) allocated into no exercise (NOE, N = 5) control, and isotonic exercise (ITE, N = 7) and isokinetic exercise (IKE, N = 7) training groups. Exercise training was conducted supine for two 30-min periods per day for 6 d per week: ITE training was intermittent at 60-90% peak VO2; IKE training was 10 sets of 5 repetitions of peak knee flexion-extension force at a velocity of 100 degrees s-1. Cardiac output was measured with the indirect Fick CO2 method, and plasma volume with Evans blue dye dilution. RESULTS: Supine submaximal exercise VO2 decreased significantly (*p < 0.05) by 10.3%* with ITE and by 7.3%* with IKE; similar to the submaximal cardiac output decrease of 14.5%* (ITE) and 20.3%* (IKE), but different from change in peak VO2 (+1.4% with ITE and -10.2%* with IKE) and decrease in plasma volume of -3.7% (ITE) and -18.0%* (IKE). Reduction of submaximal VO2 during bed rest correlated 0.79 (p < 0.01) with submaximal Qc, but was not related to change in peak VO2 or plasma volume. CONCLUSION: Reduction in submaximal oxygen uptake during prolonged bed rest is related to decrease in exercise but not resting cardiac output; perturbations in active skeletal muscle metabolism may be involved.

Formation of different micro-morphologies from VO2 and ZnO crystallization using macro-porous silicon substrates

NASA Astrophysics Data System (ADS)

Salazar-Kuri, U.; Antúnez, E. E.; Estevez, J. O.; Olive-Méndez, Sion F.; Silva-González, N. R.; Agarwal, V.

2017-05-01

Square-shaped macropores produced by electrochemical anodization of n- and p-type Si wafers have been used as centers of nucleation to crystallize VO2 and ZnO. Substrate roughness dependent formation of different morphologies is revealed in the form of squared particles, spheres, bars and ribbons in the case of VO2 and hexagonal piles and spheres in the case of ZnO, have been observed.The presence of nano-/micro-metric crystals was studied through field emission scanning electron microscopy and energy dispersive X-ray spectroscopy mapping. Crystal structure of metal oxides was confirmed by micro-Raman spectroscopy. The growth of the different morphologies has been explained in terms of the surface free energy of a bare Si/SiO2 substrate and its modification originated from the roughness of the surface and of the walls of the porous substrates. This energy plays a crucial role on the minimization of the required energy to induce heterogeneous nucleation and crystal growth. Present work strengthens and provides an experimental evidence of roughness dependent metal oxide crystal growth with well-defined habits from pore corners and rough sides of the pore walls, similar to already reported protein crystals.

Non-invasive measurement of the mean alveolar O(2) tension from the oxygen uptake versus tidal volume curve.

PubMed

Jordanoglou, J; Latsi, P; Chroneou, A; Koulouris, N G

2007-10-01

The classical equations for measuring the mean and the ideal alveolar O(2) tension are based on assumptions, which are shown to be invalid. So we thought to develop a new, non-invasive method for measuring the mean alveolar P,O(2) within the volume domain (PA,O(2(Bohr))). This method is based on the oxygen uptake vs. tidal volume curve (VO(2) vs. VT) obtained during tidal breathing of room air and/or air enriched with oxygen. PA,O(2(Bohr)) and the ideal alveolar PO(2) (PA,O(2(ideal))) were simultaneously measured in 10 healthy subjects and 34 patients suffering from chronic obstructive pulmonary disease (COPD) breathing tidally room air at rest. Additionally, 10 subjects (three healthy subjects and seven COPD patients) were studied while breathing initially room air and subsequently air enriched with oxygen. According to the results, PA,O(2(Bohr)) considerably differed from PA,O(2(ideal)) (P = 0.004). The cause of the difference, at the individual's R, is: (1) the difference between the arterial and Bohr's alveolar CO(2) tension, mainly in COPD patients, and (2) the inequality between Bohr's alveolar part of the tidal volume for CO(2) and O(2). Furthermore, end-tidal gas tension (PET,CO(2) and PET,O(2)) differed from Pa,CO(2) and PA,O(2(Bohr)) respectively. The deviation of PA,O(2(Bohr)) from PA,O(2(ideal)) has a definite impact on Bohr's dead space ratio for O(2) and CO(2), and on the alveolar-arterial O(2) difference. The difference (PA,O(2(Bohr)) - PA,O(2(ideal))) is not related to the pathology of the disease. So, gas exchange within the lungs should be assessed at the subject's R from PA,O(2(Bohr)) and PA,CO(2(Bohr)) but not from PA,O(2(ideal)) nor Pa,CO(2).

The Effect of Habitual Smoking on VO2max

NASA Technical Reports Server (NTRS)

Wier, Larry T.; Suminski, Richard R.; Poston, Walker S.; Randles, Anthony M.; Arenare, Brian; Jackson, Andrew S.

2008-01-01

VO2max is associated with many factors, including age, gender, physical activity, and body composition. It is popularly believed that habitual smoking lowers aerobic fitness. PURPOSE: to determine the effect of habitual smoking on VO2max after controlling for age, gender, activity and BMI. METHODS: 2374 men and 375 women employed at the NASA/Johnson Space Center were measured for VO2max by indirect calorimetry (RER>=1.1), activity by the 11 point (0-10) NASA Physical Activity Status Scale (PASS), BMI and smoking pack-yrs (packs day*y of smoking). Age was recorded in years and gender was coded as M=1, W=0. Pack.y was made a categorical variable consisting of four levels as follows: Never Smoked (0), Light (1-10), Regular (11-20), Heavy (>20). Group differences were verified by ANOVA. A General Linear Models (GLM) was used to develop two models to examine the relationship of smoking behavior on VO2max. GLM #1(without smoking) determined the combined effects of age, gender, PASS and BMI on VO2max. GLM #2 (with smoking) determined the added effects of smoking (pack.y groupings) on VO2max after controlling for age, gender, PASS and BMI. Constant errors (CE) were calculated to compare the accuracy of the two models for estimating the VO2max of the smoking subgroups. RESULTS: ANOVA affirmed the mean VO2max of each pack.y grouping decreased significantly (p<0.01) as the level of smoking exposure increased. GLM #1 showed that age, gender, PASS and BMI were independently related with VO2max (R2 = 0.642, SEE = 4.90, p<0.001). The added pack.y variables in GLM #2 were statistically significant (R2 change = 0.7%, p<0.01). Post hoc analysis showed that compared to Never Smoked, the effects on VO2max from Light and Regular smoking habits were -0.83 and -0.85 ml.kg- 1.min-1 respectively (p<0.05). The effect of Heavy smoking on VO2max was -2.56 ml.kg- 1.min-1 (p<0.001). The CE s of each smoking group in GLM #2 was smaller than the CE s of the smoking group counterparts in GLM #1

Oxidizing annealing effects on VO2 films with different microstructures

NASA Astrophysics Data System (ADS)

Dou, Yan-Kun; Li, Jing-Bo; Cao, Mao-Sheng; Su, De-Zhi; Rehman, Fida; Zhang, Jia-Song; Jin, Hai-Bo

2015-08-01

Vanadium dioxide (VO2) films have been prepared by direct-current magnetron sputter deposition on m-, a-, and r-plane sapphire substrates. The obtained VO2 films display different microstructures depending on the orientation of sapphire substrates, i.e. mixed microstructure of striped grains and equiaxed grains on m-sapphire, big equiaxed grains on a-sapphire and fine-grained microstructure on r-sapphire. The VO2 films were treated by the processes of oxidation in air. The electric resistance and infrared transmittance of the oxidized films were characterized to examine performance characteristics of VO2 films with different microstructures in oxidation environment. The oxidized VO2 films on m-sapphire exhibit better electrical performance than the other two films. After air oxidization for 600 s at 450 °C, the VO2 films on m-sapphire show a resistance change of 4 orders of magnitude over the semiconductor-to-metal transition. The oxidized VO2 films on a-sapphire have the highest optical modulation efficiency in infrared region compared to other samples. The different performance characteristics of VO2 films are understood in terms of microstructures, i.e. grain size, grain shape, and oxygen vacancies. The findings reveal the correlation of microstructures and performances of VO2 films, and provide useful knowledge for the design of VO2 materials to different applications.

Improved metal-insulator-transition characteristics of ultrathin VO2 epitaxial films by optimized surface preparation of rutile TiO2 substrates

NASA Astrophysics Data System (ADS)

Martens, Koen; Aetukuri, Nagaphani; Jeong, Jaewoo; Samant, Mahesh G.; Parkin, Stuart S. P.

2014-02-01

Key to the growth of epitaxial, atomically thin films is the preparation of the substrates on which they are deposited. Here, we report the growth of atomically smooth, ultrathin films of VO2 (001), only ˜2 nm thick, which exhibit pronounced metal-insulator transitions, with a change in resistivity of ˜500 times, at a temperature that is close to that of films five times thicker. These films were prepared by pulsed laser deposition on single crystalline TiO2(001) substrates that were treated by dipping in acetone, HCl and HF in successive order, followed by an anneal at 700-750 °C in flowing oxygen. This pretreatment removes surface contaminants, TiO2 defects, and provides a terraced, atomically smooth surface.

Temperature and electric field induced metal-insulator transition in atomic layer deposited VO2 thin films

NASA Astrophysics Data System (ADS)

Tadjer, Marko J.; Wheeler, Virginia D.; Downey, Brian P.; Robinson, Zachary R.; Meyer, David J.; Eddy, Charles R.; Kub, Fritz J.

2017-10-01

Amorphous vanadium oxide (VO2) films deposited by atomic layer deposition (ALD) were crystallized with an ex situ anneal at 660-670 °C for 1-2 h under a low oxygen pressure (10-4 to 10-5 Torr). Under these conditions the crystalline VO2 phase was maintained, while formation of the V2O5 phase was suppressed. Electrical transition from the insulator to the metallic phase was observed in the 37-60 °C range, with an ROFF/RON ratio of up to about 750 and ΔTC ≅ 7-10 °C. Lateral electric field applied across two-terminal device structures induced a reversible phase change, with a room temperature transition field of about 25 kV/cm in the VO2 sample processed with the 2 h long O2 anneal. Both the width and slope of the field induced MIT I-V hysteresis were dependent upon the VO2 crystalline quality.

Synthesis and crystal structure of two new uranyl oxychloro-vanadate layered compounds: M7(UO 2) 8(VO 4) 2O 8Cl with M=Rb, Cs

NASA Astrophysics Data System (ADS)

Duribreux, I.; Saadi, M.; Obbade, S.; Dion, C.; Abraham, F.

2003-05-01

Two new alkali uranyl oxychloro vanadates M7(UO 2) 8(VO 4) 2O 8Cl with M=Rb, Cs, have been synthesized by solid-state reactions and their structures determined from single-crystal X-ray diffraction data. They crystallize in the orthorhombic system with space groups Pmcn and Pmmn, respectively. The a and b unit cell parameters are almost identical in both compounds while the c parameter in the Rb compound is doubled: Rb— a=21.427(5) Å, b=11.814(3) Å, c=14.203(3) Å, V=3595.1(1) Å 3, Z=4, ρmes=5.93(2) g/cm 3, ρcal=5.82(1) g/cm 3; Cs— a=21.458(3) Å, b=11.773(2) Å, c=7.495(1) Å, V=1893.6(5) Å 3, Z=2, ρmes=6.09(2) g/cm 3, ρcal=6.11(1) g/cm 3. A full-matrix least-squares refinement yielded R1=0.0221, w R2=0.0562 for 2675 independent reflections and R1=0.0386, w R2=0.1042 for 2446 independent reflections, for the Rb and Cs compounds, respectively. Data were collected with Mo( Kα) radiation and a charge coupled device (CCD) detector of a Bruker diffractometer. Both structures are characterized by [(UO 2) 8(VO 4) 2O 8Cl] n7 n- layers parallel to the (001) plane. The layers are built up from VO 4 tetrahedra, UO 7 and UO 6Cl pentagonal bipyramids, and UO 6 distorded octahedra. The UO 7 and UO 6Cl pentagonal bipyramids are associated by sharing opposite equatorial edges to form infinite chains (UO 5-UO 4Cl-UO 5) n parallel to the a axis. These chains are linked together by VO 4 tetrahedra, UO 6 octahedra, UO 7 corner sharing and UO 6Cl, Cl sharing. Both structures differ simply by the symmetry of the layers. The unit cell contains one centrosymmetric layer in the Cs compound, whereas in the two-layer unit cell of the Rb compound, two non-centrosymmetric consecutive layers are related by an inversion center. The layers appear to be held together by the alkali ions. The mobility of the M+ ions within the interlayer space in M7(UO 2) 8(VO 4) 2O 8Cl and carnotite analog compounds is compared.

Hydrothermal route to VO2 (B) nanorods: controlled synthesis and characterization

NASA Astrophysics Data System (ADS)

Song, Shaokun; Huang, Qiwei; Zhu, Wanting

2017-10-01

One-dimensional vanadium dioxides have attracted intensive attention owing to their distinctive structure and novel applications in catalysis, high energy lithium-ion batteries, chemical sensors/actuators and electrochemical devices etc. In this paper, large-scale VO2 (B) nanorods have been successfully synthesized via a versatile and environment friendly hydrothermal strategy using V2O5 as vanadium source and carbohydrates/alcohols as reductant. The obtained samples are characterized by XRD, FT-IR, TEM, and XPS techniques to investigate the effects of chemical parameters such as reductants, temperature, and time of synthesis on the structure and morphology of products. Results show that pure B phase VO2 with homogeneous nanorod-like morphology can be prepared easily at 180 °C for 3 days with glycerol as reluctant. Typically, the nanorod-like products are 0.5-1 μm long and 50 nm width. Furthermore, it is also confirmed that the products are consisted of VO2, corresponding to the B phase. More importantly, this novel approach is efficient, free of any harmful solvents and surfactants. Therefore, this efficient, green, and cost-saving route will have great potential in the large-scale fabrication of 1D VO2 (B) nanorods from the economic and environmental point of view.

Catalytic properties of the VO x /Ce0.46Zr0.54O2 oxide system in the oxidative dehydrogenation of propane

NASA Astrophysics Data System (ADS)

Turakulova, A. O.; Kharlanov, A. N.; Levanov, A. V.; Isaikina, O. Ya.; Lunin, V. V.

2017-01-01

Ce0.46Zr0.54O2 solid solution prepared using a cellulose template was employed as a carrier for vanadium catalysts of the oxidative dehydrogenation of propane. The properties of VO x /Ce0.46Zr0.54O2 catalyst (5 wt % vanadium) are compared with the properties of the neat support. The carrier and catalyst are studied by means of BET, SEM, DTA, XRD, and Raman spectroscopy. It is shown that the CeVO4 phase responsible for the ODH process is formed upon interaction between vanadate ions and cerium ions on the surface of the solid solution. The catalytic properties of the catalyst and the support are studied in the propane oxidation reaction at temperatures of 450 and 500°C with pulse feeding of the reagent. It is found that the complete oxidation of propane occurs on the support with formation of CO2 and H2O. Three products (propene, CO2, and H2O) form in the presence of the vanadium catalyst. It is suggested that there are two types of catalytic centers on the catalyst's surface. It is concluded that the centers responsible for the complete oxidation of propane are concentrated mainly on the carrier, while the centers responsible for propane ODH are on the CeVO4.

Electrode Reaction Mechanism of Ag 2VO 2PO 4 Cathode

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Ruibo; Abtew, Tesfaye A.; Quackenbush, Nicholas F.

In this study, the high capacity of primary lithium-ion cathode Ag 2VO 2PO 4 is facilitated by both displacement and insertion reaction mechanisms. Whether the Ag extrusion (specifically, Ag reduction with Ag metal displaced from the host crystal) and V reduction are sequential or concurrent remains unclear. A microscopic description of the reaction mechanism is required for developing design rules for new multimechanism cathodes, combining both displacement and insertion reactions. However, the amorphization of Ag 2VO 2PO 4 during lithiation makes the investigation of the electrode reaction mechanism difficult with conventional characterization tools. For addressing this issue, a combination ofmore » local probes of pair-distribution function and X-ray spectroscopy were used to obtain a description of the discharge reaction. We determine that the initial reaction is dominated by silver extrusion with vanadium playing a supporting role. In addition, once sufficient Ag has been displaced, the residual Ag + in the host can no longer stabilize the host structure and V–O environment (i.e., onset of amorphization). After amorphization, silver extrusion continues but the vanadium reduction dominates the reaction. As a result, the crossover from primarily silver reduction displacement to vanadium reduction is facilitated by the amorphization that makes vanadium reduction increasingly more favorable.« less

Electrode Reaction Mechanism of Ag 2VO 2PO 4 Cathode

DOE PAGES

Zhang, Ruibo; Abtew, Tesfaye A.; Quackenbush, Nicholas F.; ...

2016-05-09

In this study, the high capacity of primary lithium-ion cathode Ag 2VO 2PO 4 is facilitated by both displacement and insertion reaction mechanisms. Whether the Ag extrusion (specifically, Ag reduction with Ag metal displaced from the host crystal) and V reduction are sequential or concurrent remains unclear. A microscopic description of the reaction mechanism is required for developing design rules for new multimechanism cathodes, combining both displacement and insertion reactions. However, the amorphization of Ag 2VO 2PO 4 during lithiation makes the investigation of the electrode reaction mechanism difficult with conventional characterization tools. For addressing this issue, a combination ofmore » local probes of pair-distribution function and X-ray spectroscopy were used to obtain a description of the discharge reaction. We determine that the initial reaction is dominated by silver extrusion with vanadium playing a supporting role. In addition, once sufficient Ag has been displaced, the residual Ag + in the host can no longer stabilize the host structure and V–O environment (i.e., onset of amorphization). After amorphization, silver extrusion continues but the vanadium reduction dominates the reaction. As a result, the crossover from primarily silver reduction displacement to vanadium reduction is facilitated by the amorphization that makes vanadium reduction increasingly more favorable.« less

Electronic structure and insulating gap in epitaxial VO 2 polymorphs

DOE PAGES

Lee, Shinbuhm; Meyer, Tricia L.; Sohn, Changhee; ...

2015-12-24

Here, determining the origin of the insulating gap in the monoclinic VO 2(M1) is a long-standing issue. The difficulty of this study arises from the simultaneous occurrence of structural and electronic transitions upon thermal cycling. Here, we compare the electronic structure of the M1 phase with that of single crystalline insulating VO 2(A) and VO 2(B) thin films to better understand the insulating phase of VO 2. As these A and B phases do not undergo a structural transition upon thermal cycling, we comparatively study the origin of the gap opening in the insulating VO 2 phases. By x-ray absorptionmore » and optical spectroscopy, we find that the shift of unoccupied t 2g orbitals away from the Fermi level is a common feature, which plays an important role for the insulating behavior in VO 2 polymorphs. The distinct splitting of the half-filled t 2g orbital is observed only in the M1 phase, widening the bandgap up to ~0.6 eV. Our approach of comparing all three insulating VO 2 phases provides insight into a better understanding of the electronic structure and the origin of the insulating gap in VO 2.« less

Optimizing the "priming" effect: influence of prior exercise intensity and recovery duration on O2 uptake kinetics and severe-intensity exercise tolerance.

PubMed

Bailey, Stephen J; Vanhatalo, Anni; Wilkerson, Daryl P; Dimenna, Fred J; Jones, Andrew M

2009-12-01

It has been suggested that a prior bout of high-intensity exercise has the potential to enhance performance during subsequent high-intensity exercise by accelerating the O(2) uptake (Vo(2)) on-response. However, the optimal combination of prior exercise intensity and subsequent recovery duration required to elicit this effect is presently unclear. Eight male participants, aged 18-24 yr, completed step cycle ergometer exercise tests to 80% of the difference between the preestablished gas exchange threshold and maximal Vo(2) (i.e., 80%Delta) after no prior exercise (control) and after six different combinations of prior exercise intensity and recovery duration: 40%Delta with 3 min (40-3-80), 9 min (40-9-80), and 20 min (40-20-80) of recovery and 70%Delta with 3 min (70-3-80), 9 min (70-9-80), and 20 min (70-20-80) of recovery. Overall Vo(2) kinetics were accelerated relative to control in all conditions except for 40-9-80 and 40-20-80 conditions as a consequence of a reduction in the Vo(2) slow component amplitude; the phase II time constant was not significantly altered with any prior exercise/recovery combination. Exercise tolerance at 80%Delta was improved by 15% and 30% above control in the 70-9-80 and 70-20-80 conditions, respectively, but was impaired by 16% in the 70-3-80 condition. Prior exercise at 40%Delta did not significantly influence exercise tolerance regardless of the recovery duration. These data demonstrate that prior high-intensity exercise ( approximately 70%Delta) can enhance the tolerance to subsequent high-intensity exercise provided that it is coupled with adequate recovery duration (>or=9 min). This combination presumably optimizes the balance between preserving the effects of prior exercise on Vo(2) kinetics and providing sufficient time for muscle homeostasis (e.g., muscle phosphocreatine and H(+) concentrations) to be restored.

Structure and Properties of VO2 and Titanium Dioxide Based Epitaxial Heterostructures Integrated with Silicon and Sapphire Substrates

NASA Astrophysics Data System (ADS)

Bayati, Mohammad Reza

The main focus of this study was placed on structure-property correlation in TiO2 and VO2 based epitaxial heterostructures where the photochemical and electrical properties were tuned through microstructural engineering. In the framework of domain matching epitaxy, epitaxial growth of TiO2 and VO2 heterostructures on different substrates were explained. The theta-2theta and ϕ scan X-ray diffraction measurements and detailed high resolution electron microscopy studies corroborated our understanding of the epitaxial growth and the crystallographic arrangement across the interfaces. The influence of the laser and substrate variables on structural characteristics of the films was investigated using X-ray photoelectron spectroscopy, room temperature photoluminescence spectroscopy, and UV-Vis spectrophotometry. In addition, morphological studies were performed by atomic force microscopy. Photochemical properties of the heterostructures were assessed through measuring surface wettability characteristics and photocatalytic reaction rate constant of degradation of 4-chlorophenol under ultraviolet and visible irradiations. We also studied electrical properties employing 4-probe measurement technique. The effect of post treatment processes, such as vacuum annealing and laser treatment, on structure and properties was investigated as well. The role of point defects and deviation from the stoichiometry on photochemical and electrical properties was addressed. In this research, TiO2 epilayers with controlled phase structure, defect content, and crystallographic alignments were grown on sapphire and silicon substrates. Integration with silicon was achieved using cubic and tetragonal yttria-stabilized zirconia buffer layers. I was able to tune the phase structure of the TiO2 based heterostructures from pure rutile to pure anatase and establish an epitaxial relationship across the interfaces in each case. These heterostructures were used for two different purposes. First, their

Aerobic Fitness Level Typical of Elite Athletes is not Associated With Even Faster VO2 Kinetics During Cycling Exercise

PubMed Central

Figueira, Tiago R.; Caputo, Fabrizio; Machado, Carlos E.P.; Denadai, Benedito S.

2008-01-01

The aim of this study was to address the question if the VO2 kinetics is further improved as the aerobic training status increases from trained to elite level athletes. Maximal oxygen uptake (VO2max), work-rate associated to VO2max (IVO2max) and VO2 kinetics of moderate (Mod) and maximal exercise (Max) were determined in fifty- five subjects. Then, they were assigned into three groups: low (LF), intermediate (IF) and high (HF) aerobic fitness level. In average, the VO2max of LF, IF and HF groups were, respectively, 36.0 ± 3.1, 51.1 ± 4.5 and 68.1 ± 3.9 ml·kg·min-1 (p ≤ 0.05 among each other). VO2 kinetics mean response time of both exercise intensities were significantly faster (p ≤ 0.05) in HF (Mod, 27.5 ± 5.5 s; Max, 32.6 ± 8.3 s) and IF (Mod, 25.0 ± 3.1 s; Max, 42.6 ± 10.4 s) when compared to LF (Mod, 35.7 ± 7.9 s; Max: 57.8 ± 17.8 s). We can conclude that VO2 kinetics is improved as the fitness level is increased from low to intermediate but not further improved as the aerobic fitness level increases from intermediate to high. Key points Currently, it is reasonable to believe that the rate-limiting step of VO2 kinetics depends on exercise intensity. The well known physiological adaptations induced by endurance training are likely the most extreme means to overcome rate-limiting steps determining VO2 kinetics across exercise intensities. However, exercise adaptation leading individuals to the high-end of aerobic fitness level range (VO2max > 65 ml.kg.min-1) is not able to further improve VO2 kinetics during both, moderate and maximal intensity exercise. PMID:24150145

Maintained peak leg and pulmonary VO2 despite substantial reduction in muscle mitochondrial capacity.

PubMed

Boushel, R; Gnaiger, E; Larsen, F J; Helge, J W; González-Alonso, J; Ara, I; Munch-Andersen, T; van Hall, G; Søndergaard, H; Saltin, B; Calbet, J A L

2015-12-01

We recently reported the circulatory and muscle oxidative capacities of the arm after prolonged low-intensity skiing in the arctic (Boushel et al., 2014). In the present study, leg VO2 was measured by the Fick method during leg cycling while muscle mitochondrial capacity was examined on a biopsy of the vastus lateralis in healthy volunteers (7 male, 2 female) before and after 42 days of skiing at 60% HR max. Peak pulmonary VO2 (3.52 ± 0.18 L.min(-1) pre vs 3.52 ± 0.19 post) and VO2 across the leg (2.8 ± 0.4L.min(-1) pre vs 3.0 ± 0.2 post) were unchanged after the ski journey. Peak leg O2 delivery (3.6 ± 0.2 L.min(-1) pre vs 3.8 ± 0.4 post), O2 extraction (82 ± 1% pre vs 83 ± 1 post), and muscle capillaries per mm(2) (576 ± 17 pre vs 612 ± 28 post) were also unchanged; however, leg muscle mitochondrial OXPHOS capacity was reduced (90 ± 3 pmol.sec(-1) .mg(-1) pre vs 70 ± 2 post, P < 0.05) as was citrate synthase activity (40 ± 3 μmol.min(-1) .g(-1) pre vs 34 ± 3 vs P < 0.05). These findings indicate that peak muscle VO2 can be sustained with a substantial reduction in mitochondrial OXPHOS capacity. This is achieved at a similar O2 delivery and a higher relative ADP-stimulated mitochondrial respiration at a higher mitochondrial p50. These findings support the concept that muscle mitochondrial respiration is submaximal at VO2max , and that mitochondrial volume can be downregulated by chronic energy demand. © 2015 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.

Mechanisms for •O2‑ and •OH production on flowerlike BiVO4 photocatalysis based on Electron Spin Resonance

NASA Astrophysics Data System (ADS)

Xu, Xuan; Sun, Yaofang; Fan, Zihong; Zhao, Deqiang; Xiong, Shimin; Zhang, Bingyao; Zhou, Shiyu; Liu, Guotao

2018-03-01

Many studies have focused on the use of BiVO4 as a photocatalyst, but few have investigated the production of free radicals during the photocatalytic process. Following synthesis of flowerlike BiVO4 and characterization by X-ray diffraction (XRD), Raman spectroscopy, Scanning electron microscopy (SEM) Scanning electron microscopy (EDX), UV-Vis and XPS, we successfully prepared BiVO4. Then we used electron spin resonance (ESR) to determine the production and degradation of individual active free radicals, including the superoxide radical (•O2‑) and the hydroxyl radical (•OH). In the first experiment, we used ESR to detect the signals of free radicals (•O2‑ and •OH) under varying oxygen conditions. The results shown that in addition to production by •O2‑, •OH could also be produced by oxidation of h+ to OH‑. In the next experiment, we detected •OH under varying pH to identify the result of the first experiment, and found that signal intensities increased with increasing pH, indicating the mechanism for •OH production. Finally, we conducted a trapping experiment to examine free radical degradation mechanisms. We identified •OH and h+ as the main active free radicals and showed the complete production about •OH. These results improve current knowledge of free radical production mechanisms, which can be used to enhance the photocatalytic performance of BiVO4.

Solution-processed phase-change VO(2) metamaterials from colloidal vanadium oxide (VO(x)) nanocrystals.

PubMed

Paik, Taejong; Hong, Sung-Hoon; Gaulding, E Ashley; Caglayan, Humeyra; Gordon, Thomas R; Engheta, Nader; Kagan, Cherie R; Murray, Christopher B

2014-01-28

We demonstrate thermally switchable VO2 metamaterials fabricated using solution-processable colloidal nanocrystals (NCs). Vanadium oxide (VOx) NCs are synthesized through a nonhydrolytic reaction and deposited from stable colloidal dispersions to form NC thin films. Rapid thermal annealing transforms the VOx NC thin films into monoclinic, nanocrystalline VO2 thin films that show a sharp, reversible metal-insulator phase transition. Introduction of precise concentrations of tungsten dopings into the colloidal VOx NCs enables the still sharp phase transition of the VO2 thin films to be tuned to lower temperatures as the doping level increases. We fabricate "smart", differentially doped, multilayered VO2 films to program the phase and therefore the metal-insulator behavior of constituent vertically structured layers with temperature. With increasing temperature, we tailored the optical response of multilayered films in the near-IR and IR regions from that of a strong light absorber, in a metal-insulator structure, to that of a Drude-like reflector, characteristic of a pure metallic structure. We demonstrate that nanocrystal-based nanoimprinting can be employed to pattern multilayered subwavelength nanostructures, such as three-dimensional VO2 nanopillar arrays, that exhibit plasmonic dipolar responses tunable with a temperature change.

Small effort, high impact: Focus on physical activity improves oxygen uptake (VO2peak ), quality of life, and mental health after pediatric renal transplantation.

PubMed

Thorsteinsdottir, Hjørdis; Diseth, Trond H; Lie, Anine; Tangeraas, Trine; Matthews, Iren; Åsberg, Anders; Bjerre, Anna

2018-06-19

This study estimates the effects on peak oxygen uptake (VO 2 peak ), QoL, and mental health after the introduction of an adjusted post-transplant follow-up program, that is, early physiotherapy and focus on the importance of physical activity. VO 2 peak was measured by a treadmill exercise test in 20 renal-transplanted children on the adjusted post-transplant follow-up and compared with a group of 22 patients investigated in a previously, before the implementation of our new follow-up routines. PedsQL and The Strengths and Difficulties Questionnaire (SDQ) were used to assess QoL and mental health in 45 patients on the new as compared to 32 patients on the previous follow-up strategy. The patients exposed to early physiotherapy and a higher focus on physical activity had significantly higher VO 2 peak (44.3 vs 33.5 mL kg -1  min -1 , P = .031) in addition to improved QoL (P = .003) and mental health scores (P = .012). The cardiovascular risk profile was similar in both groups aside from significantly higher triglycerides in the present cohort. Small efforts as early physiotherapy and increased focus on physical activity after pediatric renal transplantation have significant impact on cardiorespiratory fitness, QoL, and mental health. The importance of physical activity should therefore be emphasized in follow-up programs. © 2018 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.

Highly infrared sensitive VO2 nanowires for a nano-optical device.

PubMed

Bhuyan, Prabal Dev; Gupta, Sanjeev K; Kumar, Ashok; Sonvane, Yogesh; Gajjar, P N

2018-04-25

Recent studies on the electronic, magnetic and optical properties of VO2 (vanadium dioxide) materials have motivated the exploration of one dimensional VO2 nanowires. First principles calculations were performed to investigate the structural, electronic, magnetic and optical properties of the monoclinic (M) and rutile (R) phases of VO2 nanowires. The monoclinic phase shows semiconducting behaviour with a band gap of 1.17 eV, whereas the rutile phase of VO2 nanowires behaves as a spin gapless semiconducting material, as band lines cross the Fermi level due only to up spin contribution. The monoclinic structure of VO2 nanowires is found to be paramagnetic and the rutile structure shows ferromagnetic half metal behavior. The conductivity calculation for VO2 nanowires shows the metal-insulator transition (MIT) temperature to be 250 K. The possible mechanism of VO2 nanowires to be used as smart windows has been discussed, as the nanowires are highly sensitive in the infrared (IR) region. Interestingly, at low temperature, the VO2 monoclinic structure allows infrared light to be transmitted, while VO2 with the rutile phase blocks light in the IR region. Furthermore, we adsorbed CO2, N2 and SO2 gas molecules on 1D VO2 monoclinic nanowire to investigate their interaction behaviour. It was observed that the absorption and transmission properties of VO2 dramatically change upon the adsorption of CO2 and SO2 gas molecules, which is likely to open up its application as an optical gas sensor.

Influence of aerosol chemical composition on N2O5 uptake: airborne regional measurements in northwestern Europe

NASA Astrophysics Data System (ADS)

Morgan, W. T.; Ouyang, B.; Allan, J. D.; Aruffo, E.; Di Carlo, P.; Kennedy, O. J.; Lowe, D.; Flynn, M. J.; Rosenberg, P. D.; Williams, P. I.; Jones, R.; McFiggans, G. B.; Coe, H.

2015-01-01

Aerosol chemical composition was found to influence nighttime atmospheric chemistry during a series of airborne measurements in northwestern Europe in summer conditions, which has implications for regional air quality and climate. The uptake of dinitrogen pentoxide, γ (N2O5), to particle surfaces was found to be modulated by the amount of water content and ammonium nitrate present in the aerosol. The conditions prevalent in this study suggest that the net uptake rate of N2O5 to atmospheric aerosols was relatively efficient compared to previous studies, with γ (N2O5) values in the range 0.01-0.03. This is likely a consequence of the elevated relative humidity in the region, which promotes greater aerosol water content. Increased nitrate concentrations relative to particulate water were found to suppress N2O5 uptake. The results presented here contrast with previous ambient studies of N2O5 uptake, which have generally taken place in low-nitrate environments in the USA. Comparison of the N2O5 uptake derived from the measurements with a parameterised scheme that is based on the ratio of particulate water to nitrate yielded reasonably good agreement in terms of the magnitude and variation in uptake, provided the effect of chloride was neglected. An additional suppression of the parameterised uptake is likely required to fully capture the variation in N2O5 uptake, which could be achieved via the known suppression by organic aerosol. However, existing parameterisations representing the suppression by organic aerosol were unable to fully represent the variation in N2O5 uptake. These results provide important ambient measurement constraint on our ability to predict N2O5 uptake in regional and global aerosol models. N2O5 uptake is a potentially important source of nitrate aerosol and a sink of the nitrate radical, which is the main nocturnal oxidant in the atmosphere. The results further highlight the importance of ammonium nitrate in northwestern Europe as a key component

VO{sub 2} precipitates for self-protected optical surfaces

DOEpatents

Gea, L.A.; Boatner, L.A.

1999-03-23

A method for forming crystallographically coherent precipitates of vanadium dioxide in the near-surface region of sapphire and the resulting product is disclosed. Ions of vanadium and oxygen are stoichiometrically implanted into a sapphire substrate (Al{sub 2}O{sub 3}), and subsequently annealed to form vanadium dioxide precipitates in the substrate. The embedded VO{sub 2} precipitates, which are three-dimensionally oriented with respect to the crystal axes of the Al{sub 2}O{sub 3} host lattice, undergo a first-order monoclinic-to-tetragonal (and also semiconducting-to-metallic) phase transition at ca. 77 C. This transformation is accompanied by a significant variation in the optical transmission of the implanted region and results in the formation of an optically active, thermally ``switchable`` surface region on Al{sub 2}O{sub 3}. 5 figs.

VO.sub.2 precipitates for self-protected optical surfaces

DOEpatents

Gea, Laurence A.; Boatner, Lynn A.

1999-01-01

A method for forming crystallographically coherent precipitates of vanadium dioxide in the near-surface region of sapphire and the resulting product is disclosed. Ions of vanadium and oxygen are stoichiometrically implanted into a sapphire substrate (Al.sub.2 O.sub.3), and subsequently annealed to form vanadium dioxide precipitates in the substrate. The embedded VO.sub.2 precipitates, which are three-dimensionally oriented with respect to the crystal axes of the Al.sub.2 O.sub.3 host lattice, undergo a first-order monoclinic-to-tetragonal (and also semiconducting-to-metallic) phase transition at .about.77.degree. C. This transformation is accompanied by a significant variation in the optical transmission of the implanted region and results in the formation of an optically active, thermally "switchable" surface region on Al.sub.2 O.sub.3.

Nano crystalline Bi{sub 2}(VO{sub 5}) phases in lithium bismuth borate glasses containing mixed vanadium-nickel oxides

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yadav, Arti, E-mail: artidabhur@gmail.com; Khasa, S.; Dahiya, M. S.

2016-05-23

Glass composition 7V{sub 2}O{sub 5}·23Li{sub 2}O·20Bi{sub 2}O{sub 3}·50B{sub 2}O{sub 3} and x(2NiO·V{sub 2}O{sub 5})·(30-x)Li{sub 2}O·20Bi{sub 2}O{sub 3}·50B{sub 2}O{sub 3}, x=0, 2, 5, 7 and 10, were produced by conventional melt quenching technique. The quenched amorphous glass samples were annealed at temperatures 400°C and 500°C for 6 hours. The Bi{sub 2}(VO{sub 5}) crystallite were grown in all prepared glass matrix. Tn vanadium lithium bismuth borate glass (annealed), the some phrase of V{sub 2}O{sub 5}-crystal were observed along with the nano crystalline Bi{sub 2}(VO{sub 5}) phase. The sharp peaks in FTTR spectra of all annealed compositions were also compatible with the XRDmore » diffraction peaks of the system under investigation. Average crystalline size (D) of the Bi{sub 2}(VO{sub 5}) nano-crystallite was ~30 nm for samples annealed at 400°C and ~42 nm for samples annealed at 500°C. Lattice parameter and the lattice strain for all the samples was also calculated corresponding to the (113) plane of Bi{sub 2}(VO{sub 5}) crystallite.« less

VO{sub 2} (A): Reinvestigation of crystal structure, phase transition and crystal growth mechanisms

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rao Popuri, Srinivasa; University of Bordeaux, ICMCB, UPR 9048, F-33608 Pessac; National Institute for Research and Development in Electrochemistry and Condensed Matter, Timisoara, Plautius Andronescu Str. No. 1, 300224 Timisoara

2014-05-01

Well crystallized VO{sub 2} (A) microrods were grown via a single step hydrothermal reaction in the presence of V{sub 2}O{sub 5} and oxalic acid. With the advantage of high crystalline samples, we propose P4/ncc as an appropriate space group at room temperature. From morphological studies, we found that the oriented attachment and layer by layer growth mechanisms are responsible for the formation of VO{sub 2} (A) micro rods. The structural and electronic transitions in VO{sub 2} (A) are strongly first order in nature, and a marked difference between the structural transition temperatures and electronic transitions temperature was evidenced. The reversiblemore » intra- (LTP-A to HTP-A) and irreversible inter- (HTP-A to VO{sub 2} (M1)) structural phase transformations were studied by in-situ powder X-ray diffraction. Attempts to increase the size of the VO{sub 2} (A) microrods are presented and the possible formation steps for the flower-like morphologies of VO{sub 2} (M1) are described. - Graphical abstract: Using a single step and template free hydrothermal synthesis, well crystallized VO{sub 2} (A) microrods were prepared and the P4/ncc space group was assigned to the room temperature crystal structure. Reversible and irreversible phase transitions among different VO{sub 2} polymorphs were identified and their progressive nature was highlighted. Attempts to increase the microrods size, involving layer by layer formation mechanisms, are presented. - Highlights: • Highly crystallized VO{sub 2} (A) microrods were grown via a single step hydrothermal process. • The P4/ncc space group was determined for VO{sub 2} (A) at room temperature. • The electronic structure and progressive nature of the structural phase transition were investigated. • A weak coupling between structural and electronic phase transitions was identified. • Different crystallite morphologies were discussed in relation with growth mechanisms.« less

Electrical properties of crystallized 30B2O3-70V2O5 glass

NASA Astrophysics Data System (ADS)

Gwoo, Donggun; Kim, Taehee; Han, Kyungseok; Choi, Wongyu; Kim, Jonghwan; Ryu, Bongki

2013-05-01

30B2O3-70V2O5 binary-system glass was prepared, and variations in structural and electrical property were examined using crystallization. While different related research studies exist, few have evaluated the variations in the structure and properties with changes in the crystallization rate. 30B2O3-70V2O5 glass was annealed in the graphite mold above the glass transition temperature for 2 h and heat-treated at each crystallization temperature for 3 h. 30B2O3-70V2O5 glass showed predominantly electronic conductive characteristic. FTIR was preferentially used for analyzing the structural changes of B-O bond after crystallization, while XRD was utilized to verify the inferred changes in the structure array (BO3 + V2O5 ↔ BO4 + 2VO2). Structural changes induced by heat treatment were confirmed by analyzing the molecular volume determined from the sample density, and conductance was measured to correlate structural and property changes. Conductivity is discussed based on the migration of vanadate ions with different valence states because of the increase in VO2 crystallinity at 130°C, which, however, was not observed at 170°C. After VO2 structures were reinforced, a 1.8-fold increase in conductance was observed (as compared to the annealed sample) after crystallization at 130°C for 3 h.

Estimated Prestroke Peak VO2 Is Related to Circulating IGF-1 Levels During Acute Stroke.

PubMed

Mattlage, Anna E; Rippee, Michael A; Abraham, Michael G; Sandt, Janice; Billinger, Sandra A

2017-01-01

Background Insulin-like growth factor-1 (IGF-1) is neuroprotective after stroke and is regulated by insulin-like binding protein-3 (IGFBP-3). In healthy individuals, exercise and improved aerobic fitness (peak oxygen uptake; peak VO 2 ) increases IGF-1 in circulation. Understanding the relationship between estimated prestroke aerobic fitness and IGF-1 and IGFBP-3 after stroke may provide insight into the benefits of exercise and aerobic fitness on stroke recovery. Objective The purpose of this study was to determine the relationship of IGF-1 and IGFBP-3 to estimated prestroke peak VO 2 in individuals with acute stroke. We hypothesized that (1) estimated prestroke peak VO 2 would be related to IGF-1 and IGFBP-3 and (2) individuals with higher than median IGF-1 levels will have higher estimated prestroke peak VO 2 compared to those with lower than median levels. Methods Fifteen individuals with acute stroke had blood sampled within 72 hours of hospital admission. Prestroke peak VO 2 was estimated using a nonexercise prediction equation. IGF-1 and IGFBP-3 levels were quantified using enzyme-linked immunoassay. Results Estimated prestroke peak VO 2 was significantly related to circulating IGF-1 levels (r = .60; P = .02) but not IGFBP-3. Individuals with higher than median IGF-1 (117.9 ng/mL) had significantly better estimated aerobic fitness (32.4 ± 6.9 mL kg -1 min -1 ) than those with lower than median IGF-1 (20.7 ± 7.8 mL kg -1 min -1 ; P = .03). Conclusions Improving aerobic fitness prior to stroke may be beneficial by increasing baseline IGF-1 levels. These results set the groundwork for future clinical trials to determine whether high IGF-1 and aerobic fitness are beneficial to stroke recovery by providing neuroprotection and improving function. © The Author(s) 2016.

Running Performance, VO2max, and Running Economy: The Widespread Issue of Endogenous Selection Bias.

PubMed

Borgen, Nicolai T

2018-05-01

Studies in sport and exercise medicine routinely use samples of highly trained individuals in order to understand what characterizes elite endurance performance, such as running economy and maximal oxygen uptake VO 2max . However, it is not well understood in the literature that using such samples most certainly leads to biased findings and accordingly potentially erroneous conclusions because of endogenous selection bias. In this paper, I review the current literature on running economy and VO 2max , and discuss the literature in light of endogenous selection bias. I demonstrate that the results in a large part of the literature may be misleading, and provide some practical suggestions as to how future studies may alleviate endogenous selection bias.

Modulation of liver mitochondrial NOS is implicated in thyroid-dependent regulation of O(2) uptake.

PubMed

Carreras, M C; Peralta, J G; Converso, D P; Finocchietto, P V; Rebagliati, I; Zaninovich, A A; Poderoso, J J

2001-12-01

Changes in O(2) uptake at different thyroid status have been explained on the basis of the modulation of mitochondrial enzymes and membrane biophysical properties. Regarding the nitric oxide (NO) effects, we tested whether liver mitochondrial nitric oxide synthase (mtNOS) participates in the modulation of O(2) uptake in thyroid disorders. Wistar rats were inoculated with 400 microCi (131)I (hypothyroid group), 20 microg thyroxine (T(4))/100 g body wt administered daily for 2 wk (hyperthyroid group) or vehicle (control). Basal metabolic rate, mitochondrial function, and mtNOS activity were analyzed. Systemic and liver mitochondrial O(2) uptake and cytochrome oxidase activity were lower in hypothyroid rats with respect to controls; mitochondrial parameters were further decreased by L-arginine (-42 and -34%, P < 0.05), consistent with 5- to 10-fold increases in matrix NO concentration. Accordingly, mtNOS expression (75%) and activity (260%) were selectively increased in hypothyroidism and reverted by hormone replacement without changes in other nitric oxide isoforms. Moreover, mtNOS activity correlated with serum 3,5,3'-triiodothyronine (T(3)) and O(2) uptake. Increased mtNOS activity was also observed in skeletal muscle mitochondria from hypothyroid rats. Therefore, we suggest that modulation of mtNOS is a substantial part of thyroid effects on mitochondrial O(2) uptake.

Simulated swimming: a useful tool for evaluation the VO2 max of swimmers in the laboratory.

PubMed Central

Kimura, Y; Yeater, R A; Martin, R B

1990-01-01

This study was designed to develop a simulated swimming exercise (SS) so that peak VO2 would be assessed on swimmers in a laboratory setting. The subjects assumed a prone position on an incline bench and performed arm cranking on a Monark Rehab Trainer while performing a flutter kick against tension supplied by elastic cords. The SS test was compared to four peak VO2 tests: treadmill running (RN), tethered swimming (TW), bicycle ergometry (B), and arm cranking (AC). Eleven male varsity swimmers underwent each of the five VO2 max tests, and maximal cardiorespiratory indicators (HR, VE, VO2, O2 pulse, and RQ) were measured. The percentage of peak VO2 obtained during SS was compared to RN, TW, B, and AC. The SS test achieved 78 percent of RN, 91 percent of TW, 81 percent of B, and 124 percent of AC. There were no significant differences in VO2 in ml/kg.min between SS and TW. As expected, RN and B were significantly higher, while AC was lower. Ten subjects performed the SS test twice on two separate days within one week. The reliability of VO2 max in ml/kg.min was 0.95. the validity of VO2 max in ml/kg.min in the SS test vs. RN was 0.68. The SS test is reliable and can be used as effectively as TW to assess the VO2 max of swimmers in a laboratory setting. PMID:2078808

The preparation of a plasmonically resonant VO2 thermochromic pigment.

PubMed

Bai, Huaping; Cortie, Michael B; Maaroof, Abbas I; Dowd, Annette; Kealley, Catherine; Smith, Geoffrey B

2009-02-25

Vanadium dioxide (VO(2)) undergoes a reversible metal-insulator transition, normally at approximately 68 degrees C. While the properties of continuous semi-transparent coatings of VO(2) are well known, there is far less information available concerning the potential use of discrete VO(2) nanoparticles as a thermochromic pigment in opaque coatings. Individual VO(2) nanoparticles undergo a localized plasmon resonance with near-infrared light at about 1100 nm and this resonance can be switched on and off by simply varying the temperature of the system. Therefore, incorporation of VO(2) nanoparticles into a coating system imbues the coating with the ability to self-adaptively modulate its own absorptive efficiency in the near-infrared. Here we examine the magnitude and control of this phenomenon. Prototype coatings are described, made using VO(2) powder produced by an improved process. The materials are characterized using calorimetry, x-ray diffraction, high-resolution scanning electron microscopy, transmission electron microscopy, and by measurement of optical properties.

Reactions of vanadium dioxide molecules with acetylene: infrared spectra of VO2(η(2)-C2H2)(x) (x = 1, 2) and OV(OH)CCH in solid neon.

PubMed

Zhou, Xiaojie; Chen, Mohua; Zhou, Mingfei

2013-07-03

Reactions of vanadium dioxide molecules with acetylene have been studied by matrix isolation infrared spectroscopy. Reaction intermediates and products are identified on the basis of isotopic substitutions as well as density functional frequency calculations. Ground state vanadium dioxide molecule reacts with acetylene in forming the side-on-bonded VO2(η(2)-C2H2) and VO2(η(2)-C2H2)2 complexes spontaneously on annealing in solid neon. The VO2(η(2)-C2H2) complex is characterized to have a (2)B2 ground state with C2v symmetry, whereas the VO2(η(2)-C2H2)2 complex has a (2)A ground state with C2 symmetry. The VO2(η(2)-C2H2) and VO2(η(2)-C2H2)2 complexes are photosensitive. The VO2(η(2)-C2H2) complex rearranges to the OV(OH)CCH molecule upon UV-vis light excitation.

Anomalous spectral-weight transfers unraveling oxygen screening and electronic correlations in the insulator-metal transition of VO2

NASA Astrophysics Data System (ADS)

Yeo, L. H.; Srivastava, A.; Majidi, M. A.; Sutarto, R.; He, F.; Poh, S. M.; Diao, C.; Yu, X.; Motapothula, M.; Saha, S.; Ojha, S.; Kanjilal, D.; Trevisanutto, P. E.; Breese, M. B. H.; Venkatesan, T.; Rusydi, A.

2015-02-01

Vanadium dioxide (VO2) undergoes an unusual insulator-metal transition (IMT), and after decades of study, the origin of the IMT remains hotly debated. Here, by analyzing spectral-weight transfers (SWTs) of x-ray absorption spectroscopy at the V L3 ,2 and O K edges on specially designed VO2 films, we observe d||(dx2-y2) band splitting at the V L3 ,2 edges across the IMT, accompanied by anomalous SWTs as high as ˜12 eV at the O K edge, indicating strong electronic correlations. Surprisingly, a few oxygen vacancies induce dramatic SWTs at the O K edge, but the sample remains conducting. Supported by theoretical calculations, we find that in the metallic state, direct V (3 d∥) -V(3 d∥) and O(2 p ) -V(3 d∥) hybridized orbital correlations are screened by O(2 p ) -V(3 dπ) hybridized orbitals, while in the insulating state they are strongly correlated due to changes in the oxygen orbital occupancy. Our result shows the importance of screenings and electronic correlations for IMTs in VO2.

Interval training at 95% and 100% of the velocity at VO2 max: effects on aerobic physiological indexes and running performance.

PubMed

Denadai, Benedito S; Ortiz, Marcelo J; Greco, Camila C; de Mello, Marco T

2006-12-01

The objective of this study was to analyze the effect of two different high-intensity interval training (HIT) programs on selected aerobic physiological indices and 1500 and 5000 m running performance in well-trained runners. The following tests were completed (n=17): (i) incremental treadmill test to determine maximal oxygen uptake (VO2 max), running velocity associated with VO2 max (vVO2 max), and the velocity corresponding to 3.5 mmol/L of blood lactate concentration (vOBLA); (ii) submaximal constant-intensity test to determine running economy (RE); and (iii) 1500 and 5000 m time trials on a 400 m track. Runners were then randomized into 95% vVO2 max or 100% vVO2 max groups, and undertook a 4 week training program consisting of 2 HIT sessions (performed at 95% or 100% vVO2 max, respectively) and 4 submaximal run sessions per week. Runners were retested on all parameters at the completion of the training program. The VO2 max values were not different after training for both groups. There was a significant increase in post-training vVO2 max, RE, and 1500 m running performance in the 100% vVO2 max group. The vOBLA and 5000 m running performance were significantly higher after the training period for both groups. We conclude that vOBLA and 5000 m running performance can be significantly improved in well-trained runners using a 4 week training program consisting of 2 HIT sessions (performed at 95% or 100% vVO2 max) and 4 submaximal run sessions per week. However, the improvement in vVO2 max, RE, and 1500 m running performance seems to be dependent on the HIT program at 100% vVO2 max.

Nano-crystalline phase evolution and structural modification in Co/V substituted Li2O-Bi2O3-B2O3 glasses

NASA Astrophysics Data System (ADS)

Yadav, Arti; Dahiya, M. S.; Hooda, A.; Agarwal, A.; Khasa, S.

2018-05-01

Co/V substituted Li2O-Bi2O3-B2O3 glasses having composition 7CoO•23Li2O•20Bi2O3•50B2O3(CLBB) and xCoO•(30-x)Li2O•20Bi2O3•50B2O3(x = 0.0, 2.0, 5.0, 7.0 and 10.0 mol%, CVLBB1-5 respectively) developed via melt- quench route. The effect of annealing on structural properties of prepared samples was investigated by using XRD patterns and FTIR spectroscopy. Glasses annealed at 400˚C remained amorphous whereas glasses annealed at 500˚C changes from glasses to glass ceramics. The different crystalline phases i.e. Bi2(V0.9Co0.1)O5.25, LiCoVO4, V2O5 & Bi2(VO5) evolve on annealing at 500°C for 6 hours confirmed from the corresponding XRD patterns. The crystallite size of prepared samples were found to vary as 38-60nm This indicated that CoO and V2O5 introduced in matrix act as crystallizing agents and cause structural modification as studied by the FTIR spectra for all heat treated compositions.