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Sample records for highly oriented vo2

  1. High level runners are able to maintain a VO2 steady-state below VO2max in an all-out run over their critical velocity.

    PubMed

    Billat, V; Binsse, V; Petit, B; Koralsztein, J P

    1998-02-01

    During prolonged and intense running exercises beyond the critical power level, a VO2 slow component elevates VO2 above predicted VO2-work rates calculated from exercise performed at intensities below the lactate threshold. In such cases, the actual VO2 value will increase over time until it reaches VO2max. The aims of the present study were to examine whether the VO2 slow component is a major determinant of VO2 over time when running at a speed beyond critical velocity, and whether the exhaustion latency period at such intensity correlates with the magnitude of the VO2 slow component. Fourteen highly trained long-distance runners performed four exhaustive runs, each separated by one week of light training. VO2 and the velocity at VO2max (vVO2max) were determined for each by a graded treadmill exercise. The critical velocity (86.1 +/- 1.5% vVO2max) of each runner was calculated from exhaustive treadmill runs at 90, 100 and 105% of vVO2max. During supra-critical velocity runs at 90% of vVO2max, there was no significant rise in VO2max (20.9 +/- 2.1 ml min-1 kg-1 between the third and last min of tlim 90), such that the runners reached a VO2 steady-state, but did not reach their vVO2max level over time (69.5 +/- 5.0 vs 74.9 +/- 3.0 ml min-1 kg-1). Thus, subjects' time to exhaustion at 90% of vVO2max was not correlated with the VO2max slow component (r = 0.11, P = 0.69), but significantly correlated with the lactate threshold (r = 0.54, P = 0.04) and the critical velocity (% vVO2max; r = 0.65, P = 0.01). In conclusion, the present study demonstrates that for highly trained long-distance runners performing exhaustive, supra-critical velocity runs at 90% of vVO2max, there was not a VO2 slow component tardily completing the rise of VO2. Instead, runners will maintain a VO2 steady-state below VO2max, such that the time to exhaustion at 90% of vVO2max for these runners is positively correlated with the critical velocity expressed as % of vVO2max.

  2. Enhanced electrochemical performance of orientated VO2(B) raft-like nanobelt arrays through direct lithiation for lithium ion batteries

    NASA Astrophysics Data System (ADS)

    Liu, Liang; Liu, Qiang; Zhao, Wen; Li, Guochun; Wang, Limei; Shi, Weidong; Chen, Long

    2017-02-01

    Lithiation modification of VO2(B) has been carried out by a facile hydrothermal process, and the compact and locally ordered VO2(B) raft-like nanobelt arrays have been prepared. The synthesis route provides a new approach to elaborate a VO2(B) nanostructure under a mild environment condition. It is found that the growth mechanism of VO2(B) raft-like nanobelt arrays is different from the traditional nucleation-growth process. A novel chemical lithiating-exfoliating-splitting model is proposed. Compared with the bulk counterpart, the lithiated VO2(B) raft-like nanobelt arrays as cathodes exhibit a higher discharge capacity and an enhanced high-rate performance owing to their increased structural anisotropy and decreased polarization. This work indicates that VO2(B) raft-like nanobelt arrays have great potential applications as cathode materials for lithium ion batteries.

  3. Enhanced electrochemical performance of orientated VO2(B) raft-like nanobelt arrays through direct lithiation for lithium ion batteries.

    PubMed

    Liu, Liang; Liu, Qiang; Zhao, Wen; Li, Guochun; Wang, Limei; Shi, Weidong; Chen, Long

    2017-02-10

    Lithiation modification of VO2(B) has been carried out by a facile hydrothermal process, and the compact and locally ordered VO2(B) raft-like nanobelt arrays have been prepared. The synthesis route provides a new approach to elaborate a VO2(B) nanostructure under a mild environment condition. It is found that the growth mechanism of VO2(B) raft-like nanobelt arrays is different from the traditional nucleation-growth process. A novel chemical lithiating-exfoliating-splitting model is proposed. Compared with the bulk counterpart, the lithiated VO2(B) raft-like nanobelt arrays as cathodes exhibit a higher discharge capacity and an enhanced high-rate performance owing to their increased structural anisotropy and decreased polarization. This work indicates that VO2(B) raft-like nanobelt arrays have great potential applications as cathode materials for lithium ion batteries.

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

    NASA Astrophysics Data System (ADS)

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

    2016-06-01

    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.

  5. 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

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

    PubMed

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

    2016-06-14

    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.

  7. Effects of high-intensity interval training on the VO2 response during severe exercise.

    PubMed

    Duffield, Rob; Edge, Johann; Bishop, David

    2006-06-01

    This study examined the effect of high-intensity interval training on the VO2 response during severe, constant-load exercise. Prior to, and following training, 10 females (V O2 peak 37.4+/-6.0 mL kg-1 min-1) performed a graded exercise test to determine VO2 peak and lactate threshold (LT) and a 6 min cycle test (CT) at the pre-training VO2 peak intensity. Training involved high-intensity intervals (2 min work, 1 min rest) performed 3x week for 8 weeks. Breath-by-breath data from 0 to 6 min during the CT were smoothed using 5s averages and fit to a bi-exponential model starting from 20s. Training resulted in significant improvements in VO2 max (2.34+/-0.37-2.78+/-0.30 L min-1), power at VO2 max (170+/-26-204+/-25 W) and power at LT (113+/-17-136+/-20 W) (p<0.05). Following training, the VO2 response showed a significant increase in the amplitude of the primary phase (A1) (1396+/-103-1695+/-100 mL min-1; p<0.05) and end-exercise VO2 (VO2 EE), with no difference (p>0.05) in the time constants of either phase or the amplitude of the slow component (318+/-67-380+/-48 mL; p=0.15). In conjunction, accumulated oxygen deficit (AOD) (43.7+/-9.8-17.2+/-2.8 mL O2 eq kg-1) and anaerobic contribution to the CT (19.4+/-4.4-7.2+/-1.2%) were significantly reduced. In contrast to previous moderate-intensity research, a high-intensity interval training program increased A1 and VO2 EE for the same absolute exercise intensity, decreasing the AOD during a severe-intensity CT.

  8. Self-Assembly and Horizontal Orientation Growth of VO2 Nanowires

    PubMed Central

    Cheng, Chun; Guo, Hua; Amini, Abbas; Liu, Kai; Fu, Deyi; Zou, Jian; Song, Haisheng

    2014-01-01

    Single-crystalline vanadium dioxide (VO2) nanostructures have attracted an intense research interest recently because of their unique single-domain metal-insulator phase transition property. Synthesis of these nanostructures in the past was limited in density, alignment, or single-crystallinity. The assembly of VO2 nanowires (NWs) is desirable for a “bottom-up” approach to the engineering of intricate structures using nanoscale building blocks. Here, we report the successful synthesis of horizontally aligned VO2 NWs with a dense growth mode in the [1-100]quartz direction of a polished x-cut quartz surface using a simple vapor transport method. Our strategy of controlled growth of VO2 NWs promisingly paves the way for designing novel metal-insulator transition devices based on VO2 NWs. PMID:24965899

  9. VO2max trainability and high intensity interval training in humans: a meta-analysis.

    PubMed

    Bacon, Andrew P; Carter, Rickey E; Ogle, Eric A; Joyner, Michael J

    2013-01-01

    Endurance exercise training studies frequently show modest changes in VO2max with training and very limited responses in some subjects. By contrast, studies using interval training (IT) or combined IT and continuous training (CT) have reported mean increases in VO2max of up to ~1.0 L · min(-1). This raises questions about the role of exercise intensity and the trainability of VO2max. To address this topic we analyzed IT and IT/CT studies published in English from 1965-2012. Inclusion criteria were: 1)≥ 3 healthy sedentary/recreationally active humans <45 yrs old, 2) training duration 6-13 weeks, 3) ≥ 3 days/week, 4) ≥ 10 minutes of high intensity work, 5) ≥ 1:1 work/rest ratio, and 6) results reported as mean ± SD or SE, ranges of change, or individual data. Due to heterogeneity (I(2) value of 70), statistical synthesis of the data used a random effects model. The summary statistic of interest was the change in VO2max. A total of 334 subjects (120 women) from 37 studies were identified. Participants were grouped into 40 distinct training groups, so the unit of analysis was 40 rather than 37. An increase in VO2max of 0.51 L · min(-1) (95% CI: 0.43 to 0.60 L · min(-1)) was observed. A subset of 9 studies, with 72 subjects, that featured longer intervals showed even larger (~0.8-0.9 L · min(-1)) changes in VO2max with evidence of a marked response in all subjects. These results suggest that ideas about trainability and VO2max should be further evaluated with standardized IT or IT/CT training programs.

  10. Effect of high-intensity interval training on cardiovascular function, VO2max, and muscular force.

    PubMed

    Astorino, Todd A; Allen, Ryan P; Roberson, Daniel W; Jurancich, Matt

    2012-01-01

    The purpose of this study was to examine the effects of short-term high-intensity interval training (HIIT) on cardiovascular function, cardiorespiratory fitness, and muscular force. Active, young (age and body fat = 25.3 ± 4.5 years and 14.3 ± 6.4%) men and women (N = 20) of a similar age, physical activity, and maximal oxygen uptake (VO2max) completed 6 sessions of HIIT consisting of repeated Wingate tests over a 2- to 3-week period. Subjects completed 4 Wingate tests on days 1 and 2, 5 on days 3 and 4, and 6 on days 5 and 6. A control group of 9 men and women (age and body fat = 22.8 ± 2.8 years and 15.2 ± 6.9%) completed all testing but did not perform HIIT. Changes in resting blood pressure (BP) and heart rate (HR), VO2max, body composition, oxygen (O2) pulse, peak, mean, and minimum power output, fatigue index, and voluntary force production of the knee flexors and extensors were examined pretraining and posttraining. Results showed significant (p < 0.05) improvements in VO2max, O2 pulse, and Wingate-derived power output with HIIT. The magnitude of improvement in VO2max was related to baseline VO2max (r = -0.44, p = 0.05) and fatigue index (r = 0.50, p < 0.05). No change (p > 0.05) in resting BP, HR, or force production was revealed. Data show that HIIT significantly enhanced VO2max and O2 pulse and power output in active men and women.

  11. Increases in .VO2max with "live high-train low" altitude training: role of ventilatory acclimatization.

    PubMed

    Wilhite, Daniel P; Mickleborough, Timothy D; Laymon, Abigail S; Chapman, Robert F

    2013-02-01

    The purpose of this study was to estimate the percentage of the increase in whole body maximal oxygen consumption (.VO(2max)) that is accounted for by increased respiratory muscle oxygen uptake after altitude training. Six elite male distance runners (.VO(2max) = 70.6 ± 4.5 ml kg(-1) min(-1)) and one elite female distance runner (.VO(2max)) = 64.7 ml kg(-1) min(-1)) completed a 28-day "live high-train low" training intervention (living elevation, 2,150 m). Before and after altitude training, subjects ran at three submaximal speeds, and during a separate session, performed a graded exercise test to exhaustion. A regression equation derived from published data was used to estimate respiratory muscle .VO(2) (.VO(2RM)) using our ventilation (.VE) values. .VO(2RM) was also estimated retrospectively from a larger group of distance runners (n = 22). .VO(2max) significantly (p < 0.05) increased from pre- to post-altitude (196 ± 59 ml min(-1)), while (.VE) at .VO(2max) also significantly (p < 0.05) increased (13.3 ± 5.3 l min(-1)). The estimated .VO(2RM) contributed 37 % of Δ .VO(2max). The retrospective group also saw a significant increase in .VO(2max) from pre- to post-altitude (201 ± 36 ml min(-1)), along with a 10.8 ± 2.1 l min(-1) increase in (.VE), thus requiring an estimated 27 % of Δ .VO(2max) Our data suggest that a substantial portion of the improvement in .VO(2max) with chronic altitude training goes to fuel the respiratory muscles as opposed to the musculature which directly contributes to locomotion. Consequently, the time-course of decay in ventilatory acclimatization following return to sea-level may have an impact on competitive performance.

  12. 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

  13. Epitaxial stabilization and phase instability of VO2 polymorphs

    DOE PAGES

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

    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. Bymore » 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. In conclusion, 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.« less

  14. A VO2-Based Multifunctional Window with Highly Improved Luminous Transmittance

    NASA Astrophysics Data System (ADS)

    Jin, Ping; Xu, Gang; Tazawa, Masato; Yoshimura, Kazuki

    2002-03-01

    A novel window structure composed of VO2 thermochromic film with TiO2 antireflection (AR) coating was proposed. TiO2 was chosen as the best AR candidatefor reasons that it is an AR material superior to the reported SiO2, and that it is capable to make the window multifunctional with excellent photocatalytic properties. Optical calculation was done for the proposed structure, which predicts a strong enhancement in luminous transmittance (Tlum). A TiO2 (40 nm)/VO2 (50 nm) structure, optimized to a maximum integrated luminous transmittance by calculation, was formed on SiO2 glass by magnetron sputtering. A maximum increase in Tlum by 53% (from 32% to 49%) was experimentally obtained. The proposed window is the most advanced among the similarly reported in being multifunctional with automatic solar/heat control, ultraviolet stopping, and possibly a wide range of photocatalytic functions in addition to being highly luminous transmitting.

  15. A high blood lactate induced by heavy exercise does not affect the increase in submaximal VO2 with hyperoxia.

    PubMed

    Favier, F B; Prieur, F; Grataloup, O; Busso, T; Castells, J; Denis, C; Geyssant, A; Benoit, H

    2005-05-01

    Few studies evidenced an enhancement in oxygen uptake (VO2) during submaximal exercise in hyperoxia. This O2 "overconsumption" seems to increase above the lactate threshold. The aim of this study was to determine whether the hyperoxia-induced enhancement in VO2 may be related to a higher metabolism of lactate. Nine healthy males (aged 23.1 years, mean VO2 max= 53.8 ml min-1 kg-1) were randomized to two series of exercise in either normoxia or hyperoxia corresponding to an inspired O2 fraction (FIO2) of 30%. Each series consisted of 6 min cycling at 50% VO2 max (Moderate1), 5 min cycling at 95%VO2 max (Near Max) and then 6 min at 50% VO2 max (Moderate2). In both series Near Max was performed in normoxia. VO2 was significantly greater under hyperoxia than in normoxia during Moderate1 (2192 +/- 189 vs. 2025 +/- 172 ml min-1) and during Moderate2 (2352 +/- 173 vs. 2180+ /- 193 ml min-1). However, the effect of the high FIO2 was not significantly different on VO2Moderate2 (+172+/-137 ml min-1 with [La] approximately 6 mmol l-1) compared to VO2Moderate1 (+166 +/- 133 ml min-1 with [La] approximately 2.4 mmol l-1). [La] at the onset of Moderate2 was not different between normoxia and hyperoxia (10.1 +/- 2.2 vs. 10.9 +/- 1.6 mmol l-1). The results show that VO2 is significantly increased during moderate exercise in hyperoxia. But this O2 overconsumption was not modified by a high [La] induced by a prior heavy exercise. It could be concluded that lactate accumulation is not directly responsible for the increase in O2 overconsumption with intensity during exercise in hyperoxia.

  16. Recruitment pattern of muscle fibre type during high intensity exercise (60-100% VO2max) in thoroughbred horses.

    PubMed

    Yamano, S; Eto, D; Hiraga, A; Miyata, H

    2006-02-01

    To consider the optimal training programme for Thoroughbred horses, we examined the recruitment pattern of muscle fibres including hybrid muscle fibres in well-trained Thoroughbred horses. The horses performed exercise at three different intensities and durations; i.e., 100% VO2max for 4 min, 80% and 60% VO2max for 8 min on a treadmill with 10% incline. Muscle samples were obtained from the middle gluteal muscle before, during (4 min at 80% and 60% VO2max), and after exercise. Four muscle fibre types (types I, IIA, IIA/IIX, and IIX) were immunohistochemically identified, and optical density of periodic acid Schiff staining (OD-PAS) in each fibre type, and the glycogen content of the muscle sample, were determined by quantitative histochemical and biochemical procedures. The changes in OD-PAS showed that the recruitment of all fibre types were identical at the final time stage of each exercise bout, i.e., 4 min running at 100% VO2max, and 8 min running at 80% and 60% VO2max. The changes in OD-PAS of type IIA/IIX fibre were very similar to those of type IIX fibre. The recruitment of these fibres were obviously more facilitated by 4 min running at 100% VO2max than by 4 min running at 80% or 60% VO2max. Short duration with high intensity exercise, such as 4 min running at 100% VO2max or 8 min running at 80% or 60% VO2max, is effective to stimulate type IIX fibre and IIA/IIX fibres that have the fastest speed of contraction.

  17. VO2/TiO2 Nanosponges as Binder-Free Electrodes for High-Performance Supercapacitors

    NASA Astrophysics Data System (ADS)

    Hu, Chenchen; Xu, Henghui; Liu, Xiaoxiao; Zou, Feng; Qie, Long; Huang, Yunhui; Hu, Xianluo

    2015-11-01

    VO2/TiO2 nanosponges with easily tailored nanoarchitectures and composition were synthesized by electrostatic spray deposition as binder-free electrodes for supercapacitors. Benefiting from the unique interconnected pore network of the VO2/TiO2 electrodes and the synergistic effect of high-capacity VO2 and stable TiO2, the as-formed binder-free VO2/TiO2 electrode exhibits a high capacity of 86.2 mF cm-2 (~548 F g-1) and satisfactory cyclability with 84.3% retention after 1000 cycles. This work offers an effective and facile strategy for fabricating additive-free composites as high-performance electrodes for supercapacitors.

  18. VO2/TiO2 Nanosponges as Binder-Free Electrodes for High-Performance Supercapacitors

    PubMed Central

    Hu, Chenchen; Xu, Henghui; Liu, Xiaoxiao; Zou, Feng; Qie, Long; Huang, Yunhui; Hu, Xianluo

    2015-01-01

    VO2/TiO2 nanosponges with easily tailored nanoarchitectures and composition were synthesized by electrostatic spray deposition as binder-free electrodes for supercapacitors. Benefiting from the unique interconnected pore network of the VO2/TiO2 electrodes and the synergistic effect of high-capacity VO2 and stable TiO2, the as-formed binder-free VO2/TiO2 electrode exhibits a high capacity of 86.2 mF cm−2 (~548 F g−1) and satisfactory cyclability with 84.3% retention after 1000 cycles. This work offers an effective and facile strategy for fabricating additive-free composites as high-performance electrodes for supercapacitors. PMID:26531072

  19. 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)

  20. 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.

  1. High-intensity interval training every second week maintains VO2max in soccer players during off-season.

    PubMed

    Slettaløkken, Gunnar; Rønnestad, Bent R

    2014-07-01

    Reduced endurance training among semiprofessional soccer players during off-season may have negative effect on game performance during the competition season. This negative effect can be prevented by adding high-intensity interval training (HIT) to normal activity. In this study, we want to compare 2 different frequencies of HIT (5 bouts of 4 minutes on 87-97% peak heart rate) session on maintenance of aerobic fitness among semiprofessional soccer players during a 6-week off-season period. Seventeen male players at second and third highest soccer division in Norway participated. The subjects were randomized into 1 HIT session every second week (HIT 0.5) or 1 HIT session per week (HIT 1). All participants performed a 20-m shuttle run test and a maximal oxygen uptake (VO2max) test on treadmill before and after the training intervention. VO2max (HIT 0.5, 63.4 ± 5.9 ml·kg-1·min-1; HIT 1, 65.6 ± 2.1 ml·kg-1·min-1) and 20-m shuttle run performance (HIT 0.5, 2335 ± 390 m, HIT 1, 2531 ± 106 m) were not different between the groups before the training intervention. VO2max was maintained after the training intervention in both HIT 0.5 and HIT 1 (64.0 ± 5.9 ml·kg-1·min-1 and 64.3 ± 1.3 ml·kg-1·min-1, respectively). There was a reduction in distance covered during the 20-m shuttle run test in HIT 1 and when groups were pooled (-7.9 ± 5.7% and -6.4 ± 7.9%, respectively, p ≤ 0.05). In conclusion, HIT 1 did not maintain VO2max better than HIT 0.5 when added to normal off-season activity. However, performance in 20-m shuttle run, which is a more soccer-specific fitness test than VO2max test, was slightly reduced when both groups was pooled.

  2. 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”.

  3. High-performance thermal sensitive W-doped VO2(B) thin film and its identification by first-principles calculations

    NASA Astrophysics Data System (ADS)

    Wan, Dongyun; Xiong, Ping; Chen, Lanli; Shi, Siqi; Ishaq, Ahmad; Luo, Hongjie; Gao, Yanfeng

    2017-03-01

    VO2(B) is currently a preferred phase structure for the application as bolometer material, which, however, suffers from low temperature-coefficient-of-resistance (TCR) values and large resistances. Here we present the combined experimental and first-principles calculations study on both doped and undoped VO2(B) thin films enabling us to attain high TCR (-3.9%/k) and suitable square-resistance (32.7 kΩ) by controlled W doping employing the widely used magnetron sputtering technique. The TCR value is 50% larger than reported ones at the similar resistance. The underlying microscopic mechanism for the performance improvement was studied and results indicated that the introduction of extra electrons and the variation in the band structure resulting from the incorporation of W6+ ions in the VO2(B) crystal lattice contribute to the enhancement of the electronic conductivity. Moreover, the special two-dimensional octahedral structure of monoclinic (C2/m) B-phase VO2 favors the strain control with W-doping for achieving a large TCR, which overcomes the analogous predicament between the high conductivity and large TCR generated by dopants in the M-phase VO2. The present findings provides a facile and simple pathway for the design and fabrication of high performance W-doped VO2(B) thin films rendering superior optical and electrical properties for its wide applications in thermo-opto-electro sensing devices.

  4. 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.

  5. Effect of Oxide Buffer Layer on the Thermochromic Properties of VO2 Thin Films

    NASA Astrophysics Data System (ADS)

    Koo, Hyun; Xu, Lu; Ko, Kyeong-Eun; Ahn, Seunghyun; Chang, Se-Hong; Park, Chan

    2013-12-01

    VO2 thin films were deposited on soda lime glass substrates with ZnO, TiO2, SnO2, and CeO2 thin films applied as buffer layers between the VO2 films and the substrates in order to investigate the effect of buffer layer on the formation and the thermochromic properties of VO2 film. Buffer layers with thicknesses over 50 nm were found to affect the formation of VO2 film, which was confirmed by XRD spectra. By using ZnO, TiO2, and SnO2 buffer layers, monoclinic VO2 (VO2(M)) film was successfully fabricated on soda lime glass at 370 °C. On the contrary, films of VO2(B), which is known to have no phase transition near room temperature, were formed rather than VO2(M) when the film was deposited on CeO2 buffer layer at the same film deposition temperature. The excellent thermochromic properties of the films deposited on ZnO, TiO2, and SnO2 buffer layers were confirmed from the temperature dependence of electrical resistivity from room temperature to 80 °C. Especially, due to the tendency of ZnO thin film to grow with a high degree of preferred orientation on soda lime glass at low temperature, the VO2 film deposited on ZnO buffer layer exhibits the best thermochromic properties compared to those on other buffer layer materials used in this study. These results suggest that deposition of VO2 films on soda lime glass at low temperature with excellent thermochromic properties can be achieved by considering the buffer layer material having structural similarity with VO2. Moreover, the degree of crystallization of buffer layer is also related with that of VO2 film, and thus ZnO can be one of the most effective buffer layer materials.

  6. 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.

  7. Formation of highly ordered VO2 nanotubular/nanoporous layers and their supercooling effect in phase transitions.

    PubMed

    Yang, Yang; Lee, Kiyoung; Zobel, Mirijam; Maćković, Mirza; Unruh, Tobias; Spiecker, Erdmann; Schmuki, Patrik

    2012-03-22

    The fabrication of self-organized VO(2) nanotubular/nanoporous layers is demonstrated by self-organizing anodization, followed by a suitable heat treatment. These VO(2) layers show a reversible metal to insulator transition (MIT) at 70 and 44 °C, when heating and cooling, respectively.

  8. High resolution Hall measurements across the VO2 metal-insulator transition reveal impact of spatial phase separation

    PubMed Central

    Yamin, Tony; Strelniker, Yakov M.; Sharoni, Amos

    2016-01-01

    Many strongly correlated transition metal oxides exhibit a metal-insulator transition (MIT), the manipulation of which is essential for their application as active device elements. However, such manipulation is hindered by lack of microscopic understanding of mechanisms involved in these transitions. A prototypical example is VO2, where previous studies indicated that the MIT resistance change correlate with changes in carrier density and mobility. We studied the MIT using Hall measurements with unprecedented resolution and accuracy, simultaneously with resistance measurements. Contrast to prior reports, we find that the MIT is not correlated with a change in mobility, but rather, is a macroscopic manifestation of the spatial phase separation which accompanies the MIT. Our results demonstrate that, surprisingly, properties of the nano-scale spatially-separated metallic and semiconducting domains actually retain their bulk properties. This study highlights the importance of taking into account local fluctuations and correlations when interpreting transport measurements in highly correlated systems. PMID:26783076

  9. Electric field-induced transport modulation in VO2 FETs with high-k oxide/organic parylene-C hybrid gate dielectric

    NASA Astrophysics Data System (ADS)

    Wei, Tingting; Kanki, Teruo; Fujiwara, Kohei; Chikanari, Masashi; Tanaka, Hidekazu

    2016-02-01

    We report on the observation of reversible and immediate resistance switching by high-k oxide Ta2O5/organic parylene-C hybrid dielectric-gated VO2 thin films. Resistance change ratios at various temperatures in the insulating regime were demonstrated to occur in the vicinity of phase transition temperature. We also found an asymmetric hole-electron carrier modulation related to the suppression of phase transition temperature. The results in this research provide a possibility for clarifying the origin of metal-insulator transition in VO2 through the electrostatic field-induced transport modulation.

  10. VO2 responses to running speeds above VO2max.

    PubMed

    Duffield, R; Bishop, D

    2008-06-01

    This study compared VO2, heart rate (HR) and electromyographic (iEMG) responses to speeds above the velocity associated with VO2max (v-VO2max). Eight male, middle-distance runners performed a graded exercise test to determine VO2max and v-VO2max and runs to fatigue at 100 % and 110 % v-VO2max. Breath-by-breath VO2 and HR were continuously recorded; lactate [La (-)] measured pre- and post-run and iEMG measures of rectus femoris (RF) and vastus lateralis were recorded during the first and last 20 s of each run. Analysis indicated longer time to fatigue in the 100 % v-VO2max run with no differences between conditions for VO2 or HR amplitudes or post-run [La (-)] (p > 0.05). There were significantly faster tau values (p < 0.05) in the 110 % condition in VO2 and HR. No significant correlations were observed between VO2 or HR tau values and time to fatigue. RF iEMG was significantly larger in 110 % compared to 100 % run in the first 20 s (p < 0.05). While no association between treadmill performance and VO2 response was evident, faster running speeds resulted in faster VO2 and HR responses, with no difference in amplitude or % VO2max attained. This may potentially be as a result of an increased muscle fibre recruitment stimulus during the faster running velocity resulting in faster cardiodynamic responses.

  11. Improved VO2max and time trial performance with more high aerobic intensity interval training and reduced training volume: a case study on an elite national cyclist.

    PubMed

    Støren, Øyvind; Bratland-Sanda, Solfrid; Haave, Marius; Helgerud, Jan

    2012-10-01

    The present study investigated to what extent more high aerobic intensity interval training (HAIT) and reduced training volume would influence maximal oxygen uptake (VO2max) and time trial (TT) performance in an elite national cyclist in the preseason period. The cyclist was tested for VO2max, cycling economy (C(c)), and TT performance on an ergometer cycle during 1 year. Training was continuously logged using heart rate monitor during the entire period. Total monthly training volume was reduced in the 2011 preseason compared with the 2010 preseason, and 2 HAIT blocks (14 sessions in 9 days and 15 sessions in 10 days) were performed as running. Between the HAIT blocks, 3 HAIT sessions per week were performed as cycling. From November 2010 to February 2011, the cyclist reduced total average monthly training volume by 18% and cycling training volume by 60%. The amount of training at 90-95% HRpeak increased by 41%. VO2max increased by 10.3% on ergometer cycle. TT performance improved by 14.9%. C(c) did not change. In conclusion, preseason reduced total training volume but increased amount of HAIT improved VO2max and TT performance without any changes in C(c). These improvements on cycling appeared despite that the HAIT blocks were performed as running. Reduced training time, and training transfer from running into improved cycling form, may be beneficial for cyclists living in cold climate areas.

  12. [VO2 max, a true exercise test].

    PubMed

    Saunier, Carole

    2013-01-01

    VO2 max is nowadays an essential examination performed in the monitoring of heart failure. The nurse has a role to play during the test and in supporting the patient, although this test remains highly technical and complex.

  13. Magnetic phase transition of high-pressure phase (VO)2P2O7 studied by high-field ESR measurements

    NASA Astrophysics Data System (ADS)

    Hiraka, K.; Nagasaka, Y.; Kunimoto, T.; Inagaki, Y.; Okubo, S.; Ohta, H.; Saito, T.; Azuma, M.; Takano, M.

    2004-05-01

    The high-pressure phase of (VO)2P2O7 (HP-VOPO) is a S=1/2 Heisenberg antiferromagnetic alternating chain compound with one spin gap. The high-field ESR measurements of the HP-VOPO single crystal have been performed using the pulsed magnetic field up to 30T. Small anomaly is observed in ESR mode for both a- and b-axis. The linewidth became broad around Bc=20T when the field is applied along the a- and b-axis. The magnetic state of HP-VOPO above Bc will be discussed.

  14. Magnetic Irreversibility in VO2/Ni Bilayers

    NASA Astrophysics Data System (ADS)

    de La Venta, Jose; Lauzier, Josh; Sutton, Logan

    The temperature dependence of the coercivity and magnetization of VO2/Ni bilayers was studied. VO2 exhibits a well-known Structural Phase Transition (SPT) at 330-340 K, from a low temperature monoclinic (M) to a high temperature rutile (R) structure. The SPT of VO2 induces an inverse magnetoelastic effect that strongly modifies the coercivity and magnetization of the Ni films. In addition, the growth conditions allow tuning of the magnetic properties. Ni films deposited on top of VO2 (M) show an irreversible change in the coercivity after the first cycle through the high temperature phase, with a corresponding change in the surface morphology of VO2. On the other hand, the Ni films grown on top of VO2 (R) do not show this irreversibility. These results indicate that properties of magnetic films are strongly affected by the strain induced by materials that undergo SPT and that it is possible to control the magnetic properties by tuning the growth conditions.

  15. High-intensity interval training improves VO(2peak), maximal lactate accumulation, time trial and competition performance in 9-11-year-old swimmers.

    PubMed

    Sperlich, Billy; Zinner, Christoph; Heilemann, Ilka; Kjendlie, Per-Ludvik; Holmberg, Hans-Christer; Mester, Joachim

    2010-11-01

    Training volume in swimming is usually very high when compared to the relatively short competition time. High-intensity interval training (HIIT) has been demonstrated to improve performance in a relatively short training period. The main purpose of the present study was to examine the effects of a 5-week HIIT versus high-volume training (HVT) in 9-11-year-old swimmers on competition performance, 100 and 2,000 m time (T(100 m) and T(2,000 m)), VO(2peak) and rate of maximal lactate accumulation (Lac(max)). In a 5-week crossover study, 26 competitive swimmers with a mean (SD) age of 11.5 ± 1.4 years performed a training period of HIIT and HVT. Competition (P < 0.01; effect size = 0.48) and T(2,000 m) (P = 0.04; effect size = 0.21) performance increased following HIIT. No changes were found in T(100 m) (P = 0.20). Lac(max) increased following HIIT (P < 0.01; effect size = 0.43) and decreased after HVT (P < 0.01; effect size = 0.51). VO(2peak) increased following both interventions (P < 0.05; effect sizes = 0.46-0.57). The increases in competition performance, T(2,000 m), Lac(max) and VO(2peak) following HIIT were achieved in significantly less training time (~2 h/week).

  16. Electric Field-induced Resistance Switching in VO2 Channels using Hybrid Gate Dielectric of High- k Ta2O5/Organic material Parylene-C

    NASA Astrophysics Data System (ADS)

    Wei, Tingting; Kanki, Teruo; Fujiwara, Kohei; Chikanari, Masashi; Tanaka, Hidekazu

    Electrostatic approach utilizing field-effect transistor (FET) with correlated electron materials provides an avenue to realize the novel devices (Mott-transistor) and to clarify condensed matter physics. In this study, we have prepared Mott-transistors using vanadium dioxide (VO2) channels and employed hybrid gate dielectric consisted of high- k material Ta2O5 and organic polymer parylene-C to trigger carrier transport modulation in VO2. Obvious resistance modulations were observed in insulating regime through time-dependent resistance measurement at varied square-shaped gate bias (VG) . Contrasting to the hysteretic response in electric double layer transistor (EDLT), an abrupt resistance switching in less than of 2-second-interval enables us to attribute such immediate modulation to pure electrostatic effect. Moreover, the maximum of resistance change was identified to appear around phase transition temperature (TMI) , which confirmed the disordered heterogeneous regime at TMI. Taking advantage of systematic modulation using VO2-based devices, we demonstrated the pronounced shifts of TMI by gate bias. Another fascinating behavior on asymmetric drop in TMI by hole-electron carrier doping was observed.

  17. Time to exhaustion and time spent at a high percentage of VO2max in severe intensity domain in children and adults.

    PubMed

    Leclair, Erwan; Mucci, Patrick; Borel, Benoit; Baquet, Georges; Carter, Helen; Berthoin, Serge

    2011-04-01

    The aim of the study was to compare time spent at a high percentage of VO2max (>90% of VO2max) (ts90%), time to achieve 90% of VO2max (ta90%), and time to exhaustion (TTE) for exercise in the severe intensity domain in children and adults. Fifteen prepubertal boys (10.3 ± 0.9 years) and 15 men (23.5 ± 3.6 years) performed a maximal graded exercise to determine VO2max, maximal aerobic power (MAP) and power at ventilatory threshold (PVTh). Then, they performed 4 constant load exercises in a random order at PVTh plus 50 and 75% of the difference between MAP and PVTh (PΔ50 and PΔ75) and 100 and 110% of MAP (P100 and P110). VO2max was continuously monitored. The P110 test was used to determine maximal accumulated oxygen deficit (MAOD). No significant difference was found in ta90% between children and adults. ts90% and TTE were not significantly different between children and adults for the exercises at PΔ50 and PΔ75. However, ts90% and TTE during P100 (p < 0.05 and p < 0.01, respectively) and P110 (p < 0.001) exercises were significantly shorter in children. Children had a significantly lower MAOD than adults (34.3 ± 9.4 ml · kg vs. 53.6 ± 11.1 ml · kg). A positive relationship (p < 0.05) was obtained between MAOD and TTE values during the P100 test in children. This study showed that only for intensities at, or higher than MAP, lower ts90% in children was linked to a reduced TTE, compared to adults. Shorter TTE in children can partly be explained by a lower anaerobic capacity (MAOD). These results give precious information about exercise intensity ranges that could be used in children's training sessions. Moreover, they highlight the implication of both aerobic and anaerobic processes in endurance performances in both populations.

  18. Role of surface defects and microstructure in infrared optical properties of thermochromic VO2 materials

    NASA Astrophysics Data System (ADS)

    Guinneton, Frédéric; Sauques, Laurent; Valmalette, Jean-Christophe; Cros, Frédéric; Gavarri, Jean-Raymond

    2005-01-01

    Thermochromic vanadium dioxide VO2 exhibits a semi-conducting to metallic phase transition at Tc=68 °C, involving strong variations in optical transmittance, reflectance and emissivity. However, the optical contrasts observed in thin films or nanostructured compacted samples seem to depend on both surface microstructure and surface crystal texture. In the case of opaque materials, surface defects might play a drastic role in optical reflectivity. As the high temperature metallic phase of VO2 is opaque for infrared radiations, we used aluminum samples as standards allowing us to correlate reflectivity responses with porosity and surface defects. Then, various polycrystalline and nanostructured VO2 samples compacted at various pressures and presenting variable surface roughness were prepared. Thin films were deposited by radio frequency sputtering process. The samples were characterized using X-ray diffraction, scanning electron microscopy and transmission electron microscopy. Optical properties (reflectance and emissivity) were analyzed above and below the transition temperature, making use of specific FTIR equipments. In thin films, the deposited VO2 phase was systematically oriented and surface porosity was very weak. In polycrystalline samples, as the compaction pressure increased, surface porosity decreased, and infrared optical contrast increased. In such samples, preferred orientations were favored for low applied pressures. These features clearly show that the main parameters conditioning the optical contrast should be the surface defects and porosity, not the preferred crystal orientations. As an additional interesting result, the surfaces formed from compacted nanocrystalline VO2 powders present improved optical contrast for reflectance and emissivity properties.

  19. Joule-heat-driven high-efficiency electronic-phase switching in freestanding VO2/TiO2 nanowires

    NASA Astrophysics Data System (ADS)

    Higuchi, Yoshiyuki; Kanki, Teruo; Tanaka, Hidekazu

    2017-03-01

    In this study, we demonstrated that an insulator-to-metal transition is driven by a low electric power using freestanding structures with two different sizes. The critical power (P C) required to induce the insulator-to-metal transition was measured with clamped and freestanding nanowires. The required P C for 400-nm-wide freestanding nanowires was 483 nW at a temperature 2 K lower than the temperature of the insulator-to-metal transition. This P C value is approximately 1 order of magnitude smaller than that for freestanding microwires with a width of 1 µm. The thermal dissipation model explains the changes in P C. These results provide guidelines for achieving significant reductions in P C in two-terminal VO2 phase-switching devices.

  20. The influence of exercise duration at VO2 max on the off-transient pulmonary oxygen uptake phase during high intensity running activity.

    PubMed

    Billat, V L; Hamard, L; Koralsztein, J P

    2002-12-01

    The purpose of this study was to examine the influence of time run at maximal oxygen uptake (VO2 max) on the off-transient pulmonary oxygen uptake phase after supra-lactate threshold runs. We hypothesised: 1) that among the velocities eliciting VO2 max there is a velocity threshold from which there is a slow component in the VO2-off transient, and 2) that at this velocity the longer the duration of this time at VO2 max (associated with an accumulated oxygen kinetics since VO2 can not overlap VO2 max), the longer is the off-transient phase of oxygen uptake kinetics. Nine long-distance runners performed five maximal tests on a synthetic track (400 m) while breathing through the COSMED K4b2 portable, telemetric metabolic analyser: i) an incremental test which determined VO2 max, the minimal velocity associated with VO2 max (vVO2 max) and the velocity at the lactate threshold (vLT), ii) and in a random order, four supra-lactate threshold runs performed until exhaustion at vLT + 25, 50, 75 and 100% of the difference between vLT and vVO2 max (vdelta25, vdelta50, vdelta75, vdelta100). At vdelta25, vdelta50 (= 91.0 +/- 0.9% vVO2 max) and vdelta75, an asymmetry was found between the VO2 on (double exponential) and off-transient (mono exponential) phases. Only at vdelta75 there was at positive relationship between the time run at VO2 max (%tlimtot) and the VO2 recovery time constant (Z = 1.8, P = 0.05). In conclusion, this study showed that among the velocities eliciting VO2 max, vdelta75 is the velocity at which the longer the duration of the time at VO2 max, the longer is the off-transient phase of oxygen uptake kinetics. It may be possible that at vdelta50 there is not an accumulated oxygen deficit during the plateau of VO2 at VO2 max and that the duration of the time at VO2 max during the exhaustive runs at vdelta100, could be too short to induce an accumulating oxygen deficit affecting the oxygen recovery.

  1. 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.

  2. VO2@RER1.0: a novel submaximal cardiopulmonary exercise index.

    PubMed

    Chin, Clifford; Kazmucha, Jeffrey; Kim, Nancy; Suryani, Reny; Olson, Inger

    2010-01-01

    Maximal oxygen consumption (VO2max) is the "gold standard" by which to assess functional capacity; however, it is effort dependent. VO2@RER1.0 is defined when VO2 = VCO2. Between December 22, 1997 and November 9, 2004, 305 pediatric subjects underwent cycle ergometer cardiopulmonary exercise testing, exercised to exhaustion, and reached a peak respiratory exchange ratio > or = 1.10. Group 1 subjects achieved a peak VO2 > or = 80% of predicted VO2max; group 2 subjects achieved a peak VO2 < or = 60% of predicted VO2max; and group 3 subjects achieved a peak VO2 between 61 and 79% of predicted VO2max. Linear regression analysis was performed for VO2@RER1.0 as a function of predicted VO2 for group 1 subjects. A -2 SD regression line and equation was created. VO2@RER1.0 data from groups 2 and 3 were plotted onto the normative graph. Contingency table and relative-risk analysis showed that an abnormal VO2@RER1.0 predicted an abnormal peak VO2(positive-predictive value 83%, negative-predictive value 85%, sensitivity 84%, and specificity 84%). VO2@RER1.0 is a highly sensitive, specific, and predictive submaximal index of functional capacity. This submaximal index is easy to identify without subjectivity. This index may aid in the evaluation of subjects who cannot exercise to maximal parameters.

  3. 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.

  4. Sol-gel preparation and characterization of SiO2 coated VO2 films with enhanced transmittance and high thermochromic performance

    NASA Astrophysics Data System (ADS)

    Li, Dezeng; Shan, Yongkui; Huang, Fuqiang; Ding, Shangjun

    2014-10-01

    Vanadium dioxide (VO2) films prepared at low-temperature with a low cost are considerable for energy-saving applications. Here, SiO2 coated VO2 films with clearly enhanced visible transmittance by introducing antireflection coatings (ARCs) and excellent thermochromic performance were present. The VO2 films have been prepared via a stable and low-cost sol-gel synthesis route using vanadium pentaoxide powder as precursor, and their structural, morphological, optical and electrical properties and thermochromic performance were systemically characterized. The resistance of VO2 films varies by 4 orders of magnitude and the transmittance changes from 11.8% to 69.3% at 2500 nm while no significant deviation appears in the visible region during metal-insulator transition (MIT). Nanoporous SiO2 coating with good optical transparency was coated on the surface of VO2 film via sol-gel dip-coating technique to enhance its optical transmittance, and the visible transmittance is increased by 14.6% due to the significantly decreased reflectance. The critical transition temperature (63 °C) and infrared switching properties of VO2 films are not much deteriorated by applying SiO2 layer. The synergistic effect of antireflection and thermochromism on SiO2 coated VO2 films was investigated.

  5. Influence of work-interval intensity and duration on time spent at a high percentage of VO2max during intermittent supramaximal exercise.

    PubMed

    Wakefield, Benjamin R; Glaister, Mark

    2009-12-01

    The purpose of this study was to examine the effect of work-interval duration (WID) and intensity on the time spent at, or above, 95% VO2max (T95 VO2max) during intermittent bouts of supramaximal exercise. Over a 5-week period, 7 physically active men with a mean (+/-SD) age, height, body mass, and VO2max of 22 +/- 5 years, 181.5 +/- 5.6 cm, 86.4 +/- 11.4 kg, and 51.5 +/- 1.5 ml.kg-1.min-1, respectively, attended 7 testing sessions. After completing a submaximal incremental test on a treadmill to identify individual oxygen uptake/running velocity relationships, subjects completed a maximal incremental test to exhaustion to VO2max and subsequently (from the aforementioned relationship) the minimum velocity required to elicit VO2max (vVO2max). In a random order, subjects then carried out 3 intermittent runs to exhaustion at both 105% and 115% vVO2max. Each test used a different WID (20 s, 25 s, or 30 s) interspersed with 20-second passive recovery periods. Results revealed no significant difference in T95 vVO2max for intermittent runs at 105% versus 115% vVO2max (p = 0.142). There was, however, a significant effect (p < 0.001) of WID on T95 VO2max, with WIDs of 30 seconds enabling more time relative to WIDs of 20 seconds (p = 0.018) and 25 seconds (p = 0.009). Moreover, there was an interaction between intensity and duration such that the effect of WID was magnified at the lower exercise intensity (p = 0.046). In conclusion, despite a number of limitations, the results of this investigation suggest that exercise intensities of approximately 105% vVO2max combined with WIDs greater than 25 seconds provide the best way of optimizing T95 VO2max when using fixed 20-second stationary rest periods.

  6. 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.

  7. High temperature coefficient of resistance of low-temperature-grown VO2 films on TiO2-buffered SiO2/Si (100) substrates

    NASA Astrophysics Data System (ADS)

    Miyazaki, Kenichi; Shibuya, Keisuke; Suzuki, Megumi; Wado, Hiroyuki; Sawa, Akihito

    2015-08-01

    The introduction of a TiO2 buffer layer significantly improved the temperature coefficient of resistance (TCR), a measure of the sharpness of the metal-insulator transition, for films of VO2 grown on SiO2/Si (100) substrates at growth temperatures below 670 K. X-ray diffraction and Raman scattering measurements revealed that polycrystalline VO2 films were formed on the TiO2-buffered substrates at low temperatures below 600 K, whereas amorphous films were formed at these temperatures on SiO2/Si (100) substrates without a TiO2 buffer layer. Electron microscopy studies confirmed that the TiO2 buffer layer enhanced the grain growth of VO2 films at low growth temperatures. The VO2 films grown at 600 K on TiO2-buffered substrates showed a large TCR of more than 80%/K as a result of the improved crystallinity and grain size of the VO2 films. Our results provide an effective approach toward the integration of VO2-based devices onto Si platforms at process temperatures below 670 K.

  8. Metal-insulator transition of valence-controlled VO2 thin film prepared by RF magnetron sputtering using oxygen radical

    NASA Astrophysics Data System (ADS)

    Suetsugu, Takaaki; Shimazu, Yuichi; Tsuchiya, Takashi; Kobayashi, Masaki; Minohara, Makoto; Sakai, Enju; Horiba, Koji; Kumigashira, Hiroshi; Higuchi, Tohru

    2016-06-01

    We have prepared b-axis-oriented VO2 thin films by RF magnetron sputtering using oxygen radicals as the reactive gas. The VO2 thin films consist of a mixed-valence V3+/V4+ state formed by oxygen vacancies. The V3+ ratio strongly depends on the film thickness and the oxygen partial pressure of the radical gun during deposition. The lattice constant of the b-axis increases and the metal-insulator transition (MIT) temperature decreases with decreasing V3+ ratio, although the VO2 thin films with a high V3+ ratio of 42% do not exhibit MIT. The bandwidths and spectral weights of V 3d a1g and \\text{e}\\text{g}σ bands at around the Fermi level, which correspond to the insulating phase at 300 K, are smaller in the VO2 thin films with a low V3+ ratio. These results indicate that the control of the mixed-valence V3+/V4+ state is important for the MIT of b-axis-oriented VO2 thin films.

  9. Infrared Response and Optoelectronic Memory Device Fabrication Based on Epitaxial VO2 Film.

    PubMed

    Fan, Lele; Chen, Yuliang; Liu, Qianghu; Chen, Shi; Zhu, Lei; Meng, Qiangqiang; Wang, Baolin; Zhang, Qinfang; Ren, Hui; Zou, Chongwen

    2016-12-07

    In this work, high-quality VO2 epitaxial films were prepared on high-conductivity n-GaN (0001) crystal substrates via an oxide molecular beam epitaxy method. By fabricating a two-terminal VO2/GaN film device, we observed that the infrared transmittance and resistance of VO2 films could be dynamically controlled by an external bias voltage. Based on the hysteretic switching effect of VO2 in infrared range, an optoelectronic memory device was achieved. This memory device was operated under the "electrical writing-optical reading" mode, which shows promising applications in VO2-based optoelectronic device in the future.

  10. The preparation of a plasmonically resonant VO2 thermochromic pigment

    NASA Astrophysics Data System (ADS)

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

    2009-02-01

    Vanadium dioxide (VO2) undergoes a reversible metal-insulator transition, normally at ~68 °C. While the properties of continuous semi-transparent coatings of VO2 are well known, there is far less information available concerning the potential use of discrete VO2 nanoparticles as a thermochromic pigment in opaque coatings. Individual VO2 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 VO2 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 VO2 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.

  11. Thermochromic VO2 on Zinnwaldite Mica by pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    Mathevula, L.; Ngom, B. D.; Kotsedi, L.; Sechogela, P.; Doyle, T. B.; Ghouti, M.; Maaza, M.

    2014-09-01

    VO2 thin films have been deposited by pulsed laser deposition on Zinnwaldite Mica substrates. The crystal structure, chemical composition, morphology were determined and the semiconductor/metal transition (SMT) properties of the deposited films were investigated. Without any post annealing, the films exhibit a textured nature with a VO2 (0 1 1) preferred crystallographic orientation and an elevated thermal variation of the electric resistance ratio RS/RM through the SMT at T ≈ 68 °C of the order of 104 and a narrow ∼7 °C hysteresis. In addition, the growth of the VO2 crystallites seem to be governed likely by a Volmer-Weber or Stranski-Krastanov mechanisms and certainly not a Frank-van Der Merwe process.

  12. Preparation and Characterization of VO 2 Nanopowders

    NASA Astrophysics Data System (ADS)

    Zheng, Chenmou; Zhang, Xinmin; Zhang, Jianhui; Liao, Kairong

    2001-02-01

    VO2 powders with sizes of <30 nm were successfully synthesized by pyrolysis of the precursor, [NH4]5[(VO)6(CO3)4(OH)9]·10H2O. The effects of various pyrolysis conditions on VO2 stoichiometries and crystal states were investigated in detail. The results of IR measurements show that for the stoichiometric VO2, from micro- to nanocrystals and to amorphous state, the absorptions shifted to lower wavenumbers, the numbers of bands decreased gradually, and the widths of the bands broadened. Moreover, the IR spectra of nanocrystals were obviously different from those of microcrystals and amorphism. In comparison with stoichiometric VO2 crystals, the IR absorptions of oxygen-rich VO2 crystals clearly were blue shift, and those of oxygen-deficient VO2 crystals lightly red shift. The heats and temperatures of phase transition from VO1.96 to VO2.07 were determined. The results indicate that the phase transition temperature of VO2.02 is 70.1°C and has the maximum phase transition heat.

  13. Biology of VO2 max: looking under the physiology lamp.

    PubMed

    Lundby, C; Montero, D; Joyner, M

    2016-11-07

    In this review, we argue that several key features of maximal oxygen uptake (VO2 max) should underpin discussions about the biological and reductionist determinants of its interindividual variability: (i) training-induced increases in VO2 max are largely facilitated by expansion of red blood cell volume and an associated improvement in stroke volume, which also adapts independent of changes in red blood cell volume. These general concepts are also informed by cross-sectional studies in athletes that have very high values for VO2 max. Therefore, (ii) variations in VO2 max improvements with exercise training are also likely related to variations in these physiological determinants. (iii) All previously untrained individuals will respond to endurance exercise training in terms of improvements in VO2 max provided the stimulus exceeds a certain volume and/or intensity. Thus, genetic analysis and/or reductionist studies performed to understand or predict such variations might focus specifically on DNA variants or other molecular phenomena of relevance to these physiological pathways.

  14. Thermochromic characteristics of Ti-doped VO2 thin film

    NASA Astrophysics Data System (ADS)

    Lee, Hwasoo; Ko, Kyung Hyun; Choi, Jun Oh

    2014-03-01

    Utilizing metal-to-insulator transition (MIT) properties of V-oxide film, stable VO2 phase is necessary. In sputtering deposition of VO2, simple target preparation and high deposition rate are recommendable. For this, VO2 film was deposited on quartz substrate by RF magnetron sputter system under low working pressure using V2O5 target. Due to the lower sputtering yield of oxygen compared to vanadium, oxygen ion contents is usually deficient from that of target. So, the reduction of V ions was a result of charge compensation with the oxygen ions. Under lower working pressure, deposition rate become higher so that this deficiency is getting larger to cause further reduction to destabilize VO2. Preventing this, titanium oxide co-deposition was suggested to enrich oxygen source. When TiO2 was used, Ti ion has stable +4 charge state so that extra oxygen sputtered prevents V ion reduction below +4 state. But, in case of TiO, Ti ions were oxidized from +2 to +3 and +4 state and V ions with less oxidation potential should be reduced to +3 or so. Pure VO2 film had MIT at 66°C and large resistivity ratio of 4 orders of magnitude from 30°C to 90°C. Under low working pressure, (V2O5 + TiO2) system yield fairly good films, while films with poor or absence of MIT were produced with TiO case.

  15. Optimization of VO2 nanowire polymer composite thermochromic films by optical simulation

    NASA Astrophysics Data System (ADS)

    Naoi, Yuki; Amano, Jun

    2016-12-01

    Thermochromic films with high efficiency, transparency, and flexibility are highly desirable for energy-efficient smart window films. Vanadium oxide (VO2)-nanoparticle-embedded flexible polymer composite films are the most promising thermochromic films because of the sharp phase transition of insulating to metallic phases of VO2 at 68 °C with visible transparency and a large change in transmittance at near-infrared wavelengths before and after the metal-insulator phase transition. This paper describes the simulation of high-efficiency thermochromic polymer composite films embedded with VO2 nanoparticles of various sizes to investigate the optimum VO2 nanowire size and length.

  16. Thermochromic VO2 nanorods made by sputter deposition: Growth conditions and optical modeling

    NASA Astrophysics Data System (ADS)

    Li, Shu-Yi; Namura, Kyoko; Suzuki, Motofumi; Niklasson, Gunnar A.; Granqvist, Claes G.

    2013-07-01

    Reactive dc magnetron sputtering onto glass-based substrates yielded deposits of thermochromic VO2 with well-developed nanorods and nanowires. Their formation was promoted by high substrate temperature (above ˜500 °C), sufficient film thickness, proper inlet of the reactive gas, dispersed gold "seeds," and pronounced substrate roughness. Rutherford back scattering ascertained mass thicknesses, scanning electron microscopy depicted the nanostructures, and glancing incidence X-ray diffraction proved that single-phase VO2 was normally formed. Spectrophotometric measurements of total and diffuse transmittance and reflectance on VO2 thin films, at room temperature and ˜100 °C, allowed us to determine complex dielectric functions below and above the "critical" temperature for thermochromic switching (˜68 °C). These data were then used in computations based on the Bruggeman effective medium theory applied to randomly oriented prolate spheroidal structural units to derive the optical properties of the deposits. Experimental and computed data on spectral absorptance were found to be in good qualitative agreement.

  17. Persistent Electrochemical Performance in Epitaxial VO2(B).

    PubMed

    Lee, Shinbuhm; Sun, Xiao-Guang; Lubimtsev, Andrew A; Gao, Xiang; Ganesh, Panchapakesan; Ward, Thomas Z; Eres, Gyula; Chisholm, Matthew F; Dai, Sheng; Lee, Ho Nyung

    2017-04-12

    Discovering high-performance energy storage materials is indispensable for renewable energy, electric vehicle performance, and mobile computing. Owing to the open atomic framework and good room temperature conductivity, bronze-phase vanadium dioxide [VO2(B)] has been regarded as a highly promising electrode material for Li ion batteries. However, previous attempts were unsuccessful to show the desired cycling performance and capacity without chemical modification. Here, we show with epitaxial VO2(B) films that one can accomplish the theoretical limit for capacity with persistent charging-discharging cyclability owing to the high structural stability and unique open pathways for Li ion conduction. Atomic-scale characterization by scanning transmission electron microscopy and density functional theory calculations also reveal that the unique open pathways in VO2(B) provide the most stable sites for Li adsorption and diffusion. Thus, this work ultimately demonstrates that VO2(B) is a highly promising energy storage material and has no intrinsic hindrance in achieving superior cyclability with a very high power and capacity in a Li-ion conductor.

  18. Direct and continuous synthesis of VO2 nanoparticles

    NASA Astrophysics Data System (ADS)

    Powell, M. J.; Marchand, P.; Denis, C. J.; Bear, J. C.; Darr, J. A.; Parkin, I. P.

    2015-11-01

    Monoclinic VO2 nanoparticles are of interest due to the material's thermochromic properties, however, direct synthesis routes to VO2 nanoparticles are often inaccessible due to the high synthesis temperatures or long reaction times required. Herein, we present a two-step synthesis route for the preparation of monoclinic VO2 nanoparticles using Continuous Hydrothermal Flow Synthesis (CHFS) followed by a short post heat treatment step. A range of particle sizes, dependent on synthesis conditions, were produced from 50 to 200 nm by varying reaction temperatures and the residence times in the process. The nanoparticles were characterised by powder X-ray diffraction, Raman and UV/Vis spectroscopy, transmission electron microscopy (TEM), scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). The nanoparticles were highly crystalline with rod and sphere-like morphologies present in TEM micrographs, with the size of both the rod and spherical particles being highly dependent on both reaction temperature and residence time. SEM micrographs showed the surface of the powders produced from the CHFS process to be highly uniform. The samples were given a short post synthesis heat treatment to ensure that they were phase pure monoclinic VO2, which led to them exhibiting a large and reversible switch in optical properties (at near-IR wavelengths), which suggests that if such materials can be incorporated into coatings or in composites, they could be used for fenestration in architectural applications.

  19. Microstructure and Transport properties of epitaxial VO2 thin films on TiO2 substrates

    NASA Astrophysics Data System (ADS)

    Lu, Jiwei

    2008-10-01

    Vanadium oxides are paradigms of strongly correlated oxides and have attracted attention because of the metal insulator transitions (MIT) that several of the oxides and sub-oxides exhibit. In particular, VO2 has a metal--semiconductor transition at 340 K. This transition in VO2 combines the properties of a pure Mott Hubbard electronic transition with those of a Peierls structural transition. The Mott transition is responsible for the extreme speed of the optical switching that has been observed (faster than 100 fs). Understanding this transition and how to control it remains a challenge for both theory and experimental physics. We used a novel deposition technique, Reactive Bias Target Ion Beam Deposition, to grow 40 nm epitaxial VO2 thin films on rutile TiO2 substrates with various crystal orientations. X-ray diffraction (XRD) was used to explore the epitaxy of VO2 and we found that all VO2 thin films on TiO2 substrates showed tetragonal symmetry at room temperature due to the constrain from rutile substrates. We also characterized the metal-insulator transition of VO2 films as the function of the crystal orientation of rutile TiO2. We also characterized the anisotropy of VO2 thin films. In collaboration with Kevin West and Stuart Wolf, University of Virginia.

  20. Characterization of nanostructured VO2 thin films grown by magnetron controlled sputtering deposition and post annealing method.

    PubMed

    Chen, Sihai; Lai, Jianjun; Dai, Jun; Ma, Hong; Wang, Hongchen; Yi, Xinjian

    2009-12-21

    By magnetron controlled sputtering system, a new nanostructured metastable monoclinic phase VO2 (B) thin film has been fabricated. The testing result shows that this nanostructured VO2 (B) thin film has high temperature coefficient of resistance (TCR) of -7%/K. Scanning electron microscopy measurement shows that the average grain diameter of the VO2 (B) crystallite is between 100 and 250 nm. After post annealed, VO2 (B) crystallite is changed into monoclinic (M) phase VO2 (M) crystallite with the average grain diameter between 20 and 50 nm. A set up of testing the thin film switching time is established. The test result shows the switching time is about 50 ms. With the nanostructured VO2 (B) and VO2 (M) thin films, optical switches and high sensitivity detectors will be presented.

  1. Is peak VO2 a maximal index of children's aerobic fitness?

    PubMed

    Armstrong, N; Welsman, J; Winsley, R

    1996-07-01

    A levelling of oxygen uptake (VO2 plateau) at high exercise intensities is conventionally used as the criterion for establishing VO2max during progressive, incremental exercise testing. Only a minority of children, however, demonstrate a VO2 plateau during exercise to voluntary exhaustion. This study was therefore designed to investigate whether a VO2 plateau is required before peak VO2 can be considered a maximal index of children's aerobic fitness. Eighteen girls and 17 boys (age 9.9 +/- 0.4 yrs) carried out three treadmill tests to exhaustion one week apart. The first test comprised a discontinuous, incremental protocol to voluntary exhaustion. In test two each child warmed up and then ran to exhaustion at the same belt speed but on a gradient 2.5% greater than that which had produced an exhaustive effort on the first test. The third test was conducted similarly but the treadmill gradient was raised to 5% greater than that which had produced an exhaustive effort on the first test. Seven girls and 6 boys demonstrated a VO2 plateau (< or = 2 ml.kg-1.min-7) on the first test but no significant differences in either anthropometrical or peak physiological data were detected between those who demonstrated a plateau and those who did not. Mean peak VO2 values during tests two and three (supramaximal tests) did not increase significantly above that achieved on test one although indicators of an increased anaerobic contribution were significantly higher in both supramaximal tests. These findings indicate that peak VO2 in test one was a maximal value despite the absence of a VO2 plateau. The requirement of a VO2 plateau before peak VO2 can be regarded as a maximal index of young children's aerobic fitness is therefore untenable.

  2. 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.

  3. Electrical and optical properties of VO2 thin films grown on various sapphire substrates by using RF sputtering deposition

    NASA Astrophysics Data System (ADS)

    Jung, Dae Ho; So, Hyeon Seob; Ko, Kun Hee; Park, Jun Woo; Lee, Hosun; Nguyen, Trang Thi Thu; Yoon, Seokhyun

    2016-12-01

    VO2 thin films were grown on a-, c-, m-, and r-plane sapphire and SiO2/Si substrates under identical conditions by using RF sputtering deposition from a VO2 target. The structural and the morphological properties of all VO2 films were investigated. The grain sizes of the VO2 films varied between 268 nm and 355 nm depending on the substrate's orientation. The electrical and the optical properties of all VO2 thin films were examined in detail. The metal-insulator transition temperature (TMI) varied with the substrate's orientation. The (200)/(bar 211 )-oriented VO2 films on the a-plane sapphire showed the lowest TMI of about 329.3 K (56.3 °C) while the (020)/(002)-VO2 films on the c-plane sapphire displayed the highest TMI of about 339.6 K (66.6 °C). The VO2 films showed reversible changes in the resistivity as large as 1.19 × 105 and a hysteresis of 2 K upon traversing the transition temperature. The variations observed in the TMI with respect to the substrate's orientation were due to changes in the lattice strain and the grain size distribution. Raman spectroscopy showed that metal (rutile) - insulator (monoclinic) transitions occurred via the M2 phase for VO2 films on the c-plane substrate rather than the direct M1 to rutile transition. The shifts in the phonon frequencies of the VO2 film grown on various sapphire substrates were explained in terms of the strain along the V-V atomic bond direction (cR). Our work shows a possible correlation between the transition parameters ( e.g., TMI, sharpness, and hysteresis width) and the width ( σ) of the grain size distribution. It also shows a possible correlation between the TMI and the resistivities at the insulating and the metallic phases for VO2 films grown on various sapphire substrates.

  4. Epitaxial growth of higher transition-temperature VO2 films on AlN/Si

    NASA Astrophysics Data System (ADS)

    Slusar, Tetiana; Cho, Jin-Cheol; Kim, Bong-Jun; Yun, Sun Jin; Kim, Hyun-Tak

    2016-02-01

    We report the epitaxial growth and the mechanism of a higher temperature insulator-to-metal-transition (IMT) of vanadium dioxide (VO2) thin films synthesized on aluminum nitride (AlN)/Si (111) substrates by a pulsed-laser-deposition method; the IMT temperature is TIMT ≈ 350 K. X-ray diffractometer and high resolution transmission electron microscope data show that the epitaxial relationship of VO2 and AlN is VO2 (010) ‖ AlN (0001) with VO2 [101] ‖ AlN [ 2 1 ¯ 1 ¯ 0 ] zone axes, which results in a substrate-induced tensile strain along the in-plane a and c axes of the insulating monoclinic VO2. This strain stabilizes the insulating phase of VO2 and raises TIMT for 10 K higher than TIMT single crystal ≈ 340 K in a bulk VO2 single crystal. Near TIMT, a resistance change of about four orders is observed in a thick film of ˜130 nm. The VO2/AlN/Si heterostructures are promising for the development of integrated IMT-Si technology, including thermal switchers, transistors, and other applications.

  5. 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

  6. Silica-shell encapsulation and adhesion of VO2 nanowires to glass substrates: integrating solution-derived VO2 nanowires within thermally responsive coatings

    NASA Astrophysics Data System (ADS)

    Pelcher, Kate E.; Crawley, Matthew R.; Banerjee, Sarbajit

    2014-09-01

    The binary vanadium oxide VO2 undergoes a reversible insulator—metal phase transition in response to increasing temperature accompanied by an orders of magnitude alteration of optical transmittance; the low-temperature monoclinic phase of VO2 is infrared-transmissive, whereas the high-temperature rutile phase is infrared-reflective. This remarkable property portends applications in thermally responsive spectral mirrors that can modulate infrared transmittance as a function of temperature. Using a modified Stöber process, we demonstrate the constitution of conformal SiO2 shells around the VO2 nanowires. The SiO2 shells enhance the robustness of the VO2 nanowires towards thermal oxidation; the thickness of the shells is observed to depend on the reaction time. Notably, the deposition of conformal shells does not deleteriously impact the metal—insulator transitions of the VO2 nanowire cores. A modification of this approach allows for the VO2 nanowires to be embedded within a SiO2 matrix bonded to glass. The applied coatings are strongly adhered to glass as evaluated using standardized ASTM methods. The coatings exhibit promising thermochromic response and attenuate transmission of near-infrared radiation with increasing temperature.

  7. Terbium-Doped VO2 Thin Films: Reduced Phase Transition Temperature and Largely Enhanced Luminous Transmittance.

    PubMed

    Wang, Ning; Duchamp, Martial; Dunin-Borkowski, Rafal E; Liu, Shiyu; Zeng, XianTing; Cao, Xun; Long, Yi

    2016-01-26

    Vanadium dioxide (VO2) is a well-known thermochromic material with large IR modulating ability, promising for energy-saving smart windows. The main drawbacks of VO2 are its high phase transition temperature (τ(c) = 68°C), low luminous transmission (T(lum)), and weak solar modulating ability (ΔT(sol)). In this paper, the terbium cation (Tb(3+)) doping was first reported to reduce τ(c) and increase T(lum) of VO2 thin films. Compared with pristine VO2, 2 at. % doping level gives both enhanced T(lum) and ΔT(sol) from 45.8% to 54.0% and 7.7% to 8.3%, respectively. The T(lum) increases with continuous Tb(3+) doping and reaches 79.4% at 6 at. % doping level, representing ∼73.4% relative increment compared with pure VO2. This has surpassed the best reported doped VO2 thin films. The enhanced thermochromic properties is meaningful for smart window applications of VO2 materials.

  8. Is time limit at the minimum swimming velocity of VO2 max influenced by stroking parameters?

    PubMed

    Fernandes, Ricardo J; Marinho, Daniel A; Barbosa, Tiago M; Vilas-Boas, J Paulo

    2006-08-01

    The aim of this study was to observe the relationship between time limit at the minimum velocity that elicits maximal oxygen consumption (TLim-v VO2 max) and stroke rate, stroke length, and stroke index. 13 men and 10 women, highly trained swimmers, performed an intermittent incremental test for v VO2 max assessment and an all-out swim to estimate TLim-v VO2 max. The mean +/- SD TLim-v VO2 max, v VO2 max, stroke rate, stroke length, and stroke index values were 233.36 +/- 53.92 sec., 1.40 +/- .06 meter/sec., 35.58 +/- 2.89 cycles/min., 2.39 +/- .22 meter/cycle, and 3.36 +/- .41 meter2/(cycle x sec.), respectively. The correlation between TLim-v VO2 max and stroke rate was -.51 (p < .01), and values for TLim-v VO2 max with stroke length (r = .52, p < .01) and stroke index (r = .45, p < .05). These results seem to suggest that technical skill is a key factor in typical efforts requiring prolonged aerobic power.

  9. A theoretical analysis of factors determining VO2 MAX at sea level and altitude.

    PubMed

    Wagner, P D

    1996-12-01

    When maximal VO2 (VO2 MAX) is limited by O2 supply, it is generally thought that cardiac output (QT) is mostly responsible, but other O2 transport conductances [ventilation (VA); [Hb]; pulmonary (DLO2) and muscle (DMO2) diffusion capacities] may also influence VO2 MAX. A numerical analysis interactively linking the lungs, circulation and muscles was designed to compare the influences of each conductance component on VO2 MAX at three altitudes: PB = 760, 464 and 253 Torr. For any given set of conductances the analysis simultaneously solved six equations for alveolar, arterial, and venous PO2 and PcO2. The equations represent pulmonary mass balance, pulmonary diffusion, and muscle diffusion for both gases. At PB = 760, [Hb], DLO2 and DMO2 were as influential as QT in limiting VO2 MAX. With increasing altitude, the influence of QT and [Hb] fell while that of VA, DLO2 and DMO2 progressively increased until at PB = 253, VO2 MAX was independent of QT and [Hb]. Neither the fall in maximal QT nor rise in [Hb] with chronic hypoxia therefore appear to affect VO2 MAX. However, high values of ventilation, DLO2 and DMO2 appear to be advantageous for exercise at altitude.

  10. Instantaneous band gap collapse in photoexcited monoclinic VO2 due to photocarrier doping.

    PubMed

    Wegkamp, Daniel; Herzog, Marc; Xian, Lede; Gatti, Matteo; Cudazzo, Pierluigi; McGahan, Christina L; Marvel, Robert E; Haglund, Richard F; Rubio, Angel; Wolf, Martin; Stähler, Julia

    2014-11-21

    Using femtosecond time-resolved photoelectron spectroscopy we demonstrate that photoexcitation transforms monoclinic VO2 quasi-instantaneously into a metal. Thereby, we exclude an 80 fs structural bottleneck for the photoinduced electronic phase transition of VO2. First-principles many-body perturbation theory calculations reveal a high sensitivity of the VO2 band gap to variations of the dynamically screened Coulomb interaction, supporting a fully electronically driven isostructural insulator-to-metal transition. We thus conclude that the ultrafast band structure renormalization is caused by photoexcitation of carriers from localized V 3d valence states, strongly changing the screening before significant hot-carrier relaxation or ionic motion has occurred.

  11. .VO2max is not altered by self-pacing during incremental exercise.

    PubMed

    Chidnok, Weerapong; Dimenna, Fred J; Bailey, Stephen J; Burnley, Mark; Wilkerson, Daryl P; Vanhatalo, Anni; Jones, Andrew M

    2013-02-01

    We tested the hypothesis that incremental cycling to exhaustion that is paced using clamps of the rating of perceived exertion (RPE) elicits higher .VO2max values compared to a conventional ramp incremental protocol when test duration is matched. Seven males completed three incremental tests to exhaustion to measure .VO2max. The incremental protocols were of similar duration and included: a ramp test at 30 W min(-1) with constant cadence (RAMP1); a ramp test at 30 W min(-1) with cadence free to fluctuate according to subject preference (RAMP2); and a self-paced incremental test in which the power output was selected by the subject according to prescribed increments in RPE (SPT). The subjects also completed a .VO2max 'verification' test at a fixed high-intensity power output and a 3-min all-out test. No difference was found for .VO2max between the incremental protocols (RAMP1 = 4.33 ± 0.60 L min(-1); RAMP2 = 4.31 ± 0.62 L min(-1); SPT = 4.36 ± 0.59 L min(-1); P > 0.05) nor between the incremental protocols and the peak.VO2max measured during the 3-min all-out test (4.33 ± 0.68 L min(-1)) or the .VO2max measured in the verification test (4.32 ± 0.69 L min(-1)). The integrated electromyogram, blood lactate concentration, heart rate and minute ventilation at exhaustion were not different (P > 0.05) between the incremental protocols. In conclusion, when test duration is matched, SPT does not elicit a higher .VO2max compared to conventional incremental protocols. The striking similarity of .VO2max measured across an array of exercise protocols indicates that there are physiological limits to the attainment of .VO2max that cannot be exceeded by self-pacing.

  12. Estimated V(O2)max from the rockport walk test on a nonmotorized curved treadmill.

    PubMed

    Seneli, Rhiannon M; Ebersole, Kyle T; OʼConnor, Kristian M; Snyder, Ann C

    2013-12-01

    The Rockport Walk Test (RWT) is a 1-mile walk used to estimate the maximal volume of oxygen uptake (V(O2)max). The purpose of this study was to validate the RWT on a nonmotorized curved treadmill (CT). Twenty-three healthy adults (10 females; 19-44 years old) participated. One trial of the RWT was performed on a measured indoor track (RWTO) and another on the CT (RWTC) on different days in randomized order. Heart rate (HR) and completion time were used to calculate V(O2)max using 6 different general and gender specific equations from previous research. Subjects also performed a treadmill graded exercise test (GXT), which was used as the criterion measure for V(O2)max. Completion times and HR between the 2 RWT were compared using dependent t-tests. Estimated V(O2)max values were compared between the RWTC, RWTO, and GXT through repeated measures analysis of variance, Pearson's correlations (r), and Bland-Altman's plots. There was no difference between completion times for the RWTO and RWTC but HRs were significantly higher with RWTC. When the same equation was applied to the RWTO and RWTC, there were no similar results. All V(O2)max estimations were different from observed V(O2)max except for the estimation from the relative general Kline et al. equation on the RWTO. Despite high correlations (r = 0.75-0.91), the RWTC underestimated V(O2)max. The RWTC underestimates V(O2)max but may be beneficial if a new equation were created specifically for the CT. With appropriate equations for the CT, the RWTC would provide an alternate form of V(O2)max testing.

  13. Lithium-inserted vanadium dioxide (LixVO2) thin films

    NASA Astrophysics Data System (ADS)

    Khan, Mohammad S. R.

    1996-04-01

    Thermochromic switching between a low-temperature and high-temperature less transparent state is possible in thin films based on vanadium dioxide (VO2). The critical temperature Tc at which the transition takes place in VO2 is on the order of 68 degrees Celsius which can be depressed towards a comfortable temperature by several techniques, including dopants. Dopants can be inserted by electrochemical means. This work is an exploratory study of the electrochromism of LixVO2 with a view to 'smart window' applications. Thin films of LixVO2 (0 less than or equal to x less than or equal to 0.43) were made by reactive sputtering and annealing electrolyte of LiClO4 and propylene carbonate. A maximum lithium content of x equals 0.43 was accomplished. Optical spectral response at wavelength pertinent to solar radiation was reported. Lithium insertion increased the transmittance gradually and reversibly i.e. LixVO2 showed electrochromism and bleached under Li insertion. LixVO2 also showed thermochroism, although to a smaller degree than VO2 and was most transparent at low temperature. Temperature- dependent electrical conductivity and thermoelectric power measurements were also performed. A conductivity transition by approximately 3 orders of magnitude was seen at approximately 60 degrees Celsius in VO2. This transition decreased in proportion with the amount of Li intercalation and was less than one order of magnitude in Li0.43VO2. Lithiation also decreased Tc by a few degrees Celsius. The thermoelectric power showed a well defined increase when Tc was exceeded.

  14. Time at or near VO2max during continuous and intermittent running. A review with special reference to considerations for the optimisation of training protocols to elicit the longest time at or near VO2max.

    PubMed

    Midgley, A W; Mc Naughton, L R

    2006-03-01

    Several authors have suggested that training at or near VO2max (i.e. > or = 95% VO2max) is the most effective training intensity to enhance VO2max and that for highly trained endurance athletes, training at or near VO2max may be necessary to increase it further. Consequently, there is an interest in characterising training protocols that allow the longest time at or near VO2max (T@VO2max). Intermittent running protocols have been found to be more effective than continuous protocols for increasing T@VO2max. Intermittent protocols can be manipulated by altering the warm-up intensity and timing, work and relief interval velocity and duration, amplitude, interval number per set, and the number of sets performed. To increase T@VO2max it is recommended that work interval intensity should generally range between 90% and 105% vVO2max and relief interval intensity between 50% vVO2max and the lactate threshold velocity. Work and relief interval durations should be between 15 and 30 seconds. The warm-up period prior to the intermittent protocol should be about 10 to 15 minutes in duration at 1 or 2 km x h(-1) below the lactate threshold velocity, with no gap between the warm-up and the intermittent protocol. When designing intermittent training protocols for the enhancement of VO2max, the simultaneous enhancement of other physiological performance determinants should also be considered. Further experimental research is required to identify the specific physiological responses and adaptations to various intermittent running protocols that are designed to elicit the longest time at or near VO2max, before recommendations can be given to competitive endurance runners.

  15. Synthesis and Electrochemical Properties of Nano-VO2 (B).

    PubMed

    Yang, Yun; Lu, Yong; Wang, Wei; Feng, Chuanqi; Yang, Shuijin

    2016-03-01

    The nano-VO2 (B) has been self-assembly synthesized by hydrothermal method using different templates, which may give them some interesting properties. The as-prepared samples were characterized by X-ray powder diffraction (XRD) and scanning electron microscopy (SEM). The electrochemical properties of the samples were investigated. The results show that the hexadecyltrimethyl ammonium bromide (CTAB) (soft template) was used to obtain the VO2 (B1) nanobelts. The flake graphite (hard template) was taken to get the VO2 (B2) nanosheets. The VO2 (B1) nanobelts have higher initial capacity to compare with VO2 (B2). But the VO2 (B2) nanosheets showed better cycling performance than that of VO2 (B1) nanobelts. The nano VO2 (B2) is a promising anode material for lithium ion battery application.

  16. VO2 max in an Indian population: a study to understand the role of factors determining VO2 max.

    PubMed

    Nitin, Y M; Sucharita, S; Madhura, M; Thomas, T; Sandhya, T A

    2013-01-01

    VO2 max is the maximum amount of oxygen a person can consume and the value does not change despite an increase in workload. There is lack of data evaluating the impact of factors, which could affect VO2 max measurement, particularly in Indian population. The objectives of the present study were (i) to estimate VO2 max in a young healthy Indian population and to compare it with available prediction equations for Indian population (ii) to correlate time to achieve VO2 max with the relative VO2 max (iii) to assess the factors affecting the time to achieve VO2 max measurement (body composition and physical activity level). Twenty healthy adult males (18-30 years) underwent detailed anthropometry, physical activity level and modified Bruce protocol for VO2 max assessment. Breath by breath VO2, VCO2, oxygen saturation, heart rate, blood pressure were measured continuously and following exercise protocol. There was an internal validity between the estimated VO2 max and the maximum heart rate (MHR) (r = 0.51, P < 0.05). Respiratory rate and tidal volume significantly correlated with VO2 max P < 0.01). Linear regression analysis indicated physical activity level (PAL) was a strong predictor of time to reach VO2 max. Out of the 3 prediction equations computed to estimate VO2 max, 2 equations significantly overestimated VO2 max. In Conclusion, physical activity level emerged to be a strong predictor of time to VO2 max. Time to achieve VO2 max is an important factor to be considered when determining VO2 max. There was an overestimation in the VO2 max values derived from predicted equations.

  17. 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

  18. Size and composition-controlled fabrication of VO2 nanocrystals by terminated cluster growth

    SciTech Connect

    Anders, Andre; Slack, Jonathan

    2013-05-14

    A physical vapor deposition-based route for the fabrication of VO2 nanoparticles is demonstrated, consisting of reactive sputtering and vapor condensation at elevated pressures. The oxidation of vanadium atoms is an efficient heterogeneous nucleation method, leading to high nanoparticle throughtput. Fine control of the nanoparticle size and composition is obtained. Post growth annealing leads to crystalline VO2 nanoparticles with optimum thermocromic and plasmonic properties.

  19. Effect of protocol on determination of velocity at VO2 max and on its time to exhaustion.

    PubMed

    Billat, V L; Hill, D W; Pinoteau, J; Petit, B; Koralsztein, J P

    1996-01-01

    The velocity associated with the achievement of VO2 max during an incremental treadmill test (v VO2 max) has been reported to be an indicator of performance in middle distance running events. Previous study has shown the reproducibility of the time to exhaustion (time limit: tlim) at v VO2 max performed by well-trained males in the same condition at one week of interval (Billat et al., 1994b). It is essential in studies involving tlim at v VO2 max that the v VO2 max be precisely determined, or else the measured tlim will be meaningless. The purpose of this study was to examine the influence of the stage duration and velocity incrementation on the velocity at VO2 max and, consequently, on the two times to exhaustion (tlim) associated with the two v VO2 max generated by the two protocols. v VO2 max was determined in 15 trained male endurance athletes as the lowest speed at which VO2 max was attained in speed-incremented 0%-slope treadmill tests. For one test, increments were 1.0 km.h-1 and stages were 2 min in duration; for the other test, increments were 0.5 km.h-1 and stages were 1 min in duration. Results of paired means t-tests revealed no difference in v VO2 max obtained using the two protocols. v VO2 max was 20.7 +/- 1.0 km.h-1 with the 1.0 km.h-1 x 2 min protocol and 20.8 +/- 0.9 km.h-1 with the 0.5 km.h-1 x 1 min protocol. In addition, VO2, VCO2, VE, VE/VO2 and respiratory exchange ratio at the submaximal intensities that were common to both protocols (e.g., 17.0 km.h-1, 18.0 km.h-1, 19.0 km.h-1, 20.0 km.h-1) did not differ. Times to exhaustion at the two v VO2 max demonstrated a high degree of inter-individual variability (coefficients of variation were 35% and 45%) but did not differ (345 +/- 120 s versus 373 +/- 169 s). These results demonstrated that small changes in protocol have no significant impact on the value of v VO2 max and in consequence on tlim v VO2 max.

  20. Modification of Mott phase transition characteristics in VO2@TiO2 core/shell nanostructures by misfit-strained heteroepitaxy.

    PubMed

    Li, Yamei; Ji, Shidong; Gao, Yanfeng; Luo, Hongjie; Jin, Ping

    2013-07-24

    Vanadium dioxide (VO2) is a key material for thermochromic smart windows that can respond to environmental temperature and modulate near-infrared irradiation by changing from a transparent state at low temperature to a more reflective state at high temperature, while maintaining visible transmittance. Here, we demonstrate for the first time that the Mott phase transition characteristics in VO2 nanoparticles can be remarkably modified by misfit strains occurring at the epitaxial interface between VO2 and the anatase TiO2 of VO2/TiO2 core-shell particles. The heteroepitaxial growth of the as-synthesized particles followed an unprecedented orientation relationship, and an epitaxial growth mechanism is proposed to explain this behavior. A relatively small theoretical coherent misfit (3-11%) and a moderate heating rate (20 °C·min(-1)) in the preparation of the core-shell structure were critically important from the thermodynamic and kinetic perspectives, respectively. The misfit-induced interfacial strain along the uniaxial cR axis increased the transition temperatures, especially on the cooling portion of the heating-cooling cycle, leading to a notably reduced transition hysteresis loop width (from 23.5 to 12.0 °C). Moreover, the optical band gap was also engineered by the interfacial effect. Such a reduced hysteresis showed a benefit for enhancing a rapid response for energy saving thermochromic smart windows.

  1. Epitaxial growth and electronic structure of oxyhydride SrVO2H thin films

    NASA Astrophysics Data System (ADS)

    Katayama, Tsukasa; Chikamatsu, Akira; Yamada, Keisuke; Shigematsu, Kei; Onozuka, Tomoya; Minohara, Makoto; Kumigashira, Hiroshi; Ikenaga, Eiji; Hasegawa, Tetsuya

    2016-08-01

    Oxyhydride SrVO2H epitaxial thin films were fabricated on SrTiO3 substrates via topotactic hydridation of oxide SrVO3 films using CaH2. Structural and composition analyses suggested that the SrVO2H film possessed one-dimensionally ordered V-H--V bonds along the out-of-plane direction. The synthesis temperature could be lowered by reducing the film thickness, and the SrVO2H film was reversible to SrVO3 by oxidation through annealing in air. Photoemission and X-ray absorption spectroscopy measurements revealed the V3+ valence state in the SrVO2H film, indicating that the hydrogen existed as hydride. Furthermore, the electronic density of states was highly suppressed at the Fermi energy, consistent with the prediction that tetragonal distortion induces metal to insulation transition.

  2. Reversible phase modulation and hydrogen storage in multivalent VO2 epitaxial thin films

    NASA Astrophysics Data System (ADS)

    Yoon, Hyojin; Choi, Minseok; Lim, Tae-Won; Kwon, Hyunah; Ihm, Kyuwook; Kim, Jong Kyu; Choi, Si-Young; Son, Junwoo

    2016-10-01

    Hydrogen, the smallest and the lightest atomic element, is reversibly incorporated into interstitial sites in vanadium dioxide (VO2), a correlated oxide with a 3d1 electronic configuration, and induces electronic phase modulation. It is widely reported that low hydrogen concentrations stabilize the metallic phase, but the understanding of hydrogen in the high doping regime is limited. Here, we demonstrate that as many as two hydrogen atoms can be incorporated into each VO2 unit cell, and that hydrogen is reversibly absorbed into, and released from, VO2 without destroying its lattice framework. This hydrogenation process allows us to elucidate electronic phase modulation of vanadium oxyhydride, demonstrating two-step insulator (VO2)-metal (HxVO2)-insulator (HVO2) phase modulation during inter-integer d-band filling. Our finding suggests the possibility of reversible and dynamic control of topotactic phase modulation in VO2 and opens up the potential application in proton-based Mottronics and novel hydrogen storage.

  3. Transmission of reactive pulsed laser deposited VO2 films in the THz domain

    NASA Astrophysics Data System (ADS)

    Émond, Nicolas; Hendaoui, Ali; Ibrahim, Akram; Al-Naib, Ibraheem; Ozaki, Tsuneyuki; Chaker, Mohamed

    2016-08-01

    This work reports on the characteristics of the insulator-to-metal transition (IMT) of reactive pulsed laser deposited vanadium dioxide (VO2) films in the terahertz (THz) frequency range, namely the transition temperature TIMT, the amplitude contrast of the THz transmission over the IMT ΔA, the transition sharpness ΔT and the hysteresis width ΔH. XRD analysis shows the sole formation of VO2 monoclinic structure with an enhancement of (011) preferential orientation when varying the O2 pressure (PO2) during the deposition process from 2 to 25 mTorr. THz transmission measurements as a function of temperature reveal that VO2 films obtained at low PO2 exhibit low TIMT, large ΔA, and narrow ΔH. Increasing PO2 results in VO2 films with higher TIMT, smaller ΔA, broader ΔH and asymmetric hysteresis loop. The good control of the VO2 IMT features in the THz domain could be further exploited for the development of advanced smart devices, such as ultrafast switches, modulators, memories and sensors.

  4. No Effect of Acute and 6-Day Nitrate Supplementation on VO2 and Time-Trial Performance in Highly Trained Cyclists.

    PubMed

    Nyakayiru, Jean M; Jonvik, Kristin L; Pinckaers, Philippe J M; Senden, Joan; van Loon, Luc J C; Verdijk, Lex B

    2017-02-01

    While the majority of studies reporting ergogenic effects of dietary nitrate have used a multiday supplementation protocol, some studies suggest that a single dose of dietary nitrate before exercise can also improve subsequent performance. We aimed to compare the impact of acute and 6-day sodium nitrate supplementation on oxygen uptake (V̇O2) and time-trial performance in trained cyclists. Using a randomized, double-blind, cross-over design, 17 male cyclists (25 ± 4 y, V̇O2peak 65 ± 4 ml·kg(-1)·min(-1), Wmax 411 ± 35 W) were subjected to 3 different trials; 5 days placebo and 1 day sodium nitrate supplementation (1-DAY); 6 days sodium nitrate supplementation (6-DAY); 6 days placebo supplementation (PLA). Nitrate was administered as 1097 mg sodium nitrate providing 800 mg (~12.9 mmol) nitrate per day. Three hours after ingestion of the last supplemental bolus, indirect calorimetry was performed while subjects performed 30 min of exercise at 45% Wmax and 30 min at 65% Wmax on a cycle ergometer, followed by a 10 km time-trial. Immediately before exercise, plasma [nitrate] and [nitrite] increased to a similar extent during the 6-DAY and 1-DAY trial, but not with PLA (plasma nitrite: 501 ± 205, 553 ± 278, and 239 ± 74 nM, respectively; p < .001). No differences were observed between interventions in V̇O2 during submaximal exercise, or in time to complete the time-trial (6-DAY: 1004 ± 61, 1-DAY: 1022 ± 72, PLA: 1017 ± 71 s; p = .28). We conclude that both acute and 6-days of sodium nitrate supplementation do not alter V̇O2 during submaximal exercise or improve time-trial performance in highly trained cyclists, despite increasing plasma [nitrate] and [nitrite].

  5. Ultrafast dynamics during the photoinduced phase transition in VO2

    NASA Astrophysics Data System (ADS)

    Wegkamp, Daniel; Stähler, Julia

    2015-12-01

    The phase transition of VO2 from a monoclinic insulator to a rutile metal, which occurs thermally at TC = 340 K, can also be driven by strong photoexcitation. The ultrafast dynamics during this photoinduced phase transition (PIPT) have attracted great scientific attention for decades, as this approach promises to answer the question of whether the insulator-to-metal (IMT) transition is caused by electronic or crystallographic processes through disentanglement of the different contributions in the time domain. We review our recent results achieved by femtosecond time-resolved photoelectron, optical, and coherent phonon spectroscopy and discuss them within the framework of a selection of latest, complementary studies of the ultrafast PIPT in VO2. We show that the population change of electrons and holes caused by photoexcitation launches a highly non-equilibrium plasma phase characterized by enhanced screening due to quasi-free carriers and followed by two branches of non-equilibrium dynamics: (i) an instantaneous (within the time resolution) collapse of the insulating gap that precedes charge carrier relaxation and significant ionic motion and (ii) an instantaneous lattice potential symmetry change that represents the onset of the crystallographic phase transition through ionic motion on longer timescales. We discuss the interconnection between these two non-thermal pathways with particular focus on the meaning of the critical fluence of the PIPT in different types of experiments. Based on this, we conclude that the PIPT threshold identified in optical experiments is most probably determined by the excitation density required to drive the lattice potential change rather than the IMT. These considerations suggest that the IMT can be driven by weaker excitation, predicting a transiently metallic, monoclinic state of VO2 that is not stabilized by the non-thermal structural transition and, thus, decays on ultrafast timescales.

  6. Tuning the work function of VO2(1 0 0) surface by Ag adsorption and incorporation: Insights from first-principles calculations

    NASA Astrophysics Data System (ADS)

    Chen, Lanli; Wang, Xiaofang; Shi, Siqi; Cui, Yuanyuan; Luo, Hongjie; Gao, Yanfeng

    2016-03-01

    VO2 is an attractive material for application to thermochromic optoelectronic devices such as smart windows, and Ag/VO2 double-layered structure can effectively decrease the phase transition temperature (Tc) of VO2 thin film, which is very important for practical application of VO2. Previous works has shown that the decrease in phase transition temperature (Tc) seems to be relevant with the work function of VO2 in Ag/VO2 double-layered thin film, although the underlying mechanism of tuning its Tc by Ag incorporation and adsorption on the VO2(1 0 0) surface has been rarely investigated. Our first-principles calculations reveal that the adsorption of Ag atoms on the VO2(1 0 0) surface rather than incorporation of Ag exhibits a lower work function, which is ascribed to an integrated effect of charge transfer from Ag to VO2(1 0 0) surface and enhanced surface dipole moment. The results suggest that the decrease in work function of VO2 with Ag adsorption favors the reduction in Tc. The current findings are helpful to understand the fundamental mechanism for yielding high-efficiency VO2-based optoelectronic devices.

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

    PubMed

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

    2016-12-15

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2016-12-01

    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.

  9. Hydrogen-doping induced reduction in the phase transition temperature of VO2: a first-principles study.

    PubMed

    Cui, Yuanyuan; Shi, Siqi; Chen, Lanli; Luo, Hongjie; Gao, Yanfeng

    2015-08-28

    VO2 is a promising thermochromic material that can intelligently control the transmittance of sunlight in the near-infrared region in response to temperature change, although the high phase transition temperature (Tc) of 340 K restricts its wide application. Our first-principles calculations show that hydrogen is an efficient dopant which can stabilize the metallic VO2 phase at ambient temperature through reducing Tc by 38 K/at% H. The reduction in Tc is coupled with the changes in atomic and electronic structures, i.e., the V-V chains feature the dimerization characteristics in H-doped VO2(R) and the V-O bonds become less ionic due to the formation of a typical H-O covalent bond. In addition, hydrogen-doped VO2 is more sensitive to external strain as compared with pure VO2, implying that Tc can be further regulated through a combination of H-doping and strain.

  10. 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

  11. The effects of uphill vs. level-grade high-intensity interval training on VO2max, Vmax, V(LT), and Tmax in well-trained distance runners.

    PubMed

    Ferley, Derek D; Osborn, Roy W; Vukovich, Matthew D

    2013-06-01

    Uphill running represents a frequently used and often prescribed training tactic in the development of competitive distance runners but remains largely uninvestigated and unsubstantiated as a training modality. The purpose of this investigation included documenting the effects of uphill interval training compared with level-grade interval training on maximal oxygen consumption (VO2max), the running speed associated with VO2max (Vmax), the running speed associated with lactate threshold (V(LT)), and the duration for which Vmax can be sustained (Tmax) in well-trained distance runners. Thirty-two well-trained distance runners (age, 27.4 ± 3.8 years; body mass, 64.8 ± 8.9 kg; height, 173.6 ± 6.4 cm; and VO2max, 60.9 ± 8.5 ml·min(-1)·kg(-1)) received assignment to an uphill interval training group (G(Hill) = 12), level-grade interval training group (G(Flat) = 12), or control group (G(Con) = 8). G(Hill) and G(Flat) completed 12 interval and 12 continuous running sessions over 6 weeks, whereas G(Con) maintained their normal training routine. Pre- and posttest measures of VO2max, Vmax, V(LT), and Tmax were used to assess performance. A 3 × 2 repeated measures analysis of variance was performed for each dependent variable and revealed a significant difference in Tmax in both G(Hill) and G(Flat) (p < 0.05). With regard to running performance, the results indicate that both uphill and level-grade interval training can induce significant improvements in a run-to-exhaustion test in well-trained runners at the speed associated with VO2max but that traditional level-grade training produces greater gains.

  12. Electrical Switching in Semiconductor-Metal Self-Assembled VO2 Disordered Metamaterial Coatings

    NASA Astrophysics Data System (ADS)

    Kumar, Sunil; Maury, Francis; Bahlawane, Naoufal

    2016-11-01

    As a strongly correlated metal oxide, VO2 inspires several highly technological applications. The challenging reliable wafer-scale synthesis of high quality polycrystalline VO2 coatings is demonstrated on 4” Si taking advantage of the oxidative sintering of chemically vapor deposited VO2 films. This approach results in films with a semiconductor-metal transition (SMT) quality approaching that of the epitaxial counterpart. SMT occurs with an abrupt electrical resistivity change exceeding three orders of magnitude with a narrow hysteresis width. Spatially resolved infrared and Raman analyses evidence the self-assembly of VO2 disordered metamaterial, compresing monoclinic (M1 and M2) and rutile (R) domains, at the transition temperature region. The M2 mediation of the M1-R transition is spatially confined and related to the localized strain-stabilization of the M2 phase. The presence of the M2 phase is supposed to play a role as a minor semiconducting phase far above the SMT temperature. In terms of application, we show that the VO2 disordered self-assembly of M and R phases is highly stable and can be thermally triggered with high precision using short heating or cooling pulses with adjusted strengths. Such a control enables an accurate and tunable thermal control of the electrical switching.

  13. Electrical Switching in Semiconductor-Metal Self-Assembled VO2 Disordered Metamaterial Coatings

    PubMed Central

    Kumar, Sunil; Maury, Francis; Bahlawane, Naoufal

    2016-01-01

    As a strongly correlated metal oxide, VO2 inspires several highly technological applications. The challenging reliable wafer-scale synthesis of high quality polycrystalline VO2 coatings is demonstrated on 4” Si taking advantage of the oxidative sintering of chemically vapor deposited VO2 films. This approach results in films with a semiconductor-metal transition (SMT) quality approaching that of the epitaxial counterpart. SMT occurs with an abrupt electrical resistivity change exceeding three orders of magnitude with a narrow hysteresis width. Spatially resolved infrared and Raman analyses evidence the self-assembly of VO2 disordered metamaterial, compresing monoclinic (M1 and M2) and rutile (R) domains, at the transition temperature region. The M2 mediation of the M1-R transition is spatially confined and related to the localized strain-stabilization of the M2 phase. The presence of the M2 phase is supposed to play a role as a minor semiconducting phase far above the SMT temperature. In terms of application, we show that the VO2 disordered self-assembly of M and R phases is highly stable and can be thermally triggered with high precision using short heating or cooling pulses with adjusted strengths. Such a control enables an accurate and tunable thermal control of the electrical switching. PMID:27883052

  14. 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

  15. VO2 kinetics during heavy and severe exercise in swimming.

    PubMed

    Pessoa Filho, D M; Alves, F B; Reis, J F; Greco, C C; Denadai, B S

    2012-09-01

    The purpose of this study was to describe the VO2 kinetics above and below respiratory compensation point (RCP) during swimming. After determination of the gas-exchange threshold (GET), RCP and VO(2max), 9 well-trained swimmers (21.0 ± 7.1 year, VO(2max)=57.9 ± 5.1 ml.kg (- 1).min (- 1)), completed a series of "square-wave" swimming transitions to a speed corresponding to 2.5% below (S - 2.5%) and 2.5% above (S+2.5%) the speed observed at RCP for the determination of pulmonary VO2 kinetics. The trial below (~2.7%) and above RCP (~2%) was performed at 1.28 ± 0.05 m.s (- 1) (76.5 ± 6.3% VO(2max)) and 1.34 0.05 m.s (- 1) (91.3 ± 4.0% VO(2max)), respectively. The time constant of the primary component was not different between the trials below (17.8 ± 5.9 s) and above RCP (16.5 ± 5.1 s). The amplitude of the VO(2)slow component was similar between the exercise intensities performed around RCP (S - 2.5%=329.2 ± 152.6 ml.min (- 1) vs. S+2.5%=313.7 ± 285.2 ml.min (- 1)), but VO(2max) was attained only during trial performed above RCP (S-2.5%=91.4 ± 5.9% VO(2max) vs. S+2.5%=103.0 ± 8.2% VO(2max)). Thus, similar to the critical power during cycling exercise, the RCP appears to represent a physiological boundary that dictates whether VO(2) kinetics is characteristic of heavy- or severe-intensity exercise during swimming.

  16. Leg strength and the VO2 max of older men.

    PubMed

    Lovell, D; Cuneo, R; Delphinus, E; Gass, G

    2011-04-01

    The purpose of the study was to determine if leg strength limits VO2 max and the ability to reach a plateau during VO2 max test in older men during cycle ergometry. Men aged 70-80 years were randomly selected into a strength training (ST, n=12) 3 times weekly for 16 weeks, followed by 4 weeks detraining or a non-training control group (C, n=12). Leg strength and VO2 max were assessed every 4 weeks for 20 weeks; body composition and cardiac function were assessed before and after 16 weeks training and after 4 weeks detraining. Leg strength, upper leg muscle mass (ULMM), arterial-venous O2 difference (a-v O2 difference) and VO2 max increased in the ST group (95±0.6%, 7±0.7%. 6.2±0.5% and 8±0.8%, respectively; P<0.05) after 16 weeks training. After 4 weeks detraining, gains in ULMM (50%) and strength (75%) were retained, but VO2 max and a-v O2 difference returned to pre-training levels. There was no change in the ability of the participants to reach a plateau during VO2 max testing over the 20-week study. These findings indicate that leg strength may not limit either VO2 max or the ability to plateau during VO2 max tests in older men during cycle ergometry.

  17. CORP: Measurement of the Maximum Oxygen Uptake (VO2max): VO2peak is no longer acceptable.

    PubMed

    Poole, David C; Jones, Andrew M

    2017-02-02

    The maximum rate of VO2 uptake (i.e., VO2max), as measured during large muscle mass exercise such as cycling or running, is widely considered to be the gold standard measurement of integrated cardiopulmonary-muscle oxidative function. The development of rapid-response gas analyzers, enabling measurement of breath-by-breath pulmonary gas exchange, has led to replacement of the discontinuous progressive maximal exercise test (that produced an unambiguous VO2-work rate plateau definitive for VO2max) with the rapidly-incremented or ramp testing protocol. Whilst this expedient is more suitable for clinical and experimental investigations and enables measurement of the gas exchange threshold, exercise efficiency, and VO2 kinetics, a VO2-work rate plateau is not an obligatory outcome. This shortcoming has led to investigators resorting to so-called secondary criteria such as respiratory exchange ratio, maximal heart rate and/or maximal blood lactate concentration, the acceptable values of which may be selected arbitrarily and result in grossly inaccurate VO2max determination. Whereas this may not be an overriding concern in young, healthy subjects with experience of performing exercise to volitional exhaustion, exercise test naïve subjects, patient populations and less motivated subjects may stop exercising before their VO2max is reached. When VO2max is a or the criterion outcome of the investigation this represents a major experimental design issue. This CORP presents the rationale for incorporation of a second, constant-work rate test performed at 105-110% of the work rate achieved on the initial ramp test to resolve the classic VO2-work rate plateau that is the unambiguous validation of VO2max. The broad utility of this procedure has been established for children, adults of varying fitness, obese individuals and patient populations.

  18. Nanoporous thermochromic VO(2) films with low optical constants, enhanced luminous transmittance and thermochromic properties.

    PubMed

    Kang, Litao; Gao, Yanfeng; Luo, Hongjie; Chen, Zhang; Du, Jin; Zhang, Zongtao

    2011-02-01

    Nanoporous thermochromic VO(2) films with low optical constants and tunable thicknesses have been prepared by polymer-assisted deposition. The film porosity and thickness change the interference relationship of light reflected from the film-substrate and the air-film interfaces, strongly influencing the optical properties of these VO(2) films. Our optimized single-layered VO(2) films exhibit high integrated luminous transmittance (T(lum,l) = 43.3%, T(lum,h) = 39.9%) and solar modulation (ΔT(sol) = 14.1%, from T(sol,l) = 42.9% to T(sol,h) = 28.8%), which are comparable to those of five-layered TiO(2)/VO(2)/TiO(2)/VO(2)/TiO(2) films (T(lum,l) = 45%, T(lum,h) = 42% and ΔT(sol) = 12%, from T(sol,l) = 52% to T(sol,h) = 40%, from Phys. Status Solidi A2009, 206, 2155-2160.). Optical calculations suggest that the performance could be further improved by increasing the porosity.

  19. A new submaximal cycle ergometer test for prediction of VO2max.

    PubMed

    Ekblom-Bak, E; Björkman, F; Hellenius, M-L; Ekblom, B

    2014-04-01

    Maximal oxygen uptake (VO2max) is an important, independent predictor of cardiovascular health and mortality. Despite this, it is rarely measured in clinical practice. The aim of this study was to create and evaluate a submaximal cycle ergometry test based on change in heart rate (HR) between a lower standard work rate and an individually chosen higher work rate. In a mixed population (n = 143) with regard to sex (55% women), age (21-65 years), and activity status (inactive to highly active), a model included change in HR per unit change in power, sex, and age for the best estimate of VO2max. The association between estimated and observed VO2max for the mixed sample was r = 0.91, standard error of estimate = 0.302 L/min, and mean measured VO2max = 3.23 L/min. The corresponding coefficient of variation was 9.3%, a significantly improved precision compared with one of the most commonly used submaximal exercise tests, the Åstrand test, which in the present study was estimated to be 18.1%. Test-retest reliability analysis over 1 week revealed no mean difference in the estimated VO2max (-0.02 L/min, 95% confidence interval: -0.07-0.03). The new test is low-risk, easily administered, and valid for a wide capacity range, and is therefore suitable in situations as health evaluations in the general population.

  20. Hybrid metamaterial switching for manipulating chirality based on VO2 phase transition

    PubMed Central

    Lv, T. T.; Li, Y. X.; Ma, H. F.; Zhu, Z.; Li, Z. P.; Guan, C. Y.; Shi, J. H.; Zhang, H.; Cui, T. J.

    2016-01-01

    Polarization manipulations of electromagnetic waves can be obtained by chiral and anisotropic metamaterials routinely, but the dynamic and high-efficiency modulations of chiral properties still remain challenging at the terahertz range. Here, we theoretically demonstrate a new scheme for realizing thermal-controlled chirality using a hybrid terahertz metamaterial with embedded vanadium dioxide (VO2) films. The phase transition of VO2 films in 90° twisted E-shaped resonators enables high-efficiency thermal modulation of linear polarization conversion. The asymmetric transmission of linearly polarized wave and circular dichroism simultaneously exhibit a pronounced switching effect dictated by temperature-controlled conductivity of VO2 inclusions. The proposed hybrid metamaterial design opens exciting possibilities to achieve dynamic modulation of terahertz waves and further develop tunable terahertz polarization devices. PMID:27000427

  1. The identification of defect structures for oxygen pressure dependent VO2 crystal films

    NASA Astrophysics Data System (ADS)

    Fan, Shaojuan; Fan, Lele; Li, Qiang; Liu, Jiandang; Ye, Bangjiao

    2014-12-01

    The defect structures of vanadium dioxide (VO2) films prepared at different oxygen pressures have been investigated using positron annihilation spectroscopy for the first time. It is found that the concentration of vanadium vacancies is not dependent on oxygen pressure for the range studied, implying that at high oxygen pressure, the point defects which have an effect on transition properties are O-interstitials. The variations of oxygen pressures are more probable to cause changes of the type or concentration of oxygen related defects (such as O-interstitials or O-vacancies) and further influence the transition characters. No matter what kind of the defects they are, the localized point defects have a great impact on the metal-insulator phase transition (MIT) process and the corresponding influence mechanisms are discussed. In addition, the stability of the VO2 films is also studied. The present results are valuable for the achievement of VO2-based devices.

  2. Field Effect and Strongly Localized Carriers in the Metal-Insulator Transition Material VO(2).

    PubMed

    Martens, K; Jeong, J W; Aetukuri, N; Rettner, C; Shukla, N; Freeman, E; Esfahani, D N; Peeters, F M; Topuria, T; Rice, P M; Volodin, A; Douhard, B; Vandervorst, W; Samant, M G; Datta, S; Parkin, S S P

    2015-11-06

    The intrinsic field effect, the change in surface conductance with an applied transverse electric field, of prototypal strongly correlated VO(2) has remained elusive. Here we report its measurement enabled by epitaxial VO(2) and atomic layer deposited high-κ dielectrics. Oxygen migration, joule heating, and the linked field-induced phase transition are precluded. The field effect can be understood in terms of field-induced carriers with densities up to ∼5×10(13)  cm(-2) which are trongly localized, as shown by their low, thermally activated mobility (∼1×10(-3)  cm(2)/V s at 300 K). These carriers show behavior consistent with that of Holstein polarons and strongly impact the (opto)electronics of VO(2).

  3. Durability of VO2-based thin films at elevated temperature: Towards thermochromic fenestration

    NASA Astrophysics Data System (ADS)

    Ji, Yu-Xia; Niklasson, Gunnar A.; Granqvist, Claes G.

    2014-11-01

    An explorative study was performed on sputter-deposited thermochromic VO2 films with top coatings of Al oxide and Al nitride. The films were exposed to dry air at a high temperature. Bare 80-nm-thick VO2 films rapidly converted to non-thermochromic V2O5 under the chosen conditions. Al oxide top coatings protected the underlying VO2 films and, expectedly, increased film thickness yielded improved protection. Specifically, it was found that a 30-nm-thick sputter-deposited Al oxide top coating delayed the oxidation by more than one day upon heating at 300°C. The results demonstrate the importance of protective layers in thermochromic windows for practical application.

  4. Factors determining the time course of VO2(max) decay during bedrest: implications for VO2(max) limitation.

    PubMed

    Capelli, C; Antonutto, G; Kenfack, M Azabji; Cautero, M; Lador, F; Moia, C; Tam, E; Ferretti, G

    2006-09-01

    The aim of this study was to characterize the time course of maximal oxygen consumption VO2(max) changes during bedrests longer than 30 days, on the hypothesis that the decrease in VO2(max) tends to asymptote. On a total of 26 subjects who participated in one of three bedrest campaigns without countermeasures, lasting 14, 42 and 90 days, respectively, VO2(max) maximal cardiac output (Qmax) and maximal systemic O2 delivery (QaO2max) were measured. After all periods of HDT, VO2max, Qmax, and QaO2max were significantly lower than before. The VO2max decreased less than qmax after the two shortest bedrests, but its per cent decay was about 10% larger than that of Qmax after 90-day bedrest. The VO2max decrease after 90-day bedrest was larger than after 42- and 14-day bedrests, where it was similar. The Qmax and QaO2max declines after 90-day bedrest was equal to those after 14- and 42-day bedrest. The average daily rates of the VO2max, Qmax, and QaO2max decay during bedrest were less if the bedrest duration were longer, with the exception of that of VO2max in the longest bedrest. The asymptotic VO2max decay demonstrates the possibility that humans could keep working effectively even after an extremely long time in microgravity. Two components in the VO2max decrease were identified, which we postulate were related to cardiovascular deconditioning and to impairment of peripheral gas exchanges due to a possible muscle function deterioration.

  5. DC sputtered W-doped VO2 thermochromic thin films for smart windows with active solar control.

    PubMed

    Batista, C; Ribeiro, R; Carneiro, J; Teixeira, V

    2009-07-01

    Doped VO2 thin films, with different W at.% and consequent dissimilar transition temperatures, were successfully deposited onto SiO2-coated float-glass substrates by reactive direct current (DC) magnetron sputtering. Structural analyses have shown, for undoped films, single phase VO2(M) films with c-axis (002) direction as the preferred crystal orientation. The addition of tungsten into the VO2 solid solution favored the crystallization in the (011) direction which became dominant above a critical level of dopant concentration. The surface morphology of pure VO2 films revealed elongated grains oriented within the film plane. The doped films evidenced an increased tendency to be oriented out of the film plane which has resulted in increased roughness levels. The doping methodology associated with optimized processing conditions allowed the production of W-doped VO2 films with reduced transition temperatures, from 63 down to 28 degrees C, and maximum transmittances at the visible region ranging 40%. The relationship between tungsten content in the film and consequent transition temperature expressed a linear behavior.

  6. Tailoring of Luminous Transmittance upon Switching for Thermochromic VO2 Films by Thickness Control

    NASA Astrophysics Data System (ADS)

    Xu, Gang; Jin, Ping; Tazawa, Masato; Yoshimura, Kazuki

    2004-01-01

    The difference in luminous transmittance (Δ Tlum) upon switching of VO2 films strongly affects its solar controllability when used as a thermochromic window. It was found that Δ Tlum is controllable by film thickness. Optical calculation for a VO2 film on quartz glass revealed that the low-temperature semiconductor phase exhibits lower Tlum than the high-temperature metallic phase for thickness below 50 nm, while the relationship is reversed above 50 nm. The calculation was confirmed by film deposition and measurement. Maximum Δ Tlum is located near 80 nm. An enhanced Δ Tlum contributes largely to solar efficiency.

  7. 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 VO2) 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 VO2 in individuals with acute stroke. We hypothesized that (1) estimated prestroke peak VO2 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 VO2 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 VO2 was estimated using a nonexercise prediction equation. IGF-1 and IGFBP-3 levels were quantified using enzyme-linked immunoassay. Results Estimated prestroke peak VO2 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.

  8. Interaction of VO2+ ion with human serum transferrin and albumin.

    PubMed

    Sanna, Daniele; Garribba, Eugenio; Micera, Giovanni

    2009-04-01

    The complexation of VO(2+) ion with the high molecular mass components of the blood serum, human serum transferrin (hTf) and albumin (HSA), has been re-examined using EPR spectroscopy. In the case of transferrin, the results confirm those previously obtained, showing that VO(2+) ion occupies three different binding sites, A, B(1) and B(2), distinguishable in the X-band anisotropic spectrum recorded in D(2)O. With albumin the results show that a dinuclear complex (VO)(2)(d)HSA is formed in equimolar aqueous solutions or with an excess of protein; in the presence of an excess of VO(2+), the multinuclear complex (VO)(x)(m)HSA is the prevalent species, where x=5-6 indicates the equivalents of metal ion coordinated by HSA. The structure of the dinuclear species is discussed and the donor atoms involved in the metal coordination are proposed on the basis of the measured EPR parameters. Two different binding modes of albumin can be distinguished varying the pH, with only one species being present at the physiological value. The results show that the previously named "strong" site is not the N-terminal copper binding site, and some hypothesis on the metal coordination is discussed, with the (51)V A(z) values for the proposed donor sets obtained by DFT (density functional theory) calculations. Finally, preliminary results obtained in the ternary system VO(2+)/hTf/HSA are shown in order to determine the different binding strength of the two proteins. Due to the low VO(2+) concentration used, the recording of the EPR spectra through the repeated acquisition of the weak signals is essential to obtain a good signal to noise ratio in these systems.

  9. 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.

  10. 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.

  11. Percent utilization of VO2 max at 5-km competition velocity does not determine time performance at 5 km among elite distance runners.

    PubMed

    Støa, Eva Maria; Støren, Øyvind; Enoksen, Eystein; Ingjer, Frank

    2010-05-01

    The present study investigated to what extent maximum oxygen uptake (VO2 max) and fractional utilization (%VO2 max) in 5-km competition speed correlate with 5-km performance times among elite long distance runners. Eight elite long distance runners with 5-km performance times of 15.10 minutes ( +/- 32 seconds) were tested for VO2 max during an incremental protocol and for %VO2 max during an 8-minute treadmill test at the velocity representing their 5-km seasonal best performance time. There was no correlation between fractional utilization and 5-km performance. The study showed no significant difference between VO2 max obtained during an incremental VO2 max test and %VO2 max when running for 8 minutes at the runner's individual 5-km competition speed. The 5-km time was related to the runner's VO2 max even in a homogenous high-level performance group. In conclusion, the present study found no relationship between fractional utilization and 5-km performance time. Training aiming to increase %VO2 max may thus be of little or no importance in performance enhancement for competitions lasting up to approximately 20 minutes.

  12. Depressed phase transition in solution-grown VO2 nanostructures.

    PubMed

    Whittaker, Luisa; Jaye, Cherno; Fu, Zugen; Fischer, Daniel A; Banerjee, Sarbajit

    2009-07-01

    The first-order metal-insulator phase transition in VO(2) is characterized by an ultrafast several-orders-of-magnitude change in electrical conductivity and optical transmittance, which makes this material an attractive candidate for the fabrication of optical limiting elements, thermochromic coatings, and Mott field-effect transistors. Here, we demonstrate that the phase-transition temperature and hysteresis can be tuned by scaling VO(2) to nanoscale dimensions. A simple hydrothermal protocol yields anisotropic free-standing single-crystalline VO(2) nanostructures with a phase-transition temperature depressed to as low as 32 degrees C from 67 degrees C in the bulk. The observations here point to the importance of carefully controlling the stoichiometry and dimensions of VO(2) nanostructures to tune the phase transition in this system.

  13. ESR spectra of VO2+ ions adsorbed on calcium phosphates.

    PubMed

    Oniki, T; Doi, Y

    1983-07-01

    The ESR spectra of oxovanadium(IV) ions, (VO2+), adsorbed on hydroxyapatite(OHAp), fluorhydroxyapatite(FHAp), Mg-containing tricalcium phosphate(Mg-TCP), .octacalcium phosphate (OCP), dicalcium phosphate dihydrate (DCPD), and amorphous calcium phosphate(ACP) were measured at room temperature. The ESR parameters of VO2+ adsorbed on these compounds were slightly different from one another and accordingly, the ESR technique by use of VO2+ was useful for an analysis of the calcium phosphates precipitated from supersaturated solutions. The ESR parameters of VO2+ adsorbed on ACP and Mg-TCP were found to be very similar to each other, suggesting that ACP and TCP resemble each other in the structure of their crystal surfaces.

  14. Sequential electronic and structural transitions in VO2 observed using X-ray absorption spectromicroscopy.

    PubMed

    Kumar, Suhas; Strachan, John Paul; Pickett, Matthew D; Bratkovsky, Alexander; Nishi, Yoshio; Williams, R Stanley

    2014-11-26

    The popular dual electronic and structural transitions in VO2 are explored using X-ray absorption spectromicroscopy with high spatial and spectral resolutions. It is found that during both heating and cooling, the electronic transition always precedes the structural Peierls transition. Between the two transitions, there are intermediate states that are spectrally isolated here.

  15. Enhanced optical response of hybridized VO2/graphene films

    NASA Astrophysics Data System (ADS)

    Kim, Hyeongkeun; Kim, Yena; Kim, Taeyoung; Jang, A.-Rang; Jeong, Hu Young; Han, Seung Ho; Yoon, Dae Ho; Shin, Hyeon Suk; Bae, Dong Jae; Kim, Keun Soo; Yang, Woo Seok

    2013-03-01

    Application of graphene as transparent electrodes is an active research area due to its excellent electrical and optical properties. Vanadium dioxide (VO2) is an attractive material since it is a thermochromic material that undergoes a structural phase transition when heat is applied. The phase transition results in the change of electrical and optical characteristics. We report optical characteristics of hybrid materials of graphene and VO2. We observed a 12% improvement in infrared transmittance with VO2 films deposited on graphene sapphire substrates compared to that of bare sapphire substrates. We also found that the phase transition temperature decreases as the number of graphene layers on the substrates increases. In the case of VO2 films on the substrate that was coated with four layers of graphene, the mean phase transition temperature was lowered to ~56 °C.Application of graphene as transparent electrodes is an active research area due to its excellent electrical and optical properties. Vanadium dioxide (VO2) is an attractive material since it is a thermochromic material that undergoes a structural phase transition when heat is applied. The phase transition results in the change of electrical and optical characteristics. We report optical characteristics of hybrid materials of graphene and VO2. We observed a 12% improvement in infrared transmittance with VO2 films deposited on graphene sapphire substrates compared to that of bare sapphire substrates. We also found that the phase transition temperature decreases as the number of graphene layers on the substrates increases. In the case of VO2 films on the substrate that was coated with four layers of graphene, the mean phase transition temperature was lowered to ~56 °C. Electronic supplementary information (ESI) available. See DOI: 10.1039/c3nr34054f

  16. Cardiovascular factors explain genetic background differences in VO2max.

    PubMed

    Roy, Jane L P; Hunter, Gary R; Fernandez, Jose R; McCarthy, John P; Larson-Meyer, D Enette; Blaudeau, Tamilane E; Newcomer, Bradley R

    2006-01-01

    The purpose of this study was to further explore factors that may be related to ethnic differences in the maximum rate at which an individual can consume oxygen (VO2max) between 20 African American (AA) and 30 European American (EA) sedentary women who were matched for body weight (kg) and fat-free mass (FFM). VO2max (l/min) was determined during a graded treadmill exercise test. Submaximal steady-state heart rate and submaximal VO2 were determined at a treadmill speed of 1.3 m/sec and a 2.5% grade. Hemoglobin (Hb) was determined by the cyanide method, muscle oxidative capacity by 31P magnetic resonance spectroscopy (ADP time constant), and FFM (kg) by dual-energy x-ray absorptiometry. Genetic classification was self-reported, and in a subset of the sample (N = 32), the determinants of ethnicity were measured by African genetic admixture. AA women had significantly reduced VO2max, Hb levels, and muscle oxidative capacity (longer ADP time constants, P < or = 0.05) than EA women. Submaximal oxygen pulse (O2Psubmax), ADP time constant, Hb, and ethnic background were all significantly related to VO2max (ml/kg/min and ml/kg FFM/min, all P < or = 0.01). By multiple regression modeling, Hb, O2Psubmax, muscle oxidative capacity, and ethnicity were found to explain 61% and 57% of the variance of VO2max in ml/kg/min and ml/kg FFM/min, respectively. Muscle oxidative capacity and O2Psubmax were both significantly and independently related to VO2max in all three models (P < or = 0.05), whereas Hb and ethnicity were not. These results suggest that mitochondrial muscle oxidative capacity and oxygen delivery capabilities, as determined by O2Psubmax, account for most if not all of the ethnic differences in VO2max.

  17. Interference systems for wideband mid-IR VO2 mirrors

    NASA Astrophysics Data System (ADS)

    Danilov, Oleg B.; Konovalova, O. P.; Sidorov, Aleksandr I.; Shaganov, Igor I.

    1999-01-01

    We performed the analyze of principles of wide-band VO2- mirrors creation for mid-IR (2.5 - 12 micrometers ) laser radiation control. It was shown, that the choice of interference system of VO2-mirror makes possible to extend region of maximum reflection change up to 1 - 2 (mu) . Calculations and experimental results are presented for mirrors with dR/d>0 and <0 with the change of reflection coefficient from 0.1 up to 94 - 98%.

  18. Structural and electrical properties of large area epitaxial VO2 films grown by electron beam evaporation

    NASA Astrophysics Data System (ADS)

    Théry, V.; Boulle, A.; Crunteanu, A.; Orlianges, J. C.; Beaumont, A.; Mayet, R.; Mennai, A.; Cosset, F.; Bessaudou, A.; Fabert, M.

    2017-02-01

    Large area (up to 4 squared inches) epitaxial VO2 films, with a uniform thickness and exhibiting an abrupt metal-insulator transition with a resistivity ratio as high as 2.85 × 10 4 , have been grown on (001)-oriented sapphire substrates by electron beam evaporation. The lattice distortions (mosaicity) and the level of strain in the films have been assessed by X-ray diffraction. It is demonstrated that the films grow in a domain-matching mode where the distortions are confined close to the interface which allows growth of high-quality materials despite the high film-substrate lattice mismatch. It is further shown that a post-deposition high-temperature oxygen annealing step is crucial to ensure the correct film stoichiometry and provide the best structural and electrical properties. Alternatively, it is possible to obtain high quality films with a RF discharge during deposition, which hence do not require the additional annealing step. Such films exhibit similar electrical properties and only slightly degraded structural properties.

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

    PubMed

    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 pointsCurrently, 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.

  20. Orientational high-entropy alloys

    NASA Astrophysics Data System (ADS)

    Kumar, Nitesh; Subramaniam, Anandh

    2014-12-01

    In high-entropy alloys (HEA), the configurational entropy arising from the presence of multiple elements, stabilizes a disordered solid solution in preference to the possible formation of compounds. In the current work, we identify cluster compounds (of the type AM4X8) as orientational analogues of HEA (as a first report on orientational high-entropy systems). In cluster compounds, orientational disorder increases the entropy and plays a role analogous to positional disorder in HEA. In the GaMo4S8 compound, at temperatures greater than 50 K, the entropic benefit more than makes up for the strain energy cost and stabilizes the disordered phase in preference to an orientationally ordered compound.

  1. Effect of CO on VO2 of carotid body and chemoreception with and without Ca2+.

    PubMed

    Lahiri, S; Buerk, D G; Osanai, S; Mokashi, A; Chugh, D K

    1997-09-10

    This study was done using high PCO (> 500 Torr at PO2 of 120 Torr) in the carotid body perfusate in vitro, and recording simultaneously the activity of the whole carotid sinus nerve (CSN) and VO2 of the carotid body. In the cascade of excitation of CSN by high PCO in the dark [light eliminated the excitation; S. Lahiri, News Physiol. Sci. 9 (1992) 161-165], Ca2+ effects occur at the level of neurosecretion after the level of oxygen consumption, according to the following scheme: CO-hypoxia-->VO2 decrease-->K+ conductance decrease-->cell depolarization-->cytosolic Ca2+ rise-->neurosecretion-->neural discharge. Thus, a part of the hypothesis was that [Ca2+] decrease, being a downstream event, may not affect VO2 of the carotid body. Also, to determine to what extent the intracellular calcium stores contribute to cystolic [Ca2+] and chemosensory discharge with high PCO, we tested the effect of interruption of perfusate flow with medium nominally free of [Ca2+] on CSN excitation and VO2 of the carotid body with and without high PCO. High PCO in the dark decreased carotid body VO2, independent of [Ca2+]o. CSN excitation was always enhanced by high PCO, and its sensitivity to perfusate flow interruption. Also, nominally Ca(2+)-free solution increased the latency and decreased the rate of rise and peak activity of CSN during interruption of perfusate flow, but CO augmented the responses. This reversal effect by CO suggests that Ca2+ is released from intracellular stores, because CO has no other way to excite the chemoreceptors than by acting on the intracellular stores.

  2. 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.

  3. Metal-VO2 hybrid grating structure for a terahertz active switchable linear polarizer.

    PubMed

    Shin, Jun-Hwan; Moon, Kiwon; Lee, Eui Su; Lee, Il-Min; Park, Kyung Hyun

    2015-08-07

    An active terahertz (THz) wave hybrid grating structure of Au/Ti metallic grating on VO2/Al2O3 (0001) was fabricated and evaluated. In our structure, it is shown that the metallic gratings on the VO2 layer strengthen the metallic characteristics to enhance the contrast of the metallic and dielectric phases of a VO2-based device. Especially, the metal grating-induced optical conductivity of the device is greatly enhanced, three times more than that of a metallic phase of bare VO2 films in the 0.1-2.0 THz spectral range. As an illustrative example, we fabricated an actively on/off switchable THz linear polarizer. The fabricated device has shown commercially comparable values in degree of polarization (DOP) and extinction ratio (ER). A high value of 0.89 in the modulation depth (MD) for the transmission field amplitude, superior to other THz wave modulators, is achieved. The experimental results show that the fabricated device can be highly useful in many applications, including active THz linear polarizers, THz wave modulators and variable THz attenuators.

  4. VO2 kinetics and metabolic contributions whilst swimming at 95, 100, and 105% of the velocity at VO2max.

    PubMed

    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 (τ1--15, 18, and 16 s, A1--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.

  5. 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.

  6. Effect of buffer layer on thermochromic performances of VO2 films fabricated by magnetron sputtering

    NASA Astrophysics Data System (ADS)

    Zhu, Benqin; Tao, Haizheng; Zhao, Xiujian

    2016-03-01

    As a well-developed industrial fabricating method, magnetron sputtering technique has its distinct advantages for the large-scale production. In order to investigate the effect of buffer layer on the formation and thermochromic performances of VO2 films, using RF magnetron sputtering method, we fabricated three kinds of buffer layers SiO2, TiO2 and SnO2 on soda lime float-glass. Then according to the reactive DC magnetron sputtering method, VO2 films were deposited. Due to the restriction of heat treatment temperature when using soda lime float-glass as substrates, dense rutile phase TiO2 cannot be formed, leading to the formation of vanadium oxide compounds containing Na ions. When using SnO2 as buffer layer, we found that relatively high pure VO2 can be deposited more easily. In addition, compared with the effect of SiO2 buffer layer, we observed an enhanced visible transparency, a decreased infrared emissivity, which should be mainly originated from the modified morphology and/or the hetero-structured VO2/SnO2 interface.

  7. 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.

  8. Electrically controllable terahertz square-loop metamaterial based on VO2 thin film

    NASA Astrophysics Data System (ADS)

    Shin, Jun-Hwan; Park, Kyung Hyun; Ryu, Han-Cheol

    2016-05-01

    An electrically controllable square-loop metamaterial based on vanadium dioxide (VO2) thin film was proposed in the terahertz frequency regime. The square-loop shaped metamaterial was adopted to perform roles not only as a resonator but also as a micro-heater for the electrical control of the VO2. A dual-resonant square-loop structure was designed to realize band-pass characteristics in the desired frequency band. The measured Q-factors of the basic and scaled-down metamaterials fabricated on VO2 thin films were 2.22 and 1.61 at the center frequencies of 0.44 and 1.14 THz in the passbands, respectively. The transmittances of the proposed metamaterial were successfully controlled by applying a bias voltage without an external heater. The measured transmittance on-off ratios of the metamaterials were over 40 at the center frequencies in the passbands. In the future, electrically controllable terahertz metamaterial based on VO2 metamaterial could be employed as high-performance active filters or sensors.

  9. Shape-controlled synthesis and influence of W doping and oxygen nonstoichiometry on the phase transition of VO2

    PubMed Central

    Chen, Ru; Miao, Lei; Liu, Chengyan; Zhou, Jianhua; Cheng, Haoliang; Asaka, Toru; Iwamoto, Yuji; Tanemura, Sakae

    2015-01-01

    Monoclinic VO2(M) in nanostructure is a prototype material for interpreting correlation effects in solids with fully reversible phase transition and for the advanced applications to smart devices. Here, we report a facile one-step hydrothermal method for the controlled growth of single crystalline VO2(M/R) nanorods. Through tuning the hydrothermal temperature, duration of the hydrothermal time and W-doped level, single crystalline VO2(M/R) nanorods with controlled aspect ratio can be synthesized in large quantities, and the crucial parameter for the shape-controlled synthesis is the W-doped content. The dopant greatly promotes the preferential growth of (110) to form pure phase VO2(R) nanorods with high aspect ratio for the W-doped level = 2.0 at% sample. The shape-controlled process of VO2(M/R) nanorods upon W-doping are systematically studied. Moreover, the phase transition temperature (Tc) of VO2 depending on oxygen nonstoichiometry is investigated in detail. PMID:26373612

  10. Difference in Physiological Components of VO2 Max During Incremental and Constant Exercise Protocols for the Cardiopulmonary Exercise Test.

    PubMed

    Yamamoto, Junshiro; Harada, Tetsuya; Okada, Akinori; Maemura, Yuko; Yamamoto, Misaki; Tabira, Kazuyuki

    2014-08-01

    [Purpose] VO2 is expressed as the product of cardiac output and O2 extraction by the Fick equation. During the incremental exercise test and constant high-intensity exercise test, VO2 results in the attainment of maximal O2 uptake at exhaustion. However, the differences in the physiological components, cardiac output and muscle O2 extraction, have not been fully elucidated. We tested the hypothesis that constant exercise would result in higher O2 extraction than incremental exercise at exhaustion. [Subjects] Twenty-five subjects performed incremental exercise and constant exercise at 80% of their peak work rate. [Methods] Ventilatory, cardiovascular, and muscle oxygenation responses were measured using a gas analyzer, Finapres, and near-infrared spectroscopy, respectively. [Results] VO2 was not significantly different between the incremental exercise and constant exercise. However, cardiac output and muscle O2 saturation were significantly lower for the constant exercise than the incremental exercise at the end of exercise. [Conclusion] These findings indicate that if both tests produce a similar VO2 value, the VO2 in incremental exercise would have a higher ratio of cardiac output than constant exercise, and VO2 in constant exercise would have a higher ratio of O2 extraction than incremental exercise at the end of exercise.

  11. Time at VO2max during intermittent treadmill running: test protocol dependent or methodological artefact?

    PubMed

    Midgley, A W; McNaughton, L R; Carroll, S

    2007-11-01

    Effects of methodological differences on the determination of time at VO (2max) (t (VO2max)) during intermittent treadmill running were investigated. Subjects performed three incremental tests to volitional exhaustion: a continuous protocol with 1-min stages (Cont-INC ([1-min])), and two discontinuous protocols of 2-min (Dis-INC ([2-min])) and 3-min (Dis-INC ([3-min])) stage durations. For each test, VO (2max) and the running velocity associated with V.O (2max) (vVO (2max)) were determined. On a fourth visit, subjects performed an intermittent test with 30-s work and relief intervals run at 105 % and 60 %, respectively, of the vV. (2max) determined during Cont-INC ((1-min)). The t (VO2max) during the intermittent test was determined using three different criteria: VO (2) data points > or = 100 % VO (2max) determined in Cont-INC ((1-min)) (t (VO2max[100 %])), > or = 95 % VO (2max) (t (VO2max[95 %])) and > or = VO (2max) minus 2.1 ml . kg (-1) . min (-1) (t (VO2max[- 2.1])). The V.O (2max) means (SD) for Cont-INC ((1-min)), Dis-INC ((2-min)) and Dis-INC ((3-min)) were 4093 (538), 4096 (516), and 3980 (488) mL . min (-1), respectively. The t (VO2max) means (SD) were: t (VO2max(100 %)) 163 (227) s, t (VO2max(95 %)) 418 (439) s, and t (VO2max(- 2.1)) 358 (395) s. All differences in t (V.O2max) were significantly different (p < 0.05). Differences in t (VO2max) due to using V.O (2max) values derived from using different V.O (2) time-averages were significantly different (p < 0.05). Methodological differences should be considered during interpretation of previous studies.

  12. Phase transition in bulk single crystals and thin films of VO2 by nanoscale infrared spectroscopy and imaging

    DOE PAGES

    Liu, Mengkun; Sternbach, Aaron J.; Wagner, Martin; ...

    2015-06-29

    We have systematically studied a variety of vanadium dioxide (VO2) crystalline forms, including bulk single crystals and oriented thin films, using infrared (IR) near-field spectroscopic imaging techniques. By measuring the IR spectroscopic responses of electrons and phonons in VO2 with sub-grain-size spatial resolution (~20nm), we show that epitaxial strain in VO2 thin films not only triggers spontaneous local phase separations, but leads to intermediate electronic and lattice states that are intrinsically different from those found in bulk. Generalized rules of strain- and symmetry-dependent mesoscopic phase inhomogeneity are also discussed. Furthermore, these results set the stage for a comprehensive understanding ofmore » complex energy landscapes that may not be readily determined by macroscopic approaches.« less

  13. 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

  14. Group training in adolescent runners: influence on VO2max and 5-km race performance.

    PubMed

    Loprinzi, Paul D; Cardinal, Bradley J; Karp, Jason R; Brodowicz, Gary R

    2011-10-01

    The aims of this study were to (a) examine the interrelationships between training intensity, VO2max, and race performance in adolescent crosscountry runners and (b) determine if adolescent runners participating in a group crosscountry training program differ in the amount of training time at various intensities. In this study, 7 adolescent runners performed a laboratory-based VO2max test before and after a 9-week high-school crosscountry season. Heart rate (HR) and ventilatory threshold (VT) were used to identify 3 training zones for each runner based on the HR at ventilator threshold (HR(VT)): zone 1: >15 b·min(-1) below HR(VT); zone 2: between zone 1 and HR(VT); zone 3: >HR(VT). During each training session throughout the season, HR was measured to quantify the amount of training time in each of these 3 intensity zones. Results showed that the time in each of the 3 zones was not significantly associated with 5-km race performance. Zone 3 training time was positively associated with postseason VO2max (r = 0.73, p = 0.06); VO2max was significantly inversely associated with 5-km race performance (r = -0.77, p = 0.04). Each week, the amount of training time at, above, and below the VT was significantly different among the participants even though the training prescription for the group was standardized. The results suggest that, among adolescent crosscountry runners, training above the VT may be important in increasing VO2max and ultimately, race performance. Given the between-participant differences in the amount of training time in each HR zone, coaches should apply individual, rather than group, training programs.

  15. Metal-semiconductor phase transition of order arrays of VO2 nanocrystals

    NASA Astrophysics Data System (ADS)

    Lopez, Rene; Suh, Jae; Feldman, Leonard; Haglund, Richard

    2004-03-01

    The study of solid-state phase transitions at nanometer length scales provides new insights into the effects of material size on the mechanisms of structural transformations. Such research also opens the door to new applications, either because materials properties are modified as a function of particle size, or because the nanoparticles interact with a surrounding matrix material, or with each other. In this paper, we describe the formation of vanadium dioxide nanoparticles in silicon substrates by pulsed laser deposition of ion beam lithographically selected sites and thermal processing. We observe the collective behavior of 50 nm diameter VO2 oblate nanoparticles, 10 nm high, and ordered in square arrays with arbitrary lattice constant. The metal-semiconductor-transition of the VO2 precipitates shows different features in each lattice spacing substrate. The materials are characterized by electron microscopy, x-ray diffraction, Rutherford backscattering. The features of the phase transition are studied via infrared optical spectroscopy. Of particular interest are the enhanced scattering and the surface plasmon resonance when the particles reach the metallic state. This resonance amplifies the optical contrast in the range of near-infrared optical communication wavelengths and it is altered by the particle-particle coupling as in the case of noble metals. In addition the VO2 nanoparticles exhibit sharp transitions with up to 50 K of hysteresis, one of the largest values ever reported for this transition. The optical properties of the VO2 nanoarrays are correlated with the size of the precipitates and their inter-particle distance. Nonlinear and ultra fast optical measurements have shown that the transition is the fastest known solid-solid transformation. The VO2 nanoparticles show the same bulk property, transforming in times shorter than 150 fs. This makes them remarkable candidates for ultrafast optical and electronic switching applications.

  16. Photoluminescence of monolayer transition metal dichalcogenides integrated with VO2

    NASA Astrophysics Data System (ADS)

    Lin, Yu-Chuan; DeLello, Kursti; Zhang, Hai-Tian; Zhang, Kehao; Lin, Zhong; Terrones, Mauricio; Engel-Herbert, Roman; Robinson, Joshua A.

    2016-12-01

    Integrating a phase transition material with two-dimensional semiconductors can provide a route towards tunable opto-electronic metamaterials. Here, we integrate monolayer transition metal dichalcogenides with vanadium dioxide (VO2) thin films grown via molecular beam epitaxy to form a 2D/3D heterostructure. Vanadium dioxide undergoes an insulator-to-metal transition at 60-70 °C, which changes the band alignment between MoS2 and VO2 from a semiconductor-insulator junction to a semiconductor-metal junction. By switching VO2 between insulating and metallic phases, the modulation of photoluminescence emission in the 2D semiconductors was observed. This study demonstrates the feasibility to combine TMDs and functional oxides to create unconventional hybrid optoelectronic properties derived from 2D semiconductors that are linked to functional properties of oxides through proximity coupling.

  17. Manipulation of avalanche characteristics in nanoscaled VO2 devices

    NASA Astrophysics Data System (ADS)

    Wang, Siming; West, Kevin G.; Schuller, Ivan K.

    2011-03-01

    The temperature driven metal insulator transition (MIT) in nanoscaled VO2 devices occurs through a series of resistance jumps ranging over two decades in magnitude. A power law distribution of the jump sizes, demonstrates that the transition is caused by avalanches across the percolation transition. We investigate the effect of a DC write current on the intrinsic behavior of the MIT transition in nanoscaled VO2 devices. We find an increase in the maximum resistance jump size by as much as a factor of 10x after application of a DC write current at room temperature. Interestingly, we find no significant changes in the exponent of the power law distribution as a function of an applied DC write current. The observations suggest that the DC current changes the intrinsic properties of the VO2 thin film and may be related to spatial confinement which leads to an increase in the maximum resistance jump size. Work supported by US-DOE.

  18. Dynamics of photothermally driven VO2-coated microcantilevers

    NASA Astrophysics Data System (ADS)

    Cabrera, Rafmag; Merced, Emmanuelle; Sepúlveda, Nelson; Fernández, Félix E.

    2011-11-01

    The dynamic response of VO2-coated silicon microcantilevers thermally driven over the film's insulator-to-metal transition was studied using laser light pulses directly incident on the cantilevers. The measured photothermal response revealed very high curvature changes of approximately 2500 m-1 up to pulse frequencies greater than 100 Hz and readily observable vibrations up to frequencies of a few kHz with no amplitude degradation after tens of thousands of pulses. Maximum tip amplitudes for 300-μm-long, 1-μm-thick cantilevers used in these experiments were nearly 120 μm and correspondingly less for 2-μm-thick cantilevers. The main mechanism limiting oscillation amplitude was found to be heat transport response during heating and cooling, which depends mainly on thermal conduction through the cantilever itself to the massive anchor and chip body, which acted as a heat sink at room temperature. For the laser-driven oscillations studied, damping by the surrounding air is unimportant in the range of frequencies probed. Large-curvature response is expected to extend to higher pulse frequencies for cantilevers with smaller dimensions.

  19. Accuracy of the VO2peak prediction equation in firefighters

    PubMed Central

    2014-01-01

    Background A leading contributing factor to firefighter injury and death is lack of fitness. Therefore, the Fire Service Joint Labor Management Wellness-Fitness Initiative (WFI) was established that includes a focus on providing fitness assessments to all fire service personnel. The current fitness assessment includes a submaximal exercise test protocol and associated prediction equation to predict individual VO2peak as a measure of fitness. There is limited information on the accuracy, precision, and sources of error of this prediction equation. This study replicated previous research by validating the accuracy of the WFI VO2peak prediction equation for a group of firefighters and further examining potential sources of error for an individual firefighters’ assessment. Methods The sample consisted of 22 firefighters who completed a maximal exercise test protocol similar to the WFI submaximal protocol, but the test was terminated when firefighters reached a maximal level of exertion (i.e., measured VO2peak). We then calculated the predicted VO2peak based on the WFI prediction equation along with individual firefighters’ body mass index (BMI) and 85% of maximum heart rate. The data were analyzed using paired samples t-tests in SPSS v. 21.0. Results The difference between predicted and measured VO2peak was -0.77 ± 8.35 mL•kg-1•min-1. However, there was a weak, statistically non-significant association between measured VO2peak and predicted VO2peak (R2 = 0.09, F(1,21) = 2.05, p = 0.17). The intraclass correlation coefficient (ICC = 0.215, p > 0.05) and Pearson (r = 0.31, p = 0.17) and Spearman (ρ = 0.28, p = 0.21) correlation coefficients were small. The standard error of the estimate (SEE) was 8.5 mL•kg-1•min-1. Further, both age and baseline fitness level were associated with increased inaccuracy of the prediction equation. Conclusions We provide data on the inaccuracy and sources of error for the WFI VO2peak

  20. 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.

  1. Influence of doping with alkaline earth metals on the optical properties of thermochromic VO2

    NASA Astrophysics Data System (ADS)

    Dietrich, Marc K.; Kramm, Benedikt G.; Becker, Martin; Meyer, Bruno K.; Polity, Angelika; Klar, Peter J.

    2015-05-01

    Thin films of doped VO2 were deposited, analyzed, and optimized with regard to their solar energy transmittance (Tsol) and visible/luminous light transmittance (Tlum) which are important parameters in the context of smart window applications in buildings. The doping with alkaline earth metals (AEM) like Mg, Ca, Sr, or Ba increased both Tsol and Tlum due to a bandgap widening and an associated absorption edge blue-shift. Thereby, the brown-yellowish color impression of pure VO2 thin films, which is one major hindrance limiting the usage of VO2 as thermochromic window coating, was overcome. Transparent thin films with excellent switching behavior were prepared by sputtering. Highly doped V1-xMexO2 (Me = Ca, Sr, Ba) kept its excellent thermochromic switching behavior up to x(Me) = Me/(Me + V) = 10 at. % doping level, while the optical bandgap energy was increased from 1.64 eV for undoped VO2 to 2.38 eV for x(Mg) = 7.7 at. %, 1.85 eV for x(Ca) = 7.4 at. %, 1.84 eV for x(Sr) = 6.4 at. % and 1.70 eV for x(Ba) = 6.8 at. %, as well as the absorption edge is blue shifted by increasing AEM contents. Also, the critical temperature ϑc, at which the semiconductor-to-metal transition (SMT) occurs, was decreased by AEM doping, which amounted to about -0.5 K/at. % for all AEM on average. The critical temperature was determined by transmittance-temperature hysteresis measurements. Furthermore, Tsol and Tlum were calculated and were found to be significantly enhanced by AEM doping. Tlum increased from 32.0% in undoped VO2 to 43.4% in VO2 doped with 6.4 at. % Sr. Similar improvements were found for other AEM. The modulation of the solar energy transmittance ΔTsol, which is the difference of the Tsol values in the low and high temperature phase, was almost constant or even slightly increased when the doping level was increased up to about 10 at. % Ca, Sr, or Ba.

  2. Optical diffraction in ordered VO2 nanoparticle arrays

    NASA Astrophysics Data System (ADS)

    Lopez, Rene; Feldman, Leonard; Haglund, Richard

    2006-03-01

    The potential of oxide electronic materials as multifunctional building blocks is one of the driving concepts of the field. In this presentation, we show how nanostructured particle arrays with long-range order can be used to modulate an optical response through exploiting the metal-insulator transition of vanadium dioxide. Arrays of VO2 nanoparticles with long-range order were fabricated by pulsed laser deposition in an arbitrary pattern defined by focused ion-beam lithography. The interaction of light with the nanoparticles is controlled by the nanoparticle size, spacing and geometrical arrangement and by switching between the metallic and semiconducting phases of VO2. In addition to the near-infrared surface plasmon response observed in previous VO2 studies, the VO2 nanoparticle arrays exhibit size-dependent optical resonances in the visible region that likewise show an enhanced optical contrast between the semiconducting and metallic phases. The collective optical response as a function of temperature gives rise to an enhanced scattering state during the evolving phase transition, while the incoherent coupling between the nanoparticles produces an order-disorder-order transition.

  3. Validity of 3 protocols for verifying VO2 max.

    PubMed

    Kirkeberg, J M; Dalleck, L C; Kamphoff, C S; Pettitt, R W

    2011-04-01

    The verification bout has emerged as a technique for confirming 'true' VO2 max; however, validity during a single visit is unknown. We evaluated 3 different GXT durations with severe intensity verification bouts. On 3 separate days, in counterbalanced order, 12 recreational-trained men completed short (9±1 min), middle (11±1 min), and long (13±2 min) duration GXTs followed by exhaustive, sine wave verification bouts during the same visit. Intensities for verification were set at speeds equivalent to 2-stages minus end-GXT speed. No differences (p<0.05) in VO2 max (mL/kg/min) were observed between short (49.1), middle (48.2), and long (48.8) protocols. In addition, no differences in verification bout duration occurred between protocols (3±1 min). Validity of VO2 max was strongest for the middle duration protocol (ICC α=0.97; typical error=1 mL/kg/min; CV=2%). A small, but significantly higher HR (max) (∼1-2 bpm) was observed for the long protocol. Maximum respiratory exchange ratios were inconsistent (ICC α ranged 0.58-0.68). Our findings indicate GXT-verification bout testing during a single visit is a valid means of measuring 'true' VO2 max. The 10 min target for GXT duration was the optimum.

  4. Matching of Male and Female Subjects Using VO2 Max.

    ERIC Educational Resources Information Center

    Cureton, Kirk J.

    1981-01-01

    The increasing use of various VO2 max expressions as test measures is a problem because the magnitude of sex difference varies considerably with each expression. A valid match of male and female test subjects would consider physical activity history and the amount of endurance exercise done in the previous year. (Author/FG)

  5. VO2 prediction and cardiorespiratory responses during underwater treadmill exercise.

    PubMed

    Greene, Nicholas P; Greene, Elizabeth S; Carbuhn, Aaron F; Green, John S; Crouse, Stephen F

    2011-06-01

    We compared cardiorespiratory responses to exercise on an underwater treadmill (UTM) and land treadmill (LTM) and derived an equation to estimate oxygen consumption (VO2) during UTM exercise. Fifty-five men and women completed one LTM and five UTM exercise sessions on separate days. The UTM sessions consisted of chest-deep immersion, with 0, 25, 50, 75, and 100% water-jet resistance. All session treadmill velocities increased every 3 min from 53.6 to 187.8 m x min(-1). Cardiorespiratory responses were similar between LTM and UTM when jet resistance for UTM was 50%. Using multiple regression analysis, weight-relative VO2 could be estimated as: VO2 (mLO2 c kg(-1) x min(-1)) = 0.19248 x height (cm) + 0.17422 x jet resistance (% max) + 0.14092 x velocity (m x min(-1)) -0.12794 x weight (kg)-27.82849, R2 = .82. Our data indicate that similar LTM and UTM cardiorespiratory responses are achievable, and we provide a reasonable estimate of UTM VO2.

  6. A minimal model for the structural energetics of VO2

    NASA Astrophysics Data System (ADS)

    Kim, Chanul; Marianetti, Chris; The Marianetti Group Team

    Resolving the structural, magnetic, and electronic structure of VO2 from the first-principles of quantum mechanics is still a forefront problem despite decades of attention. Hybrid functionals have been shown to qualitatively ruin the structural energetics. While density functional theory (DFT) combined with cluster extensions of dynamical mean-field theory (DMFT) have demonstrated promising results in terms of the electronic properties, structural phase stability has not yet been addressed. In order to capture the basic physics of the structural transition, we propose a minimal model of VO2 based on the one dimensional Peierls-Hubbard model and parameterize this based on DFT calculations of VO2. The total energy versus dimerization in the minimal mode is then solved numerically exactly using density matrix renormalization group (DMRG) and compared to the Hartree-Fock solution. We demonstrate that the Hartree-Fock solution exhibits the same pathologies as DFT+U, and spin density functional theory for that matter, while the DMRG solution is consistent with experimental observation. Our results demonstrate the critical role of non-locality in the total energy, and this will need to be accounted for to obtain a complete description of VO2 from first-principles. The authors acknowledge support from FAME, one of six centers of STARnet, a Semiconductor Research Corporation program sponsored by MARCO and DARPA.

  7. Can We Confidently Study VO2 Kinetics in Young People?

    PubMed Central

    Fawkner, Samantha G.; Armstrong, Neil

    2007-01-01

    The study of VO2 kinetics offers the potential to non-invasively examine the cardiorespiratory and metabolic response to dynamic exercise and limitations to every day physical activity. Its non-invasive nature makes it hugely attractive for use with young people, both healthy and those with disease, and yet the literature, whilst growing with respect to adults, remains confined to a cluster of studies with these special populations. It is most likely that this is partly due to the methodological difficulties involved in studying VO2 kinetics in young people which are not present, or present to a lesser degree, with adults. This article reviews these methodological issues, and explains the main procedures that might be used to overcome them. Key pointsThe VO2 kinetic response to exercise represents the combined efficiency of the cardiovascular, pulmonary and metabolic systems, and an accurate assessment of the response potentially provides a great deal of useful information via non-invasive methodology.An accurate assessment of the VO2 kinetic response is however inherently difficult with children and especially those with reduced exercise tolerance, due primarily to the apparent breath-by-breath noise which masks the true underlying physiological response, and the small amplitudes of the response signal.Despite this, it is possible to assess and quantify the VO2 kinetic response with children if appropriate steps are taken to apply carefully selected methodologies and report response variables with confidence intervals. In this way, both the researcher and the reader can be confident that the data reported is meaningful. PMID:24149413

  8. VO2sim 0.1: Using Simulation to Understand Measurement Error in Indirect Calorimetry

    DTIC Science & Technology

    2015-08-01

    illness. The Army has recognized the importance of understanding oxygen consumption in the field and is developing models to aid in operational decision...acclimatize to high altitude (Amann et al. 2013) and hypoxia (Self et al. 2013). The Army has recognized the importance of understanding oxygen consumption...Atwater and Benedict 1983). The cumbersome direct calorimetry method was later updated so that volumes of expired oxygen (VO2) and carbon dioxide

  9. Exploring the interplay between the motivational climate and goal orientation in predicting maximal oxygen uptake.

    PubMed

    Buch, Robert; Nerstad, Christina G L; Aandstad, Anders; Säfvenbom, Reidar

    2016-01-01

    Drawing upon achievement goal theory, this study explored the interplay between the perceived motivational climate, achievement goals and objective measurements of maximal oxygen uptake (VO2max). The results of a study of 123 individuals from three Norwegian military academies revealed that under the condition of a high-performance orientation there is a stronger positive relationship between performance climate and VO2max for individuals reporting a low (rather than high)-mastery orientation. Furthermore, we found that for individuals with a high-mastery orientation there is a stronger positive relationship between mastery climate and VO2max for individuals reporting a low (rather than high)-performance orientation. These findings contribute to achievement goal theory by providing support for an interactionist person-environment fit perspective. Implications for future research and practice are discussed.

  10. Efficiency of Photocarrier Injection in a VO2/TiO2:Nb Heterostructure

    NASA Astrophysics Data System (ADS)

    Hiroi, Zenji; Yamauchi, Tohru; Muraoka, Yuji; Muramatsu, Takaki; Yamaura, Jun-Ichi

    2003-12-01

    The efficiency of photocarrier injection in a VO2/TiO2:Nb heterostructure is studied by measuring I-V characteristics at room temperature under ultraviolet light irradiation. It is revealed that photogenerated hole carriers in the TiO2:Nb substrate are injected and accumulated in the VO2 film by the photovoltaic effect. The surface charge density is controlled successfully in a wide range of 109-1013 cm-2 as a function of light irradiance. The maximum hole density of 9× 1018 cm-3 is attained at a light irradiance of 133 mW/cm2, which is estimated by assuming the uniform distribution of holes in the film. It is suggested that high efficiency can be achieved by utilizing the large dielectric constant of titanium oxide substrates.

  11. [Effect of 4 weeks of training on the limit time at VO2 max].

    PubMed

    Heubert, Richard; Bocquet, Valéry; Koralsztein, Jean Pierre; Billat, Véronique

    2003-10-01

    The purpose of this study was to examine the effect of 4 weeks training in running on the time spent at VO2max (tlim VO2max). Eight athletes carried out, before and after an aerobic training, an incremental and five exhaustive tests at 90, 95, 100, 115% vVO2max and at the critical power at VO2max (CV'; slope of the linear relation between the tlim VO2max and the distance limit at VO2max). This training did not significantly improve VO2max (p = 0.17) or tlim VO2max (p = 0.72). However, the "tlim VO2max-intensity" curve was shifted toward the right, meaning that the athlete had to run at a higher intensity after training to obtain the same tlim VO2max. Tlim VO2max at CV' before training was significantly higher than tlim VO2max at 90, 95, 100, and 115% vVO2max (p < 0.05). This training increased CV' in absolute value (13.9 +/- 1.3 vs. 14.9 +/- 1.2 km.h-1, p < 0.05; n = 6) but not in relative value (86 +/- 4 vs. 86 +/- 5% vVO2max; p = 0.9). In conclusion, in spite of the shift of the "tlim VO2max-intensity" curve, tlim VO2max was not significantly increased by this training. Furthermore, CV' allowed subjects to spend the longest time of exercise at VO2max during a continuous exercise with constant speed, but CV', expressed in % vVO2max, did not improve with this training.

  12. Suppression of Structural Phase Transition in VO2 by Epitaxial Strain in Vicinity of Metal-insulator Transition

    PubMed Central

    Yang, Mengmeng; Yang, Yuanjun; Bin Hong; Wang, Liangxin; Hu, Kai; Dong, Yongqi; Xu, Han; Huang, Haoliang; Zhao, Jiangtao; Chen, Haiping; Song, Li; Ju, Huanxin; Zhu, Junfa; Bao, Jun; Li, Xiaoguang; Gu, Yueliang; Yang, Tieying; Gao, Xingyu; Luo, Zhenlin; Gao, Chen

    2016-01-01

    Mechanism of metal-insulator transition (MIT) in strained VO2 thin films is very complicated and incompletely understood despite three scenarios with potential explanations including electronic correlation (Mott mechanism), structural transformation (Peierls theory) and collaborative Mott-Peierls transition. Herein, we have decoupled coactions of structural and electronic phase transitions across the MIT by implementing epitaxial strain on 13-nm-thick (001)-VO2 films in comparison to thicker films. The structural evolution during MIT characterized by temperature-dependent synchrotron radiation high-resolution X-ray diffraction reciprocal space mapping and Raman spectroscopy suggested that the structural phase transition in the temperature range of vicinity of the MIT is suppressed by epitaxial strain. Furthermore, temperature-dependent Ultraviolet Photoelectron Spectroscopy (UPS) revealed the changes in electron occupancy near the Fermi energy EF of V 3d orbital, implying that the electronic transition triggers the MIT in the strained films. Thus the MIT in the bi-axially strained VO2 thin films should be only driven by electronic transition without assistance of structural phase transition. Density functional theoretical calculations further confirmed that the tetragonal phase across the MIT can be both in insulating and metallic states in the strained (001)-VO2/TiO2 thin films. This work offers a better understanding of the mechanism of MIT in the strained VO2 films. PMID:26975328

  13. First-principles investigation on solar radiation shielding performance of rutile VO2 filters for smart windows

    NASA Astrophysics Data System (ADS)

    Xiao, Lihua; Su, Yuchang; Qiu, Wei; Ran, Jingyu; Liu, Yike; Wu, Jianming; Lu, Fanghai; Shao, Fang; Peng, Ping

    2016-11-01

    Vanadium dioxide (VO2) undergoing reversible metal-insulator phase transition could allow for the formation of an efficient thermochromic material for smart windows. However, solar radiation shielding performance is determined by transparent rutile VO2 filters, and the puzzling metal-insulator transition mechanism makes it challenging to explain the origin of the coexistence of strong near infrared absorption with high optical transparency. The band structure, the density of states, and the optical properties of rutile VO2 were calculated using the first-principles calculations. The calculated results of the structural and optical properties are in good agreement with the previously reported experimental findings. The calculated dielectric functions, electron energy-loss function and solar radiation shielding performance of the rutile VO2 filters indicate that rutile VO2 is a promising near-infrared absorption/reflectance material with the near-infrared radiation insulating abilities and a visible light transmittance. These properties arise from plasma oscillation and a collective oscillation (volume plasmons) of carrier electrons.

  14. Resistance noise at the metal-insulator transition in thermochromic VO2 films

    NASA Astrophysics Data System (ADS)

    Topalian, Zareh; Li, Shu-Yi; Niklasson, Gunnar A.; Granqvist, Claes G.; Kish, Laszlo B.

    2015-01-01

    Thermochromic VO2 films were prepared by reactive DC magnetron sputtering onto heated sapphire substrates and were used to make 100-nm-thick samples that were 10 μm wide and 100 μm long. The resistance of these samples changed by a factor ˜2000 in the 50 < Ts < 70 °C range of temperature Ts around the "critical" temperature Tc between a low-temperature semiconducting phase and a high-temperature metallic-like phase of VO2. Power density spectra S(f) were extracted for resistance noise around Tc and demonstrated unambiguous 1/f behavior. Data on S(10 Hz)/Rs2 scaled as Rsx, where Rs is sample resistance; the noise exponent x was -2.6 for Ts < Tc and +2.6 for Ts > Tc. These exponents can be reconciled with the Pennetta-Trefán-Reggiani theory [Pennetta et al., Phys. Rev. Lett. 85, 5238 (2000)] for lattice percolation with switching disorder ensuing from random defect generation and healing in steady state. Our work hence highlights the dynamic features of the percolating semiconducting and metallic-like regions around Tc in thermochromic VO2 films.

  15. Influence of grain size on transition temperature of thermochromic VO2

    NASA Astrophysics Data System (ADS)

    Miller, Mark J.; Wang, Junlan

    2015-01-01

    Vanadium(IV) oxide (VO2) is a unique material that undergoes a reversible phase transformation around 68 °C. The material could potentially be used as an energy-efficient coating for windows since its reflectance in the infrared (IR) increases significantly more than in the visible region. Currently, VO2 is limited by a transition temperature ( τ c ) that is too high, luminous transmittance that is too low or both. In this study, a transition temperature of 45 °C is achieved for a reactively sputtered, undoped film by restricting grain size to approximately 30 nm. It is concluded that a higher density of grain boundaries (smaller grain size) provides a greater number of nucleating defects which in turn reduces τ c . Similarly, a higher density of grain boundaries may reduce the hysteresis width (difference between transition temperatures in heating and cooling). Also in this study, a new set of optical performance metrics is proposed in which the solar spectrum is divided into the ultraviolet (UV), visible and near infrared (NIR) regions. This approach is more closely aligned with the goals of limiting UV, allowing luminous and modulating NIR transmission. Using these metrics, the optical properties of the low- τ c sample were: 2% UV transmittance, 47% luminous transmittance, and 23% NIR modulation (decrease from 43 to 33%). This study demonstrates that the grain size of VO2 should be viewed as an important parameter for controlling the transition temperature of the material.

  16. A novel terahertz device with multi-function of polarization and switch based on phase transition of VO2

    NASA Astrophysics Data System (ADS)

    Gu, Wen-hao; Chang, Sheng-jiang; Fan, Fei

    2016-11-01

    A terahertz (THz) polarizer and switch structure is proposed based on the phase transition of vanadium dioxide (VO2). When VO2 is in the insulation phase, the resonance frequencies of the proposed structure are 1.49 THz and 1.22 THz for the x- and y-polarization, respectively. It can perform as a THz polarizer with extinction ratios of 52.5 dB and 17 dB for the y- and x-polarization, respectively; When VO2 transforms into metallic phase, the resonance frequency for x-polarization wave shifts from 1.49 THz to 1.22 THz, while that remains still for the y-polarization component. It means that the structure can work as a polarization-dependent THz switch with a high extinction ratio of 32 dB.

  17. Relationship between body and leg VO2 during maximal cycle ergometry

    NASA Technical Reports Server (NTRS)

    Knight, D. R.; Poole, D. C.; Schaffartzik, W.; Guy, H. J.; Prediletto, R.; Hogan, M. C.; Wagner, P. D.

    1992-01-01

    It is not known whether the asymptotic behavior of whole body O2 consumption (VO2) at maximal work rates (WR) is explained by similar behavior of VO2 in the exercising legs. To resolve this question, simultaneous measurements of body and leg VO2 were made at submaximal and maximal levels of effort breathing normoxic and hypoxic gases in seven trained male cyclists (maximal VO2, 64.7 +/- 2.7 ml O2.min-1.kg-1), each of whom demonstrated a reproducible VO2-WR asymptote during fatiguing incremental cycle ergometry. Left leg blood flow was measured by constant-infusion thermodilution, and total leg VO2 was calculated as the product of twice leg flow and radial arterial-femoral venous O2 concentration difference. The VO2-WR relationships determined at submaximal WR's were extrapolated to maximal WR as a basis for assessing the body and leg VO2 responses. The differences between measured and extrapolated maximal VO2 were 235 +/- 45 (body) and 203 +/- 70 (leg) ml O2/min (not significantly different). Plateauing of leg VO2 was associated with, and explained by, plateauing of both leg blood flow and O2 extraction and hence of leg VO2. We conclude that the asymptotic behavior of whole body VO2 at maximal WRs is a direct reflection of the VO2 profile at the exercising legs.

  18. VO2 Reserve vs. Heart Rate Reserve During Moderate Intensity Treadmill Exercise.

    PubMed

    Solheim, Tanner J; Keller, Brad G; Fountaine, Charles J

    VO2 and heart rate (HR) are widely used when determining appropriate training intensities for clinical, healthy, and athletic populations. It has been shown that if the % reserve (%R) is used, rather than % of max, HR and VO2 can be used interchangeably to accurately prescribe exercise intensities. Thus, heart rate reserve (HRR) can be prescribed if VO2 reserve (VO2R) is known. Therefore, the purpose of this study was to compare VO2 R and HRR during moderate intensity exercise (50%R). Physically active college students performed a maximal treadmill test to exhaustion. During which VO2 and HR were monitored to determine max values. Upon completion of the maximal test, calculations were made to determine the % grade expected to yield approximately 50% of the subjects VO2R. Subjects then returned to complete the submaximal test (50%R) at least two days later. The %VO2R and %HRR were calculated and compared to the predicted value as well as to each other. Statistical analysis revealed that VO2 at 50%R was significantly greater than the actual VO2 achieved, p < .001. Conversely, the mean predicted HR at 50%R was significantly less than the actual HR achieved, p < .001. In conclusion, this study indicated that VO2 could be more accurately predicted than HR during moderate intensity exercise. The weak correlation between VO2R and HRR indicates that caution should be used when relying on a HR to determine VO2.

  19. VO2 thermochromic smart window for energy savings and generation

    NASA Astrophysics Data System (ADS)

    Zhou, Jiadong; Gao, Yanfeng; Zhang, Zongtao; Luo, Hongjie; Cao, Chuanxiang; Chen, Zhang; Dai, Lei; Liu, Xinling

    2013-10-01

    The ability to achieve energy saving in architectures and optimal solar energy utilisation affects the sustainable development of the human race. Traditional smart windows and solar cells cannot be combined into one device for energy saving and electricity generation. A VO2 film can respond to the environmental temperature to intelligently regulate infrared transmittance while maintaining visible transparency, and can be applied as a thermochromic smart window. Herein, we report for the first time a novel VO2-based smart window that partially utilises light scattering to solar cells around the glass panel for electricity generation. This smart window combines energy-saving and generation in one device, and offers potential to intelligently regulate and utilise solar radiation in an efficient manner.

  20. VO2 thermochromic smart window for energy savings and generation

    PubMed Central

    Zhou, Jiadong; Gao, Yanfeng; Zhang, Zongtao; Luo, Hongjie; Cao, Chuanxiang; Chen, Zhang; Dai, Lei; Liu, Xinling

    2013-01-01

    The ability to achieve energy saving in architectures and optimal solar energy utilisation affects the sustainable development of the human race. Traditional smart windows and solar cells cannot be combined into one device for energy saving and electricity generation. A VO2 film can respond to the environmental temperature to intelligently regulate infrared transmittance while maintaining visible transparency, and can be applied as a thermochromic smart window. Herein, we report for the first time a novel VO2-based smart window that partially utilises light scattering to solar cells around the glass panel for electricity generation. This smart window combines energy-saving and generation in one device, and offers potential to intelligently regulate and utilise solar radiation in an efficient manner. PMID:24157625

  1. Voltage-Controlled Switching and Thermal Effects in VO2 Nano-Gap Junctions

    DTIC Science & Technology

    2014-06-09

    material1, vanadium dioxide (VO2), has attracted significant attention in optics2–9 and electronics10–15 for its applications in low power, compact and...lateral VO2 junctions as illustrated in Fig. 1(a). A t = 100 nm VO2 film was deposited using magnetron sputtering of a vanadium target on a 2 μm thick

  2. Estimation of VO2 Max: A Comparative Analysis of Five Exercise Tests.

    ERIC Educational Resources Information Center

    Zwiren, Linda D.; And Others

    1991-01-01

    Thirty-eight healthy females measured maximal oxygen uptake (VO2max) on the cycle ergometer and treadmill to compare five exercise tests (run, walk, step, and two tests using heart-rate response on the bicycle ergometer) in predicting VO2max. Results indicate that walk and run tests are satisfactory predictors of VO2max in 30- to 39-year-old…

  3. Graphene-Nanowall-Decorated Carbon Felt with Excellent Electrochemical Activity Toward VO2(+)/VO(2+) Couple for All Vanadium Redox Flow Battery.

    PubMed

    Li, Wenyue; Zhang, Zhenyu; Tang, Yongbing; Bian, Haidong; Ng, Tsz-Wai; Zhang, Wenjun; Lee, Chun-Sing

    2016-04-01

    3D graphene-nanowall-decorated carbon felts (CF) are synthesized via an in situ microwave plasma enhanced chemical vapor deposition method and used as positive electrode for vanadium redox flow battery (VRFB). The carbon fibers in CF are successfully wrapped by vertically grown graphene nanowalls, which not only increase the electrode specific area, but also expose a high density of sharp graphene edges with good catalytic activities to the vanadium ions. As a result, the VRFB with this novel electrode shows three times higher reaction rate toward VO2(+)/VO(2+) redox couple and 11% increased energy efficiency over VRFB with an unmodified CF electrode. Moreover, this designed architecture shows excellent stability in the battery operation. After 100 charging-discharging cycles, the electrode not only shows no observable morphology change, it can also be reused in another battery and practical with the same performance. It is believed that this novel structure including the synthesis procedure will provide a new developing direction for the VRFB electrode.

  4. Graphene‐Nanowall‐Decorated Carbon Felt with Excellent Electrochemical Activity Toward VO2 +/VO2+ Couple for All Vanadium Redox Flow Battery

    PubMed Central

    Li, Wenyue; Zhang, Zhenyu; Bian, Haidong; Ng, Tsz‐Wai

    2015-01-01

    3D graphene‐nanowall‐decorated carbon felts (CF) are synthesized via an in situ microwave plasma enhanced chemical vapor deposition method and used as positive electrode for vanadium redox flow battery (VRFB). The carbon fibers in CF are successfully wrapped by vertically grown graphene nanowalls, which not only increase the electrode specific area, but also expose a high density of sharp graphene edges with good catalytic activities to the vanadium ions. As a result, the VRFB with this novel electrode shows three times higher reaction rate toward VO2 +/VO2+ redox couple and 11% increased energy efficiency over VRFB with an unmodified CF electrode. Moreover, this designed architecture shows excellent stability in the battery operation. After 100 charging–discharging cycles, the electrode not only shows no observable morphology change, it can also be reused in another battery and practical with the same performance. It is believed that this novel structure including the synthesis procedure will provide a new developing direction for the VRFB electrode. PMID:27774399

  5. Porous carbon derived from disposable shaddock peel as an excellent catalyst toward VO2+/VO2+ couple for vanadium redox battery

    NASA Astrophysics Data System (ADS)

    Liu, J.; Wang, Z. A.; Wu, X. W.; Yuan, X. H.; Hu, J. P.; Zhou, Q. M.; Liu, Z. H.; Wu, Y. P.

    2015-12-01

    Functional porous carbon (PC) derived from bio-friendly shaddock peel has been firstly explored as catalyst for vanadium redox flow battery (VRB). The prepared PC is micro-mesoporous with high BET surface area of 882.7 m2 g-1, has some surface oxygen-containing functional groups, and is doped with N and P heteroatoms. These three factors greatly favor the electrochemical reactions of VO2+/VO2+ on the PC modified glass carbon (PC-GC). Compared with the naked GC and graphite modified GC, the PC-GC presents a lower peak separation (66 mV), higher anodic current density (17.1 mA cm-2) and cathodic current density (15.0 mA cm-2). The VRB using PC modified graphite felt (GF) as positive electrode demonstrates an enhanced voltage efficiency of 82.7% at the current density of 60 mA cm-2, and a better rate performance than that from the virginal GF.

  6. Impact of Body Composition and Vo2 Max on the Competitive Success in Top-Level Handball Players.

    PubMed

    Ilic, Vladimir; Ranisavljev, Igor; Stefanovic, Dorde; Ivanovic, Vuk; Mrdakovic, Vladimir

    2015-09-01

    The purpose of the study was to determine the morphological and functional characteristics of 32 Serbian national U20 handball players (age 20.43 +/- 1.16 y; training experience 8.12 +/- 1.89 y) before European championship in Switzerland (2006) and to determinate their impact on competitive performance and outstanding success achieved. The results show that wing players differ from other players in morphological characteristics. Values for body height, weight, BMI, muscle mass and fat mass were significantly lower compared to the other playing positions. Extremely low values of maximal oxygen uptake (VO2 max) were measured in all players (ranged from 2.68 to 4.66 l x min(-1)). Pivots had the highest VO2 max in absolute values (3.76 l x min(-1)), and wing players in relative terms (40.83 ml x kg(-1) x min(-1)). Handball is characterized by high intensity intermittent play, followed by a number of walking breaks and quick substitutions. This makes possible to retain high playing intensity during whole match, because players can be given rest periods whenever needed. This will result in a high intensity game that does not necessarily require high VO2 max. Competitive success in modern top-level handball might be more reliant on optimal tactical preparation than on the body composition and VO2 max of an individual athlete.

  7. The Effect of CeO2 Antireflection Layer on the Optical Properties of Thermochromic VO2 Film for Smart Window System

    NASA Astrophysics Data System (ADS)

    Koo, Hyun; Shin, Dongmin; Bae, Sung-Hwan; Ko, Kyeong-Eun; Chang, Se-Hong; Park, Chan

    2013-11-01

    CeO2-VO2 bilayer structure was fabricated to investigate the effect of depositing CeO2 film on the optical properties of VO2 film for smart window application. CeO2 was employed as an antireflection (AR) layer material of VO2 film because of its advantages which include high transparency in the visible-near infrared range and high refractive index. All the films were deposited on soda-lime glass substrate by pulsed laser deposition method. Optical calculations were carried out using transfer-matrix method for the purpose of designing CeO2-VO2 bilayer structure with enhanced integrated luminous transmittance (T lum) and switching efficiency (ΔT sol). The optical constants of VO2 and CeO2 films needed for the optical calculation were measured by spectroscopic ellipsometer. The curve of T lum the shape of which depends on the thickness of CeO2 layer, was calculated in each VO2 sample, which showed two maxima. The samples were divided into two groups; one for the highest enhancement of T lum and the other for balanced enhancement between T lum and ΔT sol. The sample with the structure of ~60 nm CeO2 AR layer on 39-nm thick VO2 film showed large increase of T lum (~27%) with ΔT sol of ~5%, which is the largest increase in T lum reported so far. Two samples in the other group showed the balanced enhancement in T lum (~57, ~50%) and ΔT sol (~9, ~10.5%). The effect of CeO2 AR layer on the optical properties of VO2 film was confirmed with the optical calculation and the experimental results. CeO2-VO2 bilayer structure showed notable improvement of optical properties compared to the single VO2 film, indicating that CeO2 layer can be effectively used as the antireflection layer while working as a protective layer that can prevent the oxidation of VO2 layer as well.

  8. "Tailored" submaximal step test for VO2max prediction in healthy older adults.

    PubMed

    Pogliaghi, Silvia; Bellotti, Cecilia; Paterson, Donald H

    2014-04-01

    The authors developed and validated a "tailored" version of the Astrand-Rhyming step test (tA-R) and a new equation for VO2max prediction in older adults (OA). Sixty subjects (age 68 ± 4 yr, 30 male, 30 female) performed their tA-R step test (5-min, 30-cm step, tailored stepping rate) and an incremental cycling test to exhaustion. VO2max was (a) predicted using the standard A-R equation (predicted VO2max), (b) predicted based on the authors' new multiple linear equation (equation VO2max), and (c) directly measured by incremental cycling test (direct VO2max). Agreement among values of VO2max was evaluated by Bland-Altman analysis. The predicted VO2max was not significantly different from the direct VO2max, yet with relatively large imprecision. The equation VO2max allowed more precise as well as accurate predictions of VO2max compared with standard A-R prediction. The "tailored" version of the Astrand-Rhyming step test and the new prediction equation appear suitable for a rapid (5-min), safe (submaximal), accurate, and precise VO2max prediction in healthy OA.

  9. K3VO2(V2As2O12)

    PubMed Central

    Ezzine, Safa; Zid, Mohamed Faouzi; Driss, Ahmed

    2009-01-01

    A new potassium vanadium arsenate, tripotassium trivanadium bis­(arsenate) hexa­oxide, K3VO2(V2As2O12), was synthesized by a solid-state reaction at 743 K. The structure is built up from VO5 pyramids, VO4 tetra­hedra (.m. symmetry) and AsO4 tetra­hedra linked together by corner-sharing to form a three-dimensional framework. The two crystallographically independent K+ cations, one of which has .m. symmetry, are located in the inter­connected tunnels running along the a and b directions. PMID:21583723

  10. Thermochromic light scattering from particulate VO2 layers

    NASA Astrophysics Data System (ADS)

    Montero, José; Ji, Yu-Xia; Granqvist, Claes G.; Niklasson, Gunnar A.

    2016-02-01

    Particulate layers of thermochromic (TC) VO2 were made by reactive DC magnetron sputtering of vanadium onto In2O3:Sn-coated glass. The deposits were characterized by scanning electron microscopy, atomic force microscopy, and X-ray diffraction. Specular and diffuse optical transmittance and reflectance were recorded in the 300-2500-nm wavelength range and displayed pronounced TC effects. These properties could be reconciled with a semi-quantitative model based on Lorentz-Mie theory applied to the distribution of particle sizes and accounting for particle shapes by the Grenfell-Warren approach with equal-volume-to-area spheres.

  11. 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

  12. Decoupling of structural and electronic phase transitions in VO2.

    PubMed

    Tao, Zhensheng; Han, Tzong-Ru T; Mahanti, Subhendra D; Duxbury, Phillip M; Yuan, Fei; Ruan, Chong-Yu; Wang, Kevin; Wu, Junqiao

    2012-10-19

    Using optical, TEM, and ultrafast electron diffraction experiments we find that single crystal VO(2) microbeams gently placed on insulating substrates or metal grids exhibit different behaviors, with structural and metal-insulator transitions occurring at the same temperature for insulating substrates, while for metal substrates a new monoclinic metal phase lies between the insulating monoclinic phase and the metallic rutile phase. The structural and electronic phase transitions in these experiments are strongly first order and we discuss their origins in the context of current understanding of multiorbital splitting, strong correlation effects, and structural distortions that act cooperatively in this system.

  13. Improving the Accuracy of Predicting Maximal Oxygen Consumption (VO2pk)

    NASA Technical Reports Server (NTRS)

    Downs, Meghan E.; Lee, Stuart M. C.; Ploutz-Snyder, Lori; Feiveson, Alan

    2016-01-01

    Maximal oxygen (VO2pk) is the maximum amount of oxygen that the body can use during intense exercise and is used for benchmarking endurance exercise capacity. The most accurate method to determineVO2pk requires continuous measurements of ventilation and gas exchange during an exercise test to maximal effort, which necessitates expensive equipment, a trained staff, and time to set-up the equipment. For astronauts, accurate VO2pk measures are important to assess mission critical task performance capabilities and to prescribe exercise intensities to optimize performance. Currently, astronauts perform submaximal exercise tests during flight to predict VO2pk; however, while submaximal VO2pk prediction equations provide reliable estimates of mean VO2pk for populations, they can be unacceptably inaccurate for a given individual. The error in current predictions and logistical limitations of measuring VO2pk, particularly during spaceflight, highlights the need for improved estimation methods.

  14. A simple model implementation to measure breath by breath the VO2 and VCO2 by the indirect calorimetry technique.

    PubMed

    Cadena, M; Sacristan, E; Infante, O; Rodriguez, F; Escalante, B; Pérez, P; Azpiroz, J

    2006-01-01

    This paper proposes a discrete random time series modeling for the VO2 and VCO2 measurement in the indirect calorimetry technique (ICT). Mathematical equations are developed in order to establish clear differences between the breath-by-breath and mixing chamber measurement based calorimeters. This simple model offers not only a physiological ICT definition approach but also defines the idea of VO2 and VCO2 short-term variability information for research. The preliminary results show a new physiological information when a computer oriented algorithm model implementation was applied to a data acquisition system in order to obtain the power spectrum analysis from a typical observation subject submitted to the clino-ortho maneuver.

  15. Thermochromic films of VO2:W for smart solar energy applications

    NASA Astrophysics Data System (ADS)

    Paone, A.; Joly, M.; Sanjines, R.; Romanyuk, A.; Scartezzini, J.-L.; Schüler, A.

    2009-08-01

    Overheating is a common problem both with the use of active and passive solar energy in thermal solar energy systems and in highly glazed buildings. In solar thermal collectors, the elevated temperatures occurring during stagnation result in reduced lifetime of the collector materials. Highly glazed building facades provide high solar gains in winter, but imply in most cases high energy needs for air conditioning in summer. A solution to such problems might be provided by "smart" thermochromic coatings. A durable inorganic thermochromic material is vanadium dioxide. At 68°C, VO2 undergoes a reversible crystal structural phase transition accompanied by a strong variation in optical properties. By doping the material with tungsten, it is possible to lower the transition temperature making it suitable as a window coating. In order to simulate the optical behaviour of multilayered solar coatings, precise knowledge on the optical material properties is necessary. Experimental data reported in the literature are rare and controversial. We determined the complex dielectric function for VO2:W by spectroscopic UV-VIS-NIR ellipsometry above and below the transition temperature and subsequent point-by-point analysis of the ellipsometric psi/delta data. For a validation, the solar reflectance, absorptance and transmittance were measured by spectrophotometry in the visible range and in the near infrared range up to 2500 nm. The experimental reflectance spectra have been compared with the computer simulations based on the determined optical material properties. Finally, we collected optical data in a more extended wavelength range by digital infrared imaging to detect the switch in thermal emissivity of VO2:W at around 45°C.

  16. 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 VO2 (a-VO2 ) colloids were synthesized by electrochemical anodic oxidation of metallic vanadium. It was found that the a-VO2 colloids have a cotton-like morphology composed of very small clusters, and that the crystallization temperature of the a-VO2 colloids can be adjusted either by the electrolyte of the anodic oxidation or/and the dispersion agent of the colloids. VO2 (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-VO2 colloids at 310 °C under air, which is beneficial for practical applications. The VO2 (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 VO2 (M) NP film.

  17. Challenging a dogma of exercise physiology: does an incremental exercise test for valid VO 2 max determination really need to last between 8 and 12 minutes?

    PubMed

    Midgley, Adrian W; Bentley, David J; Luttikholt, Hans; McNaughton, Lars R; Millet, Gregoire P

    2008-01-01

    A widely cited recommendation is that to elicit valid maximal oxygen uptake (VO(2 max)) values, incremental exercise tests should last between 8 and 12 minutes. However, this recommendation originated from the findings of a single experimental study conducted by Buchfuhrer et al. in 1983. Although this study is an important contribution to scientific knowledge, it should not be viewed as sufficient evidence to support the recommendation for eliciting valid VO(2 max) values. At least eight studies have reported that durations as short as 5 minutes and as long as 26 minutes elicit VO(2 max) values similar to those derived from tests of 8-12 minutes' duration. Two studies reported that the shorter test protocols elicited significantly higher VO(2 max) values in untrained men and women. In three studies that reported significantly higher VO(2 max) values determined during tests of 8-12 minutes than during more prolonged tests, the prolonged tests were associated with maximal treadmill grades of 20-25%, compared with 6-10% in the shorter tests. Therefore, intolerable treadmill grades, rather than the prolonged test duration, may have limited the ability to elicit VO(2 max). In view of the available evidence, test administrators, reviewers and journal editors should not view 8-12 minutes' duration for incremental exercise tests as obligatory for valid VO(2 max) determination. Current evidence suggests that to elicit valid VO(2 max) values, cycle ergometer tests should last between 7 and 26 minutes and treadmill tests between 5 and 26 minutes. This is dependent on the qualification that short tests are preceded by an adequate warm-up and that treadmill grades do not exceed 15%. Current research is too limited to indicate appropriate test duration ranges for discontinuous test protocols, or protocols incorporating high treadmill grades.

  18. Band dispersion near the Fermi level for VO2 thin films grown on TiO2 (001) substrates

    NASA Astrophysics Data System (ADS)

    Saeki, K.; Wakita, T.; Muraoka, Y.; Hirai, M.; Yokoya, T.; Eguchi, R.; Shin, S.

    2009-09-01

    We have performed angle-resolved photoemission spectroscopy (ARPES) measurements of VO2 using epitaxial thin films and observed the band dispersion near the Fermi level (EF) for this compound. The VO2 thin films have been grown on TiO2 (001) single-crystal substrates using pulsed laser deposition. The films exhibit a first-order metal-insulator transition (MIT) at 305 K. In the ARPES spectra of the metallic phase for the films, the O2p band shows highly dispersive features in the binding-energy range of 3-8 eV along the Γ-Z direction. Also, the V3d state shows two dispersive bands around the Γ point near EF , indicative of two electron pockets centered at the Γ point. Both electron pockets have an occupied bandwidth of about 0.4 eV. Assuming the parabolic energy bands around the Γ point, the effective-mass ratios of the two electron pockets are estimated to be about 0.2 and 1. The present work indicates that the ARPES measurements using epitaxial thin films are promising for determining the band structure of VO2 and thus would play a crucial role to elucidate the mechanism of the MIT in VO2 .

  19. Electrolysis-induced protonation of VO2 thin film transistor for the metal-insulator phase modulation

    NASA Astrophysics Data System (ADS)

    Katase, Takayoshi; Endo, Kenji; Ohta, Hiromichi

    2016-02-01

    Compared to state-of-the-art modulation techniques, protonation is the most ideal to control the electrical and optical properties of transition metal oxides (TMOs) due to its intrinsic non-volatile operation. However, the protonation of TMOs is not typically utilized for solid-state devices because of imperative high-temperature annealing treatment in hydrogen source. Although one solution for room temperature (RT) protonation of TMOs is liquid-phase electrochemistry, it is unsuited for practical purposes due to liquid-leakage problem. Herein we demonstrate solid-state RT-protonation of vanadium dioxide (VO2), which is a well-known thermochromic TMO. We fabricated the three terminal thin-film-transistor structure on an insulating VO2 film using a water-infiltrated nanoporous glass, which serves as a solid electrolyte. For gate voltage application, water electrolysis and protonation/deprotonation of VO2 film surface occurred, leading to reversible metal-insulator phase conversion of ~11-nm-thick VO2 layer. The protonation was clearly accompanied by the structural change from an insulating monoclinic to a metallic tetragonal phase. Present results offer a new route for the development of electro-optically active solid-state devices with TMO materials by engineering RT protonation.

  20. Preparation and modification of VO2 thin film on R-sapphire substrate by rapid thermal process

    NASA Astrophysics Data System (ADS)

    Zhu, Nai-Wei; Hu, Ming; Xia, Xiao-Xu; Wei, Xiao-Ying; Liang, Ji-Ran

    2014-04-01

    The VO2 thin film with high performance of metal-insulator transition (MIT) is prepared on R-sapphire substrate for the first time by magnetron sputtering with rapid thermal process (RTP). The electrical characteristic and THz transmittance of MIT in VO2 film are studied by four-point probe method and THz time domain spectrum (THz-TDS). X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and search engine marketing (SEM) are employed to analyze the crystalline structure, valence state, surface morphology of the film. Results indicate that the properties of VO2 film which is oxidized from the metal vanadium film in oxygen atmosphere are improved with a follow-up RTP modification in nitrogen atmosphere. The crystallization and components of VO2 film are improved and the film becomes compact and uniform. A better phase transition performance is shown that the resistance changes nearly 3 orders of magnitude with a 2-°C hysteresis width and the THz transmittances are reduced by 64% and 60% in thermal and optical excitation respectively.

  1. Optical Switching in VO2 films by below-gap excitation

    SciTech Connect

    Dipartimento di Fisica, Universita?di Brescia, Italy; Universite du Quebec, INRS energie et materiaux, Varennes, Quebec; Department of Physics. Clarendon Laboratory, University of Oxford, UK; Department of Physics, University of Tokyo; Institute of Physics, University of Tsukuba, Ibaraki, Japan; Cavalleri, Andrea; Rini, Matteo; Giannetti, Claudio; Fourmaux, Sylvain; Wall, Simon; Hao, Zhao; Parmigiani, Fulvio; Fujimori, Atsushi; Onoda, Masashige; Kieffer, Jean-Claude; Schoenlein, Robert W.; Cavalleri, Andrea

    2008-03-14

    We study the photo-induced insulator-metal transition in VO2, correlating threshold and dynamic evolution with excitation wavelength. In high-quality single crystal samples, we find that switching can only be induced with photon energies above the 670-meV gap. This contrasts with the case of polycrystalline films, where formation of the metallic state can also be triggered with photon energies as low as 180 meV, well below the bandgap. Perfection of this process may be conducive to novel schemes for optical switches, limiters and detectors, operating at room temperature in the mid-IR.

  2. Erythropoietin elevates VO2,max but not voluntary wheel running in mice.

    PubMed

    Kolb, E M; Kelly, S A; Middleton, K M; Sermsakdi, L S; Chappell, M A; Garland, T

    2010-02-01

    Voluntary activity is a complex trait, comprising both behavioral (motivation, reward) and anatomical/physiological (ability) elements. In the present study, oxygen transport was investigated as a possible limitation to further increases in running by four replicate lines of mice that have been selectively bred for high voluntary wheel running and have reached an apparent selection limit. To increase oxygen transport capacity, erythrocyte density was elevated by the administration of an erythropoietin (EPO) analogue. Mice were given two EPO injections, two days apart, at one of two dose levels (100 or 300 microg kg(-1)). Hemoglobin concentration ([Hb]), maximal aerobic capacity during forced treadmill exercise (VO2,max) and voluntary wheel running were measured. [Hb] did not differ between high runner (HR) and non-selected control (C) lines without EPO treatment. Both doses of EPO significantly (P<0.0001) increased [Hb] as compared with sham-injected animals, with no difference in [Hb] between the 100 microg kg(-1) and 300 microg kg(-1) dose levels (overall mean of 4.5 g dl(-1) increase). EPO treatment significantly increased VO2,max by approximately 5% in both the HR and C lines, with no dosexline type interaction. However, wheel running (revolutions per day) did not increase with EPO treatment in either the HR or C lines, and in fact significantly decreased at the higher dose in both line types. These results suggest that neither [Hb] per se nor VO2,max is limiting voluntary wheel running in the HR lines. Moreover, we hypothesize that the decrease in wheel running at the higher dose of EPO may reflect direct action on the reward pathway of the brain.

  3. 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.

  4. Advancements in Optical Properties of Thermochromic VO 2 Films through Experimental and Numerical Investigations

    NASA Astrophysics Data System (ADS)

    Miller, Mark J.

    The Department of Energy reports that buildings consume more than 40% of primary energy in the U.S. and that this trend will continue for the foreseeable future. Furthermore, windows constitute a major path for energy losses from buildings and therefore also present a significant opportunity for efficiency improvement and waste reduction. With this in mind, the work in this dissertation is focused on improving the control of solar and thermal radiation through windows. These radiation spectra can be controlled independently because they peak at different wavelengths due to the much higher temperature (5500 °C) of the Sun compared to objects on Earth (25 °C). In this work, a thermochromic material is utilized to control solar irradiance and a low-emissive (low-E) material is used to control thermal radiation. Thermochromic materials possess optical properties that change in response to temperature and low-E coatings are reflective in the mid-infrared (thermal) region. VO 2 is an exciting candidate for thermochromic coatings because its transmittance in the visible region is relatively constant, but its reflectance in the IR increases significantly with temperature. The main technical issues limiting VO2 are luminous transmittance (Tlum) that is too low and a transition temperature (tauc) that is too high. For the low-E coating, (SnO2)x(In 2O3)1-x (ITO glass) was chosen because it has both high luminous transmittance and low emissivity. In this dissertation it is shown that tauc of VO2 can be lowered from 50 to 45 °C by reducing the grain size of the film from 70 to 31 nm. In the area of luminous transmittance, TiO2 is investigated as an anti-reflective coating which can be used to increase Tlum. Later in this work, it is demonstrated that the energy efficiency gained through VO2 can be further improved by combining it with a low-E coating. The multilayer design combines anti-reflection in the visible region, thermochromism the near-IR and low emissivity in the

  5. Nanoscale probing of electronic band gap and topography of VO2 thin film surfaces by scanning tunneling microscopy

    NASA Astrophysics Data System (ADS)

    Yin, W.; Wolf, S.; Ko, C.; Ramanathan, S.; Reinke, P.

    2011-01-01

    The metal-insulator transition (MIT) in vanadium dioxide in the vicinity of room temperature makes it one of the most interesting materials for novel switching device applications. It is therefore essential to have a fundamental understanding of the VO2 surface when it is incorporated into multilayer structures or nanodevices. This study focuses on the surface modification of VO2 in response to the thermal treatment during phase transition. Vacuum annealing at temperatures in the vicinity of the MIT triggers a partial reduction in the surface, and thus initiates a chemical phase transition. Scanning tunneling microscopy and spectroscopy are used to investigate the electronic properties and surface structure of the VO2 thin film on (0001) sapphire substrates. Band gap maps with a high spatial resolution and single point spectroscopy I-V curves are measured as the sample is cycled through the MIT, and thus provide a direct observation of the surface phase transition at the nanoscale. The VO2 surface exhibits a homogeneous insulating behavior with a typical band gap of ˜0.5 eV at room temperature, and the surface becomes more metallic and spatially inhomogeneous in conductivity during MIT, and wide range of surface oxides can be identified. The surface still remains partially metallic after cooling down from a long period anneal, and such irreversible surface electrical change is attributed to the loss of oxygen. The location of metallic islands after thermal cycling is strongly coupled to the topography of the film, and relaxation processes and continued modification of the spatial distribution of the metallic regions are recognized on a longer timescale. The impact of film morphology, strain, surface chemistry, and structural phase transition on the electronic characteristics of VO2 surfaces are discussed.

  6. A bioinspired solution for spectrally selective thermochromic VO2 coated intelligent glazing.

    PubMed

    Taylor, Alaric; Parkin, Ivan; Noor, Nuruzzaman; Tummeltshammer, Clemens; Brown, Mark S; Papakonstantinou, Ioannis

    2013-09-09

    We present a novel approach towards achieving high visible transmittance for vanadium dioxide (VO(2)) coated surfaces whilst maintaining the solar energy transmittance modulation required for smart-window applications. Our method deviates from conventional approaches and utilizes subwavelength surface structures, based upon those present on the eyeballs of moths, that are engineered to exhibit broadband, polarization insensitive and wide-angle antireflection properties. The moth-eye functionalised surface is expected to benefit from simultaneous super-hydrophobic properties that enable the window to self-clean. We develop a set of design rules for the moth-eye surface nanostructures and, following this, numerically optimize their dimensions using parameter search algorithms implemented through a series of Finite Difference Time Domain (FDTD) simulations. We select six high-performing cases for presentation, all of which have a periodicity of 130 nm and aspect ratios between 1.9 and 8.8. Based upon our calculations the selected cases modulate the solar energy transmittance by as much as 23.1% whilst maintaining high visible transmittance of up to 70.3%. The performance metrics of the windows presented in this paper are the highest calculated for VO(2) based smart-windows.

  7. Monitoring changes in VO2max via the Polar FT40 in female collegiate soccer players.

    PubMed

    Esco, Michael R; Snarr, Ronald L; Williford, Hank N

    2014-01-01

    This study was conducted to determine if the Polar FT40 could accurately track changes in maximal oxygen consumption (VO2max) in a group of female soccer players. Predicted VO2max (pVO2max) via the Polar FT40 and observed VO2max (aVO2max) from a maximal exercise test on a treadmill were determined for members of a collegiate soccer team (n = 20) before and following an 8-week endurance training protocol. Predicted (VO2max and aVO2max measures were compared at baseline and within 1 week post-training. Change values (i.e., the difference between pre to post) for each variable were also determined and compared. There was a significant difference in aVO2max (pre = 43.6 ± 2.4 ml · kg · min(-1), post = 46.2 ± 2.4 ml · kg · min(-1), P < 0.001) and pVO2max (pre = 47.3 ± 5.3 ml · kg · min(-1), post = 49.7 ± 6.2 ml · kg · min(-1), P = 0.009) following training. However, predicted values were significantly greater at each time point compared to observed values (P < 0.001 at pre and P = 0.008 at post). Furthermore, there was a weak correlation between the change in aVO2max and the change in pVO2max (r = 0.18, P = 0.45). The Polar FT40 does not appear to be a valid method for predicting changes in individual VO2max following 8 weeks of endurance training in female collegiate soccer players.

  8. Effects of body mass on exercise efficiency and VO2 during steady-state cycling.

    PubMed

    Berry, M J; Storsteen, J A; Woodard, C M

    1993-09-01

    Oxygen uptake (VO2) and exercise efficiency during cycle ergometer exercise are considered to be independent of body mass. To determine the validity of this assumption, 50 females ranging in body mass from 41.5-98.9 kg exercised on a cycle ergometer with no load at 60 rpm and at 25, 50, 75, and 100 W at 60 and 90 rpm. Gross VO2 and efficiency, net VO2 and efficiency, work VO2 and efficiency, and delta efficiency were computed. Gross and net VO2 were significantly and positively correlated with body mass at all work rates and pedal frequencies. Gross efficiency was significantly and negatively correlated with body mass at all work rates and pedal frequencies. Work VO2 and body mass were not significantly correlated. The correlations between work and delta efficiency and body mass were not significant. Since body mass was found to be significantly correlated with gross VO2, the following equation was developed using stepwise multiple regression to predict gross VO2: VO2 (ml.min-1) = 10.9 (work rate, W) + 8.2 (pedal rate, rpm) + 8.3 (body mass, kg) - 559.6. These data suggest that body mass should be considered when estimating the oxygen uptake during cycle ergometer exercise.

  9. EPR study of VO2+ doped glycine zinc sulphate single crystal

    NASA Astrophysics Data System (ADS)

    Prabakaran, R.; Subramanian, P.

    2015-06-01

    Single crystals Of GZS:VO2+ were grown by slow evaporation of solvent at room temperature. The EPR study was carried out at room temperature. Single crystal rotations in each of the three mutually orthogonal planes indicate single site occupation of VO2+ in the lattice. g and A tensors were calculated from the recorded EPR spectra. The principal values of g and A indicates existence of rhombic symmetry around the VO2+ ion. From the direction cosines of the g and A tensors, the locations of VO2+ in the lattice have been identified as substitutional site.

  10. Utility of a Non-Exercise VO2max Prediction Model for Designing Ramp Test Protocols.

    PubMed

    Cunha, F A; Midgley, A; Montenegro, R; Vasconcellos, F; Farinatti, P

    2015-10-01

    This study investigated the validity of determining the final work rates of cycling and walking ramp-incremented maximal cardiopulmonary exercise tests (CPETs) using a non-exercise model to predict maximal oxygen uptake VO2max and the American College of Sports Medicine ACSM's metabolic equations. The validity of using this methodology to elicit the recommended test duration of between 8 and 12 min was then evaluated. First, 83 subjects visited the laboratory once to perform a cycling (n=49) or walking (n=34) CPET to investigate the validity of the methodology. Second, 25 subjects (cycling group: n=13; walking group: n=12) performed a CPET on 2 separate days to test the reliability of CPET outcomes. Observed VO2max was 1.0 ml·kg(-1)·min(-1) lower than predicted in the cycling CPET (P=0.001) and 1.4 ml·kg(-1)·min(-1) lower in the walking CPET (P=0.001). Only one of the 133 conducted CPETs was outside the test duration range of 8-12 min. Test-retest reliability was high for all CPET outcomes, with intraclass correlation coefficients of 0.90 to 0.99. In conclusion, the non-exercise model is a valid and reliable method for establishing the final work rate of cycling and walking CPETs for eliciting test durations of between 8 and 12 min.

  11. Electrode Reaction Mechanism of Ag2VO2PO4 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 Ag2VO2PO4 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 Ag2VO2PO4 during lithiation makes the investigation of the electrode reaction mechanism difficult with conventional characterization tools. For addressing this issue, a combination of local probes of pair-distribution function andmore » 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

  12. Increase of Structural Phase Transition Temperature with Cr doping in Cr:VO2 Thin Films

    NASA Astrophysics Data System (ADS)

    Brown, B. L.; Lee, Mark; Clem, P.; Nordquist, C. D.; Jordan, T. S.; Wolfley, S. L.; Leonhardt, D.; Custer, J. A.

    2013-03-01

    Bulk crystal VO2 has a well-known structural phase transition near Tc = 68 °C that separates a low-temperature insulating phase from a high-temperature metallic phase with several orders-of-magnitude resistance contrast between the two phases. We report electrical and optical studies of the effect of Cr doping on the Tc in Cr:VO2 thin films. Resistivity, Hall effect, and infrared reflectivity all show that Cr doping systematically increases Tc from 50 °C up to ~ 75 °C at 11% Cr with similar transition width and hysteresis from DC to infrared, but the effect appears to saturate. At the same time, there is a modest decrease in resistance contrast. We will discuss possible effects of both carrier density and scattering changes across Tc on the resistance. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

  13. Laser-processing of VO2 thin films synthesized by polymer-assisted-deposition

    NASA Astrophysics Data System (ADS)

    Breckenfeld, Eric; Kim, Heungsoo; Gorzkowski, Edward P.; Sutto, Thomas E.; Piqué, Alberto

    2017-03-01

    We investigate a novel route for synthesis and laser-sintering of VO2 thin films via solution-based polymer-assisted-deposition (PAD). By replacing the traditional solvent for PAD (water) with propylene glycol, we are able to control the viscosity and improve the environmental stability of the precursor. The solution stability and ability to control the viscosity makes for an ideal solution to pattern simple or complex shapes via direct-write methods. We demonstrate the potential of our precursor for printing applications by combining PAD with laser induced forward transfer (LIFT). We also demonstrate large-area film synthesis on 4 in. diameter glass wafers. By varying the annealing temperature, we identify the optimal synthesis conditions, obtaining optical transmittance changes of 60% at a 2500 nm wavelength and a two-order-of-magnitude semiconductor-to-metal transition. We go on to demonstrate two routes for improved semiconductor-to-metal characteristics. The first method uses a multi-coating process to produce denser films with large particles. The second method uses a pulsed-UV-laser sintering step in films annealed at low temperatures (<450° C) to promote particle growth and improve the semiconductor-to-metal transition. By comparing the hysteresis width and semiconductor-to-metal transition magnitude in these samples, we demonstrate that both methods yield high quality VO2 with a three-order-of-magnitude transition.

  14. The effect of trial familiarisation on the validity and reproducibility of a field-based self-paced VO2max test.

    PubMed

    Lim, W; Lambrick, D; Mauger, A R; Woolley, B; Faulkner, J

    2016-09-01

    The self-paced maximal oxygen uptake (VO2max) test (SPV), which is based on the Borg 6-20 Ratings of Perceived Exertion (RPE) scale, allows participants to self-regulate their exercise intensity during a closed-loop incremental maximal exercise test. As previous research has assessed the utility of the SPV test within laboratory conditions, the purpose to this study was to assess the effect of trial familiarisation on the validity and reproducibility of a field-based, SPV test. In a cross-sectional study, fifteen men completed one laboratory-based graded exercise test (GXT) and three field-based SPV tests. The GXT was continuous and incremental until the attainment of VO2max. The SPV, which was completed on an outdoor 400m athletic track, consisted of five x 2 min perceptually-regulated (RPE11, 13, 15, 17 and 20) stages of incremental exercise. There were no differences in the VO2max reported between the GXT (63.5±10.1 ml·kg(-1)·min(-1)) and each SPV test (65.5±8.7, 65.4±7.0 and 66.7±7.7 ml·kg(-1)·min(-1) for SPV1, SPV2 and SPV3, respectively; P>.05). Similar findings were observed when comparing VO2max between SPV tests (P>.05). High intraclass correlation coefficients were reported between the GXT and the SPV, and between each SPV test (≥.80). Although participants ran faster and further during SPV3, a similar pacing strategy was implemented during all tests. This study demonstrated that a field-based SPV is a valid and reliable VO2max test. As trial familiarisation did not moderate VO2max values from the SPV, the application of a single SPV test is an appropriate stand-alone protocol for gauging VO2max.

  15. Low-temperature CVD synthesis of patterned core-shell VO2@ZnO nanotetrapods and enhanced temperature-dependent field-emission properties.

    PubMed

    Yin, Haihong; Yu, Ke; Song, Changqing; Wang, Zhiliang; Zhu, Ziqiang

    2014-10-21

    VO2 nanostructures are attractive materials because of their reversible metal-insulator transition (MIT) and wide applications in devices. When they are used as field emitters, a new type of temperature-controlled field emission device can be fabricated. Vapor transport methods used to synthesize traditional VO2 nanostructures are energy-intensive, low yield, and produce simple morphology (quasi-1D) that exhibits substrate clamping; thus they are not suitable for field emission applications. To overcome these limitations, ZnO nanotetrapods were used as templates, and patterned core-shell VO2@ZnO nanotetrapods were successfully grown on an ITO/glass substrate via a low-temperature CVD synthesis. SEM, TEM, EDX, XPS analyses and X-ray diffraction revealed that the cores and shells of these nanotetrapods were single crystal wurtzite-type ZnO and polycrystalline VO2, respectively. The VO2@ZnO nanotetrapods show strongly MIT-related FE properties, the emission current density at low temperature is significantly enhanced in comparison with pure VO2 nanostructures, and the emission current density increased by about 20 times as the ambient temperature increased from 25 to 105 °C at a fixed field of 5 V μm(-1). Although the VO2@ZnO nanotetrapods show a worse FE performance at low temperatures compared with pure ZnO nanotetrapods, the FE performance was substantially improved at high temperatures, which was attributed to the MIT-related band bending near the interface and the abrupt resistance change across the MIT.

  16. 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 (τ1—15, 18, and 16 s, A1—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

  17. The Effect of Aging on Relationships between Lean Body Mass and VO2max in Rowers.

    PubMed

    Kim, Chul-Ho; Wheatley, Courtney M; Behnia, Mehrdad; Johnson, Bruce D

    2016-01-01

    Aging is associated with a fall in maximal aerobic capacity as well as with a decline in lean body mass. The purpose of the study was to investigate the influence of aging on the relationship between aerobic capacity and lean body mass in subjects that chronically train both their upper and lower bodies. Eleven older rowers (58±5 yrs) and 11 younger rowers (27±4 yrs) participated in the study. Prior to the VO2max testing, subjects underwent a dual energy X-ray absorptiometry scan to estimate total lean body mass. Subsequently, VO2max was quantified during a maximal exercise test on a rowing ergometer as well as a semi-recumbent cycle ergometer. The test protocol included a pre-exercise stage followed by incremental exercise until VO2max was reached. The order of exercise modes was randomized and there was a wash-out period between the two tests. Oxygen uptake was obtained via a breath-by-breath metabolic cart (Vmax™ Encore, San Diego, CA). Rowing VO2max was higher than cycling VO2max in both groups (p<0.05). Older subjects had less of an increase in VO2max from cycling to rowing (p<0.05). There was a significant relationship between muscle mass and VO2max for both groups (p<0.05). After correcting for muscle mass, the difference in cycling VO2max between groups disappeared (p>0.05), however, older subjects still demonstrated a lower rowing VO2max relative to younger subjects (p<0.05). Muscle mass is associated with the VO2max obtained, however, it appears that VO2max in older subjects may be less influenced by muscle mass than in younger subjects.

  18. The Effect of Aging on Relationships between Lean Body Mass and VO2max in Rowers

    PubMed Central

    Kim, Chul-Ho

    2016-01-01

    Aging is associated with a fall in maximal aerobic capacity as well as with a decline in lean body mass. The purpose of the study was to investigate the influence of aging on the relationship between aerobic capacity and lean body mass in subjects that chronically train both their upper and lower bodies. Eleven older rowers (58±5 yrs) and 11 younger rowers (27±4 yrs) participated in the study. Prior to the VO2max testing, subjects underwent a dual energy X-ray absorptiometry scan to estimate total lean body mass. Subsequently, VO2max was quantified during a maximal exercise test on a rowing ergometer as well as a semi-recumbent cycle ergometer. The test protocol included a pre-exercise stage followed by incremental exercise until VO2max was reached. The order of exercise modes was randomized and there was a wash-out period between the two tests. Oxygen uptake was obtained via a breath-by-breath metabolic cart (Vmax™ Encore, San Diego, CA). Rowing VO2max was higher than cycling VO2max in both groups (p<0.05). Older subjects had less of an increase in VO2max from cycling to rowing (p<0.05). There was a significant relationship between muscle mass and VO2max for both groups (p<0.05). After correcting for muscle mass, the difference in cycling VO2max between groups disappeared (p>0.05), however, older subjects still demonstrated a lower rowing VO2max relative to younger subjects (p<0.05). Muscle mass is associated with the VO2max obtained, however, it appears that VO2max in older subjects may be less influenced by muscle mass than in younger subjects. PMID:27479009

  19. Removing the thermal component from heart rate provides an accurate VO2 estimation in forest work.

    PubMed

    Dubé, Philippe-Antoine; Imbeau, Daniel; Dubeau, Denise; Lebel, Luc; Kolus, Ahmet

    2016-05-01

    Heart rate (HR) was monitored continuously in 41 forest workers performing brushcutting or tree planting work. 10-min seated rest periods were imposed during the workday to estimate the HR thermal component (ΔHRT) per Vogt et al. (1970, 1973). VO2 was measured using a portable gas analyzer during a morning submaximal step-test conducted at the work site, during a work bout over the course of the day (range: 9-74 min), and during an ensuing 10-min rest pause taken at the worksite. The VO2 estimated, from measured HR and from corrected HR (thermal component removed), were compared to VO2 measured during work and rest. Varied levels of HR thermal component (ΔHRTavg range: 0-38 bpm) originating from a wide range of ambient thermal conditions, thermal clothing insulation worn, and physical load exerted during work were observed. Using raw HR significantly overestimated measured work VO2 by 30% on average (range: 1%-64%). 74% of VO2 prediction error variance was explained by the HR thermal component. VO2 estimated from corrected HR, was not statistically different from measured VO2. Work VO2 can be estimated accurately in the presence of thermal stress using Vogt et al.'s method, which can be implemented easily by the practitioner with inexpensive instruments.

  20. 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)

  1. Porous silicon-VO2 based hybrids as possible optical temperature sensor: Wavelength-dependent optical switching from visible to near-infrared range

    NASA Astrophysics Data System (ADS)

    Antunez, E. E.; Salazar-Kuri, U.; Estevez, J. O.; Campos, J.; Basurto, M. A.; Jiménez Sandoval, S.; Agarwal, V.

    2015-10-01

    Morphological properties of thermochromic VO2—porous silicon based hybrids reveal the growth of well-crystalized nanometer-scale features of VO2 as compared with typical submicron granular structure obtained in thin films deposited on flat substrates. Structural characterization performed as a function of temperature via grazing incidence X-ray diffraction and micro-Raman demonstrate reversible semiconductor-metal transition of the hybrid, changing from a low-temperature monoclinic VO2(M) to a high-temperature tetragonal rutile VO2(R) crystalline structure, coupled with a decrease in phase transition temperature. Effective optical response studied in terms of red/blue shift of the reflectance spectra results in a wavelength-dependent optical switching with temperature. As compared to VO2 film over crystalline silicon substrate, the hybrid structure is found to demonstrate up to 3-fold increase in the change of reflectivity with temperature, an enlarged hysteresis loop and a wider operational window for its potential application as an optical temperature sensor. Such silicon based hybrids represent an exciting class of functional materials to display thermally triggered optical switching culminated by the characteristics of each of the constituent blocks as well as device compatibility with standard integrated circuit technology.

  2. A new non-exercise-based Vo2max prediction equation for aerobically trained men.

    PubMed

    Malek, Moh H; Housh, Terry J; Berger, Dale E; Coburn, Jared W; Beck, Travis W

    2005-08-01

    The purposes of the present study were to (a) modify previously published Vo(2)max equations using the constant error (CE = mean difference between actual and predicted Vo(2)max) values from Malek et al. (28); (b) cross-validate the modified equations to determine their accuracy for estimating Vo(2)max in aerobically trained men; (c) derive a new non- exercise-based equation for estimating Vo(2)max in aerobically trained men if the modified equations are not found to be accurate; and (d) cross-validate the new Vo(2)max equation using the predicted residual sum of squares (PRESS) statistic and an independent sample of aerobically trained men. One hundred and fifty-two aerobically trained men (Vo(2)max mean +/- SD = 4,154 +/- 629 ml.min(-1)) performed a maximal incremental test on a cycle ergometer to determine actual Vo(2)max. An aerobically trained man was defined as someone who had participated in continuous aerobic exercise 3 or more sessions per week for a minimum of 1 hour per session for at least the past 18 months. Nine previously published Vo(2)max equations were modified for use with aerobically trained men. The predicted Vo(2)max values from the 9 modified equations were compared to actual Vo(2)max by examining the CE, standard error of estimate (SEE), validity coefficient (r), and total error (TE). Cross-validation of the modified non-exercise-based equations on a random subsample of 50 subjects resulted in a %TE > or = 13% of the mean of actual Vo(2)max. Therefore, the following non-exercise-based Vo(2)max equation was derived from a random subsample of 112 subjects: Vo(2)max (ml.min(-1)) = 27.387(weight in kg) + 26.634(height in cm) - 27.572(age in years) + 26.161(h.wk(-1) of training) + 114.904(intensity of training using the Borg 6-20 scale) + 506.752(natural log of years of training) - 4,609.791 (R = 0.82, R(2) adjusted = 0.65, and SEE = 378 ml.min(-1)). Cross-validation of this equation on the remaining sample of 40 subjects resulted in a %TE of 10

  3. Thermochromic properties of VO2 thin film on SiNx buffered glass substrate

    NASA Astrophysics Data System (ADS)

    Koo, Hyun; You, HyunWoo; Ko, Kyeong-Eun; Kwon, O.-Jong; Chang, Se-Hong; Park, Chan

    2013-07-01

    VO2 thin films were deposited on soda lime glass substrates with silicon nitride sodium-diffusion barrier layer as diffusion barrier, in order to investigate the effect of sodium ion diffusion on the formation of VO2. SiNx layers with thicknesses over 30 nm were found to successfully prevent sodium ion diffusion in VO2 thin film and also contribute to the formation of VO2 thin film, which was confirmed by XRD spectra and XPS measurements. The change of infrared transmittance at 2500 nm wavelength with temperature change from room temperature to 80 °C was increased significantly, and the optical hysteresis width of the sample decreased by almost 6 K as well. The results suggest that applying diffusion barrier can improve the thermochromic properties of the VO2 films for energy-saving smart coatings, and silicon nitride can be one of the effective materials to prevent sodium ion diffusion.

  4. Changes in body temperature influence the scaling of VO2max and aerobic scope in mammals.

    PubMed

    Gillooly, James F; Allen, Andrew P

    2007-02-22

    Debate on the mechanism(s) responsible for the scaling of metabolic rate with body size in mammals has focused on why the maximum metabolic rate (VO2max ) appears to scale more steeply with body size than the basal metabolic rate (BMR). Consequently, metabolic scope, defined as VO2max/BMR, systematically increases with body size. These observations have led some to suggest that VO2max, and BMR are controlled by fundamentally different processes, and to discount the generality of models that predict a single power-law scaling exponent for the size dependence of the metabolic rate. We present a model that predicts a steeper size dependence for VO2max than BMR based on the observation that changes in muscle temperature from rest to maximal activity are greater in larger mammals. Empirical data support the model's prediction. This model thus provides a potential theoretical and mechanistic link between BMR and VO2 max.

  5. High Resolution Orientation Imaging Microscopy

    DTIC Science & Technology

    2012-05-02

    Functions, ICCES 2010, Las Vegas. 17. David Fullwood, Brent Adams, Mike Miles, Stuart Rogers, Ali Khosravani, Raj Mishra, Design for Ductility : Defect... Pseudo -Symmetries by High Resolution EBSD Methods, MS&T. 2009: Pittsburgh. 27. Oliver Johnson, Calvin Gardner, David Fullwood, Brent Adams, George...applied to strain measurements ................................... 6 2.3 Recovery of Lattice Tetragonality and Pseudo -Symmetry Resolution

  6. Li/Ag2VO2PO4 batteries: the roles of composite electrode constituents on electrochemistry

    DOE PAGES

    Bock, David C.; Bruck, Andrea M.; Pelliccione, Christopher J.; ...

    2016-11-01

    In this study, we utilize silver vanadium phosphorous oxide, Ag2VO2PO4, as a model system to systematically study the impact of the constituents of a composite electrode, including polymeric and conductive additives, on electrochemistry. Notably, although highly resistive, this bimetallic cathode can be discharged as a pure electroactive material in the absence of a conductive additive as it generates an in situ conductive matrix via a reduction displacement reaction resulting in the formation of silver metal nanoparticles. Also, three different electrode compositions were investigated: Ag2VO2PO4 only, Ag2VO2PO44 with binder, and Ag2VO2PO4 with binder and carbon. Constant current discharge, pulse testing andmore » impedance spectroscopy measurements were used to characterize the electrochemical properties of the electrodes as a function of depth of discharge. In situ EDXRD was used to spatially resolve the discharge progression within the cathode by following the formation of Ag0. Ex situ XRD and EXAFS modeling were used to quantify the amount of Ag0 formed. Results indicate that the metal center reduced (V5+ or Ag+) was highly dependent on composite composition (presence of PTFE, carbon), depth of discharge (Ag0 nanoparticle formation), and spatial location within the cathode. The addition of a binder was found to increase cell polarization, and the percolation network provided by the carbon in the presence of PTFE was further increased with reduction and formation of Ag0. Lastly, this study provides insight into the factors controlling the electrochemistry of resistive active materials in composite electrodes.« less

  7. VO2+-hydroxyapatite complexes as models for vanadyl coordination to phosphate in bone

    NASA Astrophysics Data System (ADS)

    Dikanov, Sergei A.; Liboiron, Barry D.; Orvig, Chris

    2013-10-01

    We describe a 1D and 2D electron spin echo envelope modulation investigation of VO2+ adsorbed on hydroxyapatite (HA) at different concentrations and compare with VO2+-triphosphate (TPH) complexes studied previously in detail, in an effort to provide more insight into the structure of VO2+ coordination in bone. Structures of this interaction are important because of the role of bone in the long-term storage of administered vanadium, and the likely role of bone in the steady-state release of vanadium leading to the chronic insulin-enhancing anti-diabetic effects of vanadyl complexes. Three similar sets of cross-peaks from phosphorus nuclei observed in the 31P hyperfine sublevel correlation (HYSCORE) spectra of VO2+-HA, VO2+-TPH and VO2+-bone suggest a common tridentate binding motif for triphosphate moieties to the vanadyl ion. The similarities between the systems present the possibility that in vivo vanadyl coordination in bone is relatively uniform. Experiments with HA samples containing different amounts of adsorbed VO2+ demonstrate additional peculiarities of the ion-adsorbent interaction which can be expected in vivo. The HYSCORE spectra of HA samples show varying relative intensities of 31P lines from phosphate ligands and 1H lines, especially lines from protons of coordinated water molecules. This result suggests that the number of equatorial phosphate ligands in HA could be different depending on the water content of the sample and the VO2+ concentration; complexes of different structures probably contribute to the spectra of VO2+-HA. Similar behaviour can also be expected in vivo during VO2+ accumulation in bones.

  8. Reduction of [VO2(ma)2]- and [VO2(ema)2]- by ascorbic acid and glutathione: kinetic studies of pro-drugs for the enhancement of insulin action.

    PubMed

    Song, Bin; Aebischer, Nicolas; Orvig, Chris

    2002-03-25

    To shed light on the role of V(V) complexes as pro-drugs for their V(IV) analogues, the kinetics of the reduction reactions of [VO2(ma)2]- or [VO2(ema)2]- (Hma = maltol, Hema = ethylmaltol), with ascorbic acid or glutathione, have been studied in aqueous solution by spectrophotometric and magnetic resonance methods. EPR and 51V NMR studies suggested that the vanadium(V) in each complex was reduced to vanadium(IV) during the reactions. All the reactions studied showed first-order kinetics when the concentration of ascorbic acid or glutathione was in large excess and the observed first-order rate constants have a linear relationship with the concentrations of reductant (ascorbic acid or glutathione). Potentiometric results revealed that the most important species in the neutral pH range is [VO2(L)2]- for the V(V) system where L is either ma- or ema-. An acid dependence mechanism was proposed from kinetic studies with varying pH and varying maltol concentration. The good fits of the second order rate constant versus pH or the total concentration of maltol, and the good agreement of the constants obtained between fittings, strongly supported the mechanism. Under the same conditions, the reaction rate of [VO2(ma)2]- with glutathione is about 2000 times slower than that of [VO2(ma)2]- with ascorbic acid, but an acid dependence mechanism can also be used to explain the results for the reduction with glutathione. Replacing the methyl group in maltol with an ethyl group has little influence on the reduction rate with ascorbic acid, and the kinetics are the same no matter whether [VO2(ma)2]- or [VO2(ema)2]- is reduced.

  9. Evidence of O2 supply-dependent VO2 max in the exercise-trained human quadriceps.

    PubMed

    Richardson, R S; Grassi, B; Gavin, T P; Haseler, L J; Tagore, K; Roca, J; Wagner, P D

    1999-03-01

    Maximal O2 delivery and O2 uptake (VO2) per 100 g of active muscle mass are far greater during knee extensor (KE) than during cycle exercise: 73 and 60 ml. min-1. 100 g-1 (2.4 kg of muscle) (R. S. Richardson, D. R. Knight, D. C. Poole, S. S. Kurdak, M. C. Hogan, B. Grassi, and P. D. Wagner. Am. J. Physiol. 268 (Heart Circ. Physiol. 37): H1453-H1461, 1995) and 28 and 25 ml. min-1. 100 g-1 (7.5 kg of muscle) (D. R. Knight, W. Schaffartzik, H. J. Guy, R. Predilleto, M. C. Hogan, and P. D. Wagner. J. Appl. Physiol. 75: 2586-2593, 1993), respectively. Although this is evidence of muscle O2 supply dependence in itself, it raises the following question: With such high O2 delivery in KE, are the quadriceps still O2 supply dependent at maximal exercise? To answer this question, seven trained subjects performed maximum KE exercise in hypoxia [0.12 inspired O2 fraction (FIO2)], normoxia (0.21 FIO2), and hyperoxia (1.0 FIO2) in a balanced order. The protocol (after warm-up) was a square wave to a previously determined maximum work rate followed by incremental stages to ensure that a true maximum was achieved under each condition. Direct measures of arterial and venous blood O2 concentration in combination with a thermodilution blood flow technique allowed the determination of O2 delivery and muscle VO2. Maximal O2 delivery increased with inspired O2: 1.3 +/- 0.1, 1.6 +/- 0.2, and 1.9 +/- 0.2 l/min at 0.12, 0.21, and 1.0 FIO2, respectively (P < 0.05). Maximal work rate was affected by variations in inspired O2 (-25 and +14% at 0.12 and 1.0 FIO2, respectively, compared with normoxia, P < 0.05) as was maximal VO2 (VO2 max): 1.04 +/- 0.13, 1. 24 +/- 0.16, and 1.45 +/- 0.19 l/min at 0.12, 0.21, and 1.0 FIO2, respectively (P < 0.05). Calculated mean capillary PO2 also varied with FIO2 (28.3 +/- 1.0, 34.8 +/- 2.0, and 40.7 +/- 1.9 Torr at 0.12, 0.21, and 1.0 FIO2, respectively, P < 0.05) and was proportionally related to changes in VO2 max, supporting our previous finding that a

  10. Effects of training on muscle O2 transport at VO2max

    NASA Technical Reports Server (NTRS)

    Roca, J.; Agusti, A. G.; Alonso, A.; Poole, D. C.; Viegas, C.; Barbera, J. A.; Rodriguez-Roisin, R.; Ferrer, A.; Wagner, P. D.

    1992-01-01

    To quantify the relative contributions of convective and peripheral diffusive components of O2 transport to the increase in leg O2 uptake (VO2leg) at maximum O2 uptake (VO2max) after 9 wk of endurance training, 12 sedentary subjects (age 21.8 +/- 3.4 yr, VO2max 36.9 +/- 5.9 ml.min-1.kg-1) were studied. VO2max, leg blood flow (Qleg), and arterial and femoral venous PO2, and thus VO2leg, were measured while the subjects breathed room air, 15% O2, and 12% O2. The sequence of the three inspirates was balanced. After training, VO2max and VO2leg increased at each inspired O2 concentration [FIO2; mean over the 3 FIO2 values 25.2 +/- 17.8 and 36.5 +/- 33% (SD), respectively]. Before training, VO2leg and mean capillary PO2 were linearly related through the origin during hypoxia but not during room air breathing, suggesting that, at 21% O2, VO2max was not limited by O2 supply. After training, VO2leg and mean capillary PO2 at each FIO2 fell along a straight line with zero intercept, just as in athletes (Roca et al. J. Appl. Physiol. 67: 291-299, 1989). Calculated muscle O2 diffusing capacity (DO2) rose 34% while Qleg increased 19%. The relatively greater rise in DO2 increased the DO2/Qleg, which led to 9.9% greater O2 extraction. By numerical analysis, the increase in Qleg alone (constant DO2) would have raised VO2leg by 35 ml/min (mean), but that of DO2 (constant Qleg) would have increased VO2leg by 85 ml/min, more than twice as much. The sum of these individual effects (120 ml/min) was less (P = 0.013) than the observed rise of 164 ml/min (mean). This synergism (explained by the increase in DO2/Qleg) seems to be an important contribution to increases in VO2max with training.

  11. Intensity-dependent tolerance to exercise after attaining V(O2) max in humans.

    PubMed

    Coats, Edward M; Rossiter, Harry B; Day, James R; Miura, Akira; Fukuba, Yoshiyuki; Whipp, Brian J

    2003-08-01

    The tolerable duration of high-intensity, constant-load cycle ergometry is a hyperbolic function of power, with an asymptote termed critical power (CP) and a curvature constant (W') with units of work. It has been suggested that continued exercise after exhaustion may only be performed below CP, where predominantly aerobic energy transfer can occur and W' can be partially replenished. To test this hypothesis, six volunteers each performed cycle-ergometer exercise with breath-by-breath determination of ventilatory and pulmonary gas exchange variables. Initially, four exercise tests to exhaustion were made: 1). a ramp-incremental and 2). three high-intensity constant-load bouts at different work rates, to estimate lactate (theta(L)) and CP thresholds, W', and maximum oxygen uptake (Vo2 max). Subsequently, subjects cycled to the limit of tolerance (for approximately 360 s) on three occasions, each followed by a work rate reduction to 1). 110% CP, 2). 90% CP, and 3). 80% theta(L) for a 20-min target. W' averaged 20.9 +/- 2.35 kJ or 246 +/- 30 J/kg. After initial fatigue, 110% CP was tolerated for only 30 +/- 12 s. Each subject completed 20 min at 80% theta(L), but only two sustained 20 min at 90% CP; the remaining four subjects fatigued at 577 +/- 306 s, with oxygen consumption at 89 +/- 8% Vo2 max. The results support the suggestion that replenishing W' after fatigue necessitates a sub-CP work rate. The variation in subjects' responses during 90% CP was unexpected but consistent with mechanisms such as reduced CP consequent to prior high-intensity exercise, variation in lactate handling, and/or regional depletion of energy substrates, e.g., muscle glycogen.

  12. Expression of VO2peak in Children and Youth, with Special Reference to Allometric Scaling.

    PubMed

    Loftin, Mark; Sothern, Melinda; Abe, Takashi; Bonis, Marc

    2016-10-01

    The aim of this review was to highlight research that has focused on examining expressions of peak oxygen uptake (VO2peak) in children and youth, with special reference to allometric scaling. VO2peak is considered the highest VO2 during an increasing workload treadmill or bicycle ergometer test until volitional termination. We have reviewed scholarly works identified from PubMed, One Search, EBSCOhost and Google Scholar that examined VO2peak in absolute units (L·min(-1)), relative units [body mass, fat-free mass (FFM)], and allometric expressions [mass, height, lean body mass (LBM) or LBM of the legs raised to a power function] through July 2015. Often, the objective of measuring VO2peak is to evaluate cardiorespiratory function and fitness level. Since body size (body mass and height) frequently vary greatly in children and youth, expressing VO2peak in dimensionless units is often inappropriate for comparative or explanatory purposes. Consequently, expressing VO2peak in allometric units has gained increased research attention over the past 2 decades. In our review, scaling mass was the most frequent variable employed, with coefficients ranging from approximately 0.30 to over 1.0. The wide variance is probably due to several factors, including mass, height, LBM, sex, age, physical training, and small sample size. In summary, we recommend that since skeletal muscle is paramount for human locomotion, an allometric expression of VO2peak relative to LBM is the best expression of VO2peak in children and youth.

  13. Influence of Prior Exercise on VO2 Kinetics Subsequent Exhaustive Rowing Performance

    PubMed Central

    Sousa, Ana; Ribeiro, João; Sousa, Marisa; Vilas-Boas, João Paulo; Fernandes, Ricardo J.

    2014-01-01

    Prior exercise has the potential to enhance subsequent performance by accelerating the oxygen uptake (VO2) kinetics. The present study investigated the effects of two different intensities of prior exercise on pulmonary VO2 kinetics and exercise time during subsequent exhaustive rowing exercise. It was hypothesized that in prior heavy, but not prior moderate exercise condition, overall VO2 kinetics would be faster and the VO2 primary amplitude would be higher, leading to longer exercise time at VO2max. Six subjects (mean ± SD; age: 22.9±4.5 yr; height: 181.2±7.1 cm and body mass: 75.5±3.4 kg) completed square-wave transitions to 100% of VO2max from three different conditions: without prior exercise, with prior moderate and heavy exercise. VO2 was measured using a telemetric portable gas analyser (K4b2, Cosmed, Rome, Italy) and the data were modelled using either mono or double exponential fittings. The use of prior moderate exercise resulted in a faster VO2 pulmonary kinetics response (τ1 = 13.41±3.96 s), an improved performance in the time to exhaustion (238.8±50.2 s) and similar blood lactate concentrations ([La−]) values (11.8±1.7 mmol.L−1) compared to the condition without prior exercise (16.0±5.56 s, 215.3±60.1 s and 10.7±1.2 mmol.L−1, for τ1, time sustained at VO2max and [La−], respectively). Performance of prior heavy exercise, although useful in accelerating the VO2 pulmonary kinetics response during a subsequent time to exhaustion exercise (τ1 = 9.18±1.60 s), resulted in a shorter time sustained at VO2max (155.5±46.0 s), while [La−] was similar (13.5±1.7 mmol.L−1) compared to the other two conditions. Although both prior moderate and heavy exercise resulted in a faster pulmonary VO2 kinetics response, only prior moderate exercise lead to improved rowing performance. PMID:24404156

  14. Evaluation of the American College of Sports Medicine submaximal treadmill running test for predicting VO2max.

    PubMed

    Marsh, Clare E

    2012-02-01

    The purpose of this study was to assess the validity of the American College of Sports Medicine's (ACSM's) submaximal treadmill running test in predicting VO2max. Twenty-one moderately well-trained men aged 18-34 years performed 1 maximal treadmill test to determine maximal oxygen uptake (M VO2max) and 2 submaximal treadmill tests using 4 stages of continuous submaximal exercise. Estimated VO2max was predicted by extrapolation to age-predicted maximal heart rate (HRmax) and calculated in 2 ways: using data from all submaximal stages between 110 b·min(-1) and 85% HRmax (P VO2max-All), and using data from the last 2 stages only (P VO2max-2). The measured VO2max was overestimated by 3% on average for the group but was not significantly different to predicted VO2max (1-way analysis of variance [ANOVA] p = 0.695; M VO2max = 53.01 ± 5.38; P VO2max-All = 54.27 ± 7.16; P VO2max-2 = 54.99 ± 7.69 ml·kg(-1)·min(-1)), although M VO2max was not overestimated in all the participants--it was underestimated in 30% of observations. Pearson's correlation, standard error of estimate (SEE), and total error (E) between measured and predicted VO2max were r = 0.646, 4.35, 4.08 ml·kg(-1)·min(-1) (P VO2max-All) and r = 0.642, 4.21, 3.98 ml·kg(-1)·min(-1) (P VO2max-2) indicating that the accuracy in prediction (error) was very similar whether using P VO2max-All or P VO2max-2, with up to 70% of the participants predicted scores within 1 SEE (∼4 ml·kg(-1)·min(-1)) of M VO2max. In conclusion, the ACSM equation provides a reasonably good estimation of VO2max with no difference in predictive accuracy between P VO2max-2 and P VO2max-All, and hence, either approach may be equally useful in tracking an individual's aerobic fitness over time. However, if a precise knowledge of VO2max is required, then it is recommended that this be measured directly.

  15. Predicting maximal aerobic capacity (VO2max) from the critical velocity test in female collegiate rowers.

    PubMed

    Kendall, Kristina L; Fukuda, David H; Smith, Abbie E; Cramer, Joel T; Stout, Jeffrey R

    2012-03-01

    The objective of this study was to examine the relationship between the critical velocity (CV) test and maximal oxygen consumption (VO2max) and develop a regression equation to predict VO2max based on the CV test in female collegiate rowers. Thirty-five female (mean ± SD; age, 19.38 ± 1.3 years; height, 170.27 ± 6.07 cm; body mass, 69.58 ± 0.3 1 kg) collegiate rowers performed 2 incremental VO2max tests to volitional exhaustion on a Concept II Model D rowing ergometer to determine VO2max. After a 72-hour rest period, each rower completed 4 time trials at varying distances for the determination of CV and anaerobic rowing capacity (ARC). A positive correlation was observed between CV and absolute VO2max (r = 0.775, p < 0.001) and ARC and absolute VO2max (r = 0.414, p = 0.040). Based on the significant correlation analysis, a linear regression equation was developed to predict the absolute VO2max from CV and ARC (absolute VO2max = 1.579[CV] + 0.008[ARC] - 3.838; standard error of the estimate [SEE] = 0.192 L·min(-1)). Cross validation analyses were performed using an independent sample of 10 rowers. There was no significant difference between the mean predicted VO2max (3.02 L·min(-1)) and the observed VO2max (3.10 L·min(-1)). The constant error, SEE and validity coefficient (r) were 0.076 L·min(-1), 0.144 L·min(-1), and 0.72, respectively. The total error value was 0.155 L·min(-1). The positive relationship between CV, ARC, and VO2max suggests that the CV test may be a practical alternative to measuring the maximal oxygen uptake in the absence of a metabolic cart. Additional studies are needed to validate the regression equation using a larger sample size and different populations (junior- and senior-level female rowers) and to determine the accuracy of the equation in tracking changes after a training intervention.

  16. 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..

  17. Effects of muscle electrical stimulation on peak VO2 in cardiac transplant patients.

    PubMed

    Vaquero, A F; Chicharro, J L; Gil, L; Ruiz, M P; Sánchez, V; Lucía, A; Urrea, S; Gómez, M A

    1998-07-01

    Peak oxygen consumption (peak VO2) has become a critical component in the evaluation of heart transplant recipients (HTR). In these patients, peak VO2 remains low after cardiac transplantation mainly because of persisting peripheral limitations in the working muscles. Muscular electrical stimulation, on the other hand, has been shown to enhance the oxidative capacity of healthy muscle. It was the purpose of our investigation to study the effects of ES on the peak VO2 of HTR. Fourteen (11 males and 3 females) HTR (age: 57+/-7yr, mean +/- SD; height: 163+/-7 cm, weight: 70.5+/-8.6 kg) were selected as subjects and each of them was randomly assigned to one of two groups: (a) group EXP (n = 7), receiving electrical stimulation on both quadriceps muscles during a period of 8 weeks, and (b) group CONT (n = 7), not receiving electrical stimulation. Before (PRE) and after (POST) the aforementioned 8-week period, respectively, all the subjects performed a cardiopulmonary exercise test (ramp protocol) on a cycle ergometer for peak VO2 determination. PRE values of peak VO2 were similar in both groups (17.1+/-2.0 vs 16.9+/-3.8ml x kg(-1) x min(-1) in EXP and CONT, respectively). However, peak values of VO2 significantly increased in EXP (p < 0.05) after the period of electrical stimulation (POST peak VO2: 18.7+/-2.0ml x kg(-1)), whereas no change was observed in CONT (POST peak VO2: 16.2+/-3.2 ml x kg(-1) x min(-1)). In conclusion, electrical stimulation could therefore be used to improve the functional capacity of HTR, and might be included in the rehabilitation programs of this population group.

  18. Properties of VO2 Films Sputter-Deposited from V2O5 Target

    NASA Astrophysics Data System (ADS)

    Tsai, Kuang-Yue; Chin, Tsung-Shune; Shieh, Han-Ping D.

    2003-07-01

    Rutile VO2 is a thermochromic material that exhibits a reversible metal-insulator phase transition upon thermal cycling. A new deposition process of rutile VO2 from a V2O5 target was developed using reactive oxygen instead of hydrogen. Adjusting the substrate temperature and the oxygen flow ratio changes the compositions and phases of the as-deposited films into rutile VO2 under optimum deposition conditions on the Si and thick glass substrates. Crystalline phases analyzed by X-ray diffraction shows the relationship among V4O9, V6O13, and VO2 films prepared under different deposition conditions. Analysis by AFM shows that VO2 films grown at higher substrate temperatures have larger grain size. The optical switching property of VO2 was measured at a wavelength of 1.5 μm and transition temperature around 45°C was also measured. Inhomogeneity and the strained structure of the film are suggested to be the reasons of transition temperature lower than typical reported value because the impurity in the target is too low to be detected quantatively by ICP.

  19. Comparison of intensities and rest periods for VO2max verification testing procedures.

    PubMed

    Nolan, P B; Beaven, M L; Dalleck, L

    2014-11-01

    We sought to determine the incidence of 'true' VO2max confirmation with the verification procedure across different protocols. 12 active participants (men n=6, women n=6) performed in random order 4 different maximal graded exercises tests (GXT) and verification bout protocols on 4 separate days. Conditions for the rest period and verification bout intensity were: A - 105% intensity, 20 min rest; B - 105% intensity, 60 min rest; C - 115% intensity, 20 min rest; D - 115% intensity, 60 min rest. VO2max confirmation (difference between peak VO2 GXT and verification trial<±3%) using the verification trial was 12/12 (100%), 12/12 (100%), 8/12 (66.70%), and 7/12 (58.33%) for protocols A, B, C, and D. There was a significant (p<0.05) effect of verification intensity on VO2max confirmation across all exercise test conditions (intensity effect within recovery 20 min (χ(2) (1)=4.800, p<0.05), intensity effect within recovery 60 min (χ(2) (1)=6.316, p<0.05)). No significant effect was found for incidence of VO2max confirmation with different rest periods. We recommend the use of 105% of the maximal GXT workload and 20 min rest periods when using verification trials to confirm VO2max in normally active populations.

  20. Verification Testing to Confirm VO2max in Altitude-Residing, Endurance-Trained Runners.

    PubMed

    Weatherwax, R M; Richardson, T B; Beltz, N M; Nolan, P B; Dalleck, L

    2016-06-01

    We sought to explore the utility of the verification trial to confirm individual attainment of 'true' VO2max in altitude-residing, endurance-trained runners during treadmill exercise. 24 elite endurance-trained men and women runners (age=21.5±3.3 yr, ht=174.8±9.3 cm, body mass=60.5±6.7 kg, PR 800 m 127.5±13.1 s) completed a graded exercise test (GXT) trial (VO2max=60.0±5.8 mL·kg(-1)·min(-1)), and returned 20 min after incremental exercise to complete a verification trial (VO2max=59.6±5.7 mL·kg(-1)·min(-1)) of constant load, supramaximal exercise. The incidence of 'true' VO2max confirmation using the verification trial was 24/24 (100%) with all participants revealing differences in VO2max≤3% (the technical error of our equipment) between the GXT and verification trials. These findings support use of the verification trial to confirm VO2max attainment in altitude-residing, endurance-trained runners.

  1. Comparison of VO2max in obese and non-obese young Indian population.

    PubMed

    Patkar, Kshitija Umesh; Joshi, Anjali S

    2011-01-01

    Incidence of obesity in early life is increasing nowadays because of faulty food habits and lack of exercise. This study was aimed to find out whether obesity affects cardiorespiratory efficiency of young adults. As VO2max is the most accepted indicator of cardiorespiratory efficiency it was compared in 30 obese and 30 non-obese subjects aged around 18-20 years. VO2mx was estimated by Queen's college step test. Various other parameters measured and calculated are weight, height, BMI, skin fold thickness, percentage body fat, lean body mass, fat mass. The results showed that cardiorespiratory efficiency (absolute VO2max & VO2max/kg lean body mass) was not affected (P > 0.05) in obese group in both sexes. Ability to do exhausting work (VO2max/kg body weight) was less in obese group (P = 0.001) compared to non-obese group & in obese males (P < 0.01) as compared to non-obese males. Percentage body fat (r = -0.416), triceps skin fold thickness (r = -0.427) and calf skin fold thickness (r = -0.381) strongly correlate to VO2max/kg body weight. Therefore the exercise programs can be best designed to increase caloric expenditure and thus to decrease body fat rather than to improve aerobic fitness.

  2. Synthesis and characterization of VO2-based thermochromic thin films for energy-efficient windows

    NASA Astrophysics Data System (ADS)

    Batista, Carlos; Ribeiro, Ricardo M.; Teixeira, Vasco

    2011-12-01

    Thermochromic VO2 thin films have successfully been grown on SiO2-coated float glass by reactive DC and pulsed-DC magnetron sputtering. The influence of substitutional doping of V by higher valence cations, such as W, Mo, and Nb, and respective contents on the crystal structure of VO2 is evaluated. Moreover, the effectiveness of each dopant element on the reduction of the intrinsic transition temperature and infrared modulation efficiency of VO2 is discussed. In summary, all the dopant elements--regardless of the concentration, within the studied range-- formed a solid solution with VO2, which was the only compound observed by X-ray diffractometry. Nb showed a clear detrimental effect on the crystal structure of VO2. The undoped films presented a marked thermochromic behavior, specially the one prepared by pulsed-DC sputtering. The dopants effectively decreased the transition of VO2 to the proximity of room temperature. However, the IR modulation efficiency is markedly affected as a consequence of the increased metallic character of the semiconducting phase. Tungsten proved to be the most effective element on the reduction of the semiconducting-metal transition temperature, while Mo and Nb showed similar results with the latter being detrimental to the thermochromism.

  3. Synthesis and characterization of VO2-based thermochromic thin films for energy-efficient windows.

    PubMed

    Batista, Carlos; Ribeiro, Ricardo M; Teixeira, Vasco

    2011-04-07

    Thermochromic VO2 thin films have successfully been grown on SiO2-coated float glass by reactive DC and pulsed-DC magnetron sputtering. The influence of substitutional doping of V by higher valence cations, such as W, Mo, and Nb, and respective contents on the crystal structure of VO2 is evaluated. Moreover, the effectiveness of each dopant element on the reduction of the intrinsic transition temperature and infrared modulation efficiency of VO2 is discussed. In summary, all the dopant elements--regardless of the concentration, within the studied range-- formed a solid solution with VO2, which was the only compound observed by X-ray diffractometry. Nb showed a clear detrimental effect on the crystal structure of VO2. The undoped films presented a marked thermochromic behavior, specially the one prepared by pulsed-DC sputtering. The dopants effectively decreased the transition of VO2 to the proximity of room temperature. However, the IR modulation efficiency is markedly affected as a consequence of the increased metallic character of the semiconducting phase. Tungsten proved to be the most effective element on the reduction of the semiconducting-metal transition temperature, while Mo and Nb showed similar results with the latter being detrimental to the thermochromism.

  4. Familial resemblance for VO2max in the sedentary state: the HERITAGE family study.

    PubMed

    Bouchard, C; Daw, E W; Rice, T; Pérusse, L; Gagnon, J; Province, M A; Leon, A S; Rao, D C; Skinner, J S; Wilmore, J H

    1998-02-01

    This study investigates the familial resemblance of maximal oxygen uptake (VO2max) based on data from 86 nuclear families of Caucasian descent participating in the HERITAGE Family Study. In the current study, VO2max was measured twice on a cycle ergometer in 429 sedentary individuals (170 parents and 259 of their offspring), aged between 16 and 65 yr. The VO2max was adjusted by regression procedures for the effects of 1) age and sex; 2) age, sex, and body mass; and 3) age, sex, body mass, fat mass, and fat-free mass, as determined by underwater weighing. Evidence for significant familial resemblance was observed for each of the three VO2max phenotypes. Spouse, sibling, and parent-offspring correlations were significant, suggesting that both genetic and environmental factors contribute to the familial resemblance for VO2max. Maximal heritability estimates were at least 50%, a value inflated to an undetermined degree by nongenetic factors. The hypothesis of maternal inheritance, with the father's contribution being environmental, was also found to fit the data with estimates of maternal heritability, potentially associated in part with mitochondrial inheritance, reaching about 30%. These results suggest that genetic and nongenetic factors as well as maternal influences contribute to the familial aggregation of VO2max in sedentary individuals.

  5. Block training periodization in alpine skiing: effects of 11-day HIT on VO2max and performance.

    PubMed

    Breil, Fabio A; Weber, Simone N; Koller, Stefan; Hoppeler, Hans; Vogt, Michael

    2010-08-01

    Attempting to achieve the high diversity of training goals in modern competitive alpine skiing simultaneously can be difficult and may lead to compromised overall adaptation. Therefore, we investigated the effect of block training periodization on maximal oxygen consumption (VO2max) and parameters of exercise performance in elite junior alpine skiers. Six female and 15 male athletes were assigned to high-intensity interval (IT, N = 13) or control training groups (CT, N = 8). IT performed 15 high-intensity aerobic interval (HIT) sessions in 11 days. Sessions were 4 x 4 min at 90-95% of maximal heart rate separated by 3-min recovery periods. CT continued their conventionally mixed training, containing endurance and strength sessions. Before and 7 days after training, subjects performed a ramp incremental test followed by a high-intensity time-to-exhaustion (tlim) test both on a cycle ergometer, a 90-s high-box jump test as well as countermovement (CMJ) and squat jumps (SJ) on a force plate. IT significantly improved relative VO2max by 6.0% (P < 0.01; male +7.5%, female +2.1%), relative peak power output by 5.5% (P < 0.01) and power output at ventilatory threshold 2 by 9.6% (P < 0.01). No changes occurred for these measures in CT. tlim remained unchanged in both groups. High-box jump performance was significantly improved in males of IT only (4.9%, P < 0.05). Jump peak power (CMJ -4.8%, SJ -4.1%; P < 0.01), but not height decreased in IT only. For competitive alpine skiers, block periodization of HIT offers a promising way to efficiently improve VO2max and performance. Compromised explosive jump performance might be associated with persisting muscle fatigue.

  6. Continuous Tuning of Phase Transition Temperature in VO2 Thin Films on c-Cut Sapphire Substrates via Strain Variation.

    PubMed

    Jian, Jie; Wang, Xuejing; Li, Leigang; Fan, Meng; Zhang, Wenrui; Huang, Jijie; Qi, Zhimin; Wang, Haiyan

    2017-02-15

    Vanadium dioxide (VO2) thin films with controlled thicknesses are deposited on c-cut sapphire substrates with Al-doped ZnO (AZO) buffer layers by pulsed laser deposition. The surface roughness of AZO buffer layers is varied by controlling oxygen pressure during growth. The strain in the VO2 lattice is found to be dependent on the VO2 thickness and the VO2/AZO interface roughness. The semiconductor-to-metal transition (SMT) properties of VO2 thin films are characterized and the transition temperature (Tc) is successfully tuned by the VO2 thickness as well as the VO2/AZO interface roughness. It shows that the Tc of VO2 decreases with the decrease of film thickness or VO2/AZO interface roughness. Other SMT properties of the VO2 films are maintained during the Tc tuning. The results suggest that the strain tuning induced by AZO buffer provides an effective approach for tuning Tc of VO2 continuously.

  7. Validation of a Ramp Running Protocol for Determination of the True VO2max in Mice

    PubMed Central

    Ayachi, Mohamed; Niel, Romain; Momken, Iman; Billat, Véronique L.; Mille-Hamard, Laurence

    2016-01-01

    In the field of comparative physiology, it remains to be established whether the concept of VO2max is valid in the mouse and, if so, how this value can be accurately determined. In humans, VO2max is generally considered to correspond to the plateau observed when VO2 no longer rises with an increase in workload. In contrast, the concept of VO2peak tends to be used in murine studies. The objectives of the present study were to determine whether (i) a continuous ramp protocol yielded a higher VO2peak than a stepwise, incremental protocol, and (ii) the VO2peak measured in the ramp protocol corresponded to VO2max. The three protocols (based on intensity-controlled treadmill running until exhaustion with eight female FVB/N mice) were performed in random order: (a) an incremental protocol that begins at 10 m.min−1 speed and increases by 3 m.min−1 every 3 min. (b) a ramp protocol with slow acceleration (3 m.min−2), and (c) a ramp protocol with fast acceleration (12 m.min−2). Each protocol was performed with two slopes (0 and 25°). Hence, each mouse performed six exercise tests. We found that the value of VO2peak was protocol-dependent (p < 0.05) and was highest (59.0 ml.kg 0.75.min−1) for the 3 m.min−2 0° ramp protocol. In the latter, the presence of a VO2max plateau was associated with the fulfillment of two secondary criteria (a blood lactate concentration >8 mmol.l−1 and a respiratory exchange ratio >1). The total duration of the 3 m.min−2 0° ramp protocol was shorter than that of the incremental protocol. Taken as a whole, our results suggest that VO2max in the mouse is best determined by applying a ramp exercise protocol with slow acceleration and no treadmill slope. PMID:27621709

  8. Validation of a Ramp Running Protocol for Determination of the True VO2max in Mice.

    PubMed

    Ayachi, Mohamed; Niel, Romain; Momken, Iman; Billat, Véronique L; Mille-Hamard, Laurence

    2016-01-01

    In the field of comparative physiology, it remains to be established whether the concept of VO2max is valid in the mouse and, if so, how this value can be accurately determined. In humans, VO2max is generally considered to correspond to the plateau observed when VO2 no longer rises with an increase in workload. In contrast, the concept of VO2peak tends to be used in murine studies. The objectives of the present study were to determine whether (i) a continuous ramp protocol yielded a higher VO2peak than a stepwise, incremental protocol, and (ii) the VO2peak measured in the ramp protocol corresponded to VO2max. The three protocols (based on intensity-controlled treadmill running until exhaustion with eight female FVB/N mice) were performed in random order: (a) an incremental protocol that begins at 10 m.min(-1) speed and increases by 3 m.min(-1) every 3 min. (b) a ramp protocol with slow acceleration (3 m.min(-2)), and (c) a ramp protocol with fast acceleration (12 m.min(-2)). Each protocol was performed with two slopes (0 and 25°). Hence, each mouse performed six exercise tests. We found that the value of VO2peak was protocol-dependent (p < 0.05) and was highest (59.0 ml.kg (0.75).min(-1)) for the 3 m.min(-2) 0° ramp protocol. In the latter, the presence of a VO2max plateau was associated with the fulfillment of two secondary criteria (a blood lactate concentration >8 mmol.l(-1) and a respiratory exchange ratio >1). The total duration of the 3 m.min(-2) 0° ramp protocol was shorter than that of the incremental protocol. Taken as a whole, our results suggest that VO2max in the mouse is best determined by applying a ramp exercise protocol with slow acceleration and no treadmill slope.

  9. 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.

  10. Formation mechanism of a microscale domain and effect on transport properties in strained VO2 thin films on TiO2(001)

    NASA Astrophysics Data System (ADS)

    Kawatani, Kenichi; Kanki, Teruo; Tanaka, Hidekazu

    2014-08-01

    We investigated film thickness dependence of domain size and transport property in VO2 thin films on rutile TiO2 (001) substrates and identified formation mechanism of the microscaled domain. It was found that domain size decreased with increasing film thickness and the domain boundary consisted of cracks and dislocations, clarified by high-resolution transmission electron microscopy. The detailed images showed, the tensile-strained VO2 lattices received by TiO2 (001) were partially relaxed around the cracks and dislocations. The relaxed lattice is likely to return the original metal-insulator transition temperature of 340 K, whereas the tensile-strained lattice has the transition at 300 K in a VO2/TiO2 (001) system. Thus, the mixed states of strained and relaxed crystal lattice and the increase in dislocation density in thicker films cause the overly broad resistance behavior against temperature. Furthermore, the origin of the dislocations and the thickness dependence of the domain size could be explained by the energy release of shear stress generated by competition between the pinning layers at near-interface VO2 layers holding the tetragonal structure and the near-surface layers separated from the substrate attempting the lattice transformation to a monoclinic structure. This understanding enables us to more precisely design the size and configuration of these domains and their transport properties.

  11. 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

  12. Microwave-Assisted Synthesis of Silver Vanadium Phosphorus Oxide, Ag2VO2PO4 : Crystallite Size Control and Impact on Electrochemistry

    DOE PAGES

    Huang, Jianping; Marschilok, Amy C.; Takeuchi, Esther S.; ...

    2016-03-07

    We study silver vanadium phosphorus oxide, Ag2VO2PO4, that is a promising cathode material for Li batteries due in part to its large capacity and high current capability. Herein, a new synthesis of Ag2VO2PO4 based on microwave heating is presented, where the reaction time is reduced by approximately 100× relative to other reported methods, and the crystallite size is controlled via synthesis temperature, showing a linear correlation of crystallite size with temperature. Notably, under galvanostatic reduction, the Ag2VO2PO4 sample with the smallest crystallite size delivers the highest capacity and shows the highest loaded voltage. Further, pulse discharge tests show a significantmore » resistance decrease during the initial discharge coincident with the formation of Ag metal. Thus, the magnitude of the resistance decrease observed during pulse tests depends on the Ag2VO2PO4 crystallite size, with the largest resistance decrease observed for the smallest crystallite size. Additional electrochemical measurements indicate a quasi-reversible redox reaction involving Li+ insertion/deinsertion, with capacity fade due to structural changes associated with the discharge/charge process. In summary, this work demonstrates a faster synthetic approach for bimetallic polyanionic materials which also provides the opportunity for tuning of electrochemical properties through control of material physical properties such as crystallite size.« less

  13. Effects of specific muscle training on VO2 on-response and early blood lactate.

    PubMed

    Cerretelli, P; Pendergast, D; Paganelli, W C; Rennie, D W

    1979-10-01

    The relationship between half time of the O2 uptake on-response (t1/2 VO2on, seconds) and early blood lactate accumulation (delta Lab, mmol.1(-1) at the onset of submaximal arm and/or leg exercise was the object of a cross-sectional study of sedentary subjects (S,n = 3), and kayakers (K, n = 8), and of a longitudinal study on 11 untrained subjects of specific arm vs. leg training. In supine arm cranking (W = 125 watts) S had an average t1/2 VO2on of 82 s and a delta Aab of 9.2 mmol.1(-1) compared to 47 +/- 7 s and 4 +/- 1.4 mmol.1(-1), respectively, for K. In longitudinal trainees shorter t1/2 VO2on was accompanied by lower Lab for the trained limbs. Specific limb conditioning in swimmers and runners resulted in shorter t1/2 VO2on. A linear relationship was observed between delta Lab and t1/2 VO2on having an intercept on the time axis at congruent to 20 s and a slope proportional to muscle mass. Trained muscles were grouped closest to the intercept indicating local acceleration of the rate of O2 transfer approaching the t1/2 VO2on for isolated perfused muscle at the onset of work. Since t1/2 VO2on, we conclude that factors distal to the capillary are specifically involved in the local training response.

  14. Markers of inflammation are inversely associated with VO2 max in asymptomatic men.

    PubMed

    Kullo, Iftikhar J; Khaleghi, Mahyar; Hensrud, Donald D

    2007-04-01

    We investigated whether markers of inflammation, including a cytokine (IL-6), acute-phase reactants [C-reactive protein (CRP) and fibrinogen], and white blood cell (WBC) count are associated with maximal O(2) consumption (Vo(2 max)) in men without coronary heart disease (CHD). In asymptomatic men (n = 172, 51 +/- 9.3 yr old), Vo(2 max) was measured during a symptom-limited graded treadmill exercise test. Physical activity level was assessed by a standardized questionnaire. IL-6 and CRP were measured by immunoassays, fibrinogen by the Clauss method, and WBC count with a Coulter counter. IL-6 and CRP were logarithmically transformed to reduce skewness. Multivariable regression was used to assess whether markers of inflammation were associated with Vo(2 max) after adjustment for age, body mass index, CHD risk factors, and lifestyle variables (physical activity level, percent body fat, and alcohol intake). Vo(2 max) was 34.5 ml.kg(-1).min(-1) (SD 6.1). Log IL-6 (r = -0.38, P < 0.001), log CRP (r = -0.40, P < 0.001), fibrinogen (r = -0.42, P < 0.001), and WBC count (r = -0.22, P = 0.004) were each correlated with Vo(2 max). In separate multivariable linear regression models that adjusted for age, body mass index, CHD risk factors, and lifestyle variables, log IL-6 [beta-coeff = -1.66 +/- 0.63 (SE), P = 0.010], log CRP [beta-coeff = -0.99 +/- 0.33 (SE), P = 0.003], fibrinogen [beta-coeff = -1.51 +/- 0.44 (SE), P = 0.001], and WBC count [beta-coeff = -0.52 +/- 0.30 (SE), P = 0.088] were each inversely associated with Vo(2 max). In conclusion, higher circulating levels of IL-6, CRP, and fibrinogen are independently associated with lower Vo(2 max) in asymptomatic men.

  15. VO2 max is associated with ACE genotype in postmenopausal women.

    PubMed

    Hagberg, J M; Ferrell, R E; McCole, S D; Wilund, K R; Moore, G E

    1998-11-01

    Relationships have frequently been found between angiotensin-converting enzyme (ACE) genotype and various pathological and physiological cardiovascular outcomes and functions. Thus we sought to determine whether ACE genotype affected maximal O2 consumption (VO2 max) and maximal exercise hemodynamics in postmenopausal women with different habitual physical activity levels. Age, body composition, and habitual physical activity levels did not differ among ACE genotype groups. However, ACE insertion/insertion (II) genotype carriers had a 6.3 ml . kg-1 . min-1 higher VO2 max (P < 0.05) than the ACE deletion/deletion (DD) genotype group after accounting for the effect of physical activity levels. The ACE II genotype group also had a 3.3 ml . kg-1 . min-1 higher VO2 max (P < 0.05) than the ACE insertion/deletion (ID) genotype group. The ACE ID group tended to have a higher VO2 max than the DD genotype group, but the difference was not significant. ACE genotype accounted for 12% of the variation in VO2 max among women after accounting for the effect of habitual physical activity levels. The entire difference in VO2 max among ACE genotype groups was the result of differences in maximal arteriovenous O2 difference (a-vDO2). ACE genotype accounted for 17% of the variation in maximal a-vDO2 in these women. Maximal cardiac output index did not differ whatsoever among ACE genotype groups. Thus it appears that ACE genotype accounts for a significant portion of the interindividual differences in VO2 max among these women. However, this difference is the result of genotype-dependent differences in maximal a-vDO2 and not of maximal stroke volume and maximal cardiac output.

  16. A comparison of time to exhaustion at VO2 max in élite cyclists, kayak paddlers, swimmers and runners.

    PubMed

    Billat, V; Faina, M; Sardella, F; Marini, C; Fanton, F; Lupo, S; Faccini, P; de Angelis, M; Koralsztein, J P; Dalmonte, A

    1996-02-01

    A recent study has shown the reproducibility of time to exhaustion (time limit: tlim) at the lowest velocity that elicits the maximal oxygen consumption (vVO2 max). The same study found an inverse relationship between this time to exhaustion at vVO2 max and vVO2 max among 38 élite long-distance runners (Billat et al. 1994b). The purpose of the present study was to compare the time to exhaustion at the power output (or velocity) at VO2 max for different values of VO2 max, depending on the type of exercise and not only on the aerobic capacity. The time of exhaustion at vVO2 max (tlim) has been measured among 41 élite (national level) sportsmen: 9 cyclists, 9 kayak paddlers, 9 swimmers and 14 runners using specific ergometers. Velocity or power at VO2 max (vVO2 max) was determined by continuous incremental testing. This protocol had steps of 2 min and increments of 50 W, 30 W, 0.05 m s-1 and 2 km-1 for cyclists, kayak paddlers, swimmers and runners, respectively. One week later, tlim was determined under the same conditions. After a warm-up of 10 min at 60% of their vVO2 max, subjects were concluded (in less than 45 s) to their vVO2 max and then had to sustain it as long as possible until exhaustion. Mean values of vVO2 max and tlim were respectively equal to 419 +/- 49 W (tlim = 222 +/- 91 s), 239 +/- 56 W (tlim = 376 +/- 134 s), 1.46 +/- 0.09 m s-1 (tlim = 287 +/- 160 s) and 22.4 +/- 0.8 km h-1 (tlim = 321 +/- 84 s), for cyclists, kayak paddlers, swimmers and runners. Time to exhaustion at vVO2 max was only significantly different between cycling and kayaking (ANOVA test, p < 0.05). Otherwise, VO2 max (expressed in ml min-1 kg-1) was significantly different between all sports except between cycling and running (p < 0.05). In this study, time to exhaustion at vVO2 max was also inversely related to VO2 max for the entire group of élite sportsmen (r = -0.320, p < 0.05, n = 41). The inverse relationship between VO2 max and tlim at vVO2 max has to be explained, it

  17. Electronic, thermoelectric and optical properties of vanadium oxides: VO2, V2O3 and V2O 5

    NASA Astrophysics Data System (ADS)

    Lamsal, Chiranjivi

    Correlated electrons in vanadium oxides are responsible for their extreme sensitivity to external stimuli such as pressure, temperature or doping. As a result, several vanadium oxides undergo insulator-to-metal phase transition (IMT) accompanied by structural change. Unlike vanadium pentoxide (V2O5), vanadium dioxide (VO2) and vanadium sesquioxide (V2O3) show IMT in their bulk phases. In this study, we have performed one electron Kohn-Sham electronic band-structure calculations of VO2, V2O3 and V2O 5 in both metallic and insulating phases, implementing a full ab-initio simulation package based on Density Functional Theory (DFT), Plane Waves and Pseudopotentials (PPs). Electronic band structures are found to be influenced by crystal structure, crystal field splitting and strong hybridization between O2p and V3d bands. "Intermediate bands", with narrow band widths, lying just below the higher conduction bands, are observed in V2O 5 which play a critical role in optical and thermoelectric processes. Similar calculations are performed for both metallic and insulating phases of bulk VO2 and V2O3. Unlike in the metallic phase, bands corresponding to "valence electrons" considered in the PPs are found to be fully occupied in the insulating phases. Transport parameters such as Seebeck coefficient, electrical conductivity and thermal (electronic) conductivity are studied as a function of temperature at a fixed value of chemical potential close to the Fermi energy using Kohn-Sham band structure approach coupled with Boltzmann transport equations. Because of the layered structure and stability, only V2O5 shows significant thermoelectric properties. All the transport parameters have correctly depicted the highly anisotropic electrical conduction in V2O 5. Maxima and crossovers are also seen in the temperature dependent variation of Seebeck coefficient in V2O5, which can be consequences of "specific details" of the band structure and anisotropic electron-phonon interactions

  18. Service Oriented Architecture for High Level Applications

    SciTech Connect

    Chu, Chungming; Chevtsov, Sergei; Wu, Juhao; Shen, Guobao; /Brookhaven

    2012-06-28

    Standalone high level applications often suffer from poor performance and reliability due to lengthy initialization, heavy computation and rapid graphical update. Service-oriented architecture (SOA) is trying to separate the initialization and computation from applications and to distribute such work to various service providers. Heavy computation such as beam tracking will be done periodically on a dedicated server and data will be available to client applications at all time. Industrial standard service architecture can help to improve the performance, reliability and maintainability of the service. Robustness will also be improved by reducing the complexity of individual client applications.

  19. 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.

  20. Echinacea purpurea supplementation does not enhance VO2max in distance runners.

    PubMed

    Baumann, Cory W; Bond, Kelsey L; Rupp, Jeffrey C; Ingalls, Christopher P; Doyle, J Andrew

    2014-05-01

    Oral supplementation of Echinacea purpurea (ECH) has been reported to increase levels of serum erythropoietin and as a result improve endurance performance in untrained subjects. The purpose of this study was to determine if ECH supplementation alters maximal oxygen uptake (VO2max) in trained endurance runners. Using a double-blind design, 16 trained endurance runners (9 ECH and 7 placebo [PLA]) supplemented with either 8,000 mg·d(-1) of ECH or wheat flour (PLA) for 6 weeks. Maximal aerobic treadmill tests and blood samples were measured before and after supplementation to determine VO2max, hematocrit (Hct), and hemoglobin (Hb). VO2max, Hct, and Hb did not differ between the ECH and PLA groups before or after supplementation. Furthermore, supplementation of ECH failed to improve VO2max (67.37 ± 4.62 vs. 67.23 ± 5.82 ml·kg(-1)·min(-1)), Hct (43.57 ± 2.38 vs. 42.85 ± 1.46%), or Hb (14.93 ± 1.27 vs. 15.55 ± 0.80 g·dL(-1)) from baseline measurements. Echinacea purpurea supplementation of 8,000 mg·d(-1) for 6 weeks failed to increase VO2max, Hct, or Hb in trained endurance runners and thus does not seem to influence physiological variables that affect distance running performance.

  1. Scaling of VO2max and its relationship with insulin resistance in children.

    PubMed

    Ahn, Bumsoo; McMurray, Robert; Harrell, Joanne

    2013-02-01

    The relationship between insulin resistance (HOMA-IR), percent body fat, and aerobic fitness (VO2max per unit fat free mass; mL/kgFFM/min) was examined in 1,710 children. Percent body fat was estimated from sum of skinfolds, and VO2max was estimated from submaximal cycle ergometer tests. Overnight fasting blood samples were obtained. VO2max (mL/kgFFM/min) and percent body fat were correlated with HOMA-IR (r = -0.076, p < .002; r = .420, p < .001, respectively); as was VO2max in units of mL/kg/min (r = -0.264, p < .001). When VO2max in mL/kg/min was used, a progressive increase in HOMA-IR was found with decreasing fitness (p < .05). However, when mL/kgFFM/min was used, HOMA-IR scores remained similar between moderate-fit and low-fit group. The stronger association between aerobic fitness (mL/kg/min) and HOMA-IR is partially due to the significant association of fat mass to HOMA-IR. Therefore, our recommendation is to express aerobic fitness in units of mL/kgFFM/min to eliminate the confounding factor of adiposity and better understand the influence of muscle on insulin resistance.

  2. Echinacea Purpurea Supplementation does not Enhance VO2max in Distance Runners.

    PubMed

    Baumann, Cory W; Bond, Kelsey L; Rupp, Jeffrey C; Ingalls, Christopher P; Doyle, J Andrew

    2013-11-20

    Oral supplementation of echinacea purpurea (ECH) has been reported to increase levels of serum erythropoietin (EPO) and as a result improve endurance performance in untrained subjects. The purpose of this study was to determine if ECH supplementation alters maximal oxygen uptake (VO2max) in trained endurance runners. Using a double-blind design, 16 trained endurance runners (9 ECH and 7 placebo-PLA) supplemented with either 8000 mg·d of ECH or wheat flour (PLA) for 6 weeks. Maximal aerobic treadmill tests and blood samples were measured before and after supplementation to determine VO2max, hematocrit (Hct) and hemoglobin (Hb). VO2max, Hct and Hb did not differ between the ECH and PLA group before or after supplementation. Furthermore, supplementation of ECH failed to improve VO2max (67.37 ± 4.62 vs. 67.23 ± 5.82 mL⋅kg⋅min), Hct (43.57 ± 2.38 vs. 42.85 ± 1.46%) or Hb (14.93 ± 1.27 vs. 15.55 ± .80 g·dL) from baseline measurements. Echinacea purpurea (ECH) supplementation of 8000 mg·d for 6 weeks failed to increase VO2max, Hct or Hb in trained endurance runners and thus does not appear to influence physiological variables that affect distance-running performance.

  3. Concentration Dependence of VO2+ Crossover of Nafion for Vanadium Redox Flow Batteries

    SciTech Connect

    Lawton, Jamie; Jones, Amanda; Zawodzinski, Thomas A

    2013-01-01

    The VO2+ crossover, or permeability, through Nafion in a vanadium redox flow battery (VRFB) was monitored as a function of sulfuric acid concentration and VO2+ concentration. A vanadium rich solution was flowed on one side of the membrane through a flow field while symmetrically on the other side a blank or vanadium deficit solution was flowed. The blank solution was flowed through an electron paramagnetic resonance (EPR) cavity and the VO2+ concentration was determined from the intensity of the EPR signal. Concentration values were fit using a solution of Fick s law that allows for the effect of concentration change on the vanadium rich side. The fits resulted in permeability values of VO2+ ions across the membrane. Viscosity measurements of many VO2+ and H2SO4 solutions were made at 30 60 C. These viscosity values were then used to determine the effect of the viscosity of the flowing solution on the permeability of the ion. 2013 The Electrochemical Society. [DOI: 10.1149/2.004306jes] All rights reserved.

  4. Transport Anisotropy of Epitaxial VO2 films grown on (100) TiO2

    NASA Astrophysics Data System (ADS)

    Kittiwatanakul, Salinporn; Lu, Jiwei; Wolf, Stuart

    2011-03-01

    Vanadium dioxide (VO2) exhibits a metal semiconductor transition (MST) at 340 K. This transition is accompanied by the abrupt change in the electrical conductivity, optical transmittance and reflectance in infrared region, which can be used in the electronic devices such as temperature sensors and electric switches. In this study, Reactive Bias Target Ion Beam Deposition was used for epitaxial VO2 thin film growth on Ti O2 (100) substrates. The out-of-plane and the in-plane XRD scans have been performed to confirm the single phase VO2 and the epitaxial relationship between the film and the substrate. The hall bars along the in-plane c-axis and b-axis of R-VO2 were fabricated via the photolithographic process. It is found that the maximum conductivity was parallel to c-axis, while the minimum conductivity was parallel to b-axis. The conductivity anisotropy persisted through the metal semiconductor transition. The conductivity anisotropy ratio σc / σb was found to be ~ 16.2 at 300 K, much larger than that of single crystal VO2 . The temperature dependent anisotropy of the carrier concentration and the mobility is to be discussed.

  5. Negative capacitance switching via VO2 band gap engineering driven by electric field

    NASA Astrophysics Data System (ADS)

    He, Xinfeng; Xu, Jing; Xu, Xiaofeng; Gu, Congcong; Chen, Fei; Wu, Binhe; Wang, Chunrui; Xing, Huaizhong; Chen, Xiaoshuang; Chu, Junhao

    2015-03-01

    We report the negative capacitance behavior of an energy band gap modulation quantum well with a sandwich VO2 layer structure. The phase transition is probed by measuring its capacitance. With the help of theoretical calculations, it shows that the negative capacitance changes of the quantum well device come from VO2 band gap by continuously tuning the temperature or voltage. Experiments reveal that as the current remains small enough, joule heating can be ignored, and the insulator-metal transition of VO2 can be induced by the electric field. Our results open up possibilities for functional devices with phase transitions induced by external electric fields other than the heating or electricity-heat transition.

  6. Direct observation of the M2 phase with its Mott transition in a VO2 film

    NASA Astrophysics Data System (ADS)

    Kim, Hoon; Slusar, Tetiana V.; Wulferding, Dirk; Yang, Ilkyu; Cho, Jin-Cheol; Lee, Minkyung; Choi, Hee Cheul; Jeong, Yoon Hee; Kim, Hyun-Tak; Kim, Jeehoon

    2016-12-01

    In VO2, the explicit origin of the insulator-to-metal transition is still disputable between Peierls and Mott insulators. Along with the controversy, its second monoclinic (M2) phase has received considerable attention due to the presence of electron correlation in undimerized vanadium ions. However, the origin of the M2 phase is still obscure. Here, we study a granular VO2 film using conductive atomic force microscopy and Raman scattering. Upon the structural transition from monoclinic to rutile, we observe directly an intermediate state showing the coexistence of monoclinic M1 and M2 phases. The conductivity near the grain boundary in this regime is six times larger than that of the grain core, producing a donut-like landscape. Our results reveal an intra-grain percolation process, indicating that VO2 with the M2 phase is a Mott insulator.

  7. Theoretical investigation of the optical and EPR parameters for VO 2+ion in some complexes

    NASA Astrophysics Data System (ADS)

    Kalfaoğlu, Emel; Karabulut, Bünyamin

    2012-04-01

    The molecular orbital coefficients and the EPR parameters of trisodium citrate dihydrate, sodium hydrogen oxalate monohydrate, potassium d-gluconate monohydrate and L-Alanine vanadyl complexes are calculated theoretically. Two d-d transition spectra and EPR parameters for the VO2+ complex are calculated theoretically by using crystal-field theory. The calculated g and A paramaters have indicated that paramagnetic center is axially symmetric. Having the relations of g∥A⊥ for VO2+ ions, it can be concluded that VO2+ ions are located in distorted octahedral sites (C4v) elongated along the z-axis and the ground state of the paramagnetic electron is dxy.

  8. Effects of simulated weightlessness and sympathectomy on maximum VO2 of male rats

    NASA Technical Reports Server (NTRS)

    Woodman, C. R.; Stump, C. S.; Beaulieu, S. M.; Rahman, Z.; Sebastian, L. A.

    1989-01-01

    The effects of simulated weightlessness (hind-limb suspension) and chemical sympathectomy (by repeated injections with guanethidine sulfate) on the maximum oxygen consumption (VO2 max) of female rats were investigated in rats assigned for 14 days to one of three groups: a head-down hind-limb suspension, a horizontal suspension with hind limbs weight bearing, or the caged control. The VO2 max values were assessed by having rats run on a treadmill enclosed in an airtight chamber. The hind-limb-suspended sympathectomized rats were found to exhibit shorter run times and lower mechanical efficiencies, compared to their presuspension values or the values from saline-injected suspended controls. On the other hand, the suspended sympathectomized rats did not demonstrate a decrease in the VO2 max values that was observed in saline-injected controls.

  9. Hydrothermal synthesis of Mo-doped VO2/TiO2 composite nanocrystals with enhanced thermochromic performance.

    PubMed

    Li, Dengbing; Li, Ming; Pan, Jing; Luo, Yuanyuan; Wu, Hao; Zhang, Yunxia; Li, Guanghai

    2014-05-14

    This paper reports a one-step TiO2 seed-assistant hydrothermal synthesis of Mo-doped VO2(M)/TiO2 composite nanocrystals. It was found that excess Mo doping can promote formation of the VO2(M) phase, and rutile TiO2 seed is beneficial to morphology control, size reduction, and infrared modulation of Mo-doped VO2(M) nanocrystals. The Mo-doped VO2 nanocrystals epitaxially grow on TiO2 seeds and have a quasi-spherical shape with size down to 20 nm and a nearly 35% infrared modulation near room temperature. The findings of this work demonstrate important progress in the near-room-temperature thermochromic performance of VO2(M) nanomaterials, which will find potential application in constructing VO2(M) nanocrystal-based smart window coatings.

  10. Prediction of VO2peak from the 20-m shuttle-run test in youth with Down syndrome.

    PubMed

    Agiovlasitis, Stamatis; Pitetti, Kenneth H; Guerra, Myriam; Fernhall, Bo

    2011-04-01

    This study examined whether 20-m shuttle-run performance, sex, body mass index (BMI), age, height, and weight are associated with peak oxygen uptake (VO2peak) in youth with Down syndrome (DS; n = 53; 25 women, age 8-20 years) and whether these variables can be used to develop an equation to predict VO2peak. BMI, 20-m shuttle-run performance, and sex were significantly associated with VO2peak in youth with DS, whereas age, height, and weight were not. A regression model included only shuttle-run performance as a significant predictor of VO2peak; however, the developed prediction equation had low individual predictability. Therefore, 20-m shuttle-run performance alone does not provide valid prediction of VO2peak in youth with DS. Sex, BMI, age, height, and weight do not improve the prediction of VO2peak.

  11. Optical properties of correlated materials: Generalized Peierls approach and its application to VO2

    NASA Astrophysics Data System (ADS)

    Tomczak, Jan M.; Biermann, Silke

    2009-08-01

    The aim of this paper is to present a versatile scheme for the computation of optical properties of solids, with particular emphasis on realistic many-body calculations for correlated materials. Geared at the use with localized basis sets, we extend the commonly known lattice “Peierls substitution” approach to the case of multiatomic unit cells. We show in how far this generalization can be deployed as an approximation to the full Fermi-velocity matrix elements that enter the continuum description of the response of a solid to incident light. We further devise an upfolding scheme to incorporate optical transitions that involve high-energy orbitals that had been downfolded in the underlying many-body calculation of the electronic structure. As an application of the scheme, we present results on a material of longstanding interest, vanadium dioxide, VO2 . Using dynamical mean-field data of both, the metallic and the insulating phase, we calculate the corresponding optical conductivities, elucidate optical transitions and find good agreement with experimental results.

  12. Ultrafast nano-imagining of the photoinduced phase transition dynamics in VO2

    NASA Astrophysics Data System (ADS)

    Doenges, Sven A.; Khatib, Omar; O'Callahan, Brian T.; Atkin, Joanna M.; Park, Jae Hyung; Cobden, David H.; Raschke, Markus B.

    Many quantum phase transitions in correlated matter exhibit spatial inhomogeneities with expected yet unexplored effects on the associated ultrafast dynamics. Here we demonstrate the combination of ultrafast non-degenerate pump-probe spectroscopy with scattering scanning near-field optical microscopy (s-SNOM) for ultrafast nano-imaging. In a femtosecond near-field non-degenerate near-IR (NIR) pump and mid-IR (MIR) probe experiment, we study the photoinduced insulator-to-metal (IMT) transition in nominally homogeneous VO2 micro-crystals using far-from equilibrium excitation. We observe spatial heterogeneity on 50-100 nm length scales in the fluence dependent IMT dynamics, ranging from sub-100 fs to 1 ps. With pump fluences as high as nominally 10 mJ/cm2 we can reach distinct excitation and saturation regimes. These results suggest a large sensitivity of the IMT with respect to local variations in strain, doping, or defects difficult to discern microscopically.

  13. Wafer-scale growth of VO2 thin films using a combinatorial approach

    PubMed Central

    Zhang, Hai-Tian; Zhang, Lei; Mukherjee, Debangshu; Zheng, Yuan-Xia; Haislmaier, Ryan C.; Alem, Nasim; Engel-Herbert, Roman

    2015-01-01

    Transition metal oxides offer functional properties beyond conventional semiconductors. Bridging the gap between the fundamental research frontier in oxide electronics and their realization in commercial devices demands a wafer-scale growth approach for high-quality transition metal oxide thin films. Such a method requires excellent control over the transition metal valence state to avoid performance deterioration, which has been proved challenging. Here we present a scalable growth approach that enables a precise valence state control. By creating an oxygen activity gradient across the wafer, a continuous valence state library is established to directly identify the optimal growth condition. Single-crystalline VO2 thin films have been grown on wafer scale, exhibiting more than four orders of magnitude change in resistivity across the metal-to-insulator transition. It is demonstrated that ‘electronic grade' transition metal oxide films can be realized on a large scale using a combinatorial growth approach, which can be extended to other multivalent oxide systems. PMID:26450653

  14. Development of a rowing-specific VO2max field test.

    PubMed

    Huntsman, Heather D; DiPietro, Loretta; Drury, Daniel G; Miller, Todd A

    2011-06-01

    The purpose of this study was to develop an aerobic capacity test for rowers using minimal equipment that could be used in the field. Thirty rowers (15 men and 15 women) between the ages of 18 and 26 years were recruited on a volunteer basis from the District of Columbia metro area. The testing protocol consisted of a maximum of 7 2-minute stages on a rowing ergometer, separated by 30-second breaks where lactic acid concentrations were analyzed. Starting intensity for men was 200 W, although women started at 150 W, and each stage increased by 50 W. Expired gasses were collected during the test, and athletes were asked to row until maximal volition so that the directly measured VO2max could be compared to predicted values. Peak heart rates from each completed stage were plotted, and regression equations were calculated to predict VO2max. Separate regression equations were calculated for men and women. The predicted VO2max values were approximately 23 and 25% lower than what was actually achieved for men and women, respectively. Heart rate was a stronger correlate of VO2max in men compared with in women. Among men, we observed a moderate and statistically significant correlation (r = 0.55; p = 0.05), whereas among women, no such agreement was observed (r = -0.05; p > 0.85). The principle finding of this study was that the test was adequate in predicting VO2max in men but was inadequate in its prediction in women. With slight modifications to the testing protocol, stronger correlations and a more accurate prediction of VO2max is expected in men.

  15. Influences of chemical sympathectomy, demedullation, and hindlimb suspension on the VO2max of rats

    NASA Technical Reports Server (NTRS)

    Woodman, C. R.; Stump, C. S.; Sebastian, L. A.; Tipton, C. M.

    1992-01-01

    Results from previous studies have shown that the reduction in maximal oxygen consumption (VO2max) with simulated microgravity is attenuated in chemically sympathectomized rats. To determine the contributions of the catecholamines from the adrenal medulla in this process, investigations were conducted with 65 saline injected (SAL) and chemically sympathectomized (SX) female rats that were either surgically demedullated (DM), or intact (IN). Microgravity conditions were simulated by head-down suspension (HDS) while controls were assigned to individual cages (CC). The experimental period was 14 d. The rats were tested for VO2max, treadmill run time (RT), and submaximal mechanical efficiency (ME) prior to suspension and on days 7 and 14. Saline injected rats that had intact adrenal medullas (SAL-IN) exhibited significantly reduced measures of VO2max after 7 and 14 d by 15% and 21%, respectively. No significant reduction in VO2max was observed with HDS in the SX-IN animals. Sympathectomized rats that were demedullated (SX-DM) also exhibited a significant reduction in VO2max (12%). In addition, HDS was associated with a marked and significant reduction in RT in all groups. ME for submaximal exercise was significantly reduced after HDS in SAL-IN rats but not in the SX-IN rats. SX-DM rats experienced significant reductions in ME similar in magnitude to the SAL-IN rats. These results confirm that chemical sympathectomy attenuates the expected decrease in VO2max with HDS and suggests that circulating epinephrine contributes to this response.

  16. Relationship between Maximal Oxygen Consumption (VO2max) and Home Range Area in Mammals.

    PubMed

    Albuquerque, Ralph L; Sanchez, Gabriela; Garland, Theodore

    2015-01-01

    Home range is defined as the area traversed during normal daily activities, such as foraging, avoiding predators, and social or antagonistic behaviors. All else being equal, larger home ranges should be associated with longer daily movement distances and/or higher average movement speeds. The maximal rate of oxygen consumption (VO2max) generally sets an upper limit to the intensity of work (e.g., speed of locomotion) that an animal can sustain without fatigue. Therefore, home range area and VO2max are predicted to evolve in concert (coadapt). We gathered literature data on home range and VO2max for 55 species of mammals. We computed residuals from log-log (allometric) regressions on body mass with two different regression models: ordinary least squares (OLS) and phylogenetic generalized least squares (PGLS). Residuals were weakly positively related for both the OLS (r = 0.278, one-tailed P < 0.05) and PGLS (r = 0.210, P > 0.05) regressions. For VO2max, the PGLS regression model had a slightly higher likelihood than the OLS model, but the situation was reversed for home range area. In addition, for both home range area and VO2max, models that fit better than either OLS or PGLS were obtained by modeling residual variation with the Ornstein-Uhlenbeck process to mimic stabilizing selection (RegOU), indicating that phylogenetic signal is present in both size-adjusted traits, consistent with findings of previous studies. (However, residuals from the RegOU models cannot be tested for correlation due to mathematical complexities.) We conclude that the best estimate of the residual correlation is probably somewhere between these two values reported above. Possible reasons for the low correlation between residual home range area and VO2max are discussed.

  17. 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.

  18. Direct correlation of structural and electrical properties of electron-doped individual VO2 nanowires on devised TEM grids

    NASA Astrophysics Data System (ADS)

    Jo, Y.-R.; Kim, M.-W.; Kim, B.-J.

    2016-10-01

    Nano-scale VO2 wires with controlled parameters such as electron-doping have attracted intense interest due to their capability of suppressing the temperature of the metal-insulator transition (MIT). However, because their diameters are smaller than the spatial resolutions of the conventional measuring equipment, the ability to perform a thorough examination of the wires has been hindered. Here, we report the fabrication of a transmission electron microscopy (TEM) grid with an optimum design of Si3N4 windows on which the photolithography for individual electron-doped VO2 nanowire devices can be safely accomplished, allowing the cross-examination of the structural and electrical properties. TEM dark-field imaging was used to quantitatively investigate the fractions of rutile and M1 phases, and their lattice alignments were observed using high-resolution TEM (HRTEM) with small area diffraction. Moreover, electron energy loss spectroscopy (EELS) revealed that the rutile domain would be created by the strain induced by oxygen vacancies. Importantly, we successfully tuned the transition temperature by changing the rutile fraction while maintaining a high level of resistivity change. The resistivity at room temperature linearly decreased with the rutile fraction, following a simple model. Furthermore, the T dependence of the threshold voltage can be attributed to the Joule heating, exhibiting an identical thermal dependence, irrespective of the rutile fraction.

  19. Thermochromic VO2 thin films deposited by magnetron sputtering for smart window applications

    NASA Astrophysics Data System (ADS)

    Fortier, Jean-Philippe

    objectives in mind. To start, we had to find a first recipe to obtain our first samples of the material. Using the literature as a starting point, several samples were deposited by magnetron sputtering while improving certain deposition conditions as well as varying influential deposition parameters. Once the oxide obtained, it was necessary to optimize the parameters not only to render thermochromic coatings with the highest possible quality, but also to determine each parameter's sensitivity. Characterization techniques such as microscopy, spectroscopy, ellipsometry, scanning electron microscopy, atomic force microscopy, Raman spectroscopy, x-ray diffraction and finally, time-of-flight secondary ion mass spectrometry were used to analyze different aspects of our multiple samples. Indeed, to mention only the ix most relevant observations, we were able to confirm that the microstructure, composition, most relevant observations, we were able to confirm that the microstructure, composition, crystallinity and film thickness have a significant impact on the coating's thermochromic behavior as well as on its optical properties. As a result, the oxygen concentration and the thickness had to be optimized and the deposition temperature, maximized. Reactive poisoning of the sputtering target is also a phenomenon that needs to be considered during deposition. Then, our sputtering target and substrate cleaning procedures were improved following certain observations. VO2 was equally found to be sensitive to small temperature gradients in addition of being highly dependent upon high deposition temperatures. Finally, the use of different substrates has subsequently shown that the film composition and microstructure can be altered. After mastering the deposition of thin VO2 films, we explored another path that we found to be quite innovative. A relatively new deposition technique called HiPIMS was put to the test based on its new characteristics, leading to believe that it had the

  20. Preliminary investigation of energy comparation between gyroscope, electromyography and VO2 wearable sensors.

    PubMed

    Williams, Gareth; Saiyi Li; Pathirana, Pubudu N

    2016-08-01

    Building on previous experiments in the domain of energy expenditure estimation using wearable sensors, the measurements of energy ratios of a runner on a treadmill were analyzed to observe any commonalities between an inertia measurement unit and an electromyograph sensor. The subjects were equipped with a VO2 gas measurement device, an Inertial Measurement Unit (IMU) measuring gyroscopic activity and an electromyography (EMG) sensor network whilst running at 5 different speeds on a calibrated treadmill. The observed results established a co-linear relationship with the gyroscope based measurements, EMG based measurements with the VO2 measurements.

  1. Frequency of the VO2max plateau phenomenon in world-class cyclists.

    PubMed

    Lucía, A; Rabadán, M; Hoyos, J; Hernández-Capilla, M; Pérez, M; San Juan, A F; Earnest, C P; Chicharro, J L

    2006-12-01

    We aimed to determine the frequency of the VO2max plateau phenomenon in top-level male professional road cyclists (n = 38; VO2max [mean +/- SD]: 73.5 +/- 5.5 ml.kg(-1).min(-1)) and in healthy, sedentary male controls (n = 37; VO2max: 42.7 +/- 5.6 ml.kg(-1).min(-1)). All subjects performed a continuous incremental cycle-ergometer test of 1-min workloads until exhaustion. Power output was increased from a starting value of 25 W (cyclists) or 20 W (controls) at the rate of 25 W.min(-1) (cyclists) or 20 W.min(-1) (controls) until volitional exhaustion. We measured gas-exchange and heart rate (HR) throughout the test. Blood concentrations of lactate (BLa) were measured at end-exercise in both groups. We defined maximal exercise exertion as the attainment of a respiratory exchange rate (RER) >or= 1.1; HR > 95 % age-predicted maximum; and BLa > 8 mmo.l(-1). The VO2max plateau phenomenon was defined as an increase in two or more consecutive 1-min mean VO2 values of less than 1.5 ml.kg(-1).min(-1). Most cyclists met our criteria for maximal exercise effort (RER > 1.1, 100 %; 95 % predicted maximal HR [HRmax], 82 %; BLa > 8 mmol.l(-1), 84 %). However, the proportion of cyclists attaining a V.O (2max) plateau was considerably lower, i.e., 47 %. The majority of controls met the criteria for maximal exercise effort (RER > 1.1, 100 %; predicted HRmax, 68 %; BLa > 8 mmol. l(-1), 73 %), but the proportion of these subjects with a VO2max plateau was only 24 % (significantly lower proportion than in cyclists [p < 0.05]). Scientists should consider 1) if typical criteria of attainment of maximal effort are sufficiently stringent, especially in elite endurance athletes; and 2) whether those humans exhibiting the VO2max plateau phenomenon are those who perform an absolute maximum effort or there are additional distinctive features associated with this phenomenon.

  2. Development of a submaximal test to predict elliptical cross-trainer VO2max.

    PubMed

    Dalleck, Lance C; Kravitz, Len; Robergs, Robert A

    2006-05-01

    The purpose of this study was to develop an equation to predict VO2max from a submaximal elliptical cross-trainer test. Fifty-four apparently healthy subjects (25 men and 29 women, mean +/- SD age: 29.5 +/- 7.1 years, height: 173.3 +/- 12.6 cm, weight: 72.3 +/- 7.9 kg, percent body fat: 17.3 +/- 5.0%, and elliptical cross-trainer VO2max: 43.9 +/- 7.2 ml x kg(-1) x min(-1)) participated in the study and were randomly assigned to an original sample group (n = 40) and a cross-validation group (n = 14). Each subject completed an elliptical cross-trainer submaximal (3 5-minute submaximal stages) and a VO2max test on the same day, with a 15-minute rest period in between. Stepwise multiple regression analyses were used to develop an equation for estimating elliptical cross-trainer VO2max from the data of the original sample group. The accuracy of the equation was tested by using data from the cross-validation group. Because there was no shrinkage in R2 between the original sample group and the cross-validation group, data were combined in the final prediction equation (R2 = 0.732, standard error of the estimate = 3.91 ml x kg(-1) x min(-1), p < 0.05): VO2max = 73.676 + 7.383(gender) - 0.317(weight) + 0.003957(age x cadence) - 0.006452(age x heart rate at stage 2). The correlation coefficient between the predicted and measured VO2max values was r = 0.86. Dependent t-tests resulted in no significant differences (p > 0.05) between predicted (43.8 ml x kg(-1) x min(-1)) and measured (43.9 ml x kg(-1) x min(-1)) VO2max measurements. Results indicate that the protocol and equation developed in the current study can be used by exercise professionals to provide acceptably accurate estimates of VO2max in non-laboratory-based settings.

  3. Microwave-assisted synthesis and electrochemical evaluation of VO2 (B) nanostructures

    DOE PAGES

    Ashton, Thomas E.; Borras, David Hevia; Iadecola, Antonella; ...

    2015-12-01

    Understanding how intercalation materials change during electrochemical operation is paramount to optimising their behaviour and function and in situ characterisation methods allow us to observe these changes without sample destruction. Here, we first report the improved intercalation properties of bronze phase vanadium dioxide VO2 (B) prepared by a microwave assisted route which exhibits a larger electrochemical capacity (232 mAh g-1) compared to VO2 (B) prepared by a solvothermal route (197 mAh g-1). These electrochemical differences have also been followed using in situ X-ray absorption spectroscopy allowing us to follow oxidation state changes as they occur during battery operation.

  4. A thermochromic low-emittance coating: Calculations for nanocomposites of In2O3:Sn and VO2

    NASA Astrophysics Data System (ADS)

    Li, S.-Y.; Niklasson, G. A.; Granqvist, C. G.

    2011-09-01

    Calculations based on the Bruggeman effective medium theory were applied to thin films comprising a heavily doped wide band gap semiconductor (specifically In2O3:Sn (ITO)) and VO2. Films with ˜20 vol. % of VO2 can combine a 10% thermochromic modulation of the solar energy throughput with a luminous transmittance of 50%-60% and low thermal emittance. The maximum thermochromic modulation is ˜13% and occurs at ˜35 vol. % VO2. Coatings of ITO-VO2 are of interest for energy efficient fenestration.

  5. Resistance switching of epitaxial VO2/Al2O3 heterostructure at room temperature induced by organic liquids

    NASA Astrophysics Data System (ADS)

    Yang, Mengmeng; Yang, Yuanjun; Hong, Bin; Huang, Haoliang; Hu, Sixia; Dong, Yongqi; Wang, Haibo; He, Hao; Zhao, Jiyin; Liu, Xuguang; Luo, Zhenlin; Li, Xiaoguang; Zhang, Haibin; Gao, Chen

    2015-03-01

    We studied using organic liquids (cyclohexane, n-butanol, and ethylene glycol) to modulate the transport properties at room temperature of an epitaxial VO2 film on a VO2/Al2O3 heterostructure. The resistance of the VO2 film increased when coated with cyclohexane or n-butanol, with maximum changes of 31% and 3.8%, respectively. In contrast, it decreased when coated with ethylene glycol, with a maximum change of -7.7%. In all cases, the resistance recovered to its original value after removing the organic liquid. This organic-liquid-induced reversible resistance switching suggests that VO2 films can be used as organic molecular sensors.

  6. Sex differences in the effects of 12 weeks sprint interval training on body fat mass and the rates of fatty acid oxidation and VO2max during exercise

    PubMed Central

    Bagley, Liam; Slevin, Mark; Bradburn, Steven; Liu, Donghui; Murgatroyd, Chris; Morrissey, George; Carroll, Michael; Piasecki, Mathew; Gilmore, William S; McPhee, Jamie S

    2016-01-01

    Background The purpose of this study was to examine whether very short duration, very high intensity sprint interval training (SIT) leads to loss of body fat mass in association with improvements to VO2max and fatty acid oxidation, and to assess the extent of sex dimorphism in these physiological responses. Methods A total of 24 men and 17 women (mean (SEM) age: 39 (±2) years; body mass index 24.6 (0.6)) completed measurements of the maximal rate of oxygen uptake (VO2max) and fatty acid oxidation (FATmax). Body fat and lean mass were measured by dual emission x-ray absorptiometry, and fasting blood lipid, glucose and insulin profiles were assessed before and after training. SIT consisted of 4×20 s sprints on a cycle ergometer at approximately 175% VO2max, three times per week for 12 weeks. Results Fat mass decreased by 1.0 kg, although men lost statistically significantly more fat than women both when expressed in Kg and as % body fat. VO2max increased by around 9%, but women improved VO2max significantly more than men. FATmax improved by around 13%, but fasting plasma glucose, insulin, total triglyceride, total cholesterol and high-density lipoprotein (HDL) did not change after training, while low-density lipoprotein decreased by 8% (p=0.028) and the HDL:Total Cholesterol ratio improved by 6%. There were no sex differences in these metabolic responses to training. Conclusions These results show lower body fat %, and higher rates of fatty acid oxidation and VO2max after 12 weeks of training for just 4 min per week. Notably, women improved VO2max more than men, while men lost more fat than women. PMID:27900150

  7. Phase coexistence and pressure-temperature phase evolution of VO2(A ) nanorods near the semiconductor-semiconductor transition

    NASA Astrophysics Data System (ADS)

    Samanta, Sudeshna; Li, Quanjun; Cheng, Benyuan; Huang, Yanwei; Pei, Cuiying; Wang, Qinglin; Ma, Yanzhang; Wang, Lin

    2017-01-01

    A comprehensive understanding of the physical origins of the phase transition behaviors of transition metal oxides is still complex due to the interplay among competing interactions of comparable strengths tuning their nature. Widespread interest in such phase transitions has motivated explorations of nanocrystalline vanadium dioxide (VO2) in various forms and a long-running debate persists over the roles played by electron-electron correlation with lattice distortion. External stimuli like pressure and temperature have strong effects on the appearance, stability, and spacial distribution of the high-resistive (HR) and low-resistive (LR) phases accompanying their structural modification. Our comprehensive experiments establish the pressure-induced and thermally driven evolution of phase coexistence in VO2(A ) nanorods. Our experimental evidence supports coexisting HR and LR phases, where compression suppressed coexistence at ˜7 GPa, followed by a semiconductor-semiconductor transition at around ˜10 GPa with the absence of pressure-induced metallization. X-ray diffraction revealed lattice distortion with local microscopic strain inhomogeneity in the nanorods, without any discontinuity in the pressure-volume data. We further investigated the vibrational modes and relaxations of the samples related to their thermal expansions. We also found that the pressure-dependent hierarchy of microstructural densification contributed significantly to the resulting transport properties.

  8. Periodic porous thermochromic VO2(M) films with enhanced visible transmittance.

    PubMed

    Zhou, Min; Bao, Jian; Tao, Minshan; Zhu, Rui; Lin, Yingting; Zhang, Xiaodong; Xie, Yi

    2013-07-11

    A periodic porous structure is introduced for the first time into a VO2(M) film to block only heat rather than light. The as-obtained 2D and 3D films show excellent visible transmittance and solar modulation efficiency.

  9. Prediction VO2max during cycle ergometry based on submaximal ventilatory indicators.

    PubMed

    Nunes, Rodolfo Alkmim Moreira; Vale, Rodrigo Gomes de Souza; Simão, Roberto; de Salles, Belmiro Freitas; Reis, Victor Machado; Novaes, Jefferson da Silva; Miranda, Humberto; Rhea, Matthew R; Medeiros, Aldo da Cunha

    2009-09-01

    There are several equations to predict maximum oxygen consumption (VO2max) from ergometric test variables on different ergometers. However, a similar equation using ventilatory thresholds of ergospirometry in a submaximal test on a cycle ergometer is unavailable. The aim of the present study was to assess the accuracy of VO2max prediction models based on indicators of submaximal effort. Accordingly, 4,640 healthy, nonathlete women ages 20 years and older volunteered to be tested on a cycle ergometer using a maximum incremental protocol. The subjects were randomly assigned to 2 groups: group A (estimation) and group B (validation). From the independent variables of weight in kilograms, the second workload threshold (WT2), and heart rate of the second threshold (HRT2), it was possible to build a multiple linear regression model to predict maximal oxygen consumption (VO2max = 40.302 - 0.497 [Weight] - 0.001 [HRT2] + 0.239 [WT2] in mL O2/kg/min(-1); r = 0.995 and standard error of the estimate [SEE] = 0.68 mL O2/kg/min(-1)). The cross-validation method was used in group B with group A serving as the basis for building the model and the validation dataset. The results showed that, in healthy nonathlete women, it is possible to predict VO2max with a minimum of error (SEE = 1.00%) from submaximal indicators obtained in an incremental test.

  10. Nano-optical investigations of the metal-insulator phase behavior of individual VO(2) microcrystals.

    PubMed

    Jones, Andrew C; Berweger, Samuel; Wei, Jiang; Cobden, David; Raschke, Markus B

    2010-05-12

    Despite the relatively simple stoichiometry and structure of VO(2), many questions regarding the nature of its famous metal-insulator transition (MIT) remain unresolved. This is in part due to the prevailing use of polycrystalline film samples and the limited spatial resolution in most studies, hindering access to and control of the complex phase behavior and its inevitable spatial inhomogeneities. Here, we investigate the MIT and associated nanodomain formation in individual VO(2) microcrystals subject to substrate stress. We employ symmetry-selective polarization Raman spectroscopy to identify crystals that are strain-stabilized in either the monoclinic M1 or M2 insulating phase at room-temperature. Raman measurements are further used to characterize the phase dependence on temperature, identifying the appearance of the M2 phase during the MIT. The associated formation and spatial evolution of rutile (R) metallic domains is studied with nanometer-scale spatial resolution using infrared scattering-scanning near-field optical microscopy (s-SNOM). We deduce that even for small crystals of VO(2), the MIT is influenced by the competition between the R, M1, and M2 crystal phases with their different lattice constants subjected to the external substrate-induced stress. The results have important implications for the interpretation of the investigations of conventional polycrystalline thin films where the mutual interaction of constituent crystallites may affect the nature of the MIT in VO(2).

  11. 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.

  12. Thermally driven sign switch of static dielectric constant of VO2 thin film

    NASA Astrophysics Data System (ADS)

    Kana Kana, J. B.; Vignaud, G.; Gibaud, A.; Maaza, M.

    2016-04-01

    Smart multifunctional materials exhibiting phase transition and tunable optical and/electrical properties provide a new direction towards engineering switchable devices. Specifically, the reversible, tunable and sign switch dielectric constants via external temperature stimuli observed in vanadium dioxide (VO2) make it a candidate of choice for tunable and switchable technologies devices. Here we report new aspect of the metal-insulator transition (MIT) through the sign switch of the static dielectric constant εS of pure VO2. As it is shown, the static dielectric constant showed an abrupt change from positive at T < 70 °C to negative at T > 70 °C. εS > 0 confirms the insulating phase where charges are localized while εS < 0 confirms the metallic phase of VO2 where charges are delocalized. We report for the first time the tunability of the dielectric constant from a negative sign for the static dielectric constant of VO2 thin film rarely found in real physical systems. We also demonstrate the tunability and switchability of the real and imaginary part of the dielectric constant (ε) via external temperature stimuli. More specifically, the real (ε) and Imaginary (ε) showed an abrupt thermal hysteresis which clearly confirms the phase transition.

  13. The reproducibility of VO2max, ventilatory, and lactate thresholds in elderly women.

    PubMed

    Foster, V L; Hume, G J; Dickinson, A L; Chatfield, S J; Byrnes, W C

    1986-08-01

    The reproducibility of VO2max, ventilatory, and lactate thresholds in elderly women. Med. Sci. Sports Exerc., Vol. 18, No. 4, pp. 425-430, 1986. This investigation examined the reproducibility of maximal (VO2max) and submaximal measures of fitness for elderly women. Eight subjects [age (yr): mean = 80.6 +/- 3.7; range = 73-86] volunteered to repeat three continuous, incremental maximal effort treadmill tests. Blood lactate determinations were made for each increment from blood samples taken from an indwelling venous catheter located in the back of the hand. Average VO2max values (ml X min-1 X kg X l-1) were 13.21 + 1.95 for test 1, 13.44 +/- 1.83 for test 2, and 13.62 + 2.95 for test 3. In all but one subject, a threshold was not definable by either ventilatory or lactate measurements. Maximal lactate values were low, with the average values for tests 1, 2, and 3 being 1.89, 1.46, and 1.86 mmol X l-1, respectively. The data demonstrates that VO2max is reproducible for older women and can, therefore, be used for fitness assessment and exercise prescription. The use of ventilatory or lactate thresholds as submaximal measures of fitness or as minimal intensities for exercise prescription was determined not to be applicable for women in the eighth and ninth decades of life.

  14. Thermal tuning of infrared resonant absorbers based on hybrid gold-VO2 nanostructures

    NASA Astrophysics Data System (ADS)

    Kocer, Hasan; Butun, Serkan; Banar, Berker; Wang, Kevin; Tongay, Sefaatttin; Wu, Junqiao; Aydin, Koray

    2015-04-01

    Resonant absorbers based on plasmonic materials, metamaterials, and thin films enable spectrally selective absorption filters, where absorption is maximized at the resonance wavelength. By controlling the geometrical parameters of nano/microstructures and materials' refractive indices, resonant absorbers are designed to operate at wide range of wavelengths for applications including absorption filters, thermal emitters, thermophotovoltaic devices, and sensors. However, once resonant absorbers are fabricated, it is rather challenging to control and tune the spectral absorption response. Here, we propose and demonstrate thermally tunable infrared resonant absorbers using hybrid gold-vanadium dioxide (VO2) nanostructure arrays. Absorption intensity is tuned from 90% to 20% and 96% to 32% using hybrid gold-VO2 nanowire and nanodisc arrays, respectively, by heating up the absorbers above the phase transition temperature of VO2 (68 °C). Phase change materials such as VO2 deliver useful means of altering optical properties as a function of temperature. Absorbers with tunable spectral response can find applications in sensor and detector applications, in which external stimulus such as heat, electrical signal, or light results in a change in the absorption spectrum and intensity.

  15. VO2 Max in Variable Type Exercise Among Well-Trained Upper Body Athletes.

    ERIC Educational Resources Information Center

    Seals, Douglas R.; Mullin, John P.

    1982-01-01

    The maximal oxygen consumption (VO2 max) of well-trained upper body athletes was compared to that of untrained individuals in four types of exercise: arm cranking, legs only cycling, graded treadmill running, and combined arm cranking and leg cycling. Results of the study showed that well-trained upper body athletes attained a significantly higher…

  16. Local temperature redistribution and structural transition during joule-heating-driven conductance switching in VO2.

    PubMed

    Kumar, Suhas; Pickett, Matthew D; Strachan, John Paul; Gibson, Gary; Nishi, Yoshio; Williams, R Stanley

    2013-11-13

    Joule-heating induced conductance-switching is studied in VO2 , a Mott insulator. Complementary in situ techniques including optical characterization, blackbody microscopy, scanning transmission X-ray microscopy (STXM) and numerical simulations are used. Abrupt redistribution in local temperature is shown to occur upon conductance-switching along with a structural phase transition, at the same current.

  17. Mediated proton transport through Nafion 117 membranes imbibed with varying concentrations of aqueous VOSO4 (VO2+) and NH4VO3 (VO2+) in 2 M H2SO4

    NASA Astrophysics Data System (ADS)

    Suarez, Sophia; Paterno, Domenec

    2016-11-01

    We performed an extensive study on Nafion 117 membrane imbibed with various concentrations of aqueous ammonium metavanadate (NH4VO3), and vanadyl sulfate (VOSO4), in 2 M H2SO4 over the temperature range of 20-100 °C, using 1H NMR and AC Impedance spectroscopies. The objective was to determine the effect of the tetravalent (VO2+) and pentavalent (VO2+) vanadium ions on the proton transport of Nafion 117.1H NMR chemical shift and linewidth data show greater short-range proton transport for the VO2+ imbibed membranes compared with the VO2+. However, the local environments seem to differ in that while the data for VO2+ imbibed membranes seem to follow more the trends observed for water hydrated Nafion 117, those for the VO2+ followed the trend of its aqueous bulk vanadium solvents, indicating that viscosity plays a larger role for the VO2+ imbibed membranes compared to the VO2+.

  18. Contributions of Astronauts Aerobic Exercise Intensity and Time on Change in VO2peak during Spaceflight

    NASA Technical Reports Server (NTRS)

    Downs, Meghan E.; Buxton, Roxanne; Moore, Alan; Ploutz-Snyder, Robert; Ploutz-Snyder, Lori

    2014-01-01

    There is considerable variability among astronauts with respect to changes in maximal aerobic capacity (VO2peak) during International Space Station (ISS) missions, ranging from a 5% increase to 30% decline. Individual differences may be due to in-flight aerobic exercise time and intensity. PURPOSE: To evaluate the effects of in-flight aerobic exercise time and intensity on change in VO2peak during ISS missions. METHODS: Astronauts (N=11) performed peak cycle tests approx 60 days before flight (L-60), on flight day (FD) approx 14, and every approx 30 days thereafter. Metabolic gas analysis and heart rate (HR) were measured continuously during the test using the portable pulmonary function system. HR and duration of each in-flight cycle ergometer and treadmill (TM) session were recorded and averaged in time segments corresponding to each peak test. Mixed effects linear regression with exercise mode (TM or cycle) as a categorical variable was used to assess the contributions of exercise intensity (%time >70% peak HR or %time >90% peak HR) and time (min/wk), adjusted for body weight, on %change in VO2peak during the mission, and incorporating the repeated-measures experimental design. RESULTS: 110 observations were included in the model (4-6 peak cycle tests per astronaut, 2 exercise devices). VO2peak was reduced from preflight throughout the mission (FD14: 13+/-13% and FD 105: 8+/-10%). Exercise intensity (%peak HR: FD14=66+/-14; FD105=75+/-8) and time (min/wk: FD14=82+/-46; FD105=158+/-40) increased during flight. The models showed main effects for exercise time and intensity with no interactions between time, intensity, and device (70% peak HR: time [z-score=2.39; P=0.017], intensity [z-score=3.51; P=0.000]; 90% peak HR: time [zscore= 3.31; P=0.001], intensity [z-score=2.24; P=0.025]). CONCLUSION: Exercise time and intensity independently contribute to %change in VO2peak during ISS missions, indicating that there are minimal values for exercise time and intensity

  19. The effects of exercise modality on the incidence of plateau at VO2max.

    PubMed

    Gordon, Dan; Mehter, Mashihullah; Gernigon, Marie; Caddy, Oliver; Keiller, Don; Barnes, Richard

    2012-09-01

    The purpose of this study was to determine the effect of exercise modality on the incidence of plateau at VO2max. Twelve recreationally active men (age, 21·7 ± 2·3 year; mass, 74·8 ± 6·5 kg; height, 177·6 ± 5·6 cm) completed four incremental tests to volitional exhaustion, of which two were completed on a treadmill (TRE) and two were completed using a cycle ergometer (CYC). The work rate employed for CYC was 1 W·2 s(-1) from an initial loading of 100 W with cadence being maintained at 60 rpm. For TRE, the workload (gradient) increased at a rate of 0·5% · 30 s(-1) while maintaining a constant running speed of 10 kph. Throughout all the trials, VO2 was determined on a breath-by-breath basis using a precalibrated metabolic cart. The criteria adopted for determination of a plateau was a Δ VO2 over the final two consecutive 30-s sampling periods of ≤50 ml · min(-1). Averaging across the two trials per each exercise modality showed a significant difference for plateau incidence between CYC (8%) and TRE (58%) (P = 0·017). This was aligned with a significant difference in the slope of the regression line during the final 60 s of the VO2max test, CYC (99·9 ± 49·7 ml · min(-1)) and TRE (49·6 ± 42·6 ml · min(-1)) (P = 0·017). Repeat measures ANOVA of these data suggests that plateau incidence rates at VO2max differ between treadmill- and cycle ergometry-based exercises. Future studies need to address whether these response rates are replicated in well-trained athletes.

  20. Bone mass in girls according to their BMI, VO2 max, hours and years of practice.

    PubMed

    Ubago-Guisado, Esther; Martinez-Rodriguez, Alejandro; Gallardo, Leonor; Sánchez-Sánchez, Javier

    2016-11-01

    The accumulation of bone mass during puberty is related with bone health in adulthood. This accumulation is influenced by diverse factors such as body mass index (BMI), maximal oxygen uptake (VO2 max), hours of training and years of sport practice. For this reason, the objective of this study is to analyse the influence of these variables on bone mass in young female athletes. The sample is formed of 120 healthy girls with ages between 9 and 13 (11.32 ± 1.6 years old), divided into two groups depending on their BMI, VO2 max, hours of training and years of sport practice. The participants completed a series of tests to evaluate level of sexual development, body composition (fat mass, lean mass and bone mass) and physical condition. The results show higher values of total lean mass, total fat mass and percentage of body fat in the groups with higher BMI in prepubertal girls and pubertal girls (p < .05). In relation to VO2 max, in the prepubertal group, girls with lower VO2 max had higher values of total fat mass (p < .05) and percentage of body fat (p < .05). In the pubertal group, girls with lower VO2 max also showed a higher total fat mass (p < .05). The studied variables account for a 85% and 75.4% of the variance of total bone mineral content and bone mineral density (BMD), respectively. In conclusion, the content and BMD are closely related with muscle mass and sports practice in young females. The amount of fat mass showed no association with bone mass and physical condition has an indirect relationship with bone development.

  1. Influence of simulated microgravity on the VO2 max of nontrained and trained rats

    NASA Technical Reports Server (NTRS)

    Woodman, C. R.; Monnin, K. A.; Sebastian, L. A.; Tipton, C. M.

    1993-01-01

    Head-down suspension (HDS) of rats has evolved as a useful model for the simulation of a microgravity environment. Previous HDS experiments with rats have shown an impaired capacity to perform aerobic exercise as demonstrated by reductions in maximum oxygen consumption (VO2 max), treadmill run time (RT), and mechanical efficiency (ME) of treadmill running at submaximal conditions. To determine whether endurance training (TR) before HDS would modify exercise performance, male Sprague-Dawley rats were assigned to nontrained (NT) or TR groups for 6 wk and exposed to HDS or cage control (CC) conditions for 29 days. The rats were tested for VO2 max, RT, and ME before treatment and on days 7, 14, 21, and 28. In addition, water and electrolyte excretion was measured on days 1 and 21 of the experimental period. Before HDS, the TR rats had significantly higher measures of VO2 max (15%) and RT (22%) than the NT rats. On day 28, HDS was associated with significant reductions in absolute VO2 max (ml/min) in TR (-30%) and NT (-14%) rats. Relative VO2 max (ml.min-1.kg-1) was significantly reduced in TR (-15%) but not NT rats. Similar reductions in RT occurred in TR (-37%) and NT (-35%) rats by day 28. ME was reduced 22% in both TR and NT rats after 28 days of suspension. HDS elicited diuresis, natriuresis, and kaliuresis in TR rats after 21 days but not after 24 h. In contrast, HDS-NT rats exhibited no diuretic, natriuretic, or kaliuretic responses.(ABSTRACT TRUNCATED AT 250 WORDS).

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

    PubMed Central

    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. PMID:28319189

  3. Thermochromic VO2 thin films: solution-based processing, improved optical properties, and lowered phase transformation temperature.

    PubMed

    Zhang, Zongtao; Gao, Yanfeng; Chen, Zhang; Du, Jing; Cao, Chuanxiang; Kang, Litao; Luo, Hongjie

    2010-07-06

    This paper describes a solution-phase synthesis of high-quality vanadium dioxide thermochromic thin films. The films obtained showed excellent visible transparency and a large change in transmittance at near-infrared (NIR) wavelengths before and after the metal-insulator phase transition (MIPT). For a 59 nm thick single-layer VO(2) thin film, the integral values of visible transmittance (T(int)) for metallic (M) and semiconductive (S) states were 54.1% and 49.1%, respectively, while the NIR switching efficiencies (DeltaT) were as high as 50% at 2000 nm. Thinner films can provide much higher transmittance of visible light, but they suffer from an attenuation of the switching efficiency in the near-infrared region. By varying the film thickness, ultrahigh T(int) values of 75.2% and 75.7% for the M and S states, respectively, were obtained, while the DeltaT at 2000 nm remained high. These results represent the best data for VO(2) to date. Thicker films in an optimized range can give enhanced NIR switching efficiencies and excellent NIR blocking abilities; in a particularly impressive experiment, one film provided near-zero NIR transmittance in the switched state. The thickness-dependent performance suggests that VO(2) will be of great use in the objective-specific applications. The reflectance and emissivity at the wavelength range of 2.5-25 microm before and after the MIPT were dependent on the film thickness; large contrasts were observed for relatively thick films. This work also showed that the MIPT temperature can be reduced simply by selecting the annealing temperature that induces local nonstoichiometry; a MIPT temperature as low as 42.7 degrees C was obtained by annealing the film at 440 degrees C. These properties (the high visible transmittance, the large change in infrared transmittance, and the near room-temperature MIPT) suggest that the current method is a landmark in the development of this interesting material toward applications in energy-saving smart

  4. Preparation and characterization of self-supporting thermochromic films composed of VO2(M)@SiO2 Nanofibers.

    PubMed

    Li, Shaotang; Li, Yamei; Jiang, Meng; Ji, Shidong; Luo, Hongjie; Gao, Yanfeng; Jin, Ping

    2013-07-24

    Nanofibers of VO2(A) with the diameter and length averagely at 100 nm and 10-20 μm were prepared via a facile one-step hydrothermal method by reducing NH4VO3 with 1,3-propylene glycol in an acidic solution. The obtained VO2(A) was coated by SiO2 to form VO2(A)@SiO2 core-shell nanocomposites, which were then transformed into VO2(M)@SiO2 by annealing under nitrogen atmosphere. The resulted composites maintained the original fibrous morphology, particularly with a large amount of pores emerging inside the fiber due to the volume shrinkage during the phase transition, which may improve its thermal insulation ability in real applications. The VO2(M)@SiO2 nanofibers were arranged into a self-supporting film by filtration, which shows excellent thermochromic properties.

  5. Successive orbital ordering transitions in NaVO_2

    SciTech Connect

    Klimczuk, Tomasz W; Mcqueen, T; Stephens, P W; Huang, Q; Ronning, Filip; Cava, R

    2008-01-01

    Temperature-dependent dc susceptibility, heat capacity, and x-ray and neutron diffraction measurements on powder samples of the layered triangular-lattice material NaY02 reveal two successive phase transitions. At high temperature the structure is rhomobohedral, with all six inplane V-V distances equivalent. At T = 98K, the system undergoes a second order phase transition to a monoclinic intermediate temperature phase in which the in-plane Y -Y distances separate into four short and two long bonds, corresponding to orbital ordering of one electron per y3+. Below T 93K, there is a first order phase transition to a low temperature monoclinic phase, in which there are four long and two short in-plane Y -Y distances, consistent with orbital ordering of two electrons per y 3+ on a triangular lattice. Long range magnetic ordering of 0.98(2),uB per y 3 + (3d2) sets in at the T 93K structural transition. The low temperature structure ofNa Y02 displays orbital ordering that, although predicted by first principle calculations, has not previously been observed in this class of materials.

  6. 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.

  7. Crossvalidation of two heart rate-based equations for predicting VO2max in white and black men.

    PubMed

    Esco, Michael R; Olson, Michele S; Williford, Henry N; Mugu, Emmanuel M; Bloomquist, Barbara E; McHugh, Aindrea N

    2012-07-01

    The purpose of this investigation was to crossvalidate 2 equations that use the ratio of maximal heart rate (HRmax) to resting HR (HRrest) for predicting maximal oxygen consumption (VO2max) in white and black men. One hundred and nine white (n = 51) and black (n = 58) men completed a maximal exercise test on a treadmill to determine VO2max. The HRrest and HRmax were used to predict VO2max via the HRindex and HRratio equations. Validity statistics were done to compare the criterion versus predicted VO2max values across the entire cohort and within each race separately. For the entire group, VO2max was significantly overestimated with the HRindex equation, but the HRratio equation yielded no significant difference compared with the criterion. In addition, there were no significant differences shown between VO2max and either HR-based prediction equation for the white subgroup. However, both equations significantly overestimated VO2max in the black group. Furthermore, large standard error of estimates (ranging from 6.92 to 7.90 ml·kg(-1)·min(-1)), total errors (ranging from 8.30 to 8.62 ml·kg(-1)·min(-1)), and limits of agreement (ranging from upper limits of 16.65 to lower limits of -18.25 ml·kg(-1)·min(-1)) were revealed when comparing the predicted to criterion VO2max for both the groups. Considering the results of this investigation, the HRratio and HRindex methods appear to crossvalidate and prove useful for estimating the mean VO2max in white men as a group but not for an age-matched group of black men. However, because of inflated values for error, caution should be exercised when using these methods to predict individual VO2max.

  8. Slow VO2 off-kinetics in skeletal muscle is associated with fast PCr off-kinetics--and inversely.

    PubMed

    Korzeniewski, Bernard; Zoladz, Jerzy A

    2013-09-01

    The computer model of the bioenergetic system in skeletal muscle, developed previously, was used to study the effect of the characteristic decay time of the parallel activation of oxidative phosphorylation [τ(OFF)] during muscle recovery on the muscle oxygen consumption rate (Vo2) and phosphocreatine (PCr) work-to-rest transition (off)-kinetics and on the relationship between the Vo2 and PCr rest-to-work transition (on)- and off-kinetics in moderate and heavy exercise. An increase in τ(OFF) slows down the initial phase of the muscle Vo2 off-kinetics and accelerates the PCr off-kinetics. As a result, the relationship between the initial phase of the Vo2 off-kinetics (lasting approximately 3-60 s in computer simulations) and the PCr off-kinetics is inverse: the slower the former, the faster the latter. A faster initial phase of the Vo2 off-kinetics is associated with a slower late phase of the Vo2 off-kinetics, and as a result, the integral of Vo2 above baseline during recovery, representing the oxygen debt, is identical in all cases [values of τ(OFF)] for a given PCr decrease. Depending on τ(OFF), the muscle Vo2 on-kinetics was either equally fast or slower than the Vo2 off-kinetics in moderate exercise and always slower in heavy exercise. PCr on-kinetics was always faster than PCr off-kinetics. This study clearly demonstrates that τ(OFF) has a pronounced impact on the mutual relations between the muscle Vo2 and PCr on- and off-kinetics.

  9. Visualization of one-dimensional diffusion and spontaneous segregation of hydrogen in single crystals of VO2.

    PubMed

    Kasırga, T Serkan; Coy, Jim M; Park, Jae H; Cobden, David H

    2016-08-26

    Hydrogen intercalation in solids is common, complicated, and very difficult to monitor. In a new approach to the problem, we have studied the profile of hydrogen diffusion in single-crystal nanobeams and plates of VO2, exploiting the fact that hydrogen doping in this material leads to visible darkening near room temperature connected with the metal-insulator transition at 65 °C. We observe hydrogen diffusion along the rutile c-axis but not perpendicular to it, making this a highly one-dimensional diffusion system. We obtain an activated diffusion coefficient, [Formula: see text] applicable in metallic phase. In addition, we observe dramatic supercooling of the hydrogen-induced metallic phase and spontaneous segregation of the hydrogen into stripes implying that the diffusion process is highly nonlinear, even in the absence of defects. Similar complications may occur in hydrogen motion in other materials but are not revealed by conventional measurement techniques.

  10. Monitoring VO2max during fourteen weeks of endurance training using the CardioCoach.

    PubMed

    Vehrs, Pat R; Keller, David M; George, James D; Hager, Ronald L; Fellingham, Gilbert W

    2007-02-01

    This study evaluated the validity of the desktop CardioCoach metabolic system to measure VO2max and VEmax. Sixteen subjects (mean age = 19.5 +/- 3.2 years) completed 2 maximal graded exercise tests following the same protocol before and after 7 and 14 weeks of endurance training. Subjects' VO2max and VEmax were measured by either the CardioCoach or the ParvoMedics TrueOne 2400 metabolic measurement system (TrueOne). An alpha level of significance of p < 0.05 was maintained for all statistical analyses. The time to test completion and the final treadmill grade of the exercise tests performed by both the CardioCoach and the TrueOne increased over the 3 testing periods, confirming an improvement in cardiorespiratory fitness resulting from the 14 weeks of training. A linear growth curve analysis indicated that there were statistically significant differences between VO2max (ml x kg(-1) x min(-1)) as measured by the TrueOne and the CardioCoach before (44.4 +/- 5.0 and 49.3 +/- 5.4) and after 7 weeks (46.0 +/- 5.2 and 48.2 +/- 5.4) of training but not after 14 weeks of training (47.8 +/- 5.6 and 48.4 +/- 5.2). Significant differences also existed in VEmax (L x min(-1)) as measured by the TrueOne and the CardioCoach before (76.8 +/- 17.7 and 71.9 +/- 13.7), after 7 weeks (81.4 +/- 16.2 and 72.8 +/- 14.1), and after 14 weeks (86.8 +/- 19.4 and 74.2 +/- 13.1) of training. Although significant growth of VO2max (0.24 ml x kg(-1) x min(-1) x wk(-1)) and VEmax (0.71 L x min(-1) x wk(-1)) was measured by the TrueOne over 14 weeks of training, the CardioCoach was unable to detect growth in VO2max (-0.02 ml x kg(-1) x min(-1) x wk(-1)) or VEmax (0.17 L x min(-1) x wk(-1)). This study indicates that the CardioCoach did not accurately measure or monitor changes in VO2max or VEmax resulting from training.

  11. Presence of Peierls pairing and absence of insulator-to-metal transition in VO2 (A): a structure-property relationship study.

    PubMed

    Popuri, S R; Artemenko, A; Decourt, R; Villesuzanne, A; Pollet, M

    2017-03-01

    Layered vanadium oxides have been extensively explored due to their interesting metal-insulator transitions and energy conversion/storage applications. In the present study, we have successfully synthesized VO2 (A) polymorph powder samples by a single-step hydrothermal synthesis process and consolidated them using spark plasma sintering. The structural and electronic properties of VO2 (A) are measured over a large temperature range from liquid helium, across the structural transition (400-440 K) and up to 500 K. The structural analysis around this transition reveals an antiferrodistorsive to partially ferrodistorsive ordering upon cooling. It is followed by a progressive antiferromagnetic spin pairing which fully settles at about 150 K. The transport measurements show that, in contrast to the rutile archetype VO2 (R/M1), the structural transition comes with a transition from semiconductor to band-type insulator. Under these circumstances, we propose a scenario with a high temperature antiferrodistorsive paramagnetic semiconducting phase, followed by an intermediate regime with a partially ferrodistorsive paramagnetic semiconducting phase, and finally a low temperature partially ferrodistorsive antiferromagnetic band insulator phase with a possible V-V Peierls-type pairing.

  12. Direct formation of single crystal VO 2(R) nanorods by one-step hydrothermal treatment

    NASA Astrophysics Data System (ADS)

    Ji, Shidong; Zhao, Yangang; Zhang, Feng; Jin, Ping

    2010-01-01

    Pure phase VO 2(R) nanorods were directly synthesized via the reduction of V 2O 5 by oxalic acid during one-step hydrothermal treatment. The products were characterized by X-ray diffraction, field-emission scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, FT-IR and UV-vis spectroscopy. By adding a proper amount of H 2SO 4 as morphology control agent, monodispersed single crystal VO 2(R) nanorods were obtained from the hydrothermal solution for the first time at relatively lower temperature (260 °C) and even shorter time (4 h). The prepared nanorods showed very excellent thermochromic property with narrower hysteresis and lower phase transformation temperature compared with bulk materials.

  13. Intensity tunable infrared broadband absorbers based on VO2 phase transition using planar layered thin films

    PubMed Central

    Kocer, Hasan; Butun, Serkan; Palacios, Edgar; Liu, Zizhuo; Tongay, Sefaattin; Fu, Deyi; Wang, Kevin; Wu, Junqiao; Aydin, Koray

    2015-01-01

    Plasmonic and metamaterial based nano/micro-structured materials enable spectrally selective resonant absorption, where the resonant bandwidth and absorption intensity can be engineered by controlling the size and geometry of nanostructures. Here, we demonstrate a simple, lithography-free approach for obtaining a resonant and dynamically tunable broadband absorber based on vanadium dioxide (VO2) phase transition. Using planar layered thin film structures, where top layer is chosen to be an ultrathin (20 nm) VO2 film, we demonstrate broadband IR light absorption tuning (from ~90% to ~30% in measured absorption) over the entire mid-wavelength infrared spectrum. Our numerical and experimental results indicate that the bandwidth of the absorption bands can be controlled by changing the dielectric spacer layer thickness. Broadband tunable absorbers can find applications in absorption filters, thermal emitters, thermophotovoltaics and sensing. PMID:26294085

  14. Thermoelectric effect across the metal-insulator domain walls in VO2 microbeams.

    PubMed

    Cao, J; Fan, W; Zheng, H; Wu, J

    2009-12-01

    We report on measurements of Seebeck effect in single-crystal VO(2) microbeams across their metal-insulator phase transition. One-dimensionally aligned metal-insulator domain walls were reversibly created and eliminated along single VO(2) beams by varying temperature, which allows for accurate extraction of the net contribution to the Seebeck effect from these domain walls. We observed significantly lower Seebeck coefficient in the metal-insulator coexisting regime than predicted by a linear combination of contributions from the insulator and metal domains. This indicates that the net contribution of the domain walls has an opposite sign from that of the insulator and metal phases separately. Possible origins that may be responsible for this unexpected effect were discussed in the context of complications in this correlated electron material.

  15. Correlation of plume dynamics and oxygen pressure with VO2 stoichiometry during pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    Lafane, S.; Kerdja, T.; Abdelli-Messaci, S.; Khereddine, Y.; Kechouane, M.; Nemraoui, O.

    2013-07-01

    Vanadium dioxide thin films have been deposited on Corning glass substrates by a KrF laser ablation of V2O5 target at the laser fluence of 2 J cm-2. The substrate temperature and the target-substrate distance were set to 500 ∘C and 4 cm, respectively. X-ray diffraction analysis showed that pure VO2 is only obtained at an oxygen pressure range of 4×10-3-2×10-2 mbar. A higher optical switching contrast was obtained for the VO2 films deposited at 4×10-3-10-2 mbar. The films properties were correlated to the plume-oxygen gas interaction monitored by fast imaging of the plume.

  16. Resolving the VO2 controversy: Mott mechanism dominates the insulator-to-metal transition

    NASA Astrophysics Data System (ADS)

    Nájera, O.; Civelli, M.; Dobrosavljević, V.; Rozenberg, M. J.

    2017-01-01

    We consider a minimal model to investigate the metal-insulator transition in VO2. We adopt a Hubbard model with two orbitals per unit cell, which captures the competition between Mott and singlet-dimer localization. We solve the model within dynamical mean-field theory, characterizing in detail the metal-insulator transition and finding new features in the electronic states. We compare our results with available experimental data, obtaining good agreement in the relevant model parameter range. Crucially, we can account for puzzling optical conductivity data obtained within the hysteresis region, which we associate with a metallic state characterized by a split heavy quasiparticle band. Our results show that the thermal-driven insulator-to-metal transition in VO2 is compatible with a Mott electronic mechanism, providing fresh insight to a long-standing "chicken-and-egg" debate and calling for further research of "Mottronics" applications of this system.

  17. Reconfigurable anisotropy and functional transformations with VO2-based metamaterial electric circuits

    NASA Astrophysics Data System (ADS)

    Savo, Salvatore; Zhou, You; Castaldi, Giuseppe; Moccia, Massimo; Galdi, Vincenzo; Ramanathan, Shriram; Sato, Yuki

    2015-04-01

    We demonstrate an innovative multifunctional artificial material that combines exotic metamaterial properties and the environmentally responsive nature of phase-change media. The tunable metamaterial is designed with the aid of two interwoven coordinate-transformation equations and implemented with a network of thin-film resistors and vanadium dioxide (VO2). The strong temperature dependence of VO2 electrical conductivity results in a significant modification of the resistor network behavior, and we provide experimental evidence for a reconfigurable metamaterial electric circuit that not only mimics a continuous medium, but is also capable of responding to thermal stimulation through dynamic variation of its spatial anisotropy. Upon external temperature change, the overall effective functionality of the material switches between a "truncated cloak" and a "concentrator" for electric currents. Possible applications may include adaptive matching resistor networks, multifunctional electronic devices, and equivalent artificial materials in the magnetic domain. Additionally, the proposed technology could also be relevant for thermal management of integrated circuits.

  18. Comparison of V'O2 kinetics in upright and supine position

    NASA Astrophysics Data System (ADS)

    Hoffmann, U.; Eßfeld, D.; Stegemann, J.; Schütze, H.

    Oxygen uptake (V'O2) kinetics during exercise depends in particular on muscular aerobic capacity and cardio-vascular parameters. The objective of this study was to investigate the influence of body position on the V'O2 kinetics as determined by means of the PRBS technique. 9 healthy male volunteers performed bicycle ergometer exercise in both upright and supine position. No significant changes were seen in normalized gains and phase shifts of the power-V'O2-relationship. It is concluded that the differences in venous blood volume distribution and cardiac output associated with upright and supine position do not have major effects on power-V'O2-gains.

  19. Infrared micro-spectroscopy of strained VO2 micro-crystals

    NASA Astrophysics Data System (ADS)

    Qazilbash, M. M.; Huffman, T.; Walter, E. J.; Krakauer, H.; Wei, Jiang; Cobden, D. H.; Bechtel, H. A.; Martin, M. C.; Carr, G. L.; Basov, D. N.

    2012-02-01

    The temperature-driven insulator-to-metal transition (IMT) in vanadium dioxide (VO2) is accompanied by a structural instability (SI). The IMT and SI lead to a drastic change in the electronic properties, crystal structure, and lattice dynamics. We performed infrared micro-spectroscopy on single crystal platelets of VO2 deposited on oxidized silicon substrate by physical vapor deposition. The firm attachment of these micro-crystals to the substrate causes strain which can alter their properties compared to bulk samples. We report infrared data on these micro-crystals and demonstrate both their electronic and phonon properties in the monoclinic M1 phase and the rutile phase. We also compare their infrared conductivity to that of bulk single crystals and thin films. Finally, we compare infrared-active phonon features to first-principles density functional theory calculations.

  20. Local Peltier-effect-induced reversible metal-insulator transition in VO2 nanowires

    NASA Astrophysics Data System (ADS)

    Takami, Hidefumi; Kanki, Teruo; Tanaka, Hidekazu

    2016-06-01

    We report anomalous resistance leaps and drops in VO2 nanowires with operating current density and direction, showing reversible and nonvolatile switching. This event is associated with the metal-insulator phase transition (MIT) of local nanodomains with coexistence states of metallic and insulating phases induced by thermoelectric cooling and heating effects. Because the interface of metal and insulator domains has much different Peltier coefficient, it is possible that a significant Peltier effect would be a source of the local MIT. This operation can be realized by one-dimensional domain configuration in VO2 nanowires because one straight current path through the electronic domain-interface enables theoretical control of thermoelectric effects. This result will open a new method of reversible control of electronic states in correlated electron materials.

  1. Determinants of maximal oxygen uptake (VO2 max) in fire fighter testing.

    PubMed

    Vandersmissen, G J M; Verhoogen, R A J R; Van Cauwenbergh, A F M; Godderis, L

    2014-07-01

    The aim of this study was to evaluate current daily practice of aerobic capacity testing in Belgian fire fighters. The impact of personal and test-related parameters on the outcome has been evaluated. Maximal oxygen uptake (VO2 max) results of 605 male fire fighters gathered between 1999 and 2010 were analysed. The maximal cardio respiratory exercise tests were performed at 22 different centres using different types of tests (tread mill or bicycle), different exercise protocols and measuring equipment. Mean VO2 max was 43.3 (SD = 9.8) ml/kg.min. Besides waist circumference and age, the type of test, the degree of performance of the test and the test centre were statistically significant determinants of maximal oxygen uptake. Test-related parameters have to be taken into account when interpreting and comparing maximal oxygen uptake tests of fire fighters. It highlights the need for standardization of aerobic capacity testing in the medical evaluation of fire fighters.

  2. Separation observation of metal-insulator transition and structural phase transition in VO2

    NASA Astrophysics Data System (ADS)

    Kim, Hyun-Tak; Kim, Bong-Jun; Lee, Yong Wook; Chae, Byung Gyu; Yun, Sun Jin; Oh, Soo-Young; Lim, Yong-Sik

    2007-03-01

    An intermediate monoclinic metal phase between the metal-insulator transition (MIT) and the structural phase transition (SPT) is observed with VO2-based two-terminal devices and can be explained in terms of the Mott MIT. The conductivity of this phase linearly increases with increasing temperature up to TSPT 68^oC and becomes maximum at TSPT. The SPT is confirmed by micro-Raman spectroscopy. Optical microscopic observation reveals the absence of a local current path in the metal phase. The current uniformly flows throughout the surface of the VO2 film when the MIT occurs. This device can be used as a programmable critical temperature sensor. (References: New J. Phys. 6 (1994) 52 (http://www.njp.org); Appl. Phys. Lett. 86 (2005) 24210); Physica B 369 (2005) 76; cond-mat/0607577; cond-mat/0608085; cond-mat/0609033).

  3. Effects of concurrent training on explosive strength and VO(2max) in prepubescent children.

    PubMed

    Marta, C; Marinho, D A; Barbosa, T M; Izquierdo, M; Marques, M C

    2013-10-01

    The purpose of this study was to compare the effects of an 8-weeks training period of resistance training alone (GR), combined resistance and endurance training (GCON) and a control group (GC) on explosive strength and V(O2max) in a large sample of prepubescent boys and girls. 125 healthy children (58 boys, 67 girls), aged 10-11 years old (10.8±0.4 years) were assigned into 2 training groups to train twice a week for 8 weeks: GR (19 boys, 22 girls), GCON (21 boys, 24 girls) and a control group (GC: 18 boys, 21 girls; no training program). A significant but medium-sized increase from pre- to the post-training in the vertical jump (Effect size=0.22, F=34.44, p<0.01) and V(O2max) (Effect size=0.19, F=32.89, p<0.01) was observed. A significant large increase in the 1 kg (Effect size=0.53, F=202.17, p<0.01) and 3 kg (Effect size=0.48, F=132.1, p<0.01) ball throwing, standing long jump (Effect size=0.53, F=72.93, p<0.01) and running speed (Effect size=0.45, F=122.21, p<0.01) was also observed. The training group (GR and GCON) and sex factors did not significantly influence the evolution of strength variables from pre- to the post-training. The V(O2max) increased significantly only in GCON. Concurrent training is equally effective on training-induced explosive strength, and more efficient than resistance training only for V(O2max), in prepubescent boys and girls. This should be taken into consideration in order to optimize strength training school-based programs.

  4. Effects of ozone exposure on four consecutive days on work performance and VO2max

    SciTech Connect

    Foxcroft, W.J.; Adams, W.C.

    1986-09-01

    The effects of 4 consecutive days of 1-h exposure to 0.35 ppm ozone (O/sub 3/) on maximal O/sub 2/ uptake (VO2max), performance time, pulmonary function, and subjective symptom responses were studied in eight aerobically trained males. Each subject was first exposed in random order to filtered air (FA) and 0.35 ppm O/sub 3/ while exercising on a bicycle ergometer for 50 min at a work load eliciting minute ventilation of approximately 60 1/min. A rapidly incremented VO2max test to volitional fatigue was completed within 10 min following each of these exposures, as well as on day 4 of the consecutive daily exposures to O/sub 3/. Initial exposure to O/sub 3/ induced the occurrence of subjective symptoms, as well as significant pulmonary function impairment and decrements in maximal exercise performance time (from 253 to 211 s) and VO2max (from 3.85 to 3.62 l/min). Following the fourth consecutive day of exposure to O/sub 3/, pulmonary function impairment was not significantly different from initial exposure to O/sub 3/, although subjective symptom severity was significantly reduced. Exercise performance time (239 s) and VO2max (3.79 l/min) on the fourth consecutive daily exposure to O/sub 3/ were not significantly different from FA values. These data indicate no significant adaptation to initial O/sub 3/ exposure-induced pulmonary function impairment following four consecutive daily exposures to O/sub 3/, although reduced subjective symptom severity and enhanced exercise performance time on day 4 suggest an habituation effect. Our results also suggest that O/sub 3/ adaptation may be a more complex phenomena than identified previously.

  5. Gas sensor based on metal-insulator transition in VO2 nanowire thermistor.

    PubMed

    Strelcov, Evgheni; Lilach, Yigal; Kolmakov, Andrei

    2009-06-01

    Using temperature driven sharp metal-insulator phase transition in single crystal VO(2) nanowires, the realization of a novel gas sensing concept has been tested. Varying the temperature of the nanowire close to the transition edge, the conductance of the nanowire becomes extremely responsive to the tiny changes in molecular composition, pressure, and temperature of the ambient gas environment. This gas sensing analog of the transition edge sensor radiometry used in astrophysics opens new opportunities in gas sensorics.

  6. Development of a hockey-specific, skate-treadmill VO2 max protocol.

    PubMed

    Dreger, R W; Quinney, H A

    1999-12-01

    The purpose of this study was to investigate a protocol for the determination of VO2 max utilizing a motor-driven skate treadmill (ST). On separate days, 6 male hockey players completed a ST and a cycle ergometer (BK) VO2 max protocol. The results showed no significant difference between the ST and BK protocols for relative (60.4 +/- 5.09 vs. 59.0 +/- 8.31 ml.kg-1.min-1) and absolute VO2 max values (4.51 +/- 0.50 vs. 4.39 +/- 0.59 L.min-1), respectively. Significantly higher HR max was recorded during the ST protocol (202.3 +/- 4.27 vs. 200.7 +/- 4.55 b.min-1) (p < 0.05). Peak VE and VT were nonsignificant between the two conditions. However, peak f was higher for the ST protocol (63.0 +/- 7.56 vs. 60.2 +/- 7.76 breath.min-1) (p < 0.05). Although the physiological response to both protocols was similar, the ST protocol replicates a hockey stride, which may provide more applicable information for the development of training programs.

  7. The band structure of VO2 measured by angle-resolved photoemission

    NASA Astrophysics Data System (ADS)

    Moreschini, Luca; Chang, Young Jun; Innocenti, Davide; Walter, Andrew L.; Kim, Young Su; Gaines, Geoffrey; Bostwick, Aaron; Denlinger, Jonathan; Rotenberg, Eli

    2011-03-01

    The origin of the 340K metal-insulator transition (MIT) in VO2 is still under debate. the main reason is that no direct experimental verifications of the electronic structure of VO2 exist up to this point. The quality of the available single crystals is not sufficient for ARPES measurements, so that photoemission is limited to angle-integrated mode. New opportunities are offered by oxide films, on which data of equal or even higher quality have been reported (Saeki et al., PRB 2009). WIth the in situ pulsed-laser-deposition (PLD) system available on beamline 7.0.1 at the Advanced Light Source we have grown VO2(001) films on a TiO2 substrate and measured the Fermi surface of the metallic phase. These results will permit a direct comparison with the existing band calculations and open the way to the study of the MIT as a function, e.g., of film thickness or electron doping with Cr. Work supported by U.S. DOE (DE-AC02-05CH11231 for ALS), the Max Planck Society, and the Swiss National Science Foundation (PBELP2-125484).

  8. Determinants of VO2 max decline with aging: an integrated perspective.

    PubMed

    Betik, Andrew C; Hepple, Russell T

    2008-02-01

    Aging is associated with a progressive decline in the capacity for physical activity. Central to this decline is a reduction in the maximal rate of oxygen utilization, or VO2 max. This critical perspective examines the roles played by the factors that determine the rate of muscle oxygen delivery versus those that determine the utilization of oxygen by muscle as a means of probing the reasons for VO2 max decline with aging. Reductions in muscle oxygen delivery, principally due to reduced cardiac output and perhaps also a maldistribution of cardiac output, appear to play the dominant role up until late middle age. On the other hand, there is a decline in skeletal muscle oxidative capacity with aging, due in part to mitochondrial dysfunction, which appears to play a particularly important role in extreme old age (senescence) where skeletal muscle VO2 max is observed to decline by approximately 50% even under conditions of similar oxygen delivery as young adult muscle. It is noteworthy that at least the structural aspects of the capillary bed do not appear to be reduced in a manner that would compromise the capacity for muscle oxygen diffusion even in senescence.

  9. Nanothermochromics: Calculations for VO2 nanoparticles in dielectric hosts show much improved luminous transmittance and solar energy transmittance modulation

    NASA Astrophysics Data System (ADS)

    Li, S.-Y.; Niklasson, G. A.; Granqvist, C. G.

    2010-09-01

    VO2-based films are thermochromic and show infrared reflectance above a "critical" temperature in the vicinity of room temperature. Implementations on energy efficient windows have been discussed for decades but have been severely curtailed since the luminous absorptance is undesirably large and the solar energy transmittance modulation is too small. Here we show by calculations based on effective medium theory that dilute composites with VO2 nanoparticles embedded in hosts with properties mimicking glass or polymer can yield significantly decreased luminous absorption jointly with much enhanced transmittance modulation of solar energy. These results demonstrate that VO2-based nanothermochromics opens new avenues toward energy efficient fenestration.

  10. Crossvalidation of two 20-m shuttle-run tests for predicting VO2max in female collegiate soccer players.

    PubMed

    Green, Michael S; Esco, Michael R; Martin, Tyler D; Pritchett, Robert C; McHugh, Aindrea N; Williford, Henry N

    2013-06-01

    The aim of this study was twofold: (a) to compare the maximal attained speed (MAS) from the 20-m shuttle (MST) and 20-m square-shuttle (SST) tests and (b) to crossvalidate 2 equations for predicting maximal oxygen consumption (VO2max) that were previously developed from MST and SST in a group of female collegiate soccer players. Thirty-nine subjects (age: 20.1 ± 1.5 years) participated in the study. A maximal graded exercise treadmill test was used to measure VO2max. In addition, VO2max was predicted from the MAS obtained during MST ((pred)VO2maxMST) and SST ((pred)VO2maxSST) using previously developed equations. Measured VO2max for the group was 44.2 ± 3.3 ml·kg(-1)·min(-1). The MAS was 12.5 ± 0.6 km·h(-1) for MST and 13.3 ± 0.8 km·h(-1) for SST (p < 0.05). The prediction methods yielded a (pred)VO2maxMST of 49.6 ± 3.9 ml·kg(-1)·min(-1) and predVO2maxSST of 41.8 ± 3.1 ml·kg(-1)·min(-1), which were significantly different from measured VO2max (p < 0.05). The validity statistics revealed the following constant error (CE), correlation coefficient (r), standard error of estimate (SEE), and total error (TE) for (pred)VO2maxMST and (pred)VO2maxSST: CE = 5.35 ± 3.83, r = 0.45 (p < 0.05), SEE = 2.97 ml·kg(-1)·min(-1), TE = 6.39 ml·kg(-1)·min(-1); and CE = -2.43 ± 2.49, r = 0.69 (p < 0.05), SEE = 2.39 ml·kg(-1)·min(-1), TE = 3.43 ml·kg(-1)·min(-1), respectively. Residual plots indicated no proportional bias for either prediction model. The results of this study suggest that female collegiate soccer players had a higher MAS from SST compared with that from MST. In addition, SST appeared to be a more accurate predictor of VO2max than MST in the group of athletes.

  11. Adjustment for gas exchange threshold enhances precision of heart rate-derived VO2 estimates during heavy exercise.

    PubMed

    Pettitt, Robert W; Symons, J David; Taylor, Julie E; Eisenman, Patricia A; White, Andrea T

    2008-02-01

    Overestimates of oxygen uptake (VO2) are derived from the heart rate reserve-VO2 reserve (HRR-VO2R) model. We tested the hypothesis that adjusting for differences above and below gas exchange threshold (HRR-GET model) would tighten the precision of HR-derived VO2 estimates during heavy exercise. Seven men and 7 women of various VO2 max levels, on 2 separate days, cycled for 6 min at intensities equal to power at GET, 15% the difference between GET and VO2 max (15% above), and at 30% above GET. A second bout at 15% above GET (15% above (bout 2)) after 3 min of recovery was performed to assess estimates during interval training. Actual VO2 was compared with estimates derived from the HRR-VO2R and the HRR-GET. VO2 values were summed over the 6 min duration of data collection (6 min LO2) and compared with Bland-Altman plots. HRR-VO2R yielded 6 min LO2 (+/-2 SD) overestimates of 2.0 (+/-2.5), 1.9 (+/-2.7), and 1.3 (+/-3.3) for GET, 15% over, and 30% over, respectively, whereas corresponding 6 min LO2 difference values for the HRR-GET model were -0.42 (+/-1.6), -0.23 (+/-1.1), and -0.55 (+/-1.8), respectively. For 15% above (bout 2), the 6 min LO2 difference for HRR-VO2R was 1.8 (+/-2.9), whereas the difference for HRR-GET was 0.17 (+/-1.4). The 6 min LO2 values relative to the subjects' VO2 max did not vary (r=0.05 to 0.36); therefore, fitness level did not affect estimates. Sex did not affect accuracy of either estimate model (sex X estimate model interaction, p>0.95). We observed accurate estimates from the HRR-GET model during heavy exercise.

  12. High Performance Object-Oriented Scientific Programming in Fortran 90

    NASA Technical Reports Server (NTRS)

    Norton, Charles D.; Decyk, Viktor K.; Szymanski, Boleslaw K.

    1997-01-01

    We illustrate how Fortran 90 supports object-oriented concepts by example of plasma particle computations on the IBM SP. Our experience shows that Fortran 90 and object-oriented methodology give high performance while providing a bridge from Fortran 77 legacy codes to modern programming principles. All of our object-oriented Fortran 90 codes execute more quickly thatn the equeivalent C++ versions, yet the abstraction modelling capabilities used for scentific programming are comparably powereful.

  13. Testing the Jacob's ladder of density functionals for electronic structure and magnetism of rutile VO2

    NASA Astrophysics Data System (ADS)

    Xiao, Bing; Sun, Jianwei; Ruzsinszky, Adrienn; Perdew, John P.

    2014-08-01

    We employ semilocal density functionals [local spin-density approximation (LSDA), Perdew-Burke-Ernzerhof (PBE) generalized gradient approximation (GGA), and meta-GGAs)], LSDA plus Hubbard U (LSDA+U) theory, a nonlocal range-separated Heyd-Scuseria-Ernzerhof hybrid functional (HSE06), and the random-phase approximation (RPA) to assess their performances for the ground-state magnetism and electronic structure of a strongly correlated metal, rutile VO2. Using recent quantum Monte Carlo results as the benchmark, all tested semilocal and hybrid functionals as well as the RPA (with PBE inputs) predict the correct magnetic ground states for rutile VO2. The observed paramagnetism could arise from temperature-disordered local spin moments or from the thermal destruction of these moments. All semilocal functionals also give the correct ground-state metallicity for rutile VO2. However, in the ferromagnetic (FM) and antiferromagnetic (AFM) phases, LSDA+U and HSE06 incorrectly predict rutile VO2 to be a Mott-Hubbard insulator. For the computed electronic structures of FM and AFM phases, we find that the Tao-Perdew-Staroverov-Scuseria (TPSS) and revised TPSS (revTPSS) meta-GGAs give strong 2p-3d hybridizations, resulting in a depopulation of the 2p bands of O atoms, in comparison with other tested meta-GGAs. The regularized TPSS (regTPSS) and meta-GGAs made simple, i.e., MGGA_MS0 and MGGA_MS2, which are free of the spurious order-of-limits problem of TPSS and revTPSS, give electronic states close to those of the PBE GGA and LSDA. In comparison to experiment, semilocal functionals predict better equilibrium cell volumes for rutile VO2 in FM and AFM states than in the spin-unpolarized state. For meta-GGAs, a monotonic decrease of the exchange enhancement factor Fx(s,α) with α for small s, as in the MGGA_MS functionals, leads to large (probably too large) local magnetic moments in spin-polarized states.

  14. 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.

  15. Significance of antibody orientation unraveled: well-oriented antibodies recorded high binding affinity.

    PubMed

    Tajima, Nobuyuki; Takai, Madoka; Ishihara, Kazuhiko

    2011-03-15

    To investigate the effect of antibody orientation on its immunological activities, we developed a novel and versatile platform consisting of a well-defined phospholipid polymer surface on which staphylococcal protein A (SpA) was site-selectively immobilized. The application of a biocompatible phospholipid-based platform ensured minimal denaturation of immobilized antibodies, and the site-selective immobilization of SpA clarified the effect of antibody orientation on immunological activities. The phospholipid polymer platform was prepared on silicon substrates using the surface-initiated atom transfer radical polymerization (SI-ATRP) technique. An enzymatic reaction was performed for orientation-selective coupling of SpA molecules to the polymer brush surface. Orientation-controlled antibodies were achieved using enzymatic reactions, and these antibodies captured 1.8 ± 0.1 antigens on average, implying that at least 80% of immobilized antibodies reacted with two antigens. Theoretical multivalent binding analysis further revealed that orientation-controlled antibodies had antigen-antibody reaction equilibrium dissociation constants (K(d)) as low as 8.6 × 10(-10) mol/L, whereas randomly oriented and partially oriented antibodies showed K(d) values of 2.0 × 10(-7) and 1.2 × 10(-7) mol/L, respectively. Strict control of antibody orientation not only formed an approximately 100-fold stronger antigen-antibody complex than the controls but also sustained the native antibody K(d) (10(-10)-10(-9) mol/L). These findings support the significance of antibody orientation because controlling the orientation resulted in high reactivity and theoretical binding capacity.

  16. Program Orientation for High School Sport Coaches. Position Statement

    ERIC Educational Resources Information Center

    National Association for Sport and Physical Education, 2005

    2005-01-01

    The National Association for Sport and Physical Education (NASPE) believes that prior to the start of each season, all high school head coaches, assistant coaches, and volunteer coaches should be required to participate in a comprehensive orientation to the sport program. This orientation should be planned and conducted by the athletic director or…

  17. Thermochromic properties of Sn, W co-doped VO2 nanostructured thin film deposited by pulsed laser deposition.

    PubMed

    Hur, M G; Masaki, T; Yoon, D H

    2014-12-01

    Tin (Sn) and tungsten (W) co-doped vanadium dioxide (VO2) nanostructured thin films with 50-nm thickness were deposited by pulsed laser deposition (PLD) to reduce the transition temperature and improve the IR transmittance. The crystal structure of the nanostructured thin films and the presence of elements were evaluated by XRD and XPS analysis. The transition temperature (T(c)) of 1 at% Sn-1 at% W co-doped VO2 nanostructured thin film was decreased to about 22 degrees C (from 70.3 to 48.5 degrees C) compared with the undoped VO2 nanostructured thin film. The transmittance width in the IR range of the co-doped nanostructured thin film decreased from 37.5% to 27% compared with the undoped VO2 nanostructured thin film. Also, the width of hysteresis was narrowed by Sn doping.

  18. Achievement of VO2max criteria during a continuous graded exercise test and a verification stage performed by college athletes.

    PubMed

    Mier, Constance M; Alexander, Ryan P; Mageean, Amanda L

    2012-10-01

    The purpose of this study was to determine the incidence of meeting specific VO2max criteria and to test the effectiveness of a VO2max verification stage in college athletes. Thirty-five subjects completed a continuous graded exercise test (GXT) to volitional exhaustion. The frequency of achieving various respiratory exchange ratio (RER) and age-predicted maximum heart rate (HRmax) criteria and a VO2 plateau within 2 and 2.2 ml·kg(-1)·min(-1) (<2SD of the expected increase in VO2) were measured and tested against expected frequencies. After 10 minutes of active recovery, 10 subjects who did not demonstrate a plateau completed a verification stage performed at supramaximal intensity. From the GXT, the number of subjects meeting VO2max plateau was 5 (≤2 ml·kg(-1)·min(-1)) and 7 (≤2.2 ml·kg(-1)·min(-1)), RER criteria 34 (≥1.05), 32 (≥1.10), and 24 (≥1.15), HRmax criteria, 35 (<85%), 29 (<10 b·min(-1)) and 9 (HRmax). The VO2max and HRmax did not differ between GXT and the verification stage (53.6 ± 5.6 vs. 55.5 ± 5.6 ml·kg(-1)·min(-1) and 187 ± 7 vs. 187 ± 6 b·min(-1)); however, the RER was lower during the verification stage (1.15 ± 0.06 vs. 1.07 ± 0.07, p = 0.004). Six subjects achieved a similar VO2 (within 2.2 ml·kg(-1)·min(-1)), whereas 4 achieved a higher VO2 compared with the GXT. These data demonstrate that a continuous GXT limits the college athlete's ability to achieve VO2max plateau and certain RER and HR criteria. The use of a verification stage increases the frequency of VO2max achievement and may be an effective method to improve the accuracy of VO2max measurements in college athletes.

  19. VO2max and ventilatory threshold of trained cyclists are not affected by 28-day L-arginine supplementation.

    PubMed

    Sunderland, Kyle L; Greer, Felicia; Morales, Jacobo

    2011-03-01

    The ergogenic effect of L-arginine on an endurance-trained population is not well studied. The few studies that have investigated L-arginine on this population have not been conducted in a laboratory setting or measured aerobic variables. The purpose of the current study is to determine if 28 days of L-arginine supplementation in trained male cyclists affects VO2max and ventilatory threshold (VT). Eighteen (18) endurance-trained male cyclists (mean ± SD, age: 36.3 ± 7.9 years; height: 182.4 ± 4.6 cm; and body mass: 79.5 ± 4.7 kg) performed a graded exercise test (GXT; 50 W + 25 W·min) before and after 28 days of supplementation with L-arginine (ARG; 2 × 6 g·d) or placebo (PLA; cornstarch). The GXT was conducted on the subject's own bicycle using the RacerMate CompuTrainer (Seattle, WA, USA). VO2 was continuously recorded using the ParvoMedics TrueOne 2400 metabolic cart (Salt Lake City, UT, USA) and VT was established by plotting the ventilatory equivalent for O2 (VE/VO2) and the ventilatory equivalent for CO2 (VE/VCO2) and identifying the point at which VE/VO2 increases with no substantial changes in VE/VCO2. L-arginine supplementation had no effect from initial VO2max (PL, 58.7 ± 7.1 ml·kg·min; ARG, 63.5 ± 7.3 ml·kg·min) to postsupplement VO2max (PL, 58.9 ± 6.0 ml·kg·min; ARG, 63.2 ± 7.2 ml·kg·min). Also, no effect was seen from initial VT (PL, 75.7 ± 4.6% VO2max; ARG, 76.0 ± 5.3% VO2max) to postsupplement VT (PL, 74.3 ± 8.1% VO2max; ARG, 74.2 ± 6.4% VO2max). These results indicate that L-arginine does not impact VO2max or VT in trained male cyclists.

  20. Antepartum cardiorespiratory fitness (CRF) quantification by estimation of maximal oxygen consumption (Vo2 max) in pregnant South Indian women.

    PubMed

    Chakaravertty, Biswajit; Parkavi, K; Coumary, Sendhil A; Felix, A J W

    2012-04-01

    The aim of the study was to calculate the maximal oxygen consumption (Vo2max) for pregnant women of varying trimesters and to quantify the cardiorespiratory fitness (CRF)with the objective of being able to determine the exercise dose for antenatal women which can be prescribed to achieve optimal exercise benefits during various trimesters. A study group comprising 64 pregnant women with uncomplicated singleton pregnancy and control group with 77 non-pregnant women were subjected to Cooper's 12 minutes walk test. From the distance covered in 12 minutes, Vo2max was calculated. The Vo2max values were statistically analysed between the non-pregnant and pregnant and also its variability among the trimesters. Percentile tables of Vo2max were drawn and multiple comparisons were applied. Results show that the Vo2max values among non-pregnant and first trimester ranges between 18 and 22 ml/kg/minute. Trimesters II and III had a range of Vo2max values between 16-20 and 14-18 ml/kg/minute respectively. The CRF of pregnant women significantly reduced to 6%, 9% and 18% in each trimester respectively when compared with the reference table framed out of non-pregnant Vo2max values. Among the study group the reduction in Vo2max values had no statistical significance between first 2 trimesters but trimester III significantly differs from other trimesters. The exercise prescription cannot be the same for pregnant and non-pregnant women. Even among the pregnant women, III trimester needs separate exercise prescription from the other two trimesters as CRF is markedly compromised towards term.

  1. Angle-independent VO2 Thin Film on Glass Fiber Cloth as a Soft-Smart-Mirror (SSM)

    PubMed Central

    Cai, Nianjin; Zhang, Wang; Wang, Wanlin; Zhu, Yuchen; Zada, Imran; Gu, Jiajun; Liu, Qinglei; Su, Huilan; Guo, Cuiping; Zhang, Zhijian; Zhang, Jianzhong; Wu, Liping; Zhang, Di

    2016-01-01

    Designing materials with a negative feedback function is beneficial for achieving temperature regulation inside a greenhouse. VO2 has been studied extensively because of its low insulator-to-metal transition temperature (IMT). In this study, reflection changes during a VO2 phase transition were investigated. Glass fiber cloth was used as a substrate, as it is stable and soft. A VO2 thin film on a glass fiber cloth whose surface contained 96% V4+ and 4% V5+ was prepared using an inorganic sol-gels method. The insulator-to-metal transition temperature was decreased by 38 °C, which was observed from the reflection curve detected using an angle-resolved spectrometer. This decrease in IMT occurred mainly because of the presence of V5+, which causes destabilization of the monoclinic phase of VO2. When the greenhouse temperature was increased from 30 °C to 40 °C, the reflected intensity of VO2 on glass fiber cloth decreased by 22% for the wavelength range of 400 nm to 800 nm. In addition, the angle-independent property of the VO2 thin film was observed using an angle-resolved spectrometer. Owing to its thermo-reflective properties, the thin film can serve as a soft-smart-mirror (SSM) inside a greenhouse to stabilize the temperature, playing a negative feedback role. PMID:27849051

  2. Initial Weekly HRV Response is Related to the Prospective Change in VO2max in Female Soccer Players.

    PubMed

    Esco, M R; Flatt, A A; Nakamura, F Y

    2016-06-01

    The aim of this study was to determine whether the early response in weekly measures of HRV, when derived from a smartphone application, were related to the eventual change in VO2max following an off-season training program in female soccer athletes. 9 female collegiate soccer players participated in an 11-week off-season conditioning program. In the week immediately before and after the training program, each participant performed a test on a treadmill to determine maximal oxygen consumption (VO2max). Daily measures of the log-transformed root mean square of successive R-R intervals (lnRMSSD) were performed by the participants throughout week 1 and week 3 of the conditioning program. The mean and coefficient of variation (CV) lnRMSSD values of week 1 showed small (r=- 0.13, p=0.74) and moderate (r=0.57, p=0.11), respectively, non-significant correlations to the change in VO2max at the end of the conditioning program (∆VO2max). Significant and near-perfect correlation was found between the change in the weekly mean lnRMSSD values from weeks 1 and 3 (∆lnRMSSDM) and ∆VO2max (r=0.90, p=0.002). The current results have identified that the initial change in weekly mean lnRMSSD from weeks 1 to 3 of a conditioning protocol was strongly associated with the eventual adaptation of VO2max.

  3. The phase transition in VO2 probed using x-ray, visible and infrared radiations

    NASA Astrophysics Data System (ADS)

    Kumar, Suhas; Strachan, John Paul; Kilcoyne, A. L. David; Tyliszczak, Tolek; Pickett, Matthew D.; Santori, Charles; Gibson, Gary; Williams, R. Stanley

    2016-02-01

    Vanadium dioxide (VO2) is a model system that has been used to understand closely occurring multiband electronic (Mott) and structural (Peierls) transitions for over half a century due to continued scientific and technological interests. Among the many techniques used to study VO2, the most frequently used involve electromagnetic radiation as a probe. Understanding of the distinct physical information provided by different probing radiations is incomplete, mostly owing to the complicated nature of the phase transitions. Here, we use transmission of spatially averaged infrared (λ = 1.5 μm) and visible (λ = 500 nm) radiations followed by spectroscopy and nanoscale imaging using x-rays (λ = 2.25-2.38 nm) to probe the same VO2 sample while controlling the ambient temperature across its hysteretic phase transitions and monitoring its electrical resistance. We directly observed nanoscale puddles of distinct electronic and structural compositions during the transition. The two main results are that, during both heating and cooling, the transition of infrared and visible transmission occurs at significantly lower temperatures than the Mott transition, and the electronic (Mott) transition occurs before the structural (Peierls) transition in temperature. We use our data to provide insights into possible microphysical origins of the different transition characteristics. We highlight that it is important to understand these effects because small changes in the nature of the probe can yield quantitatively, and even qualitatively, different results when applied to a non-trivial multiband phase transition. Our results guide more judicious use of probe type and interpretation of the resulting data.

  4. Aging attenuates vascular and metabolic plasticity but does not limit improvement in muscle VO(2) max.

    PubMed

    Lawrenson, L; Hoff, J; Richardson, R S

    2004-04-01

    The interactions between exercise, vascular and metabolic plasticity, and aging have provided insight into the prevention and restoration of declining whole body and small muscle mass exercise performance known to occur with age. Metabolic and vascular adaptations to normoxic knee-extensor exercise training (1 h 3 times a week for 8 wk) were compared between six sedentary young (20 +/- 1 yr) and six sedentary old (67 +/- 2 yr) subjects. Arterial and venous blood samples, in conjunction with a thermodilution technique facilitated the measurement of quadriceps muscle blood flow and hematologic variables during incremental knee-extensor exercise. Pretraining, young and old subjects attained a similar maximal work rate (WR(max)) (young = 27 +/- 3, old = 24 +/- 4 W) and similar maximal quadriceps O(2) consumption (muscle Vo(2 max)) (young = 0.52 +/- 0.03, old = 0.42 +/- 0.05 l/min), which increased equally in both groups posttraining (WR(max), young = 38 +/- 1, old = 36 +/- 4 W, Muscle Vo(2 max), young = 0.71 +/- 0.1, old = 0.63 +/- 0.1 l/min). Before training, muscle blood flow was approximately 500 ml lower in the old compared with the young throughout incremental knee-extensor exercise. After 8 wk of knee-extensor exercise training, the young reduced muscle blood flow approximately 700 ml/min, elevated arteriovenous O(2) difference approximately 1.3 ml/dl, and increased leg vascular resistance approximately 17 mmHg x ml(-1) x min(-1), whereas the old subjects revealed no training-induced changes in these variables. Together, these findings indicate that after 8 wk of small muscle mass exercise training, young and old subjects of equal initial metabolic capacity have a similar ability to increase quadriceps muscle WR(max) and muscle Vo(2 max), despite an attenuated vascular and/or metabolic adaptation to submaximal exercise in the old.

  5. Limitations to vasodilatory capacity and .VO2 max in trained human skeletal muscle.

    PubMed

    Barden, Jeremy; Lawrenson, Lesley; Poole, Jennifer G; Kim, Jeannie; Wray, D Walter; Bailey, Damian M; Richardson, Russell S

    2007-05-01

    To further explore the limitations to maximal O(2) consumption (.VO(2 max)) in exercise-trained skeletal muscle, six cyclists performed graded knee-extensor exercise to maximum work rate (WR(max)) in hypoxia (12% O(2)), hyperoxia (100% O(2)), and hyperoxia + femoral arterial infusion of adenosine (ADO) at 80% WR(max). Arterial and venous blood sampling and thermodilution blood flow measurements allowed the determination of muscle O(2) delivery and O(2) consumption. At WR(max), O(2) delivery rose progressively from hypoxia (1.0 +/- 0.04 l/min) to hyperoxia (1.20 +/- 0.09 l/min) and hyperoxia + ADO (1.33 +/- 0.05 l/min). Leg .VO(2 max) varied with O(2) availability (0.81 +/- 0.05 and 0.97 +/- 0.07 l/min in hypoxia and hyperoxia, respectively) but did not improve with ADO-mediated vasodilation (0.80 +/- 0.09 l/min in hyperoxia + ADO). Although a vasodilatory reserve in the maximally working quadriceps muscle group may have been evidenced by increased leg vascular conductance after ADO infusion beyond that observed in hyperoxia (increased blood flow but no change in blood pressure), we recognize the possibility that the ADO infusion may have provoked vasodilation in nonexercising tissue of this limb. Together, these findings imply that maximally exercising skeletal muscle may maintain some vasodilatory capacity, but the lack of improvement in leg .VO(2 max) with significantly increased O(2) delivery (hyperoxia + ADO), with a degree of uncertainty as to the site of this dilation, suggests an ADO-induced mismatch between O(2) consumption and blood flow in the exercising limb.

  6. Individual versus Standardized Running Protocols in the Determination of VO2max.

    PubMed

    Sperlich, Paula F; Holmberg, Hans-Christer; Reed, Jennifer L; Zinner, Christoph; Mester, Joachim; Sperlich, Billy

    2015-06-01

    The purpose of this study was to determine whether an individually designed incremental exercise protocol results in greater rates of oxygen uptake (VO2max) than standardized testing. Fourteen well-trained, male runners performed five incremental protocols in randomized order to measure their VO2max: i) an incremental test (INCS+I) with pre-defined increases in speed (2 min at 8.64 km·h(-1), then a rise of 1.44 km·h(-1) every 30 s up to 14.4 km·h(-1)) and thereafter inclination (0.5° every 30 s); ii) an incremental test (INCI) at constant speed (14.4 km·h(-1)) and increasing inclination (2° every 2 min from the initial 0°); iii) an incremental test (INCS) at constant inclination (0°) and increasing speed (0.5 km·h(-1) every 30 s from the initial 12.0 km·h(-1)); iv) a graded exercise protocol (GXP) at a 1° incline with increasing speed (initially 8.64 km·h(-1) + 1.44 km·h(-1) every 5 min); v) an individual exercise protocol (INDXP) in which the runner chose the inclination and speed. VO2max was lowest (-4.2%) during the GXP (p = 0.01; d = 0.06-0.61) compared to all other tests. The highest rating of perceived exertion, heart rate, ventilation and end-exercise blood lactate concentration were similar between the different protocols (p < 0.05). The time to exhaustion ranged from 7 min 18 sec (INCS) to 25 min 30 sec (GXP) (p = 0.01).The VO2max attained by employing an individual treadmill protocol does not differ from the values derived from various standardized incremental protocols. Key pointsThe mean maximum oxygen uptake during the GXP was lower than for all other tests.Differences in the maximum rate of oxygen uptake between the various protocols exhibited considerable inter-individual variation.From the current findings, it can be concluded that well trained athletes are able to perform an individually designed treadmill running protocol.

  7. Highly oriented graphene growth and characterization

    NASA Astrophysics Data System (ADS)

    Saheed, Mohamed Salleh Mohamed; Mohamed, Norani Muti; Singh, Balbir Singh Mahinder; Saheed, Mohamed Shuaib Mohamed

    2016-11-01

    Combination of the highly ordered monolayers to form the multilayer interconnected graphene is essential to produce robust and free standing graphene unlike its counterpart 2D monolayers. Here, chemical vapor deposition (CVD) technique is employed to produce highly flexible and high mobility 3D graphene. In this study, the 3D graphene is grown via direct carbon deposition on sacrificial template. With the use of polymer coating such as poly methyl methacrylate (PMMA), it is observed that the graphene is bendable without any degradation. Great potential in term of electrical conductivity and flexibility can be exploited for future work for this CVD grown 3D graphene.

  8. Hydrogen incorporation induced the octahedral symmetry variation in VO2 films

    NASA Astrophysics Data System (ADS)

    Lee, Dooyong; Kim, Hyegyeong; Kim, Ji Woong; Lee, Ik Jae; Kim, Yooseok; Yun, Hyung-Joong; Lee, Jouhahn; Park, Sungkyun

    2017-02-01

    This study examined the microscopic aspects of macroscopic physical property variations of hydrogen annealed VO2 films, deposited on Al2O3(0001) substrates by RF magnetron sputtering. The temperature-dependent electrical resistivity showed that the as-grown film exhibited a metal-insulator-transition (MIT) at 55.20 °C and 49.26 °C during heating and cooling, respectively. On the other hand, no MIT was observed for the film annealed under a hydrogen environment. Spectroscopic measurements during the in-situ hydrogenation process showed that hydrogen annealing (∼0.3 mbar, up to 300 °C) promoted the V3+ state above 100 °C. Raman spectroscopy and X-ray diffraction confirmed that the as-grown film changed from a monoclinic to rutile structure during hydrogen annealing. In addition, the shift of the (020) diffraction peak position of the hydrogen-annealed film to a lower angle compare to that of the known rutile VO2 film was attributed to the expansion of the unit cell. In addition, local structure analysis showed that an increase in octahedral symmetry after hydrogen annealing is one of the main explanations for the metallic characteristics of the hydrogen-annealed film.

  9. Analysis of square-wave bouts to verify VO2max.

    PubMed

    Sedgeman, D; Dalleck, L; Clark, I E; Jamnick, N; Pettitt, R W

    2013-12-01

    Submaximal and supramaximal square-wave bouts have been reported to consistently verify 'true' VO2max. Although a direct comparison between both protocols exists, knowledge on the statistical consistency between the protocols using the same group of participants is lacking. The purpose of this study was to conduct an analysis of the submaximal and supramaximal verification bout performed shortly subsequent to a graded exercise test (GXT). On 2 separate occasions, 6 males and 7 females (age: 29±9 years) completed a GXT protocol and an exhaustive, square-wave bout at either end-GXT power minus 2-stages or 105% end-GXT power. No differences (p>0.05) in VO2max were observed between the GXT and square-wave bouts. The typical error (ml/kg/min) for submaximal (1.09) and supramaximal (1.04) trials was similar. Likewise, similar relative measures of consistency were observed for the submaximal (ICC α=0.97, CV=2.4%) and supramaximal trials (ICC α=0.95, CV=2.3%). For a GXT lasting ~10-12 min, the submaximal or supramaximal protocols appear to be equally effective.

  10. Tuning a strain-induced orbital selective Mott transition in epitaxial VO2

    NASA Astrophysics Data System (ADS)

    Mukherjee, Shantanu; Quackenbush, N. F.; Paik, H.; Schlueter, C.; Lee, T.-L.; Schlom, D. G.; Piper, L. F. J.; Lee, Wei-Cheng

    2016-06-01

    We present evidence of strain-induced modulation of electron correlation effects and increased orbital anisotropy in the rutile phase of epitaxial VO2/TiO2 films from hard x-ray photoelectron spectroscopy and soft V L-edge x-ray absorption spectroscopy, respectively. By using the U(1) slave spin formalism, we further argue that the observed anisotropic correlation effects can be understood by a model of orbital selective Mott transition at a filling that is noninteger but close to the half filling. Because the overlaps of wave functions between d orbitals are modified by the strain, orbital-dependent renormalizations of the bandwidths and the onsite energy occur. These renormalizations generally result in different occupation numbers in different orbitals. We find that if the system has a noninteger filling number near the half filling such as for VO2, certain orbitals could reach an occupation number closer to half filling under the strain, resulting in a strong reduction in the quasiparticle weight Zα of that orbital. Our work demonstrates that such an orbital selective Mott transition, defined as the case with Zα=0 in some but not all orbitals, could be accessed by epitaxial-strain engineering of correlated electron systems.

  11. Large phonon entropy drives the metallization of vanadium dioxide (VO2)

    NASA Astrophysics Data System (ADS)

    Hong, Jiawang

    2015-03-01

    Vanadium dioxide (VO2) exhibits a first-order metal-insulator transition (MIT) near room temperature, where conductivity is suppressed and the lattice changes from tetragonal to monoclinic on cooling. This MIT in VO2 has attracted intense interest from both fundamental and technological perspectives. However, most studies performed in the past 50 years have focused on the electronic structure and energetics of the transition, ignoring the role of phonons and their entropic contribution to the phase stability. Much of the reason is that the standard tool of neutron scattering does not yield coherent scattering from V nuclei, and first-principles methods with harmonic approximation cannot capture the stable phonons for the rutile phase. We close this gap by using a combination of ab initio molecular dynamics calculations and neutron/x-ray scattering to establish that the entropy driving the MIT is dominated by soft, anharmonic phonons of the metallic phase. The MIT results from the competition between lower electronic energy in insulating M1 phase due to the Peierls instability, and the higher entropy of the metallic rutile phase resulting from soft anharmonic phonons. This understanding of the role of lattice dynamics and their relationship to electronic structure provides a critical component for developing more complete physical models of phase competition in functional transition metal oxides. Theoretical calculations were performed using the NERSC at LBNL. Modeling of neutron data was performed in CAMM, measurements were funded by the US DOE, BES, Materials Science and Engineering Division.

  12. Switching dynamics of single and coupled VO2-based oscillators as elements of neural networks

    NASA Astrophysics Data System (ADS)

    Velichko, Andrey; Belyaev, Maksim; Putrolaynen, Vadim; Pergament, Alexander; Perminov, Valentin

    2017-01-01

    In the present paper, we report on the switching dynamics of both single and coupled VO2-based oscillators, with resistive and capacitive coupling, and explore the capability of their application in oscillatory neural networks. Based on these results, we further select an adequate SPICE model to describe the modes of operation of coupled oscillator circuits. Physical mechanisms influencing the time of forward and reverse electrical switching, that determine the applicability limits of the proposed model, are identified. For the resistive coupling, it is shown that synchronization takes place at a certain value of the coupling resistance, though it is unstable and a synchronization failure occurs periodically. For the capacitive coupling, two synchronization modes, with weak and strong coupling, are found. The transition between these modes is accompanied by chaotic oscillations. A decrease in the width of the spectrum harmonics in the weak-coupling mode, and its increase in the strong-coupling one, is detected. The dependences of frequencies and phase differences of the coupled oscillatory circuits on the coupling capacitance are found. Examples of operation of coupled VO2 oscillators as a central pattern generator are demonstrated.

  13. Nanoscale Engineering in VO2 Nanowires via Direct Electron Writing Process.

    PubMed

    Zhang, Zhenhua; Guo, Hua; Ding, Wenqiang; Zhang, Bin; Lu, Yue; Ke, Xiaoxing; Liu, Weiwei; Chen, Furong; Sui, Manling

    2017-02-08

    Controlling phase transition in functional materials at nanoscale is not only of broad scientific interest but also important for practical applications in the fields of renewable energy, information storage, transducer, sensor, and so forth. As a model functional material, vanadium dioxide (VO2) has its metal-insulator transition (MIT) usually at a sharp temperature around 68 °C. Here, we report a focused electron beam can directly lower down the transition temperature of a nanoarea to room temperature without prepatterning the VO2. This novel process is called radiolysis-assisted MIT (R-MIT). The electron beam irradiation fabricates a unique gradual MIT zone to several times of the beam size in which the temperature-dependent phase transition is achieved in an extended temperature range. The gradual transformation zone offers to precisely control the ratio of metal/insulator phases. This direct electron writing technique can open up an opportunity to precisely engineer nanodomains of diversified electronic properties in functional material-based devices.

  14. Mechanism and observation of Mott transition in VO2-based two- and three-terminal devices

    NASA Astrophysics Data System (ADS)

    Kim, Hyun-Tak; Chae, Byung-Gyu; Youn, Doo-Hyeb; Maeng, Sung-Lyul; Kim, Gyungock; Kang, Kwang-Yong; Lim, Yong-Sik

    2004-05-01

    When holes of about 0.018% are induced into a conduction band (breakdown of critical on-site Coulomb energy), an abrupt first-order Mott metal-insulator transition (MIT) rather than a continuous Hubbard MIT near a critical on-site Coulomb energy U/Uc=1, where U is on-site Coulomb energy between electrons, is observed on an inhomogeneous VO2 film, a strongly correlated Mott insulator. As a result, discontinuous jumps of the density of states on the Fermi surface are observed and inhomogeneity inevitably occurs. The off-current and temperature dependences of the abrupt MIT in a two-terminal device and the gate effect in a three-terminal device are clear evidence that the abrupt Mott MIT was induced by the excitation of holes. Raman spectra measured by a micro-Raman system show an MITs without the structural phase transition. Moreover, the magnitude of the observed jumps DgrJobserved at the abrupt MIT is an average over an inhomogeneous measurement region of the maximum true jump, DgrJtrue, deduced from the Brinkman-Rice picture. A brief discussion of whether VO2 is a Mott insulator or a Peierls insulator is presented.

  15. The effects of an acute bout of sleep on running economy and VO2 max.

    PubMed

    Pierce, E F; McGowan, R W; Barkett, E; Fry, R W

    1993-04-01

    Synchronized human sleep has been shown to decrease activation of the sympathetic nervous system, resulting in reduced levels of oxygen consumption. This is in direct conflict with sympathetic arousal, which coincides with the initiation of exercise. Although a considerable body of research has investigated the effects of sleep deprivation on exercise performance, the effects of an acute bout of sleep on exercise response have not been previously reported. This question appears relevant considering the occurrence of acute sleep bouts among athletes competing in prolonged multi-event competition (e.g. swimming, track and field). To investigate the effects of an acute bout of sleep on submaximal (running economy) and maximal oxygen consumption, seven male volunteers participated in a continuous, progressive treadmill test to volitional exhaustion immediately following a 1-h bout of sleep (SB) or no sleep (Control). The subjects served as their own controls and the order of trials was randomized. A MANOVA with repeated measures indicated no difference between groups for running economy or VO2 (P < 0.05). However, a significant interaction effect was observed in which SB resulted in greater running economy (lower VO2) through the first two stages of the protocol, while the control treatment yielded a greater economy throughout the remaining stages. While the implications of the findings are uncertain, they may indicate differences in psychological arousal or anxiety as a result of treatments or the possibility of a delayed sympathetic arousal in the early stages of exercise following sleep.

  16. Metallization of Epitaxial VO2 Films by Ionic Liquid Gating through Initially Insulating TiO2 Layers.

    PubMed

    Passarello, Donata; Altendorf, Simone G; Jeong, Jaewoo; Samant, Mahesh G; Parkin, Stuart S P

    2016-09-14

    Ionic liquid gating has been shown to metallize initially insulating layers formed from several different oxide materials. Of these vanadium dioxide (VO2) is of especial interest because it itself is metallic at temperatures above its metal-insulator transition. Recent studies have shown that the mechanism of ionic liquid gated induced metallization is entirely distinct from that of the thermally driven metal-insulator transition and is derived from oxygen migration through volume channels along the (001) direction of the rutile structure of VO2. Here we show that it is possible to metallize the entire volume of 10 nm thick layers of VO2 buried under layers of rutile titanium dioxide (TiO2) up to 10 nm thick. Key to this process is the alignment of volume channels in the respective oxide layers, which have the same rutile structure with clamped in-plane lattice constants. The metallization of the VO2 layers is accompanied by large structural expansions of up to ∼6.5% in the out-of-plane direction, but the structure of the TiO2 layer is hardly affected by gating. The TiO2 layers become weakly conducting during the gating process, but in contrast to the VO2 layers, the conductivity disappears on exposure to air. Indeed, even after air exposure, X-ray photoelectron spectroscopy studies show that the VO2 films have a reduced oxygen content after metallization. Ionic liquid gating of the VO2 films through initially insulating TiO2 layers is not consistent with conventional models that have assumed the gate induced carriers are of electrostatic origin.

  17. Synthesis and supercapacitor electrode of VO2(B)/C core-shell composites with a pseudocapacitance in aqueous solution

    NASA Astrophysics Data System (ADS)

    Zhang, Yifu; Zheng, Jiqi; Hu, Tao; Tian, Fuping; Meng, Changgong

    2016-05-01

    VO2(B)/C core-shell composites were successfully prepared using commercial V2O5, glucose and water as the starting materials by a facile one-pot hydrothermal method. The composition of the products was characterized by the techniques including X-ray powder diffraction, infrared spectroscopy, Raman, energy-dispersive X-ray spectrometer and elemental analysis. The morphology of the products was observed by scanning electron microscopy and transmission electron microscopy tests. The results showed the products consisted of the crystal VO2(B) phase and the amorphous carbon phase. The amorphous carbon contained lots of organic groups, such as sbnd OH, Csbnd H, Cdbnd O and Cdbnd C, etc., which suggested that the carbon here was organic carbon. The morphology of the as-obtained VO2(B)/C composites was well-defined nanobelts, and each VO2(B) core was encapsulated into carbon. Furthermore, the electrochemical properties of VO2(B)/C core-shell composites were investigated by cyclic voltammetry and galvanostatic charge-discharge. The results showed the measured capacitance of VO2(B)/C composites was mainly based on the pseudocapacitance. VO2(B)/C composites displayed the specific capacitance of 203, 190, 182, 173, 164, and 147 F g-1 at the current density of 0.2, 0.5, 1, 5, 10 and 20 A g-1, respectively. They also showed an excellent energy density of 198.9 W h kg-1 at a power density of 504.5 W kg-1 and a rapidly reversible redox Faraday response.

  18. Structure and stability of VO2+ in aqueous solution: a Car-Parrinello and static ab initio study.

    PubMed

    Sadoc, Aymeric; Messaoudi, Sabri; Furet, Eric; Gautier, Régis; Le Fur, Eric; le Pollès, Laurent; Pivan, Jean-Yves

    2007-06-11

    Quantum chemical calculations have been carried out to get some insight concerning the effects of temperature and solvent acidity on the structure and stability of solvated VO2+ as the elementary chemical unit involved in the nucleation of vanadophosphates. First, because some recent theoretical studies have suggested a tendency of density functional theory (DFT) to favor lower coordination numbers for such systems, static calculations have been performed on [VO2(H2O)(4-n)]+.nH2O (n=0-2) conformers at the MP2 and DFT level of theory, using two different combinations of basis sets. The results of two pure-GGA (BP86 and PBEPBE), two hybrid-GGA (PBE1PBE and mPWPW91), and two hybrid-meta-GGA (mPW1B95 and B1B95) functionals were analyzed on these systems. The comparison of the results indicates that the stability differences between the two methodologies are resolved when hydration energy is taken into account, provided that some amount of HF exchange is introduced in the DFT calculations. In a second step, Car-Parrinello simulations have been carried out starting from VO2(H2O)4+ surrounded by water molecules. The calculations at 300 K show the natural tendency of VO2(H2O)4+ to decompose to VO2(OH)2- and the requirements to work with an already acidified medium to be able to investigate the coordination sphere of VO2+ for an extended period of time. Under such conditions, we have obtained a clear preference for a five-coordinated vanadium. The molecular dynamics simulations performed at 500 K starting from hydrated VO2+ in a protonated medium found VO(OH)3 to be the most stable structure, whereas this ideal candidate for oxolation reactions is expected to be a very minor species at room temperature.

  19. Extracting cardiac myofiber orientations from high frequency ultrasound images

    NASA Astrophysics Data System (ADS)

    Qin, Xulei; Cong, Zhibin; Jiang, Rong; Shen, Ming; Wagner, Mary B.; Kirshbom, Paul; Fei, Baowei

    2013-03-01

    Cardiac myofiber plays an important role in stress mechanism during heart beating periods. The orientation of myofibers decides the effects of the stress distribution and the whole heart deformation. It is important to image and quantitatively extract these orientations for understanding the cardiac physiological and pathological mechanism and for diagnosis of chronic diseases. Ultrasound has been wildly used in cardiac diagnosis because of its ability of performing dynamic and noninvasive imaging and because of its low cost. An extraction method is proposed to automatically detect the cardiac myofiber orientations from high frequency ultrasound images. First, heart walls containing myofibers are imaged by B-mode high frequency (<20 MHz) ultrasound imaging. Second, myofiber orientations are extracted from ultrasound images using the proposed method that combines a nonlinear anisotropic diffusion filter, Canny edge detector, Hough transform, and K-means clustering. This method is validated by the results of ultrasound data from phantoms and pig hearts.

  20. Determination of both the time constant of vO2 and DeltavO2/DeltaW from a single incremental exercise test: validation and repeatability.

    PubMed

    Wisén, Anita G M; Wohlfart, Björn

    2004-09-01

    A single incremental cycle exercise test including a steady-state load, combined with respiratory gas exchange, was performed with the objective of determining the time constant (tauVO(2)) and the amount of oxygen required at each load (DeltaVO(2)/DeltaW) by using a novel equation. The protocol was validated using four exercise tests at different constant loads and conventionally fitted mono-exponential functions to determine tauVO(2), and interpolation of VO(2) versus load to determine DeltaVO(2)/DeltaW. No significant differences were seen between the means of either tauVO(2) or DeltaVO(2)/DeltaW determined with the two protocols. The correlation coefficient was 0.62 for tauVO(2) and 0.48 for DeltaVO(2)/DeltaW. The absolute differences (2 SD) were 11.6 s for tauVO(2) and 1.1 ml min(-1) W(-1) for DeltaVO(2)/DeltaW. The equations were compared in the same steady-state test and good agreement of tauVO(2) was obtained (R = 0.99). The 5-6-week repeatability (incremental test) was evaluated. No statistical differences were seen between the mean of the repeated tests. The difference between the tests (2 SD) were 20 s for tauVO(2) and 1.2 ml min(-1) W(-1) for DeltaVO(2)/DeltaW. In conclusion, tauVO(2) and DeltaVO(2)/DeltaW can be determined from a single incremental test. The validation showed an acceptable agreement, although the variations in absolute values were not negligible. This could partly be explained by the natural day-to-day variation and fluctuations in incoming raw data. The test-retest variation in absolute values was considerable, which must be taken into account when using tauVO(2) and DeltaVO(2)/DeltaW for evaluation of aerobic function.

  1. Theoretical Study of Electronic Properties of X-Doped (X = F, Cl, Br, I) VO2 Nanoparticles for Thermochromic Energy-Saving Foils.

    PubMed

    Ren, Qinghua; Wan, Jinyu; Gao, Yanfeng

    2014-11-20

    First-principles density functional theory (DFT) electronic structure calculations were carried out for the model halogen-doped VO2 (M1 phase) to evaluate the effect of halogen (X = F, Cl, Br, I) doping on the band edges. The model structures of X-doped VO2 with X at V site or O site were constructed on the basis of 96-atom 2 × 2 × 2 supercell of monoclinic M1 phase of VO2. Our results showed that the band gap Eg2 for Cl-doped VO2 at O1 site (0.51 eV) is smaller than that of F-doped VO2 at O1 site (0.61 eV) and that of pure VO2 (0.78 eV). We also investigated the substitution of chlorine, bromine, and iodine for vanadium in VO2, where the band gaps Eg2 are 0.40, 0.45, and 0.37 eV for Cl-, Br-, and I-doped VO2 at V site, respectively. The Cl-doped VO2 at V site is the best one for achieving good VO2 thermochromic energy-saving foils.

  2. Effects of sprint interval training on VO2max and aerobic exercise performance: A systematic review and meta-analysis.

    PubMed

    Sloth, M; Sloth, D; Overgaard, K; Dalgas, U

    2013-12-01

    Recently, several studies have examined whether low-volume sprint interval training (SIT) may improve aerobic and metabolic function. The objective of this study was to systematically review the existing literature regarding the aerobic and metabolic effects of SIT in healthy sedentary or recreationally active adults. A systematic literature search was performed (Bibliotek.dk, SPORTDiscus, Embase, PEDro, SveMed+, and Pubmed). Meta-analytical procedures were applied evaluating effects on maximal oxygen consumption (VO2max). Nineteen unique studies [four randomized controlled trials (RCTs), nine matched-controlled trials and six noncontrolled studies] were identified, evaluating SIT interventions lasting 2-8 weeks. Strong evidence support improvements of aerobic exercise performance and VO2max following SIT. A meta-analysis across 13 studies evaluating effects of SIT on VO2max showed a weighted mean effects size of g = 0.63 95% CI (0.39; 0.87) and VO2max increases of 4.2-13.4%. Solid evidence support peripheral adaptations known to increase the oxidative potential of the muscle following SIT, whereas evidence regarding central adaptations was limited and equivocal. Some evidence indicated changes in substrate oxidation at rest and during exercise as well as improved glycemic control and insulin sensitivity following SIT. In conclusion, strong evidence support improvement of aerobic exercise performance and VO2max following SIT, which coincides with peripheral muscular adaptations. Future RCTs on long-term SIT and underlying mechanisms are warranted.

  3. Effects of optimal pacing strategies for 400-, 800-, and 1500-m races on the VO2 response.

    PubMed

    Hanon, Christine; Thomas, Claire

    2011-06-01

    The aim of this study was to compare the evolution of oxygen uptake (VO2) in specifically trained runners during running tests based on the 400-, 800-, and 1500-m pacing strategies adopted by elite runners to optimize performance. Final velocity decreased significantly for all three distances, with the slowest velocity in the last 100 m expressed relative to the peak velocity observed in the 400 m (77%), 800 m (88%), and 1500 m (96%). Relative to the previously determined VO2max values, the respective VO 2peak corresponded to 94% (400 m) and 100% (800 and 1500 m). In the last 100 m, a decrease in VO2 was observed in all participants for the 400-m (15.6 ± 6.5%) and 800-m races (9.9 ± 6.3%), whereas a non-systematic decrease (3.6 ± 7.6%) was noted for the 1500 m. The amplitude of this decrease was correlated with the reduction in tidal volume recorded during the last 100 m of each distance (r = 0.85, P < 0.0001) and with maximal blood lactate concentrations after the three races (r = 0.55, P < 0.005). The present data demonstrate that the 800 m is similar to the 400 m in terms of decreases in velocity and VO2.

  4. PREDICTION OF VO2PEAK USING OMNI RATINGS OF PERCEIVED EXERTION FROM A SUBMAXIMAL CYCLE EXERCISE TEST

    PubMed Central

    Mays, Ryan J.; Goss, Fredric L.; Nagle-Stilley, Elizabeth F.; Gallagher, Michael; Schafer, Mark A.; Kim, Kevin H.; Robertson, Robert J.

    2015-01-01

    Summary The primary aim of this study was to develop statistical models to predict peak oxygen consumption (VO2peak) using OMNI Ratings of Perceived Exertion measured during submaximal cycle ergometry. Men (mean ± standard error: 20.90 ± 0.42 yrs) and women (21.59 ± 0.49 yrs) participants (n = 81) completed a load-incremented maximal cycle ergometer exercise test. Simultaneous multiple linear regression was used to develop separate VO2peak statistical models using submaximal ratings of perceived exertion for the overall body, legs, and chest/breathing as predictor variables. VO2peak (L·min−1) predicted for men and women from ratings of perceived exertion for the overall body (3.02 ± 0.06; 2.03 ± 0.04), legs (3.02 ± 0.06; 2.04 ± 0.04) and chest/breathing (3.02 ± 0.05; 2.03 ± 0.03) were similar with measured VO2peak (3.02 ± 0.10; 2.03 ± 0.06, ps > .05). Statistical models based on submaximal OMNI Ratings of Perceived Exertion provide an easily administered and accurate method to predict VO2peak. PMID:25068750

  5. Visualization of one-dimensional diffusion and spontaneous segregation of hydrogen in single crystals of VO2

    NASA Astrophysics Data System (ADS)

    Serkan Kasırga, T.; Coy, Jim M.; Park, Jae H.; Cobden, David H.

    2016-08-01

    Hydrogen intercalation in solids is common, complicated, and very difficult to monitor. In a new approach to the problem, we have studied the profile of hydrogen diffusion in single-crystal nanobeams and plates of VO2, exploiting the fact that hydrogen doping in this material leads to visible darkening near room temperature connected with the metal-insulator transition at 65 °C. We observe hydrogen diffusion along the rutile c-axis but not perpendicular to it, making this a highly one-dimensional diffusion system. We obtain an activated diffusion coefficient, ˜ 0.01 {{{e}}}-0.6\\text{eV/{{k}}{{B}}{T}} {{{cm}}}2 {{{s}}}-1, applicable in metallic phase. In addition, we observe dramatic supercooling of the hydrogen-induced metallic phase and spontaneous segregation of the hydrogen into stripes implying that the diffusion process is highly nonlinear, even in the absence of defects. Similar complications may occur in hydrogen motion in other materials but are not revealed by conventional measurement techniques.

  6. Detraining increases body fat and weight and decreases VO2peak and metabolic rate.

    PubMed

    Ormsbee, Michael J; Arciero, Paul J

    2012-08-01

    Competitive collegiate swimmers commonly take a month off from swim training after their last major competition. This abrupt cessation of intense physical training has not been well studied and may lead to physiopsychological decline. The purpose of this investigation was to examine the effects of swim detraining (DT) on body composition, aerobic fitness, resting metabolism, mood state, and blood lipids in collegiate swimmers. Eight healthy endurance-trained swimmers (V(O2)peak, 46.7 ± 10.8 ml · kg(-1) · min(-1)) performed 2 identical test days, 1 in the trained (TR) state and 1 in the detrained (~5 weeks) state (DT). Body composition and circumferences, maximal oxygen consumption (V(O2)peak), resting metabolism (RMR), blood lipids, and mood state were measured. After DT, body weight (TR, 68.9 ± 9.7 vs. DT, 69.8 ± 9.8 kg; p = 0.03), fat mass (TR, 14.7 ± 7.6 vs. DT, 16.5 ± 7.4 kg; p = 0.001), and waist circumference (TR, 72.7 ± 3.1 vs. DT, 73.8 ± 3.6 cm; p = 0.03) increased, whereas V(O2)peak (TR, 46.7 ± 10.8 vs. DT, 43.1 ± 10.3 ml · kg(-1) · min(-1); p = 0.02) and RMR (TR, 1.34 ± 0.2 vs. DT, 1.25 ± 0.17 kcal · min(-1); p = 0.008) decreased, and plasma triglycerides showed a trend to increase (p = 0.065). Our data suggest that DT after a competitive collegiate swim season adversely affects body composition, fitness, and metabolism. Athletes and coaches need to be aware of the negative consequences of detraining from swimming, and plan off-season training schedules accordingly to allow for adequate rest/recovery and prevent overuse injuries. It's equally important to mitigate the negative effects on body composition, aerobic fitness and metabolism so performance may continue to improve over the long term.

  7. Maximally anisotropic point Fermi surface system: VO2 films embedded in TiO2

    NASA Astrophysics Data System (ADS)

    Pardo, Victor

    2010-03-01

    Oxide heterostructures provide an unusually rich canvas for the design of unprecedented electronic states. Here we will discuss multilayer (TiO2)m/(VO2)n nanostructures, namely V^4+:d^1 - Ti^4+:d^0 interfaces, with no polar discontinuity, studied by density functional theory techniques[1]. This system shows a metal-insulator transition with respect to the VO2 layer thickness in our first principles calculations[2]. For n = 1 and 2 VO2 layers, the system is insulating. For 5 and more layers, it is ferromagnetic and half-metallic. For the quantum confined cases of n = 3 and 4 the system is neither insulating nor conducting, instead an unexpected state arises: the Fermi surface is point-like as in graphene, except that extreme anisotropy is present[3]. The electrons (or holes, depending on doping) behave as massless fermions along the zone diagonal in k-space, and as conventional (massive) fermions along the perpendicular direction. Certain characteristics identify this ``semi-Dirac'' phase as resulting from quantum confinement, rather than being an interface phenomenon. This point Fermi surface system differs from graphene not only in its extreme anisotropy, but that it arises in a half-metallic system, so spin degrees of freedom are removed. In this presentation an analysis of the evolution of the electronic structure through this unprecedented insulator-to-metal transition will be provided, and the role of a non-intuitive orbital ordering of the V d^1 ions will be discussed. Also the robustness of the semi-Dirac electronic structure to interfacial disorder and the introduction of spin-orbit coupling in the calculations will be analyzed. [4pt] [1] V. Pardo and W.E. Pickett, Phys. Rev. Lett. 102, 107003 (2009).[0pt] [2] V. Pardo and W.E. Pickett, arXiv:0910.4411.[0pt] [3] S. Banerjee, R.R.P. Singh, V. Pardo and W.E. Pickett, Phys. Rev. Lett. 103, 016402 (2009).

  8. A JUNIOR HIGH SCHOOL ORIENTATION CAMP, A COORDINATED CAMPING EXPERIENCE.

    ERIC Educational Resources Information Center

    NEALE, DANIEL; AND OTHERS

    A 2-WEEK SUMMER CAMPING PROGRAM WAS OFFERED TO 61 DISADVANTAGED STUDENTS ABOUT TO ENTER LINCOLN JUNIOR HIGH IN MINNEAPOLIS, MINNESOTA. THE PROGRAM'S PRIMARY PURPOSE WAS TO EASE THE STUDENT'S TRANSITION INTO JUNIOR HIGH SCHOOL. THROUGH CAMPING ACTIVITIES AND SCHOOL ORIENTATION CLASSES CONDUCTED BY THE LINCOLN STAFF, CAMPERS WOULD BECOME ACQUAINTED…

  9. The structures of interstitial hydrogen centers in VO2 in the dilute limit from their vibrational properties and theory

    NASA Astrophysics Data System (ADS)

    Yin, Weikai; Qin, Ying; Fowler, W. Beall; Stavola, Michael; Boatner, Lynn A.

    2016-10-01

    The introduction of a large concentration of H into VO2 is known to suppress the insulating phase of the metal-insulator transition that occurs upon cooling below 340 K. We have used infrared spectroscopy and complementary theory to study the properties of interstitial H and D in VO2 in the dilute limit to determine the vibrational frequencies, thermal stabilities, and equilibrium positions of isolated interstitial H and D centers. The vibrational lines of several OH and OD centers were observed to have thermal stabilities similar to that of the hydrogen that suppresses the insulating phase. Theory associates two of the four possible OH configurations for Hi in the insulating VO2 monoclinic phase with OH lines seen by experiment. Furthermore, theory predicts the energies and vibrational frequencies for configurations with Hi trapped near a substitutional impurity and suggests such defects as candidates for additional OH centers that have been observed.

  10. The structures of interstitial hydrogen centers in VO2 in the dilute limit from their vibrational properties and theory

    DOE PAGES

    Yin, W.; Qin, Ying; Fowler, W. B.; ...

    2016-07-28

    The introduction of a large concentration of H into VO2 is known to suppress the insulating phase of the metal-insulator transition that occurs upon cooling below 340 K. We have used infrared spectroscopy and complementary theory to study the properties of interstitial H and D in VO2 in the dilute limit to determine the vibrational frequencies, thermal stabilities, and equilibrium positions of isolated interstitial H and D centers. The vibrational lines of several OH and OD centers were observed to have thermal stabilities similar to that of the hydrogen that suppresses the insulating phase. Theory associates two of the fourmore » possible OH configurations for Hi in the insulating VO2 monoclinic phase with OH lines seen by experiment. Furthermore, theory predicts the energies and vibrational frequencies for configurations with Hi trapped near a substitutional impurity and suggests such defects as candidates for additional OH centers that have been observed.« less

  11. Role of thermal heating on the voltage induced insulator-metal transition in VO2.

    PubMed

    Zimmers, A; Aigouy, L; Mortier, M; Sharoni, A; Wang, Siming; West, K G; Ramirez, J G; Schuller, Ivan K

    2013-02-01

    We show that the main mechanism for the dc voltage or dc current induced insulator-metal transition in vanadium dioxide VO(2) is due to local Joule heating and not a purely electronic effect. This "tour de force" experiment was accomplished by using the fluorescence spectra of rare-earth doped micron sized particles as local temperature sensors. As the insulator-metal transition is induced by a dc voltage or dc current, the local temperature reaches the transition temperature indicating that Joule heating plays a predominant role. This has critical implications for the understanding of the dc voltage or dc current induced insulator-metal transition and has a direct impact on applications which use dc voltage or dc current to externally drive the transition.

  12. Origin of variation in switching voltages in threshold-switching phenomena of VO2 thin films

    NASA Astrophysics Data System (ADS)

    Lee, S. B.; Kim, K.; Oh, J. S.; Kahng, B.; Lee, J. S.

    2013-02-01

    We investigated the origin of the variation in switching voltages in threshold-switching of VO2 thin films. When a triangular-waveform voltage signal was applied, the current changed abruptly at two switching voltages, i.e., VON (insulator-to-metal) and VOFF (metal-to-insulator). VON and VOFF were measured by changing the period of the voltage signal, the temperature of the environment, and the load resistance. We observed that either VON or VOFF varied significantly and had different dependences with respect to the external parameters. Based on the mechanism of the metal-insulator transition induced by Joule heating, numerical simulations were performed, which quantitatively reproduced all of the experimental results. From the simulation analysis, the variation in the switching voltages for threshold-switching was determined to be thermal in origin.

  13. The bistability phenomenon in single and coupled oscillators based on VO2 switches

    NASA Astrophysics Data System (ADS)

    Belyaev, M. A.; Putrolaynen, V. V.; Velichko, A. A.

    2017-01-01

    New operation regimes of single and coupled oscillators in circuits based on planar VO2 switches have been studied. The phenomenon of bistability is discovered, which consists in controlled switching of self-sustained oscillations by external pulses, which is a promising basis for the creation of oscillatory memory cells and implementation of pulse coupling regimes in artificial neural networks (ANNs). The duration of switch-on and switch-off pulses is no less that 20 μs and 30 ms, respectively. It is established that the region of threshold voltages for bistable switching in coupled oscillators is much wider than in a single oscillator and the hysteresis width in the former case can reach 2 V. A regime of initiation of switching packets has been observed that models the ANN packet activity.

  14. Local coexistence of VO2 phases revealed by deep data analysis

    PubMed Central

    Strelcov, Evgheni; Ievlev, Anton; Belianinov, Alex; Tselev, Alexander; Kolmakov, Andrei; Kalinin, Sergei V.

    2016-01-01

    We report a synergistic approach of micro-Raman spectroscopic mapping and deep data analysis to study the distribution of crystallographic phases and ferroelastic domains in a defected Al-doped VO2 microcrystal. Bayesian linear unmixing revealed an uneven distribution of the T phase, which is stabilized by the surface defects and uneven local doping that went undetectable by other classical analysis techniques such as PCA and SIMPLISMA. This work demonstrates the impact of information recovery via statistical analysis and full mapping in spectroscopic studies of vanadium dioxide systems, which is commonly substituted by averaging or single point-probing approaches, both of which suffer from information misinterpretation due to low resolving power. PMID:27384473

  15. Fast hydrogen sorption from MgH2-VO2(B) composite materials

    NASA Astrophysics Data System (ADS)

    Milošević, Sanja; Kurko, Sandra; Pasquini, Luca; Matović, Ljiljana; Vujasin, Radojka; Novaković, Nikola; Novaković, Jasmina Grbović

    2016-03-01

    The hydrogen sorption kinetics of MgH2‒VO2(B) composites synthesised by mechanical milling have been studied. The microstructural properties of composites were characterized by means of X-ray diffraction (XRD), Raman spectroscopy, Scanning electron microscopy (SEM), Particle size analysis (PSD), while sorption behaviour was followed by differential scanning calorimetry (DSC) and Sievert measurements. Results have shown that although desorption temperature reduction is moderate; there is a substantial improvement in hydrogen sorption kinetics. The complete desorption of pure MgH2 at elevated temperature takes place in more than 30 min while the composite fully desorbs in less than 2 min even at lower temperatures. It has been shown that the metastable γ-MgH2 phase and the point defects have a decisive role in desorption process only in the first sorption cycle, while the second and the subsequent sorption cycles are affected by microstructural and morphological characteristics of the composite.

  16. Local coexistence of VO2 phases revealed by deep data analysis

    DOE PAGES

    Strelcov, Evgheni; Ievlev, Anton; Tselev, Alexander; ...

    2016-07-07

    We report a synergistic approach of micro-Raman spectroscopic mapping and deep data analysis to study the distribution of crystallographic phases and ferroelastic domains in a defected Al-doped VO2 microcrystal. Bayesian linear unmixing revealed an uneven distribution of the T phase, which is stabilized by the surface defects and uneven local doping that went undetectable by other classical analysis techniques such as PCA and SIMPLISMA. This work demonstrates the impact of information recovery via statistical analysis and full mapping in spectroscopic studies of vanadium dioxide systems, which is commonly substituted by averaging or single point-probing approaches, both of which suffer frommore » information misinterpretation due to low resolving power.« less

  17. Bending in VO2-coated microcantilevers suitable for thermally activated actuators

    NASA Astrophysics Data System (ADS)

    Rúa, Armando; Fernández, Félix E.; Sepúlveda, Nelson

    2010-04-01

    The curvature of VO2-coated silicon microcantilevers was measured as the temperature was cycled through the coating's insulator-to-metal transition (IMT), which drives the curvature change mainly through the strain generated during this reversible structural transformation. The films were grown by pulsed laser deposition (PLD) on heated substrates. Cantilever tip displacement was measured for a 130 μm long cantilever as the temperature was changed by recording the deflection of a laser beam, and the curvature change and estimated film stress were calculated from this data. A change in curvature of over 2000 m-1 was observed through the narrow temperature range of the IMT, with a maximum rate of ˜485 m-1 per degree. Estimated recoverable stress was ˜1 GPa through the transition region. These results suggest applications in actuator devices with reduced dimensions, including submicron lengths, multifunctional capabilities, and possibly with higher operational frequencies than other thermally actuated devices.

  18. Variation of optical properties of gel-derived VO2 thin films with temperature

    NASA Astrophysics Data System (ADS)

    Hou, Lisong; Lu, Song W.; Gan, Fuxi

    1991-11-01

    VO2 thin films are prepared on three kinds of substrates by the sol-gel dip-coating method followed by heat treatment under vacuum conditions. The IR and UV-visible spectra of the films are studied during heating and cooling between room temperature and 100 degree(s)C. The experimental results show that the films exhibit thermally-induced reversible phase transition and, as a result, the maximum changes in transmittance and reflectivity are 58% and 25%, respectively, in the case of vacuum heat treatment at 400 degree(s)C and silica glass substrates. The refractive index n decreases and the extinction coefficient k increases when heating these films from room temperature to 100 degree(s)C, and vice versa. The reasons why the optical constants and IR absorption spectra change so remarkably are discussed.

  19. V(O2) max is unaffected by altering the temporal pattern of stimulation frequency in rat hindlimb in situ.

    PubMed

    Hepple, Russell T; Krause, Daniel J; Hagen, Jason L; Jackson, Cory C

    2003-08-01

    It might be anticipated that fatiguing contractions would impair the aerobic metabolic response in skeletal muscle if significant fatigue developed before full activation of aerobic metabolism. On the basis of this premise, we examined two groups of rats to test the hypothesis that a gradual increase in stimulation frequency would yield a higher maximal O2 uptake (Vo2 max) than beginning immediately with an intense stimulation frequency because of a slower progression of fatigue under the former conditions. In one group of animals, the distal hindlimb muscles were electrically stimulated at a frequency of 60 tetani/min for 4 min (F60; n = 6 rats); in the other group, the muscles were incrementally stimulated for 1 min at each of 7.5, 15, 30, and 60 tetani/min and for 2 min at 90 tetani/min (FInc; n = 5 rats). Despite large differences in rate of fatigue [time to 60% of initial force was 47 +/- 3 (SE) vs. 188 +/- 1 s in F60 and FInc, respectively] and the time at which Vo2 max occurred (120 +/- 15 vs. 264 +/- 6 s), Vo2 max was not different (419 +/- 24 vs. 381 +/- 44 micromol x min-1. 100 g-1). Furthermore, time x tension integral at Vo2 max (3.82 +/- 0.41 vs. 4.07 +/- 0.31 N. s) and peak lactate efflux (910 +/- 45 vs. 800 +/- 98 micromol x min-1. 100 g-1) were not different between groups. Thus our results show that the more rapid progression of fatigue in F60 did not compromise the aerobic metabolic response in electrically stimulated rat hindlimb muscles. However, in both groups, O2 uptake and lactate efflux declined after Vo2 max was attained in similar proportion to a further fall in force, suggesting that ongoing fatigue with intense contractions reduced ATP demand below that requiring maximal aerobic and glycolytic metabolic responses once Vo2 max was reached.

  20. VO2 Kinetics in All-out Arm Stroke, Leg Kick and Whole Stroke Front Crawl 100-m Swimming.

    PubMed

    Rodríguez, F A; Lätt, E; Jürimäe, J; Maestu, J; Purge, P; Rämson, R; Haljaste, K; Keskinen, K L; Jürimäe, T

    2016-03-01

    The VO2 response to extreme-intensity exercise and its relationship with sports performance are largely unexplored. This study investigated the pulmonary VO2 kinetics during all-out 100-m front crawl whole stroke swimming (S), arm stroke (A) and leg kick (L). 26 male and 10 female competitive swimmers performed an all-out S trial followed by A and L of equal duration in random order. Breath-by-breath VO2 was measured using a snorkel attached to a portable gas analyzer. Mean (±SD) primary component parameters and peak blood lactate (Lapeak) during S, A, and L were, respectively: time delay (s), 14.2 ± 4.7, 14.3 ± 4.5, 15.6 ± 5.1; amplitude (ml·kg(-1)·min(-1)), 46.8 ± 6.1, 37.3 ± 6.9, 41.0 ± 4.7; time constant (τ, s): 9.2 ± 3.2, 12.4 ± 4.7, 10.1 ± 3.2; Lapeak (mmol·l(-1)), 6.8 ± 3.1, 6.3 ± 2.5, 7.9 ± 2.8. During A and L respectively, 80% and 87% of amplitude in S was reached, whereas A+L were 68% greater than in S. 100-m performance was associated to shorter cardiodynamic phase and greater VO2 amplitude and Lapeak (accounting up to 61% of performance variance), but not to τ. We conclude that (i) VO2 gain was proportional to exercise intensity and muscle mass involved, (ii) kicking is metabolically less efficient, and (iii) the main limiting factor of peak VO2 appears to be O2 delivery and not muscle extraction.

  1. 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.

  2. ARTICLES: Nonlinear interaction of infrared waves on a VO2 surface at a semiconductor-metal phase transition

    NASA Astrophysics Data System (ADS)

    Berger, N. K.; Zhukov, E. A.; Novokhatskiĭ, V. V.

    1984-04-01

    The use of a semiconductor-metal phase transition for wavefront reversal of laser radiation was proposed. An investigation was made of nonlinear reflection of CO2 laser radiation at a phase transition in VO2. A three-wave interaction on a VO2 surface was achieved using low-power cw and pulsed CO2 lasers. In the first case, the intensity reflection coefficient was 0.5% for a reference wave intensity of 0.9 W/cm2 and in the second case, it was 42% for a threshold reference wave energy density of 0.6-0.8 mJ/cm2.

  3. A thermally tunable terahertz bandpass filter with insulator-metal phase transition of VO2 thin film

    NASA Astrophysics Data System (ADS)

    Li, Wei; Chang, Sheng-jiang; Wang, Xiang-hui; Lin, Lie; Bai, Jin-jun

    2014-05-01

    A terahertz bandpass filter with the sandwich structure consisting of thermally tunable vanadium dioxide (VO2) thin film, silica substrate and subwavelength rectangular Cu hole arrays is designed and theoretically analyzed. The results show that the transmittance of the filter can be actively tuned by controlling the temperature of VO2, the narrow band terahertz (THz) waves with the transmittance from 85.2% to 10.5% can be well selected at the frequency of 1.25 THz when the temperature changes from 50 °C to 80 °C, and the maximum modulation depth of this terahertz bandpass filter can achieve 74.7%.

  4. Analysis of performance in orienteering with treadmill tests and physiological field tests using a differential global positioning system.

    PubMed

    Larsson, Peter; Burlin, Lennart; Jakobsson, Erkki; Henriksson-Larsén, Karin

    2002-07-01

    The aim of this study was to determine the physiological responses to orienteering by examining the interrelationships between the information provided by a differential global positioning system (dGPS) about an orienteer's route, speed and orienteering mistakes, portable metabolic gas analyser data during orienteering and data from incremental treadmill tests. Ten male orienteers completed a treadmill threshold test and a field test; the latter was performed on a 4.3 km course on mixed terrain with nine checkpoints. The anaerobic threshold, threshold of decompensated metabolic acidosis, respiratory exchange ratio, onset of blood lactate accumulation and peak oxygen uptake (VO2peak) were determined from the treadmill test. Time to complete the course, total distance covered, mean speed, distance and timing of orienteering mistakes, mean oxygen uptake, mean relative heart rate, mean respiratory exchange ratio and mean running economy were computed from the dGPS data and metabolic gas analyser data. Correlation analyses showed a relationship between a high anaerobic threshold and few orienteering mistakes (r = - 0.64, P < 0.05). A high threshold of decompensated metabolic acidosis and VO2peak were related to a fast overall time (r = -0.70 to -0.72, P < 0.05) and high running speed (r = 0.64 to 0.79, P < 0.05 and P < 0.01, respectively), and were thus the best predictors of performance.

  5. Moderate acute exercise (70% VO2 peak) induces TGF-β, α-amylase and IgA in saliva during recovery.

    PubMed

    Rosa, L; Teixeira, Aas; Lira, Fs; Tufik, S; Mello, Mt; Santos, Rvt

    2014-03-01

    Strenuous exercise promotes changes in salivary IgA and can be associated with a high incidence of upper respiratory tract Infections. However, moderate exercise enhances immune function. The effect of exercise on salivary IgA has been well studied, but its effect on other immunological parameters is poorly studied. Thus, this study determined the effect of moderate acute exercise on immunological salivary parameters, such as the levels of cytokines (TGF-β and IL-5), IgA, α-amylase and total protein, over 24 h. Ten male adult subjects exercised for 60 min at an intensity of 70% VO2 peak. Saliva samples were collected before ('basal') and 0, 12 and 24 h after an exercise session. The total salivary protein was lower after 12 and 24 h than immediately after exercise, whereas α-amylase increased at 12 and 24 h after exercise compared with basal levels. The IgA concentration was increased at 24 h after exercise relative to immediately after exercise, and there was no difference in the IL-5 while TGF-β concentration increased in recovery. In conclusion, 70% VO2 peak exercise does not induce changes immediately after exercise, but after 24 h, it produces an increase in salivary TGF-β without changing IL-5.

  6. Combined Thermochromic And Plasmonic: Optical Responses In Novel Nanocomposite Au-VO2 Films Prepared By RF Inverted Cylindrical Magnetron Sputtering

    NASA Astrophysics Data System (ADS)

    Kana, J. B. Kana; Ndjaka, J. M.; Manyala, N.; Nemraoui, O.; Beye, A. C.; Maaza, M.

    2008-09-01

    We prepared gold/Vanadium dioxide nanocomposites thin films by the rf reactive inverted cylindrical magnetron sputtering (ICMS) for the first time and report their enhanced surface plasmon resonance (SPR) tunable shift reversibility. ICMS has been attracting much attention for its ability for uniform coating of three-dimensional objects and high-rate deposition of dielectric materials. To investigate the optical properties of gold nanoparticles embedded in an active matrix (VO2) composite film was synthesized on corning glass substrates for several substrate temperatures ranging from 400 °C to 600 °C. The X-ray diffraction results demonstrated that the Au and VO2 were well crystallized. The optical transmission properties were measured from 300nm to 1100nm and the absorption peak due to the surface plasmon resonance (SPR) of Au nanoparticles were observed. Under external temperature stimuli, the tunable reversibility of the SPR shift was observed when the nanocomposites temperature varies from 20 °C to 100 °C. The enhancement of this shift of SPR was observed as the substrate temperature increases and it was found that the shift of SPR increased rapidly with increasing substrate temperature but then remained constant at ˜57 nm for substrate temperature higher than 500 °C.

  7. Velocity at V(.)O(2 max) and peak treadmill velocity are not influenced within or across the phases of the menstrual cycle.

    PubMed

    Burrows, M; Bird, S R

    2005-03-01

    Velocity at VO(2 max) (vV(.)O(2 max)) and peak treadmill velocity (PTV) are variables highly predictive of endurance performance. However, how these variables are affected by the menstrual cycle is unknown. The aim of this study was to assess the effect of the menstrual cycle on vV(.)O(2 max) and PTV. Ten, female runners were studied across three menstrual cycles. Training, menstrual history and mood states were assessed for 2 months, with daily salivary samples taken to detect menstrual phases. During the third menstrual cycle, participants completed a maximal test to determine V(.)O(2 max), vV(.)O(2 max) and PTV in the early follicular phase, late follicular phase, early luteal phase, late luteal phase and menses. Progesterone increased at the onset of the luteal phase [mean (SEM); 490 (73.6) pmol l(-1)] compared to the follicular phase [344.6 (59.7) pmol l(-1)). No significant differences in the psychological mood states between the phases of the menstrual cycle were found (P>0.05). No significant differences in vV(.)O(2 max) (P=0.611), or PTV (P=0.472) were found between the phases of the menstrual cycle. Thus, vV(.)O(2 max) and PTV are not affected by the monthly menstrual cycle in female endurance runners.

  8. The effects of weekly exercise time on VO2max and resting metabolic rate in normal adults

    PubMed Central

    Gim, Mi-Na; Choi, Jung-Hyun

    2016-01-01

    [Purpose] The present study examined the effect of individual weekly exercise time on resting metabolic rate and VO2max (maximal oxygen uptake), which are important components of individual health indexes. [Subjects and Methods] Thirty healthy adults participated in this study. Questionnaires were used to divide the participants into groups based on average weekly walking. Resting metabolic rate was measured using a respiratory gas analyzer. Graded exercise tests were conducted using a treadmill, and the modified Bruce protocol was used as an exercise test method. [Results] VO2max, anaerobic threshold, and resting metabolic rate were significantly different among the groups. [Conclusion] Average weekly exercise time affected VO2max, resting metabolic rate, and anaerobic threshold, all of which are indicators of individual physical ability and health. These values increased as the individual amount of exercise increased. In addition, VO2max, resting metabolic rate, and anaerobic threshold were found to be closely correlated. These findings were consistent with the results of similar previous studies. PMID:27190483

  9. Hydrogen-incorporation stabilization of metallic VO2(R) phase to room temperature, displaying promising low-temperature thermoelectric effect.

    PubMed

    Wu, Changzheng; Feng, Feng; Feng, Jun; Dai, Jun; Peng, Lele; Zhao, Jiyin; Yang, Jinlong; Si, Cheng; Wu, Ziyu; Xie, Yi

    2011-09-07

    Regulation of electron-electron correlation has been found to be a new effective way to selectively control carrier concentration, which is a crucial step toward improving thermoelectric properties. The pure electronic behavior successfully stabilized the nonambient metallic VO(2)(R) to room temperature, giving excellent thermoelectric performance among the simple oxides with wider working temperature ranges.

  10. The effects of weekly exercise time on VO2max and resting metabolic rate in normal adults.

    PubMed

    Gim, Mi-Na; Choi, Jung-Hyun

    2016-04-01

    [Purpose] The present study examined the effect of individual weekly exercise time on resting metabolic rate and VO2max (maximal oxygen uptake), which are important components of individual health indexes. [Subjects and Methods] Thirty healthy adults participated in this study. Questionnaires were used to divide the participants into groups based on average weekly walking. Resting metabolic rate was measured using a respiratory gas analyzer. Graded exercise tests were conducted using a treadmill, and the modified Bruce protocol was used as an exercise test method. [Results] VO2max, anaerobic threshold, and resting metabolic rate were significantly different among the groups. [Conclusion] Average weekly exercise time affected VO2max, resting metabolic rate, and anaerobic threshold, all of which are indicators of individual physical ability and health. These values increased as the individual amount of exercise increased. In addition, VO2max, resting metabolic rate, and anaerobic threshold were found to be closely correlated. These findings were consistent with the results of similar previous studies.

  11. Graded Exercise Testing Protocols for the Determination of VO2max: Historical Perspectives, Progress, and Future Considerations.

    PubMed

    Beltz, Nicholas M; Gibson, Ann L; Janot, Jeffrey M; Kravitz, Len; Mermier, Christine M; Dalleck, Lance C

    2016-01-01

    Graded exercise testing (GXT) is the most widely used assessment to examine the dynamic relationship between exercise and integrated physiological systems. The information from GXT can be applied across the spectrum of sport performance, occupational safety screening, research, and clinical diagnostics. The suitability of GXT to determine a valid maximal oxygen consumption (VO2max) has been under investigation for decades. Although a set of recommended criteria exists to verify attainment of VO2max, the methods that originally established these criteria have been scrutinized. Many studies do not apply identical criteria or fail to consider individual variability in physiological responses. As an alternative to using traditional criteria, recent research efforts have been directed toward using a supramaximal verification protocol performed after a GXT to confirm attainment of VO2max. Furthermore, the emergence of self-paced protocols has provided a simple, yet reliable approach to designing and administering GXT. In order to develop a standardized GXT protocol, additional research should further examine the utility of self-paced protocols used in conjunction with verification protocols to elicit and confirm attainment of VO2max.

  12. Graded Exercise Testing Protocols for the Determination of VO2max: Historical Perspectives, Progress, and Future Considerations

    PubMed Central

    Gibson, Ann L.; Janot, Jeffrey M.; Kravitz, Len; Dalleck, Lance C.

    2016-01-01

    Graded exercise testing (GXT) is the most widely used assessment to examine the dynamic relationship between exercise and integrated physiological systems. The information from GXT can be applied across the spectrum of sport performance, occupational safety screening, research, and clinical diagnostics. The suitability of GXT to determine a valid maximal oxygen consumption (VO2max) has been under investigation for decades. Although a set of recommended criteria exists to verify attainment of VO2max, the methods that originally established these criteria have been scrutinized. Many studies do not apply identical criteria or fail to consider individual variability in physiological responses. As an alternative to using traditional criteria, recent research efforts have been directed toward using a supramaximal verification protocol performed after a GXT to confirm attainment of VO2max. Furthermore, the emergence of self-paced protocols has provided a simple, yet reliable approach to designing and administering GXT. In order to develop a standardized GXT protocol, additional research should further examine the utility of self-paced protocols used in conjunction with verification protocols to elicit and confirm attainment of VO2max. PMID:28116349

  13. Voltage- and current-activated metal-insulator transition in VO2-based electrical switches: a lifetime operation analysis

    NASA Astrophysics Data System (ADS)

    Crunteanu, Aurelian; Givernaud, Julien; Leroy, Jonathan; Mardivirin, David; Champeaux, Corinne; Orlianges, Jean-Christophe; Catherinot, Alain; Blondy, Pierre

    2010-12-01

    Vanadium dioxide is an intensively studied material that undergoes a temperature-induced metal-insulator phase transition accompanied by a large change in electrical resistivity. Electrical switches based on this material show promising properties in terms of speed and broadband operation. The exploration of the failure behavior and reliability of such devices is very important in view of their integration in practical electronic circuits. We performed systematic lifetime investigations of two-terminal switches based on the electrical activation of the metal-insulator transition in VO2 thin films. The devices were integrated in coplanar microwave waveguides (CPWs) in series configuration. We detected the evolution of a 10 GHz microwave signal transmitted through the CPW, modulated by the activation of the VO2 switches in both voltage- and current-controlled modes. We demonstrated enhanced lifetime operation of current-controlled VO2-based switching (more than 260 million cycles without failure) compared with the voltage-activated mode (breakdown at around 16 million activation cycles). The evolution of the electrical self-oscillations of a VO2-based switch induced in the current-operated mode is a subtle indicator of the material properties modification and can be used to monitor its behavior under various external stresses in sensor applications.

  14. Validity of VO(2 max) in predicting blood volume: implications for the effect of fitness on aging

    NASA Technical Reports Server (NTRS)

    Convertino, V. A.; Ludwig, D. A.

    2000-01-01

    A multiple regression model was constructed to investigate the premise that blood volume (BV) could be predicted using several anthropometric variables, age, and maximal oxygen uptake (VO(2 max)). To test this hypothesis, age, calculated body surface area (height/weight composite), percent body fat (hydrostatic weight), and VO(2 max) were regressed on to BV using data obtained from 66 normal healthy men. Results from the evaluation of the full model indicated that the most parsimonious result was obtained when age and VO(2 max) were regressed on BV expressed per kilogram body weight. The full model accounted for 52% of the total variance in BV per kilogram body weight. Both age and VO(2 max) were related to BV in the positive direction. Percent body fat contributed <1% to the explained variance in BV when expressed in absolute BV (ml) or as BV per kilogram body weight. When the model was cross validated on 41 new subjects and BV per kilogram body weight was reexpressed as raw BV, the results indicated that the statistical model would be stable under cross validation (e.g., predictive applications) with an accuracy of +/- 1,200 ml at 95% confidence. Our results support the hypothesis that BV is an increasing function of aerobic fitness and to a lesser extent the age of the subject. The results may have implication as to a mechanism by which aerobic fitness and activity may be protective against reduced BV associated with aging.

  15. Reactive pulsed-DC sputtered Nb-doped VO2 coatings for smart thermochromic windows with active solar control.

    PubMed

    Batista, C; Carneiro, J; Ribeiro, R M; Teixeira, V

    2011-10-01

    Thermochromic VO2 thin films have successfully been grown on SiO2-coated float glass by reactive pulsed-DC magnetron sputtering. Different Nb doping amounts were introduced in the VO2 solid solution during the film growing which resulted in films with distinct semiconducting-metal phase transition temperatures. Pure VO2 showed improved thermochromic behavior as compared with VO2 films prepared by conventional DC sputtering. The transition temperatures were linearly decreased from 59 down to 34 degrees C with the increase in Nb content. However, the luminous transmittance and the infrared modulation efficiency were markedly affected. The surface morphology of the films was examined by scanning electron microscopy (SEM) and showed a tendency for grain sized reduction due to Nb addition. Moreover, the films were found to be very dense with no columnar microstructure. Structural analyses carried out by X-ray diffractometry (XRD) revealed that Nb introduces significant amount of defects in the crystal lattice which clearly degrade the optical properties.

  16. Crystalline, highly oriented MOF thin film: the fabrication and application.

    PubMed

    Fu, Zhihua; Xu, Gang

    2016-10-24

    The thin film of metal-organic frameworks (MOFs) is a rapidly developing research area which has tremendous potential applications in many fields. One of the major challenges in this area is to fabricate MOF thin film with good crystallinity, high orientation and well-controlled thickness. In order to address this challenge, different appealing approaches have been studied intensively. Among various oriented MOF films, many efforts have also been devoted to developing novel properties and broad applications, such as in gas separator, thermoelectric, storage medium and photovoltaics. As a result, there has been a large demand for fundamental studies that can provide guidance and experimental data for further applications. In this account, we intend to present an overview of current synthetic methods for fabricating oriented crystalline MOF thin film and bring some updated applications. We give our perspective on the background, preparation and applications that led to the developments in this area and discuss the opportunities and challenges of using crystalline, highly oriented MOF thin film.

  17. Repeated Sprint Performance in Male and Female College Athletes Matched for VO2max Relative to Fat Free Mass.

    PubMed

    Mageean, Amanda L; Alexander, Ryan P; Mier, Constance M

    The purpose of this study was to examine gender differences in repeated sprint exercise (RSE) performance among male and female athletes matched for VO2max relative to FFM (VO2max FFM). Thirty nine male and female college athletes performed a graded exercise test for VO2max and hydrostatic weighing to determine FFM. From the results, 11 pairs of males and females matched for VO2max FFM (mean ± SD; 58.3 ± 4.3 and 58.9 ± 4.6 ml·kg FFM(-1)·min(-1); men and women, respectively) were identified. On a separate day, matched participants performed a RSE protocol that consisted of five 6-sec cycle sprints with 30-sec recovery periods, followed by 5-min active recovery and a 30-sec all-out sprint. Repeated 6-sec sprint performance did not differ between men and women; both maintained power output (PO) until sprint 4. POFFM (W·kg(-1) FFM) did not differ between men and women during the five sprints. During the 30-sec sprint, men achieved a lower peak POFFM than women (11.7 ± 1.5 vs 13.2 ± 1.2); however, the decline in POFFM over 30 sec was greater in women. VO2 (ml·kg FFM(-1)·min(-1)) was lower in men during recovery (24.4 ± 3.8 vs 28.7 ± 5.7) and at the beginning (29.2 ± 4.0 vs 34.7 ± 4.9) and end (49.4 ± 5.0 vs 52.3 ± 4.0). of the 30-sec sprint. These data indicate that men and women with similar aerobic capacities do not respond differently to short repeated sprints but may differ in their ability to recover and perform sprints of longer duration.

  18. Why is VO2 max after altitude acclimatization still reduced despite normalization of arterial O2 content?

    PubMed

    Calbet, J A L; Boushel, R; Radegran, G; Sondergaard, H; Wagner, P D; Saltin, B

    2003-02-01

    Acute hypoxia (AH) reduces maximal O2 consumption (VO2 max), but after acclimatization, and despite increases in both hemoglobin concentration and arterial O2 saturation that can normalize arterial O2 concentration ([O2]), VO2 max remains low. To determine why, seven lowlanders were studied at VO2 max (cycle ergometry) at sea level (SL), after 9-10 wk at 5,260 m [chronic hypoxia (CH)], and 6 mo later at SL in AH (FiO2 = 0.105) equivalent to 5,260 m. Pulmonary and leg indexes of O2 transport were measured in each condition. Both cardiac output and leg blood flow were reduced by approximately 15% in both AH and CH (P < 0.05). At maximal exercise, arterial [O2] in AH was 31% lower than at SL (P < 0.05), whereas in CH it was the same as at SL due to both polycythemia and hyperventilation. O2 extraction by the legs, however, remained at SL values in both AH and CH. Although at both SL and in AH, 76% of the cardiac output perfused the legs, in CH the legs received only 67%. Pulmonary VO2 max (4.1 +/- 0.3 l/min at SL) fell to 2.2 +/- 0.1 l/min in AH (P < 0.05) and was only 2.4 +/- 0.2 l/min in CH (P < 0.05). These data suggest that the failure to recover VO2 max after acclimatization despite normalization of arterial [O2] is explained by two circulatory effects of altitude: 1) failure of cardiac output to normalize and 2) preferential redistribution of cardiac output to nonexercising tissues. Oxygen transport from blood to muscle mitochondria, on the other hand, appears unaffected by CH.

  19. High Frequency Scattering from Arbitrarily Oriented Dielectric Disks

    NASA Technical Reports Server (NTRS)

    Levine, D. M.; Meneghini, R.; Lang, R. H.; Seker, S. S.

    1982-01-01

    Calculations have been made of electromagnetic wave scattering from dielectric disks of arbitrary shape and orientation in the high frequency (physical optics) regime. The solution is obtained by approximating the fields inside the disk with the fields induced inside an identically oriented slab (i.e. infinite parallel planes) with the same thickness and dielectric properties. The fields inside the disk excite conduction and polarization currents which are used to calculate the scattered fields by integrating the radiation from these sources over the volume of the disk. This computation has been executed for observers in the far field of the disk in the case of disks with arbitrary orientation and for arbitrary polarization of the incident radiation. The results have been expressed in the form of a dyadic scattering amplitude for the disk. The results apply to disks whose diameter is large compared to wavelength and whose thickness is small compared to diameter, but the thickness need not be small compared to wavelength. Examples of the dependence of the scattering amplitude on frequency, dielectric properties of the disk and disk orientation are presented for disks of circular cross section.

  20. F-doped VO2 nanoparticles for thermochromic energy-saving foils with modified color and enhanced solar-heat shielding ability.

    PubMed

    Dai, Lei; Chen, Shi; Liu, Jianjun; Gao, Yanfeng; Zhou, Jiadong; Chen, Zhang; Cao, Chuanxiang; Luo, Hongjie; Kanehira, Minoru

    2013-07-28

    F-doped VO2 (M1) nanoparticles were prepared via one-pot hydrothermal synthesis. The F-doping can minimise the size of the VO2 (M1) nanoparticles, induce a homogeneous size distribution and effectively decrease the phase transition temperature to 35 °C at 2.93% F in VO2. VO2 smart glass foils obtained by casting these nanoparticles exhibit excellent thermochromism in the near-infrared region, which suggests that these foils can be used for energy-efficient glass. Compared to a pure VO2 foil, the 2.93% F-doped VO2 foil exhibits an increased solar-heat shielding ability (35.1%) and a modified comfortable colour, while still retaining an excellent solar modulation ability (10.7%) and an appropriate visible transmittance (48.7%). The F-doped VO2 foils are the first to simultaneously meet the requirements of a reduced phase transition temperature, diluted colour and excellent thermochromic properties, and these properties make the further improved F-doped VO2 foils suitable for commercial applications in energy efficient glass.

  1. Excess VO2 during ramp exercise is positively correlated to intercostal muscles deoxyhemoglobin levels above the gas exchange threshold in young trained cyclists.

    PubMed

    Oueslati, Ferid; Girard, Olivier; Tabka, Zouhair; Ahmaidi, Said

    2016-07-01

    We assessed respiratory muscles oxygenation responses during a ramp exercise to exhaustion and further explored their relationship with the non-linear increase of VO2 (VO2 excess) observed above the gas-exchange threshold. Ten male cyclists completed a ramp exercise to exhaustion on an electromagnetically braked cycle-ergometer with a rate of increment of 30Wmin(-1) with continuous monitoring of expired gases (breath-by-breath) and oxygenation status of intercostal muscles. Maximal inspiratory and expiratory pressure measurements were taken at rest and at exhaustion. The VO2 excess represents the difference between VO2max observed and VO2max expected using linear equation between the VO2 and the intensity before gas-exchange threshold. The deoxyhemoglobin remained unchanged until 60% of maximal aerobic power (MAP) and thereafter increased significantly by 37±18% and 40±22% at 80% and 100% of MAP, respectively. Additionally, the amplitude of deoxyhemoglobin increase between 60 and 100% of MAP positively correlated with the VO2 excess (r=0.69, p<0.05). Compared to exercise start, the oxygen tissue saturation index decreased from 80% of MAP (-4.8±3.2%, p<0.05) onwards. At exhaustion, maximal inspiratory and expiratory pressures declined by 7.8±16% and 12.6±10% (both p<0.05), respectively. In summary, our results suggest a significant contribution of respiratory muscles to the VO2 excess phenomenon.

  2. Microcracks in nuclear graphite and highly oriented pyrolytic graphite (HOPG)

    NASA Astrophysics Data System (ADS)

    Wen, Keyun; Marrow, James; Marsden, Barry

    2008-10-01

    Microcracks with varied length and width are observed in nuclear grade graphite and highly oriented pyrolytic graphite (HOPG) by transmission electron microscopy. In situ observations show that these cracks tend to close up on heating the sample. The crystal dimensional change from in situ electron-irradiation also causes the closure of the cracks. Although some of the cracks may be identifiable as accommodation porosity (i.e. Mrozowski cracks), others appear to have already formed prior to carbonization and graphitization.

  3. Bedrest-induced peak VO2 reduction associated with age, gender, and aerobic capacity

    NASA Technical Reports Server (NTRS)

    Convertino, V. A.; Goldwater, D. J.; Sandler, H.

    1986-01-01

    A study measuring the peak oxygen uptake (V02), heart rate (HR), and exercise tolerance time of 15 men of 55 + or - 2 yr and 17 women of 55 + or - 1 yr after 10 days of continuous bed rest (BR) is presented. The experimental conditions and procedures are described. Following BR a decrease in peak VO2 of 8.4 percent in men and 6.8 percent in women, a reduction in exercise tolerance time by 8.1 percent in men and 7.3 percent in women, and an increse in HR of 4.4 percent and 1.3 percent for men and women, respectively, are observed. These data are compared with data from Convertino et al. (1977) for men 21 + or - 1 yr and women 28 + or - 2yr. It is concluded that BR-induced aerobic deconditioning is independent of age and sex, since the relative decrease in peak V02 in the older and younger subjects and men and women are similar.

  4. Metallic bubbles nucleation and growth in VO2 nanofilms: insights from TDDFT+DMFT

    NASA Astrophysics Data System (ADS)

    Turkowski, Volodymyr; Galicia-Hernandez, Jose Mario; Hernandez-Cocoletzi, Gregorio; Rahman, Talat S.

    We apply a time-dependent density-functional theory + dynamical mean-field theory (TDDFT+DMFT) approach to model the response of insulating nanofilms of VO2 to perturbations by ultrafast laser pulses. We focus on the spatially-resolved metallization of the systems, and especially on the process of nucleation and time-dependence of the size of the ''surface'' and ''bulk'' metallic domains (bubbles) as a function of film width. In particular, we find that the initial universal (parameter-independent) growth of the domains (radius R ~t 1 / 2), changes by the bubbles shrinking (R ~t-a , a ~ 1) as a result of Coulomb scattering effects, and eventually by post-femto-second phonon-involved relaxation of the systems to the equilibrium accompanied by infrared photoemission. The time-dependent conductivity obtained from the above results is in a good agreement with available experimental data. Work supported in part by DOE Grant No. DOE-DE-FG02-07ER46354 and by CONACYT Scholarship # 23210 (J.M.G.H.).

  5. Carbohydrate beverage ingestion and neutrophil degranulation responses following cycling to fatigue at 75% VO2 max.

    PubMed

    Bishop, N C; Blannin, A K; Walsh, N P; Gleeson, M

    2001-04-01

    Carbohydrate (CHO) beverage ingestion appears to influence neutrophil functional responses to prolonged exercise of a fixed duration. The aim of this randomised study was to examine the effect of CHO (5% w/v) beverage ingestion on lipopolysaccharide (LPS)-stimulated neutrophil degranulation responses in nine recreationally active males who cycled at 75% VO2 max until fatigue. On two separate occasions, subjects ingested either placebo (PLA) or CHO beverages before and at 15 min intervals during the exercise. Subjects exercised for 31% longer on the CHO trial compared with the PLA trial (P < 0.05). At fatigue plasma glucose concentration was significantly lower on the PLA trial compared with the CHO trial (P < 0.05). Plasma cortisol concentrations had increased similarly on both trials at this time. A marked neutrophilia was evident at fatigue and throughout the 4 h recovery period, the magnitude of which was similar on both trials. At fatigue LPS-stimulated elastase release per neutrophil had fallen similarly on both trials compared with pre-exercise values (47% and 50% on the PLA and CHO trials, respectively). In conclusion, our results suggest that CHO beverage ingestion has negligible influence on the hormonal, circulating neutrophil and LPS-stimulated neutrophil degranulation responses when exercise is performed to fatigue.

  6. Body composition and Vo2max of exceptional weight-trained athletes.

    PubMed

    Fahey, T D; Akka, L; Rolph, R

    1975-10-01

    The maximal oxygen uptake and body composition of 30 exceptional athletes who have trained extensively with weights was measured. The sample included 3 world record holders, 8 other world class athletes, and 19 national class competitors. The sports represented were shot-putting, discus throwing, body building, power lifting, wrestling, and olympic lifting. Vo2max as determined on a bicycle ergometer by the open-circuit method was 4.6 +/- 0.7 1-min-1 (mean +/- SD) (48.8 +/- 7 ml-kg-1., 56.4 +/- 8.6 ml-(kg LBW)-1). The mean maximal heart rate was 185.3 +/- 11.6 beats-min-1. The subjects attained a work rate of 1,728.2 +/- 223 kpm-min-1 on a continuous progressive bicycle ergometer test and had mean maximal ventilations of 152.5 +/- 27.7 1-min-1 BTPS. Body composition was determined by densitometry. Body weight averaged 96.0 +/- 14.9 kg, with mean percent fat of 13.8 +/- 4.5. The results of this study indicate that exceptional weight-trained athletes are within the normal college-age population range in body fat and of somewhat higher physical working capacity.

  7. A Reference Equation for Normal Standards for VO2 max: Analysis from the Fitness Registry and the Importance of Exercise National Database (FRIEND Registry).

    PubMed

    Myers, Jonathan; Kaminsky, Leonard A; Lima, Ricardo; Chistle, Jeffrey; Ashley, Euan; Arena, Ross

    2017-04-01

    Existing normal standards for maximal oxygen uptake (VO2 max) are problematic because they tend to be population specific, lack normal distribution and portability, and are poorly represented by women. The objective of the current study was to apply the Fitness Registry and the Importance of Exercise: A National Data Base (FRIEND) Registry to improve upon previous regression formulas for normal standards for VO2 max using treadmill testing. Maximal treadmill tests were performed in 7783 healthy men and women (20-79years; maximal RER >1.0) from the FRIEND registry and a separate validation cohort of 1287 subjects. A regression equation for VO2 max was derived from the FRIEND registry and compared to the validation cohort and two commonly used equations (Wasserman and European). Age, gender, and body weight were the only significant predictors of VO2 max (multiple R=0.79, R(2)=0.62, p<0.001). The equation for predicting VO2 max was: [Formula: see text] Marked differences were observed in percentage predicted VO2 max achieved between commonly used reference equations, particularly among women, overweight and obese subjects. In the validation sample, the FRIEND equation closely paralleled measured VO2 max, with the validation group yielding a percent predicted VO2 max of 100.4% based on the FRIEND equation. An equation for age-predicted VO2 max derived from the FRIEND registry provided a lower average error between measured and predicted VO2 max than traditional equations, and thus may provide a more suitable normal standard relative to traditional equations.

  8. Highly oriented carbon fiber–polymer composites via additive manufacturing

    SciTech Connect

    Tekinalp, Halil L.; Kunc, Vlastimil; Velez-Garcia, Gregorio M.; Duty, Chad E.; Love, Lonnie J.; Naskar, Amit K.; Blue, Craig A.; Ozcan, Soydan

    2014-10-16

    Additive manufacturing, diverging from traditional manufacturing techniques, such as casting and machining materials, can handle complex shapes with great design flexibility without the typical waste. Although this technique has been mainly used for rapid prototyping, interest is growing in using this method to directly manufacture actual parts of complex shape. To use 3D-printing additive manufacturing in wide spread applications, the technique and the feedstock materials require improvements to meet the mechanical requirements of load-bearing components. Thus, we investigated the short fiber (0.2 mm to 0.4 mm) reinforced acrylonitrile-butadiene-styrene composites as a feedstock for 3D-printing in terms of their processibility, microstructure and mechanical performance; and also provided comparison with traditional compression molded composites. The tensile strength and modulus of 3D-printed samples increased ~115% and ~700%, respectively. 3D-printer yielded samples with very high fiber orientation in printing direction (up to 91.5 %), whereas, compression molding process yielded samples with significantly less fiber orientation. Microstructure-mechanical property relationships revealed that although the relatively high porosity is observed in the 3D-printed composites as compared to those produced by the conventional compression molding technique, they both exhibited comparable tensile strength and modulus. Furthermore, this phenomena is explained based on the changes in fiber orientation, dispersion and void formation.

  9. Highly oriented carbon fiber–polymer composites via additive manufacturing

    DOE PAGES

    Tekinalp, Halil L.; Kunc, Vlastimil; Velez-Garcia, Gregorio M.; ...

    2014-10-16

    Additive manufacturing, diverging from traditional manufacturing techniques, such as casting and machining materials, can handle complex shapes with great design flexibility without the typical waste. Although this technique has been mainly used for rapid prototyping, interest is growing in using this method to directly manufacture actual parts of complex shape. To use 3D-printing additive manufacturing in wide spread applications, the technique and the feedstock materials require improvements to meet the mechanical requirements of load-bearing components. Thus, we investigated the short fiber (0.2 mm to 0.4 mm) reinforced acrylonitrile-butadiene-styrene composites as a feedstock for 3D-printing in terms of their processibility, microstructuremore » and mechanical performance; and also provided comparison with traditional compression molded composites. The tensile strength and modulus of 3D-printed samples increased ~115% and ~700%, respectively. 3D-printer yielded samples with very high fiber orientation in printing direction (up to 91.5 %), whereas, compression molding process yielded samples with significantly less fiber orientation. Microstructure-mechanical property relationships revealed that although the relatively high porosity is observed in the 3D-printed composites as compared to those produced by the conventional compression molding technique, they both exhibited comparable tensile strength and modulus. Furthermore, this phenomena is explained based on the changes in fiber orientation, dispersion and void formation.« less

  10. Effects of acute inhalation of albuterol on submaximal and maximal VO2 and blood lactate.

    PubMed

    Fleck, S J; Lucia, A; Storms, W W; Wallach, J M; Vint, P F; Zimmerman, S D

    1993-07-01

    The acute effects of inhaled albuterol, a selective beta-2 adrenergic agonist, on measures of endurance cycling performance and pulmonary function were assessed in 21 competitive road cyclists. A 5 step methacholine challenge revealed all cyclists to be non-asthmatic. Albuterol (A) total dose 360 micrograms or a saline placebo (P) was administered by inhaler, in 4 metered doses of 90 micrograms each, 15 minutes before cycle ergometry exercise. Heart rate, whole blood lactate, perceived exertion and VO2 were determined at the submaximal workloads of 150, 200, 225, 250, 275, 300 watts and at max. Pulmonary function tests determining forced vital capacity, forced expiratory volume during the first second of expiration, forced mid-expiratory flow and maximal voluntary ventilation were performed prior to and 10 minutes after inhalation; and 5, 10 and 15 minutes after termination of the exercise protocol. Heart rate was significantly greater during the A compared to the P treatment at 200 (150.8 +/- 2.5 vs 146.7 +/- 2.8 beats per minute), 225 (159.7 +/- 2.4 vs 154.6 +/- 2.7 beats per minute) and 250 watts (166.9 +/- 2.4 vs 164.4 +/- 2.6 beats per minute). Whole blood lactate was significantly greater during the A compared to the P treatment at 275 watts (4.7 +/- 0.3 vs 4.2 +/- 0.4 mmol.l-1). No other significant differences were found between the 2 treatments at any time point. These data indicate that the acute effect of albuterol inhalation at twice the recommended dosage has no positive effect on endurance performance measures or pulmonary function in athletes who are not asthmatic.

  11. Investigations of the spin Hamiltonian parameters for VO2+ ions in KZnClSO4 ṡ 3H2O single crystals

    NASA Astrophysics Data System (ADS)

    Tu, Chao; Xie, Linhua; Du, Xiangrong

    2017-01-01

    The spin Hamiltonian parameters of VO2+ in KZnClSO4ṡ3H2O single crystals are calculated from the third-order perturbation formulas based on the double spin-orbit coupling model for the tetragonal transition-ion clusters in crystals with the ground state |dxy>. In the paper, both the crystal-field (CF) mechanism and the charge-transfer (CT) mechanism (double-mechanism model) are considered to calculate the spin Hamiltonian parameters. The calculated results are in agreement with the experimental data. Moreover, the calculated results show that the CT mechanism cannot be omitted for a high-valence state V4+ ions in KZnClSO4ṡ3H2O single crystals. The tetragonal field parameters are also acquired in the paper.

  12. Dynamically tracking the joule heating effect on the voltage induced metal-insulator transition in VO2 crystal film

    NASA Astrophysics Data System (ADS)

    Liao, G. M.; Chen, S.; Fan, L. L.; Chen, Y. L.; Wang, X. Q.; Ren, H.; Zhang, Z. M.; Zou, C. W.

    2016-04-01

    Insulator to metal phase transitions driven by external electric field are one of the hottest topics in correlated oxide study. While this electric triggered phenomena always mixes the electric field switching effect and joule thermal effect together, which are difficult to clarify the intrinsic mechanism. In this paper, we investigate the dynamical process of voltage-triggered metal-insulator transition (MIT) in a VO2 crystal film and observe the temperature dependence of the threshold voltages and switching delay times, which can be explained quite well based on a straightforward joule thermal model. By conducting the voltage controlled infrared transmittance measurement, the delayed infrared transmission change is also observed, further confirming the homogeneous switching process for a large-size film. All of these results show strong evidences that joule thermal effect plays a dominated role in electric-field-induced switching of VO2 crystal.

  13. Temperature dependence of the first-order metal-insulator transition in VO2 and programmable critical temperature sensor

    NASA Astrophysics Data System (ADS)

    Kim, Bong-Jun; Lee, Yong Wook; Chae, Byung-Gyu; Yun, Sun Jin; Oh, Soo-Young; Kim, Hyun-Tak; Lim, Yong-Sik

    2007-01-01

    For VO2-based two-terminal devices, the first-order metal-insulator transition (MIT, jump) is controlled by an applied voltage and temperature, and an intermediate monoclinic metal phase between the MIT and the structural phase transition (SPT) is observed. The conductivity of this phase linearly increases with increasing temperature up to TSPT≈68°C and becomes maximum at TSPT. Optical microscopic observation reveals the absence of a local current path in the metal phase. The current uniformly flows throughout the surface of the VO2 film when the MIT occurs. This device can be used as a programmable critical temperature sensor where the applied voltage is controlled by a program.

  14. 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.

  15. Fast-start strategy increases the time spent above 95 %VO2max during severe-intensity intermittent running exercise.

    PubMed

    de Aguiar, Rafael Alves; Turnes, Tiago; de Oliveira Cruz, Rogério Santos; Caputo, Fabrizio

    2013-04-01

    This study aimed to use the intermittent critical velocity (ICV) model to individualize intermittent exercise and analyze whether a fast-start strategy could increase the time spent at or above 95 %VO(2max) (t95VO(2max)) during intermittent exercise. After an incremental test, seven active male subjects performed three intermittent exercise tests until exhaustion at 100, 110, and 120 % of the maximal aerobic velocity to determine ICV. On three occasions, the subjects performed an intermittent exercise test until exhaustion at 105 % (IE105) and 125 % (IE125) of ICV, and at a speed that was initially set at 125 %ICV but which then decreased to 105 %ICV (IE125-105). The intermittent exercise consisted of repeated 30-s runs alternated with 15-s passive rest intervals. There was no difference between the predicted and actual Tlim for IE125 (300 ± 72 s and 284 ± 76 s) and IE105 (1,438 ± 423 s and 1,439 ± 518 s), but for IE125-105 the predicted Tlim underestimated the actual Tlim (888 ± 211 s and 1,051 ± 153 s, respectively). The t95VO(2max) during IE125-105 (289 ± 150 s) was significantly higher than IE125 (113 ± 40 s) and IE105 (106 ± 71 s), but no significant differences were found between IE125 and IE105. It can be concluded that predicting Tlim from the ICV model was affected by the fast-start protocol during intermittent exercise. Furthermore, fast-start protocol was able to increase the time spent at or above 95 %VO2max during intermittent exercise above ICV despite a longer total exercise time at IE105.

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

    DTIC Science & Technology

    2014-11-27

    Electronic and thermal effects in the insulator -metal phase transition in VO2 nano-gap junctions Arash Joushaghani,1 Junho Jeong,1 Suzanne Paradis,2...voltage waveforms, the electronically induced insulator -metal phase transition is investigated in the adiabatic heating and transient carrier injection...the complete insulator -metal phase transition is limited by thermal redistribution times to hundreds of nanoseconds. The dynamics of the insulator

  17. Coherent control of optical absorption and the energy transfer pathway of an infrared quantum dot hybridized with a VO2 nanoparticle

    NASA Astrophysics Data System (ADS)

    Hatef, Ali; Zamani, Naser; Johnston, William

    2017-04-01

    We systematically investigate the optical response of a semiconductor quantum dot (QD) hybridized with a vanadium dioxide nanoparticle (VO2NP) in the infrared (IR) region. The VO2NP features a semiconductor to metal phase change characteristic below and above a critical temperature that leads to an abrupt change in the particle’s optical properties. This feature means that the QD-VO2NP hybrid system can support the coherent coupling of exciton-polaritons and exciton-plasmon polaritons in the semiconductor and metal phases of the VO2NP, respectively. In our calculations, the VO2NP phase transition is modelled with a filling fraction (f), representing the fraction of the VO2NP in the metallic phase. The phase transition is driven by the hybrid system’s interaction with a continuous wave (CW) IR laser field. In this paper, we show how control over the filling fraction results in the enhancement or suppression of the QD’s linear absorption. These variations in the QD absorption is due to dramatic changes in the effective local field experienced by the QD and the non-radiative energy transfer from the QD to the VO2NP. The presented results have the potential to be applied to the design of thermal sensors at the nanoscale.

  18. The visible transmittance and solar modulation ability of VO2 flexible foils simultaneously improved by Ti doping: an optimization and first principle study.

    PubMed

    Chen, Shi; Dai, Lei; Liu, Jianjun; Gao, Yanfeng; Liu, Xinling; Chen, Zhang; Zhou, Jiadong; Cao, Chuanxiang; Han, Penggang; Luo, Hongjie; Kanahira, Minoru

    2013-10-28

    The Mott phase transition compound vanadium dioxide (VO2) shows promise as a thermochromic smart material for the improvement of energy efficiency and comfort in a number of applications. However, the use of VO2 has been restricted by its low visible transmittance (Tvis) and limited solar modulation ability (ΔTsol). Many efforts have been made to improve both of these limitations, but progress towards the optimization of one aspect has always come at the expense of the other. This paper reports that Ti doping results in the improvement of both the Tvis and ΔTsol of VO2-nanoparticle-derived flexible foils to the best levels yet reported. Compared with an undoped VO2 foil, a 15% increase (from 46.1% to 53%) in Tvis and a 28% increase (from 13.4% to 17.2%) in ΔTsol are achieved at a Ti doping level of 1.1%, representing the best performance reported for similar foils or films prepared using various methods. Only a defined doping level of less than 3% is beneficial for simultaneous improvement in Tvis and ΔTsol. First principle calculations suggest that an increase in the intrinsic band gap of VO2 (M) and the reduced electron density at Fermi level of VO2 (R) cooperate to result in the improvement of ΔTsol and that an enhancement in the optical band gap of VO2 (M) leads to the increase of Tvis.

  19. Coherent control of optical absorption and the energy transfer pathway of an infrared quantum dot hybridized with a VO2 nanoparticle.

    PubMed

    Hatef, Ali; Zamani, Naser; Johnston, William

    2017-04-20

    We systematically investigate the optical response of a semiconductor quantum dot (QD) hybridized with a vanadium dioxide nanoparticle (VO2NP) in the infrared (IR) region. The VO2NP features a semiconductor to metal phase change characteristic below and above a critical temperature that leads to an abrupt change in the particle's optical properties. This feature means that the QD-VO2NP hybrid system can support the coherent coupling of exciton-polaritons and exciton-plasmon polaritons in the semiconductor and metal phases of the VO2NP, respectively. In our calculations, the VO2NP phase transition is modelled with a filling fraction (f), representing the fraction of the VO2NP in the metallic phase. The phase transition is driven by the hybrid system's interaction with a continuous wave (CW) IR laser field. In this paper, we show how control over the filling fraction results in the enhancement or suppression of the QD's linear absorption. These variations in the QD absorption is due to dramatic changes in the effective local field experienced by the QD and the non-radiative energy transfer from the QD to the VO2NP. The presented results have the potential to be applied to the design of thermal sensors at the nanoscale.

  20. EPR and optical studies of VO2+ doped potassium succinate-succinic acid single crystal - Substitutional incorporation

    NASA Astrophysics Data System (ADS)

    Juliet sheela, K.; Radha Krishnan, S.; Shanmugam, V. M.; Subramanian, P.

    2017-03-01

    EPR and optical absorption studies of VO2+ doped potassium succinate-succinic acid (KSSA) single crystal has been examined at room temperature. EPR spectrum shows that well resolved hyperfine lines. The angular variation of the EPR spectra has shown that two different VO2+ complexes are located in different chemical environments. Among the number of sites, two sites have been followed and reported here. From the EPR analysis, spin Hamiltonian parameters g and A tensors and their directional cosines are evaluated. Both the sites experience rhombic crystal field symmetry around the impurity ion. The VO2+ ion entering the site location of potassium ion has coordination of eight oxygen atoms in a distorted dodecahedral arrangement. The Optical absorption spectrum studied at room temperature shows bands corresponding to C4v symmetry. The crystal field parameter and tetragonal field parameters are calculated. From the Optical and EPR data various molecular orbital coefficients are evaluated and the nature of bonding in the crystal is discussed.

  1. Carbon Quantum Dot Surface-Engineered VO2 Interwoven Nanowires: A Flexible Cathode Material for Lithium and Sodium Ion Batteries.

    PubMed

    Balogun, Muhammad-Sadeeq; Luo, Yang; Lyu, Feiyi; Wang, Fuxin; Yang, Hao; Li, Haibo; Liang, Chaolun; Huang, Miao; Huang, Yongchao; Tong, Yexiang

    2016-04-20

    The use of electrode materials in their powdery form requires binders and conductive additives for the fabrication of the cells, which leads to unsatisfactory energy storage performance. Recently, a new strategy to design flexible, binder-, and additive-free three-dimensional electrodes with nanoscale surface engineering has been exploited in boosting the storage performance of electrode materials. In this paper, we design a new type of free-standing carbon quantum dot coated VO2 interwoven nanowires through a simple fabrication process and demonstrate its potential to be used as cathode material for lithium and sodium ion batteries. The versatile carbon quantum dots that are vastly flexible for surface engineering serve the function of protecting the nanowire surface and play an important role in the diffusion of electrons. Also, the three-dimensional carbon cloth coated with VO2 interwoven nanowires assisted in the diffusion of ions through the inner and the outer surface. With this unique architecture, the carbon quantum dot nanosurface engineered VO2 electrode exhibited capacities of 420 and 328 mAh g(-1) at current density rate of 0.3 C for lithium and sodium storage, respectively. This work serves as a milestone for the potential replacement of lithium ion batteries and next generation postbatteries.

  2. Mesoscopic structural phase progression in photo-excited VO2 revealed by time-resolved x-ray diffraction microscopy

    NASA Astrophysics Data System (ADS)

    Zhu, Yi; Cai, Zhonghou; Chen, Pice; Zhang, Qingteng; Highland, Matthew J.; Jung, Il Woong; Walko, Donald A.; Dufresne, Eric M.; Jeong, Jaewoo; Samant, Mahesh G.; Parkin, Stuart S. P.; Freeland, John W.; Evans, Paul G.; Wen, Haidan

    2016-02-01

    Dynamical phase separation during a solid-solid phase transition poses a challenge for understanding the fundamental processes in correlated materials. Critical information underlying a phase transition, such as localized phase competition, is difficult to reveal by measurements that are spatially averaged over many phase separated regions. The ability to simultaneously track the spatial and temporal evolution of such systems is essential to understanding mesoscopic processes during a phase transition. Using state-of-the-art time-resolved hard x-ray diffraction microscopy, we directly visualize the structural phase progression in a VO2 film upon photoexcitation. Following a homogenous in-plane optical excitation, the phase transformation is initiated at discrete sites and completed by the growth of one lattice structure into the other, instead of a simultaneous isotropic lattice symmetry change. The time-dependent x-ray diffraction spatial maps show that the in-plane phase progression in laser-superheated VO2 is via a displacive lattice transformation as a result of relaxation from an excited monoclinic phase into a rutile phase. The speed of the phase front progression is quantitatively measured, and is faster than the process driven by in-plane thermal diffusion but slower than the sound speed in VO2. The direct visualization of localized structural changes in the time domain opens a new avenue to study mesoscopic processes in driven systems.

  3. Mesoscopic structural phase progression in photo-excited VO2 revealed by time-resolved x-ray diffraction microscopy

    PubMed Central

    Zhu, Yi; Cai, Zhonghou; Chen, Pice; Zhang, Qingteng; Highland, Matthew J.; Jung, Il Woong; Walko, Donald A.; Dufresne, Eric M.; Jeong, Jaewoo; Samant, Mahesh G.; Parkin, Stuart S. P.; Freeland, John W.; Evans, Paul G.; Wen, Haidan

    2016-01-01

    Dynamical phase separation during a solid-solid phase transition poses a challenge for understanding the fundamental processes in correlated materials. Critical information underlying a phase transition, such as localized phase competition, is difficult to reveal by measurements that are spatially averaged over many phase separated regions. The ability to simultaneously track the spatial and temporal evolution of such systems is essential to understanding mesoscopic processes during a phase transition. Using state-of-the-art time-resolved hard x-ray diffraction microscopy, we directly visualize the structural phase progression in a VO2 film upon photoexcitation. Following a homogenous in-plane optical excitation, the phase transformation is initiated at discrete sites and completed by the growth of one lattice structure into the other, instead of a simultaneous isotropic lattice symmetry change. The time-dependent x-ray diffraction spatial maps show that the in-plane phase progression in laser-superheated VO2 is via a displacive lattice transformation as a result of relaxation from an excited monoclinic phase into a rutile phase. The speed of the phase front progression is quantitatively measured, and is faster than the process driven by in-plane thermal diffusion but slower than the sound speed in VO2. The direct visualization of localized structural changes in the time domain opens a new avenue to study mesoscopic processes in driven systems. PMID:26915398

  4. 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 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.

  5. Mesoscopic structural phase progression in photo-excited VO2 revealed by time-resolved x-ray diffraction microscopy

    DOE PAGES

    Zhu, Yi; Cai, Zhonghou; Chen, Pice; ...

    2016-02-26

    Dynamical phase separation during a solid-solid phase transition poses a challenge for understanding the fundamental processes in correlated materials. Critical information underlying a phase transition, such as localized phase competition, is difficult to reveal by measurements that are spatially averaged over many phase seperated regions. The ability to simultanousely track the spatial and temporal evolution of such systems is essential to understanding mesoscopic processes during a phase transition. Using state-of- the-art time-resolved hard x-ray diffraction microscopy, we directly visualize the structural phase progression in a VO2 film upon photoexcitation. Following a homogenous in-plane optical excitation, the phase transformation is initiatedmore » at discrete sites and completed by the growth of one lattice structure into the other, instead of a simultaneous isotropic lattice symmetry change. The time-dependent x-ray diffraction spatial maps show that the in-plane phase progression in laser-superheated VO2 is via a displacive lattice transformation as a result of relaxation from an excited monoclinic phase into a rutile phase. The speed of the phase front progression is quantitatively measured, which is faster than the process driven by in-plane thermal diffusion but slower than the sound speed in VO2. Lastly, the direct visualization of localized structural changes in the time domain opens a new avenue to study mesoscopic processes in driven systems.« less

  6. Mesoscopic structural phase progression in photo-excited VO2 revealed by time-resolved x-ray diffraction microscopy.

    PubMed

    Zhu, Yi; Cai, Zhonghou; Chen, Pice; Zhang, Qingteng; Highland, Matthew J; Jung, Il Woong; Walko, Donald A; Dufresne, Eric M; Jeong, Jaewoo; Samant, Mahesh G; Parkin, Stuart S P; Freeland, John W; Evans, Paul G; Wen, Haidan

    2016-02-26

    Dynamical phase separation during a solid-solid phase transition poses a challenge for understanding the fundamental processes in correlated materials. Critical information underlying a phase transition, such as localized phase competition, is difficult to reveal by measurements that are spatially averaged over many phase separated regions. The ability to simultaneously track the spatial and temporal evolution of such systems is essential to understanding mesoscopic processes during a phase transition. Using state-of-the-art time-resolved hard x-ray diffraction microscopy, we directly visualize the structural phase progression in a VO2 film upon photoexcitation. Following a homogenous in-plane optical excitation, the phase transformation is initiated at discrete sites and completed by the growth of one lattice structure into the other, instead of a simultaneous isotropic lattice symmetry change. The time-dependent x-ray diffraction spatial maps show that the in-plane phase progression in laser-superheated VO2 is via a displacive lattice transformation as a result of relaxation from an excited monoclinic phase into a rutile phase. The speed of the phase front progression is quantitatively measured, and is faster than the process driven by in-plane thermal diffusion but slower than the sound speed in VO2. The direct visualization of localized structural changes in the time domain opens a new avenue to study mesoscopic processes in driven systems.

  7. Computational Study of Orientation-dependent Molecular High Harmonic Spectra

    NASA Astrophysics Data System (ADS)

    Dutoi, Anthony; Seideman, Tamar

    2007-03-01

    Recently, there has been much interest in high harmonic generation (HHG) by aligned molecules [Phys. Rev. A 67 023819, Nature 432 867, Nature 435 470]. During HHG, an electron is ionized and driven back to the cation by a strong, low-frequency field, and radiation is emitted at harmonics of this driving pulse. Because this process is sensitive to the orientation of a molecule, rotational dynamics can be probed on very short time scales. We are working to predict the time-dependent HHG spectra for aligned rotational wavepackets. In conjunction with experiment, these simulations should be valuable for studying the loss of rotational coherence in media such as dense gases. Within the presented formalism, Born-Oppenheimer rotational dynamics are handled exactly, while HHG at any given orientation is estimated by numerical time integration of a one-electron Schr"odinger equation. Propagation outside of the integration grid can be handled using an analytical Volkov propagator at the expense of ignoring the cation field at this distance.

  8. 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.

  9. Oxidative stress-mediated selective antimicrobial ability of nano-VO2 against Gram-positive bacteria for environmental and biomedical applications.

    PubMed

    Li, Jinhua; Zhou, Huaijuan; Wang, Jiaxing; Wang, Donghui; Shen, Ruxiang; Zhang, Xianlong; Jin, Ping; Liu, Xuanyong

    2016-06-09

    Vanadium dioxide (VO2) is a unique thermochromic material as a result of its semiconductor-metal transition, holding great promise for energy-saving intelligent windows. Herein, pure nano-VO2 from discrete nanoparticles to continuous films were successfully deposited on quartz glass by controlling the sputtering parameters. It was demonstrated that, for Gram-positive S. aureus and S. epidermidis, the nano-VO2 could effectively disrupt bacteria morphology and membrane integrity, and eventually cause death. By contrast, the nano-VO2 did not exhibit significant toxicity towards Gram-negative E. coli and P. aeruginosa. To our knowledge, this is the first report on a selective antimicrobial effect of nano-VO2 materials on Gram-positive bacteria. Based on the experimental results, a plausible mechanism was proposed for the antimicrobial selectivity, which might originate from the different sensitivity of Gram-positive and Gram-negative bacteria to intracellular reactive oxygen species (ROS) level. Elevated intracellular ROS levels exceed the threshold that bacteria can self-regulate to maintain cellular redox homeostasis and thus cause oxidative stress, which can be alleviated by the intervention of glutathione (GSH) antioxidant. In addition, nano-VO2 did not produce significant cytotoxicity (hemolysis) against human erythrocytes within 12 h. Meanwhile, potential cytotoxicity against HIBEpiC revealed a time- and dose-dependent behavior that might be controlled and balanced by careful design. The findings in the present work may contribute to understanding the antimicrobial behavior of nano-VO2, and to expanding the new applications of VO2-based nanomaterials in environmental and biomedical fields.

  10. Oxidative stress-mediated selective antimicrobial ability of nano-VO2 against Gram-positive bacteria for environmental and biomedical applications

    NASA Astrophysics Data System (ADS)

    Li, Jinhua; Zhou, Huaijuan; Wang, Jiaxing; Wang, Donghui; Shen, Ruxiang; Zhang, Xianlong; Jin, Ping; Liu, Xuanyong

    2016-06-01

    Vanadium dioxide (VO2) is a unique thermochromic material as a result of its semiconductor-metal transition, holding great promise for energy-saving intelligent windows. Herein, pure nano-VO2 from discrete nanoparticles to continuous films were successfully deposited on quartz glass by controlling the sputtering parameters. It was demonstrated that, for Gram-positive S. aureus and S. epidermidis, the nano-VO2 could effectively disrupt bacteria morphology and membrane integrity, and eventually cause death. By contrast, the nano-VO2 did not exhibit significant toxicity towards Gram-negative E. coli and P. aeruginosa. To our knowledge, this is the first report on a selective antimicrobial effect of nano-VO2 materials on Gram-positive bacteria. Based on the experimental results, a plausible mechanism was proposed for the antimicrobial selectivity, which might originate from the different sensitivity of Gram-positive and Gram-negative bacteria to intracellular reactive oxygen species (ROS) level. Elevated intracellular ROS levels exceed the threshold that bacteria can self-regulate to maintain cellular redox homeostasis and thus cause oxidative stress, which can be alleviated by the intervention of glutathione (GSH) antioxidant. In addition, nano-VO2 did not produce significant cytotoxicity (hemolysis) against human erythrocytes within 12 h. Meanwhile, potential cytotoxicity against HIBEpiC revealed a time- and dose-dependent behavior that might be controlled and balanced by careful design. The findings in the present work may contribute to understanding the antimicrobial behavior of nano-VO2, and to expanding the new applications of VO2-based nanomaterials in environmental and biomedical fields.

  11. 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.

  12. Thermochromic properties of W-doped VO2 thin films deposited by aqueous sol-gel method for adaptive infrared stealth application

    NASA Astrophysics Data System (ADS)

    Liu, Dongqing; Cheng, Haifeng; Xing, Xin; Zhang, Chaoyang; Zheng, Wenwei

    2016-07-01

    The W doped VO2 thin films with various W contents were successfully deposited by aqueous sol-gel method followed by a post annealing process. The derived thin films were characterized by X-ray diffraction, Raman spectra, scanning electron microscopy and atomic force microscopy. Besides, the resistance-temperature relationship and infrared emissivity in the waveband 7.5-14 μm were analyzed, and the effects of W doping on the thermochromic properties of VO2 thin films were studied. The results show that W atoms enter the crystal lattice of VO2 and the transition temperature decreases gradually with increasing doping amount of W. The emissivity of VO2-W-4% thin films has dropped to 0.4 when its real temperature is above 30 °C. The thermal infrared images were also examined under different temperature by thermal imager. The results indicate that the temperature under which W doped VO2 thin films begin to have lower emissivity decreases gradually with increasing doping amount of W. W doped VO2 thin films can control its infrared radiation intensity actively at a lower temperature level of 30 °C, which has great application prospects in the adaptive infrared stealth technology.

  13. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2013-04-01

    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.

  15. 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

  16. Plasma volume expansion does not increase maximal cardiac output or VO2 max in lowlanders acclimatized to altitude.

    PubMed

    Calbet, José A L; Rådegran, Göran; Boushel, Robert; Søndergaard, Hans; Saltin, Bengt; Wagner, Peter D

    2004-09-01

    With altitude acclimatization, blood hemoglobin concentration increases while plasma volume (PV) and maximal cardiac output (Qmax) decrease. This investigation aimed to determine whether reduction of Qmax at altitude is due to low circulating blood volume (BV). Eight Danish lowlanders (3 females, 5 males: age 24.0 +/- 0.6 yr; mean +/- SE) performed submaximal and maximal exercise on a cycle ergometer after 9 wk at 5,260 m altitude (Mt. Chacaltaya, Bolivia). This was done first with BV resulting from acclimatization (BV = 5.40 +/- 0.39 liters) and again 2-4 days later, 1 h after PV expansion with 1 liter of 6% dextran 70 (BV = 6.32 +/- 0.34 liters). PV expansion had no effect on Qmax, maximal O2 consumption (VO2), and exercise capacity. Despite maximal systemic O2 transport being reduced 19% due to hemodilution after PV expansion, whole body VO2 was maintained by greater systemic O2 extraction (P < 0.05). Leg blood flow was elevated (P < 0.05) in hypervolemic conditions, which compensated for hemodilution resulting in similar leg O2 delivery and leg VO2 during exercise regardless of PV. Pulmonary ventilation, gas exchange, and acid-base balance were essentially unaffected by PV expansion. Sea level Qmax and exercise capacity were restored with hyperoxia at altitude independently of BV. Low BV is not a primary cause for reduction of Qmax at altitude when acclimatized. Furthermore, hemodilution caused by PV expansion at altitude is compensated for by increased systemic O2 extraction with similar peak muscular O2 delivery, such that maximal exercise capacity is unaffected.

  17. Electron paramagnetic resonance study of 14N and 19F superhyperfine interaction in VO 2+ doped propylenediammonium hexafluorozirconate

    NASA Astrophysics Data System (ADS)

    Lakshmi^Kasturi, T.; Krishnan, V. G.

    1998-05-01

    Electron paramagnetic resonance spectra have been recorded at X-band frequencies at room temperature on VO 2+ molecular ion in propylenediammonium hexafluorozirconate, [H 3N(CH 2) 3NH 3]ZrF 6, single crystals. The superhyperfine structure caused by 14N and 19F has been clearly observed in the spectra. The two sets of spectra observed are related to each other by the symmetry operations of the host crystals and represent vanadyl ion at two magnetically distinguishable interstitial sites in the unit cell.

  18. The effect of an active arm action on heart rate and predicted VO(2max) during the Chester step test.

    PubMed

    Elliott, Dave; Abt, Grant; Barry, Tim

    2008-04-01

    This study examined whether the predictive outcomes of the Chester step test (CST) would be influenced by arm dynamics. Participants completed the CST on two separate occasions, once using active arms and once using passive arms. Results revealed that when compared to the passive arm protocol, the use of active arms led to a mean increase in heart rate of approximately 7 beats per minute across all of the incremental stages. However, this increase had little impact upon predicted VO(2max). Consequently, these results indicate that when performing the CST, participants are able to adopt an arm action that is compatible with personal preference.

  19. Picosecond soft X-ray absorption measurement of the photo-inducedinsulator-to-metal transition in VO2.

    SciTech Connect

    Cavalleri, Andrea; Chong, Henry H.W.; Fourmaux, Sylvain; Glover,Thornton E.; Heimann, Phil A.; Kieffer, Jean Claude; Mun, B. Simon; Padmore, Howard A.; Schoenlein, Robert W.

    2004-02-01

    We directly measure the photoinduced insulator-to-metal transition in VO2 using time-resolved near-edge x-ray absorption. Picosecond pulses of synchrotron radiation are used to detect the redshift in the vanadium L3edge at 516 eV, which is associated with the transient collapse of the low-temperature band gap. We identify a two-component temporal response, corresponding to an ultrafast transformation over a 50 nm surface layer, followed by 40 m/s thermal growth of the metallic phase into the bulk.

  20. Silver Vanadium Phosphorous Oxide, Ag(2)VO(2)PO(4): Chimie Douce Preparation and Resulting Lithium Cell Electrochemistry.

    PubMed

    Kim, Young Jin; Marschilok, Amy C; Takeuchi, Kenneth J; Takeuchi, Esther S

    2011-08-15

    Recently, we have shown silver vanadium phosphorous oxide (Ag(2)VO(2)PO(4), SVPO) to be a promising cathode material for lithium based batteries. Whereas the first reported preparation of SVPO employed an elevated pressure, hydrothermal approach, we report herein a novel ambient pressure synthesis method to prepare SVPO, where our chimie douce preparation is readily scalable and provides material with a smaller, more consistent particle size and higher surface area relative to SVPO prepared via the hydrothermal method. Lithium electrochemical cells utilizing SVPO cathodes made by our new process show improved power capability under constant current and pulse conditions over cells containing cathode from SVPO prepared via the hydrothermal method.

  1. Nonlinear interaction of infrared waves on a VO2 surface at a semiconductor-metal phase transition

    NASA Astrophysics Data System (ADS)

    Berger, N. K.; Zhukov, E. A.; Novokhatskii, V. V.

    1984-04-01

    Nonlinear interactions (including wavefront reversal) of light from CW or pulsed 10.6-micron CO2 lasers at the semiconductor-metal phase transition in a VO2 film are investigated experimentally. The results are presented in graphs and characterized in detail. The intensity reflection coefficients of the three-wave interactions are found to be 0.5 percent for a CW reference wave of intensity 900 mW/sq cm and 42 percent for a pulsed reference wave of threshold density 600-800 microjoule/sq cm.

  2. High pressure dielectric studies on the structural and orientational glass.

    PubMed

    Kaminska, E; Tarnacka, M; Jurkiewicz, K; Kaminski, K; Paluch, M

    2016-02-07

    High pressure dielectric studies on the H-bonded liquid D-glucose and Orientationally Disordered Crystal (ODIC) 1,6-anhydro-D-glucose (levoglucosan) were carried out. It was shown that in both compounds, the structural relaxation is weakly sensitive to compression. It is well reflected in the low pressure coefficient of the glass transition and orientational glass transition temperatures which is equal to 60 K/GPa for both D-glucose and 1,6-anhydro-D-glucose. Although it should be noted that ∂Tg(0)/∂p evaluated for the latter compound seems to be enormously high with respect to other systems forming ODIC phase. We also found that the shape of the α-loss peak stays constant for the given relaxation time independently on the thermodynamic condition. Consequently, the Time Temperature Pressure (TTP) rule is satisfied. This experimental finding seems to be quite intriguing since the TTP rule was shown to work well in the van der Waals liquids, while in the strongly associating compounds, it is very often violated. We have also demonstrated that the sensitivity of the structural relaxation process to the temperature change measured by the steepness index (mp) drops with pressure. Interestingly, this change is much more significant in the case of D-glucose with respect to levoglucosan, where the fragility changes only slightly with compression. Finally, kinetics of ODIC-crystal phase transition was studied at high compression. It is worth mentioning that in the recent paper, Tombari and Johari [J. Chem. Phys. 142, 104501 (2015)] have shown that ODIC phase in 1,6-anhydro-D-glucose is stable in the wide range of temperatures and there is no tendency to form more ordered phase at ambient pressure. On the other hand, our isochronal measurements performed at varying thermodynamic conditions indicated unquestionably that the application of pressure favors solid (ODIC)-solid (crystal) transition in 1,6-anhydro-D-glucose. This result mimics the impact of pressure on the

  3. Very short (15s-15s) interval-training around the critical velocity allows middle-aged runners to maintain VO2 max for 14 minutes.

    PubMed

    Billat, V L; Slawinksi, J; Bocquet, V; Chassaing, P; Demarle, A; Koralsztein, J P

    2001-04-01

    The purpose of this study was to compare the effectiveness of three very short interval training sessions (15-15 s of hard and easier runs) run at an average velocity equal to the critical velocity to elicit VO2 max for more than 10 minutes. We hypothesized that the interval with the smallest amplitude (defined as the ratio between the difference in velocity between the hard and the easy run divided by the average velocity and multiplied by 100) would be the most efficient to elicit VO2 max for the longer time. The subjects were middle-aged runners (52 +/- 5 yr, VO2 max of 52.1 +/- 6 mL x min(-1) x kg(-1), vVO2 max of 15.9 +/- 1.8 km x h(-1), critical velocity of 85.6 +/- 1.2% vVO2 max) who were used to long slow distance-training rather than interval training. They performed three interval-training (IT) sessions on a synthetic track (400 m) whilst breathing through the COSMED K4b2 portable metabolic analyser. These three IT sessions were: A) 90-80% vVO2 max (for hard bouts and active recovery periods, respectively), the amplitude= (90-80/85) 100=11%, B) 100-70% vVO2 max amplitude=35%, and C) 60 x 110% vVO2 max amplitude = 59%. Interval training A and B allowed the athlete to spend twice the time at VO2 max (14 min vs. 7 min) compared to interval training C. Moreover, at the end of interval training A and B the runners had a lower blood lactate than after the procedure C (9 vs. 11 mmol x l(-1)). In conclusion, short interval-training of 15s-15s at 90-80 and 100-70% of vVO2 max proved to be the most efficient in stimulating the oxygen consumption to its highest level in healthy middle-aged long-distance runners used to doing only long slow distance-training.

  4. Chemical solution deposition of the highly c-axis oriented apatite type lanthanum silicate thin films.

    PubMed

    Hori, Shigeo; Takatani, Yasuhiro; Kadoura, Hiroaki; Uyama, Takeshi; Fujita, Satoru; Tani, Toshihiko

    2015-10-28

    Highly c-axis oriented apatite-type lanthanum silicate (LSO) thin films were fabricated by a simple solution coating method. In the solution coating method, LSO thin films are obtained by crystallization of initially deposited amorphous LSO precursor thin films. The degree of orientation was influenced by the precursor morphologies and a dense LSO precursor led to a high c-axis orientation perpendicular to the substrate. The oriented LSO thin films were composed of columnar grains with a single crystal orientation over the entire film thickness. In-plane orientation was not detected, which indicates that the c-axis orientation of the LSO thin films can be attributed to self-orientation.

  5. Researches on High Accuracy Prediction Methods of Earth Orientation Parameters

    NASA Astrophysics Data System (ADS)

    Xu, X. Q.

    2015-09-01

    The Earth rotation reflects the coupling process among the solid Earth, atmosphere, oceans, mantle, and core of the Earth on multiple spatial and temporal scales. The Earth rotation can be described by the Earth's orientation parameters, which are abbreviated as EOP (mainly including two polar motion components PM_X and PM_Y, and variation in the length of day ΔLOD). The EOP is crucial in the transformation between the terrestrial and celestial reference systems, and has important applications in many areas such as the deep space exploration, satellite precise orbit determination, and astrogeodynamics. However, the EOP products obtained by the space geodetic technologies generally delay by several days to two weeks. The growing demands for modern space navigation make high-accuracy EOP prediction be a worthy topic. This thesis is composed of the following three aspects, for the purpose of improving the EOP forecast accuracy. (1) We analyze the relation between the length of the basic data series and the EOP forecast accuracy, and compare the EOP prediction accuracy for the linear autoregressive (AR) model and the nonlinear artificial neural network (ANN) method by performing the least squares (LS) extrapolations. The results show that the high precision forecast of EOP can be realized by appropriate selection of the basic data series length according to the required time span of EOP prediction: for short-term prediction, the basic data series should be shorter, while for the long-term prediction, the series should be longer. The analysis also showed that the LS+AR model is more suitable for the short-term forecasts, while the LS+ANN model shows the advantages in the medium- and long-term forecasts. (2) We develop for the first time a new method which combines the autoregressive model and Kalman filter (AR+Kalman) in short-term EOP prediction. The equations of observation and state are established using the EOP series and the autoregressive coefficients

  6. The Effect of Training Intensity on VO2max in Young Healthy Adults: A Meta-Regression and Meta-Analysis.

    PubMed

    Scribbans, Trisha D; Vecsey, Stephan; Hankinson, Paul B; Foster, William S; Gurd, Brendon J

    Exercise training at a variety of intensities increases maximal oxygen uptake (VO2max), the strongest predictor of cardiovascular and all-cause mortality. The purpose of the present study was to perform a systematic review, meta-regression and meta-analysis of available literature to determine if a dose-response relationship exists between exercise intensity and training-induced increases in VO2max in young healthy adults. Twenty-eight studies involving human participants (Mean age: 23±1 yr; Mean VO2max: 3.4±0.8 l·min(-1)) were included in the meta-regression with exercise training intensity, session dose, baseline VO2max, and total training volume used as covariates. These studies were also divided into 3 tertiles based on intensity (tertile 1: ~60-70%; 2: ~80-92.5%; 3: ~100-250%VO2max), for comparison using separate meta-analyses. The fixed and random effects meta-regression models examining training intensity, session dose, baseline VO2max and total training volume was non-significant (Q4=1.36; p=0.85; R(2)=0.05). There was no significant difference between tertiles in mean change in VO2max (tertile 1:+0.29±0.15 l/min, ES (effect size) =0.77; 2:+0.26±0.10 l/min, ES=0.68; 3:+0.35±0.17 l/min, ES=0.80), despite significant (p<0.05) reductions in session dose and total training volume as training intensity increased. These data suggest that exercise training intensity has no effect on the magnitude of training-induced increases in maximal oxygen uptake in young healthy human participants, but similar adaptations can be achieved in low training doses at higher exercise intensities than higher training doses of lower intensity (endurance training).

  7. The Effect of Training Intensity on VO2max in Young Healthy Adults: A Meta-Regression and Meta-Analysis

    PubMed Central

    SCRIBBANS, TRISHA D.; VECSEY, STEPHAN; HANKINSON, PAUL B.; FOSTER, WILLIAM S.; GURD, BRENDON J.

    2016-01-01

    Exercise training at a variety of intensities increases maximal oxygen uptake (VO2max), the strongest predictor of cardiovascular and all-cause mortality. The purpose of the present study was to perform a systematic review, meta-regression and meta-analysis of available literature to determine if a dose-response relationship exists between exercise intensity and training-induced increases in VO2max in young healthy adults. Twenty-eight studies involving human participants (Mean age: 23±1 yr; Mean VO2max: 3.4±0.8 l·min−1) were included in the meta-regression with exercise training intensity, session dose, baseline VO2max, and total training volume used as covariates. These studies were also divided into 3 tertiles based on intensity (tertile 1: ~60–70%; 2: ~80–92.5%; 3: ~100–250%VO2max), for comparison using separate meta-analyses. The fixed and random effects meta-regression models examining training intensity, session dose, baseline VO2max and total training volume was non-significant (Q4=1.36; p=0.85; R2=0.05). There was no significant difference between tertiles in mean change in VO2max (tertile 1:+0.29±0.15 l/min, ES (effect size) =0.77; 2:+0.26±0.10 l/min, ES=0.68; 3:+0.35±0.17 l/min, ES=0.80), despite significant (p<0.05) reductions in session dose and total training volume as training intensity increased. These data suggest that exercise training intensity has no effect on the magnitude of training-induced increases in maximal oxygen uptake in young healthy human participants, but similar adaptations can be achieved in low training doses at higher exercise intensities than higher training doses of lower intensity (endurance training). PMID:27182424

  8. Fabrication of highly oriented hexagonal boron nitride nanosheet/elastomer nanocomposites with high thermal conductivity.

    PubMed

    Kuang, Zhiqiao; Chen, Yulong; Lu, Yonglai; Liu, Li; Hu, Shui; Wen, Shipeng; Mao, Yingyan; Zhang, Liqun

    2015-04-08

    A homogeneous dispersion of hexagonal boron nitride nanosheets (BNNSs) in elastomers is obtained by solution compounding methods, and a high orientation of BNNSs is achieved by strong shearing. The composites show high thermal conductivities, especially when BNNS loading exceeds 17.5 vol%, indicating that the material is promising for thermal-management applications which need high thermal conductivity, low dielectric constant, and adequate softness.

  9. Asymmetrically modulating the insulator-metal transition of thermochromic VO2 films upon heating and cooling by mild surface-etching

    NASA Astrophysics Data System (ADS)

    Kang, Litao; Xie, Lingli; Chen, Zhang; Gao, Yanfeng; Liu, Xuguang; Yang, Yongzhen; Liang, Wei

    2014-08-01

    The reversible thermochromic insulator-metal transition (IMT) of VO2 is believed to start from suitable nucleating defects, but the role of specific defects during the IMT has remained elusive. In this work, we performed a simple, mild but effective acid etching treatment on pure-phase VO2 films to adjust the surface state of the VO2 particles while leaving the phase composition, crystallinity, grain size, and stoichiometry unchanged. By continuously etching VO2 particles, the poor crystallized layers on the particle surface were removed, and the particle connections became loose, resulting in significant shifts of the IMT toward higher temperatures. In stark contrast, the reversal IMT (i.e., metal-insulator transition, MIT) parameters remained relatively steady during the etching process. These experimental results correlate directly the IMT characteristics with the states (e.g., local defects, stress, and connection) of the particle surface, and further enable us to asymmetrically modulate the IMT parameters, while keeping the MIT (i.e., metal-insulator transition, the reversal of IMT) almost constant. This work illustrates the potential for particle surface engineering in thermochromic VO2 films.

  10. 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.

  11. Polymorphism of NaVO2F2: a P2₁/c superstructure with pseudosymmetry of P2₁/m in the subcell.

    PubMed

    Yu, Zi-Qun; Wang, Jing-Quan; Huang, Ya-Xi; Botis, Sanda M; Pan, Yuanming; Mi, Jin-Xiao

    2015-06-01

    The ADDSYM routine in the program PLATON [Spek (2015). Acta Cryst. C71, 9-18] has helped researchers to avoid structures of (metal-)organic compounds being reported in an unnecessarily low symmetry space group. However, determination of the correct space group may get more complicated in cases of pseudosymmetric inorganic compounds. One example is NaVO2F2, which was reported [Crosnier-Lopez et al. (1994). Eur. J. Solid State Inorg. Chem. 31, 957-965] in the acentric space group P2₁ based on properties but flagged by ADDSYM as (pseudo)centrosymmetric P2₁/m within default distance tolerances. Herein a systematic investigation reveals that NaVO2F2 exists in at least four polymorphs: P2₁, (I), P2₁/m, (II), P2₁/c, (III), and one or more low-temperature ones. The new centrosymmetric modification, (III), with the space group P2₁/c has a similar atomic packing geometry to phase (I), except for having a doubled c axis. The double-cell of phase (III) arises from atomic shifts from the glide plane c at (x, ¼, z). With increasing temperature, the number of observed reflections decreases. The odd l reflections gradually become weaker and, correspondingly, all atoms shift towards the glide plane, resulting in a gradual second-order transformation of (III) into high-temperature phase (II) (P2₁/m) at below 493 K. At least one first-order enantiotropic phase transition was observed below 139 K from both the single-crystal X-ray diffraction and the differential scanning calorimetry analyses. Periodic first-principles calculations within density functional theory show that both P2₁/c superstructure (III) and P2₁ substructure (I) are more stable than P2₁/m structure (II), and that P2₁/c superstructure (III) is more stable that P2₁ substructure (I).

  12. Synthesis, characterisation and catalytic potential of hydrazonato-vanadium(V) model complexes with [VO]3+ and [VO2]+ cores.

    PubMed

    Maurya, Mannar R; Agarwal, Shalu; Bader, Cerstin; Ebel, Martin; Rehder, Dieter

    2005-02-07

    Reaction between [VO(acac)2] and H2L (H2L are the hydrazones H2sal-nah I or H2sal-fah II; sal = salicylaldehyde, nah = nicotinic acid hydrazide and fah = 2-furoic acid hydrazide) in methanol leads to the formation of oxovanadium(IV) complexes [VOL.H2O](H2L = I: 1, H2L = II: 4). Aerial oxidation of the methanolic solutions of 1 and 4 yields the dinuclear oxo-bridged monooxovanadium(V) complexes [{VOL}2mu-O](H2L = I: 2, H2L = II: 5). These dinuclear complexes slowly convert, in excess methanol, to [VO(OMe)(MeOH)L](H(2)L = I: 9, H(2)L = II: 10), the crystal and molecular structures of which have been determined, confirming the ONO binding mode of the dianionic ligands in their enolate form. Reaction of aqueous K[VO3] with the ligands at pH ca. 7.5 results in the formation of [K(H2O)][VO2L](H2L = I: 3, H2L = II: 6). Treatment of 3 and 6 with H2O2 yields (unstable) oxoperoxovanadium(v) complexes K[VO(O2)L], the formation of which has been monitored spectrophotometrically. Acidification of methanolic solutions of 3 and 6 with HCl affords oxohydroxo complexes, while the neutral complexes [VO2(Hsal-nah)] 7 and [VO2(Hsal-fah)] 8 were isolated on treatment of aqueous solutions of 3 and 6 with HClO4. These complexes slowly transform into 9 and 10 in methanol, as confirmed by 1H, 13C and 51V NMR. The anionic complexes 3 and 6 catalyse the oxidative bromination of salicylaldehyde in water in the presence of H2O2/KBr to 5-bromosalicylaldehyde and 3,5-dibromosalicylaldehyde, a reaction similar to that exhibited by vanadate-dependent haloperoxidases. They are also catalytically active for the oxidation of benzene to phenol and phenol to catechol and p-hydroquinone.

  13. Living and training in moderate hypoxia does not improve VO2 max more than living and training in normoxia.

    PubMed

    Henderson, K K; Clancy, R L; Gonzalez, N C

    2001-06-01

    The objective of these experiments was to determine whether living and training in moderate hypoxia (MHx) confers an advantage on maximal normoxic exercise capacity compared with living and training in normoxia. Rats were acclimatized to and trained in MHx [inspired PO2 (PI(O2)) = 110 Torr] for 10 wk (HTH). Rats living in normoxia trained under normoxic conditions (NTN) at the same absolute work rate: 30 m/min on a 10 degrees incline, 1 h/day, 5 days/wk. At the end of training, rats exercised maximally in normoxia. Training increased maximal O2 consumption (VO2 max) in NTN and HTH above normoxic (NS) and hypoxic (HS) sedentary controls. However, VO2 max and O2 transport variables were not significantly different between NTN and HTH: VO2 max 86.6 +/- 1.5 vs. 86.8 +/- 1.1 ml x min(-1) x kg(-1); maximal cardiac output 456 +/- 7 vs. 443 +/- 12 ml x min(-1) x kg(-1); tissue blood O2 delivery (cardiac output x arterial O2 content) 95 +/- 2 vs. 96 +/- 2 ml x min(-1) x kg(-1); and O2 extraction ratio (arteriovenous O2 content difference/arterial O2 content) 0.91 +/- 0.01 vs. 0.90 +/- 0.01. Mean pulmonary arterial pressure (Ppa, mmHg) was significantly higher in HS vs. NS (P < 0.05) at rest (24.5 +/- 0.8 vs. 18.1 +/- 0.8) and during maximal exercise (32.0 +/- 0.9 vs. 23.8 +/- 0.6). Training in MHx significantly attenuated the degree of pulmonary hypertension, with Ppa being significantly lower at rest (19.3 +/- 0.8) and during maximal exercise (29.2 +/- 0.5) in HTH vs. HS. These data indicate that, despite maintaining equal absolute training intensity levels, acclimatization to and training in MHx does not confer significant advantages over normoxic training. On the other hand, the pulmonary hypertension associated with acclimatization to hypoxia is reduced with hypoxic exercise training.

  14. Role of microstructures on the M1-M2 phase transition in epitaxial VO2 thin films

    PubMed Central

    Ji, Yanda; Zhang, Yin; Gao, Min; Yuan, Zhen; Xia, Yudong; Jin, Changqing; Tao, Bowan; Chen, Chonglin; Jia, Quanxi; Lin, Yuan

    2014-01-01

    Vanadium dioxide (VO2) with its unique sharp resistivity change at the metal-insulator transition (MIT) has been extensively considered for the near-future terahertz/infrared devices and energy harvesting systems. Controlling the epitaxial quality and microstructures of vanadium dioxide thin films and understanding the metal-insulator transition behaviors are therefore critical to novel device development. The metal-insulator transition behaviors of the epitaxial vanadium dioxide thin films deposited on Al2O3 (0001) substrates were systematically studied by characterizing the temperature dependency of both Raman spectrum and Fourier transform infrared spectroscopy. Our findings on the correlation between the nucleation dynamics of intermediate monoclinic (M2) phase with microstructures will open a new avenue for the design and integration of advanced heterostructures with controllable multifunctionalities for sensing and imaging system applications. PMID:24798056

  15. Reversible switching between pressure-induced amorphization and thermal-driven recrystallization in VO2(B) nanosheets

    PubMed Central

    Wang, Yonggang; Zhu, Jinlong; Yang, Wenge; Wen, Ting; Pravica, Michael; Liu, Zhenxian; Hou, Mingqiang; Fei, Yingwei; Kang, Lei; Lin, Zheshuai; Jin, Changqing; Zhao, Yusheng

    2016-01-01

    Pressure-induced amorphization (PIA) and thermal-driven recrystallization have been observed in many crystalline materials. However, controllable switching between PIA and a metastable phase has not been described yet, due to the challenge to establish feasible switching methods to control the pressure and temperature precisely. Here, we demonstrate a reversible switching between PIA and thermally-driven recrystallization of VO2(B) nanosheets. Comprehensive in situ experiments are performed to establish the precise conditions of the reversible phase transformations, which are normally hindered but occur with stimuli beyond the energy barrier. Spectral evidence and theoretical calculations reveal the pressure–structure relationship and the role of flexible VOx polyhedra in the structural switching process. Anomalous resistivity evolution and the participation of spin in the reversible phase transition are observed for the first time. Our findings have significant implications for the design of phase switching devices and the exploration of hidden amorphous materials. PMID:27426219

  16. Silver Vanadium Phosphorous Oxide, Ag2VO2PO4: Chimie Douce Preparation and Resulting Lithium Cell Electrochemistry

    PubMed Central

    Kim, Young Jin; Marschilok, Amy C.; Takeuchi, Kenneth J.; Takeuchi, Esther S.

    2010-01-01

    Recently, we have shown silver vanadium phosphorous oxide (Ag2VO2PO4, SVPO) to be a promising cathode material for lithium based batteries. Whereas the first reported preparation of SVPO employed an elevated pressure, hydrothermal approach, we report herein a novel ambient pressure synthesis method to prepare SVPO, where our chimie douce preparation is readily scalable and provides material with a smaller, more consistent particle size and higher surface area relative to SVPO prepared via the hydrothermal method. Lithium electrochemical cells utilizing SVPO cathodes made by our new process show improved power capability under constant current and pulse conditions over cells containing cathode from SVPO prepared via the hydrothermal method. PMID:21765587

  17. Evidence for a structurally-driven insulator-to-metal transition in VO2 : A view from the ultrafast timescale

    NASA Astrophysics Data System (ADS)

    Cavalleri, A.; Dekorsy, Th.; Chong, H. H. W.; Kieffer, J. C.; Schoenlein, R. W.

    2004-10-01

    We apply ultrafast spectroscopy to establish a time-domain hierarchy between structural and electronic effects in a strongly correlated electron system. We discuss the case of the model system VO2 , a prototypical nonmagnetic compound that exhibits cell doubling, charge localization, and a metal-insulator transition below 340 K. We initiate the formation of the metallic phase by prompt hole photo-doping into the valence band of the low- T insulator. The insulator-to-metal transition is, however, delayed with respect to hole injection, exhibiting a bottleneck time scale, associated with the phonon connecting the two crystallographic phases. This structural bottleneck is observed despite faster depletion of the d bands and is indicative of important bandlike character for this controversial insulator.

  18. Ultra-compact electro-absorption VO2–Si modulator with TM to TE conversion

    NASA Astrophysics Data System (ADS)

    Sánchez Diana, Luis David; Cortés Juan, Frederic; Rosa Escutia, Alvaro; Sanchis Kilders, Pablo

    2017-03-01

    An ultra-compact (6 μm length) electro-absorber modulator with transverse magnetic (TM) to transverse-electric (TE) conversion is proposed. The device performance is controlled by means of the semiconductor-to-metal transition of the vanadium dioxide. For the insulating state, the device performs as a TM–TE converter with insertion losses of 0.3 dB and extinction ratio of 36 dB at a wavelength of 1.55 μm. Changing to the metallic state, the TE generated component is attenuated due to the increase of losses in the VO2 and the mode mismatch. This electro-absorber modulator shows a broadband operation with an extinction ratio higher than 10 dB and insertion losses below 0.5 dB for a range of 60 nm covering the whole C-band.

  19. Reversible switching between pressure-induced amorphization and thermal-driven recrystallization in VO2(B) nanosheets.

    PubMed

    Wang, Yonggang; Zhu, Jinlong; Yang, Wenge; Wen, Ting; Pravica, Michael; Liu, Zhenxian; Hou, Mingqiang; Fei, Yingwei; Kang, Lei; Lin, Zheshuai; Jin, Changqing; Zhao, Yusheng

    2016-07-18

    Pressure-induced amorphization (PIA) and thermal-driven recrystallization have been observed in many crystalline materials. However, controllable switching between PIA and a metastable phase has not been described yet, due to the challenge to establish feasible switching methods to control the pressure and temperature precisely. Here, we demonstrate a reversible switching between PIA and thermally-driven recrystallization of VO2(B) nanosheets. Comprehensive in situ experiments are performed to establish the precise conditions of the reversible phase transformations, which are normally hindered but occur with stimuli beyond the energy barrier. Spectral evidence and theoretical calculations reveal the pressure-structure relationship and the role of flexible VOx polyhedra in the structural switching process. Anomalous resistivity evolution and the participation of spin in the reversible phase transition are observed for the first time. Our findings have significant implications for the design of phase switching devices and the exploration of hidden amorphous materials.

  20. Reversible switching between pressure-induced amorphization and thermal-driven recrystallization in VO2(B) nanosheets

    DOE PAGES

    Wang, Yonggang; Zhu, Jinlong; Yang, Wenge; ...

    2016-07-18

    Pressure-induced amorphization (PIA) and thermal-driven recrystallization have been observed in many crystalline materials. However, controllable switching between PIA and a metastable phase has not been described yet, due to the challenge to establish feasible switching methods to control the pressure and temperature precisely. Here, we demonstrate a reversible switching between PIA and thermally-driven recrystallization of VO2(B) nanosheets. Comprehensive in situ experiments are performed to establish the precise conditions of the reversible phase transformations, which are normally hindered but occur with stimuli beyond the energy barrier. Spectral evidence and theoretical calculations reveal the pressure–structure relationship and the role of flexible VOxmore » polyhedra in the structural switching process. Anomalous resistivity evolution and the participation of spin in the reversible phase transition are observed for the first time. Lastly, our findings have significant implications for the design of phase switching devices and the exploration of hidden amorphous materials.« less

  1. Reversible switching between pressure-induced amorphization and thermal-driven recrystallization in VO2(B) nanosheets

    NASA Astrophysics Data System (ADS)

    Wang, Yonggang; Zhu, Jinlong; Yang, Wenge; Wen, Ting; Pravica, Michael; Liu, Zhenxian; Hou, Mingqiang; Fei, Yingwei; Kang, Lei; Lin, Zheshuai; Jin, Changqing; Zhao, Yusheng

    2016-07-01

    Pressure-induced amorphization (PIA) and thermal-driven recrystallization have been observed in many crystalline materials. However, controllable switching between PIA and a metastable phase has not been described yet, due to the challenge to establish feasible switching methods to control the pressure and temperature precisely. Here, we demonstrate a reversible switching between PIA and thermally-driven recrystallization of VO2(B) nanosheets. Comprehensive in situ experiments are performed to establish the precise conditions of the reversible phase transformations, which are normally hindered but occur with stimuli beyond the energy barrier. Spectral evidence and theoretical calculations reveal the pressure-structure relationship and the role of flexible VOx polyhedra in the structural switching process. Anomalous resistivity evolution and the participation of spin in the reversible phase transition are observed for the first time. Our findings have significant implications for the design of phase switching devices and the exploration of hidden amorphous materials.

  2. Dynamically tracking the strain across the metal-insulator transition in VO2 measured using electromechanical resonators.

    PubMed

    Parikh, Pritesh; Chakraborty, Chitraleema; Abhilash, T S; Sengupta, Shamashis; Cheng, Chun; Wu, Junqiao; Deshmukh, Mandar M

    2013-10-09

    We study the strain state of doubly clamped VO2 nanobeam devices by dynamically probing resonant frequency of the nanoscale electromechanical device across the metal-insulator transition. Simultaneous resistance and resonance measurements indicate M1-M2 phase transition in the insulating state with a drop in resonant frequency concomitant with an increase in resistance. The resonant frequency increases by ~7 MHz with the growth of metallic domain (M2-R transition) due to the development of tensile strain in the nanobeam. Our approach to dynamically track strain coupled with simultaneous resistance and resonance measurements using electromechanical resonators enables the study of lattice-involved interactions more precisely than static strain measurements. This technique can be extended to other phase change systems important for device applications.

  3. Dissipation function of the first-order phase transformation in VO2 ceramics by internal-friction measurements

    NASA Astrophysics Data System (ADS)

    Zhang, J. X.; Yang, Z. H.; Fung, P. C. W.

    1995-07-01

    In order to apply the concept of the dissipation function during the first-order phase transition (FOPT) in solids, we measured the internal friction Q-1 and shear modulus μ for a range of frequencies of polycrystalline ceramics VO2 as the sample passed through a FOPT across the temperature range of 300-420 K. The experiment was repeated for different temperature variation rate T˙. We have found that for each frequency, a maximum of Q-1 and a minimum of μ occurred at the same temperature Tp when T˙ was kept constant. The numerical values of the dissipation function ΔGR plus other FOPT parameters have been deduced using Q-1 data. The general trend of ΔGR-T and other results are found to be consistent with known physical aspects.

  4. Joule Heating-Induced Metal-Insulator Transition in Epitaxial VO2/TiO2 Devices.

    PubMed

    Li, Dasheng; Sharma, Abhishek A; Gala, Darshil K; Shukla, Nikhil; Paik, Hanjong; Datta, Suman; Schlom, Darrell G; Bain, James A; Skowronski, Marek

    2016-05-25

    DC and pulse voltage-induced metal-insulator transition (MIT) in epitaxial VO2 two terminal devices were measured at various stage temperatures. The power needed to switch the device to the ON-state decrease linearly with increasing stage temperature, which can be explained by the Joule heating effect. During transient voltage induced MIT measurement, the incubation time varied across 6 orders of magnitude. Both DC I-V characteristic and incubation times calculated from the electrothermal simulations show good agreement with measured values, indicating Joule heating effect is the cause of MIT with no evidence of electronic effects. The width of the metallic filament in the ON-state of the device was extracted and simulated within the thermal model.

  5. X-ray Spectroscopy of Ultra-thin Oxide/oxide Heteroepitaxial Films: A Case Study of Single-nanometer VO2/TiO2

    SciTech Connect

    Quackenbush, Nicholas F.; Paik, Hanjong; Woicik, Joseph C.; Arena, Dario A.; Schlom, Darrell G.; Piper, Louis F. J.

    2015-08-21

    Epitaxial ultra-thin oxide films can support large percent level strains well beyond their bulk counterparts, thereby enabling strain-engineering in oxides that can tailor various phenomena. At these reduced dimensions (typically < 10 nm), contributions from the substrate can dwarf the signal from the epilayer, making it difficult to distinguish the properties of the epilayer from the bulk. This is especially true for oxide on oxide systems. Here, we have employed a combination of hard X-ray photoelectron spectroscopy (HAXPES) and angular soft X-ray absorption spectroscopy (XAS) to study epitaxial VO2/TiO2 (100) films ranging from 7.5 to 1 nm. We observe a low-temperature (300 K) insulating phase with evidence of vanadium-vanadium (V-V) dimers and a high-temperature (400 K) metallic phase absent of V-V dimers irrespective of film thickness. Results confirm that the metal insulator transition can exist at atomic dimensions and that biaxial strain can still be used to control the temperature of its transition when the interfaces are atomically sharp. Generally, our case study highlights the benefits of using non-destructive XAS and HAXPES to extract out information regarding the interfacial quality of the epilayers and spectroscopic signatures associated with exotic phenomena at these dimensions.

  6. Positive-bias gate-controlled metal–insulator transition in ultrathin VO2 channels with TiO2 gate dielectrics

    PubMed Central

    Yajima, Takeaki; Nishimura, Tomonori; Toriumi, Akira

    2015-01-01

    The next generation of electronics is likely to incorporate various functional materials, including those exhibiting ferroelectricity, ferromagnetism and metal–insulator transitions. Metal–insulator transitions can be controlled by electron doping, and so incorporating such a material in transistor channels will enable us to significantly modulate transistor current. However, such gate-controlled metal–insulator transitions have been challenging because of the limited number of electrons accumulated by gate dielectrics, or possible electrochemical reaction in ionic liquid gate. Here we achieve a positive-bias gate-controlled metal–insulator transition near the transition temperature. A significant number of electrons were accumulated via a high-permittivity TiO2 gate dielectric with subnanometre equivalent oxide thickness in the inverse-Schottky-gate geometry. An abrupt transition in the VO2 channel is further exploited, leading to a significant current modulation far beyond the capacitive coupling. This solid-state operation enables us to discuss the electrostatic mechanism as well as the collective nature of gate-controlled metal–insulator transitions, paving the pathway for developing functional field effect transistors. PMID:26657761

  7. Optimal V.O2max-to-mass ratio for predicting 15 km performance among elite male cross-country skiers

    PubMed Central

    Carlsson, Tomas; Carlsson, Magnus; Hammarström, Daniel; Rønnestad, Bent R; Malm, Christer B; Tonkonogi, Michail

    2015-01-01

    The aim of this study was 1) to validate the 0.5 body-mass exponent for maximal. oxygen uptake (V.O2max) as the optimal predictor of performance in a 15 km classical-technique skiing competition among elite male cross-country skiers and 2) to evaluate the influence of distance covered on the body-mass exponent for V.O2max among elite male skiers. Twenty-four elite male skiers (age: 21.4±3.3 years [mean ± standard deviation]) completed an incremental treadmill roller-skiing test to determine their V.O2max. Performance data were collected from a 15 km classical-technique cross-country skiing competition performed on a 5 km course. Power-function modeling (ie, an allometric scaling approach) was used to establish the optimal body-mass exponent for V.O2max to predict the skiing performance. The optimal power-function models were found to be racespeed=8.83⋅(V˙O2maxm−0.53)0.66 and lapspeed=5.89⋅(V˙O2maxm−(0.49+0.0181lap))0.43e0.010age, which explained 69% and 81% of the variance in skiing speed, respectively. All the variables contributed to the models. Based on the validation results, it may be recommended that V.O2max divided by the square root of body mass (mL · min−1 · kg−0.5) should be used when elite male skiers’ performance capability in 15 km classical-technique races is evaluated. Moreover, the body-mass exponent for V.O2max was demonstrated to be influenced by the distance covered, indicating that heavier skiers have a more pronounced positive pacing profile (ie, race speed gradually decreasing throughout the race) compared to that of lighter skiers. PMID:26719730

  8. Study-Orientation of High and Low Academic Achievers at Secondary Level in Pakistan

    ERIC Educational Resources Information Center

    Sarwar, Muhammad; Bashir, Muhammad; Khan, Muhammad Naemullah; Khan, Muhammad Saeed

    2009-01-01

    The study orientation of low and high academic achievers was compared, measured through a self-developed study orientation scale (SOS) primarily based on 47 items comparing study habits and attitude. Students' marks obtained in the 10th grade Examination determined the measure of academic performance. The analysis revealed that the high achievers…

  9. Evaluation of Maximal Oxygen Uptake (V02max) and Submaximal Estimates of VO2max Before, During and After Long Duration ISS Missions

    NASA Technical Reports Server (NTRS)

    Moore, Alan; Evetts, Simon; Feiveson, Alan; Lee, Stuart; McCleary, Frank; Platts, Steven

    2009-01-01

    NASA's Human Research Program Integrated Research Plan (HRP-47065) serves as a road-map identifying critically needed information for future space flight operations (Lunar, Martian). VO2max (often termed aerobic capacity) reflects the maximum rate at which oxygen can be taken up and utilized by the body during exercise. Lack of in-flight and immediate postflight VO2max measurements was one area identified as a concern. The risk associated with not knowing this information is: Unnecessary Operational Limitations due to Inaccurate Assessment of Cardiovascular Performance (HRP-47065).

  10. rf-microwave switches based on reversible semiconductor-metal transition of VO2 thin films synthesized by pulsed-laser deposition

    NASA Astrophysics Data System (ADS)

    Dumas-Bouchiat, F.; Champeaux, C.; Catherinot, A.; Crunteanu, A.; Blondy, P.

    2007-11-01

    Microwave switching devices based on the semiconductor-metal transition of VO2 thin films were developped on two types of substrates (C-plane sapphire and SiO2/Si), and in both shunt and series configurations. Under thermal activation, the switches achieved up to 30-40dB average isolation of the radio-frequency (rf) signal on 500MHz -35GHz frequency band with weak insertion losses. These VO2-based switches can be electrically activated with commutation times less than 100ns, which make them promising candidates for realizing efficient and simple rf switches.

  11. Magnetic field alignment of randomly oriented, high aspect ratio silicon microwires into vertically oriented arrays.

    PubMed

    Beardslee, Joseph A; Sadtler, Bryce; Lewis, Nathan S

    2012-11-27

    External magnetic fields have been used to vertically align ensembles of silicon microwires coated with ferromagnetic nickel films. X-ray diffraction and image analysis techniques were used to quantify the degree of vertical orientation of the microwires. The degree of vertical alignment and the minimum field strength required for alignment were evaluated as a function of the wire length, coating thickness, magnetic history, and substrate surface properties. Nearly 100% of 100 μm long, 2 μm diameter, Si microwires that had been coated with 300 nm of Ni could be vertically aligned by a 300 G magnetic field. For wires ranging from 40 to 60 μm in length, as the length of the wire increased, a higher degree of alignment was observed at lower field strengths, consistent with an increase in the available magnetic torque. Microwires that had been exposed to a magnetic sweep up to 300 G remained magnetized and, therefore, aligned more readily during subsequent magnetic field alignment sweeps. Alignment of the Ni-coated Si microwires occurred at lower field strengths on hydrophilic Si substrates than on hydrophobic Si substrates. The magnetic field alignment approach provides a pathway for the directed assembly of solution-grown semiconductor wires into vertical arrays, with potential applications in solar cells as well as in other electronic devices that utilize nano- and microscale components as active elements.

  12. Crystallographic orientation variation of isothermal pearlite under high magnetic field

    SciTech Connect

    Meng, Lan Zhou, Xiaoling Chen, Jianhao

    2015-07-15

    Crystallographic orientation (CO) variation of magnetic-induced pearlite (MIP) during its microstructure evolution in 19.8 T was investigated by electron back-scatter diffraction (EBSD). It is closely related to the isothermal temperatures (ITs) and the applied magnetic time (MT) during the process of MIP formation. The <100> easy magnetization direction in MIP colonies is strengthened with the MT within the certain transformed fraction of MIP (f{sub MIP}) at the relatively lower IT (983 K) above the eutectoid temperature but below the magnetically shifted upward eutectoid temperature, while this special CO tends to be weakened at a relatively higher IT (995 K). For the same MT, the higher the IT, the relatively larger is the proportion in <100> orientation for MIP colonies at the early growth stage. These results have demonstrated that the change of <100> orientation of MIP is closely related to the growth rate of pearlite ferrite (PF), and strengthened mainly at early transformation stage. When f{sub MIP} reaches some value, the growth rate of MIP at other COs, such as <110>, even at the hard magnetization direction, turns to present speed-up. - Highlights: • HMF can induce pearlite with different fractions above the eutectoid temperature. • CO is closely related to isothermal temperatures and applied magnetic time. • <100> direction is related to the growth rate of PF, and strengthened at early stage. • When f{sub MIP} reaches some value, the growth rate at other COs turns to present speed-up.

  13. Growth of diamond microcrystals by the oriented attachment mechanism at high pressure and high temperature

    NASA Astrophysics Data System (ADS)

    Kidalov, S. V.; Shakhov, F. M.; Shvidchenko, A. V.; Smirnov, A. N.; Sokolov, V. V.; Yagovkina, M. A.; Vul', A. Ya.

    2017-01-01

    For the first time it has been experimentally shown that a powder of detonation nanodiamonds (DND) and a saturated acyclic hydrocarbon, mono- or dibasic alcohol, used as the reaction mixture after treatment at high pressures (5-8 GPa) and high temperatures (1300-1800°C) results in the formation of diamond single crystals up to 15 micron in size. The Raman spectrum indicates that the diamonds have a perfect of crystal structure. It has been suggested that the oriented attachment mechanism is responsible for growth of micrometer-size diamond single crystals out of DND particles with sizes of about 5 nm under these technological conditions.

  14. Decoupling the Lattice Distortion and Charge Doping Effects on the Phase Transition Behavior of VO2 by Titanium (Ti(4+)) Doping.

    PubMed

    Wu, Yanfei; Fan, Lele; Liu, Qinghua; Chen, Shi; Huang, Weifeng; Chen, Feihu; Liao, Guangming; Zou, Chongwen; Wu, Ziyu

    2015-05-07

    The mechanism for regulating the critical temperature (TC) of metal-insulator transition (MIT) in ions-doped VO2 systems is still a matter of debate, in particular, the unclear roles of lattice distortion and charge doping effects. To rule out the charge doping effect on the regulation of TC, we investigated Ti(4+)-doped VO2 (Ti(x)V(1-x)O2) system. It was observed that the TC of Ti(x)V(1-x)O2 samples first slightly decreased and then increased with increasing Ti concentration. X-ray absorption fine structure (XAFS) spectroscopy was used to explore the electronic states and local lattice structures around both Ti and V atoms in Ti(x)V(1-x)O2 samples. Our results revealed the local structure evolution from the initial anatase to the rutile-like structure around the Ti dopants. Furthermore, the host monoclinic VO2 lattice, specifically, the VO6 octahedra would be subtly distorted by Ti doping. The distortion of VO6 octahedra and the variation of TC showed almost the similar trend, confirming the direct effect of local structural perturbations on the phase transition behavior. By comparing other ion-doping systems, we point out that the charge doping is more effective than the lattice distortion in modulating the MIT behavior of VO2 materials.

  15. 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 (V2O3), dioxide (VO2), and pentoxide (V2O5) 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 V2O5, VO2, and V2O3 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 V2O5, VO2, and V2O3 are illustrated by the characterization of the electrochromic properties of V2O5 films, a discussion about the metal to insulator transition of VO2 on the basis of in situ measurements versus temperature of its electrical and optical properties, and the characterization of the magnetic transition of V2O3 powder from SQUID measurements. For the latter compound, the influence of the crystallite size on the magnetic properties is discussed.

  16. Comparing the effects of two in-flight aerobic exercise protocols on standing heart rates and VO(2peak) before and after space flight

    NASA Technical Reports Server (NTRS)

    Siconolfi, S. F.; Charles, J. B.; Moore, A. D. Jr; Barrows, L. H.

    1994-01-01

    The effects of regular aerobic exercise on orthostatic tolerance have been the subject of a long-standing controversy that will influence the use of exercise during space flight. To examine these effects, astronauts performed continuous (CE) aerobic exercise (n = 8), interval (IE) aerobic exercise (n = 4), or no (NE) exercise (n = 5) during flights of 7 to 11 days. Heart rate (HR) responses to an orthostatic challenge (stand test) were measured 10 days before flight and on landing day. VO(2peak) (graded treadmill exercise) was measured 7 to 21 days before and 2 days after flight. No significant differences across the groups were observed in standing HRs before or after flight. However, the within-group mean HRs significantly increased in the NE (71-89 beats/min) and CE (60-85 beats/min) groups after space flight. The HRs for the IE group did not significantly increase (75-86 beats/min) after space flight. VO(2peak) decreased (P < .05) in the NE (-9.5%) group, but did not change in the CE (-2.4%) and IE (1%) groups. The relationship (r = 0.237) between the delta HR and delta VO(2peak) was not significant. These preliminary results indicate that: (1) continuous exercise does not affect the orthostatic HR response after space flight; (2) interval exercise may minimize an increase in the postflight orthostatic HR; and (3) both exercise protocols can maintain VO(2peak).

  17. 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.

  18. Decoupling the Lattice Distortion and Charge Doping Effects on the Phase Transition Behavior of VO2 by Titanium (Ti4+) Doping

    PubMed Central

    Wu, Yanfei; Fan, Lele; Liu, Qinghua; Chen, Shi; Huang, Weifeng; Chen, Feihu; Liao, Guangming; Zou, Chongwen; Wu, Ziyu

    2015-01-01

    The mechanism for regulating the critical temperature (TC) of metal-insulator transition (MIT) in ions-doped VO2 systems is still a matter of debate, in particular, the unclear roles of lattice distortion and charge doping effects. To rule out the charge doping effect on the regulation of TC, we investigated Ti4+-doped VO2 (TixV1-xO2) system. It was observed that the TC of TixV1-xO2 samples first slightly decreased and then increased with increasing Ti concentration. X-ray absorption fine structure (XAFS) spectroscopy was used to explore the electronic states and local lattice structures around both Ti and V atoms in TixV1-xO2 samples. Our results revealed the local structure evolution from the initial anatase to the rutile-like structure around the Ti dopants. Furthermore, the host monoclinic VO2 lattice, specifically, the VO6 octahedra would be subtly distorted by Ti doping. The distortion of VO6 octahedra and the variation of TC showed almost the similar trend, confirming the direct effect of local structural perturbations on the phase transition behavior. By comparing other ion-doping systems, we point out that the charge doping is more effective than the lattice distortion in modulating the MIT behavior of VO2 materials. PMID:25950809

  19. Submaximal Exercise VO